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Peptide therapeutics https://en.wikipedia.org/wiki/Peptide_therapeutics

Peptide therapeutics are peptides or polypeptides (oligomers or short polymers of amino acids) which are used to for the treatment of diseases. Naturally occurring peptides may serve as hormones, growth factors, neurotransmitters, ion channel ligands, and anti-infectives

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Peptide Therapy https://delawareintegrativemedicine.com/therapies/peptide-therapy

Peptide therapy is the targeted use of peptides to produce a specific reaction in the body. Some peptides, for example have been shown to assist with weight loss by stimulating the breakdown of visceral fat. They may also be utilized to reduce inflammation. Some peptides stimulate the production of human growth hormone and are utilized in anti-aging therapies or to increase muscle mass. Peptides are typically administered through the skin as a subcutaneous injection

 

Peptides are so numerous and variable in structure, there effects are also widespread and varied. One of these classes of peptides are know as growth hormone Secretaogoues, and cause one's own natural human growth hormone (hCG) in the body. These peptides have been shown to be very useful in the treatment of age-related conditions such as osteoporosis, obesity and many chronic inflammatory diseases, and have several advantages over traditional hCG treatments.

 

Another type of peptide is composed of part of the hCG molecule that is responsible for fat cell death, and has been shown to be very effective as an anti-obesity drug. These peptides lead to increased lean muscle mass and decreased body fat, in addition to decreasing inflammation.

 

A certain class of peptide has been used to help prevent skin cancer by increasing the melanin in one's skin, causing a darkening effect that mimics a quality sun tan. This peptide has also been shown to increased lean muscle mass and improve sex drive

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Best Nootropics for Traumatic Brain Injury as PDF, viewed on page 9 or https://nootropicsexpert.com/best-nootropics-for-traumatic-brain-injury

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Pharmacological Approaches to Treating Traumatic Brain Injury: a Case for Arginine-Rich Peptides
https://pubmed.ncbi.nlm.nih.gov/27844291

 

Peptides are rapidly emerging as useful therapeutic agents because they can possess beneficial therapeutic properties such as the ability to cross membranes, high specificity and affinity for target molecules, and low immunogenicity and toxicity [18, 84]. In addition, chemical modifications can be easily introduced into peptides to increase serum and oral stability, and improve pharmacokinetic properties [85]. The global peptide therapeutic market is predicted to increase to US$25.4 billion in 2018 [86, 87].

 

Given that peptide based therapeutics have been widely used in the treatment of diabetes, cardiovascular disease, asthma, allergies, cancer, and infectious diseases, the fact that they have been used so sparingly in CNS disorders is striking. Because of the high social and economic burden associated with TBI and stroke alone, these diseases represent an enormous pharmaceutical market segment and a major area of unmet need [21, 87]. Given that a number of peptides have already shown efficacy in preclinical TBI models, it seems logical to suggest that future effective neuroprotective agents may be peptide based therapeutics.

 

evidence that suggests arginine rich peptides represent a new class of neuroprotective agent and have argued that they should be considered in the context of neuroprotective therapeutic drug development for TBI. Adding to this, past studies using TAT fused and other cationic peptides as a potential neuroprotective agent for TBI have produced some promising results that warrant additional investigation. This class of peptides have established efficacy in other brain injury models such as stroke, suggesting that they may be equally efficacious in TBI. Importantly, it appears that the arginine residues are especially critical in allowing these peptides to cross the BBB and be internalised by neurons and other neural cells. Upon being internalised, these peptides appear to act via multiple mechanisms, namely, maintaining mitochondrial integrity, reducing destruction of the brain extracellular matrix, and pre serving BBB by inhibiting MMPs. Given these findings, there is growing evidence that arginine rich peptides, including poly arginine peptides such as R18, warrant consideration as neuro protective agents for TBI

 

Peptide therapy encompasses numerous different biological amino acid sequences with varied effects, ranging from immune modulation and tissue repair to fat loss and muscle building. The benefits of peptide therapy may include improved sleep cycle, hormone production, brain function and inflammatory mediators. Peptides can also be used in the treatment of injuries. They also have the capabilities that help prevent aging, illness, and enhance peak performance. Peptides play a major role in how your body responds to diet and exercise. The body will not perform at an optimal level if it isn't producing enough peptides or essential amino acids.

 

Peptides may help regulate processes within the body. Patients with Lyme disease, chronic inflammation, autoimmune disease and other chronic degenerative diseases may benefit from peptides in their treatment plan

 

Sermorelin Acetate is a compound similar in structure to growth hormone releasing hormone (GHRH). Sermorelin has been known to stimulate the pituitary gland to produce and secrete growth hormone. It is a bioidentical synthetic hormone peptide sequence comprised of 29 amino acids. Sermorelin is affordable and is available in lyophilized injectable form and oral preparation.

 

Growth hormone releasing peptides stimulate the pituitary gland’s natural production of endogenous human growth hormone. Sermorelin is an analogue of growth hormone releasing hormone (GHRH). Sermorelin has been shown to be effective in raising growth hormone/insulin like growth factor which helps to:

• Increase bone density
• Strengthen the cardiovascular system
• Increase muscle mass
• Improve ability to burn fat
• Increase sex drive
• Improve recovery and repair from injuries
• Regenerate nerve tissue
• Strengthen the immune system
• Enhance energy levels
• Improve cognition and memory
• Improve bone and mineral density

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From: GH deficiency as the most common pituitary defect after TBI: clinical implications
https://www.ncbi.nlm.nih.gov/pubmed/16508711

 

Recent studies have demonstrated that hypopituitarism, and in particular growth hormone deficiency (GHD), is common among survivors of traumatic brain injury (TBI) tested several months or years following head trauma. In addition, it has been shown that post-traumatic neuroendocrine abnormalities occur early and with high frequency. These findings may have significant implications for the recovery and rehabilitation of patients with TBI. The subjects at risk are those who have suffered moderate-to severe head trauma although mild intensity trauma may precede hypopituitarism also. Particular attention should be paid to this problem in children and adolescents. GH deficiency is very common in TBI, particularly isolated GHD. For the assessment of the GH-IGF axis in TBI patients, plasma IGF-I concentrations plus GH response to a provocative test is mandatory. Growth retardation secondary to GHD is a predominant feature of GHD after TBI in children. Clinical features of adult GHD are variable and in most obesity is present. Neuropsychological examinations of patients with TBI show that a significant portion of variables like attention, concentration, learning, memory, conceptual thinking, problem solving and language are impaired in patients with TBI. In the few case reports described, hormone replacement therapy in hormone deficient head-injured patients resulted in major neurobehavioral improvements. Improvements in mental-well being and cognitive function with GH replacement therapy in GHD adults have been reported. The effect of GH replacement in posttraumatic GHD needs to be examined in randomized controlled studies.

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From: Chronic cognitive sequelae after traumatic brain injury are not related to growth hormone deficiency in adults. - PubMed – NCBI https://www.ncbi.nlm.nih.gov/pubmed/20050894

 

GHD persists long after the TBI, independently of trauma severity and age at traumatic event. GH secretion is more sensitive to TBI than other pituitary hormones.

 

From: Clearfield Panhypopituitarism and TBI http://www.nevadaosteopathic.org/attachments/article/33/Clearfield%20Panhypopituitarism%20and%20TBI.pdf

 

Growth Hormone Deficiency (GHD) – First and most common deficiency – Acute Injury Incidence rate: 20%. – 12 month follow up rate increases to 35-40% of survivors.

 

TBI with GHD • Rapid weight gain • Excessive anxiety • Depression along • Deficits in: – Attention – Executive Functioning – Memory – Emotion – Cognition – Mood Anxiety/Depression • Poor overall physical health and quality of life

 

GH Replacement – Improvements in: • Cardiovascular Risk – Reduces IL-6, Il-1, cRP, Homocysteine • Concentration • Memory • Depression • Anxiety • Fatigue • Lean body mass • Lumbar vertebral bone density • 14.4 % decrease in adipose\- tissue mass • Skin thickness

 

GH Deficiency Associated w Cognitive Dysfunction and “Atypical Depression”

 

Correction of GHD : Tempers: Intensity of Outbursts Hostility Paranoid Ideation Anxiety, Phobia Somatization Obsessive Compulsive S/S Improves: Verbal and Non-Verbal Memory Cognition Mental Alertness Work Capacity

 

GH Lab Values and Rx. Lab Values: GH 5.0 ng/ml IGF-1 200 ng/ml IGFBP-3 4000 ng/ml RX: Injectables: HGH 0.8-1.2 IU/day SQ5-7 IU day/wk. Semorelean w or W/O GNRH 2 or 6 (2 causes nausea, 6 hunger) Peptide CJC 1295 with DAC 0.5-2.0 mg q. week (Can cause hot flash for 5\- 15 minutes ) Oral Spray: Secretropin, Dynotropin

 

Case study Olivia G.

Diagnosis: Treatment Resistant Depression

Growth Hormone

(Morning Lab Draw)

 

> > > > > > Olivia                                     Median

Growth Hormone             0.6 ng/ml                             5 ng/ml

IGF-1                                78 ng/ml                              > 200 ng/ml

IGFBP3                              2950 ng/ml                         > 4000 ng/ml

 

IGF-1 as proxy

IGFBP 3 logarithmic relation to GH Pulse

Estrogen and Quercetin can stimulate IGf BP 3

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Pharmacological Approaches to Treating Traumatic Brain Injury: a Case for Arginine-Rich Peptides https://pubmed.ncbi.nlm.nih.gov/27844291

 

Peptides are rapidly emerging as useful therapeutic agents because they can possess beneficial therapeutic properties such as the ability to cross membranes, high specificity and affinity for target molecules, and low immunogenicity and toxicity [18, 84]. In addition, chemical modifications can be easily introduced into peptides to increase serum and oral stability, and improve pharmacokinetic properties [85]. The global peptide therapeutic market is predicted to increase to US$25.4 billion in 2018 [86, 87].

 

Given that peptide based therapeutics have been widely used in the treatment of diabetes, cardiovascular disease, asthma, allergies, cancer, and infectious diseases, the fact that they have been used so sparingly in CNS disorders is striking. Because of the high social and economic burden associated with TBI and stroke alone, these diseases represent an enormous pharmaceutical market segment and a major area of unmet need [21, 87]. Given that a number of peptides have already shown efficacy in preclinical TBI models, it seems logical to suggest that future effective neuroprotective agents may be peptide based therapeutics.

 

evidence that suggests arginine rich peptides represent a new class of neuroprotective agent and have argued that they should be considered in the context of neuroprotective therapeutic drug development for TBI. Adding to this, past studies using TAT fused and other cationic peptides as a potential neuroprotective agent for TBI have produced some promising results that warrant additional investigation. This class of peptides have established efficacy in other brain injury models such as stroke, suggesting that they may be equally efficacious in TBI. Importantly, it appears that the arginine residues are especially critical in allowing these peptides to cross the BBB and be internalised by neurons and other neural cells. Upon being internalised, these peptides appear to act via multiple mechanisms, namely, maintaining mitochondrial integrity, reducing destruction of the brain extracellular matrix, and pre serving BBB by inhibiting MMPs. Given these findings, there is growing evidence that arginine rich peptides, including poly arginine peptides such as R18, warrant consideration as neuro protective agents for TBI

 

Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults https://pubmed.ncbi.nlm.nih.gov/16352683

 

Subcutaneous administration of CJC-1295 resulted in sustained, dose-dependent increases in GH and IGF-I levels in healthy adults and was safe and relatively well tolerated, particularly at doses of 30 or 60 microg/kg. There was evidence of a cumulative effect after multiple doses. These data support the potential utility of CJC-1295 as a therapeutic agent

 

Peptide CJC 1295 https://en.wikipedia.org/wiki/CJC-1295

 

CJC-1295, also known as DAC:GRF (short for drug affinity complex:growth hormone-releasing factor), is a synthetic analogue of growth hormone-releasing hormone (GHRH) (also known as growth hormone-releasing factor (GRF)) and a growth hormone secretagogue (GHS) which was developed by ConjuChem Biotechnologies.[1][2][3] It is a modified form of GHRH (1-29) with improved pharmacokinetics, especially in regard to half-life.[1][2][3][4]

 

CJC-1295 markedly increases plasma growth hormone (GH) and insulin-like growth factor 1 (IGF-1) levels in both animals and humans.[1][2][3][5] With a single injection, in human subjects, CJC-1295 increases plasma GH levels by 2- to 10-fold for 6 days or longer and plasma IGF-1 levels by 0.5- to 3-fold for 9 to 11 days.[3] The drug has an estimated half-life of about 6 to 8 days in humans.[3] With multiple doses of CJC-1295, IGF-1 levels were found to remain elevated in humans for up to 28 days.[3]

CJC-1295 has been shown to extend the half-life and bioavailability of growth-hormone-releasing hormone 1-29 and stimulate insulin-like growth factor 1 secretion. It increases the half-life of acting agents by bioconjugation.[6]

 

CJC-1295 was under investigation for the treatment of lipodystrophy and growth hormone deficiency and reached phase II clinical trials but was discontinued upon the death of one of the trial subjects.[7][8] The attending physician of the trial believed that the most likely explanation for the incident was that the patient had asymptomatic coronary artery disease with plaque rupture and occlusion, and that the occurrence was unrelated to treatment with CJC-1295.[8] In any case, research was terminated nonetheless as a precaution.[8] CJC-1295 has found grey market use for bodybuilding purposes, with this, in some countries such as the Netherlands, being an illicit use

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Peptide Therapy Education https://limitlessmale.com/treatments/peptide-therapy

 

BPC-157 is a pentadecapeptide made up of 15 amino acids. It is a partial sequence of the body protection compound (BPC) derived from human gastric juice. Research has shown that it heightens the healing of many different types of tissues, including: tendon, muscle, nervous system, and is superior at healing damaged ligaments.

 

Patients who suffer from discomfort due to sprains, tears, and tissue damage may benefit from treatment with this peptide as it can increase blood flow back to the injured sites. BPC-157 may protect organs, prevent stomach ulcers, and heal skin burns. Benefits over time may include:

• Accelerated wound healing
• Anti-inflammatory properties
• Increased growth hormone receptors
• Improves digestive function
• May decrease pain in damaged areas

 

AOD 9604 (Advanced Obesity Drug) is a modified form of amino acids 176-191 of the GH polypeptide, which enhances fat reducing effects. One of the advantages of this peptide is the absence of adverse effects on blood sugar and insulin resistance.

 

AOD 9604 has shown potential effects to repair cartilage and muscle and is often used in the treatment of osteoarthritis.

 

AOD-9604 works by mimicking the function of human growth hormone in the regulation of burning fat metabolism. At the same time, it increases the activity of beta-3 receptors, which are relevant to overall metabolism. It is also known for its properties in the lipolysis stimulation, resulting in fat destruction. Benefits may include:

• Reduction of body fat
• Triggers fat release from obese fat cells predominately more than lean ones
• Mimics the way natural growth hormone regulates fat metabolism
• No adverse effects on blood sugar or growth
• Stimulate lipolysis
• Inhibits lipogenesis that's the transformation of non-fatty foods into body fat

 

AOD 6904 has been shown to have very favorable cartilage repair and regenerative properties, particularly when paired with peptide BPC 157

 

Thymosin is a hormone secreted from the thymus. Its primary function is to stimulate the production of T cells, which are an important part of the immune system. Thymosin also assists in the development of B cells to plasma cells to produce antibodies. The predominant form of thymosin, thymosin beta 4, is an actin, a cell building protein. One of the main mechanisms of action of Thymosin Beta-4 is its regulation of Actin.

 

This cell-building protein is an essential component of cell structure and movement which leads to its role in tissue repair. Tβ 4 has been found to play an important role in protection, regeneration, and remodeling of injured or damaged tissues. After an injury, Tβ 4 is released by platelets and numerous other types of cells to protect the most damaged cells and tissues and to reduce inflammation and microbial growth. Benefits may include:

• Calms muscle spasm
• Improved muscle tone
• Increased exchange of substances between cells
• Encourages tissue repair
• Stretches connective tissue
• Helps maintain flexibility
• Reduced inflammation of tissue in joints
• Encourages the growth of new blood cells in tissue
• Increased endurance and strength
• Prevents formation of adhesions and fibrous bands in muscles, tendons, and ligaments
• Effective in fighting infectious disease like Lyme disease by stimulating T cells and B cells

 

Peptides LL-37 + BPC-157 1

LL-37 is a broad-spectrum antimicrobial peptide naturally made in the body. Anecdotally, supplemental LL-37 helps fix gut issues. BPC-157 is a peptide naturally found in the stomach which may promote healing and tissue regeneration.

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https://en.wikipedia.org/wiki/Neuropeptidergic

Neuropeptidergic means "related to neuropeptides".

A neuropeptidergic agent (or drug) is a chemical which functions to directly modulate the neuropeptide systems in the body or brain. An example is opioidergics.

 

See also

Adenosinergic

Cannabinoidergic

Cholinergic

GABAergic

Glutamatergic

Glycinergic

Histaminergic

Monoaminergic

Opioidergic

 

Specifically designed peptides like Cerebrolysin, Dihexa, Selank, and Semax increase the brain-derived nootropic factor and neuro growth factor. These factors impact the metabolism of the brain and subsequently your ability to focus and overall brain health.

 

In addition, peptides offer a potential improvement to the ability of your brain to create synapses. This separates peptides from nootropic regimens, as peptides can introduce long term benefits that would disappear after discontinuing other nootropic modalities.

 

Many supplements offer “natural remedies” but peptides are naturally occurring in the body. Clinical introduction of peptides only enhances functions that are already being performed by your brain

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Pharmacological Approaches to Treating Traumatic Brain Injury: a Case for Arginine-Rich Peptides (full https://pubmed.ncbi.nlm.nih.gov/27844291

 

Many attempts have been made to use experimental neuroprotective agents for the treatment of TBI with little or no success. Early experimental neuroprotective agents focused on targeting a single pathophysiological event, such as attenuating excitotoxicity. Dexanabinol, magnesium sulphate, and Selfotel [78] were some of the compounds investigated in this category. Although beneficial outcomes were reported from some of these agents in clinical trials, others had no significant effects [79, 80]. Similarly, other interventions have sought to block calcium ion channels, since cellular homeostatic disruption is a major factor in triggering excitotoxic injury. Originally used to treat high blood pressure, nimodipine and nicardipine are voltage gated calcium channel blockers with neuroprotective effects in preclinical experiments; however, efficacy has not been confirmed in clinical trials [79].

While the exact reasons for the failure of previous therapeutics in TBI is beyond the scope of this review, several explanations have been proposed. For example, a drug may be beneficial in the acute neuro destructive phases following injury, but persistent antagonistic effects on a receptor or cellular target may hinder neuronal survival [81]. Moreover, the therapeutic agent may only target one neuro damaging event; therefore, any neuroprotective actions are eclipsed by other aspects of the secondary injury cascade, lending credence to multifunctional drug investigations [82]. It is also possible that the drug has not reached therapeutic levels at the appropriate time following TBI, perhaps due to pharmacokinetic alterations [83]. Alternatively, there may be inherent problems in the way therapeutic efficacy of compounds are assessed, ranging from poor extrapolation of preclinical data, clinical irrelevance, and model variations [17]. Recently, the Operation Brain Trauma Therapy consortium screened a number of small compounds that had reported favourable preclinical outcomes. Of the three therapies, only levetiracetam had beneficial effects [16]. Simvastatin [19] and nicotinamide [15] both had sporadic results which led the consortium to conclude that further exploring their potential was largely not worthwhile [20].

 

Towards a Peptide Based Therapeutic

 

Peptides are rapidly emerging as useful therapeutic agents because they can possess beneficial therapeutic properties such as the ability to cross membranes, high specificity and affinity for target molecules, and low immunogenicity and toxicity [18, 84]. In addition, chemical modifications can be easily introduced into peptides to increase serum and oral stability, and improve pharmacokinetic properties [85]. The global peptide therapeutic market is predicted to increase to US$25.4 billion in 2018 [86, 87].

 

Given that peptide based therapeutics have been widely used in the treatment of diabetes, cardiovascular disease, asthma, allergies, cancer, and infectious diseases, the fact that they have been used so sparingly in CNS disorders is striking. Because of the high social and economic burden associated with TBI and stroke alone, these diseases represent an enormous pharmaceutical market segment and a major area of unmet need [21, 87]. Given that a number of peptides have already shown efficacy in preclinical TBI models, it seems logical to suggest that future effective neuroprotective agents may be peptide based therapeutics. Below, we highlight the peptides that have been assessed in animal TBI models, and discuss their mechanisms of action, with an emphasis on arginine rich peptides. The outcomes of preclinical TBI studies utilising peptides are summarised in Table 1.

 

Cyclosporin A

 

Cyclosporin A (CsA) is a powerful immunosuppressant and calcineurin inhibitor originally derived from an isolate of soil fungi. The peptide is an 11amino acid cyclic structure (aLLVTAbuSarLVLA; where a = Dalanine; Abu = Lal phaaminobutyric acid; Sar = sarcosine) consisting of mostly hydrophobic amino acids such as tyrosine, leucine, and valine. In addition, most of the amino acids in CsA are chemically modified or are atypical amino acids (e.g. Dalanine and sarcosine). CsA is widely used in organ transplantation

 

procedures to prevent rejection, and its neuroprotective properties are attributable to its ability to interact with the mitochondrial protein, cyclophilin D, preventing MPTP opening (Fig. 1) [88, 89]. Evidence suggests that by inhibiting the opening of the MPTP, CsA reduces excitotoxic mediated mitochondrial calcium uptake and ROS production [22, 90–92]. It has also been suggested that the neuroprotective action of CsA may in part be due to its ability to inhibit calcineurin [22, 23]; however, a study using a noncalcineurin inhibitory ana logue of CsA has shown that this is not the case [24].

 

The positive effects of CsA on mitochondria prompted a preclinical assessment of CsA as a potential therapeutic for acute brain injuries, including TBI. In rats modelling both cortical impact and diffuse axonal injuries (CCI and DAI, respectively), administration of CsA within half an hour of the injury attenuated mitochondrial dysfunction and limited axonal dam age [22, 91]. In a subsequent CsA dose response study, a 16,630 nmol/kg dose was shown to be optimal for neuroprotection when administered up to 24 h after TBI [93]. Later studies demonstrated that a lower dose of CsA (8315 nmol/ kg) administered daily after TBI was also neuroprotective and improved functional outcomes (Table 1) [23, 92].

 

The positive outcomes achieved with CsA in animal stud ies have led to clinical studies of its efficacy in humans. Early phase studies established a good safety profile for CsA when infused at a dose of 4158 nmol/kg over 24 h [94, 95]. However, no clear evidence of neuroprotective efficacy for CsA in TBI could be demonstrated, mostly due to its powerful immunosuppressant activity having detrimental side effects. Despite this lack of demonstrable clinical efficacy in TBI, there have been renewed studies of CsA (ClinicalTrials.gov Identifiers: NCT01825044, NCT02496975) investigating its pharmacokinetics, other effects on acute administration, and as candidate in combined therapies for TBI [96].

 

Mixed results from past preclinical trials have recently prompted one group to investigate the efficacy of CsA in different TBI animal models [25]. Doses of 8315 and 16,650 nmol/kg were given at 15 min and 24 h after fluid percussion injury (FPI), CCI, and penetrating ballisticlike brain injury (PBBI) models (Table 1). In the milder FPI and CCI models, CsA had limited beneficial effects, whereas del eterious and toxic effects were observed in the more severe PBBI model, leading the investigators to conclude that there is little reason for further clinical translation for the peptide [25].

 

Conopeptides

 

Conotoxins are a class of peptides derived from the venom of sea snails, a subset of which was first utilised as an analgesic for severe and chronic pain before its discovery as a potential neuroprotective agent for TBI. Purported to act as Ntype voltage dependent calcium channel blockers (VDCC) (Fig. 1), ω conotoxins have shown to be potently neuroprotective in preclinical TBI studies but not in subsequent clinical trials. Despite these past failures, studies on the neuroprotective po tential of other similar conotoxins continue.

 

SNX111 (also Ziconotide; CKGKGAKCSRLMY DCCTGSCRSGKC) is a synthetic derivative of ω conotoxin from the venom of Conus magus sea snails. It is a highly potent and selective antagonist of VDCCs (Fig. 1), its interactions with which are highly dependent on lysine and arginine residues in the peptide [97]. Following reports of neuroprotective effects in animal models of cerebral ischaemia [98–100], Bowersox and Luther [101] suggested that SNX111 may be efficacious in other neurological disorders. Subsequent investiga tions showed that SNX111 was effective in animal models of TBI, where it was capable of reducing intra cellular neuronal calcium accumulation and mitochondri al dysfunction (Table 1) [102, 103]. In another study using a rat DAI model, SNX111 improved behavioural outcomes when administered 3, 5, and 24 h postinjury (Table 1) [104]. Additionally, when SNX111 peptide was combined with the brainpenetrating antioxidant U101033E (known to reduce infarct size in rat models of middle cerebral artery occlusion) following TBI, mi tochondrial dysfunction was also significantly reduced [105]. Given the positive outcomes of these preclinical TBI studies, clinical trials were undertaken with a phase I trial showing good safety and tolerability profiles for SNX111, after  a 24h infusion  at a dose of up to 16 nmol/kg/h [26]. Subsequently, a phase II study in 160 headinjured patients was commenced, but was suspended after a higher mortality rate was observed in SNX111treated patients (25 %) compared to placebo (15 %) [106].

 

Despite this setback with SNX111, research on other conopeptides as potential neuroprotective agents has contin ued. SNX185 (CLSPGSSCSPTSYNCCRSCNPYSRKC) is the synthetic form of another ωconotoxin peptide, derived from the Conus tulipa sea snail. SNX185 shares a 46 % ami no acid homology with SNX111 and has a similar inhibitory effect on VDCCs (Fig. 1), but greater bioavailability and a longer halflife in the rodent brain following intravenous ad ministration compared to SNX111, a feature attributed to its greater resistance to proteolytic degradation [107]. In a fluid percussion injury (FPI)induced focal model of TBI, SNX 185 administration into the ipsilateral CA2–3 subregion of the hippocampus 5 min postinjury increased neuronal surviv al after 42 days, and improved behavioural outcomes (Table 1) [27]. More recently, in vitro investigations have revealed that SNX185 increases cell survival in cortical neuronal [28] and astrocytic cultures [108] subjected to mechanical strain and/or a secondary low pH insult. Despite these positive preclinical findings for SNX185, there have been no further reports ex amining its neuroprotective capabilities in TBI.

 

EPODerivatives

 

Erythropoietin (EPO) is a protein that has potential neuropro tective actions due to its ability to decrease inflammation and neuronal death, and promote neurogenesis [109–112]. However, EPO given either by intravenous infusion or subcu taneous injections after TBI in humans does not improve neu rological outcomes, but contributes to raised intracranial pres sure and deep vein thrombosis [113, 114]. Given these nega tive findings, the focus has switched to peptides derived from the EPO in an attempt to circumvent detrimental side effects while still retaining the neuroprotective activities of the full length protein.

 

An 11amino acid peptide (QEQLERALNSS) synthe sised from the helix B region of EPO (designated HBSP) has been demonstrated to be nonerythropoietic and capa ble of reducing the degree of injury in a nonTBI CNS injury model to a molarequivalent extent compared to EPO [29]. The Nterminal glutamine in the HBSP peptide, however, is prone to cyclisation to pyroglutamate (pHBSP; pyrEQLERALNSS; pyr = pyroglutamate). Furthermore, pHBSP, unlike EPO, has the added advantage of stability for up to 12 months at room temperature, or 24 months at 4 °C [30]. Having established its cytoprotective activity in a number of nonTBI models of injury [29, 115, 116], pHBSP has been identified as a potential therapeutic neuroprotective agent. In a mild model of TBI (mTBI) induced by CCI, rats intraperitoneally administered 23.5 nmol/kg pHBSP every 12 h for 3 days, beginning at either 1 or 24 h postinjury, improved histological and functional out comes when compared to rats treated with a scrambled version of the peptide [117]. Even more promising results are reported for pHBSP by the same group in an mTBI model compounded with haemorrhagic hypotension [30].

 

A peptide (GCAEHCSLNENITVPDTKV) known as JM4 derived from the EPO protein AB loop is nonerythropoietic and shows neuroprotective properties [118]. The presence of two cysteine residues has been identified as a desirable char acteristic that enables the peptide to form a stable cyclic struc ture due to the formation of disulphide bonds. In a mouse CCI TBI model, intraperitoneal administration of JM4 reduced le sion size when given up to 9 h postinjury (Table 1).

 

The neuroprotective mechanism of EPOderived peptides such as pHBSP and JM4 is yet to be fully elucidated. Since these peptides are derived from regions of the EPO protein that interact with the EPO receptor, it is believed that their neuroprotective activity is mediated via this receptor, leading to suppression of the inflammatory response (Fig. 1) and stim ulated expression of protective molecules such as brain derived neurotrophic factor [117]. To date, no clinical trials of EPOderived peptides have been reported, although a pat ent for the JM4 peptide as a therapeutic for CNS injuries has been filed.

 

Pituitary Adenylate Cyclase Activating Polypeptide

 

The pituitary adenylate cyclase activating polypeptide (PACAP) consists of 175 amino acids and is a member of the vasoactive intestinal peptide (VIP)/secretin/glucagon pep tide family. It is widely distributed in the central and peripheral nervous systems where it plays an important role in neurogenesis and neuroregeneration, and for these reasons has been investigated for the assessment of its neuroprotective potential [119]. Administration of PACAP in TBIinduced rats via impact acceleration reported therapeutic benefit [120, 121]. Despite this, the native polypeptide does has a number of drawbacks that limit its therapeutic potential, such as poor bioavailability, low tissue absorption, and short biological halflife [122].

 

More recently, shorter peptides derived from PACAP have emerged. In particular, a 38amino acid form (PACAP38: HSDGIFTDSYSRYRKQMAVKKYLAAVLGKRYKQRVKNK) was found to have beneficial effects on nutrient deprived PC12 cells, increasing intracellular calcium and po tassium levels, and protecting cells from apoptosis [31]. Additionally, suppression of microglial activity was observed using a much shorter, 3amino acid PACAPderived peptide (GIF) in cell culture following 2.5 ng/mL lipopolysaccharide exposure [123]. In vivo studies of PACAP38 have also pro duced positive results. Early studies demonstrated that intra cerebroventricular or intravenous infusion of PACAP38 could reduce CA1 hippocampal cell death in rats exposed to cerebral global ischaemia [32]. For TBI studies, intracerebro ventricular administration of PACAP38 to rats prior to induc tion of injury using a modified Feeney weightdrop model improved behavioural outcomes and reduced inflammatory responses and tissue injury (Table 1) [124]. Miyamoto et al.

 

[125] investigated PACAP38 in a mouse CCI model and suggested that its neuroprotective effects were mediated by enhancing cellular antioxidant activity (Table 1).

There has been speculation as to the mechanisms associat ed with PACAP38 peptidemediated cytoprotection and, more specifically, its antiapoptotic and antiinflammatory ac tivities (Fig. 1). It was hypothesised that the neuroprotective activity of PACAP38 may be attributed to its ability to acti vate calcium channels, thus increasing intracellular calcium, which combines with nerve growth factor expression to pro mote neurite outgrowth and cell survival [31]. However, the exact means by which calcium channels are activated are still unknown. PACAP38 is also believed to attenuate the TLR4/MyD88/NFκB signalling pathway in microglia and neurons [124], a response that plays a crucial role in inflam matory aspects of TBI pathogenesis. It has been suggested that PACAP38, by attenuating microglial NADPH oxidase activ ity and ROS production, reduces microglial proinflammatory signalling, and enhances the action of microglia SOD2 and GPx1 antioxidants [123, 125].

 

Intranasal administration delivery of PACAP38 has been recommended by some, as the peptide binds to blood proteins resulting in reduced effectiveness when administered intrave nously [126]. The proven neuroprotective properties of PACAP38 suggest that the peptide warrants investigation in other areas of CNS injury such as brain ischaemia and spinal cord injury (SCI) [126]. The ability of cyclodextrincoupled PACAP38 to target specific areas in the brain has also been explored as a therapeutic option in the treatment of Alzheimer’s disease [127].

 

Other Endogenous Neurotrophic Protein Derivatives

 

Neuronal wellbeing is reliant on endogenous neurotrophic polypeptides and proteins, such as the aforementioned VIP. The neuroprotective and growthpromoting actions of VIP are purported to be mediated by two gliaderived proteins, activitydependent neurotrophic factor (ADNF) [128] and activitydependent neuroprotective protein (ADNP) [129]. The latter is essential for brain formation, while the former plays a vital role in protecting neurons from death associated with electrical blockade.

Brenneman and Gozes [128] were the first to isolate an active 14amino acid portion of the ADNF protein (ADNF 14: VLGGGSALLRSIPA) and report its exceptional potency in the femtomolar range in preventing neuronal cell death in electrically blocked spinal neuronal cultures. These re searchers commented on the similarity of the peptide’s se quence to those in molecular chaperones that are induced by a variety of cellular stresses. Subsequent studies also reported positive neuroprotective effects of ADNF14, and a shorter 9 amino acid ADNF peptide (ADNF9: SALLRSIPA) [130–133] (Table 1). An 8amino acid ADNPderived peptide (NAP: NAPVSIPQ) that shares structural and immunological similarities with ADNF9 also possesses neuroprotective properties [129, 132, 133] (Table 1). Although both ADNF 9 and NAP are thought to be neuroprotective by promoting neurite outgrowth, NAP is considered the preferred lead pep tide due to its greater capacity to stimulate production of VIP, allowing interaction with glial cells (Fig. 1), and secretion of proteins that increase cell survival [129].

With respect to neuroprotective efficacy, a single subcuta neous dose of NAP (363 nmol/kg) is reported to reduce brain injury, purportedly by inhibiting the longterm accumulation of TNFα in a mouse model of closed head injury (CHI) (Table 1) [134–136]. It is also thought that the neuroprotective effects of NAP are mediated by the peptide acting as a chap erone to protect against toxic βamyloid plaque (Aβ) aggre gation [33]. Furthermore, it is also believed that NAP protects against tau hyperphosphorylation [137], an event implicated in both traumatic brain injury and Alzheimer’s disease.

Clinical studies on NAP for TBI have not progressed, al though its application in other neurodegenerative diseases has

 

been investigated. Similar to PACAP38, NAP was initially developed for intranasal administration and marketed as Davunetide. Although it proved to be safe in human phase 1 studies (ClinicalTrials.gov Identifiers: NCT00404014, NCT00422981, NCT01110720) [ 138 ], no further

developments for Davunetide have been reported since June 2015.

 

Nogo Extracellular Peptide 1–40

 

The myelinderived neurite outgrowth inhibitor, Nogo pro tein, is a wellknown inhibitor of neurite outgrowth in mature neurons. Of its three isoforms, NogoA is the most studied in terms on its effects on the CNS in injury. Nogo66 is the functional domain common to all three isoforms and forms part of the extracellular loop that binds to the Nogo66 recep tor 1 (NgR1) to transduce growth inhibitory signals [139]. Nogo66 receptor 1 signalling has been confirmed as a poten tial neuroprotective target in TBI based on the finding that NgR knockout mice subjected to a CCI have a better cognitive outcome than wildtype mice [139].

A 40amino acid peptide derived from the Nogo66 do main (NEP1–40; RIYKGVIQAIQKSDEGHPFRAY

LESEVAISEELVQKYSNS) has been shown to possess neuroprotective properties in vitro [140] via a mechanism thought to be mediated by the peptide acting as a competitive antago nist for NogoNgR binding (Fig. 1). To provide a more effec tive means of delivery of NEP1–40 across the blood brain barrier (BBB), NEP1–40 was fused to the cationic arginine rich cellpenetrating peptide (CPP) TAT (named TATNEP1– 40) [141]. The resultant TATNEP1–40 peptide was able to protect cultured PC12 cells from cell death induced by oxygenglucose deprivation, an effect mediated by the peptide upregulating Bcl2, and promoting neurite outgrowth [141]. While the neuroprotective mechanism associated NEP1– 40 and TATNEP1–40 has centred on their ability to disrupt binding of Nogo to NgR, conflicting evidence for this mech anism has come to light. Hånell et al. [142] reported that genetic deletion and pharmacological inhibition of NgR1 re sulted in poorer outcomes in mice following TBI. Although there is potential for the application of NEP1–40 and TAT NEP1–40 in TBI therapy and related injuries (stroke and SCI), further studies are required to validate the neuroprotec tive potential of these peptides and better elucidate their mech

anism of action.

 

APP96–110

 

The amyloid precursor protein (APP) is a ubiquitously expressed transmembrane protein that is particularly concen trated in the synapses of neurons. Increasing levels of APP in the brain have been implicated in the events following TBI for having deleterious effects due to the production of neurotoxic

 

Aβ plaques, that allows for its use as a biomarker [34, 143]. Despite the potentially toxic effects of APP, a derivative of the protein generated from the nonamyloidogenic processing pathway was found to have neuroprotective and neurotrophic properties [35, 36]. Similarly, early studies into the therapeutic potential of secreted forms of APP have revealed that they are protective against calciuminduced neuronal injury, and atten uate the neurotoxicity of Aβ [37]. Further, intracerebroven tricular administration of the soluble α form of APP (sAPPα) is neuroprotective in rats with TBI where it reduces neuronal cell loss and axonal injury, as well as improving functional outcome [38] (Table 1). Recently, an APPderived peptide comprising residues 9 6 t o 110 (APP9 6 – 110; NWCKRGRKQCKTHPH) of the heparin binding D1 domain was also shown to improve functional outcomes in mouse TBI models [35, 39] (Table 1).

 

The mechanism(s) by which APP96–110 exerts its neuro protective effect is not known, but appears to be related to the heparan sulphate proteoglycan (HSPG) binding abilities of the peptide (Fig. 1). Currently, it has been proposed that the for mation of a βhairpin loop within the peptide as a result of a disulphide bond between cysteine residues 98 and 105 facili tates HSPGs binding and triggers physiological changes such as the promotion of neurite outgrowth [40, 144]. Despite un certainties regarding the neuroprotective mechanism of APP96–110, research continues on the therapeutic potential of the peptide in TBI [40].

 

APOEDerivatives

 

The 299amino acid apolipoprotein E (APOE) protein has multiple biological functions, most notably in relation to lipo protein metabolism and transport. Moreover, APOE is anti inflammatory and has neuroprotective effects within the CNS. APOE can protect primary mixed neuronal glial cell cultures from NMDA excitotoxicity [145] via mechanisms thought to involve the protein interacting with the lowdensity lipopro tein receptorrelated protein (LRP) receptor [146, 147]. Due to its inability to readily cross the BBB, a major focus has been on developing an APOEderived peptide that retains the neuroprotective properties of the fulllength protein but has im proved CNS bioavailability.

 

The first APOEderived peptide investigated was COG133 (LRVRLASHLRKLRKRLL), generated from amino acids 133–149 of the APOE protein. Initial in vitro investigations with COG133 demonstrated that the peptide was able to pro tect cultured neurons from NMDA excitotoxicity, but efficacy was slightly less than the APOE protein [148]. In animal models of TBI, intravenous administration of COG133 within 30 min of injury favourably modifies systemic and CNS in flammatory responses [41, 149]. Despite these positive ef fects, the 30 min therapeutic window is too short for therapeu tic use [150] (Table 1). As a consequence, the COG133

 

peptide was further modified to generate COG1410 (ASAib LRKLAibKRLL; Aib = 2aminoisobutyric acid).

Compared to COG133, COG1410 has an extended thera peutic time window and can improve histological and func tional outcomes following TBI [150–155]. A dosage regimen consisting of five daily intravenous injections of COG1410 at 710 nmol/kg provides a therapeutic time window of 2 h post injury in rats following FPI (Table 1) [154]. Similarly, the same daily intravenous dose of COG1410 over 3 days im proves outcomes after subarachnoid haemorrhage [156] and TBI in rats by suppressing MMP9 activity, thus preserving brain extracellular matrix integrity and reducing BBB disrup tion [155] (Table 1). Further investigation into the safety and toxicity of COG1410 are underway by the pharmaceutical company Cognosci, Inc. as a preliminary to clinical trials.

 

As mentioned above, the neuroprotective action of APOE derived peptides is thought to be related to their interaction with the LRP receptor (Fig. 1). A study by Wang and Gruenstein [147] reported that a 9mer peptide consisting of a tandem repeat of APOE residues 141–149 (RKLRKRLL) rapidly and irreversibly increases neuronal cytoplasmic calci um. Interestingly, the increase in intracellular calcium was associated with the APOE 9mer peptide stimulating the syn thesis of IP3 mediated by activation of a Gprotein [146], suggesting that the calcium originated from the endoplasmic reticulum. Leupold et al. [157] subsequently proposed the involvement of HSPGs in the transport of APOEderived pep tides across the plasma membrane of target cells as an impor tant event associated with neuroprotection.

 

Other TATFused Peptides

 

The collapsin response mediator protein 2 (CRMP2) is a high lyexpressed, brainspecific protein involved in axonal guid ance during development, and pre and postsynaptic calcium regulation. CRMP2 is also implicated in various neurological disorders and is suspected to play a role in neuronal regener ation. Following injury, CRMP2, as well as CRMP1, and CRMP4 are degraded by calpain [158–161], a process that correlates with neuronal intracellular calcium influx, cell inju ry, and neurite damage. A 15amino acid peptide (CBD3: ARSRLAELRGVPRGL) derived from the calciumbinding domain of CRMP2, fused to the CPP TAT (named TAT CBD3) was demonstrated to have neuroprotective properties following excitotoxic injury in cultured neurons [162–164]. Subsequent studies demonstrated that the TATCBD3 also im proved outcomes following TBI in mice [162] (Table 1).

 

It is believed the CBD3 peptide can alter the location and/ or function of voltagegated ion channels (e.g. CaV2.3), glu tamate receptors (e.g. NMDA receptor), and calcium trans porters (e.g. NCX3) on the plasma membrane (Fig. 1), thereby reducing calcium influx. Consequently, the neuroprotective mechanism of action for TATCBD3 is commonly thought to

 

relate to its ability to suppress the excitotoxic influx of calci um. In vitro experiments with CBD3 have shown that, as long as the peptide is fused to the TAT carrier peptide, neuropro tection is achieved [162–164]. Interestingly, the neuroprotec tive properties of CBD3 are enhanced when the TAT peptide is replaced with the polyarginine9 (R9) CPP (R9CBD3) [164]. While this effect could be due to the enhanced uptake of R9CBD3, it could equally reflect the properties of the CPP conjugate itself, an effect that might be further enhanced by the arginine content of the cargo peptide [165, 166].

 

Another TATfused peptide (gp91dsTAT; RKKRRQRRR CSTRIRRQL) developed for its ability to inhibit activity of the plasma membranebound enzyme complex NADPH oxi dase 2 has been shown to mitigate ROS and improve out comes following TBI in mice. [167]. However, given the number of arginine residues present in the gp91dsTAT pep tide, it is equally possible that the neuroprotective action of the peptide is not mediated by its proposed inhibitory actions on NADPH oxidase 2, but rather, via the arginine rich TAT pep tide itself, with further enhancement due to the arginine con tent of gp91ds.

 

A Case for arginine rich Peptides

 

Because of past therapeutic failures and the complex patholo gy of TBI, current thinking has focused on developing phar macological therapies that target multiple facets of TBI path ophysiology. The National Institutes of Health has encouraged trials of combination therapies in an attempt to explore the potential of combined agents with complementary mecha nisms of action [96]. Of the trials that had been funded, many of these failed to demonstrate any significant difference when compared to their respective monotherapies, with one trial producing poorer outcomes [168]. As an alternative approach, we propose that arginine rich peptides be considered, given that they showed neuroprotection in preclinical stroke models, and have the potential to target several neurodamaging pro cesses such as excitotoxicity, mitochondrial dysfunction, ROS production, and activation of proteolytic enzymes (Fig. 1) [14]. The identification of a range of peptides rich in the cat ionic amino acid arginine and, to a lesser extent, lysine, as neuroprotective suggests that arginine rich peptides may be considered as a new class of neuroprotective agent for assess ment in TBI and other acute CNS injuries.

 

Past Approaches with Peptides Containing Arginine Residues

 

A range of peptides containing positively charged arginine and/or lysine residues, lending to the peptide’s overall cationic state, have shown to be neuroprotective in TBI. The SNX111 conopeptide (with 2 arginine and 4 lysine residues), for

 

example, was highly effective in preclinical studies [106] compared to other drugs at the time. The ability for it to antagonise calcium channels and attenuate mitochondrial dys function initially made it an attractive drug candidate for TBI, characteristics which were attributed to its arginine and lysine content [97]. Unfortunately, clinical development of SNX111 was abandoned following adverse outcomes in a phase 2 TBI study. Other cationic peptides investigated for use in either TBI or other CNS injuries include PACAP38, APP96–110, APOEderived, and TATfused neuroprotective peptides, whereas neutral peptides such as CsA [25] and NAP have been largely discontinued as potential treatments for TBI.

 

TAT and Neuroprotective Peptides Fused to TAT

 

As the most commonly used CPP for drug delivery, TAT has been widely used in CNS studies due to its ability to traverse the BBB. The TAT peptide (TAT48–57: GRKKRRQRRR) was derived from the protein transduction domain (PTD) within the human immunodeficiency virustype 1 transactivator of transcription (HIVTAT) protein [169]. The membrane traversing properties of TAT and other cationic arginine rich peptides are attributable to peptide electrostatic interactions with negatively charged plasma membrane moieties, and sub sequent uptake by endocytic and/or nonendocytic pathways [169, 170]. Over 30 different putative neuroprotective pep tides have been fused to the TAT peptide with the vast major ity showing neuroprotection in various animal models associated with CNS disorders, including TBI, stroke, perinatal hypoxicischaemia, SCI, and pain. However, several years ago, our laboratory and others reported that the TAT peptide possessed modest neuroprotective properties in its own right [171–173].

 

Additional studies from our laboratory have demonstrated that the related cationic arginine rich CPPs, polyarginine9 (R9), and penetratin (RQIKIWFQNRRMKWKK) are even more neuroprotective than TAT [174]. Further analysis of dif ferent polyarginine and arginine rich peptides, as well as some previously described TATfused neuroprotective pep tides has led us to conclude that the mode of action of neuro protective peptides fused to arginine rich CPPs is mediated exclusively by the carrier peptide itself, with efficacy being further enhanced by the arginine content of the cargo peptide [165, 166]. On this basis, we have identified arginine content and peptide positive charge as critical factors in determining neuroprotective capacity, a finding supported by an earlier study from Ferrer Montiel et al. [175] who screened a 6mer peptide library for the ability to block glutamate evoked ionic currents in Xenopus oocytes, and later by Marshal et al. [176] who screened a range of arginine rich peptides in a NMDA retinal ganglion cell excitotoxicity model. There is evidence that other amino acid residues can also influence the efficacy of arginine rich peptides. For example, cationic lysine, highly hydrophobic tryptophan, and disulphide bondforming cysteine residues appear to increase the level of neuroprotection, while alanine appears to decrease neuroprotection [166, 176].

 

Our research increasingly supports the view that peptides rich in the cationic amino acid arginine, including poly arginine peptides and other neuroprotective peptides fused to TAT, represent a new and promising class of neuroprotective agents for the treatment of CNS disorders, including TBI [14, 165, 166]. Furthermore, based on the biological properties of arginine containing peptides, it is highly likely that this class of peptide operates through several different neuroprotective mechanisms of action, a property that is highly advantageous as neurodegenerative disorders invariably involve multiple neuro damaging processes operating in tandem. A summary of our current understanding of the neuroprotective mechanisms for arginine rich peptide is provided below.

 

arginine rich Peptide Interactions with Cell Surface Structures

 

The neuroprotective ability and efficacy of arginine rich peptides is critically reliant on their arginine content and peptide charge, which correlate with the endocytic or cellular uptake properties of the peptide [166]. These two critical properties, which are attributed to the guanidino chemical head group, are only found with the amino acid arginine [177, 178]. The guanidino head group confers a cationic charge and uniquely allows arginine residues present in arginine rich peptides to undergo bidentate hydrogen bond ing with anionic sulphate, phosphate, or carboxylate moie ties on the plasma membrane [179], and thereby induce cel lular uptake by endocytic and nonendocytic  pathways. Consistent with this critical structural feature of arginine res idues, polylysine peptides containing cationic lysine residues that can only form monodentate electrostatic bonds with sulphate, phosphate, or carboxylate moieties on the plasma membrane show poor cellular uptake and neuroprotective properties compared to polyarginine peptides [165]. Our laboratory has demonstrated that arginine rich pep tides are potent inhibitors of glutamate excitotoxic neuronal death with neuroprotective potency increasing with the number of arginine residues [165]. Based on the ability of arginine rich peptides to reduce excitotoxic calcium influx, we have hypothesised that the peptides downregulate and/or interfere with plasma membrane glutamate receptors during peptide uptake. Furthermore, we have conjectured that arginine rich peptides have the capacity to alter the function of other cell surface receptors, ion channels, and transporters during internalisation and/or interaction with the plasma membrane. For example, we have highlighted [165, 166] that many studies with arginine rich peptides, including putative B neuroprotective peptides^ fused to TAT, can interfere with or reduce the expression of cell surface ion channels and

 

receptors, including NMDAR, VR1, CaV2.2, CaV3.2, and NCX. Investigators studying the neuroprotective properties of conopeptides also noted the significance of arginine (and lysine) residues, particularly in relation to calcium channel inhibition [97]. Moreover, TAT, penetratin, and R9 have been shown to induce the endocytic internalisation of TNF recep tors and/or the EGF receptor in HeLa cells [180]. More recent ly, we have shown that exposure of cortical neurons to R12 (polyarginine12) reduces cell surface levels of the NMDA receptor subunit protein, NR2B (unpublished observation). Similarly, the interaction of the APP96–110 peptide with neg atively charged cell surface HSPGs structures, which is known to trigger endocytosis, may be necessary for the pep tide to exert a neuroprotective effect. Interestingly, HSPGs and LRPs have also been implicated in the uptake of the HIV1 TAT protein [181], which may partly explain the neuroprotec tive actions of APOEderived peptides.

 

Overall, we believe it is highly likely that arginine rich peptides have neuroprotective actions that are associated with the suppression of the toxic effects of ion channels and receptors that are activated following TBI and are involved in neurodamaging pathways, such as excitotoxicity, cell death signalling, and inflammation. Notwithstanding the above, it is also possible that the correlation of peptide uptake with neuroprotective efficacy is related to increased intracellular bioavailability of the peptide and hence increased opportunities to positively interact with intracellular targets, such as mitochondria.

 

arginine rich Peptide Interactions with Mitochondria

 

As discussed previously, mitochondrial disturbances in the form of reduced ATP synthesis, excessive ROS production, release of proapoptotic proteins, and opening of the MPTP play a major role in damaging brain tissue following TBI. arginine rich peptides are known to target mitochondria [182, 183] primarily due to their cationic property conferred by the incorporation of basic amino acid residues. Moreover, arginine residues within arginine rich peptides are thought to electrostatically interact with phosphate head groups on the negatively charged mitochondrial inner membrane phospho lipid, cardiolipin [184]. Increasing evidence suggests that arginine rich peptides have a positive effect on mitochondria in terms of maintaining mitochondrial integrity in times of stress, as occurs in the brain following TBI. By modulating the MPTP, arginine rich peptides are able to rescue cells from oxidative stress as a result of an influx of calcium. Calcium induced mitochondrial swelling is reduced [185, 186], protecting the mitochondrial cristae architecture. There is also inhibition of complex I activity and ROS production, acceler ating ATP recovery, and preventing cytochrome c release.

The SzetoSchiller (SS) peptides are a class of poly cationic peptides that have proven to be incredibly effective

 

in mitigating ROS production [187–189], a capability that may be extended to PACAP38 and APOEderived peptides. The main neuroprotective ability of the SSpeptides is pur portedly due to their action on mitochondria, protecting the organelle against oxidative damage by inhibiting ROS production, preventing swelling, cytochrome c release, and apoptosis [190, 191]. Like a number of the other peptides discussed, SSpeptides are cationic, containing both arginine and lysine residues, with the arginine residue considered particularly critical for activity. Since oxidative stress is also a product of other forms of injury, it is not surprising that SS peptides have shown to be efficacious in heart and renal dis orders [188, 192, 193]. PACAP38 reportedly had a similar effect in mice, suppressing cortical damage through antioxidant activity [125]. APOE similarly downregulates microglial activity, reducing ROS production, and resulting in protection from oxidative stress [148, 150, 194, 195]. Since the cationic state appears crucial to determining the neuroprotective efficacy of peptides in mitigating mitochondrial ROS production, it could be argued that arginine rich peptides may also provide neuroprotection via the described mechanisms with mitochondria.

 

Other Potential Neuroprotective Actions of arginine rich Peptides

 

arginine rich peptides, in particular polyarginine peptides, have been shown to inhibit the activity of proteolytic enzymes, such as matrix metalloproteinases (MMPs), the proteasome, and cathepsin C. The activation of proteases, especially matrix metalloproteinases, is known to be implicated in tissue injury following TBI [71, 196]. MMPs are responsible for the degradation of extracellular matrix proteins leading to BBB disruption and cerebral oedema after TBI [70, 71]. MMPs can be activated following cleavage by the proprotein convertase furin, of which arginine rich CPPs [197] and especially polyarginine peptides [198] are potent inhibitors. Furin is expressed in the brain and can activate MMP2, MMP3, and MMP14 (also known as MT1MMP) [ 199 ]. Furthermore, MMP14 activates MMP2, which in turn along with MMP3 activates MMP9 [200, 201]. Importantly, MMP2, MMP3, and MMP9 have all been associated with tissue injury and BBB disruption in TBI [71, 72, 202]. By extension, it would also be reasonable to associate MMP14 with the deleterious TBI cascade as it is activated in other acute brain injuries such as stroke. Therefore, it is possible that the inhibition of furin by arginine rich peptides reduces the damaging effects MMPs following TBI.

arginine rich peptides may have additional beneficial effects by inhibiting the activity of the intracellular proteasome complex in brain cells affected by TBI [203–205]. Proteasome activity is known to increase following TBI [206, 207], and is thought to be involved in accelerating the degree of axonal shearing [208]. In addition, inhibition of the ubiquitin proteasome system may rescue mitochondria from mitophagy [209] and disrupt the NFκβ pathway, thereby reducing inflammation [210].

 

Designing an arginine rich Therapeutic for TBI

 

Axonal injury is a prominent feature across all severities of TBI [211] that produces the worst outcomes in human patients, making it a vital target for therapy. Mechanical stretching of the axon acutely increases intracellular calcium, leading to delayed Wallerian degeneration [212]. Additionally, the influx of calcium has detrimental effects on mitochondria, such as opening the MPTP, ROS production, mitochondrial swelling, and cristae disruption [213, 214]. Mechanoporation has been suggested in the past as a major mechanism associated with intracellular calcium influx, but this is not supported by more recent findings [215]. Together, these insults result in a breakdown of the axon’s structural integrity, eliciting microstructural changes in the white and grey matter [216]. By targeting the plasma membrane and calcium channels/influx, and mitochondria, arginine rich peptides have great potential to counteract DAI damaging pathways.

 

To be clinically effective in TBI, arginine rich peptides need to exhibit several characteristics. Specifically, arginine rich peptides are very stable, do not require refrigeration for storage, and are easily transported (e.g. protamine sulphate). On this basis, and coupled with the effectiveness of intravenous delivery, arginine rich peptides have features that make it feasible for them to be administered in the field at the site of the TBI prior to hospital admission, thereby providing a means for early intervention to reduce brain injury and maximise patient outcomes.

 

Efficacy of Arginine Rich Peptides in Stroke Models

 

The similarities between stroke and TBI are well known [217] and have provided the basis for numerous therapeutics developed in a stroke context, and subsequently applied in the treat ment of TBI. In our laboratory, arginine rich peptides, particularly polyarginine peptides, have been shown to have highly potent neuroprotective effects in various in vitro and in vivo models of ischaemic stroke [165, 173, 174, 218]. Recently, the R18 polyarginine peptide was shown to be more effective than the highly characterised TATfused NR2B9c neuroprotective peptide (TATNR2B9c; also known as NA1) in permanent and transient middle cerebral artery occlusion models of stroke [218]. The TATNR2B9c peptide is neuroprotective in a number of rodent [219–224] and nonhuman primate [225, 226] stroke models, and it reduces ischaemic brain lesions in humans following endovascular aneurysm repair [227]. R18 contains significantly more arginine residues and has a higher cationic charge than TATNR2B9c, and we believe that this is the main reason for its enhanced neuroprotective activity compared to TATNR2B9c peptide. Based on the efficacy of R18 in experimented stroke, our intention in the near future is to assess the potential of this peptide in a rat model of TBI.

 

Conclusion

 

The clinical impact of a lack of an effective pharmacological therapy for such a devastating condition as TBI cannot be overstated. Many previous attempts at therapy have failed, and consequently, a new direction for the development of neuroprotective agents for TBI is urgently needed. Here, we have drawn attention to evidence that suggests arginine rich peptides represent a new class of neuroprotective agent and have argued that they should be considered in the context of neuroprotective therapeutic drug development for TBI. Adding to this, past studies using TAT fused and other cationic peptides as a potential neuroprotective agent for TBI have produced some promising results that warrant additional investigation. This class of peptides have established efficacy in other brain injury models such as stroke, suggesting that they may be equally efficacious in TBI. Importantly, it appears that the arginine residues are especially critical in allowing these peptides to cross the BBB and be internalised by neurons and other neural cells. Upon being internalised, these peptides appear to act via multiple mechanisms, namely, maintaining mitochondrial integrity, re ducing destruction of the brain extracellular matrix, and pre serving BBB by inhibiting MMPs. Given these findings, there is growing evidence that arginine rich peptides, including poly arginine peptides such as R18, warrant consideration as neuroprotective agents for TBI

 

What Is Peptide Therapy, and How Can It Improve Your Health? Here's Everything You Need to Know https://parade.com/1233367/kaitlin-vogel/peptide-therapy

 

WHAT ARE PEPTIDES & WHY DO YOU WANT THEM https://www.theresurgeclinic.com/blog/what-are-peptides-why-do-you-need-them

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                                                   'World's 2nd Highest IQ and His Nootropic Stack'Nootropics Expert newsletter nootropicsexpert.comRick Rosner has the 2nd highest IQ in the world. And he starts his day with a nootropic stack because he’s convinced it makes his brain work better and he’ll live longer.  The World Genius Directory records Rosner’s IQ as 192. Average IQ is around 100.  So, it seems to me that if the world’s 2nd most intelligent man uses nootropics …  … I’d like to know what he’s using.  But first, it helps to know how IQ is measured because then we’ll know which nootropics work best for boosting IQ.  Organizations like Mensa International test IQ by evaluating your:      knowledge base (crystallized intelligence)    reasoning and problem-solving ability (fluid intelligence)    using visual images to solve problems (visual intelligence)    processing speed    working memory    mathematical reasoning and problem-solving ability (quantitative intelligence)  Crystallized intelligence is all the stuff you’ve learned over a lifetime. You can use nootropics to boost long-term memory.  Fluid intelligence includes using the stuff stored in memory for problem solving and changing our behavior based on circumstances.[i] All based on working memory and processing speed. And can be boosted by using nootropics.  Rosner’s daily nootropic stack includes:      Omega-3    Metformin (natural alternative is Berberine)    Multivitamin/mineral supplement    Prebiotic    Curcumin    SAM-e    CoQ10    L-Carnosine    Acetyl-L-Carnitine (ALCAR)    Vitamin D3    Vitamin C    Vitamin E with selenium    Benfotiamine (alternative is Sulbutiamine)    N-Acetyl Cysteine (NAC)    Vitamin K    Caffeine    Phosphatidylserine (PS)    DMAE    Centrophenoxine    Piracetam or Aniracetam    Alpha GPC (Cognitex® by Life Extension)    Quercetin + bromelain    Vinpocetine    Methylene Blue[ii]  You’ll find full reviews for each of the nootropics Rosner uses by scrolling down and clicking on each in the Nootropics List here.  And these are the supplements I use and recommend which contain the many of the same nootropics Rosner uses: Performance Lab® Omega-3 Performance Lab® NutriGenesis Multi Performance Lab® Prebiotic Performance Lab® Energy (CoQ10 and ALCAR) Performance Lab® Caffeine+ (caffeine) Mind Lab Pro® v4.0 (Phosphatidylserine)  P.S.  If you are determined to boost your IQ, or simply to make this your best year yet, consider booking a Personal Consultation with me.  I've helped hundreds of people around the world and just like you both beginner and experienced deciding what nootropics will work best for you.  You will find a link to my calendar on this page: Personal Consultations  "I’m so grateful as you’ve had an impact in my life but are also empowering me to help my loved ones as well. From the bottom of my heart thank you for your knowledge, expertise and sharing". ~ Ashley Warren  P.P.S. I’ve reviewed in detail all of the most popular nootropics used in the world today in my book Head First.  The full review of each supplement includes what it is, what it does for you, why you'd want to use it, dosage recommendations, side effects and types or forms to buy.  Head First also includes two chapters on recommended nootropic stacks for anxiety, depression, ADHD, memory, longevity and more.  Get your copy of Head First for only $37 right here → Head First – The Complete Guide to Healing and Optimizing Your Brain with Nootropic Supplements  "Many thanks for all your great work. Between you and Dr. Bredesen, my wife's Alzheimer's it totally stalled" ~ Eric Fletcher  [i] Friedel E. et. al. “The effects of life stress and neural learning signals on fluid intelligence” European Archives of Psychiatry and Clinical Neuroscience 2015; 265: 35–43.[ii] Specter D. “The World's 2nd-Smartest Man Reveals The 'Brain Drugs' That He Thinks Make Him Smarter” Business Insider December 2, 2014 

 

 

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