What is Tetrahydrobiopterin (BH4)?

Tetrahydrobiopterin (BH4), also known as sapropterin (INN), plays a key role in a number of physiological processes. It is involved in the formation of neurotransmitters, heart and endothelial dysfunction, the immune response, and pain sensitivity [R].

BH4 is essential for the action of several enzymes, including ones responsible for neurotransmitter synthesis, host defense, and formation of lipids [R].

BH4 helps in the biosynthesis of the neurotransmitters serotonin, melatonin, dopamine, norepinephrine, epinephrine, and is important for the production of nitric oxide (NO).

Reduction in vascular BH₄ bioavailability is a central mechanism for the development of impaired NO-mediated microvascular (smaller blood vessels) function in a wide variety of conditions, including diabetes, hypertension, hypercholesterolemia, atherosclerosis, and aging [R].

Tetrahydrobiopterin has clinical trials on autism, ADHD, hypertension, endothelial dysfunction, and chronic kidney disease [R].

The aforementioned disorders also are associated with elevated vascular oxidative stress, and BH₄ is particularly susceptible to oxidation by peroxynitrite (ONOO⁻), a reactive oxygen species byproduct of the NO and superoxide anion (O₂⁻) reaction.

Oxidation of BH₄ results in promoting the transfer of electrons to molecular oxygen resulting in the production of Superoxide rather than Nitric Oxide.

One hypothesis is that exogenously administered BH₄ is oxidized rapidly to BH₂ upon entering circulation, diffuses into the cell as BH₂, and then is recycled back to BH₄ via the “salvage” pathway enzyme DHFR.

Potential Health Benefits of BH4

Prescription Sapropterin for PKU

Before we discuss new research, it’s important to note that BH4, as sapropterin, has only been approved to help manage phenylketonuria, or PKU.

Tetrahydrobiopterin deficiency can cause excess phenylalanine concentration, or phenylketonuria. PKU can cause severe brain damage, mental retardation, seizures, and other abnormalities [R].

Treatment with BH4 can help normalize phenylalanine levels and brain neurotransmitters and correct a deficiency of other chemicals [R, R].

Treatment of BH4 deficiencies is usually very efficient especially if initiated at an early stage. However, not everyone

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