Taurine

Taurine, or 2-aminoethanesulfonic acid, is an organic acid. It is also a major constituent of bile, and can be found in lower amounts in the tissues of many animals including humans. ^[1][2] Taurine is a derivative of the sulfur-containing (sulfhydryl) amino acid, cysteine. Taurine is the only known naturally occurring sulfonic acid.^[3]

Taurine is named after the Latin taurus, which means bull or ox, as it was first isolated from ox bile in 1827 by Austrian scientists Friedrich Tiedemann and Leopold Gmelin. It is often called an amino acid, even in scientific literature,^[4][5][6] but as it lacks a carboxyl group it is not strictly an amino acid.^[7] It does contain a sulfonate group and may be called an amino sulfonic acid. Small polypeptides have been identified which contain taurine but to date no aminoacyl tRNA synthetase has been identified as specifically recognizing taurine and capable of incorporating it onto a tRNA.^[8]

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Physiological roles

Taurine is conjugated via its amino terminal group with its chenodeoxycholic acid and cholic acid to form the bile salts sodium taurochenodeoxycholate and sodium taurocholate (see bile). The low pKa (1.5) of taurine's sulfonic acid group ensures that this moiety is negatively charged in the pH ranges normally found in the intestinal tract and thus improves the surfactant properties of the cholic acid conjugate. Taurine has also been implicated in a wide array of other physiological phenomena including inhibitory neurotransmission,^[9] long-term potentiation in the striatum/hippocampus, membrane stabilization, feedback inhibition of neutrophil/macrophage respiratory bursts, adipose tissue regulation, and calcium homeostasis.

Prematurely born infants who lack the enzymes needed to convert cystathionine to cysteine may become deficient in taurine. Thus, taurine is a dietary essential nutrient in these individuals and is often added to many infant formulas as a measure of prudence. There is also evidence that taurine in adult humans reduces blood pressure.^[10]

Obese mice demonstrate reduced blood levels of taurine, which may promote further weight gain, and taurine supplementation prevented obesity in mice fed a high-fat, low-taurine diet.^[11] Recent studies have also shown that taurine can influence (and possibly reverse) defects in nerve blood flow, motor nerve conduction velocity, and nerve sensory thresholds in experimental diabetic neuropathic rats.^[12][13] Taurine levels were found to be significantly lower in vegans than in a control group on a standard American diet. Plasma taurine was 78% of control values, and urinary taurine 29%.^[14]

According to some animal studies, taurine produced an anxiolytic-like effect in mice and may act as a modulator or anti-anxiety agent in the central nervous system.^[15]

In recent years, taurine has become a common ingredient in energy drinks. Taurine is often used in combination with bodybuilding supplements such as creatine and anabolic steroids, partly due to recent findings in mice that taurine alleviates muscle fatigue in strenuous workouts and raises exercise capacity.^[16] Taurine is also used in some contact lens solutions.^{[citation needed]}

Taurine has also been shown in diabetic rats to decrease weight and decrease blood sugar.^[17]

Taurine and cats

Taurine is essential for cat health, as a cat cannot synthesize the compound. The absence of taurine causes a cat's retina to slowly degenerate, causing eye problems and (eventually) irreversible blindness. This condition is called central retinal degeneration (CRD).^[18][19] In addition, taurine deficiency can cause feline dilated cardiomyopathy, and supplementation can reverse left ventricular systolic dysfunction. However, the vegetarian lioness Little Tyke survived for years in captivity without imbibing the normal required dose of taurine.^[20][21] Taurine is now a requirement of the AAFCO and any dry or wet food product labeled approved by the AAFCO should have a minimum of 0.1% taurine.^[22]

Synthesis and Production

In 1993, approximately 5,000–6,000 t of taurine (synthetic and natural) were produced; 50% for pet food manufacture, 50% in pharmaceutical applications.^[3] Synthetic taurine is obtained from isethionic acid (2-hydroxyethanesulfonic acid), which in turn is obtained from the reaction of ethylene oxide with aqueous sodium bisulfite.^[23] Another approach is the reaction of aziridine with sulfurous acid. This leads directly to taurine.

Energy drinks

Taurine is an ingredient in many energy drinks and energy products.

Despite its presence in many energy drinks, taurine has not been shown to be energy-giving. A study of mice hereditarily unable to transport taurine suggests that it is needed for proper maintenance and functioning of skeletal muscles.^[24]

References