Spotlight on Taurine

Taurine: A Unique Amino Acid

Amino acids, when strung together, make up the proteins found in our diet. The bonds connecting these building blocks of protein are broken during digestion, releasing amino acids for absorption. Once absorbed, the amino acids can be re-assembled to form proteins of different shapes, sizes and properties that the body needs to repair tissue, form muscle, manufacture enzymes, produce immune cells and perform a host of other functions.

A few amino acids are also manufactured within the body in addition to being provided by the protein foods we consume. Taurine is one example. This amino acid occurs naturally in foods such as seafood, meats, poultry and eggs - although it can also be synthesized internally from two sulfur-containing amino acids, methionine and cysteine, in the presence of vitamin B6. Unlike most proteins, however, taurine is not incorporated into proteins or enzymes but is found as a free amino acid in body tissues. The chemical structure of taurine is also unique, making it well-suited to perform its physiologic functions.

Taurine "Wears Many Hats" in the Body

Taurine's role in the body is diverse: from working with bile acids to help digest and absorb fats, to its involvement in regulating water balance by helping to transport magnesium and potassium into cells. Taurine is found throughout the body, but is concentrated in muscle, where it is thought to help regulate heart beat and muscle contraction. Taurine has antioxidant activity, and is gaining attention for its potential clinical use in ischemia-reperfusion injury - the free radical damage that can occur when blood flow is restored to oxygen deprived tissue, such as after heart valve or coronary artery bypass surgeries. Researchers are also investigating taurine's involvement in mediating the inflammatory response.

Because taurine is needed for the development of retinal and nervous tissue, dietary sources are important for premature and newborn infants who can't manufacture sufficient amounts on their own and obtain taurine through breast milk. For those with chronic kidney, liver or heart failure, taurine is often considered a "conditionally essential" amino acid, which means that under certain conditions, diseases or injury, the body may not be able to make enough taurine to meet demands.

The Role of Taurine in the Eye

Taurine plays a role in the visual system of adults: it interacts with zinc to stabilize membranes and helps make photoreceptors (rods) in the retina, resistant to injury. Some also postulate a role for antioxidant taurine in helping to maintain clarity of the eye's lens, though this remains speculative.

In addition to taurine's function in the adult eye, new research has shed some light on how this amino acid helps to initially develop rod photoreceptors - the specialized light-gathering cells that line the retina. In the early 1990s, it was found that adding taurine to immature retinal cells could get more of them to turn into rods. Yet it was unclear what was making the cells susceptible to taurine's instructions. New findings from Harvard suggest that taurine works its transforming effects through neurotransmitter receptors, with similar findings reported by UC San Francisco researchers. According to the Harvard team, this discovery provides information that someday could lead to new methods of restoring or replacing these delicate cells, which are lost in various retinal diseases and decline with age.

Bibliography

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