Taurine

Discovery and name

Taurine was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin. Another German scientist Von H. Demarcay first used its common chemical name Taurine in 1838, derived from the Latin (cognate to Ancient Greek , grc) meaning bull or ox. It was subsequently identified in human bile in 1846 by Edmund Ronalds.

In nature

Taurine is widely distributed in nature, particularly in animal tissues. Moreover, it is abundant in nature, including in animal organs, and further, as substrates in the biosynthesis of bile salts. Taurine concentrations in human cells may derive from at least three processes:

• biosynthesis from the sulfur amino acids (e.g., cysteine);
• active uptake by a possible taurine transporter; and
• the extent of its release from cells by a "volume-sensitive leak pathway".

It is not an essential human dietary nutrient, resulting in the absence of taurine from compounds having a Reference Daily Intake. Its role in human physiology is unknown.

Taurine is a major constituent of bile, and can be found in the large intestine. Its concentrations in land plants are low or undetectable, but up to a substantial wet weight has been found in algae.

Chemical and biochemical features

Taurine exists as a zwitterion , as verified by X-ray crystallography. The sulfonic acid has a low pKa ensuring that it is fully ionized to the sulfonate at the pHs found in the intestinal tract.

Biosynthesis

Among the diverse pathways by which natural taurine can be biosynthesized, its pathways in the human liver are from cysteine and/or methionine. With regard to the route from cysteine: mammalian taurine synthesis occurs in the liver via the cysteine sulfinic acid pathway. In this pathway, cysteine is first oxidized to its sulfinic acid, catalyzed by the enzyme cysteine dioxygenase. Cysteine sulfinic acid, in turn, is decarboxylated by sulfinoalanine decarboxylase to form hypotaurine. Hypotaurine is enzymatically oxidized to yield taurine by hypotaurine dehydrogenase.

Taurine is also produced by the transsulfuration pathway, which converts homocysteine into cystathionine. The cystathionine is then converted to hypotaurine by the sequential action of three enzymes: cystathionine gamma-lyase, cysteine dioxygenase, and cysteine sulfinic acid decarboxylase. Hypotaurine is then oxidized to taurine as described above.

A pathway for taurine biosynthesis from serine and sulfate is reported in microalgae, developing chicken embryos, and chick liver. Serine dehydratase converts serine to 2-aminoacrylate, which is converted to cysteic acid by 3-phosphoadenylyl sulfate:2-aminoacrylate C-sulfotransferase. Cysteic acid is converted to taurine by cysteine sulfinic acid decarboxylase.

Chemical synthesis

Synthetic taurine is obtained by the ammonolysis of isethionic acid (2-hydroxyethanesulfonic acid), which in turn is obtained from the reaction of ethylene oxide with aqueous sodium bisulfite. A direct approach involves the reaction of aziridine with sulfurous acid.

In 1993, about of taurine were produced for commercial purposes: 50% for pet food and 50% in pharmaceutical applications.

In the laboratory, taurine can be produced by alkylation of ammonia with bromoethanesulfonate salts.

In food

Taurine occurs naturally in fish and meat. The mean daily intake from omnivore diets was determined to be around (range ), and to be low or negligible from a vegan diet. Typical taurine consumption in the American diet is about per day.

Taurine is partially destroyed by heat in processes such as baking and boiling. This is a concern for cat food, as cats have a dietary requirement for taurine and can easily become deficient. Either raw feeding or supplementing taurine can satisfy this requirement.

Both lysine and taurine can mask the metallic flavor of potassium chloride, a salt substitute.

Breast milk

Taurine is present in breast milk, and has been added to many infant formulas as a measure of prudence since the early 1980s. However, this practice has never been rigorously studied, and as such it has yet to be proven to be necessary, or even beneficial.

Energy drinks and dietary supplements

Taurine is an ingredient in some energy drinks in amounts of per serving.

Research

Taurine is not regarded as an essential human dietary nutrient, and has not been assigned recommended intake levels. High-quality clinical studies to determine possible effects of taurine in the body or following dietary supplementation are absent from the literature. Preliminary human studies on the possible effects of taurine supplementation have been inadequate due to low subject numbers, inconsistent designs, and variable doses. In one review of preliminary human studies, use of taurine as a supplement had positive effects on biomarkers of metabolic syndrome.

Safety and toxicity

According to the European Food Safety Authority, taurine is "considered to be a skin and eye irritant and skin sensitiser, and to be hazardous if inhaled"; it may be safe to consume up to 6 grams of taurine per day. Other sources indicate that taurine is safe for supplemental intake in normal healthy adults at up to 3 grams per day.

A 2008 review found no documented reports of negative or positive health effects associated with the amount of taurine used in energy drinks, concluding, "The amounts of guarana, taurine, and ginseng found in popular energy drinks are far below the amounts expected to deliver either therapeutic benefits or adverse events".

Animal dietary requirement

Cats

Cats lack the enzyme sulfinoalanine decarboxylase to produce taurine and must therefore acquire it from their diet. A taurine deficiency in cats can lead to retinal degeneration and eventually blindness ‒ a condition known as central retinal degeneration, as well as hair loss and tooth decay. Other effects of a diet lacking in taurine are dilated cardiomyopathy and reproductive failure in female cats.

Decreased plasma taurine concentration has been demonstrated to be associated with feline dilated cardiomyopathy. Unlike central retinal degeneration, the heart condition is reversible with supplementation.

Taurine is now a requirement of the Association of American Feed Control Officials (AAFCO) and any dry or wet food product labeled approved by the AAFCO should have a minimum of 0.1% taurine in dry food and 0.2% in wet food. Studies suggest the amino acid should be supplied at of bodyweight per day for domestic cats.

Other mammals

A number of other mammals also have a requirement for taurine. While the majority of dogs can synthesize taurine, case reports have described a singular American cocker spaniel, 19 Newfoundland dogs, and a family of golden retrievers suffering from taurine deficiency treatable with supplementation. Foxes on fur farms also appear to require dietary taurine. The rhesus, cebus and cynomolgus monkeys each require taurine at least in infancy. The giant anteater also requires taurine.

Birds

Taurine appears to be essential for the development of passerine birds. Many passerines seek out taurine-rich spiders to feed their young, particularly just after hatching. Researchers compared the behaviours and development of birds fed a taurine-supplemented diet to a control diet and found the juveniles fed taurine-rich diets as neonates were much larger risk takers and more adept at spatial learning tasks. Under natural conditions, each blue tit nestling receive of taurine per day from parents.

Taurine can be synthesized by chickens. Supplementation has no effect on chickens raised under adequate lab conditions, but seems to help with growth under stresses such as heat and dense housing.

Fish

Species of fish, mostly carnivorous ones, show reduced growth and survival when the fish-based feed in their food is replaced with soy meal or feather meal. Taurine has been identified as the factor responsible for this phenomenon; supplementation of taurine to plant-based fish feed reverses these effects. Future aquaculture is expected to use more of these more environmentally-friendly protein sources, so supplementation would become more important.

The need of taurine in fish is conditional, differing by species and growth stage. The olive flounder, for example, has lower capacity to synthesize taurine compared to the rainbow trout. Juvenile fish are less efficient at taurine biosyntheis due to reduced cysteine sulfinate decarboxylase levels.

Derivatives

• Taurine is used in the preparation of the anthelmintic drug, Totabin
• Taurolidine
• Taurocholic acid and tauroselcholic acid
• Tauromustine
• 5-Taurinomethyluridine and 5-taurinomethyl-2-thiouridine are modified uridines in (human) mitochondrial tRNA.
• Tauryl is the functional group attaching at the sulfur, 2-aminoethylsulfonyl.
• Taurino is the functional group attaching at the nitrogen, 2-sulfoethylamino.
• Thiotaurine
• Peroxytaurine which is a degradation product by both superoxide and heat degradation.

References

References

1. "Oxford Learner's Dictionaries -- Taurine". Oxford University Press.
2. "Taurine".
3. (September 2003). "Taurine: new implications for an old amino acid". FEMS Microbiology Letters.
4. (2013). "Lehninger Principles of Biochemistry". W.H. Freeman.
5. (2013). "Fundamentals of Biochemistry: Life at the Molecular Level". John Wiley & Sons.
6. Hendler, Sheldon Saul. (1990). "The Doctors' Vitamin and Mineral Encyclopedia". Simon & Schuster.
7. (2021). "Lehninger Principles of Biochemistry". W.H. Freeman.
8. (15 May 2023). "Taurine". Drugs.com.
9. (1827). "Einige neue Bestandtheile der Galle des Ochsen". Annalen der Physik.
10. (January 1992). "Physiological actions of taurine". Physiological Reviews.
11. (1838). "Ueber die natur der Galle". Journal für Praktische Chemie.
12. (2012). "Review: taurine: a "very essential" amino acid". Molecular Vision.
13. (2019). "Bringing Together Academic and Industrial Chemistry: Edmund Ronalds' Contribution". Substantia.
14. (2004). "Regulation of the Cellular Content of the Organic Osmolyte Taurine in Mammalian Cells". Neurochemical Research.
15. (12 November 2012). "Taurine: A "Very Essential" Amino Acid". Molecular Vision.
16. (25 February 2022). "Daily Value on the New Nutrition and Supplement Facts Labels". US Food and Drug Administration.
17. (1986). "Occurrence of Taurine in Plants". Agricultural and Biological Chemistry.
18. (2014). "Amino acid content of selected plant, algae and insect species: a search for alternative protein sources for use in pet foods". Journal of Nutritional Science.
19. (2000). "Taurine". Acta Crystallographica Section C.
20. (October 1980). "13C nuclear magnetic resonance study of the complexation of calcium by taurine". Journal of Inorganic Biochemistry.
21. (25 May 2024). "Taurine". PubChem, US National Library of Medicine.
22. (September 1962). "Oxidation of hypotaurine in rat liver". Biochimica et Biophysica Acta.
23. (2012). "Review: taurine: a "very essential" amino acid". Molecular Vision.
24. (1955). "The Utilization of Sulfate Sulfur for the Synthesis of Taurine in the Developing Chick Embryo". The Journal of Biological Chemistry.
25. (1972-03-01). "The Synthesis of Taurine from Sulfate III. Further Evidence for the Enzymatic Pathway in Chick Liver". Proceedings of the Society for Experimental Biology and Medicine.
26. (2000). "Sulfonic Acids, Aliphatic".
27. (2000). "Kirk-Othmer Encyclopedia of Chemical Technology". John Wiley & Sons, Inc.
28. (1938). "Taurine". Organic Syntheses.
29. (June 2006). "The sulfur-containing amino acids: an overview". The Journal of Nutrition.
30. (1999-01-21). "Opinion on Caffeine, Taurine and D-Glucurono –γ-Lactone as constituents of so-called 'energy' drinks". Directorate-General Health and Consumers, European Commission, European Union.
31. (October 1987). "Rhodopsin topography and rod-mediated function in cats with the retinal degeneration of taurine deficiency". Experimental Eye Research.
32. (Aug 2003). "Taurine concentrations in animal feed ingredients; cooking influences taurine content". Journal of Animal Physiology and Animal Nutrition.
33. (January 2014). "Monosodium glutamate, disodium inosinate, disodium guanylate, lysine and taurine improve the sensory quality of fermented cooked sausages with 50% and 75% replacement of NaCl with KCl". Meat Science.
34. (November 2004). "Taurine in neonatal nutrition – revisited". Archives of Disease in Childhood. Fetal and Neonatal Edition.
35. (May 2021). "Taurine in sports and exercise". Journal of the International Society of Sports Nutrition.
36. (2024-05-16). "Taurine reduces the risk for metabolic syndrome: a systematic review and meta-analysis of randomized controlled trials". Nutrition & Diabetes.
37. EFSA Panel on Additives and Products or Substances used in Animal Feed. (2012). "Scientific Opinion on the safety and efficacy of taurine as a feed additive for all animal species". EFSA Journal.
38. (April 2008). "Risk assessment for the amino acids taurine, L-glutamine and L-arginine". Regulatory Toxicology and Pharmacology.
39. (2008). "Safety issues associated with commercially available energy drinks". Journal of the American Pharmacists Association.
40. (May 1978). "Taurine: an essential nutrient for the cat". The Journal of Nutrition.
41. (1975). "Retinal Degeneration Associated with Taurine Deficiency in the Cat". Science.
42. (1986). "Nutrient Requirements of Cats, Revised Edition". Board On Agriculture.
43. (May 1975). "Retinal degeneration associated with taurine deficiency in the cat". Science.
44. (1990). "Taurine: an essential nutrient for cats". Journal of Small Animal Practice.
45. (August 1987). "Myocardial failure in cats associated with low plasma taurine: a reversible cardiomyopathy". Science.
46. "AAFCO Cat Food Nutrient Profiles".
47. (1982). "The taurine requirement of the adult cat". Journal of Small Animal Practice.
48. (January 2014). "Clinical significance of taurine". Amino Acids.
49. (October 2007). "Parental prey selection affects risk-taking behaviour and spatial learning in avian offspring". Proceedings. Biological Sciences.
50. (February 2020). "Taurine in poultry nutrition". Animal Feed Science and Technology.
51. (February 2015). "Taurine: a critical nutrient for future fish feeds". Aquaculture.
52. (November 2020). "Roles of dietary taurine in fish nutrition". Marine Life Science & Technology.
53. (December 2002). "Taurine as a constituent of mitochondrial tRNAs: new insights into the functions of taurine and human mitochondrial diseases". The EMBO Journal.
54. (2007). "Systematic nomenclature of organic, organometallic and coordination chemistry". EPFL Press.