Taurine (), or 2-aminoethanesulfonic acid, is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
that is widely distributed in animal tissues. It is a major constituent of
bile
Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bi ...
and can be found in the
large intestine, and accounts for up to 0.1% of total human body weight. It is named after
Latin
Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
(
cognate
In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical ef ...
to
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
ταῦρος, ''taûros'') meaning
bull or
ox, as it was first isolated from ox bile in 1827 by German scientists
Friedrich Tiedemann and
Leopold Gmelin. It was discovered in human bile in 1846 by
Edmund Ronalds.
It has many biological roles, such as conjugation of
bile acids,
antioxidation,
osmoregulation,
membrane stabilization, and modulation of
calcium signaling. It is essential for
cardiovascular function, and development and function of
skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...
, the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
, and the
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...
.
It is an unusual example of a naturally occurring
sulfonic acid
In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is k ...
.
Chemical and biochemical features
Taurine exists as a
zwitterion , as verified by
X-ray crystallography
X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
. The sulfonic acid has a low
p''K''a ensuring that it is fully ionized to the sulfonate at the
pHs found in the intestinal tract.
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
Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite in fact is not a real compound, but a mixture of salts that dissolve in water to give solutio ...
. A direct approach involves the reaction of
aziridine
Aziridine is an organic compound consisting of the three-membered heterocycle . It is a colorless, toxic, volatile liquid that is of significant practical interest. Aziridine was discovered in 1888 by the chemist Siegmund Gabriel. Its derivat ...
with
sulfurous acid
Sulfurous acid (also sulfuric(IV) acid, sulphurous acid (UK), sulphuric(IV) acid (UK)) is the chemical compound with the formula . There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase ...
.
In 1993, about 5,000–6,000 tonnes of taurine were produced for commercial purposes: 50% for pet food and 50% in pharmaceutical applications.
As of 2010, China alone has more than 40 manufacturers of taurine. Most of these enterprises employ the
ethanolamine method to produce a total annual production of about 3,000 tonnes.
In the laboratory taurine can be produced by alkylation of ammonia with bromoethanesulfonate salts.
Biosynthesis
Taurine is naturally derived from
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, some ...
. Mammalian taurine synthesis occurs in the pancreas via the
cysteine sulfinic acid pathway. In this pathway,
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, some ...
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
In enzymology, a hypotaurine dehydrogenase () is an enzyme that catalyzes the chemical reaction
:hypotaurine + H2O + NAD+ \rightleftharpoons taurine + NADH + H+
The 3 substrates of this enzyme are hypotaurine, H2O, and NAD+, whereas its 3 prod ...
.
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.
Nutritional significance
Taurine occurs naturally in fish and meat.
The mean daily intake from omnivore diets was determined to be around 58 mg (range from 9 to 372 mg) and to be low or negligible from a strict vegan diet. In another study, taurine intake was estimated to be generally less than 200 mg/day, even in individuals eating a high-meat diet. According to a third study, taurine consumption was estimated to vary between 40 and 400 mg/day.
The availability of taurine is affected depending on how the food is prepared,
raw diets retaining the most taurine, and baking or boiling resulting in the greatest taurine loss.
Taurine levels were found to be significantly lower in
vegan
Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. ...
s than in a control group on a standard American diet. Plasma taurine was 78% of control values, and urinary taurine was 29%.
Prematurely born infants are believed to lack the enzymes needed to convert
cystathionine to
cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile.
When present as a deprotonated catalytic residue, some ...
, and may, therefore, become deficient in taurine. 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 workout supplements
Taurine is an ingredient in some
energy drinks. Many contain 1000 mg per serving, and some as much as 2000 mg.
It is also found in various
dietary supplements aimed towards athletes.
Physiological functions
Taurine is essential for cardiovascular function and development and function of skeletal muscle, the retina, and the central nervous system.
It is a biosynthetic precursor to the bile salts sodium
taurochenodeoxycholate and
sodium taurocholate.
Taurine functions as an antioxidant, suppressing the toxicity of
hypochlorite
In chemistry, hypochlorite is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite (household bleach) and calcium hypochlorite (a component of ...
and
hypobromite produced physiologically. Taurine reacts with these halogenating agents to form N-chloro- and N-bromotaurine, which are less toxic than their precursors hypohalides.
Role in liver function
Taurine has been shown to reduce the secretion of
apolipoprotein B100 and lipids in
HepG2
Hep G2 (or HepG2) is a human liver cancer cell line.
Hep G2 is an immortal cell line which was derived in 1975 from the liver tissue of a 15-year-old Caucasian male from Argentina with a well-differentiated hepatocellular carcinoma. T ...
cells.
Role in the muscular system
Taurine is necessary for normal skeletal muscle functioning.
Mice with a genetic taurine deficiency had a nearly complete depletion of skeletal and cardiac muscle taurine levels and a reduction of more than 80% of exercise capacity compared to control mice.
Taurine can influence (and possibly reverse) defects in nerve blood flow, motor nerve conduction velocity, and nerve sensory thresholds in experimental diabetic neuropathic rats.
Pharmacology
Taurine crosses the
blood–brain barrier and has been implicated in a wide array of physiological phenomena including inhibitory
neurotransmission,
long-term potentiation in the
striatum
The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives gluta ...
/
hippocampus
The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic syste ...
,
membrane stabilization feedback inhibition of
neutrophil
Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...
/
macrophage
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...
respiratory burst,
adipose tissue regulation and possible prevention of obesity,
calcium
homeostasis
In biology, homeostasis ( British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
, recovery from
osmotic shock, protection against glutamate
excitotoxicity, and prevention of epileptic seizures.
According to the single study on human subjects, daily administration of 1.5 g of taurine had no significant effect on insulin secretion or insulin sensitivity.
There is evidence that taurine may exert a beneficial effect in preventing diabetes-associated
microangiopathy and tubulointerstitial injury in
diabetic nephropathy.
According to animal studies, taurine produces an
anxiolytic effect and may act as a modulator or antianxiety agent in the central nervous system by activating the
glycine receptor
The glycine receptor (abbreviated as GlyR or GLR) is the receptor of the amino acid neurotransmitter glycine. GlyR is an ionotropic receptor that produces its effects through chloride current. It is one of the most widely distributed inhibitor ...
.
Taurine acts as a glycation inhibitor. Taurine-treated diabetic rats had a decrease in the formation of
advanced glycation end products (AGEs) and AGEs content. The
United States Department of Agriculture
The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...
has found a link between cataract development and lower levels of vitamin B
6, folate, and taurine in the diets of the elderly.
Animal physiology and nutrition
In diabetic rats, taurine supplementation slightly reduced abdominal body fat while improving
glucose tolerance.
Taurine is effective in removing fatty liver deposits in rats, preventing liver disease, and reducing
cirrhosis
Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...
in tested animals.
Likewise, taurine administration to diabetic
rabbit
Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit sp ...
s resulted in 30% decrease in serum glucose levels.
Cats
The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members o ...
lack the enzymatic machinery (
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. Other effects of a diet lacking in this essential amino acid are dilated cardiomyopathy and reproductive failure in females.
The absence of taurine causes a cat's
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
to slowly degenerate, causing eye problems and (eventually) irreversible blindness – a condition known as
central retinal degeneration (CRD), as well as hair loss and tooth decay. Decreased plasma taurine concentration has been demonstrated to be associated with
feline dilated cardiomyopathy. Unlike CRD, the 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 10 mg/kg of bodyweight/day for domestic cats.
Taurine appears essential to the development of
passerine
A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by th ...
birds. Many passerines seek out taurine-rich
spider
Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...
s 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.
Taurine has been used in some
cryopreservation mixes for animal
artificial insemination.
Safety and toxicity
A substantial increase in the plasma concentration of
growth hormone
Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...
was reported in some epileptic patients during taurine tolerance testing (oral dose of 50 mg per kg body mass per day), suggesting a potential to stimulate the
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...
and to modify neuroendocrine function. A 1966 study found an indication that taurine (2 g/day) has some function in the maintenance and possibly in the induction of
psoriasis
Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to comple ...
.
[ Three later studies failed to support that finding.
It may also be necessary to take into consideration that absorption of taurine from beverages may be more rapid than from foods.][
Taurine has an observed safe level of supplemental intake in normal healthy adults at up to 3 g/day.] Even so, a study by the European Food Safety Authority found no adverse effects for up to 1,000 mg of taurine per kilogram of body weight per day.
A review published in 2008 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
Guaraná ( from the Portuguese ''guaraná'' ), ''Paullinia cupana'', syns. ''P. crysan, P. sorbilis'') is a climbing plant in the family Sapindaceae, native to the Amazon basin and especially common in Brazil. Guaraná has large leaves and cl ...
, taurine, and ginseng found in popular energy drinks are far below the amounts expected to deliver either therapeutic benefits or adverse events".
Other uses
In cosmetics and contact lens solutions
Since the 2000s cosmetic compositions containing taurine have been introduced, possibly due to its antifibrotic properties. It has been shown to prevent the damaging effects of TGFB1 to hair follicles. It also helps to maintain skin hydration.
Taurine is also used in some contact lens solutions.
Derivatives
*Taurine is used in the preparation of the anthelmintic drug netobimin (Totabin).
* Taurolidine
* Taurocholic acid and tauroselcholic acid
*Tauromustine
*5-Taurinomethyluridine and 5-taurinomethyl-2-thiouridine are modified uridines in (human) mitochondrial tRNA
Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ...
.
*Tauryl is the functional group attaching at the sulfur, 2-aminoethylsulfonyl.
*Taurino is the functional group attaching at the nitrogen, 2-sulfoethylamino.
See also
* Homotaurine (tramiprosate), precursor to acamprosate
* Taurates, a substance group.
References
External links
Mass Spectrum of Taurine
Taurine bound to proteins
in the PDB
{{Authority control
Amines
Sulfonic acids
Glycine receptor agonists
Inhibitory amino acids