Taurine in human nutrition

Dr. Yousef Elshrek

Taurine • Definition :Taurine is an oxidized sulfur-containing

amine occurring conjugated in the bile, usually as cholyltaurine (a bile salt, the taurine conjugate of cholic acid) or chenodeoxycholyltaurine (A bile salt formed in the liver by conjugation of chenodeoxycholate* with taurine, usually as the sodium salt. It acts as detergent to solubilize fats in the small intestine and is

itself absorbed. It is used as a cholagogue* and choleretic**); it may also be a central nervous system neurotransmitter or neuromodulatora derivative of the amino acid cysteine.

• It is present in bile in combination with cholic acid.

• It is used in the synthesis of bile salts. ______________________________________

• *An agent that promotes the flow of bile into the intestine, especially as a result of contraction of the gallbladder.

• **An agent, usually a drug, that stimulates the liver to increase output of bile.

• 0r It is a colorless crystalline substance formed by the hydrolysis of taurocholic acid and found in the fluids of the muscles and lungs of many animals

• 0r It is an amino acid often found in nerve and muscle tissues.

• Has been reported as an adjuvant treatment for congestive heart failure, viral hepatitis, alcoholism, cataracts, cerebrovascular accidents, diabetes, gallbladder conditions, high blood pressure, multiple sclerosis, psoriasis, and seizure disorders.

• No known precautions.

• Also called L-taurine.

Taurine structure • Taurine is a derivative of cysteine, an amino acid which

contains a thiol group.

• Taurine is one of the few known naturally occurring sulfonic acids.

• In the strict sense, it is not an amino acid, as it lacks a carboxyl group, but it is often called one, even in scientific literature

• 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 into a tRNA

Taurine, or 2-aminoethanesulfonic acid

Taurine Biosynthesis

• Within the body, taurine is synthesized within the pancreas through a pathway in which cysteine is oxidized to create cysteine sulphuric acid.

• Positioned behind the stomach, the pancreas is a gland which manufactures hormones and digestive enzymes.

• In adult males, taurine is also produced within the testes (testicles)

Taurine synthesis and physiological roles in mammalian cells

Role of taurine in neural cell volume regulation

• Release of taurine and other amino acids was monitored from cultured astrocytes and neurons under isomotic and hyposmotic conditions as well as during exposure of the cells to 56 mM KCl.

• The release was correlated with swelling, as determined by the 3-O-methylglucose method.

• It was shown that release of taurine from astrocytes cultured from cerebral cortex and cerebellum of rats and mice regardless of the stimulating agent is a consequence of cell swelling. The release is unrelated to depolarization.

• This conclusion is also valid regarding release of taurine from cerebellar granule neurons.

• Comparison of release of different amino acids showed that not only .

• On the other hand, glutamine is not released under these conditions.

• Studies of uptake of taurine under isosmotic and hyposmotic conditions as well as the dependency of the release on sodium and temperature strongly suggest that the release process is mediated by diffusional forces and not by a reversal of the high-affinity carrier.

• It is proposed that taurine may play an important role as an osmotically active substance in the brain involved in cell volume regulation.

• Taurine but also to some extent glutamate, aspartate, and glycine are released during cell swelling

• Nowadays, you will often find taurine added to creatine or amino acid preparations in bodybuilding supplements for a heightened effect. The best time to consume these combinations might be 30 minutes before training and again immediately after.

Taurine and neural cell damage • The inhibitory amino acid taurine is an osmoregulator and

neuromodulator, also exerting neuroprotective actions in neural tissue.

• The involvement of taurine in neuron-damaging conditions, including hypoxia, hypoglycemia, ischemia, oxidative stress, and the presence of free radicals, metabolic poisons and an excess of ammonia.

• The brain concentration of taurine is increased in several models of ischemic injury in vivo.

• Cell-damaging conditions which perturb the oxidative metabolism needed for active transport across cell membranes generally reduce taurine uptake in vitro, immature brain tissue being more tolerant to the lack of oxygen.

• In ischemia non saturable diffusion increases considerably.

• Both basal and K+-stimulated release of taurine in the hippocampus in vitro is markedly enhanced under cell-damaging conditions, ischemia, free radicals and metabolic poisons being the most potent.

• Hypoxia, hypoglycemia, ischemia, free radicals and oxidative stress also increase the initial basal release of taurine in cerebellar granule neurons, while the release is only moderately enhanced in hypoxia and ischemia in cerebral cortical astrocytes.

• The taurine release induced by ischemia is for the most part Ca2+-independent , a Ca2+ -dependent mechanism being discernible only in hippocampal slices from developing mice.

• Moreover, a considerable portion of hippocampal taurine release in ischemia is mediated by the reversal of Na+-dependent transporters.

• The enhanced release in adults may comprise a swelling-induced component through Cl− channels, which is not discernible in developing mice.

• Excitotoxic concentrations of glutamate also potentiate taurine release in mouse hippocampal slices.

• The ability of ionotropic glutamate receptor agonists to evoke taurine release varies under different cell-damaging conditions, the N-methyl-D-aspartate-evoked release being clearly receptor-mediated in ischemia.

• Neurotoxic ammonia has been shown to provoke taurine release from different brain preparations, indicating that the ammonia-induced release may modify neuronal excitability in hyperammonic conditions.

• Taurine released simultaneously with an excess of excitatory amino acids in the hippocampus under ischemic and other neuron-damaging conditions may constitute an important protective mechanism against excitotoxicity, counteracting the harmful effects which lead to neuronal death.

• The release of taurine may prevent excitation from reaching neurotoxic levels.

Role of the Liver in Regulation of Body Cysteine and Taurine Levels

• The first-pass metabolism of dietary sulfur amino acids by the liver and the robust up regulation of hepatic cysteine dioxygenase activity in response to an increase in dietary protein or sulfur amino acid level gives the liver a primary role in the removal of excess cysteine and in the synthesis of taurine.

• Hepatic taurine synthesis is largely restricted by the low availability of cysteinesulfinate as substrate for cysteinesulfinate decarboxylase, and taurine production is increased when cysteinesulfinate increases in response to an increase in the hepatic cysteine concentration and the associated increase in cysteine dioxygenase activity.

• The up regulation of cysteine dioxygenase in the presence of cysteine is a consequence of diminished ubiquitination of cysteine dioxygenase and a slower rate of degradation by the 26S proteasome.

Taurine and human nutrition

• Taurine (2-aminoethane sulphonic acid), a ubiquitous β-

amino acid not incorporated into proteins but found either

free or in some simple peptides is considered as a

conditionally semi-essential amino acid in man.

• Once thought of as no more than an innocuous end

product of cysteine metabolism, taurine has in recent

years generated much interest due to research findings

indicating a role in numerous physiological processes.

• These roles are varied and include membrane

stabilization, detoxification, antioxidation,

osmoregulation, maintenance of calcium homeostasis,

and stimulation of glycolysis and glycogenesis.

• Intracellular and plasma taurine levels are high and although cellular taurine is tightly regulated, plasma levels are known to decrease in response to surgical injury and numerous pathological conditions including cancer, trauma and sepsis.

• Decreased plasma concentrations can be restored with supplementary taurine. Although the importance of taurine as a physiological agent with pharmacological properties is now recognized, the potential advantages of dietary supplementation with taurine have not as yet been fully exploited and this is an area which could prove to be of benefit to the patient.

• Because the role of elemental sulfur in human nutrition has not been studied extensively, it is the purpose to emphasize the importance of this element in humans and discuss the therapeutic applications of sulfur compounds in medicine.

• Sulfur is the sixth most abundant macromineral in breast milk and the third most abundant mineral based on percentage of total body weight

• The sulfur-containing amino acids (SAAs) are methionine, cysteine, cystine, homocysteine, homocystine, and taurine.

• Dietary SAA analysis and protein supplementation may be indicated for vegan athletes, children, or patients with HIV, because of an increased risk for SAA deficiency in these groups.

• Methylsulfonylmethane (MSM), a volatile component in the sulfur cycle, is another source of sulfur found in the human diet.

• Increases in serum sulfate may explain some of the therapeutic effects of MSM, DMSO, and glucosamine sulfate. Organic sulfur, as SAAs, can be used to increase synthesis of S- adenosylmethionine (SAMe), glutathione

• (GSH), taurine, and N- acetylcysteine (NAC).

• MSM may be effective for the treatment of allergy, pain syndromes, athletic injuries, and bladder disorders.

• Other sulfur compounds such as SAMe, dimethylsulfoxide (DMSO), taurine, glucosamine or chondroitin sulfate, and reduced glutathione may also have clinical applications in the treatment of a number of conditions such as depression, fibromyalgia, arthritis, interstitial cystitis, athletic injuries, congestive heart failure, diabetes, cancer, and AIDS.

• The low toxicological profiles of these sulfur compounds, combined with promising therapeutic effects, warrant continued human clinical trails

Taurine in Pediatric Nutrition

• Taurine was long considered an end product of the metabolism of the sulfur-containing amino acids, methionine and cyst(e)ine.

• Its only clearly recognized biochemical role had been as a substrate in the conjugation of bile acids. Taurine is found free in millimolar concentrations in animal tissues, particularly those that are excitable, rich in membranes, and generate oxidants.

• Various lines of evidence suggest one major nutritional role as protecting cell membranes by attenuating toxic substances and/or by acting as an osmoregulator.

• The totality of evidence suggests that taurine is nonessential in the rodent, it is an essential amino acid in the cat, and it is conditionally essential in man and monkey.

• from the diet of a conditionally essential nutrient does not produce immediate deficiency disease but, in the long term, can cause problems.

• Taurine is now added to many infant formulas as a measure of prudence to provide improved nourishment with the same margin of safety for its newly identified physiologic functions as that found in human milk.

• Such supplementation can be justified by the finding of improved fat absorption in preterm infants and in children with cystic fibrosis, as well as by salutary effects on auditory brainstem-evoked responses in preterm infants.

• Experimental findings in animal models and in human cell models provide further justification for taurine supplementation of infant formulas.

Taurine Sources

• Taurine occurs naturally in food, especially in seafood 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

• Natural sources of taurine come from a variety of food items. taurine levels in vegans

• Foods rich in taurine include:

1. eggs

2. fish

3. meat

4. milk

5. seafood

• As foods rich in taurine include meat and fish, levels of taurine in vegans can be lower than non-vegans who include meat and fish in their die

• One benefit of taurine is using taurine supplements to raise