General
Taurine was first isolated from ox bile in 1827 where it is found in high concentration. (Tiedemann F., Gmelin L., 1827: Einige neue Bestandteile der Galle des Ochsen, Ann. Physik. Chem., 9, 326-337). The bovine connection (latin name "bos taurus") clearly explains  the descriptive name "Taurine" was chosen.

Taurine, one of the lesser-known amino acids, plays several important roles in the body and is essential to newborns of many species. Along with methionine, cystine and cysteine, it is a sulfur amino acid. The taurine molecule (H2N-CH2-CH2-SO2H) is small and consists of hydrogen (H), nitrogen (N), carbon (C), sulfur (S) and oxygen (O).

Most amino acids have a L- or D-configuration, which means the molecule when put into a solution will rotate light either to the left (Levo=L) or the right (Dextro=D). Taurine, like the amino acid Glycine does not polarize light and consequently does not have an L- or D-configuration.

It occurs in the body as a free molecule and is never incorporated into muscle proteins. The taurine molecule is water soluble and thus doesn’t easily cross the mostly fatty membranes of the body’s cell but it is present in all membranes.

For a long time, taurine was considered a nonessential nutrient for humans. However, in recent years it has become clear that Taurine is a very important amino acid involved in a large number of metabolic processes and can become essential under certain circumstances. Taurine is important in the visual pathways, the brain and nervous system, cardiac function, and it is a conjugator of bile acids. Basically, its function is to facilitate the passage of sodium, potassium and possibly calcium and magnesium ions into and out of cells and to stabilize electrically the cell membranes. Dr. G. E. Gaull (1984) suggests that since human never develop a high level of cysteinsulfinic acid decarboxylase, an enzyme necessary for the formation of taurine from the amino acid cysteine, people are probably all somewhat dependent upon dietary taurine. Under certain conditions of high stress or in disease states the need for taurine probably increases. Another important function of taurine is detoxification.Taurine is required for efficent fat absorption & solubilization. Studies also showed that dietary taurine supplementation ameliorates experimental renal disease including models of refractory nephrotic syndrome and diabetic nephropathy. The benefinical effects of taurine are mediated by its antioxidant action. (Trachtman H. and Sturman J.A., 1996, Amino Acids, 11:1-13). Taurine may also have an important role in renal development. One study with rats showed protective effect of taurine on TNBS-induced inflammatory bowel disease. With all these discoveries and more on the horizon taurine research is accelerating rapidly.

Taurine is extremely well-absorbed and a good blood level is readily obtained.

Main Functions of Taurine in Mammals Bile acid conjugation Detoxification Osmoregulation Membrane Stabilization Regulation of intracellular Ca2+ Homeostasis

Males in some species seem to have higher levels of the enzymes needed for taurine synthesis than do females. In monkeys, dietary taurine deficiency has a greater effect on females than on males.

Major locations in the body: In 1984, Dr. M. Shimada and his colleagues fed radioactively tagged taurine to rats. They found that the taurine went mostly to the cortex of the kidney, the liver, pituitary, thymus and adrenal glands, the eye, basal mucous membranes, salivary glands, heart and the mucous membranes lining the digestive tract. Unfortunately, they had no data on the brain. Taurine is found in high concentrations in the eye. It is the most abundant amino acid in the retina of all species studied.

Cats and Taurine
Taurine is an essential dietary nutrient for cats because the rate of synthesis under most conditions is less than the rate of loss from the body. Although some taurine is synthesized from methionine and cysteine, the main pathway of taurine biosynthesis appears to be limited by the high flux through the desulfhydrase pathways and a low flux through the cysteinesulfinate decarboxylase rather than to a low activity of the enzyme cysteinesulfinate decarboxylase (James H. Morris & Quinton R. Rogers, Department of Physiological Sciences School of Veterinary Medicine, University of California Davis) and therefore cats are unable to use the strategy of many other mammals of switching to the glycine conjugation and conserving taurine when dietary taurine becomes scarce. Also, the loss of taurine from the body is dependent on the composition of the diet AND the method by which the diet is processed.   Dietary fiber levels also alter taurine requirements. Cats which are fed a taurine deficient diet may become blind. This blindness, usually in kittens, is due to degeneration of the light- sensitive cells in the eye. It can be reversed if it is caught early enough and the animal’s diet is supplemented with taurine. Myocardial failure based on echocardiographic evidence of dilated hearts in domestic cats has been associated with low plasma taurine concentrations. This condition is also reversible by nutritional taurine therapy if treated in time. Interestingly, the two clinical conditions (feline central retinal degeneration or FCRD and dilated cardiomyopathy) do not always occur together in the same cat, each can occur without presence of the other. Clinical signs of taurine deficiency occur only after prolonged periods of depletion (e.g. five months up to two years).

Furthermore, a number of studies have shown that immune responsiveness can be adversely affected by inappropriate taurine levels. Studies have shown, that there are changes in the host defense mechanisms in cats fed diets deficient in taurine. These host-defense mechanisms are present to protect individuals against infections with pathogenic organisms (bacteria, viruses, parasites) and against the development and spread of malignant tumors. Histological changes in the spleens of taurine-depleted cats were consistent with depletion of B-cells and T-cells and follicular center reticular cells. Lung lavage fluid from cats fed taurine-deficient diets also contained a reduced proportion of neutrophils and macrophages wich produced increased quantities of reactive oxygen intermediates associated with lower Taurine concentrations.

Taurine deficiency has also a profound adverse effect on feline pregnancy and outcome of the progeny. Such females have difficulties in maintaining their pregnancies, frequently resorbing or aborting their fetuses. Pregnancies which do reach term,  frequently result in stillborn and low-birth-weight kitttens, survivors have abnormally slow growth rates and exhibit a variety of neurological symptoms. Abnormal hind-limb development and thoracic kyphosis, which appears as a dorsoventral flattening of the thoracic cavity, may happen.

The determination of a "safe" minimal dietary requirement of taurine for cats has been particularly challenging, as loss of taurine from the body is dependent on diet composition. While minimal requirements of taurine for various physiological states of cats are not known, the metabolic basis for the requirement varying with diet is at least partially understood. Expanded dry diets containing 1200mg taurine/kg DM and canned diets containing 2500 mg taurine/kg DM would appear to meet the requirements of the majority of cats. 0

Little attention has been paid to potential effects of high taurine diets, however. One study reported adverse effects in the guinea pig comprising of fatty changes in the liver accompanied by changes in the lipid content after 14 days of oral administration of taurine (Cantafora A. Mantovani A. Masella R. Mechelli M. and Alvaro D, 1986, Effect of taurine administration on liver lipids in guinea pig, Experientia 42:407).

But a study done by John A. Sturman and Jeffrey M. Messing (Department of Developmental Biochemistry, Institute for Basic Research in Developmental Disabilities Staten Island, NY) showed no adverse effect of prolonged feeding of a high taurine diet (1% DM). The diet had no effect on appetite, food consumption, weight gain or estrus cycle of the adult females. The reproductive performance, if anything, was slightly better in the females fed the high taurine diet compared to the control (0.05% and 0.2% DM). The only significant difference between cats fed either a 0.05% or a 1% fortified diet was seen in the liver lipid composition.

Interaction, Synthesis, Excretion
Like all nutrients, taurine enhances or decreases the action of other nutrients. Monosodium glutamate (MSG) is the sodium salt of the amino acid glutamic acid. If glutamic acid supplementation is given, as is sometimes done with alcoholics, it tends to reduce taurine. MSG itself can also reduce taurine levels. The amino acids beta-alanine and beta-hypotaurine, as well as the B-vitamin pantothenic acid, may also interfere with taurine’s functions. Zinc, on the other hand, enhances taurine’s effects. Zinc deficiency and combined vitamin A and zinc deficiency are associated with an increased excretion of taurine in the urine and with depleted taurine levels in the tissues where it is normally found. Cysteine and vitamin B6 are the most critical nutrients to support the manufacture of taurine in the body of human beings or those species that are able to synthesize enough.

Taurine, as the most abundant urinary metabolite after sulfate, is formed primarily from the amino acid cysteine. Pyridoxal phosphate (active vitamin B6) is necessary for this to take place. Taurine excretion is reduced in B6 deficiency, which suggests that adequate B6 intake is necessary for the production of taurine. Some taurine may be made directly from sulfate, thus bypassing the need for cysteine. Cysteine and B6 are useful to boost taurine levels without giving taurine directly when there is concern about an irritating effect on the digestive tract. Taurine is excreted in two ways. It is readily eliminated in the urine if body taurine levels are adequate. In times of taurine depletion, however, the kidney reabsorbs taurine and does not allow it to be lost in the urine. Taurine is also excreted in the bile, where it is bound to bile acids. It probably keeps bile acids soluble, preventing gallstone formation. Interesting: When a normal nutrient balance study is done on cats consuming diets adequate in taurine, the sum of the quantity of taurine recovered in feces and urine is considerably less than the taurine ingested, even disregarding synthesis. The reason for this disparity between taurine ingested and taurine excreted must be due to microbial degradation in the gut. Anaerobic bacteria deconjugate the bile acid and degrade taurine as well as modifying the structure of the steroid moiety to produce secondary bile acids. The metabolism in the gut is therefore important in determining the taurine status of cats.

Hormonal Effects
The number of peptides with reported hormonal effects has skyrocketed. Recently, a hormone called glutataurine was discovered in the parathyroid gland of rats. Dr. L. Feuer and colleagues (1982, 1983) found that this peptide had highly selective action on adrenal hormones, which are involved in the body’s response to stress and on rat brain neurotransmitters. The nutritional basis of glandular therapies may be in the ingested peptides. Glutataurine has vitamin A-like effects. It antagonizes cortisone and thyroxine and increases the development of the thymus; increased levels of taurine have been found in hypothyroid patients. Dr. W. G. Lampson and his colleagues (1983) have found that taurine increases some of the effects of insulin. Because insulin can have hypoglycemic effects, taurine should be given with caution to patients with blood sugar problems. Taurine can inhibit the release of adrenalin from the adrenal gland. Taurine and hypotaurine have physiochemical properties similar to the sperm motility factor. A role for taurine and hypotaurine has been demonstrated in preparing the sperm of experimental animals for fertilization. Conceivably, some problems of infertility may be related to taurine deficiency.

In the mother, taurine increases blood levels of the hormone prolactin, which triggers the production and release of milk. Taurine is thus a useful supplement for nursing mothers, because it promotes lactation in the mother and better development in the infant. In a study of three groups of mouse pups on high-, normal- and low-protein diets, taurine added to the mother’s drinking water increased the pups’ survival rate by increasing the supply of milk. (The Healing Nutrients within, Braverman).

Detoxification
Due to its ability to neutralize hypochlorous acid, a potent oxidizing substance, taurine is able to attenuate DNA damage caused by aromatic amine compounds in vitro. (Kozumbo et al, Breakage and binding of DNA by reaction products of hypochlorous acid with aniline, l-…, Toxicol Appl Pharmacol, 1992, 115,107-115). Because of taurine’s unique structure, containing a sulfonic acid moiety rather than carboxylic acid, it does not form an aldehyde from hypochlorous acid, forming instead a relatively stable chloroamine compound. Hence, taurine is an antioxidant that specifically mediates the chloride ion and hypochlorous acid concentration, and protects the body from potentially toxic effects of aldehyde release. Taurine has also been reported to protect against carbon tetrachloride-induced toxicity. (ref). Another striking finding: Retinol [vitamin A] in excess amounts, i.e., unbound to retinol-binding protein, can act as a poison. When the long-term lymphoid cell lines are exposed to 10 mc M retinol, their viability decreases strikingly over a 90-minute period]. Addition of zinc improves the viability slightly. Further addition of taurine protects the cells even more. If a combination of zinc and taurine is added, there is a striking protective effect. (Gaull, 1986). If the above said suggests that taurine and zinc - both found in animal foods - provide protection from excess vitamin A - a vitamin found in full form only in animal foods - then this is certainly an interesting synergism, to say the least. Another study showed that taurine could reduce the toxic effects of copper.

Exposure to bacterial endotoxins has been suggested as one factor which can augment the magnitude of individual response to xenobiotics (ref). Circulating endotoxins of intestinal origin have been found to create a positive feedback on endotoxin translocation from the gut, stimulating increases in serum endo-toxin levels. In experimental animals, taurine was found to significantly inhibit intestinal translocation and to protect the animals from endotoxemic injury (ref). Therefore, it is possible that taurine might be able to modify factors underlying susceptibility to toxic chemicals.

Taurine content in foods
It is present in high concentration in algae (ref) and in the animal kingdom, including insects and arthropods, but is generally absent or present in traces in the bacterial and plant kingdom. In many animals, including mammals, it is one of the most abundant of the low-molecular-weight organic constituents. A 70-kg human contains up to 70 g of taurine. In the plant kingdom, taurine occurs in traces, averaging ~0.01 mc mol/g fresh wt of green tissue according to one report (ref). This is <1% of the content of the most abundant free amino acids. Taurine occurs in red algae, but not brown or green algae. Taurine has been reported at levels up to 0.046 mc mol/g, wet weight, in a few plant foods (nuts). Taurine is also present, at high levels, in insects. (Huxtable 1992). But Huxtable warns of the difficulty in assaying plant foods for taurine content. Due to the precision with which taurine must be measured, the taurine content of plant foods given by an analysis may be incorrect due to contamination of the sample with insects, insect parts, animal droppings. Huxtable summarizes that taurine concentrations in plants, when taurine is present at all, are measured in nmol (billionths of a mole), whereas in animal foods taurine is present in micro-moles (millionths of a mole), i.e., an order of magnitude difference of one thousand.

Interesting: A recent study done in 1990 by Laidlaw Stewart A. et al. came to somewhat different measures than Roe and Weston (published in Nutrient Requirements of Cats, Revised Edition, 1986).

Taurine Content of Selected Foods (mg/kg, wet weight) taken from Nutrient Requirements of Cats, Revised Edition, 1986 which in turn has adapted from Roe and Weston, 1965, Potential significance of free taurine in the diet, Nature,  205:287.
Item	Uncooked Mean	Range	Baked Mean	Range	Boiled Mean	Range
Beef muscle	362	150-472	133	96-125	60	58-63
Beef liver	192	144-270	141	68-184	73	36-95
Beef kidney	225	180-247	138	130-144	76	68-88
Lamb muscle	473	446-510	257	220-284	126	91-184
Lamb kidney	239	128-440	154	81-290	51	47-55
Pork muscle	496	394-690	219	126-390	118	91-184
Pork liver	169	110-228	85	70-100	43	30-54
Chicken muscle	337	300-380	229	140-310	82	71-180
Cod Fish	314	233-396	294	260-328	161	125-198
Oysters	698	390-1238	264	217-308	89	59-122
Clams	2400	1450-3700	1017	587-1700	446	264-794

The results were either comparable or higher than those reported by these latter authors: the differences ranged from 19% and 23% higher for uncooked beef and pork, respectively to 768% higher for cooked, dark chicken meat. These differences may, in part, be a reflection of improved detection methods, differences in sample selection methods or differences in definitions of edible portions. Roe and Weston consistently found that appreciable losses of taurine occurred when meats were baked (range of losses 7-63%). When samples were boiled, the losses of taurine were even higher, ranging from 49 to 87% of the taurine found in uncooked samples. In contrast, Laidlaw et al. were generally unable to demonstrate appreciable losses of taurine from cooked meat samples by the cooking methods they used, which generally resembled baking.

High levels of taurine were observed in some seafoods as has been reported previously. However, not all sea creatures contain large amounts of taurine. Shrimp, eg. have levels of taurine similar to that found in most meats.

Very high amounts (values are always mg/100g wet weight) were found in raw scallop (827 +/- 15 mg), raw mussel (655 +/- 72mg), raw clam (520 +/- 97mg), raw oyster (396 +/-29mg) and raw squid (356 +/- 95mg). White fish raw still contained 151 +/-23mg, cooked 172 +/- 54mg. In meat, the taurine content of dark turkey and chicken tended to be substantially greater than beef, veal and pork, whereas the three latter ones were considerably higher than light turkey or chicken. Chicken light raw 18 +/-3mg, chicken light cooked 15mg. Chicken dark raw 169mg, broiled 199mg. Turkey light raw 30mg, roasted 11mg, turkey dark raw 306 +/- 69 mg, roasted 299 +/-52 mg. Beef raw 43mg, broiled 38mg. Veal raw 40mg, broiled 47mg. Pork loin raw 81 mg, roasted 57mg. (Laidlaw Stewart A., Grosvenor M., Kopple Joel D. The Taurine Content of Common Foodstuffs, Journal of Parenteral and Enteral Nutrition, 1990, 14, No. 2, 183-188).

Here are some more values for taurine content of meat, poultry, aquatic and other products (adapted from Zhao Xi-he in Asia Pacific J Clin Nutr, 1994, 3, 131-134; Boren JC, Lochmiller RL, Leslie Jr. DM in Proc Okla Acad Sci, 1996, 76, 55-65; Pasantes-Morales H, Quesada O, Alcocer L, Sanchez-Olea R in Nutr Rep Int, 1989, 40, 793-801 and Laidlaw SA, Grosvenor M, Kopple JD, opiter cited). Values are mg/kg except for quail serum and yogurt which is mg/l.

Food	Taurine content	Food	Taurine content
Conch (Strombus gigas)	8500	Eel	910
Inkfish	6720	Pork meat	1180
Blood Clam	6170	Pork heart	2000
Shellfish	3320	Pork kidney	1200
Crab	2780	Pork liver	420
Prawn	1430	Chicken breast	260
Sole	2560	Chicken leg	3780
Crucial carp	2050	Quail muscle	95-280*
Silver carp	900	Quail serum	0,50-0,9*
Hairtail fish	560	Tuna canned	3320
Yellowfish	880	Low-fat plain yogurt	7.8
Octopus	3900	Shrimp	1150
Cat, entire body	2000	Cheetah serum	0.8-6.3
.	.	Cat serum	6-14

* Taurine content considerably declined in tissue and serum when quails where fed a high protein diet.

Cow's milk and milk products in general don't contain a lot of taurine, eggs virtually none. Taurine content in milk varies greatly beween species and depends also on time of lactation. Rassin et al. has established an interesting overview in 1978 about various taurine concentrations in milk of diverse species:

Taurine Concentration in Milk of Diverse Species
Species	Concentration mmol/l	Amount of free AA %
Gerbil	5.95	43.8
Cat	2.87	71.8
Dog	1.91	75.5
Rhesus Monkey	0.56	33.1
Mouse	0.75	25.4
Human	0.34	13.0
Chimpanzee	0.26	6.6
Rat	0.15	9.6
Sheep	0.14	14.2
Rabbit	0.14	4.2
Cow	0.01	1.8
Horse	0.03	1.6
Guinea Pig	0.56	3.4