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A Review on the Biomedical Importance of Taurine

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MK Vanitha et al. Volume 3 (3), 2015, Page-680-686
680
IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
CODEN (USA)-IJPRUR, e-ISSN: 2348-6465
Review Article
A Review on the Biomedical Importance of Taurine
M K Vanitha1, *, K Baskaran1, K Periyasamy1, D Saravanan1, A Ilakkia1, S Selvaraj1, R Venkateswari1, B
Revathi Mani1, P Anandakumar2, D Sakthisekaran1
1Department of Medical Biochemistry, Dr ALMPGIBMS, University of Madras, Taramani campus, Chennai-113, India.
2Department of Biomedical Sciences, College of Health Sciences, Arsi University, Asella, Ethiopia.
A RT I C LE IN FO A B S T R A C T
_______________________________________________________________________________
1. INTRODUCTION
Taurine originated from the Latin word taurus, which
means bull or ox, as it was first isolated from ox bile in
1827 by Austrian scientists Friedrich Tiedemann and
Leopold Gmelin.1It is often considered an amino acid
in scientific literatures. It is a vital nutrient for cats, and
probably also for primates, since it is essential for the
development and survival of neural cell.2In healthy
humans, dietary foodstuffs are the main sources of
taurine. High concentrations of taurine are found in
animal sources whilst undetectable in vegetables.3
International Journal of Pharma Research and Health Sciences
Available online at www.pharmahealthsciences.net
Received: 22 Jun 2015
Accepted: 03 July 2015
Objectives: To briefly outline the effects of taurine on different organs, in order to
elucidate the biomedical importance of taurine. Summary: Taurine is a sulfur-
containing amino acid that is found in mammalian tissues. Taurine has different
biological and physiological functions. It is a component of bile acids, which are
used to help absorb fats and fat-soluble vitamins. It also helps regulate the
heartbeat, maintain cell membrane stability and prevent brain cell over -activity. In
addition, taurine chloramine, an endogenous product derived from activated
neutrophils, has been reported to suppress obesity-induced oxidative stress and
inflammation in adipocytes. Conclusion: This review is an attempt to reveal the
biomedical importance of taurine including its effect on heart, lung, kidney, bone,
fetal tissue, retinal photoceptors, oxidative stress and cancer
Key words:Taurine, endothelium, lung, kidney, antioxidant
Corresponding author *
M.K.Vanitha, Research Scholar, Department of Medical
Biochemistry, University of Madras, Taramani Campus, Chennai-
600 113.
E-mail: vanithakalappan@gmail.com
MK Vanitha et al. Volume 3 (3), 2015, Page-680-686
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IIIIIIIII© International Journal of Pharma Research and Health Sciences. All rights reserved
Fig 1: Structure of taurine
Since vegetarians have no dietary intake of taurine and
often eat low sulphur amino acid diets, plasma
concentrations are lower in vegetarians.
Methionine and cysteine are precursors of taurine,
however synthesis ability varies widely amongst
species, the maximal human synthesis rate is unknown.
The average daily synthesis in adults ranges between
0.4 - 1.0 mmol (50-125 mg) 4under stress the synthesis
capacity may be impaired; therewith some authors
consider taurine as a conditionally essential amino
acid, whereas for others it remains non essential. Fish
is a good source of taurine and tests for taurine content
for a variety of fish have been conducted.
Fig 2: Biosynthesis of taurine
2. CHEMISTRY OF TAURINE
The molecular formula of taurine is C2H7NO3S and its
molecular weight is 125.15. It has a pKa of 1.5 (at 25
°C) and a melting point of 300 °C (decomposition) and
shows a bulk density of 0.650.75g/cm3 and a density
of approximately 1.7g/cm3. It is soluble in water (10 g
dissolves in 100 mL at 25 °C) and insoluble in ethanol,
ethyl ether and acetone. The pH of a 5 % solution in
water is 4.1 5.6. Taurine is a white crystalline powder
that is almost odourless but with a slightly acidic taste.
It contains by specification at least 98.0 % taurine in
dried substance. Taurine is a monobasic acid that has
unique physical constants compared to other
neuroactive amino acids. The uniqueness of taurine is
mainly due to the functional group containing sulfur,
the sulfonic group, unlike the carboxylic group typical
of all the other natural amino acids. This difference
may provide the rationale behind the unique biological
nature of taurine which is not shared with other
neuroactive amino acids. With its sulfonate group, it is
a stronger acid (pKa 1.5) than glycine, aspartic acid, β-
alanine, and γ-aminobutyric acid (GABA). Similarly,
having a pKb value of 8.82, it is less basic than GABA,
β-alanine and glycine. Its solubility in water is
10.48g/100mL at 258°C, which is lower than that of β-
alanine, GABA or glycine.
Table 1: Properties of taurine
Molecular formula
C2H7NO3S
Molecular mass
125.14 g/mol
Density
1.734 g/cm3
Melting point
305.110C
3. BIOMEDICAL IMPORTANCE OF
TAURINE
3.1 Taurine in Fetal Development and Neonatal
Growth
The human fetus has no ability to synthesize taurine,
but considerably high levels of taurine have been
recorded, and this may be due to a very efficient
placental role of taurine in disease prevention. The
amount of taurine was found to be very high in human
breast milk compared to cow’s milk, on which a large
portion of infants are fed, and this may be due to the
high concentration of taurine in placenta. Thus, taurine
is now added to many infant formulas to provide
improved nourishment.5Several types of organ
dysfunction develop from abnormalities of taurine
levels in growing children. In neonatal cardiomyocytes
(as in adult ones), taurine functions as an organic
osmolyte. During pregnancy, taurine accumulates in
the maternal tissues, from where it is periodically
released to the fetus via the placenta. In infants, taurine
is acquired through the mother’s milk. This is the stage
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when taurine accumulates more in fetal and neonatal
brain. A low maternal taurine concentration will lead to
low fetal taurine concentration.6
3.2 Taurine and the Central Nervous System (CNS)
Taurine is the most abundant amino acid in the brain
after glutamate, and it is found in all cell types in the
CNS. A high concentration of taurine occurs in the
developing brain, but with maturity, its levels fall to
30%.7Taurine is extensively involved in neurological
activities, including protection, modulation of neural
excitability, maintenance of cerebellar functions and
modulation of motor behavior through interaction with
dopaminergic, adrenergic, serotonergic and cholinergic
receptors and through glutamate.8Free radicals are
particularly detrimental to brain tissue where there is a
high concentration of lipids, suitable target for
oxidation. Taurine is now being explored for its
capacity to protect tissues against oxidative stress. In
cerebellar neurons, stimulation by excitatory agents
was effectively countered by taurine. While taurine
may not directly decrease the levels of free radicals, it
does increase cell viability. This may become an
important alternate protective mechanism against free
radical damage to brain cells.
3.3 Taurine and the Liver
Liver synthesizes bile, which is a mixture of bile acids,
salts, bilirubin, cholesterol and fatty acids, stored in the
gallbladder. It is also responsible for the detoxification
of harmful substances, but only if available in
sufficient quantities. The bile acids act as detergents to
solubilize or emulsify food into digestible components.
This detergent action is due to the presence of both
lipophilic and hydrophilic ends in the bile acids. The
hydrophilic regions include sulfonates or carboxylate
backbones. Mammals mainly use taurine and, to a
lesser extent glycine, as the major amino acids that
conjugate with bile acids to form biliary salts. Among
the tauro-conjugates, taurocholic acid (TC),
taurodeoxycholic acid (TDC), taurolithocholic acid
(TLC), and taurocheno- deoxycholic acid (TCDC), can
act as cholagogues (agents that promote the flow of
bile into the intestine) or choleretics (agents that
stimulate the liver to increase production of bile). The
ratio between tauro-conjugates and glycocholate in
humans is about 3: 1 and this ratio is adversely affected
in cases of low taurine supply. In the absence of TC,
bile salts can precipitate and form gallstones.9
3.4 Taurine and Hypercholesterolemia
In blood, cholesterol is carried in low density
lipoproteins (LDL) and high density lipoproteins
(HDL). Elevated LDL levels are implicated in a range
of heart and vascular diseases, including myocardial
infarction (heart attack) and atherosclerosis (clogging
of the arteries). Taurine can attenuate the increased
levels in total and LDL cholesterol in animals
consuming a high fat, high cholesterol diet.10 High fat
diets produce hypercholesterolemia, atherosclerosis,
and accumulation of lipids on the aortic valve of the
heart. Dietary taurine supplements are known to be
beneficial in situations when the body cholesterol
status is high, as well as normal. In particular, it has
been demonstrated that taurine is capable of reducing
plasma lipid concentration and visceral fat in diabetic
rats as well as in obese humans.11
3.5 Taurine and Occupational Environmental Liver
Damage
Exposure to toxic chemicals, which is a common
hazard for industrial workers, has been linked to birth
defects, sterility, headache, chronic fatigue, arthritic-
like inflammation and many other symptoms. These
chemicals have a deleterious effect on the liver and
taurine is able to moderate the extent and severity of
their side. Furthermore, it reduces the number of cancer
antigen-positive hepatocytes and in several cases of
chemical exposure, taurine also protected against DNA
damage.12
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3.6 Taurine and Diabetes
Type II diabetes mellitus is one of the most common
human diseases and its prevalence is constantly
growing. This pathology is characterized by the
reduced sensitivity of the cellular targets, mainly
adipose and muscle cells, to insulin stimulation. Such
alteration can lead to insulin resistance, hyper-
insulinemia, hyperglycemia, and several other
metabolic dysfunctions. Lifestyle, dietary habits, and
environment can influence the appearance of
diabetes.13 Taurine supplements administered to
patients with type 2 diabetes were proven to be
beneficial. Also, taurine alleviates clinical
complications of diabetes, having beneficial effects on
nephropathy and retinopathy. In animal models of
experimental insulin resistance, it has been
demonstrated that the metabolic alterations associated
with diabetes are ameliorated by taurine
administration.14
3.7 Taurine and the Cardiovascular System
Taurine concentration is found to be high in the
mammalian heart. The maintenance of cardiac taurine
content is governed by a series of processes, which
include transport, accumulation, binding, release, as
well as metabolism. The availability of taurine in
cardiac tissue is generally dependent on the transport
process, because of its limited ability to be effectively
synthesized in the cardiac tissue. Taurine deficiency
may possibly be linked to cardiomyopathy, as it has
been well reported in cats. Furthermore, conclusive
evidence of the relationship between taurine and heart
health was provided by studies with transgenic mice
knocked out of its taurine transporter.15
3.8 Taurine and Endothelial Dysfunction
Endothelial dysfunction is common among
cardiovascular diseases and diabetes and it is known as
one of the primary events in the development of
atherosclerosis and diabetic angiopathies.16 Taurine has
been shown to be a protector of endothelial structure
and function after exposure to inflammatory cells, their
mediators, or other chemicals. Treatment of activated
macrophages with taurine inhibits the generation of
NO and other inflammatory mediators, which is
present in high amounts in inflammatory cells, seems
to be uniquely capable of modifying homeostasis in
both target and receptor cells through antioxidant
calcium flux and the osmo regulatory pathway. Finally,
taurine was proven to protect endothelial cells from
damage induced by hyperglycemia and oxidized
LDL.17
3.9 Taurine and Lung Function
The depletion of taurine is particularly harmful to
pulmonary tissue. Alveolar macrophages, which reside
on the surface of lung alveoli, ingest inhaled
particulates to clear the alveolar spaces. However,
alveolar macrophages, much like the general
macrophages, become more susceptible to ROS and
more pro-inflammatory when deprived of the
antioxidant protective capacity that taurine provides.
Fibrosis may also result from toxic chemical exposure.
There are numerous factors responsible for toxin-
induced damage to lung cells and tissue in animal
models of induced interstitial pulmonary fibrosis. In
several cases, the administration of taurine, niacin or a
combination of both, yielded promising results, and
can reverse increased lung lipid peroxidation.
Furthermore, the ability to scavenge ROS and to
stabilize cell membranes contributed to the suppression
of lung collagen accumulation and oxidative stress
damage. Asthma is a chronic disease characterized by
bronchial obstruction and airway hyper reactivity with
neutrophil accumulation. There is increasing evidence
that excessive production of ROS along with defective
endogenous antioxidant defense mechanisms may be
responsible for asthma. In an animal model of allergic
asthma, taurine content was found to be reduced and
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oral treatment with taurine produced anti-inflammatory
responses. Similar effects have also been demonstrated
in humans.18
3.10 Taurine and The Kidney
In the kidneys, taurine is found at a high concentration,
which is regulated by the reabsorption at the
modulating proximal tubule according to its dietary
intake. In alleviating the diabetic nephropathy, taurine
serves as an osmolyte, an endogenous antioxidant and
an inhibitor of phosphokinase C (PKC) in mesangial
cells. The beneficial effects of taurine may be due to its
well-known anti-oxidative, anti-inflammatory and anti-
apoptotic activities.19
3.11 Taurine and Retinal Photoreceptor Activity
The common eye disease cataract demonstrates the
importance of lens condition. It is speculated that
cataract formation may be largely due to the oxidation
of protein in the lens. Consequently, a lack of
antioxidants could be a major factor in the
development of cataracts. Since taurine acts as an
antioxidant directly, it prevents changes in the levels of
glutathione, ATP and insoluble proteins, molecular
factors that predispose to cataract formation.20
Furthermore, taurine plays a critical role in the
structure and function of the photoreceptors,
specifically rods, which are responsible for seeing in
both low illumination and night conditions. The
promotional effect of taurine in cellular regeneration is
compromised with drugs that induce the activation of
PKC or phosphate inhibitors.21 Retinitis pigmentosa
(RP) is characterized by visual field loss and night
blindness. Nutritional factors are now recognized as
important factors in the reversal of RP. Experimental
finding suggests that RP patients recover their visual
capacities with the addition of nutrients, including
taurine, which has been found to be beneficial. Taurine
and zinc interact with each other to influence the
development of the retinal structure and function in the
eye. Both molecules promote the healthy oscillatory
potentials necessary for vision. Deficiency of taurine
has been identified as the cause of all these diseases
and clearly demonstrates its vital role in vision.22
3.12 Taurine in Bone Tissue Formation And
Inhibition of Bone Loss
Bone tissue contains cells and the extracellular matrix,
which is composed of collagen fibers and
noncollagenous proteins. In bone tissue, taurine is
found in high concentration, similar to that found in the
liver and kidneys. This taurine-bone interaction is one
of the latest added to its long list of actions.23 In bones,
taurine acts as a double agent. It is involved in both
bone formation and inhibition of bone loss. In addition
to these two major actions, taurine has beneficial
effects in wound healing and bone repair.
3.13 Anticancer Activity of Taurine
Taurine has been found that taurine has radio
protective properties and anti-mutagenic effect,
reducing nucleic acid damage. The chemo-preventive
activity of taurine and, in particular, 1-(2-chloroethyl)-
3(2-dimethyl sulfony) ethyl-11-nitrosourea derivative
(e.g., tauromustine), have been used against colon and
hepatic cancers. In hepato-carcinogenesis, the degree
of membrane damage and the fall in glutathione
function were reduced when oral taurine was given
prior to exposure to carcinogens. These findings
suggest that taurine, by inhibiting lipo-peroxidation
and preserving the glutathione antioxidant system,
offers protection against membrane breakdown.24
Recombinant interleukin-2 immunotherapy is utilized
as a therapeutic approach in certain types of cancers.
However, it may produce a cytotoxic effect on both
tumor cells and healthy vascular endothelial cells. In
such cancer therapy programs, taurine reduces
interleukin endothelial cell cytotoxicity without
compromising the antitumor activity of the
immunotherapy. In addition, when taurine is used in
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conjunction with interleukin, it actually increases the
tumor cytotoxicity. For the treatment of intra peritoneal
(abdominal) tumors, researchers have studied a taurine
derivative, taurolidine, as both an alternative and an
adjunct to heparin, a standard substance used to
prolong the clotting time of blood. In certain cancers,
the amino acid profile yields data about the disease that
is useful to better assess the therapeutic approach.
Colorectal cancer patients exhibit a characteristic
amino acid profile with significantly lower intracellular
levels of taurine, glutamic acid, methionine, and
ornithine and elevated levels of valine. Likewise,
squamous cell carcinoma of the head and neck exhibit
a profile that is marked by decreased taurine.25
4. CONCLUSION
This review highlights the divergent effects of taurine
on different tissues. Thus, further studies on taurine
could exemplify the beneficial role of taurine in human
health and disease.
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Conflict of Interest: None
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Taurine (2-Amino ethane sulfonic acid) is a naturally occurring sulphur amino acid, found in several mammalian and non mammalian tissues. Taurine is believed to be involved in several life processes. Its deficiency is a cause of concern in developing abnormalities in many organs like eye, heart, kidney, brain etc during developmental stages and even later on. Taurine contents are believed to be high in bone tissue mostly due to accumulation by transport, as taurine synthesis in bone is yet to be recorded. A strong stimulating role of taurine in bone matrix formation and collagen synthesis has been observed in osteoblast like UMR-106 cells; together with this, inhibition of bone resorption and osteoclast formation by taurine has also been identified, making taurine an agent for preventing inflammatory bone resorption in periodontal diseases. Thus, taurine acts as a double beneficial agent; stimulating bone formation and inhibiting bone loss. Along with these actions in bone, it also has beneficial action in radio protection, wound healing, bone gain through exercise and many others. Taurine has the potential to replace bisphosphonates; suitable taurine analogues may further accelerate this. An extensive analytical study of taurine contents in both the stages of bone formation and bone loss may make taurine as a single marker of bone metabolism. However taurine-bone interaction needs more deep study towards regulation of taurine, interaction with ions, and many other pharmacological and physiological actions. An in depth clinical study of its actions in bone may make taurine an ideal agent for desired effect; yet, all these recorded taurine - bone interactions, are milestones for future research.
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Taurine (2-aminoethanesulfonic acid) is known to protect hepatocyte injury induced by hydrazine or carbon tetrachloride. We investigated whether cellular polyamines are involved in the protective mechanism of taurine in the hepatocyte injury caused by hydrazine or carbon tetrachloride. The agents decreased cellular polyamine concentrations, but the treatment with taurine prevented this decrease. The protection of taurine against hepatic injury was not observed in hepatocytes treated with alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase which is a key enzyme in polyamine biosynthesis. The protection of taurine was recovered by the addition of polyamines to DFMO-treated hepatocytes. These results suggest that cellular polyamines play an important role in the protection of taurine in hydrazine or carbon tetrachloride-induced hepatocyte injury.
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Gestational diabetes compromises fetal development and induces a diabetogenic effect in the offspring, including the development of gestational diabetes and the transmission of the effect to the next generation. Changes are not limited to glucose and insulin metabolism, and appear to be modulated by alterations at the hypothalamo-hypophyseal axis. In the present work, serum concentrations are given for the non-protein amino-acids taurine and gamma-aminobutyric acid (GABA), both neurotransmitters essential for normal brain development, and for the endogenous neuroprotector carnosine, a known anti-oxydans. Taurine levels are significantly below normal values in mildly diabetic mothers, in their fetal and adult offspring, virgin and pregnant, and in the fetuses of these pregnant offspring. GABA and carnosine levels are at the limit of detection in the diabetic mothers and their offspring at every stage. It is concluded that the low taurine, GABA and carnosine levels in diabetic mothers and their fetuses might compromise the normal structural and functional development of the fetal brain. When adult, these offspring present a deficiency of the circulating levels of these neurotransmitters involved in the hypothalamo-hypophyseal regulation of insulin secretion. This might contribute to the development of impaired glucose tolerance and gestational diabetes, thereby transmitting the effect to the next generation.