Taurine is a sulfur-containing amino acid that is found in high concentrations in the heart, the brain, the skeletal muscle, and the retina, and it is the most abundant free amino acid in the human body (with a total body pool of approximately 70g, most of which is in the heart and the skeletal muscle). Taurine is not incorporated into proteins — it exists as a free amino acid in the cytoplasm and in the mitochondria, where it performs multiple physiological functions, including the regulation of the calcium homeostasis (as an intrinsic calcium modulator in the cardiac and the skeletal muscle), the regulation of the cardiac contractility (through the modulation of the calcium channels and of the calcium-sensitive enzymes), the antioxidant defence (through the direct neutralisation of the hypochlorous acid and through the support of the glutathione synthesis), and the osmoregulation (through the adjustment of the intracellular osmolarity in response to the metabolic stress). The heart has the highest concentration of taurine of any organ (approximately 20-30 micromol/g wet weight), and this high concentration is maintained by the active transport of taurine into the cardiac myocytes by the taurine transporter (TAUT), which is regulated by the osmotic pressure, by the beta-adrenergic stimulation, and by the thyroid hormone. Without adequate taurine, the cardiac calcium homeostasis is disrupted, the cardiac contractility is impaired, and the cardiac arrhythmias and the cardiomyopathy develop — these are the most sensitive and most clinically significant manifestations of the taurine deficiency.
Taurine and the Calcium Homeostasis
Taurine is an intrinsic modulator of the calcium homeostasis in the cardiac myocytes — it regulates the calcium influx through the L-type and T-type calcium channels, the calcium release from the sarcoplasmic reticulum (via the ryanodine receptors and the IP3 receptors), and the calcium extrusion by the sodium-calcium exchanger (NCX) and by the calcium-ATPase. This calcium-modulating effect of taurine is one of the most important mechanisms of its antiarrhythmic and cardioprotective effects — by stabilising the cardiac myocyte calcium dynamics, taurine prevents the calcium overload that is the primary trigger of the cardiac arrhythmias and of the myocardial cell death during the ischaemia-reperfusion injury. The taurine depletion in the cardiac myocytes (which occurs in the heart failure, in the chronic tachycardia, and in the chronic ischaemia) sensitises the cardiac myocytes to the calcium overload and predisposes to the arrhythmias and to the contractile dysfunction — and the taurine supplementation reverses these effects by restoring the normal calcium homeostasis and the normal contractile function.
The clinical importance of taurine for the cardiac function is underscored by the observation that the taurine supplementation improves the cardiac function in patients with the congestive heart failure (CHF) — multiple small RCTs have demonstrated that taurine supplementation at 1-3g daily improves the exercise tolerance, reduces the symptoms of the CHF (dyspnoea, fatigue, peripheral oedema), and improves the left ventricular ejection fraction in patients with the CHF. The proposed mechanism of this benefit involves the restoration of the normal calcium homeostasis in the cardiac myocytes, the reduction of the oxidative stress in the myocardium, and the improvement of the cardiac contractile efficiency. These findings are consistent with the traditional use of the taurine-rich seafood diets (particularly in Japan, where the fish and the shellfish are dietary staples) for the prevention of the heart disease.
Taurine and the Neurological Function
Taurine is also abundant in the brain, where it functions as an inhibitory neurotransmitter and as an osmoregulator. In the brain, taurine activates the GABA-A receptors (making it an inhibitory neuromodulator that reduces the neuronal excitability), and it调节s the intracellular osmolarity in response to the metabolic stress and to the neuronal activity. The taurine deficiency in the brain produces the hyperexcitability, the seizures, and the epilepsy — which are the most dramatic manifestations of the taurine deficiency in the central nervous system. The taurine supplementation has been studied for its effects on the epilepsy — with some clinical evidence supporting its use as an adjunctive therapy for the treatment of the drug-resistant epilepsy, particularly in children.
Practical Application
For general taurine supplementation, the evidence-based approach is to supplement with 1-3g of taurine daily (as the free amino acid form, which is well absorbed and well tolerated). The taurine is found in high concentrations in the meat, the fish, and the shellfish, and the typical dietary intake of taurine is 40-400mg daily (with much higher intake in people who eat fish regularly). The taurine supplementation is particularly important for people with the heart failure, with the chronic liver disease (where the taurine synthesis is impaired), and with the epilepsy. For comprehensive cardiac and neurological support, taurine pairs well with the magnesium (which is a natural calcium channel blocker and which has complementary effects on the cardiac and the neurological function), with the omega-3 fatty acids (which have anti-inflammatory and cardioprotective effects), and with the CoQ10 (which supports the mitochondrial energy production in the cardiac and the skeletal muscle).
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