Hidehiko Yokogoshi

Dietary Taurine Enhances Cholesterol Degradation and Reduces Serum and Liver Cholesterol Concentrations in Rats Fed a High-Cholesterol Diet

Summary.u2002The effect of taurine on hypercholesterolemia induced by feeding a high-cholesterol (HC) diet (10u2009g/kg) to rats was examined. When taurine was supplemented to HC for 2u2009wk, serum total cholesterol significantly decreased and serum HDL-cholesterol increased compared with the HC diet group. In the hypercholesterolemic rats fed the HC diet, the excretion of fecal bile acids and hepatic cholesterol 7α-hydroxylase (CYP7A1) activity and its mRNA level increased significantly, and the supplementation of taurine further enhanced these indexes, indicating an increase in cholesterol degradation. Agarose gel electrophoresis revealed that, in hypercholesterolemic rats fed the HC diet, the serum level of the heavier VLDL increased significantly, but taurine repressed this increase and normalized this pattern. Significant correlations were observed between the time-dependent increase of CYP7A1 gene expression and the decrease of blood cholesterol concentration in rats fed the HC diet supplemented with taurine. These results suggest that the hypocholesterolemic effects of taurine observed in the hypocholesterolemic rats fed the HC diet were mainly due to the enhancement of cholesterol degradation and the excretion of bile acid.

Hypotensive effect of γ-glutamylmethylamide in spontaneously hypertensive rats.

The effect of gamma-glutamylmethylamide(GMA), one of the components of green tea extract, on the blood pressure in spontaneously hypertensive rats (SHR) was investigated. The effect of glutamic acid and r-glutamylethylamide (theanine), which is structurally similar to GMA, was also examined. When SHR were injected with glutamic acid (2000mg/kg), the blood pressure was not altered. The same dose of theanine decreased it significantly. GMA administration to SHR reduced the blood pressure significantly, and its degree of hypotensive action was more effective than that by theanine administration.

ANTIHYPERCHOLESTEROLEMIC ACTION OF TAURINE ON STREPTOZOTOCIN-DIABETIC RATS OR ON RATS FED A HIGH CHOLESTEROL DIET

Taurine is especially abundant in excitable tissues, membrane-rich cells, and tissues producing oxidants and toxic substances including brain, retina, myocardium, skeletal muscle, liver, platelets, and leucocytes. Suggested biological actions of taurine include cell membrane stabilization, antioxidation, detoxification, osmoregulation, neuromodulation, and brain-retinal development. It also has antiarrhythmic, hypotensive, anticonvulsant, inotropic and thermoregulatory actions2, 4, 6.

Amplified Effect of Taurine on PCB-Induced Hypercholesterolemia in Rats

The physiological functions of taurine such as membrane-stabilization, antioxidation, detoxification, osmoregulation, neuromodulation and brain-retinal development have been investigated in detail. Currently, we have been examining the hypercholesterolemic action of taurine in several conditions. In a previous study we reported that feeding a normal diet with taurine supplementation did not change the serum cholesterol levels, but in animals fed a high cholesterol diet, in which serum cholesterol significantly increased, taurine supplementation significantly reduced the cholesterol level11,19. This hypocholesterolemic action of taurine is explained by an increase in the activity of cholesterol 7 α-hydroxylase and also by the enhancement of fecal steroid excretion. Also, when the serum lipoprotein distribution was monitored by agarose-gel electrophoresis, the heavier very low density lipoprotein (VLDL), namely β-VLDL, significantly increased by feeding a high cholesterol diet. However, taurine repressed this increase and normalized the lipoprotein pattern. Many other investigators also examined the mechanism of hypercholesterolemia induced by feeding a high cholesterol diet, and demonstrated the elevation of both low density lipoprotein (LDL) and VLDL-cholesterol10,19.

Dietary Taurine Changes Ascorbic Acid Metabolism and Cholesterol Metabolism In Rats Fed Diets Containing Polychlorinated Biphenyls

The effect of dietary taurine on ascorbic acid metabolism and hepatic drug-metabolizing enzymes wasinvestigated in rats fed diets containing 0.02% PCB. The rats fed the PCB containing diets showed greater liver weight, and greater activities of drug metabolizing enzymes in the liver than control rats. In PCB-fed rats, urinary ascorbic acid excretion was enhanced, and serum cholesterol concentration (especially HDL-cholesterol) was significantly elevated compared with those in normal rats. Dietary taurine potentiated the increases of urinary excretion of ascorbic acid and the rise in the levels of cytochrome P-450 which were induced by PCB. On the other hand, the supplementation of taurine to normal diet did not alter these parameters. These results suggested that taurine might enhance the hepatic drug-metabolizing systems, leading consequently to the stimulation of the ascorbic acid metabolism in rats fed PCB-containingdiet.