Dietary protein and atherosclerosis

Effects of puffer (Sphoeroides rubripes) supplementation on disruption of antioxidant defense systems in ethanol-treated rats

We investigated the effects of puffer (Sphoeroides rubripes) supplementation on antioxidant metabolism in ethanol-treated rats. Sprague-Dawley rats were randomly assigned into 4 groups of 7 rats each and fed (1) an AIN-93G diet (NC), (2) 25% ethanol (E), (3) 25% ethanol and an AIN-93G diet containing 1% puffer flesh (E+F), or (4) 25% ethanol and an AIN-93G diet containing 1% puffer skin (E+S) for 5 wk. At the end of the experimental period, the rats were sacrificed and their blood and organs were collected. To evaluate the effect of puffer supplementation, lipid-soluble antioxidant vitamin and conjugated diene (CD) levels, DNA damage, and mRNA expression of heme oxygenase-1 (HO-1) were assessed. Animals that were fed ethanol showed reduced plasma levels of lipid-soluble antioxidant vitamin and significantly increased levels of lipid peroxides, DNA damage, and HO-1 expression. Dietary supplementation with puffer conferred an antioxidant effect by significantly increasing the levels of γ-tocopherol, a lipid-soluble antioxidant vitamin, and by significantly decreasing the plasma levels of CD, DNA damage, and HO-1 expression. These results suggest that consumption of puffer improves the antioxidant status of ethanol-treated rats.

Digestibilities of casein and soya-bean protein in relation to their effects on serum cholesterol in rabbits

Diets containing isolated soya-bean protein induce lower levels of serum cholesterol in animals than diets containing casein. Experiments were conducted to investigate whether differences in digestibility of the proteins might explain this effect. At pH 8 with pancreatic enzymes or intestinal peptidase, soya-bean protein was hydrolysed in vitro much less rapidly than casein. However, with pepsin (EC 3.4.23.1) at acid pH, soya-bean protein was hydrolysed more rapidly than casein. These differences in digestibility may be due to pH-dependent changes in solubility of the proteins. Casein and soya-bean protein were most soluble at alkaline and acid pH respectively. Heat treatment of the proteins resulted in lower solubilities and digestibilities. Sonication of soya-bean protein at pH 7.8 increased solubility but only slightly raised digestibility. When fed to rabbits, enzymically hydrolysed soya-bean protein induced a 2.3-fold higher concentration of serum cholesterol than did intact soya-bean protein. The hypocholesterolaemic effect of soya-bean protein may be partly attributable to its low solubility and digestibility at alkaline pH.

Effects of dietary proteins on the regulation of liver lipoprotein receptors in rats

Female rats fed a 1.2% cholesterol diet with animal proteins (casein) develop a significant hypercholesterolemia, with a marked increase of very low density lipoprotein (VLDL)-associated cholesterol. Substitution of soy proteins for casein in the diet counteracts the increase of both total and VLDL cholesterol. Studies of liver receptor activity were carried out with both casein and soybean-cholesterol diets, to define the site of action of soy proteins. Binding of a cholesterol-rich lipoprotein fraction (beta-VLDL) to hepatic membranes is normal when a soybean-cholesterol diet is administered, and markedly reduced with casein-cholesterol. The activity of receptor-linked enzymes, HMG-CoA reductase, cholesterol 7 alpha-hydroxylase and acyl-CoA:cholesterol O-acyltransferase (ACATase), is differently affected by the two diets. HMG-CoA reductase activity is reduced by both diets with, however, significantly higher enzyme activities in the soybean-cholesterol-fed group. Both 7 alpha-hydroxylase and ACATase activity levels are significantly raised by casein-cholesterol but are in a normal range with soybean-cholesterol. These findings suggest that the hepatic receptor regulation of cholesterol metabolism is differently affected by animal and vegetable proteins in the diet.