Selective Effects of Different Antioxidants on Oxidation of Lipoproteins from Rats

Abstract

Lipoprotein oxidation may contribute to development of atherosclerosis, and supplementation with antioxidants may reduce risk for atherosclerotic events. Genistein, a major isoflavone from soy protein, and catechins from green tea have important antioxidant properties. This study compared the effects of various diets containing antioxidant-rich foods or supplements on serum lipids and lipoprotein oxidation of male Sprague-Dawley rats. The control diet used was devoid of vitamin E. Test diets included these ingredients: green tea powder, 20 g/kg; beta-carotene, 250 mg/kg; a low isoflavone soy protein isolate; a genistein-rich soy protein isolate; and vitamin E, 4000 mg/kg. Ten-week-old rats were acclimatized for 1 week on a special custom diet without vitamin E. Following randomization and allocation to different diet groups, rats were fed the test diets for 3 weeks. Blood was drawn by cardiac puncture, and the plasma was separated by centrifugation. The VLDL-LDL fraction was isolated by ultracentrifugation. Oxidation kinetics of the VLDL-LDL fraction were determined by measuring the lag phase and formation of conjugated dienes, lipid peroxides, and TBARS. The vitamin E diet (P < 0.001) and high-genistein diet profoundly decreased all parameters of lipoprotein oxidation. The following alterations were noted with the high-genistein diet compared to the control diet: the lag phase was 49% longer (P=0.002); conjugated diene formation was decreased by 28% (P=0.01); lipid peroxide formation was decreased 31% (P=0.0059); and TBARS production was 35% lower (P=0.019). The low-isoflavone diet increased the lag phase by 43% (P=0.0019) but did not significantly alter other measures of oxidation. Green tea increased only the lag phase by 33% (P=0.012) compared to the control diet. Beta-Carotene had no significant effect on the oxidation of lipoproteins. The effect of genistein-rich soy protein isolates on lipoprotein oxidation in vitro suggests that either soy isoflavones or other antioxidants derived from soy protein, like vitamin E, may be transported in these lipoproteins. The minimal effects of the isoflavone-poor soy protein isolate suggests that either the small amount of isoflavones present have a potent effect or other components of soy protein are exerting these effects. Further studies are required to examine these results.

Health Benefits of Soy Isoflavones

“…Rats consuming soy protein isolates for 3 wk develop a VLDL (very-low-density lipoprotein) ILDL fraction that becomes significantly more resistant to oxidative damage, although the antioxidant improvement in the low-genistein group was only slightly less than that observed in the high-genistein group (23). A more recent study of humans consuming soy diets confirmed these observations.…”

Hormonal and metabolic effects of genistein and daidzein in male rat

“…Genistein has an important antioxidant properties. In Sprague-Dawley rats it profoundly decreased all parameters of lipoprotein oxidation (Anderson et al, 1998). There were also observed antitumor effects of isoflavones in animals.…”

Genistein supplementation to the quail: Effects on egg production and egg yolk genistein, daidzein, and lipid peroxidation levels

“…Soy isoflavones are structurally and functionally similar to natural estrogens and can weakly bind to estrogen receptors and may exert either estrogenic or antiestrogenic effects. Soy isoflavones are also shown to prevent certain types of cancer (Adlercreutz, 1995;Franke et al, 1995), reduce the risk of osteoporosis (Adlercreutz, 1995;Zhang et al, 2008), lower plasma cholesterol (Anderson et al, 1998;Arjmandi et al, 1998;Ho et al, 2000), and can act as antioxidant agents (Adlercreutz, 1995;Kirk et al, 1998;Ho et al, 2000;Munro et al, 2003;Onderci et al, 2004;Jiang et al, 2007) and immune enhancers (Adlercreutz, 1995) in humans and laboratory animals.…”