A study on the antioxidative and antiatherogenic effects of barley leaf extract

Autor: Ya-Mei Yu, 余雅美
Rok vydání: 2002
Druh dokumentu: 學位論文 ; thesis
Popis: 90
Atherosclerosis is a major cause of coronary heart disease. Previous studies have indicated that the oxidative modification of low-density lipoprotein (LDL) plays a primary key role on the pathogenesis of atherosclerosis. Young barley leaf extract (BL) is a good natural source of vitamins and minerals. It contains phenolic compounds which has been found to have antioxidant activity in a lipid peroxidation system. In this study, the total content of phenolics and total equivalent antioxidants capacity (TEAC) of BL after extraction was determined. The effects of supplementation of 15 g/d BL on plasma lipids, LDL subsceptibility to oxidation, free radical scavenging activities in hyperlipidemic smokers and type 2 diabetes were investigated. The molecular mechanisms of the antioxidative and antiatherogenic effects of BL in animal model were also elucidated. Results in trial 1 showed that the total contents of polyphenols in BL was 29.6 mg/100 g (as gallic acid), and the total antioxidant capacity of daily BL intake (15 g) was equal to 100-150 mg of Trolox. In hyperlipidemic smokers’ study in trial 2, the plasma total cholesterol (TC) and LDL-C levels were reduced, and HDL-C levels were enhanced following treatment with either BL or adlay. However, it seemed that BL had stronger antioxidative effect on the prevention of LDL oxidation than adlay. The results also indicated that antioxidative effect was less pronounced in smokers compared to non-smokers. In trial 3, forty-eight type 2 diabetic patients received one of the following supplements daily for 4 weeks: 15 g BL, vitamin C (200 mg) and vitamin E (200 mg) (CE), or BL plus CE (BL+CE), or BL plus olive oil-replaced diet (BL+O). The plasma TC and LDL-C levels were reduced following supplementation. Vitamin E content and lag times of LDL subfractions increased significantly following any treatment supplementation especially for BL+CE or BL+O group. The percent increase of lag times in the BL and CE groups showed similar increases. The antioxidative effects of BL+CE and BL+O were greater for small, dense LDL (Sd-LDL) than large buoyant LDL (B-LDL) with further increases in percentage of lag times 4 and 2 folds compared to BL alone. The lucigenin-chemiluminescence (CL) and luminol-CL levels in blood were significantly reduced in all groups. The results indicate that supplementation with BL may help to scavenge oxygen free radicals, save LDL-vitamin E content, and inhibit LDL oxidation. Furthermore, supplementation with the addition of vitamins C and E or olive oil-replaced diet to BL can inhibit Sd-LDL oxidation more effectively, which may protect against vascular diseases in type 2 diabetic patients. An animal study in trial 4, six groups of Syrian hamster were fed with one of the following diets: a normal diet (rat chow diet, n=6); a control diet (normal diet with 14 % sunflower oil and 0.2 % cholesterol, n=6); 1 % BL diet (control diet with 1 % BL, w/w, n=6); 3 % BL diet (control diet with 3 % BL, w/w, n=6); 5 % BL diet (control diet with 5 % BL, w/w, n=6). RNA and protein were extracted from liver to study the gene expression of antioxidative enzymes after four weeks feeding. With Western blot assay, it was found that the protein levels of CuZn-SOD were significantly increased in hamster fed with 3 %, 5 % BL and vitamin E (1.63, 1.54, 1.49 folds compared to control, respectively). With RT-PCR analysis, it showed that the mRNA levels of GPx were significantly potentiated by 3 %, 5 % BL or vitamin E (3.09, 2.11, 3.04 folds compared to control, respectively). These data suggested that CuZn-SOD and GSH-Px gene expression can be upregulated by BL or vitamin E which in turn scavenged superoxide anion and hydrogen peroxide to reduce the oxidative stress in livers. Another animal study in trial 5, twenty-four New Zealand White (NZW) male rabbits were assigned randomly into four dietary groups. The normal group was fed regular rabbit chow and the control group was fed a chow containing 10 % corn oil and 0.5 % cholesterol. The BL and the probucol groups were fed the same diet as the control diet containing 1 % (w/w) BL or 1 % (w/w) probucol, respectively. The plasma levels of triacyglycerol (TG), TC, lucigenin-CL, luminol-CL were increased in the control group compared to the normal group, and decreased in the BL group and probucol group compared to the control group. The value of T50 of RBC hemolysis and the lag phase of LDL oxidation increased in the BL group and probucol group compared to the controls. Ninety percent of the intimal surface of the thoracic aorta was covered with atherosclerotic lesions in the control group but only 60 % of the surface was covered in the BL group. This 30 % reduction of hyperlipidemic atherosclerosis by BL was associated with a decrease in plasma TC、LDL-C and TG, and an increase in antioxidative abilities (as measured by T50, lag phase, and CL). These results suggest that the antioxidative and hypolipidemic effects of BL could be useful in the prevention of atherosclerosis which may cause cardiovascular disease. In conclusion, BL contains antioxidative vitamins and polyphenols, and was proved to have antioxidative ability in vitro. In human studies, supplementation with BL can decrease plasma TC and LDL-C, and increase a-tocopherol content of LDL and inhibit LDL oxidation. In animal studies, the antiatherogenic effect of BL seems to be associated with induction of the gene expression of two major antioxidant enzymes, namely CuZn-SOD and GPx in liver, an increase in scavenging oxygen free radicals in blood, and a decrease in plasma TG、TC and LDL-C.
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