Inhibition of LDL oxidation

The cytotoxicity of LDL can also be inferred from the study by Blake et al. (1985). In this study of human cultured endothelial cells, stored sera from patients with necrotizing arteritis demonstrated an enhanced tendency to develop oxidized LDL, which correlated closely with endothelial cell cytotoxicity. This process appears to require the presence of both oxygen and transition metal ions such as iron in the presence of a reducing agent (Gebicki ef /., 1991). There is considerable evidence that transition metals are involved in cell-induced modifications of LDL including the inhibitory effects of EDTA and desfer-rioxamine (Hiramatsu et 1987). A role for Of in LDL modification by endothelial cells and fibroblasts comes from studies showing inhibition of LDL oxidation by SOD (Steinbrecher, 1988). 

Esterbauer, H., Waeg, G., Puhl, H., Dieber-Rotheneder, M. and Tatzber, F. (1992). Inhibition of LDL oxidation by antioxidants. In Free Radicals and Aging (eds. I. Emerit and B. Chance) pp. 145-157. Birkhauser Verlag, Basel. 

Flavonoids protect LDL from oxidation, delaying the onset of lipid peroxidation, however, the prevention of atherosclerosis by flavonoids occurs not only by the inhibition of LDL oxidation, but also by the increase of cellular resistance to harmful effects of the oxidized LDL (de Luis and Aller, 2008). The antioxidant activity of anthocyanidins, as well as their protective role against LDL oxidation, has been well demonstrated in different in vitro systems (Aviram and Fuhrman, 2002 Satue-Gracia and others 1997 Teissedre and others 1996). 

Zuckerman SH, Bryan N (1996) Inhibition of LDL oxidation and myeloperoxidase dependent tyrosyl radical formation by the selective estrogen receptor modulator raloxifene (LY139481 HCL). Atherosclerosis 126 65-75... 

Besides cholesterol efflux from arterial wall and its role in RCT, additional properties of HDL have been proposed for its protective anti-atherogenic activities. HDL protects vascular function by a number of potential alternative mechanisms, including inhibition of LDL oxidation [8,9], platelet aggregation and coagulation [10], and endothelial monocyte adhesion [11], as well as promotion of endothelial nitric oxide synthase (eNOS) [12], and prostacyclin synthesis [13-15]. The proposed alternate protective mechanisms for HDL are attractive but many of them lack validation under in vivo conditions. 

Sevanian, A., Shen, L., and Ursini, P., 2000, Inhibition of LDL oxidation and oxidized LDL-induced cytotoxicity by dihydropyridine calcium antagonists, Pbami. Res. 17 999-1006. 

It was postulated that the inhibition of LDL oxidation by red wine may help to explain the French paradox. Since Frankel and co-workers [73] showed that red wine inhibit the oxidation of LDL, several in vitro studies have confirmed this finding [26,74,75]. There is controversy over whether or not the consumption of red wine by humans reduces the oxidation of LDL ex vivo. While several studies found resistance of LDL oxidation after 2 weeks of red wine consumption in healthy subjects [75,76], others found no effect on the oxidation of LDL ex vivo [26,77]. Recently, Stein and coworkers [78] showed that short-term ingestion of purple grape juice (7.7 1.2 mL/Kg/day for 14 days) reduced the susceptibility to oxidation in coronary artery disease patients and that this is a potential mechanism by which flavonoids in purple grape products may prevent cardiovascular events, independent of alcohol content. 

Vaya J, Mahmood S, Goldblum A, Aviram M, Volkova N, Shaalan A, Musa R, Tamir S. 2003. Inhibition of LDL oxidation by flavonoids in relation to their structure and calculated enthalpy. Phytochemistry 62 89-99. 

Plaque stabilization Reduced CD40 expression and CD40-related activation of vascular cells Reduced leukocyte-endothelial cell interactions Reduced C-reactive protein levels and proinflammatory cytokines Inhibition of LDL oxidation Reduced cytotoxicity of T-lymphocytes Inhibition of proinflammatoiy T helper 1 cell development and augmentation of anti-inflammatoy T helper 2 cell development Reduced oxidized LDL uptake... 

Other drugs that have an impact on serum lipids have also been examined. Probucol pretreatment has been shown to lower the rate of restenosis after balloon angioplasty in clinical trials (88,89). Although its lipid-lowering effect is due to an increase in the fractional catabolic rate of LDL cholesterol (90), its antirestenotic effect is believed to be related to other properties, including inhibition of LDL oxidation, promotion of endothelial regeneration, and anti-inflammatory effects (91). However, probucol is not widely available due to its ability to lower HDL-cholesterol and concerns relating to proarrhythmia. 

Hwang, J. Sevanian, A. Hodis, H.N. Ursini, F. 2000. Synergistie inhibition of LDL oxidation by phytoestrogens and aseorbic acid. J. Free Radie. Biol. Med. 29 79-89. 

SUMMARY OF PREVIOUS STUDIES FROM THIS LABORATORY Inhibition of LDL Oxidation by Resveratrol... 

The antioxidant activities of red and white commercial grape juices have been studied using in vitro inhibition of the copper-catalyzed oxidation of human LDL (Frankel et al., 1998). The correlation between total phenols, expressed as GAE, and relative percent of inhibition of LDL oxidation was r = 0.99. In red Concord grape juices, the antioxidant activity was related to the anthocyanin levels. In the white grape juice, the antioxidant activity was associated with the levels of hydrox-ycinnamates (caffeic acid) and flavanols (catechin). When compared at the same level of total phenolics (10 pM GAE), the antioxidant activities of the grape juices were comparable to the antioxidant activities of red wine (Frankel et al., 1995). Laplaud et al. (1997) found protective action of copper-mediated LDL oxidation in aqueous V. myrtillus extracts. On a molar base, the extracts were more efficient than ascorbic acid and BHT in inhibiting LDL oxidation. 

Several cohort studies have been performed in which the relationships between flavonoid intake and the risk of coronary heart disease have been investigated. The studies have shown that the mortality from coronary heart diseases (CHD) is inversely correlated with the intake of flavonoids in the diet. Hollman and Katan (1998) summarize that in three out of five cohort studies, in addition to one cross-cultural study, flavonoids from the flavonol and flavone subgroups demonstrated a protective role toward cardiovascular disease. The protective effect of the flavonoids is partly explained by the inhibition of LDL oxidation and by reduced platelet aggregability. As reviewed by Cook and Samman (1996), there are several possible routes as to how LDL is oxidized by free radicals generated in the cells and how the oxidized LDL initiates and promotes atherosclerosis in the human body. 

The ability of the constituents of tea, particularly (+)-catechin, to inhibit LDL oxidation has been investigated [46] as expected, LDL modified by cells or copper-induced oxidation was endocytosed and degraded by macrophages more quickly than native LDL. However, in the presence of (-i-)-catechin, the rates of endocytosis and degradation were similar to those of native LDL [46]. In addition to the inhibition of LDL oxidation, flavonoids such as catechin, rutin, and quercetin, at levels of 10-20 mmol/L, minimize the cytotoxicity of oxidized LDL [47]. Moreover, cells preincubated with these flavonoids were observed to be resistant to the cytotoxic effects of previously oxidized LDL (47, 48). The postulated mechanisms by which flavonoids protect against the cytotoxicity of oxidized LDL are consistent with their antioxidant and free radical-scavenging properties [4]. 

Lavy, A., Ben Amotz, A., and Aviram, M., Preferential inhibition of LDL oxidation by the all-trans isomer of P-carotene in comparison with 9-cis P-carotene, Eur. J. Clin. Chem. Clin. Biochem., 31, 83, 1993. 

Given the proposed role of oxLDL in the development of atherosclraosis, studies have been performed to evaluate the role of antioxidants such as resvraatrol on inhibition of LDL oxidation. For example, short-term consumption of grape jirice by patients with coronary heart disease increases the mean lag time of LDL oxidation in vitro ... 

Isolation of LDL and Measurement of the Inhibition of LDL Oxidation. Blood samples were obtained from food-deprived cholesterol-fed rabbits with or without drug treatment. Plasma lipoproteins were isolated by discontinuous NaCl/KBr density gradient ultracentrifugation in a SW 50 Ti rotor (Beckman Instruments, Palo Alto, CA) for 20 h at 4°C. LDL was isolated in a density range of 1.019-1.063 g/mL, and was dialyzed extensively at 4 C under Nj against PBS (5 mM phosphate and 145 mM NaCl, pH 7.4) in darkness. LDL cholesterol was determined enzymatically. All samples were diluted in normal saline to give a final concentration of 150 mg/dL cholesterol for the oxidation susceptibility studies. 

The inhibition of LDL oxidation was measured by the method of Esterbauer et al. (40). A 50-pL aliquot of LDL was added to each well in a 96-weU microfilter plate. LDL was preincubated with test compounds at 37 C for 1 h. A 50-p.L aliquot of CuSO solution was added to make a final Cu concentration of 20 pM to induce oxidation. The microfilter plate was again incubated at 37°C for 0.5,1,1.5,2, 2.5,3,3.5,4, or 4.5 h. After incubation, 150 pL of EDTA (2 mM) was added. A 100-pL aliquot from each well was transferred to a minivial. After the addition of 0.9 mL 2-propanol, the mixture was centrifuged. The concentration of conjugated dienes in the supernatant was determined by ultraviolet (UV) absorption at 232 nm. 

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