Original Contribution
Effects of vitamin E on peroxisome proliferator-activated receptor γ and nuclear factor-erythroid 2-related factor 2 in hypercholesterolemia-induced atherosclerosis

https://doi.org/10.1016/j.freeradbiomed.2014.02.017Get rights and content

Highlights

  • ABCA1 mediates cholesterol efflux from macrophages via the PPARγ pathway.

  • PPARγ regulates matrix metalloproteinase expression.

  • Nrf2 may play both proatherosclerotic and antiatherosclerotic roles.

  • Vitamin E may afford protection against atherosclerosis by affecting gene expression in the PPARγ and Nrf2 pathways.

Abstract

Atherosclerosis and associated cardiovascular complications such as stroke and myocardial infarction are major causes of morbidity and mortality. We have previously reported a significant increase in mRNA levels of the scavenger receptor CD36 in aortae of cholesterol-fed rabbits and shown that vitamin E treatment attenuated increased CD36 mRNA expression. In the present study, we further investigated the redox signaling pathways associated with protection against atherogenesis induced by high dietary cholesterol and correlated these with CD36 expression and the effects of vitamin E supplementation in a rabbit model. Male albino rabbits were assigned to either a control group fed with a low vitamin E diet alone or a test group fed with a low vitamin E diet containing 2% cholesterol in the absence or presence of daily intramuscular injections of vitamin E (50 mg/kg). To elucidate the mechanisms by which vitamin E supplementation alters the effects of hypercholesterolemia in rabbit aortae, we measured peroxisome proliferator-activated receptor γ (PPARγ), ATP-binding cassette transporter A1 (ABCA1), and matrix metalloproteinase-1 (MMP-1) mRNA levels by quantitative RT-PCR and the expression of MMP-1, nuclear factor-erythroid 2-related factor 2 (Nrf2), and glutathione S-transferase α (GSTα) protein by immunoblotting. The increased MMP-1 and decreased GSTα expression observed suggests that a cholesterol-rich diet contributes to the development of atherosclerosis, whereas vitamin E supplementation affords protection by decreasing MMP-1 and increasing PPARγ, GSTα, and ABCA1 levels in aortae of rabbits fed a cholesterol-rich diet. Notably, protein expression of Nrf2, the antioxidant transcription factor, was increased in both the cholesterol-fed and the vitamin E-supplemented groups. Although Nrf2 activation can promote CD36-mediated cholesterol uptake by macrophages, the increased induction of Nrf2-mediated antioxidant genes is likely to contribute to decreased lesion progression. Thus, our study demonstrates that Nrf2 can mediate both pro- and antiatherosclerotic effects.

Section snippets

Animals and diets

All experimental procedures were approved by the Marmara University Animal Care and Use Committee, Istanbul (Protocol 062008). Twenty-one male albino rabbits (2–3 months of age) were assigned randomly to three groups, which were fed: (i) vitamin E-poor diet, (ii) vitamin E poor-diet containing 2% cholesterol, or (iii) vitamin E-poor diet containing 2% cholesterol with daily intramuscular injections of vitamin E (50 mg/kg). After 4 weeks, after overnight fasting, rabbits were anesthetized using 50

Effects of cholesterol and vitamin E supplementation on blood serum levels

Supplementation with 2% cholesterol for 4 weeks resulted in ~30-fold increase in serum cholesterol in the cholesterol and cholesterol + vitamin E groups compared to the control group (Table 1). Intramuscular vitamin E injections increased serum vitamin E levels ~11-fold in the cholesterol + vitamin E group (Table 1). In the cholesterol group, serum vitamin E levels appeared to increase, mostly as vitamin E is a fat-soluble vitamin carried by LDL cholesterol in blood, but the values corrected

Discussion

A high-cholesterol diet leads to metabolic changes involving endothelial damage, an increase in extracellular matrix synthesis, smooth muscle cell proliferation, and altered antioxidant and pro-oxidant enzyme activity related to the progression of atherosclerotic lesions. To investigate the relationship between hypercholesterolemia and atherogenesis in vivo, feeding rabbits a 2% cholesterol-containing diet for 4 weeks was found to be sufficient to elicit formation of atherosclerotic lesions in

Conclusions

In summary, our findings demonstrate that a high-cholesterol diet significantly enhances lipid accumulation via Nrf2-mediated induction of CD36 expression during atherogenesis. We also provided evidence for the role of vitamin E supplementation on gene expression through the upregulation of PPARγ and Nrf2 and induction of their downstream targets ABCA1 and GSTα, respectively, and through inhibition of MMP-1. ABCA1 upregulation results in cholesterol efflux from macrophages and inhibition of

Acknowledgments

This study was supported by COST B35 Action; TUBITAK (106S121); Marmara University Research Funds SAG-C-YLP-130511-014, SAG-C-YLP-070211-0038, SAG-C-YLP-050608-0125; and Heart Research UK (G.E.M., R.C.M.S.).

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