Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC111
Induction of vascular antioxidant defences in response to dietary lipids and atherogenesis in hypercholesterolemic rabbits
P. Bozaykut1,2, B. Catalgol1, B. Yazgan1, E. Sozen1, R. Siow2, G. E. Mann2, N. Kartal Ozer1
1. Deparment of Biochemistry, Marmara University, Istanbul, Turkey. 2. Cardiovascular Division, King`s College London, London, United Kingdom.
Atherosclerosis and complications such as stroke and myocardial infarction are major causes of the death worldwide. Besides several genetic and environmental factors, increased serum cholesterol and oxLDL are considered to be inducing factors of atherosclerosis (1). We have previously reported a significant increase in CD36 mRNA levels in cholesterol fed rabbits and shown that vitamin E pretreatment prevented the dietary lipid induced increase in CD36 mRNA expression. In the present study, we further investigated redox signalling pathways involved in cellular defence against oxidative stress associated with atherogenesis in hypercholesterolemic rabbits. All experimental procedures were approved by the Marmara University Ethics Committee. Twenty-one male albino rabbits were assigned randomly to three groups fed: (i) vitamin E deficient diet, (ii) vitamin E deficient diet containing 2% cholesterol, and (iii) vitamin E deficient diet containing 2% cholesterol with daily intramuscular injections of vitamin E (50 mg/kg). After four weeks, serum cholesterol and vitamin E levels were determined. Supplementation with cholesterol resulted in ~30-fold increase of plasma cholesterol while vitamin E treatment increased serum vitamin E levels 11-fold (mean±S.D., n=7, p< 0.001, Student’s t-test). When thoracic aortae stained with hemotoxylene eosin were examined by light microscopy, cholesterol fed rabbits exhibited atherosclerotic lesions and endothelial damage compared to control rabbits. Notably, lipid accumulation and foam cell formation was detectable in animals fed cholesterol and treated with vitamin E. The consequences of hypercholestrolemic diet were further examined determining protein levels of Nrf2 and MMP-1 (n=3 per each group) by immunoblotting and PPARγ, ABCA1 and MMP-1 mRNA levels (n=5 per each group) by quantitative RT-PCR. Nrf2 protein expression was increased in the cholesterol group. Both MMP-1 protein and mRNA expression was increased in cholesterol group but decreased in cholesterol and vitamin E treated group. PPARγ and ABCA1 mRNA levels were decreased in the cholesterol group and increased in vitamin E treated group. Enhanced expression of Nrf2 supports our previous findings of Nrf2 regulated CD36 expression (2) and may reflect the fact that Nrf2 may be proatherogenic (3). Increased protein and mRNA expression of MMP-1 in cholesterol fed group may underlie its key role in extracellular matrix remodelling in atherosclerosis (4). As PPARγ is known to inhibit MMP-1 via the AP-1 pathway (5), this may account for our finding of decreased PPARγ in hypercholestrolemic rabbits. Our findings suggest that vitamin E may afford protection in part by decreasing MMP-1 expression and increasing PPARγ and ABCA1 expression.
Where applicable, experiments conform with Society ethical requirements