Aortic valve sclerosis in rabbits

BACKGROUND AND AIM OF THE STUDY: Aortic valve sclerosis is fairly common and is currently seen as a marker of systemic atherosclerosis. For unclear reasons only a minority of those sclerotic valves will evolve to become stenotic suggesting that atherogenic factors alone are insufficient to explain the development of valve stenosis. We had reported in a model of cholesterol fed rabbits that a combination of high cholesterol with vitamin D supplementation was necessary to induce valve stenosis and significant calcium deposition whereas high cholesterol alone only induced a sclerosis of the valve. In this study, we further evaluated the role of vitamin D treatment in the development of aortic valve disease (sclerosis or stenosis) in this rabbit model. METHODS: Rabbits were divided in 4 groups followed for 12 weeks: 1) no treatment; 2) cholesterol-enriched diet, 3) cholesterol-enriched diet + vitamin D2 (VD; 50000IU, daily) 4) VD alone for 12 weeks. Echocardiographic assessment of the aortic valve was done at baseline, and every 4 weeks thereafter. Aortic valve area, maximal and mean transvalvular gradients were recorded and compared over time. Immunohistological study of the valves of AS rabbits was also realized for several classical atherosclerosis markers. RESULTS: Vitamin D2 treated animal did not develop any stenosis of the valve despite increased echogenicity due to diffuse calcium deposits on the leaflets without any atherosclerotic lesions. Only the combination of high cholesterol with VD resulted in a decrease of aortic valve area. Immunohistological analysis of aortic valves from VD rabbits showed the presence of calcium deposits, T-cell infiltration in addition to positive labeling for alpha-smooth muscle cell actin. We did not observe macrophage infiltration in aortic valve leaflets of VD rabbits. CONCLUSION: Hypercholesterolemia or vitamin D supplements alone could not induce aortic valve stenosis in our animal model whereas the combination resulted in a decreased aortic valve area. These findings support the hypothesis that a combination of atherosclerotic and calcifying factors is necessary to induce aortic valve stenosis in this model