Effects Of Acipimox On Atherosclerosis Induced By A Palmitate-rich Diet

Backgrounds：Saturated fatty acids (FA) have been linked to an increased risk ofcardiovascular disease. It has been demonstrated that nonesterified free FAwhich is also known as free fatty acids contribute to overall mortality,especifically cardiovascular death. Palmitate, a saturated long chain FA, isabundant in the diet and associated with oxidative stress and inflammation.However, the role of palmitate in the growth of atherosclerotic plaques andplaque stability remains to be elucidated.Acipimox,5-methyl-pyrazine-2-carboxylic acid-4-oxide, is a nicotinicacid derivative that inhibits lipolysis and attenuates the release of free FA fromadipose tissue. It has been reported that acipimox might ameliorateatherosclerosis in ritonavir-treated LDLR-null mice, an animal model withlipoatrophy and elevated plasma FA concentrations. Additionally, our previousstudy demonstrated that acipimox might inhibit the growth of atheroscleroticplaques in ApoE-/-mice fed an oleate-rich diet. However, the effects ofacipimox on the growth of atherosclerotic plaque and plaque stability in ApoE-/-mice fed a palmitate-rich diet are unknown.Objectives:The present study aimed to investigate whether a palmitate-rich diet could accelerate atherosclerosis and promote instability and that can be blocked bytreatment with acipimox in ApoE-/-mice.Materials and Methods：Male ApoE-/-mice,6to8weeks of age, were randomized into three groups.The animals were fed a normal chow diet in the control group, a diet containing5%palmitic acid in the palmitate group, and a diet containing5%palmitic acidand0.02%acipimox in the acipimox group, respectively, for12weeks. Then,the following measurements were performed.1. Plasma parameters such as triglycerides, total cholesterol, low-densitylipoprotein cholesterol, high-density lipoprotein cholesterol and free fatty acids(FFA) levels in plasma were measured by colorimetric assays.2. The atherosclerotic lesions of the thoraco-abdominal aorta wereanalyzed by Oil-red-O staining. Atherosclerotic lesions in the aortic roots wereexamined in cross-sections of the aortic origin and were stained withhematoxylin and eosin.3. Paraffin sections (5μm) were obtained from the aortic sinus and theplaque collagen content was detected using a fast Masson dye kit.4. The expression of matrix metalloproteinase (MMP-2, MMP-3, MMP-9,and MMP-14) and the tissue inhibitor of MMP (TIMP-1, and TIMP-2) weredetermined by immunohistochemical analysis.Results：1. The plasma TG，TC，LDL-C and HDL-C concentrations were notaffected by the palmitate-rich diet or acipimox treatment（P＞0.05）. But the palmitate-rich diet induced hyper-free fatty acidemia in the ApoE-/-mice (P <0.01). In addition, the increased plasma FFA concentration was significantlyattenuated by co-treatment with acipimox (P <0.05).2. After a12-week treatment, the atherosclerotic plaque size in thethoraco-abdominal aorta was significantly increased in the palmitate groupcompared to the control group (P <0.01). Furthermore, the mice in thepalmitate group showed a slight but not significant increase in the size of aorticroot plaques compared to the aortic root plaques in the control mice. Asexpected, the plaque sizes in both the thoraco-abdominal aorta and aortic rootwere significantly attenuated by co-treatment with acipimox (both P <0.01).3. The collagen content in atherosclerotic plaques in the aortic root wassignificantly decreased in the palmitate-fed mice relative to the plaques in thecontrol mice (P <0.01). Moreover, the palmitate-induced decrease in collagencontent was significantly reduced by treatment with acipimox (P <0.01).4. There was no distinct staining for MMP-3or TIMP-1in the aorticsections. MMP-2was significantly upregulated by the palmitate-rich diet,whereas this effect was remarkably attenuated by co-treatment with acipimox(P <0.05and P <0.01). The palmitate-rich diet significantly decreased theexpression of MMP-9(P <0.01), which was not affected by co-treatment withacipimox. The protein expression levels of MMP-14and TIMP-2were notaffected by palmitate or acipimox（P＞0.05）.Conclusion:1. The palmitate-rich diet can induce hyper-free fatty acidemia in mice. In addition, the palmitate-rich diet not only significantly enhances the growth ofatherosclerotic plaques but also promotes plaque instability.2. Acipimox significantly alleviates palmitate-induced hyper-free fattyacademia, atherosclerotic lesion development and plaque instability.3. One mechanism by which acipimox could relieve palmitate-inducedplaque instability is to reverse the upregulation of MMP-2.