Plasma insulin levels predict atherosclerotic lesion burden in obese hyperlipidemic mice

Despite a clear association between obesity, insulin resistance and atherosclerosis in humans, to date, no animal models have been described in which insulin resistance is associated with atherosclerotic lesion burden. Using two mouse models of obesity-induced hyperlipidemia:leptin deficient (ob/ob) mice on an apolipoprotein E deficient (apoE−/−) or low density lipoprotein receptor deficient (LDLR−/−) background, we sought to determine metabolic parameters most closely associated with atherosclerotic lesion burden. Total plasma cholesterol (TC) levels in ob/ob;apoE−/− mice and ob/ob;LDLR−/− mice were indistinguishable (682 ± 48 versus 663 ± 16, respectively). Analysis of lipoprotein profiles showed that cholesterol was carried primarily on VLDL in the ob/ob;apoE−/− mice and on LDL in the ob/ob;LDLR−/− mice. Plasma triglycerides (TG) were 55% lower (P < 0.001), non-esterified fatty acids (NEFA) were 1.5-fold higher (P < 0.01), and insulin levels were 1.7-fold higher (NS) in ob/ob;apoE−/− mice compared to ob/ob;LDLR−/− mice. Other parameters such as body weight, fat pad weight, and glucose levels were not different between the groups. Aortic sinus lesion area of ob/ob;apoE−/− mice was increased 3.2-fold above ob/ob;LDLR−/− mice (102,455 ± 8565 μm2/section versus 31,750 ± 4478 μm2/section, P < 0.001). Lesions in ob/ob;apoE−/− mice were also more complex as evidenced by a 7.7-fold increase in collagen content (P < 0.001). Atherosclerotic lesion area was positively correlated with body weight (P < 0.005), NEFA (P = 0.007), and insulin (P = 0.002) levels in the ob/ob;LDLR−/− mice and with insulin (P = 0.014) in the ob/ob;apoE−/− mice. In contrast, lesion burden was neither associated with TC and TG, nor with individual lipoprotein pools, in either animal model. These data provide a direct demonstration of the pathophysiologic relevance of hyperinsulinemia, NEFA, and increased body weight to atherosclerotic lesion formation.