Regression of poloxamer 407-induced atherosclerotic lesions in C57BL/6 mice using atorvastatin

HMG-CoA reductase inhibitor drugs or ‘statins’ have been shown to effectively reduce plasma total cholesterol (CHOL), CHOL associated with low-density-lipoprotein (LDL), and triglycerides (TG). In addition, slight elevations in HDL-CHOL are also typically observed. Poloxamer 407 (P-407), a nonionic surfactant, effectively elevates both plasma CHOL and especially TG in a dose-controlled fashion and results in formation of atherosclerotic lesions in the aortas of C57BL/6 mice without the requirement of dietary cholic acid [1 and 2]. The purpose of the present study was to assess whether a typical statin, namely atorvastatin (Lipitor®) would significantly reduce P-407-induced hypercholesterolemia and hypertriglyceridemia as well as cause regression of atherosclerotic lesions resulting from administration of P-407 to C57BL/6 mice. C57BL/6 mice in the present study were treated with either normal saline (C, controls), 0.5 g/kg of P-407 (P), or a high-fat, high-cholesterol, cholate-containing diet (HF) for 120 days. Mice in all groups were then equally and randomly divided and treated with either atorvastatin or saline for an additional 120 days. Beginning at Day 121 and using mice in groups P and HF as an example, one-fourth of the mice in each group received 20 mg/kg per day of atorvastatin with either concomitant HF feeding or P-407 administration (‘progression’ treatment groups), one-fourth received 20 mg/kg per day of atorvastatin following cessation of HF feeding or P-407 administration, one-fourth received saline (placebo) with either simultaneous HF feeding or P-407 administration (‘progression’ placebo groups), and one-fourth received saline (placebo) following cessation of HF feeding or P-407 administration. Total plasma CHOL was significantly (P<0.01) lower for mice in groups P and HF when administered atorvastatin relative to saline, but remained significantly (P<0.05) elevated compared to total plasma CHOL of C mice. With discontinuation of either P-407 administration or HF feeding, total plasma CHOL declined rapidly in both P and HF mice with atorvastatin-treated mice generally demonstrating lower plasma CHOL concentrations relative to saline-treated mice. Total plasma TG was significantly (P<0.01) lower for mice in group P administered atorvastatin relative to saline, but remained significantly (P<0.05) elevated compared to plasma TG of C mice. With discontinuation of P-407 administration, total plasma TG declined rapidly in P mice with atorvastatin-treated mice typically demonstrating lower plasma TG concentrations relative to saline-treated P mice. Aortas of mice treated with 20 mg/kg per day of atorvastatin in both groups P and HF, whether maintained on the HF-diet or treated with P-407 from Day 120 to 240 or whether each treatment was terminated at Day 120, revealed no presence of atherosclerotic lesions relative to saline-treated mice and were indistinguishable from aortas retrieved from C mice. Atorvastatin at a dose of 20 mg/kg per day not only significantly reduced the plasma CHOL and TG concentrations, but also resulted in regression of atherosclerotic lesions induced in C57BL/6 mice by administration of P-407 or ingestion of a HF-diet containing cholic acid.