Simvastatin, an HMG-CoA reductase inhibitor, induces the synthesis and secretion of apolipoprotein AI in HepG2 cells and primary hamster hepatocytes

Abstract

Clinical studies have recently suggested that statin treatment may beneficially elevate plasma concentrations of high density lipoprotein (HDL)–cholesterol in patients with hyperlipidemia. Here, we have investigated the effect of a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase on the synthesis and secretion of apolipoprotein AI (apoAI) in two model systems, HepG2 cells and primary hamster hepatocytes. Cultured cells were incubated with different doses of simvastatin (0.1–10 μM) for a period of 18 h. A dose-dependent increase in synthesis and secretion of apoAI was observed in both cell types. There was a significant increase in the synthesis of apoAI in HepG2 cells (44.3±12.1%), and hamster hepatocytes (212±2%) after treatment with 10 μM of the statin. The increase in apoAI synthesis appeared to result in a higher level of apoAI secreted into the culture media in both cell types (49.2±7.8% in HepG2, 197±0.2% in hamster hepatocytes). ApoAI mRNA levels were also significantly increased in both cell types in response to statin treatment. Control experiments with transferrin confirmed specificity of the effect on apoAI secretion. Analysis of a density fraction containing HDL particles in culture media revealed an increase in HDL-associated apoAI of 94.3±2.1% in HepG2 cells and 27.0±0.03% in hamster hepatocytes following 10 μM simvastatin-treatment. Comparative studies of simvastatin and lovastatin indicated a differential ability to induce apoAI synthesis and secretion, with simvastatin having a more significant effect. Thus, acute statin treatment of cultured hepatocytes (transformed as well as primary) resulted in a significant upregulation of apoAI mRNA and apoAI synthesis, causing oversecretion of apoAI and HDL extracellularly. The stimulatory effect on apoAI synthesis and secretion may thus explain the clinical observation of an elevated plasma HDL–cholesterol level in hyperlipidemic patients treated with certain statins.