Fluvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl-CoA reductase, scavenges free radicals and inhibits lipid peroxidation in rat liver microsomes

Abstract

We investigated the effect of fluvastatin sodium (fluvastatin) and pravastatin, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, on the formation of thiobarbituric acid reactive substances both in vivo and in vitro in rat liver microsomes and on active oxygen species. Oral administration of fluvastatin at low doses (3.13 and 6.25 mg/kg) inhibited the formation of thiobarbituric acid reactive substances in rat liver microsomes, but high doses (12.5 and 25 mg/kg) did not change the formation of thiobarbituric acid reactive substances. Fluvastatin at any dose used had no effect on the content of cytochrome P-450 and the activity of NADPH-cytochrome P-450 reductase. In in vitro experiments, concentrations of fluvastatin ranging from 1×10⁻⁶–1×10⁻⁴ M markedly inhibited NADPH-dependent lipid peroxidation in liver microsomes, but pravastatin weakly inhibited lipid peroxidation. The order of magnitude of inhibition of each drug on in vitro lipid peroxidation was butylated hydroxytoluene>probucol≥fluvastatin>pravastatin. Moreover, fluvastatin chemically scavenged active oxygen species such as hydroxyl radicals and superoxide anion generated by the Fenton reaction and by the xanthine–xanthine oxidase system, respectively, but pravastatin showed no scavenging of superoxide anion. These results indicate that the suppression of in vivo and in vitro lipid peroxidation in liver microsomes may be, at least in part, due to the scavenging by fluvastatin of free radicals.

Introduction

Fluvastatin is a new and potent inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, the rate-limiting enzyme of cholesterol biosynthesis. Cholesterol synthesis in the liver, the major organ supplying serum cholesterol, is regulated by cellular HMG-CoA reductase and low-density lipoprotein (LDL) receptors. Hussein et al. (1997)have demonstrated that fluvastatin reduces the LDL level in plasma. The oxidative modification of the LDL level in plasma or tissue is related to the progression of atherosclerotic disease (Rudling and Collins, 1996; Rifici and Khachadurian, 1996). The antiatherogenic properties of fluvastatin are related to its ability to reduce the susceptibility of LDL to lipid peroxidation (Hussein et al., 1997). There is evidence that LDL oxidation occurs in vivo (Rifici and Khachadurian, 1996), but the mechanism for this is not well known.

Recently, we also reported that fluvastatin was more potent than pravastatin in inhibiting both ex vivo and in vivo sterol synthesis in rat liver (Yamamoto et al., 1995, Transon et al., 1996). Transon et al. (1995), Transon et al. (1996)described that fluvastatin competitively inhibited cytochrome P-450_TB (CYP2C9) in vivo and in vitro. Cytochrome P-450 in hepatic microsomes is believed to be predominant in causing oxidative damage, that is, radical species (Ingelman-Sundberg, 1986; Hu et al., 1994; Bestervelt et al., 1995). In this connection, Afanas'ev et al. (1993)reported that the lipid-rich microsomal membranes are potential targets of injury in cells exposed to active oxygen species. The increased production of reactive oxygen species contributes to pathological processes, including membrane lipid peroxidation (Puntarulo and Cederbaum, 1996).

The present study, therefore, was undertaken to examine the influence of fluvastatin on both drug-metabolizing enzymes and lipid peroxidation in rat liver microsomes. Moreover, the in vitro effects of fluvastatin on lipid peroxidation were also included for comparison with the effects of another HMG-CoA reductase inhibitor, pravastatin, and the antioxidant agents, butylated hydroxytoluene and probucol. This study was undertaken to examine the hydroxyl radical and superoxide scavenging activity of fluvastatin, using both electron spin resonance (ESR) spectrometry and chemiluminescence.