Effect of Cyclosporine on HMG-CoA Reductase, Cholesterol 7a-Hydroxylase, LDL Receptor, HDL Receptor, VLDL Receptor, and Lipoprotein Lipase Expressions

Long-term administration of cyclosporine (CsA) has been shown to cause hypercholesteremia, hypertriglyceridemia, and elevations of plasma low-density and very low-density lipoprotein (LDL and VLDL) levels in humans. This study was undertaken to explore the effects of CsA on expressions of the key lipid regulatory enzymes and receptors. Thus, hepatic expressions of cholesterol 7a-hydroxylase (the rate-limiting step in cholesterol conversion to bile acids), LDL receptor, and highdensity lipoprotein (HDL) receptor proteins, as well as 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were determined in rats treated with CsA (18 mg/kg/day) or placebo for 3 weeks. In addition, skeletal muscle and adipose tissue expressions of lipoprotein lipase and VLDL receptor were measured. Western blot analysis was used for all protein measurements using appropriate antibodies against the respective proteins. CsA-treated animals showed mild but significant elevations of plasma cholesterol and triglyceride concentrations. This was associated with a marked down-regulation of cholesterol 7a-hydroxylase in the liver and a severe reduction of lipoprotein lipase abundance in skeletal muscle and adipose tissue. However, hepatic LDL receptor and HDL receptor expressions and HMG-CoA reductase activity were not altered by CsA therapy. Likewise, skeletal muscle and adipose tissue VLDL receptor protein expressions were unaffected by CsA administration under the given condition. In conclusion, CsA administration for 3 weeks resulted in a significant reduction of hepatic cholesterol 7a-hydroxylase and marked down-regulation of skeletal muscle and adipose tissue lipoprotein lipase abundance in rats. The former abnormality can contribute to hypercholesterolemia by limiting cholesterol catabolism, whereas the latter may contribute to hypertriglyceridemia and VLDL accumulation by limiting triglyceride-rich lipoprotein clearance in CsA-treated animals. Since its introduction and release as an anti-rejection agent two decades ago, cyclosporine (CsA) has become the cornerstone of immunosuppressive therapy in organ transplant recipients. Administration of CsA is accompanied by a variety of side effects, including hypertension, nephrotoxicity, microvascular thrombosis, and hyperlipidemia. Long-term administration of CsA has been reported to raise plasma total cholesterol and triglyceride concentrations and to increase plasma low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) levels in humans (Raine et al., 1988; Ballantyne et al., 1989; Drueke et al., 1991; Schorn et al., 1991; Webb et al., 1992; Kuster et al., 1994; Edwards et al., 1995; Verpooten et al., 1996). Moreover, CsA administration enhances generation of oxygen-free radicals leading to oxidation of lipoproteins and formation of proatherogenic oxidized LDL (Lopez-Miranda et al., 1993; Sutherland et al., 1995). It should be noted, however, that the residual renal insufficiency and concomitant administration of corticosteroids, diuretics, and beta blockers, which are commonly used in transplant recipients, can independently affect lipid metabolism. For instance, Arnadottir et al. (1991) reported a significant elevation of serum cholesterol and triglyceride concentrations in their transplant recipients treated with CsA, compared with the non-CsA-treated group. However, their CsA-treated group had a greater impairment of renal function, received a higher corticosteroid dosage, and were more frequently treated with diuretics and beta blockers. Moreover, multiple regression analysis failed to demonstrate a clear association between CsA administration and hyperlipidemia in the latter study (Arnadottir et al., 1991). Thus, the presence of multiple confounding factors in the clinical setting hinders the ability to draw definitive conclusions as to the direct role of CsA in the pathogenesis of the associated dyslipidemia. Available data on the mechanisms of CsA-induced dyslipidemia are limited. We considered that a systematic study of Received for publication January 21, 2000. 1 This study was generously supported by Mr. and Mrs. William Chou. ABBREVIATIONS: CsA, cyclosporine; HDL, high-density lipoprotein; HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; IDL, intermediatedensity lipoprotein; LDL, low-density lipoprotein; VLDL, very low-density lipoprotein. 0022-3565/00/2942-0778$03.00/0 THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Vol. 294, No. 2 Copyright © 2000 by The American Society for Pharmacology and Experimental Therapeutics Printed in U.S.A. JPET 294:778–783, 2000 /2521/841108 778 at A PE T Jornals on N ovem er 3, 2017 jpet.asjournals.org D ow nladed from the key lipid-regulatory factors might help to uncover the molecular basis of CsA-induced hyperlipidemia. To this end, we explored the effect of CsA therapy on hepatic 3-hydroxy3-methylglutaryl coenzyme A (HMG-CoA) reductase (the rate-limiting enzyme in cholesterol synthesis), LDL, and high-density lipoprotein (HDL) receptors (the critical factors in metabolism of the cholesterol-rich LDL and HDL particles), and of cholesterol 7a-hydroxylase, (the rate-limiting step in cholesterol catabolism to bile acids). In addition, we determined the effects of CsA therapy on skeletal muscle and adipose tissue abundance of lipoprotein lipase and the novel VLDL receptor, which are the principal clearance pathways of triglyceride-rich lipoproteins, namely, chylomicrons and VLDL. Materials and Methods