Previous in vitro
studies have shown that metabolic syndrome associated ectopic lipid accumulation regulates the expression and activity of drug metabolizing enzymes (DME) and transporters (1, 2). The lipogenic enzyme stearoyl-CoA desaturase-1 (SCD1) is associated with ectopic lipid deposition and has emerged as a target for the treatment of the metabolic syndrome. Sterculic oil (SO) is a known natural inhibitor of SCD1 and we hypothesized that SO supplementation would alter obesity-associated changes in DME and transporter expression and activity. Therefore, the current study examines the role of SO treatment on expression and activity of DME and transporters in lean LETO and obese OLETF rats. Liver tissue samples were isolated from 14 week old male LETO and OLETF rats fed with a standard AIN-93G diet or OLETF animals that were fed an AIN-93G diet supplemented with 0.5% SO (OLETF-SO). Microsomes were isolated from the livers using a previously described method, while RNA was isolated using a Qiagene® RNA isolation kit. CYP1A, NAT and XO activity was determined using Ethoxyresorufin, p-aminobenzoic acid as probe substrates and Cayman® XO assay kit respectively. The mRNA expression was determined using qRT-PCR. Our results indicate that the hepatic XO activity was 2.5 times higher in the OLETF obese rats when compared to the LETO lean rats (891.2 units/mg vs. 374.8 units/mg protein). The addition of SO to the diets of OLETF rats resulted in significant reversal of the elevated XO activity (450.4 units/mg protein) similar to that of the LETO lean rats. The hepatic mRNA expression of SLCO1A4
transporters was 5 and 2.5 fold lower in the OLETF rats when compared to lean LETO rats, (p< 0.001, 0.01) respectively; however, this effect was not reversed in the OLETF-SO rats. Interestingly OLETF rats fed an AIN-93G diet supplemented with SO showed an increase in hepatic mRNA expression of ABCB1
(2.5 fold, p < 0.01) and SLC22A6
(1.63 fold; p < 0.05) as compared to the OLETF and LETO rats. No differences were observed between LETO, OLETF, and OLETF-SO rats with respect to hepatic CYP1A and NAT enzyme activity and hepatic ABCC1
mRNA levels. In conclusion, this study demonstrates that inhibition of SCD1 by SO reverses the upregulation of XO activity. Also SO was found to differentially alter transporter mRNA expression levels. Additional studies are required to determine the exact mechanism of the SO mediated alterations and its role in affecting the disposition of drugs.
1. Hirunpanich V, Sethabouppha B, Sato H. Inhibitory effects of saturated and polyunsaturated fatty acids on the cytochrome P450 3A activity in rat liver microsomes. Biol Pharm Bull. 2007 Aug;30(8):1586-8.
2. Zangar RC, Novak RF. Effects of fatty acids and ketone bodies on cytochromes P450 2B, 4A, and 2E1 expression in primary cultured rat hepatocytes. Arch Biochem Biophys. 1997 Jan 15;337(2):217-24.