Role of Intestinal Cytochrome P450 (P450) in Modulating the Bioavailability of Oral Lovastatin: Insights from Studies on the Intestinal Epithelium-Specific P450 Reductase Knockout Mouse

Abstract

ABSTRACT:The extents to which small intestinal (SI) cytochrome P450 (P450) enzymes control the bioavailability of oral drugs are not well defined, particularly for drugs that are substrates for both P450 and the P-glycoprotein (P-gp). In this study, we have determined the role of SI P450 in the clearance of orally administered lovastatin (LVS), an anti-hypercholesterolemia drug, using an intestinal epithelium (IE)-specific P450 reductase knockout (IE-Cpr-null) mouse model. In the IE-Cpr-null mouse, which has little P450 activities in the IE, the oral bioavailability of LVS was substantially higher than that in wild-type (WT) mice (15 and 5%, respectively). In control experiments, the clearance rates were not different between the two strains, either for intraperitoneally dosed LVS, which bypasses SI metabolism, or for orally administered pravastatin, which is known to be poorly metabolized by P450. Thus, our results demonstrate a predominant role of SI P450 enzymes in the first-pass clearance of oral LVS. The absence of IE P450 activities in the IE-Cpr-null mice also facilitated the identification of the molecular targets for orally administered grapefruit juice (GFJ), which is known to inhibit LVS clearance in humans. We found that pretreatment of mice with oral GFJ enhanced the systemic exposure of LVS in WT, but not in IE-Cpr-null mice, a result suggesting that the main target of GFJ action in the small intestine is P450, but not P-gp.

Commentary: Theoretical Predictions of Flow Effects on Intestinal and Systemic Availability in Physiologically Based Pharmacokinetic Intestine Models: The Traditional Model, Segregated Flow Model, and QGutModel

“…These aspects are especially pertinent when intestinal metabolic activity is substantial relative to that in the liver, and when different extents of induction/inhibition of intestinal and hepatic enzymes or transporters are the result of treatment with the culprit compound, which usually shows a higher induction/inhibition effect with oral administration (Fromm et al, 1996;Paine et al, 1996;Thummel et al, 1996;Eeckhoudt et al, 2002;Mouly et al, 2002;Fang and Zhang, 2010;Liu et al, 2010;Lledó-García et al, 2011;Zhu et al, 2011).…”

Regulation of Intestinal Cytochrome P450 Expression by Hepatic Cytochrome P450: Possible Involvement of Fibroblast Growth Factor 15 and Impact on Systemic Drug Exposure

“…While examining the respective roles of liver and SI P450 enzymes in the first-pass metabolism of several oral drugs (Zhu et al, 2011;Zhu and Zhang, 2012), we made an intriguing observation that the clearance of oral LVS was not decreased (at 25 mg/kg), or even increased (at 5 mg/kg), in the LCN mice, which led to the hypothesis that SI LVS metabolism and P450 expression are upregulated by the loss of hepatic P450 function. After successful validation of this hypothesis using LCN mice compared with wild-type (WT) mice, we further explored the mechanisms that underlie the interorgan "cross-talk" by examining the bile acid (BA) pool and expression of BA target genes in the SI.…”

“…Those drugs surviving the first-pass metabolism in the SI will undergo further extraction in the liver before they reach systemic circulation. Therefore, P450 enzymes in the SI as well as those in the liver play essential roles in controlling the systemic exposure of oral drugs, as we have demonstrated for nifedipine and lovastatin (LVS) (Zhang et al, 2009;Zhu et al, 2011) using an intestinal epithelium (IE)-Cpr-null mouse model (Zhang et al, 2009), in which the Cpr gene is specifically deleted in the intestinal epithelium.…”

“…The assay for microsomal metabolism of LVS and the liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis for determination of its two metabolites (69b-hydroxy LVS and 69-exomethylene LVS) were performed as described (Zhu et al, 2011). Control experiments were performed in which NADPH was omitted.…”

“…Both LVS and LVA are CYP3A substrates (Ishigami et al, 2001). The extraction and LC-MS/MS analysis of LVA were performed as described (Zhu et al, 2011). Pharmacokinetic parameters were calculated by noncompartmental analysis using the PK Solver software (in Microsoft Excel).…”