Title Site-dependent contributions of P-glycoprotein and CYP 3 A to cyclosporinA absorption , and effect of dexamethasone in small intestine of mice

We examined whether the oral bioavailability of cyclosporin A is controlled primarily by Pglycoprotein (P-gp) or CYP3A in the small intestine. In situ loop method was used to evaluate the uptake of cyclosporin A (40 nmol) at the upper and lower intestine of wild-type and mdr1a/1b knockout mice treated or not treated with dexamethasone (75 mg/kg/day, 7 days, i.p.). Expression of CYP3A mRNA in the control group was higher in the upper than the lower intestine, while that of the multidrug resistance-1a (mdr1a) mRNA was in the opposite order. Dexamethasone administration potently induced CYP3A andmdr1a mRNAs in the lower and upper intestine, respectively. At 45 min after cyclosporin A administration into an upper intestinal loop of the control group of wild-type mice, the ratio of residual cyclosporin A to dose did not differ significantly from that of mdr1a/1b knockout mice, whereas in dexamethasone-treated wild-type mice, the residual ratio was increased significantly. The ratio of the cyclosporin A metabolite M17 to cyclosporin A in portal venous blood at an upper intestinal loop of mdr1a/1b knockout mice was much higher than that a lower intestinal loop. The M17/cyclosporin A ratio of portal venous blood at a lower intestinal loop in mdr1a/ 1b knockout mice was increased significantly by dexamethasone treatment. These results suggest that, under physiological conditions, the oral bioavailability of cyclosporin A is mainly controlled by CYP3A in the upper intestine, rather than liver, but when P-gp is induced by steroid, the intestinal absorption of cyclosporin A may be inhibited. # 2006 Published by Elsevier Inc. * Corresponding author at: Department of Hospital Pharmacy, School of Medicine, Kanazawa University, 13-1 Takara-machi, Kanazawa 920-8641, Japan. Tel.: +81 76 265 2045; fax: +81 76 234 4280. E-mail address: miyaken@pharmacy.m.kanazawa-u.ac.jp (K.-I. Miyamoto). avai lab le at www.sc iencedi rect .com journal homepage: www.e lsev ier .com/ locate /b iochempharm 0006-2952/$ – see front matter # 2006 Published by Elsevier Inc. doi:10.1016/j.bcp.2006.07.020 Please cite this article as: Mingji Jin et al., Site-dependent contributions of P-glycoprotein and CYP3A to cyclosporin A absorption, and effect of dexamethasone in small intestine of mice, Biochemical Pharmacology (2006), doi:10.1016/j.bcp.2006.07.020. U N C O R R E C TE D P R O O F intestinal P-gp, rather than intestinal CYP3A, plays a key role in the interpatient variation in oral bioavailability of cyclosporin A. On the other hand, CYP3A accounts for about 30 and 70% of total CYP activity in the liver and small intestine, respectively [12–14], and intestinal first-pass metabolism mediated by CYP3A has been shown to be clinically relevant for several drugs, including cyclosporin A [15,16]. However, it remains to be fully clarified whether P-gp and/or CYP3A controls the oral bioavailability of cyclosporin A by limiting absorption from the small intestine. We have reported that the blood concentrations of cyclosporin A [17] and tacrolimus [18] were decreased by combined steroid hormones due to induction of P-gp and/or CYP3A in the liver and small intestine. Hsiu et al. [19] also suggested that quercetin significantly decreased the oral bioavailability of cyclosporin A by inducing P-gp and/or CYP3A4. Further, Konishi et al. [20] demonstrated that the oral bioavailability of cyclosporin A is decreased by methylprednisolone, and the mechanism involves enhancement of small-intestinal P-gp function. Based on a study comparing the effects of high-dose dexamethasone (75 mg/ kg/day intraperitoneally, for 7 days) in mdr1a/1b knockout mice and wild-type mice, we concluded that P-gp plays only a small role in the absorption of cyclosporin A under physiological conditions, but after induction by dexamethasone, P-gp functions as an absorption barrier to cyclosporin A in the small intestine [21]. In the present study, we used an in situ intestinal loop method to examine in detail the effects of both P-gp and CYP3A on the absorption of cyclosporin A from the upper and lower small intestine in wild-type and mdr1a/1b knockout mice treated with or without dexamethasone. 2. Materials and methods