Limited Role of P-Glycoprotein in the Intestinal Absorption of Cyclosporin A

Abstract

Cyclosporin A (CsA), a powerful immunosuppressive agent, is orally administered to prevent rejection in new organ transplants and to treat a variety of autoimmune diseases.1) The intestinal absorption of CsA following oral administration is poor (typically 20-50%) and varies greatly among patients, 2) owing to its relatively high molecular weight (1202.6), poor solubility in aqueous fluids, 3) site-specific absorption in the small intestine, 4) and intestinal firstpass metabolism by the Cyp450 system. 5) Furthermore, Pglycoprotein (P-gp), an ATP-dependent efflux transporter, has been proposed as a factor in the poor absorption of CsA [6][7][8] via various experiments, including the effect of single nucleotide polymorphism of P-gp 9) and P-gp related herb-CsA drug interaction. 10) However, little is known to date concerning the quantitative contribution of P-gp to the absorption of CsA. Only a limited number of experiments, such as an in vitro transport study employing the Caco-2 cell system, 11) a speculative in vivo experiment in mice 12) and human clinical trials, 13) have been reported. Thus, the quantitative contribution of P-gp to the absorption of CsA was investigated in the present study. For this purpose, the absorption of CsA in P-gp knockout (Mdr1a/1b knockout) mice and wildtype mice was compared, and the concentration dependency of the transport of CsA across Caco-2 cell monolayers was investigated. MATERIALS AND METHODS Chemicals and Dosage Forms3 H-CsA (Amersham, Okaville, ON, U.S.A.), CsA (Galena Co., Czecho) and Neoral ® (a CsA microemulsion by Norvatis Pharma AG, Basle, Switzerland) were used. 3 H-CsA was diluted with the Neoral ® solution in saline to give a specific activity of 10 mCi/ml. All other chemicals were of reagent grade and were used without further purification.Animal Experiments P-gp knockout (Mdr1a/1b knockout) mice (Tarconic, U.S.A.) and wild-type control, FVB mice, weighing 28Ϯ5 g (9-18 weeks of age), were used in all experiments. For the pharmacokinetic study, CsA (as Neoral ® solution, 1 mg/kg) was intravenously administered to mice via the tail vein or orally.8,12) This dose was comparable to an usual dose of CsA in human (i.e., 175 mg/body). In order to avoid possible chronopharmacokinetic changes, 14) the administration was always performed at around 10:30 a.m. Blood samples (10 ml) were collected from the tail artery at designated time intervals, solubilized using a Soluene350 ® : propanol mixture (1 : 1, v/v) and decolorized by the addition of 30% H 2 O 2 . Brain was removed 24 h after the each administration, and solubilized in a similar manner. Total radioactivity was determined by liquid scintillation counting (LS 6000SE; Beckman Coulter, Fullerton, CA, U.S.A.), and used for the calculation of blood and brain concentration of CsA.The area under the blood CsA concentration from time 0 to 24 h after administration (AUC 0-24 ) was determined by the standard log-linear trapezoidal rule. The apparent absolute oral bioavailability (F, %) was calculated by comparing the AUC 0-...

Long‐Term Changes in Cyclosporine Pharmacokinetics After Renal Transplantation in Children: Evidence for Saturable Presystemic Metabolism and Effect of NR1I2 Polymorphism

“…In 1 study in 60 adult liver transplant patients, cyclosporine AUC 0–24 h increased by 30% when the patients were changed from bid dosing (1.1‐mg/kg single doses) to once‐daily dosing (2.2‐mg/kg single dose) 35 . Thus, it can be hypothesized that the inhibitory effects of cyclosporine on CYP3A4 and P‐glycoprotein 13 , 36 – 38 result in auto‐inhibition and dose‐dependent pharmacokinetics at low single doses, such as those used in our patients, whereas complete saturation of CYP3A4 or P‐glycoprotein renders cyclosporine pharmacokinetics dose‐linear after a certain threshold dose is exceeded 39 …”

“…35 Thus, it can be hypothesized that the inhibitory effects of cyclosporine on CYP3A4 and P-glycoprotein 13,[36][37][38] result in auto-inhibition and dose-dependent pharmacokinetics at low single doses, such as those used in our patients, whereas complete saturation of CYP3A4 or P-glycoprotein renders cyclosporine pharmacokinetics dose-linear after a certain threshold dose is exceeded. 39 As young children have a larger clearance/body weight than older children, 9 their cyclosporine halflife is shorter, leading to greater peak-to-trough ratios. Therefore, to avoid high cyclosporine peaks associated with acute nephrotoxicity 40 and tremor, 41 we divided the daily dose into 3 single doses in young children in our center.…”

Utility of In Vitro Systems and Preclinical Data for the Prediction of Human Intestinal First-Pass Metabolism during Drug Discovery and Preclinical Development

“…Nifedipine is a P-gp substrate but neither the PBPK nor the indirect method can distinguish between P-gp-mediated efflux and intestinal metabolism. P-gp-mediated intestinal efflux is often expected to be minimal due to high intestinal concentrations, especially for high-solubility drugs (Kwon et al, 2004;Cao et al, 2005) and a limited role of P-gp has been reported for cyclosporine A (Lee et al, 2005), tacrolimus (Saitoh et al, 2006), and verapamil (Cao et al, 2005).…”

Modest Effect of Impaired P-glycoprotein on the Plasma Concentrations of Fexofenadine, Quinidine, and Loperamide following Oral Administration in Collies

“…A number of studies, particularly using Mdr1a Ϫ/Ϫ and Mdr1a/ 1b Ϫ/Ϫ mice, have demonstrated that P-gp limits oral availability and penetration into the brain and mediates biliary and urinary excretion by actively extruding xenobiotics into the adjacent luminal space (Chen et al, 2003;Mizuno et al, 2003). For instance, Mdr1a/1b Ϫ/Ϫ mice exhibited greater plasma concentrations than wild-type mice after oral administration of paclitaxel (Sparreboom et al, 1997), fexofenadine (Tahara et al, 2005), cyclosporin A (Lee et al, 2005), etoposide (Allen et al, 2003), and vinblastine (Ogihara et al, 2006). For daunomycin, loperamide, quinidine, ritonavir, and verapamil, the permeability-surface area product in the small intestine increased more than three times in Mdr1a/1b Ϫ/Ϫ mice (Adachi et al, 2003).…”