title: Altered disposition and antinociception of [D-penicillamine(2,5)] enkephalin in mdr1a-gene-deficient mice.
abstract: This study was undertaken to test the hypothesis that P-glycoprotein (P-gp) modulates opioid peptide pharmacodynamics. [D-Penicillamine2, 5]enkephalin (DPDPE) (10 mg/kg i.v.) was administered to mdr1a(-/-) and wild-type mice to assess systemic disposition and antinociception. A subsequent dose-response experiment examined the impact of P-gp on DPDPE antinociception. In addition, the time course of antinociception was determined after a 0.9-mg/kg [mdr1a(-/-) mice] or 24-mg/kg (FVB mice) i.v. dose. Data were fit with a series of pharmacokinetic-pharmacodynamic models to compare the disposition and action of DPDPE in the two mouse strains. A 10-mg/kg dose produced >80% maximum possible response at all time points in mdr1a(-/-) mice; peak antinociception was <20% maximum possible response in FVB mice. DPDPE systemic disposition did not differ between the two mouse strains. Although brain tissue concentrations were 2- to 4-fold higher in mdr1a(-/-) compared to FVB mice, the dose required to elicit comparable antinociception was nearly 30-fold lower in mdr1a(-/-) mice; brain tissue EC50 differed by an order of magnitude in the two mouse strains. Pharmacokinetic-pharmacodynamic modeling indicated that the difference in antinociception between mdr1a(-/-) and FVB mice was a function of DPDPE distribution within brain, as well as between blood and brain, and not due to differences in intrinsic response. The results of this study suggest that DPDPE is a substrate of P-gp, and that P-gp is responsible, in part, for the low penetration of DPDPE into brain. The substantial difference in brain tissue EC50 in the absence vs. presence of P-gp suggests that P-gp modulates DPDPE-associated antinociception at sites other than the blood-brain interface.
authors.affiliation: Division of Drug Delivery and Disposition, School of Pharmacy, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
authors.forename: C
authors.initials: C
authors.lastname: Chen
authors.forename: G M
authors.initials: GM
authors.lastname: Pollack
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000700:Analgesics / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000493:pharmacokinetics* / Q000494:pharmacology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D014018:Tissue Distribution
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000700:Analgesics; D004745:Enkephalins; D020881:Enkephalin, D-Penicillamine (2,5)-