Significance of peptide transporter 1 in the intestinal permeability of valacyclovir in wild-type and PepT1 knockout mice

Abstract

The purpose of this study was to quantitatively determine the contribution of PepT1 [peptide transporter 1 (SLC15A1)] to the intestinal permeability of valacyclovir, an ester prodrug of the antiviral drug acyclovir. In situ single-pass intestinal perfusions were employed (pH 6.5 3 90 minutes) to assess the effective permeability (Peff) of 100 mM [3H]valacyclovir in wild-type and PepT1 knockout mice. Acyclovir pharmacokinetics was also evaluated after oral administration of 25 nmol/g valacyclovir. In wild-type mice, jejunal uptake of valacyclovir was best described by both saturable (Km = 10.2 mM) and nonsaturable components where the saturable pathway accounted for 82% of total transport. Valacyclovir Peff was 2.4 3 1024 cm/s in duodenum, 1.7 3 1024 cm/s in jejunum, 2.1 3 1024 cm/s in ileum, and 0.27 3 1024 cm/s in colon. In Pept1 knockout mice, Peff values were about 10% of that in wild-type animals for these small intestinal segments. Valacyclovir Peff was similar in the colon of both genotypes. There were no differences in valacyclovir Peff between any of the intestinal segments of PepT1 knockout mice. Valacyclovir Peff was significantly reduced by the dipeptide glycylsarcosine and the aminocephalosporin cefadroxil, but not by the amino acids L-valine or L-histidine, the organic acid p-aminohippurate, or the organic base tetraethylammonium (all at 25 mM). PepT1 ablation resulted in 3-to 5-fold reductions in the in vivo rate and extent of valacyclovir absorption. Our findings conclusively demonstrate, using in situ and in vivo validations in genetically modified mice, that PepT1 has a major influence in improving the oral absorption of valacyclovir. Copyright © 2013 by The American Society for Pharmacology and Experimental Therapeutics.