Abstract
The purpose of this study was to determine if glycylsarcosine (a model dipeptide) and oseltamivir (an antiviral prodrug) exhibited a species-dependent uptake in yeast Pichia pastoris expressing the rat, mouse, and human homologues of PEPT1. Experiments were performed with [3H]glycylsarcosine (GlySar) in yeast Pichia pastoris expressing human, mouse and rat PEPT1, in which uptake was examined as a function of time, concentration, potential inhibitors and the dose-response inhibition of GlySar by oseltamivir. Studies with [14C]oseltamivir were also performed under identical experimental conditions. We found that GlySar exhibited a saturable uptake in all three species, with Km values for human (0.86 mM) > mouse (0.30 mM) > rat (0.16 mM). GlySar uptake in the yeast transformants was specific for peptides (GlyPro) and peptide-like drugs (cefadroxil, cephradine, valacyclovir), but was unaffected by glycine, L-histidine, cefazolin, cephalothin, cephapirin, acyclovir, SITS, TEA and elacridar. Although oseltamivir caused a dose-dependent inhibition of GlySar uptake [IC50 values for human (27.4 mM) > rat (18.3 mM) > mouse (10.7 mM)], the clinical relevance of this interaction would be very low in humans. Importantly, oseltamivir was not a substrate for the intestinal PEPT1 transporter in yeast expressing the three mammalian species tested. Instead, the prodrug exhibited nonspecific binding to the yeast vector and PEPT1 transformants. Finally, the mouse appeared to be a better animal model than rat for exploring the intestinal absorption and pharmacokinetics of peptides and peptide-like drugs in human.
- Received February 9, 2012.
- Accepted April 9, 2012.
- The American Society for Pharmacology and Experimental Therapeutics