Influence of Fed-Fasted State on Intestinal PEPT1 Expression and In Vivo Pharmacokinetics of Glycylsarcosine in Wild-Type and Pept1 Knockout Mice

Abstract

To determine if fasting would affect the intestinal expression and in vivo functional activity of PEPT1 as determined after oral dosing of the dipeptide glycylsarcosine (GlySar). Systemic exposure and tissue distribution studies were performed in wild-type and Pept1 knockout mice, under fed and fasted conditions, following both intravenous and oral doses of [(14)C]GlySar at 5nmol/g body weight. Intestinal PEPT1 expression was evaluated by real-time PCR and immunoblot analyses. We found that expression of PEPT1 protein in the small intestine was increased ~2-fold in wild-type mice during fasted as compared to fed conditions. In agreement, systemic exposure and peak plasma concentrations of orally administered GlySar were 40 and 65% greater, respectively, in wild-type mice during fasted vs. fed state. No significant differences were observed between fed and fasted animals during PEPT1 ablation. Tissue distribution of GlySar was unchanged after oral dosing for all four treatment groups. As little as 16h of fasting can cause significant upregulation of PEPT1 protein expression in the small intestine, which then translates into a significant increase in in vivo oral absorption of GlySar.