New methods to evaluate intestinal drug absorption mediated by oligopeptide transporter from in vitro study using Caco-2 cells.

The aim of the present work is to develop a convenient and rapid screening system in vitro for intestinal drug absorption mediated by oligopeptide transporter (PepT1). In this study, (1) Transports of cephalexin (CEX) and L-phenylalanine (L-Phe) across Caco-2 monolayers were measured and compared with those of passively transported drugs, (2) Inhibitory effects of various drugs on the transport of [(14)C]glycylsarcosine (Gly-Sar) across Caco-2 monolayers were measured and correlated with their in vivo permeability to rat small intestine, (3) Intracellular pH-change induced by co-transport of drugs with proton into Caco-2 cells was monitored by using Fluorometric Imaging Plate Reader (FLIPR, Molecular Devices Corp.). Concentration-dependent transport was observed in Caco-2 monolayers for CEX and L-Phe, although their permeability was relatively low compared to those of passively transported drugs. Inhibitory effects of various drugs including beta-lactam antibiotics and angiotensin converting enzyme-inhibitors on the transport of Gly-Sar correlated well with their in vivo permeability to rat small intestine. It was demonstrated that CEX, but not cefazolin, induced gradual decrease in the intracellular pH of Caco-2 cells. The degree of intracellular pH-change caused by various drugs showed a sigmoidal or saturable relationship with their permeability to rat small intestine. These in vitro approaches with Caco-2 cells should be useful to evaluate in vivo intestinal permeability of drugs mediated by PepT1, suggesting a possibility of high throughput screening of drug absorption.