Stability, metabolism and transport of D-Asp(OBzl)-Ala - a model prodrug with affinity for the oligopeptide transporter

The model prodrug D-Asp(OBzl)-Ala has previously been shown to have affinit y and to be transported by the oligopeptide transporter PepT(1) expressed i n Caco-2 cells. The main objective of the present study was to investigate the aqueous stability of D-Asp(OBzl)-Ala and its in vitro metabolism in dif ferent gastrointestinal media arising from rats and humans, as well as in h uman plasma. The second major aim of the study was to evaluate our previous study in Caco-2 cell culture, by determining the effective intestinal perm eability (P-eff) of D-Asp(OBzl)-Ala in situ using the single-pass rat perfu sion model. The aqueous stability studies show water, general buffer, as we ll as specific acid and base catalysis of D-Asp(OBzl)-Ala. The degradation of the model prodrug was independent of ionic strength. The half-lives in r at jejunal fluid and homogenate were >3 h. In human gastric and intestinal fluids, the half-lives were >3 h and 2.3+/-0.03 h, respectively. rising the rat single-pass perfusion technique, the effective jejunal permeability (P -eff) of D-Asp(OBzl)-Ala was determined to be high (1.29+/-0.5.10(-4) cm/s) . The 32 times higher P-eff value found in the perfusion model compared to Caco-2 cells is most likely due to a higher functional expression of the ol igopeptide transporter. Rat jejuna P-eff was reduced by approximately 50% i n the presence of well known oligopeptide transporter substrates, such as G ly-Sar and cephalexin. It may be that D-Asp(OBzl)-Ala is primarily absorbed intact by the rat jejunal oligopeptide transporter, since the stability in the intestinal homogenate and fluids was rather high (t(1/2)>2.3 h). (C) 1 999 Elsevier Science BN. All rights reserved.