Investigation of the absorption pathways of some poorly absorbed drugs using human intestinal (CAC0-2) cell monolayers

Abstract

Absorption across the gastro-intestinal epithelium is via two pathways; the transcellular and paracellular pathway. Caco-2 cells, when cultured on polycarbonate filters, formed a confluent monolayer with many properties of differentiated intestinal epithelial cells, As a model of human gastro-intestinaJ tract epithelia they were used to elucidate and characterise the transepithelial transport of two protein kinase C inhibitors, N-(3-chlorophenyl)-4-[2-(3-hydroxypropylamino)-4-pyridyl]-2-pyrimidinamin (CHPP) and N-benzoyl-staurosporine (NBS), and the polypeptide, human calcitonin.
Lanthanum ions are proposed as a paracellular pathway inhibitor and tested with D-mannitol permeability and transepithelial electrical resistance measurements. The effect La³⁺ has on the carrier-mediated transport of D-glucose and Sodium taurocholate as well as the vesicularly transcytosed horseradish peroxidase was also investigated.
As expected, 2 mM apical La³⁺ increases transepithelial electrical resistance 1.S-fold and decreases mannitol permeability by 63.0 % ± 1.37 %. This inhibition was not repeated by other cations. Apical 2 mM La³⁺ was found to decrease carrier-mediated D-glucose and taurocholate permeability by only 8.7 % ± 1.6 %, 26.3 % ± 5.0 %. There was no inhibitory effect on testosterone or PEG 4000 permeability observed with La³⁺. However, for horseradish peroxidase and human calcitonin permeability was decreased by 98.7 % ± 11.7%, and 96.2 % ± 0.8 % respectively by 2 mM La³⁺. Indicating that human calcitonin could also be transported by vesicular transcytosis.
The addition of 2 mM La³⁺ to the apical surface of Caco-2 monolayers produces a paracellular pathway inhibition. Therefore, La³⁺ could be a useful additional tool in delineating the transepithelial pathway of passive drug absorption.