CYTOTOXIC EFFECTS OF PAMIDRONATE ON MONOLAYERS OF HUMAN INTESTINAL EPITHELIAL (CACO-5) CELLS AND ITS EPITHELIAL TRANSPORT

Pamidronate (APD) is a new drug in the treatment of osteolytic bone di seases. Caco-2 cells were used to study the cytotoxic effects of APD o n intestinal epithelium and also the transport (mechanism) of APD acro ss the intestinal epithelium. We investigated the cytotoxic effect of APD by combining two spectrophotometric assays [neutral red (NR) uptak e and lactate dehydrogenase (LDH) release] with a morphological assay (electron microscopy). The amount of APD transported across the Caco-2 monolayer was measured by HPLC. The permeability of the monolayer was studied by determining the transepithelial electrical resistance (TEE R). The results show that after exposing the Caco-2 cells to increasin g concentrations of APD [dose range calculated on the basis of relevan ce to the oral dose administered to patients] the NR uptake decreased while LDH loss increased, which is indicative of a cytotoxic effect of APD. Ultrastructural alterations, including a widening in intercellul ar spaces and, at higher doses, complete cell death, were observed. Th e transport percentage of nontoxic doses of APD was low, while the TEE R decreased with increasing doses of APD. In conclusion, APD is cytoto xic for Caco-2 cells. As the transport percentage of nontoxic doses of APD is low and APD reduces the TEER, it is hypothesized that APD is t ransported paracellularly.