Jason Zastre1, John Jackson, Helen Burt. 1. Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z3.
Abstract
PURPOSE: The purpose of this study was to investigate the pathways involved in rhodamine 123 (R-123) accumulation enhancement in Caco-2 cells with a low molecular-weight methoxypolyethylene glycol-block-polycaprolactone (MePEG-b-PCL) diblock copolymer. METHODS: R-123 accumulation by Caco-2 cells with MePEG17-b-PCL5 was measured in the presence of endocytosis inhibitors or under ATP depletion conditions. Directional flux studies were conducted with cell monolayers on Transwell plates. RESULTS: Endocytosis inhibitors had no effect on reducing R-123 accumulation with MePEG17-b-PCL5. The apical to basolateral (AP-->BL) flux of R-123 with MePEG17-b-PCL5 or verapamil was similar to R-123 alone. However the BL-->AP flux was significantly decreased with MePEG17-b-PCL5 and verapamil. The efflux ratio for R-123 flux was 3.2 and was reduced to 1.06 with MePEG17-b-PCL5 confirming the inhibition of P-glycoprotein (P-gp)-mediated efflux. R-123 accumulation at the conclusion of each of the flux experiments was similar for MePEG17-b-PCL5 and verapamil in the BL-->AP direction. The AP-->BL direction demonstrated a 2-fold increase for verapamil and a 5-fold increase with MePEG17-b-PCL5. This difference in R-123 accumulation was possibly due to the diblock enhancing passive membrane diffusion of R-123. CONCLUSIONS: MePEG17-b-PCL5 diblock reduced R-123 efflux through inhibition of P-gp efflux, and unimers may interact with cell membranes, increasing permeability and enhancing R-123 influx through increased transmembrane diffusion.
PURPOSE: The purpose of this study was to investigate the pathways involved in rhodamine 123 (R-123) accumulation enhancement in Caco-2 cells with a low molecular-weight methoxypolyethylene glycol-block-polycaprolactone (MePEG-b-PCL) diblock copolymer. METHODS:R-123 accumulation by Caco-2 cells with MePEG17-b-PCL5 was measured in the presence of endocytosis inhibitors or under ATP depletion conditions. Directional flux studies were conducted with cell monolayers on Transwell plates. RESULTS: Endocytosis inhibitors had no effect on reducing R-123 accumulation with MePEG17-b-PCL5. The apical to basolateral (AP-->BL) flux of R-123 with MePEG17-b-PCL5 or verapamil was similar to R-123 alone. However the BL-->AP flux was significantly decreased with MePEG17-b-PCL5 and verapamil. The efflux ratio for R-123 flux was 3.2 and was reduced to 1.06 with MePEG17-b-PCL5 confirming the inhibition of P-glycoprotein (P-gp)-mediated efflux. R-123 accumulation at the conclusion of each of the flux experiments was similar for MePEG17-b-PCL5 and verapamil in the BL-->AP direction. The AP-->BL direction demonstrated a 2-fold increase for verapamil and a 5-fold increase with MePEG17-b-PCL5. This difference in R-123 accumulation was possibly due to the diblock enhancing passive membrane diffusion of R-123. CONCLUSIONS: MePEG17-b-PCL5 diblock reduced R-123 efflux through inhibition of P-gp efflux, and unimers may interact with cell membranes, increasing permeability and enhancing R-123 influx through increased transmembrane diffusion.
Authors: T J Lampidis; C Castello; A del Giglio; B C Pressman; P Viallet; K W Trevorrow; G K Valet; H Tapiero; N Savaraj Journal: Biochem Pharmacol Date: 1989-12-01 Impact factor: 5.858