Effect of poly(ethylene glycol)-block-polylactide nanoparticles on hepatic cells of mouse: Low cytotoxicity, but efflux of the nanoparticles by ATP-binding cassette transporters

The objective of this paper is to study the effects of poly(ethylene glycol) -block-polylactide (PLA-PEG) nanoparticles on hepatic cells of mouse. Blank PLA-PEG nanoparticles have been successfully prepared and MTT assay suggested that the nanoparticles with HepG2 cell co-culture model did not cause significant changes in membrane integrity in controlled concentration range (0.001-0.1 mg/ml). Immunohistochemical analysis demonstrated that large dose of PLA-PEG nanoparticles injection (42.04 mg/kg, i.v.) did not induce hepatic cell apoptosis. From biochemical assay experiments, although the levels of SOD decreased and those of MDA, NOS increased after treatment with large dose of PLA-PEG nanoparticles injection (42.04 mg/kg, i.v.), they were all not significant (p > 0.05). Then Kunming mice were treated with large dose of PLA-PEG nanoparticles (42.04 mg/kg, i.v.) and after 4 days total RNA was isolated to elucidate patterns of gene expression using a mouse cDNA-microarray (SuperArray). Treatment with nanoparticles resulted in over-exoression of a lot of ATP-binding cassette (ABC) transporters, especially two ABC transporters (ABCA8 and ABCC5/MRP5), and down-regulation of GSTP1, in comparison with the control. ABCA8 could extrude low molecular weight polymers after PLA-PEG nanoparticles hydrolysis outside the cells. We also discovered that ABCC5 expressed multidrug resistance protein 5 (MRP5) to pump out conjugate (GS-X) of PLA-PEG nanoparticles with GSH. The results were confirmed by RT-PCR. Results of in vitro accumulation and efflux experiments indicated that about 51-52% (51.5% and 52.0%) intracellular PLA-PEG nanoparticles was expulsed after mouse primary hepatocytes reached a saturation uptake of nanoparticles during the concentration range of 750-1000 mu g/ml. The results suggested that ABC transporters (especially ABCA8) pump out the polymers after hydrolysis from mouse hepatic cells and large dose of PLA-PEG nanoparticles make mouse hepatic cells gain drug resistance to PLA-PEG nanoparticles. (C) 2006 Elsevier B.V. All rights reserved.