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-expression 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 μg/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.