Mechanism of RPE Cell Death in α-Crystallin Deficient Mice: A Novel and Critical Role for MRP1-Mediated GSH Efflux

Absence of α-crystallins (αA and αB) in retinal pigment epithelial (RPE) cells renders them susceptible to oxidant-induced cell death. We tested the hypothesis that the protective effect of α-crystallin is mediated by changes in cellular glutathione (GSH) and elucidated the mechanism of GSH efflux. In α-crystallin overexpressing cells resistant to cell death, cellular GSH was >2 fold higher than vector control cells and this increase was seen particularly in mitochondria. The high GSH levels associated with α-crystallin overexpression were due to increased GSH biosynthesis. On the other hand, cellular GSH was decreased by 50% in murine retina lacking αA or αB crystallin. Multiple multidrug resistance protein (MRP) family isoforms were expressed in RPE, among which MRP1 was the most abundant. MRP1 was localized to the plasma membrane and inhibition of MRP1 markedly decreased GSH efflux. MRP1-suppressed cells were resistant to cell death and contained elevated intracellular GSH and GSSG. Increased GSH in MRP1-supressed cells resulted from a higher conversion of GSSG to GSH by glutathione reductase. In contrast, GSH efflux was significantly higher in MRP1 overexpressing RPE cells which also contained lower levels of cellular GSH and GSSG. Oxidative stress further increased GSH efflux with a decrease in cellular GSH and rendered cells apoptosis-prone. In conclusion, our data reveal for the first time that 1) MRP1 mediates GSH and GSSG efflux in RPE cells; 2) MRP1 inhibition renders RPE cells resistant to oxidative stress-induced cell death while MRP1 overexpression makes them susceptible and 3) the antiapoptotic function of α-crystallin in oxidatively stressed cells is mediated in part by GSH and MRP1. Our findings suggest that MRP1 and α crystallin are potential therapeutic targets in pathological retinal degenerative disorders linked to oxidative stress

Preparation, Characterization and Optimization of Ibuprofen Ointment Intended for Topical and Systemic Delivery

Purpose: To develop an ibuprofen ointment with a potential for both topical and systemic delivery of the drug. Method: A co-solvency technique with a trial and error approach was used to develop a 10% ibioprofen ointment in petrolatum base, with the entire drug dissolved in the base. An insertion cell was used to evaluate drug release from the formulations. Further, factorial design multiple regression (FDMRA) analysis, a statistical optimization technique, was used in the optimization of the final formulation. Result: The desired ibuprofen ointments were developed. Release depended on vehicle and proportion of co-solvents. Best fit equations for optimization purposes including various fluxes (initial, steady-state and total) and diffusion coefficient as dependent variables and the concentrations of co-solvents as independent variables were obtained using SAS programme. Dependent variables strongly depended (p<0.05) on the independent variables and followed the polynomial equations generated. Conclusion: The ointments consisting of petrolatum base (80%), PEG 400 (6%) and propylene glycol (4%) and ibuprofen (10%) and that consisting of petrolatum base (75%), PEG 400 (6%), propylene glycol (4%), menthol (5%) and ibuprofen (10%) can be used for topical and systemic delivery of the active, ingredient respectively