Functional and energetic characterization of P-gp-mediated doxorubicin transport in rainbow trout (Oncorhynchus mykiss) hepatocytes

An assessment of energetic costs associated with P-glycoprotein (P-gp)-mediated xenobiotic efflux is important in understanding the energy budgets, tradeoffs, and fitness of organisms inhabiting contaminated environments. Here, a functional characterization and determination of the energetic costs associated with doxorubicin (DOX) efflux was examined in isolated hepatocytes of rainbow trout. The accumulation and efflux of DOX were both concentration dependent. The efflux of DOX over a 3 h incubation period resulted in a significant decrease in intracellular ATP concentrations (maximum decrease 25%) compared to control baseline levels, while significant increases in concentrations of ADP (max. 26%), AMP (max. 36%) and inorganic phosphate (max. 11%). were observed. In addition, significant reductions in the adenylate energy charge ([AEC]: max 11%), and phosphorylation potential ([PP]: max. 53%) were shown in cells incubated with DOX compared to control cells. Inhibition of DOX efflux (max. 61%) by the non-competitive P-gp inhibitor tariquidar (XR9576), demonstrated that changes in ATP, ADP, AMP, inorganic phosphate concentrations, AEC and PP in DOX-exposed hepatocytes were mainly due to P-gp activity. Overall, these results indicate that the exposure of trout hepatocytes to DOX increases energetic and metabolic costs that are associated specifically with P-gp efflux activity.