The cytotoxic effect of paraquat to isolated renal proximal tubular segments from rabbits

Abstract

Paraquat (PQ) induces lung, liver and kidney damage. Since PQ mainly is eliminated by the kidney, the kidney damage is of particular importance to the outcome of PQ poisoning. The exact toxic mechanism of PQ is still unclear but it is assumed to involve redox cycling and formation of reactive oxygen species. In this study, further investigations on the toxic mechanism and metabolic effects of PQ were performed using isolated renal proximal tubules from rabbits. Proximal tubules were isolated using a combined iron perfusion and collagenase method. Suspended tubules were incubated for varying periods and concentrations of PQ at 25 or 37°C in Krebs-Ringer phosphate buffer or HCO 3 −/CO 2 buffer. The cytotoxic effect of PQ was evaluated by (1) markers of oxidative stress: status of glutathione (GSH/GSSG) and formation of malondialdehyde (MDA); and (2) markers of tubular metabolism: oxygen consumption (QO 2), transport of 14C- p-aminohippuric acid (PAH) and 14C-tetraethylammonium (TEA). Using 0.5 and 5 mM PQ, the GSH/GSSG ratio decreased whereas formation of MDA increased indicating oxidative stress. PQ reduced the accumulation of PAH and TEA, the basal QO 2 and the ouabain sensitive QO 2 indicating inhibition of the Na/K-ATPase. Nystatin-stimulated QO 2 was reduced by PQ, excluding inhibition of Na + entry as a possible cytotoxic mechanism and suggesting mitochondrial injury. This was confirmed by measuring FCCP-uncoupled QO 2. Thus high concentrations of PQ appear to disrupt mitochondrial electron chain transfer resulting in reduction of metabolic functions.