Albumin-bound fatty acids induce mitochondrial oxidant stress and impair antioxidant responses in proximal tubular cells

Albumin induces oxidative stress and cytokine production in proximal tubular cells (PTECs). Albumin-bound fatty acids (FAs) enhance tubulopathic effects of albumin in vivo. We proposed that FA aggravation of albumin-induced oxidative stress in PTECs might be involved. We hypothesized that mitochondria could be a source of such stress. Using a fluorescent probe, we compared reactive oxygen species (ROS) production after exposure of PTECs to bovine serum albumin (BSA) alone or loaded with oleic acid (OA-BSA) (3-30 g/l for 2 h). There was no difference in cellular albumin uptake, but OA-BSA dose-dependently induced more ROS than BSA alone (P < 0.001). OA-BSA-induced ROS was significantly alleviated by mitochondrial inhibition, but not by inhibitors of nicotinamide adenine dinucleotide phosphate hydrogenase ( NADPH) oxidase, xanthine oxidase, or nitric oxide synthase. Gene expression analysis showed that neither the NADPH oxidase component p22phox nor xanthine oxidase was induced by BSA or OA-BSA. OA-BSA, in contrast to BSA, failed to induce mitochondrial manganese superoxide dismutase 2 (SOD2) expression. OA-BSA showed a greater capacity than BSA to downregulate heme oxygenase-1 mRNA expression and accentuate inflammatory cytokine mRNA and protein. Supplementation of SOD activity with EUK-8 reduced ROS, and interleukin-6 protein expression was suppressed by both mitochondrial inhibition and SOD augmentation. Thus, in PTECs, FAs accentuate albumin-induced oxidative stress and inflammatory cytokine expression via increased mitochondrial ROS, while frustrating protective antioxidant responses.