Received for publication March 8, 2006.
Revised April 6, 2006.
Accepted for publication April 11, 2006.

The Anti-Inflammatory Drug, Nimesulide Uncouples Mitochondria and Induces Mitochondrial Permeability Transition in Human Hepatoma Cells. Protection by Albumin

Abstract

Like other nonsteroidal anti-inflammatory drugs, nimesulide triggers hepatitis in a few recipients. Although nimesulide has been shown to uncouple mitochondrial respiration and cause hepatocyte necrosis in the absence of albumin, mechanisms for cell death are incompletely understood, and comparisons with human concentrations are difficult because 99% of nimesulide is albumin-bound. We studied the effects of nimesulide, with or without a physiological concentration of albumin, in isolated rat liver mitochondria or microsomes, and in human hepatoma cells. Nimesulide did not undergo monoelectronic nitro reduction in microsomes. In mitochondria incubated without albumin, nimesulide (50 µM) decreased the mitochondrial membrane potential (_m), increased basal respiration, and potentiated the mitochondrial permeability transition (MPT) triggered by calcium preloading. In HUH-7 cells incubated for 24 hours without albumin, nimesulide (1 mM) decreased the _m and cell NAD(P)H, and increased the glutathione disulfide/reduced glutathione ratio and cell peroxides; nimesulide triggered MPT, ATP depletion, high cell calcium, and caused mostly necrosis, with rare apoptotic cells. Co-incubation with either cyclosporin A (an MPT inhibitor) or the combination of fructose-1,6-diphosphate (a glycolysis substrate) and oligomycin (an ATPase inhibitor) prevented the decrease in _m, ATP depletion and cell death. A physiological concentration of albumin abolished the effects of nimesulide on isolated mitochondria or HUH-7 cells. In conclusion, the weak acid, nimesulide uncouples mitochondria and triggers MPT and ATP depletion in isolated mitochondria or hepatoma cells incubated without albumin. However, in the presence of albumin, only a fraction of the drug enters cells or organelles, and uncoupling and toxicity are not observed.

Key words: Hepatitis, Mitochondria, Mitochondrial permeability transition, Nimesulide, Nonsteroidal anti-inflammatory drug, Uncoupling