Oxidative stress alters mitochondrial bioenergetics and modifies pancreatic cell death independently of cyclophilin D, resulting in an apoptosis-to-necrosis shift

Mitochondrial dysfunction lies at the core of acute pancreatitis (AP). Diverse AP stimuli induce Ca(2+)-dependent formation of the mitochondrial permeability transition pore (MPTP), a solute channel modulated by cyclophilin D (CypD), the formation of which causes ATP depletion and necrosis. Oxidative stress reportedly triggers MPTP formation and is elevated in clinical AP, but how reactive oxygen species influence cell death is unclear. Here, we assessed potential MPTP involvement in oxidant-induced effects on pancreatic acinar cell bioenergetics and fate. H(2)O(2) application promoted acinar cell apoptosis at low concentrations (1–10 μm), whereas higher levels (0.5–1 mm) elicited rapid necrosis. H(2)O(2) also decreased the mitochondrial NADH/FAD(+) redox ratio and ΔΨ(m) in a concentration-dependent manner (10 μm to 1 mm H(2)O(2)), with maximal effects at 500 μm H(2)O(2). H(2)O(2) decreased the basal O(2) consumption rate of acinar cells, with no alteration of ATP turnover at <50 μm H(2)O(2). However, higher H(2)O(2) levels (≥50 μm) diminished spare respiratory capacity and ATP turnover, and bioenergetic collapse, ATP depletion, and cell death ensued. Menadione exerted detrimental bioenergetic effects similar to those of H(2)O(2), which were inhibited by the antioxidant N-acetylcysteine. Oxidant-induced bioenergetic changes, loss of ΔΨ(m), and cell death were not ameliorated by genetic deletion of CypD or by its acute inhibition with cyclosporine A. These results indicate that oxidative stress alters mitochondrial bioenergetics and modifies pancreatic acinar cell death. A shift from apoptosis to necrosis appears to be associated with decreased mitochondrial spare respiratory capacity and ATP production, effects that are independent of CypD-sensitive MPTP formation.