Ischemia-reperfusion injury-induced pulmonary mitochondrial damage.

Background: Mitochondrial dysfunction is a key factor in solid organ ischemia-reperfusion (IR) injury. Impaired mitochondrial integrity predisposes to cellular energy depletion, free radical generation, and cell death. This study analyzed mitochondrial damage induced by warm pulmonary IR.

Methods: Anesthetized Wistar rats received mechanical ventilation. Pulmonary clamping was followed by reperfusion to generate IR injury. Rats were subjected to control, sham, and to 2 study group conditions: 30 minutes of ischemia without reperfusion (IR30/0), or ischemia followed by 60 minutes of reperfusion (IR30/60). Pulmonary edema was quantified by wet/dry-weight ratio. Polarography determined activities of respiratory chain complexes. Mitochondrial viability was detected by using Ca(2+)-induced swelling, and integrity by citrate synthase assay. Enzyme-linked immunosorbent assay determined cytochrome C content. Mitochondrial membrane potential (ΔΨm) stability was analyzed by flow cytometry using JC1, inflammation by myeloperoxidase (MPO) activity, and matrix-metalloproteinase-9 (MMP-9) activity by gel zymography, respectively.

Results: In IR30/60 rats, tissue water content was elevated from 80.6 % (sham) to 86.9%. After ischemia, ΔΨm showed hyperpolarization and rapid decline after uncoupling compared with controls. IR, but not ischemia alone, impaired respiratory chain function complexes I, II and III (p < 0.05). Mitochondrial viability (p < 0.001) and integrity (p < 0.01) was impaired after ischemia and IR, followed by mitochondrial cytochrome C loss (p < 0.05). Increased activation of MPO (p < 0.01) and MMP-9 (p < 0.001) was induced by reperfusion after ischemia.

Conclusions: Ischemia-related ΔΨm hyper-polarization induces reperfusion-associated mitochondrial respiratory chain dysfunction in parallel with tissue inflammation and degradation. Controlling ΔΨm during ischemia might reduce IR injury.