Objectives: 

Sepsis induces the mitochondrial iNOS (i-mtNOS) and subsequent production of nitric oxide (NO•). NO• reacts with the superoxide anion generating the highly toxic peroxynitrites that impair the respiratory complexes, reducing ATP production. This condition favours the electron leak and, hence, the formation of reactive oxygen species (ROS). Melatonin is a potent antioxidant and anti-inflammatory molecule and, thus, we evaluated here its effects against mitochondrial dysfunction during sepsis.

Materials: 

Studies were performed in isolated liver mitochondria of male C57/Bl6 mice (3 mo.), and sepsis was induced by cecal ligation and puncture (CLP). The animals were divided as follows: control group; CLP group, and CLP+melatonin group. Mice were sacrificed at 8 and at 24 h after sepsis. Melatonin was sc injected at 30 mg/kg bw. Mitochondrial respiration was assessed by a high resolution respirometry. We also analysed the content and expression of UCP2 by WB and qRT-PCR, respectively, and the content of mitochondrial cytochromes by spectrophotometry.

Results: 

A significant decrease in the ADP-stimulated state 3 respiration and in the efficiency of OXPHOS in septic mice was observed. The RCR decreased along the sepsis, reaching the lowest value 24 hrs after sepsis. RCR decrease reflects a loss of the mitochondrial membrane integrity and a respiratory uncoupling. We found a decline of the cytochrome c in mitochondria of septic mice, suggesting its release to the cytosol and activation of apoptosis. Sepsis was also followed by an increased leak state and UCP2 expression.

Conclusions: 

The data suggest a severe mitochondrial dysfunction during sepsis. Melatonin treatment restored the normal mitochondrial physiology. Thus, melatonin is able to maintain mitochondrial homeostasis, preventing its failure in sepsis.