Identification of mitochondrial deficits and melatonin targets in liver of septic mice by high-resolution respirometry

Aims: Previous data showed that melatonin maintains liver mitochondrial homeostasis during sepsis, but neither the mechanisms underlying mitochondrial dysfunction nor the target of melatonin are known. Main methods: Here, we analyzed mitochondrial respiration in isolated mouse liver mitochondria with different substrate combinations (glutamate/malate, glutamate/malate/sucinate or succinate/rotenone) to identify mitochondrial defects and melatonin targets during sepsis. Other bioenergetic parameters including a + a(3), b, and c + c(1) content, mitochondrial mass, and mitochondrial supercomplexes formation were analyzed. Mitochondrial function was assessed during experimental sepsis induced by cecal ligation and puncture (CLP) in livers of 3 mo. C57BL/6 mice at early and late phases of sepsis, i.e., at 8 and 24 h after sepsis induction. Key findings: Septic mice showed mitochondrial injury with a decrease in state 3, respiratory control rate, mitochondrial mass, and cytochrome b and c + c(1) content, which was prevented by melatonin treatment. Mitochondrial dysfunction in sepsis was mainly linked to complex I damage, because complex II was far less impaired. These mitochondria preserved the respiratory supramolecular organization, maintaining their electron transport system capacity. Significance: This work strengthens the use of substrate combinations to identify specific respiratory defects and selective melatonin actions in septic mitochondria. Targeting mitochondrial complex I should be a main therapeutical approach in the treatment of sepsis, whereas the use of melatonin should be considered in the therapy of clinical sepsis. (C) 2014 Elsevier Inc. All rights reserved.