Electron transport chain function during endotoxin-induced sepsis. Increased ROS emission through electron leak from the respiratory chain in mitochondria may exacerbate mitochondrial impairment and 
induce mitochondrial AbMole 3,4,5-Trimethoxyphenylacetic acid AbMole LOUREIRIN-B Oxidative stress. Since IA LPS injection promotes systemic oxidative stress and an inflammatory response in the preterm fetal lamb, we hypothesised that LPS-induced weakness in the preterm diaphragm would be associated with inhibition of mitochondrial complex activity and oxidative stress. This hypothesis is supported by our findings that a 2 d IA LPS exposure depresses the activity of electron transport chain complexes II and IV, and that a longer LPS exposure increased oxidative modified protein content, compared with the 2 d exposure group. An alternative possibility is that impaired mitochondrial complex activity enhanced the production of ROS and was primarily responsible for the oxidative stress that occurred after a 7din utero LPS exposure. The mitochondrial electron transport chain generates superoxide at complexes I, II, and III. Complex III is the principal site of ROS production by generating superoxide at the Qo site, resulting in superoxide accumulation in the intermembrane space or the matrix. Although activity of complex III did not change, the pattern of decreasing complex III activity with increasing duration of fetal exposure to LPS was consistent with that observed for complex IV. Complex IV activity was significantly decreased in both 2 d and 7 d LPS groups. Complex IV has not been reported to generate ROS; however, cytochrome c participates in the generation of hydrogen peroxide by providing electrons to p66 Shc. Oxidative stress occurs when the production of ROS overwhelms the scavenging capacity of antioxidant system. Under physiological conditions, an increase in ROS stimulates further antioxidant enzyme expression, increasing the capacity of the antioxidant defence system to maintain redox homeokinesis and protect cells from ROS-induced oxidative damage. This adaptive response to accumulation of free radicals is also observed in diaphragm preparations weakened after exposure to controlled mechanical ventilation of diaphragm or soleus muscle preparations after immobilization and represents a cell-protective mechanism for managing oxidative stress. Unlike the adult, the antioxidant system of the fetus is underdeveloped and susceptible to environmental insults resulting in oxidative stress during fetal development. Consequently, an increase in production of ROS may overwhelm the compromised preterm oxidant defensive system, promoting the development of oxidative stress. We examined gene expression and protein hydrogen peroxide, which are subsequently converted to water and oxygen by catalase. Similarly, GPX1 utilizes reduced glutathione as a reducing equivalent to reduce hydrogen peroxide to form oxidized glutathione and water. We showed that a 7 d in utero LPS exposure inhibited catalase and SOD2 gene and protein expression, but not GPX1, reflecting a decrease in ROS scavenging which coincides with mitochondrial oxidative protein accumulation. Thus, down-regulation of antioxidant enzymes may be a secondary mechanism leading to mitochondrial oxidative stress in the preterm lamb. Nrf2 transcriptional factor regulates the expression of antioxidant genes through antioxidant response cis-elements. We analysed Nrf2 protein levels in the cell lysate and nuclear fraction of diaphragm muscle to investigate whether Nrf2 signalling participates in down-regulation of antioxidant genes after fetal exposure to IA LPS.