Figure 1.

Different intracellular ROS sources participate in ROS generation by adipocytes. Mitochondria, as the core machinery for energy production through oxidative phosphorylation, is considered as a main source of O₂ ^•−, predominantly produced at complexes I and III. Superoxide anions will be further converted to H₂O₂ by mitochondrial manganese superoxide dismutase (MnSOD). ROS can also be produced by NADPH oxidases enzymes, in which Nox4 is the main isoform in adipocytes. This isoform presents the particularity to primarily generate H₂O₂, whereas other NADPH oxidases would generate O₂ ^•− later converted to H₂O₂ by endogenous SOD. Nitric oxide synthase, whose eNOS and iNOS isoforms are abundantly expressed by adipocytes, might represent another source of ROS since they can be uncoupled to produce O₂ ^•− in the absence of sufficient amounts of substrates.