NADPH oxidase subunit gp91phox, known also as Nox2, is an enzyme solely dedicated to the generation of ROS.22 Gp91phox expression is upregulated in the ischemic heart and salvages cardiomyocytes from ROS-induced injury.23 Knockdown of Nox2-NADPH oxidase using siRNA improves cardiac function following myocardial infarction.24 Loss of NOX2 (gp91phox) further reduces oxidative stress and prevents progression to advanced heart failure.25 In this study, we showed that the apelin overexpression significantly inhibited gp91phox expression in heart of STZ mice. The gene discussed is FMO5; the disease is heart failure.