Intermedin protects against renal ischemia-reperfusion injury by inhibition of oxidative stress.

Reactive oxygen species (ROS) play a critical role in renal ischemia-reperfusion injury (IRI). Intermedin (IMD) reportedly protected against myocardial IRI via its antioxidant effects; however, its protective role in renal IRI has not been investigated. We overexpressed IMD in rat kidneys and examined how the kidneys respond to renal IRI. Eukaryotic expression plasmid encoding the rat IMD gene or control empty vector was transfected into the left kidney using an ultrasound-microbubble-mediated delivery system. This method yielded high expression of IMD in kidney cells. Renal IRI was induced by clamping the left renal artery followed by reperfusion. In response to IRI, overexpression of IMD in the kidney significantly improved renal function and pathology compared with the kidney transfected with control plasmid. We investigated the mechanisms by which IMD protects against renal IRI. We examined renal superoxide dismutase (SOD) activity and malondialdehyde (MDA) content and found SOD activity was significantly increased, while MDA level was markedly decreased in kidneys transfected with IMD, suggesting ROS production and oxidative stress were reduced by IMD overexpression. We also measured myeloperoxidase (MPO) activity, tubular cell apoptosis, and the expression of intercellular adhesion molecule-1 (ICAM-1), P-selectin, and endothelin-1 (ET-1) in the kidney. Renal MPO activity and the expression of ICAM-1, P-selectin, and ET-1 stimulated by IRI were significantly inhibited by IMD overexpression. Moreover, IMD overexpression prevented kidney cells from apoptosis caused by IRI. Our results demonstrate that overexpression of IMD in the kidney protects against renal IRI, apparently by reducing oxidative stress, consequently suppressing inflammation and vasoconstrictor production and apoptosis.