α-Melanocyte-stimulating hormone protects against renal injury after ischemia in mice and rats

Reperfusion after ischemia induces cytokines, chemoattractaut chemokines, adhesion molecules, and nitric oxide (NO). The resultant neutrophil adherence and NO potentiates renal injury. α-Melanocyte- stimulating hormone (α-MSH) is a potent anti-inflammatory agent that inhibits neutrophil migration and production of neutrophil chemokines and NO. Since neutrophils and NO promote renal ischemic injury, we sought to determine if α-MSH inhibits renal injury in a model of bilateral renal ischemia. α-MSH significantly reduced ischemia-induced renal damage, measured by changes in renal histology and plasma blood urea nitrogen and creatinine in mice. α-MSH significantly decreased tubule necrosis, neutrophil plugging, and capillary congestion. Delay of α-MSH treatment for 6 h after ischemia also significantly inhibited renal damage. α-MSH also significantly inhibited ischemic damage in rats. To begin to determine the mechanism of action of α-MSH, we measured its effects on mediators of neutrophil trafficking and induction of the inducible isoform of NO synthase- II. α-MSH inhibited ischemia-induced increases in mRNA for the murine neutrophil chemokine KC/IL-8. α-MSH also inhibited induction of mRNA for the adhesion molecule ICAM-1, which is known to be critical in renal ischemic injury. α-MSH inhibited nitration of kidney proteins and induction of NO synthase-II. We conclude: (a) α-MSH protects against renal ischemia/reperfusion injury; and (b) it may act, in part, by inhibiting the maladaptive activation of genes that cause neutrophil activation and adhesion, and induction of NO synthase.