Inhibition of the Rac1 GTPase protects against nonlethal ischemia/reperfusion-induced necrosis and apoptosis in vivo

Reperfusion of ischemic tissue results in the generation of reactive oxygen species that contribute to tissue injury. The sources of reactive oxygen s pecies in reperfused tissue are not fully characterized. We hypothesized th at the small GTPase Rac1 mediates the oxidative burst in reperfused tissue and thereby contributes to reperfusion injury. Zn an in vivo model of mouse hepatic ischemia/reperfusion injury, recombinant adenoviral expression of a dominant negative Rac1 (Rac1N17) completely suppressed the ischemia/reper fusion-induced production of reactive oxygen species and lipid peroxides, a ctivation of nuclear factor-kappa B, and resulted in a significant reductio n of acute liver necrosis, Expression of Rac1N17 also suppressed ischemia/r eperfusion-induced acute apoptosis, The protection offered by Rac1N17 was a lso evident in knockout mice deficient for the gp91phox component of the ph agocyte NADPH oxidase. This work demonstrates the crucial role of a Rac1-re gulated oxidase in mediating the production of injurious reactive oxygen sp ecies, which contribute to acute necrotic and apoptotic cell death induced by ischemia/reperfusion in vivo. Targeted inhibition of this oxidase, which is distinct from the phagocyte NADPH oxidase, should provide a new avenue for in vivo therapy aimed at protecting organs at risk from ischemia/reperf usion injury.