Regulation of JNK/ERK activation, cell apoptosis, and tissue regeneration by monoamine oxidases after renal ischemia-reperfusion.

Reactive oxygen species (ROS) contribute to the ischemia-reperfusion injury. In kidney, the intracellular sources of ROS during ischemia-reperfusion are still unclear. In the present study, we investigated the role of the catecholamine-degrading enzyme monoamine oxidases (MAOs) in hydrogen peroxide (H2O2) generation after reperfusion and their involvement in cell events leading to tissue injury and recovery. In a rat model of renal ischemia-reperfusion, we show concomitant MAO-dependent H2O2 production and lipid peroxidation in the early reperfusion period. Rat pretreatment with the irreversible MAO inhibitor pargyline resulted in the following: i) prevented H2O2 production and lipid peroxidation; ii) decreased tubular cell apoptosis and necrosis, measured by TUNEL staining and histomorphological criteria; and iii) increased tubular cell proliferation as determined by proliferating cell nuclear antigen expression. MAO inhibition also prevented Jun N-terminal kinase phosphorylation and promoted extracellular signal-regulated kinase activation, two mitogen-activated protein kinases described as a part of a "death" and "survival" pathway after ischemia-reperfusion. This work demonstrates the crucial role of MAOs in mediating the production of injurious ROS, which contribute to acute apoptotic and necrotic cell death induced by renal ischemia-reperfusion in vivo. Targeted inhibition of these oxidases could provide a new avenue for therapy to prevent renal damage and promote renal recovery after ischemia-reperfusion.

Prevention of apoptotic and necrotic cell death, caspase-3 activation, and renal dysfunction by melatonin after ischemia/reperfusion.

The pineal hormone melatonin has been reported to protect tissue from oxidative damage. This study was designed to determine whether melatonin could prevent cell events leading to tissue injury and renal dysfunction after ischemia/reperfusion (I/R). Using an in vivo rat model of I/R, we show a significant increase in kidney malondialdehyde concentrations, reflecting lipid peroxidation, and cell apoptosis measured by TUNEL staining. This apoptotic cell death was associated with an increase in the activity of the proapoptotic factor caspase-3, determined by fluorometric protease activity assay. Histomorphological analysis of ischemic kidneys revealed that the most extensive tubular necrosis occurred at 24 and 48 h after reperfusion, which correlated with peak elevations in blood urea nitrogen and creatinine. Rat pretreatment with melatonin prevented lipid peroxidation, cell apoptosis, and necrosis and blocked caspase-3 activity. The prevention of tissue injury was associated with the improvement of renal function as shown by the decrease in blood urea nitrogen and creatinine concentrations. The demonstration that melatonin prevents postreperfusion apoptotic and necrotic cell death and improves renal function suggests that melatonin may represent a novel therapeutic approach for prevention of I/R injury.

Involvement of peripheral benzodiazepine receptor in the oxidative stress, death-signaling pathways, and renal injury induced by ischemia-reperfusion.

The peripheral benzodiazepine receptor (PBR) is a critical component of the mitochondrial permeability transition pore, which is involved in the regulation of cell death. In the present study we investigated the role of PBR in the regulation of signaling pathways leading to apoptotic and necrotic damage and renal dysfunction in a rat model of ischemia-reperfusion. Renal ischemia-reperfusion led to extended tubular apoptosis and necrosis that were associated with peroxidative damage, high levels of proapoptotic Bax expression, and low levels of antiapoptotic Bcl-2 expression, cleavage of death substrate, poly(ADP-ribose) polymerase (PARP), and activation of a key effector of apoptosis, caspase-3. Rat pretreatment with a novel PBR antagonist, SSR180575, significantly decreased postreperfusion oxidative stress and tubular apoptosis and necrosis. This effect was associated with inhibition of caspase-3 activation and PARP cleavage, upregulation of Bcl-2, and downregulation of Bax. Furthermore, inhibition of PBR accelerated the recovery of normal renal function, as assessed by measurement of levels of plasma creatinine and blood urea nitrogen. These findings reveal a role for PBR as a modulator of necrotic and apoptotic cell death induced by ischemia-reperfusion and suggest that regulation of PBR may provide new therapeutic implications for the prevention of acute renal failure.