The nitric oxide donor, V-PYRRO/NO, protects against acetaminophen-induced hepatotoxicity in mice

The liver-selective nitric oxide (NO) donor, O-2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V PYRRO/NO), is metabolized by P-450 enzymes to release NO in the liver, and is shown to protect the liver from tumor necrosis factor a (TNF-alpha)-induced apoptosis and D-glactosamine/endotoxin-induced hepatotoxicity. This study was undertaken to examine the effects of V PYRRO/NO on acetaminophen-induced hepatotoxicity in mice. Mice were given V PYRRO/NO via osmotic pumps (1.8-5.4 mg/ml,, 8 muL/h) 4 to 16 hours before a hepatotoxic dose of acetaminophen (600 mg/kg, intraperitoneally [ip]). V PYRRO/NO administration dramatically reduced acetaminophen-induced hepatotoxicity in a dose- and time-dependent manner, as evidenced by reduced serum alanine aminotransferase (ALT) activity, reduced hepatic congestion, apoptosis, and improved hepatocellular pathology. The protection afforded by V PYRRO/NO does not appear to be caused by a decrease in the formation of toxic acetaminophen metabolites, which consumes glutathione (GSH), because V PYRRO/NO did not alter acetaminophen-induced hepatic GSH depletion. Acetaminophen-induced lipid peroxidation, as determined by the concentrations of 4-hydroxyalkenals (4-HNE) and malondialdehyde (MDA), was reduced significantly by V PYRRO/NO treatment. Although pretreatment was most effective, administration of V PYRRO/NO simultaneously with acetaminophen also was able to reduce acetaminophen hepatotoxicity. Genomic analysis of the liver samples 10 hours after acetaminophen intoxication showed the enhanced expression of genes associated with stress/oxidative stress, apoptosis/cell death, and DNA damage/repair. Acetaminophen-induced alterations in gene expression were attenuated significantly by V PYRRO/NO. Real-time reverse-transcription polymerase chain reaction (RT-PCR) and Western-blot analysis confirmed microarray results. In conclusion, V PYRRO/NO is effective in blocking acetaminophen -induced hepatotoxicity in mice. This protection may involve the reduction of oxidative stress, the inhibition of apoptosis, and possibly the maintenance of hepatic vasculature to prevent congestion.