Effects of ozone oxidative preconditioning on nitric oxide generation and cellular redox balance in a rat model of hepatic ischaemia-reperfusion

Background: Many studies indicate that oxygen free-radical formation after reoxygenation of liver may initiate the cascade of hepatocellular injury. It has been demonstrated that controlled ozone administration may promote an oxidative preconditioning or adaptation to oxidative stress, preventing the damage induced by reactive oxygen species and protecting against liver ischaemia-reperfusion (I/R) injury. Aims: In the present study, the effects of ozone oxidative preconditioning (OzoneOP) on nitric oxide (NO) generation and the cellular redox balance have been studied. Methods: Six groups of rats were classified as follows: (1) sham-operated; (2) sham-operated+L-NAME (N-omega-nitro-L-arginine methyl ester); (3) I/R (ischaemia 90 min-reperfusion 90 min); (4) OzoneOP+I/R; (5) OzoneOP+L-NAME+I/R; and (6) L-NAME+I/R. The following parameters were measured: plasma transaminases (aspartate aminotransferase, alanine aminotransferase) as an index of hepatocellular injury; in homogenates of hepatic tissue: nitrate/nitrite as an index of NO production: superoxide dismutase (SOD), catalase (CAT) and glutathione levels as markers of endogenous antioxidant system; and finally malondialdehyde+4-hydroxyalkenals (MDA+4-HDA) and total hydroperoxides (TH) as indicators of oxidative stress. Results: A correspondence between liver damage and the increase of NO, CAT, TH, glutathione and MDA+4-HDA concentrations were observed just as a decrease of SOD activity. OzoneOP prevented and attenuated hepatic damage in I/R and OzoneOP+L-NAME+I/R, respectively, in close relation with the above-mentioned parameters. Conclusions: These results show that OzoneOP protected against liver I/R injury through mechanisms that promote a regulation of endogenous NO concentrations and maintenance of cellular redox balance. Ozone treatment may have important clinical implications, particularly in view of the increasing hepatic transplantation programs.