Effects of antioxidant vitamins on glutathione depletion and lipid peroxidation induced by restraint stress in the rat liver

Abstract

Background and aim: Stress as a cofactor has been reported to affect the progression and severity of several diseases. The influence of stress on the liver is of interest from the clinical point of view because stress plays a potential role in aggravating liver diseases in general and hepatic inflammation in particular, probably through generation of reactive oxygen species. The present study was undertaken to investigate the potential of the antioxidant vitamins A (retinol), E (tocopherol) and C (ascorbic acid) individually and in combination (vitamin E + C) to modulate restraint stress-induced oxidative changes. These effects were determined by measuring changes in hepatic levels of free radical scavenging enzymes such as superoxide dismutase (SOD), glutathione-S-transferase (GST) and catalase, as well as levels of total glutathione (GSH), malondialdehyde (MDA), aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

Methods: Immobilisation was achieved by placing the animals in wire mesh cages of their size. The rats were orally administered vitamins A, E and C individually and in combination (E + C) prior to and after 6 hours of immobilisation stress exposure. The hepatic levels of SOD, GST, catalase, GSH and MDA were determined by spectrophotometric methods. Liver SOD activity was assayed by monitoring the amount of enzyme required to inhibit autoxidation of pyrogallol by 50%. Hepatic GST was monitored by following the increase in absorbance at 340 nm of CDNB-GSH conjugate generated due to GST catalysis between GSH and CDNB. Catalase activity in liver tissues was determined using peroxidase as the substrate. Lipid peroxidation was measured by determining the level of thiobarbituric acid reactive substances. ALT and AST were determined by commercial kits.

Results: Six hours of immobilisation stress caused a decrease in liver levels of SOD (p = 0.001), catalase (p = 0.031), GST (p = 0.021) and GSH (0.013), while levels of MDA (p = 0.0015), AST (p = 0.05) and ALT (p = 0.046) were increased compared with non-stressed control rats. Both pre-vitamin stress and post-vitamin stress treatments either alone or in combination were associated with increased normalisation of these parameters towards control values, with post-vitamin treatment being the more effective of the two. Vitamins E and C individually were found to be more effective in restoring the endogenous antioxidant system than vitamin A. The combined vitamin (E + C) post-stress treatment was found to be effective but not additive in combating hepatic oxidative stress. The beneficial effects of these vitamin treatments were also reflected in reversions of altered AST and ALT levels towards their control values.

Conclusion: Vitamins E or C alone or in combination can be given as prophylactic/therapeutic supplements for combating scavenging free radicals generated in liver tissue. This approach may reduce oxidative stress caused by diseases such as cirrhosis.