Pre-treatment with N-acetylcysteine upregulates superoxide dismutase 2 and catalase genes in cadmium-induced oxidative stress in the chick omphalocele model.

PURPOSE

In the chick embryo, administration of the heavy metal Cadmium (Cd) induces omphalocele phenotype. Cd is a potent inhibitor of antioxidant enzymes and causes accumulation of reactive oxygen species (ROSs) such as hydrogen peroxide. Previous work with the Cd chick model has demonstrated that increased levels of MDA, as a marker for oxidative stress, 24 h post Cd treatment (24H) are identical in chick embryos exposed to Cd. Furthermore, of the several antioxidants assessed, only N-acetylcysteine (NAC) has been shown to reduce MDA levels to control values in the Cd-treated chick embryo. However, the molecular mechanisms by which NAC acts to maintain oxidative stress in the Cd-induced ventral body wall defect chick model remains to be unclear. We designed this study to investigate the hypothesis that gene expression levels of antioxidant enzymes are downregulated in malformed embryos exposed to Cd compared to controls and to determine the effect of pre-treatment with NAC on the expression levels of genes encoding antioxidant enzymes.

METHODS

After 60 h incubation, chick embryos were pre-treated with NAC and exposed to either chick saline or Cd. Chicks were then harvested at 24H and divided into five groups: control, Cd group without malformation [Cd(-)], Cd group with malformation [Cd(+)], NAC + Cd(-) and NAC + Cd(+). Real-time PCR was performed to evaluate the relative mRNA expression levels of antioxidant enzymes, including superoxide dismutase (SOD)-1, SOD2, catalase (CAT) and glutathione peroxidase (GPX)-4. Differences between five groups were tested by Tukey-Kramer post-hoc test following one-way ANOVA. Statistical significance was accepted at p < 0.05. Immunohistochemistry was also performed to evaluate protein expression.

RESULTS

The mRNA expression levels of SOD2 and CAT were significantly decreased in Cd(+) as compared to controls, whereas there was no significant difference between controls and Cd(-) (p < 0.05 vs. controls). In addition, gene expression levels of SOD2 and CAT were significantly increased in NAC + Cd(-) as compared to Cd(+) and NAC + Cd(+) (p < 0.05 vs. controls). However, there were no significant differences in the expression levels of SOD1 and GPX4 among any groups. Increased immunoreactivity of SOD2 and CAT was also observed in NAC + Cd(-) as compared to Cd(+) and NAC + Cd(+).

CONCLUSION

Our results suggest that SOD2 and CAT may play an important role in preventing Cd-induced teratogenesis. Prenatal treatment with drugs which can upregulate SOD2 and CAT transcripts may have a therapeutic potential in preventing omphalocele phenotype.