Gene expression of glutathione S-transferase alpha, glutathione S-transferase rho, glutathione peroxidase, uncoupling protein 2, cytochrome P450 1A, heat shock protein 70 in liver of Oreochromis niloticus upon exposure of microcystin-LR, microcystin-RR and toxic cyanobacteria crude

Objective: Microcystins (MCs) are considered to be one of the most hazard groups of cyanobacteria and are known as a group of cyclic polypeptide hepatotoxins of varying potency. The study determined the variation of gene expression of GSTA, GSTR, GPX, UCP2, CYP1A1 and HSP70 genes in liver of tilapia fish (Oreochromis niloticus) under the effect of MC-LR or MC-RR toxins. Methods: Tilapia fish adult male fishes (n = 20; 120-178 g) obtained from fish farm. Fishes injected i.p. with a single dose of 50 mu g/kg MC-LR, and 20 fishes injected with 500 mu g/kg MC-RR. Whereas the control group was only received the vehicle solution. Total mRNA was isolated from 50 mg of hepatic sections. The relative levels of GSTA, GSTR, GPX, UCP2, HSP70/beta actin mRNA were determined by RT-real time PCR. Results: Significantly increased in GSTA mRNA expression was observed in the liver of fish after exposure to all exposure groups. Variable alterations in the levels of GPx, GSTR, UCP2 and CYP1A mRNA expression were observed post exposure groups. Whereas, the relative level of HSP70 mRNA was increased at 12 h after MCs exposure and was elevated gradually at 24 h until 7 days post treatment. Conclusion: The presence of inducible expression of GSTA, GSTR and GPx, and no significant changes of CYP1A mRNA expression in the liver of tilapia post MCs exposure, indicates that it should be the phase II detoxification enzyme in the liver of tilapia, but not the phase I detoxification enzyme. In addition to restrain over production of ROS, increasing of UCP2 and HSP70 expression may play an important role as a molecular chaperone against oxidative stress consequently, preventing hepatic cells from apoptosis.

Automated summary

This study investigated the gene expression variation in the liver of tilapia fish under the effect of MC-LR or MC-RR toxins. The results showed increased expression of GSTA mRNA, variable alterations in GPx, GSTR, UCP2, and CYP1A mRNA, and gradually elevated expression of HSP70 mRNA after MCs exposure. These findings indicate that tilapia liver expresses phase II detoxification enzymes and increased UCP2 and HSP70 expression may protect against oxidative stress and prevent apoptosis.