Naringin attenuates the cytotoxicity of hepatotoxin microcystin-LR by the curious mechanisms to OATP1B1- and OATP1B3-expressing cells.

Microcystin-LR, which is an inhibitor of serine/threonine protein phosphatase (PP)1 and PP2A, induces liver injury by its selective uptake system into the hepatocyte. It is also thought that microcystin-LR induces reactive oxygen species (ROS). We tried to establish the chemical prevention of microcystin-LR poisoning. We investigated the effect of grapefruit flavanone glycoside naringin on cytotoxicity of microcystin-LR using human hepatocyte uptake transporter OATP1B3-expressing HEK293-OATP1B3 cells. We found cytotoxicity of microcystin-LR was attenuated by naringin in a dose dependent manner. The inhibition magnitude of total cellular serine/threonine protein phosphatase activity induced by microcystin-LR was suppressed by naringin. In addition, uptake of microcystin-LR into HEK293-OATP1B3 cells was inhibited by naringin. Furthermore, microcystin-LR induced phosphorylation of p53 was inhibited by naringin. Regardless of the difference in the exposure pattern of pre-processing and post-processing of naringin, the toxicity of microcystin-LR was comparable. These results suggested that naringin is promising remedy as well as preventive medicine for liver damage with microcystin-LR. In addition, involvement of ROS production after exposure to the sublethal concentrations of microcystin-LR in the onset of cytotoxicity was negligible. Therefore, inhibition of microcystin-LR uptake and the pathway other than ROS production would be involved in the effect of naringin on the attenuation of microcystin-LR toxicity.

Inhibitory effect of naringin on microcystin-LR uptake in the freshwater snail Sinotaia histrica.

Gastropods are an important food source for aquatic animals, and have been demonstrated to transfer microcystin (MC) to higher trophic levels through the food web. In this study, we performed an oral administration experiment to evaluate whether naringin can inhibit MC-LR uptake in the freshwater snail Sinotaia histrica. We also observed the effect of MC-LR on the organizational pathology of the hepatopancreas in S. histrica. Following exposure to cells of Microcystis ichthyoblabe, S. histrica showed vacuolization and separation of the basal lamina from cells in the hepatopancreas. Initial treatment with 1mM naringin resulted in the prevention of MC-LR uptake rate by approximately 60% over 8days, whereas initial treatment with 10mM naringin suppressed microcystin uptake in 2days, despite an increase in MC-LR levels in the snail from days 5 to 8. With continuous treatment of 10mM naringin, the uptake prevention rate was 100%. Overall, we observed a strong inhibitory effect against MC-LR with naringin treatment. This study provides a potential mechanism to prevent the uptake of microcystin in the aquatic food web, thereby limiting its toxicity in cyanobacterial bloom-polluted areas where the environment can be controlled and may have further applications in the aquaculture of gastropods.