Genotoxic effects of microcystins mediated by nitric oxide and mitochondria

Microcystins-LR induced apoptosis via S-nitrosylation of GAPDH in colorectal cancer cells

Microcystins-LR (MC-LR), a cyanobacterial toxins, initiate apoptosis in normal and tumor cells. Nitric oxide produced by iNOS is necessary for MC-LR-induced apoptosis. However, the underlying mechanism of NO mediated MC-LR cytotoxicity remains unclear. Here, we performed in vitro experiments on MC-LR cytotoxicity associated with NO induced S-nitrosyation of GAPDH in human colon cancer cells SW480. MTT assay indicated that MC-LR decreased the cellular viability by high concentration (>1 μM). Flow cytometer assay revealed that apoptosis was core mode for MC-LR cytotoxicity. Griess assay showed that MC-LR exposure increased the release of NO through the function of NOS1 and NOS2 in SW480 cells. In turn, NO stress induced the S-nitrosylated modification of GAPDH leading to its nuclear translocation following Siah1 binding. CHIP assay showed that the nuclear GADPH increased P53 transcript of a panner of apoptosis related genes. Moreover, apoptosis induced by MC-LR could be reduced by GAPDH or si-Siah1 or NOSs inhibitor, L-NAME. Thus, our study verified a molecular mechanism of NO/GAPDH/Siah1 cascade in MC-LR mediated apoptosis in colorectal cancer cells, providing a further understanding the in vitro molecular mechanism of MC-LR colorectal toxicity.

Amelioratory effect of coenzyme Q10 on potential human carcinogen Microcystin-LR induced toxicity in mice

Microcystins are a group of cyclic heptapeptide toxins produced by cyanobacteria. More than 100 microcystin analogues have been detected, among which microcystin-LR is the most abundant and toxic variant. Present study was designed to reveal whether potential human carcinogen microcystin-LR could imbalance the glycolytic-oxidative-nitrosative status of heart, kidney and spleen of mice and also to explore the amelioratory effect of coenzyme Q10 on microcystin-LR induced toxicity. Microcystin-LR was administered at a dose of 10 μg/kg bw/day, ip for 14 days in male mice. In microcystin-LR treated mice as compared to control, significant increase in the level of lipid peroxidation, hydrogen peroxide, lactate dehydrogenase, nitric oxide with a concomitant decrease in the level of glutathione was observed, suggesting microcystin-LR induced toxicity via induction of oxidative-nitrosative-glycolytic pathway. Although several studies have evaluated numerous antioxidants but still there is no effective chemoprotectant against microcystin-LR induced toxicity. When microcystin-LR treated mice were co-administered coenzyme Q10 (10 mg/kg bw/day, im) for 14 days, it was observed that coenzyme Q10 ameliorates microcystin-LR induced toxicity via modulation of glycolytic-oxidative-nitrosative stress pathway. Thus, the results suggest that coenzyme Q10 has a potential to be developed as preventive agent against microcystin-LR induced toxicity.

Effect of algal flocculation on dissolved organic matters using cationic starch modified soils

Modified soils (MSs) are being increasingly used as geo-engineering materials for the sedimentation removal of cyanobacterial blooms. Cationic starch (CS) has been tested as an effective soil modifier, but little is known about its potential impacts on the treated water. This study investigated dissolved organic matters in the bloom water after algal removal using cationic starch modified soils (CS-MSs). Results showed that the dissolved organic carbon (DOC) could be decreased by CS-MS flocculation and the use of higher charge density CS yielded a greater DOC reduction. When CS with the charge density of 0.052, 0.102 and 0.293meq/g were used, DOC was decreased from 3.4 to 3.0, 2.3 and 1.7mg/L, respectively. The excitation-emission matrix fluorescence spectroscopy and UV254 analysis indicated that CS-MS exhibits an ability to remove some soluble organics, which contributed to the DOC reduction. However, the use of low charge density CS posed a potential risk of DOC increase due to the high CS loading for effective algal removal. When CS with the charge density of 0.044meq/g was used, DOC was increased from 3.4 to 3.9mg/L. This study suggested, when CS-MS is used for cyanobacterial bloom removal, the content of dissolved organic matters in the treated water can be controlled by optimizing the charge density of CS. For the settled organic matters, other measures (e.g., capping treatments using oxygen loaded materials) should be jointly applied after algal flocculation.