Food Chemistry and Toxicology, University of Kaiserslautern, Kaiserslautern 67659, Germany.
Department of Food Chemistry, Friedrich-Schiller-University, Jena, Germany.
Toxicology. 2012 Mar 11;293(1-3):59-67. doi: 10.1016/j.tox.2011.12.011. Epub 2012 Jan 3.
Contamination of water, foods and food supplements by various genera of cyanobacteria is a serious health problem worldwide for humans and animals, largely due to the toxic effects of microcystins (MCs) and nodularin (NOD), a group of hepatotoxic cyclic peptides. The toxins occur in variable structures resulting in more than 90 different MCs and 8 different NODs, many of them not having been investigated for their toxic potency. Potent MCs such as MC-LR have been shown to elicit their hepatotoxic potency via inhibition of hepatic protein phosphatases (PP) 1 and 2A leading to over-phosphorylation of vital cellular proteins. This mechanism of action is also thought to be responsible for the long term tumor promoting action of certain MCs and NOD in the liver. Here, we report on the isolation of certain MCs and NOD as well as a number of their desmethylated derivatives from algae bloom. Subsequently, we determined the cytotoxicity of these compounds in isolated primary human and rat hepatocytes in culture. In parallel experiments, we analyzed the inhibitory potency of these congeners on PP1 and 2A using commercially available enzymes. We found in primary rat hepatocytes that MC-LR, -YR and NOD were cytotoxic, namely in the 10 to >50 nM range, while MC-RR was not. The desmethylated congeners of MC-LR, -YR, and NOD were equally or more-toxic as/than their fully methylated counterparts. In primary human hepatocytes we could show that MC-LR, NOD and the desmethylated variants [³Asp]MC-LR, [⁷Dha]MC-LR and [¹Asp]NOD were cytotoxic in the 20 to >600 nM range. Inhibition data with human, bovine and rabbit protein phosphatases 1 and 2A were roughly in accordance with the cytotoxicity findings in human and rat hepatocytes, i.e. desmethylation had no pronounced effects on the inhibitory potencies. Thus, a variety of naturally occurring desmethylated MC and NOD congeners have to be considered as being at least as toxic as the corresponding fully methylated derivatives.
水、食物和食品补充剂被各种蓝藻属污染是一个严重的全球健康问题，对人类和动物都有很大的影响，这主要是由于微囊藻毒素（MCs）和节球藻毒素（NOD）的毒性作用，这是一组肝毒性环肽。这些毒素以不同的结构存在，导致出现 90 多种不同的 MCs 和 8 种不同的 NOD，其中许多毒素的毒性尚未得到研究。研究表明，强毒性的 MCs，如 MC-LR，通过抑制肝蛋白磷酸酶（PP）1 和 2A 发挥其肝毒性，导致重要细胞蛋白过度磷酸化。这种作用机制也被认为是某些 MCs 和 NOD 在肝脏中具有长期促进肿瘤作用的原因。在这里，我们报告了从藻类大量繁殖中分离出某些 MCs 和 NOD 以及它们的一些去甲基衍生物。随后，我们在体外培养的分离原代人源和大鼠肝细胞中测定了这些化合物的细胞毒性。在平行实验中，我们使用市售的酶分析了这些同系物对 PP1 和 2A 的抑制能力。我们在原代大鼠肝细胞中发现，MC-LR、-YR 和 NOD 具有细胞毒性，即在 10 至 >50 nM 范围内，而 MC-RR 则没有。MC-LR、-YR 和 NOD 的去甲基同系物的毒性与它们的完全甲基化对应物相同或更高。在原代人源肝细胞中，我们可以证明 MC-LR、NOD 以及去甲基变体 [³Asp]MC-LR、[⁷Dha]MC-LR 和 [¹Asp]NOD 在 20 至 >600 nM 范围内具有细胞毒性。用人类、牛和兔蛋白磷酸酶 1 和 2A 的抑制数据与人类和大鼠肝细胞的细胞毒性发现大致相符，即去甲基化对抑制能力没有明显影响。因此，各种天然存在的去甲基 MC 和 NOD 同系物至少与相应的完全甲基化衍生物一样具有毒性。
