title: Oxidative damage and apoptosis induced by microcystin-LR in the liver of Rana nigromaculata in vivo.
abstract: Microcystins (MCs) are hepatotoxins with potent inhibitor activity of protein phosphatases PP1 and PP2A. The present study shows that MC-LR can induce severe oxidative damage and apoptosis in the livers of frogs (Rana nigromaculata) exposed to 1μg/L MC-LR for 7 and 14d in vivo. Ultrastructural observation showed the apoptotic morphology of perinuclear chromatin margination and swollen mitochondria, indicating that MC-LR can significantly damage frog liver. Reactive oxygen species (ROS) production and malondialdehyde (MDA) content were positively correlated with exposure time. Meanwhile, reduced glutathione (GSH) content and GSH peroxidase (GPx) activity rapidly decreased after prolonged exposure to 1μg/L MC-LR in a time-dependent manner. These results imply that the antioxidant defense systems of the liver were damaged. Enhanced apoptosis of cells in the livers of MC-treated frogs was detected by terminal deoxynucleotidyl transferase-mediated deoxy-UTP nick end labeling (TUNEL) associated with up-regulation of the mitochondrial system. MC-LR significantly stimulated the livers to release cytochrome c, which improved the protein expressions of Bax, caspase-3, and caspase-9 (p<0.01) and inhibited the protein expression of Bcl-2 with prolonged exposure (p<0.01) via the mitochondrial pathway. These results imply that the mitochondrial pathway has a key function in toxin-induced liver cell apoptosis. The expression of caspase-8 was induced significantly (p<0.01), which illustrates the mechanism that the death receptor pathway is also involved in apoptosis. The present findings show that MC-LR can induce apoptosis in frog liver, which may be related with the decline of amphibian populations. The World Health Organization-recommended drinking water limit for MC-LR in water may be not safe for amphibians.
authors.affiliation: Department of Environmental Sciences, Hangzhou Normal University, Xuelin Road 16#, Xiasha Gaojiao Dongqu, Hangzhou, Zhejiang Province 310036, China.
authors.forename: Hangjun
authors.initials: H
authors.lastname: Zhang
authors.forename: Chenchen
authors.initials: C
authors.lastname: Cai
authors.forename: Wendi
authors.initials: W
authors.lastname: Fang
authors.forename: Jia
authors.initials: J
authors.lastname: Wang
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jiayu
authors.initials: J
authors.lastname: Liu
authors.forename: Xiuying
authors.initials: X
authors.lastname: Jia
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000633:toxicity; D005978:Glutathione / Q000378:metabolism; D005979:Glutathione Peroxidase / Q000378:metabolism; D020287:In Situ Nick-End Labeling; D008099:Liver / Q000187:drug effects* / Q000648:ultrastructure; D008315:Malondialdehyde / Q000378:metabolism; D008387:Marine Toxins; D052998:Microcystins / Q000633:toxicity*; D008928:Mitochondria / Q000187:drug effects; D010084:Oxidation-Reduction / Q000187:drug effects*; D011898:Ranidae / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; D008315:Malondialdehyde; D005979:Glutathione Peroxidase; C057862:cyanoginosin LR; D005978:Glutathione
keywords: Apoptosis; Liver; Oxidative damage; Rana nigromaculata