Protective Effects And Mechanisms Of The Natural Antioxitant EGCG Against Nodnlarin-induced Hepatotoxicity In Mice

With the serious eutrophication in water bodies, algae blooms frequently outbreak. The secondary metabolite of the algae with strong toxicity was widely cared. Nodularin (NOD) is one type of algae biotoxins with its strong hepatotoxicity. In order to reveal the hepatic toxic effects induced by nodularin in huamans, mice (ICR grade) were taken as experimental subjects and exposured to low does of nodularin (10μg/kg/d; LD50=50μg/kg) in a long period (21d) with the measurements of body and liver weight, LBI%, the changes of liver functions and the ultrastructure in morphology and pathology. Results showed:(1) Under the exposure of NOD in21d, body and liver weight of mice and so dose the LBI%were declined significantly;(2) ALT/AST levels, and the leakage of LDH in the serum were remarkablely increased in the treatment of NOD (63.6%,9.5%,6.8%);(3) Visible morphological changes emerged as "strawberry like skin" in mice livers in NOD-treatment;(4) In H&E staining, pathobiological changes such as small nodules, acidophilic degeneration, inflammatory infiltration, chronic cholestasis and steatosis were observed in mice livers of NOD treatment, and some hepatocytes with acidophilic degeneration deteriorated to be acidophilic bodies after the exposure period were prolonged to28d.(5) Karyopyknosis, agglutination or frontier set of chromatin, deepen of mitochondrial cristae bands and chaos distribution, endoplasmic reticulum swelling, ribosomal threshing were captured under the TEM observation. Besides, microvesicular steatosis and devour vesicles were also observed in some cytoplasms. These changes observed aboved fully indicated that, NOD still possessed strong hepatotoxicity under the long period and low dose exposure, and acidophilic degeneration of hepatic cells and the induction of inflammation may be the majoy reasons of NOD-induced chronic hepatotoxicity, and further deterioration came up. such as more serious structural damages of the hepatic plate and further damages to the liver, when the experimental period were extended.As one kind of natural antioxidant. Epigallocatechin gallate (EGCG) possesses strong ability of scavenging free radicals, which was taken as protective agent and used in pretreatment of mice before the NOD-contaminated. The protective effects of EGCG against the toxicity induced by NOD were evaluated through H&E staining, TEM observation and the determination of antioxidation parameters, gene and protein expression of cytokines related to apoptosis and inflammation. Results indicated:(1) Pretreatment of high dose of EGCG suppressed the formation of "strawberry like skin" effectively;(2) Acidophilic degeneration, chronic cholestasis, spotty necrosis, inflammatory infiltration, steatosis and hydropic degeneration were restrained efficiently with the pretreatment of high does EGCG;(3) Karyopyknosis, agglutination or frontier set of chromatin, deepen of mitochondrial cristae bands and chaos distribution, endoplasmic reticulum swelling, ribosomal threshing and mitochondrial swelling were also well inhibited;(4) Compared to the NOD treatment, GSH content in hepatocytes in EGCG pretreatment was increased by50%, lipid peroxidation product MDA was declined (73.9%), and the enzyme activity of CAT and SOD were elevated by45.8%and15.8%, respectively, thus, the ability of antioxidation was enhanced;(5) In EGCG pretreatment, gene and protein expressions of proapoptosis factor Bax were reduced in74.3%and33.3%, respectively (P<0.01). Otherwise, the expressions of antiapoptosis factor Bcl-2in gene and protein levels were well increased in23.1%and33.3%, respectively (P<0.01). Meanwhile, susceptibility of apoptosis was enhanced (79.2%, P<0.01);(6) Content of TNF-a in hepatocytes was increased significantly both in gene (87.2%; P<0.01) and protein levels (72.2%; P<0.01) in the group of NOD-treated contrast to control, and with the protective effect of EGCG (200mg/kg), expression of TNF-a in gene and protein levels were decreased in81.2%and47.4%, respectively. In conclusion, natural antioxidant EGCG could inhibit the hepatotoxicity induced by nodularin in mice through the anti-oxidative stress, anti-inflammation and the regulations of genes and proteins expressions related to apoptosis.