Nitrite, a highly toxic environmental contaminant, induces various physiological toxicities in aquatic animals. Herein, we investigate the in vivo effects of nitrite exposure at concentrations of 0, 0.2, 2, and 20 mg/L on glucose and lipid metabolism in zebrafish. Our results showed that exposure to nitrite induced mitochondrial oxidative stress in zebrafish liver and ZFL cells, which were evidenced by increased levels of malondialdehyde (MDA) and reactive oxygen species (ROS) as well as decreased mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP). Changes in these oxidative stress markers were accompanied by alterations in the expression levels of genes involved in HIF-1α pathway (hif1α and phd), which subsequently led to the upregulation of glycolysis and gluconeogenesis-related genes (gk, pklr, pdk1, pepck, g6pca, ppp1r3cb, pgm1, gys1 and gys2), resulting in disrupted glucose metabolism. Moreover, nitrite exposure activated ERs (Endoplasmic Reticulum stress) responses through upregulating of genes (atf6, ern1 and xbp1s), leading to increased expression of lipolysis genes (pparα, cpt1aa and atgl) and decreased expression of lipid synthesis genes (srebf1, srebf2, fasn, acaca, scd, hmgcra and hmgcs1). These results were also in consistent with the observed changes in glycogen, lactate and decreased total triglyceride (TG) and total cholesterol (TC) in the liver of zebrafish. Our in vitro results showed that co-treatment with Mito-TEMPO and nitrite attenuated nitrite-induced oxidative stress and improved mitochondrial function, which were indicated by the restorations of ROS, MMP, ATP production, and glucose-related gene expression recovered. Co-treatment of TUDCA and nitrite prevented nitrite-induced ERs response and which was proved by the levels of TG and TC ameliorated as well as the expression levels of lipid metabolism-related genes. In conclusion, our study suggested that nitrite exposure disrupted hepatic glucose and lipid metabolism through mitochondrial dysfunction and ERs responses. These findings contribute to the understanding of the potential hepatotoxicity for aquatic animals in the presence of ambient nitrite.

中文翻译：

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亚硝酸盐通过线粒体功能障碍和 ERs 反应诱导斑马鱼肝脏糖脂代谢紊乱


亚硝酸盐是一种剧毒的环境污染物，可在水生动物中诱导各种生理毒性。在此，我们研究了浓度为 0、0.2、2 和 20 mg/L 的亚硝酸盐暴露对斑马鱼体内葡萄糖和脂质代谢的影响。我们的结果表明，暴露于亚硝酸盐会诱导斑马鱼肝脏和 ZFL 细胞的线粒体氧化应激，丙二醛 （MDA） 和活性氧 （ROS） 水平升高以及线粒体膜电位 （MMP） 和三磷酸腺苷 （ATP） 降低。这些氧化应激标志物的变化伴随着 HIF-1α 通路相关基因 （hif1α 和 phd） 表达水平的改变，随后导致糖酵解和糖异生相关基因 （gk、pklr、pdk1、pepck、g6pca、ppp1r3cb、pgm1、gys1 和 gys2） 的表达水平上调，导致葡萄糖代谢中断。此外，亚硝酸盐暴露通过上调基因 （atf6、ern1 和 xbp1s） 激活 ERs （内质网应激） 反应，导致脂肪分解基因 （pparα、cpt1aa 和 atgl） 表达增加，脂质合成基因 （srebf1、srebf2、fasn、acaca、scd、hmgcra 和 hmgcs1） 表达降低。这些结果也与观察到的斑马鱼肝脏中糖原、乳酸以及总甘油三酯 （TG） 和总胆固醇 （TC） 降低的变化一致。我们的体外结果表明，Mito-TEMPO 和亚硝酸盐的共同处理减轻了亚硝酸盐诱导的氧化应激并改善了线粒体功能，这表现为 ROS 、 MMP 、 ATP 产生的恢复和葡萄糖相关基因表达的恢复。 TUDCA 和亚硝酸盐的共同处理阻止了亚硝酸盐诱导的 ER 反应，这可以通过改善的 TG 和 TC 水平以及脂质代谢相关基因的表达水平来证明。总之，我们的研究表明，亚硝酸盐暴露通过线粒体功能障碍和 ER 反应破坏了肝脏葡萄糖和脂质代谢。这些发现有助于了解在环境亚硝酸盐存在下对水生动物的潜在肝毒性。