Chronic exposure to 3,6-dichlorocarbazole exacerbates non-alcoholic fatty liver disease in zebrafish by disrupting lipid metabolism and inducing special lipid biomarker accumulation.

Most previous studies have focused primarily on the adverse effects of environmental chemicals on organisms of good healthy. Although global prevalence of non-alcoholic fatty liver disease (NAFLD) has reached approximately 25%, the impact of environmentally persistent organic chemicals on organisms with NAFLD is substantially unknown. Polyhalogenated carbazoles (PHCZs) as emerging contaminants have been frequently detected in the environment and organisms. In this study, we investigated the impact of the most frequently detected PHCZs, 3,6-dichlorocarbazole (36-CCZ), on zebrafish with high-fat diet (HFD)-induced NAFLD. After 4 weeks exposure to environmentally relevant concentrations of 36-CCZ (0.16-0.45 µg/L), the accumulation of lipid in zebrafish liver dramatically increased, and the transcription of genes involved in lipid synthesis, transport and oxidation was significantly upregulated, demonstrating that 36-CCZ had exacerbated the NAFLD in zebrafish. Lipidomic analysis indicated that 36-CCZ had significantly affected liver lipid metabolic pathways, mainly including glycerolipids and glycerophospholipids. Additionally, fifteen lipids were identified as potential lipid biomarkers for 36-CCZ exacerbation of NAFLD, including diacylglycerols (DGs), triglycerides (TGs), phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidic acid (PA), and phosphatidylinositol (PI). These findings demonstrate that long-term exposure to 36-CCZ can promote the progression of NAFLD, which will contribute to raising awareness of the health risks of PHCZs.

Tissue-specific accumulation, depuration and histopathological effects of 3,6-dichlorocarbazole and 2,7-dibromocarbazole in adult zebrafish (Danio rerio).

Although polyhalogenated carbazoles have been detected with increasing frequency in aquatic ecosystems, their bioaccumulation in fish and corresponding pathological effects related to bioaccumulation are still unclear. Here, we investigated the tissue-specific accumulation, depuration, and histopathological effects of two typical PHCZs, 3,6-dichlorocarbazole (36-CCZ) and 2,7-dibromocarbazole (27-BCZ), in adult zebrafish at three levels (0, 0.15 µg/L (5 × environmentally relevant level), and 50 µg/L (1/10 LC50). The lowest concentrations of 36-CCZ (1.2 µg/g ww) and 27-BCZ (1.4 µg/g ww) were observed in muscle, and the greatest concentrations of 36-CCZ (3.6 µg/g ww) and 27-BCZ (4 µg/g ww) were detected in intestine among the tested tissues. BCFww of 36-CCZ and 27-BCZ in zebrafish ranged from 172.9 (muscle) to 606.6 (intestine) and 285.2 (muscle) to 987.5 (intestine), respectively, indicating that both 36-CCZ and 27-BCZ have high potential of bioaccumulation in aquatic system. The 0.15 µg/L level of 36-CCZ or 27-BCZ caused lipid accumulation in liver, while 50 µg/L of 36-CCZ or 27-BCZ induced liver lesions such as fibrous septa, cytolysis, and nuclear dissolution. Brain damage such as multinucleated cells and nuclear solidification were only observed at 50 µg/L of 27-BCZ. This study provided valuable information in assessing the health and ecological risks of 36-CCZ and 27-BCZ.