Effects of Two Sublethal Concentrations of Mercury Chloride on the Morphology and Metallothionein Activity in the Liver of Zebrafish (Danio rerio)

Abstract

Mercury (Hg) is a highly hazardous pollutant widely used in industrial, pharmaceutical and agricultural fields. Mercury is found in the environment in several forms, elemental, inorganic (iHg) and organic, all of which are toxic. Considering that the liver is the organ primarily involved in the regulation of metabolic pathways, homeostasis and detoxification we investigated the morphological and ultrastructural effects in Danio rerio liver after 96 h exposure to two low HgCl 2 concentrations (7.7 and 38.5 µg/L). We showed that a short-term exposure to very low concentrations of iHg severely affects liver morphology and ultrastructure. The main effects recorded in this work were: cytoplasm vacuolization, decrease in both lipid droplets and glycogen granules, increase in number of mitochondria, increase of rough endoplasmic reticulum and pyknotic nuclei. Pathological alterations observed were dose dependent. Trough immunohistochemistry, in situ hybridization and real-time PCR analysis, the induction of metallothionein (MT) under stressor conditions was also evaluated. Some of observed alterations could be considered as a general response of tissue to heavy metals, whereas others (such as increased number of mitochondria and increase of RER) may be considered as an adaptive response to mercury.

Mercury Exposure in Association With Decrease of Liver Function in Adults: A Longitudinal Study

“…In an animal study of male rats exposed to Hg, AST, ALT, and GGT were significantly elevated, and marked damage or necrotic changes were observed in most of the liver tissue samples upon a histological examination [ 17 ]. Degenerative changes and large lysed areas in liver parenchyma in Hg-exposed zebrafish have been observed [ 18 ]. In addition, Hg exposure in zebrafish induced deregulation of oxidative stress, intrinsic apoptotic pathways, and nuclear receptor and kinase activity [ 19 ], suggesting that gluconeogenesis and adipogenesis occur in these processes and that hepatotoxicity occurs through cell death, mitochondrial dysfunction, endocrine disruption, and metabolic disorders.…”

Effect of arsenic (As) and lead (Pb) on glycogen content and on the activities of selected enzymes involved in carbohydrate metabolism in freshwater catfish, Heteropneustes fossilis

“…Glycogen granules were shown to be depleted in the fish exposed to an acute concentration of heavy metals (As and Pb) as evidenced from the TEM studies. Depletion in glycogen granules in liver of zebra fish is also reported by Macirella et al (2016) when treated with mercury chloride. The depletion of glycogen may be due to rapid turnover of the glycogen.…”

Assessment of mercury contamination in Brycon falcatus (Characiformes: Bryconidae) and human health risk by consumption of this fish from the Teles Pires River, Southern Amazonia

“…The primary target tissues of Hg are the central nervous system and the kidney, causing brain damage, abnormal motor coordination, behavioral changes, alterations that impair growth, reproduction and development of the fish (Clarkson et al, 2003). Mercuryinduced toxicity in the liver can severely affect morphology and structure, impairing its functional role by interfering with key physiological and metabolic processes (Macirella et al, 2016). Some fish organs are commonly used to determine the bioaccumulation of total mercury (THg), such as the liver, as it plays vital roles in the accumulation, biotransformation and excretion of contaminants (Figueiredo-Fernandes et al, 2006).…”