Effect of long-term manganese exposure on oxidative stress, liver damage and apoptosis in grouper Epinephelus moara x Epinephelus lanceolatus

Manganese is an indispensable trace element, however, it may be present at high concentrations in water and sediments of aquatic ecosystems due to natural and anthropogenic activities, and can interfere with physiological and biochemical mechanisms in fish. This study was conducted to determine the toxic effects associated with exposure to Mn2+ (0, 0.5, 1, 2, and 4 mg/L) for 30 d, regarding liver damage and apoptosis in Yunlong grouper (Epinephelus moara female xE. lanceolatus male). Expression of superoxide dismutase (sod) and catalase (cat) genes in the liver was significantly increased on days 10 and 20 following Mn2+ exposure (4 mg/L), but was reduced on day 30. Similarly, expression of glutathione peroxidase (gpx) and glutathione reductase (gr) genes was elevated after 10 d of exposure to 2 and 4 mg/L Mn2+, but decreased after 20 and 30 d. After 30 d of exposure to high concentrations (2 and 4 mg/L) of Mn2+, liver tissue showed hepatic sinusoidal gap congestion, dilatation, cell vacuolation, and necrosis. In addition, the activities of alanine aminotransferase (ALT) and aspartate transaminase (AST) as well as 8-hydroxydeoxyguanosine (8-OHdG) levels were significantly increased after Mn2+ exposure. Moreover, Mn2+ exposure altered the expression pattern of some pivotal genes associated to apoptosis (p53, bax, bcl-2, apaf-1, caspase-9, and caspase-3), which suggested that Mn2+ exposure induces apoptosis through the mitochondrial pathway. The above results showed that excessive Mn2+ induced apoptosis and liver damage in grouper through elicitation of oxidative stress. These insights help elucidate the mechanism by which Mn2+ induces toxicity in marine fish, and provide a new perspective regarding the detrimental effects of heavy metals in fish.