Waterborne zinc induced lobe-dependent effect on oxidative stress and energy metabolism in hepatopancreas of Larimichthys crocea.

The study aimed to compare differences in oxidative stress and energy metabolism between the left and right lobe of hepatopancreas in large yellow croaker Larimichthys crocea exposed to 0 (control)， 20， and 100 μM Zn for 96 h. Tipical biomarkers were examined including the proportion of white hepatopancreas， lipid content， malondialdehyde (MDA) level， glutathione (GSH) content， activity levels of enzymes (Cu/Zn-superoxide dismutase， Cu/Zn-SOD; catalase， CAT; glutathione peroxidase， GPx; glutathione reductase， GR; mitochondrial ATP synthase， F-ATPase; malate dehydrogenase， MDH; succinate dehydrogenase， SDH; hepatic lipase， HTGL; lipoprotein lipase， LPL)， mRNA levels of genes encoding these enzymes (sod1， cat， gpx1a， gr， atp5b， mdh， sdh， htgl， and lpl)， and gene expression of signaling molecules the NF-E2-related nuclear factor 2 (nrf2) and Kelch-like ECH-associated protein 1 (keap1). A whitish color in the left lobe of hepatopancreas was observed in the control and Zn-exposed fish. Contrarily， the right lobe of hepatopancreas tended towards red with increasing Zn levels. The phenomenon was further confirmed by that lipid content was reduced in the right lobe and was not significantly affected in the left lobe by Zn. The right lobe showed higher energy consumption than the left lobe as reflected by the up-regulation of activity levels of HTGL， LPL， F-ATPase， MDH， and SDH. Lipid peroxidation declined by 20 μM Zn and was unchanged by 100 μM Zn in both lobes， which could be explained by increased activity levels of Cu/Zn-SOD and GPx. However， the magnitude of increase in Cu/Zn-SOD activity was greater in the right lobe than that in the left one. The difference in enzyme activity between two lobes may be involved in changes in mRNA levels of sod1， gr， atp5b， sdh， htgl， lpl， and nrf2， which was further confirmed by positive relationships between enzyme activity and gene expression. Our data also showed positive correlations between nrf2 expression and mRNA levels of its target genes， suggesting that Nrf2 was required for the protracted induction of these genes. Our results demonstrated the potential molecular mechanism of Zn-induced differences between lobes of hepatopancreas， suggesting that the sampling part of hepatopancreas should be considered with caution when assessing metal contamination.