Histopathological and Molecular Alterations in the Liver of <scp> <i>Hoplias intermedius</i> </scp> (Pisces: Erythrinidae) Contaminated by Heavy Metals in a Neotropical River

Heavy metals, originating from human activities and natural processes, are a threat to aquatic organisms and the environment. As the main organ responsible for detoxification, the liver plays a fundamental role in regulating potentially harmful chemicals such as heavy metals, and the interaction between heat shock protein 70 and metallothionein may be important in processes related to cellular protection, since both participate in responses to oxidative stress and redox balance. To analyze the effects of heavy metals on the morphology and biomarkers expression in the liver of Hoplias intermedius, specimens from the Paraopeba River-contaminated environment and Abaete River-control environment were collected, and fragments of liver were sampled for histopathological and immunohistochemical analyses. Additionally, the levels of Al, Cd, Pb, Cu, Cr, Fe, Mn, and Zn were measured in water and liver from all individuals. The results showed concentrations above the permitted levels of Al, Cd, and Mn in the water, and Cd, Pb, Cr, and Fe in liver samples of Paraopeba River. Furthermore, dilatation and congestion of sinusoidal capillaries and lobular veins were observed; vacuolization of hepatocytes; formation of melanomacrophage centers; and signs of tissue necrosis were detected. In immunohistochemical analysis, metallothionein and heat shock proteins (HSP70) markings increased when compared to fish from the control environment. These results indicate the severity of the toxic effects of chronic exposure to heavy metals on aquatic biota, and a possible human health threat due to the consumption of contaminated fish.