The in vivo effects of copper, manganese and mercury mixtures on the heart, lung and brain and the coagulation system in the Sprague-Dawley rat model

Abstract

Anthropogenic activities are the main sources of the increased heavy metal concentrations in the environment, including water. Drinking or the use of contaminated water can have harmful effects on human health contributing to cardiovascular, respiratory and neurodegenerative diseases. There is some data on the effects of metal exposure and potential toxic effects, but more information is needed regarding copper, manganese and mercury exposure, especially as part of metal mixtures. The aim of this study was to investigate the in vivo effects of copper, manganese and mercury, alone and in mixtures, on the aorta, heart, lung and brain as well as the coagulation system of male Sprague-Dawley rats by measuring blood markers of tissue damage, evaluating tissue structure as well as blood cellular composition and coagulation using biochemical analysis, light microscopy, scanning electron microscopy and transmission electron microscopy. The in vivo model was implemented successfully over a 28-day exposure period, where male Sprague-Dawley rats received daily dosages of the metals, alone or in metal mixtures at X100 that of the World Health Organization’s safety limit for drinking water, which is 2.0 mg/L, 0.4 mg/L and 0.006 mg/L for copper, manganese and mercury, respectively. Aorta, heart, lung and brain samples were collected and analysed for morphological and ultrastructural alterations using light- and transmission electron microscopy, respectively. Blood was analysed by measuring full blood count parameters, methaemoglobin and blood markers of tissue damage, including lactate dehydrogenase, total serum protein and creatinine. Morphological alterations to the cellular components of the blood were analysed using scanning electron microscopy. The average weight gain of the Sprague-Dawley rats was also determined. The heavy metals under investigation and their mixtures demonstrated varying toxicities dependent on the target. For the single metal groups, manganese showed the highest degree of toxicity. In the double metal mixtures, the copper and manganese combination group demonstrated the most alterations overall. The triple mixture group demonstrated a significant decrease in multiple blood parameters, the lowest weight gain overall and caused the most severe alterations to cardiac and brain ultrastructure, making it the most toxic group in the study. In conclusion, copper, manganese and mercury, alone and in metal mixtures, had an effect on blood parameters, morphology of blood constituents, histology and ultrastructure of the tissues. This in turn influences the function of these organs and makes them susceptible to early ageing and disease development. Keywords: aorta, brain, copper, damage, disease, heart, lung, manganese, mercury, mixtures.