Global Human Threat: The Potential Synergism between Mercury Intoxication and COVID-19

The COVID-19 pandemic affected billions of people worldwide, and exposure to toxic metals has emerged as an important risk factor for COVID-19 severity. Mercury is currently ranked as the third toxic substance of global concern for human health, and its emissions to the atmosphere have increased globally. Both COVID-19 and mercury exposure present a high prevalence in similar regions: East and Southeast Asia, South America and Sub-Saharan Africa. Since both factors represent a multiorgan threat, a possible synergism could be exacerbating health injuries. Here, we discuss key aspects in mercury intoxication and SARS-CoV-2 infection, describing the similarities shared in clinical manifestations (especially neurological and cardiovascular outcomes), molecular mechanisms (with a hypothesis in the renin-angiotensin system) and genetic susceptibility (mainly by apolipoprotein E, paraoxonase 1 and glutathione family genes). Literature gaps on epidemiological data are also highlighted, considering the coincident prevalence. Furthermore, based on the most recent evidence, we justify and propose a case study of the vulnerable populations of the Brazilian Amazon. An understanding of the possible adverse synergism between these two factors is crucial and urgent for developing future strategies for reducing disparities between developed and underdeveloped/developing countries and the proper management of their vulnerable populations, particularly considering the long-term sequelae of COVID-19.

Methylmercury inhibits prolactin release in a cell line of pituitary origin

Heavy metals, such as methylmercury, are key environmental pollutants that easily reach human beings by bioaccumulation through the food chain. Several reports have demonstrated that endocrine organs, and especially the pituitary gland, are potential targets for mercury accumulation; however, the effects on the regulation of hormonal release are unclear. It has been suggested that serum prolactin could represent a biomarker of heavy metal exposure. The aim of this study was to evaluate the effect of methylmercury on prolactin release and the role of the nitrergic system using prolactin secretory cells (the mammosomatotroph cell line, GH3B6). Exposure to methylmercury (0-100 μM) was cytotoxic in a time- and concentration-dependent manner, with an LC₅₀ higher than described for cells of neuronal origin, suggesting GH3B6 cells have a relative resistance. Methylmercury (at exposures as low as 1 μM for 2 h) also decreased prolactin release. Interestingly, inhibition of nitric oxide synthase by N-nitro-L-arginine completely prevented the decrease in prolactin release without acute neurotoxic effects of methylmercury. These data indicate that the decrease in prolactin production occurs via activation of the nitrergic system and is an early effect of methylmercury in cells of pituitary origin.

Mercury exposure and antioxidant defenses in women: a comparative study in the Amazon

Mercury is a hazardous metal that has become an important issue of environmental contamination in Amazon areas. Human intoxication by mercury causes sensory deficits, motor dysfunction, delayed psychomotor development, genotoxicity, and several other health problems. One of the major cellular mechanisms of mercury toxicity is the oxidative stress which may lead to membrane peroxidation and generation of reactive oxygen species. The antioxidant defense, which includes scavenger compounds such as glutathione and antioxidant enzymes such as catalase, might prevent these injuries to occur. Thus, the objective of this work was to evaluate hair mercury levels and the strength of antioxidant defenses, evaluated by glutathione levels and catalase activity in the blood of exposed and non-exposed women living in Amazon populations. For each location, no statistically significant difference (P<0.05) was detected for age versus mercury content. However, women from populations under the influence of gold mining activity exhibit high mercury levels in hair samples, above the tolerance limit accepted by the World Health Organization. In addition, a significant correlation was found between high mercury content, high glutathione level, and lower catalase activity. These data suggest that chronic mercury intoxication may deplete antioxidant enzymatic activity, which can be used as an important peripheral marker. Knowledge originated by this monitoring will better assist the development of preventive strategies and governmental actions against the problem of mercury contamination.