60-Day chronic exposure to low concentrations of HgCl2 impairs sperm quality: hormonal imbalance and oxidative stress as potential routes for reproductive dysfunction in rats.

Stefan Schlatt,Caroline S Martinez,María J Alonso,Janete A Anselmo-Franci,João Guilherme D Torres,Mercedes Salaices,Giulia A Wiggers,Franck M Peçanha,Dalton V Vassallo

doi:10.1371/journal.pone.0111202

Abstract

Mercury is a toxic and bio-accumulative heavy metal of global concern. While good deals of research have been conducted on the toxic effects of mercury, little is known about the mechanisms involved in the pathogenesis of male reproductive dysfunction induced by mercury. Therefore, the purpose of this study was to assess the effects and underlying mechanisms of chronic mercury exposure at low levels on male reproductive system of rats. Three-month-old male Wistar rats were divided into two groups and treated for 60 days with saline (i.m., Control) and HgCl2 (i.m. 1st dose: 4.6 µg/kg, subsequent doses 0.07 µg/kg/day). We analyzed sperm parameters, hormonal levels and biomarkers of oxidative stress in testis, epididymis, prostate and vas deferens. Mercury treatment decreased daily sperm production, count and motility and increased head and tail morphologic abnormalities. Moreover, mercury treatment decreased luteinizing hormone levels, increased lipid peroxidation on testis and decreased antioxidant enzymes activities (superoxide dismutase and catalase) on reproductive organs. Our data demonstrate that 60-day chronic exposure to low concentrations of HgCl2 impairs sperm quality and promotes hormonal imbalance. The raised oxidative stress seems to be a potential mechanism involved on male reproductive toxicity by mercury.

Highlights

Mercury is a persistent toxic and bio-accumulative heavy metal of global concern since their anthropogenic and natural emissions still pose high risk to human and environmental health
The main contribution to human exposure is the ingestion of fish and seafood; it can occur from dental amalgam fillings, vaccines and contaminated water and air [1,2]
Rats were divided into two groups (n = 10 each) and treated for 60 days as follows: a) Control; b) Mercury (HgCl2 - mercury chloride (1st dose 4.6 mg/kg, subsequent doses 0.07 mg/kg/day, i.m., to cover daily loss, using the model described by Wiggers et al [26], with an extended exposure for 60 days)

Summary

Introduction

Mercury is a persistent toxic and bio-accumulative heavy metal of global concern since their anthropogenic and natural emissions still pose high risk to human and environmental health. The main contribution to human exposure is the ingestion of fish and seafood (methylmercury); it can occur from dental amalgam fillings (metallic mercury), vaccines (ethylmercury) and contaminated water and air (mercury chloride) [1,2]. Within the US population, the chronic mercury exposure and average population of mercury concentrations rose sharply from 1999 to 2006 [3]. At Tapajos River Basin, Amazon, Brazil, known for mercury occupational exposure from gold mining and, bioaccumulation, exposure to mercury have decreased between 1999–2012 among women of reproductive age; the potential risk is still an issue because 22% of the women shows high mercury levels. In the aforementioned cohort studies, the mercury levels are close to or above the tolerance limit established by WHO [4,5,6]

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