Cytotoxicity and genotoxicity of low doses of mercury chloride and methylmercury chloride on human lymphocytes in vitro

L.C Silva-Pereira,M.A.C Smith,P.C.S Cardoso,M.O Bahia,R.R Burbano,W.R Bastos,D.S Leite

doi:10.1590/s0100-879x2005000600012

Abstract

Mercury is a xenobiotic metal that is a highly deleterious environmental pollutant. The biotransformation of mercury chloride (HgCl2) into methylmercury chloride (CH3HgCl) in aquatic environments is well-known and humans are exposed by consumption of contaminated fish, shellfish and algae. The objective of the present study was to determine the changes induced in vitro by two mercury compounds (HgCl2 and CH3HgCl) in cultured human lymphocytes. Short-term human leukocyte cultures from 10 healthy donors (5 females and 5 males) were set-up by adding drops of whole blood in complete medium. Cultures were separately and simultaneously treated with low doses (0.1 to 1000 microg/l) of HgCl2 and CH3HgCl and incubated at 37 degrees C for 48 h. Genotoxicity was assessed by chromosome aberrations and polyploid cells. Mitotic index was used as a measure of cytotoxicity. A significant increase (P < 0.05) in the relative frequency of chromosome aberrations was observed for all concentrations of CH3HgCl when compared to control, whether alone or in an evident sinergistic combination with HgCl2. The frequency of polyploid cells was also significantly increased (P < 0.05) when compared to control after exposure to all concentrations of CH3HgCl alone or in combination with HgCl2. CH3HgCl significantly decreased (P < 0.05) the mitotic index at 100 and 1000 microg/l alone, and at 1, 10, 100, and 1000 microg/l when combined with HgCl2, showing a synergistic cytotoxic effect. Our data showed that low concentrations of CH3HgCl might be cytotoxic/genotoxic. Such effects may indicate early cellular changes with possible biological consequences and should be considered in the preliminary evaluation of the risks of populations exposed in vivo to low doses of mercury.

Highlights

Mercury, one of the most widely diffused and hazardous organ-specific environmental contaminants, exists in a wide variety of physical and chemical states, each of which with unique characteristics of target organ specificity [1]
Once introduced into the environment, mercury compounds can undergo a wide variety of transformations
CH3HgCl has been an environmental concern to public health and regulatory agencies for over 50 years because of its neurotoxicity

Summary

Introduction

One of the most widely diffused and hazardous organ-specific environmental contaminants, exists in a wide variety of physical and chemical states, each of which with unique characteristics of target organ specificity [1]. Once introduced into the environment, mercury compounds can undergo a wide variety of transformations. Inorganic mercury (HgCl2) may be converted into methyl (CH3HgCl) and dimethyl (CH3CH2HgCl) forms by methanogenic bacteria. This biotransformation constitutes a serious environmental risk, given that CH3HgCl is the most toxic of the mercury compounds and accumulates in the aquatic food chain, eventually reaching human diets [2]. The three modern “faces” of mercury are our perceptions of risk from the exposure of billions of people to CH3HgCl in fish, mercury vapor from amalgam tooth fillings and CH3CH2HgCl in the form of thimerosal added as an antiseptic to widely used vaccines [4]

Objectives

Methods

Results