PARENT SESSION
41 - Physiological and Molecular Mechanisms of Toxicity
8:00 AM to 6:30 PM, Tuesday, 14 May 2002
Exhibition Area

(41-07) Inhibition of spontaneous apoptosis in human neutrophil by low-level mercury.

Moisan, Eliane^*,1, Arbour, Sylvie¹, Ngguyen, Nhi¹, Hébert, Marie-José¹, Girard, Denis, Bernier, Jacques¹, Fournier, Michel¹, Kouassi, Edouard¹, ¹ INRS-Institut Armand-Frappier, Pointe-Claire, Québec, Canada

ABSTRACT- Low levels of organic and inorganic mercury compounds have been reported previously to induce cell death by apoptosis in human peripheral blood mononuclear cells (MNC) but little is known about their potential effects on the viability and death of polymorphonuclear neutrophils (PMN). In contrast to MNC, PMN are known to undergo readily spontaneous apoptosis both in vivo and in vitro. Therefore, it was hypothesized that PMN may differ from MNC in their reactions to low mercury levels. The effects of methylmercuric chloride (MeHgCl) and mercuric chloride (HgCl₂) were evaluated in concentration-response and time course studies on human PMN viability and on their modes of cell death after in vitro incubation at 37⁰C. Cell death by apoptosis or necrosis was assessed by annexin V-fluorescein isothiocyanate binding to externalized phosphatidylserine in conjunction with propidium iodide, and flow cytometry analysis. Morphologic counting of pyknotic nuclei, as well as the fluorescence properties of the DNA-binding dye Hoechst 33342 in combination with propidium iodide were used to further confirm apoptotic cell death, and to characterize the sequence of Hg-induced cell death. Results show that low concentrations of MeHgCl (1-7.5 M) that were cytotoxic to MNC actually inhibited PMN spontaneous apoptosis. Low-level HgCl₂ reproduced the anti-apoptotic effects of MeHgCl on PMN, but to a lower extent. Higher concentrations of MeHgCl and HgCl2 were necrogenic to PMN, but MeHgCl was about an order of magnitude more toxic, and discrete differences were observed in the modalities of cell death induced by both species. These data reveal for the first time that (i) low levels of organic and inorganic mercury species protect human PMN from cell death via inhibition of spontaneous apoptosis, and that (ii) PMN are more resistant than MNC to mercury-induced cytotoxicity. These findings may have implications for mercury-induced autoimmunity and inflammation. Supported by the Canadian Toxic Substance

Key words: Neutrophils, Mercury, Apoptosis