Clastogenic but Not Apoptotic Effects on Human Artery Endothelial Cells by Concentrations of Inorganic Lead Inhibiting Their Nitric Oxide Production

Abstract

Human coronary artery endothelial cells (HCAEC 5156) were cultured as monolayers and exposed to concentrations of lead (as acetate, Pb) in the culture medium similar or lower than those commonly found in the blood of human beings occupationally or environmentally exposed to this element. Only at the concentration of 200 ng/mL, Pb reduced growth rate of HCAEC 5156 cells starting from the 3rd day and up to the 5th day of incubation. On the other hand, Pb (0.2, 2 and 200 ng/mL) increased concentration-dependently micronuclei formation in binucleated HCAEC5156 cells, as it was shown by the cytokinesis-blocked micronucleus assay (CBMN assay) carried out after 48 hours of exposure to the metal. However, Pb was unable, at all the above concentrations, to induce apoptosis in HCAEC 5156 cells following a 48 hour-exposure, as shown by an electrophoretic apoptotic DNA fragmentation test. Moreover, Pb (2 and 200 ng/mL) reduced significantly the concentration of nitric oxide (NO, determined analytically as L-citrulline) in both culture medium and cytosol of HCAEC 5156 cells following a 7 day-exposure to the element. Results were discussed also in relation to evidences of other studies reporting genotoxic and/or apoptotic effects of Pb on various cell types at very elevated dosages or concentrations. The observed clastogenic effects of Pb were explained through a series of mechanisms involving interactions between oxygen reactive species and NO and/or reduced NO synthesis in the endothelium, thus leading to a depressed NO bioavailability. This research first shows that Pb is provided with clastogenic but not apoptotic effects on cultured human endothelial cells. It was emphasized that such effects are induced by Pb concentrations similar to those commonly found in blood and tissues of laboratory animals showing Pb induced cardiovascular and/or neuropsychological alterations.