Abstract
A rapid and sensitive quantitative fluorometric assay was developed to measure the response of endothelial cells to hydrogen peroxide (H2O2). The response of an endothelial cell-derived cell line, EA-hy-926, or human umbilical vein endothelial cells to H2O2 was determined using calcein-AM, a dye which becomes fluorescent upon cleavage by intracellular esterase(s). The ability of the cells to take up and convert calcein-AM was measured directly in the wells of 96-well flat-bottomed tissue culture plates with cell monolayers using a computerised microplate fluorimeter, or in cell suspensions using flow cytometry. The results obtained by these techniques were compared with each other and with a standard 51Cr release cytotoxicity assay. We found that calcein-AM is a highly sensitive probe for measuring H2O2-mediated cell injury, as it can not only detect the irreversible cyotoxicity measured by 51Cr release assay, but can also distinguish sublethal and reversible injury seen at low H2O2 concentrations.