Efficiency of homocysteine plus copper in inducing apoptosis is inversely proportional to γ-glutamyl transpeptidase activity

Hyperhomocysteinemia represents an independent risk factor for atherosclerosis, but the mechanisms leading to cellular dysfunctions remain unknown. Using ECV304 cells, we found that homocysteine (Hcy) plus copper (Cu2+) induced cytotoxic effects: loss of cell adhesion, increased permeability to PI, and the occurrence of morphologically apoptotic cells. This form of apoptosis, inhibited by Z-VAD-fmk, was associated with a loss of mitochondrial potential, a cytosolic release of cytochrome c, activation of caspase-3, degradation of poly( ADP-ribose) polymerase, and internucleosomal DNA fragmentation. However, the ability of Hcy plus Cu2+ to induce apoptosis decreased when the pretreatment culture time increased. As a positive correlation was found between the length of time of culture before treatment and the enhancement of gamma -glutamyl transpeptidase (gamma -GT) activity, we asked whether gamma -GT was involved in the control of Hcy plus Cu2+-induced apoptosis. Therefore, ECV304 cells were treated with either acivicin or dexamethasone, inhibiting and stimulating gamma -GT, respectively. In ECV304 cells and human umbilical venous endothelial cells, acivicin favored Hcy plus Cu2+-induced apoptosis whereas dexamethasone counteracted the apoptotic process. As acivicin and dexamethasone were also capable of modulating cell death in ECV304 cells treated with antitumoral drugs, our data emphasize that the involvement of gamma -GT in the control of apoptosis is not restricted to Hcy but also concerns other chemical compounds.