The cell-damaging effects of low amounts of homocysteine and copper ions in human cell line cultures are caused by oxidative stress.

In the present study, we have investigated the increase of cell protein and the concentration of glutathione, cysteine and homocysteine in cell culture systems (HeLa cell line) after addition of low amounts (100-500 micromol/l) of homocysteine and/or copper. The thiols and cell protein were determined in cell cultures with daily additions of new medium with and without homocysteine and/or copper ions for 3 days. The present study shows that extracellularly added homocysteine (500 and 2000 micromol/l) resulted in signs of cell toxicity (decreased intracellular glutathione level and/or retarded cell growth). After the addition of copper ions (10, 50 or 100 micromol/l), complex changes in the concentrations of thiols in cell cultures occurred but cell growth was normal. After the addition of both homocysteine and copper ions, changes similar to those seen with the addition of copper ions and homocysteine alone were noted. However, synergistic features after addition of 500 micromol/l homocysteine and 10 or 50 micromol/l of copper ions were a significantly retarded cell growth and decreased concentration of cellular glutathione. In HeLa cell lines with initial low cell density and in an endothelial cell line (ECV 304), even the presence of 100 micromol/l of homocysteine and 10 micromol/l of copper ions inhibited cell growth and decreased the cellular level of glutathione. Whilst the level of homocysteine in our 3-day cell-culture experiments is higher than the mild hyperhomocysteinemia thought to be atherogenic in humans (20-30 micromol/l), it is conceivable that over a longer time course (several decades), this mild hyperhomocysteinemia could be sufficient to induce cellular effects similar to those found in the present study, eventually leading to atherosclerosis.