Arsenic induces telomerase expression and maintains telomere length in human cord blood cells

Inorganic arsenic (iAs) is a human carcinogen, well known as a clastogenic compound. To evaluate the molecular mechanism of arsenite (iAsIII) toxicity, we investigated the effects on cell growth and apoptosis, telomere length, telomerase expression, as well as the formation of reactive oxygen species (ROS) in male and female human cord blood cells in vitro. Incubation with iAsIII at the concentration of 0.0001 μM increased telomerase mRNA and protein expression maintained both telomere length and cellular growth, and induced mRNA over-expression of the two oncogenes ras and myc. Our results suggest that female cord blood cells are more sensitive than male ones to iAsIII induced telomerase stimulation at low concentrations, possibly related to the increased expression of ras and myc oncogenes. On the contrary, at the concentration of 1 μM, iAsIII decreased telomerase expression and telomere length, and induced apoptosis, necrosis and production of reactive oxygen species. Buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, markedly increased the percentage of apoptotic cells, suggesting that GSH is fundamental for detoxification of iAsIII in cord blood cells. The reactive oxygen species (ROS) scavenger, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), protected cord blood cells from iAsIII toxicity, and prevented telomere shortening and telomerase down-modulation. It can be concluded that telomerase expression and telomere length are associated with iAsIII induced cell death, via production of reactive oxygen species, as well as with iAsIII induced effects on cell differentiation processes and rate of cell growth.