Effect of nitrosative stress on extracellular nucleotide metabolism in endothelial cells.

Mechanisms of free radical injury involve chemical modification of proteins, lipid derivatives and nucleic acids and consequent loss of its function. However, specific targets and exact sequence of events has not been fully clarified. We determined whether extracellular enzymes that are involved in adenosine formation such as ecto-5'nucleotidase (e5N) and removal such as extracellular form of adenosine deaminase (eADA) could be affected by peroxynitrite. We used intact cell assay system that involves exposure of cultured HMEC-1 cells to substrates followed by HPLC analysis of conversion of substrates into products. We found that e5N and ADA activities decreased by 20-40% after incubation for 20 or 60 minutes with 30 μM peroxynitrite. Decrease of cellular ATP and NAD was also observed. We conclude that besides other cytotoxic effects modification of extracellular enzymes of nucleotide metabolism could be important target for free radical injury.