Differential degradation by nitric oxide and peroxynitrite of heparin and hyaluronic acid

Endothelial cells produce nitric oxide (NO), a strong vasorelaxing agent, from arginine by the enzyme nitric oxide synthase (NOS). These cells also produce Superoxide, which can combine with NO to form peroxynitrite (PN). In water, NO converts to nitrous acid, an agent which is known to depolymerize heparin (H) and heparan sulfate (HS) of the extracellular matrix. PN decomposes to hydroxyl radical, which is a potent nonspecific degradative agent. The purpose of this study is to determine which species degrades H (and HS), using the degradation of hyaluronic acid (which is resistant to nitrous acid) for comparison. H and HA were treated with nitrous acid, NO gas, or synthetic PN. H degradation was determined by gel filtration, while HA degradation was observed by electrophoresis. Pure NO gas degraded H to small fragments, similar to the products from exhaustive nitrous acid treatment. NO gas had no effect on HA. PN degraded bacterial HA from a molecular weight of 2.7 x 106 to 0.6 x 106, but PN did not degrade heparin. Endothelial cells degrade exogenous H, but not HA, and this degradation can be inhibited by NOS inhibitors. These data describe a new chemical reaction and suggest that endothelial cells may degrade HS of the extracellular matrix by NO through a nitrous acid pathway.