The Role of Superoxide Nitric Oxide and Peroxynitrite in Neutrophil-Mediated Human Microvascular Cell Injury

Abstract

Neutrophil-derived oxygen radicals have been implicated in many pathophysiological states, such as the tissue injury associated with inflammation, organ ischemia associated with thrombosis, adult respiratory distress syndrome, rheumatoid arthritis, atherosclerosis, and asthma. The identity of the oxygen species responsible for oxidative cell injury is still largely in dispute. Evidence suggests that it may differ for each disease state, depend on the intrinsic antioxidant defenses of the target cell and the mode of neutrophil activation. In this study, we show that peroxynitrite, formed upon the interaction of superoxide and nitric oxide, may be the primary toxic oxygen radical species generated in vitro by neutrophils primed with TNF-alpha, then stimulated with C5a or N-formyl-Met-Leu-Phe (fMLP). Phorbol myristate acetate (PMA) induced cell injury also appears to cause the generation of peroxynitrite, however, superoxide and hydrogen peroxide may also play a role. Immune complex induced injury appears not to be mediated by peroxynitrite in this system. Neutrophils stimulated by TNF-alpha/C5a, TNF- alpha/fMLP, or PMA generated superoxide and nitrate (a product of peroxynitrite decomposition), both of which correlated with human dermal microvascular endothelial (HDME) cell injury. The addition of authentic nitric oxide caused a dose-dependent amplification of injury only when the neutrophils were stimulated to generate superoxide and nitrate. Furthermore, superoxide dismutase (SOD) mimics or oxygemoglobin (oxyHb), a nitric oxide scavenger, attenuated TNF-alpha/C5a or TNF-alpha/fMLP stimulated neutrophil-mediated injury. PMA-induced cell injury was inhibited by SOD mimic or a combination of catalase and SOD mimic, but not oxyHb.