EXOGENOUS NITRIC OXIDE (NO) ENHANCES APOPTOTIC NEUTROPHIL CELL DEATH.▴ 266

Inhaled NO may modulate immune response at clinically relevant concentrations (20 ppm) by depressing neutrophil (PMN) oxidative function¹. NO could affect function by causing cell necrosis or by inducing apoptosis, an “anti-inflammatory” form of programmed cell death by which aging PMNs are terminated². We hypothesize that NO exposure hastens PMN death by enhancing apoptosis.

Methods: Isolated human PMNs were exposed to room air (RA), 80% oxygen (O₂), NO at 20 ppm in RA (NO/RA), or NO/O₂ for 2 hours; or in RA alone for 2-24 hours (control). PMNs were also incubated in the absence or presence of NO donor S-nitroso-N-penicillamine (SNAP; 1mM), NO synthase inhibitor N^G-mono-methyl-L-arginine (L-NMMA; 0.5 mM), and PMN stimulant fMLP(10 nM). PMN cell viability was measured by fluorescence viability/cytotoxicity assay (Molecular Probes). PMN apoptosis was assessed by cell death detection ELISA for histone-associated DNA fragments (Boehringer Mannheim), TdT transferase-mediated fluorescence-labeled dUTP nick end labeling (TUNEL) assay, and DNA fragmentation gel electrophoresis.

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