Background. We examined the role of nitrosative stress in allograft destruction. Methods. Rats undergoing cardiac transplants received NOX-100, a water-soluble nitric oxide (NO) scavenger with antioxidant properties, with or without low-dose cyclosporine (CsA). Graft survival, NO production, and nuclear factor kappa B (NF-κB) activity were studied. Results. Using NOX-100 daily until rejection prolonged graft survival (11.6±0.6 vs. 7.4±0.2 days; P<0.05). Daily low-dose CsA (2.5 mg/kg im) for 7 days or until rejection also prolonged survival (12.6±0.5 and 21.6±1.6 days, respectively; P<0.01 vs. Controls). Low-dose CsA for 7 days and NOX-100 for 30 days prolonged graft survival (45.0±4.7 days; P<0.01 vs. all groups.). NOX-100 had no effect on whole blood CsA levels. Combination therapy until Day 100 resulted in 1 graft loss at Day 116 and indefinite survival in 3 animals (>300 days), which accepted a second WF strain heart without further immunosuppressive therapy but promptly rejected a third party (ACI) cardiac allograft. NOX-100 and CsA reduced nitrate and nitrite, and combination therapy completely normalized NO through to Day 30. Electron paramagnetic resonance spectroscopic analysis demonstrated reduction of signals for nitrosylmyoglobin and nitrosylheme with NOX-100 and elimination of signals with CsA alone or combination therapy. Activity of myocardial NF-κB decreased with monotherapy vs. untreated allografts. Combination therapy resulted in further inhibition of NF-κB up to Day 30. The extent of graft survival correlated with the extent of NO scavenging and NF-κB inhibition. Short-term combination therapy had no effect on graft lymphocytic infiltrate on Days 15, 20, and 30. Conclusion. These data support a role for both oxidative and nitrosative stress in rejection and the immunoregulatory potential of antioxidant therapy after transplantation.
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