Protective effect of poly(ADP-ribose) synthetase inhibition on multiple organ failure after zymosan-induced peritonitis in the rat

Background and Methods: In the present study, we tested the hypothesis that peroxynitrite and subsequent activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS) play a role in the pathogenesis of multiple organ failure induced by peritoneal injection of zymosan in the rat. Animals were randomly divided into six groups (ten rats for each group). The first group was treated with ip administration of saline solution (0.9% NaCl) and served as the sham group. The second group was treated with ip administration of zymosan (500 mg/kg suspended in saline solution). In the third and fourth groups, rats received ip administration of 3-aminobenzamide (10 mg/kg) 1 and 6 hrs after zymosan or saline administration, respectively. In the fifth and sixth groups, rats received ip administration of nicotinamide (50 mg/kg) 1 and 6 hrs after zymosan or saline administration, respectively. After zymosan or saline injection, animals were monitored for 72 hrs to evaluate systemic toxicity (conjunctivitis, ruffled fur, diarrhea, and lethargy), loss of body weight, and mortality. Results: A severe inflammatory response, characterized by peritoneal exudation, high plasma and peritoneal levels of nitrate/nitrite (the breakdown products of nitric oxide), and leukocyte infiltration into peritoneal exudate, was induced by zymosan administration. This inflammatory process coincided with the damage of lung, small intestine, and liver as assessed by histologic examination and by an increase of myeloperoxidase activity, which is indicative of neutrophil infiltration. Zymosan-treated rats showed signs of systemic illness, significant loss of body weight, acid high mortality rates. Peritoneal administration of zymosan in the rat also induced a significant increase in the plasma levels of peroxynitrite as measured by the oxidation of the fluorescent dihydrorhodamine 123. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to nitrotyrosine, a specific "footprint" of peroxynitrite, in the lung of zymosan-shocked rats. In vivo treatment with ip administration of 3-aminobenzamide (10 mg/kg, 1 and 6 hrs after zymosan injection) or nicotinamide (50 mg/kg, 1 and 6 hrs after zymosan injection) significantly decreased mortality, inhibited the development of peritonitis, and reduced peroxynitrite formation. In addition, PARS inhibitors were effective in preventing the development of organ failure because tissue injury and neutrophil infiltration, by myeloperoxidase evaluation, were reduced in the lung, small intestine, and liver. Conclusions: In conclusion, the major findings of our study are that peroxynitrite and the consequent PARS activation exert a role in the development of multiple organ failure and that PARS inhibition is an effective anti-inflammatory therapeutic tool.