Concentrations of nitric oxide (NO) metabolites in the liver of Neisseria meningitidis-infected mice: The effect of bacterial nitric oxide detoxification

Abstract

Rationale and hypothesis Meningococcal septicaemia is characterised by high bacterial titres in blood and an increased production of circulating nitric oxide metabolites, including nitrates NO 3 - , nitrites NO 2 - and S-nitrosothiol [SNO]. The formation of SNO, termed S-nitrosylation, is an important form of post-translational protein modification akin to phosphorylation. Previously, bacterial NO detoxification was demonstrated to reduce the concentration of host-cell SNO. We hypothesise that bacterial NO detoxification during sepsis interferes with host NO homeostasis within the liver, a vital organ in physiological response to infection, and contributes toward pathogenesis. Objectives 1. To establish an in vivo murine model of acute fulminant meningococcal sepsis. 2. To study the link between bacterial NO detoxification and circulating NO metabolites in murine liver. Methodology Female C57 Bl/6 mice were infected by intraperitoneal injection of wild type Neisseria meningitidis (serogroup B strain MC58) or an isogenic mutant unable to detoxify NO (ΔnorB). Eight hours after infection, livers were extracted and lysates were subjected to ozone-based chemiluminescence-based measurement of multiple NO metabolites. We obtained reproducibly high bacterial titres both in blood and liver lysates. Findings 1. Increased bacterial burden in liver lysates is positively and significantly correlated with hepatic nitrite concentrations NO 2 - (Spearman’s rank correlation, r = 0.5682, p = 0.0020, n = 9), negatively and significantly correlated with the hepatic concentration of all NO [NOx] deriviatives (r = −0.4390, p = 0.0220, n = 9) 2. In an acute fulminant meningococcal sepsis model, the production of NO metabolites was found to be unperturbed by the presence of bacterial NO detoxification machinery (p = 0.2704, n = 9).