Pseudomonas aeruginosa is associated with increased lung cytokines and asymmetric dimethylarginine compared with methicillin-resistant Staphylococcus aureus.

The objective of the study was to investigate pulmonary responses to Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) using ovine and mice models of sepsis with emphasis on lung cytokine expression, asymmetric dimethylarginine (ADMA) concentration, and the arginase pathway. Sheep were instilled with either MRSA, P. aeruginosa, or saline under deep anesthesia; mechanically ventilated; resuscitated with fluid; and killed after 24 h. Mice were instilled with either MRSA, P. aeruginosa, or saline under deep anesthesia and killed after 8 h. Lungs were assessed for ADMA concentration, arginase activity, oxidative stress, and cytokine expression, and plasma was assessed for nitrate/nitrite concentrations. The severity of lung injury was more pronounced in P. aeruginosa sepsis compared with MRSA. The significant changes in sheep lung function after P. aeruginosa sepsis were associated with significantly increased ADMA concentrations and arginase activity compared with MRSA. However, the plasma concentration of nitrites and nitrates were significantly increased in MRSA sepsis compared with P. aeruginosa sepsis. In the mice model, P. aeruginosa significantly increased lung cytokine expression (IL-1 and IL-13), protein oxidation, and arginase activity compared with MRSA. Our data suggest that the greater expression of cytokines and ADMA concentrations may be responsible for severity of acute lung injury in P. aeruginosa sepsis. The lack of arginase activity may explain the greater nitric oxide production in MRSA sepsis.

Molecular biological effects of selective neuronal nitric oxide synthase inhibition in ovine lung injury.

Neuronal nitric oxide synthase is critically involved in the pathogenesis of acute lung injury resulting from combined burn and smoke inhalation injury. We hypothesized that 7-nitroindazole, a selective neuronal nitric oxide synthase inhibitor, blocks central molecular mechanisms involved in the pathophysiology of this double-hit insult. Twenty-five adult ewes were surgically prepared and randomly allocated to 1) an uninjured, untreated sham group (n = 7), 2) an injured control group with no treatment (n = 7), 3) an injury group treated with 7-nitroindazole from 1-h postinjury to the remainder of the 24-h study period (n = 7), or 4) a sham-operated group subjected only to 7-nitroindazole to judge the effects in health. The combination injury was associated with twofold increased activity of neuronal nitric oxide synthase and oxidative/nitrosative stress, as indicated by significant increases in plasma nitrate/nitrite concentrations, 3-nitrotyrosine (an indicator of peroxynitrite formation), and malondialdehyde lung tissue content. The presence of systemic inflammation was evidenced by twofold, sixfold, and threefold increases in poly(ADP-ribose) polymerase, IL-8, and myeloperoxidase lung tissue concentrations, respectively (each P < 0.05 vs. sham). These molecular changes were linked to tissue damage, airway obstruction, and pulmonary shunting with deteriorated gas exchange. 7-Nitroindazole blocked, or at least attenuated, all these pathological changes. Our findings suggest 1) that nitric oxide formation derived from increased neuronal nitric oxide synthase activity represents a pivotal reactive agent in the patho-physiology of combined burn and smoke inhalation injury and 2) that selective neuronal nitric oxide synthase inhibition represents a goal-directed approach to attenuate the degree of injury.

Cardiovascular collapse and vascular permeability changes in an ovine model of methicillin-resistant Staphylococcus aureus sepsis.

Methicillin-resistant Staphylococcus aureus (MRSA) infections with severe outcomes such as sepsis and septic shock are progressively increasing in both the community and in hospital settings. We hypothesized that overexpression of reactive nitrogen and oxygen species and vascular endothelial growth factor (VEGF) play a pivotal role in cardiovascular collapse associated with vascular hyperpermeability in MRSA sepsis. Twelve sheep were surgically prepared and randomized into a control (noninjured; n = 6) and a sepsis (injured; n = 6) group. Animals in the sepsis group were subjected to cotton smoke inhalation and instillation of 2.5 x 10(11) colony-forming units of live MRSA into both lungs. Cardiovascular variables in the control group remained stable, whereas the MRSA sepsis group developed a hypotensive and hyperdynamic circulatory shock state beginning at 6 h associated with significantly increased vascular permeability evidenced by increased prefemoral lymph flow starting at 12 h and permeability index from 12 to 18 h, higher fluid accumulation from 12 to 24 h, and significantly decreased plasma protein concentration and oncotic pressure beginning at 6 h compared with control animals. Myocardial 3-nitrotyrosine (3-NT) protein, poly (adenosine diphosphate-ribose), and VEGF mRNA expressions measured after the 24-h experiment were significantly increased in the injured animals as well. These results evidence that excessive production of reactive radicals and VEGF may play a major role in cardiovascular collapse and vascular hyperpermeability in MRSA sepsis.

Pulmonary vascular permeability changes in an ovine model of methicillin-resistant Staphylococcus aureus sepsis.

INTRODUCTION: Endothelial dysfunction is a hallmark of sepsis, associated with lung transvascular fluid flux and pulmonary dysfunction in septic patients. We tested the hypothesis that methicillin-resistant Staphylococcus aureus (MRSA) sepsis following smoke inhalation increases pulmonary transvascular fluid flux via excessive nitric oxide (NO) production. METHODS: Ewes were chronically instrumented, and randomised into either a control or MRSA sepsis (MRSA and smoke inhalation) group. RESULTS: Pulmonary function remained stable in the control group, whereas the MRSA sepsis group developed impaired gas exchange and significantly increased lung lymph flow, permeability index and bloodless wet-to-dry weight-ratio (W/D ratio). The plasma nitrate/nitrite (NOx) levels, lung inducible nitric oxide synthases (iNOS) and endothelial nitric oxide synthases (eNOS), vascular endothelial growth factor (VEGF) protein expressions and poly-(ADP)-ribose (PAR) were significantly increased by MRSA challenge. CONCLUSIONS: These results provide evidence that excessive NO production may mediate pulmonary vascular hyperpermeability in MRSA sepsis via up regulation of reactive radicals and VEGF.

Effects of the bradykinin B2 receptor antagonist icatibant on microvascular permeability after thermal injury in sheep.

Peptide kinins are potent vasoactive agents in the microcirculation that might be released after burn injury. The present study was designed to test the hypothesis that Icatibant (JE 049), a potent, selective peptidomimetic bradykinin-B2 receptor antagonist, would reduce the cardiovascular pathology occurring in sheep exposed to 40% total body surface area (TBSA), third-degree burn. Female sheep were surgically prepared for chronic study. After 5 to 7 days' recovery from the operative procedure, they were randomized to five groups: sham (n = 6, noninjured, nontreated), medicated sham (n = 4, noninjured, treated with 20 microg kg h Icatibant), control (n = 7, 40% TBSA third-degree burn, nontreated), Icatibant-4 (n = 6, 40% TBSA third-degree burn, treated with 4 microg kg h Icatibant [low dose]), Icatibant-20 (n = 8, 40% TBSA third-degree burn, treated with 20 microg kg h Icatibant [high dose]). Prefemoral lymph flow (milliliters per hour) remained constant in the sham and medicated sham groups but increased after injury: control (0 h, 3.9 +/- 0.5; 24 h, 28 +/- 4.2; 48 h, 33.0 +/- 8.1). The increased fluid flux was associated with enhanced protein flux. Both low and high doses of Icatibant significantly reduced the microvascular fluid flux: Icatibant-4 (0 h, 5.3 +/- 0.6; 24 h, 17.5 +/- 3.5; 48 h, 20.3 +/- 3.4); Icatibant-20 (0 h, 5.3 +/- 1.1; 24 h, 15.2 +/- 2; 48 h, 17.6 +/- 4.1). Total prefemoral protein leak was reduced in all treatment groups. The low dose of Icatibant significantly reduced prefemoral lymph flow without adversely affecting the hemodynamic changes observed after burn injury in sheep, suggesting that the bradykinin antagonist would reduce edema formation and improve fluid management of thermally injured patients.