Complement partially mediates acid aspiration-induced remote organ injury in the rat

Aspiration pneumonia and pneumonitis: a spectrum of infectious/noninfectious diseases affecting the lung

PURPOSE OF REVIEW

Our purpose is to describe aspiration pneumonia/pneumonitis as a spectrum of infectious/noninfectious diseases affecting the lung. We summarize diagnosis, risk factors, treatment, and strategies for prevention of aspiration.

RECENT FINDINGS

Aspiration is present in normal individuals, and disease manifestation depends on the chemical characteristics, frequency, and volume of inoculum. Anaerobes, though present, are no longer the predominant microbes isolated in aspiration pneumonia. Targets for preventing aspiration including improved oral hygiene and positional feeding have had mixed results. Patients diagnosed by clinicians with aspiration pneumonia experience greater morbidity and mortality than patients with community-acquired pneumonia.

SUMMARY

Aspiration pneumonia and pneumonitis are part of the pneumonia continuum and share similarities in pathophysiology, microbiology, and treatment. Modern microbiology demonstrates that the lung is not sterile, and isolates in aspiration pneumonia frequently include aerobes or mixed cultures. Treatment for aspiration pneumonia should include antibiotic coverage for oral anaerobes, aerobes associated with community-acquired pneumonia, and resistant organisms depending on appropriate clinical context. Additional studies targeting prevention of aspiration and investigating the increased morbidity and mortality associated with aspiration pneumonia are warranted.

Causative treatment of acid aspiration induced acute lung injury - Recent trends from animal experiments and critical perspective

Aspiration of low-pH gastric fluid leads to an initial pneumonitis, which may become complicated by subsequent pneumonia or acute respiratory distress syndrome. Current treatment is at best supportive, but there is growing experimental evidence on the significant contribution of both neutrophils and platelets in the development of this inflammatory pulmonary reaction, a condition that can be attenuated by several medicinal products. This review aims to summarize novel findings in experimental models on pathomechanisms after an acid-aspiration event. Given the clinical relevance, specific emphasis is put on deduced potential experimental therapeutic approaches, which make use of the characteristic alteration of microcirculation in the injured lung.

Sublytic terminal complement attack induces c-fos transcriptional activation in myotubes

Sublytic C5b-9 alters the molecular phenotype of myotubes by inhibiting muscle-specific gene expression. Here, we showed that C5b-9 induced c-fos mRNA and transcription. Using c-fos promoter-CAT constructs and electrophoretic mobility shift assay (EMSA), the minimal c-fos promoter activity was shown to increase within 30-min exposure to serum C5b-9, which also induced the binding of serum response factor (SRF), along with ternary complex factor (TCF) Elk1 and Sap1a to the serum response element. C5b-9 activated ERK1, which in turn activated Elk1 in myotubes. We propose that c-fos gene transcription associated with myotube dedifferentiation is induced by C5b-9 through ERK1-mediated assembly of serum response factor-ternary complex.

Activation of alveolar macrophages in acid-injured lung in rats: different effects of pentoxifylline on tumor necrosis factor-alpha and nitric oxide production

OBJECTIVE

To determine whether acid instillation augments tumor necrosis factor-alpha and nitric oxide production by alveolar macrophages in rats, and to study the effects of treatment with pentoxifylline before acid instillation on the production of these inflammatory mediators.

DESIGN

Controlled laboratory investigation on tumor necrosis factor-alpha and nitric oxide production by alveolar macrophages of rats that had acid-induced lung injury.

SETTING

University research laboratory.

SUBJECT

Alveolar macrophages of rats.

INTERVENTIONS

Alveolar macrophages were recovered by bronchoalveolar lavage at 4, 10, 16, 24, and 72 hrs after unilateral hydrochloric acid (pH, 1.0; volume, 0.1 mL) instillation into the lungs of rats. Alveolar macrophages then were cultured with or without lipopolysaccharide. One group of rats was pretreated with pentoxifylline before acid instillation.

MEASUREMENTS AND MAIN RESULTS

Alveolar macrophages from both acid-instilled and contralateral lungs, which had recovered 24 hrs after acid instillation, produced significantly greater tumor necrosis factor-alpha and nitric oxide. Subsequent exposure to lipopolysaccharide, as a surrogate for bacterial infection, further promoted tumor necrosis factor-alpha and nitric oxide release. Alveolar macrophages from rats pretreated with pentoxifylline before acid instillation produced significantly less tumor necrosis factor-alpha and did not overproduce tumor necrosis factor-alpha when exposed to lipopolysaccharide. In contrast, pretreatment with pentoxifylline had no effect on nitric oxide production by alveolar macrophages.

CONCLUSIONS

Acid instillation stimulates alveolar macrophages to produce tumor necrosis factor-alpha and nitric oxide. Pentoxifylline preserved innate production of tumor necrosis factor-alpha to lipopolysaccharide and did not inhibit the production of bactericidal nitric oxide. This may partly explain why pentoxifylline reduces acid aspiration-induced lung injury while maintaining the host's ability to combat bacterial infection after acid aspiration.

Acid instillation enhances the inflammatory response to subsequent lipopolysaccharide challenge in rats

Aspiration of gastric contents is one of leading causes of the acute respiratory distress syndrome (ARDS). The pathogenesis of acid aspiration-induced acute lung injury is well understood. Less clear is why patients who have suffered acid aspiration are susceptible to ARDS. We studied the effects of acid instillation on the inflammatory response to subsequent lipopolysaccharide (LPS) challenge in rats. Instillation of acid into the right lung worsened the pathology induced by LPS that was administered 24 h after acid instillation. This included worsened oxygenation, increased pulmonary edema, increased production of tumor necrosis factor-alpha (TNF-alpha) and cytokine-induced neutrophil chemoattractant, neutrophil accumulation and mobilization to the alveolar spaces, and nitric oxide (NO) production. Of interest, neutrophil mobilization, NO production, and protein permeability were also magnified in the left lung. These effects were attenuated by administration of the protein tyrosine kinase (PTK) inhibitors genistein and tyrphostin AG556. These data suggest that acid instillation primes the rat to enhance the inflammatory response to subsequent endotoxin challenge and that at least part of the augmented inflammatory response depends on PTK.

Complement inhibitors: a resurgent concept in anti-inflammatory therapeutics

In addition to its essential role in immune defense, the complement system contributes to tissue damage in many clinical conditions. Thus, there is a pressing need to develop therapeutically effective complement inhibitors to prevent these adverse effects. This concept, though old, received little scientific attention until recently. Data from animal models of diseases that have been produced using complement-deficient, knockout, and transgenic animals, as well as data demonstrating that complement proteins are produced in many important tissue sites (including the brain) have attracted the interest of many basic research scientists and applied scientists from the biotechnology field and larger pharmaceutical firms. This resurgence of interest has generated a wealth of new information in the field of complement inhibition. In this article, we comprehensively review up-to-date information in the field of complement inhibitors.

Pulmonary aspiration and lung injury

Lung injury after aspiration, although very rare, is a feared and potentially devastating sequela after anaesthesia. This paper summarizes the most recent studies in aspiration lung injury focusing on its clinical epidemiology, new insights in its pathophysiology and innovative concepts in its prevention and therapy.