Nitric oxide deficiency contributes to impairment of airway relaxation in cystic fibrosis mice.

The pulmonary disease of cystic fibrosis (CF) is characterized by persistent airway obstruction, which has been attributed to chronic endobronchial infection and inflammation. The levels of exhaled nitric oxide (NO) are reduced in CF patients, which could contribute to bronchial obstruction through dysregulated constriction of airway smooth muscle. Because airway epithelium from CF mice has been shown to have reduced expression of inducible NO synthase, we examined airway responsiveness and relaxation in isolated tracheas of CF mice. Airway relaxation as measured by percent relaxation of precontracted tracheal segments to electrical field stimulation (EFS) and substance P, a nonadrenergic, noncholinergic substance, was significantly impaired in CF mice. The airway relaxation in response to prostaglandin E2 was similar in CF and non-CF animals. Treatment with the NO synthase inhibitor NG-nitro-L-arginine methylester reduced tracheal relaxation induced by EFS in wild-type animals but had virtually no effect in the CF mice. Conversely, exogenous NO and L-arginine, a NO substrate, reversed the relaxation defect in CF airway. We conclude that the relative absence of NO compromises airways relaxation in CF, and may contribute to the bronchial obstruction seen in the disease.

Effect of Pseudomonas infection on weight loss, lung mechanics, and cytokines in mice.

Poor growth, Pseudomonas aeruginosa endobronchitis, pulmonary inflammation, and decline of lung function are hallmarks of cystic fibrosis (CF), yet the relationship between these features is poorly understood. Because animal models of chronic bronchopulmonary infection with P. aeruginosa used to study pulmonary inflammation in CF have also been associated with weight loss, we sought to determine whether this weight loss was due to the inflammatory process and/or to changes in lung function. P. aeruginosa-laden agarose beads were instilled into the lungs of mice. Weight loss was greatest 3 d after Pseudomonas infection. Infected mice had a rapid though transient rise in absolute neutrophil counts, mTNF-alpha, mIL-1beta, mIL-6, mip-2, and KC in bronchoalveolar lavage fluid. There was no difference in lung resistance or lung compliance measured by body plethysmography between infected and control mice. Weight loss did correlate with the concentration of proinflammatory cytokine levels 3 d after inoculation of mice with Pseudomonas, and body composition analysis revealed loss of skeletal muscle mass. These results suggest that weight loss in P. aeruginosa-infected mice was associated with the inflammatory process and not with altered pulmonary responsiveness. These findings may provide insights into the cause of cachexia and weight loss seen in patients with CF.

Tumor necrosis factor alpha, interleukin-1 alpha, interleukin-6, and prostaglandin E2 production in murine peritoneal macrophages infected with Ehrlichia risticii.

Ehrlichia risticii is a gram-negative obligate intracellular bacterium which primarily infects macrophages and crypt epithelial cells in the intestinal wall and is the etiologic agent of Potomac horse fever. To understand the pathogenesis of the disease, we tested whether E. risticii induces inflammation-associated products in thioglycolate-induced mouse peritoneal macrophages. Mouse peritoneal macrophages produced larger amounts of interleukin-1 alpha (IL-1 alpha) but lower levels of tumor necrosis factor alpha (TNF-alpha), IL-6, and prostaglandin E2 (PGE2) when exposed to live or killed E. risticii than when exposed to Escherichia coli lipopolysaccharide (LPS). Preincubation of macrophages with live or killed E. risticii suppressed TNF-alpha, IL-6, and PGE2 generation but not IL-1 alpha production in response to LPS. Murine gamma interferon treatment of macrophages did not influence TNF-alpha, IL-1 alpha, IL-6, or PGE2 production regardless of exposure to E. risticii. Intracellular cyclic AMP was significantly greater in E. risticii-infected macrophages than in uninfected macrophages. These results suggest that increased levels of IL-1 alpha but not TNF-alpha or PGE2 production by macrophages may be primarily involved in the pathogenesis of the disease caused by E. risticii. Increased intracellular concentration of cyclic AMP in infected macrophages may be chiefly responsible for the high level of IL-1 alpha and inhibition of TNF-alpha production in response to LPS.