Arginase has been suggested to compete with nitric oxide synthase (NOS) for their common substrate, L-arginine. To study the mechanisms underlying this interaction, we compared arginase expression in isolated airways and the consequences of inhibiting arginase activity in vivo with NO production, lung inflammation, and lung function in both C57BL/6 and NOS2 knockout mice undergoing ovalbumin-induced airway inflammation, a mouse model of asthma.Arginases I and II were measured by western blot in isolated airways from sensitized C57BL/6 mice exposed to ovalbumin aerosol. Physiological and biochemical responses---inflammation, lung compliance, airway hyperreactivity, exhaled NO concentration, arginine concentration--were compared with the responses of NOS2 knockout mice. NOS2 knockout mice had increased total cells in lung lavage, decreased lung compliance, and increased airway hyperreactivity. Both arginase I and arginase II were constitutively expressed in the airways of normal C57BL/6 mice. Arginase I was up-regulated approximately 8-fold in the airways of C57BL/6 mice exposed to ovalbumin. Expression of both arginase isoforms were significantly upregulated in NOS2 knockout mice exposed to ovalbumin, with about 40-and 4-fold increases in arginases I and II, respectively. Arginine concentration in isolated airways was not significantly different in any of the groups studied. Inhibition of arginase by systemic treatment of C57BL/6 mice with a competitive inhibitor, Nω-hydroxy-nor-L-arginine (nor-NOHA), significantly decreased the lung inflammatory response to ovalbumin in these animals.We conclude that NOS2 knockout mice are more sensitive to ovalbumin-induced airway inflammation and its sequelae than are C57BL/6 mice, as determined by increased total cells in lung lavage, decreased lung compliance, and increased airway hyperreactivity, and that these findings are strongly correlated with increased expression of both arginase isoforms in the airways of the NOS2 knockout mice exposed to ovalbumin.

Control of airway inflammation is critical in asthma treatment. Soluble epoxide hydrolase (sEH) has recently been demonstrated as a novel therapeutic target for treating inflammation, including lung inflammation. We hypothesized that pharmacological inhibition of sEH can modulate the inflammatory response in a murine ovalbumin (OVA) model of asthma. BALB/c mice were sensitized and exposed to OVA over 6 weeks. A sEH inhibitor (sEHI) was administered for 2 weeks. Respiratory system compliance, resistance, and forced exhaled nitric oxide were measured. Lung lavage cell counts were performed, and selected cytokines and chemokines in the lung lavage fluid were measured. A LC/MS/MS method was used to measure 87 regulatory lipids mediators in plasma, lung tissue homogenates, and lung lavage fluid. The pharmacological inhibition of sEH increased concentrations of the antiinflammatory epoxy eicosatrienoic acids and simultaneously decreased the concentrations of the proinflammatory dihydroxyeicosatrienoic acids and dihydroxyoctadecenoic acids. All monitored inflammatory markers, including FeNO levels, and total cell and eosinophil numbers in the lung lavage of OVA-exposed mice were reduced by sEHI. The type 2 T helper cell (Th2) cytokines (IL-4, IL-5) and chemokines (Eotaxin and RANTES) were dramatically reduced after sEHI administration. Resistance and dynamic lung compliance were also improved by sEHI. We demonstrated that sEHI administration attenuates allergic airway inflammation and airway responsiveness in a murine model. sEHI may have potential as a novel therapeutic strategy for allergic asthma.Keywords: soluble epoxide hydrolase; asthma; inflammation; lipid mediators; type 2 T helper cell cytokines Clinical RelevanceWe demonstrated that inhibition of soluble epoxide hydrolase attenuates allergic airway inflammation and airway responsiveness in a murine model. Therefore, sEH inhibitors may have potential as a novel therapeutic strategy for allergic asthma.Three hundred million people worldwide suffer from episodic or persistent asthma (1). The cornerstones of treatment for persistent asthma are inhaled corticosteroids and b-agonist bronchodilators; however, a significant minority of patients with asthma does not respond well to these therapies (2). Thus, there are ongoing efforts to develop novel treatment strategies (3), such as specific antagonists of type 2 T helper cell (Th2) cytokines and mediators.

Arginase gene expression in the lung has been linked to asthma both in clinical studies of human patients and in the well-studied mouse model of ovalbumin-induced airway inflammation. Arginase is thought to regulate NO levels in the lung by its ability to divert arginine, the substrate for nitric oxide synthases that produce citrulline and NO, into an alternative metabolic pathway producing ornithine and urea. In the present study arginase I and arginase II concentrations were measured in isolated microdissected airway preparations from sensitized Balb/c mice exposed to ovalbumin aerosol. We found that arginase II was constitutively expressed in the airways of normal mice, whereas arginase I was undetectable in normal airways, while its expression was increased in airways of mice exposed to ovalbumin. The expression of arginase I strongly correlated with the presence of lung inflammation, as quantified by differential cell counts in lung lavage, suggesting that most, or all, of the arginase I in lungs of mice exposed to ovalbumin is present in the inflammatory cells rather than in the airway epithelium. There was also a significant correlation between increased expression of arginase I in the isolated airways and decreased lung compliance. On the other hand, while we found arginase II expression to also be significantly increased in airways from mice exposed to ovalbumin as compared with normal airways, the relative increase was much less than that observed for arginase I, suggesting that there was a smaller contribution of inflammatory cells to the arginase II content of the airways in mice exposed to ovalbumin. There was no apparent correlation between the content of arginase in isolated airways and exhaled NO concentration in the expired air from mice exposed to ovalbumin. However, there was a correlation between exhaled NO concentration from mice exposed to ovalbumin and the lymphocyte content of the lung lavage.The concentration of arginine found in isolated airways from Balb/c mice exposed for 2 weeks to ovalbumin was about half of the value found in isolated microdissected airways from normal mice. Treatment of mice systemically with an arginase inhibitor significantly increased the amount of NO produced, as measured as the amount of nitrite + nitrate (NOx) in lung lavage supernatant prepared from mice exposed to ovalbumin. Our results are consistent with the hypothesis that the response of the lung to ovalbumin challenge includes an adaptive response in the large airways regulating the concentration of arginine within cells of the airway epithelium and subepithelial layer, by shunting of arginine into the metabolic pathway for increased synthesis of NO.

The presence of eosinophilic inflammation is a characteristic feature of chronic and acute inflammation in asthma. An estimated 5%–10% of the 300 million people worldwide who suffer from asthma have a severe form. Patients with eosinophilic airway inflammation represent approximately 40%–60% of this severe asthmatic population. This form of asthma is often uncontrolled, marked by refractoriness to standard therapy, and shows persistent airway eosinophilia despite glucocorticoid therapy. This paper reviews personalized novel therapies, more specifically benralizumab, a humanized anti-IL-5Rα antibody, while also being the first to provide an algorithm for potential candidates who may benefit from anti-IL-5Rα therapy.

Airway remodeling in asthma contributes to airway hyperreactivity, loss of lung function, and persistent symptoms. Current therapies do not adequately treat the structural airway changes associated with asthma. The statins are cholesterol-lowering drugs that inhibit the enzyme 3-hydroxy-3-methyl-glutaryl-CoA reductase, the rate-limiting step of cholesterol biosynthesis in the mevalonate pathway. These drugs have been associated with improved respiratory health and ongoing clinical trials are testing their therapeutic potential in asthma. We hypothesized that simvastatin treatment of ovalbumin-exposed mice would attenuate early features of airway remodeling, by a mevalonate-dependent mechanism. BALB/c mice were initially sensitized to ovalbumin, and then exposed to 1% ovalbumin aerosol for 2 weeks after sensitization for a total of six exposures. Simvastatin (40 mg/kg) or simvastatin plus mevalonate (20 mg/kg) were injected intraperitoneally before each ovalbumin exposure. Treatment with simvastatin attenuated goblet cell hyperplasia, arginase-1 protein expression, and total arginase enzyme activity, but did not alter airway hydroxyproline content or transforming growth factor-β1. Inhibition of goblet cell hyperplasia by simvastatin was mevalonate-dependent. No appreciable changes to airway smooth muscle cells were observed in any of the control or treatment groups. In conclusion, in an acute mouse model of allergic asthma, simvastatin inhibited early hallmarks of airway remodeling, indicators that can lead to airway thickening and fibrosis. Statins are potentially novel treatments for airway remodeling in asthma. Further studies utilizing sub-chronic or chronic allergen exposure models are needed to extend these initial findings.