Prevalence of food allergies in the United States is on the rise. Eosinophils are recruited to the intestinal mucosa in substantial numbers in food allergen-driven gastrointestinal (GI) inflammation. Soluble epoxide hydrolase (sEH) is known to play a pro-inflammatory role during inflammation by metabolizing anti-inflammatory epoxyeicosatrienoic acids (EETs) to pro-inflammatory diols. We investigated the role of sEH in a murine model of food allergy and evaluated the potential therapeutic effect of a highly selective sEH inhibitor (trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]-cyclohexyloxy}-benzoic acid [t-TUCB]). Oral exposure of mice on a soy-free diet to soy protein isolate (SPI) induced expression of intestinal sEH, increased circulating total and antigen-specific IgE levels, and caused significant weight loss. Administration of t-TUCB to SPI-challenged mice inhibited IgE levels and prevented SPI-induced weight loss. Additionally, SPI-induced GI inflammation characterized by increased recruitment of eosinophils and mast cells, elevated eotaxin 1 levels, mucus hypersecretion, and decreased epithelial junction protein expression. In t-TUCB-treated mice, eosinophilia, mast cell recruitment, and mucus secretion were significantly lower than in untreated mice and SPI-induced loss of junction protein expression was prevented to variable levels. sEH expression in eosinophils was induced by inflammatory mediators TNF-α and eotaxin-1. Treatment of eosinophils with t-TUCB significantly inhibited eosinophil migration, an effect that was mirrored by treatment with 11,12-EET, by inhibiting intracellular signaling events such as ERK (1/2) activation and eotaxin-1-induced calcium flux. These studies suggest that sEH induced by soy proteins promotes allergic responses and GI inflammation including eosinophilia and that inhibition of sEH can attenuate these responses.

Arachidonic acid metabolites resulting from the cyclooxygenase (COX), lipoxygenase, and cytochrome P450 oxidase enzymatic pathways play pro- and anti-inflammatory roles in allergic airway inflammation (AAI) and asthma. Expression of COX-2 and soluble epoxide hydrolase (sEH) are elevated in allergic airways and their enzymatic products (e.g., prostaglandins and diols of epoxyeicosatrienoic acids, respectively) have been shown to participate in the pathogenesis of AAI. Here, we evaluated the outcome of inhibiting the COX-2 and sEH enzymatic pathways with a novel dual inhibitor, PTUPB, in A. alternata-induced AAI. Allergen-challenged mice were administered with 10 or 30 mg/kg of PTUPB, celecoxib (selective COX-2 inhibitor), t-TUCB (selective sEH inhibitor) or vehicle daily by gavage and evaluated for various features of AAI. PTUPB and t-TUCB at 30 mg/kg, but not celecoxib, inhibited eosinophilic infiltration and significantly increased levels of anti-inflammatory EETs in the lung tissue of allergen-challenged mice. t-TUCB significantly inhibited allergen-induced IL-4 and IL-13, while a less pronounced reduction was noted with PTUPB and celecoxib. Additionally, t-TUCB markedly inhibited eotaxin-2, an eosinophil-specific chemokine, which was only marginally reduced by PTUPB and remained elevated in celecoxib-treated mice. PTUPB or t-TUCB administration reversed allergen-induced reduction in levels of various lipid mediators in the lungs, with only a minimal effect noted with celecoxib. Despite the anti-inflammatory effects, PTUPB or t-TUCB did not reduce allergen-induced airway hyperresponsiveness (AHR). However, development of structural changes in the allergic airways, such as mucus hypersecretion and smooth muscle hypertrophy, was significantly inhibited by both inhibitors. Celecoxib, on the other hand, inhibited only airway smooth muscle hypertrophy, but not mucus hypersecretion. In conclusion, dual inhibition of COX-2 and sEH offers no additional advantage relative to sEH inhibition alone in attenuating various features associated with A. alternata-induced AAI, while COX-2 inhibition exerts only moderate or no effect on several of these features. Dual sEH/COX-2 inhibition may be useful in treating conditions where eosinophilic inflammation co-exists with pain-associated inflammation.

Background

Altered epithelial physical and functional barrier properties along with T_H1/T_H2 immune dysregulation are features of allergic asthma. Regulation of junction proteins to improve barrier function of airway epithelial cells has the potential for alleviation of allergic airway inflammation.

Objective

We sought to determine the immunomodulatory effect of knob protein of the adenoviral capsid on allergic asthma and to investigate its mechanism of action on airway epithelial junction proteins and barrier function.

Methods

Airway inflammation, including junction protein expression, was evaluated in allergen-challenged mice with and without treatment with knob. Human bronchial epithelial cells were exposed to knob, and its effects on expression of junction proteins and barrier integrity were determined.

Results

Administration of knob to allergen-challenged mice suppressed airway inflammation (eosinophilia, airway hyperresponsiveness, and IL-5 levels) and prevented allergen-induced loss of airway epithelial occludin and E-cadherin expression. Additionally, knob decreased expression of T_H2-promoting inflammatory mediators, specifically IL-33, by murine lung epithelial cells. At a cellular level, treatment of human bronchial epithelial cells with knob activated c-Jun N-terminal kinase, increased expression of occludin and E-cadherin, and enhanced epithelial barrier integrity.

Conclusion

Increased expression of junction proteins mediated by knob leading to enhanced epithelial barrier function might mitigate the allergen-induced airway inflammatory response, including asthma.