Inhaled Bile Acids are Implicated in Airway Functional Changes and Cytokine Release

Abstract

Bile acids are potent TGR5 ligands previously identified in bronchial washings of post-lung transplant patients and have been implicated in airway contractility ex-vivo and derangement of innate immunity. Particularly, metabolomics revealed primary bile acids GCA, GCDCA, CA, CDCA, DCA and TCA as presenting in the largest quantities. We hypothesized that bile acids may also have chronic and acute effects on airway function in vivo by affecting central resistance as well as cytokine release. A/J Mice were administered IP diluted Pentobarbital: tracheostomy/cannulation performed prior to a 20s BA nebulization (1mM BA, 25% EtOH) and incremental methacholine (MCh) challenge. Lung resistance (Rn) measured on Flexivent apparatus. C57BL6 mice were administered a bile acids cocktail of 4mM including GCA, GCDCA, CA, CDCA, DCA and TCA was chronically administered via intranasal instillation for a period of one month. BAL and tissue were collected, cytokine levels were analyzed. Statistical analyses were performed using ANOVA-Bonferroni and Student T Test. In-vivo acute inhalation of BAs prior to MCh challenge showed a general decrease in Rn compared to control. GCA (p=0.005) and GCDCA (p=0.035) showed the greatest decrease in airway resistance upon acute nebulization followed by GLCA (p=0.007) and a trending CDCA (p=0.07), as shown in the figure. Cytokine output from BALs post 1-month instillation revealed a significantly lower level of IL-6 (p=0.0068), IL-1B (p=0.0063), IL-17 (p=0.0273), MIP-1a (p=0.0076), and MIP-1B (p=0.012). The acute and chronic inhalation of bile acids commonly detected as major species in brochoalveolar lavages show an impact on airway resistance by reducing the methacholine induced constriction and affecting cytokine release. Interestingly, cytokines were decreased upon chronic exposure which may indicate a macrophagic inhibition affecting the airway immune responses.