(213) Fecal Microbiota with 1 Month of Elexacaftor/Tezacaftor/Ivacaftor in Pediatric Patients with Cystic Fibrosis: Preliminary Findings from PROMISE Pediatrics Study

Background: Cystic fibrosis (CF) gastrointestinal (GI) disease includes malabsorption, intestinal obstruction, and inflammation. While these manifestations are thought to result from pancreatic insufficiency, they are incompletely corrected by enzyme replacement therapy, suggesting other factors in the CF GI tract contribute to dysfunction. Children with CF were recently shown to have fecal dysbioses relative to children without CF, and measures of these dysbioses correlated with increased fecal measures of inflammation and fat. Further studies identified significant associations between this dysbiosis and fecal bile acid abundances, suggesting a role for bile acids in CF GI inflammation and malabsorption. Intestinal bacteria modify GI bile acid content through enzymatic activities including deconjugation, carried out by bile salt hydrolases (BSHs), and transformation of primary bile acids into secondary bile acids, which affects nutrient uptake and intestinal epithelium integrity. Impaired bile acid homeostasis has been observed in CF, resulting in altered signaling by the bile acid-activated farnesoid X receptor system, which transcriptionally regulates multiple host functions, including endocrine and GI activities and expression of CFTR. However, the causes and consequences of observed alterations in CF GI bile acid constituency are not well studied. We hypothesize that different microbiota, abundances of primary and secondary bile acids, and bile salt hydrolase (BSH)-encoding genes will differ in CF fecal samples from children with high versus low fecal inflammatory marker levels. We further hypothesize that treatment with triple combination therapy elexacaftor/tezacaftor/ivacaftor (TCT) will reduce fecal abundances of pro-inflammatory pathogens and primary bile acids and increase fecal abundances of secondary bile acids and BSH genes relative to pre-treatment values. To test these hypotheses, we are conducting an ancillary analysis of samples from PROMISE, a prospective, multi-center observational study of children with CF 6-11 years old to determine the relationship between CF fecal microbiota and bile acid abundances before and after CFTR modulator initiation. Our goal is to define the mechanisms and clinical effects of bile acid homeostasis in CF, and to inform its potential as a novel therapeutic target.

Methods: This study will analyze stool samples collected 30 days prior to (baseline) and 1 month after TCT from children with CF participating in the PROMISE study. Fecal microbiota and BSH gene abundance will be defined via the Illumina NextSeq DNA sequencing platform coupled with bioinformatic analytical methods (MetaPhlAn3, HUMAnN2). Fecal bile acids will be measured using mass spectrometry. Baseline fecal microbiota and bile acid abundances will be compared among subjects in the highest and lowest quartiles of fecal calprotectin (a measure of inflammation) prior to initiation of TCT. For all subjects, fecal microbiota, bile acid abundance, and BSH gene abundance will be compared between baseline and 1 month after TCT.

Results: 190 fecal samples collected at baseline and 1 month after TCT will complete sequencing by April 2022. Fecal bile acid measurements are expected by July 2022. The final analysis is expected to be completed prior to NACFC 2022.

Conclusions: Our goal is to define the mechanisms and clinical effects of bile acid homeostasis in CF, and to inform its potential as a novel therapeutic target.

Acknowledgements: This work was supported by CFF

References: