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Abstract

We thank Verburgt et al1Verburgt CM, et al. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.010Google Scholar and Kaunitz and Hollander2Kaunitz JD, Hollander D. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.011Google Scholar for their interest in our research findings and for the opportunity to respond to the questions related to our article investigating the associations of fecal gut microbiome and intestinal permeability in healthy first-degree relatives (FDRs) of subjects with Crohn’s disease (CD).3Leibovitzh H. et al.Gastroenterology. 2022; 163: 1364-1376.e10Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar Indeed, a better understanding of the mechanism that regulates gut barrier homeostasis is required. This is especially true because healthy FDRs with baseline abnormal paracellular permeability are more than 3 times more likely to develop CD.4Turpin W. et al.Gastroenterology. 2020; 159: 2092-2100.e5Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar Our study of healthy FDRs identified multiple associations of gut microbiome with barrier function. We agree that comparing such findings in the general population could help us generalize these observations, although this is more challenging because the incidence of abnormal lactulose-to-mannitol ratio (LMR) in healthy individuals from the general population is much lower than in healthy FDRs. In this context, we read with great interest the findings reported by Verburgt et al.1Verburgt CM, et al. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.010Google Scholar Their study suggests that diet can be used to modulate gut barrier function with various degrees of responses that can be partially explained by specific baseline microbiome composition. Despite the differences in study design and patient population, several findings were in line with our results in participants that had improved gut barrier function after the dietary intervention, including increased levels of Clostridiales and an increase in microbial pathway of pyruvate fermentation to acetate and lactate in participants with normal barrier function. This highlights the role of gut microbiota modulation as a potential target to improve barrier function that should be further explored in at-risk populations such as FDRs. We are grateful for the comments made by Kaunitz and Hollander.2Kaunitz JD, Hollander D. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.011Google Scholar It is especially important to recognize their work as first establishing the increase in LMR in FDRs. This has given us the impetus to formally show that elevated LMR in healthy FDRs predicts risk of onset of CD.4Turpin W. et al.Gastroenterology. 2020; 159: 2092-2100.e5Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar Indeed, considerable progress has been made in tight-junction research5Khoshbin K. et al.Gastroenterology. 2021; 161: 463-475.e13Abstract Full Text Full Text PDF PubMed Scopus (11) Google Scholar as well as enhanced understanding of the complex relationship of tight-junction proteins and the gut microbiome based on in vitro and in vivo non-human animal models. However, translating findings from such animal studies to humans is challenging, and as Kaunitz and Hollander so correctly highlight, there are signficant limitations and challenges in defining these mechanisms from human studies. We fully agree that the LMR assay has limitations and does not address the specifics of alterations in tight-junction proteins. Moreover, the use of fecal 16S-rRNA sequencing data to assess the gut microbiome composition also has limitations. Although we agree with Kaunitz and Hollander that more information may be obtained from mucosa-associated microbiome via endoscopic procedures, this is very difficult to do on a large scale in healthy human subjects. Nonetheless, fecal gut microbiome composition still has its value, because it has been shown to be associated with multiple diseases affecting organs even outside the intestinal tract.6de Vos W.M. et al.Gut. 2022; 71: 1020-1032Crossref PubMed Scopus (129) Google Scholar Moreover, the transplantation of fecal samples from animals with increased gut permeability into recipient gnotobiotic mice was shown to transfer the increased gut permeability phenotype.7Parker A. et al.Microbiome. 2022; 29 (10): 68Crossref Scopus (23) Google Scholar Therefore, it remains plausible that fecal microbiome reflects changes in the composition of the entire gut, and given the compositional differences seen associated with altered LMR, this suggests a starting point to explore how these changes may be mechanistically related to changes in LMR in humans. We think that the impaired gut paracellular permeability is related to Crohn’s pathogenesis independently from systemic inflammation, because we previously showed that pre-CD patients have increased LMR4Turpin W. et al.Gastroenterology. 2020; 159: 2092-2100.e5Abstract Full Text Full Text PDF PubMed Scopus (85) Google Scholar as well as antimicrobial antibody8Lee S.H. et al.Gastroenterology. 2021; 161: 1540-1551Abstract Full Text Full Text PDF PubMed Scopus (9) Google Scholar many years before disease onset, even after adjusting for fecal calprotectin. In our current study,3Leibovitzh H. et al.Gastroenterology. 2022; 163: 1364-1376.e10Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar we also provided information on the potential confounding effect of gut subclinical inflammation and validated that both Colidextribacter and Clostridia UCG 014 were associated with impaired gut barrier function regardless of fecal calprotectin. We agree that future mechanistic studies are needed to support our results. We thank Verburgt et al1Verburgt CM, et al. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.010Google Scholar and Kaunitz and Hollander2Kaunitz JD, Hollander D. Gastroenterology. Published online December 20, 2022. https://doi.org/10.1053/j.gastro.2022.12.011Google Scholar for their comments regarding our study. We welcome future experiments to assess more directly some of the issues raised. Notably, our plan to broaden the functional assessment of the gut microbiome is ongoing. We think the GEM (Genetic, Environmental, Microbial) cohort will allow us to better elucidate the mechanism(s) involved in the onset of CD. Finally, we think that prospective cohorts are necessary to understand the pathogenesis of CD and draw conclusions that cannot be derived from cross-sectional case-control studies or deduced from nonhuman animal studies. ReplyGastroenterologyPreviewWe read with great interest the study by Leibovitzh et al.1 We add to their findings with our experience with intestinal permeability (IP), looking at pediatric Crohn’s disease (CD) patients on dietary therapy (with either CD exclusion diet or exclusive enteral nutrition). We have previously described that IP improves in children during dietary therapy within the first 3 weeks (mainly with CD exclusion diet).2 Using the present cutoff (urinary lactulose-to-mannitol ratio ≤ 0.025), 30 of 53 patients (57%) had normal barrier integrity at baseline, which improved to 36 of 53 patients (68%) after the dietary therapy at 3 weeks. Full-Text PDF Revisiting the Stool Microbiome: Intestinal Paracellular Permeability ConnectionGastroenterologyPreviewThe initial discovery of increased small intestinal paracellular permeability in healthy first-degree relatives (FDRs) of patients with Crohn’s disease1 is one of the more striking observations that may bear on the pathogenesis of Crohn’s disease. Although the genetic basis for this observation has been reinforced by subsequent studies and a vast amount of knowledge has accumulated regarding the structure and regulation of intestinal tight junctions,2 this observation remains unexplained. Full-Text PDF