Background/Purpose:

The gastro-intestinal tract (GIT) is frequently involved in Systemic sclerosis (SSc). Perturbation in the gut microbiota may affect the body well-being and function and intestinal disbiosis has been associated with a number of autoimmune diseases, including SSc. To date no attempt has been made to characterize the functional consequences of intestinal disbioisis in SSc and autoimmunity.

Methods:

A total of 59 SSc patients and 28 healthy controls (HCs) were included. Intestinal microbiota was studied via 16s-RNA sequencing on stool samples; in parallel, plasma metabolites were analyzed by high-performance liquid chromatography coupled to electrospray ionisation and quadrupole time-of-flight mass spectrometry (HPLC-MS-ESI-QTOF). Interaction models capable of explaining the disease were built via data mining algorithms with internal validation (20 x 10-fold cross-validation) and feature selection. Microbic and metabolic results were correlated by means of Spearman’s rho and results corrected via 100K-fold permutation testing. The severity of intestinal symptoms was assessed via the UCLA GIT questionnaire.

Results:

random forest model showed that HCs and SSc patients differ at the genus taxonomic rank (AUROC = 0.706 ± 0.023). Model reduction identified 9 genera relevant to the disease status (AUROC = 0.711 ± 0.042). A naïve Bayes algorithm found a unique metabolic pattern associated with SSc (AUROC = 0.707 ± 0.029) with just 17 relevant metabolites after feature selection (AUROC = 0.744 ± 0.029). Cross correlation between the 9 genera and the 17 metabolites (Figure, left panel) found significant interactions between desulfovibrio and alpha-N-Phenylacetyl-L-glutamine (rho = 0.389, p_c = 0.03) and 2,4-dinitrobenzenesulfonic acid (rho = 0.39, p_c = 0.029). Gut microbiota of SSc patients was capable of explaining 12.7 ± 4.1% of the variance of GIT scores. A model of 10 bacteria could jointly discriminate HCs and SSc patients with or without intestinal involvement (weighted AUROC = 0.679 ± 0.021). Among these bacteria, desulfovibrio was significantly associated with the presence of intestinal involvement (figure, right panel).

Conclusion:

SSc patients present unique microbic and metabolic fingertips. SSc-related disbiosis is characterized by an increase in pro-inflammatory microbial groups which compete with commensal bacteria. This microbiomic shift may promote the accumulation of metabolites, including a a sulfonate compound which has direct pro-inflammatory and immuno-modulating properties and that may serve as electron acceptor in anaerobic respiration of desulfovibrio strains. The toxic end-product of desulfovibrio respiratory metabolism (hydrogen sulfide) may contribute to intestinal damage and altered motility.

This work received support from the EU/EFPIA IMI Joint Undertaking PRECISESADS grant n° 115565. www.precisesads.eu