Intestinal Metabolites Are Profoundly Altered in the Context of HLA-B27 Expression and Functionally Modulate Disease in a Rat Model of Spondyloarthritis

Objective HLA-B27 associated spondyloarthropathies are associated with an altered intestinal microbiota and bowel inflammation. Therefore, we sought to identify B27-dependent changes in both host and microbial metabolites in the HLA-B27/β2m rat and whether microbiota-derived metabolites could impact disease in this major model of spondyloarthropathy. Methods Cecal contents were collected from 6wk (pre-diseased) and 16wk (diseased) Fischer 344 HLA-B27/β2m transgenic rats and WT controls. Metabolomic profiling was performed by high-throughput gas- and liquid-chromatography-based mass spectrometry. HLA-B27/β2m rats were treated with microbial metabolites propionate or butyrate in drinking water for 10wks and disease activity subsequently assessed. Results Our screen identified 582 metabolites, of which over half were significantly altered by B27 expression at 16wks. Both microbial and host metabolites were altered, with multiple pathways including amino acid, carbohydrate, xenobiotic and medium chain fatty acid metabolism affected. Differences were even observed at 6wks, with upregulation of histidine, tyrosine, spermidine, N-acetylmuramate and glycerate in HLA-B27/β2m rats. Administration of the short chain fatty acid propionate significantly attenuated B27-associated inflammatory disease, albeit was not associated with increased FoxP3+ T cell induction, or altered expression of cytokines IL-10, IL-33 or tight junction protein ZO-1. HLA-B27 expression was also associated with altered host expression of microbial metabolite receptor genes FFAR2, FFAR3 and NIACR1. Conclusion HLA-B27 expression profoundly impacts the intestinal metabolome, with changes evident in rats even at 6wks of age. Critically, we demonstrate a microbial metabolite, propionate attenuates development of B27-associated inflammatory disease. These and other microbiota-derived bioactive mediators may provide novel treatment modalities in B27-associated spondyloathropathies. This article is protected by copyright. All rights reserved.