Gut microbiota-derived inosine from dietary barley leaf supplementation attenuates colitis through PPARγ signaling activation

Abstract

Background Ulcerative colitis is a type of chronic inflammatory bowel disease closely associated with gut microbiota dysbiosis and intestinal homeostasis dysregulation. Barley leaf (BL) has a long history of use in Traditional Chinese Medicine with potential health-promoting effects on intestinal functions. However, its mechanism of action is not yet clear. Here, we explore the potential modulating roles of gut microbial metabolites of BL to protect against colitis and elucidate the underlying molecular mechanisms. Results Using 16S rRNA gene-based microbiota analysis, we first found that dietary supplementation of BL ameliorated dextran sulfate sodium (DSS)-induced gut microbiota dysbiosis. The mechanisms by which BL protected against DSS-induced colitis were resulted from improved intestinal mucosal barrier functions via the activation of peroxisome proliferator-activated receptor (PPAR)γ signaling. In addition, metabolomic profiling analysis showed that the gut microbiota modulated BL-induced metabolic reprograming in the colonic tissues particularly by the enhancement of glycolysis process. Notably, dietary BL supplementation resulted in the enrichment of microbiota-derived purine metabolite inosine, which could activate PPARγ signaling in human colon epithelial cells. Furthermore, exogenous treatment of inosine reproduced similar protective effects as BL to protect against DSS-induced colitis through improving adenosine 2A receptor (A2AR)/PPARγ-dependent mucosal barrier functions. Conclusions Overall, our findings suggest that the gut microbiota-inosine-A2AR/PPARγ axis plays an important role in the maintenance of intestinal homeostasis, which may represent a novel approach for colitis prevention via manipulation of the gut microbial purine metabolite.

Dietary Barley Leaf Mitigates Tumorigenesis in Experimental Colitis-Associated Colorectal Cancer

“…The BL was prepared as previously described [23] and its nutritional composition is shown in Supplementary Table S1. The contents of nutritional components including protein, fat, soluble dietary fiber, insoluble dietary fiber, moisture, and ash were detected based on the National Standard Test Method by PONY (Beijing, China).…”

“…Colonic slides were stained with hematoxylin and eosin (HE) to assess the extent of histological and crypt injury. In addition, colonic sections were also stained with Alcian blue (AB) to evaluate mucosal barrier damage by counting the goblet cells [23].…”

“…The protein concentration of the supernatants was measured. The cytokine levels in the colon, including interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ, were quantified by commercial ELISA kits as described previously [23].…”

“…The barrier permeability of the intestinal tract was measured using the fluorescein isothiocyanate (FITC)-dextran (Sigma-Aldrich, Saint Louis MO, USA) method [23]. Before the assay, mice were fasted for 4 h, followed by the administration of FITC-dextran by gavage.…”

“…Barley leaf (BL) is rich in natural nutrients and is also a functional food with various health-promoting activities [21]. We and others have shown that BL has protective effects against colitis through the regulation of gut microbiota [22][23][24]. However, evidence of dietary BL in the prevention of colitis-associated colorectal cancer is still lacking.…”