【Introduction】
Barley β-glucan promotes the production of short-chain fatty acids via fermentation by gut bacteria. Short-chain fatty acids stimulate the immune system and contribute to the regulation of anti-inflammatory effects. Therefore, an increase in the amount of short-chain fatty acids in the gut due to barley consumption is predicted to enhance gut-derived immune function.
Although there have been previous studies*1 suggesting that administration of oat β-glucan activates white blood cells and intestinal epithelial cells in the intestines of mice, most studies have been conducted using β-glucan extracts, and there have been few studies focusing on changes in the immune system when barley is consumed as a food.
Consumption of high-fat diets has adverse effects on the immune system. Recent studies have shown that administration of a high-fat diet decreases serum IgA levels in mice*2. Therefore, the primary purpose of this study was to investigate the changes in the secretion of secretory immunoglobulin A (sIgA) and mRNA expression levels of various cytokines in diet-induced obese mice treated with β-glucan-rich barley (high β-glucan barley). The relationship between the intestinal microbiota and the production of short-chain fatty acids was also investigated.
【Materials and Methods】
Four-week-old male C57BL/6J mice were acclimated for 11 days. The mice were fed a high-fat diet (50% lipid energy ratio) with the addition of powder of "white fiber", a variety of high β-glucan barley (HGB), or with the addition of cellulose (C). The total dietary fiber content was adjusted to be 5% in both groups. Eight mice in each group were fed the experimental diets for 90 days.
Bodyweight and feed intake were measured two or three times a week and collected feces for five days at 11 weeks. At the end of the study period, mice were dissected and measured the weight of the cecum, abdominal adipose tissue, and liver.
GC-MS determined short-chain fatty acid levels in the cecum and feces. sIgA and various cytokine levels in the cecum and serum were determined using ELISA methods. Gut microflora of the cecum and mRNA expression related to immunity in the ileum were analyzed by real-time PCR.
【Results】
There was no significant difference in feed intake between the two groups, therefore energy intake during the study period was equivalent. However, weight gain was significantly slower, and final weight was significantly lower in HGB than in C.
Liver, retroperitoneal fat, and mesenteric fat weights were significantly lower in HGB than in C. The cecum was significantly higher in HGB than in C.
The concentrations of sIgA in the cecum and serum were significantly higher in HGB than in C, but there were no significant differences in the concentrations of IL-6 and IL-10 in serum.
Total short-chain fatty acids, propionic acid, isobutyric acid, isovaleric acid, lactic acid, and succinic acid in the cecal contents were significantly higher in HGB than in C.
Butyric acid, propionic acid, isobutyric acid, valeric acid, isovaleric acid, lactic acid, and succinic acid in the feces were significantly higher in HGB than in C.
The total bacterial count in the cecum was significantly higher in HGB than in C. The bacterial count was significantly higher in Bacteroidetes and Firmicutes at the phylum level and Bacteroides, Bifidobacterium, Lactobacillus, and Atopobium clusters genus level.
The expression level of IL-10 mRNA in the ileum was significantly higher in HGB than in C, but there were no significant differences in other cytokines (IFN-γ, IL-12, IL-17, IL-1β, IL-33, IL-4, IL-5, IL-6, TGF-β, TNF-α). The expression level of multimeric immunoglobulin receptor (pIgR) mRNA was significantly higher in HGB than in C.
Correlation of sIgA levels with immune system-related parameters in the ileum and cecum showed a positive correlation between cecal sIgA levels and isobutyric acid, lactate, succinate, Lactobacillus, and pIgR. A strong positive correlation between serum sIgA levels and most gut bacteria. A positive correlation was shown with propionate, lactate, succinate, Bifidobacterium, Lactobacillus, and pIgR.
【Discussion and Conclusion】
We confirmed that barley consumption increased the sIgA concentration in the cecum and serum and increased the expression level of pIgR, which is involved in the secretion of sIgA into the intestinal lumen. There was also a positive correlation between the sIgA concentrations in the cecum and serum and the increase in gut bacteria and intestinal fermentation metabolites. We suggested that changes in the intestinal microflora caused by barley consumption increased immune function and IgA secretion, especially when consuming a high-fat diet.
Previous study reported that acetic acid and propionic acid promote migration of regulatory T cells (Treg) via G protein-coupled receptor 43 (GPR43) *3. IL-10 secreted by Treg inhibits the production of proinflammatory cytokines. IL-10 secreted by Treg inhibits the production of proinflammatory cytokines. Since there was a positive correlation between propionic acid concentration and IL-10 mRNA expression, barley intake may have affected Treg migration and IL-10 secretion via propionic acid. In addition, there was a positive correlation between sIgA concentration in the cecum and serum and Lactobacillus and lactic acid concentrations. Since It has been reported that Lactobacillus increases IL-10 expression*4, an increase in lactic acid-producing bacteria may increase sIgA concentration through the intestinal immune response.
【Research institution】
Otsuma Women's University (Japan)
Hakubaku Co., Ltd. (Japan)
*1 Nutr Res 30, 1, 40–8, 2010
*2 Biosci Microbiota Food Health 38, 2, 55–64, 2019
*3 Science 341, 6145, 569–73, 2013
*4 J Allergy Clin Immunol 115, 6, 1260–7, 2005
Ingestion of High β-Glucan Barley Flour Enhances the Intestinal Immune System of Diet-Induced Obese Mice by Prebiotic Effects
Nutrients 13, 3, 907, 2021
