【Introduction】
Barley β-glucan has beneficial physiological effects such as normalization of cholesterol levels, improving glucose tolerance, and reducing visceral fat. These effects suggest due to delayed digestion and absorption and improvement of energy metabolism by gut bacteria-derived short-chain fatty acids. However, few reports have simultaneously confirmed the effects on glucose and lipid metabolism in the liver, adipose tissue, and intestinal tract.
The purpose of this study was to investigate the effect of barley flour, rich in barley β-glucan, on the expression levels of genes related to glucose and lipid metabolism in the liver, adipose tissue, and ileum of mice fed on a high-fat diet.
【Materials and Methods】
Four-week-old male C57BL/6J mice were randomized into two groups (10 mice in each group) and kept for 92 days after one week of acclimation.: a group fed a high-fat diet (50% fat to energy ratio) supplemented with “Beaufiber” (BF) and a control group fed the same diet supplemented with cellulose (C). Experimental diets were adjusted to contain 5% dietary fiber.
Feed intake and body weight were measured, and an oral glucose tolerance test was performed in the 11th week. At the end of the study period, mice were dissected and subjected to various biochemical tests in serum, weight measurements of the liver, cecum, and adipose tissue, measurement of the short-chain fatty acid content of cecum contents, DNA microarray analysis of liver, adipose tissue, and ileum, and mRNA expression analysis by real-time PCR. The relationship between gene expression levels in each tissue and the amount of short-chain fatty acids in the cecum contents was also examined.
【Results】
There were no significant differences in body weight, feed intake, and feed efficiency. Liver weight and fat of retroperitoneal and abdominal were significantly lower in BF than in C, and the weight of the cecum was significantly higher in BF than in C.
Cholesterol and triglycerides in the liver, serum total cholesterol and LDL-cholesterol, and leptin concentrations were significantly lower in BF than in C. Serum triglycerides were significantly higher in BF than in C. Oral glucose tolerance test was significantly lower in BF than in C at 15 and 60 minutes.
The amounts of acetic acid, propionic acid, lactic acid, succinic acid, and total short-chain fatty acids in cecum contents were significantly higher in BF than in C. There was no significant difference in the amount of butyric acid.
DNA microarray analysis showed that genes involved in steroid biosynthesis in BF were suppressed by more than 50% in the liver and adipose tissue and by more than 10% in the ileum. Other genes whose expression was suppressed by 10% or more in each tissue and whose expression was promoted were as follows.
Suppression of expression
Liver: Elongation of fatty acids, glycerolipid metabolism, primary bile acid synthesis, biosynthesis of unsaturated fatty acids, α-linolenic acid metabolism
Adipose tissue: fatty acid degradation, glycerolipid metabolism, ether lipid metabolism, α-linolenic acid metabolism
Promotion of expression
Liver: steroid hormone biosynthesis, linoleic acid metabolism, fatty acid biosynthesis
Adipose tissue: fatty acid biosynthesis
Ileum: steroid hormone biosynthesis, ether lipid metabolism, arachidonic acid metabolism, linoleic acid metabolism, α-linolenic acid metabolism
On the other hand, there were only minor changes in the expression levels of genes involved in glucose metabolism.
The expression levels of mRNAs were found in the liver as fatty acid synthase (FAS), acyl CoA oxidase (ACOX), diacylglycerol o-acyltransferase-1 (DGAT1), stearoyl-CoA-desaturase-1 (SCD-1) carnitine palmitoyltransferase-1 (CPT-1), 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoAr), and cytochrome P450 7A1 (CYP7a1) were significantly lower in BF than in C. In adipose tissue, the mRNA expression level of hormone-sensitive lipase (HSL) was higher in BF than in C. The mRNA expression of monocyte chemotaxis protein 1 (MCP-1), F4 / 80, and NADPH oxidase subunit p67 phox, markers of inflammation, was significantly lower in BF than in C. There was no significant difference in the mRNA expression levels of genes involved in lipid metabolism in the ileum.
Analysis of the correlation between mRNA expression in the liver and adipose tissue with the concentrations of various short-chain fatty acids in the cecum showed the following negative correlations.
Liver
Acetic acid: ACOX, HMG-CoAr, CYP7a1
Propionic acid: ACOX, CPT1, DGAT1, DGAT2, HMG-CoAr, CYP7a1
Lactic acid: CYP7a1
Succinic acid: CYP7a1
Adipose tissue
Lactic acid: MCP-1
A positive correlation showed between HSL expression in adipose tissue and the concentration of propionate and lactate.
【Discussion and Conclusion】
Barley intake suppressed the postprandial increase in blood glucose in a high-fat diet obesity model mouse. However, there were only minor changes in the expression levels of genes related to glucose metabolism in the liver, adipose tissue, and ileum. We speculated that the effect of barley intake on glucose metabolism was mainly due to the inhibition of sugar absorption and gastrointestinal hormones and less due to changes in gene expression.
On the other hand, reducing cholesterol in the liver and serum is thought to be due to the suppression of the expression level of genes involved in the biosynthesis of cholesterol, including HMG-CoAr, the rate-limiting enzyme for cholesterol synthesis. The tissues in which barley intake is involved in lipid metabolism at the gene expression level are mainly liver and adipose tissue. In the ileum, barley may affect lipid metabolism via delayed digestion and absorption and gut fermentation.
【Research institution】
Otsuma Women's University (Japan)
Hakubaku Co., Ltd. (Japan)
Effects of β-glucan Rich Barley Flour on Glucose and Lipid Metabolism in the Ileum, Liver, and Adipose Tissues of High-Fat Diet Induced-Obesity Model Male Mice Analyzed by DNA Microarray
Nutrients 12, 11, 3546, 2020
