Structural Studies of Water-Insoluble β-Glucan from Oat Bran and Its Effect on Improving Lipid Metabolism in Mice Fed High-Fat Diet

Abstract

Water-insoluble β-glucan has been reported to have beneficial effects on human health. However, no studies have thoroughly characterized the structure and function of water-insoluble β-glucan in oat bran. Thus, the structure and effect of water-insoluble β-glucan on weight gain and lipid metabolism in high-fat diet (HFD)-fed mice were analyzed. First, water-insoluble β-glucan was isolated and purified from oat bran. Compared with water-soluble β-glucan, water-insoluble β-glucan had higher DP3:DP4 molar ratio (2.12 and 1.67, respectively) and molecular weight (123,800 and 119,200 g/mol, respectively). Notably, water-insoluble β-glucan exhibited more fibrous sheet-like structure and greater swelling power than water-soluble β-glucan. Animal experiments have shown that oral administration of water-insoluble β-glucan tended to lower the final body weight of obese mice after 10 weeks treatment. In addition, water-insoluble β-glucan administration significantly improved the serum lipid profile (triglyceride, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol levels) and epididymal adipocytes size. What is more, water-insoluble β-glucan reduced the accumulation and accelerated the decomposition of lipid in liver. In conclusion, water-insoluble β-glucan (oat bran) could alleviate obesity in HFD-fed mice by improving blood lipid level and accelerating the decomposition of lipid.

Keywords: lipid metabolism; physicochemical properties; structure characterization; water-insoluble β-glucan.

Figure 1

Overview of experimental design.

Figure 2

MALDI-TOF mass spectra of β-glucan. (a) Water-insoluble β-glucan and (b) water-soluble β-glucan. Fragment DP3 (M_w: 526.91); fragment DP4 (M_w: 689.16).

Figure 3

Spectroscopic analysis of water-insoluble β-glucans. (a) ¹H spectrum of β-glucan in D₂O. (b) ¹³C spectrum of β-glucan in D₂O. (c) FT-IR spectra of β-glucan in oat bran. (d) X-ray diffraction patterns of β-glucan in oat bran. Soluble, water-soluble β-glucan; Insoluble, water-insoluble β-glucan.

Figure 4

Scanning electron microscopy for (a) water-insoluble β-glucan and (b) water-soluble β-glucan.

Figure 5

The apparent viscosities of β-glucan at various shear rates with a concentration of 3.0% (w/v) at 25 °C. Soluble, water-soluble β-glucan; Insoluble, water-insoluble β-glucan.

Figure 6

Effect of oral administration of water-insoluble β-glucan on body weight, fat tissue to body weight ratio, lean to body weight ratio, and food intake in HFD-fed mice. (a) Changes in body weight over 10 weeks. (b) Body weight gain at the end of week 10. Weight gain (%) = [(final weight(g)−initial weight (g))/initial weight (g)] × 100. (c) Fat tissue to body weight ratio (%) = fat weight/body weight × 100. (d) Lean to body weight ratio (%) = lean meat weight/body weight × 100. (e) Daily energy intake of HFD-fed mice. (f) Food efficiency ratio (%) = mean body weight gain (g)/mean food consumption (g) × 100. NC, normal control group; HFD, obesity model group; Insoluble, mice fed with HFD and given oral administration of water-insoluble β-glucan. Data are presented as mean ± standard deviation (n = 6). Groups labeled with different letters are different from one another (p < 0.05).

Figure 7

Effect of oral administration of water-insoluble β-glucan on serum biochemical concentrations and shape of epididymis in HFD-fed mice. (a) The concentration of triglycerides in serum. (b) The concentration of total cholesterol in serum. (c) The concentration of HDL-C in serum. HDL-C, high-density lipoprotein cholesterol. (d) The concentration of LDL-C in serum. LDL-C, low-density lipoprotein cholesterol. (e) Hematoxylin and eosin (H&E) staining of epididymal adipose (200× magnification). (f) Adipocyte size = total cell area/the number of cells. NC, normal control group; HFD, obesity model group; Insoluble, mice fed with HFD and given oral administration of water-insoluble β-glucan. Data are presented as mean ± standard deviation (n = 6). Groups labeled with different letters are different from one another (p < 0.05).

Figure 8

Effect of water-insoluble β-glucan on the expression of lipid metabolism-associated proteins in the liver tissues of HFD-fed mice. (a) Representative western blot for FAS and HSL. Quantification of FAS (b) and HSL (c) protein expression levels. NC, normal control group; HFD, obesity model group; Insoluble, mice fed HFD and given oral administration of water-insoluble β-glucan. Data are presented as mean ± standard deviation (n = 6). Groups labeled with different letters are different from one another (p < 0.05).