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Front Nutr
2021 Apr 16;8:628571. doi: 10.3389/fnut.2021.628571.
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Beta-Glucan From Barley Attenuates Post-prandial Glycemic Response by Inhibiting the Activities of Glucose Transporters but Not Intestinal Brush Border Enzymes and Amylolysis of Starch.
Malunga LN
,
Ames N
,
Zhouyao H
,
Blewett H
,
Thandapilly SJ
.
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Beta (β)-glucan (BG) from cereal grains is associated with lowering post-prandial blood glucose but the precise mechanism is not well-elucidated. The main aim of this study was to understand the mechanism through which BG from barley affects post-prandial glycemic response. Waffles containing 0, 1, 2, and 3 g barley BG and the same amount of available carbohydrate (15 g) were fed to the TIM-1 dynamic gastrointestinal digestion system to study the effect of BG on starch hydrolysis. Intestinal acetone powder and Xenopus laevis oocytes were used to study BG's effect on mammalian intestinal α-glucosidase and glucose transporters. The presence of BG did not significantly affect the in vitro starch digestion profiles of waffles suggesting that BG does not affect α-amylase activity. Intestinal α-glucosidase and glucose transport activities were significantly (p < 0.0001) inhibited in the presence of barley BG. Interestingly, BG viscosity did not influence α-amylase, α-glucosidase, GLUT2, and SGLT1 activities. This study provides the first evidence for the mechanism by which BG from barley attenuates post-prandial glycemic response is via alteration of α-glucosidase, GLUT2, and SGLT1 activity, but not amylolysis of starch. The decrease in post-prandial blood glucose in the presence of BG is likely a consequence of the interaction between BG and membrane active proteins (brush border enzymes and glucose transporters) as opposed to the commonly held hypothesis that increased viscosity caused by BG inhibits starch digestion.
Figure 1. The in vitro digestibility of waffle carbohydrates using TIM-1 digestion model. Waffles containing ~15 g of available carbohydrate were fed to the TIM-1 system and the dialysates were collected from jejunum and ileum compartments every 60 min for glucose analysis after acid hydrolysis. The data represent mean ± SD (n = 2). (A) The release of glucose in hydrolysates over time. (B) Total carbohydrate released over 360 min of digestion.
Figure 2. Effect of BG on mammalian intestinal alpha-glucosidase activity. Maltose (30 mg/mL) was mixed buffer (control) or buffers containing different amounts barley BG (BG-HMW: 650,000 average molecular weight; BG-LMW: 229,000 average molecular weight). Data are mean + standard deviation (n = 6). No statistical difference (p < 0.0001) was observed between means of treatment groups.
Figure 3. Effect of BG on glucose uptake in oocytes expressing human GLUT2. Oocytes expressing human GLUT2 and oocytes injected with water (SHAM, negative control) incubated in buffer containing radiolabeled glucose only (control) or buffers containing different amounts barley BG (BG-HMW: 650,000 average molecular weight; BG-LMW: 229,000 average molecular weight). Data are mean + SEM (n = 12–15 oocytes per treatment). *Significantly different from all other treatment groups p < 0.0001.
Figure 4. Effect of BG on glucose uptake in oocytes expressing human SGLT1. Oocytes expressing human SGLT1 and oocytes injected with water (SHAM, negative control) were incubated in buffer containing radiolabeled glucose only (control) or buffers containing different amounts barley BG (BG-HMW: 650,000 average molecular weight; BG-LMW: 229,000 average molecular weight). Data are means ± SEM (n = 10–12 oocytes per treatment). *Significantly different from all other treatment groups p < 0.0001.
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