Blueberry polyphenol-enriched soybean flour reduces hyperglycemia, body weight gain and serum cholesterol in mice

Abstract

Defatted soybean flour (DSF) can sorb and concentrate blueberry anthocyanins and other polyphenols, but not sugars. In this study blueberry polyphenol-enriched DSF (BB-DSF) or DSF were incorporated into very high fat diet (VHFD) formulations and provided ad libitum to obese and hyperglycemic C57BL/6 mice for 13 weeks to investigate anti-diabetic effects. Compared to the VHFD containing DSF, the diet supplemented with BB-DSF reduced weight gain by 5.6%, improved glucose tolerance, and lowered fasting blood glucose levels in mice within 7 weeks of intervention. Serum cholesterol of mice consuming the BB-DSF-supplemented diet was 13.2% lower than mice on the diet containing DSF. Compounds were eluted from DSF and BB-DSF for in vitro assays of glucose production and uptake. Compared to untreated control, doses of BB-DSF eluate containing 0.05-10μg/μL of blueberry anthocyanins significantly reduced glucose production by 24-74% in H4IIE rat hepatocytes, but did not increase glucose uptake in L6 myotubes. The results indicate that delivery of blueberry polyphenols stabilized in a high-protein food matrix may be useful for the dietary management of pre-diabetes and/or diabetes.

Copyright © 2012 Elsevier Ltd. All rights reserved.

Figures

Figure 1

BB-DSF diet reduces weight gain, but not food intake in C57BL/6 mice. (A) Body weights (g) of mice (mean ± SD) consuming the indicated diets for the 13-week intervention period. At each time point one-way ANOVA followed by unequal N HSD post-hoc test was used. Significant difference between groups for each week is signified by letter a, b or c; different letters indicate significant difference (p <0.05) between groups while the same letter or absence of a letter indicates no difference. (B) Food intake of mice on indicated diets during the intervention period. Data are expressed as the mean for the VHFD group and mean ± SD for BB-DSF and DSF groups. T-tests (2-tailed) were performed between BB-DSF and DSF groups at each time point; ** p< 0.01.

Figure 2

BB-DSF diet improves oral glucose tolerance and decreases fasting blood glucose. A. (Top row) Blood glucose concentrations (mg/dL) expressed as mean ± SD were measured at the indicated time points (0 - 180 min) after administration of 2 g/kg glucose to mice after consumption of BB-DSF or DSF diets for 0, 7, 9 and 12 weeks. (Bottom row) Mean area under the curves for blood glucose data obtained for BB-DSF and DSF groups at each of the above indicated weeks. Each bar represents the mean ± SD (n=15) for group. T-test (2-tailed): * p

Figure 3

BB-DSF-e is hypoglycemic in C57BL/6 mice. Blood glucose levels of mice before and 6 h after treatment with 75% Labrasol (VEH), BB-DSF-e, DSF-e or 300 mg/kg Metformin® (MET). BB-DSF-e dosed at 127 mg/kg (dry wt.) delivered 1.8 mg of anthocyanins (ACNs) per kg. This BB-DSF-e preparation was composed of 33% DSF compounds, therefore the DSF-e control was dosed at 42 mg/kg (dry wt.). Each bar represents mean ± SD (n = 5). ** p= 0.01 (Paired T-test comparing before and after treatment). As described in text, BB-DSF-e and DSF-e refer to the C-18 SPE column-purified acidic methanol eluates produced from BB-DSF or DSF; BBJ-c18 refers to C-18 SPE column-purified blueberry juice.

Figure 4

BB-DSF-e and DSF-e repress glucose production in H4IIE cells. (A) Release of glucose from starved control cells treated with medium alone (Ctl) was set as 100% glucose release. Triplicate wells of cells were treated with 2 mM metformin (Met), 50 nM insulin (Ins) or the indicated amounts of BB-DSF-e, DSF-e and BBJ-c18. The BB-DSF-e and BBJ-c18 samples were normalized to deliver equivalent amounts of anthocyanins (ACNs) as indicated. The dry weight amounts of DSF-e delivered was 20% of the amount of BB-DSF-e delivered. Bars represent mean ± SD (n=6) of data combined from two independent experiments performed in triplicate. Asterisks directly above each bar represent significant difference relative to Ctl as determined by ANOVA followed by Dunnett’s test (* p< 0.05; ** p< 0.01; *** p< 0.001). Asterisks above graph represent differences between indicated pairs of BB-DSF-e and DSF-e samples as well as differences between pairs of DSF-e and BBJ-c18 samples, as determined by T-test (2-tailed): * p< 0.05; ** p< 0.01; *** p< 0.001. (B) Triplicate wells of cells were treated with medium only or the indicated doses and combinations of 10 nM insulin (Ins), BB-DSF-e, or DSF-e. Bars represent mean ± SD (n=3) of data from triplicate samples. Asterisks above graph represent differences between treatment in the absence or presence of 10 nM insulin, as determined by T-test (2-tailed): * p< 0.05; ** p< 0.01. As detailed in text, BB-DSF-e and DSF-e refer to the C-18 SPE column-purified eluates produced from BB-DSF or DSF; BBJ-c18 refers to a C-18 SPE column-purified blueberry juice.