J Nutr Health.  2016 Feb;49(1):18-27. 10.4163/jnh.2016.49.1.18.

Postprandial hypoglycemic effects of mulberry twig and root bark in vivo and in vitro

• Park SY
• Jin BR
• Lee YR
• Kim YJ
• Park JB
• Jeon YH
• Choi SW
• Kwon O

• KMID: 2158302
• DOI: http://doi.org/10.4163/jnh.2016.49.1.18

Abstract

PURPOSE
Our previous study demonstrated the hypoglycemic effects of mulberry (Morus alba L.) leaf and the underlying mechanisms. Here we explored the potency of mulberry twigs (TW) and root barks (RB) in postprandial hypoglycemic effects in vitro and in vivo.
METHODS
The major components of TW and RB were determined by high performance liquid chromatography (HPLC). Alpha-glucosidase inhibition and glucose/fructose uptake inhibition in Caco-2 cells were determined for TW, RB, and their major components, followed by an oral sugar tolerance test (OSTT) in streptozotocin-induced diabetic rats. Male Wistar rats were fed a high-fat diet for 2 weeks and then a single dose of streptozotocin (35 mg/kg B.W) was administered by intraperitoneal injection. Rats with fasting blood glucose levels above 126 mg/dL were randomly divided into 5 groups (n = 8/group) for the following treatments by gavage for 4 weeks: vehicle (normal control and diabetic control), 200 mg/kg B.W of TW or RB or 100 mg/kg B.W of oxyresveratrol (OXY).
RESULTS
OXY and mulberroside A were identified as the major components of TW and OXY, mongolicin, and kuwanon H for RB. A significant inhibitory activity on alpha-glucosidase was found for TW, RB, and OXY (p = 0.0099). There was a dose-dependent inhibition of TW and RB on the intestinal sugar uptakes in Caco-2 cells, showing a greater impact on fructose compared to glucose. The OSTT showed that TW and RB significantly delayed time to maximal concentration (p = 0.0088) and decreased maximal concentration (p = 0.0043) compared to the control group.
CONCLUSION
These results suggest that TW and RB may have a postprandial hypoglycemic effect, particularly in the case of high fructose or sucrose intake. OXY was suggested as a contributor to the hypoglycemic effect of TW and RB. Further studies are needed for the systemic effect of TW and RB in circulation.

Keyword

mulberry; postprandial hypoglycemic effect; alpha-glucosidase inhibition; Caco-2 cells

MeSH Terms

alpha-Glucosidases
Animals
Blood Glucose
Caco-2 Cells
Chromatography, Liquid
Diet, High-Fat
Fasting
Fructose
Glucose
Humans
Hypoglycemic Agents*
Injections, Intraperitoneal
Male
Morus*
Rats
Rats, Wistar
Streptozocin
Sucrose
Blood Glucose
Fructose
Glucose
Hypoglycemic Agents
Streptozocin
Sucrose
alpha-Glucosidases

Figure

• 

  Fig. 1 HPLC chromatograms of mulberry twigs (A) and root barks (B). Analytical conditions are described in the method section.

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  Fig. 2 Inhibitory effects of mulberry twigs, root barks, and their major components on α-glucosidase activity. Values are mean ± SE. Different letters indicate significant differences at the p < 0.05 level using Duncan's multiple range test.

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  Fig. 3 Inhibitory effects of mulberry twigs, root barks, and oxyresveratrol on α-glucosidase activity with maltose (A) and sucrose (B) as substrates. Values are mean ± SE.

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  Fig. 4 The effects of mulberry twigs (A) and root barks (B) on cell viability of Caco-2 cells. Cell were incubated with mulberry twigs or root barks at different concentrations ranging from 0 to 1,000 µg/mL for 1 hr. Data was normalized to that of the vehicle. Values are mean ± SE. Different letters indicate significant differences at the p < 0.05 level using Duncan's multiple range test.

• 

  Fig. 5 Inhibitory effects of mulberry twigs and mulberry root barks on sugar uptake in Caco-2-cells: glucose (A) and fructose (B). Caco-2 cells were grown on 24-well plates and incubated in 10 mM Kreb's buffer containing [3H]-2-deoxyglucose or [14C]-fructose for 5 min at 37℃. Inhibition of [3H]-2-deoxyglucose uptake or [14C]-fructose uptake was measured at the increasing concentrations of mulberry twigs (●), mulberry root barks (○), by quantitation of radioactivity using scintillation counter. Values represent mean ± SE.

• 

  Fig. 6 Effects of mulberry extracts on postprandial blood glucose responses (AUC levels, C max, T max) in streptozotocin-incduced Diabetic Wistar rats (A) Day 0 or (B) Day 28. The inset graph is comparison of fasting blood glucose level between CON and DB CON. The animals received orally administered sucrose (2 g/kg B.W.) with mulberry twigs, root barks extract and OXY after overnight fasting for 12 h. Blood glucose levels were determined from tail blood samples at 0, 15, 30, 60, 90, and 120 min. CON, normal control (n = 13); DB CON, Diabetes control (n = 8); TW, Mulberry twigs extract 200 mg/kg B.W. (n = 7); RB, Mulberry root barks extract 200 mg/kg B.W. (n = 8); OXY, Oxyresveratrol 100mg/kg B.W. (n = 8); Values represent mean ± SE. Different letters indicate significant differences at the p < 0.05 level using repeated measure analysis of variance (ANOVA) with post hoc Duncan's multiple comparison tests. Asterisks in the inset graph denote significant differences relative to control group (p < 0.05 by Student's t-test).

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