British Journal of Nutrition

Full Papers

Molecular Nutrition

Antidiabetic effects of bitter gourd extracts in insulin-resistant db/db mice

Sandra D. Klomanna1 c1, Andreas S. Muellera2, Josef Pallaufa3 and Michael B. Krawinkela1

a1 Institute of Nutritional Sciences, Justus Liebig University Giessen, Wilhelmstrasse 20, 35392 Giessen, Germany

a2 Preventive Nutrition Group, Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle Wittenberg, Von-Danckelmann-Platz 2, 06120 Halle/Saale, Germany

a3 Department of Animal Nutrition and Nutritional Physiology, Interdisciplinary Research Centre, Justus Liebig University Giessen, Heinrich-Buff-Ring 26–32, 35392 Giessen, Germany

Abstract

Bitter gourd (BG, Momordica charantia) exerts proven blood glucose- and body weight-lowering effects. To develop an effective and safe application, it is necessary to identify the bioactive compounds and biochemical mechanisms responsible for these effects in type 2 diabetes. A total of forty-five 4-week-old male db/db mice were assigned to five groups of nine each. The mice were given sterile tap water as a control, a whole fruit powder, the lipid fraction, the saponin fraction or the hydrophilic residue of BG at a daily oral dosage of 150 mg/kg body weight for 5 weeks, respectively. Weight gain was significantly decreased in all the BG-treated groups (P ≤ 0·05). Glycated Hb levels were the highest in the control mice compared with all the four BG-treated mice (P = 0·02). The lipid fraction had the strongest effect, and it tended (P = 0·075) to reduce glycated Hb levels from 9·3 % (control mice) to 8·0 % (lipid fraction-treated mice). The lipid and saponin fractions reduced lipid peroxidation of adipose tissue significantly (P ≤ 0·01). Additionally, the saponin fraction and the lipid fraction reduced protein tyrosine phosphatase 1B (PTP 1B) activity in skeletal muscle cytosol by 25 % (P = 0·05) and 23 % (P = 0·07), respectively. PTP 1B is the physiological antagonist of the insulin signalling pathway. Inhibition of PTP 1B increases insulin sensitivity. This is the first study to demonstrate that BG is involved in PTP 1B regulation, and thus explains one possible biochemical mechanism underlying the antidiabetic effects of BG in insulin resistance and type 2 diabetes.

(Received March 02 2010)

(Revised May 28 2010)

(Accepted June 01 2010)

(Online publication July 09 2010)

Correspondence:

c1 Corresponding authors: S. D. Klomann, fax +49 641 99 39 039, email sandra.d.klomann@ernaehrung.uni-giessen.de; M. B. Krawinkel, email michael.krawinkel@ernaehrung.uni-giessen.de

Footnotes

Abbreviations: BG, bitter gourd; PTP 1B, protein tyrosine phosphatase 1B; TBA-RS, thiobarbituric acid-reactive substances

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