Prevention Effects and Possible Molecular Mechanism of Mulberry Leaf Extract and its Formulation on Rats with Insulin-Insensitivity

PLoS One. 2016 Apr 7;11(4):e0152728. doi: 10.1371/journal.pone.0152728. eCollection 2016.

Abstract

For centuries, mulberry leaf has been used in traditional Chinese medicine for the treatment of diabetes. This study aims to test the prevention effects of a proprietary mulberry leaf extract (MLE) and a formula consisting of MLE, fenugreek seed extract, and cinnamon cassia extract (MLEF) on insulin resistance development in animals. MLE was refined to contain 5% 1-deoxynojirimycin by weight. MLEF was formulated by mixing MLE with cinnamon cassia extract and fenugreek seed extract at a 6:5:3 ratio (by weight). First, the acute toxicity effects of MLE on ICR mice were examined at 5 g/kg BW dose. Second, two groups of normal rats were administrated with water or 150 mg/kg BW MLE per day for 29 days to evaluate MLE's effect on normal animals. Third, to examine the effects of MLE and MLEF on model animals, sixty SD rats were divided into five groups, namely, (1) normal, (2) model, (3) high-dose MLE (75 mg/kg BW) treatment; (4) low-dose MLE (15 mg/kg BW) treatment; and (5) MLEF (35 mg/kg BW) treatment. On the second week, rats in groups (2)-(5) were switched to high-energy diet for three weeks. Afterward, the rats were injected (ip) with a single dose of 105 mg/kg BW alloxan. After four more days, fasting blood glucose, post-prandial blood glucose, serum insulin, cholesterol, and triglyceride levels were measured. Last, liver lysates from animals were screened with 650 antibodies for changes in the expression or phosphorylation levels of signaling proteins. The results were further validated by Western blot analysis. We found that the maximum tolerance dose of MLE was greater than 5 g/kg in mice. The MLE at a 150 mg/kg BW dose showed no effect on fast blood glucose levels in normal rats. The MLE at a 75 mg/kg BW dose and MLEF at a 35 mg/kg BW dose, significantly (p < 0.05) reduced fast blood glucose levels in rats with impaired glucose and lipid metabolism. In total, 34 proteins with significant changes in expression and phosphorylation levels were identified. The changes of JNK, IRS1, and PDK1 were confirmed by western blot analysis. In conclusion, this study demonstrated the potential protective effects of MLE and MLEF against hyperglycemia induced by high-energy diet and toxic chemicals in rats for the first time. The most likely mechanism is the promotion of IRS1 phosphorylation, which leads to insulin sensitivity restoration.

MeSH terms

  • Animals
  • Blood Glucose / metabolism
  • Cinnamomum zeylanicum / chemistry
  • Drugs, Chinese Herbal* / chemistry
  • Drugs, Chinese Herbal* / pharmacology
  • Fasting / blood
  • Hyperglycemia* / blood
  • Hyperglycemia* / chemically induced
  • Hyperglycemia* / prevention & control
  • Insulin Resistance*
  • Lipid Metabolism / drug effects
  • Male
  • Mice
  • Morus / chemistry*
  • Plant Leaves / chemistry*
  • Rats
  • Rats, Sprague-Dawley
  • Seeds / chemistry
  • Trigonella / chemistry

Substances

  • Blood Glucose
  • Drugs, Chinese Herbal

Grants and funding

The authors YL and MJL are paid employees of Amway, China. The author YGB is a paid employee of Beijing Pepnoch Co., Ltd. The author Zhong Zhong is a paid employee of Botanic Century (Beijing) Co., Ltd. The funder provided support in the form of salaries for authors (YL, YGB, ZZ and MJL), but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.