Hypoglycemic effect of Du-zhong (Eucommia ulmoides Oliv.) leaves in streptozotocin-induced diabetic rats

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Abstract

The current study investigated whether Du-zhong (Eucommia ulmoides Oliv.) leaves could improve the hyperglycemia in streptozotocin (STZ)-induced diabetic rats. Male Sprague–Dawley rats were divided into a non-diabetic group (NDM), diabetic group (DM), diabetic group supplemented with powdered Du-zhong leaves (DM–PDZ) and diabetic group supplemented with a water extract of the powdered Du-zhong leaves (DM–WDZ). Diabetes was induced by injecting STZ (70 mg/kg B.W., i.p.). The powdered Du-zhong leaves or its powdered water extract was add to a standard diet based on 1% dried Du-zhong leaves (1 g PDZ/100 g diet and 0.187 g WDZ/100 g diet, respectively) for 3 weeks. Body weight was significantly higher in both types of Du-zhong leaves supplemented groups than in the DM group. The blood glucose levels were significantly lower in the DM–PDZ and DM–WDZ groups than in the DM group (20.05 ± 0.88 and 18.96 ± 1.23 mmol/l versus 24.42 ± 1.07 mmol/l, P < 0.05), whereas the plasma insulin and C-peptide levels were significantly higher in the PDZ and WDZ supplemented groups than in the DM group (7.45 ± 0.27 and 7.62 ± 0.69 μl U/ml versus 3.75 ± 0.27 μl U/ml for the plasma insulin, and 224.52±14.6 and 239.76 ± 15.52 pmol/l versus 166.5 ± 10.4 pmol/l for the plasma C-peptide, respectively, P < 0.05). The supplementation of PDZ and WDZ also resulted in lower plasma urea nitrogen levels compared to the DM group. Du-zhong leaves supplement seemed to be helpful to preserve the normal histological appearance of pancreatic islets as well as to preserve insulin-positive β-cells but it did not reverse the effect of STZ to a great extent. Accordingly, the reduction in plasma glucose by the powdered Du-zhong leaves and its water extract is quite small but significant, nevertheless, this was occurred with simultaneous the increase in plasma insulin and C-peptide. They improved hyperglycemia and seemingly enhance the function of pancreatic β-cells in STZ-induced diabetic rats.

Introduction

Eucommiae cortex obtained from the bark of a 15–20-year-old Du-zhong (Eucommia ulmoides Oliv.) tree [1] is a traditional medicine used in China, Japan, and Korea. According to ancient records, roasted Eucommiae cortex is recommended to reinforce the muscles and lungs, lower blood pressure, prevent miscarriages, improve the tone of the liver and kidneys, and increase longevity [2].

Recently, Du-zhong leaves that contain the same components as Eucommiae cortex have been the focus of medical research [3]. Du-zhong tea, the aqueous extract of Du-zhong leaves, is already known as a functional health food and commonly used in the treatment of hypertension [4], plus the extract of Du-zhong leaves has been suggested to have recuperative effects for hypercholesterolemia and a fatty liver [5]. Yen and Hsieh [6] reported that the water extract of Du-zhong leaves exhibits antioxidant activity toward various lipid peroxidation models with a good correlation between the polyphenol content in the water extract and the antioxidant activity.

Accordingly, the aim of the current study was to investigate the effect of Du-zhong leaves on hyperglycemia and the immunohistochemical localization of pancreatic insulin in streptozotocin (STZ)-induced diabetic rats.

Section snippets

Preparation of Du-zhong (Eucommia ulmoides Oliv.) leaves

Dried Du-zhong leaves were purchased from a herbal medicine market (Daegu, Korea), homogenized to a fine powder, and stored at room temperature (20 ± 2 °C) until use. The extraction with water was performed as follows: 100 g of powdered material was boiled in water (1:10 (w/v)) for 4 h. The water extract was then filtered through Whatman No. 1 filter paper, evaporated under a vacuum at 40 °C, and further dried to a powder using a freeze-dryer at −50 °C. Water extract yield after freeze-drying was

Body weight and survival

During the experimental period, the body weights were significantly lower in all the diabetic rats compared to the NDM group. However, the body weight was significantly higher in the DM–PDZ and DM–WDZ groups than in the DM group at third week. Accordingly, supplementation of the powdered Du-zhong leaves or its water extract had an effect to improve weight gain in the diabetic rats but not to the extent as seen in non-diabetic rats (Table 1). In addition, the food intakes were 32–34% higher for

Discussion

Type I diabetes mellitus is a chronic disease characterized by high blood glucose levels due to an absolute or relative deficiency of circulating insulin levels. Although various types of oral hypoglycemic agent are currently available along with insulin for treating diabetes mellitus, there is a growing interest in herbal remedies due to the side effects associated with the existing therapeutic hypoglycemic agents [9], [10].

As such, this study focused on evaluating the hypoglycemic activity of

Acknowledgements

This work was supported by a Korea Research Foundation Grant (KRF-2002-050-C00021).

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