Elsevier

Nutrition

Volume 21, Issue 6, June 2005, Pages 756-761
Nutrition

Basic nutritional investigation
Inhibitory effect of pine extract on α-glucosidase activity and postprandial hyperglycemia

https://doi.org/10.1016/j.nut.2004.10.014Get rights and content

Abstract

Objective

This study investigated the inhibitory effect of pine bark extract (PBE) and needle extract on carbohydrate-hydrolyzing enzymes and the hypoglycemic effect in diabetic mice (Lepob [ob/ob]).

Methods

Pine bark and needle were dried and then placed in ethanol, and the extracts were assayed for the measurement of inhibition mode of PBE against α-amylase (EC 3.2.1.1) and α-glucosidase (EC 3.2.1.20). We also investigated the effect of long-term treatment with extracts on levels of postprandial blood glucose, body weight, food efficiency ratio, and gene expression of glucose transporter-4 in quadriceps muscle in diabetic mice (Lepob [ob/ob]).

Results

The PBE showed competitive inhibition against salivary α-amylase and the combination of non-competitive and uncompetitive inhibition against yeast α-glucosidase. In animal experiments, PBE effectively suppressed the increase of postprandial blood glucose level by delaying absorption of diet, and body weights of the group that received PBE were significantly lower than that in the group administered 0.5% carboxylmethyl cellulose (control) 21 d after administration.

Conclusions

PBE can be used to suppress postprandial hyperglycemia of diabetic patients. It also can be applied for control of obesity by decreasing the food efficiency ratio, especially carbohydrates.

Introduction

Diabetes mellitus is the most serious, chronic metabolic disorder and is characterized by high blood glucose levels [1], [2]. Worldwide, the number of patients is rapidly growing with an increase in obesity and aging in the general population [3]. The best way to control postprandial plasma glucose levels is with medication in combination with dietary restriction and an exercise program [4], [5]. Nevertheless, the control of postprandial hyperglycemia is critical in the early therapy for diabetes [6], [7]. One therapeutic approach to decrease postprandial hyperglycemia is to retard absorption of glucose through inhibition of carbohydrate-hydrolyzing enzymes, e.g., α-amylase and α-glucosidase, in the digestive organs [8], [9], [10], [11]. There are reports of established α-glucosidase inhibitors such as acarbose [12], miglitol [13], and voglibose [10] from micro-organs, and nojirimycin and 1-deoxynojirimycin [14], [15], [16] from plants and its effects on blood glucose levels after food uptake [16], [17], [18]. In addition, several α-glucosidases have been recently screened and developed from natural sources [19], [20], [21], [22].

Pine needle and bark are rich in polyphenols [23]. Various biological and health-beneficial effects have recently been demonstrated by polyphenol contained in plants [24], [25], [26], [27]. Phenolic contents of pine bark are catechin, epicatechin, quercetin, dihydroquercetin, taxifolin, phenolic acids, and procyanidin dimers, trimers, oligomers, and polymers formed from catechin and epicatechin [23], [28], [29]. We previously reported that pine needle and bark extracts have high inhibition activity against several carbohydrate-hydrolyzing enzymes [30].

In this study, we investigated the inhibitory effect and thermal and acidic stabilities of pine needle and bark extracts on α-amylase and α-glucosidase activity. We also investigated the pattern of inhibition and the inhibitory mode of action of pine bark extract (PBE). We investigated the effect of α-glucosidase inhibitor on plasma glucose levels by examining disaccharides such as maltose and sucrose, but not with a meal. Thus, we examined the effect of PBE on postprandial blood glucose levels after a meal. We also examined the effects of long-term treatment with PBE on body weight gain, food efficiency ratio (FER), and gene expression of glucose transporter-4 (GLUT4) in quadriceps muscle.

Section snippets

Materials

α-Amylase from salivary, pancreatin, Bacillus sp., Aspergillus oryzae, and barley malt and α-glucosidase from yeast Saccharomyces cerevisiae and Bacillus stearothermophilus were purchased from Sigma Chemical Co. (St, Louis, MO, USA). p-Nitrophenyl α-d-glucopyranoside as a synthetic substrate of α-glucosidase and other chemicals including maltose were also obtained from Sigma Chemical Co.

Preparation of PBE

Pine bark and needles were dried and extracted with 10 times their weight of 70% EtOH for 12 h at room

Results

PBE and needle extract showed high inhibition activity against several carbohydrate-hydrolyzing enzymes [30]. We investigated the inhibitory activity between PBE and needle extract against α-amylase from saliva and the pancreas (Fig. 1). PBE and needle extract showed similar inhibitory activities against α-amylase. According to origin, inhibitory activity against α-amylase from saliva was more effective than that from the pancreas. We also investigated the inhibitory activity of PBE against

Discussion

PBE and needle extract showed similar inhibitory activities against α-amylase. According to origin, inhibitory activity against α-amylase from saliva was more effective than that from the pancreas. This result contrasts with that of acarbose, which showed similar inhibitory activity against both enzymes [9]. However, investigation of the inhibitory activity against α-amylase from human salivary and porcine pancreatic glands showed that PBE and acarbose had a similar inhibitory activity against

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    This study was supported by a grant from the Ministry of Health and Welfare, Republic of Korea (01-PJ4-PG4-01VN01-0146).

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