Basic nutritional investigationInhibitory effect of pine extract on α-glucosidase activity and postprandial hyperglycemia
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).