Applied nutritional investigationPrevention of diet-induced obesity by dietary black tea polyphenols extract in vitro and in vivo
Introduction
Excess energy intake and reduced energy expenditure result in abnormal excessive growth of adipose tissue, which can lead to the development of obesity [1]. Obesity is strongly associated with metabolic syndrome, which is characterized by the presence of insulin resistance, hypertension, and hyperlipidemia [2]. Metabolic syndrome, which is closely linked with atherosclerosis, is widely recognized as a major public health problem. Recently, pancreatic lipase inhibitors from food and natural sources have been shown to suppress intestinal lipid absorption [3], which may contribute to reduced weight gain.
Worldwide, tea is a widely consumed beverage of which there are three principal types: green tea (unfermented), oolong tea (partially fermented), and black tea (fully fermented) [4]. Recent studies have described the effects of green and oolong teas on the prevention of obesity. It was reported that green tea has physiologic effects in vivo, including reduction in body weight and fat mass, and suppression of blood cholesterol, glucose, and triglyceride levels [5], [6], [7], [8]. It was also reported that oolong tea has beneficial effects relative to reducing body weight and inhibiting pancreatic lipase activity. Oolong tea is also known to have hypolipidemic and hypoglycemic effects [9], [10], [11], [12], [13], [14]. Black tea has been shown to reduce serum cholesterol levels in rats [15], [16] and hamsters fed a high-cholesterol diet [17]. Furthermore, administration of black tea improved blood glucose levels in streptozotocin-diabetic rats [18]. Epidemiologic evidence has also shown that increased consumption of black tea (>480 mL/d) is associated with lower levels of serum glucose [19]. These reports suggest the possibility that black tea may prevent obesity. Another recent study reported that consumption of 1 g of instant black tea reduced plasma glucose levels measured 120 min after consumption of glucose in healthy humans [20]. In this study, caffeine had no effect on glucose levels. Therefore, the reduction in glucose may have been attributable to the presence of phenolic compounds in the instant black tea.
The most abundant polyphenols in green tea are catechins consisting of (-)epicatechin (EC), (-)epicatechin-3-gallate (ECG), (-)epigallocatechin (EGC), and (-)epigallocatechin-3-gallate (EGCG) [21]. In the case of black tea, catechins are oxidized during the fermentation process to yield polymerized polyphenols including theaflavins and thearubigins, which contribute to its color and taste [4]. Theaflavins consist mainly of the following four compounds: theaflavin (TF1), theaflavin-3-gallate (TF2A), theaflavin-3′-gallate (TF2B), and theaflavin-3,3′-digallate (TF3). On the other hand, thearubigins are very complex mixtures of uncharacterized polymerized polyphenols [4]. In the present study, these polymerized polyphenols (specific to black tea) are defined as black tea polyphenols (BTP). Catechins and theaflavins have been reported to inhibit the activity of the pancreatic lipase in vitro [3] and oral administration of catechins [8] or gallic acid [22] have been shown to suppress diet-induced obesity in rodents. However, the effect of BTP on obesity has not been fully evaluated. Thus, more in-depth studies are required.
In the present study, we prepared an extract from black tea (BTPE), which contains BTP as principal polyphenolic components, and then determined the effects of BTPE on intestinal lipid absorption and body weight gain. Furthermore, the active component of BTPE was investigated.
Section snippets
Preparation of BTPE
Ninety grams of commercial black tea leaves was extracted in 810 mL boiling water for 45 min. To remove caffeine and catechins from the extract, 8 g of activated charcoal (Futamura Chemical, Aichi, Japan) was added to the extract. After filtration, this extract was lyophilized and used as BTPE. Polyphenolic components in the BTPE were determined as described [23], [24]. The catechins contained in the BTPE were analyzed using high-performance liquid chromatography (HPLC) [23]. The total catechin
Total catechin, total theaflavin, gallic acid, and total polyphenol contents in BTPE
Total polyphenol, catechins, and gallic acid contents in BTPE were 26.6%, 2.4%, and 0.3%, respectively (Table 1). The estimated contribution of catechins and gallic acid to the total polyphenol content was 9.0% and 1.1%, respectively. Therefore, the black tea-derived polymerized polyphenols seemed to be the major polyphenolic components in the BTPE.
Effect of BTP or BTPE on pancreatic lipase activity
Porcine pancreatic lipase activity was inhibited 50% in the presence of 15.5 μg/mL BTP or 36.4 μg/mL BTPE, indicating that BTP was more inhibitory
Discussion
This study demonstrates that BTPE inhibits pancreatic lipase activity and also suppresses intestinal lipid absorption and body weight gain. BTP and BTPE inhibited pancreatic lipase activity with IC50 values of 15.5 and 36.4 μg/mL, respectively, indicating that the effect of BTP on pancreatic lipase was greater than that of the BTPE. This result suggested that the major active component in the BTPE was BTP, which consists of polymerized polyphenols. The increase in plasma triglyceride levels in
Acknowledgments
We thank members of our group for excellent technical support.
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