Prevention of diet-induced obesity by dietary black tea polyphenols extract in vitro and in vivo

Abstract

Objective

The effects of certain tea components on the prevention of obesity in humans have recently been reported, although it is still unclear whether black tea consumption is beneficial. We obtained black tea extract (BTPE) consisting of polyphenols specific to black tea, and from it, prepared a polymerized polyphenol fraction (BTP). The effectiveness of oral administration of the BTPE was examined in in vitro and in vivo experiments.

Methods

Effects of BTPE or BTP on pancreatic lipase activity were investigated in vitro. Male Wistar rats were administered an oral lipid emulsion containing BTPE at a concentration of 500 or 1000 mg/kg body weight and sequential plasma lipid levels were measured. Female C57BL/6N mice were fed a standard or high-fat diet supplemented with 1% or 5% (w/w) BTPE for 8 wk and changes in body weight were examined.

Results

BTP and BTPE inhibited pancreatic lipase activity with an IC₅₀ of 15.5 and 36.4 μg/mL in vitro, respectively. BTPE suppressed increases in rat plasma triglyceride levels in a dose-dependent manner after oral administration of a lipid emulsion. Furthermore, administration of the 5% BTPE suppressed increases in body weight (P < 0.05), parametrial adipose tissue mass, and liver lipid content (reduced to 56.9% and 81.7% of control mice, respectively, P < 0.05) in mice fed a high-fat diet.

Conclusion

The BTPE may prevent diet-induced obesity by inhibiting intestinal lipid absorption. It was suggested that the major active component in the BTPE was BTP.

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.