Hibiscus sabdariffa L. water extract inhibits the adipocyte differentiation through the PI3-K and MAPK pathway

Abstract

Hibiscus sabdariffa L., a tropical beverage material and medical herb, is used commonly as in folk medicines against hypertension, pyrexia, inflammation, liver disorders, and obesity. This report was designed to investigate the inhibitory mechanisms of hibiscus extract on adipocyte differentiation in 3T3-L1 preadipocytes. The possible inhibitory pathways that regulate the adipocyte differentiation contain the adipogenic transcription factors, C/EBPα and PPARγ, PI3-kinase, and MAPK pathway. In this study, we examined whether hibiscus extract affected the adipogenesis via these three pathways. To differentiate preadipocyte in adipocyte, confluent 3T3-L1 preadipocytes were treated with the hormone mixture including isobutylmethylxanthine, dexamethasone, and insulin (MDI). Hibiscus extract inhibited significantly the lipid droplet accumulation by MDI in a dose-dependent manner and attenuated dramatically the protein and mRNA expressions of adipogenic transcriptional factors, C/EBPα and PPARγ, during adipogenesis. The increase of phosphorylation and expression of PI3-K/Akt during adipocytic differentiation was markedly inhibited by treatment with hibiscus extract or PI3-K inhibitors. Furthermore, the phosphorylation and expression of MEK-1/ERK known to regulate the early phase of adipogenesis were clearly decreased with the addition of hibiscus extract. Taken together, this report suggests that hibiscus extract inhibits the adipocyte differentiation through the modulation of PI3-K/Akt and ERK pathway that play pivotal roles during adipogenesis.

Introduction

Adipose tissue is recognized as the major energy depot in higher eukaryotes. Its prominent purposes are storing triglyceride in periods of energy excess and its mobilization during energy deprivation. Recently, there has been a dramatic increase of obesity resulting from an excess of adipose tissue. Obesity is a prevalent health risk in industrialized countries and is mostly associated with a lot of pathological disorders, including diabetes (Sartipy and Loskutoff, 2003), hypertension (Pi-Sunyer, 2002), cancer (Lagra et al., 2004), gallbladder disease (Galal, 2003), and atherosclerosis (Wofford et al., 1999). It has been reported that weight loss reduces lipid levels, blood pressure, and the incidence of type 2 diabetes mellitus (Sheard, 2003). In these days, as a beverage or tea, natural alternatives that produce weight loss with minimal adverse effects have been used in the treatment of obesity (Mochizuki and Hasegawa, 2004, Swenson et al., 2006). Several reports show that natural products, including garcinia extract, hibiscus tea, marine algae, green tea, and digestive enzyme inhibitors from l-arabinose have potential as anti-obesity agents that may not have unfavorable side-effects (Sayama et al., 2000, Kim et al., 2003, Kim et al., 2004).

Hibiscus (Hibiscus sabdariffa L.) is usually used as a traditional drink material and folk medicine against hypertension, pyrexia, liver disorders, inflammation, kidney and urinary bladder stones, and obesity (Haji Faraji and Haji Tarkhani, 1999, Liu et al., 2006). The aqueous extract of hibiscus is shown to possess the anti-oxidant at dose (Hirunpanich et al., 2005) and anti-tumor effects (Sharma and Sultana, 2004, Chang et al., 2005). In addition, hibiscus extract is known to inhibit porcine pancreatic amylase and to be effective for decreasing the levels of total lipids, cholesterol, and triglycerides in rats (Hansawasdi et al., 2001, Carvajal-Zarrabal et al., 2005). Recently, the inhibitory effect of hibiscus water extract on adipogenesis was also confirmed by our group in 3T3-L1 preadipocytes (Kim et al., 2003). However, it needs more profound studies about the mechanism by which hibiscus extract inhibits the adipocyte differentiation in vitro. Adipocyte differentiation is an intricate course accompanied by changes in morphology, hormone sensitivity, and gene expression. Confluent preadipocytes go into adipocytes through the clonal expansion, growth arrest, and expression of adipocyte markers by hormonal induction (Cornelius et al., 1994). CCAAT element binding protein (C/EBP) β and C/EBPδ induced by response to isobutylmethylxanthine, dexamethasone, and insulin (MDI) activate in turn peroxisome proliferator-activated receptor (PPAR)-γ and C/EBPα. PPARγ and C/EBPα are the adipogenic transcription factors that are implicated to activate a number of genes induced during adipocyte differentiation as a master regulator of adipogenesis and keep up the adipogenesis (Tontonoz et al., 1994, Rosen, 2005). Not only adipogenic transcription factors but also external hormones affect adipocyte differentiation. Insulin, a major hormone controlling critical energy functions, stimulates glucose transport, glycogen synthesis, and mitogenesis via activation of its downstream kinases, phosphoinositol 3-kinase (PI3-K) and Akt, as well as gene expression regulation (Cheatham and Kahn, 1995). In addition, the MAPK pathway is considered to be involved in nuclear effects, proliferation and differentiation, while the PI3-K pathway plays a major role in insulin functions (Hansen et al., 2002).

It has gained an important interest in the local drink market as a diet food, although its biological and pharmacological effects are still poorly defined. Therefore, this study was designed to characterize the effects of hibiscus extract on adipogenic differentiation of 3T3-L1 cells and its inhibitory mechanism on adipocyte differentiation at the cellular and molecular levels.