Uncovering potential of Indonesian medicinal plants on glucose uptake enhancement and lipid suppression in 3T3-L1 adipocytes

Abstract

Ethnopharmacological relevance

As obesity is a key factor in the development of type 2 diabetes, lowering lipid accumulation in adipose tissues is as important as increasing insulin sensitivity in diabetic patients. The selected plant extracts used in this screen have been traditionally used in Indonesian medicine for the treatment of diabetes and its complications.

Aim of the study

To investigate the ability of the selected plants to both increase insulin sensitivity through the enhancement of glucose uptake after insulin induction in adipocytes and suppress lipid production in the same target cells.

Materials and methods

Dried Indonesian medicinal plants were extracted with 50% (v/v) aq. methanol. The extracts were dissolved in 50% DMSO when tested in 3T3-L1 adipocytes. The screening platform consists of insulin-induced glucose uptake, lipid accumulation, and cell viability. Initially, an enzymatic fluorescence assay was designed to demonstrate the enhancement of 2-deoxyglucose (2-DG) uptake after insulin induction. Different concentrations of the extracts that enhanced glucose uptake were subjected to lipid accumulation assay using Oil Red O staining. Potential extracts based on lipid suppression were subsequently assessed by CCK-8 cell viability assay to distinguish lipid reduction activity from cytotoxicity.

Results

Out of 59 plants, 13 plants demonstrated their ability to increase glucose uptake in 3T3-L1 adipocytes after insulin induction, and 4 of these plants׳ extracts suppressed lipid production of the cells. The CCK-8 assay results of those 4 plant extracts suggest that the lipid inhibition activity of Eurycoma longifolia Jack (root) and Piper nigrum L. (fruits) extracts is not attributed to their cytotoxicity in the adipose cells. Both of the plant extracts increased glucose uptake by more than 200% at 50 μg/mL and suppressed lipid accumulation in a concentration-dependent manner.

Conclusions

Screening of selected Indonesian medicinal plants has uncovered the potentials of E. longifolia Jack (root) and P. nigrum L. (fruits) with dual active functions, increasing insulin sensitivity through the enhancement of glucose uptake and reducing lipid accumulation in adipose cells. These findings suggest that the ability of both plants to suppress lipid production would provide additional benefits in the treatment of diabetes.

Introduction

In 2014, the International Diabetes Federation (IDF) reported that 387 million of the world׳s population was living with diabetes, and this number is anticipated to rise beyond 592 million within the next two decades (International Diabetes Federation, 2014). As a complex metabolic disorder, type-2 diabetes mellitus (T2DM) is associated with impaired insulin release and insulin resistance, which result in high levels of glucose in the blood. Meanwhile, obesity involves an abnormal accumulation of adipose tissue, characterized by an increasing adipocyte number (hyperplasia) and size (hypertrophy). The association between obesity and T2DM, which has been well-recognized for decades, is mainly due to the insulin resistance of target cells, which affects glucose utilization and energy production.

Insulin sensitizers are commonly prescribed to treat insulin resistance, the primary clinical issue in T2DM. Thiazolidinediones (TZDs) reduce insulin resistance by activating peroxisome proliferator activated receptor gamma (PPARγ). Clinical studies undertaken by Mayerson et al. (2002) and Virtanen et al. (2003) reported that TZDs reduce plasma insulin and increase glucose uptake. However, these improvements result in weight gain and undesirable lipid profiles. Therefore, there is on-going debate as to whether it is appropriate to use TZDs for the treatment of obesity associated with T2DM. In agreement with the reported results of TZDs, non-TZD PPARγ agonists from natural compounds have the capacity to activate PPARγ (Yang et al., 2007, Choi et al., 2009, Han et al., 2006). However, one consequence is the promotion of adipogenesis. For this reason, there is a growing need to identify novel bioactive compounds from local medicinal plants that have the capacity to increase insulin sensitivity and reduce lipid production at the same time.

This study investigates and identifies plants with dual active functions that could serve as anti-diabetes and anti-obesity agents. Those plants listed in Table 1 were selected for use in this study because they are commonly used by local herbal industries in Indonesia (Elfahmi et al., 2014). Other plants that are often used locally for curing diabetes complications were also selected (Dalimartha, 2000, Hariana, 2006, Wijayakusuma, 2006). Certain plants in this study were expected to have unique mechanisms that could increase glucose uptake, while simultaneously suppressing lipid production.

To the best of our knowledge, this work is the first to report the in vitro screening of Indonesian medicinal plants for insulin-induced glucose uptake enhancement and lipid lowering activity in 3T3-L1 adipocyte model cells. The findings of the study were anticipated to corroborate the traditional application of Indonesian medicines, known as jamu, in treating T2DM and its complications, thus contributing to a more complete understanding of their efficacy.