Development Of Cell-Free Assay System For The Screening Of PPAR Ligands From Natural Products : In Search For Positive Therapeutic Agents For Type 2 Diabetes
Loading...
Date
2013-10
Authors
Lau, Wai Kwan
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
Peroxisome proliferator-activated receptor-(PPAR) is an essential
regulator of glucose metabolic genes, of which upon activation by ligands, enhances
the actions of cellular insulin to promote glucose uptake to overcome insulin
resistance in Type 2 diabetes patients. Thiazolidinediones (TZD) is a common class
of drugs for type 2 diabetes and they function as synthetic ligands for PPAR.
However, many adverse effects are associated with these synthetic ligands.
Therefore there is an urgent need to find alternatives to TZD such as natural ligands
from plant source. In this study, a cell-free assay system was developed in order to
be used as a platform to screen for plant extracts with compounds that had the ability
to bind to PPAR as ligands which in turn, increased the binding of PPAR to its
coactivator. Truncated recombinant plasmids of PPAR and p300 coactivator were
constructed and their His-tagged recombinant proteins were expressed and column
purified. An ELISA-based PPAR ligand binding assay system was adopted to
evaluate the presence of potential PPAR ligand in plants. With Rosiglitazone, a
known synthetic ligand for PPAR as control, the extracts of six local plants found
in Malaysia namely Ficus deltoidea, Garcinia mangostana, Momordica charantia,
Swietenia macrophylla, Orthosiphon stamineus and Tinospora crispa were screened
for their activity as natural ligands for PPAR. It was found that methanol extracts of
F. deltoidea, G. mangostana, M. charantia, S. macrophylla and O. Stamineus increased the binding rate of PPAR to its coactivator which indicate that these extracts may contain potential PPAR ligands. Further anti-diabetic studies were performed on S. macrophylla seed extracts which were previously examined tocontain the putative PPAR activating components. Three isolated natural compounds from S. macrophylla namely 6-O-acetylswietenolide, diacetyl swietenolide and swietenine, were shown to possess PPAR ligand characteristics interms of PPAR binding, recruitment of coactivator as well as activation of PPAR to regulate downstream adipocyte differentiation and the expression of genes responsible for adipocyte differentiation. Moreover, the compounds also induced
GLUT4 expression in muscle cells and increased GLUT4 translocation to plasma
membrane. Their potential in modulating glucose uptake activity by enhancing 2-
NBDG uptake partly via AMPK activation in muscle cells were also demonstrated
in the study. Thus, these natural compounds in S. macrophylla seeds may have vast
potential to be developed and used as therapeutic agents against type 2 diabetes.
Description
Keywords
diabetes , ligand