TITLE:
An Optimum Dose of Olive Leaf Extract Improves Insulin Receptor Substrate-1, Tyrosine Kinase, and Glucose Transporters, While High Doses Have Genotoxic and Apoptotic Effects
AUTHORS:
Abdurrahim Kocyigit, Burçin Kasap, Eray Metin Guler, Humeyra Nur Kaleli, Mustafa Kesmen, Murat Dikilitas, Ersin Karatas
KEYWORDS:
Phytotherapy, Diabetes Mellitus, Olive Leaf Extract, Glucose Transporters, Insulin Receptors
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.10 No.11,
November
6,
2019
ABSTRACT: Type 2 diabetes is the most common type of diabetes.
Conventionally many drugs are used for the treatment of diabetes such as
biguanides, sulfonylureas, meglitinides, etc. But the desired effective
treatment is still not to be achieved. So researches are going on for the
development of effective alternative therapy against diabetes. Olive leaves are
traditionally used in the treatment of the disease. However, studies on its
mechanism of action are not yet enough. The aim of this study was to
investigate whether olive leaf extract (OLE) improves insulin receptor
substrate-1 (IRS-1), tyrosine kinase (TK), GLUT-2, and GLUT-4. Oleuropein
levels were analyzed from OLE obtained by using four different solvents, and
the highest content of methanol extract was selected for the study. Different
concentrations of OLE (2.5 to 320 μg/mL)
were incubated with hepatocellular carcinoma (HepG2) cells for 24 hours. After
incubation, cell viability was assessed based on luminometric ATP cell
viability assay kit. Intracellular reactive oxygen species (ROS) generating
level was detected using 2,7dichlorodihydrofluorescein-diacetate (H2DCF-DA)
fluorescent probes. Apoptosis was evaluated by acridine orange/ethidium bromide
double staining method. Genotoxicity was evaluated by alkaline single cell gel
electrophoresis assay (Comet Assay). Protein expression levels of IRS-1, TK,
GLUT-2, and GLUT-4 were analyzed by western blotting technique from the
obtained cell lysates. Although an optimum doses of OLE (10 μg/mL)
maximally increased cell proliferation, decreased ROS generation improved
IRS-1, TK, GLUT-2, and GLUT-4 protein expression levels (about fivefold),
higher doses (10 to 320 μg/mL) markedly decreased the cell viability, increased DNA damage,
apoptosis and ROS generation in a concentration-dependent manner. OLE can be
used in the treatment of type 2 diabetes. However, in order to find the most
effective and non-toxic concentration, dose optimization is required.