Author(s)

Abdurrahim Kocyigit^1,2*, Burçin Kasap¹, Eray Metin Guler^1,2, Humeyra Nur Kaleli³, Mustafa Kesmen⁴, Murat Dikilitas⁵, Ersin Karatas⁶

¹Department of Medical Biochemistry, Medical Faculty, Bezmialem Vakif University, Istanbul, Turkey.
²Traditional and Complementary Medicine Advanced Research and Application Center (GETAMER), Bezmialem Vakif University, Istanbul, Turkey.
³Department of Molecular Biology, Genetics, and Bioengineering, Sabanci University, Istanbul, Turkey.
⁴Republic of Turkey Ministry of Agriculture and Forestry Istanbul Pendik Veterinary Control Institute, Istanbul, Turkey.
⁵Department of Plant Protection, Agricultural Faculty, Harran University, S. Urfa, Turkey.
⁶Department of Molecular Biology and Genetics, Gebze Technical University, Kocaeli, Turkey.

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.

Phytotherapy, Diabetes Mellitus, Olive Leaf Extract, Glucose Transporters, Insulin Receptors

Kocyigit, A. , Kasap, B. , Guler, E. , Kaleli, H. , Kesmen, M. , Dikilitas, M. and Karatas, E. (2019) 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. American Journal of Plant Sciences, 10, 1933-1948. doi: 10.4236/ajps.2019.1011136.