Therapeutic effects of Ishige okamurae extract and its constituent Ishophloroglucin A against diabetic-related angiogenesis

Abstract

Diabetes mellitus is associated with secondary metabolic complications, such as insulin resistance and hyperinsulinemia leading to abnormal angiogenesis. Development of new microvessels from the existing vessels is known as angiogenesis. Diabetes is characterized by inadequate angiogenesis in some organs as well as excessive angiogenesis in some others. Apart from its role in several pathological conditions, angiogenesis plays a crucial role in normal growth and development as well. Excessive angiogenesis causes degradation of vascular endothelial cells from the extracellular matrix, enhancement of cell proliferation, migration and formation of extravascular networks. Excessive angiogenesis is also observed in diabetic retinopathy resulting in loss of vision. Marine algae are considered as a prolific source of important bioactive compounds that aid in maintaining normal health and mitigating disease risks. Among the marine algae, brown algae and its constituent phlorotannins are widely studied for various biological effects by several research groups globally. Ishige okamurae (IO) is an edible brown alga found abundantly in the coastal areas of Jeju island. It has been reported that IO exerts several biological activities, such as anti-α-glucosidase, free-radical scavenging, cytoprotective, anti-obesity, and anti-inflammatory activities. Ishophloroglucin A (IPA) is a novel phlorotannin isolated from IO extract which has been studied for standardizing the anti-αglucosidase activity of IO. However, IO extract and IPA have not been examined for diabetic-related pathologies. Therefore, in the present study, IO extract and IPA were studied for their anti-angiogenic effects on high glucose-induced vascular growth. Zebrafish model is widely used in studies on angiogenesis. Transgenic zebrafish lines are more convenient for imaging of the vessels due to fluorescent labeling. In this study, transgenic zebrafish Tg(flk:EGFP), was used to evaluate the anti-angiogenesis effects. The vascular endothelium is a biologically important layer present in the blood vessels and itsdysfunction results in various vascular pathologies. The EA.hy926 cell line is frequently used in different angiogenesis studies. These cells are more convenient than primary vascular cells because they are mortal and do not possess variations associated with the donor. In this study, the anti-angiogenic effects of IPA were evaluated in EA.hy926 cells. IPA treatment decreased cell proliferation, cell migration, and capillary-like structure formation in high glucose-treated EA.hy926 cells. In silico stimulations revealed that IPA binds to the active site of VEGFR-2 (PDB ID: 2OH4) with a binding energy of -656.948 kcal/mol. IPA treatment down regulated vascular endothelial growth factor receptor 2 (VEGFR-2) expression and its downstream signaling molecules. As the chapter 1, the attenuation of high glucose-induced angiogenesis by Ishige okamurae extract and its constituent Ishophloroglucin A was discussed. Furthermore, the effects of IPA was studied for diabetes retinopathy in high glucose-treated human retinal microvascular endothelial cells (HRMEC) in the chapter 2 of the study. The results showed that IPA treatment suppressed the angiogenesis in retinal endothelial cells by down regulating the vascular permeability in vitro and in vivo. Overall, these findings suggest that IO extract and IPA are potential agents for the development of therapeutics against diabetes-related angiogenesis. Key Words: Angiogenesis; Diabetes; Ishige okamurae; Ishophloroglucin A