Pathogenesis of diabetic macular edema: the role of pro-inflammatory and vascular factors. Aliterature review

Abstract

The review presents data on the pathogenesis of diabetic macular edema (DME). DME is a major cause of visual impairment in type 2 diabetes mellitus (DM) patients. Non-specific inflammation is an important factor of the underlying processes of DME. The importance of vascular endothelial growth factor (VEGF), interleukin-6, tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1, vascular cell adhesion molecule-1 in the development of diabetes microvascular complications is indicated. Intercellular adhesion molecules (ICAM), particularly, soluble ICAM-1 (sICAM-1), are a local inflammatory mediator involved in the pathogenesis of diabetic injury to the layers of the eye. The literature is scant on the assessment of sICAM-1 in type2 DM patients with diabetic injury to the neurovascular system of the eye (i.e. adhesion of leukocytes to the vascular endothelium (leukostasis) and the concurrent endothelial apoptosis). There are three main stages of microvascular changes due to nonspecific inflammation: dilation of capillaries and increased blood flow, microvascular structural changes and leakage of plasma proteins from the bloodstream, transmigration of leukocytes through the endothelium and accumulation at the site of injury. Vascular dysfunction in diabetic retinopathy (DR) and DMЕ is caused primarily by leukostasis, which is based on the recruitment and adhesion of leukocytes to the retinal vascular system. Leukostasis is the first step in the sequence of adhesion and activation events that lead to the infiltration of leukocytes through the endothelium. Leukocytes involved in leukostasis induce vascular permeability by releasing cytokines, including VEGF and TNF-α, contributing to endothelial protein binding, increasing levels of reactive oxidative substances, and killing pericytes and astrocytes surrounding the endothelium. Thus, the existing data on the main aspects of the pathogenesis of DMЕ indicate that inflammation is an important factor in the processes underlying the development of DMЕ and DR. But a new understanding of the physiology of the retina suggests that the pathogenesis of retinal lesions in type 2 DM can be considered as a change in the neurovascular unit of the retina.