Vitreous Antioxidants, Degeneration, and Vitreo-Retinopathy: Exploring the Links

Abstract

The transparent vitreous body, which occupies about 80% of the eye’s volume, is laden with numerous enzymatic and non-enzymatic antioxidants that could protect the eye from oxidative stress and disease. Aging is associated with degeneration of vitreous structure as well as a reduction in its antioxidant capacity. A growing body of evidence suggests these age-related changes may be the precursor of numerous oxidative stress-induced vitreo-retinopathies, including vision degrading myodesopsia, the clinically significant entoptic phenomena that can result from advanced vitreous degeneration. Adequate intravitreal antioxidant levels may be protective against vitreous degeneration, possibly preventing and even improving vision degrading myodesopsia as well as mitigating various other vitreo-retinopathies. The present article is, therefore, a review of the different antioxidant molecules within vitreous and the inter-relationships between vitreous antioxidant capacity and degeneration.

Importance of the Use of Oxidative Stress Biomarkers and Inflammatory Profile in Aqueous and Vitreous Humor in Diabetic Retinopathy

“…An antioxidant is frequently defined as the substance that, when present in low concentration compared to that of an oxidizable substrate, significantly delays or inhibits the oxidation of the substrate [43]. Overproduction or inadequate elimination of ROS beyond the ability to counteract the antioxidant system can cause OS and overload the eye tissues [44]. Tear film and aqueous humor are important components of defense mechanisms on the ocular surface.…”

“…The vitreous body has a total volume of approximately 4 mL, mainly composed of water (98-99%), collagen fibers, glycosaminoglycans, non-collagen proteins, and small amounts of trace elements [48]. The nature of the vitreous gel is attributed to the interaction between its two main components: collagen and hyaluronan (HA) [44]. The concentration of HA within the vitreous gel varies between 0.02 and 1 mg/cm3 and plays a synergistic role with collagen and other proteoglycans for the regulation of vitreous stiffness [44,49].…”

“…The nature of the vitreous gel is attributed to the interaction between its two main components: collagen and hyaluronan (HA) [44]. The concentration of HA within the vitreous gel varies between 0.02 and 1 mg/cm3 and plays a synergistic role with collagen and other proteoglycans for the regulation of vitreous stiffness [44,49]. The vitreous cortex is a lamellar structure attached to the ILM of the retina posterior to the peripheral vitreous base by an extracellular matrix "adhesive" consisting of laminin, opticin, fibronectin, chondroitin sulfate, and heparan sulfate.…”

“…Nutrient non-enzymatic antioxidants include those obtained exogenously through food and supplements, such as vitamin C, vitamin B2, and trace metals like zinc and selenium. Metabolic antioxidants are endogenous antioxidants produced by the body itself, such as GSH, metal-chelating proteins like transferrin, and uric acid [44,54].…”

“…As an antioxidant, glutathione can directly remove selected oxygen radicals and indirectly aid in the recycling of vitamins C and E [61], it also functions as a cofactor for glutathione peroxidase (GPx) activity allowing the reduction of lipid hydroperoxides [62]. Transferrin (molecular weight~80 kDa), is found in an average concentration in the vitreous of 0.0878 g/L [44]. As an antioxidant, transferrin is an iron chelator that keeps ionic iron sequestered at physiological pH, and thus minimizes the participation of iron in radical iron-dependent reactions; its activity helps reduce the toxicity of intravitreal iron during vitreous hemorrhage [63].…”