Abstract
The human eye, the highly specialized organ of vision, is greatly influenced by oxidants of endogenous and exogenous origin. Oxidative stress affects all structures of the human eye with special emphasis on the ocular surface, the lens, the retina and its retinal pigment epithelium, which are considered natural barriers of antioxidant protection, contributing to the onset and/or progression of eye diseases. These ocular structures contain a complex antioxidant defense system slightly different along the eye depending on cell tissue. In addition to widely studied enzymatic antioxidants, including superoxide dismutase, glutathione peroxidase, catalase, peroxiredoxins and selenoproteins, inter alia, metallothioneins (MTs) are considered antioxidant proteins of growing interest with further cell-mediated functions. This family of cysteine rich and low molecular mass proteins captures and neutralizes free radicals in a redox-dependent mechanism involving zinc binding and release. The state of the art of MTs, including the isoforms classification, the main functions described to date, the Zn-MT redox cycle as antioxidant defense system, and the antioxidant activity of Zn-MTs in the ocular surface, lens, retina and its retinal pigment epithelium, dependent on the number of occupied zinc-binding sites, will be comprehensively reviewed.
Highlights
Received: 18 December 2020Accepted: 4 January 2021Published: 11 January 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.The eye is subjected to a highly oxidative environment due to its intense exposure to light, its robust metabolic activity, and its high oxygen tension
Oxidative stress affects all structures of the human eye, the ocular surface, the lens and the retina, which are considered antioxidant natural barriers against external insults
The imbalance between reactive oxygen species (ROS) production and the neutralizing ability of the antioxidant defense results in an excessive oxidative milieu that contributes to the onset or progression of age-related eye diseases
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The external part is the fibrous tunic, containing the sclera and cornea, the middle part is the uvea or vascular tunic composed of iris, ciliary body (CB), and choroid, and the inner part is the neural layer formed by the retina and its retinal pigment epithelium (RPE). These coats surround the lens and the transparent media, namely anterior chamber with aqueous humor and. The lens, responsible for light refraction and focus over the retina, possesses than the cornea This transparent body is composed of long-fibre like cells and epithelial less refractive power than the cornea. The RPE cell monolayer that nourishes and maintains the adhesion of the neurosensory retina and isreduces a pigmented cell monolayer light scattering withinthat thenourishes eye [2]. and maintains the adhesion of the neurosensory retina and reduces light scattering within the eye [2]
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