Differential Mechanisms of Action and Efficacy of Vitamin E Components in Antioxidant Cytoprotection of Human Retinal Pigment Epithelium

R Scott Duncan, Daniel T Hurtado, Conner W Hall, Peter Koulen

Front Pharmacol . 2022 Jan 4;12:798938. doi: 10.3389/fphar.2021.798938. eCollection 2021.


The purpose of this study was to determine if different vitamin E components exhibit similar efficacy and mechanism of action in protecting Retinal pigment epithelium (RPE) cells from oxidative damage. We hypothesized that α-tocopherol (αT) is unique among vitamin E components in its cytoprotective mechanism of action against oxidative stress in RPE cells and that it requires protein synthesis for optimal antioxidant effect. We used cell viability assays, fluorescent chemical labeling of DNA and actin and immuno-labeling of the antioxidant proteins Nrf2 and Sod2 and of the tight junction protein, ZO-1, and confocal microscopy to determine the effects of αT and γT against oxidative stress in immortalized human RPE cells (hTERT-RPE). Using the four main vitamin E components, αT, γT, δ-tocopherol (δT) and α-tocotrienol (αTr), we ascertained that they exhibit similar, but not identical, antioxidant activity as αT when used at equimolar concentrations. In addition, we determined that the exposure time of RPE cells to α-tocopherol is critical for its ability to protect against oxidative damage. Lastly, we determined that αT, but not γT, partially requires the synthesis of new proteins within a 24-h period and prior to exposure to tBHP for optimal cytoprotection. We conclude that, unlike γT and δT, αT appears to be unique in its requirement for transport and/or signaling for it to be an effective antioxidant. As a result, more focus should be paid to which vitamin E components are used for antioxidant interventions.

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Reported evidence of vitamin E protection against cataract and glaucoma

Masaki Tanito

Free Radic Biol Med . 2021 Oct 22;177:100-119. doi: 10.1016/j.freeradbiomed.2021.10.027. Online ahead of print.


Cataract and glaucoma are the major causes of severe visual loss and blindness in older adults. This review article describes the currently available basic and clinical evidence regarding vitamin E protection against these eye diseases in the chronologic order of the publications. Experimental evidence has suggested both that oxidative stress due to the accumulation of free radicals plays a role in the pathogenesis of cataracts and glaucoma and that the process can be prevented or ameliorated by vitamin E. The results of observational studies have been inconsistent regarding the association between blood vitamin E levels and the risk of age-related cataract or glaucoma. Despite the encouraging effects of vitamin E from case series, case-control studies, and cross-sectional studies in humans, the effects on cataract formation and/or progression have not been consistent among prospective and randomized control studies; few randomized control studies have tested the effects of supplemental vitamin E on glaucoma development or progression. Given the high prevalence of cataract and glaucoma in the elderly population, even a modest reduction in the risk for these eye diseases would potentially have a substantial public health impact; however, the potential benefits of vitamin E on cataract or glaucoma remain inconclusive and need to be carefully considered.

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Effects of eye drops containing a mixture of 3% diquafosol sodium and tocopherol acetate (vitamin E) on the ocular surface of murine dry eye

Lan Li, Rujun Jin, Ying Li, Hee Su Yoon, Hyeon Jeong Yoon, Kyung Chul Yoon

Cutan Ocul Toxicol . 2021 Sep 8;1-9. doi: 10.1080/15569527.2021.1973022. Online ahead of print.


Purpose: To investigate the efficacy of topical application of 3% diquafosol sodium (DQS) and tocopherol (TCP) acetate mixtures in a mouse model of experimental dry eye (EDE).

Methods: After exposure to desiccating stress for 5 days, eye drops consisting of 3% DQS alone, 0.01% TCP alone, or 3% DQS and 0.005% or 0.01% TCP mixture were applied for the treatment of EDE. Tear volume, tear film break-up time (TBUT), corneal fluorescein staining scores (CFSS), and tear film lipid layer grades (TFLLG) were measured at 0, 5 and 10 days after treatment. The 2′,7′-dichlorodihydrofluorescein diacetate assay (DCFDA) for reactive oxygen species (ROS) production, enzyme-linked immunosorbent assay (ELISA) for malondialdehyde (MDA), and flow cytometry for CD4 + interferon (IFN)-γ+ T cells were evaluated on the ocular surface at 10 days after treatment. In addition, levels of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and chemokine CC motif ligand 4 (CCL4) in the conjunctiva were measured using a multiplex immunobead assay, and conjunctival goblet cells were counted by periodic acid-Schiff staining at 10 days after treatment.

Results: Both the TCP mixture groups indicated a significant improvement in TBUT, ROS production, and MDA concentrations compared to those in the DQS alone group. Furthermore, the 0.01% TCP mixture group also showed higher tear film lipid layer grades and conjunctival goblet cell density and lower corneal fluorescein staining scores, number of CD4 + IFN-γ+ T cells, and levels of TNF-α, IL-1β, and CCL4 than the DQS alone group (P < 0.05).

Conclusions: Application of eye drops containing the mixture of DQS and TCP could stabilize the tear film lipid layer, improve TBUT and corneal epithelial damages, decrease ROS production, inflammatory molecules, and T cells, and increase conjunctival goblet cell density on the ocular surface. Topical DQS and TCP mixtures may have a greater therapeutic effect on clinical signs, oxidative damage, and inflammation of dry eye than DQS eye drops.

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Ophthalmologic evaluation in vitamin-E deficiency: A case report

Daniele Sindaco, Francesca Cappelli, Aldo Vagge, Carlo E Traverso, Michele Iester

Eur J Ophthalmol . 2020 Nov 3;1120672120970112. doi: 10.1177/1120672120970112. Online ahead of print.


A 41-year-old woman has come to our attention complaining of decreased visual acuity and monocular diplopia associated with upper and lower limb hypoesthesia. Malabsorption syndrome with vitamin A and E deficiency developed after a bariatric biliopancreatic diversion. The clinical ophthalmological signs and symptoms improved after oral vitamin supplementation therapy. The past medical history is essential in the case of a patient complaining of visual symptoms compatible with vitamin deficiency in order to detect the cause and to start a prompt therapy to avoid irreversible neurological and visual sequelae. The clinical features of our case closely resemble other cases described in the literature of patients affected by vitamin A and E deficiency secondary to malabsorption syndrome.

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The Effect of Antioxidants on Photoreactivity and Phototoxic Potential of RPE Melanolipofuscin Granules from Human Donors of Different Age

Magdalena M Olchawa, Grzegorz M Szewczyk, Andrzej C Zadlo, Michal W Sarna, Dawid Wnuk, Tadeusz J Sarna

Antioxidants (Basel) . 2020 Oct 26;9(11):E1044. doi: 10.3390/antiox9111044.


One of the most prominent age-related changes of retinal pigment epithelium (RPE) is the accumulation of melanolipofuscin granules, which could contribute to oxidative stress in the retina. The purpose of this study was to determine the ability of melanolipofuscin granules from younger and older donors to photogenerate reactive oxygen species, and to examine if natural antioxidants could modify the phototoxic potential of this age pigment. Electron paramagnetic resonance (EPR) oximetry, EPR-spin trapping, and time-resolved detection of near-infrared phosphorescence were employed for measuring photogeneration of superoxide anion and singlet oxygen by melanolipofuscin isolated from younger and older human donors. Phototoxicity mediated by internalized melanolipofuscin granules with and without supplementation with zeaxanthin and α-tocopherol was analyzed in ARPE-19 cells by determining cell survival, oxidation of cellular proteins, organization of the cell cytoskeleton, and the cell specific phagocytic activity. Supplementation with antioxidants reduced aerobic photoreactivity and phototoxicity of melanolipofuscin granules. The effect was particularly noticeable for melanolipofuscin mediated inhibition of the cell phagocytic activity. Antioxidants decreased the extent of melanolipofuscin-dependent oxidation of cellular proteins and disruption of the cell cytoskeleton. Although melanolipofuscin might be involved in chronic phototoxicity of the aging RPE, natural antioxidants could partially ameliorate these harmful effects.

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Effects of vitamin E in a glucocorticoid induced cataract model in chicken embryo

A Vurmaz, A Ertekin, M Cem Sabaner, E Atay, E Bozkurt, A Bilir

Biotech Histochem . 2020 Sep 22;1-8. doi: 10.1080/10520295.2020.1818284. Online ahead of print.


We investigated the antioxidant effects of vitamin E on a glucocorticoid (GC) induced model of cataracts in chick embryos. We used 70 fertilized eggs divided into seven groups as follows: phosphate-buffered saline (PBS) group, olive oil treatment (OO) group, hydrocortisone treatment (HC) group, olive oil and hydrocortisone treatment (OO + HC) group, 50 mg/kg vitamin E and hydrocortisone treatment (HC + VE (50)) group, 25 mg/kg vitamin E and hydrocortisone treatment (HC + VE (25)) group and 15 mg/kg vitamin E and hydrocortisone treatment (HC + VE (15)) group. On day 17, chick embryos were removed from the eggs and lens and liver tissues were excised. Cataract formation was evaluated and total antioxidant status (TAS), total oxidant status (TOS), malondialdehyde (MDA) and glutathione peroxidase (GPx) were measured in lens and liver tissues; MDA was measured only in liver. The lenses in the HC + VE (50) group exhibited significantly higher levels of GPx and TAS, and lower levels of TOS than for HC and OO + HC groups. The livers of the HC + VE (50) group exhibited significantly higher levels of GPx and lower levels of MDA than for the HC and OO + HC groups. The HC + VE (50) group lenses were evaluated as grade 1, because the nuclei were completely free of cataracts, likely due to the antioxidative effect of high dose VE. VE is an effective antioxidant agent that exhibits a dose-response effect, for ameliorating the negative effects of GCs.

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Corneal UV Protective Effects of a Topical Antioxidant Formulation: A Pilot Study on In Vivo Rabbits

Marisa Palazzo, Francesco Vizzarri, Lubomir Ondruška, Michele Rinaldi, Luigi Pacente, Germano Guerra, Francesco Merolla, Ciro Caruso, Ciro Costagliola

Int J Mol Sci . 2020 Jul 30;21(15):E5426. doi: 10.3390/ijms21155426.


This study aimed to evaluate the protective effect of a topical antioxidant and ultraviolet (UV) shielding action formulation containing riboflavin and D-α-tocopherol polyethylene glycol succinate (TPGS) vitamin E against corneal UV-induced damage in vivo rabbit eyes. In vivo experiments were performed using male albino rabbits, which were divided into four groups. The control group (CG) did not receive any UV irradiation; the first group (IG) was irradiated with a UV-B-UV-A lamp for 30 min; the second (G30) and third (G60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with one drop of the antioxidant and shielding formulation every 15 min, starting one hour before irradiation, until the end of UV exposure. The cornea of the IG group showed irregular thickening, detachment of residual fragments of the Descemet membrane, stromal fluid swelling with consequent collagen fiber disorganization and disruption, and inflammation. The cornea of the G30 group showed edema, a mild thickening of the Descemet membrane without fibrillar collagen disruption and focal discoloration, or inflammation. In the G60 group, the cornea showed a more severe thickening, a more abundant fluid accumulation underneath the Descemet membrane with focal detachment, and no signs of severe tissue alterations, as were recorded in the IG group. Our results demonstrate that topical application of eye drops containing riboflavin and TPGS vitamin E counteracts UV corneal injury in exposed rabbits.

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Age-related macular degeneration in a randomized trial of selenium and vitamin E in men: the Select Eye Endpoints (SEE) study (SWOG S0000B)

William G Christen, Amy K Darke, John M Gaziano, Robert J Glynn, Phyllis J Goodman, Lori M Minasian, Ian M Thompson Jr

Acta Ophthalmol . 2020 Jul 23. doi: 10.1111/aos.14538. Online ahead of print.

Lettter to the Editor

Selenium and vitamin E are found in the human retina and retinal pigment epithelium and have been associated with risks of age-related macular degeneration (AMD) in observational epidemiological studies (Khoo et al. 2019). We examined a possible role for these nutrients in AMD prevention in the Select Eye Endpoints (SEE) Study, an ancillary study of the National Cancer Institute-sponsored Selenium and Vitamin E Cancer Prevention Trial (SELECT), a randomized, placebo-controlled trial of selenium (200 lg/d) and/or vitamin E (400 IU/d) in prevention of prostate cancer among 35 533 apparently healthy men aged 50 years and older (Lippman et al. 2005; Lippman et al. 2009).

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A Novel Vitamin E TPGS-Based Formulation Enhances Chlorhexidine Bioavailability in Corneal Layers

Ciro Caruso, Amalia Porta, Alessandra Tosco, Daniela Eletto, Luigi Pacente, Silvia Bartollino, Ciro Costagliola

Pharmaceutics . 2020 Jul 8;12(7):E642. doi: 10.3390/pharmaceutics12070642.


Keratitis is a severe condition characterized by inflammation of the cornea following a local trauma. The most common ocular disease is the bacterial one, which requires an antibiotic treatment. The major limitation of this therapy is the resistance of the antibiotic. For this reason, alternative procedures have been developed and consist of antimicrobial molecules. One of the most used is the chlorhexidine gluconate, which has shown activity versus Gram-positive and Gram-negative bacteria and fungi. In addition to its efficiency, chlorhexidine shows low toxicity levels for mammalian cells and is a low-cost molecule. Despite its multiple benefits, chlorhexidine, if used at concentrations higher than 0.02% (w/w), can cause local eye irritation. Additionally, its poor penetrability through the cornea makes necessary frequent instillation of eye drops for a prolonged time. Due to these limitations, alternative drug delivery strategies are required. Here, we report a novel formulation based on the combination of d-alpha-tocopherol polyethylene glycol 1000 succinate with chlorhexidine, which results in higher accumulation of the drug in human corneas measured by liquid chromatography and strong antimicrobial activity. Moreover, this formulation does not cause any toxic effect on human cells and is well tolerated by rabbit eyes. Therefore this novel formulation represents a good candidate for the treatment of keratitis that overcomes the risk of antibiotic resistance.

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