Protection by vitamin D against high-glucose-induced damage in retinal pigment epithelial cells

Relationship between histopathological findings of patients with dermatochalasis and vitamin D deficiency

PURPOSE

To compare the histopathological findings of patients who had been diagnosed with dermatochalasis (DC) and had undergone upper eyelid blepharoplasty (ULB) as well as those of controls (C-Group) according to their serum vitamin D (SVD) levels.

METHODS

The prospective study included 136 upper eyelid skin from 68 patients who underwent surgery for DC and 53 upper eyelid skin from 53 patients who underwent levator surgery with ULB. The DC Group was then divided into 3 subgroups according to the marginal reflex distance (MRD4). The lymphatic vessel (LV) count and diameter of the largest LV (DLLV) were recorded, the stromal collagen bed (SCB) was observed, and its depth was measured, the interfibrillar edema was examined, and the elastic fiber and macrophage counts and recorded, respectively, and then all of these were evaluated. The SVD levels were compared between the DC patients and the C-Group.

RESULTS

In comparison to the C-Group, significant changes were seen in the dilated LV, DLLV, SCB depth, interfibrillar edema, elastic fiber density, and macrophage count in the DC sub-Groups (P < 0.001 for all). While no difference was found between DC sub-Group 1 (MRD4 > 4 mm) and the C-Group (P > 0.05), a significant difference was found between DC sub-Group 2 (MRD4 2-4 mm) and DC sub-Group 3 (MRD4 < 2 mm) for all of the parameters (P < 0.05). A statistically significant difference was also found in the SVD levels between the DC sub-Group 1 and DC sub-Groups 2-3 (P < 0.017, P < 0.001 respectively).

CONCLUSION

According to the results of this study, SVD level was significantly lower in DC group. Moreover, an increased LV count and diameter, decreased elastic fiber count, collagen fiber and stromal edema irregularity, and increased macrophage count were found to be associated with the SVD level.

Serum vitamin D is substantially reduced and predicts flares in diabetic retinopathy patients

AIMS/INTRODUCTION

Research has suggested that vitamin D deficiency is associated with diabetic retinopathy (DR). Our study aimed to determine whether vitamin D deficiency is the cause of diabetic retinopathy or if diabetic retinopathy reduces vitamin D levels.

MATERIALS AND METHODS

Participants with type-2 diabetes were recruited for this prospective observational clinical study and were divided into a diabetic group without retinopathy and a diabetic group with retinopathy, with additional healthy volunteers serving as a control group. The differences in clinical characteristics among the three groups were also compared. Patients without retinopathy were then followed for 1 year to monitor the incidence of diabetic retinopathy. After follow-up, participants were divided into subgroups based on whether diabetic retinopathy occurred. The baseline data of the subgroups were compared, and the independent risk factors were analyzed.

RESULTS

Vitamin D levels were generally low. Participants with diabetic retinopathy had significantly lower vitamin D levels than did those without retinopathy (P < 0.01). A comparison of the two subgroups revealed lower baseline vitamin D concentrations in the new-DR subgroup than in the non-DR subgroup (P < 0.01). Vitamin D deficiency and elevated HbA1c levels were found to be independent risk factors for diabetic retinopathy (OR = 0.935, 95% CI: 0.867-0.981, P = 0.006; OR = 2.208, 95% CI: 1.764-2.764, P < 0.01). The limit of vitamin D intake according to the receiver-operating characteristic (ROC) curve was 26.01 ng/mL, and the area under the ROC curve was 0.603 (95% CI: 0.559-0.706, P = 0.002).

CONCLUSIONS

Vitamin D levels were significantly lower in patients diagnosed with diabetic retinopathy. More importantly, vitamin D deficiency may accelerate the onset of diabetic retinopathy.

The impact of vitamin D on the etiopathogenesis and the progression of type 1 and type 2 diabetes in children and adults

Diabetes is a common chronic metabolic disease with complex causes and pathogenesis. As an immunomodulator, vitamin D has recently become a research hotspot in the occurrence and development of diabetes and its complications. Many studies have shown that vitamin D can reduce the occurrence of diabetes and delay the progression of diabetes complications, and vitamin D can reduce oxidative stress, inhibit iron apoptosis, promote Ca2+ influx, promote insulin secretion, and reduce insulin resistance. Therefore, the prevention and correction of vitamin D deficiency is very necessary for diabetic patients, but further research is needed to confirm what serum levels of vitamin D3 are maintained in the body. This article provides a brief review of the relationship between vitamin D and diabetes, including its acute and chronic complications.

Visual fatigue a comprehensive review of mechanisms of occurrence, animal model design and nutritional intervention strategies

When the eyes work intensively, it is easy to have eye discomfort such as blurred vision, soreness, dryness, and tearing, that is, visual fatigue. Visual fatigue not only affects work and study efficiency, but long-term visual fatigue can also easily affect physical and mental health. In recent years, with the popularization of electronic products, although it has brought convenience to the office and study, it has also caused more frequent visual fatigue among people who use electronic devices. Moreover, studies have reported that the number of people with visual fatigue is showing a trend of increasing year by year. The range of people involved is also extensive, especially students, people who have been engaged in computer work and fine instruments (such as microscopes) for a long time, and older adults with aging eye function. More and more studies have proposed that supplementation with the proper nutrients can effectively relieve visual fatigue and promote eye health. This review discusses the physiological mechanisms of visual fatigue and the design ideas of animal experiments from the perspective of modern nutritional science. Functional food ingredients with the ability to alleviate visual fatigue are discussed in detail.

25-hydroxyvitamin D3 inhibits oxidative stress and ferroptosis in retinal microvascular endothelial cells induced by high glucose through down-regulation of miR-93

BACKGROUND

The decrease of vitamin D plays a critical role in diabetes mellitus (DM)-induced oxidative stress and vascular endothelial injury. Therefore, we investigated the effect and mechanism of 25-hydroxyvitamin D3 (25 (OH) D3) on oxidative stress and ferroptosis induced by high glucose in human retinal microvascular endothelial cells (hRMVECs). And the objective of this paper was to propose a new strategy for the prevention and treatment of diabetic retinopathy (DR).

METHODS

First, hRMVECs were transfected with mimics NC or miR-93. After that, cells were treated with 100 nM / 500 nM 25 (OH) D3 and then cultured in a high glucose (30 mM) environment. Subsequently, qRT-PCR was employed to detect the expression level of miR-93; CCK-8 for the proliferation of cells in each group; biochemical tests for the level of intracellular reactive oxygen species (ROS), malondialdehyde (MDA), reduced glutathione (GSH) and ferrous ion (Fe²⁺); and Western blot for the expression of ferroptosis-related proteins glutathione peroxidase 4 (GPX4) and SLC7A11).

RESULTS

Under a high glucose environment, 25 (OH) D3 at 100 nM/500 nM could significantly promote the proliferation of hRMVECs, remarkably decrease the level of intracellular ROS/MDA, and up-regulate the level of GSH. Besides, 25 (OH) D3 greatly reduced Fe²⁺ level in the cells while increased protein level of GPX4 and SLC7A11. Subsequently, we found that high glucose induced miR-93 expression, while 25 (OH) D3 markedly decreased high glucose-induced miR-93 overexpression. Furthermore, overexpression of miR-93 inhibited the functions of 25 (OH) D3 by activating ROS (ROS and MDA were up-regulated while GSH was down-regulated) and inducing Fe²⁺ (Fe²⁺ level was up-regulated while GPX4 and SLC7A11 level was down-regulated) in cells.

CONCLUSION

25 (OH) D3 may inhibit oxidative stress and ferroptosis in hRMVECs induced by high glucose via down-regulation of miR-93.

The effect of vitamin D supplementation on the outcome of treatment with bevacizumab in diabetic macular edema: a randomized clinical trial

Purpose

Concomitant vitamin D deficiency (VDD) is speculated to aggravate diabetic macular edema (DME). We aimed to determine the effect of hypovitaminosis D correction on the outcome of treatment with intravitreal bevacizumab (IVB) in DME eyes.

Methods

In this randomized clinical trial, 83 eyes of 83 patients with DME were recruited and divided into three groups: normal vitamin D levels + IVB administration (Group 1), vitamin D insufficient/deficient + IVB administration (Group 2), and vitamin D insufficient/deficient + IVB administration + oral vitamin D supplementation (Group 3). Participants were followed for 6 months after the intervention. Visual (corrected distance visual acuity, CDVA) and anatomical (central macular thickness, CMT) outcomes of intervention were evaluated 1, 3, and 6 months after three monthly loading doses of IVB were given. Serum vitamin D levels were measured 1 and 6 months after the third IVB administration.

Results

A total of 29, 26, and 28 eyes were enrolled in groups 1, 2, and 3, respectively. In months 1, 3, and 6, after the three basic loading doses of IVB, visual acuity and CMT improved in all three groups, but improvements (both functional and anatomical) in groups 1 and 3 in month 6 were more significant than in group 2 (mean CDVA LogMAR changes: − 0.18 ± 0.03, − 0.14 ± 0.05, and − 0.2 ± 0.06; mean CMT reductions: − 82.24 ± 11.43, − 66.62 ± 14.34, and − 86.14 ± 18.36, in groups 1, 2, and 3, respectively; p < 0.001). The mean number of IVB injections during follow-up was 5.33 (range 4–7), which did not differ between the groups.

Conclusion

Correction of vitamin D deficiency in DME patients with type 2 diabetes and vitamin D deficiency, in addition to IVB injections, may play a role in improving CDVA and CMT. However, this beneficial effect seems to be delayed by several months.

Trial registration

Iranian Registry of Clinical Trials (IRCT), IRCT20200407046978N1, registered on April 11, 2020, retrospectively registered (https://en.irct.ir/trial/46999).

Vitamin D and Ocular Diseases: A Systematic Review

The contributory roles of vitamin D in ocular and visual health have long been discussed, with numerous studies pointing to the adverse effects of vitamin D deficiency. In this paper, we provide a systematic review of recent findings on the association between vitamin D and different ocular diseases, including myopia, age-related macular degeneration (AMD), glaucoma, diabetic retinopathy (DR), dry eye syndrome (DES), thyroid eye disease (TED), uveitis, retinoblastoma (RB), cataract, and others, from epidemiological, clinical and basic studies, and briefly discuss vitamin D metabolism in the eye. We searched two research databases for articles examining the association between vitamin D deficiency and different ocular diseases. One hundred and sixty-two studies were found. There is evidence on the association between vitamin D and myopia, AMD, DR, and DES. Overall, 17 out of 27 studies reported an association between vitamin D and AMD, while 48 out of 54 studies reported that vitamin D was associated with DR, and 25 out of 27 studies reported an association between vitamin D and DES. However, the available evidence for the association with other ocular diseases, such as glaucoma, TED, and RB, remains limited.

Do serum vitamin D levels correlate with Macular Edema or with Diabetic Retinopathy?

PURPOSE

To compare serum vitamin D (25(OH)D) levels according to the presence of diabetic macular edema (DME) in Diabetes Mellitus (DM) patients with different retinopathy conditions.

METHODS

The files of all DM patients presenting for examination at the ophthalmology clinic between October 2018 and March 2020 were retrospectively examined. Data was collected from the files and included a comprehensive ophthalmological examination, laboratory results from fasting blood tests, and the internal medicine outpatient clinic examination. Patients were divided into two groups according to the presence of DME, they were divided into three groups in terms of retinopathy and DME, and in terms of retinopathy severity and presence of DME, they were divided into five groups.

RESULT

Ninety one (51.1%) of the age-sex matched participants were female and 87 (48.9%) were male. There was a statistically significant difference in vitamin D levels between the group with DME and the group without DME (p ≤ 0.001). In the comparison made according to the presence of retinopathy and DME; a significant difference was found between the DME group and the group with retinopathy but no DME (p ≤ 0.001). When the severity of retinopathy and the presence of DME were evaluated, a significant difference was found between the proliferative diabetic retinopathy (PDR) group with DME and the PDR group without DME in terms of vitamin D levels (p = 0.004).

CONCLUSION

Our study shows that the presence of DME is associated with lower serum 25(OH)D levels.

Evaluation of Retinal Structure in Pediatric Subjects With Vitamin D Deficiency

PURPOSE

To quantitatively evaluate the retinal structural parameters of pediatric patients who were determined to be deficient in vitamin D.

DESIGN

Prospective, cross-sectional study.

METHODS

Retinal structural parameters, including the peripapillary retinal nerve fiber layer (RNFL), central macula, retinal layer, and choroidal thicknesses, central retinal artery equivalent (CRAE), and central retinal vein equivalent (CRVE), in pediatric subjects with vitamin D deficiency (group 1) and those without (group 2) were compared.

RESULTS

Group 1 comprised 70 individuals, while group 2 comprised 80 individuals. The mean peripapillary RNFL (except for the nasal superior sector [P = .037]), central macula, and retinal layer thicknesses were also determined to be similar in both groups (P > .05 for both groups). The mean choroidal thickness was lower in the subfoveal (P = .006) and nasal 3000-µm-diameter areas (P = .004) in group 1. The mean CRAE was determined to be lower (P = .031) and the CRVE was higher in group 1 (P = .005); it was determined that there was a significant correlation between the vitamin D level and both the CRAE (r = 0.447, P < .001) and CRVE (r = -0.320, P = .013).

CONCLUSION

Choroidal thinning, a decrease in the CRAE, and increase in the CRVE were structural changes that occurred in the pediatric subjects who had vitamin D deficiency. The alterations in these parameters became more prominent in pediatric subjects who were determined to have lower vitamin D levels.

Role of vitamin D in diabetic retinopathy: Pathophysiological and clinical aspects

Epidemiological data predict a dramatic increase in the prevalence of diabetes and of diabetic retinopathy (DR) - the most common complication of diabetes-for which however we do not have so far effective tools for prevention and treatment. Since hypovitaminosis D is very frequent in patients with diabetes and vitamin D (VD) has vascular protective properties, several studies have addressed the association of VD deficiency with DR and its severity and progression, whereas the effects of VD supplementation on its natural history are largely unknown. Here we review the available evidence that supports the possible protective role of VD in DR and suggests to determine the VD levels in DR patients calling for a definitive randomized clinical trial to ascertain whether VD supplementation could protect against DR.

PACAP-derived mutant peptide MPAPO protects trigeminal ganglion cell and the retina from hypoxic injury through anti-oxidative stress, anti-apoptosis, and promoting axon regeneration

The purpose of this study was to determine whether the MPAPO, derived peptide of pituitary adenylate cyclase-activating polypeptide (PACAP), would protect trigeminal ganglion cells (TGCs) and the mice retinas from a hypoxic insult. The nerve endings of the ophthalmic nerve of the trigeminal nerve are widely distributed in eye tissues. In TGCs after hypoxia exposure, we discovered that reactive oxygen species level, the contents of cytosolic cytochrome c and cleaved-caspase-3 were significantly increased, in the meanwhile, m-Calpain was activated and cytoskeleton proteins (αII-spectrin and Synapsin) were degraded, neurites of TGCs disappeared, but these effects were reversed in TGCs treated with MPAPO. The structure of the mice retinas after hypoxic exposure was disordered. Increased lipid peroxidation (LPO), decreased glutathione (GSH) levels, and decreased superoxide dismutase (SOD) activity, positive cells of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL), the disintegration of nerve fibers was examined in the retinas following a hypoxic insult. Disordered retina was attenuated with MPAPO eye drops, as well as hypoxia-induced apoptosis in the developing retina, increase in LPO, and decrease in GSH levels and SOD activity of the retina. Moreover, the disintegrated retinal nerve fibers were reassembled after MPAPO treatment. These results suggest that hypoxia induces oxidative stress, apoptosis, and neurites disruption, while MPAPO is remarkably protective against these adverse effects of hypoxia in TGCs and the developing retinas by specifically activating PAC1 receptor.

Anti-Inflammatory and Anti-Oxidative Synergistic Effect of Vitamin D and Nutritional Complex on Retinal Pigment Epithelial and Endothelial Cell Lines against Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a multifactorial disease of the retina featured by dysfunction of retinal pigmented epithelial (RPE) and loss of photoreceptor cells under oxidative stress and inflammatory conditions. Vitamin D and antioxidants have beneficial effects against retinal degenerative diseases, such as AMD. We investigated the impact of associating vitamin D (ND) with a nutritional antioxidant complex (Nutrof Total^®; N) on oxidative stress and inflammation-like induced conditions by H₂O₂ and LPS, respectively, in human retinal epithelial (ARPE-19) and human retinal endothelial (HREC) cells. Application of either N or ND treatments to H₂O₂-induced media in ARPE-19 cells counteracted late apoptosis, attenuated oxidative DNA damage, and increased cell proliferation. Significant reduction in the expression levels of MCP1, IL-8, and IL6 cytokines was observed following application of either N or ND treatments under LPS-induced conditions in ARPE-19 cells and in MCP-1 and IL12p70 cytokine levels in HREC cells. ND and not N revealed significant downregulation of IFNγ in ARPE-19 cells, and of IL-6 and IL-18 in HREC cells. In conclusion, adding vitamin D to Nutrof Total^® protects in a synergistic way against oxidative and inflammatory stress-induced conditions in retinal epithelial and endothelial cells.

Polygonatum sibiricum polysaccharide inhibits high glucose-induced oxidative stress, inflammatory response, and apoptosis in RPE cells

Diabetic retinopathy is one of the major diabetic complications and remains the most common cause of adult blindness among patients with diabetes mellitus. Polygonatum sibiricum polysaccharides (PSP) are a group important component of Polygonatum sibiricum (PS) with anti-diabetic activity. However, the effect and underlying mechanism of PSP on diabetic retinopathy remains unclear. We used high glucose (HG)-stimulated ARPE-19 cells to establish in vitro diabetic retinopathy model. Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was performed to evaluate cell viability of ARPE-19 cells. The changes in the ROS production, malondialdehyde (MDA) content, and activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were detected to indicate oxidative stress. The secretion levels of tumor necrosis factor-alpha (TNF-α) and interleukin-8 (IL-8) were detected by ELISA. The protein levels of TNF-α, IL-8, bcl-2, bax, nuclear Nrf2, and anti-hemeoxygenase-1 (HO-1) were detected by western blot analysis. Our results showed that HG treatment caused a significant reduction in cell viability of ARPE-19 cells. PSP treatment improved the reduced cell viability of ARPE-19 cells. PSP also attenuated HG-induced oxidative stress with decreased ROS production and MDA content, as well as increased the activities of SOD and GPx. In addition, HG significantly increased bax expression and caspase-3 activity, and decreased bcl-2 expression. However, these changes were mitigated by PSP treatment. Furthermore, PSP markedly induced the activation of Nrf2/HO-1 pathway in HG-induced ARPE-19 cells. Knockdown of Nrf2 reversed the protective effects of PSP on HG-induced ARPE-19 cells. Taken together, these findings indicated that PSP protects ARPE-19 cells from HG-induced oxidative stress, inflammation, and cell apoptosis through regulation of Nrf2/HO-1 signaling pathway.

Tauroursodeoxycholic Acid Protects Retinal Pigment Epithelial Cells from Oxidative Injury and Endoplasmic Reticulum Stress In Vitro

Retinal degeneration is characterized by the dysfunction of retinal cells. Oxidative and endoplasmic reticulum (ER) stress play an important role in the pathogenesis and progression of retinal degeneration. Tauroursodeoxycholic acid (TUDCA) has been demonstrated to have protective effects in in vitro and in vivo retinal degeneration models. To fully understand the molecular mechanisms of TUDCA’s protection, we first treated human retinal pigment epithelial (RPE) cells, ARPE-19, with H₂O₂ or H₂O₂ plus TUDCA for 24 h. RPE cells co-exposed to TUDCA had higher cell viability and lower cell death rate compared to cells exposed to H₂O₂ alone. TUDCA significantly increased antioxidant capacity in H₂O₂-treated RPE cells by decreasing the generation of reactive oxygen species (ROS) and Malondialdehyde (MDA), upregulating the expression of antioxidant genes, and increasing the generation of glutathione (GSH). TUDCA also inhibited inflammation in H₂O₂-challenged RPE cells by decreasing the expression of proinflammatory cytokines. Furthermore, TUDCA suppressed thapsigargin-induced ER stress in RPE cells, as demonstrated by decreased the expression of CCAAT-enhancer-binding protein homologous protein (CHOP) and apoptosis. Our present study suggests that TUDCA can protect RPE cells against oxidative damage, inflammation, and ER stress and may benefit patients with retinal degeneration.

Vitamin D Protects against Oxidative Stress and Inflammation in Human Retinal Cells

Diabetic retinopathy is a vision-threatening microvascular complication of diabetes and is one of the leading causes of blindness. Oxidative stress and inflammation play a major role in its pathogenesis, and new therapies counteracting these contributors could be of great interest. In the current study, we investigated the role of vitamin D against oxidative stress and inflammation in human retinal pigment epithelium (RPE) and human retinal endothelial cell lines. We demonstrate that vitamin D effectively counteracts the oxidative stress induced by hydrogen peroxide (H₂O₂). In addition, the increased levels of proinflammatory proteins such as Interleukin (IL)-6, IL-8, Monocyte chemoattractant protein (MCP)-1, Interferon (IFN)-γ, and tumor necrosis factor (TNF)-α triggered by lipopolysaccharide (LPS) exposure were significantly decreased by vitamin D addition. Interestingly, the increased IL-18 only decreased by vitamin D addition in endothelial cells but not in RPE cells, suggesting a main antiangiogenic role under inflammatory conditions. Moreover, H₂O₂ and LPS induced the alteration and morphological damage of tight junctions in adult retinal pigment epithelium (ARPE-19) cells that were restored under oxidative and inflammatory conditions by the addition of vitamin D to the media. In conclusion, our data suggest that vitamin D could protect the retina by enhancing antioxidant defense and through exhibiting anti-inflammatory properties.

Update on the Effects of Antioxidants on Diabetic Retinopathy: In Vitro Experiments, Animal Studies and Clinical Trials

Current therapies for diabetic retinopathy (DR) incorporate blood glucose and blood pressure control, vitrectomy, photocoagulation, and intravitreal injections of anti-vascular endothelial growth factors or corticosteroids. Nonetheless, these techniques have not been demonstrated to completely stop the evolution of this disorder. The pathophysiology of DR is not fully known, but there is more and more evidence indicating that oxidative stress is an important mechanism in the progression of DR. In this sense, antioxidants have been suggested as a possible therapy to reduce the complications of DR. In this review we aim to assemble updated information in relation to in vitro experiments, animal studies and clinical trials dealing with the effect of the antioxidants on DR.