Dietary antioxidative supplements and diabetic retinopathy; a systematic review

Smoking, dietary factors and major age-related eye disorders: an umbrella review of systematic reviews and meta-analyses

BACKGROUND

There is accumulating evidence of the associations between age-related eye diseases (AREDs) and smoking or dietary factors. We aimed to provide an umbrella review of the published literature pertaining to smoking or dietary intake as risk factors for major AREDs including cataract, glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy.

METHODS

We searched for pertinent systematic reviews or meta-analyses in PubMed and Web of Science until 16 April 2022. We reperformed the meta-analysis of each association using random effects models. The heterogeneity and 95% prediction interval were calculated. The presence of small-study effect or excess significance bias was also assessed.

RESULTS

In total, 64 associations from 25 meta-analyses and 41 associations from 10 qualitative systematic reviews were evaluated. There was convincing (class I) evidence for only one association, namely current smoking and cataract. Two factors had highly suggestive (class II) evidence, namely ever smoking associated with cataract and fish consumption associated with AMD. We also found suggestive (class III) evidence for associations between the dietary intake of omega-3 polyunsaturated fatty acid, lutein, zeaxanthin, vitamin C and the risk of cataract.

CONCLUSIONS

Smoking as a risk factor for cataract was the most robust association we identified. We also identified several dietary elements associated with AREDs. Large prospective studies are warranted to further examine the associations discussed in this review.

PROSPERO REGISTRATION NUMBER

CRD42022339082.

Investigation of anti-diabetic effect of a novel coenzyme Q10 derivative

Introduction: The rising incidence of type 2 diabetes has seriously affected international public health. The search for more drugs that can effectively treat diabetes has become a cutting-edge trend in research. Coenzyme Q10 (CoQ10) has attracted much attention in the last decade due to its wide range of biological activities. Many researchers have explored the clinical effects of CoQ10 in patients with type 2 diabetes. However, CoQ10 has low bio-availability due to its high lipophilicity. Therefore, we have structurally optimized CoQ10 in an attempt to exploit the potential of its pharmacological activity. Methods: A novel coenzyme Q10 derivative (L-50) was designed and synthesized by introducing a group containing bromine atom and hydroxyl at the terminal of coenzyme Q10 (CoQ10), and the antidiabetic effect of L-50 was investigated by cellular assays and animal experiments. Results: Cytotoxicity results showed that L-50 was comparatively low toxicity to HepG2 cells. Hypoglycemic assays indicated that L-50 could increase glucose uptake in IR-HepG2 cells, with significantly enhanced hypoglycemic capacity compared to the CoQ10. In addition, L-50 improved cellular utilization of glucose through reduction of reactive oxygen species (ROS) accumulated in insulin-resistant HepG2 cells (IR-HepG2) and regulation of JNK/AKT/GSK3β signaling pathway, resulting in hypoglycemic effects. Furthermore, the animal experiments demonstrated that L-50 could restore the body weight of HFD/STZ mice. Notably, the findings suggested that L-50 could improve glycemic and lipid metabolism in HFD/STZ mice. Moreover, L-50 could increase fasting insulin levels (FINS) in HFD/STZ mice, leading to a decrease in fasting blood glucose (FBG) and hepatic glycogen. Furthermore, L-50 could recover triglycerides (TG), total cholesterol (T-CHO), lipoprotein (LDL-C) and high-density lipoprotein (HDL-C) levels in HFD/STZ mice. Discussion: The addition of a bromine atom and a hydroxyl group to CoQ10 could enhance its anti-diabetic activity. It is anticipated that L-50 could be a promising new agent for T2DM.

Is the clinical course of non-arteritic ischemic optic neuropathy associated with oxidative damage and the dynamics of the antioxidant response?

PURPOSE

Oxidative stress is known to be a decisive factor in the wide etiopathogenesis of optic neuropathy. This study aimed to comprehensively evaluate the interaction of optic neuropathy's clinical course with systemic oxidative damage and antioxidant response dynamics in a large series.

METHODS

This case-controlled clinical study included 33 non-arteritic anterior ischemic optic neuropathy (NAION) patients and 32 healthy individuals. Extensive systemic oxidation profiles were statistically compared between the two groups, and correlations between the clinical and biochemical data in the study group were analyzed.

RESULTS

Vitamin E and malondialdehyde (MDA) levels were significantly higher in the study group. Significant correlations were observed in the analyses between clinical findings and oxidative stress parameters. Correlations between vitamin E and intraocular pressure (IOP), between B12 and cup-to-disk ratio (c/d), between antioxidant glutathione and superoxide dismutase (SOD) enzyme systems, and between uric acid (UA) and age were found to be very significant. As significant correlations were found in either clinical and biochemical data or in oxidative stress parameters, correlations between vitamin E and cholesterol, MDA were found to be very significant.

CONCLUSIONS

This study not only supplies significant information regarding oxidative damage and antioxidant response in NAION, but also points out the specific interactions of neuromodulators, like vitamin E, in intracellular signaling pathways and regulation mechanisms. A better reading of these connections may help improve diagnosis, follow-ups and treatment criteria and strategies.

Coenzyme Q10 and Endocrine Disorders: An Overview

Mitochondrial dysfunction and oxidative stress have been implicated in the pathogenesis of a number of endocrine disorders; this, in turn, suggests a potential role for the vitamin-like substance coenzyme Q10 (CoQ10) in the pathogenesis and treatment of these disorders, on the basis of its key roles in mitochondrial function, and as an antioxidant. In this article we have therefore reviewed the role of CoQ10 deficiency and supplementation in disorders of the thyroid, pancreas, gonads, pituitary and adrenals, with a particular focus on hyperthyroidism, type II diabetes, male infertility and polycystic ovary syndrome.

Vitamin E and Non-Communicable Diseases: A Review

Vitamin E, a nutrient found in several foods, comprises eight lipophilic vitamers, the α-, β-, γ- and δ-tocopherols and the α-, β-, γ- and δ-tocotrienols. This vitamin is capable of exerting antioxidant and anti-inflammatory activities, and acting as immunomodulators. Despite these well-known biological activities, the findings regarding the ability of vitamin E and its serum metabolites to prevent and/or control chronic disease are often conflicting and inconsistent. In this review, we have described the metabolism of vitamin E and its interaction with the gut microbiota, considering that these factors may be partially responsible for the divergent results obtained. In addition, we focused on the correlations between vitamin E serum levels, dietary intake and/or supplementation, and the main non-communicable diseases, including diabetes mellitus, asthma, cardiovascular diseases, and the four most common cancers (breast cancer, lung cancer, colorectal cancer, and prostate cancer) with the intention of providing an overview of its health effects in the non-communicable-diseases prevention.

Micronutrients and Diabetic Retinopathy: Evidence From The National Health and Nutrition Examination Survey and a Meta-analysis

PURPOSE

To investigate the associations between circulating micronutrients (vitamins A, C, D, E, and carotenoids) and risk of diabetic retinopathy (DR).

DESIGN

Cross-sectional study and meta-analysis.

METHODS

The cross-sectional study included 517 diabetic participants aged ≥40 years in the 2005-2006 National Health and Nutrition Examination Survey. Serum vitamin D was converted to liquid chromatography-tandem mass spectrometry-equivalent results, while other micronutrients were measured using high-performance liquid chromatography. Presence of DR was determined based on non-mydriatic fundus photographs. A meta-analysis was subsequently performed, which included relevant studies published from January 01, 1990 to December 31, 2020.

RESULTS

Of the 517 included participants, DR was identified in 159 participants (25.17%). After adjusting for multiple confounders, only serum vitamin C was associated with a lower risk of DR (odds ratio [OR]: 0.60; 95% confidence interval [CI]: 0.38-0.95). A total of 35 studies were included in the subsequent meta-analysis. Comparing 1056 participants with DR to 920 controls, the pooled weighted mean difference (WMD) of vitamin C was -11.01 (95% CI: -19.35 to -2.67). Regarding vitamins D and E, the pooled WMD was -3.06 (95% CI: -5.15 to -0.96) and -3.03 (95% CI: -4.24 to -1.82), respectively. No associations were identified between DR and circulating vitamin A or carotenoids.

CONCLUSIONS

Lower levels of circulating vitamins C, D, and E were found in DR patients than those without. More high-quality studies are required to assess the real effects of micronutrients on DR.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood–retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

The Molecular Mechanism of Long Non-Coding RNA (LncRNA) Regulation of Notch Signaling in Glucose-Induced Apoptosis of Human Retinal Vascular Endothelial Cell

Diabetes, a global health concern, affects the health of more than 500 million adults. The absence of Notch protein can cause an imbalance in the retinal vascular environment and cause retinal vascular disease. Long noncoding RNA (lncRNA) is known to be involved in the regulation of many signaling pathways. We hope to understand the specific mechanism of apoptosis in retinal vascular endothelial cells (RVECs) by exploring the regulatory effect of lncRNA on the Notch pathway. In this study, we found that RVECs treated with glucose showed increased levels of Notch transcript and protein expression. The lentiviral interference with Notch RNAi reversed this response. When Notch activity decreased, oxidative stress also decreased, accompanied by increased levels of Caspase-9 and Caspase-3 and an increased rate of apoptosis. Therefore, we believe that Notch is involved in the development of diabetic retinopathy and loss of expression promotes apoptosis of human RVECs. By inhibiting the Notch pathway, lncRNA promotes apoptosis of human RVECs in a high-glucose environment.

Natural antioxidants in diabetes treatment and management: prospects of astaxanthin

Diabetes remains a major health emergency in our entire world, affecting hundreds of millions of people worldwide. In conjunction with its much-dreaded complications (e.g., nephropathy, neuropathy, retinopathy, cardiovascular diseases, etc.) it substantially reduces the quality of life, increases mortality as well as economic burden among patients. Over the years, oxidative stress and inflammation have been highlighted as key players in the development and progression of diabetes and its associated complications. Much research has been devoted, as such, to the role of antioxidants in diabetes. Astaxanthin is a powerful antioxidant found mostly in marine organisms. Over the past years, several studies have demonstrated that astaxanthin could be useful in the treatment and management of diabetes. It has been shown to protect β-cells, neurons as well as several organs including the eyes, kidney, liver, etc. against oxidative injuries experienced during diabetes. Furthermore, it improves glucose and lipid metabolism along with cardiovascular health. Its beneficial effects are exerted through multiple actions on cellular functions. Considering these and the fact that foods and natural products with biological and pharmacological activities are of much interest in the 21st-century food and drug industry, astaxanthin has a bright prospect in the management of diabetes and its complications.

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.

Lutein and zeaxanthin attenuates VEGF-induced neovascularisation in human retinal microvascular endothelial cells through a Nox4-dependent pathway

Age-related macular degeneration (AMD) and proliferative diabetic retinopathy (DR) are two of the most common and severe causes of vision loss in the population. Both conditions are associated with excessive levels of vascular endothelial growth factor (VEGF) in the eye which results in an increase in the formation of new blood vessels through a process called neovascularisation. As such, anti-VEGF therapies are currently utilised as a treatment for patients with AMD however they are associated with painful administration of injections and potential degeneration of healthy endothelium. There is therefore growing interest in alternate treatment options to reduce neovascularisation in the eye. The use of carotenoids, lutein (L) and zeaxanthin (Z), has been shown to improve vision loss parameters in patients with AMD, however the underlying mechanisms are not well-understood. We studied the impact of these compounds on neovascularisation processes using an in vitro cell model of the retinal microvascular endothelium. Our findings show that L and Z reduced VEGF-induced tube formation whilst, in combination (5:1 ratio), the compounds significantly blocked VEGF-induced neovascularisation. The carotenoids, individually and in combination, reduced VEGF-induced oxidative stress concomitant with increased activity of the NADPH oxidase, Nox4. We further demonstrated that the Nox4 inhibitor, GLX7013114, attenuated the protective effect of L and Z. Taken together, these findings indicate the protective effect of the carotenoids, L and Z, in reducing VEGF-mediated neovascularisation via a Nox4-dependent pathway. These studies implicate the potential for these compounds to be used as a therapeutic approach for patients suffering from AMD and proliferative DR.

Adjuvant Therapies in Diabetic Retinopathy as an Early Approach to Delay Its Progression: The Importance of Oxidative Stress and Inflammation

Diabetes mellitus (DM) is a progressive disease induced by a sustained state of chronic hyperglycemia that can lead to several complications targeting highly metabolic cells. Diabetic retinopathy (DR) is a multifactorial microvascular complication of DM, with high prevalence, which can ultimately lead to visual impairment. The genesis of DR involves a complex variety of pathways such as oxidative stress, inflammation, apoptosis, neurodegeneration, angiogenesis, lipid peroxidation, and endoplasmic reticulum (ER) stress, each possessing potential therapeutic biomarkers. A specific treatment has yet to be developed for early stages of DR since no management is given other than glycemic control until the proliferative stage develops, offering a poor visual prognosis to the patient. In this narrative review article, we evaluate different dietary regimens, such as the Mediterranean diet, Dietary Pattern to Stop Hypertension (DASH) and their functional foods, and low-calorie diets (LCDs). Nutraceuticals have also been assessed in DR on account of their antioxidant, anti-inflammatory, and antiangiogenic properties, which may have an important impact on the physiopathology of DR. These nutraceuticals have shown to lower reactive oxygen species (ROS), important inflammatory factors, cytokines, and endothelial damage biomarkers either as monotherapies or combined therapies or concomitantly with established diabetes management or nonconventional adjuvant drugs like topical nonsteroidal anti-inflammatory drugs (NSAIDs).