Current Approaches in Treatment of Diabetic Retinopathy and Future Perspectives

Hydrogel for light delivery in biomedical applications

Traditional optical waveguides or mediums are often silica-based materials, but their applications in biomedicine and healthcare are limited due to the poor biocompatibility and unsuitable mechanical properties. In term of the applications in human body, a biocompatible hydrogel system with excellent optical transparency and mechanical flexibility could be beneficial. In this review, we explore the different designs of hydrogel-based optical waveguides derived from natural and synthetic sources. We highlighted key developments such as light emitting contact lenses, implantable optical fibres, biosensing systems, luminating and fluorescent materials. Finally, we expand further on the challenges and perspectives for hydrogel waveguides to achieve clinical applications.

New concepts drive the development of delivery tools for sustainable treatment of diabetic complications

Diabetic complications, especially diabetic retinopathy, diabetic nephropathy and painful diabetic neuropathy, account for a large portion of patients with diabetes and display rising global prevalence. They are the leading causes of blindness, kidney failure and hypersensitivity to pain caused by diabetes. Current approved therapeutics against the diabetic complications are few and exhibit limited efficacy. The enhanced cell-specificity, stability, biocompatibility, and loading capacity of drugs are essential for the mitigation of diabetic complications. In the article, we have critically discussed the recent studies over the past two years in material sciences and biochemistry. The insightful concepts in these studies drive the development of novel nanoparticles and mesenchymal stem cells-derived extracellular vesicles to meet the need for treatment of diabetic complications. Their underlying biochemical principles, advantages and limitations have been in-depth analyzed. The nanoparticles discussed in the article include double-headed nanodelivery system, nanozyme, ESC-HCM-B system, soft polymer nanostars, tetrahedral DNA nanostructures and hydrogels. They ameliorate the diabetic complication through attenuation of inflammation, apoptosis and restoration of metabolic homeostasis. Moreover, mesenchymal stem cell-derived extracellular vesicles efficiently deliver therapeutic proteins to the retinal cells to suppress the angiogenesis, inflammation, apoptosis and oxidative stress to reverse diabetic retinopathy. Collectively, we provide a critical discussion on the concept, mechanism and therapeutic applicability of new delivery tools to treat these three devastating diabetic complications.

Stem cells as a regenerative medicine approach in treatment of microvascular diabetic complications

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by high blood glucose and is associated with high morbidity and mortality among the diabetic population. Uncontrolled chronic hyperglycaemia causes increased formation and accumulation of different oxidative and nitrosative stress markers, resulting in microvascular and macrovascular complications, which might seriously affect the quality of a patient's life. Conventional treatment strategies are confined to controlling blood glucose by regulating the insulin level and are not involved in attenuating the life-threatening complications of diabetes mellitus. Thus, there is an unmet need to develop a viable treatment strategy that could target the multi-etiological factors involved in the pathogenesis of diabetic complications. Stem cell therapy, a regenerative medicine approach, has been investigated in diabetic complications owing to their unique characteristic features of self-renewal, multilineage differentiation and regeneration potential. The present review is focused on potential therapeutic applications of stem cells in the treatment of microvascular diabetic complications such as nephropathy, retinopathy, and polyneuropathy.

Agonism of GPR120 Prevented High Glucose-Induced Apoptosis of Retinal Endothelial Cells through Inhibiting NLRP3 Inflammasome

PURPOSE

GPR120 has been reported to ameliorate inflammation in diabetes and diabetic complications. In this study, GW9508, the GPR120 agonist, was utilized in human retinal microvascular endothelial cells (HRMECs) exposed to high glucose (HG) to investigate the involvement of GPR120 in cellular viability and apoptosis as well as the association with the NLRP3 inflammasome.

METHODS

The expression of GPR120 in HRMECs cultured under HG was firstly detected by Western blotting. HRMECs were then assigned to the normal control, GW9508, HG, and HG + GW9508 groups. The expression of the NLRP3 inflammasome consists of NLRP3, ASC, and caspase-1 and was detected by Western blotting and the downstream IL-1β and IL-18 by ELISA. The cellular viability and apoptosis of HRMECs were detected by CCK-8 and flow cytometry, respectively. The expressions of apoptosis-related proteins Bax and Bcl-2 were detected by Western blotting. Finally, nonspecific siRNA (NS) or GPR120 siRNA (siGPR120) was transfected to the cells, followed by stimulation with or without GW9508 or HG, and the expression of NLRP3, ASC, and caspase-1 were detected by Western blotting in these groups.

RESULTS

GPR120 is expressed in HRMECs, and HG can reduce its expression in a time-dependent manner. GW9508 can attenuate inflammation by reducing the expression of NLRP3, ASC, caspase-1, IL-1β, and IL-18 under HG. GW9508 rescues the viability of HRMCs and reduces cell apoptosis by preventing an increase in Bax expression and the reduction in Bcl-2 expression. Additionally, knockdown of GPR120 by siRNA weakened the effects of GW9508 on NLRP3 inflammasome expression.

CONCLUSIONS

Activation of GPR120 protects retinal vascular endothelial cells from HG through inhibiting NLRP3 inflammasome. Thus, GPR120 might be a potential therapeutic target to reduce retinal endothelial damage in diabetic retinopathy.

LncRNA SNHG1 targets miR-340-5p/PIK3CA axis to regulate microvascular endothelial cell proliferation, migration, and angiogenesis in DR

Diabetic retinopathy (DR) is a serious long-term complication of diabetes. However, the current treatment of DR is still challenging. We aimed to investigate the role of lncRNA SNHG1/miR-340-5p/PIK3CA in DR and the mechanisms involved. Blood samples from clinical DR patients and healthy subjects were obtained. HRMECs were induced by high glucose for 24 h to establish the DR model. The vector for interfering or overexpressing lncRNA SNHG1, miR-340-5p, and PIK3CA was constructed. LncRNA SNHG1, miR-340-5p, and PIK3CA expressions were detected by qRT-PCR or Western blot. Cell proliferation and migration were detected by CCK-8 and Transwell assays. Blood vessel formation was detected by angiogenesis assay. Dual-luciferase reporter assay tested the interaction of lncRNA SNHG1 with miR-340-5p and miR-340-5p with PIK3CA. RIP measured the binding of miR-340-5p to PIK3CA. In the blood of DR patients and the DR model, lncRNA SNHG1 was increased and miR-340-5p expression was down-regulated. In the DR model, PIK3CA expression was elevated. Downregulation of lncRNA SNHG1 inhibited HRMECs proliferation, migration, and angiogenesis. LncRNA SNHG1 interacted with miR-340-5p, and up-regulation of miR-340-5p inhibited HRMECs proliferation, migration and angiogenesis. The inhibition of cell proliferation, migration, and angiogenesis of HRMECs caused by down-regulation of lncRNA SNHG1 was reversed by knockdown of miR-340-5p. miR-340-5p targeted PIK3CA, and downregulation of PIK3CA inhibited HRMECs proliferation, migration, and angiogenesis. The inhibition of HRMECs proliferation, migration and angiogenesis caused by down-regulation of lncRNA SNHG1 could be reversed by overexpression of PIK3CA. LncRNA SNHG1 targeted miR-340-5p/PIK3CA axis to regulate microvascular endothelial cell proliferation, migration, and angiogenesis in DR.

The ghrelin-GHSR-1a pathway inhibits high glucose-induced retinal angiogenesis in vitro by alleviating endoplasmic reticulum stress

Background

To investigate the effect of ghrelin, a brain-gut peptide hormone, on high glucose-induced retinal angiogenesis in vitro and explore its association with endoplasmic reticulum (ER) stress.

Methods

Human retinal microvascular endothelial cells (HRMECs) were first divided into control and high-glucose groups, and the mRNA and protein expression levels of the receptor for ghrelin [growth hormone secretin receptor 1a, (GHSR-1a)] in cells were determined. HRMECs were then treated with high glucose alone or in combination with ghrelin or siGHSR-1a, and cell viability, migration, tube formation and the expression of the ER stress-related proteins PERK, ATF4 and CHOP were detected. Finally, to clarify whether the effects of ghrelin are related to ER stress, tunicamycin, an inducer of ER stress, was used to treat HRMECs, and cell viability, cell migration, and tube formation were evaluated.

Results

GHSR-1a expression in HRMECs at both the mRNA and protein levels was inhibited by high-glucose treatment. Under high-glucose conditions, ghrelin promoted cell viability and inhibited migration and tube formation, which were blocked by siGHSR-1a treatment. Ghrelin inhibited the increases in the protein levels of p-PERK, ATF4 and CHOP induced by high-glucose treatment, and combination treatment with siGHSR-1a reversed this effect of ghrelin. When tunicamycin was added, the effects of ghrelin on cell viability, migration and tube formation were all weakened.

Conclusions

This study experimentally revealed that ghrelin can inhibit high glucose-induced retinal angiogenesis in vitro through GHSR-1a, and alleviation of ER stress may be one of the mechanisms underlying this effect.

Tribbles homolog 3 contributes to high glucose-induced injury in retinal pigment epithelial cells via binding to growth factor receptor-bound 2

Diabetic retinopathy (DR) is the most typical complication of diabetes, which severely threatens sight. Tribbles homolog 3 (TRB3), a kind of pseudokinase, is discovered to be highly expressed in diabetes and retinas after retinal detachment. TRB3 expression in human retinal pigment epithelial (hRPE) cells exposed to different concentrations of glucose was tested by RT-qPCR and western blot. Then, cells were induced with 30 mM high glucose (HG) to establish a DR cell model. Following TRB3 knockdown, cell viability estimation employed CCK-8 assay. The mRNA levels of inflammatory factors were detected by RT-qPCR. Reactive oxygen species (ROS) level was measured by DCFH-DA assay, and levels of oxidative stress markers were evaluated applying corresponding kits. Cell apoptosis was assayed by TUNEL assay and western blot. Following, the growth factor receptor-bound 2 (GRB2) expression was also examined by RT-qPCR and western blot. The interaction between TRB3 and GRB2 was verified by Co-IP assay. After GRB2 was overexpressed in HG-induced hRPE cells transfected with shRNA-TRB3, functional experiments were conducted again. The results manifested that TRB3 expression was elevated under HG conditions. Deficiency of TRB3 enhanced the viability while alleviated inflammation, oxidative stress, and apoptosis in HG-induced hRPE cells. GRB2 was also increased in HG-exposed hRPE cells. Moreover, GRB2 had a strong affinity with TRB3 and positively regulated by TRB3. After GRB2 overexpression, the effects of TRB3 knockdown on HG-stimulated hRPE cells were all reversed. Briefly, this study confirmed the promoting role of TRB3/GRB2 axis in the progression of DR.

Evaluation of the Effect of Garlic Tablet as a Complementary Treatment for Patients with Diabetic Retinopathy

PURPOSE

The aim of this study was to investigate the effectiveness of garlic (Allium sativum L.) tablets as a complimentary herbal medication in diabetic macular edema.

METHODS

A total of 91 diabetic participants (117 eyes) with central involved macular edema underwent a double-blind randomized trial. The patients used garlic tablets (500 mg) (2 tab/day) or placebo for 4 weeks and subsequently were examined by an expert ophthalmologist. Clinical manifestations including the best-corrected visual acuity (BCVA, logMAR), central macular thickness (CMT, μm), and intraocular pressure (IOP) were measured as the main outcomes.

RESULTS

BCVA was significantly improved by a 0.18 decrease in mean logMAR value in the garlic-treated patients in comparison with 0.06 in the control ones (P value = 0.027). CMT was decreased in both groups by a 102.99 μm decrease in the garlic group compared to 52.67 μm in the placebo group, albeit in a nonsignificant manner (P value: 0.094). IOP was decreased in the garlic group by 1.03 mmHg (P value: 0.024) and increased by 0.3 mmHg (P value: 0.468) in the placebo group.

CONCLUSION

Our trial suggests that garlic supplements can improve visual acuity, decrease the CMT and lower the IOP, and can be considered as an adjuvant treatment in patients with diabetic macular edema. Garlic was satisfactorily tolerated in diabetic patients, and no significant adverse effect interrupting the safety profile was observed.

Systemic diseases and the cornea

There is a number of systemic diseases affecting the cornea. These include endocrine disorders (diabetes, Graves' disease, Addison's disease, hyperparathyroidism), infections with viruses (SARS-CoV-2, herpes simplex, varicella zoster, HTLV-1, Epstein-Barr virus) and bacteria (tuberculosis, syphilis and Pseudomonas aeruginosa), autoimmune and inflammatory diseases (rheumatoid arthritis, Sjögren's syndrome, lupus erythematosus, gout, atopic and vernal keratoconjunctivitis, multiple sclerosis, granulomatosis with polyangiitis, sarcoidosis, Cogan's syndrome, immunobullous diseases), corneal deposit disorders (Wilson's disease, cystinosis, Fabry disease, Meretoja's syndrome, mucopolysaccharidosis, hyperlipoproteinemia), and genetic disorders (aniridia, Ehlers-Danlos syndromes, Marfan syndrome). Corneal manifestations often provide an insight to underlying systemic diseases and can act as the first indicator of an undiagnosed systemic condition. Routine eye exams can bring attention to potentially life-threatening illnesses. In this review, we provide a fairly detailed overview of the pathologic changes in the cornea described in various systemic diseases and also discuss underlying molecular mechanisms, as well as current and emerging treatments.