Neurovascular Impairment and Therapeutic Strategies in Diabetic Retinopathy

On implications of somatostatin in diabetic retinopathy

Somatostatin, a naturally produced neuroprotective peptide, depresses excitatory neurotransmission and exerts anti-proliferative and anti-inflammatory effects on the retina. In this review, we summarize the progress of somatostatin treatment of diabetic retinopathy through analysis of relevant studies published from February 2019 to February 2023 extracted from the PubMed and Google Scholar databases. Insufficient neuroprotection, which occurs as a consequence of declined expression or dysregulation of retinal somatostatin in the very early stages of diabetic retinopathy, triggers retinal neurovascular unit impairment and microvascular damage. Somatostatin replacement is a promising treatment for retinal neurodegeneration in diabetic retinopathy. Numerous pre-clinical and clinical trials of somatostatin analog treatment for early diabetic retinopathy have been initiated. In one such trial (EUROCONDOR), topical administration of somatostatin was found to exert neuroprotective effects in patients with pre-existing retinal neurodysfunction, but had no impact on the onset of diabetic retinopathy. Overall, we concluded that somatostatin restoration may be especially beneficial for the growing population of patients with early-stage retinopathy. In order to achieve early prevention of diabetic retinopathy initiation, and thereby salvage visual function before the appearance of moderate non-proliferative diabetic retinopathy, several issues need to be addressed. These include the needs to: a) update and standardize the retinal screening scheme to incorporate the detection of early neurodegeneration, b) identify patient subgroups who would benefit from somatostatin analog supplementation, c) elucidate the interactions of somatostatin, particularly exogenously-delivered somatostatin analogs, with other retinal peptides in the context of hyperglycemia, and d) design safe, feasible, low cost, and effective administration routes.

Possible retinotoxicity of long-term vardenafil treatment

Phosphodiesterase (PDE) inhibitors - such as vardenafil - are used primarily for treating erectile dysfunction via increasing cyclic guanosine monophosphate (cGMP) levels. Recent studies have also demonstrated their significant cardioprotective effects in several diseases, including diabetes, upon long-term, continuous application. However, PDE inhibitors are not specific for PDE5 and also inhibit the retinal isoform. A sustained rise in cGMP in photoreceptors is known to be toxic; therefore, we hypothesized that long-term vardenafil treatment might result in retinotoxicity. The hypothesis was tested in a clinically relevant animal model of type 2 diabetes mellitus. Histological experiments were performed on lean and diabetic Zucker Diabetic Fatty rats. Half of the animals were treated with vardenafil for six months, and the retinal effects were evaluated. Vardenafil treatment alleviated rod outer segment degeneration but decreased rod numbers in some positions and induced changes in the interphotoreceptor matrix, even in control animals. Vardenafil treatment decreased total retinal thickness in the control and diabetic groups and reduced the number of nuclei in the outer nuclear layer. Müller cell activation was detectable even in the vardenafil-treated control animals, and vardenafil did not improve gliosis in the diabetic group. Vardenafil-treated animals showed complex retinal alterations with improvements in some parameters while deterioration in others. Our results point towards the retinotoxicity of vardenafil, even without diabetes, which raises doubts about the retinal safety of long-term continuous vardenafil administration. This effect needs to be considered when approving PDE inhibitors for alternative indications.

Topical anesthesia versus topical and subconjunctival anesthesia combined in diabetic retinopathy photocoagulation

PURPOSE

comparison between two anesthetic techniques on the ability to reduce pain during panretinal photocoagulation (PRP) treatment.

METHODS

Observational retrospective single center study. Medical charts of patients who underwent PRP for proliferative diabetic retinopathy were revised. Patients were included if they had the first eye treated with oxybuprocaine hydrochloride drops, and in case of severe pain, the fellow eye received topical anesthesia in combination with 2% subconjunctival lidocaine. The groups were compared for pain perception using an analog visual scale (VAS), number of laser spots, number of interruptions, and laser session duration.

RESULTS

Forty-two eyes of 21 patients (mean age: 58.3 ± 7.6 years) were analyzed. The mean number of laser spots was significantly higher under combined anesthesia (+84.2 ± 155.9 spots, p = 0.01), with a reduced time for laser execution (-2.5 ± 3.12, p = 0.0008). The use of combined anesthesia significantly decreased the number of interruptions (-40.8%, p < 0.0001) into a single session. On the pain grading scale, the pain perception was significantly lower in the combined anesthesia group (p < 0.0001). In eyes receiving topical anesthesia the treatment was stopped for pain in 5 eyes (23.8%), while 5 eyes under combined anesthesia presented subconjunctival hemorrhage (23.8%).

CONCLUSION

Using combined anesthesia in patients subjected to PRP appeared to reduce pain perception limiting the treatment duration and the interruptions for pain without significant complications. Further studies on a larger scale would be desirable to replicate such findings and standardize the analgesic procedures in ophthalmology.

Advances in Research Related to MicroRNA for Diabetic Retinopathy

Diabetic retinopathy (DR) is a severe microvascular complication of diabetes and is one of the primary causes of blindness in the working-age population in Europe and the United States. At present, no cure is available for DR, but early detection and timely intervention can prevent the rapid progression of the disease. Several treatments for DR are known, primarily ophthalmic treatment based on glycemia, blood pressure, and lipid control, which includes laser photocoagulation, glucocorticoids, vitrectomy, and antivascular endothelial growth factor (anti-VEGF) medications. Despite the clinical efficacy of the aforementioned therapies, none of them can entirely shorten the clinical course of DR or reverse retinopathy. MicroRNAs (miRNAs) are vital regulators of gene expression and participate in cell growth, differentiation, development, and apoptosis. MicroRNAs have been shown to play a significant role in DR, particularly in the molecular mechanisms of inflammation, oxidative stress, and neurodegeneration. The aim of this review is to systematically summarize the signaling pathways and molecular mechanisms of miRNAs involved in the occurrence and development of DR, mainly from the pathogenesis of oxidative stress, inflammation, and neovascularization. Meanwhile, this article also discusses the research progress and application of miRNA-specific therapies for DR.

Salidroside protects RGC from pyroptosis in diabetes-induced retinopathy associated with NLRP3, NFEZL2 and NGKB1, revealed by network pharmacology analysis and experimental validation

OBJECTIVE

To investigate the effect of salidroside (SAL) in protecting retinal ganglion cell (RGC) from pyroptosis and explore associated molecular network mechanism in diabetic retinapathy (DR) rats.

METHODS

HE, Nissl and immunofluorescence staining were used to observe the retinal morphological change, and the related target genes for salidroside, DR and pyroptosis were downloaded from GeneCard database. Then Venny, PPI, GO, KEGG analysis and molecular docking were used to reveal molecular network mechanism of SAL in inhibiting the pyroptosis of RGC. Lastly, all hub genes were confirmed by using qPCR.

RESULTS

HE and Nissl staining showed that SAL could improve the pathological structure known as pyroptosis in diabetic retina, and the fluorescence detection of pyroptosis marker in DM group was the strongest, while they decreased in the SAL group(P < 0.05)). Network pharmacological analysis showed 6 intersecting genes were obtained by venny analysis. GO and KEGG analysis showed 9 biological process, 3 molecular function and 3 signaling pathways were involved. Importantly, molecular docking showed that NFE2L2, NFKB1, NLRP3, PARK2 and SIRT1 could combine with salidroside, and qPCR validates the convincible change of CASP3, NFE2L2, NFKB1, NLRP3, PARK2 and SIRT1.

CONCLUSION

Salidroside can significantly improve diabetes-inducedRGC pyrotosis in retina, in which, the underlying mechanism is associated with the NLRP3, NFEZL2 and NGKB1 regulation.

Neurovascular Cell Death and Therapeutic Strategies for Diabetic Retinopathy

Diabetic retinopathy (DR) is a major complication of diabetes and a leading cause of blindness worldwide. DR was recently defined as a neurovascular disease associated with tissue-specific neurovascular impairment of the retina in patients with diabetes. Neurovascular cell death is the main cause of neurovascular impairment in DR. Thus, neurovascular cell protection is a potential therapy for preventing the progression of DR. Growing evidence indicates that a variety of cell death pathways, such as apoptosis, necroptosis, ferroptosis, and pyroptosis, are associated with neurovascular cell death in DR. These forms of regulated cell death may serve as therapeutic targets for ameliorating the pathogenesis of DR. This review focuses on these cell death mechanisms and describes potential therapies for the treatment of DR that protect against neurovascular cell death.

The Ratio of Fibrinogen to Albumin is Related to the Occurrence of Retinopathy in Type 2 Diabetic Patients

Purpose

Type 2 diabetic retinopathy is a long-term chronic inflammatory disease. The aim of this study was to investigate the relationship between fibrinogen to albumin ratio (FAR) and retinopathy in type 2 diabetic patients.

Methods

This was a retrospective study that included 500 patients with type 2 diabetes mellitus (T2DM), and were divided into non-diabetic retinopathy group (NDR, n=297) and diabetic retinopathy group (DR, n=203) according to fundus examination findings, and the DR group was further divided into non-proliferative retinopathy group (NPDR, n=182) and proliferative retinopathy group (PDR, n=21). Baseline data of patients were collected, and the fibrinogen to albumin ratio (FAR) and neutrophil to lymphocyte ratio (NLR) were calculated to analyze the correlation between FAR and NLR and type 2 diabetic retinopathy.

Results

The FAR and NLR were significantly higher in the DR group compared with the NDR group (both P < 0.001). Spearman correlation analysis showed that FAR was positively correlated with NLR and DR (P < 0.05). As the FAR quartile increased, the prevalence of DR increased (14.8%, 16.7%, 25.1%, and 43.30%, respectively; P < 0.05). Multifactorial logistic regression analysis showed that FAR, diabetic course, systolic blood pressure (SBP) and diabetic peripheral neuropathy (DPN) were risk factors for the development of DR in patients with T2DM. The area under the ROC curve for FAR to predict DR progression was 0.708, with an optimal critical value of 7.04, and the area under the ROC curve for diabetes duration and SBP to predict DR was 0.705 and 0.588, respectively.

Conclusion

Our findings show for the first time that FAR is an independent risk factor for assessing DR in patients with type 2 diabetes.

Diabetic Neuropathy of the Retina and Inflammation: Perspectives

A clear connection exists between diabetes and atherosclerotic cardiovascular disease. Consequently, therapeutic approaches that target both diseases are needed. Clinical trials are currently underway to explore the roles of obesity, adipose tissue, gut microbiota, and pancreatic beta cell function in diabetes. Inflammation plays a key role in diabetes pathophysiology and associated metabolic disorders; thus, interest has increased in targeting inflammation to prevent and control diabetes. Diabetic retinopathy is known as a neurodegenerative and vascular disease that occurs after some years of poorly controlled diabetes. However, increasing evidence points to inflammation as a key figure in diabetes-associated retinal complications. Interconnected molecular pathways, such as oxidative stress, and the formation of advanced glycation end-products, are known to contribute to the inflammatory response. This review describes the possible mechanisms of the metabolic changes in diabetes that involve inflammatory pathways.

Overcoming Treatment Challenges in Posterior Segment Diseases with Biodegradable Nano-Based Drug Delivery Systems

Posterior segment eye diseases present a challenge in treatment due to the complex structures in the eye that serve as robust static and dynamic barriers, limiting the penetration, residence time, and bioavailability of topical and intraocular medications. This hinders effective treatment and requires frequent dosing, such as the regular use of eye drops or visits to the ophthalmologist for intravitreal injections, to manage the disease. Moreover, the drugs must be biodegradable to minimize toxicity and adverse reactions, as well as small enough to not affect the visual axis. The development of biodegradable nano-based drug delivery systems (DDSs) can be the solution to these challenges. First, they can stay in ocular tissues for longer periods of time, reducing the frequency of drug administration. Second, they can pass through ocular barriers, offering higher bioavailability to targeted tissues that are otherwise inaccessible. Third, they can be made up of polymers that are biodegradable and nanosized. Hence, therapeutic innovations in biodegradable nanosized DDS have been widely explored for ophthalmic drug delivery applications. In this review, we will present a concise overview of DDSs utilized in the treatment of ocular diseases. We will then examine the current therapeutic challenges faced in the management of posterior segment diseases and explore how various types of biodegradable nanocarriers can enhance our therapeutic arsenal. A literature review of the pre-clinical and clinical studies published between 2017 and 2023 was conducted. Through the advances in biodegradable materials, combined with a better understanding of ocular pharmacology, the nano-based DDSs have rapidly evolved, showing great promise to overcome challenges currently encountered by clinicians.

Advanced Glycation End-Products and Diabetic Neuropathy of the Retina

Diabetic retinopathy is a tissue-specific neurovascular impairment of the retina in patients with both type 1 and type 2 diabetes. Several pathological factors are involved in the progressive impairment of the interdependence between cells that consist of the neurovascular units (NVUs). The advanced glycation end-products (AGEs) are one of the major pathological factors that cause the impairments of neurovascular coupling in diabetic retinopathy. Although the exact mechanisms for the toxicities of the AGEs in diabetic retinopathy have not been definitively determined, the AGE-receptor of the AGE (RAGE) axis, production of reactive oxygen species, inflammatory reactions, and the activation of the cell death pathways are associated with the impairment of the NVUs in diabetic retinopathy. More specifically, neuronal cell death is an irreversible change that is directly associated with vision reduction in diabetic patients. Thus, neuroprotective therapies must be established for diabetic retinopathy. The AGEs are one of the therapeutic targets to examine to ameliorate the pathological changes in the NVUs in diabetic retinopathy. This review focuses on the basic and pathological findings of AGE-induced neurovascular abnormalities and the potential therapeutic approaches, including the use of anti-glycated drugs to protect the AGE-induced impairments of the NVUs in diabetic retinopathy.

Diabetic Retinopathy May Covariate With Stroke in Diabetes Mellitus

Diabetes mellitus is a chronic metabolic disorder with increasing prevalence per hour. Cataracts are one of the most common eye complications, and they affect all structures of the eye. The incidence of cataracts is increasing in patients with diabetes by several mechanisms. With the advancement of technology, cataract surgery is now a necessary procedure for diabetic patients. High-risk complications, like diabetic macular oedema, diabetic retinopathy (DR), phakic, postoperative cyst, and postoperative macular oedema, and macular oedema and endophthalmitis following surgery for a pseudocyst, could result in blindness. The importance of preoperative, intraoperative, and postoperative factors cannot be overestimated in managing complications and improving visual outcomes. DR can be a severe problem if it worsens and causes non-proliferative or proliferative DR or if fluid accumulation in the eye is diagnosed as macular oedema. A woman progressing to sight-threatening DR during childbearing age experiences distress and often requires ocular treatment. Diabetes that has been present for a more extended period, as well as more significant hyperglycaemia, hypertension, cardiovascular diseases, and elevated blood pressure, substantially predict the development of DR. Oxidative stress can be caused by hyperglycaemia, irregular metabolic processes, and people with DR developing neurodegeneration. Therefore, controlling postprandial hyperglycaemia is crucial for preventing DR. Femtosecond laser technology, multifocal intraocular lenses, and other surgical innovations are popularly referred to as surgical management; it will be engaged in the coming era to determine whether there will be a continued reduction in the complication of cataract surgery. This article aims to review the correlation of DR with stroke and its screening and to outline the critical management strategies. 

Harnessing retinal phagocytes to combat pathological neovascularization in ischemic retinopathies?

Ischemic retinopathies (IR) are vision-threatening diseases that affect a substantial amount of people across all age groups worldwide. The current treatment options of photocoagulation and anti-VEGF therapy have side effects and are occasionally unable to prevent disease progression. It is therefore worthwhile to consider other molecular targets for the development of novel treatment strategies that could be safer and more efficient. During the manifestation of IR, the retina, normally an immune privileged tissue, encounters enhanced levels of cellular stress and inflammation that attract mononuclear phagocytes (MPs) from the blood stream and activate resident MPs (microglia). Activated MPs have a multitude of effects within the retinal tissue and have the potential to both counter and exacerbate the harmful tissue microenvironment. The present review discusses the current knowledge about the role of inflammation and activated retinal MPs in the major IRs: retinopathy of prematurity and diabetic retinopathy. We focus particularly on MPs and their secreted factors and cell–cell-based interactions between MPs and endothelial cells. We conclude that activated MPs play a major role in the manifestation and progression of IRs and could therefore become a promising new target for novel pharmacological intervention strategies in these diseases.