Topical treatment of diabetic retinopathy: a systematic review

Diabetic retinopathy in the pediatric population: Pathophysiology, screening, current and future treatments

Diabetic retinopathy (DR) is a sight threatening complication of diabetes mellitus (DM). The incidence of DR in the pediatric population has increased in the last two decades and it is expected to further rise in the future, following the increase in DM prevalence and obesity in youth. As early stages of the retinal disease are asymptomatic, screening programs are of extreme importance to guarantee a prompt diagnosis and avoid progression to more advanced, sight threatening stages. The management of DR comprises a wide range of actions starting from glycemic control, continuing with systemic and local medical treatments, up to para-surgical and surgical approaches to deal with the more aggressive complications. In this review we will describe the pathophysiology of DR trying to understand all the possible targets for currently available or future treatments. We will briefly consider the impact of screening techniques, screening strategies and their social and economic impact. Finally a large part of the review will be dedicated to medical and surgical treatments for DR including both currently available and under development therapies. Most of the available data in the literature on DR are focused on the adult population. The aim of our work is to provide clinicians and researchers with a comprehensive overview of the state of the art regarding DR in the pediatric population, considering the increasing numbers of this diseases in youth and the inevitable consequences that such a chronic disease could have if poorly managed in children.

Repeated Topical Administration of 3 nm Cerium Oxide Nanoparticles Reverts Disease Atrophic Phenotype and Arrests Neovascular Degeneration in AMD Mouse Models

Increased oxidative stress in the retina and retinal pigment epithelium is implicated in age-related macular degeneration (AMD). Antioxidant cerium oxide nanoparticles (CeO2NPs) have been used to treat degenerative retinal pathologies in animal models, although their delivery route is not ideal for chronic patient treatment. In this work, we prepared a formulation for ocular topical delivery that contains small (3 nm), nonaggregated biocompatible CeO2NPs. In vitro results indicate the biocompatible and protective character of the CeO2NPs, reducing oxidative stress in ARPE19 cells and inhibiting neovascularization related to pathological angiogenesis in both HUVEC and in in vitro models of neovascular growth. In the in vivo experiments, we observed the capacity of CeO2NPs to reach the retina after topical delivery and a subsequent reversion of the altered retinal transcriptome of the retinal degenerative mouse model DKOrd8 toward that of healthy control mice, together with signs of decreased inflammation and arrest of degeneration. Furthermore, CeO2NP eye drops' treatment reduced laser-induced choroidal neovascular lesions in mice by lowering VEGF and increasing PEDF levels. These results indicate that CeO2NP eye drops are a beneficial antioxidant and neuroprotective treatment for both dry and wet forms of AMD disease.

New Insights into Treating Early and Advanced Stage Diabetic Retinopathy

Diabetic retinopathy (DR) is the leading cause of preventable blindness in the working-age population. The disease progresses slowly, and we can roughly differentiate two stages: early-stage (ESDR), in which there are mild retinal lesions and visual acuity is generally preserved, and advanced-stage (ASDR), in which the structural lesions are significant and visual acuity is compromised. At present, there are no specific treatments for ESDR and the current recommended action is to optimize metabolic control and maintain close control of blood pressure. However, in the coming years, it is foreseeable that therapeutic strategies based in neuroprotection will be introduced in the clinical arena. This means that screening aimed at identifying patients in whom neuroprotective treatment might be beneficial will be crucial. Regarding the treatment of ASDR, the current primary course is based on laser photocoagulation and intravitreal injections of anti-angiogenic factors or corticosteroids. Repeated intravitreal injections of anti-VEGF agents as the first-line treatment would be replaced by more cost-effective and personalized treatments based on the results of “liquid biopsies” of aqueous humor. Finally, topical administration (i.e., eye drops) of neuroprotective, anti-inflammatory and anti-angiogenic agents will represent a revolution in the treatment of DR in the coming decade. In this article, all these approaches and others will be critically discussed from a holistic perspective.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Minimum Effective Dose of DPP-4 Inhibitors for Treating Early Stages of Diabetic Retinopathy in an Experimental Model

The neurovascular unit (NVU) plays an essential role in the development of diabetic retinopathy (DR). We previously reported that the topical administration (eye drops) of sitagliptin and saxagliptin, two dipeptidyl peptidase-4 inhibitors (DPP-4i), prevents retinal neurodegeneration and vascular leakage in db/db mice. The aim of the present study is to evaluate the minimum effective dose of the topical administration of these DPP-4i. For this purpose, sitagliptin and saxagliptin were tested at different concentrations (sitagliptin: 1 mg/mL, 5 and 10 mg/mL, twice per day; saxagliptin: 1 and 10 mg/mL, once or twice per day) in db/db mice. As end points of efficacy, the hallmarks of NVU impairment were evaluated: reactive gliosis, neural apoptosis, and vascular leakage. These parameters were assessed by immunohistochemistry, cell counting, and the Evans blue method, respectively. Our results demonstrated that the minimum effective dose is 5 mg/mL twice per day for sitagliptin, and 10 mg/mL twice per day for saxagliptin. In conclusion, this study provides useful results for the design of future preclinical regulatory studies and for planning clinical trials.

Ocular Neurodegenerative Diseases: Interconnection between Retina and Cortical Areas

The possible interconnection between the eye and central nervous system (CNS) has been a topic of discussion for several years just based on fact that the eye is properly considered an extension of the brain. Both organs consist of neurons and derived from a neural tube. The visual process involves photoreceptors that receive light stimulus from the external environment and send it to retinal ganglionic cells (RGC), one of the cell types of which the retina is composed. The retina, the internal visual membrane of the eye, processes the visual stimuli in electric stimuli to transfer it to the brain, through the optic nerve. Retinal chronic progressive neurodegeneration, which may occur among the elderly, can lead to different disorders of the eye such as glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR). Mainly in the elderly population, but also among younger people, such ocular pathologies are the cause of irreversible blindness or impaired, reduced vision. Typical neurodegenerative diseases of the CSN are a group of pathologies with common characteristics and etiology not fully understood; some risk factors have been identified, but they are not enough to justify all the cases observed. Furthermore, several studies have shown that also ocular disorders present characteristics of neurodegenerative diseases and, on the other hand, CNS pathologies, i.e., Alzheimer disease (AD) and Parkinson disease (PD), which are causes of morbidity and mortality worldwide, show peculiar alterations at the ocular level. The knowledge of possible correlations could help to understand the mechanisms of onset. Moreover, the underlying mechanisms of these heterogeneous disorders are still debated. This review discusses the characteristics of the ocular illnesses, focusing on the relationship between the eye and the brain. A better comprehension could help in future new therapies, thus reducing or avoiding loss of vision and improve quality of life.

Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy

The concept of diabetic retinopathy as a microvascular disease has evolved and is now considered a more complex diabetic complication in which neurovascular unit impairment plays an essential role and, therefore, can be considered as a main therapeutic target in the early stages of the disease. However, neurodegeneration is not always the apparent primary event in the natural story of diabetic retinopathy, and a phenotyping characterization is recommendable to identify those patients in whom neuroprotective treatment might be of benefit. In recent years, a myriad of treatments based on neuroprotection have been tested in experimental models, but more interestingly, there are drugs with a dual activity (neuroprotective and vasculotropic). In this review, the recent evidence concerning the therapeutic approaches targeting neurovascular unit impairment will be presented, along with a critical review of the scientific gaps and problems which remain to be overcome before our knowledge can be transferred to clinical practice.