Association between neurodegeneration and macular perfusion in the progression of diabetic retinopathy. A 3-year longitudinal study

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

Patterns of Progression of Nonproliferative Diabetic Retinopathy Using Non-Invasive Imaging

Purpose

To identify progression of nonproliferative diabetic retinopathy (NPDR) in patients with type 2 diabetes by combining optical coherence tomography angiography (OCTA) metrics and color fundus photography (CFP) images.

Methods

This study was a post hoc analysis of a prospective longitudinal cohort study (CORDIS, NCT03696810) with 2-year duration. This study enrolled 122 eyes. Ophthalmological examinations included OCTA and CFP. OCTA metrics included skeletonized vessel density (SVD) and perfusion density (PD) at the superficial capillary plexus (SCP) and deep capillary plexus (DCP). Microaneurysm turnover analysis and Early Treatment Diabetic Retinopathy Study (ETDRS) grading for diabetic retinopathy (DR) severity assessment were performed on 7-field CFP.

Results

Eyes graded as ETDRS level 20 showed significant capillary nonperfusion predominantly in the inner ring area in the SCP (P < 0.001), whereas eyes graded as ETDRS level 35 and ETDRS levels 43 and 47 showed significant capillary nonperfusion in both the SCP and DCP in both inner and outer rings (P < 0.001). When evaluating rates of progression in capillary nonperfusion for the 2-year period of follow-up, changes were found predominantly in the DCP for SVD and PD and were better identified in the outer ring area. Microaneurysm turnover contributes to the characterization of NPDR progression by discriminating ETDRS level 35 from ETDRS levels 43 and 47 (P < 0.001), which could not be achieved using only OCTA metrics.

Conclusions

Patterns of progression of NPDR can be identified combining OCTA examinations of the superficial and deep retinal capillary plexi of central retina and determination of microaneurysm turnover from fundus photographs.

Translational Relevance

Our study reports results from a registered clinical trial that advances understanding of disease progression in NPDR.

Association of OCT and OCT angiography measures with the development and worsening of diabetic retinopathy in type 2 diabetes

OBJECTIVE

To assess if optical coherence tomography (OCT) and OCT angiography (OCTA) measures are associated with the development and worsening of diabetic retinopathy (DR) over four years.

METHODS

280 participants with type 2 diabetes underwent ultra-wide field fundus photography, OCT and OCTA. OCT-derived macular thickness measures, retinal nerve fibre layer and ganglion cell-inner plexiform layer thickness and OCTA-derived foveal avascular zone area, perimeter, circularity, vessel density (VD) and macular perfusion (MP) were examined in relation to the development and worsening of DR over four years.

RESULTS

After four years, 206 eyes of 219 participants were eligible for analysis. 27 of the 161 eyes (16.7%) with no DR at baseline developed new DR, which was associated with a higher baseline HbA1c and longer diabetes duration. Of the 45 eyes with non-proliferative DR (NPDR) at baseline, 17 (37.7%) showed DR progression. Baseline VD (12.90 vs. 14.90 mm/mm2, p = 0.032) and MP (31.79% vs. 36.96%, p = 0.043) were significantly lower in progressors compared to non-progressors. Progression of DR was inversely related to VD ((hazard ratio [HR] = 0.825) and to MP (HR = 0.936). The area under the receiver operating characteristic curves for VD was AUC = 0.643, with 77.4% sensitivity and 41.8% specificity for a cut-off of 15.85 mm/mm2 and for MP it was AUC = 0.635, with 77.4% sensitivity and 25.5% specificity for a cut-off of 40.8%.

CONCLUSIONS

OCTA metrics have utility in predicting progression rather than the development of DR in individuals with type 2 diabetes.

Retinal neurodegeneration in eyes with NPDR risk phenotypes: A two-year longitudinal study

INTRODUCTION

Diabetic retinopathy (DR) is both a microangiopathy and a neurodegenerative disease. However, the connections between both changes are not well known.

PURPOSE

To characterise the longitudinal retinal ganglion cell layer + inner plexiform layer (GCL + IPL) changes and their association with microvascular changes in type-2 diabetes (T2D) patients with nonproliferative diabetic retinopathy (NPDR).

METHODS

This two-year prospective study (CORDIS, NCT03696810) included 122 T2D individuals with NPDR identified as risk phenotypes B and C, which present a more rapid progression. Phenotype C was identified by decreased VD ≥ 2SD in healthy controls, and phenotype B, identified by subclinical macular oedema with only minimal vascular closure. The GCL + IPL thickness, vessel density, perfusion density and area of intercapillary spaces (AIS) were assessed by optical coherence tomography (OCT) and OCT angiography (OCTA). Linear mixed effects models were employed to evaluate the retinal GCL + IPL progression and its associations.

RESULTS

Regarding GCL + IPL thickness, T2D individuals presented on average 80.1 ± 7.49 μm, statistically significantly lower than the healthy control group, 82.5 ± 5.71 (p = 0.022), with only phenotype C differing significantly from controls (p = 0.006). GCL + IPL thickness steadily decreased during the two-year period in both risk phenotypes, with an annual decline rate of -0.372 μm/year (p < 0.001). Indeed, phenotype C showed a higher rate of progression (-0.459 μm/year, p < 0.001) when compared to phenotype B (-0.296 μm/year, p = 0.036). Eyes with ETDRS grade 20 showed GCL + IPL thickness values comparable to those of healthy control group (83.3 ± 5.80 and 82.7 ± 5.50 μm, respectively, p = 0.880), whereas there was a progressive decrease in GCL + IPL thickness in ETDRS grades 35 and 43-47 associated with the increase in severity of the retinopathy (-0.276 μm/year, p = 0.004; -0.585 μm/year, p = 0.013, respectively). Furthermore, the study showed statistically significant associations between the progressive thinning of GCL + IPL and the progressive increase in retinal capillary non-perfusion, with particular relevance for AIS (p < 0.001).

CONCLUSIONS

Our findings showed that, in eyes with NPDR and at risk for progression, retinal neurodegeneration occurs at different rates in different risk phenotypes, and it is associated with retinal microvascular non-perfusion.

Understanding human aging and the fundamental cell signaling link in age-related diseases: the middle-aging hypovascularity hypoxia hypothesis

Aging-related hypoxia, oxidative stress, and inflammation pathophysiology are closely associated with human age-related carcinogenesis and chronic diseases. However, the connection between hypoxia and hormonal cell signaling pathways is unclear, but such human age-related comorbid diseases do coincide with the middle-aging period of declining sex hormonal signaling. This scoping review evaluates the relevant interdisciplinary evidence to assess the systems biology of function, regulation, and homeostasis in order to discern and decipher the etiology of the connection between hypoxia and hormonal signaling in human age-related comorbid diseases. The hypothesis charts the accumulating evidence to support the development of a hypoxic milieu and oxidative stress-inflammation pathophysiology in middle-aged individuals, as well as the induction of amyloidosis, autophagy, and epithelial-to-mesenchymal transition in aging-related degeneration. Taken together, this new approach and strategy can provide the clarity of concepts and patterns to determine the causes of declining vascularity hemodynamics (blood flow) and physiological oxygenation perfusion (oxygen bioavailability) in relation to oxygen homeostasis and vascularity that cause hypoxia (hypovascularity hypoxia). The middle-aging hypovascularity hypoxia hypothesis could provide the mechanistic interface connecting the endocrine, nitric oxide, and oxygen homeostasis signaling that is closely linked to the progressive conditions of degenerative hypertrophy, atrophy, fibrosis, and neoplasm. An in-depth understanding of these intrinsic biological processes of the developing middle-aged hypoxia could provide potential new strategies for time-dependent therapies in maintaining healthspan for healthy lifestyle aging, medical cost savings, and health system sustainability.

Neuroinflammation and neurodegeneration in diabetic retinopathy

Diabetic retinopathy (DR) is the most common complication of diabetes and has been historically regarded as a microangiopathic disease. Now, the paradigm is shifting toward a more comprehensive view of diabetic retinal disease (DRD) as a tissue-specific neurovascular complication, in which persistently high glycemia causes not only microvascular damage and ischemia but also intraretinal inflammation and neuronal degeneration. Despite the increasing knowledge on the pathogenic pathways involved in DR, currently approved treatments are focused only on its late-stage vasculopathic complications, and a single molecular target, vascular endothelial growth factor (VEGF), has been extensively studied, leading to drug development and approval. In this review, we discuss the state of the art of research on neuroinflammation and neurodegeneration in diabetes, with a focus on pathophysiological studies on human subjects, in vivo imaging biomarkers, and clinical trials on novel therapeutic options.