Retinal neurodegeneration may precede microvascular changes characteristic of diabetic retinopathy in diabetes mellitus

Longitudinal Changes in the Peripapillary Retinal Nerve Fiber Layer Thickness of Patients With Type 2 Diabetes

Importance

Type 2 diabetes is expected to accelerate age-related peripapillary retinal nerve fiber layer (pRNFL) loss, but limited information on the rate of reduction in pRNFL thicknesses in patients with type 2 diabetes is available.

Objective

To investigate longitudinal changes in pRNFL thickness in patients with type 2 diabetes, with or without diabetic retinopathy (DR).

Design, Setting, and Participants

A total of 164 eyes of 63 healthy individuals and 101 patients with type 2 diabetes (49 patients without DR [non-DR group] and 52 patients with mild to moderate nonproliferative DR [NPDR group]) were enrolled in this prospective, longitudinal, observational study from January 2, 2013, through February 27, 2015. Participants were followed up for 3 years, and the peripapillary mean and sector RNFL thicknesses were measured at 1-year intervals. The mean rate of pRNFL loss was estimated using a linear mixed model and compared among the 3 groups. Follow-up was completed on March 16, 2018, and data were analyzed from April 2 through July 27, 2018.

Exposure

Type 2 diabetes.

Main Outcomes and Measures

The rate of reduction in pRNFL thickness in patients with type 2 diabetes.

Results

A total of 164 participants (88 women [53.7%]; mean [SD] age, 58.2 [8.7] years) were included in the study analysis. The mean (SD) age of the control group was 56.5 (9.3) years (39 women [61.9%]); the non-DR group, 59.1 (9.4) years (26 women [53.1%]); and the NPDR group, 59.4 (11.0) years (23 women [44.2%]). Mean (SD) duration of type 2 diabetes was 7.1 (4.4) years in the non-DR group and 13.2 (8.4) years in the NPDR group. The baseline mean (SD) pRNFL thickness was 96.2 (11.0) μm in the control group, 93.5 (6.4) μm in the non-DR group, and 90.4 (7.9) μm in the NPDR group. During 3 years of follow-up, these values decreased to 95.0 (9.2) μm in the control group, 90.3 (6.4) in the non-DR group, and 86.6 (7.9) μm in the NPDR group. In a linear mixed model, the estimated mean pRNFL loss was -0.92 μm/y in the non-DR group (P < .001) and -1.16 μm/y in the NPDR group (P < .001), which was 2.9-fold (95% CI, 1.1-14.8; P = .003) and 3.3-fold (95% CI, 1.4-18.0; P < .001) greater, respectively, than that of the control group (-0.35 μm/y; P = .01).

Conclusions and Relevance

Progressive reduction of pRNFL thickness was observed in healthy controls and patients with type 2 diabetes without and with DR; however, type 2 diabetes was associated with a greater loss of pRNFL regardless of whether DR was present. These findings suggest that pRNFL loss may occur in people with type 2 diabetes even in the absence of DR progression.

Vascular Inflammation Risk Factors in Retinal Disease

Inflammation of the blood vessels that serve the central nervous system has been increasingly identified as an early and possibly initiating event among neurodegenerative conditions such as Alzheimer's disease and related dementias. However, the causal relevance of vascular inflammation to major retinal degenerative diseases is unresolved. Here, we describe how genetics, aging-associated changes, and environmental factors contribute to vascular inflammation in age-related macular degeneration, diabetic retinopathy, and glaucoma. We highlight the importance of mouse models in studying the underlying mechanisms and possible treatments for these diseases. We conclude that data support vascular inflammation playing a central if not primary role in retinal degenerative diseases, and this association should be a focus of future research.

Emerging Insights and Interventions for Diabetic Retinopathy

PURPOSE OF REVIEW

To introduce recent advances in the understanding of diabetic retinopathy and to summarize current and emerging strategies to treat this common and complex cause of vision loss.

RECENT FINDINGS

Advances in retinal imaging and functional analysis indicate that retinal vascular and neural pathologies exist long before the development of clinically visible retinopathy. Such diagnostics could facilitate risk stratification and selective early intervention in high-risk patients. Antagonists of the vascular endothelial growth factor pathway effectively reduce vision loss in diabetes and promote regression of disease severity. Promising new strategies to treat diabetic retinopathy involve novel systemic diabetes therapy and ocular therapies that antagonize angiogenic growth factor signaling, improve blood-retina barrier function and neurovascular coupling, modulate neuroretinal metabolism, or provide neuroprotection. Long considered a pure microvasculopathy, diabetic retinopathy in fact affects the neural and vascular retina as well as neurovascular communication. Emerging therapies include those that target neuroretinal dysfunction in addition to those modulating vascular biology.

Vascular and Neuronal Protection in the Developing Retina: Potential Therapeutic Targets for Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a common retinal disease in preterm babies. To prolong the lives of preterm babies, high oxygen is provided to mimic the oxygen level in the intrauterine environment for postnatal organ development. However, hyperoxia-hypoxia induced pathological events occur when babies return to room air, leading to ROP with neuronal degeneration and vascular abnormality that affects retinal functions. With advances in neonatal intensive care, it is no longer uncommon for increased survival of very-low-birth-weight preterm infants, which, therefore, increased the incidence of ROP. ROP is now a major cause of preventable childhood blindness worldwide. Current proven treatment for ROP is limited to invasive retinal ablation, inherently destructive to the retina. The lack of pharmacological treatment for ROP creates a great need for effective and safe therapies in these developing infants. Therefore, it is essential to identify potential therapeutic agents that may have positive ROP outcomes, especially in preserving retinal functions. This review gives an overview of various agents in their efficacy in reducing retinal damages in cell culture tests, animal experiments and clinical studies. New perspectives along the neuroprotective pathways in the developing retina are also reviewed.

Neurodegeneration in Patients with Type 2 Diabetes Mellitus without Diabetic Retinopathy

Purpose

To evaluate neurodegeneration in patients with type 2 diabetes mellitus (DM2) without diabetic retinopathy and to assess the possible role of systemic vascular complications in retinal changes.

Methods

Sixty eyes of 60 patients with DM2 and without any signs of diabetic retinopathy and 60 eyes of 60 healthy controls underwent retinal evaluation using Spectralis optical coherence tomography. Macular ganglion cell layer (GCL) and retinal nerve fiber layer (RNFL) were evaluated. Peripapillary RNFL thickness was assessed using Glaucoma and Axonal Analytics applications. Comparison between patients with the presence/absence of systemic vascular complications and different disease duration was made.

Results

Macular GCL was reduced in patients compared to controls (p < 0.001). Differences in the macular RNFL thickness were only observed in the outer inferior sector (p=0.033). A reduction in the peripapillary RNFL (average, inferior, and inferotemporal thickness, p < 0.05 for all three) was observed in patients using both applications. Patients with chronic systemic vascular complications presented a reduction in the temporal RNFL (p=0.019) compared to patients without complications. The superotemporal RNFL thickness was thinner in patients with longer disease duration.

Conclusions

Patients with type 2 DM without diabetic retinopathy and good metabolic control present neurodegeneration affecting neurons in the macular area and axons in different sectors of the optic disc. Systemic vascular complications contributed to further axonal damage in these patients, suggesting a possible role of subclinical ischaemia to retinal neurodegeneration in type 2 DM.

Neuroprotective Effects of Ginsenoside Rg1 against Hyperphosphorylated Tau-Induced Diabetic Retinal Neurodegeneration via Activation of IRS-1/Akt/GSK3β Signaling

We have recently demonstrated that tau hyperphosphorylation causes diabetic synaptic neurodegeneration of retinal ganglion cells (RGCs), which might be the earliest affair during the pathogenesis of diabetic retinopathy (DR). Thus, there is a pressing need to seek therapeutic agents possessing neuroprotective effects against tau hyperphosphorylation in RGCs for arresting the progression of DR. Here, using a well-characterized diabetes model of db/db mouse, we discovered that topical ocular application of 10 mg/kg/day of ginsenoside Rg1 (GRg1), one of the major active ingredients extracted from Panax ginseng and Panax notoginseng, ameliorated hyperphosphorylated tau-triggered RGCs synaptic neurodegeneration in diabetic mice. The neuroprotective effects of GRg1 on diabetic retinae were abrogated when retinal IRS-1 or Akt was suppressed by intravitreal injection with si-IRS-1 or topically coadministered with a specific inhibitor of Akt, respectively. However, selective repression of retinal GSK3β by intravitreal administration of si-GSK3β rescued the neuroprotective properties of GRg1 when Akt was inactivated. Therefore, the present study showed for the first time that GRg1 can prevent hyperphosphorylated tau-induced synaptic neurodegeneration of RGCs via activation of IRS-1/Akt/GSK3β signaling in the early phase of DR. Moreover, our data clarify the potential therapeutic significance of GRg1 for neuroprotective intervention strategies of DR.

Longitudinal In Vivo Characterization of the Streptozotocin-Induced Diabetic Mouse Model: Focus on Early Inner Retinal Responses

Purpose

The goal of this study was to perform an extensive temporal characterization of the early pathologic processes in the streptozotocin (STZ)-induced diabetic retinopathy (DR) mouse model, beyond the vascular phenotype, and to investigate the potential of clinically relevant compounds in attenuating these processes.

Methods

Visual acuity and contrast sensitivity (CS) were studied in the mouse STZ model until 24 weeks postdiabetes onset. ERG, spectral domain optical coherence tomography (SD-OCT), leukostasis, and immunohistochemistry were applied to investigate neurodegeneration, inflammation, and gliosis during early-, mid- and late-phase diabetes. Aflibercept or triamcinolone acetonide (TAAC) was administered to investigate their efficacy on the aforementioned processes.

Results

Visual acuity and CS loss started at 4 and 18 weeks postdiabetes onset, respectively, and progressively declined over time. ERG amplitudes were diminished and OP latencies increased after 6 weeks, whereas SD-OCT revealed retinal thinning from 4 weeks postdiabetes. Immunohistochemical analyses linked these findings to retinal ganglion and cholinergic amacrine cell loss at 4 and 8 weeks postdiabetes onset, respectively, which was further decreased after aflibercept administration. The number of adherent leukocytes was augmented after 2 weeks, whereas increased micro- and macroglia reactivity was present from 4 weeks postdiabetes. Aflibercept or TAAC showed improved efficacy on inflammation and gliosis.

Conclusions

STZ-induced diabetic mice developed early pathologic DR hallmarks, from which inflammation seemed the initial trigger, leading to further development of functional and morphologic retinal changes. These findings indicate that the mouse STZ model is suitable to study novel integrative non-vascular therapies to treat early DR.

Retinal thickness as potential biomarker in posterior cortical atrophy and typical Alzheimer's disease

BACKGROUND

Retinal thickness can be measured non-invasively with optical coherence tomography (OCT) and may offer compelling potential as a biomarker for Alzheimer's disease (AD). Retinal thinning is hypothesized to be a result of retrograde atrophy and/or parallel neurodegenerative processes. Changes in the visual pathway are of particular interest in posterior cortical atrophy (PCA), the most common atypical AD phenotype predominantly affecting the parietal-occipital cortices. We therefore evaluated retinal thickness as non-invasive biomarker of neurodegeneration in well-characterized participants with posterior cortical atrophy (PCA) and typical Alzheimer's disease (tAD).

METHODS

Retinal thickness measures were acquired from 48 patient participants (N = 25 PCA; N = 23 tAD) fulfilling consensus diagnostic criteria and 70 age-matched controls. Participants were recruited between 2014 and 2016. All participants underwent optical coherence tomography (OCT) imaging, including measurement of peripapillary retinal nerve fiber layer (pRNFL) thickness and total macular thickness (mRT). Participants did not show evidence of any significant ophthalmological conditions. Subgroup analyses were performed in participants with available MRI and CSF measures, providing evidence of neurodegeneration and underlying AD pathology respectively.

RESULTS

There was no evidence of overall between-group differences in pRNFL thickness (mean PCA 98.7 ± 12.2; tAD 99.9 ± 8.7; controls 99.6 ± 10.0 μm, one-way analysis of variance (ANOVA) p = 0.92) or total mRT (mean PCA 266.9 ± 16.3; tAD 267.8 ± 13.6; controls 269.3 ± 13.6 μm, one-way ANOVA p = 0.75). Similarly, subgroup analysis with MRI biomarkers (PCA = 18, tAD = 17, controls = 31) showing neurodegeneration, and CSF biomarkers (PCA = 18, tAD = 14, controls = 13) supporting underlying AD pathology did not provide evidence of overall between-group differences in pRNFL or mRT measures (all p > 0.3).

CONCLUSIONS

Retinal thickness did not discriminate tAD and PCA from controls or from one another despite unequivocal differences on standard clinical, neuro-imaging and CSF measures. Findings from this well-characterized sample, including cases with PCA, do not support the hypothesis that retinal neurodegeneration, measured using conventional OCT, is a useful biomarker for AD or PCA.

Detailed Evaluation of Possible Ganglion Cell Loss in the Retina of Zucker Diabetic Fatty (ZDF) Rats

A thinning of the inner retina is one of the earliest potential markers of neuroretinal damage in diabetic subjects. The histological background is uncertain; retinal ganglion cell (RGC) loss and changes in the structure or thickness of the inner plexiform layer (IPL) have been suspected. Studies conducted on animal models on RGC pathology gave contradictory results. Hereby we present RGC numbers, distribution patterns and IPL thickness from Zucker Diabetic Fatty (ZDF) rats. After labelling RGCs on retinal whole mounts, isodensity maps were constructed, RGC numbers and distribution patterns analysed using a custom-built algorithm, enabling point-by-point comparison. There was no change in staining characteristics of the antibodies and no significant difference in average RGC densities was found compared to controls. The distribution patterns were also comparable and no significant difference was found in IPL thickness and stratification or in the number of apoptotic cells in the ganglion cell layer (GCL). Our results provide a detailed evaluation of the inner retina and exclude major RGC loss in ZDF rats and suggest that other factors could serve as a potential explanation for inner retinal thinning in clinical studies. Our custom-built method could be adopted for the assessment of other animal or human retinas.

HbA1c and retinal sensitivity in diabetics using microperimetry

PURPOSE

The purpose of this study was to determine the relationship between HbA1c values and retinal sensitivity at central 10° using the MP-1 microperimeter.

METHODS

A prospective study was carried out on 32 healthy subjects (control group) and 60 diabetic patients. The diabetic patients were divided into 2 groups. Group 1 comprised of 30 patients without diabetic retinopathy (DR) and group 2 had 30 patients with mild non-proliferative DR. A full-threshold microperimetry of the central 10° of retina (the macula) was performed on all subjects, utilizing 32 points with the MP-1. The relationship between light sensitivity and HbA1c value was calculated using linear regression analysis.

RESULTS

Total mean sensitivity at 10° for group 1 without DR, group 2 with mild NPDR and control group were 18.67±0.83, 17.98±1.42 and 19.45±0.34 (dB), respectively. There was a significant difference in total mean retinal sensitivity at 10° between the 3 groups (F(2,89)=18.14, p=0.001). A simple linear regression was calculated to predict HbA1c based on retinal sensitivity. A significant regression equation was found (F(1,90)=107.61, p=0.0001, with an R² of 0.545). The linear regression analysis revealed that there was a 0.64dB decline in mean retinal sensitivity within the central 10° diameter with an increase of 1mmHg of HbA1c.

CONCLUSION

Retinal sensitivity at the central 10° of the macula is affected by changes in HbA1c values.

Cone Photoreceptor Dysfunction in Early-Stage Diabetic Retinopathy: Association Between the Activation Phase of Cone Phototransduction and the Flicker Electroretinogram

Purpose

To define the nature and extent of cone photoreceptor abnormalities in diabetic individuals who have mild or no retinopathy by assessing the activation phase of cone phototransduction and the flicker ERG in these individuals.

Methods

Light-adapted single-flash and flicker ERGs were recorded from 20 diabetic individuals who have no clinically apparent retinopathy (NDR), 20 diabetic individuals who have mild nonproliferative diabetic retinopathy (NPDR), and 20 nondiabetic, age-equivalent controls. A-waves elicited by flashes of different retinal illuminance were fit with a delayed Gaussian model to derive R_mp3 (maximum amplitude of the massed photoreceptor response) and S (phototransduction sensitivity). Fundamental amplitude and phase of ERGs elicited by full-field sinusoidal flicker were obtained across a frequency range of 6 to 100 Hz.

Results

ANVOA indicated that both diabetic groups had significant S losses compared with the controls, whereas mean R_mp3 did not differ significantly among the groups. ANOVA also indicated significantly reduced flicker ERG amplitude for frequencies ≥56 Hz for both diabetic groups compared with the controls. Flicker ERG timing (phase) did not differ significantly among the groups. Log R_mp3 + log S was significantly correlated with the patients' high-frequency (62.5 Hz) flicker ERG amplitude loss (r = 0.69, P < 0.001).

Conclusions

The delayed Gaussian a-wave model is useful for characterizing abnormalities in the activation phase of cone phototransduction and can help explain flicker ERG abnormalities in early-stage diabetic retinopathy. Reduced cone sensitivity and attenuated high-frequency flicker ERGs provide evidence for impaired cone function in these individuals.

Correlation between corneal and retinal neurodegenerative changes and their association with microvascular perfusion in type II diabetes

PURPOSE

The pathophysiology of diabetic neurodegeneration and microvasculopathy remains controversial. Neurosensory layer thickness and corneal nerve fibre loss represent potential biomarkers of neuropathy. The purpose of this cross-sectional study was to determine the correlation between these neurodegenerative features and their association with retinal microvascular integrity in patients with type II diabetes without retinopathy.

METHODS

Nerve fibre length (NFL), density (NFD) and branch density (NBD) were assessed using corneal confocal microscopy. Spectralis optical coherence tomography (OCT) was used for peripapillary retinal nerve fibre layer (RNFL), and macular RNFL, ganglion cell (GCL), inner plexiform (IPL) and inner nuclear layer (INL) thicknesses. Parafoveal vessel density (PVD) was determined using OCT angiography.

RESULTS

We analysed 118 eyes of 61 patients. Peripapillary RNFL, macular RNFL, GCL, IPL and INL were 101 ± 8, 29 ± 3, 43 ± 4, 36 ± 3 and 36 ± 3 μm. NFL, NFD and NBD were 12.3 ± 4.4 mm/mm² , 17.8 ± 7.4/mm² and 26.7 ± 15.2/mm² . Corneal nerve fibre variables were neither associated with inner retinal thicknesses nor PVD. A significant positive correlation was found between macular GCL, IPL and peripapillary RNFL with deep capillary plexus PVD (p ≤ 0.05).

CONCLUSION

Our results indicate that corneal and retinal neurodegeneration are independent changes early in type II diabetes and that distinct retinal, but not corneal neurodegenerative features, are associated with retinal microvascular perfusion.

Disorganization of Retinal Inner Layers (DRIL) and Neuroretinal Dysfunction in Early Diabetic Retinopathy

Purpose

To elucidate the relationship between disorganization of retinal inner layers (DRILs) and retinal function in diabetic patients without diabetic retinopathy (DR) and with nonproliferative DR, but without diabetic macular edema (DME).

Methods

Fifty-seven participants with diabetes mellitus (DM) and 18 healthy controls underwent comprehensive ophthalmic examination, fundus photography, and spectral-domain optical coherence tomography. Scans of the fovea were evaluated for the presence of DRIL. Retinal function was evaluated using Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity, the quick contrast sensitivity function (qCSF) on the AST Sentio Platform, short-wavelength automated perimetry (SWAP), standard automated perimetry (SAP), and frequency doubling perimetry (FDP). ANOVA and Kruskal-Wallis were used to compare retinal function in subjects with and without DRIL. Tukey-Kramer test and Wilcoxon were used for post hoc analysis.

Results

DRIL was identified in 9 of 57 diabetic subjects. DRIL subjects had higher body mass index and longer diabetes duration compared to diabetic subjects without DRIL (P = 0.03 and P = 0.009, respectively). Subjects with DRIL had reduced ETDRS visual acuity (P = 0.003), contrast sensitivity function (P = 0.0003), and SAP performance (PSD, P < 0.0001) compared to controls and diabetic subjects without DRIL. Structural analysis revealed inner retinal thinning, and some outer retinal thinning, associated with DRIL.

Conclusions

Diabetic subjects with DRIL have reduced retinal function compared to those without DRIL, and defective retinal lamination may be an early cellular consequence of diabetes responsible for this in some patients. Following further longitudinal studies, DRIL may be a readily available and reliable structural biomarker for reduced retinal function in early diabetic neuroretinal disease.

Attenuating Diabetic Vascular and Neuronal Defects by Targeting P2rx7

Retinal vascular and neuronal degeneration are established pathological features of diabetic retinopathy. Data suggest that defects in the neuroglial network precede the clinically recognisable vascular lesions in the retina. Therefore, new treatments that target early-onset neurodegeneration would be expected to have great value in preventing the early stages of diabetic retinopathy. Here, we show that the nucleoside reverse transcriptase inhibitor lamivudine (3TC), a newly discovered P2rx7 inhibitor, can attenuate progression of both neuronal and vascular pathology in diabetic retinopathy. We found that the expression of P2rx7 was increased in the murine retina as early as one month following diabetes induction. Compared to non-diabetic controls, diabetic mice treated with 3TC were protected against the formation of acellular capillaries in the retina. This occurred concomitantly with a maintenance in neuroglial function, as shown by improved a- and b-wave amplitude, as well as oscillatory potentials. An improvement in the number of GABAergic amacrine cells and the synaptophysin-positive area was also observed in the inner retina of 3TC-treated diabetic mice. Our data suggest that 3TC has therapeutic potential since it can target both neuronal and vascular defects caused by diabetes.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Morphology of Inner Retina in Rhesus Monkeys of Various Ages: A Comparative Study

Purpose

To investigate the changes of thickness in each layer, the morphology and density of inner neurons in rhesus monkeys' retina at various growth stages, thus contribute useful data for further biological studies.

Methods

The thickness of nerve fiber layer (NFL), the whole retina, inner plexiform layer (IPL), and outer plexiform layer (OPL) of rhesus monkeys at different ages were observed with hematoxylin and eosin (H&E) staining. The morphology and the density of inner neurons of rhesus monkey retina were detected by immunofluorescence.

Results

The retina showed the well-known ten layers, the thickness of each retinal layer in rhesus monkeys at various ages increased rapidly after infant, and the retina was the thickest in adulthood, but the retinal thickness stop growing in senescent. Quantitative analysis showed that the maximum density of inner neurons was reached in adolescent, and then, the density of inner neurons decreased in adults and senescent retinas. And some changes in the morphology of rod bipolar cells have occurred in senescent.

Conclusions

The structure of retina in rhesus monkeys is relatively immature at infant, and the inner retina of rhesus monkeys is mature in adolescent, while the thickness of each retinal layer was the most developed in the adult group. There was no significant change in senescence for the thickness of each retinal layer, but the number of the neurons in our study has a decreasing trend and the morphological structure has changed.

Multimodal Imaging of the Initial Stages of Diabetic Retinopathy: Different Disease Pathways in Different Patients

The objective of this study was to evaluate the prevalence of different disease pathways (ischemia, neurodegeneration, and edema) in the initial stages of diabetic retinopathy. In this retrospective cross-sectional study, eyes were grouped by diabetic retinopathy severity using the 7-field Early Treatment Diabetic Retinopathy Study (ETDRS) protocol (levels 10-20, 35, and 43-47). Neurodegeneration was identified by thinning of the retinal nerve fiber layer and/or ganglion cell layer. Edema was identified by thickening of the inner nuclear layer, outer plexiform layer, or full retina. Ischemia was identified by metrics of retinal vessel density. Imaging was performed in 142 eyes from 142 patients (28% women) aged 52-88 years. Vessel density (ischemia) was significantly different between the ETDRS groups (P < 0.020). On multivariate regression analysis, it remained significantly different between stages of the disease and showed associations with age (P < 0.001), sex (P = 0.028), and metabolic control (P = 0.034). No significant differences between ETDRS groups were found in retinal thinning (neurodegeneration) or retinal thickness (edema). Eyes with the same ETDRS retinopathy grading from different patients with diabetes showed that the prevalence of different disease pathways varies between patients, even within the same severity group. Ischemia (capillary dropout) is the only disease pathway that shows correlation with retinopathy severity and metabolic control.

Retinal Neurodegeneration as an Early Manifestation of Diabetic Eye Disease and Potential Neuroprotective Therapies

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is a major cause of visual impairment and blindness throughout the world. Microvascular changes have long been regarded central to disease pathogenesis. In recent years, however, retinal neurodegeneration is increasingly being hypothesized to occur prior to the vascular changes classically associated with DR and contribute to disease pathogenesis.

RECENT FINDINGS

There is growing structural and functional evidence from human and animal studies that suggests retinal neurodegeneration to be an early component of DR. Identification of new therapeutic targets is an ongoing area of research with several different molecules undergoing testing in animal models for their neuroprotective properties and for possible use in humans. Retinal neurodegeneration may play a central role in DR pathogenesis. As new therapies are developed, it will be important to develop criteria for clinically defining retinal neurodegeneration. A standardization of the methods for monitoring neurodegeneration along with more sensitive means of detecting preclinical damage is also needed.

Proteomic Analysis of Early Diabetic Retinopathy Reveals Mediators of Neurodegenerative Brain Diseases

Purpose

Current evidence suggests that retinal neurodegeneration is an early event in the pathogenesis of diabetic retinopathy. Our main goal was to examine whether, in the diabetic human retina, common proteins and pathways are shared with brain neurodegenerative diseases.

Methods

A proteomic analysis was performed on three groups of postmortem retinas matched by age: nondiabetic control retinas (n = 5), diabetic retinas without glial activation (n = 5), and diabetic retinas with glial activation (n = 5). Retinal lysates from each group were pooled and run on an SDS-PAGE gel. Bands were analyzed sequentially by liquid chromatography-mass spectrometry (LC/MS) using an Orbitrap Mass Spectrometer.

Results

A total of 2190 proteins were identified across all groups. To evaluate the association of the identified proteins with neurological signaling, significant signaling pathways belonging to the category “Neurotransmitters and Other Nervous System Signaling” were selected for analysis. Pathway analysis revealed that “Neuroprotective Role of THOP1 in Alzheimer's Disease” and “Unfolded Protein Response” pathways were uniquely enriched in control retinas. By contrast, “Dopamine Degradation” and “Parkinson's Signaling” were enriched only in diabetic retinas with glial activation. The “Neuregulin Signaling,” “Synaptic Long Term Potentiation,” and “Amyloid Processing” pathways were enriched in diabetic retinas with no glial activation.

Conclusions

Diabetes-induced retinal neurodegeneration and brain neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases, share common pathogenic pathways. These findings suggest that the study of neurodegeneration in the diabetic retina could be useful to further understand the neurodegenerative processes that occur in the brain of persons with diabetes.

Cone photoreceptor density in type I diabetic patients measured with an adaptive optics retinal camera

Purpose: To assess the variation in cone photoreceptor density on the basis of age compatibility between healthy subjects, on one side, and type 1 diabetic patients with no diabetic retinopathy, on the other. Methods: A high resolution adaptive optics retinal camera in flood illumination regime was employed to image cones of 15 type I diabetic patients and 16 healthy controls. For each subject we scanned the cone mosaic in 4 perifoveal areas (nasally, temporally, superiorly and inferiorly) at 2, 3 and 4 degrees eccentricity. The impact of diabetes duration, gender and age were evaluated. Results: In the type I diabetic group we found a meaningful lower cone density (p<0.05), except for the temporal meridian at 2 and 4 degrees eccentricity. Moreover, a significant asymmetry of cone photoreceptor densities was proved between the horizontal and vertical meridians in both diabetic and control groups. Conclusion: The rtx1 retinal image evaluation demonstrated photoreceptors loss in DM1 diabetic patients prior to any clinical changes. Abbreviations: AO = adaptive optics, SS = swept source, OCT = optical coherence tomography, BCVA= best corrected visual acuity, DM = diabetes mellitus, DR = diabetic retinopathy.

Early Detection of Microvascular Changes in Patients with Diabetes Mellitus without and with Diabetic Retinopathy: Comparison between Different Swept-Source OCT-A Instruments

Optical coherence tomography angiography (OCT-A) has recently improved the ability to detect subclinical and early clinically visible microvascular changes occurring in patients with diabetes mellitus (DM). The aim of the present study is to evaluate and compare early quantitative changes of macular perfusion parameters in patients with DM without DR and with mild nonproliferative DR (NPDR) evaluated by two different swept-source (SS) OCT-A instruments using two scan protocols (3 × 3 mm and 6 × 6 mm). One hundred eleven subjects/eyes were prospectively evaluated: 18 healthy controls (control group), 73 eyes with DM but no DR (no-DR group), and 20 eyes with mild NPDR (DR group). All quantitative analyses were performed using ImageJ and included vessel and perfusion density, area and circularity index of the FAZ, and vascular complexity parameters. The agreement between methods was assessed according to the method of Bland-Altman. A significant decrease in the majority of the considered parameters was found in the DR group versus the controls with both instruments. The results of Bland-Altman analysis showed the presence of a systemic bias between the two instruments with PLEX Elite providing higher values for the majority of the tested parameters when considering 6 × 6 mm angiocubes and a less definite difference in 3 × 3 mm angiocubes. In conclusion, this study documents early microvascular changes occurring in the macular region of patients at initial stages of DR, confirmed with both SS OCT-A instruments. The fact that early microvascular alterations could not be detected with one instrument does not necessarily mean that these alterations are not actually present, but this could be an intrinsic limitation of the device itself. Further, larger longitudinal studies are needed to better understand microvascular damage at very early stages of diabetic retinal disease and to define the strengths and weaknesses of different OCT-A devices.

Diabetic Retinopathy-An Underdiagnosed and Undertreated Inflammatory, Neuro-Vascular Complication of Diabetes

Diabetes mellitus is a world-wide epidemic and diabetic retinopathy, a devastating, vision-threatening condition, is one of the most common diabetes-specific complications. Diabetic retinopathy is now recognized to be an inflammatory, neuro-vascular complication with neuronal injury/dysfunction preceding clinical microvascular damage. Importantly, the same pathophysiologic mechanisms that damage the pancreatic β-cell (e.g., inflammation, epigenetic changes, insulin resistance, fuel excess, and abnormal metabolic environment), also lead to cell and tissue damage causing organ dysfunction, elevating the risk of all complications, including diabetic retinopathy. Viewing diabetic retinopathy within the context whereby diabetes and all its complications arise from common pathophysiologic factors allows for the consideration of a wider array of potential ocular as well as systemic treatments for this common and devastating complication. Moreover, it also raises the importance of the need for methods that will provide more timely detection and prediction of the course in order to address early damage to the neurovascular unit prior to the clinical observation of microangiopathy. Currently, treatment success is limited as it is often initiated far too late and after significant neurodegeneration has occurred. This forward-thinking approach of earlier detection and treatment with a wider array of possible therapies broadens the physician's armamentarium and increases the opportunity for prevention and early treatment of diabetic retinopathy with preservation of good vision, as well the prevention of similar destructive processes occurring among other organs.

The Association of CEP135 rs4865047 and NPY2R rs1902491 Single Nucleotide Polymorphisms (SNPs) with Rapid Progression of Proliferative Diabetic Retinopathy in Patients with Type 1 Diabetes Mellitus

Background

Diabetic retinopathy has a varied prevalence, severity, and rate of progression. The aim of this study was to determine whether the single nucleotide polymorphisms (SNPs) of the gene encoding a 135-kD centrosomal protein CEP135 rs4865047 and the gene encoding the type 2 NPY protein NPY2R rs1902491 were associated with the development of rapidly progressive proliferative diabetic retinopathy in patients with type 1 diabetes mellitus.

Material/Methods

Patients with rapidly progressive proliferative diabetic retinopathy (n=48) were included in the study group. The control group (n=84) consisted of diabetes mellitus patients who had no proliferative diabetic retinopathy up to 15 years of diabetes duration. The reference group (n=90) included non-diabetic individuals who matched the study group by age and gender. The SNPs in the three groups were analyzed using real-time polymerase chain reaction (PCR) amplification.

Results

The analysis of the distribution of genotypes in CEP135 rs4865047 and NPY2R rs1902491 detected significant differences only in the single nucleotide polymorphism rs4865047 genotype between the case and control group in comparison to the reference group. The co-dominant model showed that CEP135 rs4865047 was significantly associated with patients with rapidly progressive proliferative diabetic retinopathy (OR 7.2, 95% CI, 2.28–22.74, p=0.001). No significant association was found for the NPY2R SNP rs1902491 genotype.

Conclusions

Our study reports a significant association of the CEP135 single nucleotide polymorphism rs4865047 genotype with rapidly progressive proliferative diabetic retinopathy and the control group. No significant association was found of the NPY2R single nucleotide polymorphism rs1902491 genotype.

Longitudinal Relationship Between Retinal Diabetic Neurodegeneration and Progression of Diabetic Retinopathy in Patients With Type 2 Diabetes

PURPOSE

To investigate the longitudinal relationship between diabetic retinal neurodegeneration and the progression of diabetic retinopathy (DR) by measuring macular ganglion cell-inner plexiform layer (mGCIPL) thickness in patients with type 2 diabetes (T2DM).

DESIGN

Retrospective cohort study.

METHODS

T2DM patients with no DR or mild nonproliferative DR (NPDR) followed up for ≥4 years were included in this study. DR was graded according to retinal photography, and mean parafoveal mGCIPL thickness was measured using optical coherence tomography with at least a 6-month interval from baseline. Hazard ratios (HR) for predicting 2-step progression and development of proliferative DR (PDR) were calculated using Cox proportional hazard modeling using baseline clinical factors.

RESULTS

Of 87 eyes of T2DM patients, 39 (44.8%) exhibited 2-step DR progression and 6 (6.9%) experienced progression to PDR. Patients with DR progression exhibited longer T2DM duration, thinner mGCIPL, greater mGCIPL thinning rate, severe cardiac autonomic neuropathy (CAN), lower peripheral nerve-conduction velocity, and higher glycated hemoglobin A1c level. Multivariate regression modeling revealed that baseline mGCIPL thickness (HR = 0.94), mGCIPL thinning rate (HR = 1.924), CAN score (HR = 1.248), and conduction velocity of peripheral nerves (HR = 0.894) were significant predictive factors for DR progression (area under the curve = 0.92).

CONCLUSION

Progressive loss of mGCIPL is an independent risk factor for progression in early-stage DR. Further assessment of autonomic and peripheral nerve functions can increase sensitivity in predicting aggravation of DR in patients with T2DM.

Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model

The aim of this study was to evaluate whether damage to the neurovascular unit in diabetes depends on reactive metabolites such as methylglyoxal (MG), and to assess its impact on retinal gene expression. Male Wistar rats were supplied with MG (50 mM) by drinking water and compared with age-matched streptozotocin-diabetic animals and untreated controls. Retinal damage was evaluated for the accumulation of MG-derived advanced glycation end products, changes in hexosamine and PKC pathway activation, microglial activation, vascular alterations (pericyte loss and vasoregression), neuroretinal function assessed by electroretinogram, and neurodegeneration. Retinal gene regulation was studied by microarray analysis, and transcription factor involvement was identified by upstream regulator analysis. Systemic application of MG by drinking water increased retinal MG to levels comparable with diabetic animals. Elevated retinal MG resulted in MG-derived hydroimidazolone modifications in the ganglion cell layer, inner nuclear layer, and outer nuclear layer, a moderate activation of the hexosamine pathway, a pan-retinal activation of microglia, loss of pericytes, increased formation of acellular capillaries, decreased function of bipolar cells, and increased expression of the crystallin gene family. MG mimics important aspects of diabetic retinopathy and plays a pathogenic role in microglial activation, vascular damage, and neuroretinal dysfunction. In response to MG, the retina induces expression of neuroprotective crystallins.-Schlotterer, A., Kolibabka, M., Lin, J., Acunman, K., Dietrich, N., Sticht, C., Fleming, T., Nawroth, P., Hammes, H.-P. Methylglyoxal induces retinopathy-type lesions in the absence of hyperglycemia: studies in a rat model.

GSK3β-mediated tau hyperphosphorylation triggers diabetic retinal neurodegeneration by disrupting synaptic and mitochondrial functions

Background

Although diabetic retinopathy (DR) has long been considered as a microvascular disorder, mounting evidence suggests that diabetic retinal neurodegeneration, in particular synaptic loss and dysfunction of retinal ganglion cells (RGCs) may precede retinal microvascular changes. Key molecules involved in this process remain poorly defined. The microtubule-associated protein tau is a critical mediator of neurotoxicity in Alzheimer’s disease (AD) and other neurodegenerative diseases. However, the effect of tau, if any, in the context of diabetes-induced retinal neurodegeneration has yet to be ascertained. Here, we investigate the changes and putative roles of endogeneous tau in diabetic retinal neurodegeneration.

Methods

To this aim, we combine clinically used electrophysiological techniques, i.e. pattern electroretinogram and visual evoked potential, and molecular analyses in a well characterized high-fat diet (HFD)-induced mouse diabetes model in vivo and primary retinal ganglion cells (RGCs) in vitro.

Results

We demonstrate for the first time that tau hyperphosphorylation via GSK3β activation causes vision deficits and synapse loss of RGCs in HFD-induced DR, which precedes retinal microvasculopathy and RGCs apoptosis. Moreover, intravitreal administration of an siRNA targeting to tau or a specific inhibitor of GSK3β reverses synapse loss and restores visual function of RGCs by attenuating tau hyperphosphorylation within a certain time frame of DR. The cellular mechanisms by which hyperphosphorylated tau induces synapse loss of RGCs upon glucolipotoxicity include i) destabilizing microtubule tracks and impairing microtubule-dependent synaptic targeting of cargoes such as mRNA and mitochondria; ii) disrupting synaptic energy production through mitochondria in a GSK3β-dependent manner.

Conclusions

Our study proposes mild retinal tauopathy as a new pathophysiological model for DR and tau as a novel therapeutic target to counter diabetic RGCs neurodegeneration occurring before retinal vasculature abnormalities.

Electronic supplementary material

The online version of this article (10.1186/s13024-018-0295-z) contains supplementary material, which is available to authorized users.

Correlation of retinal neurodegeneration with measures of peripheral autonomic neuropathy in type 1 diabetes

Purpose

To evaluate the relationship of neuroretinal layer thickness with sensitive measures of cardiovascular autonomic neuropathy in diabetic patients with non‐proliferative diabetic retinopathy (NPDR).

Methods

Twenty‐seven eyes of 27 patients with type 1 diabetes presenting with mild‐to‐moderate NPDR were compared to 27 healthy control (HC) eyes matched for age and gender. The total macular volume (TMV) and the volumes of individual neurosensory layers in the macula were analysed from spectral domain optical coherence tomography using automated layer segmentation. Cardiovascular autonomic regulation was assessed by short‐term power spectrum analysis of heart rate variability (HRV) before, during and after an orthostatic challenge.

Results

The patients had an age of 46 ± 12 years and diabetes since 28 ± 9 years. Diastolic and mean arterial pressure was lower in the patients compared to HCs. TMV (r = 0.58, p = 0.002), inner plexiform layer volume (IPLV; r = 0.39, p = 0.047) and inner nuclear layer volume (INLV; r = 0.60, p = 0.001) were associated with reduced recovery of low‐frequency (LF) spectral power of HRV after orthostatic load in diabetic patients but not in HCs. The response of LF spectral power during the orthostatic manoeuvre was blunted in patients compared to HCs (p = 0.02). Diabetes duration was negatively associated with TMV and INLV, whereas IPLV was significantly reduced in eyes with moderate NPDR compared to HCs.

Conclusion

The results indicate a correlation between inner retinal tissue loss and diminished autonomic regulation in type 1 diabetic patients with mild‐to‐moderate NPDR. The observed changes can be interpreted as congruent early signs of retinal and systemic neuropathy in diabetes.

Vitreous and intraretinal macular changes in diabetic macular edema with and without tractional components

Diabetic macular edema (DME) is still one of the main causes of visual impairment. Repeated intravitreal injections of ranibizumab are considered the gold standard treatment, but the efficacy in patients with prominent cystic characteristics remains uncertain. In diabetic retinas, the identification of both antero-posterior and, particularly, tangential tractions is crucial to prevent misdiagnosis of tractional and refractory DME, and therefore to prevent poor treatment outcomes. The treatment of tractional DME with anti-VEGF injections could be poorly effective due to the influence of a tractional force. Pars plana vitrectomy (PPV) is a surgical procedure that has been widely used in the treatment of diffuse and refractory DME. Anatomical improvement, although stable and immediate, did not result in visual improvement. PPV with internal limiting membrane (ILM) peeling for the treatment of non-tractional DME in patients with prominent cysts (> 390 μm) causes subfoveal atrophy, defined as "floor effect". Epiretinal tangential forces and intraretinal change evaluation by SD-OCT of non-tractional DME are essential for determining appropriate management.

Alterations in the polysialylated neural cell adhesion molecule and retinal ganglion cell density in mice with diabetic retinopathy

AIM

To investigate the impact of polysialylated neural cell adhesion molecule (PSA-NCAM) on the survival of retinal ganglion cells (RGCs) in the experimentally induced diabetes in mice.

METHODS

Diabetes was induced in 2.5 months old Swiss Webster mice by intraperitoneal injection of streptozotocin (STZ, 90 mg/kg) once daily for two consecutive days. Examination of the proteins of interest in the retinas from diabetic mice at 2mo after diabetes induction was performed using immunohistochemistry and Western blot analysis. RGCs were counted in the wholemounted retinas, and Brn3a marker was used.

RESULTS

Examination of retinas from diabetic mice at 2mo after diabetes induction revealed a considerable reduction in RGC density. Our experiments also demonstrated a redistribution of PSA-NCAM in the retina of diabetic animals. PSA-NCAM immunoreactivity was diminished in the inner part of the retina where RGCs were located. In contrast, an enhanced PSA-NCAM immunoreactivity was detected in the outer layers of the retina. PSA-NCAM signal was co-localized with glial fibrillary acidic protein immunoreactivity in the Müller cell branches. Previous studies have shown that matrix metalloproteinase-9 (MMP-9) is responsible for the reduction in PSA-NCAM levels in neuronal cells. The reduced levels of PSA-NCAM in inner layers (nerve fiber layer, ganglion cell layer) were accompanied by the increased expression of MMP-9. In contrast, in the outer retinal layers, the expression of MMP-9 was much less pronounced.

CONCLUSION

MMP-9 induces PSA-NCAM shedding in the inner part of the retina and the decreased level of PSA-NCAM in the inner part of the retina might be, at least in part, responsible for the loss of RGCs in diabetic mice.

Molecular Mechanisms Mediating Diabetic Retinal Neurodegeneration: Potential Research Avenues and Therapeutic Targets

Diabetic retinopathy (DR) is a devastating complication of diabetes with a prevalence rate of 35%, and no effective treatment options. Since the most visible clinical features of DR are microvascular irregularities, therapeutic interventions often attempt to reduce microvascular injury, but only after permanent retinal damage has ensued. However, recent data suggests that diabetes initially affects retinal neurons, leading to neurodegeneration as an early occurrence in DR, before onset of the more noticeable vascular abnormalities. In this review, we delineate the sequence of initiating events leading to retinal degeneration in DR, considering neuronal dysfunction as a primary event. Key molecular mechanisms and potential biomarkers associated with retinal neuronal degeneration in diabetes are discussed. In addition to glial reactivity and inflammation in the diabetic retina, the contribution of neurotrophic factors, cell adhesion molecules, apoptosis markers, and G protein signaling to neurodegenerative pathways warrants further investigation. These studies could complement recent developments in innovative treatment strategies for diabetic retinopathy, such as targeting retinal neuroprotection, promoting neuronal regeneration, and attempts to re-program other retinal cell types into functional neurons. Indeed, several ongoing clinical trials are currently attempting treatment of retinal neurodegeneration by means of such novel therapeutic avenues. The aim of this article is to highlight the crucial role of neurodegeneration in early retinopathy progression, and to review the molecular basis of neuronal dysfunction as a first step toward developing early therapeutic interventions that can prevent permanent retinal damage in diabetes. ClinicalTrials.gov: NCT02471651, NCT01492400.

Pathophysiology of Diabetic Retinopathy: The Old and the New

Vision loss in diabetic retinopathy (DR) is ascribed primarily to retinal vascular abnormalities-including hyperpermeability, hypoperfusion, and neoangiogenesis-that eventually lead to anatomical and functional alterations in retinal neurons and glial cells. Recent advances in retinal imaging systems using optical coherence tomography technologies and pharmacological treatments using anti-vascular endothelial growth factor drugs and corticosteroids have revolutionized the clinical management of DR. However, the cellular and molecular mechanisms underlying the pathophysiology of DR are not fully determined, largely because hyperglycemic animal models only reproduce limited aspects of subclinical and early DR. Conversely, non-diabetic mouse models that represent the hallmark vascular disorders in DR, such as pericyte deficiency and retinal ischemia, have provided clues toward an understanding of the sequential events that are responsible for vision-impairing conditions. In this review, we summarize the clinical manifestations and treatment modalities of DR, discuss current and emerging concepts with regard to the pathophysiology of DR, and introduce perspectives on the development of new drugs, emphasizing the breakdown of the blood-retina barrier and retinal neovascularization.

Different contributions of autophagy to retinal ganglion cell death in the diabetic and glaucomatous retinas

Diabetes mellitus and glaucoma are the two major causes of selective retinal ganglion cell (RGC) death. To determine the relationship between autophagy and RGC death, we compared autophagy and the related molecular pathways in diabetic and glaucomatous retinas and examined their effect on RGC survival. Biochemical analysis of microtubule-associated protein light chain 3 (LC3)-II and beclin-1 were observed. To determine the pathways involved in autophagy induction, adenosine monophosphate-activated protein kinase (AMPK) and the mechanistic target of rapamycin (mTOR) were also explored. Beclin-1 and the LC3B-II to LC3B-I ratio significantly elevated at 4 and 8 weeks after glaucoma induction; however, only a slight increase was apparent in the diabetic retina. Significant upregulation of phosphorylated AMPK and downregulation of phosphorylated mTOR was evident in the diabetic retina. After autophagy was inhibited with 3-methyladenine (3-MA), apoptosis of RGCs was significantly increased in the diabetic retinas. However, 3-MA inhibition of autophagy decreased the apoptosis of RGCs in glaucomatous retinas. Therefore, our results suggest that RGC death is differentially regulated by autophagy and that the pathways involved differ depending on the triggering injury.

Short-Term Administration of Astaxanthin Attenuates Retinal Changes in Diet-Induced Diabetic Psammomys obesus

OBJECTIVES

Psammomys obesus is a high-fat diet (HFD)-fed animal model of obesity and type 2 diabetes recently explored as a model of non-proliferative diabetic retinopathy. This study tested the protective effect of the pigment astaxanthin (AST) in the P. obesus diabetic retina.

METHODS

Young adult P. obesus were randomly assigned to two groups. The control group received a normal diet consisting of a plant-based regimen, and the HFD group received an enriched laboratory chow. After 3 months, control and diabetic rodents were administered vehicle or AST, daily for 7 days. Body weight, blood glucose, and plasma pentosidine were assessed. Frozen sections of retinas were immunolabeled for markers of oxidative stress, glial reactivity and retinal ganglion cell bodies, and imaged by confocal microscopy.

RESULTS

Retinal tissue from AST-treated control and HFD-diabetic P. obesus showed a greater expression of the antioxidant enzyme heme oxygenase-1 (HO-1). In retinas of HFD-diabetic AST-treated P. obesus, cellular retinaldehyde binding protein and glutamine synthetase in Müller cells were more intense compared to the untreated HFD-diabetic group. HFD-induced diabetes downregulated the expression of glial fibrillary acidic protein in astrocytes, the POU domain protein 3A in retinal ganglion cells, and synaptophysin throughout the plexiform layers.

DISCUSSION

Our results show that type 2-like diabetes induced by HFD affected glial and neuronal retinal cell homeostasis. AST treatment induced the antioxidant enzyme HO-1 and reduced glial reactivity. These findings suggest that diabetic P. obesus is a useful model of HFD-induced obesity and diabetes to evaluate early neuroglial retinal alterations and antioxidant neuroprotection mechanisms in DR.

Neurodegeneration in diabetic retinopathy: does it really matter?

The concept of diabetic retinopathy as a microvascular disease has evolved, in that it is now considered a more complex diabetic complication in which neurodegeneration plays a significant role. In this article we provide a critical overview of the role of microvascular abnormalities and neurodegeneration in the pathogenesis of diabetic retinopathy. A special emphasis is placed on the pathophysiology of the neurovascular unit (NVU), including the contributions of microvascular and neural elements. The potential mechanisms linking retinal neurodegeneration and early microvascular impairment, and the effects of neuroprotective drugs are summarised. Additionally, we discuss how the assessment of retinal neurodegeneration could be an important index of cognitive status, thus helping to identify individuals at risk of dementia, which will impact on current procedures for diabetes management. We conclude that glial, neural and microvascular dysfunction are interdependent and essential for the development of diabetic retinopathy. Despite this intricate relationship, retinal neurodegeneration is a critical endpoint and neuroprotection, itself, can be considered a therapeutic target, independently of its potential impact on microvascular disease. In addition, interventional studies targeting pathogenic pathways that impact the NVU are needed. Findings from these studies will be crucial, not only for increasing our understanding of diabetic retinopathy, but also to help to implement a timely and efficient personalised medicine approach for treating this diabetic complication.

Efficacy comparison of intravitreal injections of conbercept and ranibizumab for severe proliferative diabetic retinopathy

OBJECTIVE

To determine the efficacy of preoperative intravitreal injections of conbercept (IVC) and ranibizumab (IVR) on postoperative best-corrected visual acuity (BCVA), vitreous hemorrhage (VH), and neovascular glaucoma (NVG) in a population with proliferative diabetic retinopathy (PDR) undergoing vitrectomy.

DESIGN

Retrospective, cross-sectional study.

PARTICIPANTS

386 patients with severe PDR (428 eyes).

METHODS

The patients who did not receive IVC or IVR were assigned to group A (125 eyes), the patients who received IVR (0.5 mg) were assigned to group B (146 eyes), and the patients who received IVC (0.5 mg) were assigned to group C (157 eyes).

RESULTS

Both group B (p = 0.009) and group C (p = 0.002) had better postoperative BCVA than group A. Early postoperative VH occurred significantly less frequently in group B (22.60%; p = 0.007) and group C (12.10%; p < 0.001) than in group A (37.60%). Importantly, the incidences of postoperative NVG in group B (2.74%; p = 0.001) and group C (0.64%; p < 0.001) were both significantly less than that in group A (15.20%). However, there was no significant difference in the incidences of postoperative NVG between groups B and C (p = 0.325).

CONCLUSIONS

The contribution of preoperative IVC to an improved BCVA for patients with severe PDR was better than that of IVR, and IVC decreased the risk of postoperative early VH. Pretreatment with IVC or IVR reduced the incidence of postoperative NVG based on the 24-month follow-up data.

Plate-based Large-scale Cultivation of Caenorhabditis elegans: Sample Preparation for the Study of Metabolic Alterations in Diabetes

Culturing Caenorhabditis elegans (C. elegans) in a large-scale manner on agar plates can be time-consuming and difficult. This protocol describes a simple and inexpensive method to obtain a large number of animals for the isolation of proteins to proceed with a western blot, mass spectrometry, or further proteomics analyses. Furthermore, an increase of nematode numbers for immunostainings and the integration of multiple analyses under the same culturing conditions can easily be achieved. Additionally, a transfer between plates with different experimental conditions is facilitated. Common techniques in plate culture involve the transfer of a single C. elegans using a platinum wire and the transfer of populated agar chunks using a scalpel. However, with increasing nematode numbers, these techniques become overly time-consuming. This protocol describes the large-scale culture of C. elegans including numerous steps to minimize the impact of the sample preparation on the physiology of the worm. Fluid and shear stress can alter the lifespan of and metabolic processes in C. elegans, thus requiring a detailed description of the critical steps in order to retrieve reliable and reproducible results. C. elegans is a model organism, consisting of neuronal cells for up to one-third, but lacking blood vessels, thus providing the possibility to investigate solely neuronal alterations independent of vascular control. Recently, early neurodegeneration in diabetic retinopathy was found prior to vascular alterations. Thus, C. elegans is of special interest for studying general mechanisms of diabetic complications. For example, an increased formation of advanced glycation end products (AGEs) and reactive oxygen species (ROS) is observed, which are reproducibly found in C. elegans. Protocols to handle samples of adequate size for a broader spectrum of investigations are presented here, exemplified by the study of diabetes-induced biochemical alterations. In general, this protocol can be useful for studies requiring large C. elegans numbers and in which liquid culture is not suitable.

Confocal microscopy of corneal nerve plexus as an early marker of eye involvement in patients with type 2 diabetes

PURPOSE

To measure the thickness and length of corneal nerves and the peri-papillary retinal nerve fiber layer (RNFL) thickness in patients recently diagnosed with diabetes mellitus (DM).

METHODS

Twenty-two eyes of 22 patients recently diagnosed with type 2 DM and 22 eyes of 22 healthy individuals were consecutively enrolled. Central corneal sensitivity was measured using a Cochet-Bonnet esthesiometer, and corneal nerve length (CNL) and thickness (CNT) were evaluated through in vivo confocal microscopy. The confocal images were examined using software that could semi-automatically trace the corneal nerve pathway. Spectral domain optical coherence tomography (SD-OCT) was performed to quantify the overall and sectorial RNFL thickness.

RESULTS

Mean DM duration was 3.5 ± 1.7 months, whereas the mean glycemia and HbA1c levels were 180.5 ± 73.13 mg/dl and 8.6 ± 1.7% (65.2 ± 19.7 mmol/mol), respectively. Corneal sensation threshold was significantly lower in the DM group compared to control group (p = 0.003). CNL and CNT were reduced in the DM group (p = 0.043 and p = 0.004, respectively). Significant correlations were found between CNT and HbA1c levels (p = 0.04; r = -0.47), and between CNT and the corneal sensation threshold (p = 0.04; r = 0.69). RNFL thickness was significantly reduced in the temporal quadrants, but no correlation was found with CNT and CNL changes (p > 0.05).

CONCLUSIONS

CNL and CNT changes are evident even in the early stages of DM, and RNFL reduction was recorded in the temporal quadrants. These findings indicate that, in the eye with diabetes, neuropathy may represent an early marker of the disease.

Lack of Galectin-3 attenuates neuroinflammation and protects the retina and optic nerve of diabetic mice

Diabetic retinopathy is the leading cause of acquired blindness in working-age individuals. Recent work has revealed that neurodegeneration occurs earlier than vascular insult and that distal optic nerve damage precedes retinal degeneration and vascular insult. Since we have shown that optic nerve degeneration is reduced after optic nerve crush in Galectin-3 knockout (Gal-3 -/-) mice, we decided to investigate whether Gal-3 -/- could relieve inflammation and preserve both neurons and the structure of the retina and optic nerve following 8 weeks of diabetes. Diabetes was induced in 2-month-old male C57/bl6 WT or Gal-3 -/- mice by a single injection of streptozotocin (160 mg/kg). Histomorphometric retinal analyses showed no gross difference, except for a reduced number of retinal ganglion cells in WT diabetic mice, correlated to increased apoptosis. In the optic nerve, Gal-3 -/- mice showed reduced neuroinflammation, suggested by the smaller number of Iba1+ cells, particularly the amoeboid profiles in the distal end. Furthermore, iNOS staining was reduced in the optic nerves of Gal-3 -/- mice, as well as GFAP in the distal segment of the optic nerve. Finally, optic nerve histomorphometric analyses revealed that the number of myelinated fibers was higher in the Gal-3 -/- mice and myelin was more rectilinear compared to WT diabetic mice. Therefore, the present study provided evidence that Gal-3 is a central target that stimulates neuroinflammation and impairs neurological outcomes in visual complications of diabetes. Our findings provide support for the clinical use of Gal-3 inhibitors against diabetic visual complications in the near future.

Neural dysfunction and retinopathy in persons with type 1 diabetes

OBJECTIVE

To determine associations of microvascular and neuropathic complications of diabetes cross-sectionally and longitudinally in persons with long-term type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

Persons receiving care for T1D in South Central Wisconsin were identified in 1979-1980 and examined approximately every 5 years. Associations between neuropathic and microvascular complications were examined at most prior visits, when information on several neuropathic complications was collected. Temporal relationships were examined by modeling incidence between examinations across the visits.

RESULTS

Adjusting for duration of diabetes, glycated hemoglobin, and systolic blood pressure, the following were cross-sectionally associated with prevalent PDR (proliferative diabetic retinopathy): the presence of sensory neuropathy (SN) as reported at each Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) examination (odds ratio (OR) = 2.76, confidence interval (CI) = 1.71, 4.48) and the heartrate variability measures RMSD (square root of the mean of squared differences of successive RR intervals) (OR = 0.24, CI = 0.16, 0.37) and SDNN (standard deviation of successive RR intervals) (OR = 0.26, CI = 0.17, 0.39). Findings were similar for prevalent ME (macular edema) as assessed from spectral-domain optical coherence tomography (SD-OCT). The presence of PDR (OR = 2.13, CI = 1.63, 2.78) and ME (OR = 2.36, CI = 1.66, 3.34) were both significantly associated with incident WESDR SN. WESDR SN was associated with incident PDR (OR = 1.53, CI = 1.09, 2.15) but not incident ME (OR = 1.31, CI = 0.92, 1.87).

CONCLUSIONS

Sensory neuropathy and heartrate variability were significantly associated with prevalent PDR and ME in people with long-term T1D. PDR and ME were significantly associated with incident sensory neuropathy, and sensory neuropathy was significantly associated with incident PDR. Studies using earliest detectable markers of microvascular and neurologic abnormalities are needed to determine which of the two systems 'fails' first. Such information might suggest a temporal sequence of diabetes complications.

Diabetic Retinopathy: Pathophysiology and Treatments

Diabetic retinopathy (DR) is the most common complication of diabetes mellitus (DM). It has long been recognized as a microvascular disease. The diagnosis of DR relies on the detection of microvascular lesions. The treatment of DR remains challenging. The advent of anti-vascular endothelial growth factor (VEGF) therapy demonstrated remarkable clinical benefits in DR patients; however, the majority of patients failed to achieve clinically-significant visual improvement. Therefore, there is an urgent need for the development of new treatments. Laboratory and clinical evidence showed that in addition to microvascular changes, inflammation and retinal neurodegeneration may contribute to diabetic retinal damage in the early stages of DR. Further investigation of the underlying molecular mechanisms may provide targets for the development of new early interventions. Here, we present a review of the current understanding and new insights into pathophysiology in DR, as well as clinical treatments for DR patients. Recent laboratory findings and related clinical trials are also reviewed.

Loss-of-function mutation of serine racemase attenuates retinal ganglion cell loss in diabetic mice

Consistent results suggest the promoting roles of serine racemase (SR)/D-serine in retinal neurodegeneration in diabetic retinopathy (DR). However, the direct evidence connecting SR deficiency with retinal neuroprotection in genetic model of diabetes mellitus has not been reported. In this investigation, we explore the effect of absence of functional SR on the degeneration of retinal ganglion cells (RGCs) with a diabetic murine model, Ins2^Akita mice. We established a murine strain with double mutation, termed Ins2^Akita-Srr, by mating heterozygous Ins2^Akita mice with homozygous Srr^ochre269 mice. Ins2^Akita retained less RGC in posterior, middle, and peripheral retinae than the counterpart from non-diabetic sibling mice at the age of five or seven months. Ins2^Akita-Srr mice retained more RGC in middle and peripheral--but not in posterior-- retinae than the counterpart from Ins2^Akita sibling mice at the age of five months. By contrast, at the age of seven months, Ins2^Akita-Srr mice contained more RGC in peripheral, middle, and posterior retinae than the counterpart from Ins2^Akita. RGCs were identified with retrograde labeling in vivo or with immunolabeling against a RGC-specific transcription factor, Brn3a, in retinal flat mounts. Correspondingly, the aqueous humor of Ins2^Akita-Srr contained less amount of D-serine than sibling Ins2^Akita mice. Thus, SR deficiency significantly prevented RGC loss in diabetic mice. We conclude that D-serine is a critical factor in the degeneration of RGC in DR. Targeting SR expression or activity may be a strategy for ameliorating RGC loss in DR.

Alpha-1-antitrypsin ameliorates inflammation and neurodegeneration in the diabetic mouse retina

Diabetic retinopathy (DR) is the most common cause of blindness in the working age population. Early events of DR are accompanied by neurodegeneration of the inner retina resulting in ganglion cell loss. These findings together with reduced retinal thickness are observed within the first weeks of experimental DR. Besides, an inflammatory process is triggered in DR in which the innate immune response plays a relevant role. Alpha 1 antitrypsin (AAT), an inhibitor of serine proteases, has shown anti-inflammatory properties in several diseases. We aimed at evaluating the use of AAT to prevent the early changes induced by DR. Diabetic AAT-treated mice showed a delay on ganglion cell loss and retinal thinning. These animals showed a markedly reduced inflammatory status. AAT was able to preserve systemic and retinal TNF-α level similar to that of control mice. Furthermore, retinal macrophages found in the AAT-treated diabetic mouse exhibited M2 profile (F4/80⁺CD206⁺) together with an anti-inflammatory microenvironment. We thus demonstrated that AAT-treated mice show less retinal neurodegenerative changes and have reduced levels of systemic and retinal TNF-α. Our results contribute to shed light on the use of AAT as a possible therapeutic option in DR.

Intraretinal changes in idiopathic versus diabetic epiretinal membranes after macular peeling

Introduction

Epiretinal traction is not responsible only for epiretinal but also intraretinal changes. This study aims to describe structural and vascular intraretinal changes after macular peeling in idiopathic (iERM) vs diabetic ERM (dERM).

Methods

We conducted a prospective interventional study on forty-two eyes, 23 with iERMs and 19 with dERMs, undergoing ERM-ILM peeling. We performed SD-OCT preoperatively, 1 and 6 months postoperatively to assess central macular thickness (CMT), intraretinal cysts (IC) and/or continuous ectopic inner foveal layers (CEIFL), superficial and deep capillary free zone (CFZ) area on OCT-A. Glial fibrillary acidic protein (GFAP), as a Müller cells marker, was detected immunohistochemically on ILM specimens, to assess Müller cells iatrogenic damage.

Results

The CEIFLs were significantly more common in iERMs (12 (52.2%) in iERMs vs 2 (10.5%) in dERMs, p = 0.004), whereas ICs in dERMs (6 (26.1%) in iERMs vs 17 (89.5%) in dERMs, p<0.001). Median preoperative and postoperative BCVA was 20/50 [20/40-20/66] and 20/33 [20/25-20/40] in iERMs and 20/100 [20/66-20/200] and 20/50 [20/50-20/66] in dERMs, respectively. Median preoperative and postoperative CMT was 423 [370–488] and 364 [329–382] μm in iERM group and 465 [447–503] and 378 [359–433] μm in dERM group, respectively. The BCVA improvement and reduction of CMT thickness were significant in both groups (p<0.001). The presence of CEIFL was associated with lower BCVA in iERMs. Deep CFZ network significantly increased only in dERMs, passing from 0.34 [0.29–0.42] mm² preoperatively to 0.56 [0.46–0.6] mm² at 6-month follow-up (p<0.001). The GFAP expression was significantly higher in dERMs (p = 0.001).

Conclusion

The intraretinal changes are different in iERMs and dERMs, as increased expression of CEIFLs in iERMs vs ICs in dERMs. The CEIFLs are associated with worse anatomical and functional outcomes in iERMs, whereas GFAP espression in peeled ILMs is higher in dERMs.

The effect of fenofibrate on early retinal nerve fiber layer loss in type 2 diabetic patients: a case-control study

BACKGROUND

Previous studies suggested that use of fenofibrate could significantly reduce the rate of progression into diabetic retinopathy (DR), and that retinal nerve fiber layer (RNFL) loss, which has been considered an important indicator for retinal neurodegeneration, might precede microvascular changes. The aim of this study was to assess the effect(s) of fenofibrate on RNFL thickness at early stage of DR in patients with type 2 diabetes mellitus (DM).

METHODS

In this retrospective matched case-control study we included a cohort of 89 patients with type 2 DM, aged 40 or above, between Jan 1, 2017 and March 31, 2017. Among the subjects, 48 patients received fenofibrate therapy and the other 41 patients did not receive fenofibrate treatment. We defined use of fenofibrate as the presence of any prescription for fenofibrate within 1 year before or any time after the diagnosis of DM, and all the patients had either no DR or non-proliferative diabetic retinopathy (NPDR). The fibrate users were well matched with non-fenofibrate users for gender, age and axial length. The RNFL thickness in all quadrants of both eyes was examined with spectral domain optical coherence tomography (SD-OCT). The multiple linear regression analysis was used to assess the association of RNFL thickness with potential risk factors of DR other than fenofibrate use.

RESULTS

The non-fenofibrate users had significantly reduced RNFL thickness of the superior quadrant of the right eye compared to the fenofibrate users (t = 2.384, P = 0.019). On the contrary, BMI (p = 0.034) and ACR (p = 0.024) were both negatively correlated to the RNFL thickness of the right eye.

CONCLUSION

Oral administration of fenofibrate was suggestively associated with thicker RNFL in superior quadrant of the right eye of patents with early DR.