Visual and anatomic outcomes of sustained single agent anti-VEGF treatment versus double anti-VEGF switching in the treatment of persistent diabetic macular edema

Histopathology and electron microscopy evaluation of the sildenafil effect on diabetic rats' retinae

PURPOSE

Although there is increasing evidence that phosphodiesterase-5 (PDE-5) inhibitors modify the effect of diabetes on different tissues, its effect on diabetic retinopathy is not well studied.

METHODS

Forty male Sprague-Dawley (SD) rats were divided into four groups: group I = control group that received no treatment; group II (diabetic group), in which diabetes was induced by a single streptozotocin injection; group III (sildenafil small dose, SSD), in which diabetes was similarly introduced (however, rats received daily oral 1 mg/kg sildenafil citrate (SC) for 3 months); and group IV (sildenafil large dose, SLD), which was as in group 3, but SC was 2.5 mg/kg. After 3 months, globes were removed and retinae were dissected; one globe from each rat was examined by light microscopy (LM), and the other by electron microscopy (EM).

RESULTS

In contrast to the control group, diabetic rats in group II demonstrated well-established diabetic changes in the form of capillary congestion, decreased cell population, hyaline changes of capillary walls, and degenerated nerve fiber layer by LM. Similarly, EM demonstrated photoreceptor degeneration, mitochondrial cristolysis, and vacuolated depleted cells among other features in group II. These diabetic features were less prominent in group III and nearly absent in group IV.

CONCLUSION

SC use in the early stages of DR may prevent/delay diabetic retinopathy development or progression in diabetic rat models, an effect that seems to be dose-related.

Chronic sildenafil citrate use decreases retinal vascular endothelial growth factor expression in diabetic rats: a pilot study

BACKGROUND

Sildenafil citrate (SC) attenuates endothelial dysfunction. However, its effects on diabetic retinopathy (DR), which is mainly a microvascular disease, remain unclear. Vascular endothelial growth factor (VEGF) is known to be a critical mediator of DR. Therefore, we investigated the effects of SC on diabetic retina by measuring VEGF levels.

METHODS

In this study, twenty-eight rats were divided into the following groups: group I, the control group; group II, rats with streptozotocin-induced diabetes; group III, rats with streptozotocin-induced diabetes receiving daily oral sildenafil at 1 mg/kg; and group IV, rats with streptozotocin-induced diabetes receiving high-dose daily sildenafil at 2.5 mg/kg. After 3 months, VEGF was measured in the retina specimen in one eye and the vitreous body in the other eye by immunohistochemistry and enzyme-linked immunosorbent assay, respectively.

RESULTS

We found that VEGF expression in the retina was low in all rats from groups I and IV and in 30% of rats from group III; 80% of rats in group II demonstrated high VEGF expression in the retinae (P < 0.001). VEGF concentrations in the vitreous body samples were 32 ± 2, 61 ± 4, 44 ± 5, and 36 ± 3 pg/l in groups I-IV, respectively (P < 0.001).

CONCLUSION

VEGF decreased significantly in the eyes of diabetic rats after chronic oral sildenafil citrate treatment. SC may have a modifying/attenuating effect on DR. However, further studies are needed to evaluate its use as an adjunctive treatment.

Persistent diabetic macular edema: Definition, incidence, biomarkers, and treatment methods

Intravitreal antivascular endothelial growth factor (anti-VEGF) treatment has drastically improved the visual and anatomical outcomes in patients with diabetic macular edema (DME); however, success is not always guaranteed, and a proportion of these eyes demonstrate persistent DME (pDME) despite intensive treatment. While standardized criteria to define these treatment-resistant eyes have not yet been established, many studies refer to eyes with no clinical response or an unsatisfactory partial response as having pDME. A patient is considered to have pDME if the retinal thickness improves less than 10-25% after 6 months of treatment. A range of treatment options have been recommended for eyes with pDME, including switching anti-VEGF agents, using corticosteroids and/or antioxidant drugs in adjunct with anti-VEGF therapy, and vitrectomy. In addition, multimodal imaging of DME eyes may be advantageous in predicting the responsiveness to treatment; this is beneficial when initiating alternative therapies. We explore the literature on persistent DME regarding its defining criteria, incidence, the baseline biological markers that may be useful in anticipating the response to treatment, and the available treatment options.

Real Life Multicenter Comparison of 24-Month Outcomes of Anti-VEGF Therapy in Diabetic Macular Edema in Turkey: Ranibizumab vs. Aflibercept vs. Ranibizumab-Aflibercept Switch

The aim of this study was to compare the outcomes of diabetic macular edema (DME) treated with aflibercept (AFB) or ranibizumab (RNB) only, and after switching from RNB to AFB. This was a retrospective, real-world, multicenter (7 cities) 24 month study. Overall, 212 eyes in the AFB group, 461 in the RNB group, and 141 in the RNB to AFB group were included. The primary endpoints were differences in visual acuity (VA) and central macular thickness (CMT) from baseline to the final visit. The secondary outcomes were the percentage of eyes that achieved ≥10 letters gain and ≥10 letters loss in vision at month 12 and 24, and the percentage of eyes that achieved a thinning of ≥20% in CMT at month 3 and month 6. The results showed that VA did not significantly differ at baseline (AFB: 0.62 ± 0.38, RNB: 0.61 ± 0.36, RNB to AFB: 0.61 ± 0.38), at checkpoints, or at the final visit (AFB: 0.46 ± 0.38, RNB: 0.5 ± 0.37, RNB to AFB: 0.53 ± 0.36) (p > 0.05). Though the mean CMT at baseline was significantly thicker in the RNB to AFB group (479 ± 129.6 μm) when compared to the AFB (450.5 ± 122.6 μm) and RNB (442 ± 116 μm) groups (p < 0.01), similar measurements were obtained after 12 months. The percentages of eyes that gained or lost ≥10 letters in the AFB, RNB, and RNB to AFB groups at year 1 and 2 were similar, as was the percentages of eyes that demonstrated ≥20% CMT thinning at month 3 and 6. Our study showed similar visual improvements in non-switchers (AFB and RNB groups) and switchers (RNB to AFB group) through 2 years follow-up, however, AFB patients required fewer injections, visits, or need for additional treatments.

Efficacy and safety of intravitreal anti-VEGF therapy in diabetic retinopathy: what we have learned and what should we learn further?

INTRODUCTION

Diabetic retinopathy (DR) is one of the most frequent microvascular complications of diabetes that can lead to blindness. Laser treatment has been the gold standard treatment for diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR) for many years. Recently, the role of vascular endothelial growth factor (VEGF) has been established in the pathogenesis of DR, and the use of intravitreal anti-VEGF therapy has gained popularity for the management of DR.

AREAS COVERED

This review includes a brief overview of the efficacy and safety of currently available (bevacizumab, ranibizumab, and aflibercept) and potential future (brolucizumab, faricimab, and KSI-301) anti-VEGF agents in patients with DR based mainly on publicly available data from phase 1, 2 and 3 clinical trials.

EXPERT OPINION

Clinical trials investigating the efficacy of intravitreal bevacizumab, ranibizumab, and aflibercept injections demonstrated favorable functional and anatomical outcomes in patients with DME. Moreover, the use of these anti-VEGF agents showed a significant improvement in the severity of DR. Recent clinical research for future anti-VEGF molecules aims to provide higher target-protein binding affinity and prolonged therapeutic effect. Brolucizumab, faricimab, and KSI-301 are three novel anti-VEGF agents that demonstrate promising data for the management of DME and potentially DR.

Role of Angiopoietin-Tie axis in vascular and lymphatic systems and therapeutic interventions

The Angiopoietin (Ang)-Tyrosine kinase with immunoglobulin-like and EGF-like domains (Tie) axis is an endothelial cell-specific ligand-receptor signaling pathway necessary for vascular and lymphatic development. The Ang-Tie axis is involved in regulating angiogenesis, vascular remodeling, vascular permeability, and inflammation to maintain vascular quiescence. Disruptions in the Ang-Tie axis are involved in many vascular and lymphatic system diseases and play an important role in physiological and pathological vascular conditions. Given recent advances in the Ang-Tie axis in the vascular and lymphatic systems, this review focuses on the multiple functions of the Ang-Tie axis in inflammation-induced vascular permeability, vascular remodeling, atherosclerosis, ocular angiogenesis, tumor angiogenesis, and metastasis. A summary of relevant therapeutic approaches to the Ang-Tie axis, including therapeutic antibodies, recombinant proteins and small molecule drugs are also discussed. The purpose of this review is to provide new hypotheses and identify potential therapeutic strategies based on the Ang-Tie signaling axis for the treatment of vascular and lymphatic-related diseases.

Impact of Injection Protocol Selection by Retina Specialists on Clinical Outcomes in Patients with Diabetic Macular Edema

Intravitreal anti-VEGF injections are the current gold standard for treating diabetic macular edema (DME). However, injection practice patterns of retina specialists have varied markedly based on physician discretion. This retrospective study analyzes the impact of injection protocol selection on change in best-corrected visual acuity (BCVA) and central macular thickness (CMT) in 170 eyes treated by 4 retina specialists practicing a pro re nata (PRN) strategy between 2010 and 2020. DME patients received an average of 7.25 injections every 6.24 weeks over 56.6 weeks. There were significant differences between retina specialists in mean number of injections (p = 0.0001) and mean length of treatment (p = 0.0007) but not in mean interval between injections. Over the treatment period, average change in BCVA was −0.053 logMAR, and average change in CMT was −51.1 µm, neither of which had significant differences between retina specialists. BCVA and CMT at initial visit were found to be significantly associated with improved BCVA and CMT over the treatment period (p < 0.001). Number of injections administered and interval between injections were not found to be significant factors affecting change in BCVA or CMT. Despite significant differences in injection dosing regimen, retina specialists achieved similar outcomes in change in BCVA and CMT over the treatment period.

Mean macular intercapillary area in eyes with diabetic macular oedema after anti-vascular endothelial growth factor therapy and its association with treatment response

BACKGROUND

To evaluate the changes in the mean macular intercapillary area (ICA) from sequential enface optical coherence tomography angiography (OCTA) images following intravitreal anti-vascular endothelial growth factor (VEGF) therapy in initially treatment-naïve eyes with diabetic macular oedema (DME).

METHODS

In this multicentre retrospective study, 6 × 6 and 3 × 3 mm customised, total retinal projection enface OCTA images were collected and processed for quantitative assessment of ICA by a customised MATLAB software. Measurements were done in concentric regions centred on the fovea-with the exclusion of foveal avascular zone (FAZ)-in 0.5 mm diameter increments as well as within the intervening rings.

RESULTS

In this study, 6 × 6 mm OCTA images from 46 eyes of 29 patients, and 3 × 3 mm OCTA images from 23 eyes of 15 patients were included. There was no significant change in mean ICA after treatment in either scan size or in any measurement regions (all p > 0.05). Multivariate analysis revealed that baseline BCVA was significantly correlated with the visual outcome (p = 0.039). Additionally, after correction for age, baseline central retinal thickness (CRT), baseline BCVA, and retinopathy severity, mean ICA in the 1.5 mm circle was found to be a significant predictor of post treatment CRT, (p = 0.006).

CONCLUSIONS

Absence of significant change in mean ICA after a minimum of three intravitreal anti-VEGF injections, may indicate that, in the short term, anti-VEGF injections neither impair nor improve macular perfusion in DME. Baseline BCVA was found to be a robust predictor of functional outcome, while inner mean ICA was a significant predictor for macular thickness outcomes.

Angiopoietin/Tie2 signalling and its role in retinal and choroidal vascular diseases: a review of preclinical data

The angopoietin/tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Ang/Tie) pathway is an emerging key regulator in vascular development and maintenance. Its relevance to clinicians and basic scientists as a potential therapeutic target in retinal and choroidal vascular diseases is highlighted by recent preclinical and clinical evidence. The Ang/Tie pathway plays an important role in the regulation of vascular stability, in angiogenesis under physiological and pathological conditions, as well as in inflammation. Under physiological conditions, angiopoietin-1 (Ang-1) binds to and phosphorylates the Tie2 receptor, leading to downstream signalling that promotes cell survival and vascular stability. Angiopoietin-2 (Ang-2) is upregulated under pathological conditions and acts as a context-dependent agonist/antagonist of the Ang-1/Tie2 axis, causing vascular destabilisation and sensitising blood vessels to the effects of vascular endothelial growth factor-A (VEGF-A). Ang-2 and VEGF-A synergistically drive vascular leakage, neovascularisation and inflammation, key components of retinal vascular diseases. Preclinical evidence suggests that modulating the Ang/Tie pathway restores vascular stabilisation and reduces inflammation. This review discusses how targeting the Ang/Tie pathway or applying Ang-2/VEGF-A combination therapy may be a valuable therapeutic strategy for restoring vascular stability and reducing inflammation in the treatment of retinal and choroidal vascular diseases.