Differential systemic gene expression profile in patients with diabetic macular edema: responders versus nonresponders to standard treatment

Adverse effects of CXCR2 deficiency in mice reared under non-gnotobiotic conditions

The family of pro-inflammatory and pro-angiogenic chemokines including Interleukin-8 (IL-8, aka CXCL8) and its homologues (CXCL1,2,3,5,6, and 7) exhibit promiscuous binding and activation of several G-protein-coupled receptors (i.e., CXCR2, CXCR1, and the atypical chemokine receptor (ACKR1)). A high proportion of their biological activity is attributed to CXCR2 activation, thus many CXCR2 inhibitors are in clinical trials for several chronic diseases. However, CXCR2 inhibition is often only investigated acutely in these trials or in Cxcr2-/- mice grown in gnotobiotic conditions. Since humans do not live in germ-free environments, our first goal is to highlight novel retinal and systemic observations in Cxcr2-/- mice grown in non-gnotobiotic conditions that suggest potential harmful consequences of long-term CXCR2 deficiency or blockade. Beyond confirmation of circulating blood/immune cell-related phenotypes, we report novel findings in Cxcr2-/- mice including: (1) delayed dye transit to the retinal vasculature, (2) alterations in the density and distribution of retinal vessels, astrocytes and microglia, (3) decreased electroretinogram a- and b-wave amplitudes, (4) reduced visual acuity, and (5) increased polymorphonuclear cell accumulation in vascular lumina abutting venular walls in the retina and in vital non-ocular tissues (lung and liver). Furthermore, PheWAS of CXCR2 CXCR1, and ACKR1 gene variants using data from UK Biobank participants suggest clinical associations with both retinal and vascular disease phenotypes. We conclude that chronic CXCR2 deficiency in mice contributes to functional damage to the retina and that the long-term safety of CXCR1/2 inhibitors designed for chronic use in humans should be explored before clinical adoption to safeguard sight and overall vascular health.

DNA methyltransferase expression (DNMT1, DNMT3a and DNMT3b) as a potential biomarker for anti-VEGF diabetic macular edema response

PURPOSE

DNA methylation is involved in Diabetic Retinopathy progression showing a metabolic memory mechanism. However, the association of DNA methyltransferase with diabetic macular edema is still unknown. We aimed to describe the differences in DNA methyltransferase gene expression in patients with different diabetic macular edema responses.

METHODS

A total of 27 diabetic patients, aged 59-90 years, were prospectively enrolled in this cross-sectional study. The participants were classified into control group (CG, n = 11), diabetic macular edema responders (rDME, n = 9) and non-responder diabetic macular edema (nrDME, n = 7) after anti-vascular endothelial growth factor (anti-VEGF) treatment. Only cases with a complete ophthalmological examination, digital 133° color fundus, and SD-OCT assessments were used. After RNA extraction and first-strand cDNA synthesis, quantitative real-time PCR was performed with specific primers on the CFX Connect™ Real-Time PCR Detection System to assess differential transcriptional expression patterns.

RESULTS

The DNMT1 gene showed a positive correlation (r = 0.617; p = 0.043) with Best Corrected Visual Acuity (BCVA) in CG, a positive correlation (r = 0.917; p = 0.010) with HbA1c in nrDME and a negative correlation (r = -0.659; p = 0.049) with GCL-IPL thickness in rDME. DNMT3A gene showed a positive correlation (r = -0.890; p = 0.001) with Sub-foveal Choroidal thickness in rDME whereas DNMT3b gene showed a negative correlation (r = -0.815; p = 0.007) with HbA1c and RNFL (r = -0.664; p = 0.026) in CG.

CONCLUSIONS

Patients with similar metabolic profile risk factors showed associated DNA methyltransferase transcriptional expression patterns differences fitting with the anti-VEGF diabetic macular edema response. Further studies are needed to clarify if these results (1) reflect disease evolution, (2) translate the therapeutic impact, (3) or can help to predict the therapeutic resistance profile.

Genome-wide association study of the response of patients with diabetic macular edema to intravitreal Anti-VEGF injection

Diabetic macular edema (DME), a complication of diabetes mellitus, is a leading cause of adult-onset blindness worldwide. Recently, intravitreal anti-VEGF injection has been used as a first-line treatment. This study analyzed the association between the genetic profile of patients with DME and their response to treatment. Intravitreal anti-VEGF injections were administered monthly for three months to Korean patients diagnosed with DME, who were classified into two groups depending on whether they responded to anti-VEGF therapy or showed recurrence within six months. Peripheral blood samples were used for genetic analyses. Genome-wide association analysis results sowed that the genes DIRC3 on chromosome 2 (rs16857280, p = 1.2 × 10^-6), SLCO3A1 on chromosome 15 (rs12899055, p = 2.5 × 10^-6), and RAB2A on chromosome 8 (rs2272620, p = 4.6 × 10^-6) were associated with treatment response to intravitreal anti-VEGF injection. SLC35F1, TMEM132D, KIAA0368, HPCAL1, IGF2BP3, SPN2S, COL23A1, and CREB5 were also related to treatment response (p < 5.0 × 10^-5). Using the KEGG pathway analysis, RAB2A and CREB5 were found to be associated with AMPK signaling related to VEGF (p = 0.018). The identified genetic biomarkers can elucidate the factors affecting patient response to intravitreal anti-VEGF injection and help select appropriate therapeutic strategy.

Identifying Genetic Biomarkers Predicting Response to Anti-Vascular Endothelial Growth Factor Injections in Diabetic Macular Edema

Intraocular anti-vascular endothelial growth factor (VEGF) therapies are the front-line treatment for diabetic macular edema (DME); however, treatment response varies widely. This study aimed to identify genetic determinants associated with anti-VEGF treatment response in DME. We performed a genome-wide association study on 220 Australian patients with DME treated with anti-VEGF therapy, genotyped on the Illumina Global Screening Array, and imputed to the Haplotype Reference Consortium panel. The primary outcome measures were changes in central macular thickness (CMT in microns) and best-corrected visual acuity (BCVA in ETDRS letters) after 12 months. Association between single nucleotide polymorphism (SNP) genotypes and DME outcomes were evaluated by linear regression, adjusting for the first three principal components, age, baseline CMT/BCVA, duration of diabetic retinopathy, and HbA1c. Two loci reached genome-wide significance (p < 5 × 10−8) for association with increased CMT: a single SNP on chromosome 6 near CASC15 (rs78466540, p = 1.16 × 10−9) and a locus on chromosome 12 near RP11-116D17.1 (top SNP rs11614480, p = 2.69 × 10−8). Four loci were significantly associated with reduction in BCVA: two loci on chromosome 11, downstream of NTM (top SNP rs148980760, p = 5.30 × 10−9) and intronic in RP11-744N12.3 (top SNP rs57801753, p = 1.71 × 10−8); one near PGAM1P1 on chromosome 5 (rs187876551, p = 1.52 × 10−8); and one near TBC1D32 on chromosome 6 (rs118074968, p = 4.94 × 10−8). In silico investigations of each locus identified multiple expression quantitative trait loci and potentially relevant candidate genes warranting further analysis. Thus, we identified multiple genetic loci predicting treatment outcomes for anti-VEGF therapies in DME. This work may potentially lead to managing DME using personalized treatment approaches.

Amine oxidase copper-containing 3 (AOC3) inhibition: a potential novel target for the management of diabetic retinopathy

Background

Diabetic retinopathy (DR), a microvascular complication of diabetes, is the leading cause of visual impairment in people aged 20–65 years and can go undetected until vision is irreversibly lost. There is a need for treatments for non-proliferative diabetic retinopathy (NPDR) which, in comparison with current intravitreal (IVT) injections, offer an improved risk–benefit ratio and are suitable for the treatment of early stages of disease, during which there is no major visual impairment. Efficacious systemic therapy for NPDR, including oral treatment, would be an important and convenient therapeutic approach for patients and physicians and would reduce treatment burden. In this article, we review the rationale for the investigation of amine oxidase copper-containing 3 (AOC3), also known as semicarbazide-sensitive amine oxidase and vascular adhesion protein 1 (VAP1), as a novel target for the early treatment of moderate to severe NPDR. AOC3 is a membrane-bound adhesion protein that facilitates the binding of leukocytes to the retinal endothelium. Adherent leukocytes reduce blood flow and in turn rupture blood vessels, leading to ischemia and edema. AOC3 inhibition reduces leukocyte recruitment and is predicted to decrease the production of reactive oxygen species, thereby correcting the underlying hypoxia, ischemia, and edema seen in DR, as well as improving vascular function.

Conclusion

There is substantial unmet need for convenient, non-invasive treatments targeting moderately severe and severe NPDR to reduce progression and preserve vision. The existing pharmacotherapies (IVT corticosteroids and IVT anti-vascular endothelial growth factor-A) target inflammation and angiogenesis, respectively. Unlike these treatments, AOC3 inhibition is predicted to address the underlying hypoxia and ischemia seen in DR. AOC3 inhibitors represent a promising therapeutic strategy for treating patients with DR and could offer greater choice and reduce treatment burden, with the potential to improve patient compliance.

Endothelial Cells Derived From Patients With Diabetic Macular Edema Recapitulate Clinical Evaluations of Anti-VEGF Responsiveness Through the Neuronal Pentraxin 2 Pathway

Diabetic macular edema (DME) remains a leading cause of vision loss worldwide. DME is commonly treated with intravitreal injections of vascular endothelial growth factor (VEGF)-neutralizing antibodies. VEGF inhibitors (anti-VEGFs) are effective, but not all patients fully respond to them. Given the potential side effects, inconvenience, and high cost of anti-VEGFs, identifying who may not respond appropriately to them and why is essential. Herein we determine first the response to anti-VEGFs, using spectral-domain optical coherence tomography scans obtained from a cohort of patients with DME throughout the 1st year of treatment. We found that fluid fully cleared at some time during the 1st year in 28% of eyes ("full responders"); fluid cleared only partly in 66% ("partial responders"); and fluid remained unchanged in 6% ("nonresponders"). To understand this differential response, we generated induced pluripotent stem cells (iPSCs) from full responders and nonresponders, from subjects with diabetes but no DME, and from age-matched volunteers without diabetes. We differentiated these iPSCs into endothelial cells (iPSC-ECs). Monolayers of iPSC-ECs derived from patients with diabetes showed a marked and prolonged increase in permeability upon exposure to VEGF; the response was significantly exaggerated in iPSC-ECs from nonresponders. Moreover, phosphorylation of key cellular proteins in response to VEGF, including VEGFR2, and gene expression profiles, such as that of neuronal pentraxin 2, differed between full responders and nonresponders. In this study, iPSCs were used in order to predict patients' responses to anti-VEGFs and to identify key mechanisms that underpin the differential outcomes observed in the clinic. This approach identified NPTX2 as playing a significant role in patient-linked responses and as having potential as a new therapeutic target for DME.

Bradykinin 1 Receptor Antagonist BI1026706 Does Not Reduce Central Retinal Thickness in Center-Involved Diabetic Macular Edema

Purpose

The bradykinin 1 receptor may be important in inflammatory retinal vascular leakage in diabetic macular edema. BI 1026706 is an antagonist of bradykinin 1 receptor that has demonstrated efficacy in preclinical studies. Boehringer Ingelheim trial 1320.22 (NCT02732951) was a randomized, double-blind, placebo-controlled study. The pharmacodynamics, safety, and tolerability of oral BI 1026706 for 12 weeks were evaluated in patients with type 1 or type 2 diabetes mellitus and mild visual impairment owing to center-involved diabetic macular edema.

Methods

Patients (n = 105) were randomized to receive either oral BI 1026706 100 mg twice daily (morning and evening) or placebo for 12 weeks. The primary end point of the study was week 12 change from baseline in central subfield foveal thickness (CSFT) by spectral domain optical coherence tomography. Additional end points included absolute CSFT values, safety, and pharmacokinetics.

Results

After 12 weeks of treatment, there was no meaningful change from baseline in the adjusted mean CSFT in either treatment group (BI 1026706, 10.3 µm; placebo, –6.2 µm; adjusted mean treatment difference, 16.5 µm [95% confidence interval, –16.2 to 49.1]). There were also no differences in best-corrected visual acuity outcomes between treatment groups. Most reported adverse events were of mild or moderate intensity, and were balanced between treatment groups.

Conclusions

BI 1026706 was not superior to placebo in CSFT week-12 change from baseline. Therefore, BI 1026706 does not reduce CSFT, a morphologic sign of diabetic macular edema.

Translational Relevance

Kinin-kallikrein inhibition effects may not be apparent over 12 weeks for bradykinin 1 receptor inhibition alone.

Identifying Genetic Risk Factors for Diabetic Macular Edema and the Response to Treatment

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes mellitus (DM). DR is complex and the term encompasses several clinical subtypes of diabetic eye disease, including diabetic macular edema (DME), the most frequent cause of central vision loss in DR patients. Both genetic and environmental factors contribute to the pathophysiology of DR and its subtypes. While numerous studies have identified several susceptibility genes for DR, few have investigated the impact of genetics on DME susceptibility. This review will focus on the current literature surrounding genetic risk factors associated with DME. We will also highlight the small number of studies investigating the genetics of response to antivascular endothelial growth factor (anti-VEGF) injection, which is used to treat DME.

Targeting epigenetic modifications as a potential therapeutic option for diabetic retinopathy

Diabetic retinopathy (DR) is the leading cause of visual impairment in adults of working age (20-65 years) in developed countries. The metabolic memory phenomena (persistent effect of a glycemic insult even after retrieved) associated with it has increased the risk of developing the complication even after the termination of the glycemic insult. Hence, the need for finding early diagnosis and treatment options has been of great concern. Epigenetic modifications which generally occur during the beginning stages of the disease are responsible for the metabolic memory effect. Therefore, the therapy based on the reversal of the associated epigenetic mechanism can bring new insight in the area of early diagnosis and treatment mechanism. This review discusses the diabetic retinopathy, its pathogenesis, current treatment options, need of finding novel treatment options, and different epigenetic alterations associated with DR. However, the main focus is emphasized on various epigenetic modifications particularly DNA methylation which are responsible for the initiation and progression of diabetic retinopathy and the use of different epigenetic inhibitors as a novel therapeutic option for DR.

Factors influencing clinical outcomes in patients with diabetic macular edema treated with intravitreal ranibizumab: comparison between responder and non-responder cases

Diabetic macular edema (DME) is the leading cause of visual impairment in patients with diabetes mellitus. A retrospective study was conducted to investigate the factors influencing the clinical outcomes in 73 patients (94 eyes) with DME treated with intravitreal ranibizumab therapy. Baseline demographic, systemic, and ocular data were assessed for the association with visual and anatomic outcomes after treatment. The mean best corrected visual acuity (BCVA) improved from 0.92 ± 0.45 to 0.61 ± 0.43 logarithm of the minimum angle of resolution (LogMAR) (p < 0.001) after treatment. The mean central subfield macular thickness (CST) decreased from 425.2 ± 127.4 to 328.6 ± 99.4 μm (p < 0.001). The treatment response was significantly influenced by Age (p = 0.003) and baseline BCVA (p = 0.001). In addition, glycosylated hemoglobin (HbA1c) (p = 0.013) and proliferative diabetic retinopathy (PDR) (p = 0.019) were the prognostic factors for the visual outcome in the responders and non-responders, respectively. Moreover, baseline CST was the strongest predictor of anatomic outcome in all subjects (p < 0.001). Intravitreal ranibizumab for DME resulted in significant improvement in clinical outcomes. Younger age and better baseline BCVA were associated with better visual outcome after the treatment. In addition, glycemic control in the treatment of patients with DME is crucial to achieve better visual outcomes, especially in the responders to ranibizumab treatment.

Prefilled syringes for intravitreal drug delivery

Intravitreal injections of anti-vascular endothelial growth factor (VEGF) medications play an increasingly critical role in numerous retinal vascular diseases. Initially, anti-VEGF medications came in vials that had to be drawn up by the physician into a syringe for administration. In 2018, the US Food and Drug Administration (US FDA) approved the ranibizumab 0.3 mg prefilled syringe (PFS), and in October 2016, the US FDA approved the ranibizumab 0.5 mg PFS. This article discusses the advantages of the PFS, including reduced injection time, possible reduced risk of endophthalmitis, reduction in intraocular air bubbles and silicone oil droplets, and improved precision in the volume and dose of intravitreal ranibizumab administered, along with possible disadvantages. Implications of the innovation of the PFS on intravitreal injection technique and clinical practice pattern are discussed and reviewed.

Inflammatory mediators in the vitreal reflux of patients with diabetic macular edema

PURPOSE

To quantify inflammatory, growth/angiogenic, and tissue remodeling mediators in vitreal reflux (VR) in patients with diabetic macular edema (DME), as collected at first and third intravitreal anti-vascular endothelial growth factor (anti-VEGF, ranibizumab) injection.

METHODS

Thirty (30) consecutive patients (type-2 diabetes mellitus) with visual impairments due to DME and undergoing the first (untreated DME) or the third (treated DME) intravitreal injection of anti-VEGF were included in the study. At the time of surgery, patients were subjected to clinical assessment and spectral domain-optical coherence tomography (SD-OCT), including central retinal thickness (CRT), macular volume, and outer nuclear layer/retinal pigment epithelial (ONL/RPE) measurements. VR sampling was performed at the time of needle removal and subjected to customized protein-array, Western blotting (WB), Ella™ microfluidic, and/or enzyme-linked immunosorbent assay (ELISA) analysis. Biostrumental and biochemical data were collected just prior to the surgery and are representative of disease state. Clinical, biostrumental, and numerous biomarkers and cytokines were statistically compared.

RESULTS

Decreased CRT values were detected in treated DME retinas, as compared to untreated ones (p ≤ 0.05). Differences in VEGF and other mediator expressions between treated and untreated DME were detected in VR samples. Particularly, osteopontin (p ≤ 0.05), interleukin 6 (IL6) (p ≤ 0.05), and VEGF (p ≤ 0.1) values were decreased after treatment. Significant changes were validated by WB, ELISA, and Ella™ analysis.

CONCLUSION

Overall, the biostrumental and biochemical data suggest the presence of a specific pattern of inflammation in VR after treatment. The data would suggest the presence of other mechanisms and mediators, in addition to VEGF, accountable for DME progression.

Resveratrol reverses the adverse effects of bevacizumab on cultured ARPE-19 cells

Age-related macular degeneration (AMD) and proliferative diabetic retinopathy (PDR) are one of the major causes of blindness caused by neo-vascular changes in the retina. Intravitreal anti-VEGF injections are widely used in the treatment of wet-AMD and PDR. A significant percentage of treated patients have complications of repeated injections. Resveratrol (RES) is a polyphenol phytoalexin with anti-oxidative, anti-inflammatory and anti-proliferative properties. Hence, we hypothesized that if RES is used in combination with bevacizumab (BEV, anti-VEGF), it could reverse the adverse effects that precipitate fibrotic changes, drusen formation, tractional retinal detachment and so on. Human retinal pigment epithelial cells were treated with various combinations of BEV and RES. There was partial reduction in secreted VEGF levels compared to untreated controls. Epithelial-mesenchymal transition was lower in BEV + RES treated cultures compared to BEV treated cultures. The proliferation status was similar in BEV + RES as well as BEV treated cultures both groups. Phagocytosis was enhanced in the presence of BEV + RES compared to BEV. Furthermore, we observed that notch signaling was involved in reversing the adverse effects of BEV. This study paves way for a combinatorial strategy to treat as well as prevent adverse effects of therapy in patients with wet AMD and PDR.

M. A. Nuijts R, Ghosh A, Nallathambi J. Oxidative stress induces dysregulated autophagy in corneal epithelium of keratoconus patients

Oxidative stress is one of the key factors that contributes to the pathogenesis of keratoconus (KC). Macroautophagy is a vital cellular mechanism that is activated in response to oxidative stress. The aim of this study was to understand the role of the autophagic lysosomal pathway in the oxidative damage of KC corneal epithelium and the human corneal epithelial cell line (HCE).The corneal epithelium was collected from 78 KC patients undergoing corneal cross-linking or topography guided photorefractive keratectomy. We performed microarray, qPCR and western blot analysis for the expression of autophagy markers on this epithelium from patients with different clinical grades of KC. A differential expression pattern of autophagy related markers was observed in the diseased corneal cone-specific epithelium compared to matched peripheral epithelium from KC patients with increasing clinical severity. Human corneal epithelial cells exposed to oxidative stress were analyzed for the expression of key proteins associated with KC pathogenesis and the autophagic pathway. Oxidative stress led to an increase in reactive oxygen species and an imbalanced expression of autophagy markers in the HCE cells. Further, reduced levels of Akt/p70S6 Kinase, which is a known target of the mTOR pathway was observed in HCE cells under oxidative stress as well as in KC epithelium. Our results suggest that an altered expression of proteins suggestive of defective autophagy and is a consequence of oxidative damage. This could play a possible role in the pathogenesis of KC.

Retinal pigment epithelium-secretome: A diabetic retinopathy perspective

Diabetic retinopathy is a major complication of diabetes mellitus that can lead to retinal vascular abnormalities and visual impairment. While retinal endothelial pathology is well studied, retinal pigment epithelium (RPE) layer modifications and the patho-physiological regulations are not widely understood. The RPE is a highly specialized pigmented layer regulating not only physiological functions such as transport of nutrients, ions, absorption of light, phagocytosis of photoreceptor membranes, but also secretion of a number of cytokines, chemokines, angiogenic and anti-angiogenic factors. The RPE secretome, though crucial in health and disease, remains elusive in diabetic retinopathy. A knowledge of these secreted factors would help explain and correlate the clinical phase of the disease aiding in improved disease management. A comprehensive knowledge of the secreted factors of the RPE is a potential tool for understanding the differential treatment regime of early diabetic retinopathy, diabetic proliferative retinopathy and diabetic macular edema. In this review, we have delineated the importance of factors secreted by the retinal pigment epithelium and its regulation in the pathogenesis of diabetic retinopathy.

Moving Past Anti-VEGF: Novel Therapies for Treating Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness in working age adults, and is projected to be a significant future health concern due to the rising incidence of diabetes. The recent advent of anti-vascular endothelial growth factor (VEGF) antibodies has revolutionized the treatment of diabetic retinopathy but a significant subset of patients fail to respond to treatment. Accumulating evidence indicates that inflammatory cytokines and chemokines other than VEGF may contribute to the disease process. The current review examines the presence of non-VEGF cytokines in the eyes of patients with diabetic retinopathy and highlights mechanistic pathways in relevant animal models. Finally, novel drug targets including components of the kinin-kallikrein system and emerging treatments such as anti-HPTP (human protein tyrosine phosphatase) β antibodies are discussed. Recognition of non-VEGF contributions to disease pathogenesis may lead to novel therapeutics to enhance existing treatments for patients who do not respond to anti-VEGF therapies.

Effects of intravitreal ranibizumab on the untreated eye and systemic gene expression profile in age-related macular degeneration

The purpose of this study was to evaluate the systemic effects of intravitreal ranibizumab (Lucentis) treatment in patients with neovascular age-related macular degeneration (AMD). The impact of intravitreal ranibizumab injections on central retinal thickness (CRT) of treated and contralateral untreated eyes, and differences in gene expression patterns in the peripheral blood mononuclear cells were analyzed. The study included 29 patients aged 50 years old and over with diagnosed neovascular AMD. The treatment was defined as 0.5 mg of ranibizumab injected intravitreally in the form of one injection every month during the period of 3 months. CRT was measured by optical coherence tomography. The gene expression profile was assigned using oligonucleotide microarrays of Affymetrix HG-U133A. Studies have shown that there was a change of CRT between treated and untreated eyes, and there were differences in CRT at baseline and after 1, 2, and 3 months of ranibizumab treatment. Three months after intravitreal injection, mean CRT was reduced in the treated eyes from 331.97±123.62 to 254.31±58.75 μm, while mean CRT in the untreated fellow eyes reduced from 251.07±40.29 to 235.45±36.21 μm at the same time. Furthermore, the research has shown that among all transcripts, 3,097 expresses change after the ranibizumab treatment in relation to controls. Among these transcripts, 1,339 were up-regulated, whereas 1,758 were down-regulated. Our results show the potential systemic effects of anti-VEGF therapy for AMD. Moreover, our study indicated different gene expression in peripheral blood mononuclear cells before and after intravitreal ranibizumab treatment.

The role of pharmacogenetics and advances in gene therapy in the treatment of diabetic retinopathy

Diabetic retinopathy (DR) and its complications such as diabetic macular edema continue to remain a major cause for legal blindness in the developed world. While the introduction of anti-tVEGF agents has significantly improved visual outcomes of patients with DR, unpredictable response, largely due to genetic polymorphisms, appears to be a challenge with this therapy. With advances in identification of various genetic biomarkers, novel therapeutic strategies consisting of gene transfer are being developed and tested for patients with DR. Application of pharmacogenetic principles appears to be a promising futuristic strategy to attenuate diabetes-mediated retinal vasculopathy. In this comprehensive review, data from recent studies in the field of pharmacogenomics for the treatment of DR have been provided.

Sustained intraocular VEGF neutralization results in retinal neurodegeneration in the Ins2(Akita) diabetic mouse

Current therapies that target vascular endothelial growth factor (VEGF) have become a mainstream therapy for the management of diabetic macular oedema. The treatment involves monthly repeated intravitreal injections of VEGF inhibitors. VEGF is an important growth factor for many retinal cells, including different types of neurons. In this study, we investigated the adverse effect of multiple intravitreal anti-VEGF injections (200 ng/μl/eye anti-mouse VEGF164, once every 2 weeks totalling 5-6 injections) to retinal neurons in Ins2(Akita) diabetic mice. Funduscopic examination revealed the development of cotton wool spot-like lesions in anti-VEGF treated Ins2(Akita) mice after 5 injections. Histological investigation showed focal swellings of retinal nerve fibres with neurofilament disruption. Furthermore, anti-VEGF-treated Ins2(Akita) mice exhibited impaired electroretinographic responses, characterized by reduced scotopic a- and b-wave and oscillatory potentials. Immunofluorescent staining revealed impairment of photoreceptors, disruptions of synaptic structures and loss of amacrine and retinal ganglion cells in anti-VEGF treated Ins2(Akita) mice. Anti-VEGF-treated WT mice also presented mild amacrine and ganglion cell death, but no overt abnormalities in photoreceptors and synaptic structures. At the vascular level, exacerbated albumin leakage was observed in anti-VEGF injected diabetic mice. Our results suggest that sustained intraocular VEGF neutralization induces retinal neurodegeneration and vascular damage in the diabetic eye.

Diabetic retinopathy: variations in patient therapeutic outcomes and pharmacogenomics

Diabetes and its microvascular complications in patients poses a significant challenge and constitutes a major health problem. When it comes to manifestations in the eye, each case of diabetic retinopathy (DR) is unique, in terms of the phenotype, genotype, and, more importantly, the therapeutic response. It is therefore important to identify factors that distinguish one patient from another. Personalized therapy in DR is a new trend aimed at achieving maximum therapeutic response in patients by identifying genotypic and phenotypic factors that may result in less than optimal response to conventional therapy, and consequently, lead to poorer outcome. With advances in the identification of these genetic markers, such as gene polymorphisms and human leucocyte antigen associations, as well as development of drugs that can target their effects, the future of personalized medicine in DR is promising. In this comprehensive review, data from various studies have been analyzed to present what has been achieved in the field of pharmacogenomics thus far. An insight into future research is also provided.