Changing times for the management of diabetic retinopathy

Adeno-Associated Viral Vector 2 and 9 Transduction Is Enhanced in Streptozotocin-Induced Diabetic Mouse Retina

Adeno-associated viruses (AAVs) are currently the most popular vector platform technology for ocular gene therapy. While transduction efficiency and tropism of intravitreally administered AAV has been fairly well established in various retinal conditions, its transduction pattern in diabetic retinas has not previously been characterized. Here, we describe the transduction efficiencies of four different AAV serotypes, AAV2, 5, 8, and 9, in streptozotocin (STZ)-induced diabetic mouse retinas after intravitreal injections, which differed according to the duration of diabetic induction. STZ was intraperitoneally injected into C57/B6 diabetic mice subjected to unilateral intravitreal injection of AAV2, AAV5, AAV8, and AAV9 packaged with EGFP. Significantly enhanced AAV2 and AAV9 transduction was observed in 2-month-old diabetic mouse retinas compared to the 2-week-old diabetic mouse retinas and nondiabetic, vector uninjected or injected retinas. Intravitreal injection of AAV5 or AAV8 serotype in 2-month- and 2-week-old diabetic mouse retinas did not show any significant vector transduction enhancement compared to the nondiabetic control retinas. The tropism of AAV2 and AAV9 in diabetic mouse retinas differed. AAV2 was transduced into various retinal cells, including Müller cells, microglia, retinal ganglion cells (RGCs), bipolar cells, horizontal cells, and amacrine cells, whereas AAV9 was effectively transduced only into RGC and horizontal cells. The expression levels of receptors and co-receptors for AAV2 and AAV9 were significantly increased in 2-month-old diabetic mouse retinas. The results of our study demonstrated that AAV2 and AAV9 may be the vector of choice in treating diabetic retinopathy (DR) with gene therapy, and DR-related retinal changes may improve AAV vector transduction efficiency.

The RELATION study: efficacy and safety of ranibizumab combined with laser photocoagulation treatment versus laser monotherapy in NPDR and PDR patients with diabetic macular oedema

Purpose

To assess efficacy and safety of intravitreal ranibizumab 0.5 mg plus laser (COMBI) versus laser monotherapy (LASER) in patients with visual impairment due to diabetic macular oedema (DME) in either nonproliferative diabetic retinopathy (NPDR) or proliferative diabetic retinopathy (PDR) and to analyse the relevance of inner versus outer retinal thickness.

Methods

In this double‐masked, multicentre phase IIIb study, patients (N = 128) were randomized (2:1) to receive COMBI (n = 85) versus LASER (n = 43). Patients received four initial monthly injections of ranibizumab 0.5 mg (COMBI) or sham (LASER) followed by pro re nata (PRN) injections. In both groups, patients received laser at baseline and additional laser at 3 monthly intervals, as needed. The study was started in 2010 and was prematurely terminated due to approval of ranibizumab for DME.

Results

The least squares (LS) mean change in mean best‐corrected visual acuity (BCVA) from baseline to month 12 was higher in the COMBI (6.5) versus LASER (2.3) group (LS mean difference: 4.2 [95% CI 0.9; 7.4] letters, p = 0.01, primary end‐point). There was also a tendency in the same direction for the subgroup of 26 patients with PDR (LS mean difference 14.7, p = 0.11). Mean central retinal thickness decreased by 107.3 μm in the COMBI group and by 80.3 μm in the LASER group from baseline to month 12 (p = 0.28). Ranibizumab was well tolerated.

Conclusion

This study showed that ranibizumab plus laser is a valuable treatment option for the management of DME. Patients with DME in PDR might also benefit from combined therapy compared to laser alone.

Laser photocoagulation enhances adeno-associated viral vector transduction of mouse retina

Laser photocoagulation is a well-established treatment modality for retinal disease. Discrete laser burns can be placed anywhere in the retina, singly or multiply, and the burn intensity is controllable. This study investigates the effect of prior laser photocoagulation on the retinal transduction properties of intravitreally administered adeno-associated viral (AAV) vectors. C57BL/6J mice were subjected to unilateral laser photocoagulation 48 hr before bilateral intravitreal injection of self-complementary cytomegaloviral enhanced green fluorescent protein (EGFP) vectors packaged in AAV type 2, 5, and 8 capsids. The eyes were enucleated 4 weeks after injection and examined by histochemistry and quantitative image analysis. Laser pretreatment resulted in substantially increased localized transduction around the burn site for all AAV capsid types. Without laser pretreatment, the vectors transduced only ganglion cells (AAV2) or sporadic cells around the optic nerve head (AAV5 and AAV8). Laser pretreatment increased AAV2 vector expression throughout the entire retina and focally at the burn site. Transduced cells at the burn site included retinal pigment epithelium (RPE), photoreceptors, Müller cells, inner nuclear layer cells, and retinal ganglion cells. The AAV5 vector showed increased RPE transduction at the burn site only. The AAV8 vector showed augmented expression in RPE, photoreceptors, and Müller cells around the burn site. Migrating RPE cells, present in the neural retina near the burn site, were also transduced by all three capsid types as evidenced by colocalization of EGFP and cytokeratin. Laser photocoagulation can be used to precisely direct AAV vector transduction to discrete locations in the retina. A combination of laser and AAV-mediated gene expression may allow the development of improved therapies for diabetic retinopathy, branch and central vein occlusion, and age-related macular degeneration.

Screening and Referral of Diabetic Retinopathy: A Comparative Review of the Practice Guidelines

Diabetic retinopathy (DR) is a leading cause of preventable visual impairment in the working age group. The major risk factors for development and progression are duration of disease and the severity of hyperglycemia. The Global Diabetic Retinopathy Project developed a new classification system for DR and macular edema to enhance communication and coordination among the multidisciplinary team of physicians taking care of diabetic patients. Diabetic retinopathy progresses from nonproliferative DR to proliferative DR through a series of stages. Early detection and timely referral are critical for timely interventions to prevent further deterioration. Primary care physicians have an integral role in the community as they are the first point of contact for patients. Guidelines from various associations provide recommendations to physicians taking care of diabetic patients on how to screen and situations where referral to an ophthalmologist is needed. Dilated direct ophthalmoscopy is a convenient method to assess the fundus, but it does not replace retinal photography in the screening of DR. All patients with proliferative DR and diabetic macular edema should be referred to an ophthalmologist, whereas the situation for nonproliferative DR remains unclear as no consensus was drawn from the various guidelines.

Sustained moderate visual loss as a predictive end point for visual loss in non-proliferative diabetic retinopathy

PURPOSE

In PKC-DRS2, the efficacy of the oral PKC-beta inhibitor, ruboxistaurin 32 mg/day, was measured by the primary end point of sustained moderate visual loss (SMVL: a > or = 15 letter decrease from baseline on the ETDRS (Early Treatment Diabetic Retinopathy Study) chart sustained at least for the last 6 months of study participation). We now evaluate whether SMVL is more accurate than moderate visual loss (MVL: a single occurrence of a decrease from baseline of > or = 15 ETDRS letters) for predicting future visual loss.

METHODS

Study eyes with moderately severe to very-severe non-proliferative diabetic retinopathy, best-corrected visual acuity of at least 45 letters on the ETDRS chart (approximately Snellen 20/125), and no prior pan retinal photocoagulation were evaluated in 506 patients (869 eyes) who completed 36 months of treatment.

RESULTS

Sixty-five percentage (26/40) of study eyes with the onset of SMVL within 24 months of enrolment still had SMVL at study completion (36 months). In comparison, only 24% (30/126) with MVL within 24 months had SMVL at study completion. Analyses based on data from 6, 12, and 18 months of treatment were similar.

CONCLUSIONS

SMVL is a more predictable measure of subsequent visual loss than is a single time point measure of MVL.

Pathogenesis and classification of proliferative diabetic vitreoretinopathy

PURPOSE

To review the current knowledge regarding the pathogenesis of proliferative diabetic vitreoretinopathy (PDVR) and to present recommendations for its clinical staging.

DESIGN

Focused literature review and authors' clinical experience.

RESULTS

Although several biochemical mediators may be responsible for the pathogenesis of PDVR, no common biochemical pathway exists. Of those mediators, vascular endothelial growth factor is the one most studied so far. However, since in proliferative diabetic retinopathy (PDR) the thickened posterior vitreous cortex is one of the main factors in the development of proliferations, a consequent shrinkage of the posterior vitreous cortex leads to hemorrhages and tractive retinal detachments. Therefore, PDR should be called PDVR. In consequence, the authors present a new morphological classification of PDVR.

CONCLUSIONS

There is no consensus about the biochemical pathway responsible for the progression of PDVR. Although several classifications are described in the literature, the classification suggested here is important in the judgment of, the communication about and the therapy of diabetic retinopathy. Furthermore, it is the only reliable classification for predicting the surgical outcome in diabetics.

Diabetic macular oedema: a clinical overview

Diabetic retinopathy is the leading cause of blindness in working aged-adults in westernised countries. Diabetic macular oedema (DMO) is a manifestation of diabetic retinopathy and is the leading cause of the visual impairment that occurs with diabetic retinopathy. There are multiple ways of classifying DMO; however, none appear to be wholly satisfactory. DMO occurs more frequently in type 2 diabetes mellitus, and appears to be more prevalent as the duration of diabetes increases, and as the severity of diabetic retinopathy worsens. There are multiple risk factors in common with diabetic retinopathy, such as hyperglycaemia, hypertension and dyslipidaemia; however, specific factors such as the presence of renal disease appear to be more significantly associated with DMO. Whereas the gold standard for diagnosis of DMO is via clinical examination, there is considerable variability involved, and hence, this has led to the advent of more objective methods of quantifying the degree of retinal thickness, such as optical coherence tomography. Laser photocoagulation appears to be the only universally acceptable treatment of choice to date; however, this is a destructive therapy, and its side effects coupled with the suboptimal efficacy has led to the advent of potential new therapies which will undoubtedly compliment the existing approaches, in the future management of a patient with DMO.

Optical coherence tomography: a key to the future management of patients with diabetic macular oedema

Diabetic macular oedema is a major cause of visual loss in patients with diabetes. It usually results from the breakdown of the inner blood-retinal barrier. Early detection of retinal abnormalities is vital in preventing diabetic macular oedema and subsequent loss of vision, whilst assessment of retinal thickness is important for treatment and follow-up. Until recently, however, the methods available for detecting and evaluating diabetic macular oedema were slit-lamp biomicroscopy and stereoscopic photography, both of which are limited in detecting earlier retinal changes. Optical coherence tomography (OCT) is a new diagnostic imaging modality that provides high-resolution, cross-sectional images of the eye. It is proving to be an accurate tool for the early diagnosis, analysis and monitoring of retinopathy, with high repeatability and resolution. It allows not only the qualitative diagnosis of diabetic macular oedema, but also the quantitative assessment of oedema. This article reviews the future role of OCT in the management of patients with diabetic macular oedema.

Ophthalmic drug discovery

Millions of people suffer from a wide variety of ocular diseases, many of which lead to irreversible blindness. The leading causes of irreversible blindness in the elderly--age-related macular degeneration and glaucoma--will continue to effect more individuals as the worldwide population continues to age. Although there are therapies for treating glaucoma, as well as ongoing clinical trials of treatments for age-related macular degeneration, there still is a great need for more efficacious treatments that halt or even reverse ocular diseases. The eye has special attributes that allow local drug delivery and non-invasive clinical assessment of disease, but it is also a highly complex and unique organ, which makes understanding disease pathogenesis and ocular drug discovery challenging. As we learn more about the cellular mechanisms involved in age-related macular degeneration and glaucoma, potentially, new drug targets will emerge. This review provides insight into some of the new approaches to therapy.