Anti-VEGF therapy for diabetic macular edema

Diabetes enhances the efficacy of AAV2 vectors in the retina: therapeutic effect of AAV2 encoding vasoinhibin and soluble VEGF receptor 1

Adeno-associated virus (AAV) vector-mediated delivery of inhibitors of blood-retinal barrier breakdown (BRBB) offers promise for the treatment of diabetic macular edema. Here, we demonstrated a reversal of blood-retinal barrier pathology mediated by AAV type 2 (AAV2) vectors encoding vasoinhibin or soluble VEGF receptor 1 (sFlt-1) when administered intravitreally to diabetic rats. Efficacy and safety of the AAV2 vasoinhibin vector were tested by monitoring its effect on diabetes-induced changes in the retinal vascular bed and thickness, and in the electroretinogram (ERG). Also, the transduction of AAV2 vectors and expression of AAV2 receptors and co-receptors were compared between the diabetic and the non-diabetic rat retinas. AAV2 vasoinhibin or AAV2 sFlt-1 vectors were injected intravitreally before or after enhanced BRBB due to diabetes induced by streptozotocin. The BRBB was examined by the Evans blue method, the vascular bed by fluorescein angiography, expression of the AAV2 EGFP reporter vector by confocal microscopy, and the AAV2 genome, expression of transgenes, receptors, and co-receptors by quantitative PCR. AAV2 vasoinhibin and sFlt-1 vectors inhibited the diabetes-mediated increase in BRBB when injected after, but not before, diabetes was induced. The AAV2 vasoinhibin vector decreased retinal microvascular abnormalities and the diabetes-induced reduction of the B-wave of the ERG, but it had no effect in non-diabetic controls. Also, retinal thickness was not altered by diabetes or by the AAV2 vasoinhibin vector. The AAV2 genome, vasoinhibin and sFlt-1 transgenes, and EGFP levels were higher in the retinas from diabetic rats and were associated with an elevated expression of AAV2 receptors (syndecan, glypican, and perlecan) and co-receptors (fibroblast growth factor receptor 1, αvβ5 integrin, and hepatocyte growth factor receptor). We conclude that retinal transduction and efficacy of AAV2 vectors are enhanced in diabetes, possibly due to their elevated cell entry. AAV2 vectors encoding vasoinhibin and sFlt-1 may be desirable gene therapeutics to target diabetic retinopathy and macular edema.

Ocular Complications of Diabetes and Therapeutic Approaches

Diabetes mellitus (DM) is a metabolic disease defined by elevated blood glucose (BG). DM is a global epidemic and the prevalence is anticipated to continue to increase. The ocular complications of DM negatively impact the quality of life and carry an extremely high economic burden. While systemic control of BG can slow the ocular complications they cannot stop them, especially if clinical symptoms are already present. With the advances in biodegradable polymers, implantable ocular devices can slowly release medication to stop, and in some cases reverse, diabetic complications in the eye. In this review we discuss the ocular complications associated with DM, the treatments available with a focus on localized treatments, and what promising treatments are on the horizon.

Molecular features of interaction between VEGFA and anti-angiogenic drugs used in retinal diseases: a computational approach

Anti-angiogenic agents are biological drugs used for treatment of retinal neovascular degenerative diseases. In this study, we aimed at in silico analysis of interaction of vascular endothelial growth factor A (VEGFA), the main mediator of angiogenesis, with binding domains of anti-angiogenic agents used for treatment of retinal diseases, such as ranibizumab, bevacizumab and aflibercept. The analysis of anti-VEGF/VEGFA complexes was carried out by means of protein-protein docking and molecular dynamics (MD) coupled to molecular mechanics-Poisson Boltzmann Surface Area (MM-PBSA) calculation. Molecular dynamics simulation was further analyzed by protein contact networks. Rough energetic evaluation with protein-protein docking scores revealed that aflibercept/VEGFA complex was characterized by electrostatic stabilization, whereas ranibizumab and bevacizumab complexes were stabilized by Van der Waals (VdW) energy term; these results were confirmed by MM-PBSA. Comparison of MM-PBSA predicted energy terms with experimental binding parameters reported in literature indicated that the high association rate (Kon) of aflibercept to VEGFA was consistent with high stabilizing electrostatic energy. On the other hand, the relatively low experimental dissociation rate (Koff) of ranibizumab may be attributed to lower conformational fluctuations of the ranibizumab/VEGFA complex, higher number of contacts and hydrogen bonds in comparison to bevacizumab and aflibercept. Thus, the anti-angiogenic agents have been found to be considerably different both in terms of molecular interactions and stabilizing energy. Characterization of such features can improve the design of novel biological drugs potentially useful in clinical practice.

Hepatoma-derived growth factor-related protein-3 is a novel angiogenic factor

Hepatoma-derived growth factor-related protein-3 (Hdgfrp3 or HRP-3) was recently reported as a neurotrophic factor and is upregulated in hepatocellular carcinoma to promote cancer cell survival. Here we identified HRP-3 as a new endothelial ligand and characterized its in vitro and in vivo functional roles and molecular signaling. We combined open reading frame phage display with multi-round in vivo binding selection to enrich retinal endothelial ligands, which were systematically identified by next generation DNA sequencing. One of the identified endothelial ligands was HRP-3. HRP-3 expression in the retina and brain was characterized by Western blot and immunohistochemistry. Cell proliferation assay showed that HRP-3 stimulated the growth of human umbilical vein endothelial cells (HUVECs). HRP-3 induced tube formation of HUVECs in culture. Wound healing assay indicated that HRP-3 promoted endothelial cell migration. HRP-3 was further confirmed for its in vitro angiogenic activity by spheroid sprouting assay. HRP-3 extrinsically activated the extracellular-signal-regulated kinase ½ (ERK1/2) pathway in endothelial cells. The angiogenic activity of HRP-3 was independently verified by mouse cornea pocket assay. Furthermore, in vivo Matrigel plug assay corroborated HRP-3 activity to promote new blood vessel formation. These results demonstrated that HRP-3 is a novel angiogenic factor.

Effect of intravitreal bevacizumab on retrobulbar blood flow of patients with diabetic macular edema

PURPOSE

To determine the effect of intravitreal bevacizumab on retrobulbar blood flow of patients with diabetic macular edema.

METHODS

Peak systolic velocity, end-diastolic velocity, resistance, and pulsatility indices of central retinal artery (CRA), nasal posterior ciliary artery (NPCA), temporal posterior ciliary artery (TPCA), and ophthalmic artery (OA) were assessed by color Doppler ultrasonography in injected and uninjected eyes of 37 patients at baseline and at day 1 and day 7 after the injection.

RESULTS

At day 1 after the injection, peak systolic and end diastolic velocities of the CRA and NPCA in the injected eyes and peak systolic velocity of NPCA in the uninjected eyes decreased significantly (p<0.05, p = 0.025, respectively). Peak systolic and end diastolic velocities were not significantly different in the injected and uninjected eyes at day 7 after the injection (p>0.05). In the injected eyes, there was no significant change in resistance and pulsatility indices (p>0.05), but a decrease in resistance index of NPCA and resistance and pulsatility indices of TPCA occurred in uninjected eyes at day 7 after the injection (p = 0.016, p = 0.023, and p = 0.025, respectively).

CONCLUSIONS

Intravitreal bevacizumab affects retrobulbar blood flow in injected and uninjected eyes of patients with diabetic macular edema.

Diabetic retinopathy - ocular complications of diabetes mellitus

In industrialized nations diabetic retinopathy is the most frequent microvascular complication of diabetes mellitus and the most common cause of blindness in the working-age population. In the next 15 years, the number of patients suffering from diabetes mellitus is expected to increase significantly. By the year 2030, about 440 million people in the age-group 20-79 years are estimated to be suffering from diabetes mellitus worldwide (prevalence 7.7%), while in 2010 there were 285 million people with diabetes mellitus (prevalence 6.4%). This accounts for an increase in patients with diabetes in industrialized nations by 20% and in developing countries by 69% until the year 2030. Due to the expected rise in diabetic patients, the need for ophthalmic care of patients (i.e., exams and treatments) will also increase and represents a challenge for eye-care providers. Development of optimized screening programs, which respect available resources of the ophthalmic infrastructure, will become even more important. Main reasons for loss of vision in patients with diabetes mellitus are diabetic macular edema and proliferative diabetic retinopathy. Incidence or progression of these potentially blinding complications can be greatly reduced by adequate control of blood glucose and blood pressure levels. Additionally, regular ophthalmic exams are mandatory for detecting ocular complications and initiating treatments such as laser photocoagulation in case of clinical significant diabetic macular edema or early proliferative diabetic retinopathy. In this way, the risk of blindness can considerably be reduced. In advanced stages of diabetic retinopathy, pars-plana vitrectomy is performed to treat vitreous hemorrhage and tractional retinal detachment. In recent years, the advent of intravitreal medication has improved therapeutic options for patients with advanced diabetic macular edema.

A hypoxia-responsive glial cell-specific gene therapy vector for targeting retinal neovascularization

PURPOSE

Müller cells, the major glial cell in the retina, play a significant role in retinal neovascularization in response to tissue hypoxia. We previously designed and tested a vector using a hypoxia-responsive domain and a glial fibrillary acidic protein (GFAP) promoter to drive green fluorescent protein (GFP) expression in Müller cells in the murine model of oxygen-induced retinopathy (OIR). This study compares the efficacy of regulated and unregulated Müller cell delivery of endostatin in preventing neovascularization in the OIR model.

METHODS

Endostatin cDNA was cloned into plasmids with hypoxia-regulated GFAP or unregulated GFAP promoters, and packaged into self-complementary adeno-associated virus serotype 2 vectors (scAAV2). Before placement in hyperoxia on postnatal day (P)7, mice were given intravitreal injections of regulated or unregulated scAAV2, capsid, or PBS. Five days after return to room air, on P17, neovascular and avascular areas, as well as expression of the transgene and vascular endothelial growth factor (VEGF), were compared in OIR animals treated with a vector, capsid, or PBS.

RESULTS

The hypoxia-regulated, glial-specific, vector-expressing endostatin reduced neovascularization by 93% and reduced the central vaso-obliteration area by 90%, matching the results with the unregulated GFAP-Endo vector. Retinas treated with the regulated endostatin vector expressed substantial amounts of endostatin protein, and significantly reduced VEGF protein. Endostatin production from the regulated vector was undetectable in retinas with undamaged vasculature.

CONCLUSIONS

These findings suggest that the hypoxia-regulated, glial cell-specific vector expressing endostatin may be useful for treatment of neovascularization in proliferative diabetic retinopathy.