Current Treatment of Age-Related Macular Degeneration

Treatment avenues for age-related macular degeneration: Breakthroughs and bottlenecks

Age-related macular degeneration (AMD) is a significant factor contributing to serious vision loss in adults above 50. The presence of posterior segment barriers serves as chief roadblocks in the delivery of drugs to treat AMD. The conventional treatment strategies use is limited due to its off-targeted distribution in the eye, shorter drug residence, poor penetration and bioavailability, fatal side effects, etc. The above-mentioned downside necessitates drug delivery using some cutting-edge technology including diverse nanoparticulate systems and microneedles (MNs) which provide the best therapeutic delivery alternative to treat AMD efficiently. Furthermore, cutting-edge treatment modalities including gene therapy and stem cell therapy can control AMD effectively by reducing the boundaries of conventional therapies with a single dose. This review discusses AMD overview, conventional therapies for AMD and their restrictions, repurposed therapeutics and their anti-AMD activity through different mechanisms, and diverse barriers in drug delivery for AMD. Various nanoparticulate-based approaches including polymeric NPs, lipidic NPs, exosomes, active targeted NPs, stimuli-sensitive NPs, cell membrane-coated NPs, inorganic NPs, and MNs are explained. Gene therapy, stem cell therapy, and therapies in clinical trials to treat AMD are also discussed. Further, bottlenecks of cutting-edge (nanoparticulate) technology-based drug delivery are briefed. In a nutshell, cutting-edge technology-based therapies can be an effective way to treat AMD.

Current and Novel Therapeutic Approaches for Treatment of Neovascular Age-Related Macular Degeneration

Age-related macular degeneration AMD is one of the leading causes of blindness in the elderly population. An advanced form of AMD known as neovascular AMD (nAMD) is implicated as the main attributor of visual loss among these patients. The hallmark feature of nAMD is the presence of neovascular structures known as choroidal neovascular membranes (CNVs), along with fluid exudation, hemorrhages, and subretinal fibrosis. These pathological changes eventually result in anatomical and visual loss. A type of proangiogenic factor known as vascular endothelial growth factor (VEGF) has been known to mediate the pathological process behind nAMD. Therefore, therapy has transitioned over the years from laser therapy that ablates the lesions to using Anti-VEGF to target the pathology directly. In this work, we provide an overview of current and emerging therapies for the treatment of nAMD. Currently approved Anti-VEGF agents include ranibizumab, aflibercept, and brolucizumab. Bevacizumab, also an Anti-VEGF agent, is used to manage nAMD even though this is an off-label use. While Anti-VEGF agents have provided a favorable prognosis for nAMD, they are associated with a substantial financial burden for patients and the healthcare system, due to their high cost as well as the need for frequent repeat treatments and visits. Emerging therapies and studies aim to extend the intervals between required treatments and introduce new treatment modalities that would improve patients’ compliance and provide superior results.

Current progress in the derivation and therapeutic application of neural stem cells

Neural stem cells (NSCs) have a unique role in neural regeneration. Cell therapy based on NSC transplantation is a promising tool for the treatment of nervous system diseases. However, there are still many issues and controversies associated with the derivation and therapeutic application of these cells. In this review, we summarize the different sources of NSCs and their derivation methods, including direct isolation from primary tissues, differentiation from pluripotent stem cells and transdifferentiation from somatic cells. We also review the current progress in NSC implantation for the treatment of various neural defects and injuries in animal models and clinical trials. Finally, we discuss potential optimization strategies for NSC derivation and propose urgent challenges to the clinical translation of NSC-based therapies in the near future.

Multiphasic changes in systemic VEGF following intravitreal injections of ranibizumab in a child

PURPOSE

To investigate whether intravitreal ranibizumab injections administered to a child alter systemic plasma levels of total and free VEGF 165.

METHODS

A 9-year-old child sustained a choroidal rupture from blunt trauma. He subsequently developed a secondary choroidal neovascular membrane, which was treated with five ranibizumab injections over a period of 8 months. Peripheral venous blood samples were taken at each visit over a period of 12 months and plasma was extracted. Plasma VEGF 165 levels were determined using enzyme-linked immunosorbent assay and were assayed both pre- and post-immunodepletion to remove complexed VEGF.

RESULTS

Plasma VEGF 165 levels proved labile following intravitreal injection of ranibizumab. Levels increased by 30% above baseline following the first intravitreal ranibizumab injection, but then returned to baseline despite two subsequent injections. There was then a rebound increase of 67% in total plasma VEGF levels following a further injection, which remained above baseline for 12 weeks despite two further intravitreal ranibizumab injections. Baseline levels were re-attained 26 weeks after the final injection.

CONCLUSIONS

These results suggest intravitreal ranibizumab injections can cause significant, multiphasic changes in systemic VEGF levels. This may be of particular clinical significance in children as VEGF is known to be vital in the development of major organs, in addition to its role in the maintenance of normal organ function in adults.

Trophic factors in the pathogenesis and therapy for retinal degenerative diseases

Trophic factors are endogenously secreted proteins that act in an autocrine and/or paracrine fashion to affect vital cellular processes such as proliferation, differentiation, and regeneration, thereby maintaining overall cell homeostasis. In the eye, the major contributors of these molecules are the retinal pigment epithelial (RPE) and Müller cells. The primary paracrine targets of these secreted proteins include the photoreceptors and choriocapillaris. Retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa are characterized by aberrant function and/or eventual death of RPE cells, photoreceptors, choriocapillaris, and other retinal cells. We discuss results of in vitro and in vivo animal studies in which candidate trophic factors, either singly or in combination, were used in an attempt to ameliorate photoreceptor and/or retinal degeneration. We also examine current trophic factor therapies as they relate to the treatment of retinal degenerative diseases in clinical studies.

Complimentary imaging technologies in blunt ocular trauma

We describe complimentary imaging technologies in traumatic chorioretinal injury. Color and fundus autofluorescence (FAF) images were obtained with a non-mydriatic retinal camera. Optical coherence tomography (OCT) helped obtain detailed images of retinal structure. Microperimetry was used to evaluate the visual function. A 40-year-old man sustained blunt ocular trauma with a stone. Color fundus image showed a large chorioretinal scar in the macula. Software filters allowed detailed illustration of extensive macular fibrosis. A 58-year-old man presented with blunt force trauma with a tennis ball. Color fundus imaging showed a crescentric area of macular choroidal rupture with fibrosis. FAF imaging delineated an area of hypofluorescence greater on fundus imaging. OCT showed chorioretinal atrophy in the macula. Microperimetry delineated an absolute scotoma with no response to maximal stimuli. Fundus imaging with digital filters and FAF illustrated the full extent of chorioretinal injury, while OCT and microperimetry corroborated the structure and function correlations.

Ocular telehealth screenings in an urban community

The current U.S. economic recession has resulted in a loss of income, housing, and healthcare coverage. Our major goal in this socioeconomic setting was to provide ophthalmic remote health screenings for urban soup kitchen and homeless populations in order to identify and refer undetected vision-threatening disease (VTD). We assessed visual acuity, blood pressure, pulse/oxygen saturation, body mass index, and intraocular pressure for 341 participants at soup kitchens as part of the homeless outreach program in Newark, NJ. History of diabetes, hypertension, and smoking, last ocular examination, and ocular history were noted. Imaging was performed with an 8.2 megapixel non-mydriatic retinal camera with high-speed Internet ready for off-site second opinion image evaluation. Positive VTD findings were identified in 105 participants (31%) (mean age, 53.6 years), of whom 78% were African American, 73% males, and 62% smokers. We detected glaucoma in 34 participants (32%), significant cataract in 22 (21%), diabetic retinopathy in 5 (5%), optic atrophy in 1 (1%), age-related macular degeneration in 1 (1%), and other retinal findings in 43 (41%). The incidence of VTDs was higher among this cohort than among study groups in previous screenings (31% vs. 12%). This finding shows an increase in ocular morbidity in a younger, at-risk population with elevated rates of hypertension, diabetes, and smoking. Functional visual impairment was 2.5 times higher than the national average (16% vs. 6.4%). Comprehensive, community-based screenings can provide more sensitive detection of VTDs in high-risk groups with low access to ophthalmic care and can be an integral part of recession solutions for improving healthcare.

Lasting controversy on ranibizumab and bevacizumab

Vascular endothelial growth factor (VEGF), an important angiogenic factor that is able to stimulate the proliferation and migration of endothelial cells, is the best-studied hallmark of angiogenesis. Neovascularization is a major cause of age-related macular degeneration (AMD) which is a leading cause of blindness in the elderly population. Specific molecular inhibitors of VEGF have been proved to be useful in the treatment of AMD. Ranibizumab and Bevacizumab are structurally similar to anti-VEGF drugs in the treatment of AMD. Many studies have indicated that Ranibizumab and Bevacizumab are of roughly equal short-term efficacy and safety, Bevacizumab is an attractive alternative to Ranibizumab due to its lower cost. However, only Ranibizumab has received Food and Drug Administration (FDA) approval for the treatment of macular degeneration. More multicenter clinical trials are required to compare the relative efficacy and safety of these two drugs and some progress has been achieved. This review discusses the clinical effectiveness, safety, cost and other practical implications of Ranibizumab and Bevacizumab.

Comparative role of intravitreal ranibizumab versus bevacizumab in choroidal neovascular membrane in age-related macular degeneration

CONTEXT

Ranibizumab and bevacizumab are used widely for treating patients with choroidal neovascular membrane (CNVM) secondary to age-related macular degeneration (AMD).

AIMS

To determine and compare the efficacy and safety of intravitreal ranibizumab and bevacizumab in treatment of CNVM due to AMD.

SETTINGS AND DESIGN

Prospective comparative case series carried out in an eye institute and eye department of a hospital in Kolkata, India.

MATERIALS AND METHODS

One hundred and four eyes with CNVM due to AMD were randomized into two groups. Group A (n=54; 24 occult) received monthly intravitreal ranibizumab injections (0.5 mg in 0.05 ml) and Group B (n=50; 22 occult) received monthly bevacizumab injections (1.25 mg in 0.05 ml) for 3 consecutive months and then as per study criteria. Data analysis done using SPSS software. P-value of <0.05 was considered statistically significant.

RESULTS

The mean best corrected visual acuity (BCVA) in the ranibizumab group increased from 58.19 Early Treatment Diabetic Retinopathy Study (ETDRS) letters at baseline to 64 ETDRS letters at month 3 (P<0.001). In bevacizumab group mean BCVA increased from 56.80 to 61.72 ETDRS letters at month 3 (P<0.001). At the end of 18 months, there was no statistically significant difference between groups A and B with respect to change in BCVA (P=0.563) or central macular thickness (CMT; P=0.281), as measured by optical coherence tomography (Stratus OCT 3000). No significant sight-threatening complications developed.

CONCLUSIONS

Ranibizumab and bevacizumab are equally safe and efficacious in treating CNVM due to AMD.

Anti-inflammatory and antiangiogenic effects of nanoparticle-mediated delivery of a natural angiogenic inhibitor

PURPOSE

The purpose of this study was to evaluate the inhibitory effects of the nanoparticle-mediated delivery of plasminogen kringle 5 (K5) on choroidal neovascularization (CNV) and retinal inflammation.

METHODS

CNV was induced by laser in adult rats. Nanoparticles with an expression plasmid of K5 (K5-NP) were injected into the vitreous. K5 expression was detected by immunohistochemistry. The CNV area was measured after fluorescein angiography. Retinal vascular permeability was quantified with Evans blue as a tracer. Expression of vascular endothelial growth factor (VEGF), tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, and intercellular adhesion molecule (ICAM)-1 was measured by Western blot analysis or ELISA and real-time RT-PCR.

RESULTS

Intense K5 expression was detected in the retina 2 weeks after the injection of K5-NP. Areas of CNV were significantly decreased in the K5-NP treatment group compared with that in the control-NP group. The K5-NP injection also significantly reduced vascular permeability. The expression of VEGF was downregulated by K5-NP at both the protein and mRNA levels. Moreover, K5-NP also inhibited expression of TNF-α and ICAM-1. Similarly, K5-NP decreased retinal levels of total β-catenin. In cultured cells, K5-NP suppressed hypoxia-induced secretion of MCP-1 and TNF-α.

CONCLUSIONS

K5 has a novel anti-inflammatory activity. K5-NP mediates a sustained inhibitory effect on CNV and thus has therapeutic potential for age-related macular degeneration.

Treatment of age-related macular degeneration: focus on ranibizumab

Ranibizumab, a humanized antigen-binding fragment (Fab) that binds all isoforms of VEGF-A, significantly slows down loss of vision and causes significant visual improvement in many patients with choroidal neovascularization (CNV) due to exudative age-related macular degeneration (AMD). These benefits of intravitreal ranibizumab apply to all angiographic subtypes of neovascular AMD and across all lesion sizes when the drug is injected at monthly intervals as shown in two pivotal phase III trials (ANCHOR and MARINA). The results from the PrONTO study suggest that less frequent treatment with ranibizumab through a variable dosing regimen dependent on optical coherence tomography (OCT) findings is a treatment option that results in comparably favorable visual outcomes. Currently, it is unclear whether combination therapy of ranibizumab with photodynamic therapy (PDT) provides any significant advantage over ranibizumab monotherapy (FOCUS trial); however, the combination of PDT and ranibizumab may decrease the need for frequent retreatment. This question will be addressed in the SUMMIT trial. Therapy with ranibizumab is generally very well tolerated with a low rate of seriously adverse ocular events or systemic side-effects. The advent of vascular endothelial growth factor (VEGF) inhibitors has revolutionized the therapy of neovascular AMD. Ranibizumab at the moment appears to be the most effective approved treatment for neovascular AMD.

Suprachoroidal drug delivery to the back of the eye using hollow microneedles

PURPOSE

In this work, we tested the hypothesis that microneedles provide a minimally invasive method to inject particles into the suprachoroidal space for drug delivery to the back of the eye.

METHODS

A single, hollow microneedle was inserted into the sclera, and infused nanoparticle and microparticle suspensions into the suprachoroidal space. Experiments were performed on whole rabbit, pig, and human eyes ex vivo. Particle delivery was imaged using brightfield and fluorescence microscopy as well as microcomputed tomography.

RESULTS

Microneedles were shown to deliver sulforhodamine B as well as nanoparticle and microparticle suspensions into the suprachoroidal space of rabbit, pig, and human eyes. Volumes up to 35 μL were administered consistently. Optimization of the delivery device parameters showed that microneedle length, pressure, and particle size played an important role in determining successful delivery into the suprachoroidal space. Needle lengths of 800-1,000 μm and applied pressures of 250-300 kPa provided most reliable delivery.

CONCLUSIONS

Microneedles were shown for the first time to deliver nanoparticle and microparticle suspensions into the suprachoroidal space of rabbit, pig and human eyes. This shows that microneedles may provide a minimally invasive method for controlled drug delivery to the back of the eye.

The role of complement Factor H in age-related macular degeneration: a review

Factor H is a 155kDa sialic acid containing glycoprotein that plays an integral role in the regulation of the complement-mediated immune system that is involved in microbial defense, immune complex processing, and programmed cell death. These events take place primarily in fluid phase and on the cell surface and are particularly important in the context of distinguishing self from non-self. Activation of the complement system occurs within seconds and results in a proteolytic cascade eventually forming the membrane attack complex leading to cell lysis. Factor H protects host cells from injury resulting from unrestrained complement activation. Mutations and SNPs (single nucleotide polymorphisms) in Factor H have been implicated in a variety of human conditions including age-related macular degeneration (AMD), atypical hemolytic uremic syndrome, and membranoproliferative glomuleronephritis type II or dense deposit disease. It should not be surprising that these seemingly unrelated diseases involving mutations in Factor H may share common features. Because the immune process involves, in part, an inflammatory response and common or similar surface antigens, it is also not unexpected to observe features of inflammation, including deposition of bioactive complement fragments such as C3a and C5a, a cellular influx of immune related cells such as lymphocytes, and the potential for multiple organ involvement. We review recent developments in molecular genetics; SNPs, including Y402H; the three-dimensional structure; and mass spectroscopy of Factor H as it relates to the pathogenesis of eye disease. In addition, we discuss the concepts of molecular mimicry, sequestered or hidden antigens, and antigenic cross reactivity, and propose that AMD should not simply be considered to be an eye disease, but rather a systemic vascular disease where the eye has the ability to self regulate a local immune response. Identification of the initial event or inciting antigen has yet to be determined and will significantly advance the understanding of the pathogenesis of AMD.

Confocal scanning laser tomography analysis of choroidal neovascularization and correlation with quantitative fluorescein angiography

PURPOSE

To investigate the agreement between confocal scanning laser tomography and quantitative fluorescein angiography in the analysis of retinal-thickness changes in patients with choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD).

MATERIALS AND METHODS

The edema index of a cSLT was measured in 18 eyes of 16 patients with CNV secondary to AMD that underwent photodynamic therapy (PDT) with Visudyne. Measurements were taken 1 hour before as well as 1 hour, 1 month, and 3 months after therapy. Moreover, a custom-written algorithm was used to analyze the integrated contrast amplitude (ICA) of fluorescein angiograms acquired before as well as 1 month and 3 months after PDT. Confocal scanning laser analysis of the edema index (EI) before and after PDT and correlation of the results with quantitative fluorescein angiography was performed.

RESULTS

A statistical significant increase of the EI was observed 1 hour after PDT. Nonetheless, no other statistical significant change over time was observed either on the EI or the ICA. Significant correlation was observed between the EI and the ICA as well as their changes over time, yet better results were observed when non-parametric correlation was calculated.

CONCLUSIONS

The axial intensity profile of the cSLT and the edema index provide important information with respect to the neovascular membranes and correlate well with quantitative fluorescein angiography. The application of cSLT and the EI provide an important tool that could complement the investigation of new treatments of neovascular membranes.

Custom-devised and generic digital enhancement of images for people with maculopathy

AIM

The purpose of this study was to compare the effectivity, in terms of the potential usefulness, of digital filters based on either contrast sensitivity (CS) or supra-threshold contrast matching (CM) in enhancing pictures images for people with maculopathy and to investigate whether generic filters (not based on an individual's vision loss) are equally as effective. Effectivity is measured by changes in perceived visibility.

METHODS

Thirty-five subjects with maculopathy, aged 20-92 years, took part [13 atrophic age-related macular degeneration (ARMD), 14 exudative ARMD, and 8 juvenile macular dystrophy (JMD)]. CS and supra-threshold CM were measured. A range of CS filters (1 or 2-octave wide band-pass filter using a Gabor or polynomial envelope) with different strengths were developed based on the ratio of the individual's contrast threshold and that of a normal age-related group. Similarly filters were developed based on CM at 3.6% and 27.9% contrast. The following generic filters were also applied with different 'strengths': edge enhancement; sharpening; contrast enhancement; Peli's adaptive enhancement; difference of Gaussian; and an equi-emphasis band-pass filter. The filters were applied to images of faces and general scenes. Subjects were asked to rank the perceived visibility of images (to obtain the best version of each filter) and then to rate the perceived visibility of each image filtered with a particular filter.

RESULTS

In general, subjects with atrophic ARMD and JMD preferred the weaker versions of most of the filters, while those with exudative ARMD did not show such a clear preference. Generally, images of faces were preferred with less enhancement than scenes. The filters based on CM were rated as giving significant improvement, while those based on CS and peak emphasis were not preferred. Of the generic filters, the Peli adaptive enhancement filter was most frequently rated as giving a significant improvement (p < 0.05) followed by the contrast enhancement filter. They gave the same perceived enhancement as the custom-devised filters.

CONCLUSIONS

Generic filters, which are easier to apply than the custom-devised filters, are appropriate for rehabilitation purposes.

Intravenous transferrin, RGD peptide and dual-targeted nanoparticles enhance anti-VEGF intraceptor gene delivery to laser-induced CNV

Choroidal neovascularization (CNV) leads to loss of vision in age-related macular degeneration (AMD), the leading cause of blindness in adult population over 50 years old. In this study, we developed intravenously administered, nanoparticulate, targeted nonviral retinal gene delivery systems for the management of CNV. CNV was induced in Brown Norway rats using a 532 nm laser. We engineered transferrin, arginine-glycine-aspartic acid (RGD) peptide or dual-functionalized poly-(lactide-co-glycolide) nanoparticles to target delivery of anti-vascular endothelial growth factor (VEGF) intraceptor plasmid to CNV lesions. Anti-VEGF intraceptor is the only intracellularly acting VEGF inhibitory modality. The results of the study show that nanoparticles allow targeted delivery to the neovascular eye but not the control eye on intravenous administration. Functionalizing the nanoparticle surface with transferrin, a linear RGD peptide or both increased the retinal delivery of nanoparticles and subsequently the intraceptor gene expression in retinal vascular endothelial cells, photoreceptor outer segments and retinal pigment epithelial cells when compared to nonfunctionalized nanoparticles. Most significantly, the CNV areas were significantly smaller in rats treated with functionalized nanoparticles as compared to the ones treated with vehicle or nonfunctionalized nanoparticles. Thus, surface-functionalized nanoparticles allow targeted gene delivery to the neovascular eye on intravenous administration and inhibit the progression of laser-induced CNV in a rodent model.

Long-term vision rescue by human neural progenitors in a rat model of photoreceptor degeneration

PURPOSE

As a follow-up to previous studies showing that human cortical neural progenitor cells (hNPC(ctx)) can sustain vision for at least 70 days after injection into the subretinal space of Royal College of Surgeons (RCS) rats, the authors examined how functional rescue is preserved over long periods and how this relates to retinal integrity and donor cell survival.

METHODS

Pigmented dystrophic RCS rats (n = 15) received unilateral subretinal injections of hNPC(ctx) at postnatal day (P) 21; control rats (n = 10) received medium alone and were untreated. All animals were maintained on oral cyclosporine A. Function was monitored serially by measuring acuity (using an optomotor test) and luminance thresholds (recording from the superior colliculus) at approximately P90, P150, and P280. Eyes were processed for histologic study after functional tests.

RESULTS

Acuity and luminance thresholds were significantly better in hNPC(ctx)-treated animals than in controls (P < 0.001) at all time points studied. Acuity was greater than 90%, 82%, and 37% of normal at P90, P150, and P270, whereas luminance thresholds in the area of best rescue remained similar the whole time. Histologic studies revealed substantial photoreceptor rescue, even up to P280, despite progressive deterioration in rod and cone morphology. Donor cells were still present at P280, and no sign of donor cell overgrowth was seen.

CONCLUSIONS

Long-term rescue of function and associated morphologic substrates was seen, together with donor cell survival even in the xenograft paradigm. This is encouraging when exploring further the potential for the application of hNPC(ctx) in treating retinal disease.