Review Article. New treatments in age-related macular degeneration

Amyloid β peptides overexpression in retinal pigment epithelial cells via AAV-mediated gene transfer mimics AMD-like pathology in mice

Age-related macular degeneration (AMD) is a progressive retinal neurodegenerative disorder characterized by extracellular deposits known as drusen. A major constituent of drusen deposits are Alzheimer disease-associated amyloid β (Aβ) peptides. To understand the etiology of Aβ proteostasis in AMD, we delivered recombinant adeno-associated virus (AAV) encoding Aβ42 and Aβ40 peptides fused to BRI2 protein by intraocular injection in C57BL/6J mice. Endogenous protease cleavage of such constructs leads to production of secreted Aβ42 and Aβ40 respectively. We demonstrate that overexpression of secreted Aβ40 or Aβ42 resulted in dramatic induction of drusen-like deposits by 2 months' post-injection. These drusen-like deposits were immunopositive for Aβ and complement proteins but did not stain for conventional amyloid dyes, such as Thioflavin S. Both injected cohorts showed gliosis and degenerative changes, though ERG responses were minimally affected. Intriguingly, simultaneous overexpression of BRI-Aβ40 or BRI-Aβ42 together resulted in dose-dependent and cumulative changes reminiscent of AMD type pathology - drusen-like deposits, severe reduction in ERG responses, photoreceptor cell loss and gliosis. Here, we have established a physiological model of Aβ containing deposits in wild-type mice that recapitulates major retinal pathophysiological features of AMD and will be instrumental in mechanistic understanding and development of therapeutic strategies against AMD.

Influence of bromine substitution pattern on the singlet oxygen generation efficiency of two-photon absorbing chromophores

A molecular engineering strategy based on rational variations of the bromine substitution pattern in two-photon absorbing singlet oxygen sensitizers allows studying the relations that exist between the positioning of an inter-system crossing promoter on the charge-transfer chromophore and its ability to generate singlet oxygen.

Stimulation of aquaporin-mediated fluid transport by cyclic GMP in human retinal pigment epithelium in vitro

PURPOSE

The retinal pigment epithelium (RPE) expresses aquaporin-1 (AQP1) and components of the natriuretic peptide signaling pathway. We hypothesized that stimulation of the natriuretic signaling pathway in RPE with atrial natriuretic peptide (ANP) and with membrane-permeable analogs of cGMP would induce a net apical-to-basal transport of fluid.

METHODS

The hypothesis was tested using human RPE cultures that retain properties seen in vivo. Confluent monolayers were treated with ANP or membrane-permeable cGMP analogs in the presence of anantin, H-8, and an AQP1 inhibitor, AqB013. Fluid movement from the apical to basal chambers was measured by weight and used to calculate net fluid transport.

RESULTS

Our results demonstrated a 40% increase in net apical-to-basal fluid transport by ANP (5 μM) that was inhibited completely by the ANP receptor antagonist anantin and a 60% increase in net apical-to-basal fluid transport in response to the extracellularly applied membrane-permeable cGMP analog pCPT-cGMP (50 μM), which was not affected by the protein kinase G inhibitor H-8. The aquaporin antagonist AqB013 (20 μM) inhibited the cGMP-stimulated RPE fluid flux.

CONCLUSIONS

The effect of cGMP is consistent with an enhancement of the net fluid flux in RPE mediated by AQP1 channels. Pharmacologic activation of cGMP signaling and concomitant stimulation of fluid uptake from the subretinal space could offer insights into a new approach to treating or reducing the risk of retinal detachment.

Anti-amyloid therapy protects against retinal pigmented epithelium damage and vision loss in a model of age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of visual dysfunction worldwide. Amyloid β (Aβ) peptides, Aβ1-40 (Aβ40) and Aβ1-42 (Aβ42), have been implicated previously in the AMD disease process. Consistent with a pathogenic role for Aβ, we show here that a mouse model of AMD that invokes multiple factors that are known to modify AMD risk (aged human apolipoprotein E 4 targeted replacement mice on a high-fat, cholesterol-enriched diet) presents with Aβ-containing deposits basal to the retinal pigmented epithelium (RPE), histopathologic changes in the RPE, and a deficit in scotopic electroretinographic response, which is reflective of impaired visual function. Strikingly, these electroretinographic deficits are abrogated in a dose-dependent manner by systemic administration of an antibody targeting the C termini of Aβ40 and Aβ42. Concomitant reduction in the levels of Aβ and activated complement components in sub-RPE deposits and structural preservation of the RPE are associated with anti-Aβ40/42 antibody immunotherapy and visual protection. These observations are consistent with the reduction in amyloid plaques and improvement of cognitive function in mouse models of Alzheimer's disease treated with anti-Aβ antibodies. They also implicate Aβ in the pathogenesis of AMD and identify Aβ as a viable therapeutic target for its treatment.

Effect of flavone on the ocular blood flow and formation of choroidal neovascularization

AIM

To investigate the effect of flavone on ocular blood flow in rabbit eyes and the formation of choroidal neovascularization (CNV) in rat model of age-related macular degeneration (AMD).

METHODS

In in vivo studies, colored microsphere technique was used to determine the ocular blood flow in ocular hypertensive rabbit eyes. The rat eyes were treated with 0.5% flavone eye drops 3 times a day for 1 week before and 4 weeks after laser-induced injury of Bruch's membrane. The development of CNV was determined by fluorescein angiography (FA) performed on the 2nd and 4th after injury. In in vitro studies, the effect of flavone on the viability of human umbilical vein endothelial cells HUVECs was measured by MTT assay.

RESULTS

The ocular blood flow in rabbit eyes was significantly increased after flavone instillation. Flavone significantly inhibited the formation of laser induced CNV. In vitro results showed that flavone inhibited the proliferation of HUVECs.

CONCLUSION

Flavone could increase ocular blood flow and inhibit the formation of CNV.

Anti-angiogenic therapy of exudative age-related macular degeneration: current progress and emerging concepts

Age-related macular degeneration (AMD) is the leading cause of blindness in elderly patients. The more aggressive exudative form is characterized by abnormal blood-vessel development that occurs beneath the retina as a result of choroidal neovascularization (CNV). Vascular endothelial growth factor (VEGF) has emerged as the key mediator of CNV formation; this has led to intensive research on VEGF and the recent approval of anti-VEGF compounds by the US Food and Drug Administration. Despite this successful introduction of anti-angiogenic therapies into the clinical setting, there is still a lack of treatments that definitively reverse damaged vision. Here, we consider the importance of putative molecular targets other than VEGF that might have been underestimated. Emerging cellular mechanisms offer additional opportunities for innovative therapeutic approaches.

Is significant relevant? Validity and patient benefit of randomized controlled clinical trials on age-related macular degeneration

A large variety of new treatment options for different forms of age-related macular degeneration (ARMD) are becoming available. Not all new therapies may meet the expectations of patients and ophthalmologists. Despite the given statistical significant priority of treatment investigations, the endpoints may not be relevant to the patient's requirements. Therefore, questions inevitably arise regarding patient's benefit and the validity of the randomized controlled trials. The randomized controlled trial is regarded as the "gold standard" in terms of evaluating the effectiveness of interventions. The external validity of randomized controlled trials may be compromised, if, for example, patients assigned to the study group are unrepresentative of the reference population. This review aims to analyze problems with external validity in the randomized controlled trials on ARMD and surveys the endpoints of clinical studies with respect to the patient benefit.

A review of drug options in age-related macular degeneration therapy and potential new agents

Age-related macular degeneration (AMD) is the leading cause of legal blindness in people > 50 years of age in the developed world. AMD is both a debilitating and costly disease for the individual and the community. Greater understanding of the mechanisms and pathways involved in causing the visual loss in AMD has resulted in the advent of several newer and more effective treatment options, making it an exciting time in the management of AMD. This paper will examine the principles behind the existing drug therapies available, as well as those being developed in the management or prophylaxis of AMD and its vision-threatening complications.

Hypericin-loaded nanoparticles for the photodynamic treatment of ovarian cancer

A photodynamic approach has been suggested to improve diagnosis and therapy of ovarian cancer. As Hypericin (Hy), a natural photosensitizer (PS) extracted from Hypericum perforatum, has been shown to be efficient in vitro and in vivo for the detection or treatment of other cancers, Hy could also be a potent tool for the treatment and detection of ovarian cancer. Due to its hydrophobicity, systemic administration of Hy is problematic. Thus, polymeric nanoparticles (NPs) of polylactic acid (PLA) or polylactic-co-glycolic acid (PLGA) were used as a drug delivery system. Hy-loaded NPs were produced with the following characteristics: (i) size in the 200-300 nm range, (ii) negative zeta potential, (iii) low residual PVAL and (iv) drug loading from 0.03 to 0.15% (w/w). Their in vitro photoactivity was investigated on the NuTu-19 ovarian cancer cell model derived from Fischer 344 rats and compared to free drug. Hy-loaded PLA NPs exhibited a higher photoactivity than free drug. Increasing light dose or incubation time with cells induced an enhanced activity of Hy-loaded PLA NPs. Increased NP drug loading had a negative effect on their photoactivity on NuTu-19 cells: at the same Hy concentration, the higher was the drug loading, the lower was the phototoxic effect. The influence of NP drug loading on the Hy release from NPs was also investigated.

Impact of age related macular degeneration on quality of life

AIMS

To describe the impact of age related macular degeneration (AMD) on quality of life and explore the association with vision, health, and demographic variables.

METHODS

Adult participants diagnosed with AMD and with impaired vision (visual acuity <6/12) were assessed with the Impact of Vision Impairment (IVI) questionnaire. Participants rated the extent that vision restricted participation in activities affecting quality of life and completed the Short Form General Health Survey (SF-12) and a sociodemographic questionnaire.

RESULTS

The mean age of the 106 participants (66% female) was 83.6 years (range 64-98). One quarter had mild vision impairment, (VA<6/12-6/18) and 75% had moderate or severely impaired vision. Participants reported from at least "a little" concern on 23 of the 32 IVI items including reading, emotional health, mobility, and participation in relevant activities. Those with mild and moderate vision impairment were similarly affected but significantly different from those with severe vision loss (p<0.05). Distance vision was associated with IVI scores but not age, sex, or duration of vision loss.

CONCLUSION

AMD affects many quality of life related activities and not just those related to reading. Referral to low vision care services should be considered for people with mild vision loss and worse.

Enhancement of Two-Photon Absorption Cross-Section and Singlet-Oxygen Generation in Porphyrins upon β-Functionalization with Donor−Acceptor Substituents

The microwave-enhanced synthesis, comparative singlet oxygen sensitization efficiency, and nonlinear optical characterization of a new beta-functionalized porphyrin and its copper complex are described. We show that the introduction of a donor-acceptor push-pull conjugated fragment in the beta position strongly perturbs the porphyrin electronic structure leading to a remarkable one- and two-photon NIR absorption enhancement.

Contrast sensitivity as an outcome measure in patients with subfoveal choroidal neovascularisation due to age-related macular degeneration

PURPOSE

Although visual acuity is the most frequently used primary outcome measure in clinical trials of treatments for choroidal neovascularisation (CNV) due to age-related macular degeneration (AMD), contrast sensitivity may provide valuable additional information. This paper reviews the evidence for using contrast sensitivity as a measure of visual function and as an outcome measure in clinical trials in patients with subfoveal CNV due to AMD.

METHODS

Medline database searches were performed to retrieve relevant articles on contrast sensitivity. In addition, articles were included from the authors' knowledge of the literature and from the reference lists of retrieved articles.

RESULTS

The published literature demonstrates that contrast sensitivity is an important measure of visual function in patients with subfoveal CNV due to AMD. Most clinical trials of treatments for CNV due to AMD have reported visual acuity as the primary outcome. However, there is evidence that treatment (such as verteporfin therapy) may also provide additional benefits in terms of contrast sensitivity. These benefits may not be completely characterised by measurement of visual acuity alone.

CONCLUSIONS

The inclusion of contrast sensitivity as an outcome measure in studies of patients with CNV due to AMD may provide a more complete understanding of the effects of treatment on visual function and the likely benefits for patients.

Pegaptanib: in exudative age-related macular degeneration

Pegaptanib, an aptamer, is an antagonist of vascular endothelial growth factor that has shown efficacy in the treatment of patients with exudative age-related macular degeneration (AMD). In two randomised, double-masked trials in patients with exudative AMD (n=1208), the proportion of responders (those losing <15 letters of visual acuity) at 54 weeks was significantly higher in intravitreous pegaptanib 0.3 mg recipients than in those receiving sham injections (70% vs 55%; p<0.001). These trials were conducted concurrently and analysed as a single study; the treatments were given every 6 weeks for 48 weeks. The improvement in visual acuity with pegaptanib was maintained in a 1-year extension of these trials. Similar favourable results with pegaptanib 0.3 mg were seen in terms of the secondary efficacy endpoints (e.g. proportion of patients experiencing severe loss of visual acuity or legal blindness in the study eye). These vision-improving effects of pegaptanib were associated with beneficial angiographic effects. Intravitreous pegaptanib 0.3-3 mg was well tolerated with most ocular adverse events being mild-to-moderate and transient. Serious injection-related adverse events occurred in <or=1.3% of patients treated with pegaptanib. There were no systemic adverse events that could be definitely attributed to pegaptanib.

New π-Extended Water-Soluble Squaraines as Singlet Oxygen Generators

[graph: see text] Condensation of squaric acid with a number of differently substituted 2-pyrrolyl derivatives afforded three new classes of squaraines. Their sharp and intense absorption bands in the biological window (700-900 nm), inherent singlet oxygen generation capabilities, together with proper functionalization allowing good water solubility make them suitable candidates as new non-porphyrinic singlet oxygen photosensitizers for photodynamic therapy (PDT).

Transpupillary thermotherapy for occult subfoveal choroidal neovascularization: a 1-year, prospective randomized pilot study

PURPOSE

To evaluate the 1-year effect of transpupillary thermotherapy (TTT) on occult choroidal neovascularization membranes (CNV).

METHODS

In this prospective, randomized, controlled pilot study of 28 patients with occult or minimally classic (< 10%) neovascularization membranes with a diameter less than 4500 microm, 19 patients were treated with TTT, while nine received sham treatment. Outcome measures were membrane diameter, visual acuity and reading ability.

RESULTS

The median age of patients randomized to TTT was 78 years (range 24 years); that of patients randomized to sham was 79 years (range 9 years). There was no difference regarding membrane diameter at baseline between the two groups; the median membrane diameters were 3400 microm (range 2400 microm) in the TTT group and 3200 microm (range 2300 microm) in the sham group (p = 0.639). Visual acuity (VA) was similar, with a median of 0.2 (minimum-maximum 0.08-0.5) in the TTT group and a median of 0.16 (min-max 0.10-0.32) in the sham group. A total of 21 patients were followed for 1 year, 13 in the TTT group (2.7 treatments/patient) and eight in the sham group. Membrane diameter increased in both groups, by a median of 350 microm (range 1600 microm) in the TTT group and 800 microm (range 1700 microm) in the sham group (p = 0.414), respectively, and there was a loss in VA of > or = 15 letters in 5/13 patients (38%) in the TTT group compared with 2/8 patients (25%) in the sham group (p = 0.266). Reading ability deteriorated equally over time in both groups. Seven patients were lost to follow-up due to reluctance to continue in the study (n = 4) or development of a classical component > 50% (n = 3) requiring photodynamic therapy (PDT).

CONCLUSION

The results from this randomized, prospective pilot study of TTT for occult CNV did not indicate that TTT has a beneficial effect on visual outcome 1 year after treatment compared with the visual outcome that results from the natural course of the disease. The small study size limits statistical power and results from large control studies are needed.

Gene therapy for proliferative ocular diseases

Proliferative ocular diseases encompass a wide variety of pathological processes with adverse cellular differentiation, proliferation and migration as common features. Pathologies may involve neovascular responses associated with diabetic retinopathy, retinopathy of prematurity or age-related macular degeneration. These diseases are quite prevalent and account for substantial visual impairment and blindness worldwide. Although treatment strategies are largely surgical, advances in our understanding of the proteins crucial to cell transdifferentiation, proliferation and migration, along with better gene transfer techniques, have greatly increased the potential for biological treatment options. In this report, the most common proliferative ocular vascular diseases and existing therapeutic modalities will be reviewed and an overview of possible gene therapy options will be discussed, along with potential candidate genes.

Met72Thr polymorphism of pigment epithelium-derived factor gene and susceptibility to age-related macular degeneration

Age-related macular degeneration (ARMD) is the most common cause of acquired blindness among the people of occupational age. Although the pathogenesis of ARMD is not fully understood, several studies suggest a possible contribution of a genetic factor in the development and progression of ARMD. Pigment epithelium-derived factor (PEDF), a glycoprotein that belongs to the superfamily of serine protease inhibitors, was first purified from the conditioned media of human retinal pigment epithelial cells as a factor with potent neuronal differentiating activity in human retinoblastoma cells. Recently, PEDF has been shown to be a highly effective inhibitor of angiogenesis in cell culture and animal models. In addition, PEDF has been found in the vitreous, and its levels were decreased in angiogenic eye diseases, thus suggesting that a loss of PEDF in the eye is functionally important in the pathogenesis of ARMD. A functional amino acid change, a methionine to threonine polymorphism (Met72Thr polymorphism) at codon 72 in exon 3 (T/C polymorphism) of the PEDF gene, that results in the formation of BsstSI restriction site, has recently been identified. Since it is well known that a single nucleotide polymorphism and resultant amino acid change often alters the activity or expression level of the target protein, we would like to propose here a novel hypothesis that the Met72Thr polymorphism (T/C polymorphism) of PEDF gene may be a genetic marker for ARMD. Are genotype and allele frequencies of the Met72Thr polymorphism (T/C polymorphism) different between the patients with or without ARMD? Is this polymorphism associated with disease severity and progression? If the answer is yes, does this Met72Thr polymorphism regulate the vitreous levels of PEDF? These clinical studies could provide us with information whether this genetic variant of the PEDF gene could present an attractive candidate susceptibility gene for ARMD.

Cone function studied with flicker electroretinogram during progressive retinal degeneration in RCS rats

The Royal College of Surgeons (RCS) rat has a primary defect in retinal pigment epithelial cells that leads to the progressive loss of photoreceptors and central visual responsiveness. While most rods are lost by 90 days of age (P90), cones degenerate more slowly, and can be detected anatomically up to 2 years of age, despite massive neuronal death and retinal remodelling. To examine how this progressive degenerative process impacts on cone function, we recorded the electroretingram to white light flashes (1.37 log cd s m(-2)) presented at frequencies ranging from 3 to 50 Hz, under light adapted conditions (29.8 cd m(-2)). Pigmented dystrophic and congenic non-dystrophic RCS rats aged from 18 to 300 days were studied. In all responsive animals at all ages, maximal amplitudes were obtained at 3 Hz. In both non-dystrophic and dystrophic rats, there was an increase from P18 to P21 in response amplitude and critical fusion frequency. After P21, these two parameters declined progressively with age in dystrophic rats. Other changes included prolongation in latency, which was first detected prior to the initiation of amplitude reduction. While phase shifts were also detected in dystrophic RCS rats, they appeared at later degenerative stages. The latest age at which responses could be elicited in dystrophic rats was at P200, with positive waves being replaced by negative deflections. The effect of increments in the intensity of background illumination was tested at P50 in both groups. This caused a diminution in flicker response amplitude and critical fusion frequencies in non-dystrophics, while in dystrophic animals, response amplitudes were reduced only at low frequencies and critical fusion frequencies were unaltered. In conclusion, although dystrophic RCS rats undergo a progressive decline in cone function with age, the flicker responsiveness at P21 is comparable to that of non-dystrophic congenic rats, suggesting normal developmental maturation of the cone system in this animal model of retinal degeneration. Flicker responses can be recorded up to P200, at which point the retina has undergone severe regressive and reactive changes in its connectivity patterns. The fact that responses at this age consist of solely negative deflections might be a reflection of the highly pathological state of the retina.

A prospective study of visual function and quality of life following PDT in patients with wet age related macular degeneration

AIMS

(1) A prospective study to assess visual function measures and quality of life (QoL) in patients with wet age related macular degeneration (AMD) treated with photodynamic therapy (PDT). (2) To assess if PDT prevents severe visual loss (loss of six or more lines of distance visual acuity) in the treated eye.

METHODS

48 of 51 recruited patients with predominantly classic subfoveal choroidal neovascularisation (CNV) secondary AMD who were treated with PDT were followed up for 1 year. Assessment included distance and near visual acuity, contrast sensitivity, vision related quality of life and fluorescein angiography. Photodynamic therapy using Visudyne was carried out according to standard protocol. Patients were followed up every 3 months and treatment repeated if there was significant leakage from CNV.

RESULTS

At the 12 month follow up, 71% (n = 34) of the patients lost less than three lines of best corrected distance visual acuity. Although there were significant decreases in some of the QoL items tested, patients were significantly less anxious and more independent outdoors at the 12 month follow up.

CONCLUSION

This study is in keeping with published literature with PDT preventing severe visual loss in two thirds of treated patients with predominantly classic CNV.

In Vitro Demonstration of the Heavy-Atom Effect for Photodynamic Therapy

Photodynamic therapy (PDT) is an emerging treatment modality for a range of disease classes, both cancerous and noncancerous. This has brought about an active pursuit of new PDT agents that can be optimized for the unique set of photophysical characteristics that are required for a successful clinical agent. We now describe a totally new class of PDT agent, the BF2-chelated 3,5-diaryl-1H-pyrrol-2-yl-3,5-diarylpyrrol-2-ylideneamines (tetraarylazadipyrromethenes). Optimized synthetic procedures have been developed to facilitate the generation of an array of specifically substituted derivatives to demonstrate how control of key therapeutic parameters such as wavelength of maximum absorbance and singlet-oxygen generation can be achieved. Photosensitizer absorption maxima can be varied within the body's therapeutic window between 650 and 700 nm, with high extinction coefficients ranging from 75,000 to 85,000 M(-1) cm(-1). Photosensitizer singlet-oxygen generation level was modulated by the exploitation of the heavy-atom effect. An array of photosensitizers with and without bromine atom substituents gave rise to a series of compounds with varying singlet-oxygen generation profiles. X-ray structural evidence indicates that the substitution of the bromine atoms has not caused a planarity distortion of the photosensitizer. Comparative singlet-oxygen production levels of each photosensitizer versus two standards demonstrated a modulating effect on singlet-oxygen generation depending upon substituent patterns about the photosensitizer. Confocal laser scanning microscopy imaging of 18a in HeLa cervical carcinoma cells proved that the photosensitizer was exclusively localized to the cellular cytoplasm. In vitro light-induced toxicity assays in HeLa cervical carcinoma and MRC5-SV40 transformed fibroblast cancer cell lines confirmed that the heavy-atom effect is viable in a live cellular system and that it can be exploited to modulate assay efficacy. Direct comparison of the efficacy of the photosensitizers 18b and 19b, which only differ in molecular structure by the presence of two bromine atoms, illustrated an increase in efficacy of more than a 1000-fold in both cell lines. All photosensitizers have very low to nondeterminable dark toxicity in our assay system.

Age-related maculopathy: a genomewide scan with continued evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions

Age-related maculopathy (ARM), or age-related macular degeneration, is one of the most common causes of visual impairment in the elderly population of developed nations. In a combined analysis of two previous genomewide scans that included 391 families, containing up to 452 affected sib pairs, we found linkage evidence in four regions: 1q31, 9p13, 10q26, and 17q25. We now have added a third set of families and have performed an integrated analysis incorporating 530 families and up to 736 affected sib pairs. Under three diagnostic models, we have conducted linkage analyses using parametric (heterogeneity LOD [HLOD] scores under an autosomal dominant model) and nonparametric (Sall statistic) methods. There is ongoing evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions. If we treat the third set of families as a replication set, then two regions (10q26 and 17q25) are replicated, with LOD scores >1.0. If we pool all our data together, then four regions (1q31, 2q14.3, 10q26, and 17q25) show HLOD or Sall scores > or =2.0. Within the 1q31 region, we observed an HLOD of 2.72 (genomewide P=.061) under our least stringent diagnostic model, whereas the 17q25 region contained a maximal HLOD of 3.53 (genomewide P=.007) under our intermediate diagnostic model. We have evaluated our results with respect to the findings from several new independent genomewide linkage studies and also have completed ordered subset analyses (OSAs) with apolipoprotein E alleles, smoking history, and age at onset as stratifying covariates. The OSAs generate the interesting hypothesis that the effect of smoking on the risk of ARM is accentuated by a gene in the 10q26 region--a region implicated by four other studies.