Pathophysiology of age-related macular degeneration

Growth-related effects of oxidant-induced stress on cultured RPE and choroidal endothelial cells

Mounting evidence suggests that oxidative stress caused by reactive oxygen intermediates is a significant mechanism in the pathogenesis of age-related macular degeneration (AMD). Although vascular endothelial growth factor (VEGF) and other cytokines are involved in choroidal neovascularization (CNV) it is largely unknown whether oxidative stress may predispose the eye to increased levels of proangiogenic factors. In an in vitro study we have determined viability and proliferation of both human retinal pigment epithelial (RPE) cells and bovine choroidal endothelial cells (CECs) and assessed the release of basic fibroblast growth factor (bFGF) and VEGF from RPE cells after exposing them to oxidative stress. Permanent presence of tert-butyl-hydroperoxide (tBH), a pro-oxidative stressor, in the cell cultures resulted in decreasing viability and proliferation of RPE cells and CECs. Loss of RPE cell viability was associated with activation of apoptosis by tBH in a dose-dependent manner. The antioxidant, N-acetyl-L-cysteine (NAC), and secreted soluble mediators of RPE cells were appropriate to attenuate the effects of tBH-mediated oxidative stress. RPE cells exposed to tBH were found to release increasing amounts of bFGF but not VEGF after 24h of culture, thereby supporting proliferation of CECs. These findings suggest that oxidative stress compromises the viability of RPE cells and CECs. However, increased bFGF levels concomitantly released from RPE cells may attenuate the CEC-directed effect, protect CECs from oxidative insults, and are likely to promote CNV.

[Oxidative stress in association with risk factors for the occurrence and development of age-related macular degeneration]

<zakljucak> Niz rezultata potvrdjuje ulogu oksidativnog stresa u etiopatogenezi AMD i to bilo kao inicijalnog ili izolovanog uzrocnog faktora, ili kao dodatnog cinioca u sklopu drugih faktora rizika. Bolje poznavanje ove oblasti prosiruje mogucnosti prevencije ove, ali i drugih bolesti starijeg zivotnog doba.

Age and disease-related structural changes in the retinal pigment epithelium

As the retinal pigment epithelium (RPE) ages, a number of structural changes occur, including loss of melanin granules, increase in the density of residual bodies, accumulation of lipofuscin, accumulation of basal deposits on or within Bruch's membrane, formation of drusen (between the basal lamina of the RPE and the inner collagenous layer of Bruch's membrane), thickening of Bruch's membrane, microvilli atrophy and disorganization of the basal infoldings. Although these changes are well known, the basic mechanisms involved in them are frequently poorly understood. These age-related changes progress slowly and vary in severity in different individuals. These changes are also found in age-related macular degeneration (AMD), a late onset disease that severely impacts the RPE, but they are much more pronounced than during normal aging. However, the changes in AMD lead to severe loss of vision. Given the many supporting functions which the RPE serves for the retina, it is important to decipher the age-related changes in this epithelium in order to understand age-related changes in vision.

Survival and remodeling of melanopsin cells during retinal dystrophy

The melanopsin positive, intrinsically photosensitive retinal ganglion cells (ipRGCs) of the inner retina have been shown to send wide-ranging projections throughout the brain. To investigate the response of this important cell type during retinal dystrophy, we use the Royal College of Surgeons (RCS) dystrophic rat, a major model of retinal degeneration. We find that ipRGCs exhibit a distinctive molecular profile that remains unaltered during early stages of outer retinal pathology (15 weeks of age). In particular, these cells express βIII tubulin, α-acetylated tubulin, and microtubule-associated proteins (MAPs), while remaining negative for other RGC markers such as neurofilaments, calretinin, and parvalbumin. By 14 months of age, melanopsin positive fibers invade ectopic locations in the dystrophic retina and ipRGC axons/dendrites become distorted (a process that may involve vascular remodeling). The morphological abnormalities in melanopsin processes are associated with elevated immunoreactivity for MAP1b and a reduction in α-acetylated tubulin. Quantification of ipRGCs in whole mounts reveals reduced melanopsin cell number with increasing age. Focusing on the retinal periphery, we find a significant decline in melanopsin cell density contrasted by a stability of melanopsin positive processes. In addition to these findings, we describe for the first time, a distinct plexus of melanopsin processes in the far peripheral retina, a structure that is coincident with a short wavelength opsin cone-enriched rim. We conclude that some ipRGCs are lost in RCS dystrophic rats as the disease progresses and that this loss may involve vascular remodeling. However, a significant number of melanopsin positive cells survive into advanced stages of retinal degeneration and show indications of remodeling in response to pathology. Our findings underline the importance of early intervention in human retinal disease in order to preserve integrity of the inner retinal photoreceptive network.

alpha2 But not alpha1 AMP-activated protein kinase mediates oxidative stress-induced inhibition of retinal pigment epithelium cell phagocytosis of photoreceptor outer segments

Oxidative stress causes retinal pigment epithelium (RPE) cell dysfunction and is a major risk factor leading to the development of dry-type age-related macular degeneration. Taking pharmacological and genetic approaches, we address the mechanisms by which sublethal oxidative stress inhibits RPE cell phagocytosis. Sublethal oxidative stress dose-dependently inhibited RPE cell phagocytosis of photoreceptor outer segments (POS) and activated AMP-activated protein kinase (AMPK) as determined by increased Thr172 and Ser79 phosphorylation of AMPKalpha and its substrate acetyl-CoA carboxylase, respectively. Similar to oxidative stress, 5-aminoimidazole-4-carboxamide riboside (AICAR), a pharmacological activator of AMPK, inhibited RPE cell phagocytosis of POS in a dose-dependent manner. Inhibition of RPE cell phagocytosis by AICAR was fully reversed by blockade of AICAR translocation into cells by dipyridamole or inhibition of AICAR conversion to ZMP by adenosine kinase inhibitor 5-iodotubercidin. In agreement, AICAR-induced activation of AMPK was abolished by preincubation with dipyridamole or 5-iodotubercidin. Knock-out experiments further revealed that alpha2 but not alpha1 AMPK was involved in RPE cell phagocytosis and that activation of alpha2 AMPK contributed to the inhibition of RPE cell phagocytosis by oxidative stress. Inhibition of RPE cell phagocytosis by activation of alpha2 AMPK was associated with a dramatic increase in acetyl-CoA carboxylase phosphorylation. In comparison, AMPK had no role in oxidative stress-induced breakdown of RPE barrier function. Taken together, reduction in POS load under oxidative stress might direct RPE cells to a self-protected status. Thus, activating AMPK could have therapeutic potential in treating dry macular degeneration.

Macular function in eyes with early age-related macular degeneration with or without contralateral late age-related macular degeneration

PURPOSE

To evaluate psychophysical and electrophysiologic responses in eyes with early age-related macular degeneration (AMD) without a decrease in visual acuity and with or without late AMD in the fellow eye.

METHODS

Fifteen patients (mean age: 67.9 +/- 7.20 years) with early AMD in both eyes (AMD1 group, 15 eyes) and 15 patients (mean age: 71.40 +/- 7.06 years) with early AMD in one eye and late AMD in the fellow eye (AMD2 group, 15 eyes) were enrolled. They were compared to 15 age-similar normal control subjects. LogMAR visual acuity (VA), macular sensitivity by MP-1 microperimetry, and multifocal electroretinograms (mfERG) were assessed in control, AMD1, and AMD2 eyes. mfERG response amplitude density (RAD, nV/deg2) of the N1-P1 component of first order binary kernels was measured.

RESULTS

When compared to controls, AMD1 and AMD2 eyes showed a significant (analysis of variance, P < 0.01) decrease in MP-1 microperimetry assessed in the 0-2.5 and 2.5-5 degrees of the macula, significantly correlated (Pearson test, P < 0.01) to the corresponding significant decrease (P < 0.01) in mfERG N1-P1 RADs assessed in the 0-2.5 and 2.5-5 degrees. In AMD1 and AMD2 eyes, VA and mfERG N1-P1 RADs assessed in the 5-20 degrees were similar (P > 0.01) to controls. VA, MP-1, and mfERG values were not significantly different in AMD1 and AMD2 eyes.

CONCLUSION

In eyes with early AMD there is a dysfunction of preganglionic elements in the central 0-5 retinal degrees detectable by mfERG or MP-1 microperimetry. This impairment is not further influenced by the presence of late AMD in the fellow eye.

Embryonic stem cells and retinal repair

In this review we examine the potential of embryonic stem cells (ESCs) for use in the treatment of retinal diseases involving photoreceptors and retinal pigment epithelium (RPE). We outline the ontogenesis of target retinal cell types (RPE, rods and cones) and discuss how an understanding of developmental processes can inform our manipulation of ESCs in vitro. Due to their potential for cellular therapy, special emphasis is placed upon the derivation and culture of human embryonic stem cells (HESCs) and their differentiation towards a retinal phenotype. In terms of achieving this goal, we suggest that much of the success to date reflects permissive in vitro environments provided by established protocols for HESC derivation, propagation and neural differentiation. In addition, we summarise key factors that may be important for enhancing efficiency of retinal cell-type derivation from HESCs. The retina is an amenable component of the central nervous system (CNS) and as such, diseases of this structure provide a realistic target for the application of HESC-derived cellular therapy to the CNS. In order to further this goal, the second component of our review focuses on the cellular and molecular cues within retinal environments that may influence the survival and behaviour of transplanted cells. Our analysis considers both the potential barriers to transplant integration in the retina itself together with the remodelling in host visual centres that is known to accompany retinal dystrophy.

A variant of mitochondrial protein LOC387715/ARMS2, not HTRA1, is strongly associated with age-related macular degeneration

Genetic variants at chromosomes 1q31-32 and 10q26 are strongly associated with susceptibility to age-related macular degeneration (AMD), a common blinding disease of the elderly. We demonstrate, by evaluating 45 tag SNPs spanning HTRA1, PLEKHA1, and predicted gene LOC387715/ARMS2, that rs10490924 SNP alone, or a variant in strong linkage disequilibrium, can explain the bulk of association between the 10q26 chromosomal region and AMD. A previously suggested causal SNP, rs11200638, and other examined SNPs in the region are only indirectly associated with the disease. Contrary to previous reports, we show that rs11200638 SNP has no significant impact on HTRA1 promoter activity in three different cell lines, and HTRA1 mRNA expression exhibits no significant change between control and AMD retinas. However, SNP rs10490924 shows the strongest association with AMD (P = 5.3 x 10(-30)), revealing an estimated relative risk of 2.66 for GT heterozygotes and 7.05 for TT homozygotes. The rs10490924 SNP results in nonsynonymous A69S alteration in the predicted protein LOC387715/ARMS2, which has a highly conserved ortholog in chimpanzee, but not in other vertebrate sequences. We demonstrate that LOC387715/ARMS2 mRNA is detected in the human retina and various cell lines and encodes a 12-kDa protein, which localizes to the mitochondrial outer membrane when expressed in mammalian cells. We propose that rs10490924 represents a major susceptibility variant for AMD at 10q26. A likely biological mechanism is that the A69S change in the LOC387715/ARMS2 protein affects its presumptive function in mitochondria.

Pro-inflammatory cytokines increase reactive oxygen species through mitochondria and NADPH oxidase in cultured RPE cells

Reactive oxygen species (ROS) generated during inflammation are believed to play critical roles in various ocular diseases. However, the underlying mechanisms remain poorly understood. We investigated if pro-inflammatory cytokines, tumor necrosis factor (TNF)-alpha, interleukin-1 beta (IL-1 beta), and interferon-gamma (IFN-gamma), induce ROS in human retinal pigment epithelial (RPE) cells. TNF-alpha, IL-1 beta and IFN-gamma increased both intracellular and extracellular ROS production in a time- and dose-dependent manner. Thenoyltrifluoroacetone (TTFA), an inhibitor of mitochondrial respiratory chain, blocked TNF-alpha- and IFN-gamma-, but not IL-1 beta-induced ROS, whereas other two mitochondrial respiratory chain inhibitors, rotenone and antimycin A, had no effect. NADPH oxidase inhibitor (diphenylene iodinium) abolished the ROS production induced by IL-1 beta or IFN-gamma, but not by TNF-alpha, whereas 6-aminonicotinamide (6AN), an inhibitor of the hexose monophosphate shunt (HMS), had no significant effects on the ROS induced by all three cytokines. ROS scavengers, pyrrolidinedithiocarbamate (PDTC) and N-acetyl-cysteine (NAC), reduced the levels of ROS induced by TNF-alpha, IL-1 beta and IFN-gamma (P<0.05). Collectively, these results demonstrate that TNF-alpha, IL-1 beta and IFN-gamma increase mitochondrial- and NADPH oxidase-generated ROS in human RPE cells.

SOD2 knockdown mouse model of early AMD

PURPOSE

To test the hypothesis that oxidative injury to the retinal pigment epithelium (RPE) may lead to retinal damage similar to that associated with the early stages of age-related macular degeneration (AMD).

METHODS

A ribozyme that targets the protective enzyme manganese superoxide dismutase (MnSOD) was expressed in RPE-J cells, and adeno-associated virus (AAV) expressing the ribozyme gene was injected beneath the retinas of adult C57BL/6 mice. The RPE/choroid complex was examined for SOD2 protein levels and protein markers of oxidative damage using immunoblot analysis and LC MS/MS-identification of proteins and nitration sites. Lipids were extracted from retinal tissue and analyzed for the bis-retinoid compounds A2E and iso-A2E. The mice were analyzed by full-field electroretinography (ERG) for light response. Light and electron microscopy were used to measure cytological changes in the retinas.

RESULTS

The treatment of RPE-J cells with Rz432 resulted in decreased MnSOD mRNA and protein as well as increased levels of superoxide anion and apoptotic cell death. When delivered by AAV, Rz432 reduced MnSOD protein and increased markers of oxidative damage, including nitrated and carboxyethylpyrrole-modified proteins in the RPE-choroid of mice. Ribozyme delivery caused a progressive loss of electroretinograph response, vacuolization, degeneration of the RPE, thickening of Bruch's membrane, and shortening and disorganization of the photoreceptor outer and inner segments. Progressive thinning of the photoreceptor outer nuclear layer resulted from apoptotic cell death. Similar to the eyes of patients with AMD, ribozyme-treated eyes exhibited increased autofluorescence and elevated levels of A2E and iso-A2E, major bis-retinoid pigments of lipofuscin.

CONCLUSIONS

These results support the hypothesis that oxidative damage to the RPE may play a role in some of the key features of AMD.

Novel approaches to retinal drug delivery

Research into treatment modalities affecting vision is rapidly progressing due to the high incidence of diseases such as diabetic macular edema, proliferative vitreoretinopathy, wet and dry age-related macular degeneration and cytomegalovirus retinitis. The unique anatomy and physiology of eye offers many challenges to developing effective retinal drug delivery systems. Historically, drugs have been administered to the eye as liquid drops instilled in the cul-de-sac. However retinal drug delivery is a challenging area. The transport of molecules between the vitreous/retina and systemic circulation is restricted by the blood-retinal barrier, which is made up of retinal pigment epithelium and endothelial cells of the retinal blood vessels. An increase in the understanding of drug absorption mechanisms into the retina from local and systemic administration has led to the development of various drug delivery systems, such as biodegradable and non-biodegradable implants, microspheres, nanoparticles and liposomes, gels and transporter-targeted prodrugs. Such diversity in approaches is an indication that there is still a need for an optimized noninvasive or minimally invasive drug delivery system to the eye. A number of large molecular weight compounds (i.e., oligonucleotides, RNA aptamers, peptides and monoclonal antibodies) have been and continue to be introduced as new therapeutic entities. However, for high molecular weight polar compounds the mechanism of epithelial transport is primarily through the tight junctions in the retinal pigment epithelium, as these agents undergo limited transcellular diffusion. Delivery and administration of these new drugs in a safe and effective manner is still a major challenge facing pharmaceutical scientists. In this review article, the authors discuss various drug delivery strategies, devices and challenges associated with drug delivery to the retina.

Carotenoids and antioxidants in age-related maculopathy italian study: multifocal electroretinogram modifications after 1 year

OBJECTIVE

To evaluate the influence of short-term carotenoid and antioxidant supplementation on retinal function in nonadvanced age-related macular degeneration (AMD).

DESIGN

Randomized controlled trial.

PARTICIPANTS

Twenty-seven patients with nonadvanced AMD and visual acuity > or =0.2 logarithm of the minimum angle of resolution were enrolled and randomly divided into 2 age-similar groups: 15 patients had oral supplementation of vitamin C (180 mg), vitamin E (30 mg), zinc (22.5 mg), copper (1 mg), lutein (10 mg), zeaxanthin (1 mg), and astaxanthin (4 mg) (AZYR SIFI, Catania, Italy) daily for 12 months (treated AMD [T-AMD] group; mean age, 69.4+/-4.31 years; 15 eyes); 12 patients had no dietary supplementation during the same period (nontreated AMD [NT-AMD] group; mean age, 69.7+/-6.23 years; 12 eyes). At baseline, they were compared with 15 age-similar healthy controls.

METHODS

Multifocal electroretinograms in response to 61 M-stimuli presented to the central 20 degrees of the visual field were assessed in pretreatment (baseline) conditions and, in nonadvanced AMD patients, after 6 and 12 months.

MAIN OUTCOME MEASURES

Multifocal electroretinogram response amplitude densities (RAD, nanovolt/deg(2)) of the N1-P1 component of first-order binary kernels measured from 5 retinal eccentricity areas between the fovea and midperiphery: 0 degrees to 2.5 degrees (R1), 2.5 degrees to 5 degrees (R2), 5 degrees to 10 degrees (R3), 10 degrees to 15 degrees (R4), and 15 degrees to 20 degrees (R5).

RESULTS

At baseline, we observed highly significant reductions of N1-P1 RADs of R1 and R2 in T-AMD and NT-AMD patients when compared with healthy controls (1-way analysis of variance P<0.01). N1-P1 RADs of R3-R5 observed in T-AMD and NT-AMD were not significantly different (P>0.05) from controls. No significant differences (P>0.05) were observed in N1-P1 RADs of R1-R5 between T-AMD and NT-AMD at baseline. After 6 and 12 months of treatment, T-AMD eyes showed highly significant increases in N1-P1 RADs of R1 and R2 (P<0.01), whereas no significant (P>0.05) change was observed in N1-P1 RADs of R3-R5. No significant (P>0.05) changes were found in N1-P1 RADs of R1-R5 in NT-AMD eyes.

CONCLUSIONS

In nonadvanced AMD eyes, a selective dysfunction in the central retina (0 degrees -5 degrees ) can be improved by the supplementation with carotenoids and antioxidants. No functional changes are present in the more peripheral (5 degrees -20 degrees ) retinal areas.

Protective effects of myricetin and related flavonols against A2E and light mediated-cell death in bovine retinal primary cell culture

The present study was performed to investigate the effect of flavonols, namely myricetin and structurally related quercetin and kaempferol against A2E and blue light-induced photoreceptors death in primary retinal cell cultures. Primary retinal cell cultures were prepared from bovine retinas. Fourteen-day-old cultures were pretreated with different concentrations of myricetin, quercetin, kaempferol (1-40 microM) for 24 h, then treated with 30 microM of A2E or exposed to blue-actinic light for 20 h. Green nucleic acid stain assay was used to evaluate cell death. Photoreceptor and bipolar cells were immunolabeled with specific antibodies and were counted using automated microscope imaging and image-based cell counting software. Twenty hours exposure to blue light induced approximately 75% death of photoreceptors in bovine retinal cell cultures. Myricetin protected 100% of photoreceptors against blue-light-mediated damage with an EC(50) of 9+/-0.7 microM. Quercetin resulted in a maximum of 15% protection against light damage, and kaempferol was inactive. A2E induced photoreceptor and bipolar cell death in a concentration-dependent manner with EC(50) of 25 microM for photoreceptors and 31 microM for bipolar cells. Myricetin, quercetin and kaempferol protected against A2E-induced photoreceptors and bipolar cells death with EC(50) values of 2+/-0.3 microM, 2+/-0.3 microM, 5+/-0.09 microM and 0.8+/-0.07 microM, 0.44+/-0.06 microM, 1+/-0.4 microM, respectively. Caspase-3 inhibitor (Z-DEVD-fmk) protected 42% photoreceptors and 57% bipolar cells from A2E toxicity. In contrast, this inhibitor had no effect against light-induced photoreceptor damage. Despite the poor activity of quercetin and the inactivity of kaempferol against blue light, myricetin, quercetin and kaempferol exhibited approximately 100% protection against A2E toxicity. This suggests that light- and A2E-induced cell deaths are mediated through different pathways. These results suggest that myricetin functions as potent and effective neuroprotective agent for photoreceptor cells against A2E and light damage.

Contrast sensitivity and glare disability after implantation of AcrySof IQ Natural aspherical intraocular lens

PURPOSE

To evaluate contrast sensitivity and glare disability after implantation of an AcrySof IQ Natural SN60WF aspherical intraocular lens (IOL) (Alcon Laboratories).

SETTING

Iladevi Cataract & IOL Research Centre, Ahmedabad, India.

METHODS

One hundred twenty consecutive patients who had phacoemulsification in a prospective triple-masked trial were randomized to receive an AcrySof SA60AT IOL (40 eyes), AcrySof Natural SN60AT IOL (40 eyes), or AcrySof IQ SN60WF IOL (40 eyes). At 3 months, contrast sensitivity was measured using the CSV-1000E contrast sensitivity chart test face (Vector Vision) at 3, 6, 12, and 18 cycles per degrees (cpd) under photopic conditions (85 cd/m(2)) and mesopic conditions (2.7 cd/m(2)) with 4.0 mm and 6.0 mm fixed central apertures, with and without glare. The Kruskal-Wallis test was used and a pair-wise comparison performed. The main outcome measure was the difference in contrast sensitivity between IOLs at each spatial frequency.

RESULTS

The best corrected visual acuity was similar between the 3 IOL groups (P = .6). The AcrySof IQ group had significantly higher contrast sensitivity at 18 cpd under photopic conditions (P = .008); at 3, 6, 12, and 18 cpd during mesopic testing with a 4.0 mm aperture without glare (P = .018, P = .011, P = .007, and P = .0001, respectively) and with glare (P = .003, P = .006, P = .005, and P = .004, respectively); and at all spatial frequencies during mesopic testing with a 6.0 mm aperture without glare (P = .018, P = .006, P = .009, and P = .0001, respectively) and with glare (P = .019, P = .002, P = .01, and P = .017, respectively).

CONCLUSION

Eyes with the AcrySof IQ SN60WF IOL had significantly higher contrast sensitivity than eyes with an AcrySof SA60AT or AcrySof Natural SN60AT IOL at all spatial frequencies during mesopic testing (with and without glare) with 4.0 and 6.0 mm artificial pupil.

Surgical treatment of age-related macular degeneration: will there be a role in the future?

Surgical treatment has been shown to be able to improve vision that is lost as a result of age-related macular degeneration. Surgery is complex, such that improvement has always to be weighed against risk of complications. The availability of Ranibizumab and Bevacizumab is set to dramatically alter our management options. Surgical treatment will have a limited role to play in the next few years.

Serum dehydroepiandrosterone sulphate level in age-related macular degeneration

PURPOSE

To evaluate plasma dehydroepiandrosterone sulphate (DHEAS) levels in patients diagnosed with age-related macular degeneration (AMD) and controls.

DESIGN

Case-controlled, prospective, comparative noninterventional study.

METHODS

This study involved 32 men and 35 women with exudative AMD, 37 men and 38 women with nonexudative AMD, and 32 men and 32 women of an age-matched control group. The Wisconsin Age-Related Maculopathy Grading System was used to asses the severity of AMD lesions. DHEAS levels were measured and compared according to a gender based subdivision. Analysis of variance was used to assess the association between DHEAS and AMD. Linear regression model was used to examine the relation among DHEAS level and AMD severity scale.

RESULTS

Mean +/- SD of DHEAS levels in exudative AMD, nonexudative AMD, and controls in men was 2.67 +/- 0.68 micromol/l, 2.89 +/- 0.95 micromol/l, and 4.43 +/- 1.44 micromol/l, respectively (P = .001), and in women was 1.64 +/- 0.72 micromol/l, 1.85 +/- 0.73 micromol/l, and 2.78 +/- 0.91 micromol/l, respectively (P = .001). Post hoc Tukey analyses revealed a significant reduction in serum DHEAS level in both AMD groups, compared with controls for men and women (P = .001), while no difference was found between AMD groups in both men and women (P = .668 and 0.49, respectively). Regression analyses revealed an inverse correlation among serum DHEAS level and AMD severity scale both in men and women (P = .006 and .007, respectively).

CONCLUSIONS

This study suggests an inverse correlation between serum DHEAS level and AMD severity scale with a considerably reduced DHEAS level in AMD.

Interferon-gamma differentially regulates TGF-beta1 and TGF-beta2 expression in human retinal pigment epithelial cells through JAK-STAT pathway

Retinal pigment epithelium (RPE) and transforming growth factor-beta (TGF-beta) have been shown to be involved in various retinal diseases. We have studied the role of inflammatory cytokines on the expression and secretion of TGF-beta in human RPE cells (HRPE). Confluent cultures of HRPE derived from donor eyes were used. RT-PCR analyses showed that TNF-alpha and IL-1beta increased the mRNA levels of both TGF-beta1 and TGF-beta2. IFN-gamma enhanced constitutively expressed, as well as, TNF-alpha-and IL-1beta-induced TGF-beta1 mRNA levels but decreased TGF-beta2 mRNA. The effects of these cytokines on TGF-beta1 and TGF-beta2 secretion correlated with the mRNA levels. TGF-beta1 was always produced as the latent form while 21-31% of TGF-beta2 was in the active form. IFN-gamma reduced the production of active form of TGF-beta2 to 4-9%. TGF-beta3 secretion was not detectable under any of the conditions. The Real-Time PCR analysis of TGF-beta mRNAs confirmed the observed results. The TGF-beta1 and TGF-beta2 secretion was induced by TGF-beta2 and TGF-beta1, respectively. Under these conditions, the contrasting effects of IFN-gamma on TGF-beta1 and TGF-beta2 secretion were also observed. JAK inhibitor selectively inhibited IFN-gamma induced TGF-beta1 secretion and mRNA levels while reversing the inhibitory effects of IFN-gamma on TGF-beta2. Analyses of transcription factor activity strongly indicated the role of STAT-1 but not NFkappaB, C-Myc, C-Jun, SP-1, MEF-2. Our data demonstrate that IFN-gamma differentially regulates constitutively expressed, as well as, cytokine-induced TGF-beta1 and TGF-beta2 mRNA levels and secretion of TGF-betas by HRPE.

Synthesis of complement factor H by retinal pigment epithelial cells is down-regulated by oxidized photoreceptor outer segments

Complement activation is thought to be involved in the pathogenesis of age-related macular degeneration (AMD), in part because certain gene polymorphisms in complement factor H (CFH), an important regulator of the alternative complement activation pathway, are high risk factors for AMD. How CFH is regulated locally at the retina/choroid interface and how this contributes to AMD development remain unknown. In the present study, we have confirmed that CFH was detectable by immunohistochemistry in the choroid, and at low levels in the RPE cell and interphotoreceptor matrix, but appeared to be concentrated in dense patches in Bruch's membrane. In vitro, cultured human and mouse RPE cells expressed high levels of CFH as evidenced by immunohistochemistry and western blot. Using a stabilized mouse RPE cell line, we confirmed that RPE cells constitutively synthesise CFH. Synthesis of CFH was not affected by a short-term (2 h) photoreceptor outer segment (POS) treatment. However, long-term (24-48 h) treatment of RPE cells with oxidised POS (ox-POS) but not normal POS (n-POS) markedly down-regulated CFH mRNA expression. Phagocytosis of both ox-POS and n-POS appeared to reduce intracellular CFH protein expression in RPE cultures. Synthesis of CFH by cultured RPE cells was also reduced at the mRNA level by the proinflammatory cytokines TNF-alpha and IL-6. Other cytokines tested including IFN-gamma, IL-1alpha and IL-4 showed no effect on either CFH protein or mRNA levels. Our results support the view that RPE cells synthesise and express CFH and are probably a major local source of this protein at the retina/choroid interface, secreting CFH into the interphotoreceptor matrix as well as Bruch's membrane. Prolonged phagocytosis of POS, particularly if modified by oxidative processes as occurs in inflammation, appears to markedly impair synthesis and secretion of CFH, with potential loss of important regulatory functions in counteracting the pro-inflammatory effects of activated complement.

Plasma homocysteine and total thiol content in patients with exudative age-related macular degeneration

PURPOSE

Exudative age-related macular degeneration (ARMD) is one of the debilitating ocular complications, which results in permanent blindness. Elevated homocysteine (Hcys) levels have been associated in the development of several vascular diseases. Vascular and oxidative stress theories have been implicated for the development of choroidal neovascularization in exudative ARMD. The aim of the present study was to investigate the possible role of plasma Hcys and thiol content (tSH) as a risk factor for the development of exudative ARMD.

METHOD

A total of 16 patients with exudative ARMD and 20 age-matched controls were recruited for the study. Plasma Hcys levels were analysed using Reverse Phase High Performance Liquid Chromatography. Plasma glutathione (GSH) content was determined using o-phthalaldehyde (OPA) derivatization and subsequent detection by fluorimeter. Plasma tSH levels were determined by using thiol-specific reagent dithionitrobenzoic acid (DTNB) spectrophotometrically.

RESULTS

Plasma Hcys levels in exudative ARMD were elevated three-fold (18+/-5.0 microM) when compared to healthy controls (6.7+/-1.8 microM). There was a two-fold decrease in the GSH and tSH in exudative ARMD when compared with controls. Negative correlation was observed between diminished tSH and Hcys levels (r=-0.4837, P=0.05). Similarly plasma Hcys levels negatively correlated with GSH content (r=-0.6620, P<0.05).

CONCLUSION

Results from our present study revealed that there is an elevated Hcys level and diminished thiol pool content in exudative ARMD that are significant.

The role of radiation therapy in benign diseases

Although adequate prospective data are lacking, radiation therapy seems to be effective for many benign diseases and remains one of the treatment modalities in the armamentarium of medical professionals. Just as medication has potential adverse effects, and surgery has attendant morbidity, irradiation sometimes can be associated with acute and chronic sequelae. In selecting the mode of treatment, most radiation oncologists consider the particular problem to be addressed and the goal of therapy in the individual patient. It is the careful and judicial use of any therapy that identifies the professional. With an understanding of the current clinical data, treatment techniques, cost, and potential detriment, the goal is to provide long-term control of the disease while minimizing unnecessary treatment and potential risks of side effects. The art lies in balancing benefits against risks.

High density lipoprotein mediated lipid efflux from retinal pigment epithelial cells in culture

BACKGROUND/AIM

[corrected] The transport of radiolabelled photoreceptor outer segments (POS) lipids was investigated by cultured retinal pigment epithelial cells (RPE). Phagocytosis of POS by the RPE is essential to maintain the health and function of the photoreceptors in vivo. POS are phagocytised at the apical cell surface of RPE cells. Phagocytised POS lipids may be either recycled to the photoreceptors for reincorporation into new POS or they may be transported to the basolateral surface for efflux into the circulation.

RESULTS

The authors have demonstrated that high density lipoprotein (HDL) stimulates efflux of radiolabelled lipids, of POS origin, from the basal surface of RPE cells in culture. Effluxed lipids bind preferentially to HDL species of low and high molecular weight. Effluxed radiolabelled phosphotidyl choline was the major phospholipid bound to HDL, with lesser amounts of phosphatidyl ethanolamine, phosphatidyl inosotol. Effluxed radiolabelled triglycerides, cholesterol, and cholesterol esters also bound to HDL. Lipid free apolipoprotein A-I (apoA-I) and apoA-I containing vesicles also stimulate lipid efflux.

CONCLUSION

The findings suggest a role for HDL and apoA-I in regulating lipid and cholesterol transport from RPE cells that may influence the pathological lipid accumulation associated with age related macular degeneration.

Light-induced damage to the retina: role of rhodopsin chromophore revisited

The presence of the regenerable visual pigment rhodopsin has been shown to be primarily responsible for the acute photodamage to the retina. The photoexcitation of rhodopsin leads to isomerization of its chromophore 11-cis-retinal to all-trans-retinal (ATR). ATR is a potent photosensitizer and its role in mediating photodamage has been suspected for over two decades. However, there was lack of experimental evidence that free ATR exists in the retina in sufficient concentrations to impose a risk of photosensitized damage. Identification in the retina of a retinal dimer and a pyridinium bisretinoid, so called A2E, and determination of its biosynthetic pathway indicate that substantial amounts of ATR do accumulate in the retina. Both light damage and A2E accumulation are facilitated under conditions where efficient retinoid cycle operates. Efficient retinoid cycle leads to rapid regeneration of rhodopsin, which may result in ATR release from the opsin "exit site" before its enzymatic reduction to all-trans-retinol. Here we discuss photodamage to the retina where ATR could play a role as the main toxic and/or phototoxic agent. Moreover, we discuss secondary products of (photo)toxic properties accumulating within retinal lipofuscin as a result of ATR accumulation.

Predictive value of fundus autofluorescence for development of geographic atrophy in age-related macular degeneration

PURPOSE

It has been suggested that lipofuscin accumulation, as measured by increased fundus autofluorescence (FAF), precedes progression or development of junctional zone geographic atrophy (GA) in age-related macular degeneration (AMD). The tools of biomedical image analysis were used to measure the probabilistic relationship of GA progression to increased FAF.

METHODS

Serial AF images of eight eyes of six patients with AMD with GA were registered on computer. The images were leveled with a 12-zone quadratic polynomial mathematical model to minimize background variability. Semiautomated segmentation of GA was performed on the leveled images. Increased FAF was defined as a gray level greater than 2 standard deviations above the leveled image mean, identified on the initial image with automated segmentation, and measured as a fraction of the 250-microm border zone surrounding the initial GA lesion. Areas of GA lesions were identified on the final image. The positive predictive value (PPV) of increased FAF was determined as the probability that any pixel with increased FAF in the initial image would become part of new GA in the final image. Relative PPV was determined relative to the total quantity of new GA. The NPV (NPV) of increased FAF was calculated as the probability that any pixels without increased FAF would not become atrophic. The relative NPV was determined similarly. A similar analysis was also conducted with a 500-microm border zone to determine the predictive value of proximity to the original GA lesion ("proximity") for GA progression.

RESULTS

As a fraction of the geographic atrophy border zone, the mean new GA was 0.44+/-0.20, and the mean increased FAF was 0.06+/-0.06. The mean PPV of increased FAF for new GA formation was 0.50+/-0.26. Compared with the relative PPV of chance of 1.0, the mean relative PPV of increased FAF was 1.15+/-0.28. The mean NPV of increased FAF was 0.57+/-0.20. The mean relative NPV of increased FAF was 1.00+/-0.02. In the 500-microm border zone, the mean relative PPV of FAF and of proximity were essentially equal (1.56+/-.70 and 1.52+/-0.26, respectively), whereas the mean relative NPV of proximity was significantly greater than that of FAF (1.26+/-0.19 and 1.01+/-0.01, respectively, P=0.02)

CONCLUSIONS

The results of digital image analysis suggest that although increased FAF may have a modest PPV for new GA development, the relative PPV is generally no greater than chance. Similarly, the relative NPV demonstrates negligible difference from chance and is also lower than the relative NPV of proximity. This suggests that increased FAF, though a disease manifestation, is not a strong risk factor for development or extension of GA.

Bruch membrane aging alters the gene expression profile of human retinal pigment epithelium

We investigated the effects of age-related changes within the Bruch membrane on the gene expression profile of the RPE. Immortalized human ARPE-19 cells were seeded onto acellular human Bruch membrane from younger and older donors and harvested 72 hr later; total RNA was isolated and the gene expression profile was determined using the Affymetrix Human Genome U95A gene chip. Twelve genes were upregulated and 8 genes were downregulated with Bruch membrane aging; RT-PCR confirms that Bruch membrane aging upregulates genes in RPE cells encoding for transforming growth factor alpha and downregulates genes for vitronectin and the membrane transporter ABCC5. The role of these changes in the pathogenesis of age-related diseases such as macular degeneration remains to be elucidated.

Serum paraoxonase 1 activity and lipid peroxidation levels in patients with age-related macular degeneration

Our objective was to investigate antioxidant paraoxonase 1 (PON1) activity together with malondialdehyde (MDA) levels to evaluate oxidative stress in patients with age-related macular degeneration (AMD), an important cause of blindness in the elderly population. Serum PON1 activity and MDA levels were analyzed in 37 patients with AMD and compared with 29 healthy controls using a spectrophotometric method. Serum MDA levels were significantly higher in the patient group (2.76 +/- 1.28 nmol/ml) than controls (1.00 +/- 0.36 nmol/ml; p < 0.001), whereas PON1 activity was lower in the patient group (132.27 +/- 63.39 U/l) than controls (312.13 +/- 136.23 U/l; p < 0.001). There was a negative correlation between MDA and PON1 levels (r = -0.470, p < 0.001). We conclude that the observed increase in MDA levels may be related to decreased PON1 activity; the present data also demonstrated that an obvious negative correlation between PON1 activity and MDA levels exists in patients with AMD. PON1 is also an antioxidant agent, therefore effective antioxidant therapy to inhibit lipid peroxidation is necessary and agents to increase PON1 activity may be a therapeutic option in AMD.

Pulsatile ocular blood flow in asymmetric age-related macular degeneration

PURPOSE

Ocular perfusion abnormalities have been proposed in the pathogenesis of age-related macular degeneration (AMD) with differences in pulsatile ocular blood flow (POBF) in eyes with asymmetric AMD in Japanese and Taiwanese patients. The purpose of our study was to observe POBF difference in the fellow eyes of Caucasians with asymmetric AMD.

METHODS

This was a cross-sectional study comparing POBF in three groups of patients with asymmetric AMD in the fellow eyes: Group 1 (n=21) with drusen and active choroidal neovascularisation (CNV); Group 2 (n=18) with drusen and disciform scar; Group 3 (n=8) with CNV and disciform scar. The POBF was adjusted for intraocular pressure (IOP), pulse rate (PR), and axial length using multiple regression analysis. Generalised estimation equation model was used to include both eyes in each group.

RESULTS

The geometric mean (95% confidence interval) POBF values were as follows: Group 1 with drusen 1097.9 microl/min (957.0, 1259.7) in one eye and the fellow eye with CNV 1090.1 microl/min (932.3, 1274.7); Group 2 with drusen 946.0 microl/min (794.2, 1126.7) and disciform scar 966.2 microll/min (780.3, 1196.4); Group 3 with CNV 877.1 microl/min (628.3, 1224.6) and disciform scar 767.2 microl/min (530.5, 1109.7). Adjusting for differences in axial length, pulse rate and intraocular pressure, no statistically significant difference in POBF was found between fellow eyes in the same subject.

CONCLUSIONS

POBF is not different between fellow eyes of Caucasian patients with asymmetric AMD.

Vascular endothelial growth factor expression in the retinal pigment epithelium is essential for choriocapillaris development and visual function

The choroid in the eye provides vascular support for the retinal pigment epithelium (RPE) and the photoreceptors. Vascular endothelial growth factor (VEGF) derived from the RPE has been implicated in the physiological regulation of the choroidal vasculature, and overexpression of VEGF in this epithelium has been considered an important factor in the pathogenesis of choroidal neovascularization in age-related macular degeneration. Here, we demonstrate that RPE-derived VEGF is essential for choriocapillaris development. Conditional inactivation of VEGF expression in the RPE (in VEGFrpe-/- mice) results in the absence of choriocapillaris, occurrence of microphthalmia, and the loss of visual function. Severe abnormalities of RPE cells are already observed when VEGF expression in the RPE is only reduced (in VEGFrpe+/- mice), despite the formation of choroidal vessels at these VEGF levels. Finally, using Hif1arpe-/- mice we demonstrate that these roles of VEGF are not dependent on hypoxia-inducible factor-1alpha-mediated transcriptional regulation of VEGF expression in the RPE. Thus, hypoxia-inducible factor-1alpha-independent expression of VEGF is essential for choroid development.

Bruch's membrane and the vascular intima: is there a common basis for age-related changes and disease?

Several clinical and epidemiological studies have concurrently illuminated established cardiovascular risk factors in age-related macular degeneration (AMD), raising the possibility that cardiovascular disease and AMD may share a similar pathogenic process. The vascular intima and the Bruch's membrane share several age-related changes and are the seat of many common molecules. Diseases of these structures may represent parallel responses to the tissue injury induced by multiple intercalated factors such as genetic variations, oxidative stress, inappropriately directed immune response or inflammatory disease complex. However, there are marked differences in the age-related changes in these two structures. The strategic location of the Bruch's membrane between the retinal pigment epithelium and the choriocapillaris can at least partially explain the differential susceptibility of AMD to cardiovascular risk factors. Unlike the vascular wall that is exposed to changes from the endothelium, the Bruch's membrane is subject to changes from both the endothelium (choriocapillaris) and epithelium (retinal pigment epithelium). Moreover, although both the vascular wall and Bruch's membrane become lipid laden with age, the lipid composition is characteristically different. This review examines the morphological and biochemical alterations in the senescent Bruch's membrane and its analogy to the vascular wall to evaluate the concurrence of atherosclerosis and AMD.

AcrySof Natural SN60AT versus AcrySof SA60AT intraocular lens in patients with color vision defects

PURPOSE

To determine whether implantation of the AcrySof Natural intraocular lens (IOL) worsened the severity of existing color deficit in congenital partial red-green color deficient individuals (CPRG).

METHODS

A prospective controlled randomized double-masked analysis of 30 consecutive patients with CPRG defect and bilateral cataracts received a Natural IOL (test group) in 1 eye and a single-piece AcrySof IOL (control group) in the other eye. Patients were tested unilaterally to detect CPRG defect using Ishihara pseudoisochromatic plates and the Farnsworth D-15 test. Plates 1 to 21 measured the Ishihara error score; plates 22 to 25 indicated severity of defect based on clarity of both numerals as partial mild/moderate (both visible), partial severe defect (only 1 visible). The D-15 test is based on number of diametrical crossings on the circular diagram; severity is graded as mild (1 crossing), moderate (2 crossings), or severe (>2 crossings). Tests were performed before and after IOL implantation at 1, 3, and 6 months. At mean follow-up of 6.13 months +/- 1.2 (SD), analysis of variance test judged the difference in error scores and cross tabulation represented change in number of diametrical crossings.

RESULTS

The mean age was 62.3 +/- 8.5 years. All patients were men. Before IOL implantation, all patients had moderate CPRG defect on both tests. The Ishihara error score in the test and control groups did not reveal statistically significant differences (P = .505 and P = .119, respectively). With D-15, none of the patients in the test or control group showed >2 crossings.

CONCLUSION

The implantation of AcrySof Natural IOL did not worsen the preexisting severity of color defect in CPRG individuals.

Looking chloride channels straight in the eye: bestrophins, lipofuscinosis, and retinal degeneration

Recent evidence suggests that Cl(-) ion channels are important for retinal integrity. Bestrophin Cl(-) channel mutations in humans are genetically linked to a juvenile form of macular degeneration, and disruption of some ClC Cl(-) channels in mice leads to retinal degeneration. In both cases, accumulation of lipofuscin pigment is a key feature of the cellular degeneration. Because Cl(-) channels regulate the ionic environment inside organelles in the endosomal-lysosomal pathway, retinal degeneration may result from defects in lysosomal trafficking or function.

SOD2 protects against oxidation-induced apoptosis in mouse retinal pigment epithelium: implications for age-related macular degeneration

PURPOSE

Oxidative stress from reactive oxygen species (ROS) has been implicated in many diseases, including age-related macular degeneration (AMD), in which the retinal pigment epithelium (RPE) is considered a primary target. Because manganese superoxide dismutase (SOD2), localized in mitochondria, is known to be a key enzyme that protects the cells against oxidative stress, this study was undertaken to examine oxidation-induced apoptosis in cultured RPE cells with various levels of SOD2.

METHODS

Primary cultures of RPE cells were established from wild-type (WT), heterozygous Sod2-knockout mouse (HET) and hemizygous Sod2 mice with overexpression of the enzyme (HEMI). Purity of the RPE cell cultures was verified by immunostaining with antibody to RPE65 and quantified by flow cytometry. Oxidative stress was induced in RPE cells by exposing them to H(2)O(2) (0-500 muM) for 1 hour and reculturing them in normal medium for various times (0-24 hours). Apoptosis in the RPE was examined by TUNEL staining and quantified by cell-death-detection ELISA. Mitochondrial transmembrane potential (MTP) was measured by a cationic dye, and cytochrome c leakage from mitochondria was analyzed by Western blot analysis.

RESULTS

More than 95% of the cells in each culture were RPE65 positive, and the relative SOD2 levels in HET, WT, and HEMI cells were 0.6, 1.0, and 3.4, respectively. H(2)O(2)-induced apoptotic cell death was both dose and time dependent, and apoptosis in these cells was related to the cellular SOD2 level. Disruption of MTP and release of cytochrome c were observed to occur before apoptotic cell death, and they correlated with cellular SOD2.

CONCLUSIONS

The results demonstrate a critical role of SOD2 in protection against oxidative challenge. Cells from HET mice showed greater apoptotic cell death, whereas in those from HEMI mice, cell death induced by oxidative injury was suppressed.

The relation between C reactive protein and age related macular degeneration in the Cardiovascular Health Study

AIM

To test the hypothesis that individuals with age related macular degeneration (AMD) have increased C reactive protein (CRP) levels.

METHODS

A cross sectional study design using data from the Cardiovascular Health Study (CHS), a longitudinal study that enrolled older adults from four communities in the United States from 1989 to 1990, was employed to investigate the existence of an association between AMD and CRP levels in this population. Fundus photographs from 1997 and 1998 were used to identify individuals with (n=390) and without AMD (n=2365). The association between AMD and CRP levels (measured at baseline) was compared, adjusting for the potentially confounding effect of demographic, lifestyle, and health related characteristics.

RESULTS

Among the 2755 CHS participants with gradable fundus photographs, 390 were identified as having AMD. Overall, median CRP levels among those with AMD (1.76 mg/l) were similar to those without AMD (1.77 mg/l). CRP levels were categorised into quartiles and compared between those with and without AMD. Relative to those in the lowest quartile (0.07-0.93 mg/l), the odds ratios (OR) in the higher quartiles, adjusted for demographic, lifestyle, and health related characteristics were increased but not statistically significant (0.94-1.77 mg/l: OR=1.14, 95% CI 0.82 to 1.60; 1.78-3.04 mg/l: OR=1.24, 95% CI 0.88 to 1.75; >3.04 mg/l: OR=1.24, 95% CI 0.87 to 1.78).

CONCLUSIONS

In the CHS, there is no evidence that CRP levels are associated with AMD. These data do not support the theory alleging non-specific systemic inflammation in the aetiology and natural history of this disease.

Neovascular age-related macular degeneration: roundtable

Several recent developments may provide an opportunity to improve outcome in individuals who develop neovascular age-related maculopathy (age-related macular degeneration [ARMD]). Concurrent with progress in isolating clinically relevant subtypes of neovascular ARMD, several therapies have been introduced that show promise for halting progression of this disorder. However, data from controlled clinical trials to test the relative efficacy of different management strategies across these subtypes of disease presentation remain limited. In addition, strategies to control ARMD may evolve quickly as more is learned about how specific molecular events, such as cell-mediated inflammation and angiogenesis, contribute to disease expression. A roundtable of investigators was convened to discuss and summarize recent progress in the treatment of ARMD. Case studies were then presented to provide an opportunity for experts to reveal their specific thought processes in the approach to neovascular ARMD based on their own interpretation of current clinical data and empirical experience.

RPE lipofuscin and its role in retinal pathobiology

Emerging evidence indicates that the autofluorescent pigments that accumulate as lipofuscin in retinal pigment epithelial (RPE) cells may reach levels that contribute to a decline in cell function. Since recent findings with respect to the origin, composition and adverse effects of RPE lipofuscin have informed our view of this material, the goal of this article is to review our current understanding of these issues.

MMP-9 microsatellite polymorphism and susceptibility to exudative form of age-related macular degeneration

PURPOSE

To assess if a polymorphism (PM) of the microsatellite (CA(13-27)) in the promoter region of Matrix Metalloproteinase 9 (MMP-9) was associated with the exudative form of age-related macular degeneration (AMD) and to its risk factors.

METHODS

In 107 patients with AMD (AMD Group) and 223 age- and gender-matched controls (Control Group) with cataract, demographic, clinical data, and MMP-9 PM have been compared.

RESULTS

The comparison of allelic frequencies showed a different pattern of CA repeats between AMD and Control Group (P < 0.00005), in particular the prevalence of longer microsatellites (> or = 22 CA repeats) was higher in AMD than in Control Group (O.R. 2.49, 95% CI 1.71-3.37, P < 0.001). Analyses of genetic frequencies gave similar results. Logistic regression confirmed that 22 or more CA repeats are associated to AMD. The only association between MMP-9 PM and other risk factors for AMD was with BMI (Spearman's R = 0.298, P < 0.00005): all patients with both microsatellites > or = 22 CA repeats were overweight or obese (chi2 test P < 0.0005, compared to other genotypes).

CONCLUSIONS

Longer microsatellites in the promoter of MMP-9 are associated to the exudative form of AMD and to body mass index, a well-known risk factor for the disease.

Esterified and unesterified cholesterol in drusen and basal deposits of eyes with age-related maculopathy

To address the potential for an outer segment (OS) contribution to the sub-retinal pigment epithelium (RPE) lesions of age-related maculopathy (ARM), we quantified esterified and unesterified cholesterol (EC, UC) with the sterol-specific fluorescent probe filipin in cryosections of ARM eyes. Twenty six eyes from 20 donors were preserved <5 hr after death in 4% paraformaldehyde (n = 16) or 2.5% glutaraldehyde/1% paraformaldehyde (n = 10). Eyes had exudative late ARM (n = 6), geographic atrophy (n = 15), and drusen > or =125 microm (n = 11). Sections were stained with filipin for UC or were extracted and hydrolysed with cholesterol esterase before filipin staining for EC. Drusen varied in cholesterol content, with a rough correlation between EC and UC. Dome-shaped drusen contained distinctive, loosely packed UC-rich loops. In basal deposits, EC and UC were more prominent near Bruch's membrane than near the RPE. A UC-rich material was localized within the subretinal space (n = 4). Maximum filipin fluorescence due to UC was quantified in 47 lesions (19 drusen, 24 basal deposits, and 4 sub-retinal) from 12 ARM eyes and compared to OS and inner plexiform layer (IPL) of uninvolved retina in the same sections. Relative to IPL, UC fluorescence was higher in lesions (mean+/-s.d: 1.63+/-0.69) and lower in OS (0.64+/-0.18). If only the packing of membranes explained fluorescence intensity, then one would expect much higher intensities in membrane-rich OS than in lesions. Because the converse is true, the membranous material in lesions must be more highly enriched in cholesterol on a per unit area basis. UC in sub-RPE deposits cannot be derived directly from OS without considerable intracellular processing within RPE, additional cholesterol sources, or both.

Meta-analysis of genome scans of age-related macular degeneration

A genetic contribution to the development of age-related macular degeneration (AMD) is well established. Several genome-wide linkage studies have identified a number of putative susceptibility loci for AMD but only a few of these regions have been replicated in independent studies. Here, we perform a meta-analysis of six AMD genome screens using the genome-scan meta-analysis method, which allows linkage results from several studies to be combined, providing greater power to identify regions that show only weak evidence for linkage in individual studies. Results from non-parametric analysis for a broad AMD clinical phenotype (including two studies with quantitative traits) were extracted. For each study, 120 genomic bins of approximately 30 cM were defined and ranked according to maximum evidence for linkage within each bin. Bin ranks were weighted according to study size and summed across all studies; the summed rank (SR) for each bin was assessed empirically for significance using permutation methods. A high SR indicates a region with consistent evidence for linkage across studies. The strongest evidence for an AMD susceptibility locus was found on chromosome 10q26 where genome-wide significant linkage was observed (P=0.00025). Several other regions met the empirical significance criteria for bins likely to contain linked loci including adjacent pairs of bins on chromosomes 1q, 2p, 3p and 16. Several of the regions identified here showed only weak evidence for linkage in the individual studies. These results will help prioritize regions for future positional and functional candidate gene studies in AMD.

Lipids and lipid peroxidation products in the pathogenesis of age-related macular degeneration

In people over 50, age-related macular degeneration (ARMD) has become the most common cause for severe visual loss and legal blindness in all industrialized nations. Currently, there is no effective treatment for the majority of patients. To develop new and effective modes of therapy, understanding of the molecular basis of the disease in mandatory. However, the pathogenesis of ARMD is still poorly understood. Several lines of evidence suggest that aging changes of the retinal pigment epithelium (RPE), in particular the accumulation of autofluorescent lipofuscin granules in the lysosomal compartment of postmitotic RPE cells, play a key role in the pathogenesis of the disease. Recent studies indicate that lipidic compounds of lipofuscin, represented by the retinoid A2-E, and protein damage by lipid peroxidation products, in particular malondialdehyde and 4-hydroxynonenal, induce lysosomal dysfunction and lipofuscinogenesis in the RPE. The possible mechanisms underlying this lysosomal dysfunction and the resulting adverse effects on overall RPE function are discussed.

Expression of PDGF and their receptors in human retinal pigment epithelial cells and fibroblasts: regulation by TGF-beta

Platelet derived growth factors (PDGF) are known to be associated with vitreoretinal disorders such as proliferative vitreoretinopathy (PVR). We have studied the expression of PDGF and their receptors in human retinal pigment epithelial cells (HRPE) and choroid fibroblasts (HCHF), and the regulation of PDGF and its receptors by various cytokines and growth factors. RT-PCR analyses showed enhanced expression of PDGF-A and PDGF-B mRNA in HRPE treated with TGF-beta, but not with other cytokines. A minimal increase was observed in PDGF-A mRNA in TGF-beta treated HCHF cells. PDGF-R alpha mRNA, which was expressed prominently in HCHF and at very low levels in HRPE, was not affected by any of the agents. PDGF-R beta was not detectable in either HRPE or HCHF. HRPE secreted PDGF-AA and AB constitutively, and this secretion was significantly enhanced by TGF-beta. In contrast, HCHF cultures did not secrete detectable levels of any of the three isoforms of PDGF (AA, AB, BB). All three human recombinant PDGF isoforms enhanced HCHF cell proliferation significantly, while only a minimal increase was observed in HRPE. PDGF isoforms also induced HCHF cell elongation and promoted migration of HCHF in an in vitro wound assay. The results presented in this study demonstrate that TGF-beta activated RPE cells produce PDGF that may act on fibroblasts and other mesenchyme derived cells which express PDGF receptors. These studies indicate that the promotion of the proliferation and migration of mesenchymal cells by RPE cell derived PDGF may facilitate the formation of fibrovascular tissues associated with PVR.

Photoreceptor synapses degenerate early in experimental choroidal neovascularization

Severe visual loss in patients with age-related macular degeneration is associated with the development of choroidal neovascularization (CNV). The pathogenic mechanisms for CNV formation have been extensively investigated, but remarkably little research has addressed the mechanisms for dysfunction of the retina in CNV. Using laser-induced CNV in mice, we evaluated the mechanisms of retinal dysfunction. At 3 days, 1 week, 2 weeks, and 4 weeks after laser application, retinas under experimental CNV were characterized physiologically (ERG recordings, synaptic uptake of the exocytotic marker FM1-43, and light-induced translocation of transducin), histologically, and immunohistochemically. ERG amplitudes were reduced by 20% at 1 week after CNV. Depolarization-induced FM1-43 uptake in photoreceptor synapses was selectively reduced by 45% at 1 week after CNV. Although photoreceptor outer segments were shortened by 36%, light adaptation as measured by transducin translocation was mostly preserved. Early in CNV (3 days to 1 week), Muller cells demonstrated induction of c-fos and pERK expression. Also, the density of macrophage-like, F4/80 immunoreactive cells increased approximately 3-fold. Minimal photoreceptor death occurred during the first week, and was variable thereafter. At later times in CNV formation (> or =2 weeks), expression of photoreceptor synaptic markers was reduced in the outer plexiform layer, indicating loss of photoreceptor synaptic terminals. ERG amplitudes, synaptic uptake of FM1-43, and the induction of c-fos and pERK in Muller cells were altered within 1 week of experimental CNV, suggesting that during CNV formation, deficits in retinal function, in particular photoreceptor synaptic function, precede degeneration of photoreceptor terminals and photoreceptor cell death.

Spectroscopic properties and reactivity of free radical forms of A2E

A pyridinium bisretinoid (A2E) is the only identified blue-absorbing chromophore of retinal lipofuscin that has been linked to its aerobic photoreactivity and phototoxicity. Pulse radiolysis has been used to study both the one-electron oxidation and the one-electron reduction of A2E in aqueous micellar solutions. The reduction to the semireduced A2E (lambda(max) broad and between 500 and 540 nm) was achieved with formate radicals and the subsequent decay of A2E* was slow (over hundreds of milliseconds) via complex kinetics. The long lifetime of the A2E* should facilitate its reactions with other biomolecules. For example, with oxygen, the A2E* produced the superoxide radical anion with a rate constant of 3 x 10(8) M(-1) s(-1). The A2E was also reduced by the NAD radical, the corresponding rate constant being 2.3 x 10(8) M(-1) s(-1). Other experiments showed that the one-electron reduction potential of A2E lies in the range -640 to -940 mV. The semioxidized form of A2E (lambda(max) 590 nm) was formed via oxidation with the Br2*- radical and had a much shorter lifetime than the semireduced form. With strongly oxidizing peroxyl radicals (CCl3O2*) our kinetic data suggest the formation of a radical adduct followed by dissociation to the semioxidized A2E. With milder oxidizing peroxyl radicals such as that from methanol, our results were inconclusive. In benzene we observed an efficient oxidation of zeaxanthin to its radical cation by the A2E radical cation; this may be relevant to a detrimental effect of A2E in vision.