Significant photoreceptor rescue by treatment with a combination of antioxidants in an animal model for retinal degeneration

Chlorogenic acid supplementation improves multifocal electroretinography in patients with retinitis pigmentosa

To evaluate the effect of chlorogenic acid supplementation in patients with retinitis pigmentosa, we evaluated objective change in visual function with multifocal electroretinography, along with visual acuity, visual field, standard electroretinography, and contrast sensitivity. Eighteen patients diagnosed with retinitis pigmentosa were enrolled in this prospective, non-comparative, single-arm study. Multifocal electroretinography, best-corrected visual acuity in Early Treatment Diabetic Retinopathy Study letters, total point score on visual field examination with Humphrey Field Analyzer II, electroretinography, and contrast sensitivity were measured and repeated after 3 months supplementation with chlorogenic acid. The amplitude of ring 5 was significantly higher on multifocal electroretinography after 3 months of chlorogenic acid supplementation (7.2 ± 9.5 vs 8.3 ± 10.8 nV/deg(2), mean ± standard deviation, P = 0.022). There were no significant changes in the best-corrected visual acuity, total point score on Humphrey Field Analyzer, 30 Hz flicker amplitude on standard electroretinography, or contrast sensitivity. Chlorogenic acid may have a beneficial effect on the peripheral area at the margins of retinal degeneration, and should be considered as an anti-oxidant for the management of retinitis pigmentosa.

Oxidative stress retards vascular development before neural degeneration occurs in retinal degeneration rd1 mice

PURPOSE

To investigate the role of reactive oxygen species (ROS) in retinal development during the early postnatal stage of rd1 mice.

METHODS

Development of the three retinal vascular layers of C57BL/6 J (WT) and C3H/HeN (rd1) mice was evaluated from 9th postnatal day (P9) to P21. Retinal ROS production was semi-quantitatively measured using dihydroethidium fluorescence. Mice were treated with intraperitoneal injections of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) at a dose of 275 mg/kg body weight, and PBS as the control from P3 to P8.

RESULTS

Rd1 mice showed retardation of retinal vascular development in the deep layer at P9. No significant difference was observed in the outer nuclear layer thickness of rd1 and WT mice. ROS production in the outer nuclear layer of rd1 mice was significantly higher than that in the outer nuclear layer of WT mice at P9, P13, and P17 (P < .05). TEMPOL facilitated the development of the deep vascular layer when compared with injection of PBS.

CONCLUSIONS

Retardation of retinal vascular development is observed in rd1 mice; ROS is partially responsible for this finding. When using rd1 mice, we should be aware of this difference in comparison to other retinal degeneration animal models and human pathophysiological changes.

Altered antioxidant-oxidant status in the aqueous humor and peripheral blood of patients with retinitis pigmentosa

Retinitis Pigmentosa is a common form of hereditary retinal degeneration constituting the largest Mendelian genetic cause of blindness in the developed world. It has been widely suggested that oxidative stress possibly contributes to its pathogenesis. We measured the levels of total antioxidant capacity, free nitrotyrosine, thiobarbituric acid reactive substances (TBARS) formation, extracellular superoxide dismutase (SOD3) activity, protein, metabolites of the nitric oxide/cyclic GMP pathway, heme oxygenase-I and inducible nitric oxide synthase expression in aqueous humor or/and peripheral blood from fifty-six patients with retinitis pigmentosa and sixty subjects without systemic or ocular oxidative stress-related disease. Multivariate analysis of covariance revealed that retinitis pigmentosa alters ocular antioxidant defence machinery and the redox status in blood. Patients with retinitis pigmentosa present low total antioxidant capacity including reduced SOD3 activity and protein concentration in aqueous humor. Patients also show reduced SOD3 activity, increased TBARS formation and upregulation of the nitric oxide/cyclic GMP pathway in peripheral blood. Together these findings confirmed the hypothesis that patients with retinitis pigmentosa present reduced ocular antioxidant status. Moreover, these patients show changes in some oxidative-nitrosative markers in the peripheral blood. Further studies are needed to clarify the relationship between these peripheral markers and retinitis pigmentosa.

Optical imaging of mitochondrial redox state in rodent model of retinitis pigmentosa

Oxidative stress (OS) and mitochondrial dysfunction contribute to photoreceptor cell loss in retinal degenerative disorders. The metabolic state of the retina in a rodent model of retinitis pigmentosa (RP) was investigated using a cryo-fluorescence imaging technique. The mitochondrial metabolic coenzymes nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) are autofluorescent and can be monitored without exogenous labels using optical techniques. The cryo-fluorescence redox imaging technique provides a quantitative assessment of the metabolism. More specifically, the ratio of the fluorescence intensity of these fluorophores (NADH/FAD), the NADH redox ratio (RR), is a marker of the metabolic state of the tissue. The NADH RR and retinal function were examined in an established rodent model of RP, the P23H rat compared to that of nondystrophic Sprague-Dawley (SD) rats. The NADH RR mean values were 1.11 ± 0.03 in the SD normal and 0.841 ± 0.01 in the P23H retina, indicating increased OS in the P23H retina. Electroretinographic data revealed a significant reduction in photoreceptor function in P23H animals compared to SD nozrmal rats. Thus, cryo-fluorescence redox imaging was used as a quantitative marker of OS in eyes from transgenic rats and demonstrated that alterations in the oxidative state of eyes occur during the early stages of RP.

Concentration dependence of vitamin C in combinations with vitamin E and zeaxanthin on light-induced toxicity to retinal pigment epithelial cells

The purpose of this study was to determine the effects of increasing concentration of ascorbate alone and in combinations with α-tocopherol and zeaxanthin on phototoxicity to the retinal pigment epithelium. ARPE-19 cells were exposed to rose bengal and visible light in the presence and absence of antioxidants. Toxicity was quantified by an assay of cell-reductive activity. A 20 min exposure to visible light and photosensitizer decreased cell viability to ca 42%. Lipophilic antioxidants increased viabilities to ca 70%, 61% and 75% for α-tocopherol, zeaxanthin and their combination, respectively. Cell viabilities were ca 70%, 56% and 5% after exposures in the presence of 0.35, 0.7 and 1.4 mm ascorbate, respectively. A 45 min exposure increased cell death to ca 74% and >95% in the absence and presence of ascorbate, respectively. In the presence of ascorbate, zeaxanthin did not significantly affect phototoxicity. α-Tocopherol and its combination with zeaxanthin enhanced protective effects of ascorbate, but did not prevent from ascorbate-mediated deleterious effects. In conclusion, there is a narrow range of concentrations and exposure times where ascorbate exerts photoprotective effects, exceeding which leads to ascorbate-mediated increase in photocytotoxicity. Vitamin E and its combination with zeaxanthin can enhance protective effects of ascorbate, but do not ameliorate its deleterious effects.

Safranal, a saffron constituent, attenuates retinal degeneration in P23H rats

Saffron, an extract from Crocus sativus, has been largely used in traditional medicine for its antiapoptotic and anticarcinogenic properties. In this work, we investigate the effects of safranal, a component of saffron stigmas, in attenuating retinal degeneration in the P23H rat model of autosomal dominant retinitis pigmentosa. We demonstrate that administration of safranal to homozygous P23H line-3 rats preserves both photoreceptor morphology and number. Electroretinographic recordings showed higher a- and b-wave amplitudes under both photopic and scotopic conditions in safranal-treated versus non-treated animals. Furthermore, the capillary network in safranal-treated animals was preserved, unlike that found in untreated animals. Our findings indicate that dietary supplementation with safranal slows photoreceptor cell degeneration and ameliorates the loss of retinal function and vascular network disruption in P23H rats. This work also suggests that safranal could be potentially useful to retard retinal degeneration in patients with retinitis pigmentosa.

Carotenoids and DNA damage

Carotenoids are among the best known antioxidant phytochemicals, and are widely believed to contribute to the health-promoting properties of fruits and vegetables. Investigations of the effects of carotenoids have been carried out at different levels: in cultured cells, in experimental animals, and in humans. Studying reports from the last 5 years, we find a clear distinction between effects of vitamin A and pro-vitamin A carotenoids (the carotenes and β-cryptoxanthin), and effects of non-vitamin A carotenoids (lycopene, lutein, astaxanthin and zeaxanthin). Whereas the latter group are almost invariably reported to protect against DNA damage, whether endogenous or induced by exogenous agents, the provitamin A carotenoids show a more varied spectrum of effects, sometimes protecting and sometimes enhancing DNA damage. The tendency to exacerbate damage is seen mainly at high concentrations, and might be accounted for by pro-oxidant actions of these carotenoids.

Zinc-desferrioxamine attenuates retinal degeneration in the rd10 mouse model of retinitis pigmentosa

Iron-associated oxidative injury plays a role in retinal degeneration such as age-related macular degeneration and retinitis pigmentosa. The metallo-complex zinc-desferrioxamine (Zn/DFO) may ameliorate such injury by chelation of labile iron in combination with release of zinc. We explored whether Zn/DFO can affect the course of retinal degeneration in the rd10 mouse model of retinitis pigmentosa. Zn/DFO-treated animals showed significantly higher electroretinographic responses at 3 and 4.5 weeks of age compared with saline-injected controls. Corresponding retinal (photoreceptor) structural rescue was observed by quantitative histological and immunohistochemical techniques. When administered alone, the components of the complex, Zn and DFO, showed a lesser, partial effect. TBARS, a marker of lipid peroxidation, and levels of oxidative DNA damage as quantified by 8-OHdG immunostaining were significantly lower in Zn/DFO-treated retinas compared with saline-injected controls. Reduced levels of retinal ferritin as well as reduced iron content within ferritin molecules were measured in Zn/DFO-treated retinas. The data, taken together, suggest that the protective effects of the Zn/DFO complex are mediated through modulation of iron bioavailability, leading to attenuation of oxidative injury. Reducing iron-associated oxidative stress using complexes such as Zn/DFO may serve as a "common pathway" therapeutic approach to attenuate injury in retinal degeneration.

Excessive HDAC activation is critical for neurodegeneration in the rd1 mouse

Inherited retinal degenerations, collectively termed retinitis pigmentosa (RP), constitute one of the leading causes of blindness in the developed world. RP is at present untreatable and the underlying neurodegenerative mechanisms are unknown, even though the genetic causes are often established. Acetylation and deacetylation of histones, carried out by histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively, affects cellular division, differentiation, death and survival. We found acetylation of histones and probably other proteins to be dramatically reduced in degenerating photoreceptors in the rd1 human homologous mouse model for RP. Using a custom developed in situ HDAC activity assay, we show that overactivation of HDAC classes I/II temporally precedes photoreceptor degeneration. Moreover, pharmacological inhibition of HDACs I/II activity in rd1 organotypic retinal explants decreased activity of poly-ADP-ribose-polymerase and strongly reduced photoreceptor cell death. These findings highlight the importance of protein acetylation for photoreceptor cell death and survival and propose certain HDAC classes as novel targets for the pharmacological intervention in RP.

Calpain and PARP activation during photoreceptor cell death in P23H and S334ter rhodopsin mutant rats

Retinitis pigmentosa (RP) is a heterogeneous group of inherited neurodegenerative diseases affecting photoreceptors and causing blindness. Many human cases are caused by mutations in the rhodopsin gene. An important question regarding RP pathology is whether different genetic defects trigger the same or different cell death mechanisms. To answer this question, we analysed photoreceptor degeneration in P23H and S334ter transgenic rats carrying rhodopsin mutations that affect protein folding and sorting respectively. We found strong activation of calpain and poly(ADP-ribose) polymerase (PARP) in both mutants, concomitant with calpastatin down-regulation, increased oxidative DNA damage and accumulation of PAR polymers. These parameters were strictly correlated with the temporal progression of photoreceptor degeneration, mirroring earlier findings in the phosphodiesterase-6 mutant rd1 mouse, and suggesting execution of non-apoptotic cell death mechanisms. Interestingly, activation of caspases-3 and -9 and cytochrome c leakage-key events in apoptotic cell death--were observed only in the S334ter mutant, which also showed increased expression of PARP-1. The identification of the same metabolic markers triggered by different mutations in two different species suggests the existence of common cell death mechanisms, which is a major consideration for any mutation independent treatment.

A novel free radical scavenger rescues retinal cells in vivo

The benzopyran BP (3,4-dihydro-6-hydroxy-7-methoxy-2,2-dimethyl-1(2H)-benzopyran) is a free radical scavenger that is structurally similar to alpha-tocopherol and has provided neuro-protection in a number of disease models where oxidative stress is a causative factor. A novel derivative of BP with improved lipid solubility, which we have designated BP3, was synthesized and its neuro-protective efficacy subsequently analyzed in three mouse models of retinal disease in vivo. In the acute light damage model, balb/c mice received a single intra-peritoneal injection (200 mg/kg) of BP3 one hour prior to phototoxicity, reducing photoreceptor degeneration for up to 48 h post insult. In the rd10/rd10 mouse, a chronic model of inherited retinal degeneration, systemic dosing with BP3 on alternate days between post-natal day 18 and 25 preserved rod photoreceptor numbers and cone photoreceptor morphology. Finally, NMDA induced toxicity in retinal ganglion cells was diminished for at least 72 h after the initial insult by a single dose of BP3. In each disease model, BP3 alleviated cellular oxidative burden as MDA levels were markedly reduced. These results demonstrate that systemically administered BP3 has potent free radical scavenging capacity in the retina and may represent a single therapeutic strategy applicable across several retinopathies.

Microarray analysis of XOPS-mCFP zebrafish retina identifies genes associated with rod photoreceptor degeneration and regeneration

PURPOSE

XOPS-mCFP transgenic zebrafish experience a continual cycle of rod photoreceptor development and degeneration throughout life, making them a useful model for investigating the molecular determinants of rod photoreceptor regeneration. The purpose of this study was to compare the gene expression profiles of wild-type and XOPS-mCFP retinas and identify genes that may contribute to the regeneration of the rods.

METHODS

Adult wild-type and XOPS-mCFP retinal mRNA was subjected to microarray analysis. Pathway analysis was used to identify biologically relevant processes that were significantly represented in the dataset. Expression changes were verified by RT-PCR. Selected genes were further examined during retinal development and in adult retinas by in situ hybridization and immunohistochemistry and in a transgenic fluorescent reporter line.

RESULTS

More than 600 genes displayed significant expression changes in XOPS-mCFP retinas compared with expression in wild-type controls. Many of the downregulated genes were associated with phototransduction, whereas upregulated genes were associated with several biological functions, including cell cycle, DNA replication and repair, and cell development and death. RT-PCR analysis of a subset of these genes confirmed the microarray

RESULTS

Three transcription factors (sox11b, insm1a, and c-myb), displaying increased expression in XOPS-mCFP retinas, were also expressed throughout retinal development and in the persistently neurogenic ciliary marginal zone.

CONCLUSIONS

This study identified numerous gene expression changes in response to rod degeneration in zebrafish and further suggests a role for the transcriptional regulators sox11b, insm1a, and c-myb in both retinal development and rod photoreceptor regeneration.

Nanoceria extend photoreceptor cell lifespan in tubby mice by modulation of apoptosis/survival signaling pathways

Cerium oxide nanoparticles, nanoceria, are inorganic antioxidants that have catalytic activities which mimic those of the neuroprotective enzymes superoxide dismutase and catalase. We have previously shown that nanoceria preserve retinal morphology and prevent loss of retinal function in a rat light damage model. In this study, the homozygous tubby mutant mouse, which exhibits inherited early progressive cochlear and retinal degeneration, was used as a model to test the ability of nanoceria to slow the progression of retinal degeneration. Tubby mice were injected systemically, intracardially, with 20 μl of 1mM nanoceria in saline, at postnatal day 10 and subsequently at P20 and P30 whereas saline injected and uninjected wild type (or heterozygous tubby) served as injected and uninjected controls, respectively. Assays for retinal function, morphology and signaling pathway gene expression were performed on P34 mice. Our data demonstrate that nanoceria protect the retina by decreasing Reactive Oxygen Species (ROS), up-regulating the expression of neuroprotection-associated genes; down-regulating apoptosis signaling pathways and/or up-regulating survival signaling pathways to slow photoreceptor degeneration. These data suggest that nanoceria have significant potential as global agents for therapeutic treatment of inherited retinal degeneration and most types of ocular diseases.

Evidence of severe mitochondrial oxidative stress and a protective effect of low oxygen in mouse models of inherited photoreceptor degeneration

The role of oxidative stress within photoreceptors (PRs) in inherited photoreceptor degeneration (IPD) is unclear. We investigated this question using four IPD mouse models (Pde6b(rd1/rd1), Pde6b(atrd1/atrd1), Rho(-/-) and Prph2(rds/rds)) and compared the abundance of reduced glutathione (GSH) and the activity of mitochondrial NADH:ubiquinone oxidoreductase (complex I), which is oxidative stress sensitive, as indirect measures of redox status, in the retinas of wild type and IPD mice. All four IPD mutants had significantly reduced retinal complex I activities (14-29% of wild type) and two showed reduced GSH, at a stage prior to the occurrence of significant cell death, whereas mitochondrial citrate synthase, which is oxidative stress insensitive, was unchanged. We orally administered the mitochondrially targeted anti oxidant MitoQ in order to reduce oxidative stress but without any improvement in retinal complex I activity, GSH or rates of PR degeneration. One possible source of oxidative stress in IPDs is oxygen toxicity in the outer retina due to reduced consumption by PR mitochondria. We therefore asked whether a reduction in the ambient O(2) concentration might improve PR survival in Pde6b(rd1/rd1) retinal explants either directly, by reducing reactive oxygen species formation, or indirectly by a neuroprotective mechanism. Pde6b(rd1/rd1) retinal explants cultured in 6% O(2) showed 31% less PR death than normoxic explants. We conclude that (i) mitochondrial oxidative stress is a significant early feature of IPDs; (ii) the ineffectiveness of MitoQ may indicate its inability to reduce some mediators of oxidative stress, such as hydrogen peroxide; and (iii) elucidation of the mechanisms by which hypoxia protects mutant PRs may identify novel neuroprotective pathways in the retina.

cGMP-dependent cone photoreceptor degeneration in the cpfl1 mouse retina

Inherited retinal degeneration affecting both rod and cone photoreceptors constitutes one of the leading causes of blindness in the developed world. Such degeneration is at present untreatable, and the underlying neurodegenerative mechanisms are unknown, even though certain genetic causes have been established. The rd1 mouse is one of the best characterized animal models for rod photoreceptor degeneration, whereas the cpfl1 mouse is a recently discovered model for cone cell death. Because both animal models are affected by functionally similar mutations in the rod and cone phosphodiesterase 6 genes, respectively, we asked whether the mechanisms of photoreceptor degeneration in these two mouse lines share common pathways. In the present study, we followed the temporal progression of photoreceptor degeneration in the cpfl1 retina, correlated it with specific metabolic markers, and compared it with the wild-type and the rd1 situation. Similar to corresponding rd1 observations, cpfl1 cone photoreceptor cell death was associated with an accumulation of cyclic guanosine monophosphate (cGMP), activity of calpains, and phosphorylation of vasodilator-stimulated protein (VASP). Cone degeneration progressed rapidly, with a peak in cell death around postnatal day 24. Furthermore, cpfl1 cone photoreceptor migration during early postnatal development was delayed significantly compared with the corresponding wild-type retina. The finding that rod and cone photoreceptor degeneration was associated with the same metabolic markers suggests that in both cell types similar degenerative mechanisms are active. This raises the possibility that equivalent neuroprotective strategies may be used to prevent both rod and cone photoreceptor degeneration.

Photoreceptor degeneration: genetic and mechanistic dissection of a complex trait

The retina provides exquisitely sensitive vision that relies on the integrity of a uniquely vulnerable cell, the photoreceptor (PR). The genetic and mechanistic causes of retinal degeneration due to PR cell death--which occurs in conditions such as retinitis pigmentosa and age-related macular degeneration--are being successfully dissected. Over one hundred loci, some containing common variants but most containing rare variants, are implicated in the genetic architecture of this complex trait. This genetic heterogeneity results in equally diverse disease mechanisms that affect almost every aspect of PR function but converge on a common cell death pathway. Although genetic and mechanistic diversity creates challenges for therapy, some approaches--particularly gene-replacement therapy--are showing considerable promise.

Effect of para-aminobenzoic acid on the course of retinal degeneration in the rd10 mouse

PURPOSE

Recent evidence suggests that oxidative injury plays a significant role in the pathogenesis of retinal degenerative diseases. Para-aminobenzoic acid (PABA) is a cyclic amino acid, which may act to decrease lipid peroxidation and oxidative injury. Our aim was to evaluate the efficacy of PABA in attenuating oxidative injury and rate of retinal degeneration in the rd10 mouse.

METHODS

PABA (50 mg/kg) was administered intraperitoneally six times per week in 28 rd10 mice from postnatal day 3. Twenty-four littermate control mice were similarly injected with saline. At 3, 4.5, and 6 weeks of age, electrophysiological (full field electroretinogram-ERG), quantitative histological, and immunohistochemical techniques were used to assess the course and extent of retinal degeneration. Degree of lipid peroxidation was determined by the measurement of thiobarbituric acid reactive species (TBARS) and retinal carbonyl content was quantified using the 2,4-dinitrophenylhydrazine method.

RESULTS

Dark adapted mixed rod-cone ERG responses at 3 weeks of age were higher in the PABA-treated group as compared to saline control (P < 0.05). By 4.5 weeks, this protective effect was largely abolished and by 6 weeks ERG was unrecordable in both groups. However, at both 3 and 4.5 weeks of age, light-adapted cone ERG amplitudes were better preserved in PABA-treated animals. At 4.5 weeks, thickness of the outer nuclear layer was 28.6% higher in the peripheral retina of PABA-treated mice as compared to controls (P < 0.05). Quantitative immunohistochemistry revealed 2.4-fold higher red/green cone opsin content in the retinas of PABA-treated mice (P < 0.005). At both 3 and 4.5 weeks, levels of TBARS and protein carbonyls were 49%-69% lower in PABA-treated retinas (P < 0.05-0.0005), suggesting less oxidative injury.

CONCLUSIONS

PABA treatment may protect retinal function and attenuate the course of retinal degeneration in rd10 mice. Biochemical parameters indicate a lower degree of oxidative injury in PABA-treated retinas. PABA may potentially serve as an addition to antioxidative treatment for retinal and macular degenerations.

Beneficial effect of docosahexanoic acid and lutein on retinal structural, metabolic, and functional abnormalities in diabetic rats

PURPOSE

To assess the effect of docosahexanoic acid (DHA) and lutein (both compounds with anti-inflammatory and antioxidant properties) on experimental diabetic retinopathy.

METHODS

Male Wistar rats were studied: non-diabetic controls, untreated diabetic controls, and diabetic rats were treated with DHA and lutein or the combination of DHA + insulin and lutein + insulin for 12 weeks. Oxidative stress and inflammatory markers, apoptosis, and functional tests were studied to confirm biochemical and functional changes in the retina of diabetic rats. Malondialdehyde (MDA), glutathione concentrations (GSH), and glutathione peroxidase activity (GPx) were measured as oxidative stress markers. TUNEL assay and caspase-3 immunohistochemistry and electroretinogram were performed.

RESULTS

Diabetes increases oxidative stress, nitrotyrosine concentrations, and apoptosis in the retina. At 12 weeks after onset of diabetes, total thickness of retinas of diabetic rats was significantly less than that in control rats. Specifically, the thickness of the outer and inner nuclear layers was reduced significantly in diabetic rats and demonstrated a loss of cells in the GCL. These retinal changes were avoided by the administration of insulin and DHA and lutein alone or in combination with insulin. Impairment of the electroretinogram (b-wave amplitude and latency time) was observed in diabetic rats. DHA and lutein prevented all these changes even under hyperglycemic conditions.

CONCLUSIONS

Lutein and DHA are capable of normalizing all the diabetes-induced biochemical, histological, and functional modifications. Specifically, the cell death mechanisms involved deserve further studies to allow the proposal as potential adjuvant therapies to help prevent vision loss in diabetic patients.

The genomic, biochemical, and cellular responses of the retina in inherited photoreceptor degenerations and prospects for the treatment of these disorders

The association of more than 140 genes with human photoreceptor degenerations, together with studies of animal models of these monogenic diseases, has provided great insight into their pathogenesis. Here we review the responses of the retina to photoreceptor mutations, including mechanisms of photoreceptor death. We discuss the roles of oxidative metabolism, mitochondrial reactive oxygen species, metabolic stress, protein misfolding, and defects in ciliary proteins, as well as the responses of Müller glia, microglia, and the retinal vasculature. Finally, we report on potential pharmacologic and biologic therapies, the critical role of histopathology as a prerequisite to treatment, and the exciting promise of gene therapy in animal models and in phase 1 trials in humans.

Lutein and docosahexaenoic acid prevent cortex lipid peroxidation in streptozotocin-induced diabetic rat cerebral cortex

The mechanisms underlying diabetic encephalopathy, are largely unknown. Here, we examined whether docosahexaenoic acid (DHA) and lutein could attenuate the oxidative changes of the diabetic cerebral cortex. The levels of malondialdehyde (MDA) were significantly increased and glutathione (GSH) and glutathione peroxidase activity (GPx) were decreased in diabetic rats. The number of 4-hydroxynonenal (4-HNE) positive cells was increased. Treatment with insulin, lutein or DHA and the combination of each antioxidant with insulin, significantly restored all markers concentrations mentioned above, and the increase in 4-HNE inmunofluorescence. We combined 4-HNE immunofluorescence with NeuN (Neuronal Nuclei) staining. The latter demonstrated extensive overlap with the 4-HNE staining in the cortex from diabetic rats. Our findings demonstrate a clear participation of glucose-induced oxidative stress in the diabetic encephalopathy, and that the cells suffering oxidative stress are neurons. Lowering oxidative stress through the administration of different antioxidants may be beneficial for the central nervous tissue in diabetes.

Photoreceptor cell death mechanisms in inherited retinal degeneration

Photoreceptor cell death is the major hallmark of a group of human inherited retinal degenerations commonly referred to as retinitis pigmentosa (RP). Although the causative genetic mutations are often known, the mechanisms leading to photoreceptor degeneration remain poorly defined. Previous research work has focused on apoptosis, but recent evidence suggests that photoreceptor cell death may result primarily from non-apoptotic mechanisms independently of AP1 or p53 transcription factor activity, Bcl proteins, caspases, or cytochrome c release. This review briefly describes some animal models used for studies of retinal degeneration, with particular focus on the rd1 mouse. After outlining the major features of different cell death mechanisms in general, we then compare them with results obtained in retinal degeneration models, where photoreceptor cell death appears to be governed by, among other things, changes in cyclic nucleotide metabolism, downregulation of the transcription factor CREB, and excessive activation of calpain and PARP. Based on recent experimental evidence, we propose a putative non-apoptotic molecular pathway for photoreceptor cell death in the rd1 retina. The notion that inherited photoreceptor cell death is driven by non-apoptotic mechanisms may provide new ideas for future treatment of RP.

Orally administered epigallocatechin gallate attenuates light-induced photoreceptor damage

EGCG, a major component of green tea, has a number of properties which includes it being a powerful antioxidant. The purpose of this investigation was to deduce whether inclusion of EGCG in the drinking water of albino rats attenuates the effect of a light insult (2200lx, for 24h) to the retina. TUNEL-positive cells were detected in the outer nuclear layer of the retina, indicating the efficacy of the light insult in inducing photoreceptor degeneration. Moreover, Ret-P1 and the mRNA for rhodopsin located at photoreceptors were also significantly reduced as well as the amplitude of both the a- and b-waves of the electroretinogram was also reduced showing that photoreceptors in particular are affected by light. An increase in protein/mRNA of GFAP located primarily to Müller cells caused by light shows that other retinal components are also influenced by the light insult. However, antigens associated with bipolar (alpha-PKC), ganglion (Thy-1) and amacrine (GABA) cells, in contrast, appeared unaffected. The light insult also caused a change in the content of various proteins (caspase-3, caspase-8, PARP, Bad, and Bcl-2) involved in apoptosis. A number of the changes to the retina caused by a light insult were significantly attenuated when EGCG was in the drinking water. The reduction of the a- and b-waves and photoreceptor specific mRNAs/protein caused by light were significantly less. In addition, EGCG attenuated the changes caused by light to certain apoptotic proteins (especially at after 2 days) but did not appear to significantly influence the light-induced up-regulation of GFAP protein/mRNA. It is concluded that orally administered EGCG blunts the detrimental effect of light to the retina of albino rats where the photoreceptors are primarily affected.

CR-6 protects glutathione peroxidase activity in experimental diabetes

Antioxidants can be useful as a supportive therapy in diabetes, and we try to elucidate some of the mechanisms by which these compounds are able to protect from diabetic complications. For this purpose we have assayed, in vitro and in vivo, the ability of CR-6 (3,4-dihydro-6-hydroxy-7-methoxy-2,2-dimethyl-1(2H)-benzopyran), an antioxidant able to scavenge nitrogen reactive species, to protect glutathione peroxidase (GPx) activity. Glucose, in vitro, inhibited GPx activity in a concentration-dependent manner; CR-6 was able to protect GPx activity from glucose-induced inactivation. Alloxan-induced experimental diabetes in mice promoted oxidative stress in the retina and hippocampus, after 3 weeks of hyperglycemia. CR-6 administration prevented not only the alterations of oxidative stress markers (tissue GSH and malondialdehyde (MDA) concentration and GPx activity) but also the impairment of retinal function (as assessed by the modifications in electroretinogram b-wave amplitude). The findings herein confirm the role of nitrogen reactive species in diabetes; therefore, antioxidants effectively quenching these species, such as CR-6, should be considered for the adjuvant treatment of diabetes.

Excessive activation of poly(ADP-ribose) polymerase contributes to inherited photoreceptor degeneration in the retinal degeneration 1 mouse

Retinitis pigmentosa (RP) is an inherited blinding disease for which there is no treatment available. It is characterized by a progressive and neurodegenerative loss of photoreceptors but the underlying mechanisms are poorly understood. Excessive activation of the enzyme poly(ADP-ribose) polymerase (PARP) has recently been shown to be involved in several neuropathologies. To investigate the possible role of PARP in retinal photoreceptor degeneration, we used the retinal degeneration 1 (rd1) mouse RP model to study PARP expression, PARP activity, and to test the effects of PARP inhibition on photoreceptor viability. PARP expression was found to be equal between rd1 and wild-type counterpart retinas. In contrast to this, a dramatic increase in both PARP activity per se and PARP product formation was detected by in situ assays in rd1 photoreceptors actively undergoing cell death. Furthermore, PARP activity colabeled with oxidatively damaged DNA and nuclear translocation of AIF (apoptosis-inducing factor), suggesting activation of PARP as a bridge between these events in the degenerating photoreceptors. The PARP-specific inhibitor PJ34 [N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide x HCl[ reduced the number of cells exhibiting death markers in a short-term retinal culture paradigm, a protective effect that was translated into an increased number of surviving photoreceptors when the inhibitor was used in a long-term culture setting. Our results thus demonstrate an involvement of PARP activity in rd1 photoreceptor cell death, which could have a bearing on the understanding of neurodegenerations as such. The findings also suggest that the therapeutical possibilities of PARP inhibition should include retinal diseases like RP.

Seeing the light: New insights into the molecular pathogenesis of retinal diseases

In the past, most treatments for retinal diseases have been empirical. Steroids and/or laser photocoagulation and/or surgery have been tried for almost every condition with little or no understanding of the underlying disease. Over the past several years vision researchers have uncovered molecular components of processes, such as visual transduction and the visual cycle, that are critical for visual function, and identified other molecules that lead to dysfunction and disease processes such as neovascularization and macular edema. It is becoming clear that dysregulation of certain molecules can have major effects on retinal structure and function. Studies in animal models have suggested that inhibiting or augmenting levels of a single molecule can have major effects in complex disease processes. Although several molecules probably contribute to neovascularization and excessive vascular permeability in the eye, blockade of vascular endothelial growth factor (VEGF) has remarkable beneficial effects in animal models that have now been proven to apply to human diseases in clinical trials. Intraocular injection of VEGF antagonists has revolutionized the treatment of choroidal neovascularization (CNV) and macular edema and serves as a model of targeted ocular pharmacotherapy. Significant progress elucidating the molecular pathogenesis of several disease processes in the eye may soon lead to new treatments following the lead of VEGF antagonists. Initial treatments that provide benefit from frequent intraocular injections are likely to be followed by sustained delivery of drugs and/or prolonged protein delivery by gene transfer. The eye has entered the era of molecular therapy.