A Potential New Role for Zinc in Age-Related Macular Degeneration through Regulation of Endothelial Fenestration.

Age-related macular degeneration (AMD) is a common blinding disease in the western world that is linked to the loss of fenestration in the choriocapillaris that sustains the retinal pigment epithelium and photoreceptors in the back of the eye. Changes in ocular and systemic zinc concentrations have been associated with AMD; therefore, we hypothesized that these changes might be directly involved in fenestrae formation. To test this hypothesis, an endothelial cell (bEND.5) model for fenestrae formation was treated with different concentrations of zinc sulfate (ZnSO4) solution for up to 20 h. Fenestrae were visualized by staining for Plasmalemmal Vesicle Associated Protein-1 (PV-1), the protein that forms the diaphragms of the fenestrated endothelium. Size and distribution were monitored by transmission electron microscopy (TEM). We found that zinc induced the redistribution of PV-1 into areas called sieve plates containing ~70-nm uniform size and typical morphology fenestrae. As AMD is associated with reduced zinc concentrations in the serum and in ocular tissues, and dietary zinc supplementation is recommended to slow disease progression, we propose here that the elevation of zinc concentration may restore choriocapillaris fenestration resulting in improved nutrient flow and clearance of waste material in the retina.

Shihu Yeguang Pill protects against bright light-induced photoreceptor degeneration in part through suppressing photoreceptor apoptosis.

Photoreceptor cells are first-order retinal neurons that directly contribute to the formation of vision. Photoreceptor degeneration is the primary cause of vision impairment during the course of retinopathies such as retinitis pigmentosa and age-related macular degeneration, for which photoreceptor-targeted therapies are currently unavailable. Shihu Yeguang Pill (SYP), a classic formula in traditional Chinese medicine, has a long histology of clinical application for the treatment of a wide range of retinopathies in China. However, whether SYP is pharmacological effective at protecting photoreceptor cells is unclear. The current study thus directly addressed the pharmacological implications of SYP in photoreceptor degeneration in a mouse model characterized by bright light-induced retinal degeneration. Non-invasive full-retinal assessment was carried out to evaluate the effect of SYP on the retinal structure and function through optical coherence tomography and electroretinography, respectively. In addition, photoreceptor apoptosis, second-order neuron impairment and reactive changes in retinal microglial and müller cells, hallmark pathologies associated with photoreceptor degeneration, were assessed using immunohistochemistry and real-time PCR analyses. The results showed that SYP treatment attenuated bright light-induced impairment of the retinal structure and function. Moreover, SYP treatment suppressed photoreceptor apoptosis, alleviated the impairment of bipolar and horizontal cells and mitigated the reactive changes of müller and microglial cells in the bright light-exposed retinas. Real-time PCR analyses showed that dysregulated expression of pro-apoptotic c-fos and c-jun and anti-apoptotic bcl-2 as well as proinflammatory TNF-α in the bright light-exposed retinas was partially normalized as a result of SYP treatment. In summary, the work here demonstrates for the first time that SYP treatment protects the retinas from developing bright light-induced photoreceptor degeneration and associated alterations in second-order neurons and glial cells. The findings here thus provide experimental evidence to better support the mechanism-guided clinical application of SYP in the treatment of related retinal degenerative diseases.

The natural retinoprotectant chrysophanol attenuated photoreceptor cell apoptosis in an N-methyl-N-nitrosourea-induced mouse model of retinal degenaration.

Retinitis pigmentosa (RP) is an inherited photoreceptor-degenerative disease, and neuronal degeneration in RP is exacerbated by glial activation. Cassia seed (Jue-ming-zi) is a traditional herbal medicine commonly used to treat ocular diseases in Asia. In this report, we investigated the retina-protective effect of chrysophanol, an active component of Cassia seed, in an N-methyl-N-nitrosourea (MNU)-induced mouse model of RP. We determined that chrysophanol inhibited the functional and morphological features of MNU-induced retinal degeneration using scotopic electroretinography (ERG), optical coherence tomography (OCT), and immunohistochemistry analysis of R/G opsin and rhodopsin. Furthermore, TUNEL assays revealed that chrysophanol attenuated MNU-induced photoreceptor cell apoptosis and inhibited the expression of the apoptosis-associated proteins PARP, Bax, and caspase-3. In addition, chrysophanol ameliorated reactive gliosis, as demonstrated by a decrease in GFAP immunolabeling, and suppressed the activation of matrix metalloproteinase (MMP)-9-mediated gelatinolysis. In vitro studies indicated that chrysophanol inhibited lipopolysaccharide (LPS)-induced iNOS and COX-2 expression in the BV2 mouse microglia cell line and inhibited MMP-9 activation in primary microglia. Our results demonstrate that chrysophanol provided neuroprotective effects and inhibited glial activation, suggesting that chrysophanol might have therapeutic value for the treatment of human RP and other retinopathies.

Polyphenol-enriched Vaccinium uliginosum L. fractions reduce retinal damage induced by blue light in A2E-laden ARPE19 cell cultures and mice.

Polyphenols exert beneficial effects on vision. We hypothesized that polyphenol components of Vaccinium uliginosum L. (V.U.) extract protect retinal pigment epithelial (RPE) cells against blue light-induced damage. Our aim was to test extracts containing polyphenol components to ascertain effects to reduce damage against blue light in RPEs. We measured the activity in fractions eluted from water, ethanol, and HP20 resin (FH), and found that the FH fraction had the highest beneficial activity. We isolated the individual active compounds from the FH fraction using chromatographic techniques, and found that FH contained flavonoids, anthocyanins, phenyl propanoids, and iridoids. Cell cultures of A2E-laden ARPE-19 exposed to blue light after treatment with V.U. extract fractions and their individual constituents indicated improvement. V uliginosum L extract fractions and constituent compounds significantly reduced A2E photo-oxidation-induced RPE cell death and inhibited intracellular A2E accumulation. Furthermore, Balb/c male mice were exposed to blue light at 10000 lux for 1 h/d for 2 weeks to induce retinal damage. One week after the final blue light exposure, retinal damage evaluated revealed that the outer nuclear layer thickness and nuclei count were improved. Histologic examination of murine photoreceptor cells demonstrated that FH, rich in polyphenols, inhibited the loss of outer nuclear layer thickness and nuclei. Our findings suggest that V.U. extract and eluted fractions are a potential source of bioactive compounds that potentially serve a therapeutic approach for age-related macular degeneration.

A High-Throughput Drug Screening Strategy for Detecting Rhodopsin P23H Mutant Rescue and Degradation.

PURPOSE: Inherent instability of the P23H mutant opsin accounts for approximately 10% of autosomal dominant retinitis pigmentosa cases. Our purpose was to develop an overall set of reliable screening strategies to assess if either stabilization or enhanced degradation of mutant rhodopsin could rescue rod photoreceptors expressing this mutant protein. These strategies promise to reveal active compounds and clarify molecular mechanisms of biologically important processes, such as inhibition of target degradation or enhanced target folding. METHODS: Cell-based bioluminescence reporter assays were developed and validated for high-throughput screening (HTS) of compounds that promote either stabilization or degradation of P23H mutant opsin. Such assays were further complemented by immunoblotting and image-based analyses. RESULTS: Two stabilization assays of P23H mutant opsin were developed and validated, one based on ß-galactosidase complementarity and a second assay involving bioluminescence resonance energy transfer (BRET) technology. Moreover, two additional assays evaluating mutant protein degradation also were employed, one based on the disappearance of luminescence and another employing the ALPHA immunoassay. Imaging of cells revealed the cellular localization of mutant rhodopsin, whereas immunoblots identified changes in the aggregation and glycosylation of P23H mutant opsin. CONCLUSIONS: Our findings indicate that these initial HTS and following assays can identify active therapeutic compounds, even for difficult targets such as mutant rhodopsin. The assays are readily scalable and their function has been proven with model compounds. High-throughput screening, supported by automated imaging and classic immunoassays, can further characterize multiple steps and pathways in the biosynthesis and degradation of this essential visual system protein.

Dynamic increase in extracellular ATP accelerates photoreceptor cell apoptosis via ligation of P2RX7 in subretinal hemorrhage.

Photoreceptor degeneration is the most critical cause of visual impairment in age-related macular degeneration (AMD). In neovascular form of AMD, severe photoreceptor loss develops with subretinal hemorrhage due to choroidal neovascularization (CNV), growth of abnormal blood vessels from choroidal circulation. However, the detailed mechanisms of this process remain elusive. Here we demonstrate that neovascular AMD with subretinal hemorrhage accompanies a significant increase in extracellular ATP, and that extracellular ATP initiates neurodegenerative processes through specific ligation of Purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7; P2X7 receptor). Increased extracellular ATP levels were found in the vitreous samples of AMD patients with subretinal hemorrhage compared to control vitreous samples. Extravascular blood induced a massive release of ATP and photoreceptor cell apoptosis in co-culture with primary retinal cells. Photoreceptor cell apoptosis accompanied mitochondrial apoptotic pathways, namely activation of caspase-9 and translocation of apoptosis-inducing factor (AIF) from mitochondria to nuclei, as well as TUNEL-detectable DNA fragmentation. These hallmarks of photoreceptor cell apoptosis were prevented by brilliant blue G (BBG), a selective P2RX7 antagonist, which is an approved adjuvant in ocular surgery. Finally, in a mouse model of subretinal hemorrhage, photoreceptor cells degenerated through BBG-inhibitable apoptosis, suggesting that ligation of P2RX7 by extracellular ATP may accelerate photoreceptor cell apoptosis in AMD with subretinal hemorrhage. Our results indicate a novel mechanism that could involve neuronal cell death not only in AMD but also in hemorrhagic disorders in the CNS and encourage the potential application of BBG as a neuroprotective therapy.

The many different cellular functions of MYO7A in the retina.

Mutations in MYO7A (myosin VIIa) cause Usher syndrome type 1B, a disorder involving profound congenital deafness and progressive blindness. In the retina, most MYO7A is localized in the apical region of the RPE (retinal pigmented epithelial) cells, and a small amount is associated with the ciliary and periciliary membranes of the photoreceptor cells. Its roles appear to be quite varied. Studies with MYO7A-null mice indicate that MYO7A participates in the apical localization of RPE melanosomes and in the removal of phagosomes from the apical RPE for their delivery to lysosomes in the basal RPE. In the first role, MYO7A competes with microtubule motors, but in the second one, it may function co-operatively. An additional role of MYO7A in the RPE is indicated by the requirement for it in the light-dependent translocation of the ER (endoplasmic reticulum)-associated visual cycle enzyme RPE65 and normal functioning of the visual retinoid cycle. In photoreceptor cells lacking MYO7A, opsin accumulates abnormally in the transition zone of the cilium, suggesting that MYO7A functions as a selective barrier for membrane proteins at the distal end of the transition zone. It is likely that the progressive retinal degeneration that occurs in Usher syndrome 1B patients results from a combination of cellular defects in the RPE and photoreceptor cells.

Optic vesicle-like structures derived from human pluripotent stem cells facilitate a customized approach to retinal disease treatment.

Differentiation methods for human induced pluripotent stem cells (hiPSCs) typically yield progeny from multiple tissue lineages, limiting their use for drug testing and autologous cell transplantation. In particular, early retina and forebrain derivatives often intermingle in pluripotent stem cell cultures, owing to their shared ancestry and tightly coupled development. Here, we demonstrate that three-dimensional populations of retinal progenitor cells (RPCs) can be isolated from early forebrain populations in both human embryonic stem cell and hiPSC cultures, providing a valuable tool for developmental, functional, and translational studies. Using our established protocol, we identified a transient population of optic vesicle (OV)-like structures that arose during a time period appropriate for normal human retinogenesis. These structures were independently cultured and analyzed to confirm their multipotent RPC status and capacity to produce physiologically responsive retinal cell types, including photoreceptors and retinal pigment epithelium (RPE). We then applied this method to hiPSCs derived from a patient with gyrate atrophy, a retinal degenerative disease affecting the RPE. RPE generated from these hiPSCs exhibited a disease-specific functional defect that could be corrected either by pharmacological means or following targeted gene repair. The production of OV-like populations from human pluripotent stem cells should facilitate the study of human retinal development and disease and advance the use of hiPSCs in personalized medicine.

Taurine deficiency damages photoreceptors and retinal ganglion cells in vigabatrin-treated neonatal rats.

The anti-epileptic drug vigabatrin induces an irreversible constriction of the visual field, but is still widely used to treat infantile spasms and some forms of epilepsy. We recently reported that vigabatrin-induced cone damage is due to a taurine deficiency. However, optic atrophy and thus retinal ganglion cell degeneration was also reported in children treated for infantile spasms. We here show in neonatal rats treated from postnatal days 4 to 29 that the vigabatrin treatment triggers not only cone photoreceptor damage, disorganisation of the photoreceptor layer and gliosis but also retinal ganglion cell loss. Furthermore, we demonstrate in these neonatal rats that taurine supplementation partially prevents these retinal lesions and in particular the retinal ganglion cell loss. These results provide the first evidence of retinal ganglion cell neuroprotection by taurine. They further confirm that taurine supplementation should be administered with the vigabatrin treatment for infantile spasms or epilepsy.

[Restraining effects of acupuncture on photoreceptor cell apoptosis in rats with retinitis pigmentosa induced by N-methyl-N-nitrosourea].

OBJECTIVE: To observe the effect of acupuncture on photoreceptor cell apoptosis in rats with retinitis pigmentosa induced by N-methyl-N-nitrosourea (MNU). METHODS: Fifty-day-old female SD rats were established into model of retinitis pigmentosa by once intraperitoneal injection of 50 mg/kg MNU, and randomly grouped to the acupuncture group and the model group for observing the cell apoptosis in rats and compared with that in normal rats at the corresponding time points. RESULTS: Acupuncture showed no effect on cell apoptosis at its peak of occurring, apoptotic phenomena still could be seen on days 5 and 7, but it was significantly less in the acupuncture group than in the model group (P < 0.01). Moreover, acupuncture showed a restraining effect on the up-regulation of caspase-3 activity. CONCLUSION: Acupuncture can restrain the MNU induced apoptosis of photoreceptor cells, the effect is correlated, to a certain degree, with the status of the apoptosis occurrence.

Selective degeneration of central photoreceptors after hyperbaric oxygen in normal and metallothionein-knockout mice.

PURPOSE: Metallothioneins (MTs) in the brain and retina are believed to bind metals and reduce free radicals, thereby protecting neurons from oxidative damage. This study was undertaken to investigate whether retinal photoreceptor (PR) cells lacking MTs are more susceptible to hyperbaric oxygen (HBO)-induced cell death in vivo. METHODS: Wild-type (WT) and MT-knockout (MT-KO) mice lacking metallothionein (MT)-1 and MT-2 were exposed to three atmospheres of 100% oxygen for 3 hours, 3 times per week for 1, 3, or 5 weeks. The control animals were not exposed. Histologic analysis of PR viability was performed by counting rows of nuclei in the outer nuclear layer (ONL). Ultrastructure studies verified PR damage. RESULTS: HBO exposure produced a major loss of PR cells in the central retinas of WT and MT-KO mice, with no effect on the peripheral retina even at the longest (5 weeks) exposures. The degree of PR damage and cell death increased with duration of HBO exposure. One week of HBO exposure was insufficient to cause PR death, but tissue damage was observed in the inner and outer segments. At 3 weeks, the rows of PR nuclei in the central retina were significantly reduced by 38% in WT and 28% in MT-KO animals. At 5 weeks, PR loss was identical in WT (34%) and MT-KO (34%) animals and was comparable to that in WT at 3 weeks. CONCLUSIONS: The data suggest that MT-1 and -2 alone are not sufficient for protecting PRs against HBO-induced cell death. The selective degeneration of central PRs may provide clues to mechanisms of oxidative damage in retinal disease.

Exposure to diazinon alters in vitro retinogenesis: retinospheroid morphology, development of chicken retinal cell types, and gene expression.

Developing embryos are more vulnerable than adults to acute cholinergic intoxication by anticholinesterases, including organophosphorus pesticides. These agents affect the process of neural development itself, leading to permanent deficits in the architecture of the nervous system. Recent evidence on direct roles of acetylcholinesterase (AChE) on neuronal differentiation provides additional grounds for investigating the developmental toxicity of anticholinesterases. Therefore, the effect of the organophosphate diazinon on the development of chick retinal differentiation was studied by an in vitro reaggregate approach. Reaggregated spheres from dissociated retinal cells of the E6 chick embryo were produced in rotation culture. During the whole culture period of 10 days, experimental cultures were supplemented with different concentrations of the pesticide, from 20 to 120 microM diazinon. The pesticide-treated spheres were reduced in size, and their outer surface was irregular. More importantly, inner structural distortions could be easily traced because the structure of control spheroids can be well characterized by a histotypical arrangement of laminar parts homologous to the normal retina. Acetylcholinesterase activity in diazinon-treated spheres was reduced when compared with controls. As a dramatic effect of exposure to the pesticide, inner plexiform layer (IPL)-like areas in spheroids were not distinguishable anymore. Similarly, photoreceptor rosettes and Müller radial glia were strongly decreased, whereas apoptosis was stimulated. The expression of transcripts for choline-acetyltransferase and muscarinic receptors was affected, revealing an effect of diazinon on the cholinergic system. This further proves the significance of cholinesterases and the cholinergic system for proper nervous system development and shows that further studies of debilitating diazinon actions on development are necessary.

[Characteristics of N-methyl-N-nitrosourea-induced retinal degeneration in animals and application for the therapy of human retinitis pigmentosa].

BACKGROUND: Retinitis pigmentosa(RP) is a human disease characterized by loss of photoreceptor cells, especially rods, leading to visual disturbance and eventually to blindness. Effective treatment for RP control is still unavailable. The establishment of reliable animal models is essential for a better understanding of this disease, and for the development of therapeutic intervention. Here we summarize the establishment of N-methyl-N-nitrosourea (MNU)-induced retinal degeneration in animals, and success in disease control using this model. RESULTS: Retinal damage induced by MNU was highly reproducible and involved photoreceptor cell loss. It was obvious in all animals at approximately 7 days following a single systemic administration of MNU to adult mice (60 mg/kg), rats (60-75 mg/kg), hamsters (90 mg/kg), shrews (65 mg/kg), and monkeys (40 mg/kg). Extensive investigation in the rats revealed that MNU-induced photoreceptor cell loss was due to apoptosis with a decrease of Bcl-2 protein, increase of Bax protein, and activation of caspase families. Therapeutic to control MNU-induced photoreceptor cell loss in rats was evaluated with caspase-3 inhibitor (Ac-DEVD-CHO), nicotinamide(NAM), and docosahexaenoic acid(DHA); 4,000ng Ac-DEVD-CHO injected intravitreally 0 and 10 h after MNU suppressed disease progression, 25-1,000 mg/kg NAM subcutaneously injected concurrently or subsequently to MNU reversed retinal damage, and dietary supplementation of 9.5% DHA counteracted photoreceptor cell loss. CONCLUSION: Although the mechanisms triggering pathogenesis and the apoptotic cascade may differ between animals and humans, MNU-induced retinal degeneration is caused by photoreceptor cell apoptosis. Thus, suppression of MNU-induced photoreceptor cell apoptosis in animals may provide therapeutic information for RP control in humans.

Diets enriched in docosahexaenoic acid fail to correct progressive rod-cone degeneration (prcd) phenotype.

PURPOSE: Results of a previous study show abnormal plasma lipids in progressive rod-cone degeneration (prcd)-affected dogs, with lower docosahexaenoic acid (DHA; 22:6n-3) and cholesterol levels but no differences in other plasma fatty acids, lipids, triglycerides, and fat-soluble vitamins. There is also an increase of the DHA precursor 22:5n-3, so that the ratio of 22:5n-3 to 22:6n-3 is higher in affected than in normal dogs. Because DHA is the predominant esterified fatty acid in rod outer segment (ROS) phospholipids, these findings suggest a possible causal association between abnormal plasma lipid levels and retinal degeneration. In the current study, dietary supplements rich in 22:6n-3 were used to determine whether plasma, liver, and rod outer segment phospholipid composition can be altered to modify the prcd disease phenotype. METHODS: prcd-affected and normal control dogs were given DHA-enriched supplements for short (7- and 25-day) and long (21-week) periods, and the fatty acid composition of plasma, liver, and rod outer segment phospholipids were examined. In the long-term study, electroretinography and morphology were used to assess modification of the retinal degeneration phenotype. RESULTS: Administration of DHA-enriched supplements resulted in increases in plasma DHA and n-3 polyunsaturated fatty acids and in decreases in some n-6 fatty acids in normal and prcd-affected dogs. Similar increases in DHA and n-3 fatty acids were observed in the liver, but affected dogs had significantly higher levels at all supplementation time points examined. In contrast, the ROS of affected dogs had statistically lower (approximately 20%) DHA levels, and these levels could not be increased with dietary supplementation. The disease phenotype could not be modified by DHA-enriched supplements. CONCLUSIONS: Regardless of the sustained three- to fourfold elevation in plasma and liver DHA that occurs as the result of supplementation, the ROS DHA levels remain unchanged, and the prcd disease phenotype is not modified by the dietary manipulation. These findings could be the result of a reduction in the synthesis of DHA-containing phospholipids in the retinas of affected dogs; or, alternatively, there could be a reduction in DHA uptake, transport, or storage within the retinal pigment epithelium-photoreceptor complex.

Retinal light damage in rats with altered levels of rod outer segment docosahexaenoate.

PURPOSE: To compare retinal light damage in rats with either normal or reduced levels of rod outer segment (ROS) docosahexaenoic acid. METHODS: Weanling male albino rats were maintained in a weak cyclic light environment and fed either a nonpurified control diet or a purified diet deficient in the linolenic acid precursor of docosahexaenoic acid (DHA). Half the rats on the deficient diet were given linseed oil, containing more than 50 mol% linolenic acid, once a week to maintain ROS DHA at near normal levels. Diets and linseed oil supplementation were continued for 7 to 12 weeks. To replenish DHA in their ROS, some 10-week-old rats on the deficient diet were given linseed oil three times a week for up to 3 additional weeks. Groups of animals were killed at various times for ROS fatty acid determinations or were exposed to intense green light using intermittent or hyperthermic light treatments. The extent of retinal light damage was determined biochemically by rhodopsin or photoreceptor cell DNA measurements 2 weeks after exposure and morphologically by light and electron microscopy at various times after light treatment. RESULTS: Rats maintained for 7 to 12 weeks on the linolenic acid-deficient diet had significantly lower levels of DHA and significantly higher levels of n-6 docosapentaenoic acid (22:5n-6) in their ROS than deficient-diet animals supplemented once a week with linseed oil or those fed the nonpurified control diet. As determined by rhodopsin levels and photoreceptor cell DNA measurements, deficient diet rats exhibited protection against retinal damage from either intermittent or hyperthermic light exposure. However, the unsaturated fatty acid content of ROS from all three dietary groups was the same and greater than 60 mol%. In 10 week-old deficient-diet rats given linseed oil three times a week, ROS DHA was unchanged for the first 10 days, whereas 22:5n-6 levels declined by 50%. After 3 weeks of treatment with linseed oil, ROS DHA and 22:5n-6 were nearly the same as in rats supplemented with linseed oil from weaning. The time course of susceptibility to retinal light damage, however, was different. Hyperthermic light damage in rats given linseed oil for only 2 days was the same as for rats always fed the deficient diet. Six days after the start of linseed oil treatment, retinal light damage was the same as in rats given the linseed oil supplement from weaning. Morphologic alterations in ROS of linseed oil-supplemented rats immediately after intermittent light exposure were more extensive than in either the deficient-diet animals or those fed the control diet. The deficient-diet rats also exhibited better preservation of photoreceptor cell nuclei and structure 2 weeks after exposure. CONCLUSIONS: Rats fed a diet deficient in the linolenic acid precursor of DHA are protected against experimental retinal light damage. The relationship between retinal light damage and ROS lipids does not depend on the total unsaturated fatty acid content of ROS; the damage appears to be related to the relative levels of DHA and 22:5n-6.

Effect of dietary fish oil on acute light-induced photoreceptor damage in the rat retina.

PURPOSE: Previous studies have shown that ingestion of fish oil (FO) containing a high proportion of n-3 polyunsaturated fatty acids increases the susceptibility of cellular membranes to oxidative damage in various tissues. In the retina, lipid peroxidation is thought to be a major mechanism contributing to light-induced lesions. Therefore, we investigated the effect of FO on acute light-induced photoreceptor damage. METHODS: For 2 months, weanling rats were fed diets containing either soybean oil (SOY) or FO as main lipid component. RESULTS: Rats fed FO had significantly higher levels of eicosapentaenoic acid (EPA, 20:5n-3) and higher ratios of EPA to arachidonic acid (AA, 20:4n-6) in retinal phospholipids and diacylglycerols than rats fed SOY. The levels of docosahexaenoic acid (DHA, 22:6n-3) were similar in both dietary groups. The susceptibility to lipid peroxidation was enhanced in the isolated retina of FO-fed rats as shown by higher levels of thiobarbituric acid reactive substances after incubation of retinal membranes with Fe2+/ascorbate. The retinal content of alpha-tocopherol was similar in SOY- and FO-fed animals. Light damage consisting of acute rod outer segment (ROS) disruptions was induced by exposing dark-adapted animals to 600 to 700 lux (230 to 260 microW/cm2) of white fluorescent light for 30 minutes. Damage was quantitated using a computerized multifunctional image analysis of retinal thin sections. Although structural alterations of the ROS were present in both groups, FO-fed rats showed less damage at the base of the ROS. This occurred in spite of higher rhodopsin levels in FO-fed rats. There was no effect of diet on retinal morphology in dark-adapted rats. CONCLUSION: These results indicate that FO does not enhance the susceptibility to acute ROS disk disruptions in the rat retina. Our study further suggests that FO exerts a partial protective effect that may be related to changes in the formation of lipid mediators derived from EPA and AA in retinal phospholipids.

Failure of vitamin E to protect the retina against damage resulting from bright cyclic light exposure.

Cumulative light-mediated damage to the retina over a long time period may be involved in the development of age-related retinopathies. Light is thought to produce retinal damage by initiating autoxidative reactions among the molecular components of the retina. Experiments were therefore conducted (1) to confirm that long-term differences in cyclic light intensity affect the rate of age-related photoreceptor cell loss from the retina; and (2) to determine whether the antioxidant, vitamin E, is an effective inhibitor of damage to the retina by bright cyclic light. Albino rats were fed a basal diet either supplemented with or deficient in vitamin E. Each dietary group was divided into two light-treatment groups which were exposed to 12 hr cyclic light of either 15 lux or 750 lux. After 10 and 17 weeks of treatment, retinal photoreceptor cell densities were determined for animals in each group. Vitamin E deficiency resulted in moderate decreases in photoreceptor cell densities in the dim-light groups after both 10 and 17 weeks. Rats exposed to the bright-light condition suffered a pronounced loss of photoreceptor cells by 10 weeks, and an even greater cell loss by 17 weeks. Vitamin E deficiency did not enhance the effect of bright cyclic light in reducing photoreceptor cell densities. Thus, it appears unlikely that retinal damage by cyclic light occurs via an autoxidative mechanism.

Retinal degeneration in 3-month-old rhesus monkey infants fed a taurine-free human infant formula.

Rhesus monkey infants were raised from birth on a taurine-free soy protein-based human infant formula or on the same formula supplemented with taurine. The monkeys were killed 3 months after birth and the retinas examined by light and electron microscopy. All of the monkeys raised on formula alone showed degenerative ultrastructural changes in photoreceptor outer segments that ranged from swelling and disorientation to fragmentation and disorganization. Cones were more severely affected than rods, and changes were most pronounced in the foveal region. Changes were also noted in the fine structure of the retinal pigment epithelium. These changes were prevented in all but one monkey fed the same formula supplemented with taurine. These results provide further support for the addition of taurine to commercial human infant formulas.