Retinal safety of a new fluoroquinolone, pradofloxacin, in cats: assessment with electroretinography

PURPOSE

To investigate the safety of a new fluoroquinolone, pradofloxacin, on the cat retina using electroretinogram.

METHODS

Ganzfeld ERGs were recorded in 40 cats treated orally for 23 days in 4 groups: CTRL (n = 9): placebo-vehicle; PRADO30 (n = 10): pradofloxacin 30 mg/kg/day; PRADO50 (n = 14): pradofloxacin 50 mg/kg/day; and ENRO30 (n = 7): enrofloxacin at toxic doses of 30 mg/kg/day. ERG was performed before treatment and once weekly during the treatment period. An extended ISCEV protocol with addition of 8 steps of increasing luminance in dark adapted condition was carried out to assess: V (max) (saturated scotopic b-wave amplitude) and k (luminance inducing V (max)/2). OCT and retinal histological changes were also investigated.

RESULTS

Pradofloxacin showed no effects in respect to rod b-wave, V (max), k and maximum scotopic a-wave (P > 0.05). Oscillatory potentials, cone ERG and flicker were also unaltered (P > 0.05). Rod b-wave was undetectable after treatment in ENRO30 group, V (max) was reduced to 10.5% of the baseline (P < 0.05), accompanied by an increase of k by 1 log cd s/m(2) (P < 0.05). Oscillatory potentials, cone b-wave amplitude and 30 Hz flicker amplitude were reduced to 8.3%, 58.9% and 37.4% of the baseline, respectively (P < 0.05). Effects were also seen in OCT and retinal histology starting within one week after the start of treatment and thereafter remaining stable.

CONCLUSION

Pradofloxacin at 6 and 10 times the recommended doses was shown to have no retinal toxic effects in cats, neither on rod or cone function with ERG.

Steroidal and Nonsteroidal Antiinflammatory Medications Can Improve Photoreceptor Survival after Laser Retinal Photocoagulation

OBJECTIVE

To determine whether methylprednisolone or indomethacin can enhance photoreceptor survival after laser retinal injury in an animal model.

DESIGN

Experimental study.

PARTICIPANTS

Twenty rhesus monkeys.

METHODS

Twenty rhesus monkeys (Macaca mulatta) received a grid of argon green (514.5 nm, 10 ms) laser lesions in the macula of the right eye and a grid of neodymium:yttrium-aluminum-garnet (Nd:YAG; 1064 nm, 10 ns) lesions in the macula of the left eye, followed by randomization to 2 weeks of treatment in 1 of 4 treatment groups: high-dose methylprednisolone, moderate-dose methylprednisolone, indomethacin, or control. The lesions were assessed at day 1, day 14, 2 months, and 4 months. The authors were masked to the treatment group. This report discusses the histologic results of ocular tissue harvested at 4 months.

MAIN OUTCOME MEASURE

The number of surviving photoreceptor cell nuclei within each lesion was compared with the number of photoreceptor nuclei in surrounding unaffected retina. The proportion of surviving photoreceptor nuclei was compared between each treatment group.

RESULTS

Argon retinal lesions in the high-dose steroid treatment group and the indomethacin treatment group demonstrated improved photoreceptor survival compared with the control group (P = 0.004). Hemorrhagic Nd:YAG lesions demonstrated improved survivability with indomethacin treatment compared with controls (P = 0.003). In nonhemorrhagic Nd:YAG laser retinal lesions, the lesions treated with moderate-dose steroids demonstrated improved photoreceptor survival compared with the control group (P = 0.004).

CONCLUSIONS

Based on histologic samples of retinal laser lesions 4 months after injury, treatment with indomethacin resulted in improved photoreceptor survival in argon laser lesions and hemorrhagic Nd:YAG laser lesions. Treatment with systemic methylprednisolone demonstrated improved photoreceptor survival in argon retinal lesions and in nonhemorrhagic Nd:YAG lesions.

High-Resolution Manganese-Enhanced MRI of Experimental Retinopathy of Prematurity

PURPOSE

To test the hypothesis that in experimental retinopathy of prematurity (ROP), retinal neovascularization (NV) and vessel tortuosity have distinct spatial and temporal links with receptor and postreceptor ion demand.

METHODS

Newborn rats were raised in either room air (controls) or variable oxygen (50%/10% [50/10]). After 14 days, 50/10 rats were recovered in room air until postnatal day (P) 19 or P22. Peripheral retinal NV severity and incidence and panretinal arteriole and venule tortuosity indexes (TI(a), TI(v)) were measured from ADPase-stained retinal wholemounts. Intraretinal ion demand and retinal thickness were measured from high-resolution manganese-enhanced MRI (MEMRI). In separate experiments, intraretinal manganese uptake was also measured in adult rats pretreated with diltiazem, a Ca(2+) channel antagonist.

RESULTS

In 50/10 rats, peripheral retinal NV severity was significantly greater than in controls at P19 and was decreased by P22. Panretinal TI(a) and TI(v) were increased over control values at P19, but only TI(v) decreased by P22. Unlike control retinas at P19 that had a centroperipheral total retinal thickness gradient, 50/10 retinas had similar central and peripheral total retinal thickness. The 50/10 group also demonstrated a correlation between peripheral retinal NV and TI(a) and TI(v). Peripheral intraretinal uptake of manganese was significantly supernormal at P19 and decreased by P22. Increased peripheral intraretinal retinal manganese uptake was associated with peripheral NV severity and panretinal TI(a). In contrast, ion demand of central postreceptor, but not receptor, retina was significantly associated with peripheral NV severity and panretinal TI(a). Panretinal TI(v) was not correlated with intraretinal ion demand in any case. In adult rats, diltiazem suppressed (P < 0.05) intraretinal manganese uptake.

CONCLUSIONS

The present data raise the possibility that altered retinal layer-specific ion demand causes retinal circulation abnormalities in experimental ROP.

SIRT1 activation confers neuroprotection in experimental optic neuritis

PURPOSE

Axonal damage and loss of neurons correlate with permanent vision loss and neurologic disability in patients with optic neuritis and multiple sclerosis (MS). Current therapies involve immunomodulation, with limited effects on neuronal damage. The authors examined potential neuroprotective effects in optic neuritis by SRT647 and SRT501, two structurally and mechanistically distinct activators of SIRT1, an enzyme involved in cellular stress resistance and survival.

METHODS

Experimental autoimmune encephalomyelitis (EAE), an animal model of MS, was induced by immunization with proteolipid protein peptide in SJL/J mice. Optic neuritis developed in two thirds of eyes with significant retinal ganglion cell (RGC) loss detected 14 days after immunization. RGCs were labeled in a retrograde fashion with fluorogold by injection into superior colliculi. Optic neuritis was detected by inflammatory cell infiltration of the optic nerve.

RESULTS

Intravitreal injection of SIRT1 activators 0, 3, 7, and 11 days after immunization significantly attenuated RGC loss in a dose-dependent manner. This neuroprotective effect was blocked by sirtinol, a SIRT1 inhibitor. Treatment with either SIRT1 activator did not prevent EAE or optic nerve inflammation. A single dose of SRT501 on day 11 was sufficient to limit RGC loss and to preserve axon function.

CONCLUSIONS

SIRT1 activators provide an important potential therapy to prevent the neuronal damage that leads to permanent neurologic disability in optic neuritis and MS patients. Intravitreal administration of SIRT1 activators does not suppress inflammation in this model, suggesting that their neuroprotective effects will be additive or synergistic with current immunomodulatory therapies.

Localization of septin 8 in murine retina, and spatiotemporal expression of septin 8 in a murine model of photoreceptor cell degeneration

The septins, which form a conserved family of cytoskeletal GTP-binding proteins in mammals, comprise stable heteromeric complexes and have diverse roles in protein scaffolding, cytokinesis, vesicle trafficking and plasma membrane integrity following cell division. The goal of this study was to determine the localization of septin 8 in murine adult retina, and analyze the spatiotemporal expression of septin 8 in a murine model of photoreceptor cell degeneration. Expression of septin 8 in the normal retina of mouse and rat was observed by using immunohistochemistry and Western blotting. Furthermore, time course of the expression of septin 8 in mouse photoreceptor cell degeneration were examined by immunohistochemistry combined with hematoxylin and eosin staining, and in situ DNA fragment labeling method. In normal mouse and rat retina, localization of septin 8 is restricted in nuclei of photoreceptor cells. 96 h after intravitreal injection of cobalt chloride most photoreceptor cells lost septin 8 immunostaining at the same time as nuclear DNA fragmentation. The results of this study show that septin 8 protein is present in the specific location within the retina. Furthermore, the disappearance of septin 8 in the nuclei of photoreceptor cells is concomitant with nuclear DNA fragmentation. This suggests that loss of septin 8 could be a useful prognostic indicator for photoreceptor cell degeneration.

Effects of subretinal injection of patent blue and trypan blue in rabbits

PURPOSE

To investigate the histologic and clinical effects of subretinal injection of patent blue (PB) and trypan blue (TB) in rabbits.

METHODS

Dutch-belted rabbits (n=8) were vitrectomized followed by subretinal injection of 2.4 mg/ml PB (285 mOsm) and 1.5 mg/ml TB (312 mOsm); balanced salt solution (BSS) (300 mOsm) served as the control. Animals were examined 6, 12, and 24 hr and 14 days after the procedure by fluorescein angiography (FA) and indirect ophthalmoscopy; for retinal toxicity, histologic evaluation studies were performed by light and transmission electron microscopy.

RESULTS

FA examination demonstrated window defects suggestive of retinal pigment epithelium (RPE) atrophy in positions of subretinal TB injection, but this was not observed after subretinal injection of PB or BSS. Histologic evaluation disclosed only minimal abnormalities on the photoreceptor outer segment (POS) after subretinal injection of BSS during all follow-up. Subretinal injection of PB caused POS and photoreceptor inner segment (PIS) abnormalities 12 and 24 hr after surgery as well as outer nuclear layer (ONL) damage 14 days after surgery. Subretinal TB injection resulted in POS and PIS damage at 12 hr follow-up. The ONL damage was observed 24 hr after surgery; additionally, POS, PIS, ONL, and RPE abnormalities were observed 14 days after surgery after TB injection.

CONCLUSIONS

Subretinal injection of TB induced more significant clinical and histologic damage of neurosensory retina/RPE than did PB or BSS. Future human studies are necessary to access the clinical relevance of these in vivo experiments.

Multiple functions of cation-chloride cotransporters in the fish retina

A GABA- or glycine-induced increase in Cl(-) permeability can produce either a depolarization or hyperpolarization, depending on the Cl(-) equilibrium potential. It has been shown that retinal neurons express the chloride cotransporters, Na-K-2Cl (NKCC) and K-Cl (KCC), the primary molecular mechanisms that control the intracellular Cl(-) concentration. We thus studied (1) the localization of these cotransporters in the fish retina, and (2) how suppression of cotransporter activity in the fish retina affects function. Specific antibodies against NKCC and KCC2 revealed that both cotransporters were expressed in the outer and inner plexiform layers, and colocalized in many putative amacrine cells and in cells of the ganglion cell layer. However, the somata of putative horizontal cells displayed only NKCC immunoreactivity and many bipolar cells were only immunopositive for KCC2. In the outer retina, application of bumetanide, a specific inhibitor of NKCC activity, (1) increased the steady-state extracellular concentration of K+ ([K+](o)) and enhanced the light-induced decrease in the [K+](o), (2) increased the sPIII photoreceptor-dependent component of the ERG, and (3) reduced the extracellular space volume. In contrast, in the outer retina, application of furosemide, a specific inhibitor of KCC activity, decreased sPIII and the light-induced reduction in [K+](o), but had little effect on steady-state [K+](o). In the inner retina, bumetanide increased the sustained component of the light-induced increase in [K+](o). These findings thus indicate that NKCC and KCC2 control the [K+](o) and extracellular space volume in the retina in addition to regulating GABA- and glycine-mediated synaptic transmission. In addition, the anatomical and electrophysiological results together suggest that all of the major neuronal types in the fish retina are influenced by chloride cotransporter activity.

The Effect of intravitreal N-methyl-DL-aspartic acid on the electroretinogram in Royal College of surgeons rats

PURPOSE

To investigate how the third-order neuronal response contributes to shaping the electroretinogram (ERG) in the Royal College of Surgeons (RCS) rat.

METHODS

Full-field ERGs were recorded from dystrophic RCS rats (n = 30) at 4, 6, 8, 10, 12, or 14 weeks of age in response to different stimulus intensities (maximum intensity, 0.84 log cd-s/m(2)). N-methyl-DL: -aspartic acid (NMDA, 5 mM) was injected into the vitreous cavity of the right eyes to eliminate the third-order neuronal response. The left eyes received the vehicle and served as controls. The third-order neuronal response was isolated by digitally subtracting waveforms of the NMDA-injected eyes from those of the control eyes.

RESULTS

The ERG a- and b-waves deteriorated with the age of the rat. The third-order neuronal response was preserved to a greater degree than the b-wave despite progression of photoreceptor degeneration. Intravitreal injection of NMDA attenuated the a-wave and enhanced the b-wave across the stimulus range from low to middle intensities. This tendency became more pronounced with advancing rat age. In aged dystrophic RCS rats this phenomenon was seen even at maximum intensity. The difference between NMDA-injected and vehicle-injected eyes was larger for the threshold than for the maximum amplitude at each examined time point (P < 0.001). Intravitreal injection of NMDA decreased implicit times of the a- and b-waves after the rats reached 8 weeks of age (P < 0.005 for the a-wave).

CONCLUSION

With advancing photoreceptor degeneration, the third-order neuronal response made a greater contribution to shaping the a- and b-waves in dystrophic RCS rats.

Ultrastructural findings in the primate eye after intravitreal injection of bevacizumab

PURPOSE

To examine the ultrastructural effect of intravitreal bevacizumab on primate eyes with particular focus set on the choriocapillaris and to examine the influence of vascular endothelial growth factor (VEGF) inhibition on endothelial cell fenestration.

DESIGN

Animal study.

METHODS

Four Cynomolgus monkeys received an intravitreal injection of 1.25 mg bevacizumab. The eyes were enucleated and prepared for light and electron microscopy on days one, four, seven, and 14. Control eyes remained untreated. Choriocapillaris endothelial cell fenestrations were quantified.

RESULTS

Choriocapillaris endothelial cell fenestrations were significantly reduced after intravitreal injection of bevacizumab. Fenestration was lowest on day four (15.9 +/- 6.7 per 25 microm) and increased again from days seven to 14, but was still significantly lower than in the control (66.2 +/- 9.5 per 25 microm). Densely packed thrombocytes and leukocytes regionally occluded the choriocapillaris lumen of treated eyes. On day one an increased number of leukocytes filled in the choriocapillaris lumen. Photoreceptors were damaged in two of 40 light microscopic sections. On days one to seven, choroidal melanocytes contained giant melanosomes. None of these described features was found in controls.

CONCLUSIONS

Intravitreal bevacizumab causes ultrastructural changes in the choriocapillaris of primate eyes. A significant reduction of choriocapillaris endothelial cell fenestrations is seen as early as 24 hours after injection and their number increases again after two weeks. These findings may play a role in the early clinical effect of intravitreal bevacizumab for macular edema. Because an increased risk of circulation disturbances in the choriocapillaris cannot be excluded, patients should be carefully monitored.

Subretinal transplantation of bone marrow mesenchymal stem cells delays retinal degeneration in the RCS rat model of retinal degeneration

Because there is no effective treatment for this retinal degeneration, potential application of cell-based therapy has attracted considerable attention. Several investigations support that bone marrow mesenchymal stem cells (MSCs) can be used for a broad spectrum of indications. Bone marrow MSCs exert their therapeutic effect in part by secreting trophic factors to promote cell survival. The current study investigates whether bone marrow MSCs secrete factor(s) to promote photoreceptor cell survival and whether subretinal transplantation of bone marrow MSCs promotes photoreceptor survival in a retinal degeneration model using Royal College of Surgeons (RCS) rats. In vitro, using mouse retinal cell culture, it was demonstrated that the conditioned medium of the MSCs delays photoreceptor cell apoptosis, suggesting that the secreted factor(s) from the MSCs promote photoreceptor cell survival. In vivo, the MSCs were injected into the subretinal space of the RCS rats and histological analysis, real-time RT-PCR and electrophysiological analysis demonstrated that the subretinal transplantation of MSCs delays retinal degeneration and preserves retinal function in the RCS rats. These results suggest that MSC is a useful cell source for cell-replacement therapy for some forms of retinal degeneration.

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.

Apoptosis and autophagy in photoreceptors exposed to oxidative stress

Studies on human and animal models of retinal dystrophy have suggested that apoptosis may be the common pathway of photoreceptor cell death. Autophagy, the major cellular degradation process in animal cells, is important in normal development and tissue remodeling, as well as under pathological conditions. Previously we provided evidence that genes, whose products are involved in apoptosis and autophagy, may be coexpressed in photoreceptors undergoing degeneration. Here, we investigated autophagy in oxidative stress-mediated cell death in photoreceptors, analyzing the light-damage mouse model and 661W photoreceptor cells challenged with H(2)O(2). In the in vivo model, we demonstrated a time-dependent increase in the number of TUNEL-positive cells, concomitant with the formation of autophagosomes. In vitro, oxidative stress increased mRNA levels of apoptotic and autophagic marker genes. H(2)O(2) treatment resulted in the accumulation of TUNEL-positive cells, the majority of which contain autophagosomes. To determine whether autophagy and apoptosis might precede each other or co-occur, we performed inhibitor studies. The autophagy inhibitor 3-methyladenine (3-MA), silencing RNA (siRNA) against two genes whose products are required for autophagy (autophagy-related (ATG) gene 5 and beclin 1), as well as the pan-caspase-3 inhibitor, Zvad-fmk, were both found to partially block cell death. Blocking autophagy also significantly decreased caspase-3 activity, whereas blocking apoptosis increased the formation of autophagosomes. The survival effects of 3?MA and zVAD-fmk were not additive; rather treatment with both inhibitors lead to increased cell death by necrosis. In summary, the study first suggests that autophagy participates in photoreceptor cell death possibly by initiating apoptosis. Second, it confirms that cells that normally die by apoptosis will execute cell death by necrosis if the normal pathway is blocked. And third, these results argue that the up-stream regulators of autophagy need to be identified as potential therapeutic targets in photoreceptor degeneration.

Programmed cell death in retinal degeneration: targeting apoptosis in photoreceptors as potential therapy for retinal degeneration

Retinal degenerations are the major cause of incurable blindness characterized by loss of retinal photoreceptor cells. Several genes causing these genetic diseases have been identified, however the molecular characterization of a high percentage of patients affected by retinitis pigmentosa (RP), a common form of retinal degeneration, is still unknown. The high genetic heterogeneity of these diseases hampers the comprehension of the pathogenetic mechanism causing photoreceptor cell death. Therapies are not available yet and for this reason there is a lot of interest in understanding the etiology and the pathogenesis of these disorders at a cellular and molecular level. Some common features have been identified in different forms of RP. Apoptosis was reported to be the final outcome in all RP animal models and patients analyzed so far. We recently identified two apoptotic pathways coactivated in photoreceptors undergoing cell death in the retinal degeneration (rd1) mouse model of autosomal recessive RP. Our studies opened new perspectives together with many questions that require deeper analyses in order to take advantage of this knowledge and develop new therapeutic approaches. We believe that minimizing cell demise may represent a promising curing strategy that needs to be exploited for retinal degeneration.

Human and macaque pupil responses driven by melanopsin-containing retinal ganglion cells

Melanopsin, a novel photopigment, has recently been localized to a population of retinal ganglion cells that display inherent photosensitivity. During continuous light and following light offset, primates are known to exhibit sustained pupilloconstriction responses that resemble closely the photoresponses of intrinsically-photoreceptive ganglion cells. We report that, in the behaving macaque, following pharmacological blockade of conventional photoreceptor signals, significant pupillary responses persist during continuous light and following light offset. These pupil responses display the unique spectral tuning, slow kinetics, and irradiance coding of the sustained, melanopsin-derived ganglion cell photoresponses. We extended our observations to humans by using the sustained pupil response following light offset to document the contribution of these novel ganglion cells to human pupillary responses. Our results indicate that the intrinsic photoresponses of intrinsically-photoreceptive retinal ganglion cells play an important role in the pupillary light reflex and are primarily responsible for the sustained pupilloconstriction that occurs following light offset.

Minocycline protects photoreceptors from light and oxidative stress in primary bovine retinal cell culture

PURPOSE

To determine whether minocycline, a compound known to protect the retina against light-induced damage in rodent models, and its structurally related analogues would protect photoreceptor cells in primary bovine retinal cell culture against light and oxidative stress.

METHODS

Minocycline and its analogues were tested in primary retinal cell culture to see whether they would inhibit light or oxidative stress-induced cell death. Primary cell cultures composed of photoreceptors, bipolar cells, and glial cells were prepared from bovine retinas. The extent of cell death induced by light or oxidative stress was assessed by using Sytox Green (Invitrogen-Molecular Probes, Eugene, OR) a nucleic acid dye uptake assay. Differential protection of photoreceptor cells from stress were examined using immunocytochemistry.

RESULTS

Minocycline and methacycline were cytoprotective against light- or oxidative stress-induced damage of bovine primary photoreceptors in culture with an EC(50) < 10 microM. In contrast, structurally related analogues such as demeclocycline, meclocycline, and doxycycline were phototoxic at >3 to >10 microM. Though demeclocycline was found to be phototoxic, it was cytoprotective (EC(50) = 5 microM) against oxidative stress in the absence of exposure to light.

CONCLUSIONS

The protective action of minocycline against light-induced damage in the cell-based assays agrees with earlier reports in animal models and suggests that the in vitro assay using bovine primary retinal cell culture is a suitable model for evaluating compounds for retinal protection. Cellular protection or toxicity produced by structurally related compounds show that minor structural modifications can alter the function of minocycline and lead to potent retinal protective compounds.

Neurotrophic Factors Minimize the Retinal Toxicity of Verteporfin Photodynamic Therapy

PURPOSE

A prior study showed that brain-derived neurotrophic factor (BDNF) rescues photoreceptors from collateral retinal damage caused by photodynamic therapy (PDT). This study was conducted to determine whether ciliary neurotrophic factor (CNTF), a combination of BDNF and CNTF, or pigment epithelial cell-derived growth factor (PEDF) might protect photoreceptors and retinal function more effectively than BDNF. Also investigated was whether protection would be observed after a second round of PDT with adjunctive BDNF treatment.

METHODS

Normal rats received intravitreal injections of BDNF, CNTF, a combination of BDNF and CNTF, or PEDF in one eye and PBS in the other 2 days before PDT. Retinal function and photoreceptor survival were assessed with multifocal ERG (mfERG) and histology 1 week after PDT. Another group of rats received two courses of PDT 3 months apart, with injection of BDNF 2 days before each treatment.

RESULTS

All factors significantly increased photoreceptor survival. The combination of BDNF and CNTF rescued more photoreceptors than either factor alone. Only BDNF improved retinal function 1 week after PDT, with CNTF and the combination of BDNF and CNTF reducing mfERG responses. BDNF injection before a second round of PDT improved mfERG responses and retinal structure.

CONCLUSIONS

BDNF is the most effective single factor among those tested for neuroprotection and improvement of retinal function after PDT, although a combination of BDNF and CNTF rescues more photoreceptors. Adjunctive treatment with BDNF also protects retinal structure and function through two rounds of PDT, suggesting its potential value for patients who require multiple treatments.

Poly (ADP-ribose) polymerase inhibitor 3-aminobenzamide rescues N-methyl-N-nitrosourea-induced photoreceptor cell apoptosis in Sprague-Dawley rats through preservation of nuclear factor-kappaB activity

The activation of poly (ADP-ribose) polymerase (PARP) plays a pivotal role in mediating N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis. We examined the retinoprotective effects of the PARP inhibitor 3-aminobenzamide (3-AB) against MNU-induced retinal damage in relation to dose and timing of prescription, and the involvement of the transcription factor nuclear factor (NF)-kappaB. Female Sprague-Dawley rats were intraperitoneally injected with 60 mg/kg MNU at 50 days of age, and were then immediately given a subcutaneous injection of 0, 1, 5, 10, 30 or 50 mg/kg of 3-AB, or were injected with 50 mg/kg 3-AB 12h before, concurrently, or 4, 6 or 12h after MNU. Rats were killed 3 and 7 days after MNU, and MNU-treated and 3-AB-injected retinas were compared with MNU-untreated control retinas or MNU-treated/3-AB-uninjected retinas. Apoptosis in photoreceptor cells was detected by performing formamide-induced DNA denaturation and staining with anti-single-stranded DNA antibody. Retinal morphologies were compared and evaluated morphometrically using the photoreceptor cell ratio and retinal damage ratio as indices to evaluate the efficacy of 3-AB. We examined expression of the phosphorylated form of NF-kappaB and IkappaBalpha (p-NF-kappaB and p-IkappaBalpha, respectively) in retinas of MNU-treated rats concurrently treated with or without 50mg/kg 3-AB, compared with MNU-untreated control retinas. 3-AB dose-dependently suppressed photoreceptor cell apoptosis: 50mg/kg 3-AB injected concurrently with MNU completely rescued photoreceptor cell damage; 30 mg/kg 3-AB significantly reduced photoreceptor cell damage; 10 mg/kg 3-AB tended to suppress photoreceptor cell damage; <or=5mg/kg 3-AB was ineffective. When 50mg/kg 3-AB was injected 12h before or >or=4h after MNU, it did not exert a retinoprotective effect. p-NF-kappaB levels of MNU-treated rat retinas were significantly lower than those of MNU-untreated control retinas, while 50 mg/kg 3-AB injected concurrently with MNU preserved the p-NF-kappaB levels; p-IkappaBalpha levels tended to decrease after MNU injection, compared with untreated control retinas, but the difference was not significant. Thus, 3-AB dose-dependently suppressed MNU-induced retinal damage, and 50mg/kg 3-AB injected concurrently with MNU completely rescued photoreceptor cell apoptosis via preservation of NF-kappaB activity.

Contribution of calpains to photoreceptor cell death in N-methyl-N-nitrosourea-treated rats

The purpose of the present study was to determine if proteolysis by the calcium-dependent enzyme calpains (EC 3.4.22.17) contributed to retinal cell death in a rat model of photoreceptor degeneration induced by intraperitoneal injection of N-methyl-N-nitrosourea (MNU). Retinal degeneration was evaluated by H&E staining, and cell death was determined by TUNEL assay. Total calcium in retina was measured by atomic absorption spectrophotometry. Activation of calpains was determined by casein zymography and immunoblotting. Proteolysis of alpha-spectrin and p35 (regulator of Cdk5) were evaluated by immunoblotting. Calpain inhibitor SNJ-1945 was orally administrated to MNU-treated rats to test drug efficacy. MNU decreased the thickness of photoreceptor cell layer, composed of the outer nuclear layer (ONL) and outer segment (OS). Numerous cells in the ONL showed positive TUNEL staining. Total calcium was increased in retina after MNU. Activation of calpains and calpain-specific proteolysis of alpha-spectrin were observed after MNU injection. Oral administration of SNJ-1945 to MNU-treated rats showed a significant protective effect against photoreceptor cell loss, confirming involvement of calpains in photoreceptor degeneration. Conversion of p35 to p25 was well correlated with calpain activation, suggesting prolonged activation of Cdk5/p25 as a possible downstream mechanism for MNU-induced photoreceptor cell death. SNJ-1945 reduced photoreceptor cells death, even though MNU is one of the most severe models of photoreceptor cell degeneration. Oral calpain inhibitor SNJ-1945 may be a candidate for testing as a medication against retinal degeneration in retinitis pigmentosa.

Effects of ethanol on photoreceptors and visual function in developing zebrafish

PURPOSE

Children born to mothers who have consumed alcohol during pregnancy have an array of retinal abnormalities and visual dysfunctions. In the past, rodent systems have been used to study the teratogenic effects of ethanol on vertebrate embryonic development. The exact developmental windows in which ethanol causes specific developmental defects have been difficult to determine because rodents and other mammals develop in utero. In this study, we characterized how ethanol affects the function and development of the visual system in an ex utero embryonic system, the zebrafish.

METHODS

Zebrafish embryos were raised in fish water containing various concentrations of ethanol from 2 to 5 days after fertilization. The effects of ethanol on retinal morphology were assessed by histologic and immunohistochemical analyses and those on retinal function were analyzed by optokinetic response (OKR) and electroretinography (ERG).

RESULTS

Zebrafish embryos exposed to moderate and high levels of ethanol during early embryonic development had morphological abnormalities of the eye characterized by hypoplasia of the optic nerve and inhibition of photoreceptor outer segment growth. Ethanol treatment also caused an increased visual threshold as measured by the OKR. Analysis with the ERG indicated that there was a severe reduction of both the a- and b-waves, suggesting that ethanol affects the function of the photoreceptors. Indeed, low levels of ethanol that did not cause obvious morphologic changes in either the body or retina did affect both the OKR visual threshold and the a- and b-wave amplitudes.

CONCLUSIONS

Ethanol affects photoreceptor function at low concentrations that do not disturb retinal morphology. Higher levels of ethanol inhibit photoreceptor development and cause hypoplasia of the optic nerve.

Visual cycle and its metabolic support in gecko photoreceptors

Photoreceptors of nocturnal geckos are transmuted cones that acquired rod morphological and physiological properties but retained cone-type phototransduction proteins. We have used microspectrophotometry and microfluorometry of solitary isolated green-sensitive photoreceptors of Tokay gecko to study the initial stages of the visual cycle within these cells. These stages are the photolysis of the visual pigment, the reduction of all-trans retinal to all-trans retinol, and the clearance of all-trans retinol from the outer segment (OS) into the interphotoreceptor space. We show that the rates of decay of metaproducts (all-trans retinal release) and retinal-to-retinol reduction are intermediate between those of typical rods and cones. Clearance of retinol from the OS proceeds at a rate that is typical of rods and is greatly accelerated by exposure to interphotoreceptor retinoid-binding protein, IRBP. The rate of retinal release from metaproducts is independent of the position within the OS, while its conversion to retinol is strongly spatially non-uniform, being the fastest at the OS base and slowest at the tip. This spatial gradient of retinol production is abolished by dialysis of saponin-permeabilized OSs with exogenous NADPH or substrates for its production by the hexose monophosphate pathway (NADP+glucose-6-phosphate or 6-phosphogluconate, glucose-6-phosphate alone). Following dialysis by these agents, retinol production is accelerated by several-fold compared to the fastest rates observed in intact cells in standard Ringer solution. We propose that the speed of retinol production is set by the availability of NADPH which in turn depends on ATP supply within the outer segment. We also suggest that principal source of this ATP is from mitochondria located within the ellipsoid region of the inner segment.

Effect of gravity in long-term vitreous tamponade: in vivo investigation using perfluorocarbon liquids and semi-fluorinated alkanes

PURPOSE

In order to investigate whether gravity is the reason for retinal degeneration in long-term vitreous tamponade, perfluorohexyloctane (F6H8), perfluorodecalin (PFD), and a mixture of F6H8/PFD were compared.

MATERIALS AND METHODS

Each group of 5 rabbits received a 3-month tamponade with either PFD (pure) (1.93 g/cm(3)), F6H8 (pure) (1.33 g/cm(3)), or a 1:1 mixture of F6H8/PFD (1.62 g/cm(3)). Electroretinograms (ERG) were performed pre- and postoperatively. Lower and upper retinal areas were compared using immunohistochemical methods. Transmission electron microscopy was performed to investigate alterations in the photoreceptors.

RESULTS

All three substances were tolerated well in rabbit eyes for up to 3 months. Dispersion was seen earliest with PFD and latest with pure F6H8. None of the substances demonstrated inflammatory reactions or vascular alterations. ERGs were not considerably altered with any of the substances. Histology of the retina showed alterations in the cell counts within the inner and outer nuclear layer that were not attributable to the gravity of the tamponading agent.

CONCLUSION

In contrast to previously published work, this study did not detect any tamponade-related structural damage of the retina after a 3-months tamponade in the rabbit model. Based upon this study, we conclude that gravity might not be causally linked to retinal damage.

Visual cycle: Dependence of retinol production and removal on photoproduct decay and cell morphology

The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exposure to light. Initial steps, the liberation of all-trans retinal and its reduction to all-trans retinol by retinol dehydrogenase (RDH), take place in photoreceptors. We performed comparative microspectrophotometric and microfluorometric measurements on a variety of rod and cone photoreceptors isolated from salamander retinae to correlate the rates of photoproduct decay and retinol production. Metapigment decay rate was spatially uniform within outer segments and 50-70 times faster in the cells that contained cone-type pigment (SWS2 and M/LWS) compared to cells with rod-type pigment (RH1). Retinol production rate was strongly position dependent, fastest at the base of outer segments. Retinol production rate was 10-40 times faster in cones with cone pigments (SWS2 and M/LWS) than in the basal OS of rods containing rod pigment (RH1). Production rate was approximately five times faster in rods containing cone pigment (SWS2) than the rate in basal OS of rods containing the rod pigment (RH1). We show that retinol production is defined either by metapigment decay rate or RDH reaction rate, depending on cell type or outer segment region, whereas retinol removal is defined by the surface-to-volume ratio of the outer segment and the availability of retinoid binding protein (IRBP). The more rapid rates of retinol production in cones compared to rods are consistent with the more rapid operation of the visual cycle in these cells.

The β-Adrenergic Receptor Antagonist Metipranolol Blunts Zinc-Induced Photoreceptor and RPE Apoptosis

PURPOSE

To determine the effect of zinc on retinal cells at concentrations at which it is known to cause oxidative stress. Furthermore, the effects of metipranolol, known to prevent retinal damage, and of other antiglaucoma drugs were determined on zinc-injured retinal cells.

METHODS

Lipid peroxidation assays were conducted on rat brain and bovine retina-retinal pigment epithelial (RPE) membrane preparations. Immunohistochemistry, immunoblot analysis and the terminal-deoxynucleotidyl transferase dUTP-linked nick-end labeling (TUNEL) procedure determined the effects of zinc with or without trolox or metipranolol on photoreceptor death in situ. The effect of treatments on cultured RPE cells was analyzed using cell viability assays, immunoblot analysis, and the TUNEL procedure.

RESULTS

Zinc-induced lipid peroxidation of rat brain and bovine retina-RPE membranes, although the effect of the latter was of a (twofold) greater magnitude. Both effects, however, were similarly attenuated by metipranolol, desacetylmetipranolol, and trolox. Antiglaucoma drugs other than metipranolol had no effect. Intraocular injection of 150 microM zinc and treatment of cultured RPE cells with zinc led to mainly photoreceptor apoptosis and apoptotic death of RPE cells (50% death at 18 microM rising to 10% at 50 microM), respectively. Zinc-induced apoptosis of cultured RPE cells and photoreceptors were attenuated only by metipranolol and trolox.

CONCLUSIONS

The combined data suggest that oxidative injury to RPE cells and photoreceptors may be caused by elevated levels of zinc in diseases such as age-related macular degeneration (AMD) and that metipranolol may act as an efficacious antioxidant to blunt this process.

Protective Effect of Crocin against Blue Light– and White Light–Mediated Photoreceptor Cell Death in Bovine and Primate Retinal Primary Cell Culture

PURPOSE

The present study was performed to investigate the effect of crocin on blue light- and white light-induced rod and cone death in primary retinal cell cultures.

METHODS

Primary retinal cell cultures were prepared from primate and bovine retinas. Fifteen-day-old cultures were exposed to blue actinic light or to white fluorescent light for 24 hours. Cultures were treated by the addition of different concentrations of crocin for 24 hours before light exposure or for 8 hours after light exposure. Cultures kept in the dark were used as controls. Green nucleic acid stain assay was used to evaluate cell death. Rods and cones were immunolabeled with specific antibodies and counted. TUNEL labeling was used to detect fragmented DNA in fixed cells after light exposure.

RESULTS

Primary retinal cell cultures contained a mixture of retinal cells enriched in photoreceptors, bipolar cells, and Müller cells. Twenty-four-hour exposure to blue and white light induced death in 70% to 80% of the photoreceptors in bovine and primate retinal cell cultures. Crocin protected the photoreceptors against blue light- or white light-mediated damage in a concentration-dependent manner with an EC50 of approximately 30 microM. TUNEL assays confirmed that crocin protected photoreceptors from light damage.

CONCLUSIONS

These results show that blue and white light selectively induce rod and cone cell death in an in vitro model. Crocin protects retinal photoreceptors against light-induced cell death.

Effect of short-term, high-dose retinol on dark adaptation in aging and early age-related maculopathy

PURPOSE

To examine the effect of a short course of high-dose retinol (preformed vitamin A) on dark adaptation in older adults with normal retinal health or early age-related maculopathy (ARM).

METHODS

The study design was a randomized, double-masked, placebo-controlled experiment. Adults > or = 50 years of age whose fundus photographs for the eye to be tested psychophysically fell within steps 1 to 9 of the Age-Related Eye Disease Study (AREDS) Grading System were randomly assigned to a 30-day course of 50,000 IU oral retinol or a placebo. At baseline and 30-day follow-up, dark adaptation was tested and the Low Luminance Questionnaire (LLQ), an instrument for assessing difficulty with vision in reduced lighting, was administered. Primary outcomes of interest were rod- and cone-mediated parameters of dark adaptation, with scores on the LLQ's six subscales as secondary outcomes.

RESULTS

The sample consisted of 104 participants with 52 each in the intervention and placebo groups. There were no group differences in baseline variables. At 30-days, the dark-adaptation parameters of cone time-constant, cone threshold, rod-cone break, and rod threshold did not differ. The retinol intervention group had significantly larger (i.e., steeper) rod slopes, indicating faster sensitivity recovery, than did the placebo group (P = 0.0419). There were no group differences in scores on the LLQ subscales driving, extreme lighting, emotional distress, general lighting, or peripheral vision. The retinol group had a higher score by five points on the mobility subscale compared with the placebo group (P = 0.0141). Those who had the most self-reported change on the mobility subscale at day 30 were more likely to have greater change in the speed of dark adaptation, as indicated by the rod slope parameter (r = 0.24, P = 0.0141).

CONCLUSIONS

A short-term, high-dose course of retinol increased the rate of rod-mediated dark adaptation in older adults who were in the early phases of ARM or were exhibiting normal retinal aging. These results are consistent with the hypothesis that depositions and other structural changes in the retinal pigment epithelium and Bruch's membrane in aging and early ARM cause a localized retinoid deficiency.