N-acetylcysteine amide and di- N-acetylcysteine amide protect retinal cells in culture via an antioxidant action.

Reactive oxygen species (ROS) play a significant role in toxicity to the retina in a variety of diseases. N-acetylcysteine (NAC), N-acetylcysteine amide (NACA) and the dimeric di-N-acetylcysteine amide (diNACA) were evaluated in terms of protecting retinal cells, in vitro, in a variety of stress models. Three types of rat retinal cell cultures were utilized in the study: macroglial-only cell cultures, neuron-only retinal ganglion cell (RGC) cultures, and mixed cultures containing retinal glia and neurons. Ability of test agents to attenuate oxidative stress in all cultures was ascertained. In addition, capability of agents to protect against a variety of alternate clinically-relevant stressors, including excitotoxins and mitochondrial electron transport chain inhibitors, was also evaluated. Capacity of test agents to elevate cellular levels of reduced glutathione under normal and compromised conditions was also determined. NAC, NACA and diNACA demonstrated concentration-dependent cytoprotection against oxidative stress in all cultures. These three compounds, however, had differing effects against a variety of alternate insults to retinal cells. The most protective agent was NACA, which was most potent against the most stressors (including oxidative stress, mitochondrial impairment by antimycin A and azide, and glutamate-induced excitotoxicity). Similar to NAC, NACA increased glutathione levels in non-injured cells, although diNACA did not, suggesting a different, unknown mechanism of antioxidant activity for the latter. In support of this, diNACA was the only agent to attenuate rotenone-induced toxicity in mitochondria. NAC, NACA and diNACA exhibited varying degrees of antioxidant activity, i.e., protected cultured rat retinal cells from a variety of stressors which were designed to mimic aspects of the pathology of different retinal diseases. A general rank order of activity was observed: NACA ≥ diNACA > NAC. These results warrant further exploration of NACA and diNACA as antioxidant therapeutics for the treatment of retinal diseases, particularly those involving oxidative stress. Furthermore, we have defined the battery of tests carried out as the "Wood, Chidlow, Wall and Casson (WCWC) Retinal Antioxidant Indices"; we believe that these are of great value for screening molecules for potential to reduce retinal oxidative stress in a range of retinal diseases.

Effects of slit lamp-delivered retinal laser photobiomodulation in a rat model of choroidal neovascularization.

Neovascular age-related macular degeneration, also known as exudative or wet age-related macular degeneration, is the leading cause of blindness in the developed world. Photobiomodulation has the potential to target the up-stream hypoxic and pro-inflammatory drivers of choroidal neovascularization. This study investigated whether photobiomodulation attenuates characteristic pathological features of choroidal neovascularization in a rodent model. Experimental choroidal neovascularization was induced in Brown Norway rats with laser photocoagulation. A custom-designed, slit-lamp-mounted, 670 nm laser was used to administer retinal photobiomodulation every 3 days, beginning 6 days prior to choroidal neovascularization induction and continuing until the animals were killed 14 days later. The effect of photobiomodulation on the size of choroidal neovascular membranes was determined using isolectin-B4 immunohistochemistry and spectral domain-optical coherence tomography. Vascular leakage was determined with fluorescein angiography. The effect of treatment on levels of vascular endothelial growth factor expression was quantified with enzyme-linked immunosorbent assay. Treatment with photobiomodulation was associated with choroidal neovascular membranes that were smaller, had less fluorescein leakage, and a diminished presence of inflammatory cells as compared to sham eyes. These effects were not associated with a statistically significant difference in the level of vascular endothelial growth factor when compared to sham eyes. The data shown herein indicate that photobiomodulation attenuates pathological features of choroidal neovascularization in a rodent model by mechanisms that may be independent of vascular endothelial growth factor.

Repetitive, non-invasive imaging of neurodegeneration, and prevention of it with gene replacement, in mice with Sanfilippo syndrome.

Hampering assessment of treatment outcomes in gene therapy and other clinical trials in patients with childhood dementia is the lack of an objective, non-invasive measure of neurodegeneration. Optical coherence tomography (OCT) is a widely available, rapid, non-invasive, and quantitative method for examining the integrity of the neuroretina. Profound brain and retinal dysfunction occur in patients and animal models of childhood dementia, including Sanfilippo syndrome and we recently revealed a correlation between the age of onset and rate of progression of retinal and brain degeneration in sulfamidase-deficient Sanfilippo mice. The aim of the current study was to use OCT to visualise the discrete changes in retinal structure that occur during disease progression. A progressive decline in retinal thickness was readily observable in Sanfilippo mice using OCT, with differences seen in affected animals from 10-weeks of age. OCT applied to i.v. AAV9-sulfamidase-treated Sanfilippo mice enabled visualisation of improved retinal anatomy in living animals, an outcome confirmed via histology. Importantly, brain disease lesions were also ameliorated in treated Sanfilippo mice. The findings highlight the sensitivity, ease of repetitive use and quantitative capacity of OCT for detection of discrete changes in retinal structure and their prevention with a therapeutic. Combined with the knowledge that retinal and brain degeneration are correlated in Sanfilippo syndrome, OCT provides a window to the brain in this and potentially other childhood dementias.

Establishing human lacrimal gland cultures from biopsy-sized tissue specimens.

OBJECTIVES: To establish cultures of human lacrimal gland from patient-derived, biopsy-sized, tissue specimens. METHODS: Tissue was obtained after surgical removal from patients without dry eye disease undergoing routine procedures. Samples were subjected to mechanical and enzymatic digestion and resulting cell suspensions were plated onto collagen-coated glass coverslips and grown for up to 21 days. Cultures were analysed by immunocytochemistry and light microscopy, and resultant cellular distributions were compared to those in sections of fixed human lacrimal gland tissue. RESULTS: Dissociation of biopsy-sized pieces of human lacrimal gland and seeding onto coated surfaces allowed development of a mixed population of cells in vitro. Within 7-14 days, cellular aggregation was observed and by 21 days many cells had organised themselves into distinct three-dimensional complexes. Immunohistochemistry revealed a heterogeneous population of cells, including epithelial, myoepithelial, mesenchymal and progenitor cells. Some of the epithelia labelled positively for lysozyme and lactoferrin. CONCLUSIONS: Collection and dissociation of biopsy-sized pieces of human lacrimal gland leads to a cellular preparation that can proliferate in vitro and organise into three-dimensional structures. This is the first report detailing that biopsy-collected specimens of human lacrimal gland can be used to establish cell cultures.

Investigations into photoreceptor energy metabolism during experimental retinal detachment.

Retinal detachment is a sight-threatening disorder, which occurs when the photoreceptors are separated from their vascular supply. The aim of the present study was to shed light on photoreceptor energy metabolism during experimental detachment in rats. Retinal detachment was induced in the eyes of rats via subretinal injection of sodium hyaluronate. Initially, we investigated whether detachment caused hypoxia within photoreceptors, as evaluated by the exogenous and endogenous biomarkers pimonidazole and HIF-1α, as well as by qPCR analysis of HIF target genes. The results showed no unequivocal staining for pimonidazole or HIF-1α within any detached retina, nor upregulation of HIF target genes, suggesting that any reduction in pO2 is of insufficient magnitude to produce hypoxia-induced covalent protein adducts or HIF-1α stabilisation. Subsequently, we analysed expression of cellular bioenergetic enzymes in photoreceptors during detachment. We documented loss of mitochondrial, and downregulation of glycolytic enzymes during detachment, indicating that photoreceptors have reduced energetic requirements and/or capacity. Given that detachment did not cause widespread hypoxia, but did result in downregulated expression of bioenergetic enzymes, we hypothesised that substrate insufficiency may be critical in terms of pathogenesis, and that boosting metabolic inputs may preserve photoreceptor bioenergetic production and, protect against their degeneration. Thus, we tested whether supplementation with the bioavailable energy substrate pyruvate mitigated rod and cone injury and degeneration. Despite protecting photoreceptors in culture from nutrient deprivation, pyruvate failed to protect against apoptotic death of rods, loss of cone opsins, and loss of inner segment mitochondria, in situ, when evaluated at 3 days after detachment. The regimen was also ineffective against cumulative photoreceptor deconstruction and degeneration when evaluated after 4 weeks. Retinal metabolism, particularly the bioenergetic profiles and pathological responses of the various cellular subtypes still presents a considerable knowledge gap that has important clinical consequences. While our data do not support the use of pyruvate supplementation as a means of protecting detached photoreceptors, they do provide a foundation and motivation for future research in this area.

Histochemical Comparison of Human and Rat Lacrimal Glands: Implications for Bio-Engineering Studies.

Purpose: The purpose of this study was to determine whether rodent lacrimal glands (LGs) represent a suitable surrogate for human tissue in bio-engineering research, we undertook a meticulous histological and histochemical comparison of these two tissues. Methods: Histological techniques and immunohistochemistry were used to compare the structure of adult human and rat LG tissues and the expression of key functional tissue elements. Results: Compared with humans, the rat LG is comprised of much more densely packed acini which are devoid of an obvious central lumen. Myoepithelial, fibroblasts, dendritic cells, T cells, and putative progenitor cells are present in both tissues. However, human LG is replete with epithelium expressing cytokeratins 8 and 18, whereas rat LG epithelium does not express cytokeratin 8. Furthermore, human LG expresses aquaporins (AQPs) 1, 3, and 5, whereas rat LG expresses AQPs 1, 4, and 5. Additionally, mast cells were identified in the rat but not the human LGs and large numbers of plasma cells were detected in the human LGs but only limited numbers were present in the rat LGs. Conclusions: The cellular composition of the human and rat LGs is similar, although there is a marked difference in the actual histo-architectural arrangement of the tissue. Further variances in the epithelial cytokeratin profile, in tissue expression of AQPs and in mast cell and plasma cell infiltration, may prove significant. Translational Relevance: The rat LG can serve as a useful surrogate for the human equivalent, but there exist specific tissue differences meaning that caution must be observed when translating results to patients.

Differential Effects of Experimental Retinal Detachment on S- and M/L-Cones in Rats.

Retinal detachment is a vision-threatening condition, which occurs when the neurosensory retina is separated from its blood supply. The main purpose of this study was to examine the effect of experimental retinal detachment in rats on cone photoreceptors. Retinal detachment was induced in the eyes of rats via subretinal injection of sodium hyaluronate. Experimental detachment caused a rapid, sustained loss of short (S)- and medium/long (M/L)-wavelength cone opsins. Importantly, S-opsin+ cones were affected earlier than M/L-opsin+ cones and were affected to a greater extent than M/L-opsin+ cones throughout the duration of detachment. In comparison, to cone opsins, reductions in other cone markers-peanut agglutinin PNA and cone arrestin-were substantially less marked. These data suggest that loss of cone opsins does not reflect cone degeneration and may rather indicate prolonged downregulation of specific proteins in affected cones. This conclusion is supported by the lack of TUNEL+- cone arrestin+ double-labelled cells at the time point of greatest rod photoreceptor cell death, together with the partial recovery of cone arrestin+ cell numbers over time. Analysis of retinas that had naturally re-attached reinforced the deduction that few cones die following detachment, but also highlighted that prolonged detachment leads to deconstruction of cone segments that may not be readily reversible. Survival and functional recovery of cones following surgery for retinal detachment is vital for successful recovery of vision. The data suggest that experimental detachment in rats may offer a useful approach to model the response of S-cones to retinal detachment in humans.

Temporal Sequence of Post-Mortem Autolysis in the Mouse Retina.

In order to better differentiate ante-mortem lesions from post-mortem retinal autolysis, the temporal sequence of post-mortem changes was studied in a well-controlled mouse model. Mice were of the same strain, age and sex, and were held at a constant ambient temperature. Eyes were collected at various times up to 72 h after death and immersion-fixed in either Davidson's fixative or 10% neutral buffered formalin, paraffin-embedded and sections cut and stained with haematoxylin and eosin. The most prominent, and early, autolytic change was retinal detachment, and subsequent folding, which occurred immediately after death in formalin-fixed eyes, but not until 2 h post mortem with Davidson's fixative. Retinal separation was complete at 16 h, or almost complete by 2 h, in formalin, but in Davidson's fixative, was only partial and segmental, the latter not becoming total until much later. Retinal detachment was attended by progressively more severe disruption and dissolution of photoreceptors and, particularly in Davidson's-fixed retinas, the rod outer segment often showed marked homogenization from 30 min to 4 h after death. The other major early change was nuclear pyknosis in the inner nuclear layer. Ganglion cells initially had cytoplasmic swelling, followed by shrinkage and basophilia (at 4 h with formalin and 16 h with Davidson's), with nuclear pyknosis becoming increasingly common over time. While the three retinal neuronal layers eventually became more attenuated and depleted of cells, the thickness of these layers was augmented by severe swelling. These findings show that the post-mortem interval at which histological interpretation of retinal changes becomes potentially compromised is dependent on the duration of this interval and the fixative used.

Physiological response of the retinal pigmented epithelium to 3-ns pulse laser application, in vitro and in vivo.

BACKGROUND: To treat healthy retinal pigmented epithelium (RPE) with the 3-ns retinal rejuvenation therapy (2RT) laser and to investigate the subsequent wound-healing response of these cells. METHODS: Primary rat RPE cells were treated with the 2RT laser at a range of energy settings. Treated cells were fixed up to 7 days post-irradiation and assessed for expression of proteins associated with wound-healing. For in vivo treatments, eyes of Dark Agouti rats were exposed to laser and tissues collected up to 7 days post-irradiation. Isolated wholemount RPE preparations were examined for structural and protein expression changes. RESULTS: Cultured RPE cells were ablated by 2RT laser in an energy-dependent manner. In all cases, the RPE cell layer repopulated completely within 7 days. Replenishment of RPE cells was associated with expression of the heat shock protein, Hsp27, the intermediate filament proteins, vimentin and nestin, and the cell cycle-associated protein, cyclin D1. Cellular tight junctions were lost in lased regions but re-expressed when cell replenishment was complete. In vivo, 2RT treatment gave rise to both an energy-dependent localised denudation of the RPE and the subsequent repopulation of lesion sites. Cell replenishment was associated with the increased expression of cyclin D1, vimentin and the heat shock proteins Hsp27 and αB-crystallin. CONCLUSIONS: The 2RT laser was able to target the RPE both in vitro and in vivo, causing debridement of the cells and the consequent stimulation of a wound-healing response leading to layer reformation.

Retinal energy metabolism in health and glaucoma.

Energy metabolism refers to the processes by which life transfers energy to do cellular work. The retina's relatively large energy demands make it vulnerable to energy insufficiency. In addition, evolutionary pressures to optimize human vision have been traded against retinal ganglion cell bioenergetic fragility. Details of the metabolic profiles of the different retinal cells remain poorly understood and are challenging to resolve. Detailed immunohistochemical mapping of the energy pathway enzymes and substrate transporters has provided some insights and highlighted interspecies differences. The different spatial metabolic patterns between the vascular and avascular retinas can account for some inconsistent data in the literature. There is a consilience of evidence that at least some individuals with glaucoma have impaired RGC energy metabolism, either due to impaired nutrient supply or intrinsic metabolic perturbations. Bioenergetic-based therapy for glaucoma has a compelling pathophysiological foundation and is supported by recent successes in animal models. Recent demonstrations of visual and electrophysiological neurorecovery in humans with glaucoma is highly encouraging and motivates longer duration trials investigating bioenergetic neuroprotection.

Disturbed glucose and pyruvate metabolism in glaucoma with neuroprotection by pyruvate or rapamycin.

Intraocular pressure-sensitive retinal ganglion cell degeneration is a hallmark of glaucoma, the leading cause of irreversible blindness. Here, we used RNA-sequencing and metabolomics to examine early glaucoma in DBA/2J mice. We demonstrate gene expression changes that significantly impact pathways mediating the metabolism and transport of glucose and pyruvate. Subsequent metabolic studies characterized an intraocular pressure (IOP)-dependent decline in retinal pyruvate levels coupled to dysregulated glucose metabolism prior to detectable optic nerve degeneration. Remarkably, retinal glucose levels were elevated 50-fold, consistent with decreased glycolysis but possibly including glycogen mobilization and other metabolic changes. Oral supplementation of the glycolytic product pyruvate strongly protected from neurodegeneration in both rat and mouse models of glaucoma. Investigating further, we detected mTOR activation at the mechanistic nexus of neurodegeneration and metabolism. Rapamycin-induced inhibition of mTOR robustly prevented glaucomatous neurodegeneration, supporting a damaging role for IOP-induced mTOR activation in perturbing metabolism and promoting glaucoma. Together, these findings support the use of treatments that limit metabolic disturbances and provide bioenergetic support. Such treatments provide a readily translatable strategy that warrants investigation in clinical trials.

Is the eye a window to the brain in Sanfilippo syndrome?

Sanfilippo syndrome is an untreatable form of childhood-onset dementia. Whilst several therapeutic strategies are being evaluated in human clinical trials including i.v. delivery of AAV9-based gene therapy, an urgent unmet need is the availability of non-invasive, quantitative measures of neurodegeneration. We hypothesise that as part of the central nervous system, the retina may provide a window through which to 'visualise' degenerative lesions in brain and amelioration of them following treatment. This is reliant on the age of onset and the rate of disease progression being equivalent in retina and brain. For the first time we have assessed in parallel, the nature, age of onset and rate of retinal and brain degeneration in a mouse model of Sanfilippo syndrome. Significant accumulation of heparan sulphate and expansion of the endo/lysosomal system was observed in both retina and brain pre-symptomatically (by 3 weeks of age). Robust and early activation of micro- and macroglia was also observed in both tissues. There was substantial thinning of retina and loss of rod and cone photoreceptors by ~ 12 weeks of age, a time at which cognitive symptoms are noted. Intravenous delivery of a clinically relevant AAV9-human sulphamidase vector to neonatal mice prevented disease lesion appearance in retina and most areas of brain when assessed 6 weeks later. Collectively, the findings highlight the previously unrecognised early and significant involvement of retina in the Sanfilippo disease process, lesions that are preventable by neonatal treatment with AAV9-sulphamidase. Critically, our data demonstrate for the first time that the advancement of retinal disease parallels that occurring in brain in Sanfilippo syndrome, thus retina may provide an easily accessible neural tissue via which brain disease development and its amelioration with treatment can be monitored.

Software for Quantifying and Batch Processing Images of Brn3a and RBPMS Immunolabelled Retinal Ganglion Cells in Retinal Wholemounts.

Purpose: The ability to accurately quantify immunohistochemically labeled retinal ganglion cells (RGCs) on wholemounts is an important histopathological determinant in experimental retinal research. Traditionally, this has been performed by manual or semi-automated counting of RGCs. Here, we describe an automated software that accurately and efficiently counts immunolabeled RGCs with the ability to batch process images and perform whole-retinal analysis to permit isodensity map generation. Methods: Retinal wholemounts from control rat eyes, and eyes subjected to either chronic ocular hypertension or N-methyl-D-aspartate (NMDA)-induced excitotoxicity, were labeled by immunohistochemistry for two different RGC-specific markers, Brn3a and RNA-binding protein with multiple splicing (RBPMS). For feasibility of manual counting, images were sampled from predefined retinal sectors, totaling 160 images for Brn3a and 144 images for RBPMS. The automated program was initially calibrated for each antibody prior to batch analysis to ensure adequate cell capture. Blinded manual RGC counts were performed by three independent observers. Results: The automated counts of RGCs labeled for Brn3a and RBPMS closely matched manual counts. The automated script accurately quantified both physiological and damaged retinas. Efficiency in counting labeled RGC wholemount images is accelerated 40-fold with the automated software. Whole-retinal analysis was demonstrated with integrated retinal isodensity map generation. Conclusions: This automated cell counting software dramatically accelerates data acquisition while maintaining accurate RGC counts across different immunolabels, methods of injury, and spatial heterogeneity of RGC loss. This software likely has potential for wider application. Translational Relevance: This study provides a valuable tool for preclinical RGC neuroprotection studies that facilitates the translation of neuroprotection to the clinic.

Safety Profile of Slit-Lamp-Delivered Retinal Laser Photobiomodulation.

Purpose: Photobiomodulation (PBM) refers to therapeutic irradiation of tissue with low-energy, 630- to 1000-nm wavelength light. An increasing body of evidence supports a beneficial effect of PBM in retinal disorders. To date, most studies have utilized light-emitting diode irradiation sources. Slit-lamp-mounted retinal lasers produce a coherent beam that can be delivered with precisely defined dosages and predetermined target area; however, the use of retinal lasers raises safety concerns that warrant investigation prior to clinical application. In this study, we determined safe dosages of laser-delivered PBM to the retina. Methods: A custom-designed, slit-lamp-delivered, 670-nm, red/near-infrared laser was used to administer a range of irradiances to healthy pigmented and non-pigmented rat retinas. The effects of PBM on various functional and structural parameters of the retina were evaluated utilizing a combination of electroretinography, Spectral Domain Optical Coherence (SD-OCT), fluorescein angiography, histology and immunohistochemistry. Results: In non-pigmented rats, no adverse events were identified at any irradiances up to 500 mW/cm2. In pigmented rats, no adverse events were identified at irradiances of 25 or 100 mW/cm2; however, approximately one-third of rats that received 500 mW/cm2 displayed very localized photoreceptor damage in the peripapillary region, typically adjacent to the optic nerve head. Conclusions: A safety threshold exists for laser-delivered PBM in pigmented retinas and was identified as 500 mW/cm2 irradiance; therefore, caution should be exercised in the dosage of laser-delivered PBM administered to pigmented retinas. Translational Relevance: This study provides important data necessary for clinical translation of laser-delivered PBM for retinal diseases.

Preclinical and clinical studies of photobiomodulation therapy for macular oedema.

AIMS/HYPOTHESIS: Diabetic macular oedema (DME) is the leading cause of visual impairment in people with diabetes. Intravitreal injections of vascular endothelial growth factor inhibitors or corticosteroids prevent loss of vision by reducing DME, but the injections must be given frequently and usually for years. Here we report laboratory and clinical studies on the safety and efficacy of 670 nm photobiomodulation (PBM) for treatment of centre-involving DME. METHODS: The therapeutic effect of PBM delivered via a light-emitting diode (LED) device was tested in transgenic mice in which induced Müller cell disruption led to photoreceptor degeneration and retinal vascular leakage. We also developed a purpose-built 670 nm retinal laser for PBM to treat DME in humans. The effect of laser-delivered PBM on improving mitochondrial function and protecting against oxidative stress was studied in cultured rat Müller cells and its safety was studied in pigmented and non-pigmented rat eyes. We then used the retinal laser to perform PBM in an open-label, dose-escalation Phase IIa clinical trial involving 21 patients with centre-involving DME. Patients received 12 sessions of PBM over 5 weeks for 90 s per treatment at a setting of 25, 100 or 200 mW/cm2 for the three sequential cohorts of 6-8 patients each. Patients were recruited from the Sydney Eye Hospital, over the age of 18 and had centre-involving DME with central macular thickness (CMT) of >300 µm with visual acuity of 75-35 Log minimum angle of resolution (logMAR) letters (Snellen visual acuity equivalent of 20/30-20/200). The objective of this trial was to assess the safety and efficacy of laser-delivered PBM at 2 and 6 months. The primary efficacy outcome was change in CMT at 2 and 6 months. RESULTS: LED-delivered PBM enhanced photoreceptor mitochondrial membrane potential, protected Müller cells and photoreceptors from damage and reduced retinal vascular leakage resulting from induced Müller cell disruption in transgenic mice. PBM delivered via the retinal laser enhanced mitochondrial function and protected against oxidative stress in cultured Müller cells. Laser-delivered PBM did not damage the retina in pigmented rat eyes at 100 mW/cm2. The completed clinical trial found a significant reduction in CMT at 2 months by 59 ± 46 µm (p = 0.03 at 200 mW/cm2) and significant reduction at all three settings at 6 months (25 mW/cm2: 53 ± 24 µm, p = 0.04; 100 mW/cm2: 129 ± 51 µm, p < 0.01; 200 mW/cm2: 114 ± 60 µm, p < 0.01). Laser-delivered PBM was well tolerated in humans at settings up to 200 mW/cm2 with no significant side effects. CONCLUSIONS/INTERPRETATION: PBM results in anatomical improvement of DME over 6 months and may represent a safe and non-invasive treatment. Further testing is warranted in randomised clinical trials. TRIAL REGISTRATION: ClinicalTrials.gov NCT02181400 Graphical abstract.

Investigations Into Bioenergetic Neuroprotection of Cone Photoreceptors: Relevance to Retinitis Pigmentosa.

Recent studies suggest cone degeneration in retinitis pigmentosa (RP) may result from intracellular energy depletion. We tested the hypothesis that cones die when depleted of energy by examining the effect of two bioenergetic, nutraceutical agents on cone survival. The study had three specific aims: firstly, we, studied the neuroprotective efficacies of glucose and creatine in an in vitro model of RP. Next, we utilized a well-characterized mouse model of RP to examine whether surviving cones, devoid of their inner segments, continue to express genes vital for glucose, and creatine utilization. Finally, we analyzed the neuroprotective properties of glucose and creatine on cone photoreceptors in a mouse model of RP. Two different bioenergy-based therapies were tested in rd1 mice: repeated local delivery of glucose and systemic creatine. Optomotor responses were tested and cone density was quantified on retinal wholemounts. The results showed that glucose supplementation increased survival of cones in culture subjected to mitochondrial stress or oxidative insult. Despite losing their inner segments, surviving cones in the rd1 retina continued to express the various glycolytic enzymes. Following a single subconjunctival injection, the mean vitreous glucose concentration was significantly elevated at 1 and 8 h, but not at 16 h after injection; however, daily subconjunctival injection of glucose neither enhanced spatial visual performance nor slowed cone cell degeneration in rd1 mice relative to isotonic saline. Creatine dose-dependently increased survival of cones in culture subjected to mitochondrial dysfunction, but not to oxidative stress. Despite the loss of their mitochondrial-rich inner segments, cone somas and axonal terminals in the rd1 retina were strongly positive for both the mitochondrial and cytosolic forms of creatine kinase at each time point examined. Creatine-fed rd1 mice displayed enhanced optomotor responses compared to mice fed normal chow. Moreover, cone density was significantly greater in creatine-treated mice compared to controls. The overall results of this study provide tentative support for the hypothesis that creatine supplementation may delay secondary degeneration of cones in individuals with RP.

Creatine is Neuroprotective to Retinal Neurons In Vitro But Not In Vivo.

Purpose: To investigate the neuroprotective properties of creatine in the retina using in vitro and in vivo models of injury. Methods: Two different rat retinal culture systems (one containing retinal ganglion cells [RGC] and one not) were subjected to either metabolic stress, via treatments with the mitochondrial complex IV inhibitor sodium azide, or excitotoxic stress, via treatment with N-methyl-D-aspartate for 24 hours, in the presence or absence of creatine (0.5, 1.0, and 5.0 mM). Neuronal survival was assessed by immunolabeling for cell-specific antigens. Putative mechanisms of creatine action were investigated in vitro. Expression of creatine kinase (CK) isoenzymes in the rat retina was examined using Western blotting and immunohistochemistry. The effect of oral creatine supplementation (2%, wt/wt) on retinal and blood creatine levels was determined as well as RGC survival in rats treated with N-methyl-D-aspartate (NMDA; 10 nmol) or high IOP-induced ischemia reperfusion. Results: Creatine significantly prevented neuronal death induced by sodium azide and NMDA in both culture systems. Creatine administration did not alter cellular adenosine triphosphate (ATP). Inhibition of CK blocked the protective effect of creatine. Retinal neurons, including RGCs, expressed predominantly mitochondrial CK isoforms, while glial cells expressed exclusively cytoplasmic CKs. In vivo, NMDA and ischemia reperfusion caused substantial loss of RGCs. Creatine supplementation led to elevated blood and retinal levels of this compound but did not significantly augment RGC survival in either model. Conclusions: Creatine increased neuronal survival in retinal cultures; however, no significant protection of RGCs was evident in vivo, despite elevated levels of this compound being present in the retina after oral supplementation.

Spatio-temporal characterization of S- and M/L-cone degeneration in the Rd1 mouse model of retinitis pigmentosa.

BACKGROUND: The Pde6brd1 (Rd1) mouse is widely used as a murine model for human retinitis pigmentosa. Understanding the spatio-temporal patterns of cone degeneration is important for evaluating potential treatments. In the present study we performed a systematic characterization of the spatio-temporal patterns of S- and M/L-opsin+ cone outer segment and cell body degeneration in Rd1 mice, described the distribution and proportion of dual cones in Rd1 retinas, and examined the kinetics of microglial activation during the period of cone degeneration. RESULTS: Outer segments of S- and M/L-cones degenerated far more rapidly than their somas. Loss of both S- and M/L-opsin+ outer segments was fundamentally complete by P21 in the central retina, and 90% complete by P45 in the peripheral retina. In comparison, degeneration of S- and M/L-opsin+ cell bodies proceeded at a slower rate. There was a marked hemispheric asymmetry in the rate of S-opsin+ and M/L-opsin+ cell body degeneration. M/L-opsin+ cones were more resilient to degeneration in the superior retina, whilst S-opsin+ cones were relatively preserved in the inferior retina. In addition, cone outer segment and cell body degeneration occurred far more rapidly in the central than the peripheral retina. At P14, the superior retina comprised a minority of genuine S-cones with a much greater complement of genuine M/L-opsin cones and dual cones, whilst the other three retinal quadrants had broadly similar numbers of genuine S-cones, genuine M/L-cones and dual cones. At P60, approximately 50% of surviving cones in the superior, nasal and temporal quadrants were dual cones. In contrast, the inferior peripheral retina at P60 contained almost exclusively genuine S-cones with a tiny minority of dual cones. Microglial number and activity were stimulated during rod breakdown, remained relatively high during cone outer segment degeneration and loss of cone somas in the central retina, and decreased thereafter in the period coincident with slow degeneration of cone cell bodies in the peripheral retina. CONCLUSION: The results of the present study provide valuable insights into cone degeneration in the Rd1 mouse, substantiating and extending conclusions drawn from earlier studies.