Characterization of AAV-mediated dorsal root ganglionopathy.

Recent studies in non-human primates administered recombinant adeno-associated viruses (rAAVs) have shown lesions in the dorsal root ganglia (DRG) of unknown pathogenesis. In this study, rAAV9s manufactured using different purification methods alongside a non-expressing Null AAV9 vector was administered to groups of cynomolgus monkeys followed by neuropathological evaluation after 4 weeks. Lesions, including neuronal degeneration, increased cellularity, and nerve fiber degeneration, were observed in the DRG, regardless of purification methods. Animals did not develop any neurological signs throughout the study, and there was no loss of function observed in neuro-electrophysiological endpoints or clear effects on intraepidermal nerve fiber density. However, magnetic resonance imaging (MRI) of animals with axonopathy showed an increase in short tau inversion recovery (STIR) intensity and decrease in fractional anisotropy. In animals administered the Null AAV9 vector, DRG lesions were not observed despite vector DNA being detected in the DRG at levels equivalent to or greater than rAAV9-treated animals. This study further supports that DRG toxicity is associated with transgene overexpression in DRGs, with particular sensitivity at the lumbar and lumbosacral level. The data from this study also showed that the nerve fiber degeneration did not correlate with any functional effect on nerve conduction but was detectable by MRI.

Mutations of the opsin gene (Y102H and I307N) lead to light-induced degeneration of photoreceptors and constitutive activation of phototransduction in mice.

Mutations in the Rhodopsin (Rho) gene can lead to autosomal dominant retinitis pigmentosa (RP) in humans. Transgenic mouse models with mutations in Rho have been developed to study the disease. However, it is difficult to know the source of the photoreceptor (PR) degeneration in these transgenic models because overexpression of wild type (WT) Rho alone can lead to PR degeneration. Here, we report two chemically mutagenized mouse models carrying point mutations in Rho (Tvrm1 with an Y102H mutation and Tvrm4 with an I307N mutation). Both mutants express normal levels of rhodopsin that localize to the PR outer segments and do not exhibit PR degeneration when raised in ambient mouse room lighting; however, severe PR degeneration is observed after short exposures to bright light. Both mutations also cause a delay in recovery following bleaching. This defect might be due to a slower rate of chromophore binding by the mutant opsins compared with the WT form, and an increased rate of transducin activation by the unbound mutant opsins, which leads to a constitutive activation of the phototransduction cascade as revealed by in vitro biochemical assays. The mutant-free opsins produced by the respective mutant Rho genes appear to be more toxic to PRs, as Tvrm1 and Tvrm4 mutants lacking the 11-cis chromophore degenerate faster than mice expressing WT opsin that also lack the chromophore. Because of their phenotypic similarity to humans with B1 Rho mutations, these mutants will be important tools in examining mechanisms underlying Rho-induced RP and for testing therapeutic strategies.

Effects of photocoagulation on intraretinal PO2 in cat.

PURPOSE: To test the hypothesis that intraretinal Po(2) increases after photocoagulation. METHODS: Anesthetized cats underwent retinal argon laser photocoagulation. At least 4 weeks after treatment, Po(2)-sensitive microelectrodes were used to record intraretinal Po(2) profiles from healed photocoagulation lesions in anesthetized cats breathing air. Histopathologic examination of the retinas was used to confirm that the photoreceptors were destroyed and that the inner retinal layers were preserved, though somewhat disorganized, as in human panretinal photocoagulation (PRP). RESULTS: The retina and tapetum were thinner in the lesioned retina than in the nonphotocoagulated retina. Average Po(2) across the inner 50% of the retina was higher (22 +/- 10 mm Hg) in photocoagulated retina than in untreated retina (14 +/- 7 mm Hg; P < 0.01; n = 13 cats). The minimum Po(2) was also significantly higher, whereas choroidal Po(2) was significantly lower in the photocoagulated retina than in untreated retina. No significant difference was found in the preretinal vitreous. After lesions, inner retinal Po(2) could also be maintained above zero, even in the absence of retinal circulation. CONCLUSIONS: Previous measurements showed increased Po(2) in the preretinal vitreous of rabbits and pigs (but not cats) after photocoagulation of the outer retina. These intraretinal measurements in cats provide further evidence for a chronic increase in inner retinal Po(2) in lesioned areas during air breathing.

From vivarium to bedside: lessons learned from animal models.

In this review, we focus primarily on information obtained by studying mouse models of heritable ocular diseases. These models have proven to be important in advancing our understanding of disease etiology and of pathological consequences of heritable disorders. Careful phenotypic analyses of these models have lead to hypotheses regarding the function of various molecules as well as the mechanisms underlying the observed pathologies. Specific examples of the utility of mouse models in vision research are discussed.

Cone-Specific Promoters for Gene Therapy of Achromatopsia and Other Retinal Diseases.

Adeno-associated viral (AAV) vectors containing cone-specific promoters have rescued cone photoreceptor function in mouse and dog models of achromatopsia, but cone-specific promoters have not been optimized for use in primates. Using AAV vectors administered by subretinal injection, we evaluated a series of promoters based on the human L-opsin promoter, or a chimeric human cone transducin promoter, for their ability to drive gene expression of green fluorescent protein (GFP) in mice and nonhuman primates. Each of these promoters directed high-level GFP expression in mouse photoreceptors. In primates, subretinal injection of an AAV-GFP vector containing a 1.7-kb L-opsin promoter (PR1.7) achieved strong and specific GFP expression in all cone photoreceptors and was more efficient than a vector containing the 2.1-kb L-opsin promoter that was used in AAV vectors that rescued cone function in mouse and dog models of achromatopsia. A chimeric cone transducin promoter that directed strong GFP expression in mouse and dog cone photoreceptors was unable to drive GFP expression in primate cones. An AAV vector expressing a human CNGB3 gene driven by the PR1.7 promoter rescued cone function in the mouse model of achromatopsia. These results have informed the design of an AAV vector for treatment of patients with achromatopsia.

Safety and Biodistribution Evaluation in CNGB3-Deficient Mice of rAAV2tYF-PR1.7-hCNGB3, a Recombinant AAV Vector for Treatment of Achromatopsia.

Applied Genetic Technologies Corporation (AGTC) is developing rAAV2tYF-PR1.7-hCNGB3, a recombinant adeno-associated virus (rAAV) vector expressing the human CNGB3 gene, for treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. We report here results of a study evaluating safety and biodistribution of rAAV2tYF-PR1.7-hCNGB3 in CNGB3-deficient mice. Three groups of animals (n = 35 males and 35 females per group) received a subretinal injection in one eye of 1 µl containing either vehicle or rAAV2tYF-PR1.7-hCNGB3 at one of two dose concentrations (1 × 10(12) or 4.2 × 10(12) vg/ml) and were euthanized 4 or 13 weeks later. There were no test-article-related changes in clinical observations, body weights, food consumption, ocular examinations, clinical pathology parameters, organ weights, or macroscopic observations at necropsy. Cone-mediated electroretinography (ERG) responses were detected after vector administration in the treated eyes in 90% of animals in the higher dose group and 31% of animals in the lower dose group. Rod-mediated ERG responses were reduced in the treated eye for all groups, with the greatest reduction in males given the higher dose of vector, but returned to normal by the end of the study. Microscopic pathology results demonstrated minimal mononuclear cell infiltrates in the retina and vitreous of some animals at the interim euthanasia and in the vitreous of some animals at the terminal euthanasia. Serum anti-AAV antibodies developed in most vector-injected animals. No animals developed antibodies to hCNGB3. Biodistribution studies demonstrated high levels of vector DNA in vector-injected eyes but little or no vector DNA in nonocular tissue. These results support the use of rAAV2tYF-PR1.7-hCNGB3 in clinical studies in patients with achromatopsia caused by CNGB3 mutations.

Safety and Biodistribution Evaluation in Cynomolgus Macaques of rAAV2tYF-PR1.7-hCNGB3, a Recombinant AAV Vector for Treatment of Achromatopsia.

Applied Genetic Technologies Corporation (AGTC) is developing rAAV2tYF-PR1.7-hCNGB3, a recombinant adeno-associated viral (rAAV) vector expressing the human CNGB3 gene, for treatment of achromatopsia, an inherited retinal disorder characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. We report here results of a study evaluating the safety and biodistribution of rAAV2tYF-PR1.7-hCNGB3 in cynomolgus macaques. Three groups of animals (n = 2 males and 2 females per group) received a subretinal injection in one eye of 300 µl containing either vehicle or rAAV2tYF-PR1.7-hCNGB3 at one of two concentrations (4 × 10(11) or 4 × 10(12) vector genomes/ml) and were evaluated over a 3-month period before being euthanized. Administration of rAAV2tYF-PR1.7-hCNGB3 was associated with a dose-related anterior and posterior segment inflammatory response that was greater than that observed in eyes injected with the vehicle control. Most manifestations of inflammation improved over time except that vitreous cells persisted in vector-treated eyes until the end of the study. One animal in the lower vector dose group was euthanized on study day 5, based on a clinical diagnosis of endophthalmitis. There were no test article-related effects on intraocular pressure, visual evoked potential responses, hematology or clinical chemistry parameters, or gross necropsy observations. Histopathological examination demonstrated minimal mononuclear infiltrates in all vector-injected eyes. Serum anti-AAV antibodies developed in all vector-injected animals. No animals developed antibodies to CNGB3. Biodistribution studies demonstrated high levels of vector DNA in the injected eye but minimal or no vector DNA in any other tissue. These results support the use of rAAV2tYF-PR1.7-hCNGB3 in clinical studies in patients with achromatopsia caused by CNGB3 mutations.

Intraretinal pH in diabetic cats.

PURPOSE: To examine intraretinal extracellular H+ concentration([H+]o) in diabetic cats. METHODS: Double-barreled H+-selective microelectrodes were used to measure [H+]o as a function of retinal depth ([H+]o profiles) in four cats with different stages of diabetic retinopathy. Profiles from "normal"and "damaged" areas of the retina were compared to profiles previously obtained from healthy cats. RESULTS: In the healthy retina, [H+]o is generally highest in the middle of the retina and decreases toward the choroid and the vitreous. In 48 % of the profiles from diabetic animals with visible retinopathy, the inner retinal gradient was reversed so that the vitreous was more acidic than the middle of the retina. The profiles with reversed inner retinal gradients were classified as damaged. On the average, the inner retina tended to be 0.07-0.08 pH units more acidic in diabetic animals than in healthy normoglycemic animals, but of similar acidity to healthy hyperglycemic animals. In areas with damaged inner retinal gradients, net H+ production in the outer retina was also impaired. CONCLUSIONS: While the number of animals is small, we conclude that the [H+](O) distribution varied from normal to damaged in the same retina. Diabetes seems to lead to an acidification of the inner retina that appears to be at least partly related to hyperglycemia and which may be important in the progression of retinopathy.

Safety and Biodistribution Evaluation in Cynomolgus Macaques of rAAV2tYF-CB-hRS1, a Recombinant Adeno-Associated Virus Vector Expressing Retinoschisin.

Applied Genetic Technologies Corporation is developing rAAV2tYF-CB-hRS1, a recombinant adeno-associated virus (rAAV) vector for treatment of X-linked retinoschisis (XLRS), an inherited retinal disease characterized by splitting (schisis) of retinal layers causing poor vision. We report here results of a study evaluating the safety and biodistribution of rAAV2tYF-CB-hRS1 in normal cynomolgus macaques. Three groups of male animals (n = 6 per group) received an intravitreal injection in one eye of either vehicle, or rAAV2tYF-CB-hRS1 at one of two dose levels (4 × 10(10) or 4 × 10(11) vg/eye). Half the animals were sacrificed after 14 days and the others after 91 or 115 days. The intravitreal injection procedure was well tolerated in all groups. Serial ophthalmic examinations demonstrated a dose-related anterior and posterior segment inflammatory response that improved over time. There were no test article-related effects on intraocular pressure, electroretinography, visual evoked potential, hematology, coagulation, clinical chemistry, or gross necropsy observations. Histopathological examination demonstrated minimal or moderate mononuclear infiltrates in 6 of 12 vector-injected eyes. Immunohistochemical staining showed RS1 labeling of the ganglion cell layer at the foveal slope in vector-injected eyes at both dose levels. Serum anti-AAV antibodies were detected in 4 of 6 vector-injected animals at the day 15 sacrifice and all vector-injected animals at later time points. No animals developed antibodies to RS1. Biodistribution studies demonstrated high levels of vector DNA in the injected eye but minimal or no vector DNA in any other tissue. These results support the use of rAAV2tYF-CB-hRS1 in clinical studies in patients with XLRS.

Visual Cycle Modulation as an Approach toward Preservation of Retinal Integrity.

Increased exposure to blue or visible light, fluctuations in oxygen tension, and the excessive accumulation of toxic retinoid byproducts places a tremendous amount of stress on the retina. Reduction of visual chromophore biosynthesis may be an effective method to reduce the impact of these stressors and preserve retinal integrity. A class of non-retinoid, small molecule compounds that target key proteins of the visual cycle have been developed. The first candidate in this class of compounds, referred to as visual cycle modulators, is emixustat hydrochloride (emixustat). Here, we describe the effects of emixustat, an inhibitor of the visual cycle isomerase (RPE65), on visual cycle function and preservation of retinal integrity in animal models. Emixustat potently inhibited isomerase activity in vitro (IC50 = 4.4 nM) and was found to reduce the production of visual chromophore (11-cis retinal) in wild-type mice following a single oral dose (ED50 = 0.18 mg/kg). Measure of drug effect on the retina by electroretinography revealed a dose-dependent slowing of rod photoreceptor recovery (ED50 = 0.21 mg/kg) that was consistent with the pattern of visual chromophore reduction. In albino mice, emixustat was shown to be effective in preventing photoreceptor cell death caused by intense light exposure. Pre-treatment with a single dose of emixustat (0.3 mg/kg) provided a ~50% protective effect against light-induced photoreceptor cell loss, while higher doses (1-3 mg/kg) were nearly 100% effective. In Abca4-/- mice, an animal model of excessive lipofuscin and retinoid toxin (A2E) accumulation, chronic (3 month) emixustat treatment markedly reduced lipofuscin autofluorescence and reduced A2E levels by ~60% (ED50 = 0.47 mg/kg). Finally, in the retinopathy of prematurity rodent model, treatment with emixustat during the period of ischemia and reperfusion injury produced a ~30% reduction in retinal neovascularization (ED50 = 0.46mg/kg). These data demonstrate the ability of emixustat to modulate visual cycle activity and reduce pathology associated with various biochemical and environmental stressors in animal models. Other attributes of emixustat, such as oral bioavailability and target specificity make it an attractive candidate for clinical development in the treatment of retinal disease.

Hyperoxia promotes electroretinogram recovery after retinal artery occlusion in cats.

PURPOSE: This work assessed the hypotheses that (1) hyperoxia is preferable to air breathing during retinal arterial occlusion, (2) hyperoxia during occlusion is beneficial in promoting recovery from arterial occlusion, and (3) hyperoxia has value even if it is delayed relative to the onset of the occlusion. METHODS: Reversible branch retinal artery occlusion was produced by pressing with a glass probe onto an artery emerging from the superior part of the optic disc in the retina of anesthetized cats. During 2-hour occlusion episodes, the cats breathed 100% O(2), 1 hour of air and 1 hour of 100% O(2), 1 hour of air and 1 hour of 70% O(2), or air. Intraretinal ERGs were recorded before, during, and after the occlusion. RESULTS: Hyperoxia during occlusion preserved intraretinal b-wave amplitude at 86% +/- 12% of normal; longer durations of increased oxygenation maintained the b-wave at higher levels during occlusion and increased the probability of b-wave recovery after occlusion; higher O(2) content in the breathing gas increased b-wave amplitude during recovery; and hyperoxia during occlusion decreased the time it took for the b-wave to recover after the occlusion. CONCLUSIONS: Hyperoxia is preferable to air breathing during retinal arterial occlusion not only for maintaining b-wave amplitude during occlusion, but also for providing a shorter recovery time and better percentage recovery after the end of the occlusion. Even if it is not possible to begin hyperoxia at the onset of occlusion, it may still be valuable.

In vivo ocular efficacy profile of mapracorat, a novel selective glucocorticoid receptor agonist, in rabbit models of ocular disease.

PURPOSE: To compare the efficacy of mapracorat (formerly ZK-245186, and subsequently BOL-303242-X), a novel selective glucocorticoid receptor agonist (SEGRA), with that of dexamethasone (DEX) in rabbit models of ocular disease. The effects of topical BOL-303242-X and DEX on intraocular pressure (IOP) and body weight changes were also evaluated. METHODS: Dry eye was induced by atropine sulfate administration and was treated with saline, BOL-303242-X (0.1%-1.0%), DEX (0.1%), Restasis 0.05% (Allergan, Inc., Irvine, CA), or Refresh Endura (Allergan, Inc.) three times per day for 7 to 8 days. For paracentesis studies, vehicle, BOL-303242-X (0.1%, 0.5%, and 1.0%), or DEX (0.1%) were repeatedly administered topically 3 hours before paracentesis and continued for 90 minutes afterward. For IOP and body weight measurements, right eyes of rabbits were topically treated with vehicle, BOL-303242-X (1.0% or 0.1%), or DEX (0.1%) four times per day for 6 weeks. RESULTS: In the dry eye model, BOL-303242-X and DEX were fully efficacious, maintaining tear volume and tear breakup time (TBUT) at baseline levels. Although Restasis improved tear volume compared with vehicle, no changes were observed in TBUT. In the paracentesis study, BOL-303242-X and DEX improved ocular inflammation. BOL-303242-X reduced protein and PGE(2) levels. Finally, BOL-303242-X showed no effects on integrated IOP or body weight, whereas DEX significantly increased integrated IOP and prevented the increase of body weight observed in the vehicle-treated animals. CONCLUSIONS: BOL-303242-X shows full anti-inflammatory efficacy (similar to DEX) in experimental models of dry eye and postoperative inflammation while demonstrating reduced effects in IOP and body weight. These data indicate that mapracorat, a SEGRA, shows efficacy similar to that of traditional steroids while exhibiting an improved side effect profile in IOP and muscle wasting.

Decreased circulation in the feline choriocapillaris underlying retinal photocoagulation lesions.

PURPOSE: To investigate the effects of argon laser photocoagulation on the choroidal circulation in cats. METHODS: Three sizes of argon laser lesions designed to damage the outer retina were created in six cats: larger than 1 mm, 500 µm, and 200 µm. At least 1 month after the lesions, damage to the choroidal vasculature was studied in two ways. First, scanning laser ophthalmoscopy was used to obtain infrared reflectance (IR) photographs and indocyanine green (ICG) angiograms. Second, fluorescent microspheres (15 µm) were injected into the left ventricle. The globes were fixed, the choroid was flat mounted, and images were taken with a fluorescence microscope. Retinal histology was assessed in comparable lesions. RESULTS: Histology showed that the inner retina was preserved, but the choroid, tapetum, and outer retina were damaged. ICG angiograms revealed choriocapillaris loss in large lesions and in some 500-µm lesions, whereas the larger vessels were preserved; in 200 µm lesions, choriocapillaris loss was not detectable. However, in all lesions, the distribution of microspheres revealed little if any choriocapillaris flow. In larger lesions, the damaged region was surrounded by an area in which the number of microspheres was higher than in the lesion but lower than in the normal retina. CONCLUSIONS: Under lesions that destroyed photoreceptors, the choriocapillaris was also compromised, even when no change could be detected with ICG angiography. Panretinal photocoagulation is designed to increase retinal PO2 by allowing choroidal oxygen to reach the inner retina, but its effectiveness may be limited by damage to the choriocapillaris.

Metabolic responses to light in monkey photoreceptors.

PURPOSE: Transient changes in intraretinal oxygen tension (PO(2)) in response to light stimuli were studied in order to understand the dynamics of light-evoked changes in photoreceptor oxidative metabolism. METHODS: PO(2) changes during illumination were recorded by double-barreled microelectrodes in the outer part of the perifoveal retina in five macaques (Rhesus and Cynomolgus) and were fitted to a single exponential equation to obtain the time constant (tau) and maximum PO(2) change. RESULTS: At the onset of light, PO(2) increased at all illuminations in all animals. The magnitude of the light-evoked PO(2) change increased with increasing illumination over 3-4 log units but decreased in all animals at the maximum illumination. The median time constant of the PO(2) change (tau) was 26 sec and was not correlated with illumination. The time constant for the return to darkness was similar for illuminations below rod saturation. Since O(2) diffusion is fast over the short distance from the choroid to the inner segments, tau reflects the time course of the underlying change in oxidative metabolism. CONCLUSIONS: Previous results suggested that two competing processes influence the change in photoreceptor oxidative metabolism with light, Na(+)/K(+) pumping and cyclic guanosine monophosphate (cGMP) turnover. Because a single exponential fitted the PO(2) data, it appears that these processes have time constants that differ by no more than a few seconds in primate. In monkeys, tau is longer than previously reported values for cat and rat. Longer time constants are related to larger photoreceptor volume, possibly because metabolic rate is controlled by intracellular Na(+), and a change in intracellular Na(+) after the onset of illumination occurs more slowly in larger photoreceptors. The "metabolic threshold" illumination that reduced oxygen consumption by about 10% is approximately the same as the illumination that closes 10% of the light-dependent cation channels that are open in the dark.

Oxygen distribution and consumption in the macaque retina.

The oxygen distribution in the retina of six anesthetized macaques was investigated as a model for retinal oxygenation in the human retina in and adjacent to the fovea. P(O2) was measured as a function of retinal depth under normal physiological conditions in light and dark adaptation with O(2) microelectrodes. Oxygen consumption (Q(O2)) of the photoreceptors was extracted by fitting a steady-state diffusion model to P(O2) measurements. In the perifovea, the P(O2) was 48 +/- 13 mmHg (mean and SD) at the choroid and fell to a minimum of 3.8 +/- 1.9 mmHg around the photoreceptor inner segments in dark adaptation, rising again toward the inner retina. The P(O2) in the inner half of the retina in darkness was 17.9 +/- 7.8 mmHg. When averaged over the outer retina, photoreceptor Q(O2) (called Q(av)) was 4.6 +/- 2.3 ml O(2).100 g(-1).min(-1) under dark-adapted conditions. Illumination sufficient to saturate the rods reduced Q(av) to 72 +/- 11% of the dark-adapted value. Both perifoveal and foveal photoreceptors received most of their O(2) from the choroidal circulation. While foveal photoreceptors have more mitochondria, the Q(O2) of photoreceptors in the fovea was 68% of that in the perifovea. Oxygenation in macaque retina was similar to that previously found in cats and other mammals, reinforcing the relevance of nonprimate animal models for the study of retinal oxygenation, but there was a smaller reduction in Q(O2) with light than observed in cats, which may have implications for understanding the influence of light under some clinical conditions.

Retinal arterial occlusion leads to acidosis in the cat.

This study investigated the changes in pH during retinal artery occlusion by means of extracellular H+ concentration ([H+]o) measurements in the retina under both air and 100% O2 ventilation. Occlusion was produced in intact anesthetised cats by pressing with a probe onto a retinal artery. [H+]o profiles were recorded across the retina with pH sensitive microelectrodes. The average inner retinal [H+]o increased during occlusion, resulting in an acidification of as much as 0.10 pH units, even under 100% O2 ventilation. The inner retinal H+ profile magnitude decreased during occlusion due to impaired clearance. The average outer retinal H+ profile magnitude also increased even though outer retinal H+ production did not increase during occlusion. This might be due to H+ diffusion from the inner retina to the outer retina, which is opposite to the flux in the normal retina. After reperfusion, [H+]o returned to its preocclusion value. In conclusion, arterial occlusion leads to acidification of the retina. Enhanced oxygenation during occlusion did not decrease this acidification. This may explain why increasing PO2 in the retina by enhanced O2 breathing improves retinal function during and after occlusion, but does not totally reverse the effect of occlusion.