Improved protocol for histological and histopathological preparation of large eyes.

The development of new treatments for ocular diseases often requires investigating eyes similar in size and structure to human eyes. Such studies are challenging because analyzing the histopathology of large, human-sized eyes can be technically difficult. In particular, obtaining high-quality frozen sections is almost impossible due to the formation of ice crystals in the vitreous, which causes crush artifacts during the procedures of section and post sectioning manipulations. Herein, we describe a new method that provides high-quality frozen sections for large eyes and demonstrate its usefulness in the eyes of rabbits, pigs, minipigs, monkeys, and humans. We observed that artifactual separation of the photoreceptors from the retinal pigment epithelium is minimized and photoreceptor morphology is preserved. This method can be highly beneficial for investigators seeking to translate new treatments for ocular disease into the clinic. RESEARCH HIGHLIGHTS: Histopathological analysis of large and human-sized eyes presents significant challenges, particularly in obtaining high-quality frozen sections. A multistep fixation followed by vitreous removal and replacement ensures better cryopreservation and embedding of large eyes, minimizing the morphological and structural retinal loss found in many studies. Our results demonstrate that a multistep fixation and cryopreservation method for large eyes in histopathology consistently minimizes the artifactual separation of photoreceptors from the retinal pigment epithelium, thereby preserving photoreceptor morphology and providing high-quality frozen sections. A new method providing high-quality sections is necessary and will be highly useful for investigators aiming to translate new treatments for ocular diseases into clinical applications.

Interim Results of the Phase III Portal Extension Trial of the Port Delivery System with Ranibizumab in Neovascular Age-Related Macular Degeneration.

OBJECTIVE: The Port Delivery System with ranibizumab (PDS) is approved in the United States for neovascular age-related macular degeneration (nAMD). Portal (NCT03683251) is evaluating long-term safety and tolerability of the PDS in patients with nAMD who completed the phase II Ladder (NCT02510794) or phase III Archway (NCT03677934) trials. DESIGN: Multicenter, nonrandomized, open-label, extension clinical trial. PARTICIPANTS: All-PDS safety population (N = 555) comprises patients enrolled in Portal who completed Ladder or Archway. Because of data availability, efficacy population comprises Ladder-to-Portal patients only: patients who previously received PDS 10, 40, or 100 mg/mL pro re nata (as-needed [PRN]; n = 58, 62, and 59, respectively) or monthly intravitreal ranibizumab 0.5-mg injections (monthly ranibizumab; n = 41) in Ladder and subsequently enrolled in Portal. METHODS: Ladder patients received PDS refill-exchanges PRN or monthly ranibizumab. Archway patients received PDS 100 mg/mL with fixed refill-exchanges every 24 weeks (Q24W) or monthly ranibizumab. Once enrolled in Portal, all patients receive PDS Q24W from day 1. MAIN OUTCOME MEASURES: Ocular adverse events of special interest (AESIs); changes from baseline in best-corrected visual acuity (BCVA) and center point thickness (CPT); supplemental ranibizumab treatment between refill-exchange procedures; and PDS Patient Preference Questionnaire results. RESULTS: In the All-PDS safety population (mean follow-up, 111 weeks), 137 (24.7%) patients had ≥1 ocular AESI; most common were cataract (11.4%), vitreous hemorrhage (6.1%), and conjunctival thickening (bleb)/filtering bleb leak (6.3%). Endophthalmitis occurred in 11 of 555 (2.0%) patients. For Ladder-to-Portal patients previously treated with PDS 100 mg/mL or monthly ranibizumab, BCVA remained stable from baseline to month 48; mean (95% confidence interval) changes from baseline were 0.1 (-6.6 to 6.8; n = 31) and 2.3 (-9.4 to 14.1; n = 15) letters, respectively; CPT remained stable through month 48. Approximately 95% of patients did not need supplemental treatment before each refill-exchange for >2 years since Portal enrollment. Of Ladder-to-Portal previous monthly ranibizumab patients, 92% preferred the PDS over injections. CONCLUSIONS: Interim results from Portal suggest 4-year maintenance of visual/anatomic outcomes with PDS 100 mg/mL, with the PDS preferred to monthly injections. Long-term safety profile of the PDS is well characterized. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Gene therapy for neovascular age-related macular degeneration by subretinal delivery of RGX-314: a phase 1/2a dose-escalation study.

BACKGROUND: Frequent anti-vascular endothelial growth factor A (VEGF-A) injections reduce the risk of rapid and severe vision loss in patients with neovascular age-related macular degeneration (nAMD); however, due to undertreatment, many patients lose vision over time. New treatments that provide sustained suppression of VEGF-A are needed. RGX-314 (currently known as ABBV-RGX-314) is an adeno-associated virus serotype 8 vector that expresses an anti-VEGF-A antigen-binding fragment, which provides potential for continuous VEGF-A suppression after a single subretinal injection. We report results on the safety and efficacy of subretinal injection of RGX-314 in patients with nAMD. METHODS: For this open-label, multiple-cohort, multicentre, phase 1/2a, dose-escalation study conducted at eight sites in the USA, we enrolled participants with nAMD aged 50-89 years who had previously been treated with anti-VEGF injections into five cohorts (with five different doses of RGX-314). To be eligible, participants had to have macular neovascularisation secondary to nAMD with subretinal or intraretinal fluid in the centre subfield, be pseudophakic (after cataract removal), and have a best-corrected visual acuity (BCVA) in the study eye between 20/63 and 20/400 for the first participant in each cohort and between 20/40 and 20/400 for others. Subretinal injection of RGX-314 was done without a pre-bleb by a wet-laboratory-trained vitreoretinal surgeon. Cohort 1 received 3 × 109 genome copies per eye, cohort 2 received 1 × 1010, and cohort 3 received 6 × 1010. Two additional dose cohorts (cohort 4: 1·6 × 1011; cohort 5: 2·5 × 1011) were added. Participants were seen 1 day and 1 week after administration of RGX-314, and then monthly for 2 years (up to week 106). The primary outcome was safety of RGX-314 delivered by subretinal injection up to week 26. This analysis includes all 42 patients enrolled in the study. This study is registered with ClinicalTrials.gov, NCT03066258. FINDINGS: Between May 12, 2017, and May 21, 2019, we screened 110 patients for eligibility and enrolled 68. 42 participants demonstrated the required anatomic response to intravitreal ranibizumab and then received a single RGX-314 injection (dose range 3 × 109 to 2·5 × 1011 genome copies per eye) and were followed up for 2 years. There were 20 serious adverse events in 13 participants, of which one was possibly related to RGX-314: pigmentary changes in the macula with severe vision reduction 12 months after injection of RGX-314 at a dose of 2·5 × 1011 genome copies per eye. Asymptomatic pigmentary changes were seen in the inferior retinal periphery several months after subretinal injection of RGX-314 most commonly at doses of 6 × 1010 genome copies per eye or higher. There were no clinically determined immune responses or inflammation beyond that expected following routine vitrectomy. Doses of 6 × 1010 genome copies or higher resulted in sustained concentrations of RGX-314 protein in aqueous humour and stable or improved BCVA and central retinal thickness with few or no supplemental anti-VEGF-A injections in most participants. INTERPRETATION: Subretinal delivery of RGX-314 was generally well tolerated with no clinically recognised immune responses. RGX-314 gene therapy provides a novel approach for sustained VEGF-A suppression in patients with nAMD that has potential to control exudation, maintain vision, and reduce treatment burden after a single administration. Results from this study informed the pivotal programme to evaluate RGX-314 in patients with nAMD. FUNDING: RegenxBio.

Suprachoroidal gene transfer with nonviral nanoparticles in large animal eyes.

Suprachoroidal nonviral gene therapy with biodegradable poly(ß-amino ester) nanoparticles (NPs) provides widespread expression in photoreceptors and retinal pigmented epithelial (RPE) cells and therapeutic benefits in rodents. Here, we show in a human-sized minipig eye that suprachoroidal injection of 50 µl of NPs containing 19.2 µg of GFP expression plasmid caused GFP expression in photoreceptors and RPE throughout the entire eye with no toxicity. Two weeks after injection of 50, 100, or 200 µl, there was considerable within-eye and between-eye variability in expression that was reduced 3 months after injection of 200 µl and markedly reduced after three suprachoroidal injections at different locations around the eye. Reduction of bacterial CpG sequences in the expression plasmid resulted in a trend toward higher expression. These data indicate that nonviral suprachoroidal gene therapy with optimized polymer, expression plasmid, and injection approach has potential for treating photoreceptors throughout the entire retina of a human-sized eye.

Heterogeneity in disease activity, frequency of treatments, and visual outcomes among patients with retinal vein occlusion: relationship between injection need and vision with as-needed ranibizumab.

BACKGROUND/AIMS: We characterised the relationships between monitoring frequency, ranibizumab injection need and vision in patients receiving as-needed (pro re nata; PRN) ranibizumab for macular oedema due to branch retinal vein occlusion (BRVO) or central retinal vein occlusion (CRVO) in this post-hoc analysis of SHORE and HORIZON. METHODS: Patients aged 18 years and older with macular oedema due to BRVO/CRVO were included in this analysis. Injection frequency and best-corrected visual acuity (BCVA) were evaluated by PRN injection frequency in the PRN dosing phase (months (M) 7-15) of SHORE and through 12 months of HORIZON. Prespecified PRN re-treatment criteria for each trial were based on protocol-prespecified BCVA and optical coherence tomography outcomes. RESULTS: After the initial 7 monthly ranibizumab injections, patients in SHORE gained a mean of 18.3 letters from baseline. Patients randomised to PRN, on average, maintained these gains. However, some patients experienced additional mean gains, whereas others suffered losses (range 4.0 (95% CI 0.7 to 7.3) to -4.6 (95% CI -11.8 to 2.6) letters in patients who received 0 and 6-7 PRN injections, respectively). In BRAVO and CRUISE (lead-in trials), patients experienced mean gains from baseline to M6 (monthly dosing) of 19.3 and 15.0 letters, respectively, with gains maintained with PRN from M6 to M12. However, mean BCVA changes from baseline to M12 varied in HORIZON (range -0.4 (95% CI -2.5 to 1.6) to -3.6 (95% CI -6.2 to -1.0) letters in patients who received zero and six injections, respectively, during the preceding PRN phase of BRAVO and CRUISE). CONCLUSION: The BRVO/CRVO population is heterogenous with a varied response to ranibizumab treatment.

Exudation in Patients With Neovascular Age-Related Macular Degeneration Treated With the Port Delivery System or Monthly Injections.

PURPOSE: To evaluate for the presence, severity, and type of exudation at each study visit for a subgroup of patients with neovascular age-related macular degeneration from the Archway and Portal trials. DESIGN: Retrospective analysis of prospectively obtained data. METHODS: Spectral-domain optical coherence tomography scans from each study visit of 44 patients from the Port Delivery System (PDS) arm and 32 patients from the monthly injection arm of Archway were evaluated, and composites of horizontal scans through the fovea were created. Each composite was graded for the presence, type, and severity of exudation and impact on best-corrected visual acuity. RESULTS: After PDS implantation, 20 of 44 eyes (45%) never showed any exudation in the fovea, 2 (5%) never showed exudation in the fovea but had several missed visits, whereas 15 (34%), 3 (7%), and 4 (9%) showed mild, moderate, or severe exudation at 1 or more study visits, respectively. When exudation was present, it was most commonly subretinal fluid (50%). Of 32 patients randomized to monthly injections, 15 (47%) had no exudation in the fovea during monthly injections or after PDS implantation. Fluctuation of exudation in the fovea over time was seen in some patients after PDS implantation or during monthly injections with little or no identifiable impact on best-corrected visual acuity. In the 7 eyes with moderate or severe exudation in the fovea after PDS implantation, final vision was good in 5 (20/25 in 3, 20/40 in 1, and 20/50 in 1) and 2 had reduced vision from submacular hemorrhage. CONCLUSIONS: The PDS provides excellent control of exudation in the fovea in patients with neovascular age-related macular degeneration, and when exudation occurs, it often resolves without a negative impact on vision.

Anti-angiogenic collagen IV-derived peptide target engagement with αvß3 and α5ß1 in ocular neovascularization models.

AXT107, a collagen-derived peptide that binds integrins αvß3 and α5ß1 with high affinity, suppresses vascular endothelial growth factor (VEGF) signaling, promotes angiopoietin 2-induced Tie2 activation, and suppresses neovascularization (NV) and vascular leakage. Immunohistochemical staining for αvß3 and α5ß1 was markedly increased in NV compared with normal retinal vessels. After intravitreous injection of AXT107, there was no staining with an anti-AXT107 antibody on normal vessels but robust staining of NV that co-localized with αvß3 and α5ß1. Likewise, after intravitreous injection, fluorescein amidite-labeled AXT107 co-localized with αvß3 and α5ß1 on NV but not normal vessels. AXT107 also co-localized with αv and α5 at cell-cell junctions of human umbilical vein endothelial cells (HUVECs). AXT107-integrin binding was demonstrated by ex vivo cross-linking/pull-down experiments. These data support the hypothesis that AXT107 therapeutic activity is mediated through binding αvß3 and α5ß1 which are markedly upregulated on endothelial cells in NV providing selective targeting of diseased vessels which has therapeutic and safety benefits.

Reduced inspired oxygen decreases retinal superoxide radicals and promotes cone function and survival in a model of retinitis pigmentosa.

Retinitis pigmentosa (RP) is caused by many different mutations that promote the degeneration of rod photoreceptors and have no direct effect on cones. After the majority of rods have died cone photoreceptors begin to slowly degenerate. Oxidative damage contributes to cone cell death and it has been hypothesized that tissue hyperoxia due to reduced oxygen consumption from the loss of rods is what initiates oxidative stress. Herein, we demonstrate in animal models of RP that reduction of retinal hyperoxia by reducing inspired oxygen to continuous breathing of 11% O2 reduced the generation of superoxide radicals in the retina and preserved cone structure and function. These data indicate that retinal hyperoxia is the initiating event that promotes oxidative damage, loss of cone function, and cone degeneration in the RP retina.

Pharmacokinetics of the Port Delivery System with Ranibizumab in the Ladder Phase 2 Trial for Neovascular Age-Related Macular Degeneration.

INTRODUCTION: Ladder was a phase 2 trial that evaluated the Port Delivery System with ranibizumab (PDS) for neovascular age-related macular degeneration. Serum and aqueous humor samples were collected to characterize the pharmacokinetics (PK) of ranibizumab delivered through the PDS. METHODS: Ladder was a multicenter, randomized, active treatment-controlled, phase 2 clinical trial. Patients with neovascular age-related macular degeneration (n = 220) were randomized (3:3:3:2) to PDS 10 mg/ml, PDS 40 mg/ml, PDS 100 mg/ml, or monthly intravitreal ranibizumab 0.5 mg. Serum PK samples were collected in all arms and analyzed for ranibizumab concentration using an enzyme-linked immunosorbent assay. The main PK analyses were conducted in the PK-evaluable population (n = 68), which excluded patients who received fellow eye intravitreal treatment, supplemental ranibizumab treatment, or had previous treatment with bevacizumab in either eye within 9 months of randomization. RESULTS: In the PDS 10 mg/ml arm, median serum ranibizumab concentrations were below the serum trough concentration (Ctrough; 130 pg/ml) expected with monthly intravitreal ranibizumab 0.5 mg at all time points. In the PDS 40 mg/ml and 100 mg/ml arms, median serum ranibizumab concentrations were above the Ctrough expected with monthly intravitreal ranibizumab 0.5 mg (130 pg/ml) through month 3 and month 12 after implantation, respectively, and remained above the lower limit of quantification through month 15 and month 16 after implantation, respectively. CONCLUSIONS: These PK data indicate that the implant in the PDS 100 mg/ml arm maintained ranibizumab concentrations within the range of monthly intravitreal ranibizumab 0.5 mg injections (130-2220 pg/ml) through month 12 after implantation. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT02510794.

Viewpoints: Dual-blocking antibody against VEGF-A and angiopoietin-2 for treating vascular diseases of the eye.

Faricimab, a bispecific antibody that targets the endothelial cell growth factors vascular endothelial growth factor-A (VEGF-A) and angiopoietin-2 (Angpt2), was recently approved for treating neovascular age-related macular degeneration and diabetic macular edema. Here, Koh and Augustin review how mechanistic studies have translated into therapies, while Campochiaro evaluates their impact and value for clinical practice.

Oxidative stress-induced alterations in retinal glucose metabolism in Retinitis Pigmentosa.

Retinitis pigmentosa occurs due to mutations that cause rod photoreceptor degeneration. Once most rods are lost, gradual degeneration of cone photoreceptors occurs. Oxidative damage and abnormal glucose metabolism have been implicated as contributors to cone photoreceptor death. Herein, we show increased phosphorylation of key enzymes of glucose metabolism in the retinas of rd10 mice, a model of RP, and retinas of wild type mice with paraquat-induced oxidative stress, thereby inhibiting these key enzymes. Dietary supplementation with glucose and pyruvate failed to overcome the inhibition, but increased reducing equivalents in the retina and improved cone function and survival. Dichloroacetate reversed the increased phosphorylation of pyruvate dehydrogenase in rd10 retina and increased histone acetylation and levels of TP53-induced glycolysis and apoptosis regulator (TIGAR), which redirected glucose metabolism toward the pentose phosphate pathway. These data indicate that oxidative stress induced damage can be reversed by shifting glycolytic intermediates toward the pentose phosphate pathway which increases reducing equivalents and provides photoreceptor protection.

Using crowdsourcing to understand patients attitudes toward a clinical trial for retinitis pigmentosa requiring 4 years of participation.

BACKGROUND: Clinical trials for retinitis pigmentosa (RP) likely require long follow-ups because of the slow progression of RP. Understanding patients' attitudes toward participation in a long trial and their acceptability of strategies aimed at promoting retention/compliance is important for assessing feasibility and resource needs and optimizing trial design. METHODS: A crowdsourcing survey to adult RP patients was administered on social media in 2020 July-November. Patient enthusiasm level of study participation, acceptability of attending clinic visits every 4-5 months for 45-months, tele-visits with doctors, and of receiving text messages for medication reminders and for reporting missed dosages were surveyed. RESULTS: Among the 1473 respondents, over 95% use email or a mobile phone and receive text messages; 1157 (79%) respondents were very/somewhat enthusiastic about participation, among them, 80.6% were "very willing" to attend clinic visits every 4-5 months for 45 months; 90.3% were "very willing" to have tele-visits; 64.7% and 77.1% were willing to receive text reminders to take medication and messages surveying missed doses, respectively. The youngest age group (18-30) (22.1%) and oldest age group (70+) (26.1%) compared to the 41-50 years age group (14%) and women (23.5%) compared to men (14.2%) were statistically significantly more likely not to report high willingness to participate in clinical visits for 45 months. CONCLUSIONS: A trial requiring 4-years of commitment is feasible although retention can be challenging. Strategies including supplementing in-clinic visits with tele-visits and frequent communications may facilitate retention. This study also demonstrates a methodology useful for planning clinical trials for chronic diseases.

Archway Randomized Phase 3 Trial of the Port Delivery System with Ranibizumab for Neovascular Age-Related Macular Degeneration.

PURPOSE: To evaluate the safety and efficacy of the Port Delivery System with ranibizumab (PDS) for the treatment of neovascular age-related macular degeneration (nAMD). DESIGN: Phase 3, open-label, randomized, visual acuity assessor-masked noninferiority and equivalence trial. PARTICIPANTS: Patients with nAMD diagnosed within 9 months of screening previously treated with and responsive to anti-vascular endothelial growth factor therapy. METHODS: Patients were randomized 3:2 to treatment with the PDS with ranibizumab 100 mg/ml with fixed 24-week (Q24W) refill-exchanges (PDS Q24W) or intravitreal ranibizumab 0.5-mg injections every 4 weeks (monthly ranibizumab). MAIN OUTCOME MEASURES: Primary end point was change in best-corrected visual acuity (BCVA) Early Treatment Diabetic Retinopathy Study letter (letters) score from baseline averaged over weeks 36 and 40 (noninferiority margin,-4.5 letters; equivalence margin, ±4.5 letters). RESULTS: Archway enrolled 418 patients; 251 were randomized to and 248 received treatment with the PDS Q24W, and 167 were randomized to and received treatment with monthly ranibizumab. Baseline BCVA was 74.4 letters (PDS Q24W arm) and 75.5 letters (monthly ranibizumab arm; Snellen equivalent, 20/32). Adjusted mean change in BCVA score from baseline averaged over weeks 36 and 40 was +0.2 letters (standard error [SE], 0.5 letters) in the PDS Q24W arm and +0.5 letters (SE, 0.6 letters) in the monthly ranibizumab arm (difference, -0.3 letters; 95% confidence interval, -1.7 to 1.1 letters). PDS Q24W was both noninferior and equivalent to monthly ranibizumab. Of 246 PDS-treated patients assessed for supplemental ranibizumab treatment, 242 (98.4%) did not receive supplemental ranibizumab treatment before the first refill-exchange procedure, including 4 patients who discontinued treatment before the first refill-exchange procedure. Prespecified ocular adverse events of special interest were reported in 47 patients (19.0%) in the PDS Q24W arm and 10 patients (6.0%) in the monthly ranibizumab arm, which included, in the former arm, 4 (1.6%) endophthalmitis cases, 2 (0.8%) retinal detachments, 13 (5.2%) vitreous hemorrhages, 6 (2.4%) conjunctival erosions, and 5 (2.0%) conjunctival retractions. Most ocular adverse events in the PDS Q24W arm occurred within 1 month of implantation. CONCLUSIONS: Archway met its primary objective and PDS Q24W demonstrated noninferior and equivalent efficacy to monthly ranibizumab, with 98.4% of PDS-treated patients not receiving supplemental treatment in the first 24-week interval.

Eye of the Needle.

A retired patient visits our author, who is professor of ophthalmology and neuroscience at Johns Hopkins University School of Medicine, to find out why he is suddenly struggling with his vision and learn why but a single treatment option exists for macular degeneration, a condition that affects 200-million people worldwide.

Proteosomal degradation impairs transcytosis of AAV vectors from suprachoroidal space to retina.

Suprachoroidal injection provides a new route of delivery for AAV vectors to retinal pigmented epithelial cells and photoreceptors that can be done in an outpatient setting and is less invasive and potentially safer than subretinal injection, the most common route of delivery for ocular gene therapy. After suprachoroidal injection of AAV8 or AAV9 vectors, there is strong transduction of photoreceptors, but it is unclear how vector traverses the retinal pigmented epithelium. In this study, we found that transduction of photoreceptors was significantly increased after suprachoroidal injection of AAV2tYF-CBA-GFP versus AAV2-CBA-GFP vector. Compared with AAV2, AAV2tYF is more resistant to proteosomal degradation. Treatment with protease inhibitors significantly increased photoreceptor transduction after suprachoroidal injection of AAV5-GRK1-GFP. These data suggest that after suprachoroidal injection, AAV vectors access photoreceptors by transcytosis through retinal pigmented epithelial cells during which they are subject to proteosomal degradation, which if suppressed can enhance transduction of photoreceptors.

Locus-Level Changes in Macular Sensitivity in Patients with Retinitis Pigmentosa Treated with Oral N-acetylcysteine.

PURPOSE: To identify characteristics of loci associated with locus-level sensitivity loss or improvement during treatment with N-acetylcysteine (NAC) in retinitis pigmentosa (RP). DESIGN: Retrospective analysis of prospectively collected data in the FIGHT RP clinical trial. METHODS: Patients (n = 30) were treated with 600, 1,200, or 1,800 mg of NAC twice daily for 3 months and then 3 times/day for 3 months. Microperimetry locus-level changes between baseline and month 6 were correlated with baseline characteristics of loci using regression models. The main outcome measurement was locus-level sensitivity change ≥6 dB. RESULTS: Baseline mean sensitivity (3,468 loci; 51 evaluable eyes) was 7.7 dB and for foveal, parafoveal, and perifoveal loci were 20.2, 11.8, and 5.8 dB. During treatment, 287 loci (8.28%) increased ≥6 dB, and 119 of 1,613 loci with baseline sensitivity ≥6 dB decreased ≥6 dB (7.38%). A higher dose of NAC was associated with lower likelihood of sensitivity loss ≥6 dB (P = .033). Loci with low baseline sensitivity were more likely to decrease ≥6 dB (P = .034) but also more likely to increase ≥6 dB (P < .001). Foveal versus perifoveal loci (P < .001) and superior versus inferior loci (P = .005) were more likely to increase ≥6 dB. CONCLUSIONS: Higher doses of NAC reduced risk of macular loci sensitivity loss in RP. Greater sensitivity depression reversibility in the fovea during treatment suggests that high foveal cone density protects cones from irreversible loss of function in RP making them more likely to show improved function during NAC treatment.

The Multifaceted Therapeutic Role of N-Acetylcysteine (NAC) in Disorders Characterized by Oxidative Stress.

Oxidative stress, which results in the damage of diverse biological molecules, is a ubiquitous cellular process implicated in the etiology of many illnesses. The sulfhydryl-containing tripeptide glutathione (GSH), which is synthesized and maintained at high concentrations in all cells, is one of the mechanisms by which cells protect themselves from oxidative stress. N-acetylcysteine (NAC), a synthetic derivative of the endogenous amino acid L-cysteine and a precursor of GSH, has been used for several decades as a mucolytic and as an antidote to acetaminophen (paracetamol) poisoning. As a mucolytic, NAC breaks the disulfide bonds of heavily cross-linked mucins, thereby reducing mucus viscosity. In vitro, NAC has antifibrotic effects on lung fibroblasts. As an antidote to acetaminophen poisoning, NAC restores the hepatic GSH pool depleted in the drug detoxification process. More recently, improved knowledge of the mechanisms by which NAC acts has expanded its clinical applications. In particular, the discovery that NAC can modulate the homeostasis of glutamate has prompted studies of NAC in neuropsychiatric diseases characterized by impaired glutamate homeostasis. This narrative review provides an overview of the most relevant and recent evidence on the clinical application of NAC, with a focus on respiratory diseases, acetaminophen poisoning, disorders of the central nervous system (chronic neuropathic pain, depression, schizophrenia, bipolar disorder, and addiction), cardiovascular disease, contrast-induced nephropathy, and ophthalmology (retinitis pigmentosa).