Adeno-associated virus-mediated gene delivery of the human ND4 complex I subunit in rabbit eyes

Current Advances in Gene Therapies of Genetic Auditory Neuropathy Spectrum Disorder

Auditory neuropathy spectrum disorder (ANSD) refers to a range of hearing impairments characterized by an impaired transmission of sound from the cochlea to the brain. This defect can be due to a lesion or defect in the inner hair cell (IHC), IHC ribbon synapse (e.g., pre-synaptic release of glutamate), postsynaptic terminals of the spiral ganglion neurons, or demyelination and axonal loss within the auditory nerve. To date, the only clinical treatment options for ANSD are hearing aids and cochlear implantation. However, despite the advances in hearing-aid and cochlear-implant technologies, the quality of perceived sound still cannot match that of the normal ear. Recent advanced genetic diagnostics and clinical audiology made it possible to identify the precise site of a lesion and to characterize the specific disease mechanisms of ANSD, thus bringing renewed hope to the treatment or prevention of auditory neurodegeneration. Moreover, genetic routes involving the replacement or corrective editing of mutant sequences or defected genes to repair damaged cells for the future restoration of hearing in deaf people are showing promise. In this review, we provide an update on recent discoveries in the molecular pathophysiology of genetic lesions, auditory synaptopathy and neuropathy, and gene-therapy research towards hearing restoration in rodent models and in clinical trials.

Variation in retinal nerve fiber layer thickness at different stages of Leber's hereditary optic neuropathy in patients with the ND4 G11778A mutation

PURPOSE

To investigate retinal nerve fiber layer (RNFL) thickness changes at different stages of Leber's hereditary optic neuropathy (LHON) in patients bearing the ND4 G11778A mutation.

METHODS

Ninety-eight clinically diagnosed, G11778A-positive LHON patients underwent 538 optical coherence tomography (OCT) examinations from September 2015 to September 2017. Patients were grouped based on disease duration at examination. Fifty healthy volunteers underwent 100 examinations as controls. Differences in RNFL thickness were compared across groups.

RESULTS

During the onset of LHON patients with G11778A mutation, the thickness of nerve fiber layer in temporal quadrant decreased slowly within 1-3 months (p > .05), then entered in the rapid thinning period, which generally lasted until about 12 months of the course of disease (p < .05), and no obvious change occurred in the stable stage (p > .05); The optic nerve fiber layer in other quadrants was usually stayed in a significant thickening period within 1-3 months (p < .05), then entered in the rapid thinning period, which generally lasted until about 24 months of the course of disease (p < .05), and no obvious change occurred in the stable stage (p > .05) .

CONCLUSION

In LHON patients with G11778A mutation, the thickness of optic nerve fiber layer in the temporal side will experience slow thinning stage, rapid thinning stage and stable stage; The thickness of optic nerve fiber layer in other directions varies with the course of disease. Generally, it will experience five periods: significant thickening period, swelling period, recovery period, rapid thinning period and stable period.

Leber Hereditary Optic Neuropathy: Review of Treatment and Management

Leber hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disease that specifically targets the retinal ganglion cells by reducing their ability to produce enough energy to sustain. The mutations of the mitochondrial DNA that cause LHON are silent until an unknown trigger causes bilateral central visual scotoma. After the onset of loss of vision, most patients experience progressive worsening within the following months. Few of them regain some vision after a period of ~1 year. Management of LHON patients has been focused on understanding the triggers of the disease and its pathophysiology to prevent the onset of visual loss in a carrier. Medical treatment is recommended once visual loss has started in at least one eye. Research evaluated drugs that are thought to be able to restore the mitochondrial electron transport chain of the retinal ganglion cells. Significant advances were made in evaluating free radical cell scavengers and gene therapy as potential treatments for LHON. Although encouraging the results of clinical trial have been mixed in stopping the worsening of visual loss. In patients with chronic disease of over 1 year, efficient treatment that restores vision is yet to be discovered. In this review, we summarize the management strategies for patients with LHON before, during, and after the loss of vision, explain the rationale and effectiveness of previous and current treatments, and report findings about emerging treatments.

Peripapillary Intravitreal Injection Improves AAV-Mediated Retinal Transduction

The intravitreal (IVT) injection method is a choice when targeting the inner retina for gene therapy. However, the transduction efficiency of adeno-associated virus (AAV) vectors administered by the IVT route is usually low and may be affected by several factors. To improve the transduction efficiency, we developed a novel illuminated long-needle attached injection system and injected AAV2-CMV (cytomegalovirus)-EGFP in front of the retina in rabbit eyes. Ophthalmological examinations were performed and the levels of pro-inflammatory cytokines in the aqueous humor were assessed at the baseline and 1 month, and the results were compared with those of the conventional injection method. Retinal tissues were used for immunohistochemistry. In the ophthalmological examinations, no significant inflammatory signs were detected in both groups, except for transient, mild hyperemia. In the tissues of the rabbits in the peripapillary injection group, significantly increased GFP expression was detected at the ganglion cell and the inner nuclear layers (p < 0.01). There were no differences between groups in glial activation and expressions of interleukin (IL)-6 and IL-8. These results suggest that peripapillary IVT injection in front of the retina would be safe and efficiently transduce viral vectors into the retina of large animals and is considered as a potential method for use in clinical trials.

Multilocus Mitochondrial Mutations Do Not Directly Affect the Efficacy of Gene Therapy for Leber Hereditary Optic Neuropathy

PURPOSE

Clinical trials of gene therapy for Leber hereditary optic neuropathy (LHON) were conducted in 9 volunteers with the mitochondrial mutation, G11778A in ND4. The purpose of this study was to investigate whether multilocus mitochondrial mutations directly influence the efficacy of gene therapy for LHON.

METHODS

Nine volunteers with LHON participated in a clinical trial with intravitreal injection of an adenoviral vector expressing wild-type ND4. Patients were subsequently divided into 2 groups: according to the differences in therapy efficacy and based on improvements in visual acuity. Full mitochondrial DNA sequences of the 2 groups of patients were generated and compared using PubMed, PolyPhen, and PROVEAN. Furthermore, the association between the detected mutations and clinical effects of gene therapy was analyzed.

RESULTS

Best-corrected visual acuity (BCVA) significantly improved (≥0.3 log of minimum angle of resolution [logMAR]) in 7 patients 6 months after gene therapy, whereas there was no significant change in BCVA (<0.3 logMAR) of the remaining 2 patients. All 9 patients carried the G1178A mutation in addition to other nonsynonymous mutations. Among these mutations, some were predicted to be neutral and deleterious. Meanwhile, different mitochondrial mutations in the group in which treatment was ineffective, compared with those in responders, were at nucleotide positions 6569 (CO1; Patient 3), 9641 (CO3; Patient 3), and 4491 (ND2; Patient 5).

CONCLUSIONS

Detection of the 3 primary mitochondrial mutations causing LHON is sufficient for screening before gene therapy; sequencing of the entire mitochondrial genome is unnecessary before treatment. Patients with LHON can respond to targeted gene therapy irrespective of additional multilocus mitochondrial mutations.

Prognostic factors for visual acuity in patients with Leber's hereditary optic neuropathy after rAAV2-ND4 gene therapy

Importance

Factors affecting visual acuity prognosis after gene therapy in Leber's hereditary optic neuropathy (LHON) patients with mutation at site 11 778 are unknown.

Background

To analyse correlations between visual acuity prognosis and baseline characteristics of LHON after rAAV2‐ND4 gene therapy.

Design

Retrospective study.

Participants

Fifty‐three LHON patients with a mutation at site 11 778.

Methods

Single‐eye intravitreal injection of rAAV2‐ND4.

Main Outcome Measures

Sex, onset age, duration of disease, best‐corrected visual acuity (BCVA), visual field index (VFI) and mean deviation (MD) were recorded for all patients at baseline. BCVA was recorded at 1‐ and 3‐month follow‐up visits after gene therapy. Correlations between BCVA prognosis and baseline characteristics were analysed by univariate analysis. Logistic regression analysis was performed on independent factors affecting BCVA prognosis.

Results

Univariate analysis showed significant differences in the VFI and MD of the injected eye between BCVA improvement and non‐improvement groups after 3 months of treatment, with greater VFI and smaller absolute MD in the BCVA improvement group. Logistic regression showed that VFI and baseline BCVA were independent prognostic factors for visual acuity. The correlation between VFI and MD was statistically significant.

Conclusions and Relevance

VFI and baseline BCVA were correlated with the visual acuity prognosis of LHON patients receiving gene therapy, with greater baseline VFI and better baseline BCVA predicting better visual acuity prognosis. MD was strongly correlated with VFI and might be correlated with gene therapy prognosis. This finding may form a basis for predicting the efficacy of gene therapy in these patients and guiding subsequent treatment.

The Progress of Gene Therapy for Leber's Optic Hereditary Neuropathy

Introduction:

Leber’s Optic Hereditary Neuropathy (LHON) is a common cause of teenaged blindness in both eyes for which there is currently no effective treatment. In 1871, the German ophthal-mologist Theodor Leber was the first to describe the clinical characteristics of his namesake disease, and through unremitting efforts over the past 100 years, researchers have continued to increase their under-standing of LHON. In recent years, using gene therapy, several groups have obtained breakthroughs in the treatment of the disease.

Conclusion:

In this article, we will review the challenging journey that researchers faced towards our current understanding of LHON, and describe the transition of gene therapy research for LHON from the bench to bedside.

Evaluation of Leber's hereditary optic neuropathy patients prior to a gene therapy clinical trial

Gene therapy may be a promising approach for the treatment of Leber hereditary optic neuropathy. The aim of this study was to evaluate patients with this condition who were recruited into an upcoming gene therapy clinical trial and to assess any changes in the detection parameters to provide support for the clinical trial. Sixteen patients with Leber hereditary optic neuropathy were evaluated using visual function tests 12 months before the initiation of gene therapy. Then, the results of visual acuity (VA), visual field (VF), RNFL (retinal nerve fiber layer) thickness, and Pattern-reversal Visual evoked potential (PR-VEP) were compared and analyzed. A total of 32 eyes of 16 patients were evaluated. Based on the best-corrected visual acuity (BCVA), 24 eyes were relatively stable compared with the baseline evaluation, and 8 eyes had significant changes, including 5 eyes that showed improvement and 3 eyes that showed impairment. In all eyes, the changes in the best-corrected visual acuity were significantly correlated with the changes in the visual field index (VFI), mean defect (MD), and P100 of the visual evoked potential. In the eyes with relatively stable BCVA and those with an obvious improvement in the BCVA, only the visual mean defect showed a significant change; the other indicators were not significantly different. Aside from the patients showing a tendency of spontaneous improvement, the others were in accordance with the requirement. The effects of Leber hereditary optical neuropathy (LHON) gene therapy should be evaluated primarily based on visual acuity. Additionally, visual field, neural fiber thickness, and electrophysiology should be considered in the evaluation.

Long-term outcomes of gene therapy for the treatment of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a disease that leads to blindness. Gene therapy has been investigated with some success, and could lead to important advancements in treating LHON. This was a prospective, open-label trial involving 9 LHON patients at Tongji Hospital, Wuhan, China, from August 2011 to December 2015. The purpose of this study was to evaluate the long-term outcomes of gene therapy for LHON. Nine LHON patients voluntarily received an intravitreal injection of rAAV2-ND4. Systemic examinations and visual function tests were performed during the 36-month follow-up period to determine the safety and efficacy of this gene therapy. Based on successful experiments in an animal model of LHON, 1 subject also received an rAAV2-ND4 injection in the second eye 12 months after gene therapy was administered in the first eye. Recovery of visual acuity was defined as the primary outcome of this study. Changes in the visual field, visual evoked potential (VEP), optical coherence tomography findings, liver and kidney function, and antibodies against AAV2 were defined as secondary endpoints. Eight patients (Patients 2–9) received unilateral gene therapy and visual function improvement was observed in both treated eyes (Patients 4, 6, 7, and 8) and untreated eyes (Patients 2, 3, 4, 6 and 8). Visual regression fluctuations, defined as changes in visual acuity greater than or equal to 0.3 logMAR, were observed in Patients 2 and 9. Age at disease onset, disease duration, and the amount of remaining optic nerve fibers did not have a significant effect on the visual function improvement. The visual field and pattern reversal VEP also improved. The patient (Patient 1) who received gene therapy in both eyes had improved visual acuity in the injected eye after the first treatment. Unfortunately, visual acuity in this eye decreased 3 months after he received gene therapy in the second eye. Animal experiments suggested that ND4 expression remains stable in the contralateral eye after intravitreal injections. No serious safety problem was observed in the 3-year follow-up of the 9 participants enrolled in this virus-based gene therapy. Meanwhile, our results support the use of intravitreal rAAV2-ND4 as an aggressive maneuver in our clinical trial. Further study in additional patients and in these 9 subjects is needed to better understand the effects of rAAV2-ND4 gene therapy on LHON and to increase the applications of this technique.

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A long-term study of efficacy of gene therapy for Leber's hereditary optic neuropathy.

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No serious adverse effects were noted in the 9 participants over a 3-year period.

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Five patients experienced an improvement in visual function.

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Gene therapy is a promising treatment for Leber's hereditary optic neuropathy.

There are currently no effective treatments for Leber's hereditary optic neuropathy (LHON). Short-term studies using virus-based gene therapy have yielded promising results. We performed systemic examinations and visual function tests to evaluate the long-term safety and efficacy of gene therapy for LHON. Over a 3-year follow-up period, five out of nine patients had visual function improvement, and no serious adverse effects were noted.

A retrospective analysis of characteristics of visual field damage in patients with Leber's hereditary optic neuropathy

The objective of this study is to investigate the characteristics and the evolution of visual field damage caused by Leber’s hereditary optic neuropathy (LHON) and to provide clinical data for the diagnosis of LHON. Parameters of visual field in 32 consecutive patients (49 eyes) with LHON who were confirmed by genetic diagnostic tests were retrospectively measured within 1 week, between three to six months, and at six months after onset. Visual field defects revealed central scotoma in 26 eyes (53.1 %), paracentral scotoma in 12 eyes (24.5 %), ceco-central defects in 6 eyes (12.2 %), blind spot enlargenment in 3 eyes (6.1 %), quadrantanopia in 2 eyes (4.1 %) within 1 week after onset. After 3 to 6 months, ceco-central defects were detected in 22 eyes (44.9 %), central isopter constriction in 10 eyes (20.4 %), hemianopia or quadrantanopia in 5 eyes (10.2 %), central scotoma in 4 eyes (8.2 %), and paracentral scotoma in 1 eye (2.0 %). After 6 months, central isopter constriction was observed in 18 eyes (36.7 %), diffuse defects in 21 eyes (42.9 %), ceco-central defects in 3 eyes (6.1 %), hemianopia or quadrantanopia in 5 eyes (10.2 %), and central scotoma in 2 eyes (4.1 %). LHON at different stages was characterized by different focal visual field defects: visual field defects in LHON patients within 1 week after onset were mostly central or paracentral scotoma, which was enlarged around the ceco-central defect, or connected to form a blind spot after 3–6 months. Diffuse and central isopter constriction defects were usually developed after 6 months. Damages firstly appeared in papillomacular bundle and gradually expanded outward. These characteristics of visual field defects reported in this study might provide a clinical basis for better diagnosis of LHON.

Efficacy and Safety of rAAV2-ND4 Treatment for Leber's Hereditary Optic Neuropathy

Leber's hereditary optic neuropathy (LHON) is a mitochondrially inherited disease leading to blindness. A mitochondrial DNA point mutation at the 11778 nucleotide site of the NADH dehydrogenase subunit 4 (ND4) gene is the most common cause. The aim of this study was to evaluate the efficacy and safety of a recombinant adeno-associated virus 2 (AAV2) carrying ND4 (rAAV2-ND4) in LHON patients carrying the G11778A mutation. Nine patients were administered rAAV2-ND4 by intravitreal injection to one eye and then followed for 9 months. Ophthalmologic examinations of visual acuity, visual field, and optical coherence tomography were performed. Physical examinations included routine blood and urine. The visual acuity of the injected eyes of six patients improved by at least 0.3 log MAR after 9 months of follow-up. In these six patients, the visual field was enlarged but the retinal nerve fibre layer remained relatively stable. No other outcome measure was significantly changed. None of the nine patients had local or systemic adverse events related to the vector during the 9-month follow-up period. These findings support the feasible use of gene therapy for LHON.

Emerging aspects of treatment in mitochondrial disorders

Mitochondrial diseases are clinically, biochemically and genetically heterogeneous disorders of two genomes, for which effective curative therapies are currently lacking. With the exception of a few rare vitamin/cofactor responsive conditions (including ACAD9 deficiency, disorders of coenzyme Q(10) biosynthesis, and Leigh syndrome caused by mutations in the SLC19A3 transporter), the mainstay of treatment for the vast majority of patients involves supportive measures. The search for a cure for mitochondrial disease is the subject of intensive research efforts by many investigators across the globe, but the goal remains elusive. The clinical and genetic heterogeneity, multisystemic nature of many of these disorders, unpredictable natural course, relative inaccessibility of the mitochondrion and lack of validated, clinically meaningful outcome measures, have all presented great challenges to the design of rigorous clinical trials. This review discusses barriers to developing effective therapies for mitochondrial disease, models for evaluating the efficacy of novel treatments and summarises the most promising emerging therapies in six key areas: 1) antioxidant approaches; 2) stimulating mitochondrial biogenesis; 3) targeting mitochondrial membrane lipids, dynamics and mitophagy; 4) replacement therapy; 5) cell-based therapies; and 6) gene therapy approaches for both mtDNA and nuclear-encoded defects of mitochondrial metabolism.

Chemical and material communication between the optic nerves in rats

BACKGROUND

To examine interactions between optic nerves.

METHODS

A total of 24 Sprague-Dawley rats received unilateral intravitreal injections. The rats were equally divided into four groups: group A was administered an adeno-associated virus (AAV) carrying an exogenous gene (ND4; rAAV-ND4); group B, AAV carrying a green fluorescent protein (GFP; rAAV-GFP); group C, fluorogold (FG) nerve tracer dye; and group D, phosphate-buffered saline (PBS) as a control. Two weeks later, GFP expression was evaluated in both retinas and optic nerves of group B rats after frozen sectioning. The presence of FG was also evaluated in group C optic nerves by fluorescent microscopy after frozen sectioning. Four weeks after injection, ND4 expression was evaluated in both eyes of groups A and D using western blotting and immunofluorescence.

RESULTS

FG was observed in the optic chiasm posterior segment along the optic nerve of injected eyes. Some FG reached the anterior optic nerve of the non-injected eye. GFP fluorescence was observed only in the retina of the injected eye but not in the contralateral retina or either optic nerve. ND4 expression was significantly different between injected and non-injected eyes but not between the non-injected eyes in groups A and D.

CONCLUSION

Unilaterally injected material can reach the contralateral optic nerve through axoplasmic transport. It is possible that this the only mechanism by which the optic nerves directly communicate.