EPOS

European Paediatric Ophthalmological Society

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Novel pharmacological therapies for ocular coloboma

Moosajee Mariya¹, Bladen John², Gregory-Evans Cheryl¹, Gregory-Evans Kevin^3
1Molecular Ophthalmology, Imperial College London, UK, ²Chelsea and Westminster Hospital, London, UK, ³Western Eye Hospital, London, UK

Introduction: Ocular coloboma arises from incomplete fusion of the optic fissure between 5-7 weeks post conception, and is a significant cause of childhood visual impairment and blindness worldwide, with no effective treatment. This study introduces two novel pharmacological approaches for treating ocular coloboma in the zebrafish model. Aminoglycosides, such as gentamicin, suppress disease-causing premature stop mutations, thus partially restoring the functional protein. It has the potential to treat cases of CHARGE and renal coloboma syndrome caused by nonsense mutations. Anti-apoptotic agents, such as curcumin, may provide a safe, alternative prenatal treatment for ocular coloboma by reducing deleterious levels of cell death in a mutation-independent manner. Methods: Ocular coloboma lamb1-/- mutant embryos were treated with 100 µM gentamicin, 5 μM curcumin (diferuloylmethane, a caspase-3 inhibitor, derived from Curcuma longa) from 10 hours post fertilisation (hpf); ocular morphology was examined using histology and light microscopy at day 6. The lamb1-/- mutation causes lethality by day 5; survival times were determined for treated and untreated larvae (n=50 per group). Apoptosis at the site of the optic fissure was detected by TUNEL assay. Results: Histological analysis of lamb1-/- mutants treated with gentamicin showed complete closure of the optic fissure. Curcumin-treated embryos displayed a significantly milder coloboma phenotype. Both treated groups showed negligible TUNEL-positive staining at the site of the fissure, compared to untreated mutants. Mean survival of lamb1-/- mutants treated with both drugs resulted in a 1.7-fold (gentamicin) and 1.4-fold (curcumin) increase in survival (p>0.0001 using the Mann-Whitney Test). Conclusion: This study provides ‘proof-of-concept’ for the application of pharmacological treatments for ocular coloboma. Due to its known drug toxicity effects, gentamicin is unlikely to be used prenatally despite its overwhelming rescue of the coloboma defect seen in zebrafish. However, supplemental curcumin may provide a safe treatment which limits the severity of ocular coloboma and has applications for use in other ocular developmental anomalies displaying pathological levels of apoptosis.