Abstract
Purpose: :
Gene therapy is a promising approach for retinal ganglion cell (RGC) diseases such as glaucoma. Gene therapy with brain-derived neurotrophic factor (BDNF) has previously been shown to increase RGC survival in a rat glaucoma model, but it is unclear if gene therapy with other neurotrophic factors can also mediate a protective effect. Ciliary neurotrophic factor (CNTF) is protective in several retinal disease models. We explored the protective effect of adeno-associated virus (AAV) mediated delivery of CNTF in a rat glaucoma model.
Methods: :
One eye of 40 adult Wistar rats received a 2µl intravitreal injection of either a modified AAV carrying the genes for CNTF and green fluorescent protein (GFP) under the control of a CMV promoter (AAV-CNTF, n=20) or saline (n=20). (CNTF bioactivity was confirmed for each batch of virus by characteristic electroretinographic changes in non-glaucomatous mouse eyes following subretinal injection.) Experimental ocular hypertension was induced in saline and AAV-CNTF treated rat eyes 16 days after injection by 532nm trabecular laser treatment. Intraocular pressure was monitored by TonoLab tonometry. Four weeks after IOP elevation, optic nerve damage in optic nerve cross-sections was graded by masked observers using established semi-quantitative methods. GFP expression was confirmed in a subset of retinal wholemounts by fluorescence microscopy. To allow for any potential effect of AAV-CNTF on IOP, the primary outcome measure was optic nerve damage per unit of integral IOP exposure.
Results: :
4 weeks after IOP elevation, the mean optic nerve damage grade was 26±13% in AAV-CNTF eyes and 35±22% in saline controls (mean ± SD, P=0.16). There was no significant difference in the peak IOP of glaucoma eyes between groups. Integral IOP exposure was higher in AAV-CNTF eyes (225±75mmHg days) compared to saline controls (174±74mmHg days) (P=0.05). Optic nerve damage per unit integral IOP exposure was significantly lower in AAV-CNTF injected eyes compared to saline controls (0.12±0.05% per mmHg day compared to 0.23±0.18% per mmHg day, P<0.03).
Conclusions: :
Intravitreal AAV-CNTF reduced optic nerve damage per mmHg day of IOP exposure after 4 weeks of experimental glaucoma in the rat. Integral IOP was higher in AAV-CNTF treated eyes compared to saline treated eyes receiving the same amount of trabecular laser treatment for reasons that remain uncertain. The effect of AAV-CNTF on the ERG of rats with experimental glaucoma is currently under investigation.
Keywords: gene transfer/gene therapy • ganglion cells • neuroprotection