AB014. What is the role of sildenafil in repairing retinopathy of prematurity?

Background:Oxygen therapy provided to support the lungs of premature newborns often leads to damages to the retina called retinopathy of prematurity(ROP)and long-term visual impairments.Current treatments for ROP are invasive and aim at preventing further progression of the damages to the retina,but do not repair these damages.Our goal is to investigate the therapeutic effect of sildenafil on retinal structure in a rat model of ROP.Methods:Sprague-Dawley rats were exposed to hyperoxia(i.e.,80%oxygen)interrupted by three 0.5-hour periods of normoxia(i.e.,21%oxygen)(hyperoxic animals)per day or room air only(i.e.,21%oxygen)(control animals)from post-natal day 4(P4)to 14(P14).Pups were then housed in room air.Sildenafil(50 mg/kg)or vehicle was given per os twice daily after oxygen exposure(from P15 to P21).At P30,retinas were extracted,and sectioned.For retinal histology,eyes were stained with toluidine blue to measure the thicknesses of the different retinal layers.Immunohistochemistry was also performed to count the number of retinal ganglion cells and bipolar cells in the inner retina,as well as the number of astrocytes and microglia within the different retinal layers.Results:Hyperoxia caused a reduction in thickness of the outer plexiform layer(OPL)and a decrease in the number of bipolar cells in some parts of the retina,compared to control animals(P<0.05);in addition,the number of microglia cells was significantly increased in the rats exposed to hyperoxia,compared to controls(P<0.05).Sildenafil improved OPL thickness in ROP animals,but did not change the number of bipolar cells.In hyperoxic rats treated with sildenafil,the number of microglia were similar to control rats.The number of retinal ganglion cells and astrocytes did not differ significantly between the groups.Conclusions:Treatment with sildenafil following oxygen exposure provided some recovery of the structure of the retina.This beneficial effect may be modulated by a decrease of inflammation within the retina.

AB013.Sildenafil treatment following term neonatal hypoxia-ischemia may modulate inflammation by regulating gliosis

Background:Hypoxic-ischemic injuries following birth asphyxia often lead to long-term neurological sequelae,including visual impairments,due to cortical and retinal injuries in affected neonates.Although treatment with sildenafil has been shown to improve retinal function following term neonatal asphyxia,the underlying mode of action explaining this improvement remains yet to be elucidated.Our goal is to determine the impact of sildenafil on retinal neurons and glial cells following hypoxic-ischemic injury.Methods:Neonatal hypoxia-ischemia(HI)was induced in male Long-Evans rat pups at postnatal day 10(P10)by left common carotid ligation followed by 2-hour exposure to 8%oxygen.12 hours following HI,animals were randomly administered 0(vehicle),2,10 or 50 mg/kg of sildenafil for 7 consecutive days.At P30,rats were sacrificed and their eyes were extracted.Immunohistochemistry was performed to examine retinal ganglion cells(Brn3a),bipolar cells(Chx10),astrocytes(GFAP)and microglia(Iba1)in order to assess the neuronal count and the inflammatory response in the retina following HI and the impact of the sildenafil treatment.In addition,the ratio of activated to non-activated Muller cells was assessed by co-staining Nestin and GS respectively.Results:In the retina,HI caused a decrease in the number of retinal ganglion cells and bipolar cells,as well as an increase in inflammation marked by an increase in the number of astrocytes and an increase in the ratio of activated to non-activated Muller cells.Sildenafil treatment restored the number of retinal ganglion cells and bipolar cells,as well as reduced neuroinflammation by decreasing the number of astrocytes and the number of activated Muller cells.Conclusions:Sildenafil seems to improve retinal injuries by reestablishing retinal neuron numbers back to sham levels and modulating inflammation following HI.