Abstract
Purpose :
The mechanisms that contribute to VEGF-induced visual dysfunction in diabetic macular edema (DME) are not fully understood. Previously, we have shown that scotopic ERG is increased at 48 hours after intravitreal (IVT) injection of VEGF. This study investigates the role of plasma prekallikrein and endothelial nitric oxide synthase (eNOS) on VEGF-induced ERG responses in mice.
Methods :
Age-matched male wildtype (WT), plasma prekallikrein gene deletion (KLKB1-/-) and eNOS knock-in (SA1176) C57bl/6 mice were used Activation of eNOS by AKT is impaired in the SA1176 eNOS mutant. Mouse retinal thicknesses were measured using spectral domain optical coherence tomography (OCT) and retinal neuronal function was measured using full field dark-adapted ERG at 48 hours following intravitreal injections (1µL) of VEGF (100ng/eye) and saline control. Maximal scotopic responses were obtained using a 5ms white light flash (1.4x104 cd/m2).
Results :
At 48 hrs, VEGF induced an absolute change in total retinal thickness (RPE to RNFL) from baseline in WT mice (21.5±2.5µm) versus PBS (1.0±1.3µM, n=15, p<0.001). VEGF induced retinal thickness was reduced in KLKB1 (11.8±1.8µm, p=0.039) and SA1176 (11.6±3.0µm. p=0.025) compared to WT mice. VEGF increased ERG amplitude in WT mice for A-wave, OP2, OP3 and B-wave (255±7, 192±18, 229±22, 471±21 µV, n=11, p<0.05) compared to PBS (159±12, 126±15, 173±17, 301±12 µV), respectively. VEGF induced increase in amplitude was reduced by 77% (195±16µV), 88% (133±14µV) and 87% (350±18µV) in KLBK1 mice (n=12, p<0.01) and by 57% (196±15µV), 85% (136±19µV) and 68% (343±27µV) in SA1176 mice (n=11, p<0.01) for the A-Wave, OP2 and B-wave, respectively. B to A-wave ratio was not altered between PBS and VEGF responses (1.97 vs 1.85), (1.93 vs 1.85), (1.92 vs 1.78) in WT, KLKB1 or SA1176 mice, respectively. No differences were observed for implicit times.
Conclusions :
The effects of VEGF on ERG dysfunction requires plasma kallikrein and eNOS. VEGF causes extravasation and activation of the KKS resulting in an increase of ERG signal amplitudes. PKal deletion prevents KKS activation and stimulation of neuroretinal signaling through nitric oxide. Inactivation of eNOS via phosphomutation similarly reduces ERG neuroretinal response to VEGF. These data suggest that the effects of VEGF on visual dysfunction are mediated, in part, via the KKS and nitric oxide.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.