Intravitreally Injected Methylene Blue Protects Retina against Acute Ocular Hypertension in Rats

Purpose: To assess the neuroprotective effects of methylene blue (MB) in a rat model of acute ocular hypertension (AOH) and explore its possible mechanisms. Methods: Our AOH rat model was obtained with anterior chamber perfusion for 60 min. After that, 100 mu M MB was injected into the vitreous cavity immediately after injury. Electroretinogram, fundus photography, optical coherence tomography (OCT) and retina morphology examination were utilized to quantify retinal damage before surgery, as well as 7, 14 and 28 days after. The average number of surviving retinal ganglion cells (RGCs) was counted after fluorescent retrograde labelling with 4% DiI. And TUNEL assay was used to investigate retinal cell apoptosis at 24 hours after AOH. Nrf2 and BACE1 in the retina were determined by RT-qPCR analysis. Results: AOH did produce a severe degeneration effect on the whole retinal layer. Intravitreally injected MB maintained certain retinal thickness after AOH, reduced the destruction of electroretinograms, and enhanced RGCs survival. The average number of TUNEL-labelled cells statistically reduced in the MB-treated retina tissue compared with retina treated with normal saline. The relative mRNA level of Nrf2 was also much higher in the MB-treated retinas after AOH, and the expression of BACE1 had a decline in the AOH + MB group. Conclusions: MB can protect the retina from AOH injury and the possible mechanism might involve the inhibition of BACE1 expression and the activation of Nrf2 antioxidant pathway.