Silicone oil, an intraocular surgical adjuvant, induces retinal ferroptosis

Vitrectomy with silicone oil (SO) endotamponade is an effective treatment for vision-threatening retinal diseases. However, unexplained vision impairment has been reportedly critical side effects. Previously, we reported that the eyes with ocular toxoplasmosis showed retinal ferroptosis with the clinical sign of reduced intravitreal iron (Fe). We also found that total iron levels in sub-silicone oil fluid (SOF) in eyes with SO endotamponade were significantly reduced. We hypothesized that the cause of complications related to SO endotamponade is retinal ferroptosis and that low total iron in SOF is a secondary change that occurs similarly to the changes in ocular toxoplasmosis. In this study, we measured total iron levels in ocular fluid from patients, rabbits with SO endotamponade. Retinal iron taken up from the SOF was evaluated using laser ablation inductively coupled plasma mass spectrometry in human and rabbit eyes. Retinal ferroptosis was confirmed by immunohistochemistry of 4-hydrox-2-nonenal-modified proteins, FeRhoNox-1 staining, western blotting and RT-PCR. We found low total iron levels in the SOF, increased oxidative stress and Fe uptake from the SOF into the retinae of human and rabbit eyes, as well as decreased GPx4 expression, increased FeRhoNox-1 signals and altered Fe-related gene expression in SO-filled rabbit eyes. Of note, the target of ferroptosis was Müller cells. We generated an in vitro silicone oil-filled eye model using MIO-M1 cells (a human Müller cell line). The in vitro SO-filled eye model showed decreased GPx4 expression and increased intracellular catalytic Fe(II), an increase in ferroptosis, prevention of cell death by ferrostatin-1, a ferroptosis inhibitor, and altered Fe-related gene expression. These results indicate that the cause of complications related to SO endotamponade was the induction of retinal (Müller cell) ferroptosis, which can be prevented by ferrostatin-1.