Purchase this article with an account.
Wesley Chan, Maria-Magdalena Catrinescu, Leonard A. Levin; Cyanocobalamin is a Superoxide Anion Scavenger and Neuroprotectant in Neuronal Cells. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3162.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Damage to the optic nerve (optic neuropathy) can result in permanent loss of vision or blindness through retinal ganglion cell (RGC) death. Our prior work identified a burst of superoxide anion as a critical molecular event in RGCs prior to injury-induced cell death. Exogenous delivery of pegylated superoxide dismutase (SOD), a superoxide scavenger, can decrease RGC apoptosis caused by axonal injury. Recently, Suarez-Moreira et al (JACS 131:15078, 2009) demonstrated that vitamin B12 scavenges superoxide as effectively as SOD. Given that vitamin B12 deficiency can lead to optic neuropathy through unknown mechanisms, we investigated the relationship between superoxide scavenging by cyanocobalamin, the most abundant vitamin B12 vitamer, and its neuroprotective properties in neuronal cells.
Superoxide anion reacts with hydroethidine to produce a fluorescent product, 2-hydroxyethidium. Superoxide scavenging by cyanocobalamin in a cell-free system was measured with a fluorescent microplate reader. Superoxide scavenging in RGC-5 neuronal cells was assessed in vitro by fluorescent microscopy. Neuroprotection against menadione was evaluated by calcein-AM/propidium iodide assay to identify living and dead cells. An optic nerve transection model in Long-Evans rats was used to study superoxide scavenging and neuroprotection in vivo, with visualization of superoxide within retrograde-labelled RGCs by confocal scanning laser ophthalmoscopy.
Cyanocobalamin at concentrations of 10 μM and 100 μM reduced the rate of superoxide generation by 34% and 79% in cell free assays, respectively. In menadione-treated RGC-5 cells, cyanocobalamin concentrations above 10 nM scavenged superoxide anion similar to those treated with pegylated-SOD. Cyanocobalamin at concentrations of 100 μM and 1 mM reduced RGC-5 cell death from menadione by 20% and 32%, respectively. In rats with unilateral optic nerve transection, a single intravitreal dose of 667 μM cyanocobalamin significantly reduced the number of 2-hydroxyethidium-positive RGCs. This dose also increased RGC survival rate compared to rats injected with saline control.
These data suggest that vitamin B12 may be an endogenous neuroprotectant, which when depleted in nutritional deficiency, could cause death of retinal ganglion cells by a superoxide-dependent mechanism. Vitamin B12 could also potentially also be used as a therapy to slow progression of RGC death in patients with optic neuropathies characterized by overproduction of superoxide.
This PDF is available to Subscribers Only