Trolox aids coenzyme Q in neuroprotection against NMDA induced damage via upregulation of VEGF in rat model of glutamate excitotoxicity.

Glutamate induced damage to retinal ganglion cells (RGCs) requires tight physiological regulation of the N-methyl-D-aspartate (NMDA) receptors. Previously, studies have demonstrated the neuroprotective abilities of antioxidants like coenzyme Q (CoQ) and vitamin E analogs like α-tocopherol against neuropathies resulting from NMDA insult, but have failed to shed light on the effect of CoQ and trolox, a hydrophilic analog of vitamin E, on glaucomatous neurodegeneration. In the current study, we wanted to investigate whether the combined effect of trolox with CoQ could alleviate NMDA-induced death of retinal cells while also trying to elucidate the underlying mechanism in relation to the yet unexplained role of vascular endothelial growth factor (VEGF) in NMDA-mediated excitotoxicity. After successful NMDA-induced degeneration, we followed it up with the treatment of combination of Trolox and CoQ. The structural damage by NMDA was repaired significantly and retina retained structural integrity comparable to levels of control in the treatment group of Trolox and CoQ. Detection of ROS generation after NMDA insult showed that together, Trolox and CoQ could significantly bring down the high levels of free radicals while also rescuing mitochondrial membrane potential (MMP). A significant increase in NMDA receptor Grin2A by CoQ alone as well as by CoQ and trolox was accompanied by a lowered Grin2B receptor expression, suggesting neuroprotective action of Trolox and CoQ. Subsequently, lowered VEGFR1 and VEGFR2 receptor expression by NMDA treatment also recovered when subjected to combined treatment of Trolox and CoQ. Western blot analyses also indicated the same whereby Trolox and CoQ could increase the diminished levels of phosphorylated VEGFR2. Immunofluorescence studies also indicated a positive correlation between recovered VEGFR2 and NMDAR2A levels and diminished levels of NMDAR2D, confirming the results obtained by RT-PCR analysis. This is the first report in our knowledge that demonstrates the efficacy of trolox in combination with CoQ highlighting the importance of maintaining VEGF levels that are lowered in ocular diseases due to NMDA-related toxicities.