Synthetic regulators of the 2-oxoglutarate oxidative decarboxylation alleviate the glutamate excitotoxicity in cerebellar granule neurons

Excitotoxic glutamate increases flux through the 2-oxoglutarate dehydrogenase complex, stimulating its production of reactive species and inactivation. Phosphono analogs of 2-oxoglutarate, (PE)SP, cause neuroprotection by inhibiting these side reactions. Impairment of the 2-oxoglutarate oxidative decarboxylation by the 2-oxoglutarate dehydrogenase complex (OGDHC) is associated with the glutamate accumulation, ROS production and neuropathologies. We hypothesized that correct function of OGDHC under metabolic stress is essential to overcome the glutamate excitotoxic action on neurons. We show that synthetic phosphono analogs of 2-oxoglutarate, succinyl phosphonate and its phosphono ethyl ester, improve the catalysis by brain OGDHC through inhibiting the side reaction of irreversible inactivation of its first component, 2-oxoglutarate dehydrogenase. Under the substrate and cofactor saturation, the component and complex undergo the inactivation during catalysis with the apparent rate constant 0.2min−1. The inactivation rate is reduced by 90% and 60% in the presence of 50μM succinyl phosphonate and its phosphono ethyl ester, correspondingly. In cultured cerebellar granule neurons exposed to excitotoxic glutamate, the phosphonates (100μM) protect from the irreversible impairment of mitochondrial function and delayed calcium deregulation. The deregulation amplitude is decreased by succinyl phosphonate and its phosphono ethyl ester by 50% and 30%, correspondingly. Thus, succinyl phosphonate is more potent than its phosphono ethyl ester in protecting both the isolated brain OGDHC from inactivation and cultured neurons from the glutamate-induced calcium deregulation. The correlation of the relative efficiency of the phosphonates in vitro and in situ indicates that their cellular effects are due to targeting OGDHC, which is in accord with independent studies. We conclude that the compounds preserving the 2-oxoglutarate dehydrogenase activity are of neuroprotective value upon metabolic disbalance induced by glutamate excess.