Dietary targeting of dihydrolipoamide dehydrogenase for stroke tolerance

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DESCRIPTION (provided by applicant): New and recurrent stroke is the third leading cause of death and the leading cause of long-term disability in the United States, yet no effective endogenous targets have been defined to prevent or attenuate stroke-induced brain injury. We have discovered that mitochondrial dihydrolipoamide dehydrogenase (DLDH) could be a target for chemical preconditioning against stroke injury. The objective of this application is thus to evaluate the neuroprotective efficacy of DLDH chemical preconditioning and delineate its underlying mechanisms. Our preliminary studies show that when rats were fed a 4-week diet supplemented with 5-methoxyindole-2- carboxylic acid (MICA), a specific and competitive DLDH inhibitor, brain infarction volume decreased by c. 60% after transient middle cerebral artery occlusion (tMCAO, 1 hr ischemia and 24 hr reperfusion). This result indicates that chronic DLDH inhibition by MICA affords robust cerebroprotection against stroke. Further studies of MICA-treated rats in the absence of stroke indicate that DLDH activity was lower than in control rats whilst NAD(P)H: quinone oxidoreductase-1 (NQO1) activity increased significantly in the MICA-treated rats. NQO1 is an inducible enzyme and its expression is activated by binding of the nuclear transcription factor E2-related factor 2 (Nrf2) to the antioxidant response element (ARE). Our preliminary studies also indicate that 4 weeks' MICA dietary administration did not affect food intake, body weight gain, blood glucose concentration, or mitochondrial respiratory complexes. These preliminary results support our central hypothesis that dietary inhibition of DLDH induces persistent cerebroprotection, affording enhanced recovery of cognitive and locomotor function after ischemic stroke, via activation of the Nrf2-ARE signaling cascade. The rationale for the proposed investigation is that identifying nontoxic, blood brain barrier-permeable chemical agents that afford brain protection from stroke, and defining the protective mechanisms, will foster development and clinical implementation of such agents to minimize death and disability in human victims of stroke. We plan to test our central hypothesis and, thereby, accomplish the objective of this application by addressing the following three Specific Aims: (1) To define the extent to which Nrf2 nuclear localization and NQO1 expression increase following MICA administration and tMCAO, (2) To measure the extent to which dietary preconditioning can produce persistent neuroprotection from stroke, and (3) To evaluate the effects of MICA diet and experimental stroke on neurobehavioral function and hippocampal synaptic plasticity measured as CA1 long-term potentiation (LTP). It is expected that the successfully completed study will provide novel strategies using DLDH as a target for stroke therapeutics.