Abstract TMP113: Kynurenine-3-monooxygenase Inhibition Confers Neuroprotection After Ischemic Stroke In Aged Mice

Abstract

Background: The kynurenine pathway (KP) is the major route of tryptophan catabolism in mammals. KP branches into two major pathways - one (dependent on the kynurenine aminotransferases) implicated in neuroprotection, the other (dependent on the enzyme kynurenine-3-monooxygenase (KMO) in neurotoxicity. Under physiological conditions, the neuroprotective branch is more active, but under inflammatory conditions, such as seen in stroke, metabolism is shifted through the KP via KMO to produce toxic metabolites, including quinolinic acid. Recent studies have demonstrated that stroke leads to the activation of the KP. Here we tested whether inhibiting KMO activity after stroke could prevent and/or minimize the neuronal death and improve outcomes. Methods: WT C57Bl6 aged male mice were subjected to a 60-minute reversible middle cerebral artery occlusion (MCAO). Tissues collected from a sub-cohort of these mice was used for metabolomics. Other sub-cohort of mice was used for pharmacological studies. For this, mice received either an inhibitor of KMO (Ro 61-8048, 40mg/kg/day i.p) or vehicle immediately after stroke, and infarct was evaluated at day 3 post-stroke. Neurological deficit scores and open field analysis was performed to assess recovery. A separate cohort of aged WT and KMO knockout (KMO-/-) mice was also subjected to MCAO and assessed for infarct and recovery at 3 days after stroke to further evaluate the involvement of KMO on outcome. Results: Stroke caused significant reduction in the aged brain kynurenic acid/quinolinic acid (KYNA/QUIN) ratio, suggesting activation of the neurotoxic/KMO branch of the KP pathway. KMOi treatment administered immediately after the stroke reduced ischemic infarct size (p<.05; n=8 mice/grp) and also improved spontaneous locomotor activity by 72h after stroke compared to vehicle treatment. We also found that genetic deletion of KMO reduces ischemic injury size (p<.05; n=6-7mice/grp) and improves neurological deficit scores. Conclusions: Inhibition or deletion of KMO reduces neuronal death and improves motor function after stroke in aged male mice. Further studies are needed to ascertain if beneficial effects of KMOi on post-stroke recovery is not due to smaller injury, using aged animals of both sexes.