Abstracts

Rationale: Oxidative stress has been identified as a contributing factor to the cognitive decline associated with aging and neurodegenerative diseases such as Alzheimer's disease (AD). Most recently, oxidative stress has been implicated in temporal lobe epilepsy (TLE) however, to what degree oxidative stress products contribute to cognitive decline in TLE is unknown. Isoketals (IsoKs) are highly reactive gamma-ketoaldehydes formed via the isoprostane pathway of non-enzymatic, free radical catalyzed oxidation of arachidonic acid. IsoKs rapidly adduct to lysine residues and crosslink proteins. Methods: We tested the hypothesis that IsoKs are increased in a model of experimental TLE and that scavenging of these highly reactive species would attenuate learning and memory deficits. Adult male Sprague-Dawley rats (300-325g) were treated with a single high dose of kainic acid (KA) and monitored for behavioral seizures during status epilepticus and the progression to chronic epilepsy. Brain tissue (hippocampus) was collected 24 hours and 6 weeks post- KA, corresponding to the acute and chronic phases of epileptogenesis and subjected to mass spectrometry for analysis of IsoK lysine adduct levels. Salicylamine (SA) is an orally active scavenger of gamma-ketoaldehydes. A separate cohort of animals was treated with KA followed by a single injection of SA (200mg/kg) 30 minutes later and allowed free access to water supplemented with SA (1g/L) for 7 days. There was no difference in water consumption between groups or duration and intensity of seizures. After a 7 day medication period, animals were tested for indices of learning and memory in a novel object recognition task (NOR). The NOR task is uniquely suited for testing KA treated animals at this time point as it is minimally stressful and requires little training of the animal. Results: At the 24 hour time point, we found increased levels of IsoK adducts in isolated hippocampus of KA treated animals in a region specific manner such that the dentate gyrus had the largest increase (60% higher than control) followed by CA3 and CA1. At the 6 week time point, we found a global increase in levels of IsoK adducts in all areas of the hippocampus of KA treated animals (50% higher than control), suggesting that IsoKs may be a druggable target in TLE. On the NOR behavioral task, KA treated animals that received SA performed significantly better than animals not treated with SA (KA vs KA+SA p= 0.01), at a level equivalent to control animals (KA+SA vs Control p=0.15). Upon completion of the behavioral task, brain tissue and plasma was collected and subjected to HPLC analysis for levels of SA. As expected, SA was present in plasma samples at an average concentration of 0.818 uM and in brain tissue at an average abundance of 29.445 nmol/g tissue. Conclusions: These data suggest that IsoKs are potential mediators of cognitive dysfunction associated with experimental TLE and establish SA as a therapeutic to attenuate these deficits. Funding: CURE Multidisciplinary Award (Patel and Roberts) and NIHRO1NS039587-S1 (Patel and Pearson)