Investigating the effects of targeting nitric oxide pathways in a kainic acid mouse model of epileptogenesis

Epilepsy is one of the most common chronic neurological disorders, and the symptomatic form is characterised by the occurrence of spontaneous recurrent seizures following a neurological insult. One third of epilepsy patients are resistant to antiepileptic drugs (AEDs), therefore the development of novel treatments is required. Glutamate is implicated in epilepsy however, only a few glutamate receptor antagonists have been successful in epilepsy trials. An indirect means of modifying glutamate-mediated excitation, such as targeting nitric oxide (NO), might be a reasonable alternative approach. Selectively targeting NO signalling pathway by two drug interventions was investigated in this thesis. Post-synaptic density 95 blocking peptide (PSD95BP) is a protein that uncouples GluN2 subunits of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor from neuronal NO synthase to prevent downstream neurotoxic signalling of NO. In contrast, 1400W is a highly specific inducible NO synthase inhibitor that binds to the guanidine recognition site of the enzyme, competing with L-arginine and preventing neurotoxic production of NO. These compounds are effective in animal models of stroke and were tested here in a C57BL/6J mouse model of epileptogenesis. Kainic acid (KA) is widely used to induce status epilepticus (SE) in animals and the resulting neuropathology mimics that seen in humans with temporal lobe epilepsy. Repeated low dose administration of KA via intraperitoneal injection every 30 minutes consistently induced generalised seizures but was associated with inter-animal variability in KA sensitivity, acute seizure severity and mortality rate. Extra-dural telemetry electrodes were implanted in mice for electroencephalography (EEG) recordings. Two algorithms, measuring spike frequency and EEG coastline respectively, were used to quantify epileptiform activity. Mice that received drug interventions following KA-induced SE had significantly lower mean spike frequency and fewer extended coastline epochs per day than the control group at both 7 and 14 days after the initial insult. Label-free proteomics quantification showed significant changes to the hippocampal protein profile as a result of both PSD95BP and 1400W administration following KA-induced seizures. Drug treatment, singly or in combination, also reversed the effects of KA on the expression of both transforming growth factor β1 and inwardly rectifying potassium channel 4.1 in the hippocampus. Surgical implantation of extra-dural electrodes significantly lowered the seizure threshold to KA and was associated with an increase in brain expression of pro-inflammatory cytokines, suggesting that careful consideration is required in studies involving intracranial surgery to assess epileptogenesis or AED effects. Current research investigating novel therapeutic agents is focusing on non-NMDA glutamate receptors, such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate receptors, as potential AED targets. There are no compounds targeting the NO signalling pathway currently being investigated for the treatment of epilepsy. The data reported in this thesis give cause for optimism but further studies are needed to fully investigate the antiepileptic and possible antiepileptogenic properties of PSD95BP and 1400W and true efficacy will ultimately require clinical evaluation.