Abstracts

Rationale: Thyrotropin-releasing hormone (TRH) is known to have anticonvulsant effects in several animal seizure models and is efficacious in treating patients with certain intractable epilepsies. However, the duration of TRH's action is limited due to low bioavailability and difficulty penetrating the blood-brain barrier. Since direct nose to brain delivery of therapeutic compounds may provide a means for overcoming these barriers, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of an unprotected TRH analog, 3-Methyl-Histidine TRH (3Me-H TRH) or sustained-release TRH-loaded Polylactic Acid (PLA) nanoparticles (100nm)could significantly inhibit various seizure parameters. Methods: Kindling was accomplished using a 1s train of 60 Hz biphasic square wave (200 μAmp peak to peak) administered daily to the basolateral amygdala until the animal was fully kindled. Afterdischarge duration (ADD) was assessed via electroencephalographs (EEGs) recorded bilaterally from bipolar electrodes in the basolateral amygdala and behavioral seizure severity (stage I-V) was simultaneously recorded digitally. Kindled subjects received 3Me-H TRH (10-9, 10-8, 10-7 M) intranasally 60 and 30 min prior to amygdala stimulation. The ADD and seizure stage was compared to control kindled animals receiving physiological saline intranasally. In separate experiments, TRH nanoparticles (D,PLA) (10 to 1000 ng TRH) were given intranasaly at 2, 6, 12, 24, and 48 hr prior to a seizure stimulus. The ADD and seizure stage was compared to kindled animals receiving blank nanoparticles. Results: Intranasal application of 3Me-H TRH resulted in a concentration-dependent reduction in total seizure ADD (22%, 31.5%, 44% respectively). Additionally, the analog had significant concentration-dependent effects on behavioral stages I through IV (partial) seizures at 10-8 M (27%) and 10-7 M 100 nM (41.5%). Similarly, stage V (generalized) seizures at 10-8 M 10 nM (58.5%) and 10-7 M 100 nM (62.5%) were significantly reduced. However, 3Me-H TRH significantly reduced clonus duration only at the highest concentration (31%). Intranasal delivery of TRH-PLA nanoparticles in very low doses (10 to 1000 ng) given between 2 to 48 hr before seizure stimulation was ineffective.Conclusions: Collectively, our results indicate that intranasal delivery of TRH/analogs and biodegradable sustained-release nanoparticles may be a viable means to suppress temporal lobe seizures and perhaps other seizure disorders. (Supported by CURE: Citizens United for Research in Epilepsy)