Long-term antiepileptic effects of chronic intake of CNK-602A, a thyrotropin-releasing hormone analogue, on spontaneously epileptic rats

Advances on genetic rat models of epilepsy

Considering the suitability of laboratory rats in epilepsy research, we and other groups have been developing genetic models of epilepsy in this species. After epileptic rats or seizure-susceptible rats were sporadically found in outbred stocks, the epileptic traits were usually genetically-fixed by selective breeding. So far, the absence seizure models GAERS and WAG/Rij, audiogenic seizure models GEPR-3 and GEPR-9, generalized tonic-clonic seizure models IER, NER and WER, and Canavan-disease related epileptic models TRM and SER have been established. Dissection of the genetic bases including causative genes in these epileptic rat models would be a significant step toward understanding epileptogenesis. N-ethyl-N-nitrosourea (ENU) mutagenesis provides a systematic approach which allowed us to develop two novel epileptic rat models: heat-induced seizure susceptible (Hiss) rats with an Scn1a missense mutation and autosomal dominant lateral temporal epilepsy (ADLTE) model rats with an Lgi1 missense mutation. In addition, we have established episodic ataxia type 1 (EA1) model rats with a Kcna1 missense mutation derived from the ENU-induced rat mutant stock, and identified a Cacna1a missense mutation in a N-Methyl-N-nitrosourea (MNU)-induced mutant rat strain GRY, resulting in the discovery of episodic ataxia type 2 (EA2) model rats. Thus, epileptic rat models have been established on the two paths: ‘phenotype to gene’ and ‘gene to phenotype’. In the near future, development of novel epileptic rat models will be extensively promoted by the use of sophisticated genome editing technologies.

Novel thyrotropin-releasing hormone analogs: a patent review

INTRODUCTION

The potential therapeutic applications of thyrotropin-releasing hormone (TRH) have attracted attention, based on its broad-spectrum neuropharmacological action rather than its endocrine properties. These central nervous system (CNS)-mediated effects provide the rationale for use of TRH and its analogs in the treatment of brain and spinal injury, and CNS disorders like schizophrenia, Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis, Parkinson's disease, depression, shock and ischemia.

AREAS COVERED

This review summarizes the patent literature and advances in the discovery and development of novel TRH analogs over the past 20 years. It provides a comprehensive overview of the development of new TRH analogs, giving emphasis to their pharmaceutical profile.

EXPERT OPINION

The use of TRH in the treatment of various CNS disorders has been proven clinically. However, TRH itself is a poor drug candidate due to its short plasma half-life (5 min), poor biopharmaceutical properties (low intestinal and CNS permeability) and endocrine side effect. Nevertheless, researchers have come up with metabolically stable, more potent and selective TRH analogs and prodrugs. Taltirelin, one of the TRH analogs, has been approved under the trade name of Ceredist(®) in Japan for the treatment of spinocerebellar degeneration. Several other TRH analogs are in various stages of preclinical or clinical development.

Thyrotropin-releasing hormone d,l polylactide nanoparticles (TRH-NPs) protect against glutamate toxicity in vitro and kindling development in vivo

Thyrotropin-releasing hormone (TRH) is reported to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. However, its duration of action is limited by rapid tissue metabolism and the blood brain barrier. Direct nose-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS bioavailability. Bioactivity/neuroprotection of d,l polylactide nanoparticles containing TRH was assessed against glutamate toxicity in cultured rat fetal hippocampal neurons. Subsequently, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of nanoparticles containing TRH (TRH-NPs) could inhibit kindling development. Animals received daily treatments of either blank (control) or TRH-NPs for 7 days before initiation of kindling. On day 8 and each day thereafter until either fully kindled or until day 20, the animals received daily treatments before receiving a kindling stimulus 3 h later. Afterdischarge duration (ADD) was assessed via electroencephalographs recorded from electrodes in the basolateral amygdalae and behavioral seizure stereotypy was simultaneously recorded digitally. Intranasal application of TRH-NPs resulted in a significant reduction in seizure ADD as kindling progressed, while the number of stimulations required to reach stage V seizures and to become permanently kindled was significantly greater in TRH-NP-treated subjects. Additionally, delay to clonus was significantly prolonged while clonus duration was reduced indicating a less severe seizure in TRH-NP-treated subjects. Our results provide proof of principle that intranasal delivery of sustained-release TRH-NPs may be neuroprotective and can be utilized to suppress seizures and perhaps epileptogenesis.

Antiepileptic potential and behavioral profile of L-pGlu-(2-propyl)-L-His-L-ProNH2, a newer thyrotropin-releasing hormone analog

Thyrotropin-releasing hormone (TRH) and its analogs have a number of neurobiological functions and therapeutic uses in disorders of the central nervous system. In this study, the newly synthesized TRH analogs were evaluated for central nervous system activity in pentobarbital-induced sleeping in mice. The most potent TRH analog (L-pGlu-(2-propyl)-L-His-L-ProNH(2) coded as NP-647) was evaluated for its antiepileptic potential in various seizure models in mice in comparison with TRH. Intravenous pretreatment with NP-647 (10 and 20 micromol/kg body wt) significantly delayed the onset and reduced the frequency of convulsions in the pentylenetetrazole model, but not in the maximum electroshock seizure model. Also, it was found to be protective against picrotoxin- and kainic acid-induced seizures. However, NP-647 did not significantly affect theophylline-induced seizures. Further study of the effect of NP-647 on locomotor activity and a functional observational battery revealed that it did not significantly exhibit any undesirable effects as compared with vehicle and TRH. NP-647 did not significantly affect cerebral blood flow, whereas the native peptide TRH markedly increased cerebral blood flow. Furthermore, NP-647 exerted antiepileptic activity without significantly altering plasma thyroid-stimulating hormone levels and mean arterial blood pressure. This suggests that NP-647 is more selective for central nervous system activity and devoid of hormonal and cerebrovascular system effects. In contrast, TRH exhibited cardiac and endocrine effects as marked by significant elevation in mean arterial blood pressure and plasma thyroid-stimulating hormone levels. This study demonstrates that NP-647 has potential antiepileptic activity devoid of undesirable effects and, thus, can be exploited for the prevention and treatment of epilepsy.

Intranasal delivery of a thyrotropin-releasing hormone analog attenuates seizures in the amygdala-kindled rat

PURPOSE

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 (BBB). 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 a TRH analog, 3-methyl-histidine TRH (3Me-H TRH), could significantly inhibit various seizure parameters.

METHODS

Kindling was accomplished using a 1s train of 60 Hz biphasic square wave (200 microA 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.

RESULTS

Intranasal application of 3Me-H TRH resulted in a concentration-dependent reduction in total seizure ADD. Additionally, the analog had significant concentration-dependent effects on behavioral stages I through IV (partial) and stage V (generalized) seizures. However, 3Me-H TRH significantly reduced clonus duration only at the highest concentration.

DISCUSSION

The results indicate that intranasal delivery of TRH/analogs may be a viable means to suppress temporal lobe seizures and perhaps other seizure disorders.

Excitatory effects of thyrotropin-releasing hormone in the thalamus

The activity of the thalamus is state dependent. During slow-wave sleep, rhythmic burst firing is prominent, whereas during waking or rapid eye movement sleep, tonic, single-spike activity dominates. These state-dependent changes result from the actions of modulatory neurotransmitters. In the present study, we investigated the functional and cellular effects of the neuropeptide thyrotropin-releasing hormone (TRH) on the spontaneously active ferret geniculate slice. This peptide and its receptors are prominently expressed in the thalamic network, yet the role of thalamic TRH remains obscure. Bath application of TRH resulted in a transient cessation of both spindle waves and the epileptiform slow oscillation induced by application of bicuculline. With intracellular recordings, TRH application to the GABAergic neurons of the perigeniculate (PGN) or thalamocortical cells in the lateral geniculate nucleus resulted in depolarization and increased membrane resistance. In perigeniculate neurons, this effect reversed near the reversal potential for K+, suggesting that it is mediated by a decrease in K+ conductance. In thalamocortical cells, the TRH-induced depolarization was of sufficient amplitude to block the generation of rebound Ca2+ spikes, whereas the even larger direct depolarization of PGN neurons transformed these cells from the burst to tonic, single-spike mode of action potential generation. Furthermore, application of TRH prominently enhanced the afterdepolarization that follows rebound Ca2+ spikes, suggesting that this transmitter may also enhance Ca2+-activated nonspecific currents. These data suggest a novel role for TRH in the brain as an intrinsic regulator of thalamocortical network activity and provide a potential mechanism for the wake-promoting and anti-epileptic effects of this peptide.

Prolonged seizure suppression by a single implantable polymeric-TRH microdisk preparation

Thyrotropin-releasing hormone (TRH; Protirelin) is an endogenous neuropeptide known to have anticonvulsant effects in several seizure models and in intractable epileptic patients. Like most neuropeptides, its duration of action may be limited by a lack of sustained site-specific bioavailability. To attempt to provide long-term delivery, we attached TRH to a biodegradable polyanhydride copolymer as a sustained-release carrier. Utilizing the rat kindling model of temporal lobe epilepsy, a single TRH microdisk implanted stereotaxically into the seizure focus (amygdala) significantly suppressed kindling expression when assessed by the number of stimulations required to reach each behavioral stage and to become fully kindled (8.63 +/- 0.92 vs. 16.17 +/- 1.37; Mean +/- S.E.M.). Two indices of seizure severity, afterdischarge duration (Mean +/- S.E.M., sec.) (stimulated amygdala [87.40 +/- 5.47 vs. 51.80 +/- 15.65] and unstimulated amygdala [89.60 +/- 5.55 vs. 48.67 +/- 15.8] and clonus duration (71.2 +/- 5.94 vs. 29.40 +/- 8.87; Mean +/- S.E.M., sec.), were also significantly reduced by a single polymeric-TRH implant. Fifty days after initiation of the study a significant reduction in clonus duration (53.90 +/- 3.27 vs. 40.09 +/- 4.14) still remained in the TRH-implanted groups. This report is the first to provide evidence in support of in situ microdisk pharmacotherapy for potential neuropeptide delivery in intractable epilepsy and possibly other neurological disorders.