Thyrotropin-releasing hormone in treatment of intractable epilepsy: neurochemical analysis of CSF monoamine metabolites

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.

Alteration of regional cerebral blood flow to thyrotropin-releasing hormone therapy in acute encephalitis and encephalopathy during childhood

BACKGROUND

Thyrotropin-releasing hormone (TRH) is now used as a therapeutic agent for various neurological disorders. Animal study has shown that TRH was attributable to increased cerebral blood flow (CBF).

AIMS

There have been occasional reports that TRH therapy was effective for improving symptoms of persistent disturbance of consciousness after acute encephalitis or encephalopathy during childhood. To determine whether TRH has an effect on increasing CBF to patients who have consciousness disturbance caused by acute encephalitis or encephalopathy, and to determine the optimal method of administration.

METHODS

Sixteen patients aged 0.7-10.9 years (mean age, 3.2+/-3.1 years) who presented with persistent disturbance of consciousness resulting from acute encephalitis or encephalopathy and were treated with TRH. Regional CBF (rCBF) was measured by single photon emission computed tomography before and after TRH therapy. The alteration rates of rCBF were compared between the divided two groups concerning the dose levels, dosing periods, and treatment lags.

RESULTS

The alteration rates of rCBF of the high dose group were higher than those of the low dose group. Differences in the dosing periods and treatment lags did not cause any significant difference of the alteration rates of rCBF.

CONCLUSION

The study showed that higher alteration rates of the CBF were observed in the higher dosing group, and TRH have the potency of increasing CBF. TRH therapy would have the potential for effective treatment of persistent consciousness disturbance caused by childhood acute encephalitis or encephalopathy.

Thyrotropin-releasing hormone in the treatment of intractable epilepsy

Intractable seizures remain a significant therapeutic challenge despite current advances in the treatment of epilepsy. Thyrotropin-releasing hormone, the first neuroendocrine releasing factor to be isolated and fully characterized, was also the first releasing factor investigated as a possible neurotransmitter/neuromodulator outside the hypothalamus. Basic and clinical research has revealed a distinct neuroanatomic distribution and a neurochemical role for thyrotropin-releasing hormone in seizure modulation. Thyrotropin-releasing hormone and selected analogs were reported to have antiepileptic effects in several animal seizure paradigms, including kindling and electroconvulsive shock. Clinically, thyrotropin-releasing hormone treatment has been reported to be efficacious in such intractable epilepsies as infantile spasms, Lennox-Gastaut syndrome, myoclonic seizures, and other generalized and refractory partial seizures. Herein, we review evidence that suggests that thyrotropin-releasing hormone and selected thyrotropin-releasing hormone analogs may represent a new class of novel antiepileptic drugs, namely, antiepileptic neuropeptides and provide insights into potential new treatments for the intractable epilepsies.

Thyrotropin-releasing hormone: role in the treatment of West syndrome and related epileptic encephalopathies

Thyrotropin-releasing hormone (TRH) has been successfully used for treating children with neurologic disorders including epilepsy. The effectiveness of TRH and a TRH analog has been reported in West syndrome, Lennox-Gastaut syndrome, and early infantile epileptic encephalopathy that were intractable to anticonvulsants and adrenocorticotrophic hormone (ACTH). However, the peptide has not been widely studied as a treatment of intractable epilepsy outside Japan. TRH is safe in children and effective in some cases of West syndrome and Lennox-Gastaut syndrome. TRH is considered as a possible new strategy for treating West syndrome and Lennox-Gastaut syndrome prior to ACTH therapy, especially for the patient with an infection, immunosuppression, or severe organic lesions in the brain. The mechanisms of its antiepileptic action may differ from those of other antiepileptic drugs. One possibility is that TRH may act as an antiepileptic through a kynurenine mechanism, considering that kynurenic acid acts as an antagonist on the N-methyl-D-aspartate receptor complex.

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.

Clinical study on localization-related epilepsy in infancy without underlying disorders

A clinical study of 15 patients without underlying disorders whose first seizures occurred before 1 year of age was performed to determine the characteristics of localization-related epilepsies in infancy. The patients were retrospectively divided into two groups: the seizure-controlled group (10 patients) and the refractory group (five patients). The seizure-controlled group included patients whose seizures were controlled completely within 1 year after onset; the refractory group included all other patients. The characteristics of the refractory group were as follows: (1) interictal electroencephalography showed focal abnormalities, particularly on the left side, and (2) all of the patients exhibited developmental retardation. Even in the seizure-controlled group, 40% of the patients exhibited developmental retardation, and all of them were indistinguishable from patients with benign complex partial epilepsies in infancy at the onset of the seizures. Aggressive treatment should be re-evaluated for early-onset localization-related epilepsies.