Protective effects of TRH and its stable analogue, RGH-2202, on kainate-induced seizures and neurotoxicity in rodents

Differences in Hypothalamic Lipid Profiles of Young and Aged Male Rats With Impaired and Unimpaired Spatial Cognitive Abilities and Memory

Lipids play a major role for several brain functions, including cognition and memory. There is a series of work on individual lipids showing involvement in memory mechanisms, a concise lipidome was not reported so far. Moreover, there is no evidence for age-related memory decline and there is only work on brain of young vs. aging animals. Aging animals, however, are not a homogeneous group with respect to memory impairments, thus animals with impaired and unimpaired memory can be discriminated. Following recent studies of hippocampal lipid profiles and hypothalamus controlled hormone profiles, the aim of this study was to compare hypothalamic, lipidomic changes in male Sprague-Dawley rats between young (YM), old impaired (OMI) and old unimpaired (OMU) males. Grouping criterions for aged rats were evaluated by testing them in a spatial memory task, the hole-board. YMs were also tested. Subsequently brains were removed, dissected and hypothalami were kept at −80°C until sample preparation and analysis on liquid chromatography / mass spectrometry (LC-MS). Significant differences in the amounts of a series of lipids from several classes could be detected between young and aged and between OMI and OMU. A large number of lipids were increased in OMI and a smaller number in OMU as compared to young rats. Differences of lipid ratios (log2 of ratio) between OMI and OMU consisted of glycerophosphocholines (aPC 36:2 and 36:3; PC 34:0, 36:1, 36:3 and 40:2); Glycerophosphoethanolamines (aPE 34:2, 38:5 and 40:5; LPE 18:1, 20:1, 20:4, 22:4 and 22:6; PE36:1 and 38:4); glycerophosphoserines (PS 36:1, 40:4, and 40:6); triacylglycerol TG 52:4; ceramide Cer 17:2 and sphingomyelin SM 20:0. Thus, hypothalamic lipid profiles across different lipid classes discriminate aged male animals into OMU and OMI. The underlying mechanisms may be related to different functional networks of lipids in memory mechanisms and differences in metabolic processes. The study underlines the importance of lipidomics in the pathophysiology of age-related cognitive decline. The necessity of evaluating the cognitive status of aged subjects by behavioral tests results in more specific detection of critical lipids in memory decline, on which now can be focused in subsequent memory studies in animals and humans.

TRH Analog, Taltirelin Protects Dopaminergic Neurons From Neurotoxicity of MPTP and Rotenone

Dopaminergic neurons loss is one of the main pathological characters of Parkinson’s disease (PD), while no suitable neuroprotective agents have been in clinical use. Thyrotropin-releasing hormone (TRH) and its analogs protect neurons from ischemia and various cytotoxins, but whether the effect also applies in PD models remain unclear. Here, we showed that Taltirelin, a long-acting TRH analog, exhibited the neuroprotective effect in both cellular and animal models of PD. The in vitro study demonstrated that Taltirelin (5 μM) reduced the generation of reactive oxygen species (ROS) induced by MPP+ or rotenone, alleviated apoptosis and rescued the viability of SH-SY5Y cells and rat primary midbrain neurons. Interestingly, SH-SY5Y cells treated with Taltirelin also displayed lower level of p-tau (S396) and asparagine endopeptidase (AEP) cleavage products, tau N368 and α-synuclein N103 fragments, accompanied by a lower intracellular monoamine oxidase-B (MAO-B) activity. In the subacute MPTP-induced and chronic rotenone-induced PD mice models, we found Taltirelin (1 mg/kg) significantly improved the locomotor function and preserved dopaminergic neurons in the substantia nigra (SN). In accordance with the in vitro study, Taltirelin down-regulated the levels of p-tau (S396), p-α-synuclein (S129) tau N368 and α-synuclein N103 fragments in SN and striatum. Together, this study demonstrates that Taltirelin may exert neuroprotective effect via inhibiting MAO-B and reducing the oxidative stress and apoptosis, preventing AEP activation and its subsequent pathological cleavage of tau and α-synuclein, thus provides evidence for Taltirelin in protective treatment of PD.

Pharmacoresistant Epilepsy: A Current Update on Non-Conventional Pharmacological and Non-Pharmacological Interventions

Uncontrolled seizure or epilepsy is intricately related with an increase risk of pharmacoresistant epilepsy. The failure to achieve seizure control with the first or second drug trial of an anticonvulsant medication given at the appropriate daily dosage is termed as pharmacoresistance, despite the fact that these drugs possess different modes of action. It is one of the devastating neurological disorders act as major culprit of mortality in developed as well as developing countries with towering prevalence. Indeed, the presence of several anti-epileptic drug including carbamazepine, phenytoin, valproate, gabapentin etc. But no promising therapeutic remedies available to manage pharmacoresistance in the present clinical scenario. Hence, utility of alternative strategies in management of resistance epilepsy is increased which further possible by continuing developing of promising therapeutic interventions to manage this insidious condition adequately. Strategies include add on therapy with adenosine, verapamil etc or ketogenic diet, vagus nerve stimulation, focal cooling or standard drugs in combinations have shown some promising results. In this review we will shed light on the current pharmacological and non pharmacological mediator with their potential pleiotropic action on pharmacoresistant epilepsy.

Identification of thyrotropin-releasing hormone as hippocampal glutaminyl cyclase substrate in neurons and reactive astrocytes

Recently, Aβ peptide variants with an N-terminal truncation and pyroglutamate modification were identified and shown to be highly neurotoxic and prone to aggregation. This modification of Aβ is catalyzed by glutaminyl cyclase (QC) and pharmacological inhibition of QC diminishes Aβ deposition and accompanying gliosis and ameliorates memory impairment in transgenic mouse models of Alzheimer's disease (AD). QC expression was initially described in the hypothalamus, where thyrotropin-releasing hormone (TRH) is one of its physiological substrates. In addition to its hormonal role, a novel neuroprotective function of TRH following excitotoxicity and Aβ-mediated neurotoxicity has been reported in the hippocampus. Functionally matching this finding, we recently demonstrated QC expression by hippocampal interneurons in mouse brain. Here, we detected neuronal co-expression of QC and TRH in the hippocampus of young adult wild type mice using double immunofluorescence labeling. This provides evidence for TRH being a physiological QC substrate in hippocampus. Additionally, in neocortex of aged but not of young mice transgenic for amyloid precursor protein an increase of QC mRNA levels was found compared to wild type littermates. This phenomenon was not observed in hippocampus, which is later affected by Aβ pathology. However, in hippocampus of transgenic - but not of wild type mice - a correlation between QC and TRH mRNA levels was revealed. This co-regulation of the enzyme QC and its substrate TRH was reflected by a co-induction of both proteins in reactive astrocytes in proximity of Aβ deposits. Also, in primary mouse astrocytes a co-induction of QC and TRH was demonstrated upon Aβ stimulation.

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.

Synthesis, receptor binding, and CNS pharmacological studies of new thyrotropin-releasing hormone (TRH) analogues

As part of our search for selective and CNS-active thyrotropin-releasing hormone (TRH) analogues, we synthesized a set of 44 new analogues in which His and pGlu residues were modified or replaced. The analogues were evaluated as agonists at TRH-R1 and TRH-R2 in cells in vitro, and in vivo in mice for analeptic and anticonvulsant activities. Several analogues bound to TRH-R1 and TRH-R2 with good to moderate affinities, and are full agonists at both receptor subtypes. Specifically, analogue 21 a (R=CH3) exhibited binding affinities (Ki values) of 0.17 μM for TRH-R1 and 0.016 μM for TRH-R2; it is 10-fold less potent than TRH in binding to TRH-R1 and equipotent with TRH in binding to TRH-R2. Compound 21 a, the most selective agonist, activated TRH-R2 with a potency (EC50 value) of 0.0021 μM, but activated TRH-R1 at EC50=0.05 μM, and exhibited 24-fold selectivity for TRH-R2 over TRH-R1. The newly synthesized TRH analogues were also evaluated in vivo to assess their potencies in antagonism of barbiturate-induced sleeping time, and several analogues displayed potent analeptic activity. Specifically, analogues 21 a,b and 22 a,b decreased sleeping time by nearly 50% more than TRH. These analogues also displayed potent anticonvulsant activity and provided significant protection against PTZ-induced seizures, but failed to provide any protection in MES-induced seizures at 10 μmol kg(-1). The results of this study provide evidence that TRH analogues that show selectivity for TRH-R2 over TRH-R1 possess potent CNS activity.

Tyreoliberin (Trh) – The Regulatory Neuropeptide of Cns Homeostasis

The physiological role of thyreoliberin (TRH) is the preservation of homeostasis within four systems (i) the hypothalamic-hypophsysiotropic neuroendocrine system, (ii) the brain stem/midbrain/spinal cord system, (iii) the limbic/cortical system, and (iv) the chronobiological system. Thus TRH, via various cellular mechanisms, regulates a wide range of biological processes (arousal, sleep, learning, locomotive activity, mood) and possesses the potential for unique and widespread applications for treatment of human illnesses. Since the therapeutic potential of TRH is limited by its pharmacological profile (enzymatic instability, short half-life, undesirable effects), several synthetic analogues of TRH were constructed and studied in mono- or adjunct therapy of central nervous system (CNS) disturbances. The present article summarizes the current state of understanding of the physiological role of TRH and describes its putative role in clinical indications in CNS maladies with a focus on the action of TRH analogues.

Methamphetamine preconditioning alters midbrain transcriptional responses to methamphetamine-induced injury in the rat striatum

Methamphetamine (METH) is an illicit drug which is neurotoxic to the mammalian brain. Numerous studies have revealed significant decreases in dopamine and serotonin levels in the brains of animals exposed to moderate-to-large METH doses given within short intervals of time. In contrast, repeated injections of small nontoxic doses of the drug followed by a challenge with toxic METH doses afford significant protection against monoamine depletion. The present study was undertaken to test the possibility that repeated injections of the drug might be accompanied by transcriptional changes involved in rendering the nigrostriatal dopaminergic system refractory to METH toxicity. Our results confirm that METH preconditioning can provide significant protection against METH-induced striatal dopamine depletion. In addition, the presence and absence of METH preconditioning were associated with substantial differences in the identity of the genes whose expression was affected by a toxic METH challenge. Quantitative PCR confirmed METH-induced changes in genes of interest and identified additional genes that were differentially impacted by the toxic METH challenge in the presence of METH preconditioning. These genes include small heat shock 27 kD 27 protein 2 (HspB2), thyrotropin-releasing hormone (TRH), brain derived neurotrophic factor (BDNF), c-fos, and some encoding antioxidant proteins including CuZn superoxide dismutase (CuZnSOD), glutathione peroxidase (GPx)-1, and heme oxygenase-1 (Hmox-1). These observations are consistent, in part, with the transcriptional alterations reported in models of lethal ischemic injuries which are preceded by ischemic or pharmacological preconditioning. Our findings suggest that multiple molecular pathways might work in tandem to protect the nigrostriatal dopaminergic pathway against the deleterious effects of the toxic psychostimulant. Further analysis of the molecular and cellular pathways regulated by these genes should help to provide some insight into the neuroadaptive potentials of the brain when repeatedly exposed to drugs of abuse.

Effects of TRH and its analogues on primary cortical neuronal cell damage induced by various excitotoxic, necrotic and apoptotic agents

The tripeptide thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2) has been shown to possess neuroprotective activity in in vitro and in vivo models. Since its potential utility is limited by relatively rapid metabolism, metabolically stabilized analogues have been constructed. In the present study we investigated the influence of TRH and its three stable analogues: Montirelin (MON, CG-3703), RGH-2202 (L-6-keto-piperidine-2carbonyl-l-leucyl-l-prolinamide) and Z-TRH (N-carbobenzyloxy-pGlutamyl-Histydyl-Proline) in various models of mouse cortical neuronal cell injury. Twenty four hour pre-treatment with TRH and its analogues in low micromolar concentrations attenuated the neuronal cell death evoked by excitatory amino acids (EAAs: glutamate, NMDA, kainate, quisqualate) and hydrogen peroxide. All the peptides showed neuroprotective action on staurosporine (St)-evoked apoptotic neuronal cell death, but this effect was caspase-3 independent. Interestingly, in mixed neuronal-glial cell preparations only MON decreased St- and glutamate-evoked neurotoxicity. None of the peptides inhibited the doxorubicin- and lactacystin-induced neuronal cortical cell death, agents acting via activation of death receptor (FAS) or inhibition of proteasome function, respectively. Furthermore, we found that neither inhibitors of PI3-K (wortmannin, LY 294002) nor MAPK/ERK1/2 (PD 098059, U 0126) were able to inhibit neuroprotective properties of TRH and MON in St model of apoptosis. The protection mediated by TRH and MON it that model was also not connected with influence of peptides on the pro-apoptotic GSK-3beta and JNK protein kinase expression and activity. Further studies showed that calpains, calcium-activated proteases were induced by Glu, but not by St in cortical neurons. Moreover, the Glu-evoked increase in spectrin alpha II cleavage product induced by calpains was blocked by TRH. The obtained data showed that the potency of TRH and its analogues in inhibiting EAAs- and H(2)O(2)-induced neuronal cell death from the highest to lowest activity was: MON>TRH>Z-TRH>RHG. Interestingly, all peptides were active against St-induced apoptosis, however, on concentration basis MON was far more potent than the other peptides. None of the peptides inhibited Dox- and LC-evoked apoptotic cell death. Additionally, the data exclude potential role of pro-survival (PI3-K/Akt and MAPK/ERK1/2) and pro-apoptotic (GSK-3beta and JNK) pathways in neuroprotective effects of TRH and its analogues on St-induced neuronal apoptosis. Moreover, the results point to involvement of the inhibition of calpains in the TRH neuroprotective effect in Glu model of neuronal cell death.

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.

Attenuation of kindled seizures by intranasal delivery of neuropeptide-loaded nanoparticles

Thyrotropin-releasing hormone (TRH; Protirelin), an endogenous neuropeptide, is known to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. Its duration of action, however, is limited by rapid tissue metabolism and the blood-brain barrier. Direct nose-to-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS neuropeptide bioavailability. To provide proof of principle for this delivery approach, we used the kindling model of temporal lobe epilepsy to show that 1) TRH-loaded copolymer microdisks implanted in a seizure focus can attenuate kindling development in terms of behavioral stage, afterdischarge duration (ADD), and clonus duration; 2) intranasal administration of an unprotected TRH analog can acutely suppress fully kindled seizures in a concentration-dependent manner in terms of ADD and seizure stage; and 3) intranasal administration of polylactide nanoparticles (PLA-NPs) containing TRH (TRH-NPs) can impede kindling development in terms of behavioral stage, ADD, and clonus duration. Additionally, we used intranasal delivery of fluorescent dye-loaded PLA-NPs in rats and application of dye-loaded or dye-attached NPs to cortical neurons in culture to demonstrate NP uptake and distribution over time in vivo and in vitro respectively. Also, a nanoparticle immunostaining method was developed as a procedure for directly visualizing the tissue level and distribution of neuropeptide-loaded nanoparticles. Collectively, the data provide proof of concept for intranasal delivery of TRH-NPs as a viable means to 1) suppress seizures and perhaps epileptogenesis and 2) become the lead compound for intranasal anticonvulsant nanoparticle therapeutics.

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.

The synthetic TRH analogue taltirelin exerts modality-specific antinociceptive effects via distinct descending monoaminergic systems

BACKGROUND AND PURPOSE

Exogenously administered thyrotropin-releasing hormone (TRH) is known to exert potent but short-acting centrally-mediated antinociceptive effects. We sought to investigate the mechanisms underlying these effects using the synthetic TRH analogue taltirelin, focusing on the descending monoaminergic systems in mice.

EXPERIMENTAL APPROACH

The mice received systemic or local injections of taltirelin combined with either central noradrenaline (NA) or 5-hydroxytryptamine (5-HT) depletion by 6-hydroxydopamine (6-OHDA) or DL-p-chlorophenylalanine (PCPA), respectively, or blockade of their receptors. The degree of antinociception was determined using the tail flick and tail pressure tests.

KEY RESULTS

Subcutaneously (s.c.) administered taltirelin exhibited dose-dependent antinociceptive effects in the tail flick and tail pressure tests. These effects appeared to be primarily supraspinally mediated, since intracerebroventricularly (i.c.v.) but not intrathecally (i.t.) injected taltirelin generated similar effects. Depletion of central NA abolished only the analgesic effect of taltirelin (s.c. and i.c.v.) on mechanical nociception. By contrast, depletion of central 5-HT abolished only its analgesic effect on thermal nociception. Intraperitoneal (i.p.) and i.t. injection of the alpha2-adrenoceptor antagonist yohimbine respectively reduced the analgesic effect of taltirelin (s.c. and i.c.v.) on mechanical nociception. By contrast, the 5-HT1A receptor antagonist WAY-100635 (i.p. and i.t.) reduced the effect of taltirelin (s.c. and i.c.v.) on thermal nociception. Neither the 5-HT2 receptor antagonist ketanserin nor the opioid receptor antagonist naloxone altered the antinociceptive effect of taltirelin.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that taltirelin activates the descending noradrenergic and serotonergic pain inhibitory systems, respectively, to exert its analgesic effects on mechanical and thermal nociception.

An analog of thyrotropin-releasing hormone (TRH) is neuroprotective against glutamate-induced toxicity in fetal rat hippocampal neurons in vitro

TRH has been found to be efficacious in treating certain neurodegenerative disorders such as epilepsy, Alzheimer's disease, neurotrauma and depression, however, its mechanism of action is poorly understood. Since glutamate (Glu) toxicity has been implicated in these disorders, we utilized primary enriched cultures of rat fetal (E 17) hippocampal neurons to test the hypothesis that an analog of TRH, 3-Methyl-Histidine TRH (3Me-H TRH), given concurrently with Glu would protect such neurons against cell damage and cell death. Cell viability was assessed via Trypan Blue exclusion cell counts, and neuronal damage was determined by assaying lactic acid dehydrogenase (LDH) released in the conditioned media. Fetal hippocampal neurons were cultured in neurobasal media for 7 days. On day 7, neurons (10(6)/well) were treated with: control media, 10 microM 3Me-H TRH, 500 microM Glu or 500 microM Glu with either 10, 1, 0.1, 0.01 or 0.001 microM 3Me-H TRH. Both media and neurons were harvested 16 h after treatment. Prolonged exposure to 10 microM 3Me-H TRH was not toxic to the cells, whereas neurons exposed to 500 microM Glu resulted in maximal cell death. Notably, 10, 1 and 0.1 microM 3Me-H TRH, when co-treated with 500 microM Glu, protected fetal neurons against cell death in a concentration-dependent manner. These results provide support for an important neuroprotective effect of TRH/analogs against glutamate toxicity in primary hippocampal neuronal culture and implicate a potentially beneficial role of TRH/analogs in neurodegenerative diseases.

Evaluation of anticonvulsant and analgesic effects of benzyl- and benzhydryl ureides

The anticonvulsant effects of benzyl- and benzhydryl ureides in mice models of seizures (maximal electroshock seizure test, pentylenetetrazol test, picrotoxin-induced seizure test) and the influence on spontaneous locomotor activity has been assessed. Furthermore, the analgesic effect of ureide derivatives was studied in the hot-plate test in mice. Selected compounds were investigated for their in vitro interaction with adenosine receptors as well as the benzodiazepine binding site of GABA(A) receptors. This study demonstrated the strong anticonvulsant activity of several ureides in electrically or chemically induced seizure models, and structure-activity relationships were discussed. 1-Benzyl-3-butyrylurea (9) was found to be equipotent to ethosuximide in the pentylenetetrazol test with regard to the number of attacks as well as the time of the onset of seizures. The ureide 9 also revealed the highest protective activity against seizures in the other models, maximal electroshock seizure and picrotoxin test. Moreover, 1-benzyl-3-butyrylurea was not neurotoxic at doses up to 200 mg/kg. Benzylureides 8-10 showed affinity to the adenosine A1 receptors at low micromolar concentrations. However, the apparent anticonvulsant activity in different seizure models does not appear to result from direct activation of adenosine A1 receptors or GABA(A) receptors, respectively. In the hot-plate test, the majority of investigated compounds exhibited analgesic activity. Again, compound 9 was superior to the other substances investigated, suggesting a potential therapeutic value of that ureide derivative.

Gene profiling the response to kainic acid induced seizures

Kainic acid activates non-N-methyl-d-aspartate (NMDA) glutamate receptors where it increases synaptic activity resulting in seizures, neurodegeneration, and remodeling. We performed microarray analysis on rat hippocampal tissue following kainic acid treatment in order to study the signaling mechanisms underlying these diverse processes in an attempt to increase our current understanding of mechanisms contributing to such fundamental processes as neuronal protection and neuronal plasticity. The kainic acid-treated rats used in our array experiments demonstrated severe seizure behavior that was also accompanied by neuronal degeneration which is suggested by fluoro-jade B staining and anti-caspase-3 immunohistochemistry. The gene profile revealed 36 novel kainic acid regulated genes along with additional genes previously reported. The functional roles of these novel genes are discussed. These genes mainly have roles in transcription and to a lesser extent have roles in cell death, extracellular matrix remodeling, cell cycle progression, neuroprotection, angiogenesis, and synaptic signaling. Gene regulation was confirmed via quantitative real time polymerase chain reaction and in situ hybridization.

Thyrotropin-releasing hormone (protirelin) inhibits potassium-stimulated glutamate and aspartate release from hippocampal slices in vitro

Excess excitatory amino acid release is involved in pathways associated with seizures and neurodegeneration. Thyrotropin-releasing hormone (TRH; protirelin), a brain-derived tripeptide, has shown efficacy in the treatment of such disorders, yet its mechanism of neuroprotection is poorly understood. Using superfused hippocampal slices, we tested the hypothesis that TRH could inhibit evoked glutamate/aspartate release in vitro. Rat hippocampal slices were first equilibrated in oxygenated Krebs buffer (KRB) (120 min) then superfused for 10 min with KRB (control), or KRB containing 0.1, 1, or 10 microM TRH respectively, prior to and during 5 min depolarization with high potassium KRB (50 mM [K(+)] +/- TRH). Fractions (1 min) were collected during the 5 min stimulation and for an additional 10 min thereafter and analyzed for glutamate and aspartate by HPLC. TRH had no effect on baseline glutamate/aspartate release, while all three TRH doses significantly (P < 0.05) inhibited peak 50 mM [K(+)]-stimulated glutamate/aspartate release, and glutamate remained below control (P < 0.05) at 15 min post stimulation. A 5 min pulse of TRH (10 microM) had no affect on basal glutamate/aspartate release, whereas the TRH pre-pulsed slices failed to release glutamate/aspartate by [K(+)]-stimulation given 15 min later. These results are the first to show a potent and prolonged inhibitory effect of TRH on evoked glutamate/aspartate release in vitro. These initial studies suggest that exogenous and/or endogenous TRH may function, in part, to modulate excess glutamate release in specific CNS loci. Additional studies are in progress to fully understand the mechanism of this potent effect of TRH and its implication in various CNS disorders.

Effects of PRI-2191—A low-calcemic analog of 1,25-dihydroxyvitamin D3 on the seizure-induced changes in brain gene expression and immune system activity in the rat

Apart from the essential role of 1alpha,25-dihydroxyvitamin D3 in calcium and phosphorus metabolism, this compound and its analogs are involved in regulating the functions of the central nervous and immune systems. Active forms of vitamin D3 have been reported to stimulate neurotrophin gene expression and to prevent neuronal damage against a variety of insults. In the present study, we evaluated the effects of PRI-2191-a low-calcemic analog of 1alpha,25-dihydroxyvitamin D3 (50 ng/kg i.p., once daily for 8 days) on seizure-related neuronal degeneration, changes in some brain gene expression and immune system activity. Seizures were induced by pilocarpine (400 mg/kg; i.p.) administration. An in situ hybridization study showed that the pilocarpine-induced seizures led to time-dependent changes in the brain-derived neurotrophic factor (BDNF), heat shock protein 70 (HSP-70) and prepro-thyreoliberin (prepro-TRH) gene expression in several cortical and hippocampal regions. The maximal induction of gene expression was 3 h for BDNF and 24 h for HSP-70 and prepro-TRH; however, only in the case of prepro-TRH that effect was long-lasting. PRI-2191 alone had no effect on gene expression, but it enhanced the seizure-evoked expression of HSP-70, had an opposite effect on BDNF mRNA level and did not affect prepro-TRH mRNA level. Moreover, PRI-2191 had a moderate inhibitory effect on the seizure-related hippocampal damage in the CA1 field only. An immunological study revealed that PRI-2191 reversed the seizure-induced decrease in the proliferative activity of splenocytes and their ability to produce interferon-gamma. Summing up, the present study demonstrated that subchronic administration of PRI-2191 significantly modulated the seizure-related changes in both the brain and the peripheral immune system of rats.

Kindling and status epilepticus models of epilepsy: rewiring the brain

This review focuses on the remodeling of brain circuitry associated with epilepsy, particularly in excitatory glutamate and inhibitory GABA systems, including alterations in synaptic efficacy, growth of new connections, and loss of existing connections. From recent studies on the kindling and status epilepticus models, which have been used most extensively to investigate temporal lobe epilepsy, it is now clear that the brain reorganizes itself in response to excess neural activation, such as seizure activity. The contributing factors to this reorganization include activation of glutamate receptors, second messengers, immediate early genes, transcription factors, neurotrophic factors, axon guidance molecules, protein synthesis, neurogenesis, and synaptogenesis. Some of the resulting changes may, in turn, contribute to the permanent alterations in seizure susceptibility. There is increasing evidence that neurogenesis and synaptogenesis can appear not only in the mossy fiber pathway in the hippocampus but also in other limbic structures. Neuronal loss, induced by prolonged seizure activity, may also contribute to circuit restructuring, particularly in the status epilepticus model. However, it is unlikely that any one structure, plastic system, neurotrophin, or downstream effector pathway is uniquely critical for epileptogenesis. The sensitivity of neural systems to the modulation of inhibition makes a disinhibition hypothesis compelling for both the triggering stage of the epileptic response and the long-term changes that promote the epileptic state. Loss of selective types of interneurons, alteration of GABA receptor configuration, and/or decrease in dendritic inhibition could contribute to the development of spontaneous seizures.

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.

In vitro neuroprotection against glutamate-induced toxicity by pGlu-Glu-Pro-NH(2) (EEP)

EEP is a tripeptide structurally similar to thyrotropin releasing hormone (TRH) and, like TRH, it is found in the mammalian brain. TRH has been found to increase in brain regions after seizures and to be neuroprotective. EEP has also been shown to increase in brain regions following seizure activity. We therefore sought to determine whether the similarities between these two peptides might be extended to include neuroprotection. Both TRH and EEP were found to be neuroprotective in vitro against an excitotoxic insult. Interestingly, the two tripeptides appeared to have different mechanisms of action. Even though EEP was as much as four times more neuroprotective than TRH, its ability to reduce glutamate-stimulated increases in intraneuronal Ca(2+) was about half that of TRH.

Screening for cerebroprotective agents using an in vivo model of cerebral reversible depolarization in awake rats

The need to screen cerebroprotective compounds without anesthetic interference prompted the development of a model using hypoxic rats. In this model two outcome measures were used: (1) the time to reach isoelectric electroencephalogram (iEEG), caused by nitrogen gas inhalation in the test chamber, and (2) the time for behavioral recovery measuring the latency of restoration of the head-withdrawal reflex upon vibrissae stimulation. We report here data of blood chemistry, cerebral tissue oxygen measurements, a definition of a proposed scoring system, and the pharmacological results of RGH-2202. The findings with RGH-2202 are used here to show the utility of the screening method. Events during hypoxia: Arterial and venous pO(2), pCO(2), and pH, and brain tissue pO(2)significantly declined. Significant correlations were established among the pO(2)of cerebral tissue, blood, and the test chamber. RGH-2202 significantly and dose-dependently shortened the iEEG time; the compound's Effective Dose(30)was 227.8 mg kg(-1). Events during recovery: Immediately after the iEEG, when the atmosphere in the chamber was replaced with room air, the arterial, venous and brain tissue pO(2)increased above the control level and subsequently recovered to baseline levels. Behavioral recovery occurred before blood chemistry was otherwise normalized. RGH-2202 significantly and dose-dependently shortened the recovery time; the Effective Dose(30)was 8.71 mg kg(-1). The available data define and support the physiological basis of this practicable rat-screening model.