Effects of zonisamide on experimental tremors in rats

The Application of Zonisamide to Patients Suffering from Dementia with Lewy Bodies: Emerging Clinical Data

Zonisamide is an anti-epileptic medication with multiple mechanisms of action and a favorable safety profile. Zonisamide may interact with Lewy body dementia pathophysiology through a mechanism unrelated to its original indication. Zonisamide has shown efficacy as adjunct therapy for the management of motor symptoms in patients with Parkinson's disease (PD). Given that dementia with Lewy bodies (DLB) and PD are considered subtypes of a Lewy body disease spectrum, zonisamide was investigated for the treatment of parkinsonism in DLB. Phase II and phase III clinical trials were conducted in patients with DLB in Japan. In both studies, participants were randomized to receive 12 weeks of zonisamide 25 or 50 mg/day or placebo. Zonisamide significantly improved the Unified Parkinson's Disease Rating Scale Part III (UPDRS-III) without affecting the Mini-Mental State Examination (MMSE) or Neuropsychiatry Inventory-10 (NPI-10) scores at week 12. In 2018, zonisamide received Japanese regulatory approval for the additional indication of parkinsonism in DLB. This review discusses the emerging clinical data on zonisamide in the field of DLB.

Potential mechanisms of tremor tolerance induced in rats by the repeated administration of total alkaloid extracts from the seeds of Peganum harmala Linn

ETHNOPHARMACOLOGICAL RELEVANCE

The seeds of Peganum harmala Linn have been widely used for the treatment of nervous, cardiovascular, gastrointestinal, respiratory, and endocrine diseases and many other human ailments. However, tremor toxicity occurs after overdose and is tolerated following multiple dosing. Thus far, little is known about the underlying mechanisms of tremors and tremor tolerance.

AIM OF THE STUDY

To investigate the potential mechanisms of tremors and tremor tolerance induced in rats by the repeated administration of total alkaloid extracts from the seeds of P. harmala (TAEP).

MATERIALS AND METHODS

A tremor model was induced in male Wistar rats by administering TAEP at a dose of 150 mg/kg/day. To evaluate tremor action, behavioral assessment was conducted by using a custom-built tremor acquisition and analysis system. To investigate the relationships between tremors and neurotransmitter levels in the brain, various neurotransmitters were simultaneously quantified by an ultra-performance liquid chromatography combined with electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) system, and the association between these two parameters was analyzed using Pearson correlation coefficients. To further elucidate the potential mechanisms of the alterations of neurotransmitter levels in cortical tissues, the protein expression levels of several important enzymes and transporters that are closely related to neurotransmitter levels were investigated. In addition, neuropathological analysis was conducted to assess the effect of TAEP on neurons in the brain. To further clarify the potential mechanisms of TAEP-induced neurodegeneration in the brain, c-fos was subjected to immunohistochemical analysis, and oxidative stress markers were examined.

RESULTS

Tremors initially occurred in rats after the oral administration of TAEP at a dose of 150 mg/kg/day. However, they were tolerated following repeated dosing. The levels of 5-hydroxytryptamine (5-HT) and glycine (Gly) in cortical tissues were most likely associated with the tremor response. Tremor tolerance also likely resulted from the degeneration of cerebellar Purkinje cells. Furthermore, the alteration of 5-HT levels was mainly attributed to the downregulated expression of monoamine oxidase A (MAO-A). The degeneration of Purkinje neurons might have resulted from the overexpression of c-fos and increased oxidative stress in the cerebellum after the multiple dosing of TAEP.

CONCLUSION

The tremor response induced by TAEP at high doses is closely related to the concentrations of 5-HT and Gly in cortical tissues. Tremor tolerance may also be attributed to the degeneration of cerebellar Purkinje cells after the repeated dosing of TAEP. Further studies should be conducted to elucidate the interaction of the alkaloids on the neurotransmitter receptors, the expression of related neurotransmitter receptors, the specific signaling pathway involved in regulating MAO-A, and the mechanism of the loss and functional recovery of cerebellar Purkinje neurons.

A mechanistic approach to explore the neuroprotective potential of zonisamide in seizures

BACKGROUND

Epilepsy, a disease of the brain, is one of the most common serious neurological conditions. It is associated with a group of processes which alter energy metabolism, interrupt cellular ionic homeostasis, cause receptor dysfunction, activate inflammatory cascade, alter neurotransmitter uptake and result in neuronal damage. The increasing knowledge and understanding about the basis of neuronal changes in epilepsy lead to investigate the mechanistic pathway of neuroprotective agents in epilepsy. With this background, the present study is designed to reveal the molecular and biochemical mechanisms involved in the neuroprotective potential of zonisamide in epilepsy.

METHODS

Seizure-induced neuronal damage was produced by maximal electroshock seizures in animals. The oxidative stress and neuroinflammatory and apoptotic markers were assessed in the brain tissue of animals.

RESULTS AND DISCUSSION

The present findings revealed that zonisamide treatment prevented the development of seizures in animals. Seizures-induced free radicals production and neuroinflammation were markedly ameliorated by zonisamide administration. In conclusion, the present study demonstrated the mechanisms behind the strong neuroprotective potential of zonisamide against seizures by attenuating the oxidative stress, inflammatory cascade and neuronal death associated with progression of seizures. It can be further developed as a neuroprotective agent for epilepsy and other neurodegenerative disorders.

Zonisamide attenuates lactacystin-induced parkinsonism in mice without affecting system xc<sup/>

Zonisamide (ZNS), an anticonvulsant drug exhibiting symptomatic effects in Parkinson's disease (PD), was recently reported to exert neuroprotection in rodent models. One of the proposed neuroprotective mechanisms involves increased protein expression of xCT, the specific subunit of the cystine/glutamate antiporter system x_c^-, inducing glutathione (GSH) synthesis. Here, we investigated the outcome of ZNS treatment in a mouse model of PD based on intranigral proteasome inhibition, and whether the observed effects would be mediated by system x_c^-. The proteasome inhibitor lactacystin (LAC) was administered intranigrally to male C57BL/6J mice receiving repeated intraperitoneal injections of either ZNS 30mgkg^-1 or vehicle. Drug administration was initiated three days prior to stereotaxic LAC injection and was maintained until six days post-surgery. One week after lesion, mice were behaviorally assessed and investigated in terms of nigrostriatal neurodegeneration and molecular changes at the level of the basal ganglia, including expression levels of xCT. ZNS reduced the loss of nigral dopaminergic neurons following LAC injection and the degree of sensorimotor impairment. ZNS failed, however, to modulate xCT expression in basal ganglia of lesioned mice. In a separate set of experiments, the impact of ZNS treatment on system x_c^- was investigated in control conditions in vivo as well as in vitro. Similarly, ZNS did not influence xCT or glutathione levels in naive male C57BL/6J mice, nor did it alter system x_c^- activity or glutathione content in vitro. Taken together, these results demonstrate that ZNS treatment provides neuroprotection and behavioral improvement in a PD mouse model based on proteasome inhibition via system x_c^- independent mechanisms.

Anatomical localization of Cav3.1 calcium channels and electrophysiological effects of T-type calcium channel blockade in the motor thalamus of MPTP-treated monkeys

Conventional anti-Parkinsonian dopamine replacement therapy is often complicated by side effects that limit the use of these medications. There is a continuing need to develop nondopaminergic approaches to treat Parkinsonism. One such approach is to use medications that normalize dopamine depletion-related firing abnormalities in the basal ganglia-thalamocortical circuitry. In this study, we assessed the potential of a specific T-type calcium channel blocker (ML218) to eliminate pathologic burst patterns of firing in the basal ganglia-receiving territory of the motor thalamus in Parkinsonian monkeys. We also carried out an anatomical study, demonstrating that the immunoreactivity for T-type calcium channels is strongly expressed in the motor thalamus in normal and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. At the electron microscopic level, dendrites accounted for >90% of all tissue elements that were immunoreactive for voltage-gated calcium channel, type 3.2-containing T-type calcium channels in normal and Parkinsonian monkeys. Subsequent in vivo electrophysiologic studies in awake MPTP-treated Parkinsonian monkeys demonstrated that intrathalamic microinjections of ML218 (0.5 μl of a 2.5-mM solution, injected at 0.1-0.2 μl/min) partially normalized the thalamic activity by reducing the proportion of rebound bursts and increasing the proportion of spikes in non-rebound bursts. The drug also attenuated oscillatory activity in the 3-13-Hz frequency range and increased gamma frequency oscillations. However, ML218 did not normalize Parkinsonism-related changes in firing rates and oscillatory activity in the beta frequency range. Whereas the described changes are promising, a more complete assessment of the cellular and behavioral effects of ML218 (or similar drugs) is needed for a full appraisal of their anti-Parkinsonian potential.

Effects of cabergoline and rotigotine on tacrine-induced tremulous jaw movements in rats

OBJECTIVES

We examined the effects of two dopamine agonists, cabergoline and rotigotine, on tacrine-induced tremor and c-Fos expression in rats.

METHODS

Rats received intraperitoneal injection of cabergoline (0.5, 1.0, or 5.0mg/kg), rotigotine (1.0, 2.5, or 10.0mg/kg), or vehicle 30min before intraperitoneal injection of tacrine (5.0mg/kg). The number of tremulous jaw movements (TJMs) after tacrine administration was counted for 5min. Animals were sacrificed 2h later under deep anesthesia, and the brain sections were immunostained in order to evaluate the c-Fos expression.

RESULTS

Induction of TJMs by tacrine was dose-dependently reduced by pretreatment with cabergoline and rotigotine. The number of c-Fos-positive cells was significantly enhanced in the medial striatum, nucleus accumbens core, and nucleus accumbens shell after tacrine administration, and the enhanced expression of c-Fos in these three regions was significantly attenuated by cabergoline, while rotigotine suppressed c-Fos expression in two regions except the nucleus accumbens core.

CONCLUSIONS

These results suggest that tacrine-induced TJMs would be relieved by either cabergoline or rotigotine and that anticholinesterase-induced TJMs and the ameliorating effects of dopamine agonists would relate to neuronal activation in the striatum and nucleus accumbens.

Harmaline tremor: underlying mechanisms in a potential animal model of essential tremor

BACKGROUND

Harmaline and harmine are tremorigenic β-carbolines that, on administration to experimental animals, induce an acute postural and kinetic tremor of axial and truncal musculature. This drug-induced action tremor has been proposed as a model of essential tremor. Here we review what is known about harmaline tremor.

METHODS

Using the terms harmaline and harmine on PubMed, we searched for papers describing the effects of these β-carbolines on mammalian tissue, animals, or humans.

RESULTS

Investigations over four decades have shown that harmaline induces rhythmic burst-firing activity in the medial and dorsal accessory inferior olivary nuclei that is transmitted via climbing fibers to Purkinje cells and to the deep cerebellar nuclei, then to brainstem and spinal cord motoneurons. The critical structures required for tremor expression are the inferior olive, climbing fibers, and the deep cerebellar nuclei; Purkinje cells are not required. Enhanced synaptic norepinephrine or blockade of ionic glutamate receptors suppresses tremor, whereas enhanced synaptic serotonin exacerbates tremor. Benzodiazepines and muscimol suppress tremor. Alcohol suppresses harmaline tremor but exacerbates harmaline-associated neural damage. Recent investigations on the mechanism of harmaline tremor have focused on the T-type calcium channel.

DISCUSSION

Like essential tremor, harmaline tremor involves the cerebellum, and classic medications for essential tremor have been found to suppress harmaline tremor, leading to utilization of the harmaline model for preclinical testing of antitremor drugs. Limitations are that the model is acute, unlike essential tremor, and only approximately half of the drugs reported to suppress harmaline tremor are subsequently found to suppress tremor in clinical trials.

T-type calcium channel as a new therapeutic target for tremor

Voltage-gated calcium channels play an important role in many physiological and pathological processes. Accumulating studies suggest that the T-type calcium channel is a potential target for the treatment of various neurological disorders, such as epilepsy, insomnia, and neuropathic pain. Here, we highlight recent advances in our understanding of T-type calcium channel regulation and their implications for tremor disorders. Several T-type calcium channel blockers effectively suppressed experimental tremors that have been suggested to originate from either the cerebellum or basal ganglia. Among T-type calcium channel blockers that have been used clinically, the anti-tremor efficacy of zonisamide garnered our attention. Based on both basic and clinical studies, the possibility is emerging that T-type calcium channel blockers that transit into the central nervous system may have therapeutic potentials for tremor disorders.

Pharmacological and physiological characterization of the tremulous jaw movement model of parkinsonian tremor: potential insights into the pathophysiology of tremor

Tremor is a cardinal symptom of parkinsonism, occurring early on in the disease course and affecting more than 70% of patients. Parkinsonian resting tremor occurs in a frequency range of 3-7 Hz and can be resistant to available pharmacotherapy. Despite its prevalence, and the significant decrease in quality of life associated with it, the pathophysiology of parkinsonian tremor is poorly understood. The tremulous jaw movement (TJM) model is an extensively validated rodent model of tremor. TJMs are induced by conditions that also lead to parkinsonism in humans (i.e., striatal DA depletion, DA antagonism, and cholinomimetic activity) and reversed by several antiparkinsonian drugs (i.e., DA precursors, DA agonists, anticholinergics, and adenosine A(2A) antagonists). TJMs occur in the same 3-7 Hz frequency range seen in parkinsonian resting tremor, a range distinct from that of dyskinesia (1-2 Hz), and postural tremor (8-14 Hz). Overall, these drug-induced TJMs share many characteristics with human parkinsonian tremor, but do not closely resemble tardive dyskinesia. The current review discusses recent advances in the validation of the TJM model, and illustrates how this model is being used to develop novel therapeutic strategies, both surgical and pharmacological, for the treatment of parkinsonian resting tremor.

Oral tremor induced by galantamine in rats: a model of the parkinsonian side effects of cholinomimetics used to treat Alzheimer's disease

Anticholinesterases are the most common treatment for Alzheimer's disease, and, in recent years, a new group of cholinesterase inhibitors (i.e. rivastigmine, galantamine, and donepezil) has become available. Although these drugs improve cognitive symptoms, they also can induce or exacerbate parkinsonian symptoms, including tremor. The present studies were conducted to determine if galantamine induces tremulous jaw movements, a rodent model of parkinsonian tremor, and to investigate whether these oral motor impairments can be reversed by co-administration of adenosine A(2A) antagonists. The first experiment demonstrated that systemic injections of galantamine (0.75-6.0 mg/kg I.P.) induced a dose-related increase in tremulous jaw movements in rats. In a second study, co-administration of the muscarinic antagonist scopolamine (0.0156-0.25 mg/kg I.P.) produced a dose dependent suppression of tremulous jaw movements induced by a 3.0 mg/kg dose of galantamine, indicating that galantamine induces these tremulous oral movements through actions on muscarinic acetylcholine receptors. In two additional studies, analyses of freeze-frame video and electromyographic activity recorded from the lateral temporalis muscle indicated that the local frequency of these galantamine-induced jaw movements occurs in the 3-7 Hz frequency range that is characteristic of parkinsonian tremor. In the final experiment, the adenosine A(2A) antagonist MSX-3 significantly attenuated the tremulous jaw movements induced by the 3.0mg/kg dose of galantamine, which is consistent with the hypothesis that co-administration of adenosine A(2A) antagonists may be beneficial in reducing parkinsonian motor impairments induced by anticholinesterase treatment.

Diagnosis and treatment of common forms of tremor

Tremor is the most common movement disorder presenting to an outpatient neurology practice and is defined as a rhythmical, involuntary oscillatory movement of a body part. The authors review the clinical examination, classification, and diagnosis of tremor. The pathophysiology of the more common forms of tremor is outlined, and treatment options are discussed. Essential tremor is characterized primarily by postural and action tremors, may be a neurodegenerative disorder with pathologic changes in the cerebellum, and can be treated with a wide range of pharmacologic and nonpharmacologic methods. Tremor at rest is typical for Parkinson's disease, but may arise independently of a dopaminergic deficit. Enhanced physiologic tremor, intention tremor, and dystonic tremor are discussed. Further differential diagnoses described in this review include drug- or toxin-induced tremor, neuropathic tremor, psychogenic tremor, orthostatic tremor, palatal tremor, tremor in Wilson's disease, and tremor secondary to cerebral lesions, such as Holmes' tremor (midbrain tremor). An individualized approach to treatment of tremor patients is important, taking into account the degree of disability, including social embarrassment, which the tremor causes in the patient's life.

T-type calcium channel antagonists suppress tremor in two mouse models of essential tremor

Essential tremor is a common disorder that lacks molecular targets for therapeutic development. T-type calcium channel activation has been postulated to underlie rhythmicity in the olivo-cerebellar system that is implicated in essential tremor. We therefore tested whether compounds that antagonize T-type calcium channel currents suppress tremor in two mouse models that possess an essential tremor-like pharmacological response profile. Tremor was measured using digitized spectral motion power analysis with harmaline-induced tremor and in the GABA(A) receptor α1 subunit-null model. Mice were given ethosuximide, zonisamide, the neuroactive steroid (3β,5α,17β)-17-hydroxyestrane-3-carbonitrile (ECN), the 3,4-dihydroquinazoline derivative KYS05064, the mibefradil derivative NNC 55-0396, or vehicle. In non-sedating doses, each compound reduced harmaline-induced tremor by at least 50% (range of maximal suppression: 53-81%), and in the GABA(A) α1-null model by at least 70% (range 70-93%). Because the T-type calcium channel Cav3.1 is the dominant subtype expressed in the inferior olive, we assessed the tremor response of Cav3.1-deficient mice to harmaline, and found that null and heterozygote mice exhibit as much tremor as wild-type mice. In addition, ECN and NNC 55-0396 suppressed harmaline tremor as well in Cav3.1-null mice as in wild-type mice. The finding that five T-type calcium antagonists suppress tremor in two animal tremor models suggests that T-type calcium channels may be an appropriate target for essential tremor therapy development. It is uncertain whether medications developed to block only the Cav3.1 subtype would exhibit efficacy.

[The discovery of an antiparkinsonian drug, zonisamide]

We serendipitously found that zonisamide (ZNS), an antiepileptic agent, has beneficial effects on Parkinson disease. A 25 mg once a day of ZNS (200-600 mg/day for epilepsy), significantly improves motor function of advanced patients with Parkinson disease. Its effects maintained at least one year even in patients with advanced stage. It was finally approved as an anti parkinsonian agent in Japan on January 2009. As the mechanism of antiparkinsonian effects of ZNS, we showed that ZNS increases dopamine contents in the striatum by activating dopamine synthesis through increasing the levels of tyrosine hydroxylase (TH) mRNA and TH protein. It moderately inhibits monoamine oxydase (MAO) activity. ZNS shows significant inhibition on T-type Ca++ channel. It may also affect the beneficial effects of ZNS on Parkinson disease. ZNS also showed neuroprotective effects on several parkinsonian models. It markedly inhibited quinoprotein formation and increased the level of glutathione by enhancing the astroglial cystine transport system and/or astroglial proliferation through S100beta. We will verify the neuroprotective effects of ZNS on patients with Parkinson disease and study the factors responsible for the individual difference of the effects of ZNS by using genome wide association study (GWAS) in the near feature.

Oral tremor induced by the muscarinic agonist pilocarpine is suppressed by the adenosine A2A antagonists MSX-3 and SCH58261, but not the adenosine A1 antagonist DPCPX

Tremulous jaw movements in rats, which can be induced by dopamine (DA) antagonists, DA depletion, and cholinomimetics, have served as a useful model for studies of tremor. Although adenosine A(2A) antagonists can reduce the tremulous jaw movements induced by DA antagonists and DA depletion, there are conflicting reports about the interaction between adenosine antagonists and cholinomimetic drugs. The present studies investigated the ability of adenosine antagonists to reverse the tremorogenic effect of the muscarinic agonist pilocarpine. While the adenosine A(2A) antagonist MSX-3 was incapable of reversing the tremulous jaw movements induced by the 4.0mg/kg dose of pilocarpine, both MSX-3 and the adenosine A(2A) antagonist SCH58261 reversed the tremulous jaw movements elicited by 0.5mg/kg pilocarpine. Systemic administration of the adenosine A(1) antagonist DPCPX failed to reverse the tremulous jaw movements induced by either an acute 0.5mg/kg dose of the cholinomimetic pilocarpine or the DA D2 antagonist pimozide, indicating that the tremorolytic effects of adenosine antagonists may be receptor subtype specific. Behaviorally active doses of MSX-3 and SCH 58261 showed substantial in vivo occupancy of A(2A) receptors, but DPCPX did not. The results of these studies support the use of adenosine A(2A) antagonists for the treatment of tremor.

Effects of zonisamide on isolated head tremor

BACKGROUND AND PURPOSE

The medical treatment available for patients with essential tremor (ET) is often inadequate. Furthermore, the efficacy of the medical treatments currently available for patients with ET of cranial nerve areas is less satisfactory than that of the medical treatments available for patients with ET involving the upper extremities. This pilot study was performed to evaluate whether zonisamide (ZNS) is effective in the treatment of patients with isolated head tremor.

METHODS

All subjects with isolated head tremor were randomly treated with either ZNS or propranolol. After a washout period, the subjects were switched to the alternative drug.

RESULTS

ZNS was found to be more effective in the treatment of patients with isolated head tremor than propranolol. No severe adverse effects were reported with either ZNS or propranolol.

CONCLUSION

ZNS may be more useful than propranolol for the treatment of ET patients with head tremor.

Effects of zonisamide on c-Fos expression under conditions of tacrine-induced tremulous jaw movements in rats: a potential mechanism underlying its anti-parkinsonian tremor effect

OBJECTIVES

To examine the mechanisms underlying the anti-tremor effect of zonisamide in rats under conditions of tacrine-induced tremulous jaw movements (TJMs).

METHODS

Male adult rats received systemic administration of either zonisamide (5 or 50mg/kg) or vehicle at 20min prior to the administration of tacrine hydrochloride (5mg/kg). Animals were sacrificed 2h later, and the brains collected and immunostained for quantitative assessment of c-Fos expression.

RESULTS

There was no effect of zonisamide on tacrine-induced c-Fos expression in the ventrolateral striatum, a primary site of the pharmacological action of tacrine. Zonisamide suppressed the tacrine-induced c-Fos expression in the cortex, the dorsal striatum, and the nucleus accumbens, which are involved in the architecture of the cortico-basal ganglia-thalamocortical circuits.

CONCLUSION

The anti-TJM effect of zonisamide may not relate to suppression of neural activity specifically in primary tremor-generating sites, but may be due to a more broad inhibitory effect on tremor-related structures such as the cortex or the striatum. This effect of zonisamide may be a contributing mechanism underlying its therapeutic efficacy on parkinsonian tremor.