Effect of acute caffeine on severity of harmaline induced tremor in rats

Nabiximols (NBX) suppresses tremor in a rat Harmaline model of essential tremor

BACKGROUND

Essential tremor (ET) is one of the most prevalent movement disorders; despite this, there remains an unmet need for novel therapies. The treatment of rats with harmaline modulates the rhythmicity of inferior olivary neurons, resulting in generalized tremor with a frequency of 9-12 Hz in rats, comparable to that of human ET (4-12 Hz).

PURPOSE

Interestingly, cannabinoids reduce tremor, therefore we have assessed the cannabinoid nabiximols (NBX; marketed as Sativex) a complex botanical drug mixture, in the harmaline-rat model of ET.

METHOD

We tested the effects of acute (single dose) and subchronic (10 days) treatment of NBX (at 5.2, 10.4 and 20.8 mg kg-1 p.o.) administered prior to harmaline and acute NBX (20.8 mg kg-1) administered post-harmaline in male SD rats. Propranolol (20 mg kg-1 i.p.) was used as a positive control. Observed Scoring (OS) was carried out prior to placement in a tremor-monitoring apparatus for the calculation of Tremor Index (TI) and Motion Power Percentage (MPP).

RESULTS

Acute and subchronic NBX significantly attenuated harmaline-induced tremor at 10.4 and 20.8 mg kg-1, respectively, for each parameter (OS, TI, and MPP) when administered pre-harmaline as did propranolol (20 mg kg-1). NBX did not attenuate harmaline-induced tremor when administered post-harmaline.

CONCLUSIONS

These data suggest efficacy of acute and subchronic NBX to reduce tremors, based on OS, TI and MPP readouts if administered prior to harmaline. These data are the first to indicate the preclinical effects of an oral botanical cannabinoid formulation, NBX, in an animal model of ET.

Phytohormone abscisic acid elicits positive effects on harmaline-induced cognitive and motor disturbances in a rat model of essential tremor

OBJECTIVE

Essential tremor (ET) as a neurological disorder is accompanied by cognitive and motor disturbances. Despite the high incidence of ET, the drug treatment of ET remains unsatisfactory. Recently, abscisic acid (ABA) has been reported to have positive neurophysiological effects in mammals. Here, the effects of ABA on harmaline-induced motor and cognitive impairments were investigated in rats.

METHODS

Male Wistar rats weighing 120-140 g were divided into control, harmaline (30 mg/kg, ip), ABA vehicle (DMSO+normal saline), and ABA (10 μg/rat, icv, 30 min before harmaline injection) groups. Exploratory, balance and motor performance, anxiety, and cognitive function were assessed using footprint, open field, wire grip, rotarod, and shuttle box tests.

RESULTS

The results indicated that ABA (10 μg/rat) can improve harmaline-induced tremor in rats. The administration of ABA significantly increased time spent on wire grip and rotarod. In addition, ABA had a promising effect against the cognitive impairments induced by harmaline.

CONCLUSION

Taken together, ABA has positive effects on locomotor and cognitive impairments induced by tremor. However, further studies are required to determine the exact mechanisms of ABA on the ET.

Synthesis, in silico prediction of sites of metabolism and in-vitro hepatotoxicity evaluationofnew seriesN’-substituted 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazides

New series of 3-(1,3,7-trimethyl-xanthin-8-ylthio)propanehydrazide derivatives were designed and synthesized. The targed compounds were obtained in yields of 54 to 100% and their structures were elucidated by FTIR,1H NMR,13C NMR, MS and microanalyses.

The tested compounds were subjected to in silico prediction of sites of metabolism (SOMs). The predictions show thatthe main metabolic changes will be primarily related to oxidation of the sulfur atom in the side chain, carried out under the action of CYP2C19, as well as O-demethylation of compounds containing methoxy groups.The N-demethylation of the xanthine fragment was determined to be regulated by CYP1A2, CYP2C9, CYP2D6 and CYP3A4. Theperformed in vitro studies confirmed for two of the tested compounds to be low hepatotoxic, due to the presented prooxidant effects at subcellular level (isolated rat liver microsomes). These results highlight these molecules as promising hydrazide-hydrazone structures for the design of compounds with low hepatotoxicity.

Translational Pharmacology of PRAX-944, a Novel T-Type Calcium Channel Blocker in Development for the Treatment of Essential Tremor

Background

Essential tremor is the most common movement disorder with clear unmet need. Mounting evidence indicates tremor is caused by increased neuronal burst firing and oscillations in cerebello‐thalamo‐cortical circuitry and may be dependent on T‐type calcium channel activity. T‐type calcium channels regulate sigma band electroencephalogram (EEG) power during non‐rapid eye movement sleep, representing a potential biomarker of channel activity. PRAX‐944 is a novel T‐type calcium channel blocker in development for essential tremor.

Objectives

Using a rat tremor model and sigma‐band EEG power, we assessed pharmacodynamically‐active doses of PRAX‐944 and their translation into clinically tolerated doses in healthy participants, informing dose selection for future efficacy trials.

Methods

Harmaline‐induced tremor and spontaneous locomotor activity were used to assess PRAX‐944 efficacy and tolerability, respectively, in rats. Sigma‐power was used as a translational biomarker of T‐type calcium channel blockade in rats and, subsequently, in a phase 1 trial assessing pharmacologic activity and tolerability in healthy participants.

Results

In rats, PRAX‐944 dose‐dependently reduced tremor by 50% and 72% at 1 and 3 mg/kg doses, respectively, without locomotor side effects. These doses also reduced sigma‐power by ~30% to 50% in rats. In healthy participants, sigma‐power was similarly reduced by 34% to 50% at 10 to 100 mg, with no further reduction at 120 mg. All doses were well tolerated.

Conclusions

In rats, PRAX‐944 reduced sigma‐power at concentrations that reduced tremor without locomotor side effects. In healthy participants, comparable reductions in sigma‐power indicate that robust T‐type calcium channel blockade was achieved at well‐tolerated doses that may hold promise for reducing tremor in patients with essential tremor. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

The Pathophysiology and Treatment of Essential Tremor: The Role of Adenosine and Dopamine Receptors in Animal Models

Essential tremor (ET) is one of the most common neurological disorders that often affects people in the prime of their lives, leading to a significant reduction in their quality of life, gradually making them unable to independently perform the simplest activities. Here we show that current ET pharmacotherapy often does not sufficiently alleviate disease symptoms and is completely ineffective in more than 30% of patients. At present, deep brain stimulation of the motor thalamus is the most effective ET treatment. However, like any brain surgery, it can cause many undesirable side effects; thus, it is only performed in patients with an advanced disease who are not responsive to drugs. Therefore, it seems extremely important to look for new strategies for treating ET. The purpose of this review is to summarize the current knowledge on the pathomechanism of ET based on studies in animal models of the disease, as well as to present and discuss the results of research available to date on various substances affecting dopamine (mainly D3) or adenosine A1 receptors, which, due to their ability to modulate harmaline-induced tremor, may provide the basis for the development of new potential therapies for ET in the future.

Synthesis and preliminary hepatotoxicity evaluation of new caffeine-8-(2-thio)-propanoic hydrazid-hydrazone derivatives

New series of caffeine-8-(2-thio)-propanoic hydrazid-hydrazone derivatives were designed and synthesized. The targed compounds were obtained in yields of 51 to 96% and their structures were elucidated by FTIR,1H NMR,13C NMR, MS and microanalyses. All of the compounds were found to be “drug-like” as they fulfill the criteria of drug-likeness, which includes the MDDR-like rule. The tested compounds were subjected toin silicoprediction of substrate/metabolite specificity and Drug Induced Liver Injury (DILI). The prediction for indicated that the evaluated compounds would most probably act as CYP1A2 substrates. The performedin vitrostudies didn’t reveal statistically significant hepatotoxicity of the tested compounds, probably due to the pro-oxidant effects expressed on sub-cellular (isolated rat liver microsomes) level. The obtained experimental results confirmed the predicted low hepatotoxicity for the tested structures. Based on these results the compounds may be considered as promising structures for design of future molecules with low hepatotoxicity.

Erythropoietin ameliorates harmaline-induced essential tremor and cognition disturbances

There are conflicting reports concerning the association of motor disabilities with increased risk of mental disorders. This investigation will provide a good understanding about defining the possible association between tremor and risk of anxiety and cognitive alterations. Beside, a secondary objective of the current study was to determine the effect of erythropoietin (EPO) on harmaline-induced motor and cognitive impairments. Male Wistar rats were used for the present study. The animal model of Esential tremor (ET) was established by the intraperitoneal injection of harmaline. EPO (5000 U/kg, i.p.) administered to the animals 1 h prior to harmaline injection. Exploratory, balance, anxiety related behaviors and cognitive function were assessed using footprint, open field, wire grip, rotarod and shuttle box tests. Findings demonstrated EPO ameliorated tremor scores that was induced by harmaline. Harmaline impaired cognitive functions of the treated rats, whereas EPO showed a promising effect against the cognitive impairments induced by harmaline. EPO can be offered as a potential neuroprotective agent in the treatment of patients with ET that manifest locomotor and cognitive impairments; however, further studies are needed to clarify the exact mechanisms.

Modulation of sphingosine-1-phosphate receptor ameliorates harmaline-induced essential tremor in rat

Essential tremor (ET) is one of the most common movement disorders with unknown etiology. Despite lack of effective clinical treatments, some potential therapeutic factors and modulation of some neurotransmitters have been utilized to ameliorate motor symptoms in the animal models of tremor. In the current study, male Wistar rats (n=10 in each group) weighing 40-60g were divided into vehicle control groups (saline or DMSO), saline/DMSO+harmaline (30mg/kg, i.p.)+fingolimod (FTY720) (1mg/kg, i.p, 1h before harmaline injection) groups. Open field, rotarod, wire grip and foot print tests were used to evaluate motor function. The results demonstrated that administration of FTY720 can improve harmaline-induced tremor in rats. Moreover, FTY720 ameliorated gait disturbance. The results showed that FTY720 can recover step width, left and right step length; however, FTY720 failed to recover mobility duration. FTY720 also improved falling time and time spent in wire grip and rotarod, respectively. The current study provides the first evidence for the effectiveness of FTY720 on motor function in the harmaline model of ET. Furthermore, neuroprotective effects of FTY720 demonstrated in this study offer sphingosine-1-phosphate receptor (S1PR) modulators as a potential neuroprotective candidate against substance-induced tremor and a possible strategy for the treatment of patients with tremor.

Cannabinoid type 1 receptor antagonism ameliorates harmaline-induced essential tremor in rat

BACKGROUND AND PURPOSE

Essential tremor (ET) is a neurological disorder with unknown aetiology. Its symptoms include cerebellar motor disturbances, cognitive and personality changes, hearing and olfactory deficits. Hyperactivity of excitotoxic cerebellar climbing fibres may underlie essential tremor and has been induced in rodents by systemic harmaline administration. Cannabinoid (CB) receptor agonists can cause motor disturbances; although, there are also anecdotal reports of therapeutic benefits of cannabis in motor disorders. We set out to establish the effects of CB receptor agonism and antagonism on an established rodent model of ET using a battery of accepted behaviour assays in order to determine the risk and therapeutic potential of modulating the endocannabinoid system in ET.

EXPERIMENTAL APPROACH

Behavioural effects of systemic treatment with a CB receptor agonist (0.1, 0.5 and 1 mg kg^-1 WIN55, 212-2) or two CB₁ receptor antagonists (1 mg kg^-1  AM251 and 10 mg kg^-1 rimonabant) on tremor induced in rats by harmaline (30 mg kg^-1 ; i.p.), were assessed using tremor scoring, open field, rotarod, grip and gait tests.

KEY RESULTS

Overall, harmaline induced robust tremor that was typically worsened across the measured behavioural domains by CB receptor agonism but ameliorated by CB₁ receptor antagonism.

CONCLUSIONS AND IMPLICATIONS

These results provide the first evidence of the effects of modulating the endocannabinoid system on motor function in the harmaline model of ET. Our data suggest that CB₁ receptor manipulation warrants clinical investigation as a therapeutic approach to protection against behavioural disturbances associated with ET.

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.

The effects of caffeine on L-arginine metabolism in the brain of rats

In our study, the short-term effects of caffeine on L-arginine metabolism in the brains of rats were investigated. Caffeine was given orally at two different doses: 30 mg/kg and 100 mg/kg (a high non-toxic dose). Brain tissue arginase activity in rats from the caffeine-treated groups decreased significantly compared with the control group. Malondialdehyde (MDA) levels in the brain tissue and serum of animals in the caffeine groups also decreased significantly. Brain tissue and serum nitric oxide (NO) levels increased significantly after caffeine administration. Tumor necrosis factor-alpha (TNF-alpha) levels were also investigated in rat serum, but there was no statistically significant difference between the TNF-alpha levels of the caffeine-treated rats groups and the control rats. Our study indicates that brain arginase activity decreases after caffeine administration at doses of 30 mg/kg and 100 mg/kg. As a result, we can say that arginine induces production of NO in the organism.

Caffeine impairs short-term neurological outcome after concussive head injury in rats

OBJECTIVE

Adenosine is an endogenous neuroprotective agent that is released during ischemia, hypoxia, epilepsy, and ischemic brain injury. Caffeine is a receptor antagonist for adenosine that might interfere with the neuroprotective effect of adenosine in ischemic-hypoxic conditions. An investigation was undertaken to study the effect of caffeine on neurological function, edema formation, and blood-brain barrier permeability after experimental head injury in rats.

METHODS

Adult female Wistar rats classified into different groups received caffeine intraperitoneally at doses of 0, 50, 100, and 150 mg/kg body weight. Thirty minutes after the caffeine treatment, the animals were subjected to concussive head injury (CHI) administered by a controlled cortical impact device. Neurological severity score was recorded in each rat at 2 hours after CHI. Specific gravity, water content (as an indicator of edema), and blood-brain barrier impairment were analyzed in the cortical tissue surrounding the injury site. The levels of myeloperoxidase and malondialdehyde in the cortical region were measured as indicators of neutrophil infiltration and lipid peroxidation, respectively.

RESULTS

A significant increase in righting latency and neurological deficiency after CHI was observed in caffeine-treated rats as compared with untreated animals. Although no deaths occurred in the rats exposed to CHI after pretreatment with saline, pretreatment with caffeine caused significant mortality of animals after trauma in a dose-dependent manner. Caffeine also exacerbated neutrophil infiltration, edema, and disruption of blood-brain barrier in the traumatic cortex. Light microscopy of brain revealed more severe hemorrhage and neuronal degeneration in the injured hemisphere of caffeine-treated rats as compared with rats in the injury-alone group. A significant increase in malondialdehyde in the brain of injured rats treated with caffeine before CHI clearly indicated the role of oxidative stress.

CONCLUSION

Caffeine adversely affects outcome after CHI, possibly as a result of blockade of adenosine receptors. The findings also point toward the involvement of free radical-mediated neuronal damage in caffeine-induced exacerbation of neurotrauma.