Effects of caffeine on the freezing of gait in Parkinson's disease

Allosteric Interactions between Adenosine A2A and Dopamine D2 Receptors in Heteromeric Complexes: Biochemical and Pharmacological Characteristics, and Opportunities for PET Imaging

Adenosine and dopamine interact antagonistically in living mammals. These interactions are mediated via adenosine A_2A and dopamine D₂ receptors (R). Stimulation of A_2AR inhibits and blockade of A_2AR enhances D₂R-mediated locomotor activation and goal-directed behavior in rodents. In striatal membrane preparations, adenosine decreases both the affinity and the signal transduction of D₂R via its interaction with A_2AR. Reciprocal A_2AR/D₂R interactions occur mainly in striatopallidal GABAergic medium spiny neurons (MSNs) of the indirect pathway that are involved in motor control, and in striatal astrocytes. In the nucleus accumbens, they also take place in MSNs involved in reward-related behavior. A_2AR and D₂R co-aggregate, co-internalize, and co-desensitize. They are at very close distance in biomembranes and form heteromers. Antagonistic interactions between adenosine and dopamine are (at least partially) caused by allosteric receptor–receptor interactions within A_2AR/D₂R heteromeric complexes. Such interactions may be exploited in novel strategies for the treatment of Parkinson’s disease, schizophrenia, substance abuse, and perhaps also attention deficit-hyperactivity disorder. Little is known about shifting A_2AR/D₂R heteromer/homodimer equilibria in the brain. Positron emission tomography with suitable ligands may provide in vivo information about receptor crosstalk in the living organism. Some experimental approaches, and strategies for the design of novel imaging agents (e.g., heterobivalent ligands) are proposed in this review.

Current Perspectives on the Assessment and Management of Gait Disorders in Parkinson's Disease

Gait dysfunction is a key defining feature of Parkinson's disease (PD), and is associated with symptoms of freezing and an increased risk of falls. In this narrative review, we cover the putative mechanisms of gait dysfunction in PD, the assessment of gait abnormalities, and the management of symptoms caused by the inherent difficulty in walking. Our understanding of the causes of gait problems in PD has progressed in recent times, moving from neurocognitive theory to correlates of affected neuronal pathways. In particular, this can be shown to correspond with abnormalities in responses to dual-task paradigms and dysfunction in cholinergic signaling. Great progress has been made in the sophistication and precision of gait assessment; however, it has firmly remained in the research domain. There is significant momentum behind wearable technologies that can be used by patients in their own environment, acting as digital biomarkers that can not only reflect progression but also independently discriminate PD from non-PD individuals. The treatment of gait dysfunction has historically relied on physical therapies and training combined with a view to mitigating the impact of such consequences as falls. Pharmacological therapies that are the mainstay of treatment in PD have tended to address symptoms like bradykinesia; however, optimization of dopaminergic therapies likely has a positive effect on quality of gait. Other targets have been assessed with the goal of improving gait, of which medications that improve cholinergic signaling appear most promising. Neuromodulation techniques are increasingly used in the form of deep-brain stimulation; however, standard targets, such as the globus pallidus interna, have a modest effect on gait. Considerable benefit has been seen through targeting the pedunculopontine nucleus, and a dual-target approach may be warranted. Stimulation of the spinal cord and brain through direct or magnetic approaches has been assessed, but requires further evidence.

How do adenosine A2A receptors regulate motor function?

Adenosine A_2A receptor antagonism is a new therapeutic strategy in the symptomatic treatment of Parkinson's disease (PD). This review addresses how adenosine A_2A receptors are involved with the control of motor function via the basal ganglia-thalamocortical circuit, and considers the anatomical localization and physiological function of the receptor, along with its ultrastructural localization in critical areas/neurons of the circuit. Based on this understanding of the functional significance of the adenosine A_2A receptor in the basal ganglia, the mode of action of A_2A receptor antagonists is explored in terms of the dynamic functioning of the basal ganglia and the activity of the internal circuits of the striatum in PD. Finally, the pathophysiological differences between the normal and PD states are examined to emphasize the importance of the adenosine A_2A receptor.

Neuroprotective and Neurodegenerative Aspects of Coffee and Its Active Ingredients in View of Scientific Literature

Coffee and its components have several neuroprotective properties that lower the risk of cognitive decline and other neurodegenerative diseases. This study reviews the mechanisms by which coffee and its respective compounds affect the brain and its pathologies. Many epidemiological studies in this literature review have shown coffee to reduce the risk of developing dementia, stroke, and Alzheimer's disease. It may also have a positive impact on the disease course of amyotrophic lateral sclerosis, Parkinson's disease, and depression. The optimal benefits achieved from coffee in these pathologies rely on higher daily doses. Most of its effects are attributed to caffeine by the antagonism of adenosine receptors in the central nervous system; however, other coffee constituents like chlorogenic acids have also shown much promise in therapeutic value. Existing research considers coffee to have great potential, but additional studies are still needed to clarify the mechanisms and actual causal relationships in certain neuropathologies.

Freezing of gait in Parkinson's disease: pathophysiology, risk factors and treatments

Background

Freezing of gait (FOG) is a common, disabling symptom of Parkinson's disease (PD), but the mechanisms and treatments of FOG remain great challenges for clinicians and researchers. The main focus of this review is to summarize the possible mechanisms underlying FOG, the risk factors for screening and predicting the onset of FOG, and the clinical trials involving various therapeutic strategies. In addition, the limitations and recommendations for future research design are also discussed.

Main body

In the mechanism section, we briefly introduced the physiological process of gait control and hypotheses about the mechanism of FOG. In the risk factor section, gait disorders, PIGD phenotype, lower striatal DAT uptake were found to be independent risk factors of FOG with consistent evidence. In the treatment section, we summarized the clinical trials of pharmacological and non-pharmacological treatments. Despite the limited effectiveness of current medications for FOG, especially levodopa resistant FOG, there were some drugs that showed promise such as istradefylline and rasagiline. Non-pharmacological treatments encompass invasive brain and spinal cord stimulation, noninvasive repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) and vagus nerve stimulation (VNS), and physiotherapeutic approaches including cues and other training strategies. Several novel therapeutic strategies seem to be effective, such as rTMS over supplementary motor area (SMA), dual-site DBS, spinal cord stimulation (SCS) and VNS. Of physiotherapy, wearable cueing devices seem to be generally effective and promising.

Conclusion

FOG model hypotheses are helpful for better understanding and characterizing FOG and they provide clues for further research exploration. Several risk factors of FOG have been identified, but need combinatorial optimization for predicting FOG more precisely. Although firm conclusions cannot be drawn on therapeutic efficacy, the literature suggested that some therapeutic strategies showed promise.

Efficacy of istradefylline for gait disorders with freezing of gait in Parkinson's disease: A single-arm, open-label, prospective, multicenter study

Background: Gait disorders are common in Parkinson's disease patients who respond poorly to dopaminergic treatment. Blockade of adenosine A_2A receptors is expected to improve gait disorders. Istradefylline is a first-in-class selective adenosine A_2A receptor antagonist with benefits for motor complications associated with Parkinson's disease. Research design and methods: This multicenter, open-label, single-group, prospective interventional study evaluated changes in total gait-related scores of the Part II/III Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and Freezing of Gait Questionnaire (FOG-Q) in 31 Parkinson's disease patients treated with istradefylline. Gait analysis by portable gait rhythmogram was performed. Results: MDS-UPDRS Part III gait-related total scores significantly decreased at Weeks 4-12 from baseline with significant improvements in gait, freezing of gait, and postural stability. Significant decreases in MDS-UPDRS Part II total scores and individual item scores at Week 12 indicated improved daily living activities. At Week 12, there were significant improvements in FOG-Q, new FOG-Q, and overall movement per 48 h measured by portable gait rhythmogram. Adverse events occurred in 7/31 patients. Conclusions: Istradefylline improved gait disorders in Parkinson's disease patients complicated with freezing of gait, improving their quality of life. No unexpected adverse drug reactions were identified. Trial registration: UMIN-CTR (UMIN000020288).

The Impact of Coffee and Caffeine on Multiple Sclerosis Compared to Other Neurodegenerative Diseases

Background: The literature concerning the effect of coffee and caffeine on Multiple Sclerosis (MS) with focus on fatigue is investigated in this review. Potentially clinically relevant effects were also assessed in studies concerning comparable neurodegenerative diseases, such as Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS). Since the existing studies obtained very inconclusive results, we systematically reviewed these studies to summarize the evidence on the possible effects of coffee and caffeine on those disease entities. Previous studies suggested that coffee and caffeine intake is associated with a reduced risk of developing MS and other neurological diseases.

Methods: The PubMed database was searched using the keywords “coffee” OR “caffeine” in combination with keywords for each of the different diseases. Besides the keyword search, we included studies by reference list search. Studies on the effects of coffee and caffeine on the single neurological diseases were included for this review. A total of 51 articles met our inclusion criteria. The reviewed articles assessed the impact of coffee and caffeine on the susceptibility for neurological diseases, as well as the effect of coffee and caffeine on disease progression and possible symptomatic effects like on performance enhancement.

Results: Higher intake of coffee and caffeine was associated with a lower risk of developing PD. In some of the MS studies there, is evidence for a similar effect and experimental studies confirmed the positive impact. Interestingly in MS coffee and caffeine may have a stronger impact on disease course compared to effects on disease susceptibility. In ALS no such beneficial effect could be observed in the clinical and experimental studies.

Conclusion: This literature assessment revealed that coffee and especially caffeine could have a preventative role in the development of several neurodegenerative diseases if provided in comparatively high doses. The systematic assessment indicates that coffee and caffeine intake must not be considered as a health risk. Additional clinical studies are needed to fully understand how far coffee and caffeine intake should be considered as a potential therapeutic approach for certain disease entities and conditions.

Freezing of gait: Promising avenues for future treatment

Freezing of gait is a devastating symptom of Parkinson's disease and other forms of parkinsonism. It poses a major burden on both patients and their families, as freezing often leads to falls, fall-related injuries and a loss of independence. Treating freezing of gait is difficult for a variety of reasons: it has a paroxysmal and unpredictable nature; a multifaceted pathophysiology, with an interplay between motor elements (disturbed stepping mechanisms) and non-motor elements (cognitive decline, anxiety); and a complex (and likely heterogeneous) underlying neural substrate, involving multiple failing neural networks. In recent years, advances in translational neuroscience have offered new insights into the pathophysiology underlying freezing. Furthermore, the mechanisms behind the effectiveness of available treatments (or lack thereof) are better understood. Driven by these concepts, researchers and clinicians have begun to improve currently available treatment options, and develop new and better treatment methods. Here, we evaluate the range of pharmacological (i.e. closed-looped approaches), surgical (i.e. multi-target and adaptive deep brain and spinal cord stimulation) and behavioural (i.e. biofeedback and cueing on demand) treatment options that are under development, and propose novel avenues that are likely to play a crucial role in the clinical management of freezing of gait in the near future. The outcomes of this review suggest that the successful future management of freezing of gait will require individualized treatments that can be implemented in an on-demand manner in response to imminent freezing. With this review we hope to guide much-needed advances in treating this devastating symptom of Parkinson's disease.

Serum caffeine and metabolites are reliable biomarkers of early Parkinson disease

Objective

To investigate the kinetics and metabolism of caffeine in serum from patients with Parkinson disease (PD) and controls using liquid chromatography–mass spectrometry.

Methods

Levels of caffeine and its 11 metabolites in serum from 108 patients with PD and 31 age-matched healthy controls were examined by liquid chromatography–mass spectrometry. Mutations in caffeine-associated genes were screened by direct sequencing.

Results

Serum levels of caffeine and 9 of its downstream metabolites were significantly decreased even in patients with early PD, unrelated to total caffeine intake or disease severity. No significant genetic variations in CYP1A2 or CYP2E1, encoding cytochrome P450 enzymes primarily involved in metabolizing caffeine in humans, were detected compared with controls. Likewise, caffeine concentrations in patients with PD with motor complications were significantly decreased compared with those without motor complications. No associations between disease severity and single nucleotide variants of the ADORA2A gene encoding adenosine 2A receptor were detected, implying a dissociation of receptor sensitivity changes and phenotype. The profile of serum caffeine and metabolite levels was identified as a potential diagnostic biomarker by receiver operating characteristic curve analysis.

Conclusion

Absolute lower levels of caffeine and caffeine metabolite profiles are promising diagnostic biomarkers for early PD. This is consistent with the neuroprotective effect of caffeine previously revealed by epidemiologic and experimental studies.

Classification of evidence

This study provides Class III evidence that decreased serum levels of caffeine and its metabolites identify patients with PD.

The emerging science of precision medicine and pharmacogenomics for Parkinson's disease

Current therapies for Parkinson's disease are problematic because they are symptomatic and have adverse effects. New drugs have failed in clinical trials because of inadequate efficacy. At the core of the problem is trying to make one drug work for all Parkinson's disease patients, when we know this premise is wrong because (1) Parkinson's disease is not a single disease, and (2) no two individuals have the same biological makeup. Precision medicine is the goal to strive for, but we are only at the beginning stages of building the infrastructure for one of the most complex projects in the history of science, and it will be a long time before Parkinson's disease reaps the benefits. Pharmacogenomics, a cornerstone of precision medicine, has already proven successful for many conditions and could also propel drug discovery and improve treatment for Parkinson's disease. To make progress in the pharmacogenomics of Parkinson's disease, we need to change course from small inconclusive candidate gene studies to large-scale rigorously planned genome-wide studies that capture the nuclear genome and the microbiome. Pharmacogenomic studies must use homogenous subtypes of Parkinson's disease or apply the brute force of statistical power to overcome heterogeneity, which will require large sample sizes achievable only via internet-based methods and electronic databases. Large-scale pharmacogenomic studies, together with biomarker discovery efforts, will yield the knowledge necessary to design clinical trials with precision to alleviate confounding by disease heterogeneity and interindividual variability in drug response, two of the major impediments to successful drug discovery and effective treatment. © 2017 International Parkinson and Movement Disorder Society.

Drugs of abuse and Parkinson's disease

The term "drug of abuse" is highly contextual. What constitutes a drug of abuse for one population of patients does not for another. It is therefore important to examine the needs of the patient population to properly assess the status of drugs of abuse. The focus of this article is on the bidirectional relationship between patients and drug abuse. In this paper we will introduce the dopaminergic systems of the brain in Parkinson's and the influence of antiparkinsonian drugs upon them before discussing this synergy of condition and medication as fertile ground for drug abuse. We will then examine the relationship between drugs of abuse and Parkinson's, both beneficial and deleterious. In summary we will draw the different strands together and speculate on the future merit of current drugs of abuse as treatments for Parkinson's disease.

Adenosine 2A Receptor Antagonists for the Treatment of Motor Symptoms in Parkinson's Disease

Background

Treatment of motor fluctuations in Parkinson's disease (PD) remains an unmet challenge. Adenosine 2A (A_2A) receptors are located along the indirect pathway and represent a potential target to enhance l-3,4-dihydroxyphenylalanine (l-DOPA) antiparkinsonian action.

Methods

This article summarizes the preclinical and clinical literature on A_2A antagonists in PD, with a specific focus on their effect on off time, on time, and dyskinesia.

Findings

Several A_2A receptor antagonists have been tested in preclinical studies and clinical trials. In preclinical studies, A_2A antagonists enhanced l-DOPA antiparkinsonian action without exacerbating dyskinesia, but A_2A antagonists were generally administered in combination with a subthreshold dose of l-DOPA, which is different to the paradigms used in clinical trials, where A_2A antagonists were usually added to an optimal antiparkinsonian regimen. In clinical settings, A_2A antagonists generally reduced duration of off time, by as much as 25% in some studies. The effect of on time duration is less clear, and in a few studies an exacerbation of dyskinesia was reported. Two A_2A antagonists have been tested in phase III settings: istradefylline and preladenant. Istradefylline was effective in two phase III trials, but ineffective in another; the drug has been commercially available in Japan since 2013. In contrast, preladenant was ineffective in a phase III trial and the drug was discontinued. A phase III study with tozadenant will begin in 2015; the drug was effective at reducing off time in a phase IIb study. Other A_2A antagonists are in development at the preclinical and early clinical levels.

Variations in caffeine and chlorogenic acid contents of coffees: what are we drinking?

The effect of roasting of coffee beans and the extraction of ground coffee with different volumes of hot pressurised water on the caffeine and the total caffeoylquinic acids (CQAs) content of the resultant beverages was investigated. While caffeine was stable higher roasting temperatures resulted in a loss of CQAs so that the caffeine/CQA ratio was a good marker of the degree of roasting. The caffeine and CQA content and volume was determined for 104 espresso coffees obtained from coffee shops in Scotland, Italy and Spain, limited numbers of cappuccino coffees from commercial outlets and several instant coffees. The caffeine content ranged from 48-317 mg per serving and CQAs from 6-188 mg. It is evident that the ingestion of 200 mg of caffeine per day can be readily and unwittingly exceeded by regular coffee drinkers. This is the upper limit of caffeine intake from all sources recommended by US and UK health agencies for pregnant women. In view of the variable volume of serving sizes, it is also clear that the term "one cup of coffee" is not a reproducible measurement for consumption, yet it is the prevailing unit used in epidemiology to assess coffee consumption and to link the potential effects of the beverage and its components on the outcome of diseases. More accurate measurement of the intake of coffee and its potentially bioactive components are required if epidemiological studies are to produce more reliable information.

The safety of istradefylline for the treatment of Parkinson's disease

INTRODUCTION

Antagonism of the A2A receptor improves motor behavior in patients with Parkinson's disease (PD), according to results of clinical studies which confirm findings of previous experimental research. The xanthine derivative, istradefylline , has the longest half-life out of the available A2A receptor antagonists. Istradefylline easily crosses the blood-brain barrier and shows a high affinity to the human A2A receptor.

AREAS COVERED

This narrative review aims to discuss the safety and tolerability of istradefylline against the background of the currently available drug portfolio for the treatment of PD patients.

EXPERT OPINION

Istradefylline was safe and well tolerated in clinical trials, which have focused on l-DOPA-treated PD patients. The future of istradefylline as a complementary drug for modulation of the dopaminergic neurotransmission also relies on its potential to act like an l-DOPA plus dopamine agonist sparing future treatment alternative and to reduce the risk of predominant l-DOPA-related onset of motor complications in addition to its direct ameliorating effect on motor symptoms. Dopamine-substituting drugs may dose-dependently produce systemic side effects, particularly onset of hypotension and nausea by peripheral dopamine receptor stimulation. Istradefylline does not interfere with these peripheral receptors and therefore shows a good safety and tolerability profile.

Adenosine effects on inhibitory synaptic transmission and excitation-inhibition balance in the rat neocortex

KEY POINTS

Adenosine might be the most widespread neuromodulator in the brain, but its effects on inhibitory transmission in the neocortex are not understood. Here we report that adenosine suppresses inhibitory transmission to layer 2/3 pyramidal neurons via activation of presynaptic A1 receptors. We present evidence for functional A2A receptors, which have a weak modulatory effect on the A1-mediated suppression, at about 50% of inhibitory synapses at pyramidal neurons. Adenosine suppresses excitatory and inhibitory transmission to a different extent, and can change the excitation-inhibition balance at a set of synapses bidirectionally, but on average the balance was maintained during application of adenosine. These results suggest that changes of adenosine concentration may lead to differential modulation of excitatory-inhibitory balance in pyramidal neurons, and thus redistribution of local spotlights of activity in neocortical circuits, while preserving the balanced state of the whole network.

ABSTRACT

Adenosine might be the most widespread neuromodulator in the brain: as a metabolite of ATP it is present in every neuron and glial cell. However, how adenosine affects operation of neurons and networks in the neocortex is poorly understood, mostly because modulation of inhibitory transmission by adenosine has been so little studied. To clarify adenosine's role at inhibitory synapses, and in excitation-inhibition balance in pyramidal neurons, we recorded pharmacologically isolated inhibitory responses, compound excitatory-inhibitory responses and spontaneous events in layer 2/3 pyramidal neurons in slices from rat visual cortex. We show that adenosine (1-150 μm) suppresses inhibitory transmission to these neurons in a concentration-dependent and reversible manner. The suppression was mediated by presynaptic A1 receptors (A1Rs) because it was blocked by a selective A1 antagonist, DPCPX, and associated with changes of release indices: paired-pulse ratio, inverse coefficient of variation and frequency of miniature events. At some synapses (12 out of 24) we found evidence for A2ARs: their blockade led to a small but significant increase of the magnitude of adenosine-mediated suppression. This effect of A2AR blockade was not observed when A1Rs were blocked, suggesting that A2ARs do not have their own effect on transmission, but can modulate the A1R-mediated suppression. At both excitatory and inhibitory synapses, the magnitude of A1R-mediated suppression and A2AR-A1R interaction expressed high variability, suggesting high heterogeneity of synapses in the sensitivity to adenosine. Adenosine could change the balance between excitation and inhibition at a set of inputs to a neuron bidirectionally, towards excitation or towards inhibition. On average, however, these bidirectional changes cancelled each other, and the overall balance of excitation and inhibition was maintained during application of adenosine. These results suggest that changes of adenosine concentration may lead to differential modulation of excitatory-inhibitory balance in pyramidal neurons, and thus redistribution of local spotlights of activity in neocortical circuits, while preserving the balanced state of the whole network.

Coffee: biochemistry and potential impact on health

This article reviews the diversity of compounds found in coffee beans, the effect of roasting and the potential impact of coffee beverage on health.

Medicinal plants, human health and biodiversity: a broad review

Biodiversity contributes significantly towards human livelihood and development and thus plays a predominant role in the well being of the global population. According to WHO reports, around 80 % of the global population still relies on botanical drugs; today several medicines owe their origin to medicinal plants. Natural substances have long served as sources of therapeutic drugs, where drugs including digitalis (from foxglove), ergotamine (from contaminated rye), quinine (from cinchona), and salicylates (willow bark) can be cited as some classical examples.Drug discovery from natural sources involve a multifaceted approach combining botanical, phytochemical, biological, and molecular techniques. Accordingly, medicinal-plant-based drug discovery still remains an important area, hitherto unexplored, where a systematic search may definitely provide important leads against various pharmacological targets.Ironically, the potential benefits of plant-based medicines have led to unscientific exploitation of the natural resources, a phenomenon that is being observed globally. This decline in biodiversity is largely the result of the rise in the global population, rapid and sometimes unplanned industrialization, indiscriminate deforestation, overexploitation of natural resources, pollution, and finally global climate change.Therefore, it is of utmost importance that plant biodiversity be preserved, to provide future structural diversity and lead compounds for the sustainable development of human civilization at large. This becomes even more important for developing nations, where well-planned bioprospecting coupled with nondestructive commercialization could help in the conservation of biodiversity, ultimately benefiting mankind in the long run.Based on these findings, the present review is an attempt to update our knowledge about the diverse therapeutic application of different plant products against various pharmacological targets including cancer, human brain, cardiovascular function, microbial infection, inflammation, pain, and many more.

Activation of elements in HERV-W family by caffeine and aspirin

Caffeine and aspirin have been suggested to be involved in neurologic diseases, such as schizophrenia, and previous data have revealed that abnormal expression of HERV-W elements may be an important factor in the etiopathogenesis of those diseases. In this article, we reported that caffeine and aspirin contributed to the expression of HERV-W env and gag in Human SH-SY5Y neuroblastoma cells. Semi-quantitative RT-PCR and quantitative Real-time PCR were used to detect the mRNA of HERV-W env and gag in cells exposed to caffeine or aspirin. Western blotting was used to detect the protein of HERV-W env. Luciferase activity assay was employed to detect the activity of HERV-W env promoter. It was found that both caffeine and aspirin could increase the expression of HERV-W env and gag in human SH-SY5Y neuroblastoma cells. Caffeine could activate the HERV-W env promoter, while aspirin could not. With previous studies we can conjecture that HERVs might play a bridging role between environmental factors, such as drugs and neurologic diseases.

Caffeine has greater potency and efficacy than theophylline to reverse the motor impairment caused by chronic but not acute interruption of striatal dopaminergic transmission in rats

In order to assess whether caffeine and theophylline have the same potency and efficacy to reverse the impairment of motor function caused by acute or chronic interruption of striatal dopamine transmission, a comparison of their dose-response relationship was made in the acute model of haloperidol-induced catalepsy, and the chronic model of unilateral lesion of the dopamine nigrostriatal pathway with 6-hydroxydopamine. At equimolar doses, both drugs reduced catalepsy intensity and increased its onset latency in a dose-dependent fashion, showing comparable potencies and attaining the maximal effect at similar doses. Catalepsy intensity: caffeine ED₅₀ = 24.1 μmol/kg [95% CI, 18.4-31.5]; theophylline ED₅₀ = 22.0 μmol/kg [95% CI, 17.0-28.4]. Catalepsy latency: caffeine ED₅₀ = 27.0 μmol/kg [95% CI, 21.1-34.6]; theophylline ED₅₀ = 28.8 μmol/kg [95% CI, 22.5-36.7]. In one group of hemiparkinsonian rats (n = 5), caffeine caused a dose-dependent recovery of the contralateral forepaw stepping: ED₅₀ = 2.4 μmol/kg/day [95% CI, 1.9-3.1]), reaching its maximum at the dose of 5.15 μmol/kg/day. When the treatment of these same rats was switched to 5.15 μmol/kg/day of theophylline, the stepping recovery was only 51 ± 12% of that induced by caffeine. Assessing the dose-response relationship of theophylline in another group of hemiparkinsonian rats (n = 7) revealed that it caused stepping recovery in an all-or-none fashion. Thus, the three lower doses had no effect, but at the dose of 5.15 μmol/kg/day theophylline suddenly increased the stepping to 56 ± 5% of the maximal effect observed when the treatment of these same rats was switched to an equimolar dose of caffeine. Increasing the dose of theophylline up to 15.45 μmol/kg/day caused no further stepping improvement since it was only 41 ± 6% of the maximal effect produced by caffeine at the dose of 5.15 μmol/kg/day. Given that theophylline showed less potency and efficacy than caffeine to reverse the motor impairment caused by chronic, but not acute, interruption of striatal dopaminergic transmission in rats, it is suggested that caffeine would provide more benefits than theophylline to improve the motor function in patients with Parkinson's disease.

Caffeine for treatment of Parkinson disease: a randomized controlled trial

OBJECTIVE

Epidemiologic studies consistently link caffeine, a nonselective adenosine antagonist, to lower risk of Parkinson disease (PD). However, the symptomatic effects of caffeine in PD have not been adequately evaluated.

METHODS

We conducted a 6-week randomized controlled trial of caffeine in PD to assess effects upon daytime somnolence, motor severity, and other nonmotor features. Patients with PD with daytime somnolence (Epworth >10) were given caffeine 100 mg twice daily ×3 weeks, then 200 mg twice daily ×3 weeks, or matching placebo. The primary outcome was the Epworth Sleepiness Scale score. Secondary outcomes included motor severity, sleep markers, fatigue, depression, and quality of life. Effects of caffeine were analyzed with Bayesian hierarchical models, adjusting for study site, baseline scores, age, and sex.

RESULTS

Of 61 patients, 31 were randomized to placebo and 30 to caffeine. On the primary intention-to-treat analysis, caffeine resulted in a nonsignificant reduction in Epworth Sleepiness Scale score (-1.71 points; 95% confidence interval [CI] -3.57, 0.13). However, somnolence improved on the Clinical Global Impression of Change (+0.64; 0.16, 1.13, intention-to-treat), with significant reduction in Epworth Sleepiness Scale score on per-protocol analysis (-1.97; -3.87, -0.05). Caffeine reduced the total Unified Parkinson's Disease Rating Scale score (-4.69 points; -7.7, -1.6) and the objective motor component (-3.15 points; -5.50, -0.83). Other than modest improvement in global health measures, there were no changes in quality of life, depression, or sleep quality. Adverse events were comparable in caffeine and placebo groups.

CONCLUSIONS

Caffeine provided only equivocal borderline improvement in excessive somnolence in PD, but improved objective motor measures. These potential motor benefits suggest that a larger long-term trial of caffeine is warranted.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that caffeine, up to 200 mg BID for 6 weeks, had no significant benefit on excessive daytime sleepiness in patients with PD.

Improvement of postural adjustment steps in hemiparkinsonian rats chronically treated with caffeine is mediated by concurrent blockade of A1 and A2A adenosine receptors

Chronic treatment with the non-selective adenosine receptor antagonist caffeine produces full recovery of the contralateral adjusting steps in hemiparkinsonian rats. In order to disclose which adenosine receptor subtype mediates this effect, a group of hemiparkinsonian rats (n=9) was treated with caffeine (5.15 mumol/kg/day), or equimolar doses of selective A1 (DPCPX) or A2A (ZM 241385) adenosine receptor antagonists, administered in a counterbalanced order over periods of 3 weeks, interspersed with equivalent washout intervals. Treatment with ZM 241385 caused full recovery (102+/-6%) of the contralateral forepaw stepping, while the maximal effect of DPCPX was only 73+/-7% of that produced by caffeine. The maximal effect of caffeine and ZM 241385 remained stable throughout the treatment period. The response to DPCPX showed more fluctuations, but tolerance did not develop. Stepping improvement was significantly faster with DPCPX than with ZM 241385, while caffeine had intermediate values. Stepping decrease after treatment interruption was faster with ZM 241385 than with caffeine, while DPCPX had intermediate values. In other experiments with the same rats, addition of the A2AR agonist CGS 21680 (5.15 mumol/kg) or the A1R agonist CCPA (2.71 mumol/kg) during the second week of caffeine treatment reversed the improvement of contralateral stepping by 59+/-4% and 30+/-3%, respectively. The combined treatment with CGS 21680 and CCPA caused complete reversal of the contralateral stepping recovery afforded by caffeine, which was more than additive (114+/-5%) compared with the sum of the maximal inhibition produced by either agonist administered alone (89+/-4%). In all cases, after interrupting the adenosine agonists, the effect of caffeine was fully restored. None of the aforementioned treatments induced significant changes in the stepping of the ipsilateral forepaw. Collectively, these results suggest that the improvement of postural adjustments induced by chronic treatment with low doses of caffeine in hemiparkinsonian rats is mediated by concurrent blockade of A1 and A2A adenosine receptors, with a larger involvement of the latter.

Potential influences of complementary therapy on motor and non-motor complications in Parkinson's disease

Nearly two-thirds of patients with Parkinson's disease (PD) use vitamins or nutritional supplements, and many more may use other complementary therapies, yet <50% of patients have discussed the use of these complementary therapies with a healthcare professional. Physicians should be aware of the complementary therapies their patients with PD are using, and the possible effects of these therapies on motor and non-motor symptoms. Complementary therapies, such as altered diet, dietary supplements, vitamin therapy, herbal supplements, caffeine, nicotine, exercise, physical therapy, massage therapy, melatonin, bright-light therapy and acupuncture, may all influence the symptoms of PD and/or the effectiveness of dopaminergic therapy. Preliminary evidence suggests complementary therapy also may influence non-motor symptoms of PD, such as respiratory disorders, gastrointestinal disorders, mood disorders, sleep and orthostatic hypotension. Whenever possible, clinicians should ensure that complementary therapy is used appropriately in PD patients without reducing the benefits of dopaminergic therapy.

Ethnobotany as a pharmacological research tool and recent developments in CNS-active natural products from ethnobotanical sources

The science of ethnobotany is reviewed in light of its multi-disciplinary contributions to natural product research for the development of pharmaceuticals and pharmacological tools. Some of the issues reviewed involve ethical and cultural perspectives of healthcare and medicinal plants. While these are not usually part of the discussion of pharmacology, cultural concerns potentially provide both challenges and insight for field and laboratory researchers. Plant evolutionary issues are also considered as they relate to development of plant chemistry and accessing this through ethnobotanical methods. The discussion includes presentation of a range of CNS-active medicinal plants that have been recently examined in the field, laboratory and/or clinic. Each of these plants is used to illustrate one or more aspects about the valuable roles of ethnobotany in pharmacological research. We conclude with consideration of mutually beneficial future collaborations between field ethnobotanists and pharmacologists.

Adenosine receptors and the central nervous system

The adenosine receptors (ARs) in the nervous system act as a kind of "go-between" to regulate the release of neurotransmitters (this includes all known neurotransmitters) and the action of neuromodulators (e.g., neuropeptides, neurotrophic factors). Receptor-receptor interactions and AR-transporter interplay occur as part of the adenosine's attempt to control synaptic transmission. A(2A)ARs are more abundant in the striatum and A(1)ARs in the hippocampus, but both receptors interfere with the efficiency and plasticity-regulated synaptic transmission in most brain areas. The omnipresence of adenosine and A(2A) and A(1) ARs in all nervous system cells (neurons and glia), together with the intensive release of adenosine following insults, makes adenosine a kind of "maestro" of the tripartite synapse in the homeostatic coordination of the brain function. Under physiological conditions, both A(2A) and A(1) ARs play an important role in sleep and arousal, cognition, memory and learning, whereas under pathological conditions (e.g., Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke, epilepsy, drug addiction, pain, schizophrenia, depression), ARs operate a time/circumstance window where in some circumstances A(1)AR agonists may predominate as early neuroprotectors, and in other circumstances A(2A)AR antagonists may alter the outcomes of some of the pathological deficiencies. In some circumstances, and depending on the therapeutic window, the use of A(2A)AR agonists may be initially beneficial; however, at later time points, the use of A(2A)AR antagonists proved beneficial in several pathologies. Since selective ligands for A(1) and A(2A) ARs are now entering clinical trials, the time has come to determine the role of these receptors in neurological and psychiatric diseases and identify therapies that will alter the outcomes of these diseases, therefore providing a hopeful future for the patients who suffer from these diseases.