Do caffeine and more selective adenosine A2A receptor antagonists protect against dopaminergic neurodegeneration in Parkinson's disease?

Update: Protective and risk factors for Parkinson disease

We review the epidemiologic literature on potential protective and risk factors in Parkinson's Disease (PD). Prior research identified numerous possible protective and risk factors. Potential protective factors include tobacco abuse, physical activity, urate levels, NSAID use, calcium channel blocker use, statin use, and use of some α1-adrenergic antagonists. Some potential protective factors could be products of reverse causation, including increased serum urate, tobacco abuse, and coffee-tea-caffeine consumption. Potential risk factors include traumatic brain injury, pesticide exposure, organic solvent exposure, lead exposure, air pollution, Type 2 Diabetes, some dairy products, cardiovascular disease, and some infections including Hepatitis C, H. pylori, and COVID-19. Potential non-environmental risk factors include bipolar disorder, essential tremor, bullous pemphigoid, and inflammatory bowel disease. There is an inverse relationship with PD and risk of most cancers. Though many potential protective and risk factors for PD were identified, research has not yet led to unique, rigorous prevention trials or successful disease-modifying interventions. While efforts to reduce exposure to some industrial toxicants are well justified, PD incidence might be most effectively reduced by mitigation of risks, such as Type 2 Diabetes, air pollution, traumatic brain injury, or physical inactivity, that are general public health intervention targets.

Dietary Caffeine and Brain Dopaminergic Function in Parkinson Disease

OBJECTIVE

This study was undertaken to investigate the effects of dietary caffeine intake on striatal dopamine function and clinical symptoms in Parkinson disease in a cross-sectional and longitudinal setting.

METHODS

One hundred sixty-three early Parkinson disease patients and 40 healthy controls were investigated with [123I]FP-CIT single photon emission computed tomography, and striatal dopamine transporter binding was evaluated in association with the level of daily coffee consumption and clinical measures. After a median interval of 6.1 years, 44 patients with various caffeine consumption levels underwent clinical and imaging reexamination including blood caffeine metabolite profiling.

RESULTS

Unmedicated early Parkinson disease patients with high coffee consumption had 8.3 to 15.4% lower dopamine transporter binding in all studied striatal regions than low consumers, after accounting for age, sex, and motor symptom severity. Higher caffeine consumption was further associated with a progressive decline in striatal binding over time. No significant effects of caffeine on motor function were observed. Blood analyses demonstrated a positive correlation between caffeine metabolites after recent caffeine intake and dopamine transporter binding in the ipsilateral putamen.

INTERPRETATION

Chronic caffeine intake prompts compensatory and cumulative dopamine transporter downregulation, consistent with caffeine's reported risk reduction in Parkinson disease. However, this decline does not manifest in symptom changes. Transiently increased dopamine transporter binding after recent caffeine intake has implications for dopaminergic imaging guidelines. ANN NEUROL 2024;96:262-275.

Caffeine consumption outcomes on amyotrophic lateral sclerosis disease progression and cognition

Caffeine consumption outcomes on Amyotrophic Lateral Sclerosis (ALS) including progression, survival and cognition remain poorly defined and may depend on its metabolization influenced by genetic variants. 378 ALS patients with a precise evaluation of their regular caffeine consumption were monitored as part of a prospective multicenter study. Demographic, clinical characteristics, functional disability as measured with revised ALS Functional Rating Scale (ALSFRS-R), cognitive deficits measured using Edinburgh Cognitive and Behavioural ALS Screen (ECAS), survival and riluzole treatment were recorded. 282 patients were genotyped for six single nucleotide polymorphisms tagging different genes involved in caffeine intake and/or metabolism: CYP1A1 (rs2472297), CYP1A2 (rs762551), AHR (rs4410790), POR (rs17685), XDH (rs206860) and ADORA2A (rs5751876) genes. Association between caffeine consumption and ALSFRS-R, ALSFRS-R rate, ECAS and survival were statistically analyzed to determine the outcome of regular caffeine consumption on ALS disease progression and cognition. No association was observed between caffeine consumption and survival (p = 0.25), functional disability (ALSFRS-R; p = 0.27) or progression of ALS (p = 0.076). However, a significant association was found with higher caffeine consumption and better cognitive performance on ECAS scores in patients carrying the C/T and T/T genotypes at rs2472297 (p-het = 0.004). Our results support the safety of regular caffeine consumption on ALS disease progression and survival and also show its beneficial impact on cognitive performance in patients carrying the minor allele T of rs2472297, considered as fast metabolizers, that would set the ground for a new pharmacogenetic therapeutic strategy.

Adenosine and Cortical Plasticity

Brain plasticity is the ability of the nervous system to change its structure and functioning in response to experiences. These changes occur mainly at synaptic connections, and this plasticity is named synaptic plasticity. During postnatal development, environmental influences trigger changes in synaptic plasticity that will play a crucial role in the formation and refinement of brain circuits and their functions in adulthood. One of the greatest challenges of present neuroscience is to try to explain how synaptic connections change and cortical maps are formed and modified to generate the most suitable adaptive behavior after different external stimuli. Adenosine is emerging as a key player in these plastic changes at different brain areas. Here, we review the current knowledge of the mechanisms responsible for the induction and duration of synaptic plasticity at different postnatal brain development stages in which adenosine, probably released by astrocytes, directly participates in the induction of long-term synaptic plasticity and in the control of the duration of plasticity windows at different cortical synapses. In addition, we comment on the role of the different adenosine receptors in brain diseases and on the potential therapeutic effects of acting via adenosine receptors.

Does dietary intake of caffeine have an effect on transient global amnesia?

AIM

Amnesia is a cognitive disorder that may lead to memory loss. Caffeine is a psychoactive substance which have an effect on memory and cognitive functions. This study aimed to assess the association of transient global amnesia (TGA) with dietary intake of caffeine.

METHODS

This cross-sectional study was conducted on the Sabzevar Persian cohort data of 258 patients with TGA and 520 healthy individuals in Sabzevar, Iran. The Nutritional data were gathered in face-to-face interviews using a valid Food Frequency Questionnaire. Different models of logistic regression were used to determine the association between TGA and dietary caffeine intake after adjusting the confounders including age, sex, education, job, marital status, physical activity, BMI, and calorie intake.

RESULTS

There was no significant difference in terms of dietary calorie intake of (2279.5 ± 757.9 vs. 2365.5 ± 799.5, p = 0.19), protein (70.79 ± 25.27 vs. 72.94 ± 24.83, p = 0.31), fat (59.97 ± 23.79 vs. 60.13 ± 26.38, p = 0.93), carbohydrate (376 ± 134 vs. 393.1 ± 137.8, p = 0.14), and caffeine (196.4 ± 127.9 vs. 186.3 ± 128.5, p = 0.36) between the groups. No significant association was found between TGA and dietary intake of caffeine (OR: 0.99, 95% CI: 0.99-1.01, p = 0.36). The results did not change after adjusting the confounders.

CONCLUSIONS

No significant association was found between TGA and dietary intake of caffeine. Further prospective studies are required to confirm this finding.

Drugs targeting adenosine signaling pathways: A current view

Adenosine is an endogenous nucleoside that regulates many physiological and pathological processes. It is derived from either the intracellular or extracellular dephosphorylation of adenosine triphosphate and interacts with cell-surface G-protein-coupled receptors. Adenosine plays a substantial role in protecting against cell damage in areas of increased tissue metabolism and preventing organ dysfunction in pathological states. Targeting adenosine metabolism and receptor signaling may be an effective therapeutic approach for human diseases, including cardiovascular and central nervous system disorders, rheumatoid arthritis, asthma, renal diseases, and cancer. Several lines of evidence have shown that many drugs exert their beneficial effects by modulating adenosine signaling pathways but this knowledge urgently needs to be summarized, and most importantly, actualized. The present review collects pharmaceuticals and pharmacological or diagnostic tools that target adenosine signaling in their primary or secondary mode of action. We overviewed FDA-approved drugs as well as those currently being studied in clinical trials. Among them are already used in clinic A2A adenosine receptor modulators like istradefylline or regadenoson, but also plenty of anti-platelet, anti-inflammatory, or immunosuppressive, and anti-cancer drugs. On the other hand, we investigated dozens of specific adenosine pathway regulators that are tested in clinical trials to treat human infectious and noninfectious diseases. In conclusion, targeting purinergic signaling represents a great therapeutic challenge. The actual knowledge of the involvement of adenosinergic signaling as part of the mechanism of action of old drugs has open a path not only for drug-repurposing but also for new therapeutic strategies.

What to Test in Parkinson Disease Prevention Trials? Repurposed, Low-Risk, and Gene-Targeted Drugs

Despite the sound epidemiologic and basic science rationales underpinning numerous "disease modification" trials in manifest Parkinson disease (PD), none has convincingly demonstrated that a treatment slows progression. Rapidly expanding knowledge of the genetic determinants and prodromal features of PD now allows realistic planning of prevention trials with initiation of putatively neuroprotective therapies earlier in the disease. In this article, we outline the principles of drug selection for PD prevention trials, focused on proof-of-concept opportunities that will help establish a methodological foundation for this fledgling field. We describe prototypical, relatively low-risk drug candidates for such trials (e.g., albuterol, ambroxol, caffeine, ibuprofen), tailored to specific at-risk populations ranging from pathogenic LRRK2 or GBA gene variant carriers to those defined by prodromal PD and α-synucleinopathy. Finally, we review gene-targeted approaches currently in development targeting clinically manifest PD for their potential in future prevention trials.

The microbiome-gut-brain axis in Parkinson disease - from basic research to the clinic

Evidence for a close bidirectional link between the brain and the gut has led to a paradigm shift in neurology, especially in the case of Parkinson disease (PD), in which gastrointestinal dysfunction is a prominent feature. Over the past decade, numerous high-quality preclinical and clinical publications have shed light on the highly complex relationship between the gut and the brain in PD, providing potential for the development of new biomarkers and therapeutics. With the advent of high-throughput sequencing, the role of the gut microbiome has been specifically highlighted. Here, we provide a critical review of the literature on the microbiome-gut-brain axis in PD and present perspectives that will be useful for clinical practice. We begin with an overview of the gut-brain axis in PD, including the potential roles and interrelationships of the vagus nerve, α-synuclein in the enteric nervous system, altered intestinal permeability and inflammation, and gut microbes and their metabolic activities. The sections that follow synthesize the proposed roles of gut-related factors in the development and progression of, in responses to PD treatment, and as therapeutic targets. Finally, we summarize current knowledge gaps and challenges and delineate future directions for the field.

Life style and Parkinson's disease

The question whether life style may impair the advent or course of the disease in patients with Parkinsonism is of great importance for patients and physicians alike. We present here comprehensive information on the influence of the environment, diet (especially caffeine, nicotine, alcohol, chocolate and dairy products), physical activity and sleep on risk and course of Parkinson’s disease.

[Caffeine, Chocolate and Adenosine A2A Receptor Antagonists in the Treatment of Parkinson's Disease]

BACKGROUND

Patients with Parkinson's disease can apparently benefit from caffeine consumption, as a number of experimental and clinical studies have already shown.

METHODS

The review examined the available literature on caffeine and Parkinson's disease.

RESULTS

Caffeine can penetrate the blood-brain barrier and exerts its biological effects mainly by antagonizing adenosine receptors. Numerous studies indicate that caffeine and its derivatives theobromine and theophylline are associated with a reduced risk of Parkinson's disease. Caffeine and adenosine antagonists reduce the excitotoxicity caused by glutamate. Evidence from animal models supports the potential of A2A receptor antagonism as an innovative disease-modifying target in Parkinson's disease CONCLUSION: The present review shows that the investigation and synthesis of xanthine derivatives as well as their analysis in clinical studies could be a promising approach in the therapy of neurodegenerative diseases.

Dietary sources, health benefits, and risks of caffeine

Dietary intake of caffeine has significantly increased in recent years, and beneficial and harmful effects of caffeine have been extensively studied. This paper reviews antioxidant and anti-inflammatory activities of caffeine as well as its protective effects on cardiovascular diseases, obesity, diabetes mellitus, cancers, and neurodegenerative and liver diseases. In addition, we summarize the side effects of long-term or excessive caffeine consumption on sleep, migraine, intraocular pressure, pregnant women, children, and adolescents. The health benefits of caffeine depend on the amount of caffeine intake and the physical condition of consumers. Moderate intake of caffeine helps to prevent and modulate several diseases. However, the long-term or over-consumption of caffeine can lead to addiction, insomnia, migraine, and other side effects. In addition, children, adolescents, pregnant women, and people who are sensitive to caffeine should be recommended to restrict/reduce their intake to avoid potential adverse effects.

The Pharmacological Potential of Adenosine A2A Receptor Antagonists for Treating Parkinson's Disease

The adenosine A_2A receptor subtype is recognized as a non-dopaminergic pharmacological target for the treatment of neurodegenerative disorders, notably Parkinson’s disease (PD). The selective A_2A receptor antagonist istradefylline is approved in the US and Japan as an adjunctive treatment to levodopa/decarboxylase inhibitors in adults with PD experiencing OFF episodes or a wearing-off phenomenon; however, the full potential of this drug class remains to be explored. In this article, we review the pharmacology of adenosine A_2A receptor antagonists from the perspective of the treatment of both motor and non-motor symptoms of PD and their potential for disease modification.

A2A Adenosine Receptor Antagonists in Neurodegenerative Diseases

BACKGROUND

Alzheimer's disease (AD) is the most common form of dementia worldwide, with approximately 6 million cases reported in America in 2020. The clinical signs of AD include cognitive dysfunction, apathy, anxiety and neuropsychiatric signs, and pathogenetic mechanisms that involve amyloid peptide-β extracellular accumulation and tau hyperphosphorylation. Unfortunately, current drugs to treat AD can provide only symptomatic relief but are not disease-modifying molecules able to revert AD progression. The endogenous modulator adenosine, through A_2A receptor activation, plays a role in synaptic loss and neuroinflammation, which are crucial for cognitive impairment and memory damage.

OBJECTIVE

In this review, recent advances covering A_2A adenosine receptor antagonists will be extensively reviewed, providing a basis for the rational design of future A_2A inhibitors.

METHODS

Herein, the literature on A_2A adenosine receptors and their role in synaptic plasticity and neuroinflammation, as well as the effects of A_2A antagonism in animal models of AD and in humans, are reviewed. Furthermore, current chemical and structure-based strategies are presented.

RESULTS

Caffeine, the most widely consumed natural product stimulant and an A_2A antagonist, improves human memory. Similarly, synthetic A_2A receptor antagonists, as described in this review, may provide a means to fight AD.

CONCLUSION

This review highlights the clinical potential of A_2A adenosine receptor antagonists as a novel approach to treat patients with AD.

How Are Adenosine and Adenosine A2A Receptors Involved in the Pathophysiology of Amyotrophic Lateral Sclerosis?

Adenosine is extensively distributed in the central and peripheral nervous systems, where it plays a key role as a neuromodulator. It has long been implicated in the pathogenesis of progressive neurogenerative disorders such as Parkinson’s disease, and there is now growing interest in its role in amyotrophic lateral sclerosis (ALS). The motor neurons affected in ALS are responsive to adenosine receptor function, and there is accumulating evidence for beneficial effects of adenosine A_2A receptor antagonism. In this article, we focus on recent evidence from ALS clinical pathology and animal models that support dynamism of the adenosinergic system (including changes in adenosine levels and receptor changes) in ALS. We review the possible mechanisms of chronic neurodegeneration via the adenosinergic system, potential biomarkers and the acute symptomatic pharmacology, including respiratory motor neuron control, of A_2A receptor antagonism to explore the potential of the A_2A receptor as target for ALS therapy.

Istradefylline - a first generation adenosine A2A antagonist for the treatment of Parkinson's disease

Introduction It is now accepted that Parkinson's disease (PD) is not simply due to dopaminergic dysfunction, and there is interest in developing non-dopaminergic approaches to disease management. Adenosine A_2A receptor antagonists represent a new way forward in the symptomatic treatment of PD.Areas covered In this narrative review, we summarize the literature supporting the utility of adenosine A_2A antagonists in PD with a specific focus on istradefylline, the most studied and only adenosine A_2A antagonist currently in clinical use.Expert opinion: At this time, the use of istradefylline in the treatment of PD is limited to the management of motor fluctuations as supported by the results of randomized clinical trials and evaluation by Japanese and USA regulatory authorities. The relatively complicated clinical development of istradefylline was based on classically designed studies conducted in PD patients with motor fluctuations on an optimized regimen of levodopa plus adjunctive dopaminergic medications. In animal models, there is consensus that a more robust effect of istradefylline in improving motor function is produced when combined with low or threshold doses of levodopa rather than with high doses that produce maximal dopaminergic improvement. Exploration of istradefylline as a 'levodopa sparing' strategy in earlier PD would seem warranted.