Effects of chronic caffeine intake in a mouse model of amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis in Long-COVID Scenario and the Therapeutic Potential of the Purinergic System in Neuromodulation

Amyotrophic lateral sclerosis (ALS) involves the degeneration of motor neurons and debilitating and possibly fatal symptoms. The COVID-19 pandemic directly affected the quality of life of this group, and the SARS-CoV-2 infection accelerated the present neuroinflammatory process. Furthermore, studies indicate that the infection may have led to the development of the pathology. Thus, the scenario after this pandemic presents "long-lasting COVID" as a disease that affects people who have been infected. From this perspective, studying the pathophysiology behind ALS associated with SARS-CoV-2 infection and possible supporting therapies becomes necessary when we understand the impact on the quality of life of these patients. Thus, the purinergic system was trained to demonstrate how its modulation can add to the treatment, reduce disease progression, and result in better prognoses. From our studies, we highlight the P2X7, P2X4, and A2AR receptors and how their activity can directly influence the ALS pathway.

Integrative analysis of metabolomics and proteomics unravels purine metabolism disorder in the SOD1G93A mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with progressive paralysis of limbs and bulb in patients, the cause of which remains unclear. Accumulating studies suggest that motor neuron degeneration is associated with systemic metabolic impairment in ALS. However, the metabolic reprogramming and underlying mechanism in the longitudinal progression of the disease remain poorly understood. In this study, we aimed to investigate the molecular changes at both metabolic and proteomic levels during disease progression to identify the most critical metabolic pathways and underlying mechanisms involved in ALS pathophysiological changes. Utilizing liquid chromatography-mass spectrometry-based metabolomics, we analyzed the metabolites' levels of plasma, lumbar spinal cord, and motor cortex from SOD1^G93A mice and wildtype (WT) littermates at different stages. To elucidate the regulatory network underlying metabolic changes, we further analyzed the proteomics profile in the spinal cords of SOD1^G93A and WT mice. A group of metabolites implicated in purine metabolism, methionine cycle, and glycolysis were found differentially expressed in ALS mice, and abnormal expressions of enzymes involved in these metabolic pathways were also confirmed. Notably, we first demonstrated that dysregulation of purine metabolism might contribute to the pathogenesis and disease progression of ALS. Furthermore, we discovered that fatty acid metabolism, TCA cycle, arginine and proline metabolism, and folate-mediated one‑carbon metabolism were also significantly altered in this disease. The identified differential metabolites and proteins in our study could complement existing data on metabolic reprogramming in ALS, which might provide new insight into the pathological mechanisms and novel therapeutic targets of ALS.

Changes in adenosine receptors and neurotrophic factors in the SOD1G93A mouse model of amyotrophic lateral sclerosis: Modulation by chronic caffeine

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of corticospinal tract motor neurons. Previous studies showed that adenosine-mediated neuromodulation is disturbed in ALS and that vascular endothelial growth factor (VEGF) has a neuroprotective function in ALS mouse models. We evaluated how adenosine (A1R and A2AR) and VEGF (VEGFA, VEGFB, VEGFR-1 and VEGFR-2) system markers are altered in the cortex and spinal cord of pre-symptomatic and symptomatic SOD1G93A mice. We then assessed if/how chronic treatment of SOD1G93A mice with a widely consumed adenosine receptor antagonist, caffeine, modulates VEGF system and/or the levels of Brain-derived Neurotrophic Factor (BDNF), known to be under control of A2AR. We found out decreases in A1R and increases in A2AR levels even before disease onset. Concerning the VEGF system, we detected increases of VEGFB and VEGFR-2 levels in the spinal cord at pre-symptomatic stage, which reverses at the symptomatic stage, and decreases of VEGFA levels in the cortex, in very late disease states. Chronic treatment with caffeine rescued cortical A1R levels in SOD1G93A mice, bringing them to control levels, while rendering VEGF signaling nearly unaffected. In contrast, BDNF levels were significantly affected in SOD1G93A mice treated with caffeine, being decreased in the cortex and increased in spinal the cord. Altogether, these findings suggest an early dysfunction of the adenosinergic system in ALS and highlights the possibility that the negative influence of caffeine previously reported in ALS animal models results from interference with BDNF rather than with the VEGF signaling molecules.

The Multifaceted Role of GPCRs in Amyotrophic Lateral Sclerosis: A New Therapeutic Perspective?

Amyotrophic lateral sclerosis (ALS) is a degenerating disease involving the motor neurons, which causes a progressive loss of movement ability, usually leading to death within 2 to 5 years from the diagnosis. Much effort has been put into research for an effective therapy for its eradication, but still, no cure is available. The only two drugs approved for this pathology, Riluzole and Edaravone, are onlyable to slow down the inevitable disease progression. As assessed in the literature, drug targets such as protein kinases have already been extensively examined as potential drug targets for ALS, with some molecules already in clinical trials. Here, we focus on the involvement of another very important and studied class of biological entities, G protein-coupled receptors (GPCRs), in the onset and progression of ALS. This workaimsto give an overview of what has been already discovered on the topic, providing useful information and insights that can be used by scientists all around the world who are putting efforts into the fight against this very important neurodegenerating disease.

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.

Emerging roles of dysregulated adenosine homeostasis in brain disorders with a specific focus on neurodegenerative diseases

In modern societies, with an increase in the older population, age-related neurodegenerative diseases have progressively become greater socioeconomic burdens. To date, despite the tremendous effort devoted to understanding neurodegenerative diseases in recent decades, treatment to delay disease progression is largely ineffective and is in urgent demand. The development of new strategies targeting these pathological features is a timely topic. It is important to note that most degenerative diseases are associated with the accumulation of specific misfolded proteins, which is facilitated by several common features of neurodegenerative diseases (including poor energy homeostasis and mitochondrial dysfunction). Adenosine is a purine nucleoside and neuromodulator in the brain. It is also an essential component of energy production pathways, cellular metabolism, and gene regulation in brain cells. The levels of intracellular and extracellular adenosine are thus tightly controlled by a handful of proteins (including adenosine metabolic enzymes and transporters) to maintain proper adenosine homeostasis. Notably, disruption of adenosine homeostasis in the brain under various pathophysiological conditions has been documented. In the past two decades, adenosine receptors (particularly A₁ and A_2A adenosine receptors) have been actively investigated as important drug targets in major degenerative diseases. Unfortunately, except for an A_2A antagonist (istradefylline) administered as an adjuvant treatment with levodopa for Parkinson's disease, no effective drug based on adenosine receptors has been developed for neurodegenerative diseases. In this review, we summarize the emerging findings on proteins involved in the control of adenosine homeostasis in the brain and discuss the challenges and future prospects for the development of new therapeutic treatments for neurodegenerative diseases and their associated disorders based on the understanding of adenosine homeostasis.

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.

Coffee and Tea Consumption Impact on Amyotrophic Lateral Sclerosis Progression: A Multicenter Cross-Sectional Study

Background/objectives: Amyotrophic lateral sclerosis (ALS) is a devastating and still untreatable motor neuron disease. The causes of ALS are unknown, but nutritional factors may impact the rate of disease progression. We aimed to ascertain the influence of coffee and tea consumption on ALS progression rate.

Subjects/methods: In this multicenter cross-sectional study, we recruited 241 patients, 96 females, and 145 males; the mean age at onset was 59.9 ± 11.8 years. According to El Escorial criteria, 74 were definite ALS, 77 probable, 55 possible, and 35 suspected; 187 patients had spinal onset and 54 bulbar. Patients were categorized into three groups, according to their ΔFS (derived from ALS Functional Rating Scale-Revised score and disease duration from onset): slow (81), intermediate (80), and fast progressors (80).

Results: Current coffee consumers were 179 (74.3%), 34 (14.1%) were non-consumers, and 22 (9.1%) were former consumers, whereas six (2.5%) consumed decaffeinated coffee only. The log-ΔFS was weakly correlated with the duration of coffee consumption (p = 0.034), but not with the number of cup-years, or the intensity of coffee consumption (cups/day). Current tea consumers were 101 (41.9%), 6 (2.5%) were former consumers, and 134 (55.6%) were non-consumers. Among current and former consumers, 27 (25.2%) consumed only green tea, 51 (47.7%) only black tea, and 29 (27.1%) both. The log-ΔFS was weakly correlated only with the consumption duration of black tea (p = 0.028) but not with the number of cup-years.

Conclusions: Our study does not support the hypothesis that coffee or tea consumption is associated with the ALS progression rate.

Metabolic Aspects of Adenosine Functions in the Brain

Adenosine, acting both through G-protein coupled adenosine receptors and intracellularly, plays a complex role in multiple physiological and pathophysiological processes by modulating neuronal plasticity, astrocytic activity, learning and memory, motor function, feeding, control of sleep and aging. Adenosine is involved in stroke, epilepsy and neurodegenerative pathologies. Extracellular concentration of adenosine in the brain is tightly regulated. Adenosine may be generated intracellularly in the central nervous system from degradation of AMP or from the hydrolysis of S-adenosyl homocysteine, and then exit via bi-directional nucleoside transporters, or extracellularly by the metabolism of released nucleotides. Inactivation of extracellular adenosine occurs by transport into neurons or neighboring cells, followed by either phosphorylation to AMP by adenosine kinase or deamination to inosine by adenosine deaminase. Modulation of the nucleoside transporters or of the enzymatic activities involved in the metabolism of adenosine, by affecting the levels of this nucleoside and the activity of adenosine receptors, could have a role in the onset or the development of central nervous system disorders, and can also be target of drugs for their treatment. In this review, we focus on the contribution of 5'-nucleotidases, adenosine kinase, adenosine deaminase, AMP deaminase, AMP-activated protein kinase and nucleoside transporters in epilepsy, cognition, and neurodegenerative diseases with a particular attention on amyotrophic lateral sclerosis and Huntington's disease. We include several examples of the involvement of components of the adenosine metabolism in learning and of the possible use of modulators of enzymes involved in adenosine metabolism or nucleoside transporters in the amelioration of cognition deficits.

Targeting Adenosine Receptors in Neurological Diseases

Adenosine plays a significant role in neurotransmission process by controlling the blood pressure, while adenosine triphosphate (ATP) acts as a neuromodulator and neurotransmitter and by activation of P2 receptors, regulates the contractility of the heart. Adenosine signaling is essential in the process of regeneration by regulating proliferation, differentiation, and apoptosis of stem cells. In this review, we have selected neurological disorders (Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and epilepsy) with clinical trials using antagonists and epigenetic tools targeting adenosine receptor as a therapeutic approach in the treatment of these disorders. Promising results have been reported from many clinical trials. It has been found that higher expression levels of A2A and P2X7 receptors in neurological disorders further complicate the disease condition. Therefore, modulations of these receptors by using antagonists of these receptors or SAM (S-adenosylmethionine) therapy as an epigenetic tool could be useful in reversing the complications of these disorders. Finally, we suggest that modulation of adenosine receptors in neurological disorders can increase the regenerative phase by increasing the rate of proliferation and differentiation in the damaged tissues.

Hippocampal synaptic dysfunction in the SOD1G93A mouse model of Amyotrophic Lateral Sclerosis: Reversal by adenosine A2AR blockade

Amyotrophic Lateral Sclerosis (ALS) mostly affects motor neurons, but non-motor neural and cognitive alterations have been reported in ALS mouse models and patients. Here, we evaluated if time-dependent biphasic changes in synaptic transmission and plasticity occur in hippocampal synapses of ALS SOD1^G93A mice. Recordings were performed in hippocampal slices of SOD1^G93A and age-matched WT mice, in the pre-symptomatic and symptomatic stages. We found an enhancement of pre-synaptic function and increased adenosine A_2A receptor levels in the hippocampus of pre-symptomatic mice. In contrast, in symptomatic mice, there was an impairment of long-term potentiation (LTP) and a decrease in NMDA receptor-mediated synaptic currents, with A_2AR levels also being increased. Chronic treatment with the A_2AR antagonist KW-6002, rescued LTP and A_2AR values. Altogether, these findings suggest an increase in synaptic function during the pre-symptomatic stage, followed by a decrease in synaptic plasticity in the symptomatic stage, which involves over-activation of A_2AR from early disease stages.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Purinergic implication in amyotrophic lateral sclerosis-from pathological mechanisms to therapeutic perspectives

Amyotrophic lateral sclerosis (ALS) is a clinically heterogeneous disorder characterized by degeneration of upper motor neurons in the brainstem and lower motor neurons in the spinal cord. Multiple mechanisms of motor neuron injury have been implicated, including more than 20 different genetic factors. The pathogenesis of ALS consists of two stages: an early neuroprotective stage and a later neurotoxic. During early phases of disease progression, the immune system through glial and T cell activities provides anti-inflammatory factors that sustain motor neuron viability. As the disease progresses and motor neuron injury accelerates, a rapidly succeeding neurotoxic phase develops. A well-orchestrated purine-mediated dialog among motor neurons, surrounding glia and immune cells control the beneficial and detrimental activities occurring in the nervous system. In general, low adenosine triphosphate (ATP) concentrations protect cells against excitotoxic stimuli through purinergic P2X4 receptor, whereas high concentrations of ATP trigger toxic P2X7 receptor activation. Finally, adenosine is also involved in ALS progression since A2A receptor antagonists prevent motor neuron death. Given the complex cellular cross-talk occurring in ALS and the recognized function of extracellular nucleotides and adenosine in neuroglia communication, the comprehensive understanding of purinome dynamics might provide new research perspectives to decipher ALS and help to design more efficient and targeted drugs. This review will focus on the purinergic players involved in ALS etiology and disease progression and current therapeutic strategies to enhance neuroprotection and suppress neurotoxicity.

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.

Impaired tissue barriers as potential therapeutic targets for Parkinson's disease and amyotrophic lateral sclerosis

The blood-brain barrier and the intestinal barrier show signs of disruption in patients with idiopathic Parkinson's disease (PD) and animal models of nigrostriatal degeneration, and likewise in amyotrophic lateral sclerosis (ALS) models. A substantial body of evidence shows that defects in epithelial membrane barriers, both in the gut and within the cerebral vasculature, can result in increased vulnerability of tissues to external factors potentially participating in the pathogenesis of PD and ALS. As such, restoration of tissue barriers may prove to be a novel therapeutic target in neurodegenerative disease. In this review, we focus on the potential of new intervention strategies for rescuing and maintaining barrier functions in PD and ALS.

Amyotrophic Lateral Sclerosis (ALS) and Adenosine Receptors

In the present review we discuss the potential involvement of adenosinergic signaling, in particular the role of adenosine receptors, in amyotrophic lateral sclerosis (ALS). Though the literature on this topic is not abundant, the information so far available on adenosine receptors in animal models of ALS highlights the interest to continue to explore the role of these receptors in this neurodegenerative disease. Indeed, all motor neurons affected in ALS are responsive to adenosine receptor ligands but interestingly, there are alterations in pre-symptomatic or early symptomatic stages that mirror those in advanced disease stages. Information starts to emerge pointing toward a beneficial role of A_2A receptors (A_2AR), most probably at early disease states, and a detrimental role of caffeine, in clear contrast with what occurs in other neurodegenerative diseases. However, some evidence also exists on a beneficial action of A_2AR antagonists. It may happen that there are time windows where A_2AR prove beneficial and others where their blockade is required. Furthermore, the same changes may not occur simultaneously at the different synapses. In line with this, it is not fully understood if ALS is a dying back disease or if it propagates in a centrifugal way. It thus seems crucial to understand how motor neuron dysfunction occurs, how adenosine receptors are involved in those dysfunctions and whether the early changes in purinergic signaling are compensatory or triggers for the disease. Getting this information is crucial before starting the design of purinergic based strategies to halt or delay disease progression.

Purinergic Receptors in Neurological Diseases With Motor Symptoms: Targets for Therapy

Since proving adenosine triphosphate (ATP) functions as a neurotransmitter in neuron/glia interactions, the purinergic system has been more intensely studied within the scope of the central nervous system. In neurological disorders with associated motor symptoms, including Parkinson's disease (PD), motor neuron diseases (MND), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), Huntington's Disease (HD), restless leg syndrome (RLS), and ataxias, alterations in purinergic receptor expression and activity have been noted, indicating a potential role for this system in disease etiology and progression. In neurodegenerative conditions, neural cell death provokes extensive ATP release and alters calcium signaling through purinergic receptor modulation. Consequently, neuroinflammatory responses, excitotoxicity and apoptosis are directly or indirectly induced. This review analyzes currently available data, which suggests involvement of the purinergic system in neuro-associated motor dysfunctions and underlying mechanisms. Possible targets for pharmacological interventions are also discussed.

The D2 Dopamine Receptor Interferes With the Protective Effect of the A2A Adenosine Receptor on TDP-43 Mislocalization in Experimental Models of Motor Neuron Degeneration

The A2A adenosine receptor (A2AR) and D2 dopamine receptor (D2R) are two G-protein-coupled receptors that can form dimers and negatively regulate their partners. TAR DNA-binding protein (TDP-43) is a nuclear protein that has been implicated in amyotrophic lateral sclerosis (ALS). Mislocalization of TDP-43 from the nucleus to the cytoplasm is an early step of TDP-43 proteinopathy. Our previous studies indicated that A2AR is a potential drug target for ALS because treatment with an A2AR agonist (JMF1907; a T1-11 analog) prevents reactive oxygen species (ROS)-induced TDP-43 mislocalization in a motor neuron cell line (NSC34) and delays motor impairment in a TDP-43 transgenic ALS mouse model. Here, we set out to assess whether activation of D2R interferes with the beneficial effects of an A2AR agonist on motor neurons. We first demonstrated that A2AR and D2R are both located in motor neurons of mouse and human spinal cords and human iPSC-derived motor neurons. Expression of A2AR and D2R in NSC34 cells led to dimer formation without affecting the binding affinity of A2AR toward T1-11. Importantly, activation of D2R reduced T1-11-mediated activation of cAMP/PKA signaling and subsequent inhibition of TDP-43 mislocalization in NSC34 cells. Treatment with quinpirole (a D2 agonist) blunted the rescuing effect of T1-11 on TDP-43 mislocalization and impaired grip strength in a mouse model of ALS. Our findings suggest that D2R activation may limit the beneficial responses of an A2AR agonist in motor neurons and may have an important role in ALS pathogenesis.

Exploring targets and therapies for amyotrophic lateral sclerosis: current insights into dietary interventions

A growing number of preclinical and human studies demonstrate a disease-modifying effect of nutritional state in amyotrophic lateral sclerosis (ALS). The management of optimal nutrition in ALS is complicated, as physiological, physical, and psychological effects of the disease need to be considered and addressed accordingly. In this regard, multidisciplinary care teams play an integral role in providing dietary guidance to ALS patients and their carers. However, with an increasing research focus on the use of dietary intervention strategies to manage disease symptoms and improve prognosis in ALS, many ALS patients are now seeking or are actively engaged in using complementary and alternative therapies that are dietary in nature. In this article, we review the aspects of appetite control, energy balance, and the physiological effects of ALS relative to their impact on overall nutrition. We then provide current insights into dietary interventions for ALS, considering the mechanisms of action of some of the common dietary interventions used in ALS, discussing their validity in the context of clinical trials.

Health benefits of methylxanthines in neurodegenerative diseases

Methylxanthines (MTXs) are consumed by almost everybody in almost every area of the world. Caffeine, theophylline and theobromine are the most well-known members of this family of compounds; they are present, inter alia, in coffee, tea, cacao, yerba mate and cola drinks. MTXs are readily absorbed in the gastrointestinal tract and are able to penetrate into the central nervous system, where they exert significant psychostimulant actions, which are more evident in acute intake. Coffee has been paradigmatic, as its use was forbidden in many diseases, however, this negative view has radically changed; evidence shows that MTXs display health benefits in diseases involving cell death in the nervous system. This paper reviews data that appraise the preventive and even therapeutic potential of MTXs in a variety of neurodegenerative diseases. Future perspectives include the use of MTXs to advance the understanding the pathophysiology of, inter alia, Alzheimer's disease (AD) and Parkinson's disease (PD), and the use of the methylxanthine chemical moiety as a basis for the development of new and more efficacious drugs.

Purinergic contribution to amyotrophic lateral sclerosis

By signalling through purinergic receptors classified as ionotropic P2X (for ATP) and metabotropic P1 (for adenosine) and P2Y (mainly for ADP, UDP, UTP, ATP), the extracellular nucleotides and their metabolic derivatives originated by extracellular activity of several different ectonucleotidases, are involved in the functioning of the nervous system. Here they exert a central role during physiological processes, but also in the precarious balance between beneficial and noxious events. Indeed, in recent years, the dysregulation of extracellular purinergic homeostasis has been correlated to well-characterized acute and chronic neurodegenerative and neuroinflammatory diseases. Among these, we focus our attention on purinergic signalling occurring in amyotrophic lateral sclerosis (ALS), the most common late onset motoneuron disease, characterized by specific loss of motoneurons in brain stem and ventral horns of spinal cord. ALS is a progressive non-cell-autonomous and multifactorial neuroinflammatory disease, whose aetiology and pathological mechanisms are unidentified for most patients and initiate long before any sign or symptom becomes apparent. By combining purinergic with ALS knowledge, in this work we thus present and sustain a novel line of investigation on the purinergic contribution to ALS. In particular, here we recapitulate very early results about P2X4, P2X7 and P2Y6 receptor expression in tissues from ALS animal and cell models and patients, and more recent achievements about purinergic signalling mainly performed in vitro in microglia and lately in astrocytes and motoneurons. We finally highlight how purinergic signalling has progressively evolved up to preclinical trials, to the point of deserving now full consideration with reference to ALS. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Presymptomatic and symptomatic ALS SOD1(G93A) mice differ in adenosine A1 and A2A receptor-mediated tonic modulation of neuromuscular transmission

Amyotrophic lateral sclerosis (ALS) is a disease leading to neuromuscular transmission impairment. A2A adenosine receptor (A2AR) function changes with disease stage, but the role of the A(1) receptors (A1Rs) is unknown and may have a functional cross-talk with A2AR. The role of A1R in the SOD1(G93A) mouse model of ALS in presymptomatic (4-6 weeks old) and symptomatic (12-14 weeks old) phases was investigated by recording endplate potentials (EPPs), miniature endplate potentials (MEPPs), and quantal content (q.c.) of EPPs, from Mg(2+) paralyzed hemidiaphragm preparations. In presymptomatic mice, the A1R agonist, N (6)-cyclopentyladenosine (CPA) (50 nM), decreased mean EPP amplitude, MEPP frequency, and q.c. of EPPs, an effect quantitatively similar to that in age-matched wild-type (WT) mice. However, coactivation of A2AR with CGS 21680 (5 nM) prevented the effects of CPA in WT mice but not in presymptomatic SOD1(G93A) mice, suggestive of A1R/A2AR cross-talk disruption in this phase of ALS. DPCPX (50 nM) impaired CGS 21680 facilitatory action on neuromuscular transmission in WT but not in presymptomatic mice. In symptomatic animals, CPA only inhibited transmission if added in the presence of adenosine deaminase (ADA, 1 U/mL). ADA and DPCPX enhanced more transmission in symptomatic mice than in age-matched WT mice, suggestive of increase in extracellular adenosine during the symptomatic phase of ALS. The data documents that at the neuromuscular junction of presymptomatic SOD1(G93A) mice, there is a loss of A1R-A2AR functional cross-talk, while in symptomatic mice there is increased A1R tonic activation, and that with disease progression, changes in A1R-mediated adenosine modulation may act as aggravating factors during the symptomatic phase of ALS.

Adenosine-mediated modulation of ventral horn interneurons and spinal motoneurons in neonatal mice

Neuromodulation allows neural networks to adapt to varying environmental and biomechanical demands. Purinergic signaling is known to be an important modulatory system in many parts of the CNS, including motor control circuitry. We have recently shown that adenosine modulates the output of mammalian spinal locomotor control circuitry (Witts EC, Panetta KM, Miles GB. J Neurophysiol 107: 1925–1934, 2012). Here we investigated the cellular mechanisms underlying this adenosine-mediated modulation. Whole cell patch-clamp recordings were performed on ventral horn interneurons and motoneurons within in vitro mouse spinal cord slice preparations. We found that adenosine hyperpolarized interneurons and reduced the frequency and amplitude of synaptic inputs to interneurons. Both effects were blocked by the A₁-type adenosine receptor antagonist DPCPX. Analysis of miniature postsynaptic currents recorded from interneurons revealed that adenosine reduced their frequency but not amplitude, suggesting that adenosine acts on presynaptic receptors to modulate synaptic transmission. In contrast to interneurons, recordings from motoneurons revealed an adenosine-mediated depolarization. The frequency and amplitude of synaptic inputs to motoneurons were again reduced by adenosine, but we saw no effect on miniature postsynaptic currents. Again these effects on motoneurons were blocked by DPCPX. Taken together, these results demonstrate differential effects of adenosine, acting via A₁ receptors, in the mouse spinal cord. Adenosine has a general inhibitory action on ventral horn interneurons while potentially maintaining motoneuron excitability. This may allow for adaptation of the locomotor pattern generated by interneuronal networks while helping to ensure the maintenance of overall motor output.

Intakes of caffeine, coffee and tea and risk of amyotrophic lateral sclerosis: Results from five cohort studies

Caffeine is thought to be neuroprotective by antagonizing the adenosine A2A receptors in the brain and thereby protecting motor neurons from excitotoxicity. We examined the association between consumption of caffeine, coffee and tea and risk of amyotrophic lateral sclerosis (ALS). Longitudinal analyses based on over 1,010,000 males and females in five large cohort studies (the Nurses' Health Study, the Health Professionals Follow-up Study, the Cancer Prevention Study II Nutrition Cohort, the Multiethnic Cohort Study, and the National Institutes of Health-AARP Diet and Health Study). Cohort-specific multivariable-adjusted risk ratios (RR) and 95% confidence intervals (CI) estimates of ALS incidence or death were estimated by Cox proportional hazards regression and pooled using random-effects models. Results showed that a total of 1279 cases of ALS were documented during a mean of 18 years of follow-up. Caffeine intake was not associated with ALS risk; the pooled multivariable-adjusted RR comparing the highest to the lowest quintile of intake was 0.96 (95% CI 0.81-1.16). Similarly, neither coffee nor tea was associated with ALS risk. In conclusion, the results of this large study do not support associations of caffeine or caffeinated beverages with ALS risk.

Suppression of adenosine 2a receptor (A2aR)-mediated adenosine signaling improves disease phenotypes in a mouse model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease in which the majority of upper and lower motor neurons are degenerated. Despite intensive efforts to identify drug targets and develop neuroprotective strategies, effective therapeutics for ALS remains unavailable. The identification and characterization of novel targets and pathways remain crucial in the development of ALS therapeutics. Adenosine is a major neuromodulator that actively regulates synaptic transmission. Interestingly, adenosine levels are significantly elevated in the cerebrospinal fluid (CSF) of progressing human ALS patients. In the current study, we showed that adenosine 2a receptor (A2aR), but not adenosine 1 receptor (A1R), is highly enriched in spinal (motor) neurons. A2aR expression is also selectively increased at the symptomatic onset in the spinal cords of SOD1G93A mice and end-stage human ALS spinal cords. Interestingly, we found that direct adenosine treatment is sufficient to induce embryonic stem cell-derived motor neuron (ESMN) cell death in cultures. Subsequent pharmacological inhibition and partial genetic ablation of A2aR (A2aR(+/-)) significantly protect ESMN from SOD1G93A(+) astrocyte-induced cell death and delay disease progression of SOD1G93A mice. Taken together, our results provide compelling novel evidence that A2aR-mediated adenosine signaling contributes to the selective spinal motor neuron degeneration observed in the SOD1G93A mouse model of ALS.

Adenosine A2A receptors activation facilitates neuromuscular transmission in the pre-symptomatic phase of the SOD1(G93A) ALS mice, but not in the symptomatic phase

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease leading to motor neuron dysfunction resulting in impairment of neuromuscular transmission. A2A adenosine receptors have already been considered as a potential therapeutical target for ALS but their neuromodulatory role at the neuromuscular junction in ALS remains to be clarified. In the present work, we evaluated the effects of A2A receptors on neuromuscular transmission of an animal model of ALS: SOD1(G93A) mice either in the pre-symptomatic (4-6 weeks old) or in the symptomatic (12-14 weeks old) stage. Electrophysiological experiments were performed obtaining intracellular recordings in Mg2+ paralyzed phrenic nerve-hemidiaphragm preparations. Endplate potentials (EPPs), quantal content (q. c.) of EPPs, miniature endplate potentials (MEPPs) and giant miniature endplate potential (GMEPPs) were recorded. In the pre-symptomatic phase of the disease (4-6 weeks old mice), the selective A2A receptor agonist, CGS 21680, significantly enhanced (p<0.05 Unpaired t-test) the mean amplitude and q.c. of EPPs, and the frequency of MEPPs and GMEPPs at SOD1(G93A) neuromuscular junctions, the effect being of higher magnitude (p<0.05, Unpaired t-test) than age-matched control littermates. On the contrary, in symptomatic mice (12-14 weeks old), CGS 21680 was devoid of effect on both the amplitude and q.c. of EPPs and the frequency of MEPPs and GMEPPs (p<0.05 Paired t-test). The results herein reported clearly document that at the neuromuscular junction of SOD1(G93A) mice there is an exacerbation of A2A receptor-mediated excitatory effects at the pre-symptomatic phase, whereas in the symptomatic phase A2A receptor activation is absent. The results thus suggest that A2A receptors function changes with ALS progression.

Association between caffeine intake and age at onset in Huntington's disease

Habitual consumption of caffeine, a non-selective adenosine receptor (AR) antagonist, has been suggested to be beneficial in Parkinson's and Alzheimer's diseases. Experimental evidence support that ARs play a role in Huntington's disease (HD) raising the hypothesis that caffeine may be a life-style modifier in HD. To determine a possible relationship between caffeine consumption and age at onset (AAO) in HD, we retrospectively assessed caffeine consumption in 80 HD patients using a dietary survey and determined relationship with AAO. Following adjustment for gender, smoking status and CAG repeat length, caffeine consumption greater than 190mg/day was significantly associated with an earlier AAO. These data support an association between habitual caffeine intake and AAO in HD patients, but further studies are warranted to understand the link between these variables.

Caffeine inhibits acetylcholinesterase, but not butyrylcholinesterase

Caffeine is an alkaloid with a stimulant effect in the body. It can interfere in transmissions based on acetylcholine, epinephrine, norepinephrine, serotonin, dopamine and glutamate. Clinical studies indicate that it can be involved in the slowing of Alzheimer disease pathology and some other effects. The effects are not well understood. In the present work, we focused on the question whether caffeine can inhibit acetylcholinesterase (AChE) and/or, butyrylcholinesterase (BChE), the two enzymes participating in cholinergic neurotransmission. A standard Ellman test with human AChE and BChE was done for altering concentrations of caffeine. The test was supported by an in silico examination as well. Donepezil and tacrine were used as standards. In compliance with Dixon’s plot, caffeine was proved to be a non-competitive inhibitor of AChE and BChE. However, inhibition of BChE was quite weak, as the inhibition constant, K_i, was 13.9 ± 7.4 mol/L. Inhibition of AChE was more relevant, as K_i was found to be 175 ± 9 μmol/L. The predicted free energy of binding was −6.7 kcal/mol. The proposed binding orientation of caffeine can interact with Trp86, and it can be stabilize by Tyr337 in comparison to the smaller Ala328 in the case of human BChE; thus, it can explain the lower binding affinity of caffeine for BChE with reference to AChE. The biological relevance of the findings is discussed.