The seeming paradox of adenosine receptors as targets for the treatment of Alzheimer's disease: agonists or antagonists?

Effects of caffeine on temporal perception in Rattus norvegicus

We report two studies that tested the effects of caffeine, the world's most widely used psychoactive drug, on temporal perception. We trained Wistar rats using the Bisection Procedure (Experiment 1) or the Stubbs' Procedure (Experiment 2) to discriminate between short and long light stimuli. Once training finished, we administered caffeine orally (0, 9.6, and 96.0 mg/kg for Experiment 1 and 0, 9.6, 19.2, and 38.4 mg/kg for Experiment 2) 15 minutes prior to testing. Relative to the control condition, the 9.6 mg/kg condition (Experiments 1 and 2) and the 19.2 mg/kg condition (Experiment 2) resulted in an increase in proportion of choosing the long response. Meanwhile, overall accuracy was not affected by any condition in both experiments. Taken together, these results are consistent with the notion that caffeine, at some doses, speeds up temporal perception. However, it is not clear why the effect disappears at higher doses.

Adenosine receptor signalling in Alzheimer’s disease

Alzheimer’s disease (AD) is the most common dementia in the elderly and its increasing prevalence presents treatment challenges. Despite a better understanding of the disease, the current mainstay of treatment cannot modify pathogenesis or effectively address the associated cognitive and memory deficits. Emerging evidence suggests adenosine G protein-coupled receptors (GPCRs) are promising therapeutic targets for Alzheimer’s disease. The adenosine A₁ and A_2A receptors are expressed in the human brain and have a proposed involvement in the pathogenesis of dementia. Targeting these receptors preclinically can mitigate pathogenic β-amyloid and tau neurotoxicity whilst improving cognition and memory. In this review, we provide an accessible summary of the literature on Alzheimer’s disease and the therapeutic potential of A₁ and A_2A receptors. Although there are no available medicines targeting these receptors approved for treating dementia, we provide insights into some novel strategies, including allosterism and the targeting of oligomers, which may increase drug discovery success and enhance the therapeutic response.

Role and Function of Adenosine and its Receptors in Inflammation, Neuroinflammation, IBS, Autoimmune Inflammatory Disorders, Rheumatoid Arthritis and Psoriasis

The physiological effects of endogenous adenosine on various organ systems are very complex and numerous which are elicited upon activation of any of the four G-protein-coupled receptors (GPCRs) denoted as A1, A2A, A2B and A3 adenosine receptors (ARs). Several fused heterocyclic and non-xanthine derivatives are reported as a possible target for these receptors due to physiological problems and lack of selectivity of xanthine derivatives. In the present review, we have discussed the development of various new chemical entities as a target for these receptors. In addition, compounds acting on adenosine receptors can be utilized in treating diseases like inflammation, neuroinflammation, autoimmune and related diseases.

Caffeine and neuropsychiatric symptoms in patients with dementia: A systematic review

BACKGROUND

The consumption of caffeine has well known effects on the behavior and sleep of healthy adults. Behavioral symptoms and sleeping difficulties are common in patients with dementia which may be affected by caffeine consumption. This systematic review examines the association between caffeine intake and neuropsychiatric symptoms in patients with dementia.

METHODS

In January 2019 an extensive search was conducted in Medline (PubMed), Embase, Emcare, Cochrane, PsychInfo, Web of Science and gray literature. Studies were included when they: i) investigated patients diagnosed with dementia, ii) reported neuropsychiatric symptoms, iii) used caffeine or coffee consumption as an intervention, and iv) reported associations between caffeine or coffee consumption and neuropsychiatric symptoms. Studies were excluded when they also included participants without a diagnosis of dementia, or presented a review or expert opinion. Two reviewers independently rated the studies and reached consensus on the appraisal.

RESULTS

Of the seven studies eligible for this review, four reported on sleeping difficulties and five on behavioral symptoms. There was no consistent effect of caffeine administration on neuropsychiatric symptoms: e.g., both high caffeine consumption and eliminating caffeine were associated with less apathy, the total Neuropsychiatric Inventory (Nursing Home) decreased after both coffee therapy and after eliminating caffeine, and both caffeine consumption and eliminating caffeine improved sleep.

CONCLUSION

These findings suggest that caffeine can either induce or reduce neuropsychiatric symptoms in individual patients with dementia. Therefore, in these patients, caffeine consumption requires a prudent individualized approach and further research on the effects of caffeine on individual neuropsychiatric symptoms is required.

Computer-Aided Multi-Target Management of Emergent Alzheimer's Disease

Alzheimer's disease (AD) represents an enormous global health burden in terms of human suffering and economic cost. AD management requires a shift from the prevailing paradigm targeting pathogenesis to design and develop effective drugs with adequate success in clinical trials. Therefore, it is of interest to report a review on amyloid beta (Aβ) effects and other multi-targets including cholinesterase, NFTs, tau protein and TNF associated with brain cell death to be neuro-protective from AD. It should be noted that these molecules have been generated either by target-based or phenotypic methods. Hence, the use of recent advancements in nanomedicine and other natural compounds screening tools as a feasible alternative for circumventing specific liabilities is realized. We review recent developments in the design and identification of neuro-degenerative compounds against AD generated using current advancements in computational multi-target modeling algorithms reflected by theragnosis (combination of diagnostic tests and therapy) concern.