The β-adrenergic hypothesis of synaptic and microglial impairment in Alzheimer's disease

The lateralized LC-NAergic system distinguishes vicarious versus direct fear in mice

Fear can be induced either directly through self-experience of aversive events or vicariously by observing conspecifics experiencing such events. The locus coeruleus-norepinephrine (LC-NA) system is crucial in fear responses and cognitive processes. We investigated whether the LC-NA system differentially processes these two types of fear, direct and vicarious in male mice. The results highlighted that the right hemisphere LC→anterior cingulate cortex pathway is uniquely crucial for vicarious fear, while the two inputs to the LC-from the bed nucleus of the stria terminalis (BNST) and the central amygdala (CeA)-differentially contribute to fear processing. The BNST plays a more targeted role in vicarious fear, and the CeA has a broader influence on fear in general. This underscores the complexity and specialization within the LC-NA system for fear-processing.

Recent advancements in the therapeutic approaches for Alzheimer's disease treatment: current and future perspective

Alzheimer's disease (AD) is a complex, incurable neurological condition characterized by cognitive decline, cholinergic neuron reduction, and neuronal loss. Its exact pathology remains uncertain, but multiple treatment hypotheses have emerged. The current treatments, single or combined, alleviate only symptoms and struggle to manage AD due to its multifaceted pathology. The developmental drugs target pivotal disease factors involved in the envisaged hypotheses and include targets such as amyloid aggregation, hyperphosphorylated tau proteins, and receptors like cholinergic, adrenergic, etc. Present-day research focuses on multi-target directed ligands (MTDLs), which inhibit multiple factors simultaneously, helping slow the disease's progression. This review attempts to collate the recent information related to proposed hypotheses for AD etiology. It systematically organizes the advances in various therapeutic options for AD, with a particular emphasis on clinical candidates. Also, it is expected to help medicinal chemists design novel AD treatments based on available information, which could be helpful to AD patients.

Evidence from a mouse model supports repurposing an anti-asthmatic drug, bambuterol, against Alzheimer's disease by administration through an intranasal route

Bambuterol is a long-acting anti-asthmatic prodrug which releases terbutaline. Terbutaline is an agonist of the β2-adrenergic receptors which is formed by decarbamoylation of bambuterol by butyrylcholinesterase. Inhibition of the latter, as well as activation of β2-AR, are of interest for the treatment of Alzheimer's disease (AD). Combining these two activities, bambuterol could express a good clinical efficacy against AD. The present work firstly confirmed the capacity of bambuterol to display in cellulo neuroprotective activities, reduction of Tau hyperphosphorylation and preservation of synapses in rat hippocampal neuronal cultures intoxicated with Aβ peptides. Further, bambuterol, in the form of a liposomal gel, showed a good bioavailability in CNS after intranasal administration, which should reduce any side effects linked to peripheral terbutaline release. Indeed, even if the latter is more selective than other β2-mimetics towards bronchial β2-AR, cardiovascular effects (tachycardia, arrhythmias…) could occur upon cardiac β1-AR activation. Finally, intranasal administration of low doses of bambuterol gel in mice intoxicated with Aβ peptides, prevented long-term spatial memory impairment and showed beneficial effects on the survival of neurons and on synapse preservation.

Relationship between enriched environment and neurodegeneration: a review from mechanism to therapy

Enriched environment (EE), as a non-pharmacological intervention, has garnered considerable attention for its potential to ameliorate neurodegenerative diseases (NDs). This review delineated the impact of EE on the biological functions associated with NDs, emphasizing its role in enhancing neural plasticity, reducing inflammation, and bolstering cognitive performance. We discussed the molecular underpinnings of the effects of EE, including modulation of key signaling pathways such as extracellular regulated kinase 1/2 (ERK1/2), mitogen-activated protein kinases (MAPK), and AMPK/SIRT1, which were implicated in neuroprotection and synaptic plasticity. Additionally, we scrutinized the influence of EE on epigenetic modifications and autophagy, processes pivotal to ND pathogenesis. Animal models, encompassing both rodents and larger animals, offer insights into the disease-modifying effects of EE, underscoring its potential as a complementary approach to pharmacological interventions. In summary, EE emerges as a promising strategy to augment cognitive function and decelerate the progression of NDs.

Deciphering the Role of Adrenergic Receptors in Alzheimer's Disease: Paving the Way for Innovative Therapies

Neurodegenerative diseases are currently among the most devastating diseases with no effective disease-modifying drugs in the market, with Alzheimer's disease (AD) being the most prevalent. AD is a complex multifactorial neurodegenerative disorder characterized by progressive and severe cognitive impairment and memory loss. It is the most common cause of progressive memory loss (dementia) in the elderly, and to date, there is no effective treatment to cure or slow disease progression substantially. The role of adrenergic receptors in the pathogenesis of Alzheimer's disease and other tauopathies is poorly understood or investigated. Recently, some studies indicated a potential benefit of drugs acting on the adrenergic receptors for AD and dementias, although due to the heterogeneity of the drug classes used, the results on the whole remain inconclusive. The scope of this review article is to comprehensively review the literature on the possible role of adrenergic receptors in neurodegenerative diseases, stemming from the use of agonists and antagonists including antihypertensive and asthma drugs acting on the adrenergic receptors, but also from animal models and in vitro models where these receptors have been studied. Ultimately, we hope to obtain a better understanding of the role of these receptors, identify the gaps in knowledge, and explore the possibility of repurposing such drugs for AD, given their long history of use and safety.

Combined in vivo MRI assessment of locus coeruleus and nucleus basalis of Meynert integrity in amnestic Alzheimer's disease, suspected-LATE and frontotemporal dementia

BACKGROUND

The locus coeruleus (LC) and the nucleus basalis of Meynert (NBM) are altered in early stages of Alzheimer's disease (AD). Little is known about LC and NBM alteration in limbic-predominant age-related TDP-43 encephalopathy (LATE) and frontotemporal dementia (FTD). The aim of the present study is to investigate in vivo LC and NBM integrity in patients with suspected-LATE, early-amnestic AD and FTD in comparison with controls.

METHODS

Seventy-two participants (23 early amnestic-AD patients, 17 suspected-LATE, 17 FTD patients, defined by a clinical-biological diagnosis reinforced by amyloid and tau PET imaging, and 15 controls) underwent neuropsychological assessment and 3T brain MRI. We analyzed the locus coeruleus signal intensity (LC-I) and the NBM volume as well as their relation with cognition and with medial temporal/cortical atrophy.

RESULTS

We found significantly lower LC-I and NBM volume in amnestic-AD and suspected-LATE in comparison with controls. In FTD, we also observed lower NBM volume but a slightly less marked alteration of the LC-I, independently of the temporal or frontal phenotype. NBM volume was correlated with the global cognitive efficiency in AD patients. Strong correlations were found between NBM volume and that of medial temporal structures, particularly the amygdala in both AD and FTD patients.

CONCLUSIONS

The alteration of LC and NBM in amnestic-AD, presumed-LATE and FTD suggests a common vulnerability of these structures to different proteinopathies. Targeting the noradrenergic and cholinergic systems could be effective therapeutic strategies in LATE and FTD.

Periodontal disease and risk of Alzheimer's disease: A two-sample Mendelian randomization

BACKGROUND

Evidence from observational studies and clinical trials suggests an association between periodontal disease and Alzheimer's disease (AD). However, the causal relationship between periodontal disease and AD remains to be determined.

METHODS

We obtained periodontal disease data from the FinnGen database and two sets of AD data from the IEU consortium and PGC databases. Subsequently, we conducted a two-sample Mendelian randomization (MR) analysis to investigate the causal relationship between periodontal disease and AD.

RESULTS

The results of the random-effects IVW analysis revealed no evidence of a genetic causal relationship between periodontal disease and AD, regardless of whether the AD data from the IEU consortium or the AD data from the PGC database were utilized. No heterogeneity, multiple effects of levels, or outliers were observed in this study.

CONCLUSIONS

Our findings indicate that there is no causal relationship between periodontal disease and AD at the genetic level.

Drug repurposing for neurodegenerative diseases using Zebrafish behavioral profiles

Drug repurposing can accelerate drug development while reducing the cost and risk of toxicity typically associated with de novo drug design. Several disorders lacking pharmacological solutions and exhibiting poor results in clinical trials - such as Alzheimer's disease (AD) - could benefit from a cost-effective approach to finding new therapeutics. We previously developed a neural network model, Z-LaP Tracker, capable of quantifying behaviors in zebrafish larvae relevant to cognitive function, including activity, reactivity, swimming patterns, and optomotor response in the presence of visual and acoustic stimuli. Using this model, we performed a high-throughput screening of FDA-approved drugs to identify compounds that affect zebrafish larval behavior in a manner consistent with the distinct behavior induced by calcineurin inhibitors. Cyclosporine (CsA) and other calcineurin inhibitors have garnered interest for their potential role in the prevention of AD. We generated behavioral profiles suitable for cluster analysis, through which we identified 64 candidate therapeutics for neurodegenerative disorders.

One-Trial Appetitive Learning Tasks for Drug Targeting

One-trial appetitive learning developed from one-trial passive avoidance learning as a standard test of retrograde amnesia. It consists of one learning trial followed by a retention test, in which physiological manipulations are presented. As in passive avoidance learning, food- or waterdeprived rats or mice finding food or water inside an enclosure are vulnerable to the retrograde amnesia produced by electroconvulsive shock treatment or the injection of various drugs. In one-trial taste or odor learning conducted in rats, birds, snails, bees, and fruit flies, there is an association between a food item or odorant and contextual stimuli or the unconditioned stimulus of Pavlovian conditioning. The odor-related task in bees was sensitive to protein synthesis inhibition as well as cholinergic receptor blockade, both analogous to results found on the passive avoidance response in rodents, while the task in fruit flies was sensitive to genetic modifications and aging, as seen in the passive avoidance response of genetically modified and aged rodents. These results provide converging evidence of interspecies similarities underlying the neurochemical basis of learning.

Finding Drug Repurposing Candidates for Neurodegenerative Diseases using Zebrafish Behavioral Profiles

Drug repurposing can accelerate drug development while reducing the cost and risk of toxicity typically associated with de novo drug design. Several disorders lacking pharmacological solutions and exhibiting poor results in clinical trials - such as Alzheimer's disease (AD) - could benefit from a cost-effective approach to finding new therapeutics. We previously developed a neural network model, Z-LaP Tracker, capable of quantifying behaviors in zebrafish larvae relevant to cognitive function, including activity, reactivity, swimming patterns, and optomotor response in the presence of visual and acoustic stimuli. Using this model, we performed a high-throughput screening of FDA-approved drugs to identify compounds that affect zebrafish larval behavior in a manner consistent with the distinct behavior induced by calcineurin inhibitors. Cyclosporine (CsA) and other calcineurin inhibitors have garnered interest for their potential role in the prevention of AD. We generated behavioral profiles suitable for cluster analysis, through which we identified 64 candidate therapeutics for neurodegenerative disorders.

Confounding in observational studies evaluating the association between Alzheimer's disease and periodontal disease: A systematic review

Background

Studies investigating the association between periodontitis and Alzheimer's disease (AD) suggested indirect (periodontitis would increase the circulation of inflammation-inducible molecules) and direct (periodontopathogens might colonize brains affected by Alzheimer's disease) pathways. While there seems to be a positive relationship between periodontitis and AD, concerns have been raised about the role of confounding.

Aim

To systematically review the literature to assess confounding and their level of heterogeneity in the association between periodontitis and AD. Also, to examine data reporting and interpretation regarding confounding bias.

Methods

This review followed the PRISMA guidelines and was registered within PROSPERO. Electronic searches were performed in seven main databases and three others to capture the "grey literature". The PECO strategy was used to identify observational studies (cross-sectional, case-control, or cohort studies) assessing the association between periodontal disease and AD without restricting publication language and year. Critical appraisal was performed according to the Joanna Briggs Institute guidelines. Confounders were evaluated following a two-step approach.

Results

A total of 3255 studies were found, of which 18 (13 case-control, four cross-sectional, and one cohort) met the eligibility criteria. Participants with AD were 1399 (mean age 64 ± 9 to 84.8 ± 5.6 years), whereas those without AD were 1730 (mean age 62.6 ± 7.1 to 81.4 ± 4.6). Female patients composed most of the sample for both groups. The confounding variables "age" and "sex" were present in all studies. Four studies used the 2017 AAP/EFP periodontal classification. Most studies had a low risk of bias. Fifty percent of the articles did not consider confounding; variation in the adjustment approaches was observed. Additionally, 62% of the studies did not mention bias, and 40% did not discuss any limitations about confounders.

Conclusions

Given the study's limitations, caution must be taken to properly interpret the association between periodontitis and AD.Registration: CRD42022293884.