Cholinergic muscarinic M1/M4 receptor networks in dementia with Lewy bodies

Visual dysfunction in dementia with Lewy bodies

PURPOSE OF REVIEW

To review the literature on visual dysfunction in dementia with Lewy bodies (DLB), including its mechanisms and clinical implications.

RECENT FINDINGS

Recent studies have explored novel aspects of visual dysfunction in DLB, including visual texture agnosia, mental rotation of 3-dimensional drawn objects, and reading fragmented letters. Recent studies have shown parietal and occipital hypoperfusion correlating with impaired visuoconstruction performance. While visual dysfunction in clinically manifest DLB is well recognized, recent work has focused on prodromal or mild cognitive impairment (MCI) due to Lewy body pathology with mixed results. Advances in retinal imaging have recently led to the identification of abnormalities such as parafoveal thinning in DLB. Patients with DLB experience impairment in color perception, form and object identification, space and motion perception, visuoconstruction tasks, and illusions in association with visual cortex and network dysfunction. These symptoms are associated with visual hallucinations, driving impairment, falls, and other negative outcomes.

Alzheimer's disease and clinical trials

Alzheimer's disease (AD) is spreading its root disproportionately among the worldwide population. Many genes have been identified as the hallmarks of AD. Based upon the knowledge, many clinical trials have been designed and conducted. Attempts have been made to alleviate the pathology associated with AD by targeting the molecular products of these genes. Irrespective of the understanding on the genetic component of AD, many clinical trials have failed and imposed greater challenges on the path of drug discovery. Therefore, this review aims to identify research and review articles to pinpoint the limitations of drug candidates (thiethylperazine, CT1812, crenezumab, CNP520, and lecanemab), which are under or withdrawn from clinical trials. Thorough analysis of the cross-talk pathways led to the identification of many confounding factors, which could interfere with the success of clinical trials with drug candidates such as thiethylperazine, CT1812, crenezumab, and CNP520. Though these drug candidates were enrolled in clinical trials, yet literature review shows many limitations. These limitations raise many questions on the rationale behind the enrollments of these drug candidates in clinical trials. A meticulous prior assessment of the outcome of clinical studies may stop risky clinical trials at their inceptions. This may save time, money, and resources.

Noradrenergic and cholinergic systems take centre stage in neuropsychiatric diseases of ageing

Noradrenergic and cholinergic systems are among the most vulnerable brain systems in neuropsychiatric diseases of ageing, including Alzheimer's disease, Parkinson's disease, Lewy body dementia, and progressive supranuclear palsy. As these systems fail, they contribute directly to many of the characteristic cognitive and psychiatric symptoms. However, their contribution to symptoms is not sufficiently understood, and pharmacological interventions targeting noradrenergic and cholinergic systems have met with mixed success. Part of the challenge is the complex neurobiology of these systems, operating across multiple timescales, and with non-linear changes across the adult lifespan and disease course. We address these challenges in a detailed review of the noradrenergic and cholinergic systems, outlining their roles in cognition and behaviour, and how they influence neuropsychiatric symptoms in disease. By bridging across levels of analysis, we highlight opportunities for improving drug therapies and for pursuing personalised medicine strategies.

Effects of 3R, 16S-2-hydroxyethyl apovincaminate (HEAPO), donepezil and galantamine on learning and memory retention in naïve Wistar rats

The effects of 3R,16S-2-hydroxyethyl apovincaminate (HEAPO, RGH-10885) compared with those of two cholinesterase inhibitors, donepezil and galantamine, were examined in naïve Wistar rats using standard active and passive avoidance tests. The active avoidance test (shuttle box) and two passive avoidance tests (step-through and step-down) were performed according to the experimental design. There were 10 groups of rats (n = 8) and the substances studied were applied orally before each testing session. In the active avoidance test, the number of conditioned stimuli (avoidances), unconditioned stimuli (escapes) and intertrial crossings were observed. In step-down and step-through passive avoidance tests, the latencies of reactions were observed. All the studied compounds showed positive effects in the learning and memory tests, compared to the controls. It was concluded that HEAPO, donepezil and galantamine had a memory-enhancing effect in active and passive avoidance tests.

Structure-activity relationship of pyrazol-4-yl-pyridine derivatives and identification of a radiofluorinated probe for imaging the muscarinic acetylcholine receptor M4

There is an accumulating body of evidence implicating the muscarinic acetylcholine receptor 4 (M₄) in schizophrenia and dementia with Lewy bodies, however, a clinically validated M₄ positron emission tomography (PET) radioligand is currently lacking. As such, the aim of this study was to develop a suitable M₄ PET ligand that allows the non-invasive visualization of M₄ in the brain. Structure-activity relationship studies of pyrazol-4-yl-pyridine derivates led to the discovery of target compound 12 - a subtype-selective positive allosteric modulator (PAM). The radiofluorinated analogue, [¹⁸F]12, was synthesized in 28 ± 10% radiochemical yield, >37 GBq/μmol and an excellent radiochemical purity >99%. Initial in vitro autoradiograms on rodent brain sections were performed in the absence of carbachol and showed moderate specificity as well as a low selectivity of [¹⁸F]12 for the M₄-rich striatum. However, in the presence of carbachol, a significant increase in tracer binding was observed in the rat striatum, which was reduced by >60% under blocking conditions, thus indicating that orthosteric ligand interaction is required for efficient binding of [¹⁸F]12 to the allosteric site. Remarkably, however, the presence of carbachol was not required for high specific binding in the non-human primate (NHP) and human striatum, and did not further improve the specificity and selectivity of [¹⁸F]12 in higher species. These results pointed towards significant species-differences and paved the way for a preliminary PET study in NHP, where peak brain uptake of [¹⁸F]12 was found in the putamen and temporal cortex. In conclusion, we report on the identification and preclinical development of the first radiofluorinated M₄ PET radioligand with promising attributes. The availability of a clinically validated M₄ PET radioligand harbors potential to facilitate drug development and provide a useful diagnostic tool for non-invasive imaging.

(Dis-)Connected Dots in Dementia with Lewy Bodies-A Systematic Review of Connectivity Studies

Studies on dementia with Lewy bodies (DLB) have mainly focused on the degeneration of distinct cortical and subcortical regions related to the deposition of Lewy bodies. In view of the proposed trans-synaptic spread of the α-synuclein pathology, investigating the disease only in this segregated fashion would be detrimental to our understanding of its progression. In this systematic review, we summarize findings on structural and functional brain connectivity in DLB, as connectivity measures may offer better insights on how the brain is affected by the spread of the pathology. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we searched Web of Science, PubMed, and SCOPUS for relevant articles published up to November 1, 2021. Of 1215 identified records, we selected and systematically reviewed 53 articles that compared connectivity features between patients with DLB and healthy controls. Structural and functional magnetic resonance imaging, positron emission tomography, single-positron emission computer tomography, and electroencephalography assessments of patients revealed widespread abnormalities within and across brain networks in DLB. Frontoparietal, default mode, and visual networks and their connections to other brain regions featured the most consistent disruptions, which were also associated with core clinical features and cognitive impairments. Furthermore, graph theoretical measures revealed disease-related decreases in local and global network efficiency. This systematic review shows that structural and functional connectivity characteristics in DLB may be particularly valuable at early stages, before overt brain atrophy can be observed. This knowledge may help improve the diagnosis and prognosis in DLB as well as pinpoint targets for future disease-modifying treatments. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Selectivity mechanism of muscarinic acetylcholine receptor antagonism through in silico investigation

Structures of muscarinic acetylcholine receptors illustrate the strikingly high degree of homology of the residues among isoforms, thus leading to difficulty in achieving subtype selectivity when targeting these receptors and causing undesired side effects when treating the corresponding diseases. Considering the urgent need for more selective and potency therapies, this study is aimed at revealing the selectivity mechanism against M4/5 via in silico strategies, revealing crucial molecular interactions such as hydrogen bonds and pi-cation interaction formed between the key residues TYR416, ASN417, and TRP435 of M4, respectively, hydrophobic pocket formed by the key residues, especially CYS484 of M5. Besides, the water around TYR416^M4 and ASN459^M5, which can be replaced by substituent groups which can form the hydrogen bond interaction network by simulated bridging water and the water around ASP112^M4, whose replacement maybe not contribute to the increase in binding affinity of the compound, may affect the inhibitory selectivity among M4/5 in the aspect of the solvent. Moreover, from the point of inhibitors, compounds with a positively ionizable group could selectively bind to M4 receptors, while hydrophobic molecules may bind preferably to M5. We believe that the current study would provide a basis for the design of subsequent M4/5 selective antagonists.

PET Imaging of Cholinergic Neurotransmission in Neurodegenerative Disorders

As a neuromodulator, the neurotransmitter acetylcholine plays an important role in cognitive, mood, locomotor, sleep/wake, and olfactory functions. In the pathophysiology of most neurodegenerative diseases, such as Alzheimer disease (AD) or Lewy body disorder (LBD), cholinergic receptors, transporters, or enzymes are involved and relevant as imaging targets. The aim of this review is to summarize current knowledge on PET imaging of cholinergic neurotransmission in neurodegenerative diseases. For PET imaging of presynaptic vesicular acetylcholine transporters (VAChT), (-)-¹⁸F-fluoroethoxybenzovesamicol (¹⁸F-FEOBV) was the first PET ligand that could be successfully translated to clinical application. Since then, the number of ¹⁸F-FEOBV PET investigations on patients with AD or LBD has grown rapidly and provided novel, important findings concerning the pathophysiology of AD and LBD. Regarding the α4β2 nicotinic acetylcholine receptors (nAChRs), various second-generation PET ligands, such as ¹⁸F-nifene, ¹⁸F-AZAN, ¹⁸F-XTRA, (-)-¹⁸F-flubatine, and (+)-¹⁸F-flubatine, were developed and successfully translated to human application. In neurodegenerative diseases such as AD and LBD, PET imaging of α4β2 nAChRs is of special value for monitoring disease progression and drugs directed to α4β2 nAChRs. For PET of α7 nAChR, ¹⁸F-ASEM and ¹¹C-MeQAA were successfully applied in mild cognitive impairment and AD, respectively. The highest potential for α7 nAChR PET is seen in staging, in evaluating disease progression, and in therapy monitoring. PET of selective muscarinic acetylcholine receptors (mAChRs) is still in an early stage, as the development of subtype-selective radioligands is complicated. Promising radioligands to image mAChR subtypes M1 (¹¹C-LSN3172176), M2 (¹⁸F-FP-TZTP), and M4 (¹¹C-MK-6884) were developed and successfully translated to humans. PET imaging of mAChRs is relevant for the assessment and monitoring of therapies in AD and LBD. PET of acetylcholine esterase activity has been investigated since the 1990s. Many PET studies with ¹¹C-PMP and ¹¹C-MP4A demonstrated cortical cholinergic dysfunction in dementia associated with AD and LBD. Recent studies indicated a solid relationship between subcortical and cortical cholinergic dysfunction and noncognitive dysfunctions such as balance and gait in LBD. Taken together, PET of distinct components of cholinergic neurotransmission is of great interest for diagnosis, disease monitoring, and therapy monitoring and to gain insight into the pathophysiology of different neurodegenerative disorders.

Muscarinic Receptors Expression in the Peripheral Blood Cells Differentiate Dementia with Lewy Bodies from Alzheimer's Disease

BACKGROUND

Central nervous system disruption of cholinergic (ACh) signaling, which plays a major role in cognitive processes, is well documented in dementia with Lewy bodies (DLB) and Alzheimer's disease (AD). The expression of muscarinic ACh receptors type 1 and 4 (CHRM1 and CHRM4) has been reported to be altered in the brain of DLB patients.

OBJECTIVE

We aim to assess the peripheral gene expression of CHRM1 and 4 in DLB as a possible marker as compared to AD and healthy control (HC) subjects.

METHODS

Peripheral blood mononuclear cells were collected from 21 DLB, 13 AD, and 8 HC matched subjects. RT-PCR was performed to estimate gene expression of CHRM1 and CHRM4.

RESULTS

Peripheral CHRM1 expression was higher and CHRM4 was lower in DLB and AD compared to HC, whereas both CHRM1 and CHRM4 levels were higher in AD compared to DLB patients. Receiver operating characteristics curves, with logistic regression analysis, showed that combining peripheral CHRM1 and CHRM4 levels, DLB and AD subjects were classified with an accuracy of 76.0%.

CONCLUSION

Alterations of peripheral CHRM1 and CHRM4 was found in both AD and DLB patients as compared to HC. CHRM1 and CHRM4 gene expression resulted to be lower in DLB patients compared to AD. In the future, peripheral CHRM expression could be studied as a possible marker of neurodegenerative conditions associated with cholinergic deficit and a possible marker of response to acetylcholinesterase inhibitors.

Chemistry and Toxicology of Major Bioactive Substances in Inocybe Mushrooms

Mushroom poisoning has always been a threat to human health. There are a large number of reports about ingestion of poisonous mushrooms every year around the world. It attracts the attention of researchers, especially in the aspects of toxin composition, toxic mechanism and toxin application in poisonous mushroom. Inocybe is a large genus of mushrooms and contains toxic substances including muscarine, psilocybin, psilocin, aeruginascin, lectins and baeocystin. In order to prevent and remedy mushroom poisoning, it is significant to clarify the toxic effects and mechanisms of these bioactive substances. In this review article, we summarize the chemistry, most known toxic effects and mechanisms of major toxic substances in Inocybe mushrooms, especially muscarine, psilocybin and psilocin. Their available toxicity data (different species, different administration routes) published formerly are also summarized. In addition, the treatment and medical application of these toxic substances in Inocybe mushrooms are also discussed. We hope that this review will help understanding of the chemistry and toxicology of Inocybe mushrooms as well as the potential clinical application of its bioactive substances to benefit human beings.