Potential contributions of trace amines in Alzheimer's disease and therapeutic prospects

Trace amine-associated receptor 1 (TAAR1): an emerging therapeutic target for neurodegenerative, neurodevelopmental, and neurotraumatic disorders

Trace amines are physiologically active amines present in all organisms. They are structurally identical to traditional monoamines and are rapidly metabolized by monoamine oxidases. The mammalian neurological system generates these molecules at rates equivalent to traditional monoamines, but because of their short half-life, they are only observable in trace quantities. Their receptors are G protein-coupled receptors present in both the CNS and peripheral locations, with trace amine-associated receptor 1 (TAAR1) being the most researched. TAAR1's capacity to regulate glutamatergic and monoaminergic neurotransmission has made it a viable therapeutic target for neuropsychiatric illnesses. Although the TAAR1 role in schizophrenia and other neuropsychiatric disorders is well established, its role in the pathology of neurodegenerative and neurotraumatic disorders recently got attention. This review discusses the role of TAAR1 in neurodegenerative, neurodevelopment, and neurotraumatic disorders and explores its potential to be a novel therapeutic target in these disorders.

Effect of Chronic Dolutegravir Administration on the Trace Amine Profile in Wistar Rats

BACKGROUND

Dolutegravir (DTG), an integrase strand inhibitor, is currently used as the first-line treatment for HIV. Despite relatively poor tissue penetration, the risk of adverse effects in metabolic and excretory systems should be considered. The trace aminergic system and trace amines are emerging as relevant role players in many chronic diseases that are commonly diagnosed but poorly understood. Trace amines are biogenic amines that are endogenously produced and can also be ingested by the intake of trace amine-rich food. Trace amines are known to differentially regulate inflammatory and neurological outcome.

OBJECTIVE

This study investigated the effects of DTG on the trace amine profile in a wistar rat model.

METHODS

A total of 24 healthy wistar rats were randomly divided into four experimental groups: male and female controls and male and female DTG-treated. Blood and tissue samples were collected following a 12-week DTG administration study. Liquid chromatography-tandem mass spectroscopy (LC-MS/MS) was used to determine trace amine concentrations in urine, plasma, brain, and gastrointestinal tissue.

RESULTS

Current data illustrate that polyamines differ significantly (p < 0.05) between males and females in various matrices. DTG significantly (p < 0.05) reduced jejunal tyramine and urinary synephrine levels.

CONCLUSION

Data do not raise major concerns about DTG in the context of the trace amine profile. However, given the importance of the dysregulated trace amine profile in various diseased states, including HIV, current data warrant clinical investigation to further evaluate the significance of DTG-associated effects on the trace amine profile.

Magic Blue-Initiated SN2-Type Ring Opening of Activated Aziridines: Friedel-Crafts-Type Alkylation of Electron-Rich Arenes/Heteroarenes

A transition metal-free, atom-economical, and highly stereospecific synthetic approach to Friedel-Crafts-type alkylation of arenes/heteroarenes has been developed. The protocol involves the catalytic aminium radical-cation salt (Magic Blue)-initiated SN2-type nucleophilic ring opening of activated aziridines with arenes/heteroarenes to give the corresponding 2,2-diarylethylamines up to 99% yield and 85% ee (for nonracemic aziridines) in a very short reaction time. Moreover, on reaction with 1,3-dimethylindole and benzofuran, aziridines undergo domino-ring-opening cyclization (DROC) to give the various biologically significant heterocyclic scaffolds in moderate to good yields.

Systematic characterization of multi-omics landscape between gut microbial metabolites and GPCRome in Alzheimer's disease

Shifts in the magnitude and nature of gut microbial metabolites have been implicated in Alzheimer's disease (AD), but the host receptors that sense and respond to these metabolites are largely unknown. Here, we develop a systems biology framework that integrates machine learning and multi-omics to identify molecular relationships of gut microbial metabolites with non-olfactory G-protein-coupled receptors (termed the "GPCRome"). We evaluate 1.09 million metabolite-protein pairs connecting 408 human GPCRs and 335 gut microbial metabolites. Using genetics-derived Mendelian randomization and integrative analyses of human brain transcriptomic and proteomic profiles, we identify orphan GPCRs (i.e., GPR84) as potential drug targets in AD and that triacanthine experimentally activates GPR84. We demonstrate that phenethylamine and agmatine significantly reduce tau hyperphosphorylation (p-tau181 and p-tau205) in AD patient induced pluripotent stem cell-derived neurons. This study demonstrates a systems biology framework to uncover the GPCR targets of human gut microbiota in AD and other complex diseases if broadly applied.

Ultrasensitive quantification of trace amines based on N-phosphorylation labeling chip 2D LC-QQQ/MS

Trace amines (TAs) are metabolically related to catecholamine and associated with cancer and neurological disorders. Comprehensive measurement of TAs is essential for understanding pathological processes and providing proper drug intervention. However, the trace amounts and chemical instability of TAs challenge quantification. Here, diisopropyl phosphite coupled with chip two-dimensional (2D) liquid chromatography tandem triple-quadrupole mass spectrometry (LC-QQQ/MS) was developed to simultaneously determine TAs and associated metabolites. The results showed that the sensitivities of TAs increased up to 5520 times compared with those using nonderivatized LC-QQQ/MS. This sensitive method was utilized to investigate their alterations in hepatoma cells after treatment with sorafenib. The significantly altered TAs and associated metabolites suggested that phenylalanine and tyrosine metabolic pathways were related to sorafenib treatment in Hep3B cells. This sensitive method has great potential to elucidate the mechanism and diagnose diseases considering that an increasing number of physiological functions of TAs have been discovered in recent decades.

The Use of Yeast in Biosensing

Yeast has been used as a model for several diseases as it is the simplest unicellular eukaryote, safe and easy to culture and harbors most of the fundamental processes that are present in almost all higher eukaryotes, including humans. From understanding the pathogenesis of disease to drug discovery studies, yeast has served as an important biosensor. It is not only due to the conservation of genetics, amenable modification of its genome and easily accessible analytical methods, but also some characteristic features such as its ability to survive with defective mitochondria, making it a highly flexible microbe for designing whole-cell biosensing systems. The aim of this review is to report on how yeasts have been utilized as biosensors, reporting on responses to various stimuli.

Trace Amine Associate Receptor 1 (TAAR1) as a New Target for the Treatment of Cognitive Dysfunction in Alzheimer's Disease

Worldwide, approximately 27 million people are affected by Alzheimer’s disease (AD). AD pathophysiology is believed to be caused by the deposition of the β-amyloid peptide (Aβ). Aβ can reduce long-term potentiation (LTP), a form of synaptic plasticity that is closely associated with learning and memory and involves postsynaptic glutamate receptor phosphorylation and trafficking. Moreover, Aβ seems to be able to reduce glutamatergic transmission by increasing the endocytosis of NMDA receptors. Trace amines (TAs) are biogenic amines that are structurally similar to monoamine neurotransmitters. TAs bind to G protein-coupled receptors, called TAARs (trace amine-associated receptors); the best-studied member of this family, TAAR1, is distributed in the cortical and limbic structures of the CNS. It has been shown that the activation of TAAR1 can rescue glutamatergic hypofunction and that TAAR1 can modulate glutamate NMDA receptor-related functions in the frontal cortex. Several lines of evidence also suggest the pro-cognitive action of TAAR1 agonists in various behavioural experimental protocols. Thus, we studied, in vitro, the role of the TAAR1 agonist RO5256390 on basal cortical glutamatergic transmission and tested its effect on Aβ-induced dysfunction. Furthermore, we investigated, in vivo, the role of TAAR1 in cognitive dysfunction induced by Aβ infusion in Aβ-treated mice. In vitro data showed that Aβ 1–42 significantly decreased NMDA cell surface expression while the TAAR1 agonist RO5256390 promoted their membrane insertion in cortical cells. In vivo, RO5256390 showed a mild pro-cognitive effect, as demonstrated by the better performance in the Y maze test in mice treated with Aβ. Further studies are needed to better understand the interplay between TAAR1/Aβ and glutamatergic signalling, in order to evaluate the eventual beneficial effect in different experimental paradigms and animal models. Taken together, our data indicate that TAAR1 agonism may provide a novel therapeutic approach in the treatments of disorders involving Aβ-induced cognitive impairments, such as AD.

Genetic reduction of tyramine β hydroxylase suppresses Tau toxicity in a Drosophila model of tauopathy

Tauopathies are a class of neurodegenerative diseases characterized by the abnormal phosphorylation and accumulation of the microtubule-associated protein, Tau. These diseases are associated with degeneration and dysfunction of the noradrenergic system, a critical regulator of memory, locomotion, and the fight or flight response. Though Tau pathology accumulates early in noradrenergic neurons, the relationship between noradrenaline signaling and tauopathy pathogenesis remains unclear. The fruit fly, Drosophila melanogaster, is a valuable model organism commonly used to investigate factors that promote Tau-mediated degeneration. Moreover, Drosophila contain the biogenic amine, octopamine, which is the functional homolog to noradrenaline. Using a Drosophila model of tauopathy, we conducted a candidate modifier screen targeting tyramine β hydroxylase (tβh), the enzyme that controls the production of octopamine in the fly, to determine if levels of this enzyme modulate Tau-induced degeneration in the fly eye. We found that genetic reduction of tβh suppresses Tau toxicity, independent of Tau phosphorylation. These findings show that reduction of tβh, a critical enzyme in the octopaminergic pathway, suppresses Tau pathogenicity and establishes an interaction that can be further utilized to determine the relationship between noradrenergic-like signaling and Tau toxicity in Drosophila.

‘The awesome power of yeast’ in Alzheimer’s disease research

The difficulties in performing experimental studies related to diseases of the human brain have fostered a range of disease models from highly expensive and complex animal models to simple, robust, unicellular yeast models. Yeast models have been used in numerous studies to understand Alzheimer’s disease (AD) pathogenesis and to search for drugs targeting AD. Thanks to the conservation of fundamental eukaryotic processes including ageing and the availability of appropriate technological platforms, budding yeast are a simple model eukaryote to assist with understanding human cell biology, offering a platform to study human diseases. This article aims to provide insights from yeast models on the contributions of amyloid beta, a causative agent in AD, and recent research findings on AD chemoprevention.