TAAR1 Activation Research Articles

Vasoconstrictor Effects of Trace Amine Associated Receptor Agonists in the Isolated Perfused Rat Kidney.

Endogenous trace amines such as tryptamine and 3-iodothyronamine (T1AM) are present in mammalian tissues at very low concentrations. They produce their actions by activating surface G protein-coupled receptors known as trace amine-associated receptors (TAARs). The study was designed to investigate the possible vasoconstrictor effects of tryptamine, T1AM, and the selective TAAR1 agonist RO5263397 in isolated perfused rat kidney. Renal vascular reactivity experiment using Male Wistar Kyoto (WKY, n = 82) and Spontaneously Hypertensive Rats (SHR, n = 89) were used in this study. Tryptamine, T1AM, and RO5263397 increased perfusion pressure in preparations from WKY rats and SHRs in a dose-dependent manner, with no significant difference between the agonist's pD2 values (P > 0.05). EPPTB, a selective TAAR1 antagonist (1ηM), significantly (P < 0.05) reduced agonist-induced increase in perfusion pressure in both WKY and SHRs, suggesting a role for TAAR1 activation in these responses. The vasoconstrictor responses in both groups were significantly reduced by L-type dihydropyridine calcium channel blocker, Rho-kinase, and PKC inhibitors suggesting the involvement of extracellular calcium and enhanced calcium sensitization. Reactive oxygen species (ROS) scavenger significantly inhibited the agonist-induced increase in perfusion pressure in preparations from SHRs but not WKY. The agonist-induced increase in perfusion pressure in the kidney involves the influx of extracellular calcium, increased calcium sensitization, and ROS in SHRs only.

Vasodilator Effect of Trace Amines, 3-Iodothyronamine, and RO5263397 in the Rat Perfused Kidney: Comparison with Tryptamine

Introduction: Trace amine-associated receptors (TAARs) are a family of G protein-coupled receptors and are widely distributed in the body. Activation of TAAR1 by specific agonists can produce a variety of physiological effects centrally and peripherally. The objective of this study was to investigate the vasodilator effect of two selective TAAR1 agonists 3-iodothyronamine (T1AM) and RO5263397 in the isolated perfused rat kidney preparation. Methods: Kidneys were isolated and perfused with Krebs’ solution, gassed with 95% oxygen and 5% carbon dioxide, through the renal artery. Results: In preparations pre-constricted with methoxamine (5 × 10⁻⁶<sc>m</sc>), T1AM (10⁻¹⁰ – 10⁻⁶ mol), RO5263397 (10⁻¹⁰ – 10⁻⁶ mol), and tryptamine (10⁻¹⁰ – 10⁻⁶ mol) produced dose-dependent vasodilator responses. EPPTB (1 × 10⁻⁶<sc>m</sc>), a selective TAAR1 antagonist, had no effect on vasodilator responses induced by these agonists. A higher concentration of EPPTB (3 × 10⁻⁵<sc>m</sc>) produced a sustained increase in perfusion pressure but did not affect vasodilator responses to tryptamine, T1AM, and RO5263397. Agonist-induced vasodilator responses were slightly reduced by the removal of the endothelium but were not affected by L-NAME (1 × 10⁻⁴<sc>m</sc>), an inhibitor of nitric oxide synthesis. The vasodilator responses were significantly reduced by inhibiting calcium-activated (tetraethylammonium, 1 × 10⁻³<sc>m</sc>) and voltage-activated (4-AP, 1 × 10⁻³<sc>m</sc>) potassium channels. Tryptamine-, T1AM-, and RO5263397-induced vasodilator responses were significantly reduced by BMY7378, a 5-HT_1A receptor antagonist. Conclusion: It was concluded that vasodilator responses produced by the TAAR1 agonists, T1AM, RO5263397, and tryptamine, were not mediated via TAAR1 but were probably via activation of 5-HT_1A receptors.

Methamphetamine Activates Trace Amine Associated Receptor 1 to Regulate Astrocyte Excitatory Amino Acid Transporter-2 via Differential CREB Phosphorylation During HIV-Associated Neurocognitive Disorders

Methamphetamine (METH) use, referred to as methamphetamine use disorder (MUD), results in neurocognitive decline, a characteristic shared with HIV-associated neurocognitive disorders (HAND). MUD exacerbates HAND partly through glutamate dysregulation. Astrocyte excitatory amino acid transporter (EAAT)-2 is responsible for >90% of glutamate uptake from the synaptic environment and is significantly decreased with METH and HIV-1. Our previous work demonstrated astrocyte trace amine associated receptor (TAAR) 1 to be involved in EAAT-2 regulation. Astrocyte EAAT-2 is regulated at the transcriptional level by cAMP responsive element binding (CREB) protein and NF-κB, transcription factors activated by cAMP, calcium and IL-1β. Second messengers, cAMP and calcium, are triggered by TAAR1 activation, which is upregulated by IL-1β METH-mediated increases in these second messengers and signal transduction pathways have not been shown to directly decrease astrocyte EAAT-2. We propose CREB activation serves as a master regulator of EAAT-2 transcription, downstream of METH-induced TAAR1 activation. To investigate the temporal order of events culminating in CREB activation, genetically encoded calcium indicators, GCaMP6s, were used to visualize METH-induced calcium signaling in primary human astrocytes. RNA interference and pharmacological inhibitors targeting or blocking cAMP-dependent protein kinase A and calcium/calmodulin kinase II confirmed METH-induced regulation of EAAT-2 and resultant glutamate clearance. Furthermore, we investigated METH-mediated CREB phosphorylation at both serine 133 and 142, the co-activator and co-repressor forms, respectively. Overall, this work revealed METH-induced differential CREB phosphorylation is a critical regulator for EAAT-2 function and may thus serve as a mechanistic target for the attenuation of METH-induced excitotoxicity in the context of HAND.

Effects of a trace amine-associated receptor 1 agonist RO 5263397 on ethanol-induced behavioral sensitization

BackgroundAlcohol dependence is a chronic and severe health problem which puts a heavy burden on society. Alcohol activates mesolimbic dopamine circuity to achieve its reinforcing effect. While TAAR1 is critically involved in the modulation of dopamine, there is little evidence indicating that TAAR1 could play a role in behavioral effects of ethanol. MethodsBy using the animal model of behavioral sensitization induced by ethanol in mice, the present study was performed to investigate whether the activation of TAAR1 would affect the behavioral plasticity of ethanol. ResultsRepeated administration with ethanol induced a significant increased locomotion in WT mice with females showing higher level of sensitization to ethanol than male mice. The TAAR1 agonist RO5263397 significantly decreased the expression of ethanol-induced behavioral sensitization both in male and female WT mice (0.1 and 0.32 mg/kg). Repeated RO5263397 exposure also prevented the development of behavioral sensitization to ethanol both in male and female WT mice. Moreover, while TAAR1-KO mice developed normal levels of ethanol-induced behavioral sensitization, RO5263397 did not affect this behavior in TAAR1-KO mice. ConclusionsThese results indicated that the TAAR1 agonist RO5263397 negatively regulated the expression and development of ethanol-elicited behavioral sensitization in WT but not in TAAR1-KO mice. The present study suggests that TAAR1 is probably involved in certain addiction-like effects of alcohol and could be a useful drug target for the development of new medications to treat alcohol dependence.

TAAR1 and Psychostimulant Addiction.

Trace amine-associated receptor 1 is one of the best-characterized receptors of trace amines. Growing evidence shows that TAAR1 negatively regulates the monoaminergic activity, including dopamine transmission in the mesocorticolimbic system. Neurochemical assays demonstrated that selective TAAR1 full and partial agonists were effective to prevent psychostimulants-induced dopamine transmission in vitro and in vivo. In the last decade, many preclinical models of psychostimulant addiction such as drug-induced behavioral sensitization, drug-induced conditioned place preference, drug self-administration, drug discrimination, and relapse models were used to assess the effects of TAAR1 agonists on psychostimulants' behavioral effects. In general, activation of TAAR1 attenuated while knockout of TAAR1 potentiated psychostimulant abuse-related behaviors. Here, we review the advances in TAAR1 and its agonists in modulating psychostimulant addiction. We discuss the similarities and differences between the neurochemical and behavioral effects of TAAR1 full and partial agonists. We also discuss several concerns including the abuse liability, sleep reduction, and species-dependent effects that might affect the successful translation of TAAR1 agonists from preclinical studies to clinical application. In conclusion, although further investigations are in need to address certain concerns and the underlying neural mechanisms, TAAR1 agonists appear to be a promising pharmacotherapy to treat psychostimulant addiction and prevent relapse.

Amphetamine Stimulates Endocytosis of the Norepinephrine and Neuronal Glutamate Transporters in Cultured Locus Coeruleus Neurons

Amphetamines and amphetamine-derivatives elevate neurotransmitter concentrations by competing with endogenous biogenic amines for reuptake. In addition, AMPHs have been shown to activate endocytosis of the dopamine transporter (DAT) which further elevates extracellular dopamine (DA). We previously found that the biochemical cascade leading to this cellular process involves entry of AMPH into the cell through the DAT, stimulation of an intracellular trace amine-associated receptor, TAAR1, and activation of the small GTPase, RhoA. We also showed that the neuronal glutamate transporter, EAAT3, undergoes endocytosis via the same cascade in DA neurons, leading to potentiation of glutamatergic inputs. Since AMPH is a transported inhibitor of both DAT and the norepinephrine transporter (NET), and EAAT3 is also expressed in norepinephrine (NE) neurons, we explored the possibility that this signaling cascade occurs in NE neurons. We found that AMPH can cause endocytosis of NET as well as EAAT3 in NE neurons. NET endocytosis is dependent on TAAR1, RhoA, intracellular calcium and CaMKII activation, similar to DAT. However, EAAT3 endocytosis is similar in all regards except its dependence upon CaMKII activation. RhoA activation is dependent on calcium, but not CaMKII, explaining a divergence in AMPH-mediated endocytosis of DAT and NET from that of EAAT3. These data indicate that AMPHs and other TAAR1 agonists can affect glutamate signaling through internalization of EAAT3 in NE as well as DA neurons.

TAAR Agonists.

Trace amine-associated receptors (TAARs) are a family of G protein-coupled receptors (GPCRs) that are evolutionarily conserved in vertebrates. The first discovered TAAR1 is mainly expressed in the brain, and is able to detect low abundant trace amines. TAAR1 is also activated by several synthetic compounds and psychostimulant drugs like amphetamine. Activation of TAAR1 by specific agonists can regulate the classical monoaminergic systems in the brain. Further studies have revealed that other TAAR family members are highly expressed in the olfactory system which are termed olfactory TAARs. In vertebrates, olfactory TAARs can specifically recognize volatile or water-soluble amines. Some of these TAAR agonists are produced by decarboxylation of amino acids. In addition, some TAAR agonists are ethological odors that mediate animal innate behaviors. In this study, we provide a comprehensive review of TAAR agonists, including their structures, biosynthesis pathways, and functions.

TAAR1 AGONISTS AS A POTENTIAL TARGET IN THE THERAPY OF MENTAL DISORDERS WITH THE DEFICIT OF IMPULSIVE AND COMPULSIVE CONTROL

Receptors associated with trace amines, 1st subtype (TAAR1), are the promising targets for the development of new pharmacological approaches to the treatment of various neuropsychiatric disorders. Currently TAAR1 agonists are undergoing clinical trials as new pharmacologically active agents with antipsychotic action. At the same time, the expression of TAAR1 and the physiological significance of these receptors as regulators of the activity of catecholaminergic structures in the Central nervous system suggest that the activation of TAAR1 can have a therapeutic effect in patients suffering from mental diseases such as obsessive-compulsive disorder and attention deficit hyperactivity disorder, which are accompanied by violations of impulsive and compulsive control. This paper is an attempt to critically evaluate the currently existing data set obtained during testing of TAAR1 ligands in in vivo studies over the past 5 years. The analysis suggests that TAAR1 agonists may provide and have a limited anti-compulsive effect when used in the clinic.

Activation of TAAR1 attenuates extended access of cocaine self‐administration and stress‐induced reinstatement of cocaine‐seeking

Trace amine‐associated receptor 1 (TAAR1) is the best‐characterized sub‐family of receptors of trace amines. As a modulator of dopaminergic system, TAAR1 has been shown to play a critical role in regulating the rewarding properties of drugs of abuse such as cocaine. In our previous studies, we demonstrated that TAAR1 agonists were able to reduce cocaine intake and cue‐ and drug‐induced reinstatements of cocaine‐seeking under short‐access conditions. However, compared to the extended access of cocaine self‐administration model, the short‐access model could not mimic some core properties of addiction, such as escalation, compulsive motivation, and incubation of cocaine‐seeking. Furthermore, it remains unclear whether activation of TAAR1 would affect stress‐induced reinstatement of cocaine‐seeking. Here, we investigated the effects of TAAR1 partial agonist RO5263397 on the extended access of cocaine self‐administration. We also assessed the effects of the selective TAAR1 full agonist RO5166017 on the yohimbine‐induced reinstatement of cocaine‐seeking. We found that the TAAR1 partial agonist RO5263397 attenuated the escalation, break point, and cue‐seeking behavior in the extended access of cocaine self‐administration model. We also found that RO5166017 reduced yohimbine‐induced reinstatement of cocaine‐seeking and yohimbine‐potentiated cue‐induced reinstatement of cocaine seeking, indicating that activation of TAAR1 decreased the stress‐induced reinstatement of cocaine‐seeking. Taken together, our results suggest that TAAR1 is a promising therapeutic target for the treatment of cocaine addiction.Support or Funding InformationThis work was supported by the National Institute of Health Grants R21‐DA033426.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Case for TAAR1 as a Modulator of Central Nervous System Function.

TAAR1 is widely expressed across the mammalian brain, particularly in limbic and monoaminergic areas, allegedly involved in mood, attention, memory, fear, and addiction. However, the subcellular distribution of TAAR1 is still unclear, since TAAR1 signal is largely intracellular. In vitro, TAAR1 is activated with nanomolar to micromolar affinity by some endogenous amines, particularly p-tyramine, beta-phenylethylamine, and 3-iodothyronamine (T1AM), the latter representing a novel branch of thyroid hormone signaling. In addition, TAAR1 responds to a number of psychoactive drugs, i.e., amphetamines, ergoline derivatives, bromocriptine and lisuride. Trace amines have been identified as neurotransmitters in invertebrates, and they are considered as potential neuromodulators. In particular, beta-phenylethylamine and p-tyramine have been reported to modify the release and/or the response to dopamine, norepinephrine, acetylcholine and GABA, while evidence of cross-talk between TAAR1 and other aminergic receptors has been provided. Systemic or intracerebroventricular injection of exogenous T1AM produced prolearning and antiamnestic effects, reduced pain threshold, decreased non-REM sleep, and modulated the firing rate of adrenergic neurons in locus coeruleus. However each of these substances may have additional molecular targets, and it is unclear whether their endogenous levels are sufficient to produce significant TAAR1 activation in vivo. TAAR1 knock out mice show a worse performance in anxiety and working memory tests, and they are more prone to develop ethanol addiction. They also show increased locomotor response to amphetamine, and decreased stereotypical responses induced by apomorphine. Notably, human genes for TAARs cluster on chromosome 6 at q23, within a region whose mutations have been reported to confer susceptibility to schizophrenia and bipolar disorder. For human TAAR1, around 200 non-synonymous and 400 synonymous single nucleotide polymorphisms have been identified, but their functional consequences have not been extensively investigated yet. In conclusion, the bulk of evidence points to a significant physiological role of TAAR1 in the modulation of central nervous system function and a potential pharmacological role of TAAR1 agonists in neurology and/or psychiatry. However, the specific effects of TAAR1 stimulation are still controversial, and many crucial issues require further investigation.

Activation of TAAR1 reduces cocaine addiction: from behavior to neurobiology

Activation of TAAR1 reduces cocaine addiction: from behavior to neurobiology

Trace amine-associated receptor 1 is a stereoselective binding site for compounds in the amphetamine class

The demonstrated ability of amphetamine to functionally activate the rat trace amine associated receptor 1 (rTAAR1) and the subsequent reports of amphetamine activation of TAAR1 in rhesus monkey mouse, human, and human-rat chimeric TAAR1-expressing cell lines has led to speculation as to the role of this receptor in the central nervous system (CNS) responses associated with amphetamine and its analogs. The agonist potencies of ten pairs of enantiomeric amphetamines, including several with known CNS activity, at primate TAAR1 stably expressed in RD-HGA16 cells, robustly indicate the S-configuration to be associated with higher potency. Moreover, the rank order of potency to activate TAAR1 parallels the stimulant action reported by humans for the specific amphetamines. Taken together, these data suggest that TAAR1 is a stereoselective binding site for amphetamine and that activation of TAAR1 is involved in the modulation of the stimulant properties of amphetamine and its congeners. In addition, the observed parallel between hTAAR1 and rhTAAR1 responses supports the rhesus monkey as a highly translational model for developing novel TAAR1-directed compounds as therapeutics for amphetamine-related addictions.

Amiodarone and its putative metabolites fail to activate wild type hTAAR1

The ability of amiodarone and its putative metabolites to activate unmodified human trace amine associated receptor 1 ( hTAAR1) stably expressed in CHO cell lines was evaluated. Receptor activation was monitored by measuring the accumulation of cAMP, the putative hTAAR1 native second messenger, or calcium mobilization in cells where the receptor was coupled to the promiscuous Gq, G α16. Despite literature reports of activation of rodent TAAR1 by these agents, no response was seen in either cell line although robust activation was obtained with the endogenous ligand β-phenethylamine. These results indicate that TAAR1 activation by amiodarone and its analogs is species specific.

Trace Amine-Associated Receptor Agonists: Synthesis and Evaluation of Thyronamines and Related Analogues

We have previously shown that several thyronamines, decarboxylated and deiodinated metabolites of the thyroid hormone, potently activate an orphan G protein-coupled receptor in vitro (TAAR1) and induced hypothermia in vivo on a rapid time scale [Scanlan, T. S.; Suchland, K. L.; Hart, M. E.; Chiellini, G.; Huang, Y.; Kruzich, P. J.; Frascarelli, S.; Crossley, D. A.; Bunzow, J. R.; Ronca-Testoni, S.; Lin, E. T.; Hatton, D.; Zucchi, R.; Grandy, D. K. 3-Iodothyronamine is an endogenous and rapid-acting derivative of thyroid hormone. Nat. Med. 2004, 10 (6), 638-642]. Herein, we report the synthesis of these thyronamines. Additionally, a large number of thyroamine derivatives were synthesized in an effort to understand the molecular basis of TAAR1 activation and hypothermia induction. Several derivatives were found to potently activate both rTAAR1 and mTAAR1 in vitro (compounds 77, 85, 91, and 92). When administered to mice at a 50 mg/kg dose, these derivatives all induced significant hypothermia within 60 min and exhibited a hypothermic induction profile analogous to 3-iodothyronamine (1, T(1)AM) except 91, which proved to be more efficacious. On the basis of this result, a dose-dependent profile for 91 was generated and an ED(50) of 30 mumol/kg was calculated. Compound 91 proved to be more potent than T(1)AM for TAAR1 activation and exhibits increased potency and efficacy for hypothermia induction. These data further strengthen the pharmacological correlation linking TAAR1 activation by thyronamines and hypothermia induction in mice.