1
|
Pinckaers NET, Blankesteijn WM, Mircheva A, Shi X, Opperhuizen A, van Schooten FJ, Vrolijk MF. In Vitro Activation of Human Adrenergic Receptors and Trace Amine-Associated Receptor 1 by Phenethylamine Analogues Present in Food Supplements. Nutrients 2024; 16:1567. [PMID: 38892500 PMCID: PMC11174489 DOI: 10.3390/nu16111567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2024] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 06/21/2024] Open
Abstract
Pre-workout supplements are popular among sport athletes and overweight individuals. Phenethylamines (PEAs) and alkylamines (AA) are widely present in these supplements. Although the health effects of these analogues are not well understood yet, they are hypothesised to be agonists of adrenergic (ADR) and trace amine-associated receptors (TAARs). Therefore, we aimed to pharmacologically characterise these compounds by investigating their activating properties of ADRs and TAAR1 in vitro. The potency and efficacy of the selected PEAs and AAs was studied by using cell lines overexpressing human ADRα1A/α1B/α1D/α2a/α2B/β1/β2 or TAAR1. Concentration-response relationships are expressed as percentages of the maximal signal obtained by the full ADR agonist adrenaline or the full TAAR1 agonist phenethylamine. Multiple PEAs activated ADRs (EC50 = 34 nM-690 µM; Emax = 8-105%). Almost all PEAs activated TAAR1 (EC50 = 1.8-92 µM; Emax = 40-104%). Our results reveal the pharmacological profile of PEAs and AAs that are often used in food supplements. Several PEAs have strong agonistic properties on multiple receptors and resemble potencies of the endogenous ligands, indicating that they might further stimulate the already activated sympathetic nervous system in exercising athletes via multiple mechanisms. The use of supplements containing one, or a combination of, PEA(s) may pose a health risk for their consumers.
Collapse
Affiliation(s)
- Nicole E. T. Pinckaers
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
- Research Institute of Nutrition and Translational Research in Metabolism (NUTRIM), Maastricht University, 6200 MD Maastricht, The Netherlands
| | - W. Matthijs Blankesteijn
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
- School for Cardiovascular Diseases (CARIM), Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Anastasiya Mircheva
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Xiao Shi
- Research Service, Veterans Affairs Portland Health Care System, Portland, OR 97239, USA
- Department of Psychiatry, Oregon Health and Science University, Portland, OR 97239, USA
| | - Antoon Opperhuizen
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
- Office for Risk Assessment and Research, Netherlands Food and Consumer Product Safety Authority, 3540 AA Utrecht, The Netherlands
| | - Frederik-Jan van Schooten
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
- Research Institute of Nutrition and Translational Research in Metabolism (NUTRIM), Maastricht University, 6200 MD Maastricht, The Netherlands
| | - Misha F. Vrolijk
- Department of Pharmacology and Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands
- Research Institute of Nutrition and Translational Research in Metabolism (NUTRIM), Maastricht University, 6200 MD Maastricht, The Netherlands
| |
Collapse
|
2
|
Dicks LMT. Our Mental Health Is Determined by an Intrinsic Interplay between the Central Nervous System, Enteric Nerves, and Gut Microbiota. Int J Mol Sci 2023; 25:38. [PMID: 38203207 PMCID: PMC10778721 DOI: 10.3390/ijms25010038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 12/13/2023] [Accepted: 12/16/2023] [Indexed: 01/12/2024] Open
Abstract
Bacteria in the gut microbiome play an intrinsic part in immune activation, intestinal permeability, enteric reflex, and entero-endocrine signaling. The gut microbiota communicates with the central nervous system (CNS) through the production of bile acids, short-chain fatty acids (SCFAs), glutamate (Glu), γ-aminobutyric acid (GABA), dopamine (DA), norepinephrine (NE), serotonin (5-HT), and histamine. A vast number of signals generated in the gastrointestinal tract (GIT) reach the brain via afferent fibers of the vagus nerve (VN). Signals from the CNS are returned to entero-epithelial cells (EES) via efferent VN fibers and communicate with 100 to 500 million neurons in the submucosa and myenteric plexus of the gut wall, which is referred to as the enteric nervous system (ENS). Intercommunications between the gut and CNS regulate mood, cognitive behavior, and neuropsychiatric disorders such as autism, depression, and schizophrenia. The modulation, development, and renewal of nerves in the ENS and changes in the gut microbiome alter the synthesis and degradation of neurotransmitters, ultimately influencing our mental health. The more we decipher the gut microbiome and understand its effect on neurotransmission, the closer we may get to developing novel therapeutic and psychobiotic compounds to improve cognitive functions and prevent mental disorders. In this review, the intricate control of entero-endocrine signaling and immune responses that keep the gut microbiome in a balanced state, and the influence that changing gut bacteria have on neuropsychiatric disorders, are discussed.
Collapse
Affiliation(s)
- Leon M T Dicks
- Department of Microbiology, Stellenbosch University, Private Bag X1, Matieland, Stellenbosch 7602, South Africa
| |
Collapse
|
3
|
Yang SH, Yang E, Lee J, Kim JY, Yoo H, Park HS, Jung JT, Lee D, Chun S, Jo YS, Pyeon GH, Park JY, Lee HW, Kim H. Neural mechanism of acute stress regulation by trace aminergic signalling in the lateral habenula in male mice. Nat Commun 2023; 14:2435. [PMID: 37105975 PMCID: PMC10140019 DOI: 10.1038/s41467-023-38180-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 04/19/2023] [Indexed: 04/29/2023] Open
Abstract
Stress management is necessary for vertebrate survival. Chronic stress drives depression by excitation of the lateral habenula (LHb), which silences dopaminergic neurons in the ventral tegmental area (VTA) via GABAergic neuronal projection from the rostromedial tegmental nucleus (RMTg). However, the effect of acute stress on this LHb-RMTg-VTA pathway is not clearly understood. Here, we used fluorescent in situ hybridisation and in vivo electrophysiology in mice to show that LHb aromatic L-amino acid decarboxylase-expressing neurons (D-neurons) are activated by acute stressors and suppress RMTg GABAergic neurons via trace aminergic signalling, thus activating VTA dopaminergic neurons. We show that the LHb regulates RMTg GABAergic neurons biphasically under acute stress. This study, carried out on male mice, has elucidated a molecular mechanism in the efferent LHb-RMTg-VTA pathway whereby trace aminergic signalling enables the brain to manage acute stress by preventing the hypoactivity of VTA dopaminergic neurons.
Collapse
Affiliation(s)
- Soo Hyun Yang
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Esther Yang
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Jaekwang Lee
- Division of Functional Food Research, Korea Food Research Institute, Wanju, 55365, South Korea
| | - Jin Yong Kim
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Hyeijung Yoo
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Hyung Sun Park
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Jin Taek Jung
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Dongmin Lee
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea
| | - Sungkun Chun
- Department of Physiology, Jeonbuk National University Medical School, Jeonju, 54907, South Korea
| | - Yong Sang Jo
- School of Psychology, Korea University, Seoul, 02841, South Korea
| | - Gyeong Hee Pyeon
- School of Psychology, Korea University, Seoul, 02841, South Korea
| | - Jae-Yong Park
- Department of Integrated Biomedical and Life Science, Graduate School, Korea University, Seoul, 02841, South Korea
| | - Hyun Woo Lee
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea.
| | - Hyun Kim
- Department of Anatomy, College of Medicine, Korea University, Seoul, 02841, South Korea.
| |
Collapse
|
4
|
TAAR1 dependent and independent actions of the potential antipsychotic and dual TAAR1/5-HT 1A receptor agonist SEP-383856. Neuropsychopharmacology 2022; 47:2319-2329. [PMID: 36100653 PMCID: PMC9630386 DOI: 10.1038/s41386-022-01421-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2022] [Revised: 07/04/2022] [Accepted: 07/30/2022] [Indexed: 11/09/2022]
Abstract
SEP-383856 (SEP-856) is a novel antipsychotic under clinical development. It displays a unique pattern of receptor interaction, with only weak (partial agonist) activity at dopamine D2 receptors, yet more potent agonist activity at the trace amine associated receptor (TAAR1) and 5-hydroxytryptamine 1 A receptor (5-HT1A). Nonetheless, these observations await independent confirmation and more detailed characterization of the in vitro and in vivo actions of SEP-856 at TAAR1 and 5-HT1A receptors would be instructive. Herein, we employed luminescence complementation technology in heterologous live cell systems, confocal microscopy, voltage clamp electrophysiology, behavioral readouts and TAAR1 knockout (KO) mice to study SEP-856 in further detail. We provide evidence for the ability of SEP-856 to activate TAAR1 at the surface plasma membrane, and show that this interaction results in Gαs recruitment (pEC50: 6.08 ± 0.22 EMAX: 96.41% ± 15.26) and by extension, to G-protein inwardly rectifying potassium (GIRK) channel activation. Using TAAR1-KO mice, we find TAAR1 to be indispensable for SEP-856 control of body temperature, baseline locomotion reduction and for "antipsychotic-like" efficacy as characterized by a reversal of dizocilipine (MK-801) mediated disruption of pre-pulse inhibition. Conversely, the inhibition by SEP-856 of MK-801 induced locomotion was unaffected in TAAR1 KO mice. SEP-856 behaved as a low-potency, partial agonist at the 5-HT1A receptor, while it partially inhibited recruitment of D2 receptor-coupled Gα and GIRK by DA and acted as a weak partial agonist with low potency at the same receptor when applied alone. Our findings corroborate and extend previous observations on the molecular substrates engaged by this unique, dual TAAR1/5-HT1A receptor agonist and potential antipsychotic that could prove to have major advantages in the treatment of schizophrenia and other psychotic disorders.
Collapse
|
5
|
Sarkar S, Saika-Voivod I, Berry MD. Modelling of p-tyramine transport across human intestinal epithelial cells predicts the presence of additional transporters. Front Physiol 2022; 13:1009320. [PMID: 36505075 PMCID: PMC9733674 DOI: 10.3389/fphys.2022.1009320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2022] [Accepted: 09/22/2022] [Indexed: 11/12/2022] Open
Abstract
p-Tyramine (TYR) is an endogenous trace amine, which can also be synthesized by intestinal microbiota, and is present in commonly consumed diets. TYR is an agonist for the intracellular trace amine-associated receptor 1, which has been implicated in psychiatric, metabolic, and immune-related disorders. We have previously demonstrated TYR readily diffuses across lipid bilayers, while transport across Caco-2 cell membranes involves Organic Cation Transporter 2 (OCT2) and a Na+-dependent active transporter. Here we developed mathematical models to determine whether known kinetics for these processes are sufficient to explain observed transcellular TYR passage. Ordinary differential equations were developed for known TYR transport processes to predict concentration-time relationships. Michaelis-Menten kinetics were assumed for all transporter-mediated processes and a one phase exponential function used for simple diffusion. Modelled concentration-time plots were compared to published experimental results. Additional transporter functions were sequentially added to models to improve consistency, and a least squares error minimization approach utilized to determine added transporter kinetics. Finally, possible TYR compartmentalization was also modelled. Following apical loading, transport across the apical, but not the basolateral, membrane was modelled without additional transporters, suggesting a basolateral transporter was missing. Consistent with this, models of basolateral compartment loading did not match experimental observations, indicating missing basolateral transporters were bidirectional. Addition of a transporter with the kinetic characteristics of OCT2 did not improve models. Varying the kinetic parameters of the added transporter improved models of basolateral, but worsened apical, loading models, suggesting the need for either a directional preference in transporters, or intracellular TYR compartmentalization. Experimental parameters were recapitulated by introducing asymmetry into the apical OCT2 (Kt_OCT2_apicaltocell = 110.4 nM, Kt_OCT2_celltoapical = 1,227.9 nM), and a symmetric basolateral facilitated diffusion transporter (Vmax = 6.0 nM/s, Kt = 628.3 nM). The apparent directionality of OCT2 may reflect altered TYR ionization due to known pH differences between compartments. Models for asymmetry and compartmentalization were compared by root mean square deviation from experimental data, and it was found that TYR compartmentalization could only partially replace the need for asymmetry of OCT2. In conclusion, modelling indicates that known TYR transport processes are insufficient to explain experimental concentration-time profiles and that asymmetry of the apical membrane OCT2 combined with additional, low affinity, basolateral membrane facilitated diffusion transporters are required.
Collapse
Affiliation(s)
- Shreyasi Sarkar
- Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL, Canada,*Correspondence: Shreyasi Sarkar,
| | - Ivan Saika-Voivod
- Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John’s, NL, Canada
| | - Mark D. Berry
- Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL, Canada
| |
Collapse
|
6
|
Abstract
N,N-dimethyltryptamine (DMT) is a potent psychedelic naturally produced by many plants and animals, including humans. Whether or not DMT is significant to mammalian physiology, especially within the central nervous system, is a debate that started in the early 1960s and continues to this day. This review integrates historical and recent literature to clarify this issue, giving special attention to the most controversial subjects of DMT's biosynthesis, its storage in synaptic vesicles and the activation receptors like sigma-1. Less discussed topics, like DMT's metabolic regulation or the biased activation of serotonin receptors, are highlighted. We conclude that most of the arguments dismissing endogenous DMT's relevance are based on obsolete data or misleading assumptions. Data strongly suggest that DMT can be relevant as a neurotransmitter, neuromodulator, hormone and immunomodulator, as well as being important to pregnancy and development. Key experiments are addressed to definitely prove what specific roles DMT plays in mammalian physiology.
Collapse
Affiliation(s)
- Javier Hidalgo Jiménez
- ICEERS Foundation (International Center for Ethnobotanical Education, Research and Services), Barcelona, Spain
| | - José Carlos Bouso
- ICEERS Foundation (International Center for Ethnobotanical Education, Research and Services), Barcelona, Spain
| |
Collapse
|
7
|
Phenethylamine is a substrate of monoamine oxidase B in the paraventricular thalamic nucleus. Sci Rep 2022; 12:17. [PMID: 34996979 PMCID: PMC8742005 DOI: 10.1038/s41598-021-03885-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Accepted: 12/09/2021] [Indexed: 11/30/2022] Open
Abstract
Monoamine oxidase (MAO) is a key enzyme responsible for the degradation of neurotransmitters and trace amines. MAO has two subtypes (MAO-A and MAO-B) that are encoded by different genes. In the brain, MAO-B is highly expressed in the paraventricular thalamic nucleus (PVT); however, its substrate in PVT remains unclear. To identify the MAO-B substrate in PVT, we generated Maob knockout (KO) mice and measured five candidate substrates (i.e., noradrenaline, dopamine, 3-methoxytyramine, serotonin, and phenethylamine [PEA]) by liquid chromatography tandem mass spectrometry. We showed that only PEA levels were markedly elevated in the PVT of Maob KO mice. To exclude the influence of peripheral MAO-B deficiency, we developed brain-specific Maob KO mice, finding that PEA in the PVT was increased in brain-specific Maob KO mice, whereas the extent of PEA increase was less than that in global Maob KO mice. Given that plasma PEA levels were elevated in global KO mice, but not in brain–specific KO mice, and that PEA passes across the blood–brain barrier, the substantial accumulation of PEA in the PVT of Maob KO mice was likely due to the increase in plasma PEA. These data suggest that PEA is a substrate of MAO-B in the PVT as well as other tissues.
Collapse
|
8
|
Gut Bacteria and Neuropsychiatric Disorders. Microorganisms 2021; 9:microorganisms9122583. [PMID: 34946184 PMCID: PMC8708963 DOI: 10.3390/microorganisms9122583] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 11/23/2021] [Accepted: 11/26/2021] [Indexed: 12/11/2022] Open
Abstract
Bacteria in the gut microbiome plays an intrinsic part in immune activation, intestinal permeability, enteric reflex, and entero-endocrine signaling. Apart from physiological and structural changes brought about by gut bacteria on entero-epithelial cells and mucus layers, a vast number of signals generated in the gastro-intestinal tract (GIT) reaches the brain via the vagus nerve. Research on the gut–brain axis (GBA) has mostly been devoted to digestive functions and satiety. Less papers have been published on the role gut microbiota play in mood, cognitive behavior and neuropsychiatric disorders such as autism, depression and schizophrenia. Whether we will be able to fully decipher the connection between gut microbiota and mental health is debatable, especially since the gut microbiome is diverse, everchanging and highly responsive to external stimuli. Nevertheless, the more we discover about the gut microbiome and the more we learn about the GBA, the greater the chance of developing novel therapeutics, probiotics and psychobiotics to treat gastro-intestinal disorders such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), but also improve cognitive functions and prevent or treat mental disorders. In this review we focus on the influence gut bacteria and their metabolites have on neuropsychiatric disorders.
Collapse
|
9
|
Potential of Ligands for Trace Amine-Associated Receptor 1 (TAAR1) in the Management of Substance Use Disorders. CNS Drugs 2021; 35:1239-1248. [PMID: 34766253 PMCID: PMC8787759 DOI: 10.1007/s40263-021-00871-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/17/2021] [Indexed: 10/19/2022]
Abstract
Trace amines, including β-phenylethylamine (β-PEA), p-tyramine (TYR), tryptamine (TRP), and p-octopamine (OCT), represent a group of amines expressed at low levels in the mammalian brain. Given the close structural similarities to traditional monoamines, links between trace amines and the monoaminergic system have long been suspected. Trace amine-associated receptor 1 (TAAR1), the most well characterized receptor in the TAAR family, has been shown to be potently activated by trace amines such as TYR and PEA. Further, catecholamine metabolites and amphetamine analogs are also potent agonists of TAAR1, implicating the receptor in mediating the monoaminergic system and in substance use disorders. In the central nervous system, TAAR1 is expressed in brain regions involved in dopaminergic, serotonergic, and glutamatergic transmission, and genetic animal models and electrophysiological studies have revealed that TAAR1 is a potent modulator of the monoaminergic system. Selective and potent engineered TAAR1 ligands, including full (RO5166017 and RO5256390) and partial (RO5203648, RO5263397 and RO5073012) agonists and the antagonist EPPTB (N-(3-ethoxyphenyl)-4-(1-pyrrolidinyl)-3-(trifluoromethyl) benzamide, RO5212773), serve as invaluable tools for the investigation of TAAR1 functions and display significant potential for the development of TAAR1-based pharmacotherapies for the treatment of substance use disorders. Despite a number of advances that have been made, more clinical studies are warranted in order to test the potential and efficacy of TAAR1 ligands in the treatment of psychiatric disorders, including substance use disorders.
Collapse
|
10
|
Amphetamines signal through intracellular TAAR1 receptors coupled to Gα 13 and Gα S in discrete subcellular domains. Mol Psychiatry 2021; 26:1208-1223. [PMID: 31399635 PMCID: PMC7038576 DOI: 10.1038/s41380-019-0469-2] [Citation(s) in RCA: 50] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 04/23/2019] [Accepted: 05/03/2019] [Indexed: 12/11/2022]
Abstract
The extensive use of amphetamines to treat attention deficit hyperactivity disorders in children provides a compelling rationale for understanding the mechanisms of action of amphetamines and amphetamine-related drugs. We have previously shown that acute amphetamine (AMPH) regulates the trafficking of both dopamine and glutamate transporters in dopamine neurons by increasing activation of the small GTPase RhoA and of protein kinase A. Here we demonstrate that these downstream signaling events depend upon the direct activation of a trace amine-associated receptor, TAAR1, an intracellular G-protein coupled receptor (GPCR) that can be activated by amphetamines, trace amines, and biogenic amine metabolites. Using cell lines and mouse lines in which TAAR1 expression has been disrupted, we demonstrate that TAAR1 mediates the effects of AMPH on both RhoA and cAMP signaling. Inhibition of different Gα signaling pathways in cell lines and in vivo using small cell-permeable peptides confirms that the endogenous intracellular TAAR1 couples to G13 and to GS α-subunits to increase RhoA and PKA activity, respectively. Results from experiments with RhoA- and PKA-FRET sensors targeted to different subcellular compartments indicate that AMPH-elicited PKA activation occurs throughout the cell, whereas G13-mediated RhoA activation is concentrated near the endoplasmic reticulum. These observations define TAAR1 as an obligate intracellular target for amphetamines in dopamine neurons and support a model in which distinct pools of TAAR1 mediate the activation of signaling pathways in different compartments to regulate excitatory and dopaminergic neurotransmission.
Collapse
|
11
|
Involvement of Organic Cation Transporter 2 and a Na +-dependent active transporter in p-tyramine transport across Caco-2 intestinal cells. Life Sci 2020; 253:117696. [PMID: 32334013 DOI: 10.1016/j.lfs.2020.117696] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 04/14/2020] [Accepted: 04/16/2020] [Indexed: 11/22/2022]
Abstract
AIMS We have previously demonstrated that p-tyramine (TYR), an endogenous trace amine-associated receptor 1 agonist, passage across neuronal membranes involves a transporter exhibiting the pharmacological profile of Organic Cation Transporter 2 (OCT2). Since TYR is also a constituent of foodstuffs and produced by the intestinal microbiota, here we have investigated whether similar processes are involved in the passage of 100 nM TYR across apical and basolateral membranes of the Caco-2 human intestinal epithelial cell line. MATERIALS AND METHODS [3H]TYR transport across apical and basolateral membranes of Caco-2 cell monolayers was measured in the presence of inhibitors of TYR metabolizing enzymes. Cellular, apical, and basolateral compartments were collected at various timepoints, TYR concentrations calculated, and transport properties pharmacologically characterized. KEY FINDINGS Apical transport resulted in equimolar accumulation of TYR within cells. Pentamidine (OCT1/OCT2 inhibitor) decreased apical transport (P = 0.001) while atropine (OCT1 inhibitor) had no effect, suggesting apical transport involved OCT2. In contrast, basolateral transport resulted in 500-1000 nM cellular concentrations (P < 0.0001) indicating the presence of an active transporter. Replacement of Na+ on an equimolar basis with choline resulted in loss of TYR transport (P = 0.017). Unexpectedly, this active transport was also atropine-sensitive (P = 0.020). Kinetic analysis of the active transporter revealed Vmax = 43.0 nM/s with a Kt = 33.1 nM. SIGNIFICANCE We have demonstrated for the first time that TYR is transported across Caco-2 apical membranes via facilitated diffusion by OCT2, whereas transport across basolateral membranes is by a Na+-dependent, atropine-sensitive, active transporter.
Collapse
|
12
|
Biedermann F, Ghale G, Hennig A, Nau WM. Fluorescent artificial receptor-based membrane assay (FARMA) for spatiotemporally resolved monitoring of biomembrane permeability. Commun Biol 2020; 3:383. [PMID: 32669621 PMCID: PMC7363885 DOI: 10.1038/s42003-020-1108-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 06/19/2020] [Indexed: 02/07/2023] Open
Abstract
The spatiotemporally resolved monitoring of membrane translocation, e.g., of drugs or toxins, has been a long-standing goal. Herein, we introduce the fluorescent artificial receptor-based membrane assay (FARMA), a facile, label-free method. With FARMA, the permeation of more than hundred organic compounds (drugs, toxins, pesticides, neurotransmitters, peptides, etc.) through vesicular phospholipid bilayer membranes has been monitored in real time (µs-h time scale) and with high sensitivity (nM-µM concentration), affording permeability coefficients across an exceptionally large range from 10-9-10-3 cm s-1. From a fundamental point of view, FARMA constitutes a powerful tool to assess structure-permeability relationships and to test biophysical models for membrane passage. From an applied perspective, FARMA can be extended to high-throughput screening by adaption of the microplate reader format, to spatial monitoring of membrane permeation by microscopy imaging, and to the compartmentalized monitoring of enzymatic activity.
Collapse
Affiliation(s)
- Frank Biedermann
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz Platz 1, 76344, Eggenstein-Leopoldshafen, Germany.
- Department of Life Sciences and Chemistry, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany.
| | - Garima Ghale
- Department of Life Sciences and Chemistry, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
| | - Andreas Hennig
- Department of Life Sciences and Chemistry, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
| | - Werner M Nau
- Department of Life Sciences and Chemistry, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany.
| |
Collapse
|
13
|
Actions of Trace Amines in the Brain-Gut-Microbiome Axis via Trace Amine-Associated Receptor-1 (TAAR1). Cell Mol Neurobiol 2019; 40:191-201. [DOI: 10.1007/s10571-019-00772-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Accepted: 12/04/2019] [Indexed: 12/13/2022]
|
14
|
A Perspective: Active Role of Lipids in Neurotransmitter Dynamics. Mol Neurobiol 2019; 57:910-925. [PMID: 31595461 PMCID: PMC7031182 DOI: 10.1007/s12035-019-01775-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 09/01/2019] [Indexed: 12/30/2022]
Abstract
Synaptic neurotransmission is generally considered as a function of membrane-embedded receptors and ion channels in response to the neurotransmitter (NT) release and binding. This perspective aims to widen the protein-centric view by including another vital component—the synaptic membrane—in the discussion. A vast set of atomistic molecular dynamics simulations and biophysical experiments indicate that NTs are divided into membrane-binding and membrane-nonbinding categories. The binary choice takes place at the water-membrane interface and follows closely the positioning of the receptors’ binding sites in relation to the membrane. Accordingly, when a lipophilic NT is on route to a membrane-buried binding site, it adheres on the membrane and, then, travels along its plane towards the receptor. In contrast, lipophobic NTs, which are destined to bind into receptors with extracellular binding sites, prefer the water phase. This membrane-based sorting splits the neurotransmission into membrane-independent and membrane-dependent mechanisms and should make the NT binding into the receptors more efficient than random diffusion would allow. The potential implications and notable exceptions to the mechanisms are discussed here. Importantly, maintaining specific membrane lipid compositions (MLCs) at the synapses, especially regarding anionic lipids, affect the level of NT-membrane association. These effects provide a plausible link between the MLC imbalances and neurological diseases such as depression or Parkinson’s disease. Moreover, the membrane plays a vital role in other phases of the NT life cycle, including storage and release from the synaptic vesicles, transport from the synaptic cleft, as well as their synthesis and degradation.
Collapse
|
15
|
Paulsen P, Bauer S, Bauer F. Biogenic amines and polyamines in foods of animal origin. CHEMICAL HAZARDS IN FOODS OF ANIMAL ORIGIN 2019. [DOI: 10.3920/978-90-8686-877-3_12] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Peter Paulsen
- Institute of Meat Hygiene, Meat Technology and Food Science, Vetmeduni Vienna, Veterinaerplatz 1, 1210 Vienna, Austria
| | - Susanne Bauer
- Institute of Meat Hygiene, Meat Technology and Food Science, Vetmeduni Vienna, Veterinaerplatz 1, 1210 Vienna, Austria
| | - Friedrich Bauer
- Institute of Meat Hygiene, Meat Technology and Food Science, Vetmeduni Vienna, Veterinaerplatz 1, 1210 Vienna, Austria
| |
Collapse
|
16
|
Abstract
Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.
Collapse
Affiliation(s)
- Raul R Gainetdinov
- Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg, Russia (R.R.G.); Skolkovo Institute of Science and Technology (Skoltech), Moscow, Russia (R.R.G.); Neuroscience, Ophthalmology, and Rare Diseases Discovery and Translational Area, pRED, Roche Innovation Centre Basel, F. Hoffmann-La Roche Ltd., Basel, Switzerland (M.C.H.); and Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada (M.D.B.)
| | - Marius C Hoener
- Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg, Russia (R.R.G.); Skolkovo Institute of Science and Technology (Skoltech), Moscow, Russia (R.R.G.); Neuroscience, Ophthalmology, and Rare Diseases Discovery and Translational Area, pRED, Roche Innovation Centre Basel, F. Hoffmann-La Roche Ltd., Basel, Switzerland (M.C.H.); and Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada (M.D.B.)
| | - Mark D Berry
- Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg, Russia (R.R.G.); Skolkovo Institute of Science and Technology (Skoltech), Moscow, Russia (R.R.G.); Neuroscience, Ophthalmology, and Rare Diseases Discovery and Translational Area, pRED, Roche Innovation Centre Basel, F. Hoffmann-La Roche Ltd., Basel, Switzerland (M.C.H.); and Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada (M.D.B.)
| |
Collapse
|
17
|
Christian SL, Berry MD. Trace Amine-Associated Receptors as Novel Therapeutic Targets for Immunomodulatory Disorders. Front Pharmacol 2018; 9:680. [PMID: 30013475 PMCID: PMC6036138 DOI: 10.3389/fphar.2018.00680] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2018] [Accepted: 06/05/2018] [Indexed: 12/14/2022] Open
Abstract
Trace amines and their receptors (trace amine-associated receptors; TAARs) are an emerging pharmacological target for the treatment of human disorders. While most studies have focused on their therapeutic potential for neurologic and psychiatric disorders, TAARs are also expressed throughout the periphery, including prominent expression in human leukocytes. Furthermore, recent independent, unbiased metabolomic studies have consistently identified one or more TAAR ligands as potential etiologic factors in inflammatory bowel disease (IBD). The putative role of TAARs in diseases such as IBD that are associated with hyperactive immune responses has not, however, previously been systematically addressed. Here, we review the current state of the knowledge of the effects of TAARs on leukocyte function, in particular in the context of mucosal epithelial cells that interface with the environment; developing a model whereby TAARs may be considered as a novel therapeutic target for disorders associated with dysregulated immune responses to environmental factors. In this model, we hypothesize that altered trace amine homeostasis results in hyperactivity of the immune system. Such loss of homeostasis can occur through many different mechanisms including TAAR polymorphisms and altered trace amine load due to changes in host synthesis and/or degradative enzymes, diet, or microbial dysbiosis. The resulting alterations in TAAR functioning can then lead to a loss of homeostasis of leukocyte chemotaxis, differentiation, and activation, as well as an altered ability of members of the microbiota to adhere to and penetrate the epithelial cell layers. Such changes would generate a pro-inflammatory state at mucosal epithelial barrier layers that can manifest as clinical symptomatology such as that seen in IBD. These alterations may also have the potential to induce systemic effects, which could possibly contribute to immunomodulatory disorders in other systems, including neurological diseases.
Collapse
|
18
|
Berry MD, Gainetdinov RR, Hoener MC, Shahid M. Pharmacology of human trace amine-associated receptors: Therapeutic opportunities and challenges. Pharmacol Ther 2017; 180:161-180. [DOI: 10.1016/j.pharmthera.2017.07.002] [Citation(s) in RCA: 95] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
|
19
|
Wüst N, Rauscher-Gabernig E, Steinwider J, Bauer F, Paulsen P. Risk assessment of dietary exposure to tryptamine for the Austrian population. Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2016; 34:404-420. [DOI: 10.1080/19440049.2016.1269207] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Nadja Wüst
- Business Area Data, Statistics & Risk Assessment, Austrian Agency for Health and Food Safety, Vienna, Austria
| | - Elke Rauscher-Gabernig
- Business Area Data, Statistics & Risk Assessment, Austrian Agency for Health and Food Safety, Vienna, Austria
| | - Johann Steinwider
- Business Area Data, Statistics & Risk Assessment, Austrian Agency for Health and Food Safety, Vienna, Austria
| | - Friedrich Bauer
- Institute of Meat Hygiene, Meat Technology and Food Science, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Peter Paulsen
- Institute of Meat Hygiene, Meat Technology and Food Science, University of Veterinary Medicine Vienna, Vienna, Austria
| |
Collapse
|
20
|
Berry MD, Hart S, Pryor AR, Hunter S, Gardiner D. Pharmacological characterization of a high-affinity p-tyramine transporter in rat brain synaptosomes. Sci Rep 2016; 6:38006. [PMID: 27901065 PMCID: PMC5128819 DOI: 10.1038/srep38006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 11/03/2016] [Indexed: 11/22/2022] Open
Abstract
p-Tyramine is an archetypal member of the endogenous family of monoamines known as trace amines, and is one of the endogenous agonists for trace amine-associated receptor (TAAR)1. While much work has focused on the function of TAAR1, very little is known about the regulation of the endogenous agonists. We have previously reported that p-tyramine readily crosses lipid bilayers and that its release from synaptosomes is non-exocytotic. Such release, however, showed characteristics of modification by one or more transporters. Here we provide the first characterization of such a transporter. Using frontal cortical and striatal synaptosomes we show that p-tyramine passage across synaptosome membranes is not modified by selective inhibition of either the dopamine, noradrenaline or 5-HT transporters. In contrast, inhibition of uptake-2 transporters significantly slowed p-tyramine re-uptake. Using inhibitors of varying selectivity, we identify Organic Cation Transporter 2 (OCT2; SLC22A2) as mediating high affinity uptake of p-tyramine at physiologically relevant concentrations. Further, we confirm the presence of OCT2 protein in synaptosomes. These results provide the first identification of a high affinity neuronal transporter for p-tyramine, and also confirm the recently described localization of OCT2 in pre-synaptic terminals.
Collapse
Affiliation(s)
- Mark D Berry
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada
| | - Shannon Hart
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada
| | - Anthony R Pryor
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada
| | - Samantha Hunter
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada
| | - Danielle Gardiner
- Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada
| |
Collapse
|
21
|
Shi X, Walter NAR, Harkness JH, Neve KA, Williams RW, Lu L, Belknap JK, Eshleman AJ, Phillips TJ, Janowsky A. Genetic Polymorphisms Affect Mouse and Human Trace Amine-Associated Receptor 1 Function. PLoS One 2016; 11:e0152581. [PMID: 27031617 PMCID: PMC4816557 DOI: 10.1371/journal.pone.0152581] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 03/16/2016] [Indexed: 12/15/2022] Open
Abstract
Methamphetamine (MA) and neurotransmitter precursors and metabolites such as tyramine, octopamine, and β-phenethylamine stimulate the G protein-coupled trace amine-associated receptor 1 (TAAR1). TAAR1 has been implicated in human conditions including obesity, schizophrenia, depression, fibromyalgia, migraine, and addiction. Additionally TAAR1 is expressed on lymphocytes and astrocytes involved in inflammation and response to infection. In brain, TAAR1 stimulation reduces synaptic dopamine availability and alters glutamatergic function. TAAR1 is also expressed at low levels in heart, and may regulate cardiovascular tone. Taar1 knockout mice orally self-administer more MA than wild type and are insensitive to its aversive effects. DBA/2J (D2) mice express a non-synonymous single nucleotide polymorphism (SNP) in Taar1 that does not respond to MA, and D2 mice are predisposed to high MA intake, compared to C57BL/6 (B6) mice. Here we demonstrate that endogenous agonists stimulate the recombinant B6 mouse TAAR1, but do not activate the D2 mouse receptor. Progeny of the B6XD2 (BxD) family of recombinant inbred (RI) strains have been used to characterize the genetic etiology of diseases, but contrary to expectations, BXDs derived 30-40 years ago express only the functional B6 Taar1 allele whereas some more recently derived BXD RI strains express the D2 allele. Data indicate that the D2 mutation arose subsequent to derivation of the original RIs. Finally, we demonstrate that SNPs in human TAAR1 alter its function, resulting in expressed, but functional, sub-functional and non-functional receptors. Our findings are important for identifying a predisposition to human diseases, as well as for developing personalized treatment options.
Collapse
Affiliation(s)
- Xiao Shi
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- The Methamphetamine Abuse Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Nicole A. R. Walter
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - John H. Harkness
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Kim A. Neve
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- The Methamphetamine Abuse Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Robert W. Williams
- Department of Genetics, Genomics and Informatics, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America
| | - Lu Lu
- Department of Genetics, Genomics and Informatics, University of Tennessee Health Science Center, Memphis, Tennessee, United States of America
- Jiangsu Key Laboratory of Neuroregeneration, Nantong University, Nantong, Jiangsu, China
| | - John K. Belknap
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- The Methamphetamine Abuse Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Amy J. Eshleman
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Tamara J. Phillips
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- The Methamphetamine Abuse Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
| | - Aaron Janowsky
- Veterans Affairs Portland Health Care System, Portland, Oregon, United States of America
- The Methamphetamine Abuse Research Center, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Behavioral Neuroscience, Oregon Health & Science University, Portland, Oregon, United States of America
- Department of Psychiatry, Oregon Health & Science University, Portland, Oregon, United States of America
| |
Collapse
|
22
|
Mlinar B, Montalbano A, Baccini G, Tatini F, Berlinguer Palmini R, Corradetti R. Nonexocytotic serotonin release tonically suppresses serotonergic neuron activity. ACTA ACUST UNITED AC 2016; 145:225-51. [PMID: 25712017 PMCID: PMC4338157 DOI: 10.1085/jgp.201411330] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The firing activity of serotonergic neurons in raphe nuclei is regulated by negative feedback exerted by extracellular serotonin (5-HT)o acting through somatodendritic 5-HT1A autoreceptors. The steady-state [5-HT]o, sensed by 5-HT1A autoreceptors, is determined by the balance between the rates of 5-HT release and reuptake. Although it is well established that reuptake of 5-HTo is mediated by 5-HT transporters (SERT), the release mechanism has remained unclear. It is also unclear how selective 5-HT reuptake inhibitor (SSRI) antidepressants increase the [5-HT]o in raphe nuclei and suppress serotonergic neuron activity, thereby potentially diminishing their own therapeutic effect. Using an electrophysiological approach in a slice preparation, we show that, in the dorsal raphe nucleus (DRN), continuous nonexocytotic 5-HT release is responsible for suppression of phenylephrine-facilitated serotonergic neuron firing under basal conditions as well as for autoinhibition induced by SSRI application. By using 5-HT1A autoreceptor-activated G protein-gated inwardly rectifying potassium channels of patched serotonergic neurons as 5-HTo sensors, we show substantial nonexocytotic 5-HT release under conditions of abolished firing activity, Ca(2+) influx, vesicular monoamine transporter 2-mediated vesicular accumulation of 5-HT, and SERT-mediated 5-HT transport. Our results reveal a cytosolic origin of 5-HTo in the DRN and suggest that 5-HTo may be supplied by simple diffusion across the plasma membrane, primarily from the dense network of neurites of serotonergic neurons surrounding the cell bodies. These findings indicate that the serotonergic system does not function as a sum of independently acting neurons but as a highly interdependent neuronal network, characterized by a shared neurotransmitter pool and the regulation of firing activity by an interneuronal, yet activity-independent, nonexocytotic mechanism.
Collapse
Affiliation(s)
- Boris Mlinar
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| | - Alberto Montalbano
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| | - Gilda Baccini
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| | - Francesca Tatini
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| | - Rolando Berlinguer Palmini
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| | - Renato Corradetti
- Department of Neuroscience, Psychology, Drug Research and Child Health, University of Florence, 50121 Florence, Italy
| |
Collapse
|
23
|
A Permeability Study of O2 and the Trace Amine p-Tyramine through Model Phosphatidylcholine Bilayers. PLoS One 2015; 10:e0122468. [PMID: 26086933 PMCID: PMC4472697 DOI: 10.1371/journal.pone.0122468] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Accepted: 02/15/2015] [Indexed: 11/19/2022] Open
Abstract
We study here the permeability of the hydrophobic O2 molecule through a model DPPC bilayer at 323K and 350K, and of the trace amine p-tyramine through PC bilayers at 310K. The tyramine results are compared to previous experimental work at 298K. Nonequilibrium work methods were used in conjunction to simultaneously obtain both the potential of mean force (PMF) and the position dependent transmembrane diffusion coefficient, D(z), from the simulations. These in turn were used to calculate the permeability coefficient, P, through the inhomogeneous solubility-diffusion model. The results for O2 are consistent with previous simulations, and agree with experimentally measured P values for PC bilayers. A temperature dependence in the permeability of O2 through DPPC was obtained, with P decreasing at higher temperatures. Two relevant species of p-tyramine were simulated, from which the PMF and D(z) were calculated. The charged species had a large energetic barrier to crossing the bilayer of ~ 21 kcal/mol, while the uncharged, deprotonated species had a much lower barrier of ~ 7 kcal/mol. The effective in silico permeability for p-tyramine was calculated by applying three approximations, all of which gave nearly identical results (presented here as a function of the pKa). As the permeability value calculated from simulation was highly dependent on the pKa of the amine group, a further pKa study was performed that also varied the fraction of the uncharged and zwitterionic p-tyramine species. Using the experimental P value together with the simulated results, we were able to label the phenolic group as responsible for the pKa1 and the amine for the pKa2, that together represent all of the experimentally measured pKa values for p-tyramine. This agrees with older experimental results, in contrast to more recent work that has suggested there is a strong ambiguity in the pKa values.
Collapse
|
24
|
Gozal EA, O'Neill BE, Sawchuk MA, Zhu H, Halder M, Chou CC, Hochman S. Anatomical and functional evidence for trace amines as unique modulators of locomotor function in the mammalian spinal cord. Front Neural Circuits 2014; 8:134. [PMID: 25426030 PMCID: PMC4224135 DOI: 10.3389/fncir.2014.00134] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2014] [Accepted: 10/22/2014] [Indexed: 12/18/2022] Open
Abstract
The trace amines (TAs), tryptamine, tyramine, and β-phenylethylamine, are synthesized from precursor amino acids via aromatic-L-amino acid decarboxylase (AADC). We explored their role in the neuromodulation of neonatal rat spinal cord motor circuits. We first showed that the spinal cord contains the substrates for TA biosynthesis (AADC) and for receptor-mediated actions via trace amine-associated receptors (TAARs) 1 and 4. We next examined the actions of the TAs on motor activity using the in vitro isolated neonatal rat spinal cord. Tyramine and tryptamine most consistently increased motor activity with prominent direct actions on motoneurons. In the presence of N-methyl-D-aspartate, all applied TAs supported expression of a locomotor-like activity (LLA) that was indistinguishable from that ordinarily observed with serotonin, suggesting that the TAs act on common central pattern generating neurons. The TAs also generated distinctive complex rhythms characterized by episodic bouts of LLA. TA actions on locomotor circuits did not require interaction with descending monoaminergic projections since evoked LLA was maintained following block of all Na+-dependent monoamine transporters or the vesicular monoamine transporter. Instead, TA (tryptamine and tyramine) actions depended on intracellular uptake via pentamidine-sensitive Na+-independent membrane transporters. Requirement for intracellular transport is consistent with the TAs having much slower LLA onset than serotonin and for activation of intracellular TAARs. To test for endogenous actions following biosynthesis, we increased intracellular amino acid levels with cycloheximide. LLA emerged and included distinctive TA-like episodic bouts. In summary, we provided anatomical and functional evidence of the TAs as an intrinsic spinal monoaminergic modulatory system capable of promoting recruitment of locomotor circuits independent of the descending monoamines. These actions support their known sympathomimetic function.
Collapse
Affiliation(s)
| | | | | | - Hong Zhu
- Physiology Department, Emory University Atlanta, GA, USA
| | - Mallika Halder
- Physiology Department, Emory University Atlanta, GA, USA
| | | | - Shawn Hochman
- Physiology Department, Emory University Atlanta, GA, USA
| |
Collapse
|
25
|
Li Y, Li L, Stephens MJ, Zenner D, Murray KC, Winship IR, Vavrek R, Baker GB, Fouad K, Bennett DJ. Synthesis, transport, and metabolism of serotonin formed from exogenously applied 5-HTP after spinal cord injury in rats. J Neurophysiol 2013; 111:145-63. [PMID: 24068759 DOI: 10.1152/jn.00508.2013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Spinal cord transection leads to elimination of brain stem-derived monoamine fibers that normally synthesize most of the monoamines in the spinal cord, including serotonin (5-hydroxytryptamine, 5-HT) synthesized from tryptophan by enzymes tryptophan hydroxylase (TPH, synthesizing 5-hydroxytryptophan, 5-HTP) and aromatic l-amino acid decarboxylase (AADC, synthesizing 5-HT from 5-HTP). Here we examine whether spinal cord caudal to transection remains able to manufacture and metabolize 5-HT. Immunolabeling for AADC reveals that, while most AADC is confined to brain stem-derived monoamine fibers in spinal cords from normal rats, caudal to transection AADC is primarily found in blood vessel endothelial cells and pericytes as well as a novel group of neurons (NeuN positive and GFAP negative), all of which strongly upregulate AADC with injury. However, immunolabeling for 5-HT reveals that there is no detectable endogenous 5-HT synthesis in any structure in the spinal cord caudal to a chronic transection, including in AADC-containing vessels and neurons, consistent with a lack of TPH. In contrast, when we applied exogenous 5-HTP (in vitro or in vivo), AADC-containing vessels and neurons synthesized 5-HT, which contributed to increased motoneuron activity and muscle spasms (long-lasting reflexes, LLRs), by acting on 5-HT2 receptors (SB206553 sensitive) located on motoneurons (TTX resistant). Blocking monoamine oxidase (MAO) markedly increased the sensitivity of the motoneurons (LLR) to 5-HTP, more than it increased the sensitivity of motoneurons to 5-HT, suggesting that 5-HT synthesized from AADC is largely metabolized in AADC-containing neurons and vessels. In summary, after spinal cord injury AADC is upregulated in vessels, pericytes, and neurons but does not endogenously produce 5-HT, whereas when exogenous 5-HTP is provided AADC does produce functional amounts of 5-HT, some of which is able to escape metabolism by MAO, diffuse out of these AADC-containing cells, and ultimately act on 5-HT receptors on motoneurons.
Collapse
Affiliation(s)
- Yaqing Li
- Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada
| | | | | | | | | | | | | | | | | | | |
Collapse
|