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Margarita L. Dubocovich - One of the best experts on this subject based on the ideXlab platform.
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Therapeutic potential of Melatonin Receptor agonists and antagonists
Emerging Drugs, 2005Co-Authors: Margarita L. DubocovichAbstract:1. Summary In humans, the hormone Melatonin is produced and secreted from the pineal gland following a circadian rhythm with high levels during the normal hours of sleep at night and low levels during the day. The strong correlation between the sleep-wake cycle and the sleep-promoting effects of physiological and pharmacological doses of Melatonin has lead to the hypotheses that Melatonin can be used to treat insomnia and circadian sleep disorders. Insomnia is associated with daytime sleepiness and decrements in mental and physical performance. In the last decade, efforts from a number of pharmaceutical companies have aimed to discover and develop high affinity Melatonin Receptor agonists. Melatonin Receptor agonists currently in development for the treatment of sleep disorders are non-selective in that they activate multiple Melatonin Receptor subtypes. This review highlights the main pharmacological properties and clinical uses of these Melatonin analogues, and provides an assessment of the therapeutic potential of subtype-selective Melatonin Receptor agonists and antagonists. The efficacy and effectiveness of Melatonin Receptor agonists should be greatly increased and the side-effects reduced by targeting Receptor subtypes mediating specific functions. The current need for the synthesis and characterisation of high affinity and subtype-selective Melatonin Receptor antagonists to further elucidate the physiological role of Melatonin is also discussed. The discovery of drugs for the treatment of sleep disorders which are devoid of side-effects and which have novel mechanisms of action, is of current
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Mutagenesis studies of the human MT2 Melatonin Receptor.
Biochemical pharmacology, 2003Co-Authors: Matthew J. Gerdin, Faika Mseeh, Margarita L. DubocovichAbstract:Abstract Melatonin mediates its physiological effects through activation of high affinity G protein-coupled Receptors. The vertebrate MT1, MT2 and Mel1c Melatonin Receptors are molecularly and pharmacologically distinct. Three molecular models of Melatonin recognition for the MT1 and/or Mel1c Melatonin Receptors have been proposed. To determine if these models applied to the MT2 Melatonin Receptor, we mutated seven conserved residues to alanine in the hMT2 Melatonin Receptor and expressed the Receptors in HEK-293 cells. Competition of Melatonin for 2-[ 125 I ]-iodoMelatonin binding revealed that mutation of Asn 16 in TM4 or His 7 in TM5 of the hMT2 Melatonin Receptor significantly decreased the binding affinity for Melatonin when compared with wild-type. In addition, competition of 4P-ADOT, N-acetyltryptamine, luzindole, and 5-methoxytryptophol for 2-[ 125 I ]-iodoMelatonin binding suggested Asn 16 in TM4 may facilitate binding of the 5-methoxy group of the Melatonin molecule to the hMT2 Melatonin Receptor. Trp 13 or Phe 6 in TM6 while not critical for Melatonin binding, may interact with aromatic regions of luzindole and 4P-ADOT. Mutation of Ser 8 or Ser 12 in TM3, or Ser 6 in TM7 did not affect the affinity of Melatonin for competition with 2-[ 125 I ]-iodoMelatonin to the hMT2 Melatonin Receptor, although equivalent serines (Ser 8 and Ser 12 in TM3) were reported to be critical for Melatonin binding to the hMT1 Melatonin Receptor. Thus these results are the first to identify residues within the transmembrane regions of the hMT2 Melatonin Receptor critical for Melatonin binding, highlighting potential structural differences between the MT1 and MT2 Melatonin Receptor binding pockets.
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mt1 Melatonin Receptor overexpression enhances the growth suppressive effect of Melatonin in human breast cancer cells
Molecular and Cellular Endocrinology, 2002Co-Authors: Lin Yuan, Margarita L. Dubocovich, April R Collins, Jun Dai, Steven M HillAbstract:Melatonin inhibits the proliferation of estrogen Receptor alpha (ERα)-positive (MCF-7), but not ERα-negative (MDA-MB-231) breast cancer cells. Here, we assessed the effect of MT1 Melatonin Receptor stable overexpression in MCF-7 and MDA-MB-231 breast cancer cells on the growth-suppressive effects of Melatonin. Parental and vector-transfected MCF-7 cells demonstrated a modest, but significant, growth-suppressive response to Melatonin; however, Melatonin treatment of MT1-transfected MCF-7 cells resulted in significantly enhanced growth-suppression. This response was blocked by an MT1/MT2 Melatonin Receptor antagonist. Interestingly, MT1-overexpression did not induce a Melatonin-sensitive phenotype in Melatonin-insensitive MDA-MB-231 cells. Finally, Northern blot analysis demonstrated an enhanced inhibition of ERα mRNA expression and an enhanced induction of pancreatic spasmolytic polypeptide (pS2) by Melatonin in MT1-transfected MCF-7 cells relative to vector-transfected MCF-7 cells. These data suggest the involvement of the MT1 Melatonin Receptor in mediation of Melatonin effects on growth-suppression and gene-modulation in breast cancer cells.
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Melatonin Receptor signaling finding the path through the dark
Science Signaling, 2001Co-Authors: Monica I Masana, Margarita L. DubocovichAbstract:Melatonin, dubbed "the hormone of darkness," is involved in relaying photoperiodic information to the organism. Not only is Melatonin involved in the regulation of circadian rhythms and sleep, but it also has roles in visual, cerebrovascular, reproductive, neuroendocrine, and neuroimmunological functions. Melatonin mediates its effects through G protein-coupled Receptors: MT(1), MT(2), and, possibly, MT(3). Pharmacological agents have been instrumental in identifying these Receptor types. Masana and Dubocovich discuss how the level of Receptor expression may alter their efficacy, so that caution is necessary when extrapolating the pharmacological properties of ligands defined on recombinant systems to the Receptors in the organism. With these cautions in mind, they describe the various signaling pathways and physiological roles ascribed to the three Melatonin Receptor types.
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Melatonin Receptor subtype expression in human cerebellum.
Neuroreport, 1998Co-Authors: Walid M. Al-ghoul, Martin D. Herman, Margarita L. DubocovichAbstract:WE report the distinct cellular distribution in the human cerebellar cortex of the mammalian mt 1 (Mel 1a ) and MT 2 (Mel 1b ) (1) Melatonin Receptor subtypes. Specific binding of the non-selective radioligand 2-[ 125 ]iodoMelatonin to the outer molecular layer was significantly higher than to the granule cell layer. Melatonin Receptor subtype expression was assessed by in situ hybridization using selective and specific digoxigenin-labeled antisense oligonucleotide probes. This is the first demonstration of MT 2 Melatonin Receptor mRNA expression in human cerebellar Bergmann glia and astrocytes. On the other hand, the mt 1 Melatonin Receptor mRNA was expressed in both basket-stellate cells and granule cells. We conclude that mt 1 and MT 2 Melatonin Receptors are heterogeneously expressed in human cerebellar cortex. NeuroReport 9: 4063-4068 © 1998 Lippincott Williams & Wilkins.
Horst-werner Korf - One of the best experts on this subject based on the ideXlab platform.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto 5 nucleotidase mrna levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
Moran Homola - One of the best experts on this subject based on the ideXlab platform.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto 5 nucleotidase mrna levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
Monica I Masana - One of the best experts on this subject based on the ideXlab platform.
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Melatonin Receptor signaling finding the path through the dark
Science Signaling, 2001Co-Authors: Monica I Masana, Margarita L. DubocovichAbstract:Melatonin, dubbed "the hormone of darkness," is involved in relaying photoperiodic information to the organism. Not only is Melatonin involved in the regulation of circadian rhythms and sleep, but it also has roles in visual, cerebrovascular, reproductive, neuroendocrine, and neuroimmunological functions. Melatonin mediates its effects through G protein-coupled Receptors: MT(1), MT(2), and, possibly, MT(3). Pharmacological agents have been instrumental in identifying these Receptor types. Masana and Dubocovich discuss how the level of Receptor expression may alter their efficacy, so that caution is necessary when extrapolating the pharmacological properties of ligands defined on recombinant systems to the Receptors in the organism. With these cautions in mind, they describe the various signaling pathways and physiological roles ascribed to the three Melatonin Receptor types.
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selective mt2 Melatonin Receptor antagonists block Melatonin mediated phase advances of circadian rhythms
The FASEB Journal, 1998Co-Authors: Margarita L. Dubocovich, Kenneth Yun, Walid M Alghoul, Susan Benloucif, Monica I MasanaAbstract:This study demonstrates the involvement of the MT2 (Mel1b) Melatonin Receptor in mediating phase advances of circadian activity rhythms by Melatonin. In situ hybridization histochemistry with digoxigenin-labeled oligonucleotide probes revealed for the first time the expression of mt1 and MT2 Melatonin Receptor mRNA within the suprachiasmatic nucleus of the C3H/HeN mouse. Melatonin (0.9 to 30 μg/mouse, s.c.) administration during 3 days at the end of the subjective day (CT 10) to C3H/HeN mice kept in constant dark phase advanced circadian rhythms of wheel running activity in a dose-dependent manner [EC50=0.72 μg/mouse; 0.98±0.08 h (n=15) maximal advance at 9 μg/mouse]. Neither the selective MT2 Melatonin Receptor antagonists 4P-ADOT and 4P-PDOT (90 μ/mouse, s.c.) nor luzindole (300 μg/mouse, s.c.), which shows 25-fold higher affinity for the MT2 than the mt1 subtype, affected the phase of circadian activity rhythms when given alone at CT 10. All three antagonists, however, shifted to the right the dose-res...
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Melatonin Receptor antagonists that differentiate between the human Mel1a and Mel1b recombinant subtypes are used to assess the pharmacological profile of the rabbit retina ML1 presynaptic heteroReceptor
Naunyn-Schmiedeberg's archives of pharmacology, 1997Co-Authors: Margarita L. Dubocovich, Monica I Masana, Stanca Iacob, Daniel M. SauriAbstract:We have identified subtype selective agonists, partial agonists and antagonists, which distinguish the human recombinant Mel1a and Mel1b Melatonin Receptors expressed in COS-7 cells. Melatonin Receptor agonists showed higher affinity for competition of 2-[125I]-iodoMelatonin binding for the Mel1b than the Mel1a Melatonin Receptor. The dissociation constants (Ki) of 16 agonists determined on the recombinant human Mel1a and Mel1b Melatonin Receptor subtypes showed a significant correlation (r 2 = 0.85, slope = 0.97, P 0.1, n = 11) strongly suggest that the two human Melatonin Receptor subtypes can be distinguished pharmacologically. The partial agonist: 5-methoxyluzindole (pKi: 9.6) and the competitive Melatonin Receptor antagonists: GR128107 (pKi: 9.6), 4-phenyl-2-chloroacetamidotetraline (pKi: 9.1), 4-phenyl-2-acetamidotetraline (pKi: 8.9) and 4-phenyl-2-propionamidotetraline (pKi: 8.8) are selective Mel1b Melatonin Receptor analogues as their affinity selectivity ratios (Mel1a/Mel1b) are bigger than 100. We conclude that the 40% overall amino acid difference in the sequence of the human recombinant Mel1a and Mel1b Melatonin Receptors is reflected in distinct pharmacological profiles for the subtypes. We compared the pharmacological profile of the presynaptic ML1 Melatonin heteroReceptor of rabbit retina mediating inhibition of the calcium-dependent release of dopamine to that of the recombinant Mel1a and Mel1b Melatonin Receptors. Melatonin inhibited [3H]dopamine release by 50% (IC50) at 20 pM with a maximal inhibitory effect (80%) at 1 nM. The partial agonists, i.e., N-acetyltryptamine (IC50: 5.6, maximal inhibition 55%) and 5-methoxyluzindole (IC50: 1.3, maximal inhibition 40%) showed various degrees of efficacy while none of the competitive Melatonin Receptor antagonists did inhibit [3H]dopamine release on their own. The potency (IC50) of full Melatonin Receptor agonists significantly correlated with their affinity to compete for 2-[125I]-iodoMelatonin binding to either the Mel1a (r 2 = 0.76, slope = 0.77, P
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Melatonin Receptor antagonists that differentiate between the human mel1a and mel1b recombinant subtypes are used to assess the pharmacological profile of the rabbit retina ml1 presynaptic heteroReceptor
Naunyn-schmiedebergs Archives of Pharmacology, 1997Co-Authors: Margarita L. Dubocovich, Monica I Masana, Stanca Iacob, Daniel M. SauriAbstract:We have identified subtype selective agonists, partial agonists and antagonists, which distinguish the human recombinant Mel1a and Mel1b Melatonin Receptors expressed in COS-7 cells. Melatonin Receptor agonists showed higher affinity for competition of 2-[125I]-iodoMelatonin binding for the Mel1b than the Mel1a Melatonin Receptor. The dissociation constants (Ki) of 16 agonists determined on the recombinant human Mel1a and Mel1b Melatonin Receptor subtypes showed a significant correlation (r 2 = 0.85, slope = 0.97, P < 0.0001, n = 16). However, six agonists showed 10 to 60 fold higher affinity for the Mel1b Melatonin Receptor as indicated by the affinity selectivity ratios (Mel1a/Mel1b) [8-methoxy-2-acetamidotetraline (11); S20098 (14); 8-methoxy-2-propionamidotetraline (20); 6, 7 di-chloro-2-methylMelatonin (21); 6-chloroMelatonin (57); 6-methoxyMelatonin (59)]. Dissociation constants for competition of 11 partial agonists and antagonist for 2-[125I]-iodoMelatonin binding were between 15.5 (luzindole, pKi: 7.7) to 362 (4-phenyl-2-chloroacetamidotetraline, pKi: 9.1) fold higher for the Mel1b than for the Mel1a Melatonin Receptor. The lack of correlation between the pKi values (r 2 = 0.23, P > 0.1, n = 11) strongly suggest that the two human Melatonin Receptor subtypes can be distinguished pharmacologically. The partial agonist: 5-methoxyluzindole (pKi: 9.6) and the competitive Melatonin Receptor antagonists: GR128107 (pKi: 9.6), 4-phenyl-2-chloroacetamidotetraline (pKi: 9.1), 4-phenyl-2-acetamidotetraline (pKi: 8.9) and 4-phenyl-2-propionamidotetraline (pKi: 8.8) are selective Mel1b Melatonin Receptor analogues as their affinity selectivity ratios (Mel1a/Mel1b) are bigger than 100. We conclude that the 40% overall amino acid difference in the sequence of the human recombinant Mel1a and Mel1b Melatonin Receptors is reflected in distinct pharmacological profiles for the subtypes. We compared the pharmacological profile of the presynaptic ML1 Melatonin heteroReceptor of rabbit retina mediating inhibition of the calcium-dependent release of dopamine to that of the recombinant Mel1a and Mel1b Melatonin Receptors. Melatonin inhibited [3H]dopamine release by 50% (IC50) at 20 pM with a maximal inhibitory effect (80%) at 1 nM. The partial agonists, i.e., N-acetyltryptamine (IC50: 5.6, maximal inhibition 55%) and 5-methoxyluzindole (IC50: 1.3, maximal inhibition 40%) showed various degrees of efficacy while none of the competitive Melatonin Receptor antagonists did inhibit [3H]dopamine release on their own. The potency (IC50) of full Melatonin Receptor agonists significantly correlated with their affinity to compete for 2-[125I]-iodoMelatonin binding to either the Mel1a (r 2 = 0.76, slope = 0.77, P<0.0001, n = 17) or Mel1b (r 2 = 0.63, slope = 0.75, P<0.001, n = 17) human Melatonin Receptors. By contrast, the apparent dissociation constants (KB) for partial agonists and antagonists to antagonize the inhibition of [3H]dopamine release mediated by activation of the ML1 heteroReceptor by Melatonin, significantly correlated with the affinity constants (Ki) for 2-[125I]-iodoMelatonin binding determined on the Mel1b (r 2 = 0.77, slope = 0.55, P<0.001; n = 11) but not the Mel1a (r 2 = 0.27, P<0.1, n = 11) subtype. Together these results demonstrate that the pharmacological profile of the human recombinant Mel1b Melatonin Receptor is similar to that of the functional presynaptic Melatonin heteroReceptor of rabbit retina, which we referred as an ML1B subtype. We conclude that the selective Mel1b Melatonin partial agonists and antagonists described here can be used to identify Melatonin Receptor subtypes in native tissues and to search for subtype selective analogues with therapeutic potential.
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Melatonin Receptor antagonists that differentiate between the human mel1a and mel1b recombinant subtypes are used to assess the pharmacological profile of the rabbit retina ml1 presynaptic heteroReceptor
Naunyn-schmiedebergs Archives of Pharmacology, 1997Co-Authors: Margarita L. Dubocovich, Monica I Masana, Stanca Iacob, Daniel M. SauriAbstract:We have identified subtype selective agonists, partial agonists and antagonists, which distinguish the human recombinant Mel1a and Mel1b Melatonin Receptors expressed in COS-7 cells. Melatonin Receptor agonists showed higher affinity for competition of 2-[125I]-iodoMelatonin binding for the Mel1b than the Mel1a Melatonin Receptor. The dissociation constants (Ki) of 16 agonists determined on the recombinant human Mel1a and Mel1b Melatonin Receptor subtypes showed a significant correlation (r2 = 0.85, slope = 0.97, P 0.1, n = 11) strongly suggest that the two human Melatonin Receptor subtypes can be distinguished pharmacologically. The partial agonist: 5-methoxyluzindole (pKi: 9.6) and the competitive Melatonin Receptor antagonists: GR128107 (pKi: 9.6), 4-phenyl-2-chloroacetamidotetraline (pKi: 9.1), 4-phenyl-2-acetamidotetraline (pKi: 8.9) and 4-phenyl-2-propionamidotetraline (pKi: 8.8) are selective Mel1b Melatonin Receptor analogues as their affinity selectivity ratios (Mel1a/Mel1b) are bigger than 100. We conclude that the 40% overall amino acid difference in the sequence of the human recombinant Mel1a and Mel1b Melatonin Receptors is reflected in distinct pharmacological profiles for the subtypes. We compared the pharmacological profile of the presynaptic ML1 Melatonin heteroReceptor of rabbit retina mediating inhibition of the calcium-dependent release of dopamine to that of the recombinant Mel1a and Mel1b Melatonin Receptors. Melatonin inhibited [3H]dopamine release by 50% (1C50) at 20 pM with a maximal inhibitory effect (80%) at 1 nM. The partial agonists, i.e., N-acetyltryptamine (1C50 5.6, maximal inhibition 55%) and 5-methoxyluzindole (1C50: 1.3, maximal inhibition 40%) showed various degrees of efficacy while none of the competitive Melatonin Receptor antagonists did inhibit [3H]dopamine release on their own. The potency (1C50) of full Melatonin Receptor agonists significantly correlated with their affinity to compete for 2-[125I]-iodoMelatonin binding to either the Mel1a (r2 = 0.76, slope = 0.77, P < 0.0001, n = 17) or Mel1b (r2 = 0.63, slope = 0.75, P < 0.001, n = 17) human Melatonin Receptors. By contrast, the apparent dissociation constants (KB) for partial agonists and antagonists to antagonize the inhibition of [3H]dopamine release mediated by activation of the ML1 heteroReceptor by Melatonin, significantly correlated with the affinity constants (Ki) for 2-[125I]-iodoMelatonin binding determined of the Mel1b (r2 = 0.77, slope = 0.55, P < 0.001; n = 11) but not the Mel1a (r2 = 0.27, P < 0.1, n = 11) subtype. Together these results demonstrate that the pharmacological profile of the human recombinant Mel1b Melatonin Receptor is similar to that of the functional presynaptic Melatonin heteroReceptor of rabbit retina, which we referred as an ML1B subtype. We conclude that the selective Mel1b Melatonin partial agonists and antagonists described here can be used to identify Melatonin Receptor subtypes in native tissues and to search for subtype selective analogues with therapeutic potential.
Simon C. Robson - One of the best experts on this subject based on the ideXlab platform.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto 5 nucleotidase mrna levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.
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Melatonin Receptor deficiency decreases and temporally shifts ecto-5′-nucleotidase mRNA levels in mouse prosencephalon
Cell and Tissue Research, 2016Co-Authors: Moran Homola, Martina Pfeffer, Claudia Fischer, Simon C. Robson, Herbert Zimmermann, Horst-werner KorfAbstract:Ecto-5′-nucleotidase (eN) is the major extracellular adenosine-producing ecto-enzyme in mouse brain. Via the production of adenosine, eN participates in many physiological and pathological processes, such as wakefulness, inflammation, nociception and neuroprotection. The mechanisms regulating the expression of eN are therefore of considerable neurobiological and clinical interest. Having previously described a modulatory effect of Melatonin in the regulation of eN mRNA levels, we decided to analyze the Melatonin Receptor subtype involved in the regulation of eN mRNA levels by comparing eN mRNA patterns in Melatonin-proficient transgenic mice lacking either the Melatonin Receptor subtype 1 (MT1 KO) or both Melatonin Receptor subtypes (MT1 and MT2; MT1/2 KO) with the corresponding Melatonin-proficient wild-type (WT) controls. By means of radioactive in situ hybridization, eN mRNA levels were found to be diminished in both MT1 and MT1/2 KO mice compared with WT controls suggesting stimulatory impacts of Melatonin Receptors on eN mRNA levels. Whereas eN mRNA levels increased during the day and peaked at night in WT and MT1 KO mice, eN mRNA levels at night were reduced and the peak was shifted toward day-time in double MT1/2 KO mice. These data suggest that the MT2 Receptor subtype may play a role in the temporal regulation of eN mRNA availability. Notably, day-time locomotor activity was significantly higher in MT1/2 KO compared with WT mice. Our results suggest Melatoninergic signaling as an interface between the purinergic system and the circadian system.