14 research outputs found
An in Vitro and in Vivo Investigation of Bivalent Ligands That Display Preferential Binding and Functional Activity for Different Melanocortin Receptor Homodimers
Pharmacological
probes for the melanocortin receptors have been
utilized for studying various disease states including cancer, sexual
function disorders, Alzheimer’s disease, social disorders,
cachexia, and obesity. This study focused on the design and synthesis
of bivalent ligands to target melanocortin receptor homodimers. Lead
ligands increased binding affinity by 14- to 25-fold and increased
cAMP signaling potency by 3- to 5-fold compared to their monovalent
counterparts. Unexpectedly, different bivalent ligands showed preferences
for particular melanocortin receptor subtypes depending on the linker
that connected the binding scaffolds, suggesting structural differences
between the various dimer subtypes. Homobivalent compound <b>12</b> possessed a functional profile that was unique from its monovalent
counterpart providing evidence of the discrete effects of bivalent
ligands. Lead compound <b>7</b> significantly decreased feeding
in mice after intracerebroventricular administration. To the best
of our knowledge, this is the first report of a melanocortin bivalent
ligand’s in vivo physiological effects
A Direct in Vivo Comparison of the Melanocortin Monovalent Agonist Ac-His-DPhe-Arg-Trp-NH2 versus the Bivalent Agonist Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH2: A Bivalent Advantage
Bivalent ligands targeting putative melanocortin receptor dimers have been developed and characterized in vitro; however, studies of their functional in vivo effects have been limited. The current report compares the effects of homobivalent ligand CJL-1-87, Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-N
Comparative in Vivo Investigation of Intrathecal and Intracerebroventricular Administration with Melanocortin Ligands MTII and AGRP into Mice
Central
administration of melanocortin ligands has been used as
a critical technique to study energy homeostasis. While intracerebroventricular
(ICV) injection is the most commonly used method during these investigations,
intrathecal (IT) injection can be equally efficacious for the central
delivery of ligands. Importantly, intrathecal administration can optimize
exploration of melanocortin receptors in the spinal cord. Herein,
we investigate comparative IT and ICV administration of two melanocortin
ligands, the synthetic MTII (Ac-Nle-cÂ[Asp-His-DPhe-Arg-Trp-Lys]-NH<sub>2</sub>) MC4R agonist and agouti-related peptide [AGRPÂ(87-132)] MC4R
inverse agonist/antagonist, on the same batch of age-matched mice
in TSE metabolic cages undergoing a nocturnal satiated paradigm. To
our knowledge, this is the first study to test how central administration
of these ligands directly to the spinal cord affects energy homeostasis.
Results showed, as expected, that MTII IT administration caused a
decrease in food and water intake and an overall negative energy balance
without affecting activity. As anticipated, IT administration of AGRP
caused weight gain, increase of food/water intake, and increase respiratory
exchange ratio (RER). Unexpectantly, the prolonged activity of AGRP
was notably shorter (2 days) compared to mice given ICV injections
of the same concentrations in previous studies (7 days or more).− It appears that IT administration results in a more sensitive response
that may be a good approach for testing synthetic compound potency
values ranging in nanomolar to high micromolar in vitro EC<sub>50</sub> values. Indeed, our investigation reveals that the spine influences
a different melanocortin response compared to the brain for the AGRP
ligand. This study indicates that IT administration can be a useful
technique for future metabolic studies using melanocortin ligands
and highlights the importance of exploring the role of melanocortin
receptors in the spinal cord
Ac-Trp-DPhe(p-I)-Arg-Trp-NH<sub>2</sub>, a 250-Fold Selective Melanocortin‑4 Receptor (MC4R) Antagonist over the Melanocortin‑3 Receptor (MC3R), Affects Energy Homeostasis in Male and Female Mice Differently
The melanocortin-4
receptor (MC4R) has been indicated as a therapeutic target for metabolic
disorders such as anorexia, cachexia, and obesity. The current study
investigates the in vivo effects on energy homeostasis of a 15 nM
MC4R antagonist SKY2-23-7, Ac-Trp-DPheÂ(p-I)-Arg-Trp-NH<sub>2</sub>, that is a 3700 nM melanocortin-3 receptor (MC3R) antagonist with
minimal MC3R and MC4R agonist activity. When monitoring both male
and female mice in TSE metabolic cages, sex-specific responses were
observed in food intake, respiratory exchange ratio (RER), and energy
expenditure. A 7.5 nmol dose of SKY2-23-7 increased food intake, increased
RER, and trended toward decreasing energy expenditure in male mice.
However, this compound had minimal effect on female mice’s
food intake and RER at the 7.5 nmol dose. A 2.5 nmol dose of SKY2-23-7
significantly increased female food intake, RER, and energy expenditure
while having a minimal effect on male mice at this dose. The observed
sex differences of SKY2-23-7 administration result in the discovery
of a novel chemical probe for elucidating the molecular mechanisms
of the sexual dimorphism present within the melanocortin pathway.
To further explore the melanocortin sexual dimorphism, hypothalamic
gene expression was examined. The mRNA expression of the MC3R and
proopiomelanocortin (POMC) were not significantly different between
sexes. However, the expression of agouti-related peptide (AGRP) was
significantly higher in female mice which may be a possible mechanism
for the sex-specific effects observed with SKY2-23-7
A Direct in Vivo Comparison of the Melanocortin Monovalent Agonist Ac-His-DPhe-Arg-Trp-NH<sub>2</sub> versus the Bivalent Agonist Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH<sub>2</sub>: A Bivalent Advantage
Bivalent
ligands targeting putative melanocortin receptor dimers have been
developed and characterized in vitro; however, studies of their functional
in vivo effects have been limited. The current report compares the
effects of homobivalent ligand CJL-1-87, Ac-His-DPhe-Arg-Trp-PEDG20-His-DPhe-Arg-Trp-NH<sub>2</sub>, to monovalent ligand CJL-1-14, Ac-His-DPhe-Arg-Trp-NH<sub>2</sub>, on energy homeostasis in mice after central intracerebroventricular
(ICV) administration into the lateral ventricle of the brain. Bivalent
ligand CJL-1-87 had noteworthy advantages as an antiobesity probe
over CJL-1-14 in a fasting-refeeding in vivo paradigm. Treatment with
CJL-1-87 significantly decreased food intake compared to CJL-1-14
or saline (50% less intake 2–8 h after treatment). Furthermore,
CJL-1-87 treatment decreased the respiratory exchange ratio (RER)
without changing the energy expenditure indicating that fats were
being burned as the primary fuel source. Additionally, CJL-1-87 treatment
significantly lowered body fat mass percentage 6 h after administration
(<i>p</i> < 0.05) without changing the lean mass percentage.
The bivalent ligand significantly decreased insulin, C-peptide, leptin,
GIP, and resistin plasma levels compared to levels after CJL-1-14
or saline treatments. Alternatively, ghrelin plasma levels were significantly
increased. Serum stability of CJL-1-87 and CJL-1-14 (<i>T</i><sub>1/2</sub> = 6.0 and 16.8 h, respectively) was sufficient to
permit physiological effects. The differences in binding affinity
of CJL-1-14 compared to CJL-1-87 are speculated as a possible mechanism
for the bivalent ligand’s unique effects. We also provide in
vitro evidence for the formation of a MC3R-MC4R heterodimer complex,
for the first time to our knowledge, that may be an unexploited neuronal
molecular target. Regardless of the exact mechanism, the advantageous
ability of CJL-1-87 compared to CJL-1-14 to increase in vitro binding
affinity, increase the duration of action in spite of decreased serum
stability, decrease in vivo food intake, decrease mice’s body
fat percent, and differentially affect mouse hormone levels demonstrates
the distinct characteristics achieved from the current melanocortin
agonist bivalent design strategy
Human β‑Defensin 1 and β‑Defensin 3 (Mouse Ortholog mBD14) Function as Full Endogenous Agonists at Select Melanocortin Receptors
β-Defensin 3 (BD3) was identified
as a ligand for the melanocortin
receptors (MCRs) in 2007, although the pharmacology activity of BD3
has not been clearly elucidated. Herein, it is demonstrated that human
BD3 and mouse BD3 are full micromolar agonists at the MCRs. Furthermore,
mouse β-defensin 1 (BD1) and human BD1 are also MCR micromolar
agonists. This work identifies BD1 as an endogenous MCR ligand and
clarifies the controversial role of BD3 as a micromolar agonist
Epigenetic basis of opiate suppression of Bdnf gene expression in the ventral tegmental area
International audienceBrain-derived neurotrophic factor (BDNF) has a crucial role in modulating neural and behavioral plasticity to drugs of abuse. We found a persistent downregulation of exon-specific Bdnf expression in the ventral tegmental area (VTA) in response to chronic opiate exposure, which was mediated by specific epigenetic modifications at the corresponding Bdnf gene promoters. Exposure to chronic morphine increased stalling of RNA polymerase II at these Bdnf promoters in VIA and altered permissive and repressive histone modifications and occupancy of their regulatory proteins at the specific promoters. Furthermore, we found that morphine suppressed binding of phospho-CREB (cAMP response element binding protein) to Bdnf promoters in VIA, which resulted from enrichment of trimethylated H3K27 at the promoters, and that decreased NURR1 (nuclear receptor related-1) expression also contributed to Bdnf repression and associated behavioral plasticity to morphine. Our findings suggest previously unknown epigenetic mechanisms of morphine-induced molecular and behavioral neuroadaptations
Epigenetic basis of opiate suppression of Bdnf gene expression in the ventral tegmental area
International audienceBrain-derived neurotrophic factor (BDNF) has a crucial role in modulating neural and behavioral plasticity to drugs of abuse. We found a persistent downregulation of exon-specific Bdnf expression in the ventral tegmental area (VTA) in response to chronic opiate exposure, which was mediated by specific epigenetic modifications at the corresponding Bdnf gene promoters. Exposure to chronic morphine increased stalling of RNA polymerase II at these Bdnf promoters in VIA and altered permissive and repressive histone modifications and occupancy of their regulatory proteins at the specific promoters. Furthermore, we found that morphine suppressed binding of phospho-CREB (cAMP response element binding protein) to Bdnf promoters in VIA, which resulted from enrichment of trimethylated H3K27 at the promoters, and that decreased NURR1 (nuclear receptor related-1) expression also contributed to Bdnf repression and associated behavioral plasticity to morphine. Our findings suggest previously unknown epigenetic mechanisms of morphine-induced molecular and behavioral neuroadaptations