CGRP receptors: a headache to study, but will antagonists prove therapeutic in migraine?

Incorporation of health technologies: The importance of drug treatment of primary headaches in the Brazilian unified health system

Incorporation of health technologies: The importance of drug treatment of primary headaches in the Brazilian unified health system

The Cardiopulmonary Effects of the Calcitonin Gene-related Peptide Family

Cardiopulmonary diseases are very common among the population. They are high-cost diseases and there are still no definitive treatments. The roles of members of the calcitonin-gene related-peptide (CGRP) family in treating cardiopulmonary diseases have been studied for many years and promising results obtained. Especially in recent years, two important members of the family, adrenomedullin and adrenomedullin2/intermedin, have been considered new treatment targets in cardiopulmonary diseases. In this review, the roles of CGRP family members in cardiopulmonary diseases are investigated based on the studies performed to date.

Quinoline derivatives: candidate drugs for a class B G-protein coupled receptor, the calcitonin gene-related peptide receptor, a cause of migraines

Class B G-protein coupled receptors are involved in a wide variety of diseases and are a major focus in drug design. Migraines are a common problem, and one of their major causative agents is the class B G-protein coupled receptor, Calcitonin gene-related peptide (CGRP) receptor, a target for competitive drug discovery. The calcitonin receptor-like receptor generates complexes with a receptor activity-modifying protein, which determines the type of receptor protein formed. The CGRP receptor comprises a complex formed from the calcitonin receptor-like receptor and receptor activity-modifying protein 1. In this study, an in silico docking approach was used to target the calcitonin receptor-like receptor in the bound form with receptor activity-modifying protein 1 (CGRP receptor), as well as in the unbound form. In both cases, the resulting inhibitors bound to the same cavity of the calcitonin receptor-like receptor. The twelve evaluated compounds were competitive inhibitors and showed efficient inhibitory activity against the CGRP receptor and Calcitonin receptor-like receptor. The two studied quinoline derivatives demonstrated potentially ideal inhibitory activity in terms of binding interactions and low range nano-molar inhibition constants. These compounds could prove helpful in designing drugs for the effective treatment of migraines. We propose that quinoline derivatives possess inhibitory activity by disturbing CGRP binding in the trigeminovascular system and may be considered for further preclinical appraisal for the treatment of migraines.

Non-peptidic antagonists of the CGRP receptor, BIBN4096BS and MK-0974, interact with the calcitonin receptor-like receptor via methionine-42 and RAMP1 via tryptophan-74

The receptor for calcitonin gene-related peptide (CGRP) has been the target for the development of novel small molecule antagonists for the treatment of migraine. Two such antagonists, BIBN4096BS and MK-0974, have shown great promise in clinical trials and hence a deeper understanding of the mechanism of their interaction with the receptor is now required. The structure of the CGRP receptor is unusual since it is comprised of a hetero-oligomeric complex between the calcitonin receptor-like receptor (CRL) and an accessory protein (RAMP1). Both the CLR and RAMP1 components have extracellular domains which interact with each other and together form part of the peptide-binding site. It seems likely that the antagonist binding site will also be located on the extracellular domains and indeed Trp-74 of RAMP1 has been shown to form part of the binding site for BIBN4096BS. However, despite a chimeric study demonstrating the role of the N-terminal domain of CLR in antagonist binding, no specific residues have been identified. Here we carry out a mutagenic screen of the extreme N-terminal domain of CLR (residues 23-63) and identify a mutant, Met-42-Ala, which displays 48-fold lower affinity for BIBN4096BS and almost 900-fold lower affinity for MK-0974. In addition, we confirm that the Trp-74-Lys mutation at human RAMP1 reduces BIBN4096BS affinity by over 300-fold and show for the first time a similar effect for MK-0974 affinity. The data suggest that the non-peptide antagonists occupy a binding site close to the interface of the N-terminal domains of CLR and RAMP1.

Juxtamembranous region of the amino terminus of the family B G protein-coupled calcitonin receptor plays a critical role in small-molecule agonist action

The Family B G protein-coupled calcitonin receptor is an important drug target. The aim of this work was to elucidate the molecular mechanism of action of small-molecule agonist ligands acting at this receptor, comparing it with the action mechanism of the receptor's natural peptide ligand. cAMP responses to four non-peptidyl ligands and calcitonin were studied in COS-1 cells expressing wild-type and chimeric calcitonin-secretin receptors. All compounds were full agonists at the calcitonin receptor with no activity at the secretin receptor. Only chimeric constructs including the calcitonin receptor amino terminus exhibited responses to any of these ligands. We progressively truncated this domain and tested constructs for cAMP responses. Although calcitonin was able to activate the calcitonin receptor fully with the first 58 residues absent, its potency was 3 orders of magnitude lower than that at the wild-type receptor. After truncation of 114 residues, there was no response to calcitonin. In contrast, small-molecule ligands were fully active at receptors having up to 149 amino-terminal residues absent. Those compounds finally became inactive after truncation of 153 residues. Deletion and/or alanine replacement of the region of the calcitonin receptor between residues 150 and 153 resulted in marked reduction in cAMP responses to these compounds, with some compound-specific differences observed, supporting a critical role for this region. Binding studies further supported distinct sites of action of small molecules relative to that of calcitonin. These findings focus attention on the potential importance of the juxtamembranous region of the amino terminus of the Family B calcitonin receptor for agonist drug action.

Neuropeptide and kinin antagonists

Neuropeptides and kinins are important messengers in the nervous system and--on the basis of their anatomical localisation and the effects produced when the substances themselves are administered, to animals or to human subjects-a significant number of them have been suggested to have a role in pain and inflammation. Experiments in gene deletion (knock-out or null mutant) mice and parallel experiments with pharmacological receptor antagonists in a variety of species have strengthened the evidence that a number of peptides, notably substance P and calcitonin gene-related peptide (CGRP), and the kinins have a pathophysiological role in nociception. Clinical studies with non-peptide pharmacological antagonists are now in progress to determine if blocking the action of these peptides might have utility in the treatment of pain.

Muscle inflammation induces a rapid increase in calcitonin gene-related peptide (CGRP) mRNA that temporally relates to CGRP immunoreactivity and nociceptive behavior

Recent data support an important role for calcitonin gene-related peptide (CGRP) in deep tissue nociceptive processing. Using real-time reverse transcriptase polymerase chain reaction (RT-PCR), radioimmunoassay, immunohistochemistry and behavioral testing, we studied the early time course of CGRP mRNA and protein expression as well as nociceptive behavior following muscle inflammation. A rapid and significant increase in CGRP mRNA occurred in the mandibular division (V3) of the ipsilateral trigeminal ganglion at 30 minutes, 4 and 24 h after the injection of complete Freund's adjuvant as an inflammatory agent into rat masseter muscle. No change in mRNA occurred in the ipsilateral ophthalmic and maxillary divisions (V1/V2) or in the contralateral V3. The levels of immunoreactive calcitonin gene-related peptide (iCGRP) in the ipsilateral V3 significantly increased at 1, 4 and 24 h following muscle inflammation. In contrast, no change occurred in iCGRP levels in either the ipsilateral V1/V2 or contralateral V3. When saline was injected into the masseter muscle, the levels of mRNA or iCGRP did not change in the ipsilateral V3 suggesting that the biochemical changes are specific to CFA-induced muscle inflammation. The number of muscle afferent neurons immunoreactive for CGRP was significantly reduced compared with control at 1, 4 and 24 h in the ipsilateral but not in the contralateral trigeminal ganglion following inflammation. This decrease in the ipsilateral ganglion may indicate a loss of intrasomatic CGRP as a result of increased axonal transport away from the neuronal cell body and/or release of CGRP. Behavioral testing showed a reduction in head withdrawal thresholds bilaterally from 30 min through 24 h following muscle inflammation. Thus upregulation of CGRP mRNA and iCGRP levels are temporally related to the development of inflammation and lowered pain thresholds. The present data support the hypothesis that CGRP is upregulated during deep tissue inflammation and suggest that gene transcription is involved in this upregulation.

Biphasic neurogenic vasodilatation in the bovine intraocular long posterior ciliary artery: involvement of nitric oxide and an additional unidentified neurotransmitter

We have investigated the neurogenic factors inducing relaxation in the intraocular segment of the bovine long posterior ciliary artery. In precontracted vessels, electrical field stimulation (EFS, 0.5-128 Hz, 10 s trains) in the presence of guanethidine (30 microM) evoked biphasic relaxation: optimal relaxation for the first and second components occurred at 10 and 50 s, respectively. The first component, but not the second, was abolished by L-NAME (100 microM) or ODQ (3 microM). Relaxation to exogenous CGRP (0.1-300 nM) was inhibited by the CGRP antagonist, CGRP(8-37) (1-5 microM), but neither component of neurogenic relaxation was affected. Preincubation with the sensory nerve excitotoxin, capsaicin (1 microM), had no effect on either the first or second components of neurogenic relaxation. Substance P (0.1 nM-0.1 microM) induced relaxation, but rapid and complete desensitisation occurred within minutes. Neither desensitisation to substance P (0.1 microM) nor incubation with the NK(1) antagonist, L-733,060 (0.3 microM), had any effect on the first or second components of neurogenic relaxation.VIP (0.1 nM-0.3 microM) induced relaxation and this was followed by substantial desensitisation. Neither desensitisation to VIP (0.6 microM) nor treatment with the protease, alpha-chymotrypsin (10 U ml(-1)), had any effect on the first or second components of neurogenic relaxation. The results indicate that nitric oxide mediates the first component of neurogenic relaxation in the bovine intraocular ciliary artery. The neurotransmitter mediating the second component remains to be determined but is unlikely to be CGRP, substance P or VIP.

The assessment of vasoactive properties of CGRP and adrenomedullin in the microvasculature: a study using in vivo and in vitro assays in the mouse

The potent neuropeptide vasodilator, calcitonin gene-related peptide (CGRP), and the vasoactive peptide adrenomedullin (AM) are structurally related. Evidence from our laboratory has demonstrated that these peptides have potent microvascular actions of relevance to cardiovascular and inflammatory effects in health and disease. We wish to further investigate the actions of these peptides through studies in genetically modified mice. We have developed techniques to enable the quantitative analysis of CGRP and AM responses in the mouse microvasculature. A mouse isolated mesentery system was developed that measures changes in perfusion pressure used as an index of microvascular relaxation in the precontracted mesenteric microvascular bed. Bolus injections of CGRP and AM caused dose-dependent decreases in perfusion pressure that were proportional to vascular relaxation. An in vivo mouse skin assay was also used in which agents were injected intradermally into the dorsal skin. The effects of these agents was assessed by the extravascular accumulation of intravenously injected 125I-albumin for their ability to potentiate plasma extravasation induced by a mediator of increased microvascular permeability. CGRP and AM are not directly active in this assay, because it does not directly measure blood flow. However, the vasodilators acted in a potent and dose-dependent manner to significantly potentiate edema formation. The results demonstrate the potent activity of CGRP and the activity (although 100- to 300-fold less potent) of AM. Furthermore, the results demonstrate the increased potency of CGRP in the microvasculature when compared with the structurally distinct peptide VIP and PGE1.