Demonstration of the neurotransmitter role of calcitonin gene-related peptides (CGRP) by immunoblockade with anti-CGRP monoclonal antibodies

Calcitonin Gene-Related Peptide Modulators - The History and Renaissance of a New Migraine Drug Class

Several lines of evidence pointed to an important role for CGRP in migraine. These included the anatomic colocalization of CGRP and its receptor in sensory fibers innervating pain-producing meningeal blood vessels, its release by trigeminal stimulation, the observation of elevated CGRP in the cranial circulation during migraine with normalization concomitant with headache relief by sumatriptan, and translational studies with intravenous (IV) CGRP that evoked migraine only in migraineurs. The development of small molecule CGRP receptor antagonists (CGRP-RAs) that showed clinical antimigraine efficacy acutely and prophylactically in randomized placebo-controlled clinical trials subsequently gave definitive pharmacological proof of the importance of CGRP in migraine. More recently, CGRP target engagement imaging studies using a CGRP receptor PET ligand [¹¹ C]MK-4232 demonstrated that there was no brain CGRP receptor occupancy at clinically effective antimigraine doses of telcagepant, a prototypic CGRP-RA. Taken together, these data indicated that (1) the therapeutic site of action of the CGRP-RAs was peripheral not central; (2) that IV CGRP had most likely evoked migraine through an action at sites outside the blood-brain barrier; and (3) that migraine pain was therefore, at least in part, peripheral in origin. The evolution of CGRP migraine science gave impetus to the development of peripherally acting drugs that could modulate CGRP chronically to prevent frequent episodic and chronic migraine. Large molecule biologic antibody (mAb) approaches that are given subcutaneously to neutralize circulating CGRP peptide (fremanezumab, galcanezumab) or block CGRP receptors (erenumab) have shown consistent efficacy and tolerability in multicenter migraine prevention trials and are now approved for clinical use. Eptinezumab, a CGRP neutralizing antibody given IV, shows promise in late stage clinical development. Recently, orally administered next-generation small molecule CGRP-RAs have been shown to have safety and efficacy in acute treatment (ubrogepant and rimegepant) and prevention (atogepant) of migraine, giving additional CGRP-based therapeutic options for migraine patients.

Immunoneutralization of agmatine sensitizes mice to micro-opioid receptor tolerance

Systemically or centrally administered agmatine (decarboxylated arginine) prevents, moderates, or reverses opioid-induced tolerance and self-administration, inflammatory and neuropathic pain, and sequelae associated with ischemia and spinal cord injury in rodents. These behavioral models invoke the N-methyl-D-aspartate (NMDA) receptor/nitric-oxide synthase cascade. Agmatine (AG) antagonizes the NMDA receptor and inhibits nitric-oxide synthase in vitro and in vivo, which may explain its effect in models of neural plasticity. Agmatine has been detected biochemically and immunohistochemically in the central nervous system. Consequently, it is conceivable that agmatine operates in an anti-glutamatergic manner in vivo; the role of endogenous agmatine in the central nervous system remains minimally defined. The current study used an immunoneutralization strategy to evaluate the effect of sequestration of endogenous agmatine in acute opioid analgesic tolerance in mice. First, intrathecal pretreatment with an anti-AG IgG (but not normal IgG) reversed an established pharmacological effect of intrathecal agmatine: antagonism of NMDA-evoked behavior. This result justified the use of anti-AG IgG to sequester endogenous agmatine in vivo. Second, intrathecal pretreatment with the anti-AG IgG sensitized mice to induction of acute spinal tolerance of two micro-opioid receptor-selective agonists, [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin and endomorphin-2. A lower dose of either agonist that, under normal conditions, produces moderate or no tolerance was tolerance-inducing after intrathecal pretreatment of anti-AG IgG (but not normal IgG). The effect of the anti-AG IgG lasted for at least 24 h in both NMDA-evoked behavior and the acute opioid tolerance. These results suggest that endogenous spinal agmatine may moderate glutamate-dependent neuroplasticity.

Effect of two novel CGRP-binding compounds in a closed cranial window rat model

We investigated the in vivo effects of two novel calcitonin gene-related peptide (CGRP) binding molecules in the genuine closed cranial window model in the rat. The RNA-Spiegelmer (NOX-C89) and the monoclonal CGRP antibody are CGRP scavengers and might be used as an alternative to CGRP-receptor antagonists in the treatment of migraine. Rats were anaesthetized and a closed cranial window established. Changes in dural and pial artery diameter and mean arterial blood pressure were measured simultaneously. Infusion of the RNA-Spiegelmer or the CGRP antibody alone had no effect on the arteries or the mean arterial blood pressure. We then used a bolus of 0.3 microg/kg CGRP (n=6) or electrical stimulation (25 V, 5 Hz, 1 ms pulse width and of 10 s of duration) (n=6) to induce dilatation of dural and pial arteries (mediated via CGRP-receptors). Pre-treatment with the RNA-Spiegelmer inhibited CGRP-induced vasodilatation of the dural artery (from 38+/-17% to 7+/-3%) and the pial artery (from 14+/-1% to 3+/-2%) (P<0.05). The RNA-Spiegelmer, however, did not significantly inhibit dilatation induced by electrical stimulation (P>0.05). The CGRP antibody caused a significant reduction of the dural artery diameter caused by intravenous CGRP-infusion (from 23+/-5% to 12+/-3%) (P<0.05), but did not inhibit dilatation caused by electrical stimulation (P>0.05). In conclusion, the CGRP scavengers effectively inhibited the effect of circulating CGRP but do not modify the effect of electrical stimulation and the consequent liberation of CGRP from perivascular sensory nerve fibres.

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.

Galanin-like peptide rescues reproductive function in the diabetic rat

Galanin-like peptide (GALP) is expressed in the hypothalamic arcuate nucleus and is regulated by leptin and insulin. Centrally administered GALP stimulates gonadotropin secretion and sexual behavior in the rat. Type 1 diabetes is associated with reduced expression of GALP, as well as an overall decline in reproductive function. We postulated that tonic activity of GALP in the brain is required to sustain normal reproductive activity. To test this hypothesis, we examined whether central (intracerebroventricular) immunoblockade of GALP would reduce sexual behaviors and serum levels of luteinizing hormone (LH) in normal adult male rats. We found that GALP antibody reversibly reduced serum levels of LH and abolished male sexual behaviors (P < 0.05 and 0.001, respectively). Second, we tested whether intracerebroventricular GALP could restore normal plasma LH levels and sexual behavior in diabetic animals. We compared groups of diabetic rats that received intracerebroventricular GALP or vehicle and found that GALP increased serum levels of LH and sexual behavior. Third, we examined whether intracerebroventricular administration of affinity-purified GALP antibody could block the effect of insulin and leptin in reversing the effects of diabetes on LH and sexual behavior. We found that treatment of diabetic animals with insulin and leptin nearly normalized LH levels and sexual behaviors; however, this effect was attenuated by intracerebroventricular administration of GALP antibody (P < 0.05). These observations demonstrate that endogenous GALP provides trophic support to the neuroendocrine reproductive axis, including sexual behavior.

Endothelin-1 affects capsaicin-evoked release of neuropeptides from rat vas deferens

Capsaicin-sensitive neurones release a number of neuropeptides, such as substance P, neurokinin A, somatostatin and calcitonin gene-related peptide (CGRP), which exert a number of effects on smooth muscle tissues. Endothelin-1 was thought to potentiate the capsaicin-evoked release of neuropeptides from sensory neurones of the rat. We have investigated the neuromodulatory effects of endothelin-1 on capsaicin-induced release of neurotransmitters from rat vas deferens. Capsaicin and human alpha calcitonin gene-related peptide (human alphaCGRP) reduced the rat vas deferens twitch responses induced by electrical field stimulation. Human beta calcitonin gene-related peptide-(8-37) [human betaCGRP-(8-37)] (1 microM), a selective alphaCGRP receptor antagonist, antagonized the inhibitory effects of both drugs. Endothelin-1 concentration dependently evoked an increase in basal tone of the musculature and potentiated the amplitude of the electrically stimulated responses, blocking inhibitory effects of capsaicin but not of human alphaCGRP. Moreover, endothelin-1 did not markedly change the inhibitory effects of papaverine (0.1-100 microM) or isoprenaline (1 nM-100 microM) on responses to electrical field stimulation. FR 139317 [(N,N-hexamethylene) carbamoyl-Leu-D-Trp(N-Me)-D-2-Pya], a selective endothelin ET(A) receptor antagonist, administered 30 min before endothelin-1 restored the capsaicin effects whereas BQ 788 [Dmpc-gamma-MeLeu-D-Trp-(1-methoxycarbonyl)-D-Nle], a selective endothelin ET(B) receptor antagonist, was completely ineffective. The endothelin-1-induced block of the capsaicin effect was resistant to tetrodotoxin (1 microM) and 30-min pre-treatment with MEN 10.627 (cyclo[(Met-Asp-Trp-Phe-Dap-Leu) cyclo (2beta-5beta)]), a selective tachykinin NK2 receptor antagonist, did not abolish the endothelin-1 effect on the inhibitory response to capsaicin. These results suggest that endothelin-1 selectively inhibits the capsaicin-induced release of neurotransmitters from rat vas deferens and these effects are mediated via endothelin ET(A) receptors but not by tachykinin release.

Involvement of ATP-sensitive K+ channels in the inhibitory effect of calcitonin gene-related peptide on neurotransmission in rat vas deferens

This study investigated the inhibitory action of human calcitonin-gene-related peptide (CGRP) on neurotransmission in rat isolated vas deferens. The electrically stimulated contractile responses, which were mediated predominantly by activation of postganglionic noradrenergic nerve fibers, were concentration-dependently inhibited by human CGRP (0.1-100 nM, IC50 = 2.15 +/- 0.21 nM, n = 17). Human CGRP at concentrations greater than 3 nM reduced the contractile responses to exogenous noradrenaline and ATP. The inhibitory effect of human CGRP on the electrically stimulated or agonist-induced contractions was antagonized by human CGRP-(8-37), the CGRP receptor antagonist. Glibenclamide (3-10 microM) decreased the effect of human CGRP at a concentration greater than 1 nM whilst glibenclamide did not affect the inhibitory effect of human CGRP on the agonist-induced contractions. These results indicate that human CGRP at low concentrations exerts its inhibitory action mainly by acting on CGRP receptors at the sympathetic nerve terminals supplying rat vas deferens and the activation of ATP-sensitive K+ channels is at least in part involved in the action of human CGRP on neurotransmission.

Selective localization and regulated release of calcitonin gene-related peptide from dense-core vesicles in engineered PC12 cells

Introduction of the gene for calcitonin into the neuroendocrine PC12 cell line resulted in the expression of the neuronal-specific splice product, calcitonin gene-related peptide (CGRP). Expression of this neuropeptide did not require treatment of the PC12 cells with NGF. By all available criteria, including biochemical, immunological, and morphological analysis, we have determined that the CGRP in stably transfected PC12 cells is sorted selectively into the large, dense-core catecholamine-containing secretory vesicles. Conversely, the CGRP is excluded from the small, synaptophysin-rich vesicles present in the same cells. Stimulation conditions that trigger the release of catecholamines cause a parallel burst in the release of CGRP. In all these respects, the engineered PC12 cells process the foreign CGRP in a manner similar to that seen in spinal motor neurons in vivo. These results indicate that this small (37 amino acids) peptide contains sorting information sufficient for targeting to large, dense-core vesicles in heterologous cells, placing very narrow constraints on the possible location of sorting signals. In addition, this CGRP-expressing cell line opens the possibility of studying the physiological role of CGRP in the establishment and maintenance of neuromuscular contacts.

Increased fos expression in preoptic calcitonin gene-related peptide (CGRP) neurones following mating but not the luteinizing hormone surge in female rats

The functional relationship between sexually dimorphic neural populations and sex differences in reproductive functioning is unclear. The present study has investigated the function of the sexually dimorphic, estrogen-receptive, calcitonin gene-related peptide (CGRP) neurones in the female preoptic area by examining patterns of Fos immunoreactivity within these cells in relation to the luteinizing hormone surge and lordosis behaviour. In the first experiment, ovariectomized rats were treated with estradiol alone or estradiol plus progesterone to induce the luteinizing hormone surge. The percentage of CGRP neurones with Fos-positive nuclei was not different in estradiol alone (18 +/- 4%) and estradiol/progesterone-treated (24 +/- 3%) rats although the number of Fos-immunoreactive cells in the medial preoptic nucleus was increased 2-fold (P < 0.01) in estrogen/progesterone-treated rats and 40 +/- 5% of luteinizing hormone-releasing hormone neurones were found to express Fos in this group. In the second experiment, ovariectomized rats were treated with estradiol and progesterone and either, mated with a single male or placed in an empty cage, for 30 min. The number of Fos-immunoreactive cells in the medial preoptic nucleus was increased 4-fold in mated rats (P < 0.01) and the percentage of CGRP neurones with Fos-positive nuclei increased from 24 +/- 3% to 38 +/- 2% (P < 0.01) in mated animals. No differences were detected in the number of luteinizing hormone-releasing hormone neurones with Fos-positive nuclei in mated and non-mated animals.(ABSTRACT TRUNCATED AT 250 WORDS)