Inhibition of capsaicin-induced increase in dermal blood flow by the oral CGRP receptor antagonist, telcagepant (MK-0974)

Elevated plasma levels of calcitonin gene-related peptide in individuals with rosacea: A cross-sectional case-control study

BACKGROUND

Understanding the role of calcitonin gene-related peptide (CGRP) in the pathogenesis of rosacea might provide new therapeutic avenues for individuals with this disease.

OBJECTIVE

To compare plasma levels of CGRP between individuals with rosacea and healthy controls.

METHODS

In this cross-sectional case-control study conducted in Copenhagen, Denmark, we collected blood samples from the antecubital vein from adults with rosacea and from healthy controls.

RESULTS

We enrolled 123 individuals with rosacea and 68 healthy controls. After adjusting for age and sex, plasma levels of CGRP were significantly higher in individuals with rosacea (mean, 95% confidence interval: 140.21 pmol/L, 128.50-151.92 pmol/L), compared with controls (110.77 pmol/L, 99.91-120.14 pmol/L, p = 0.002). Plasma levels of CGRP were not affected by age, sex, BMI, concomitant migraine, rosacea sub- or phenotype, concomitant disease or current treatment.

LIMITATIONS

Participants were not age-, sex- and BMI-matched.

CONCLUSIONS AND RELEVANCE

Elevated plasma levels of CGRP in individuals with rosacea suggest a role of CGRP in the pathogenesis of rosacea. Targeting CGRP signalling might hold therapeutic promise in people affected by this disease.

CLINICALTRIALS

GOV LISTING

NCT03872050.

Antiseizure Medications for the Prophylaxis of Migraine during the Anti- CGRP Drugs Era

Migraine and epilepsy are fundamentally distinct disorders that can frequently coexist in the same patient. These two conditions significantly differ in diagnosis and therapy but share some widely- used preventive treatments. Antiseizure medications (ASMs) are the mainstay of therapy for epilepsy, and about thirty different ASMs are available to date. ASMs are widely prescribed for other neurological and non-neurological conditions, including migraine. However, only topiramate and valproic acid/valproate currently have an indication for migraine prophylaxis supported by high-quality evidence. Although without specifically approved indications and with a low level of evidence or recommendation, several other ASMs are used for migraine prophylaxis. Understanding ASM antimigraine mechanisms, including their ability to affect the pro-migraine calcitonin gene-related peptide (CGRP) signaling pathway and other pathways, may be instrumental in identifying the specific targets of their antimigraine efficacy and may increase awareness of the neurobiological differences between epilepsy and migraine. Several new ASMs are under clinical testing or have been approved for epilepsy in recent years, providing novel potential drugs for migraine prevention to enrich the treatment armamentarium and drugs that inhibit the CGRP pathway.

Non-neuronal TRPA1 encodes mechanical allodynia associated with neurogenic inflammation and partial nerve injury in rats

BACKGROUND AND PURPOSE

The pro-algesic transient receptor potential ankyrin 1 (TRPA1) channel, expressed by a subpopulation of primary sensory neurons, has been implicated in various pain models in mice. However, evidence in rats indicates that TRPA1 conveys nociceptive signals elicited by channel activators, but not those associated with tissue inflammation or nerve injury. Here, in rats, we explored the TRPA1 role in mechanical allodynia associated with stimulation of peptidergic primary sensory neurons (neurogenic inflammation) and moderate (partial sciatic nerve ligation, pSNL) or severe (chronic constriction injury, CCI) sciatic nerve injury.

EXPERIMENTAL APPROACH

Acute nociception and mechanical hypersensitivity associated with neurogenic inflammation and sciatic nerve injury (pSNL and CCI) were investigated in rats with TRPA1 pharmacological antagonism or genetic silencing. TRPA1 presence and function were analysed in cultured rat Schwann cells.

KEY RESULTS

Hind paw mechanical allodynia (HPMA), but not acute nociception, evoked by local injection of capsaicin or allyl isothiocyanate, the TRP vanilloid 1 (TRPV1) or the TRPA1 activators was mediated by CGRP released from peripheral sensory nerve terminals. CGRP-evoked HPMA was sustained by a ROS-dependent TRPA1 activation, probably in Schwann cells. HPMA evoked by pSNL, but not that evoked by CCI, was mediated by ROS and TRPA1 without the involvement of CGRP.

CONCLUSIONS AND IMPLICATIONS

As found in mice, TRPA1 mediates mechanical allodynia associated with neurogenic inflammation and moderate nerve injury in rats. The channel contribution to mechanical hypersensitivity is a common feature in rodents and might be explored in humans.

Gel-forming antagonist provides a lasting effect on CGRP-induced vasodilation

Migraine affects ∼15% of the adult population, and the standard treatment includes the use of triptans, ergotamines, and analgesics. Recently, CGRP and its receptor, the CLR/RAMP1 receptor complex, have been targeted for migraine treatment due to their critical roles in mediating migraine headaches. The effort has led to the approval of several anti-CGRP antibodies for chronic migraine treatment. However, many patients still suffer continuous struggles with migraine, perhaps due to the limited ability of anti-CGRP therapeutics to fully reduce CGRP levels or reach target cells. An alternative anti-CGRP strategy may help address the medical need of patients who do not respond to existing therapeutics. By serendipity, we have recently found that several chimeric adrenomedullin/adrenomedullin 2 peptides are potent CLR/RAMP receptor antagonists and self-assemble to form liquid gels. Among these analogs, the ADE651 analog, which potently inhibits CLR/RAMP1 receptor signaling, forms gels at a 6-20% level. Screening of ADE651 variants indicated that residues at the junctional region of this chimeric peptide are important for gaining the gel-forming capability. Gel-formation significantly slowed the passage of ADE651 molecules through Centricon filters. Consistently, subcutaneous injection of ADE651 gel in rats led to the sustained presence of ADE651 in circulation for >1 week. In addition, analysis of vascular blood flow in rat hindlimbs showed ADE651 significantly reduces CGRP-induced vasodilation. Because gel-forming antagonists could have direct and sustained access to target cells, ADE651 and related antagonists for CLR/RAMP receptors may represent promising candidates for targeting CGRP- and/or adrenomedullin-mediated headaches in migraine patients.

Schwann cell endosome CGRP signals elicit periorbital mechanical allodynia in mice

Efficacy of monoclonal antibodies against calcitonin gene-related peptide (CGRP) or its receptor (calcitonin receptor-like receptor/receptor activity modifying protein-1, CLR/RAMP1) implicates peripherally-released CGRP in migraine pain. However, the site and mechanism of CGRP-evoked peripheral pain remain unclear. By cell-selective RAMP1 gene deletion, we reveal that CGRP released from mouse cutaneous trigeminal fibers targets CLR/RAMP1 on surrounding Schwann cells to evoke periorbital mechanical allodynia. CLR/RAMP1 activation in human and mouse Schwann cells generates long-lasting signals from endosomes that evoke cAMP-dependent formation of NO. NO, by gating Schwann cell transient receptor potential ankyrin 1 (TRPA1), releases ROS, which in a feed-forward manner sustain allodynia via nociceptor TRPA1. When encapsulated into nanoparticles that release cargo in acidified endosomes, a CLR/RAMP1 antagonist provides superior inhibition of CGRP signaling and allodynia in mice. Our data suggest that the CGRP-mediated neuronal/Schwann cell pathway mediates allodynia associated with neurogenic inflammation, contributing to the algesic action of CGRP in mice.

Roles of calcitonin gene-related peptide in the skin, and other physiological and pathophysiological functions

Skin immunity is regulated by many mediator molecules. One is the neuropeptide calcitonin gene-related peptide (CGRP). CGRP has roles in regulating the function of components of the immune system including T cells, B cells, dendritic cells (DCs), endothelial cells (ECs), and mast cells (MCs).

Herein we discuss actions of CGRP in mediating inflammatory and vascular effects in various cutaneous models and disorders.

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CGRP can help to recruit immune cells through endothelium-dependent vasodilation.

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CGRP plays an important role in the pathogenesis of neurogenic inflammation.

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Functions of many components in the immune system are influenced by CGRP.

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CGRP regulates various inflammatory processes in human skin by affecting different cell-types.

Low Electrical Resistance Properties of Acupoints: Roles of NOergic Signaling Molecules and Neuropeptides in Skin Electrical Conductance

Early studies from several independent laboratories demonstrated that acupoints possess the characteristics of low electrical resistance. New devices are developing to increase the reliability of electrical skin impedance measurements for counteracting the factors including skin dryness, skin thickness, size of the sensing electrode, pressure applied on the electrode, interelectrode distance, room temperature, and humidity. Morphological studies have identified that blood vessels, hair follicles, and nervous components are enhanced in the meridians/acupoints, which represent areas of potentially high neuronal activity. Recent evidence shows that nitric oxide (NO) concentrations are enhanced in skin acupoints/meridians. L-arginine-derived NO synthesis modifies skin norepinephrine (NE) synthesis/release in acupoints/meridians, and NO-NE activations play an important role in mediating the skin conductance responses to electrical stimulation. NOergic signaling molecules interact with gap junction and transient receptor potential vanilloid type-1. Other studies reported that the high conductance at acupoints is a result of the release of the neuropeptides substance P and calcitonin gene-related peptide during neurogenic inflammation in the referred pain area. Pathological body conditions caused considerable changes in skin conductance or impedance at acupoints. Although systematic research with an improved equipment and research design to avoid the influencing factors are requested for a definite answer in this field, the results from anatomical and biochemical studies consistently show that acupoints exist higher levels of nervous components, and NOergic signaling molecules and neuropeptides involved in the skin low resistance at acupoints. The increased interest in the acupoints/meridians has led to an open-minded attitude towards understanding this system, which is fundamental important to establish the valid aspects of scientific basis of Chinese medicine mechanisms and therapies.

Relationship of the Calcitonin Gene-Related Peptide Monoclonal Antibody Galcanezumab Pharmacokinetics and Capsaicin-Induced Dermal Blood Flow in Healthy Subjects

Galcanezumab, a humanized monoclonal antibody targeting calcitonin gene-related peptide, was recently approved for migraine prophylaxis. The pharmacokinetic/pharmacodynamic (PK/PD) relationship between galcanezumab concentration and inhibition of capsaicin-induced dermal blood flow (CIDBF) was evaluated using first-in-human data following 6 single subcutaneous doses (1 to 600 mg) or multiple (4) 150-mg doses every 2 weeks in 7 cohorts (7 actively treated subjects and 2 placebo-treated healthy subjects). Galcanezumab pharmacokinetics were best described by a 1-compartment model with delayed first-order absorption/linear elimination. Apparent estimates (between-subject variability) of clearance, volume of distribution, absorption rate constant, and lag time were 0.0106 L/h (27%CV), 11.2 L (21%CV), 0.0192 h^-1 (89%CV), and 0.202 hours, respectively. Estimated elimination half-life was about 30 days. An effect compartment link model described the concentration-effect relationship; estimated maximum inhibitory effect was 70.5%, and 50% maximum inhibitory effect concentration (IC₅₀ ) was 1060 ng/mL. Galcanezumab showed dose- and concentration-dependent potent and durable inhibition of CIDBF. Simulated effect compartment concentrations were maintained above IC₅₀ after 12 weeks of dosing. Near-maximal CIDBF inhibition occurred with 150 mg biweekly for 12 weeks lasting ≥24 weeks or with ≥30 mg every 2 weeks or 195 mg every 13 weeks. Quantitative modeling of galcanezumab PK/PD supported dose selection for the phase 2 proof-of-concept study.

Structure-Based Drug Discovery of N-((R)-3-(7-Methyl-1H-indazol-5-yl)-1-oxo-1-(((S)-1-oxo-3-(piperidin-4-yl)-1-(4-(pyridin-4-yl)piperazin-1-yl)propan-2-yl)amino)propan-2-yl)-2'-oxo-1',2'-dihydrospiro[piperidine-4,4'-pyrido[2,3-d][1,3]oxazine]-1-carboxamide (HTL22562): A Calcitonin Gene-Related Peptide Receptor Antagonist for Acute Treatment of Migraine

Structure-based drug design enabled the discovery of 8, HTL22562, a calcitonin gene-related peptide (CGRP) receptor antagonist. The structure of 8 complexed with the CGRP receptor was determined at a 1.6 Å resolution. Compound 8 is a highly potent, selective, metabolically stable, and soluble compound suitable for a range of administration routes that have the potential to provide rapid systemic exposures with resultant high levels of receptor coverage (e.g., subcutaneous). The low lipophilicity coupled with a low anticipated clinically efficacious plasma exposure for migraine also suggests a reduced potential for hepatotoxicity. These properties have led to 8 being selected as a clinical candidate for acute treatment of migraine.

Development of AITC-induced dermal blood flow as a translational in vivo biomarker of TRPA1 activity in human and rodent skin

BACKGROUND AND PURPOSE

Develop a translational assay of Transient Receptor Potential Ankyrin 1 (TRPA1) activity for use as a preclinical and clinical biomarker.

EXPERIMENTAL APPROACH

Allyl isothiocyanate (AITC), capsaicin or citric acid were applied to ears of wildtype and Trpa1-knock out (Trpa1 KO) rats, and changes in dermal blood flow (DBF) were measured by laser speckle contrast imaging. In humans, the DBF, pain and itch responses to 5-20% AITC applied to the forearm were measured and safety was evaluated. Reproducibility of the DBF, pain and itch responses to topically applied 10% and 15% AITC were assessed at two visits separated by 13-15 days. DBF changes were summarized at 5-minute intervals as areas under the curve (AUC) and maxima. Intraclass correlation coefficient (ICC) was calculated to assess arm-arm and period-period reproducibility.

KEY RESULTS

AITC- and citric acid-induced DBF were significantly reduced in Trpa1 KO rats compared to wildtype (90 ± 2% and 65 ± 11% reduction, respectively), whereas capsaicin response did not differ. In humans, each AITC concentration significantly increased DBF compared to vehicle with the maximal increase occurring 5 minutes post application. Ten percent and 15% AITC were selected as safe and effective stimuli. AUC from 0 to 5 minutes was the most reproducible metric of AITC-induced DBF across arms (ICC = 0.92) and periods (ICC = 0.85). Subject-reported pain was more reproducible than itch across visits (ICC = 0.76 vs 0.17, respectively).

CONCLUSION AND IMPLICATIONS

AITC-induced DBF is a suitable target engagement biomarker of TRPA1 activity for preclinical and clinical studies of TRPA1 antagonists.

The role of erenumab in the treatment of migraine

Calcitonin gene related peptide (CGRP) monoclonal antibodies (mAbs) have been the first class of specifically developed preventive treatments for migraine. Clinical trials data suggest superiority of the CGRP mAbs to placebo in terms of prevention of migraine symptoms, migraine-specific quality of life and headache related disability. Treatment-related side effects overall did not differ significantly from placebo and discontinuation rate due to side effects has been low across the clinical trials, perhaps in view of their peripheral mode of action. Along with their route and frequency of administration, these novel class of drugs may constitute an improvement compared with the established arsenal of migraine treatments. Erenumab is a fully human antibody and the only mAb acting on the CGRP pathway by blocking its receptor. It is the first of the CGRP mAb class approved by the US Food and Drug Administration (May 2018) and the European Medicines Agency (July 2018). Erenumab exists in two different doses (70 mg and 140 mg) and it is administered with monthly subcutaneous injections. This review summarises erenumab pharmacological characteristics, clinical trials data, focusing on the potential role of this treatment in clinical practice.

Blocking the CGRP Pathway for Acute and Preventive Treatment of Migraine: The Evolution of Success

The pivotal role of calcitonin gene-related peptide (CGRP) in migraine pathophysiology was identified over 30 years ago, but the successful clinical development of targeted therapies has only recently been realized. This Perspective traces the decades long evolution of medicinal chemistry required to advance small molecule CGRP receptor antagonists, also called gepants, including the current clinical agents rimegepant, vazegepant, ubrogepant, and atogepant. Providing clinically effective blockade of CGRP signaling required surmounting multiple challenging hurdles, including defeating a sizable ligand with subnanomolar affinity for its receptor, designing antagonists with an extended confirmation and multiple pharmacophores while retaining solubility and oral bioavailability, and achieving circulating free plasma levels that provided near maximal CGRP receptor coverage. The clinical efficacy of oral and intranasal gepants and the injectable CGRP monoclonal antibodies (mAbs) are described, as are recent synthetic developments that have benefited from new structural biology data. The first oral gepant was recently approved and heralds a new era in the treatment of migraine.

Cutaneous TRPV1+ Neurons Trigger Protective Innate Type 17 Anticipatory Immunity

Cutaneous TRPV1⁺ neurons directly sense noxious stimuli, inflammatory cytokines, and pathogen-associated molecules and are required for innate immunity against some skin pathogens. Important unanswered questions are whether TRPV1⁺ neuron activation in isolation is sufficient to initiate innate immune responses and what is the biological function for TRPV1⁺ neuron-initiated immune responses. We used TRPV1-Ai32 optogenetic mice and cutaneous light stimulation to activate cutaneous neurons in the absence of tissue damage or pathogen-associated products. We found that TRPV1⁺ neuron activation was sufficient to elicit a local type 17 immune response that augmented host defense to C. albicans and S. aureus. Moreover, local neuron activation elicited type 17 responses and augmented host defense at adjacent, unstimulated skin through a nerve reflex arc. These data show the sufficiency of TRPV1⁺ neuron activation for host defense and demonstrate the existence of functional anticipatory innate immunity at sites adjacent to infection that depends on antidromic neuron activation.

Nonclinical safety evaluation of erenumab, a CGRP receptor inhibitor for the prevention of migraine

Calcitonin gene-related peptide (CGRP) and its receptor have been implicated as a key mediator in the pathophysiology of migraine. Thus, erenumab, a monoclonal antibody antagonist of the CGRP receptor, administered as a once monthly dose of 70 or 140 mg has been approved for the preventive treatment of migraine in adults. Due to the species specificity of erenumab, the cynomolgus monkey was used in the pharmacology, pharmacokinetics, and toxicology studies to support the clinical program. There were no effects of erenumab on platelets in vitro (by binding, activation or phagocytosis assays). Specific staining of human tissues with erenumab did not indicated any off-target binding. There were no erenumab-related findings in a cardiovascular safety pharmacology study in cynomolgus monkeys or in vitro in human isolated coronary arteries. Repeat-dose toxicology studies conducted in cynomolgus monkeys at dose levels up to 225 mg/kg (1 month) or up to 150 mg/kg (up to 6 months) with twice weekly subcutaneous (SC) doses showed no evidence of erenumab-mediated adverse toxicity. There were no effects on pregnancy, embryo-fetal or postnatal growth and development in an enhanced pre-postnatal development study in the cynomolgus monkey. There was evidence of placental transfer of erenumab based on measurable serum concentrations in the infants up to 3 months post birth. The maternal and developmental no-observed-effect level (NOEL) was the highest dose tested (50 mg/kg SC Q2W). These nonclinical data in total indicate no safety signal of concern to date and provide adequate margins of exposure between the observed safe doses in animals and clinical dose levels.

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.

Mechanisms underlying mechanical sensitization induced by complement C5a: the roles of macrophages, TRPV1, and calcitonin gene-related peptide receptors

The complement system significantly contributes to the development of inflammatory and neuropathic pain, but the underlying mechanisms are poorly understood. Recently, we identified the signaling pathway responsible for thermal hypersensitivity induced by the complement system component C5a. Here, we examine the mechanisms of another important action of C5a, induction of mechanical hypersensitivity. We found that intraplantar injection of C5a produced a dose-dependent mechanical sensitization and that this effect was blocked by chemogenetic ablation of macrophages in both male and female mice. Knockout of TRPV1 or pretreatment with the TRPV1 antagonists, AMG9810 or 5'-iodoresiniferatoxin (5'-IRTX), significantly reduced C5a-induced mechanical sensitization. Notably, local administration of 5'-IRTX 90 minutes after C5a injection resulted in a slow, but complete, reversal of mechanical sensitization, indicating that TRPV1 activity was required for maintaining C5a-induced mechanical hypersensitivity. This slow reversal suggests that neurogenic inflammation and neuropeptide release may be involved. Indeed, pretreatment with a calcitonin gene-related peptide (CGRP) receptor antagonist (but not an antagonist of the neurokinin 1 receptor) prevented C5a-induced mechanical sensitization. Furthermore, intraplantar injection of CGRP produced significant mechanical sensitization in both wild-type and TRPV1 knockout mice. Taken together, these findings suggest that C5a produces mechanical sensitization by initiating macrophage-to-sensory-neuron signaling cascade that involves activation of TRPV1 and CGRP receptor as critical steps in this process.

Is calcitonin gene-related peptide a modulator of menopausal vasomotor symptoms?

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed in the central and peripheral nervous systems, which is known as a potent vasodilator. Postmenopausal women who experience hot flushes have high levels of plasma CGRP, suggesting its involvement in menopausal vasomotor symptoms.

METHODS

In this review, we describe the biochemical aspects of CGRP and its effects associated with deficiencies of sexual hormones on skin temperature, vasodilatation, and sweating as well as the possible peripheral and central mechanisms involved in these events.

RESULTS

Several studies have shown that the effects of CGRP on increasing skin temperature and inducing vasodilatation are potentiated by a deficiency of sex hormones, a common condition of postmenopausal women. Additionally, the medial preoptic area of the hypothalamus, involved in thermoregulation, contains over 25-fold more CGRP-immunoreactive cells in female rodents compared with male rodents, reinforcing the role of female sex hormones on the action of CGRP. Some studies suggest that ovarian hormone deficiency decreases circulating endogenous CGRP, inducing an upregulation of CGRP receptors. Consequently, the high CGRP receptor density, especially in blood vessels, amplifies the stimulatory effects of this neuropeptide to raise skin temperature in postmenopausal women during hot flushes.

CONCLUSIONS

The duration of the perception of each hot flush in a woman is brief, while local reddening after intradermal administration of α-CGRP persists for 1 to 6 h. This contrast remains unclear.

Tachykinins modulate nociceptive responsiveness and sensitization: In vivo electrical characterization of primary sensory neurons in tachykinin knockout (Tac1 KO) mice

Since the failure of specific substance P antagonists to induce analgesia, the role of tachykinins in the development of neuropathic pain states has been discounted. This conclusion was reached without studies on the role of tachykinins in normal patterns of primary afferents response and sensitization or the consequences of their absence on the modulation of primary mechanonociceptive afferents after injury. Nociceptive afferents from animals lacking tachykinins (Tac1 knockout) showed a disrupted pattern of activation to tonic suprathreshold mechanical stimulation. These nociceptors failed to encode the duration and magnitude of natural pronociceptive stimuli or to develop mechanical sensitization as consequence of this stimulation. Moreover, paw edema, hypersensitivity, and weight bearing were also reduced in Tac1 knockout mice 24 h after paw incision surgery. At this time, nociceptive afferents from these animals did not show the normal sensitization to mechanical stimulation or altered membrane electrical hyperexcitability as observed in wild-type animals. These changes occurred despite a similar increase in calcitonin gene-related peptide immunoreactivity in sensory neurons in Tac1 knockout and normal mice. Based on these observations, we conclude that tachykinins are critical modulators of primary nociceptive afferents, with a preeminent role in the electrical control of their excitability with sustained activation or injury.

Cyclic changes in sensations to painful stimuli in migraine patients

Introduction

Migraine is characterized by cycling phases (interictal, preictal, ictal and postictal) with differing symptoms, while in chronic tension type headache pain phases are fluctuating. The question we asked is whether these phases are associated with changes in parameters of somatosensation and axon-reflex erythema.

Methods

Patients with episodic migraine and chronic tension type headache were examined psychophysically in the interictal, preictal and ictal phase and healthy subjects on five different test days. Thresholds and suprathreshold ratings of pressure and electrical pain were assessed on three different regions of the head. In migraine patients and in healthy controls, electrically induced axon-reflex erythema was measured in the area of the first trigeminal branch. All migraine patients filled out questionnaires about prodromal symptoms at every visit.

Results

The axon-reflex erythema was always larger in patients with migraine in contrast to healthy subjects. The pressure pain threshold was lower in migraine patients and chronic tension type headache in comparison to healthy subjects. Electrical pain thresholds did not differ between headache patients and healthy subjects and showed no changes between the phases. However, suprathreshold pain ratings showed less habituation solely in the preictal phase of migraine. The number of prodromal symptoms in migraine patients was increased in the preictal and ictal phase.

Discussion

Reduced habituation was the unique sign of the preictal phase in migraine patients, independently of prodromal symptoms, whereas a larger axon-reflex erythema and higher pressure pain sensitivity are constitutional and non-phase dependent properties of migraine. Reduced inhibitory mechanisms in the preictal phase may contribute to trigger headache attacks in migraine.

Pathways of CGRP Release from Primary Sensory Neurons

The benefit reported in a variety of clinical trials by a series of small molecule antagonists for the calcitonin gene-related peptide (CGRP) receptor, or four monoclonal antibodies against the neuropeptide or its receptor, has underscored the release of CGRP from terminals of primary sensory neurons, including trigeminal neurons, as one of the major mechanisms of migraine headaches. A large variety of excitatory ion channels and receptors have been reported to elicit CGRP release, thus proposing these agonists as migraine-provoking agents. On the other side, activators of inhibitory channels and receptors may be regarded as potential antimigraine agents. The knowledge of the intracellular pathways underlying the exocytotic process that results in CGRP secretion or its inhibition is, therefore, of importance for understanding how migraine pain originates and how to treat the disease.

Calcitonin gene-related peptide and pain: a systematic review

BACKGROUND

Calcitonin gene-related peptide (CGRP) is widely distributed in nociceptive pathways in human peripheral and central nervous system and its receptors are also expressed in pain pathways. CGRP is involved in migraine pathophysiology but its role in non-headache pain has not been clarified.

METHODS

We performed a systematic literature search on PubMed, Embase and ClinicalTrials.gov for articles on CGRP and non-headache pain covering human studies including experimental studies and randomized clinical trials.

RESULTS

The literature search identified 375 citations of which 50 contained relevant original data. An association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain was found. In 13 out of 20 studies in somatic pain conditions, CGRP levels had a positive correlation with pain. Increased CGRP levels were reported in plasma, synovial and cerebrospinal fluid in subjects with musculoskeletal pain. A randomized clinical trial on monoclonal antibody, which selectively binds to and inhibits the activity of CGRP (galcanezumab) in patients with osteoarthritis knee pain, failed to demonstrate improvement of pain compared with placebo. No studies to date have investigated the efficacy of monoclonal antibodies against CGRP receptor in non-headache pain conditions.

CONCLUSION

The present review revealed the association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain. These data suggest that CGRP may act as a neuromodulator in non-headache pain conditions. However, more studies are needed to fully understand the role of CGRP in nociceptive processing and therapy of chronic pain.

Gender aspects of CGRP in migraine

Background

Migraine is two to three times more prevalent in women than in men, but the mechanisms involved in this gender disparity are still poorly understood. In this respect, calcitonin gene-related peptide (CGRP) plays a key role in migraine pathophysiology and, more recently, the functional interactions between ovarian steroid hormones, CGRP and the trigeminovascular system have been recognized and studied in more detail.

Aims

To provide an overview of CGRP studies that have addressed gender differences utilizing animal and human migraine preclinical research models to highlight how the female trigeminovascular system responds differently in the presence of varying ovarian steroid hormones.

Conclusions

Gender differences are evident in migraine. Several studies indicate that fluctuations of ovarian steroid hormone (mainly estrogen) levels modulate CGRP in the trigeminovascular system during different reproductive milestones. Such interactions need to be considered when conducting future animal and human experiments, since these differences may contribute to the development of gender-specific therapies.

Phase I, Randomized, Double-blind, Placebo-controlled, Single-dose, and Multiple-dose Studies of Erenumab in Healthy Subjects and Patients With Migraine

Monoclonal antibodies (mAbs) targeting calcitonin gene-related peptide (CGRP) signaling are being explored as prophylactic treatments for migraine. Erenumab (AMG 334) is the first potent, selective, and competitive human mAb antagonist of the CGRP receptor. We report the data from two phase I studies assessing the safety, pharmacokinetics (PK), and pharmacodynamics of single and multiple administrations of erenumab in healthy subjects and patients with migraine. The results indicate that the PK profile of erenumab is nonlinear from 1 mg to 70 mg and the linear portion of the clearance from 70 mg to 210 mg is consistent with other human immunoglobulin G2 antibodies. Single doses of erenumab resulted in >75% inhibition of capsaicin-induced dermal blood flow, with no apparent dose-dependency for erenumab ≥21 mg. Erenumab was generally well tolerated, with an acceptable safety profile, supporting further clinical development of erenumab for migraine prevention.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis.

Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement.

Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF).

Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1–600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.

The relationship between migraine and rosacea: Systematic review and meta-analysis

Objective

To systematically review the association between migraine and rosacea.

Background

Migraine is a complex disorder with episodes of headache, nausea, photo- and phonophobia. Rosacea is an inflammatory skin condition with flushing, erythema, telangiectasia, papules, and pustules. Both are chronic disorders with exacerbations of symptoms almost exclusively in areas innervated by the trigeminal nerve. Previous studies found an association between these disorders. We review these findings, provide a meta-analysis, and discuss possible pathophysiological commonalities.

Methods

A search through PubMed and EMBASE was undertaken for studies investigating the association between all forms of migraine and rosacea published until November 2016, and meta-analysis of eligible studies.

Results

Nine studies on eight populations were identified. Studies differed in methodology and diagnostic process, but all investigated co-occurrence of migraine and rosacea. Four studies were eligible for meta-analysis, resulting in a pooled odds ratio of 1.96 (95% confidence interval 1.41–2.72) for migraine in a rosacea population compared to a non-rosacea population.

Conclusion

Our meta-analysis confirmed an association in occurrence of migraine and rosacea. Future studies should specifically investigate possible shared pathophysiological mechanisms between the two disorders.

The anti-migraine component of butterbur extracts, isopetasin, desensitizes peptidergic nociceptors by acting on TRPA1 cation channel

BACKGROUND AND PURPOSE

The mechanism of the anti-migraine action of extracts of butterbur [Petasites hybridus (L.) Gaertn.] is unknown. Here, we investigated the ability of isopetasin, a major constituent of these extracts, to specifically target TRPA1 channel and to affect functional responses relevant to migraine.

EXPERIMENTAL APPROACH

Single-cell calcium imaging and patch-clamp recordings in human and rodent TRPA1-expressing cells, neurogenic motor responses in rodent isolated urinary bladder, release of CGRP from mouse spinal cord in vitro and facial rubbing in mice and meningeal blood flow in rats were examined.

KEY RESULTS

Isopetasin induced (i) calcium responses and currents in rat/mouse trigeminal ganglion (TG) neurons and in cells expressing the human TRPA1, (ii) substance P-mediated contractions of rat isolated urinary bladders and (iii) CGRP release from mouse dorsal spinal cord, responses that were selectively abolished by genetic deletion or pharmacological antagonism of TRPA1 channels. Pre-exposure to isopetasin produced marked desensitization of allyl isothiocyanate (AITC, TRPA1 channel agonist)- or capsaicin (TRPV1 channel agonist)-evoked currents in rat TG neurons, contractions of rat or mouse bladder and CGRP release from mouse central terminals of primary sensory neurons. Repeated intragastric administration of isopetasin attenuated mouse facial rubbing, evoked by local AITC or capsaicin, and dilation of rat meningeal arteries by acrolein or ethanol (TRPA1 and TRPV1 channel agonists respectively).

CONCLUSION AND IMPLICATIONS

Activation of TRPA1 channels by isopetasin results in excitation of neuropeptide-containing nociceptors, followed by marked heterologous neuronal desensitization. Such atten uation in pain and neurogenic inflammation may account for the anti-migraine action of butterbur.

Pharmacokinetic-Pharmacodynamic Relationship of Erenumab (AMG 334) and Capsaicin-Induced Dermal Blood Flow in Healthy and Migraine Subjects

Purpose

Capsaicin-induced dermal blood flow (CIDBF) is a validated biomarker used to evaluate the target engagement of potential calcitonin gene-related peptide-blocking therapeutics for migraine. To characterize the pharmacokinetics (PK) and quantify the inhibitory effects of erenumab (AMG 334) on CIDBF, CIDBF data were pooled from a single- and a multiple-dose study in healthy and migraine subjects.

Methods

Repeated capsaicin challenges and DBF measurements were performed and serum erenumab concentrations determined. A population analysis was conducted using a nonlinear mixed-effects modeling approach. Effects of body weight, gender, and age on model parameters were evaluated.

Results

Two-compartment target-mediated drug disposition (TMDD) model assuming binding of erenumab in the central compartment best described the nonlinear PK of erenumab. Subcutaneous absorption half-life was 1.6 days and bioavailability was 74%. Erenumab produced a maximum inhibition of 89% (95% confidence interval: 87–91%). Erenumab concentrations required for 50% and 99% of maximum inhibition were 255 ng/mL and 1134 ng/mL, respectively. Increased body weight was associated with increased erenumab clearance but had no effect on the inhibitory effect on CIDBF.

Conclusions

Our results show that erenumab pharmacokinetics was best characterized by a TMDD model and resulted in potent inhibition of CIDBF.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-017-2183-6) contains supplementary material, which is available to authorized users.

The role of calcitonin gene-related peptide in peripheral and central pain mechanisms including migraine

Calcitonin gene-related peptide (CGRP) is a 37-amino acid peptide found primarily in the C and Aδ sensory fibers arising from the dorsal root and trigeminal ganglia, as well as the central nervous system. Calcitonin gene-related peptide was found to play important roles in cardiovascular, digestive, and sensory functions. Although the vasodilatory properties of CGRP are well documented, its somatosensory function regarding modulation of neuronal sensitization and of enhanced pain has received considerable attention recently. Growing evidence indicates that CGRP plays a key role in the development of peripheral sensitization and the associated enhanced pain. Calcitonin gene-related peptide is implicated in the development of neurogenic inflammation and it is upregulated in conditions of inflammatory and neuropathic pain. It is most likely that CGRP facilitates nociceptive transmission and contributes to the development and maintenance of a sensitized, hyperresponsive state not only of the primary afferent sensory neurons but also of the second-order pain transmission neurons within the central nervous system, thus contributing to central sensitization as well. The maintenance of a sensitized neuronal condition is believed to be an important factor underlying migraine. Recent successful clinical studies have shown that blocking the function of CGRP can alleviate migraine. However, the mechanisms through which CGRP may contribute to migraine are still not fully understood. We reviewed the role of CGRP in primary afferents, the dorsal root ganglion, and in the trigeminal system as well as its role in peripheral and central sensitization and its potential contribution to pain processing and to migraine.

A human trigeminovascular biomarker for antimigraine drugs: A randomised, double-blind, placebo-controlled, crossover trial with sumatriptan

Objective

The objective of this report is to establish a biomarker for the CGRP-interfering effect of antimigraine drugs.

Methods

We quantified the effect of sumatriptan on the trigeminal nerve-mediated rise in forehead dermal blood flow (DBF), induced by capsaicin application (0.6 mg/ml) and electrical stimulation (0.2–1.0 mA), in a randomised, double-blind, placebo-controlled, crossover study in healthy male ( n = 11, age ± SD: 29 ± 8 years) and female ( n = 11, 32 ± 7 years) individuals.

Results

DBF responses to capsaicin were attenuated by sumatriptan (ΔDBF, mean ± SEM: 82 ± 18 AU, p = 0.0002), but not by placebo (ΔDBF: 21 ± 12 AU, p = 0.1026).

Conclusion

We demonstrated that sumatriptan inhibits increases in DBF, induced by the release of, most likely, CGRP. Thus, our model may be used as a biomarker to establish the trigeminovascular effects of (potential) antimigraine drugs, such as CGRP receptor antagonists or antibodies directed against CGRP or its receptor.

The influence of migraine and female hormones on capsaicin-induced dermal blood flow

Background Migraine is much more common in females than in males, and occurrence is associated with changes in female sex hormones. Calcitonin gene-related peptide (CGRP) plays a key role in migraine, and variations in female sex hormones may affect CGRP sensitivity and/or production. Objectives Investigate repeatability, gender differences, influence of the menstrual cycle and of migraine on CGRP-dependent changes in dermal blood flow (DBF). Methods CGRP-dependent increases in DBF were assessed using laser Doppler perfusion imaging after topical application of 300 or 1000 µg capsaicin on the forearm of healthy subjects and migraine patients. Results In healthy males, DBF response did not vary over time and was comparable with DBF in male migraineurs. In healthy females, capsaicin-induced DBF responses to both doses of capsaicin were higher during menstruation compared to the late-secretory phase (p < 0.05); this menstrual cycle dependence was absent in female migraine patients. Compared to healthy subjects, female migraineurs displayed a higher DBF response both during menstruation and during the late-secretory phase (p < 0.05). Conclusions An increased capsaicin-induced, CGRP-mediated DBF response was observed during menstruation in healthy women, but in female migraine patients this increased response was not affected by the menstrual cycle.

Role of substance P in the cardiovascular system

This article provides an overview of the structure and function of substance P signalling system and its involvement in the cardiovascular regulation. Substance P is an undecapeptide originating from TAC1 gen and belonging to the tachykinin family. The biological actions of substance P are mainly mediated through neurokinin receptor 1 since substance P is the ligand with the highest affinity to neurokinin receptor 1. Substance P is widely distributed within the central and peripheral nervous systems as well as in the cardiovascular system. Substance P is involved in the regulation of heart frequency, blood pressure and in the stretching of vessels. Substance P plays an important role in ischemia and reperfusion and cardiovascular response to stress. Additionally, it has been also implicated in angiogenesis, pain transmission and inflammation. The substance P/neurokinin receptor 1 receptor system is involved in the molecular bases of many human pathological processes. Antagonists of neurokinin receptor 1 receptor could provide clinical solutions for a variety of diseases. Neurokinin receptor 1 antagonists are already used in the prevention of chemotherapy induced nausea and vomiting.

Characterizing the PK/PD relationship for inhibition of capsaicin-induced dermal vasodilatation by MK-3207, an oral calcitonin gene related peptide receptor antagonist

AIMS

Calcitonin gene related peptide (CGRP) receptor antagonists are effective acute migraine treatments. A capsaicin-induced dermal vasodilatation (CIDV) model has been developed to provide target-engagement information in healthy volunteers. In the model, CGRP release is provoked after dermal capsaicin application, by activating transient receptor potential vanilloid-type-1 (TRPV1) receptors at peripheral sensory nerves. Laser Doppler imaging is used to quantify CIDV and subsequent inhibition by CGRP receptor antagonists. We sought to evaluate a CGRP receptor antagonist, MK-3207, in the biomarker model and to assess the predictability of the CIDV response to migraine clinical efficacy.

METHODS

An integrated population pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the exposure-response relationship for CIDV inhibition by CGRP and TRPV1 receptor antagonists. MK-3207 dose-response predictions were made based on estimated potency from the PK/PD model and mean plasma concentrations observed at the doses investigated.

RESULTS

The results suggested that a 20 mg dose of MK-3207 (EC50 of 1.59 nm) would be required to attain the peripheral CIDV response at a target level that was shown previously to correlate with 2 h clinical efficacy based on phase 3 telcagepant clinical data, and that a plateau of the dose-response would be reached around 40-100 mg. These predictions provided a quantitative rationale for dose selection in a phase 2 clinical trial of MK-3207 and helped with interpretation of the efficacy results from the trial.

CONCLUSIONS

The integrated CIDV PK/PD model provides a useful platform for characterization of PK/PD relationships and predictions of dose-response relationships to aid in future development of CGRP and TRPV1 receptor antagonists.

Development of anti-migraine therapeutics using the capsaicin-induced dermal blood flow model

The efficacy of calcitonin gene-related peptide (receptor) (CGRP-(R)) blocking therapeutics in the treatment of acute migraine headache provided proof-of-concept for the involvement of CGRP in the pathophysiology of this disorder. One of the major hurdles for the development of any class of drugs, including CGRP blocking therapeutics, is the early clinical development process during which toxic and inefficacious compounds need to be eliminated as early as possible in order to focus on the most promising molecules. At this stage, human models providing proof of target engagement, combined with safety and tolerability studies, are extremely valuable in focusing on those therapeutics that have the highest engagement from the lowest exposure. They guide the go/no-go decision making, establish confidence in the candidate molecule by de-risking toxicity and safety issues and thereby speed up the early clinical development. In this review the focus is on the so called 'capsaicin model' as a typical example of a target engagement biomarker used as a human model for the development of CGRP blocking therapeutics. By applying capsaicin onto the skin, TRPV1 channels are activated and a CGRP-mediated increase in dermal blood flow can be quantified with laser Doppler perfusion imaging. Effective CGRP blocking therapeutics in turn, display blockade of this response. The translation of this biomarker model from animals to humans is discussed as well as the limitations of the assay in predicting the efficacy of anti-migraine drugs.

Novel oxazolidinone calcitonin gene-related peptide (CGRP) receptor antagonists for the acute treatment of migraine

In our efforts to develop CGRP receptor antagonists as backups to MK-3207, 2, we employed a scaffold hopping approach to identify a series of novel oxazolidinone-based compounds. The development of a structurally diverse, potent (20, cAMP+HS IC50=0.67 nM), and selective compound (hERG IC50=19 μM) with favorable rodent pharmacokinetics (F=100%, t1/2=7h) is described. Key to this development was identification of a 3-substituted spirotetrahydropyran ring that afforded a substantial gain in potency (10 to 35-fold).

Translational Pharmacodynamics of Calcitonin Gene-Related Peptide Monoclonal Antibody LY2951742 in a Capsaicin-Induced Dermal Blood Flow Model

LY2951742, a monoclonal antibody targeting calcitonin gene-related peptide (CGRP), is being developed for migraine prevention and osteoarthritis pain. To support the clinical development of LY2951742, capsaicin-induced dermal blood flow (DBF) was used as a target engagement biomarker to assess CGRP activity in nonhuman primates and healthy volunteers. Inhibition of capsaicin-induced DBF in nonhuman primates, measured with laser Doppler imaging, was dose dependent and sustained for at least 29 days after a single intravenous injection of the CGRP antibody. This information was used to generate a pharmacokinetic/pharmacodynamic model, which correctly predicted inhibition of capsaicin-induced DBF in humans starting at a single subcutaneous 5-mg dose. As expected, the degree of inhibition in capsaicin-induced DBF increased with higher LY2951742 plasma concentrations. Utilization of this pharmacodynamic biomarker with pharmacokinetic data collected in phase I studies provided the dose-response relationship that assisted in dose selection for the phase II clinical development of LY2951742.

Optimizing Central Nervous System Drug Development Using Molecular Imaging

Advances in multimodality fusion imaging technologies promise to accelerate the understanding of the systems biology of disease and help in the development of new therapeutics. The use of molecular imaging biomarkers has been proven to shorten cycle times for central nervous system (CNS) drug development and thereby increase the efficiency and return on investment from research. Imaging biomarkers can be used to help select the molecules, doses, and patients most likely to test therapeutic hypotheses by stopping those that have little chance of success and accelerating those with potential to achieve beneficial clinical outcomes. CNS imaging biomarkers have the potential to drive new medical care practices for patients in the latent phases of progressive neurodegenerative disorders by enabling the detection, preventative treatment, and tracking of disease in a paradigm shift from today's approaches that have to see the overt symptoms of disease before treating it.

The TRPA1 channel in inflammatory and neuropathic pain and migraine

The transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily of channels, is primarily localized to a subpopulation of primary sensory neurons of the trigeminal, vagal, and dorsal root ganglia. This subset of nociceptors produces and releases the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), which mediate neurogenic inflammatory responses. TRPA1 is activated by a number of exogenous compounds, including molecules of botanical origin, environmental irritants, and medicines. However, the most prominent feature of TRPA1 resides in its unique sensitivity for large series of reactive byproducts of oxidative and nitrative stress. Here, the role of TRPA1 in models of different types of pain, including inflammatory and neuropathic pain and migraine, is summarized. Specific attention is paid to TRPA1 as the main contributing mechanism to the transition of mechanical and cold hypersensitivity from an acute to a chronic condition and as the primary transducing pathway by which oxidative/nitrative stress produces acute nociception, allodynia, and hyperalgesia. A series of migraine triggers or medicines have been reported to modulate TRPA1 activity and the ensuing CGRP release. Thus, TRPA1 antagonists may be beneficial in the treatment of inflammatory and neuropathic pain and migraine.

Migraine associated with gastrointestinal disorders: review of the literature and clinical implications

Recent studies suggest that migraine may be associated with gastrointestinal (GI) disorders, including irritable bowel syndrome (IBS), inflammatory bowel syndrome, and celiac disease. Here, an overview of the associations between migraine and GI disorders is presented, as well as possible mechanistic links and clinical implications. People who regularly experience GI symptoms have a higher prevalence of headaches, with a stronger association with increasing headache frequency. Children with a mother with a history of migraine are more likely to have infantile colic. Children with migraine are more likely to have experienced infantile colic compared to controls. Several studies demonstrated significant associations between migraine and celiac disease, inflammatory bowel disease, and IBS. Possible underlying mechanisms of migraine and GI diseases could be increased gut permeability and inflammation. Therefore, it would be worthwhile to investigate these mechanisms further in migraine patients. These mechanisms also give a rationale to investigate the effects of the use of pre- and probiotics in migraine patients.

Calcitonin gene-related peptide: physiology and pathophysiology

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide. Discovered 30 years ago, it is produced as a consequence of alternative RNA processing of the calcitonin gene. CGRP has two major forms (α and β). It belongs to a group of peptides that all act on an unusual receptor family. These receptors consist of calcitonin receptor-like receptor (CLR) linked to an essential receptor activity modifying protein (RAMP) that is necessary for full functionality. CGRP is a highly potent vasodilator and, partly as a consequence, possesses protective mechanisms that are important for physiological and pathological conditions involving the cardiovascular system and wound healing. CGRP is primarily released from sensory nerves and thus is implicated in pain pathways. The proven ability of CGRP antagonists to alleviate migraine has been of most interest in terms of drug development, and knowledge to date concerning this potential therapeutic area is discussed. Other areas covered, where there is less information known on CGRP, include arthritis, skin conditions, diabetes, and obesity. It is concluded that CGRP is an important peptide in mammalian biology, but it is too early at present to know if new medicines for disease treatment will emerge from our knowledge concerning this molecule.

Development of a novel antibody to calcitonin gene-related peptide for the treatment of osteoarthritis-related pain

OBJECTIVE

Investigate a role for calcitonin gene-related peptide (CGRP) in osteoarthritis (OA)-related pain.

DESIGN

Neutralizing antibodies to CGRP were generated de novo. One of these antibodies, LY2951742, was characterized in vitro and tested in pre-clinical in vivo models of OA pain.

RESULTS

LY2951742 exhibited high affinity to both human and rat CGRP (KD of 31 and 246 pM, respectively). The antibody neutralized CGRP-mediated induction of cAMP in SK-N-MC cells in vitro and capsaicin-induced dermal blood flow in the rat. Neutralization of CGRP significantly reduced pain behavior as measured by weight bearing differential in the rat monoiodoacetate model of OA pain in a dose-dependent manner. Moreover, pain reduction with neutralization of CGRP occurred independently of prostaglandins, since LY2951742 and NSAIDs worked additively in the NSAID-responsive version of the model and CGRP neutralization remained effective in the NSAID non-responsive version of the model. Neutralization of CGRP also provided dose-dependent and prolonged (>60 days) pain reduction in the rat meniscal tear model of OA after only a single injection of LY2951742.

CONCLUSIONS

LY2951742 is a high affinity, neutralizing antibody to CGRP. Neutralization of CGRP is efficacious in several OA pain models and works independently of NSAID mechanisms of action. LY2951742 holds promise for the treatment of pain in OA patients.

Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease

The tachykinins, exemplified by substance P, are one of the most intensively studied neuropeptide families. They comprise a series of structurally related peptides that derive from alternate processing of three Tac genes and are expressed throughout the nervous and immune systems. Tachykinins interact with three neurokinin G protein-coupled receptors. The signaling, trafficking, and regulation of neurokinin receptors have also been topics of intense study. Tachykinins participate in important physiological processes in the nervous, immune, gastrointestinal, respiratory, urogenital, and dermal systems, including inflammation, nociception, smooth muscle contractility, epithelial secretion, and proliferation. They contribute to multiple diseases processes, including acute and chronic inflammation and pain, fibrosis, affective and addictive disorders, functional disorders of the intestine and urinary bladder, infection, and cancer. Neurokinin receptor antagonists are selective, potent, and show efficacy in models of disease. In clinical trials there is a singular success: neurokinin 1 receptor antagonists to treat nausea and vomiting. New information about the involvement of tachykinins in infection, fibrosis, and pruritus justifies further trials. A deeper understanding of disease mechanisms is required for the development of more predictive experimental models, and for the design and interpretation of clinical trials. Knowledge of neurokinin receptor structure, and the development of targeting strategies to disrupt disease-relevant subcellular signaling of neurokinin receptors, may refine the next generation of neurokinin receptor antagonists.

Development of an experimental model to study trigeminal nerve-mediated vasodilation on the human forehead

BACKGROUND

During migraine, trigeminal sensory nerve terminals release calcitonin gene-related peptide (CGRP), inducing nociception and vasodilation. Applied on the skin, capsaicin activates the transient receptor potential vanilloid type 1 (TRPV1) channel and releases CGRP from sensory nerve terminals, thus increasing dermal blood flow (DBF). Using capsaicin application and electrical stimulation of the forehead skin, a trigeminal nerve-innervated dermatome, we aimed to develop a model to measure trigeminal nerve-mediated vasodilation in humans.

METHODS

Using laser Doppler imaging, forehead DBF responses to application of capsaicin (0.06 mg/ml and 6.0 mg/ml) and saline, with and without iontophoresis, were studied in healthy subjects. The within-subject coefficient of variation (WCV) of repeated DBF measurements was calculated to assess reproducibility.

RESULTS

Maximal DBF responses to 6.0 mg/ml capsaicin with and without iontophoresis did not differ (Emax 459 ± 32 and 424 ± 32 arbitrary units (a.u.), WCV 6 ± 4%). In contrast, DBF responses to 0.06 mg/ml capsaicin were significantly larger with than without iontophoresis (Emax 307 ± 60 versus 187 ± 21 a.u., WCV 21 ± 13%). Saline with iontophoresis significantly increased DBF (Emax: 245 ± 26 a.u, WCV 11 ± 8%), while saline application without iontophoresis did not affect DBF.

CONCLUSION

Topical application of capsaicin and electrical stimulation induce reproducible forehead DBF increases and therefore are suitable to study trigeminal nerve-mediated vasodilation in humans.

Effect of telcagepant on spontaneous ischemia in cardiovascular patients in a randomized study

OBJECTIVE

The primary purpose of the study was to explore the safety and tolerability of telcagepant in patients with stable coronary artery disease.

BACKGROUND

Triptans are effective acute anti-migraine drugs whose vasoconstrictive effects limit their use in patients at risk for adverse cardiovascular events. Telcagepant, a calcitonin gene-related peptide receptor antagonist, is being developed for the acute treatment of migraine. Antagonism of calcitonin gene-related peptide, which does not appear to cause vasoconstriction, may allow for treatment of migraine in patients with coronary artery disease.

METHODS

In this randomized, double-blind, placebo-controlled, crossover study, patients with documented stable coronary artery disease were assigned to 1 of 2 treatment sequences: telcagepant then placebo, or placebo then telcagepant. In each treatment period, patients received 2 doses of telcagepant 300-mg or placebo 2 hours apart. They remained in the research center for 24 hours after receiving the first dose of each period, during which time continuous 12-lead ambulatory electrocardiographic (Holter) monitoring was performed.

RESULTS

Twenty-eight patients were enrolled; all patients completed the study and were included in all analyses. Telcagepant was generally well tolerated. No laboratory or serious adverse experiences were reported, and no patient discontinued due to an adverse experience. There were no consistent treatment-related changes in laboratory, vital signs or electrocardiogram safety parameters. Three patients (2 after receiving placebo and 1 after receiving telcagepant) experienced ST segment depression during the study; none of these patients reported chest pain.

CONCLUSIONS

Two doses of 300-mg telcagepant, administered 2 hours apart, did not appear to exacerbate spontaneous ischemia and were generally well tolerated in a small cohort of patients with stable coronary artery disease. Results of this study support further evaluation of telcagepant in patients with stable coronary artery disease.