mk-8825 and Disease-Models--Animal

The pain-signaling molecules, nitric oxide synthase (NOS) and calcitonin gene-related peptide (CGRP), are implicated in the pathophysiology of post-traumatic headache (PTH) as they are for migraine. This study assessed the changes of inducible NOS (iNOS) and its cellular source in the trigeminal pain circuit, as well as the relationship between iNOS and CGRP after controlled cortical impact (CCI) injury in mice. The effects of a CGRP antagonist (MK8825) and sumatriptan on iNOS messenger RNA (mRNA) and protein were compared to vehicle at 2 weeks postinjury. Changes in CGRP levels in the trigeminal nucleus caudalis (TNC) in iNOS knockouts with CCI were compared to wild-type (WT) mice at 3 days and 2 weeks post injury. Trigeminal allodynia and photosensitivity were measured. MK8825 and sumatriptan increased allodynic thresholds in CCI groups compared to vehicle (p < 0.01), whereas iNOS knockouts were not different from WT. Photosensitivity was attenuated in MK8825 mice and iNOS knockouts compared to WT (p < 0.05). MK8825 and sumatriptan reduced levels of iNOS mRNA and iNOS immunoreactivity in the TNC and ganglia (p < 0.01). Differences in iNOS cellular localization were found between the trigeminal ganglia and TNC. Although the knockout of iNOS attenuated CGRP at 3 days (p < 0.05), it did not reduce CGRP at 2 weeks. CGRP immunoreactivity was found in the meningeal layers post-CCI, while negligible in controls. Findings support the importance of interactions between CGRP and iNOS in mediating allodynia, as well as the individual roles in photosensitivity. Mitigating prolonged increases in CGRP may be a promising intervention for treating acute PTH.

Topics: Animals; Brain Injuries, Traumatic; Calcitonin Gene-Related Peptide; Disease Models, Animal; Hyperalgesia; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nitric Oxide Synthase Type II; Photic Stimulation; Photosensitivity Disorders; Pyridines; Random Allocation; Spiro Compounds; Sumatriptan; Trigeminal Nerve

Temporomandibular disorders (TMDs) are orofacial pains within the trigeminal distribution, which involve the masticatory musculature, the temporomandibular joint or both. Their pathophysiology remains unclear, as inflammatory mediators are thought to be involved, and clinically TMD presents pain and sometimes limitation of function, but often appears without gross indications of local inflammation, such as visible edema, redness and increase in temperature. Calcitonin gene-related peptide (CGRP) has been implicated in other pain disorders with trigeminal distribution, such as migraine, of which TMD shares a significant co-morbidity. CGRP causes activation and sensitization of trigeminal primary afferent neurons, independent of any inflammatory mechanisms, and thus may also be involved in TMD. Here we used a small molecule, selective CGRP receptor antagonist, MK-8825, to dissect the role of CGRP in inducing spontaneous nociceptive facial grooming behaviors, neuronal activation in the trigeminal nucleus, and systemic release of pro-inflammatory cytokines, in a mouse model of acute orofacial masseteric muscle pain that we have developed, as a surrogate of acute TMD. We show that CFA masseteric injection causes significant spontaneous orofacial pain behaviors, neuronal activation in the trigeminal nucleus, and release of interleukin-6 (IL-6). In mice pre-treated with MK-8825 there is a significant reduction in these spontaneous orofacial pain behaviors. Also, at 2 and 24h after CFA injection the level of Fos immunoreactivity in the trigeminal nucleus, used as a marker of neuronal activation, was much lower on both ipsilateral and contralateral sides after pre-treatment with MK-8825. There was no effect of MK-8825 on the release of IL-6. These data suggest that CGRP may be involved in TMD pathophysiology, but not via inflammatory mechanisms, at least in the acute stage. Furthermore, CGRP receptor antagonists may have therapeutic efficacy in the treatment of TMD, as they do with migraine.

Topics: Analysis of Variance; Animals; Calcitonin Gene-Related Peptide Receptor Antagonists; Cytokines; Disease Models, Animal; Facial Pain; Female; Freund's Adjuvant; Functional Laterality; In Vitro Techniques; Masseter Muscle; Mice; Mice, Inbred C57BL; Oncogene Proteins v-fos; Pain Measurement; Pyridines; Receptors, Calcitonin Gene-Related Peptide; Spiro Compounds; Time Factors; Trigeminal Ganglion

The release of calcitonin gene-related peptide (CGRP) from trigeminal nerves plays a central role in the pathophysiology of migraine and clinical evidence shows an antimigraine effect for CGRP receptor antagonists. Systemic administration of nitroglycerin (NTG), a nitrovasodilator, consistently provokes spontaneous-like migraine attacks in migraine sufferers; in the rat, systemic NTG induces a condition of hyperalgesia, probably through the activation of cerebral/spinal structures involved in nociceptive transmission.. The aim of this article is to test the analgesic effect of the CGRP receptor antagonist MK-8825 in two animal models of pain that may be relevant for migraine: the tail flick test and the formalin test performed during NTG-induced hyperalgesia.. MK-8825 showed analgesic activity when administered alone at both the tail flick test and the formalin test. Furthermore, the CGRP antagonist proved effective in counteracting NTG-induced hyperalgesia in both tests. MK-8825 indeed reduced the nociceptive behavior when administered either simultaneously or prior to (30-60 minutes before) NTG.. These data suggest that MK-8825 may represent a potential therapeutic tool for the treatment of migraine.

Topics: Animals; Calcitonin Gene-Related Peptide Receptor Antagonists; Disease Models, Animal; Hyperalgesia; Male; Migraine Disorders; Nitroglycerin; Nociceptors; Pain Threshold; Pyridines; Rats; Rats, Sprague-Dawley; Reaction Time; Spiro Compounds

Rational modification of the clinically tested CGRP receptor antagonist MK-3207 (3) afforded an analogue with increased unbound fraction in rat plasma and enhanced aqueous solubility, 2-[(8R)-8-(3,5-difluorophenyl)-8-methyl-10-oxo-6,9-diazaspiro[4.5]dec-9-yl]-N-[(6S)-2'-oxo-1',2',5,7-tetrahydrospiro[cyclopenta[b]pyridine-6,3'-pyrrolo[2,3-b]pyridin]-3-yl]acetamide (MK-8825) (6). Compound 6 maintained similar affinity to 3 at the human and rat CGRP receptors but possessed significantly improved in vivo potency in a rat pharmacodynamic model. The overall profile of 6 indicates it should find utility as a rat tool to investigate effects of CGRP receptor blockade in vivo.

Topics: Administration, Oral; Analgesics; Animals; Biological Availability; Calcitonin Gene-Related Peptide Receptor Antagonists; Disease Models, Animal; Dogs; Humans; Macaca mulatta; Mice; Migraine Disorders; Pyridines; Rats; Receptors, Calcitonin Gene-Related Peptide; Species Specificity; Spiro Compounds