Effects of parecoxib on plasma protein extravasation and c-fos expression in the rat

Celecoxib in the treatment of orofacial pain and discomfort in rats subjected to a dental occlusal interference model

Purpose:

To evaluate the effect of a selective cyclooxygenase 2 (COX-2) inhibitor on trigeminal ganglion changes and orofacial discomfort/nociception in rats submitted to an experimental model of dental occlusal interference (DOI).

Methods:

Female Wistar rats (180-200 g) were divided into five groups: a sham group (without DOI) (n=15); and four experimental groups with DOI treated daily with 0.1 mL/kg saline (DOI+SAL), 8, 16, or 32 mg/kg celecoxib (DOI+cel -8, -16, -32) (n=30/group). The animals were euthanized after one, three, and seven days. The bilateral trigeminal ganglia were analyzed histomorphometrically (neuron cell body area) and immunohistochemically (COX-2, nuclear factor-kappa B [NFkB], and peroxisome proliferator-activated receptor-y [PPARy]). A bilateral nociception assay of the masseter muscle was performed. The number of bites/scratches, weight, and grimace scale scores were determined daily. One-way/two-way analysis of variance (ANOVA)/Bonferroni post hoc tests were used (P < .05, GraphPad Prism 5.0).

Results:

DOI+SAL showed a reduction in neuron cell body area bilaterally, whereas DOI+cel-32 exhibited a significative increase in neuron cell body area compared with DOI+SAL group (P < 0.05). The ipsilateral (P=0.007 and P=0.039) and contralateral (P < 0.001 and P=0.005) overexpression of COX-2 and NFkB and downregulation of PPARy (P=0.016 and P < 0.001) occurred in DOI+SAL, but DOI+cel-32 reverted this alteration. DOI+SAL showed increase in isplateral (P < 0.001) and contralateral (P < 0.001) nociception, an increased number of bites (P=0.010), scratches (P < 0.001), and grimace scores (P=0.032). In the group of DOI+cel-32, these parameters were reduced.

Conclusions:

Celecoxib attenuated DOI-induced transitory nociception/orofacial discomfort resulting from trigeminal COX-2 overexpression.

Celecoxib reduces cortical spreading depression-induced macrophage activation and dilatation of dural but not pial arteries in rodents: implications for mechanism of action in terminating migraine attacks

Nonsteroidal anti-inflammatory drugs, commonly known as COX-1/COX-2 inhibitors, can be effective in treating mild to moderate migraine headache. However, neither the mechanism by which these drugs act in migraine is known, nor is the specific contribution of COX-1 vs COX-2. We sought to investigate these unknowns using celecoxib, which selectively inhibits the enzymatic activity of COX-2, by determining its effects on several migraine-associated vascular and inflammatory events. Using in vivo 2-photon microscopy, we determined intraperitoneal celecoxib effects on cortical spreading depression (CSD)-induced blood vessel responses, plasma protein extravasation, and immune cell activation in the dura and pia of mice and rats. Compared to vehicle (control group), celecoxib reduced CSD-induced dilatation of dural arteries and activation of dural and pial macrophages significantly, but not dilatation or constriction of pial arteries and veins, or the occurrence of plasma protein extravasation. Collectively, these findings suggest that a mechanism by which celecoxib-mediated COX-2 inhibition might ease the intensity of migraine headache and potentially terminate an attack is by attenuating dural macrophages' activation and arterial dilatation outside the blood-brain barrier, and pial macrophages' activation inside the blood-brain barrier.

Inhibitory effect of high-frequency greater occipital nerve electrical stimulation on trigeminovascular nociceptive processing in rats

Electrical stimulation of the greater occipital nerve (GON) has recently shown promise as an effective non-pharmacological prophylactic therapy for drug-resistant chronic primary headaches, but the neurobiological mechanisms underlying its anticephalgic action are not elucidated. Considering that the spinal trigeminal nucleus (STN) is a key segmental structure playing a prominent role in pathophysiology of headaches, in the present study we evaluated the effects of GON electrical stimulation on ongoing and evoked firing of the dura-sensitive STN neurons. The experiments were carried out on urethane/chloralose-anesthetized, paralyzed and artificially ventilated male Wistar rats. Extracellular recordings were made from 11 neurons within the caudal part of the STN that received convergent input from the ipsilateral facial cutaneous receptive fields, dura mater and GON. In each experiment, five various combinations of the GON stimulation frequency (50, 75, 100 Hz) and intensity (1, 3, 6 V) were tested successively in 10 min interval. At all parameter sets, preconditioning GON stimulation (250 ms train of pulses applied before each recording) produced suppression of both the ongoing activity of the STN neurons and their responses to electrical stimulation of the dura mater. The inhibitory effect depended mostly on the GON stimulation intensity, being maximally pronounced when a stimulus of 6 V was applied. Thus, the GON stimulation-induced inhibition of trigeminovascular nociceptive processing at the level of STN has been demonstrated for the first time. The data obtained can contribute to a deeper understanding of neurophysiological mechanisms underlying the therapeutic efficacy of GON stimulation in primary headaches.

Understanding migraine: Potential role of neurogenic inflammation

Neurogenic inflammation, a well-defined pathophysiologial process is characterized by the release of potent vasoactive neuropeptides, predominantly calcitonin gene-related peptide (CGRP), substance P (SP), and neurokinin A from activated peripheral nociceptive sensory nerve terminals (usually C and A delta-fibers). These peptides lead to a cascade of inflammatory tissue responses including arteriolar vasodilation, plasma protein extravasation, and degranulation of mast cells in their peripheral target tissue. Neurogenic inflammatory processes have long been implicated as a possible mechanism involved in the pathophysiology of various human diseases of the nervous system, respiratory system, gastrointestinal tract, urogenital tract, and skin. The recent development of several innovative experimental migraine models has provided evidence suggestive of the involvement of neuropeptides (SP, neurokinin A, and CGRP) in migraine headache. Antidromic stimulation of nociceptive fibers of the trigeminal nerve resulted in a neurogenic inflammatory response with marked increase in plasma protein extravasation from dural blood vessels by the release of various sensory neuropeptides. Several clinically effective abortive antimigraine medications, such as ergots and triptans, have been shown to attenuate the release of neuropeptide and neurogenic plasma protein extravasation. These findings provide support for the validity of using animal models to investigate mechanisms of neurogenic inflammation in migraine. These also further strengthen the notion of migraine being a neuroinflammatory disease. In the clinical context, there is a paucity of knowledge and awareness among physicians regarding the role of neurogenic inflammation in migraine. Improved understanding of the molecular biology, pharmacology, and pathophysiology of neurogenic inflammation may provide the practitioner the context-specific feedback to identify the novel and most effective therapeutic approach to treatment. With this objective, the present review summarizes the evidence supporting the involvement of neurogenic inflammation and neuropeptides in the pathophysiology and pharmacology of migraine headache as well as its potential significance in better tailoring therapeutic interventions in migraine or other neurological disorders. In addition, we have briefly highlighted the pathophysiological role of neurogenic inflammation in various other neurological disorders.

Inhibition of cyclooxygenase-2 prevents intra-abdominal adhesions by decreasing activity of peritoneal fibroblasts

BACKGROUND

Postoperative intra-abdominal adhesions are common complications after abdominal surgery. The exact molecular mechanisms that are responsible for these complications remain unclear, and there are no effective methods for preventing adhesion formation or reformation. The aim of the study reported here was to investigate the preventive effects and underlying potential molecular mechanisms of selective cyclooxygenase-2 (COX-2) inhibitors in a rodent model of postoperative intra-abdominal adhesions.

MATERIALS AND METHODS

The expression of COX-2 in postoperative intra-abdominal adhesions and normal peritoneal tissue was examined by immunohistochemistry and Western blot analysis. Assays were performed to elucidate the effect of COX-2 inhibition on hypoxia-induced fibroblast activity in vitro and on intra-abdominal adhesion formation in vivo.

RESULTS

Hypoxia-induced COX-2 expression in peritoneal fibroblasts was increased in postoperative intra-abdominal adhesions. Inhibition of COX-2 attenuated the activating effect of hypoxia on normal peritoneal fibroblasts in vitro. Data indicate that selective COX-2 inhibitor prevents in vivo intra-abdominal adhesion by inhibition of basic fibroblast growth factor and transforming growth factor-beta expression, but not through an antiangiogenic mechanism. Furthermore, using selective COX-2 inhibitors to prevent intra-abdominal adhesions did not adversely affect the weight, bowel motility, or healing of intestinal anastomoses in a rat model.

CONCLUSION

These results show that hypoxia-induced COX-2 expression in peritoneal fibroblasts is involved in the formation of intra-abdominal adhesions. Inhibition of COX-2 prevents postoperative intra-abdominal adhesions through suppression of inflammatory cytokines.

Intravenous dextromethorphan/quinidine inhibits activity of dura-sensitive spinal trigeminal neurons in rats

BACKGROUND

Migraine is a chronic neurological disorder characterized by episodes of throbbing headaches. Practically all medications currently used in migraine prophylaxis have a number of substantial disadvantages and use limitations. Therefore, the further search for principally new prophylactic antimigraine agents remains an important task. The objective of our study was to evaluate the effects of a fixed combination of dextromethorphan hydrobromide and quinidine sulphate (DM/Q) on activity of the spinal trigeminal neurons in an electrophysiological model of trigemino-durovascular nociception.

METHODS

The study was performed in 15 male Wistar rats, which were anaesthetized with urethane/α-chloralose and paralysed using pipecuronium bromide. The effects of cumulative intravenous infusions of DM/Q (three steps performed 30 min apart, 15/7.5 mg/kg of DM/Q in 0.5 mL of isotonic saline per step) on ongoing and dural electrical stimulation-induced neuronal activities were tested in a group of eight rats over 90 min. Other seven animals received cumulative infusion of equal volumes of saline and served as control.

RESULTS

Cumulative administration of DM/Q produced steady suppression of both the ongoing activity of the spinal trigeminal neurons and their responses to electrical stimulation of the dura mater.

CONCLUSIONS

It is evident that the observed DM/Q-induced suppression of trigeminal neuron excitability can lead to a reduction in nociceptive transmission from meninges to higher centres of the brain. Since the same mechanism is believed to underlie the pharmacodynamics of many well-known antimigraine drugs, results of the present study enable us to anticipate the potential efficacy of DM/Q in migraine.

Sumatriptan inhibits TRPV1 channels in trigeminal neurons

OBJECTIVE

To understand a possible role for transient potential receptor vanilloid 1 (TRPV1) ion channels in sumatriptan relief of pain mediated by trigeminal nociceptors.

BACKGROUND

TRPV1 channels are expressed in small nociceptive sensory neurons. In dorsal root ganglia, TRPV1-containing nociceptors mediate certain types of inflammatory pain. Neurogenic inflammation of cerebral dura and blood vessels in the trigeminal nociceptive system is thought to be important in migraine pain, but the ion channels important in transducing migraine pain are not known. Sumatriptan is an agent effective in treatment of migraine and cluster headache. We hypothesized that sumatriptan might modulate activity of TRPV1 channels found in the trigeminal nociceptive system.

METHODS

We used immunohistochemistry to detect the presence of TRPV1 channel protein, whole-cell recording in acutely dissociated trigeminal ganglia (TG) to detect functionality of TRPV1 channels, and whole-cell recording in trigeminal nucleus caudalis (TNC) to detect effects on release of neurotransmitters from trigeminal neurons onto second order sensory neurons. Effects specifically on TG neurons that project to cerebral dura were assessed by labeling dural nociceptors with DiI.

RESULTS

Immunohistochemistry demonstrated that TRPV1 channels are present in cerebral dura, in trigeminal ganglion, and in the TNC. Capsaicin, a TRPV1 agonist, produced depolarization and repetitive action potential firing in current clamp recordings, and large inward currents in voltage clamp recordings from acutely dissociated TG neurons, demonstrating that TRPV1 channels are functional in trigeminal neurons. Capsaicin increased spontaneous excitatory postsynaptic currents in neurons of layer II in TNC slices, showing that these channels have a physiological effect on central synaptic transmission. Sumatriptan (10 µM), a selective antimigraine drug, inhibited TRPV1-mediated inward currents in TG and capsaicin-elicited spontaneous excitatory postsynaptic currents in TNC slices. The same effects of capsaicin and sumatriptan were found in acutely dissociated DiI-labeled TG neurons innervating cerebral dura.

CONCLUSION

Our results build on previous work indicating that TRPV1 channels in trigeminal nociceptors play a role in craniofacial pain. Our findings that TRPV1 is inhibited by the specific antimigraine drug sumatriptan, and that TRPV1 channels are functional in neurons projecting to cerebral dura suggests a specific role for these channels in migraine or cluster headache.

Efficacy of parecoxib, sumatriptan, and rizatriptan in the treatment of acute migraine attacks

Triptans and analgetic nonsteroidal inflammatory drugs reduce acute pain syndromes in migraine. A further treatment option for an acute headache attack in patients with migraine may be the application of cyclooxygenase-2-specific inhibitors, as they have anti-inflammatory and analgesic properties. The objective of this pilot study was to investigate the effects of an oral fast-dissolving tablet of 10 mg of rizatriptan, an intravenous infusion of 40 mg of parecoxib, and a subcutaneous pen injection of sumatriptan (6 mg/0.5 mL) on pain relief in 3 cohorts of patients with episodic migraine. They were treated owing to the acute onset of a pain attack as a case of emergency. They were randomized to treatment with sumatriptan, rizatriptan, or parecoxib. The participants completed a visual analog scale for pain intensity at baseline before the drug administration and then after intervals of 20, 30, 60, and 120 minutes. Rizatriptan, parecoxib, and sumatriptan reduced pain symptoms. Twenty and 30 minutes after drug intake, rizatriptan was more efficacious than parecoxib and sumatriptan, and parecoxib was more effective than sumatriptan. Only a significant difference between rizatriptan and sumatriptan was found after 60 and 120 minutes. This trial demonstrates the effectiveness of a parecoxib infusion in the treatment of acute migraine and that the circumvention of the first pass effect of the liver by rizatriptan may be beneficial for fast pain relief.

NSAIDs in the Acute Treatment of Migraine: A Review of Clinical and Experimental Data

Migraine is a common disabling neurological disorder with a serious socio-economical burden. By blocking cyclooxygenase nonsteroidal anti-inflammatory drugs (NSAIDs) decrease the synthesis of prostaglandins, which are involved in the pathophysiology of migraine headaches. Despite the introduction more than a decade ago of a new class of migraine-specific drugs with superior efficacy, the triptans, NSAIDs remain the most commonly used therapies for the migraine attack. This is in part due to their wide availability as over-the-counter drugs and their pharmaco-economic advantages, but also to a favorable efficacy/side effect profile at least in attacks of mild and moderate intensity. We summarize here both the experimental data showing that NSAIDs are able to influence several pathophysiological facets of the migraine headache and the clinical studies providing evidence for the therapeutic efficacy of various subclasses of NSAIDs in migraine therapy. Taken together these data indicate that there are several targets for NSAIDs in migraine pathophysiology and that on the spectrum of clinical potency acetaminophen is at the lower end while ibuprofen is among the most effective drugs. Acetaminophen and aspirin excluded, comparative trials between the other NSAIDs are missing. Since evidence-based criteria are scarce, the selection of an NSAID should take into account proof and degree of efficacy, rapid GI absorption, gastric ulcer risk and previous experience of each individual patient. If selected and prescribed wisely, NSAIDs are precious, safe and cost-efficient drugs for the treatment of migraine attacks.

Animal models of headache: from bedside to bench and back to bedside

In recent years bench-based studies have greatly enhanced our understanding of headache pathophysiology, while facilitating the development of new headache medicines. At present, established animal models of headache utilize activation of pain-producing cranial structures, which for a complex syndrome, such as migraine, leaves many dimensions of the syndrome unstudied. The focus on modeling the central nociceptive mechanisms and the complexity of sensory phenomena that accompany migraine may offer new approaches for the development of new therapeutics. Given the complexity of the primary headaches, multiple approaches and techniques need to be employed. As an example, recently a model for trigeminal autonomic cephalalgias has been tested successfully, while by contrast, a satisfactory model of tension-type headache has been elusive. Moreover, although useful in many regards, migraine models are yet to provide a more complete picture of the disorder.

Differential Effects of Corticosteroids on The Expression of Cyclooxygenase-2, Tumour Necrosis Factor-Alpha and Matrix Metalloproteinase-9 in An Animal Model of Migraine

Nitric oxide (NO) directly activates trigeminal afferents innervating the dura mater and up-regulates inflammatory mediators. We evaluated NO-mediated up-regulation of cyclooxygenase-2 (COX-2), tumour necrosis factor-alpha (TNF-α) and matrix metalloproteinase-9 (MMP-9), and the effect of glucocorticoid administration in an experimental animal model of migraine. COX-2 and TNF-α expression and MMP-9 activity were increased after continuous intravenous infusion of glyceryl trinitrate (GTN), a NO donor. Immunofluorescence staining demonstrated strong expression of these inflammatory mediators in the meningeal blood vessels. Methylprednisolone (MP) down-regulated MMP-9, which was reversed by RU486, a glucocorticoid receptor antagonist. COX-2 and TNF-α expression was not affected by MP or RU486 administration. These results suggest proinflammatory mediators are involved in the NO-mediated cascade of migraine pathogenesis. Further understanding of the activation of these inflammatory mediators at the transcriptional level may have therapeutic implications for future migraine treatments.

Animal models of migraine headache and aura

PURPOSE OF REVIEW

Over the past 30 years, animal models of migraine have led to the identification of novel drug targets and drug treatments as well as helped to clarify a mechanism for abortive and prophylactic drugs. Animal models have also provided translational knowledge and a framework to think about the impact of hormones, genes, and environmental factors on migraine pathophysiology. Although most acknowledge that these animal models have significant shortcomings, promising new drugs are now being developed and brought to the clinic using these preclinical models. Hence, it is timely to provide a short overview examining the ways in which animal models inform us about underlying migraine mechanisms.

RECENT FINDINGS

First generation migraine models mainly focused on events within pain-generating intracranial tissues, for example, the dura mater and large vessels, as well as their downstream consequences within brain. Upstream events such as cortical spreading depression have also been modeled recently and provide insight into mechanisms of migraine prophylaxis. Mouse mutants expressing human migraine mutations have been genetically engineered to provide an understanding of familial hemiplegic migraine and possibly, by extrapolation, may reflect on the pathophysiology of more common migraine subtypes.

SUMMARY

Animal models of migraine reflect distinct facets of this clinically heterogeneous disorder and contribute to a better understanding of its pathophysiology and pharmacology.