Age-Related decrease in calcitonin gene-related peptide mRNA in the dorsal root ganglia of spontaneously hypertensive rats

Evaluation of Plasma Calcitonin Gene-Related Peptide as a Biomarker for Painful Temporomandibular Disorder and Migraine

Objective

To assess associations of plasma calcitonin gene-related peptide (CGRP) with chronic temporomandibular disorder (TMD) myalgia/arthralgia or frequent/chronic migraine, alone and in combination, and to evaluate relations between the CGRP concentration and clinical, psychological, and somatosensory characteristics of participants.

Methods

The cross-sectional study selected four groups of adult volunteers: healthy controls (HCs), TMD without migraine, migraine without TMD, and TMD with migraine. Each group comprised 20 participants, providing 94% power to detect statistically significant associations with CGRP concentration for either TMD or migraine. TMD and headache were classified according to the Diagnostic Criteria for TMD and the International Classification for Headache Disorders, 3rd edition, respectively. Plasma CGRP was quantified with a validated high-sensitivity electrochemiluminescent Meso Scale Discovery assay. Questionnaires and clinical examinations were used to evaluate characteristics of TMD, headache, psychological distress, and pressure pain sensitivity. Univariate regression models quantified associations of the CGRP concentration with TMD, migraine, and their interaction. Univariate associations of the CGRP concentration with clinical, psychological, and pressure pain characteristics were also assessed.

Results

Among 80 participants enrolled, neither TMD nor migraine was associated with plasma CGRP concentration (P = 0.761 and P = 0.972, respectively). The CGRP concentration (mean ± SD) was similar in all 4 groups: HCs 2.0 ± 0.7 pg/mL, TMD 2.1 ± 0.8 pg/mL, migraine 2.1 ± 0.9 pg/mL, and TMD with migraine 2.2 ± 0.7 pg/mL. CGRP concentration was positively associated with age (P = 0.034) and marginally with body mass index (P = 0.080) but was unrelated to other participant characteristics.

Conclusion

In this well-powered study, interictal plasma concentration of CGRP was a poor biomarker for TMD and migraine.

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.

Changes in the distribution of nerve fibers immunoreactive to calcitonin gene-related peptide according to growth and aging in rat molar periodontal ligament

OBJECTIVE

To analyze the age-dependent changes in nerve fibers immunoreactive to calcitonin gene-related peptide (CGRP-ir) in the periodontal ligaments of rats.

MATERIALS AND METHODS

Thirty male Wistar-ST rats were divided into growing groups (5, 9, and 15 weeks of age) and aging groups (6, 12, and 24 months of age) (n = 5 in each group). Eight serial sagittal sections, 5 microm thick, were cut parallel to the distobuccal root of the maxillary right first molar. These tissues were stained with a rabbit monoclonal antibody against CGRP. The observation area was divided into three parts (mesial, apical, and distal) and observed using a light microscope.

RESULTS

CGRP-ir nerve fibers were primarily distributed in the apical periodontal ligament in the growing group, with significantly more fibers than in the aging group.

CONCLUSIONS

CGRP-ir nerve fibers in the periodontal ligament are dense during the growth period and decrease gradually with aging, indicating that CGRP may affect periodontal tissue with growth and aging.

Differential Regulation of NADPH Oxidase in Sympathetic and Sensory Ganglia in Deoxycorticosterone Acetate–Salt Hypertension

We demonstrated recently that superoxide anion levels are elevated in prevertebral sympathetic ganglia of deoxycorticosterone acetate–salt hypertensive rats and that this superoxide anion is generated by reduced nicotinamide-adenine dinucleotide phosphate oxidase. In this study we compared the reduced nicotinamide-adenine dinucleotide phosphate oxidase enzyme system of dorsal root ganglion (DRG) and sympathetic celiac ganglion (CG) and its regulation in hypertension. The reduced nicotinamide-adenine dinucleotide phosphate oxidase activity of ganglion extracts was measured using fluorescence spectrometry of dihydroethidine; the activity in hypertensive dorsal root ganglion was 34% lower than in normotensive DRG. In contrast, activity was 79% higher in hypertensive CG than normotensive CG. mRNA for the oxidase subunits NOX1, NOX2, NOX4, p47 phox , and p22 phox were present in both CG and DRG; mRNA for NOX4 was significantly higher in CG than in DRG. The levels of mRNA and protein expression of the membrane-bound catalytic subunit p22 phox and of the regulatory subunits p47 phox and Rac-1 were measured in CG and DRG in normotensive and hypertensive rats. p22 phox mRNA and protein expression was greater in CG of hypertensive rats but not in DRG. Compared with normotensive controls, p47 phox mRNA and protein, as well as Rac-1 protein, were significantly decreased in hypertensive DRG but not in CG. Immunohistochemical staining of p47 phox showed translocation from cytoplasm to membrane in hypertensive CG but not in hypertensive DRG. This suggests that reduced nicotinamide-adenine dinucleotide phosphate oxidase activation in sympathetic neurons and sensory neurons is regulated in opposite directions in hypertension. This differential regulation may contribute to unbalanced vasomotor control and enhanced vasoconstriction in the splanchnic circulation.

Pathophysiology and therapeutic possibilities of calcitonin gene-related peptide in hypertension

Calcitonin gene related peptide (CGRP), a 37 amino acid neuropeptide, is the most potent vasodilator known. Participation of CGRP in hypertension and related diseases, such as preeclampsia or vasospasm after subarachnoid haemorrage, is one of the most studied topics. In this review we summarize the published roles of CGRP in pathophysiology of hypertension in humans and in experimental models. We also discuss the effects of direct administration of CGRP in the treatment of hypertension and of anti-hypertensive drugs that enhance the release or response of endogenous calcitonin gene-related peptide: angiotensin converting enzyme inhibitors, selective antagonists for the angiotensin II receptor, beta-blockers, magnesium sulphate for preeclampsia and rutaecarpine, as well as the possibilities using CGRP in gene therapy for prevention of vasospasm after subarachnoid haemorrage.

Long-term inhibition of angiotensin prevents reduction of periarterial innervation of calcitonin gene-related peptide (CGRP)-containing nerves in spontaneously hypertensive rats

The aim of this study was to investigate age-related changes in the density of calcitonin gene-related peptide (CGRP)-containing nerve fibers in spontaneously hypertensive rats (SHR) and the effects of long-term inhibition of the renin-angiotensin system on these changes. The density of immunocytochemically stained nerve fibers in the mesenteric artery was quantified by computer-assisted image processing. An age-related decrease in the density of CGRP-like immunoreactive (LI)-containing nerve fivers but not neuropeptide Y (NPY)-LI-containing sympathetic nerve fibers was found in the mesenteric artery of SHR but not Wistar Kyoto rats (WKY). The density of NPY-LI-containing sympathetic nerve fibers was significantly greater in SHR than in WKY. SHR were treated for 7 weeks with angiotensin converting enzyme inhibitor (0.005% temocapril), angiotensin II type-1 (AT1) receptor antagonist (0.025% losartan) or vasodilator (0.01% hydralazine) in their drinking water. Each drug treatment significantly lowered the systolic blood pressure measured by tail-cuff method. Long-term treatment of SHR with temocapril and losartan significantly increased the density of CGRP-LI-containing nerve fibers in mesenteric arteries. However, the density after hydralazine treatment was similar to the level in non-treated SHR. The density of NPY-LI-containing nerve fibers was not increased by any of the drug treatments. These results suggest that long-term inhibition of the renin-angiotensin system in SHR prevents remodeling of CGRPergic nerve fibers and prevents the reduction of CGRPergic nerve function.

Malfunction of vascular control in lifestyle-related diseases: distribution of adrenomedullin-containing perivascular nerves and its alteration in hypertension

The distribution and characteristics of adrenomedullin (AM)-containing perivascular nerves in the rat mesenteric artery were investigated using immunohistochemical techniques. Many fibers containing AM-like immunoreactivity (LI) were observed in the adventitia of mesenteric arteries, which were densely innervated by calcitonin gene-related peptide (CGRP)- and neuropeptide Y (NPY)-LI fibers. AM-LI, CGRP-LI, and NPY-LI fibers were abolished by cold storage denervation. Capsaicin pretreatment abolished AM-LI and NPY-LI fibers but not NPY-LI fibers. NPY-LI fibers but not AM-LI and CGRP-LI fibers disappeared after treatment with 6-hydroxydopamine. There were many AM-LI positive cells in the dorsal root ganglia, where AM mRNA was detected. In a double immunofluorescence study, AM-LI was found in CGRP-LI fibers, although some fibers contained AM-LI alone. The density of AM-LI fibers was lower in SHR than in WKY mesenteric arteries. These results suggest that the mesenteric artery is innervated by AM-containing perivascular nerves and AM may have a neurotransmitter role in the regulation of vascular tone.

Chronic angiotensin II inhibition increases levels of calcitonin gene-related peptide mRNA of the dorsal root ganglia in spontaneously hypertensive rats

We previously reported that the vasodilation mediated by calcitonin gene-related peptide (CGRP)-containing nerves and level of CGRP mRNA in the dorsal root ganglia (DRG) in spontaneously hypertensive rats (SHR) decreased with age, and that the reduced function of CGRP nerves was restored by chronic inhibition of angiotensin II. The present study was performed to investigate the effect of long-term treatment with angiotensin II type-1 receptor antagonists (L-158,809 and olmesartan), an angiotensin converting enzyme inhibitor (temocapril) and hydralazine on levels of CGRP mRNA in DRG of SHR and the contents of CGRP in the mesenteric artery and atrium. The level of CGRP mRNA and degree of CGRP-like immunoreactivities (CGRP-LI) were measured by Northern blot hybridization assay and enzyme-linked immunosorbent assay, respectively. Seven week-treatment of 8 week-old SHR with temocapril (0.005%), L-158,809 (0.001%), olmesartan (0.01%) or hydralazine (0.01%) administered in drinking water significantly lowered the systolic blood pressure of SHR. The level of CGRP mRNA in the DRG of control SHR was significantly lower than that in normotensive Wistar Kyoto rats (WKY), whereas the level of CGRP-LI in the mesenteric artery and atrium of SHR were significantly greater than those in WKY. Treatment of SHR with temocapril, L-158,809, or olmesartan, but not hydralazine, significantly elevated the levels of CGRP mRNA in DRG, markedly increased the level of CGRP-LI in the mesenteric artery, and slightly increased the CGRP-LI level in the atrium. These results suggest that long-term inhibition of angiotensin II restores the reduced expression of CGRP mRNA in DRG and may facilitate neurotransmission of CGRP-containing vasodilator nerves in SHR.

Regulation of vascular function by perivascular calcitonin gene-related peptide-containing nerves

The rat mesenteric artery is innervated by nonadrenergic noncholinergic (NANC) vasodilator nerves in which calcitonin gene-related peptide (CGRP), a potent vasodilator peptide, acts as a vasodilator transmitter. The inhibition of CGRPergic nerve function potentiates a vasoconstrictor response mediated by the sympathetic adrenergic nerve, suggesting that CGRPergic nerves inhibit adrenergic function and play a role in the regulation of mesenteric vascular tone. In contrast, norepinephrine released from adrenergic nerves presynaptically inhibits neurotransmission of CGRPergic nerves. Thus, both nerves reciprocally control the vascular tone. Pathophysiological studies have shown that an age-related decrease in CGRPergic nerve-mediated vasodilation, neurogenic CGRP release and CGRP mRNA levels in the dorsal root ganglia are found in spontaneously hypertensive rats (SHR), indicating a reduced function of CGRPergic nerves. Long-term treatment with angiotensin converting enzyme inhibitor and angiotensin II-receptor antagonist restores the reduced function of CGRPergic nerves, suggesting the involvement of angiotensin II in the malfunction of CGRPergic nerves in SHR.