Neurokinins induce relaxation of human pulmonary vessels through stimulation of endothelial NK1 receptors

Interaction of calcitonin gene related peptide (CGRP) and substance P (SP) in human skin

Calcitonin gene related peptide (CGRP) and substance P (SP) are neuropeptides that are simultaneously released from nociceptive C-fibers. CGRP is a potent vasodilator, inducing a long-lasting increase in superficial skin blood flow, whereas SP induces only a brief vasodilation but a significant plasma extravasation. CGRP and SP may play important roles in the pathophysiology of various pain states but little is known about their interaction. Different concentrations of SP (ranging from 10^-5M to 10^-9M) were applied to the volar forearm of 24 healthy subjects via dermal microdialysis. SP was applied either alone or in combination with CGRP10^-9M and CGRP 10^-6M. As expected, SP induced a transient increase in skin blood flow that decayed shortly after application. This transient blood flow peak was blunted with co-application of CGRP 10^-9M and inhibited with co-application of CGRP10^-6M. SP alone induced plasma protein extravasation (PPE). However, when CGRP10^-6M was added, the PPE significantly increased. Our results demonstrate a complex interaction of the neuropeptides CGRP and SP. CGRP10^-6M prevented SP-induced early vasodilation but augmented SP-induced PPE. These interactions might explain why vascular symptoms in chronic pain can differ strikingly between individuals.

TRPV1 and SP: key elements for sepsis outcome?

Sensory neurons play important roles in many disorders, including inflammatory diseases, such as sepsis. Sepsis is a potentially lethal systemic inflammatory reaction to a local bacterial infection, affecting thousands of patients annually. Although associated with a high mortality rate, sepsis outcome depends on the severity of systemic inflammation, which can be directly influenced by several factors, including the immune response of the patient. Currently, there is a lack of effective drugs to treat sepsis, and thus there is a need to develop new drugs to improve sepsis outcome. Several mediators involved in the formation of sepsis have now been identified, but the mechanisms underlying the pathology remain poorly understood. The transient receptor potential vanilloid 1 (TRPV1) receptor and the neuropeptide substance P (SP) have recently been demonstrated as important targets for sepsis and are located on sensory neurones and non-neuronal cells. Herein, we highlight and review the importance of sensory neurones for the modulation of sepsis, with specific focus on recent findings relating to TRPV1 and SP, with their distinct abilities to alter the transition from local to systemic inflammation and also modify the overall sepsis outcome. We also emphasize the protective role of TRPV1 in this context.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Discovery and biological characterization of (2R,4S)-1'-acetyl-N-{(1R)-1-[3,5-bis(trifluoromethyl)phenyl]ethyl}-2-(4-fluoro-2-methylphenyl)-N-methyl-4,4'-bipiperidine-1-carboxamide as a new potent and selective neurokinin 1 (NK1) receptor antagonist clinical candidate

A large body of compelling preclinical evidence supports the clinical use of neurokinin (NK) receptor antagonists in a plethora of CNS and non-CNS therapeutic areas. The significant investment made in this area over the past 2 decades culminated with the observation that NK(1) receptor antagonists elicited clinical efficacy in major depression disorders. In addition, aprepitant (Merck) was launched as a new drug able to prevent chemotherapy-induced nausea and vomiting (CINV). After the discovery by GlaxoSmithKline of vestipitant, a wide drug discovery program was launched aimed at identifying additional clinical candidates. New compounds were designed to maximize affinity at the NK(1) receptor binding site while retaining suitable physicochemical characteristics to ensure excellent pharmacokinetic and pharmacodynamic properties in vivo. Herein we describe the discovery process of a new NK(1) receptor antagonist (casopitant) selected as clinical candidate and progressed into clinical studies to treat major depression disorders.

Nerve-related characteristics of ventral paratendinous tissue in chronic Achilles tendinosis

Ultrasound and Doppler examination has shown high blood flow-neovascularisation inside and outside the ventral Achilles tendon in chronic painful tendinosis, but not in pain-free normal Achilles tendons. In patients with Achilles tendinosis, injections with the sclerosing substance polidocanol, targeting the areas with increased blood flow, have been demonstrated to give pain relief. A drawback when interpreting these findings is the fact that the pattern of nerve supply in the target area, i.e. the ventral area of the tendon, is so far unknown. In this study, therefore, tissue specimens from this area, obtained during surgical treatment of patients with chronic painful midportion Achilles tendinosis, were examined. In the examined area, containing loose connective tissue, the general finding was a presence of large and small arteries and nerve fascicles. The nerve fascicles were distinguished in sections processed for the pan-neural marker protein gene-product 9.5. The nerve fascicles contain sensory nerve fibers, as shown via staining for the sensory markers substance P (SP) and calcitonin gene-related peptide, and sympathetic nerve fibers as seen via processing for tyrosine hydroxylase. In addition, there were immunoreactions for the SP-preferred receptor, the neurokinin-1 receptor, in blood vessel walls and nerve fascicles. Some of the blood vessels were supplied by an extensive peri-vascular innervation, sympathetic nerve fibers being a distinct component of this innervation. There was also a marked occurrence of immunoreactions for the alpha1-adrenoreceptor in arterial walls as well as in the nerve fascicles. Altogether, these findings suggest that the area investigated is under marked influence by the nervous system, including sympathetic and sensory components. Thus, sympathetic/sensory influences may be involved in the pain mechanisms from this area. In conclusion, the nerve-related characteristics of the area targeted by the polidicanol injection treatment for Achilles tendinosis, are shown here for the first time.

Intermedin/adrenomedullin-2 dilates the rat pulmonary vascular bed: dependence on CGRP receptors and nitric oxide release

Intermedin/adrenomedullin-2 (IMD/AM2) is a 47 amino acid peptide formed by enzymatic degradation of preprointermedin. The present study was undertaken to investigate the effects of rat IMD (rIMD) in the isolated buffer perfused rat lung (IBPR) under resting conditions and under conditions of elevated pulmonary vasoconstrictor tone (PVT). Under resting conditions in the IBPR, rIMD had little or no activity. When PVT was actively increased by infusion of U46619, bolus injection of IMD decreased pulmonary arterial pressure (PAP) in a dose-dependent manner. Since the pulmonary perfusion rate and left atrial pressure were constant, these reductions in PAP directly reflect reductions in pulmonary vascular resistance (PVR). The pulmonary vasodilator response to rIMD, when compared to calcitonin gene-related peptide (CGRP) on a molar basis, was greater at the lowest and midrange doses. The degree of inhibition by CGRP8-37 on pulmonary vasodilator response to rIMD was significantly less when compared to CGRP. Pretreatment with L-nitro-arginine-methyl ester (L-NAME), unlike meclofenamate and glybenclamide, significantly reduced the pulmonary vasodilator responses to rIMD. rIMD administration induced cross-tachyphylaxis to the pulmonary vasodilator response to CGRP whereas CGRP administration did not alter the ability of rIMD to dilate the IBPR. Pulmonary vasodilator responses to repeated injections of rIMD did not undergo tachyphylaxis. The present data demonstrate rIMD possesses direct vasodilator activity in the rat pulmonary vascular bed. The present data suggest activation of CGRP1 receptors and release of nitric oxide (NO*) mediate the pulmonary vasodilator response to rIMD whereas cyclooxygenase products and KATP channels do not contribute to the pulmonary vasodilator response to rIMD. The ability of rIMD to induce heterologous desensitization of CGRP1 receptor activation, to retain much of its pulmonary vasodilator activity after inhibition of CGRP1 receptors, and to lack homologous desensitization together suggests the pulmonary, unlike the systemic, vasodilator response to rIMD may depend on other vasodilator mechanisms including receptors in the calcitonin-receptor-like-receptor (CRLR) family.

Extending the understanding of sensory neuropeptides

The tachykinins substance P and neurokinin A are present in human airways, in sensory nerves and immune cells. Tachykinins can be recovered from the airways after inhalation of ozone, cigarette smoke or allergen. They interact in the airways with tachykinin NK1, NK2 and NK3 receptors to cause bronchoconstriction, plasma protein extravasation, and mucus secretion and to attract and activate immune cells. In preclinical studies they have been implicated in the pathophysiology of asthma and chronic obstructive pulmonary disease, including allergen- and cigarette smoke induced airway inflammation and bronchial hyperresponsiveness and mucus secretion. Dual NK1/NK2 or triple NK1/NK2/NK3 tachykinin receptor antagonists offer therapeutic potential in airway diseases such as asthma and chronic obstructive pulmonary disease.

Increased substance P content in nerve fibers associated with mesenteric veins from deoxycorticosterone acetate (DOCA)-salt hypertensive rats

This study examined sensory nerves associated with mesenteric arteries and veins in sham and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Reactivity of arteries and veins to substances released from sensory nerves was also studied in vitro using computer-assisted video microscopy. Co-localization of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactivity (ir) was used to evaluate perivascular sensory nerves. Radioimmunoassay was used to quantify SP- and CGRP-ir content. Immunohistochemical studies revealed a plexus of SP/CGRP-ir nerves associated with arteries and veins. The intensity of SP-ir, but not CGRP-ir labeling was greater in arteries and veins from DOCA-salt compared to sham rats. RIA measurements revealed that the CGRP-ir content of arteries and veins was higher than the SP-ir content but there was a significant increase in SP-ir, but not CGRP-ir, content in arteries and veins from DOCA-salt rats. SP (0.03-1 microM) contracted veins and the NK-3 receptor agonist, senktide, mimicked this effect. There were no differences in SP or senktide reactivity of veins from sham or DOCA-salt rats. SP, but not senktide, relaxed KCl (40 mM) preconstricted arteries. CGRP (0.3 microM), acetylcholine (10 microM) and capsaicin (1 microM) relaxed KCl-preconstricted arteries and veins. The NK-1 receptor agonist, substance P methyl ester relaxed arteries but not veins. These data indicate that DOCA-salt hypertension is associated with upregulation of SP content in perivascular nerves. NK-3 receptors mediate venoconstriction which is unchanged in DOCA-salt hypertension. Increased release of SP from perivenous nerves might contribute to the increased venomotor tone in DOCA-salt hypertension.

Vascular NK-1 receptor occurrence in normal and chronic painful Achilles and patellar tendons: studies on chemically unfixed as well as fixed specimens

It is not known as to whether the Achilles and patellar tendons contain neurokinin-1 (NK-1) receptors. This is a drawback when considering the fact that pain symptoms are frequent in these and as recent studies show that the pain symptoms might be cured via interference with blood vessel function. In the present study, the human Achilles and patellar tendons were examined concerning immunohistochemical expression of the NK-1 receptor. Chemically unfixed and fixed specimens, TRITC and PAP stainings and a battery of NK-1 receptor antibodies, including antibodies against the C-terminus and the N-terminal region, were utilized. NK-1 receptor immunoreaction could be detected in inner parts of the walls of large blood vessels and in the walls of small blood vessels. To some extent, NK-1 immunoreaction was also detectable in small nerve fascicles and in tenocytes. It was found to be of utmost importance to apply both chemically unfixed and fixed specimens. The use of chemically unfixed tissue was found advantageous in order to depict the immunoreactions in the blood vessel walls. The observations represent new findings and are of relevance as substance P (SP) is known to be of importance where neurogenic angiogenesis contributes to diseases and as SP on the whole has profound effects concerning blood vessel regulation.

Neurokinin B causes concentration-dependent relaxation of isolated human placental resistance vessels

Placental neurokinin B (NKB) was recently identified as the causative agent in preeclampsia, a condition characterized by increased maternal and feto-placental vascular resistance. We hypothesized that NKB should constrict placental resistance vessels. Placentas were obtained from normotensive pregnancies. Immediately after delivery, stem villous arteries (300 microm diameter, 1.2 mm long) were dissected from macroscopically normal tissue in cold HEPES-physiological salt solution (PSS), mounted on a wire myograph system, and bathed in HEPES-PSS at 37 degrees C. After determination of the passive-tension internal circumference characteristics, the arteries were set to 90% of the internal circumference they would have under a normal physiological transmural pressure. Cumulative concentration-response curves were constructed for NKB (1 x 10(-12) to 1 x 10(-5) mol/l). Since there was no constrictive response to NKB, cumulative constrictive concentration-response curves were constructed to the thromboxane A(2) mimetic U46619 (1 x 10(-9) to 1 x 10(-5) mol/l). The vessels were then pre-constricted to 80% of maximal response and exposed to cumulative concentrations of NKB (1 x 10(-12) to 1 x 10(-6) mol/l). NKB caused a concentration-dependent relaxation (Maximal response NKB, 51+/-5%, n=5; time control, 12+/-6%, n=4; P<0.05). Removal of the endothelium did not alter the vasodilatory response to NKB. We conclude that, contrary to our hypothesis, NKB causes an endothelium-independent relaxation of the placental resistance vessels. We propose that NKB plays a role in the maintenance of high placental blood flow in normal pregnancy.