Role of hemokinin-1 in health and disease

Drug effects on neuropeptides and their receptors: Big hopes but moderate success in the treatment of chronic pain

Neuropeptides, including tachykinins, CGRP, and somatostatin, are localized in a peptidergic subgroup of nociceptive primary afferent neurons. Tachykinins and CGRP are pronociceptive, somatostatin is an antinociceptive mediator. Intensive drug research has been performed to develop tachykinin and CGRP antagonists, and somatostatin agonists as analgesics. CGRP receptor antagonists are efficacious and well-tolerated drugs in migraine. Monoclonal antibodies against CGRP or its receptor are used for the prophylactic treatment of migraine. Tachykinin NK1 receptor antagonists failed as analgesics but are used for chemotherapy-induced nausea and vomiting. New, orally active somatostatin 4 receptor agonists are promising drug candidates for treating various pain conditions.

Role of Spinal Cholecystokinin Octapeptide, Nociceptin/Orphanin FQ, and Hemokinin-1 in Diabetic Allodynia

A complication of diabetes is neuropathic pain, which is difficult to control with medication. We have confirmed that neuropathic pain due to mechanical allodynia in diabetic mice is mediated by a characteristic neuropeptide in the spinal cord. We evaluated the strength of mechanical allodynia in mice using von Frey filaments. When mice were intravenously injected with streptozotocin, mechanical allodynia appeared 3 days later. Antibodies of representative neuropeptides were intrathecally (i.t.) administered to allodynia-induced mice 7 days after the intravenous administration of streptozotocin, and allodynia was reduced by anti-cholecystokinin octapeptide antibodies, anti-nociceptin/orphanin FQ antibodies, and anti-hemokinin-1 antibodies. In contrast, i.t.-administered anti-substance P antibodies, anti-somatostatin antibodies, and anti-angiotensin II antibodies did not affect streptozotocin-induced diabetic allodynia mice. Mechanical allodynia was attenuated by the i.t. administration of CCK-B receptor antagonists and ORL-1 receptor antagonists. The mRNA level of CCK-B receptors in streptozotocin-induced diabetic allodynia mice increased in the spinal cord, but not in the dorsal root ganglion. These results indicate that diabetic allodynia is caused by cholecystokinin octapeptide, nociceptin/orphanin FQ, and hemokinin-1 released from primary afferent neurons in the spinal cord that transmit pain to the brain via the spinal dorsal horn.

Mast Cells and Their Related Gene HK-1 are Closely Associated with Discogenic Low Back Pain: A Bioinformatics and Clinical Sample Study

Background

Low back pain (LBP) is primarily caused by intervertebral disc degeneration (IVDD). Immune cells penetrating nucleus pulposus (NP) tissues may play an important role in generating IVDD and LBP.

Methods

The clinical data from 100 cases of IVDD patients was initially analyzed retrospectively. Subsequently, peripheral blood and NP tissues from 41 IVDD patients were gathered for a validated investigation. Among them, ribosome-removed-RNA sequencing (RNA-seq) was performed on 10 cases of NP tissues of specific classifications (VAS 3 and Pfirrmann 3 were used as the controls, while patients with VAS 6 and Pfirrmann 5 were used as the experimental group). Differentially expressed genes (DEGs) were identified for the subsequent bioinformatics analysis. Further methods to confirm the underlying cause of discogenic LBP included mast cell immunohistochemistry (IHC), 12 cytokine detection, Western blot (WB), and real-time polymerase chain reaction (RT-PCR).

Results

Discogenic LBP and IVDD severity are strongly associated, and immunological cell infiltration has been demonstrated to be a significant factor in LBP by bioanalytical research. Tryptase-positive mast cells were found to be significantly more abundant in the VAS 6 NP tissues of IVDD patients than in the VAS 3 NP tissues. It was initially demonstrated that IVDD and LBP were significantly impacted by hemokinin-1 (HK-1), the mast cell-related gene. Furthermore, blood levels of interleukin 12 p70 (IL-12P70) are noticeably elevated and strongly correlated with HK-1, indicating that HK-1 may be involved in the regulation of mast cell activity and IL-12P70 production.

Conclusion

The severity of LBP was observed to be positively correlated with the IVDD Pfirrmann grading. Further research indicates that patients with IVDD may experience persistent low back pain due to HK-1 activation of mast cells and the release of the cytokine IL12P70. This work will offer new insights into the diagnosis and treatment of discogenic LBP.

Association of Neurokinin-1 Receptor Signaling Pathways with Cancer

BACKGROUND

Numerous biochemical reactions leading to altered cell proliferation cause tumorigenesis and cancer treatment resistance. The mechanisms implicated include genetic and epigenetic changes, modified intracellular signaling, and failure of control mechanisms caused by intrinsic and extrinsic factors alone or combined. No unique biochemical events are responsible; entangled molecular reactions conduct the resident cells in a tissue to display uncontrolled growth and abnormal migration. Copious experimental research supports the etiological responsibility of NK-1R (neurokinin-1 receptor) activation, alone or cooperating with other mechanisms, in cancer appearance in different tissues. Consequently, a profound study of this receptor system in the context of malignant processes is essential to design new treatments targeting NK-1R-deviated activity.

METHODS

This study reviews and discusses recent literature that analyzes the main signaling pathways influenced by the activation of neurokinin 1 full and truncated receptor variants. Also, the involvement of NK-1R in cancer development is discussed.

CONCLUSION

NK-1R can signal through numerous pathways and cross-talk with other receptor systems. The participation of override or malfunctioning NK-1R in malignant processes needs a more precise definition in different types of cancers to apply satisfactory and effective treatments. A long way has already been traveled: the current disposal of selective and effective NK-1R antagonists and the capacity to develop new drugs with biased agonistic properties based on the receptor's structural states with functional significance opens immediate research action and clinical application.

Hemokinin-1 is a mediator of chronic restraint stress-induced pain

The Tac4 gene-derived hemokinin-1 (HK-1) binds to the NK1 receptor, similarly to Substance P, and plays a role in acute stress reactions and pain transmission in mice. Here we investigated Tac4 mRNA expression in stress and pain-related regions and its involvement in chronic restraint stress-evoked behavioral changes and pain using Tac4 gene-deleted (Tac4-/-) mice compared to C57Bl/6 wildtypes (WT). Tac4 mRNA was detected by in situ hybridization RNAscope technique. Touch sensitivity was assessed by esthesiometry, cold tolerance by paw withdrawal latency from 0°C water. Anxiety was evaluated in the light-dark box (LDB) and open field test (OFT), depression-like behavior in the tail suspension test (TST). Adrenal and thymus weights were measured at the end of the experiment. We found abundant Tac4 expression in the hypothalamic-pituitary-adrenal axis, but Tac4 mRNA was also detected in the hippocampus, amygdala, somatosensory and piriform cortices in mice, and in the frontal regions and the amygdala in humans. In Tac4-/- mice of both sexes, stress-induced mechanical, but not cold hyperalgesia was significantly decreased compared to WTs. Stress-induced behavioral alterations were mild or absent in male WT animals, while significant changes of these parameters could be detected in females. Thymus weight decrease can be observed in both sexes. Higher baseline anxiety and depression-like behaviors were detected in male but not in female HK-1-deficient mice, highlighting the importance of investigating both sexes in preclinical studies. We provided the first evidence for the potent nociceptive and stress regulating effects of HK-1 in chronic restraint stress paradigm. Identification of its targets might open new perspectives for therapy of stress-induced pain.

Hemokinin-1 induces transcriptomic alterations in pain-related signaling processes in rat primary sensory neurons independent of NK1 tachykinin receptor activation

The tachykinin hemokinin-1 (HK-1) is involved in immunological processes, inflammation, and pain. Although the neurokinin 1 receptor (NK1R) is described as its main target, several effects are mediated by currently unidentified receptor(s). The role of HK-1 in pain is controversial, depending on the involvement of peripheral and central sensitization mechanisms in different models. We earlier showed the ability of HK-1 to activate the trigeminovascular system, but the mechanisms need to be clarified. Therefore, in this study, we investigated HK-1-induced transcriptomic alterations in cultured rat trigeminal ganglion (TRG) primary sensory neurons. HK-1 was applied for 6 or 24 h in 1 μM causing calcium-influx in these neurons, 500 nM not inducing calcium-entry was used for comparison. Next-generation sequencing was performed on the isolated RNA, and transcriptomic changes were analyzed to identify differentially expressed (DE) genes. Functional analysis was performed for gene annotation using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Reactome databases. NK1R and Neurokinin receptor 2 (NK2R) were not detected. Neurokinin receptor 3 (NK3R) was around the detection limit, which suggests the involvement of other NKR isoforms or other receptors in HK-1-induced sensory neuronal activation. We found protease-activated receptor 1 (PAR1) and epidermal growth factor receptor (EGFR) as DE genes in calcium signaling. The transmembrane protein anthrax toxin receptor 2 (ANTXR2), a potential novel pain-related target, was upregulated. Acid-sensing ion channel 1; 3 (Asic1,3), N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptors decreased, myelin production and maintenance related genes (Mbp, Pmp2, Myef2, Mpz) and GNDF changed by HK-1 treatment. Our data showed time and dose-dependent effects of HK-1 in TRG cell culture. Result showed calcium signaling as altered event, however, we did not detect any of NK receptors. Presumably, the activation of TRG neurons is independent of NK receptors. ANTXR2 is a potential new target, PAR-1 has also important role in pain, however their connection to HK-1 is unknown. These findings might highlight new targets or key mediators to solve how HK-1 acts on TRG.

Neuropeptide substance P: A promising regulator of wound healing in diabetic foot ulcers

In the past, neuropeptide substance P (SP) was predominantly recognized as a neuroinflammatory factor, while its potent healing activity was overlooked. This paper aims to review the regulatory characteristics of neuropeptide SP in both normal and diabetic wound healing. SP actively in the regulation of wound healing-related cells directly and indirectly, exhibiting robust inflammatory properties, promoting cell proliferation and migration and restoring the activity and paracrine ability of skin cells under diabetic conditions. Furthermore, SP not only regulates healing-related cells but also orchestrates the immune environment, thereby presenting unique and promising application prospects in wound intervention. As new SP-based preparations are being explored, SP-related drugs are poised to become an effective therapeutic intervention for diabetic foot ulcers (DFU).

Development of Neuropeptide Hemokinin-1 Analogues with Antimicrobial and Wound-Healing Activity

Wound healing is a complex process that can be delayed in some pathological conditions, such as infection and diabetes. Following skin injury, the neuropeptide substance P (SP) is released from peripheral neurons to promote wound healing by multiple mechanisms. Human hemokinin-1 (hHK-1) has been identified as an SP-like tachykinin peptide. Surprisingly, hHK-1 shares similar structural features with antimicrobial peptides (AMPs), but it does not display efficient antimicrobial activity. Therefore, a series of hHK-1 analogues were designed and synthesized. Among these analogues, AH-4 was found to display the greatest antimicrobial activity against a broad spectrum of bacteria. Furthermore, AH-4 rapidly killed bacteria by membrane disruption, similar to most AMPs. More importantly, AH-4 showed favorable healing activity in all tested mouse full-thickness excisional wound models. Overall, this study suggests that the neuropeptide hHK-1 can be used as a desirable template for developing promising therapeutics with multiple functions for wound healing.

Skin codelivery of contact sensitizers and neurokinin-1 receptor antagonists integrated in microneedle arrays suppresses allergic contact dermatitis

BACKGROUND

Allergic contact dermatitis (CD) is a chronic inflammatory skin disease caused by type 1 biased adaptive immunity for which there is an unmet need for antigen (Ag)-specific immunotherapies. Exposure to skin sensitizers stimulates secretion of the proinflammatory neuropeptides substance P and hemokinin 1, which signal via the neurokinin-1 receptor (NK1R) to promote the innate and adaptive immune responses of CD. Accordingly, mice lacking the NK1R develop impaired CD. Nonetheless, the role and therapeutic opportunities of targeting the NK1R in CD remain to be elucidated.

OBJECTIVE

We sought to develop an Ag-specific immunosuppressive approach to treat CD by skin codelivery of hapten and NK1R antagonists integrated in dissolvable microneedle arrays (MNA).

METHODS

In vivo mouse models of contact hypersensitivity and ex vivo models of human skin were used to delineate the effects and mechanisms of NK1R signaling and the immunosuppressive effects of the contact sensitizer NK1R antagonist MNA in CD.

RESULTS

We demonstrated in mice that CD requires NK1R signaling by substance P and hemokinin 1. Specific deletion of the NK1R in keratinocytes and dendritic cells, but not in mast cells, prevented CD. Skin codelivery of hapten or Ag MNA inhibited neuropeptide-mediated skin inflammation in mouse and human skin, promoted deletion of Ag-specific effector T cells, and increased regulatory T cells, which prevented CD onset and relapses locally and systemically in an Ag-specific manner.

CONCLUSIONS

Immunoregulation by engineering localized skin neuroimmune networks can be used to treat cutaneous diseases that like CD are caused by type 1 immunity.

Alternative Splicing of Neuropeptide Prohormone and Receptor Genes Associated with Pain Sensitivity Was Detected with Zero-Inflated Models

Migraine is often accompanied by exacerbated sensitivity to stimuli and pain associated with alternative splicing of genes in signaling pathways. Complementary analyses of alternative splicing of neuropeptide prohormone and receptor genes involved in cell–cell communication in the trigeminal ganglia and nucleus accumbens regions of mice presenting nitroglycerin-elicited hypersensitivity and control mice were conducted. De novo sequence assembly detected 540 isoforms from 168 neuropeptide prohormone and receptor genes. A zero-inflated negative binomial model that accommodates for potential excess of zero isoform counts enabled the detection of 27, 202, and 12 differentially expressed isoforms associated with hypersensitivity, regions, and the interaction between hypersensitivity and regions, respectively. Skipped exons and alternative 3′ splice sites were the most frequent splicing events detected in the genes studied. Significant differential splicing associated with hypersensitivity was identified in CALCA and VGF neuropeptide prohormone genes and ADCYAP1R1, CRHR2, and IGF1R neuropeptide receptor genes. The prevalent region effect on differential isoform levels (202 isoforms) and alternative splicing (82 events) were consistent with the distinct splicing known to differentiate central nervous structures. Our findings highlight the changes in alternative splicing in neuropeptide prohormone and receptor genes associated with hypersensitivity to pain and the necessity to target isoform profiles for enhanced understanding and treatment of associated disorders such as migraine.

Regulatory Peptides in Asthma

Numerous regulatory peptides play a critical role in the pathogenesis of airway inflammation, airflow obstruction and hyperresponsiveness, which are hallmarks of asthma. Some of them exacerbate asthma symptoms, such as neuropeptide Y and tachykinins, while others have ameliorating properties, such as nociception, neurotensin or β-defensin 2. Interacting with peptide receptors located in the lungs or on immune cells opens up new therapeutic possibilities for the treatment of asthma, especially when it is resistant to available therapies. This article provides a concise review of the most important and current findings regarding the involvement of regulatory peptides in asthma pathology.

Novel Pituitary Actions of TAC4 Gene Products in Teleost

Tachykinin 4 (TAC4) is the latest member of the tachykinin family involved in several physiological functions in mammals. However, little information is available about TAC4 in teleost. In the present study, we firstly isolated TAC4 and six neurokinin receptors (NKRs) from grass carp brain and pituitary. Sequence analysis showed that grass carp TAC4 could encode two mature peptides (namely hemokinin 1 (HK1) and hemokinin 2 (HK2)), in which HK2 retained the typical FXGLM motif in C-terminal of tachyinin, while HK1 contained a mutant VFGLM motif. The ligand-receptor selectivity showed that HK2 could activate all 6 NKRs but with the highest activity for the neurokinin receptor 2 (NK2R). Interestingly, HK1 displayed a very weak activation for each NKR isoform. In grass carp pituitary cells, HK2 could induce prolactin (PRL), somatolactin α (SLα), urotensin 1 (UTS1), neuromedin-B 1 (NMB1), cocaine- and amphetamine-regulated transcript 2 (CART2) mRNA expression mediated by NK2R and neurokinin receptor 3 (NK3R) via activation cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholipase C (PLC)/inositol 1,4,5-triphosphate (IP3)/protein kinase C (PKC) and calcium²⁺ (Ca²⁺)/calmodulin (CaM)/calmodulin kinase-II (CaMK II) cascades. However, the corresponding stimulatory effects triggered by HK1 were found to be notably weaker. Furthermore, based on the structural base for HK1, our data suggested that a phenylalanine (F) to valine (V) substitution in the signature motif of HK1 might have contributed to its weak agonistic actions on NKRs and pituitary genes regulation.

Annotation of pituitary neuroendocrine tumors with genome-wide expression analysis

Pituitary neuroendocrine tumors (PitNETs) are common, generally benign tumors with complex clinical characteristics related to hormone hypersecretion and/or growing sellar tumor mass. PitNETs can be classified based on the expression pattern of anterior pituitary hormones and three main transcriptions factors (TF), SF1, PIT1 and TPIT that regulate differentiation of adenohypophysial cells. Here, we have extended this classification based on the global transcriptomics landscape using tumor tissue from a well-defined cohort comprising 51 PitNETs of different clinical and histological types. The molecular profiles were compared with current classification schemes based on immunohistochemistry. Our results identified three main clusters of PitNETs that were aligned with the main pituitary TFs expression patterns. Our analyses enabled further identification of specific genes and expression patterns, including both known and unknown genes, that could distinguish the three different classes of PitNETs. We conclude that the current classification of PitNETs based on the expression of SF1, PIT1 and TPIT reflects three distinct subtypes of PitNETs with different underlying biology and partly independent from the expression of corresponding hormones. The transcriptomic analysis reveals several potentially targetable tumor-driving genes with previously unknown role in pituitary tumorigenesis.

Serum level of hemokinin-1 is significantly lower in patients with chronic spontaneous urticaria than in healthy subjects

BACKGROUND

We previously reported upregulation of expression of Mas-related G protein-coupled receptor X2 (MRGPRX2) on mast cells (MCs) in the skin of patients with severe chronic spontaneous urticaria (CSU). Serum levels of substance P (SP) were reportedly significantly elevated, in correlation with the severity of CSU. Hemokinin-1 (HK-1) reportedly induced histamine release from LAD2 cells via MRGPRX2. We aimed to investigate HK-1's role in CSU.

METHODS

The concentrations of HK-1 and SP were measured using ELISAs. Skin- and synovium-derived cultured MCs were generated by culturing dispersed skin and synovial cells, respectively, with stem cell factor. MRGPRX2 expression in the MCs was reduced using a lentiviral shRNA silencing technique.

RESULTS

Anti-SP Ab used in the SP ELISA showed 100% cross-reactivity to HK-1, but anti-HK-1 Ab showed 0% cross-reactivity to SP. The serum level of HK-1 was significantly lower in patients with CSU (n = 151) than in non-atopic healthy control (NC) subjects (n = 114). The EC₅₀ of histamine release from MCs induced by HK-1 (5056 nM) was 12-fold higher than by SP (426 nM). Brief pretreatment of MCs with HK-1 at concentrations of 3.0-10 μM significantly reduced histamine release by 0.1 μM SP. However, brief incubation of MCs with HK-1 did not elicit rapid MRGPRX2 internalization.

CONCLUSIONS

In NC subjects, high HK-1 concentrations may desensitize MGRPRX2-mediated MC activation, thereby preventing MC degranulation by SP.

Neurokinin-1 Receptor Signaling Is Required for Efficient Ca2+ Flux in T-Cell-Receptor-Activated T Cells

Efficient Ca²⁺ flux induced during cognate T cell activation requires signaling the T cell receptor (TCR) and unidentified G-protein-coupled receptors (GPCRs). T cells express the neurokinin-1 receptor (NK1R), a GPCR that mediates Ca²⁺ flux in excitable and non-excitable cells. However, the role of the NK1R in TCR signaling remains unknown. We show that the NK1R and its agonists, the neuropeptides substance P and hemokinin-1, co-localize within the immune synapse during cognate activation of T cells. Simultaneous TCR and NK1R stimulation is necessary for efficient Ca²⁺ flux and Ca²⁺-dependent signaling that sustains the survival of activated T cells and helper 1 (Th1) and Th17 bias. In a model of contact dermatitis, mice with T cells deficient in NK1R or its agonists exhibit impaired cellular immunity, due to high mortality of activated T cells. We demonstrate an effect of the NK1R in T cells that is relevant for immunotherapies based on pro-inflammatory neuropeptides and its receptors.

The neurokinin 1 receptor (NK1R) induces Ca²⁺ flux in excitable cells. Here, Morelli et al. show that NK1R signaling in T cells promotes optimal Ca²⁺ flux triggered by TCR stimulation, which is necessary to sustain T cell survival and the efficient Th1- and Th17-based immunity that is relevant for immunotherapies based on pro-inflammatory neuropeptides.

Mass spectrometric studies on the peptide integrity of substance P and related human tachykinins in human biofluids

The neurokinin-1 receptor plays a profound role in inflammatory processes and is involved in immune cell differentiation, cytokine release, and mast cell activation. Due to their similar peptide structures, the neurokinin-1 receptor does not discriminate between the endogenous ligands substance P (SP) and human hemokinin-1 (hHK-1), which both demonstrate biological receptor affinity. In addition, due to cross-reactivity, the current bioanalytical method of choice-immunoassays-also displays limitations in differentiating between these peptides. Thus, a recently developed mass spectrometric assay was utilized for the selective quantification of SP and hHK-1 in various biofluids and tissue. By applying the sample processing protocols developed, SP was quantified in porcine brain tissue (4.49 ± 0.53 nM), human saliva (113.3 ± 67.0 pM), and human seminal fluid (0.52 ± 0.15 nM) by mass spectrometric analysis. As previously reported, neither SP nor hHK-1 could be detected in human plasma by mass spectrometry. Comparison with analysis using a commercial immunoassay of the same plasma sample revealed SP like-immunoreactivity concentrations of 37.1-178.0 pM. The previously reported carboxylic acid of SP, whose identity was confirmed by high-resolution mass spectrometric analysis, did not show cross-reactivity in the applied immunoassay and did not contribute to SP-like immunoreactivity results. Subsequent compound discovery of the immunocaptured substance indicated the presence of a precursor of SP as possible cross-reactor in human plasma samples. The found cross-reactivity might be the cause for the high variance of SP plasma levels in former determinations.

Hemokinin-1 as a Mediator of Arthritis-Related Pain via Direct Activation of Primary Sensory Neurons

The tachykinin hemokinin-1 (HK-1) is involved in immune cell development and inflammation, but little is known about its function in pain. It acts through the NK1 tachykinin receptor, but several effects are mediated by a yet unidentified target. Therefore, we investigated the role and mechanism of action of HK-1 in arthritis models of distinct mechanisms with special emphasis on pain. Arthritis was induced by i.p. K/BxN serum (passive transfer of inflammatory cytokines, autoantibodies), intra-articular mast cell tryptase or Complete Freund's Adjuvant (CFA, active immunization) in wild type, HK-1- and NK1-deficient mice. Mechanical- and heat hyperalgesia determined by dynamic plantar esthesiometry and increasing temperature hot plate, respectively, swelling measured by plethysmometry or micrometry were significantly reduced in HK-1-deleted, but not NK1-deficient mice in all models. K/BxN serum-induced histopathological changes (day 14) were also decreased, but early myeloperoxidase activity detected by luminescent in vivo imaging increased in HK-1-deleted mice similarly to the CFA model. However, vasodilation and plasma protein extravasation determined by laser Speckle and fluorescent imaging, respectively, were not altered by HK-1 deficiency in any models. HK-1 induced Ca2+-influx in primary sensory neurons, which was also seen in NK1-deficient cells and after pertussis toxin-pretreatment, but not in extracellular Ca2+-free medium. These are the first results showing that HK-1 mediates arthritic pain and cellular, but not vascular inflammatory mechanisms, independently of NK1 activation. HK-1 activates primary sensory neurons presumably via Ca2+ channel-linked receptor. Identifying its target opens new directions to understand joint pain leading to novel therapeutic opportunities.

Validated mass spectrometric assay for the quantification of substance P and human hemokinin-1 in plasma samples: A design of experiments concept for comprehensive method development

INTRODUCTION

Elevated plasma concentrations of the inflammatory neurokinins Substance P (SP) and human Hemokinin-1 (hHK-1) were found in infectious diseases. SP and hHK-1 plasma levels in diseased subjects are determined by immunoassays although not recommended by most immunoassay suppliers owing to their limitations to differentiate accurately between both peptides. A selective and reliable alternative (e.g. mass spectrometric (MS) assay) was missing because of a lack of sensitivity for the determination of endogenous plasma levels.

METHOD

Using a Design of Experiments (DoE) concept, a highly sensitive MS assay was developed for the quantification of SP, its inactive analog as the free acid, and hHK-1 in human plasma. Critical method aspects as the plasma extraction, peptide separation, and the method sensitivity were comprehensively optimized. The method was validated according to international bioanalytical guidelines and its applicability was evaluated in plasma of volunteers.

RESULTS

Within 106 experiments utilizing the DoE concept, the sensitivity of the assay was substantially improved to achieve limits of detection of 5.8 pg/mL for SP, 6.2 pg/mL for its free acid, and 5.3 pg/mL for hHK-1 in plasma. The lean method development was followed by the successful validation according to the regulatory guidelines resulting in a wide quantification range of 7.8-2000 pg/mL. In the volunteers' plasma, no SP and hHK-1 were detectable. Instead, the free acid of SP was quantified in individually distinct levels (202.5-1024.1 pg/mL).

CONCLUSION

An accurate and precise MS assay for the quantification of SP, its free acid, and hHK-1 in plasma was established. The mass spectrometric quantification of the free acid of SP in human plasma samples lead to the question about possible cross-reactivity of the immunoassays in former determinations.

Hemokinin-1 and substance P stimulate production of inflammatory cytokines and chemokines in human colonic mucosa via both NK1 and NK2 tachykinin receptors

There is increasing focus on the involvement of tachykinins in immune and inflammatory responses. Hemokinin-1 (HK-1) is a recently identified tachykinin that originates primarily from immune cells, and has structural similarities to substance P (SP), found mainly in neurons. However, there are species differences in HK-1, and the role of HK-1 in humans, particularly the intestine, has received minimal attention. The aim of this study was to investigate the inflammatory role of human HK-1 in the human colon. The effects of HK-1 and SP were compared on the production of multiple inflammatory cytokines and chemokines from human colonic mucosal explants. Data generated by Procarta multiplex assay and QuantiGene assay demonstrated that 4 h incubation with HK-1 (0.1 μM) significantly stimulated transcript expression and release of MCP-1, MIP-1α and β, RANTES, TNF-α, IL-1β and IL-6 from the mucosa. SP (0.1 μM) had comparable actions, but had no effect on MCP-1 or RANTES. These effects were inhibited separately by tachykinin NK₁ and NK₂ receptor antagonists SR140333 and SR48968 (both 0.1 μM), suggesting that these responses were mediated by both NK1 and NK2 receptors. In conclusion, these data support a novel inflammatory role for HK-1 in human colon, signaling via NK1 and NK2 receptors (and possibly other tachykinin-preferring receptors) to regulate the release of a broad spectrum of proinflammatory mediators. The study suggests that along with SP, HK-1 is also a proinflammatory mediator, likely involved in colonic inflammation, including inflammatory bowel disease (IBD).

Hemokinin-1 Gene Expression Is Upregulated in Trigeminal Ganglia in an Inflammatory Orofacial Pain Model: Potential Role in Peripheral Sensitization

A large percentage of primary sensory neurons in the trigeminal ganglia (TG) contain neuropeptides such as tachykinins or calcitonin gene-related peptide. Neuropeptides released from the central terminals of primary afferents sensitize the secondary nociceptive neurons in the trigeminal nucleus caudalis (TNC), but also activate glial cells contributing to neuroinflammation and consequent sensitization in chronic orofacial pain and migraine. In the present study, we investigated the newest member of the tachykinin family, hemokinin-1 (HK-1) encoded by the Tac4 gene in the trigeminal system. HK-1 had been shown to participate in inflammation and hyperalgesia in various models, but its role has not been investigated in orofacial pain or headache. In the complete Freund’s adjuvant (CFA)-induced inflammatory orofacial pain model, we showed that Tac4 expression increased in the TG in response to inflammation. Duration-dependent Tac4 upregulation was associated with the extent of the facial allodynia. Tac4 was detected in both TG neurons and satellite glial cells (SGC) by the ultrasensitive RNAscope in situ hybridization. We also compared gene expression changes of selected neuronal and glial sensitization and neuroinflammation markers between wild-type and Tac4-deficient (Tac4^-/-) mice. Expression of the SGC/astrocyte marker in the TG and TNC was significantly lower in intact and saline/CFA-treated Tac4^-/- mice. The procedural stress-related increase of the SGC/astrocyte marker was also strongly attenuated in Tac4^-/- mice. Analysis of TG samples with a mouse neuroinflammation panel of 770 genes revealed that regulation of microglia and cytotoxic cell-related genes were significantly different in saline-treated Tac4^-/- mice compared to their wild-types. It is concluded that HK-1 may participate in neuron-glia interactions both under physiological and inflammatory conditions and mediate pain in the trigeminal system.

Substance P and Hemokinin 1 in Nasal Lavage Fluid of Patients with Chronic Sinusitis and Nasal Polyposis

This pilot study was undertaken to isolate and quantify substance P (SP) and hemokinin 1 (HK-1) in the nasal lavage fluid of patients with chronic rhinosinusitis with nasal polyps to better elucidate the pathophysiology underlying this inflammatory process, which remains poorly understood. Mucus samples were collected from this introductory cohort of 10 patients diagnosed with chronic rhinosinusitis with nasal polyps at Tufts Medical Center (Boston, Massachusetts). Relative levels of SP and HK-1 were measured with enzyme-linked immunosorbent assay methods. Both inflammatory neuropeptides were found in detectable and comparable amounts in patient samples and in concentrations up to 100-fold those established in past literature. The presence of SP and HK-1 necessitates further investigation into their role in nasal polyposis and the potentiation of the chronic inflammation inherent to chronic rhinosinusitis. Downregulating these peptides could therefore provide novel treatment targets to manage this disease process.

Substance P-mediated cardiac mast cell activation: An in vitro study

The neuropeptide substance P can induce degranulation of cardiac mast cells at high concentrations. Herein, we seek to further understand substance P activation of cardiac mast cells in the context of other neuropeptides as well as modulation by non-neuropeptides. This is important given the increasingly recognized role of both cardiac mast cells and substance P in adverse cardiac remodeling. To address this, we isolated cardiac mast cells and compared their response to substance P as well as other members from the tachykinin family of peptides, including neurokinin A and hemokinin-1. We also tested the ability of other factors to manipulate the cardiac mast cell response to substance P. We found that while neurokinin A did not induce cardiac mast cell degranulation, both substance P and hemokinin-1 induced a concentration-dependent release of histamine; the maximal response to hemokinin-1 was greater than to substance P. Neurokinin-1 receptor blockade prevented substance P-induced histamine release, while only partially attenuating hemokinin-1-induced histamine release. The antioxidant N-acetylcysteine attenuated histamine release in response to hemokinin-1 and had no effect on substance P-induced histamine release. Selective PPAR-γ agonists attenuated histamine release in response to substance P. These data indicate that substance P activates cardiac mast cells via the neurokinin-1 receptor, and that the activation response is different to other tachykinins. That the response to substance P is receptor mediated and can be modulated by activation of other receptors (PPAR-γ), argues that substance P activation of cardiac mast cells has potential biological significance.

Hemokinin-1 is an important mediator of pain in mouse models of neuropathic and inflammatory mechanisms

The Tac4 gene-derived hemokinin-1 (HK-1) is present in pain-related regions and activates the tachykinin NK1 receptor, but with binding site and signaling pathways different from Substance P (SP). NK1 receptor is involved in nociception, but our earlier data showed that it has no role in chronic neuropathic hyperalgesia, similarly to SP. Furthermore, NK1 antagonists failed in clinical trials as analgesics due to still unknown reasons. Therefore, we investigated the role of HK-1 in pain conditions of distinct mechanisms using genetically modified mice. Chronic neuropathic mechanical and cold hyperalgesia after partial sciatic nerve ligation (PSL) were determined by dynamic plantar aesthesiometry and withdrawal latency from icy water, motor coordination on the accelerating Rotarod. Peripheral nerve growth factor (NGF) production was measured by ELISA, neuronal and glia cell activation by immunohistochemistry in pain-related regions. Acute somatic and visceral chemonocifensive behaviors were assessed after intraplantar formalin or intraperitoneal acetic-acid injection, respectively. Resiniferatoxin-induced inflammatory mechanical and thermal hyperalgesia by aesthesiometry and increasing temperature hot plate. Chronic neuropathic mechanical and cold hypersensitivity were significantly decreased in HK-1 deficient mice. NGF level in the paw homogenates of intact mice were significantly lower in case of HK-1 deletion. However, it significantly increased under neuropathic condition in contrast to wildtype mice, where the higher basal concentration did not show any changes. Microglia, but not astrocyte activation was observed 14 days after PSL in the ipsilateral spinal dorsal horn of wildtype, but not HK-1-deficient mice. However, under neuropathic conditions, the number of GFAP-positive astrocytes was significantly smaller in case of HK-1 deletion. Acute visceral, but not somatic nocifensive behavior, as well as neurogenic inflammatory mechanical and thermal hypersensitivity were significantly reduced by HK-1 deficiency similarly to NK1, but not to SP deletion. We provide evidence for pro-nociceptive role of HK-1, via NK1 receptor activation in acute inflammation models, but differently from SP-mediated actions. Identification of its targets and signaling can open new directions in pain research.

The Neurokinins: Peptidomimetic Ligand Design and Therapeutic Applications

The neurokinins are indisputably essential neurotransmitters in numerous pathoand physiological events. Being widely distributed in the Central Nervous System (CNS) and peripheral tissues, their discovery rapidly promoted them to drugs targets. As a necessity for molecular tools to understand the biological role of this class, endogenous peptides and their receptors prompted the scientific community to design ligands displaying either agonist and antagonist activity at the three main neurokinin receptors, called NK1, NK2 and NK3. Several strategies were implemented for this purpose. With a preference to small non-peptidic ligands, many research groups invested efforts in synthesizing and evaluating a wide range of scaffolds, but only the NK1 antagonist Aprepitant (EMENDT) and its prodrug Fosaprepitant (IVEMENDT) have been approved by the Food Drug Administration (FDA) for the treatment of Chemotherapy-Induced and Post-Operative Nausea and Vomiting (CINV and PONV, respectively). While non-peptidic drugs showed limitations, especially in side effect control, peptidic and pseudopeptidic compounds progressively regained attention. Various strategies were implemented to modulate affinity, selectivity and activity of the newly designed ligands. Replacement of canonical amino acids, incorporation of conformational constraints, and fusion with non-peptidic moieties gave rise to families of ligands displaying individual or dual NK1, NK2 and NK3 antagonism, that ultimately were combined with non-neurokinin ligands (such as opioids) to target enhanced biological impact.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.