Proteolysis controls endogenous substance P levels

The effect of substance P and its common in vivo-formed metabolites on MRGPRX2 and human mast cell activation

The tachykinin neuropeptide substance P (SP) is the canonical agonist peptide for the neurokinin 1 receptor (NK₁R). More recently, it has also been shown to activate the Mas‐related G protein‐coupled receptor X2 (MRGPRX2) receptor on mast cells (MCs), triggering degranulation and release of inflammatory mediators. SP undergoes rapid C‐terminal truncation in vivo by a number of proteases to generate the metabolites SP(1–9)‐COOH and in particular SP(1–7)‐COOH. While the C terminus of SP is critical for NK₁R activation, studies have shown that the peptide polycationic N terminus is key for MRGPRX2 and mast cell activation. The study thus aimed to determine if the C‐terminally truncated metabolites of SP, SP(1–9)‐COOH, and SP(1–7)‐COOH retained stimulatory activity at MRGPRX2. SP, SP(1–9)‐COOH, and SP(1–7)‐COOH were synthesized and tested on HEK293 cells expressing NK₁R or MRGPRX2, and LAD2 human mast cells, to determine the activity of SP and its metabolites in Ca²⁺ mobilization, degranulation, and cytokine assays. As expected from prior studies, both C‐terminally truncated SP metabolites had essentially no activity at NK₁R, even at very high concentrations. In contrast, the in vivo metabolite of SP, SP(1–9)‐COOH retained ability to activate MRGPRX2 across all parameters tested, albeit with reduced potency compared to intact SP. SP(1–7)‐COOH did not produce any significant MRGRPX2 activation. Our results suggest that the SP metabolite, SP(1–9)‐COOH, may play a regulatory role through the activation of MRGPRX2. However, given the relatively low potency of both SP and SP(1–9)‐COOH at MRGPRX2, additional work is needed to better understand the biological importance of this expanded SP/MRGPRX2 pathway.

The Impact of Post-Tear Collection Storage on Tear Film Substance P Concentration

PURPOSE

Substance P is a sensory neuropeptide increasingly used as a biomarker for ocular and systemic neuropathic conditions. Due to the limited studies on tear storage conditions compared to other bodily fluids including blood and urine, the aim of this study was to investigate whether different storage durations at 4 °C can impact on substance P concentrations prior to storage at -80 °C. This is important to assess potential practical limitations in the handling and storage of tear fluid essential.

METHODS

Tears were collected and pooled from both eyes of 31 healthy participants using the flush tears method. The samples were centrifuged and aliquoted into three sets of microcentrifuge tubes with each stored at 4 °C for <2 h, 4 h or 6 h (Timepoints 1, 2 or 3). After each respective storage duration, the aliquoted samples were than stored at -80 °C before analysis, within 6 months. Tears were analyzed for the concentration of substance P and the total protein content (TPC).

RESULTS

Substance P concentrations across the three timepoints were not significantly different (p > 0.05), including Timepoint 1 (Median [interquartile range]: 10.7 ng/ml [1.6-37.9]), Timepoint 2 (10.9 ng/ml [1.6-32.6]) and Timepoint 3 (5.2 ng/ml [1.3-25.2]). There were also no significant differences in TPC concentrations measured at the three timepoints, including Timepoint 1 (3.1 mg/ml [1.7-3.8]), Timepoint 2 (2.9 mg/ml [1.9-4.1]) and Timepoint 3 (2.7 mg/ml [1.6-3.7]).

CONCLUSIONS

While the levels of substance P were stable while stored at 4 °C prior to proper -80 °C storage and analysis, future research should investigate the impact of other storage conditions such as ambient room temperature to optimize the feasibility of using tears for biomarker purposes in clinical settings.

Neuron‒Mast Cell Cross-Talk in the Skin

Skin-resident mast cells (MCs) and cutaneous sensory neurons both play crucial roles in microbial‒host defense and inflammatory diseases. MCs can be directly activated by pathogens or their products, resulting in the release of numerous mediators that promote innate immune responses and also activate sensory neurons. Cutaneous sensory neurons can also directly detect the presence of pathogens, resulting in the release of neuropeptides that modulate MC function. In this review, we will focus on the reciprocal interactions between cutaneous sensory neurons and MCs and the importance of this cross-talk in skin diseases.

Substance P Serum Degradation in Complex Regional Pain Syndrome - Another Piece of the Puzzle?

In a previous study, we demonstrated that the serum peptidase system might be less efficient in complex regional pain syndrome (CRPS). Since the neuropeptide substanc P (SP) contributes to inflammation in CRPS, we now investigated the metabolism of SP in CRPS specifically. An SP metabolism assay was performed in 24 CRPS patients, which constitute a subgroup of our previous investigation on BK degradation. In addition, we included 26 healthy controls (24 newly recruited plus 2 from our previous investigation), and 13 patients after limb trauma, who did not fulfil the CRPS diagnostic criteria (trauma controls, TC) were included. We adapted a thin layer chromatography assay (TLC) to quantify SP disappearance after incubation with 7.5 µL of serum. These results were compared with bradykinin (BK) metabolization to BK1-8 and BK1-5 fragments from our previous study. In addition, TC were clinically and quantitative sensory testing (QST) phenotyped; the phenotyping of CRPS patients was retrieved from our existing database. SP metabolism was less efficient in CRPS and TC patient serum vs human control (HC) serum (P < .03) suggesting reduced activity of the neutral endopeptidase (NEP) and/or the angiotensin converting enzyme (ACE). Together with the decreased occurrence of BK1-5 fragment in CRPS and TC, this suggests a reduced activation of the angiotensin converting enzyme (ACE). There was no clear clinical phenotype related to impaired SP degradation; duration of disease and gender were also not associated. Most importantly, results in TC did not differ from CRPS. Collectively, our current and previous experimental results suggest that limb trauma reduces serum peptidase metabolism of SP ex vivo, specifically serum ACE activity. However, this finding is not CRPS-specific and seems to be rather a long-term consequence of the trauma itself. PERSPECTIVE: The experimental data from this study further support the hypothesis that impaired metabolism of inflammatory peptides potentially contribute to the development of posttraumatic pain in CRPS or limb trauma patients.

Inhibitors of neuropeptide peptidases engaged in pain and drug dependence

Owing to a broad spectrum of functions performed by neuropeptides, this class of signaling molecules attracts an increasing interest. One of the key steps in the regulation of biological activity of neuropeptides is proteolytic conversion or degradation by proteinases that change or terminate biological activity of native peptides. These enzymes, in turn, are regulated by inhibitors, which play integral role in controlling many metabolic pathways. Thus, the search for selective inhibitors and detailed knowledge on the mechanisms of binding of these substances to enzymes, could be of importance for designing new pharmacological approaches. The aim of this review is to summarize the current knowledge on the inhibitors of enzymes that convert selected groups of neuropeptides, such as dynorphins, enkephalins, substance P and NPFF fragments. The importance of these substances in pathophysiological processes involved in pain and drug addiction, have been discussed. This article is part of the special issue on Neuropeptides.

Measuring behavioral and physiological responses to pain mitigation for ovariectomy in Bos taurus yearling beef heifers

Ovariectomy (spaying) using the trans-vaginal dropped ovary technique (DOT) is performed to prevent pregnancy in cull female beef cattle that are not retained for breeding stock in areas practicing extensive grazing management. There are no reports describing analgesia for this surgical procedure. The objective of this study was to measure behavioral and physiological responses to determine whether an analgesic protocol of BXK [butorphanol (0.01 mg/kg), xylazine (0.02 mg/kg), and ketamine (0.04 mg/kg)] injected intramuscularly (i.m.) before spaying could mitigate procedural and immediate postsurgical pain, and whether oral meloxicam (1 mg/kg) administered at the time of spaying could mitigate postsurgical inflammatory pain. Forty-four red Angus and Angus crossbred yearling heifers (322 ± 27.0 kg BW) were randomly allocated to 1 of 3 groups: PALP (control; palpated but not spayed; n = 14), SPAY (spayed with no analgesia; n = 15), and BXKM (spayed with analgesia; n = 15). Behavioral measurements included visual analog scale (VAS) score, flight speed (FS), stride length (SL), and gait score (GS), as well as activity (lying, standing) and feeding behavior. Physiological measurements included salivary cortisol (SC), haptoglobin (Hp), serum amyloid A (SAA), substance P (SP), complete blood count (CBC), and rectal temperature (RT). Saliva and blood samples were collected, and RT, FS, SL, and GS were measured on day -1, day 0 (time of palpation/spaying), and hours 1, 2, 4, and days 1, 2, 4, and 7 after palpation/spaying. The BXKM heifers had lower SC concentrations than SPAY heifers at 1 h (P = 0.01) and 2 h (P = 0.004). Heifers treated with BXKM had Hp concentrations lower than SPAY heifers at 2 d (P = 0.01), 4 d (P < 0.001), and 7 d (P = 0.008), and lower Hp concentrations than PALP heifers at 4 d (P < 0.001). Concentrations of SAA were greater (P = 0.04) in BXKM heifers than in PALP heifers at 1 h and lower in PALP heifers than in BXKM heifers (P = 0.02) and SPAY heifers (P = 0.05) at 1 d. Heifers in the BXKM group had higher RT than PALP and SPAY heifers at 1 h (P < 0.001) and 2 h (P = 0.004). Results suggest that DOT ovariectomy is acutely stressful and painful and administration of BXK before spaying and meloxicam at the time of spaying mitigated the procedural and postsurgical stress, pain, and inflammation.

Concentration-Dependent Effects of Fibroblast-Like Synoviocytes on Collagen Gel Multiscale Biomechanics and Neuronal Signaling: Implications for Modeling Human Ligamentous Tissues

Abnormal loading of a joint's ligamentous capsule causes pain by activating the capsule's nociceptive afferent fibers, which reside in the capsule's collagenous matrix alongside fibroblast-like synoviocytes (FLS) and transmit pain to the dorsal root ganglia (DRG). This study integrated FLS into a DRG-collagen gel model to better mimic the anatomy and physiology of human joint capsules; using this new model, the effect of FLS on multiscale biomechanics and cell physiology under load was investigated. Primary FLS cells were co-cultured with DRGs at low or high concentrations, to simulate variable anatomical FLS densities, and failed in tension. Given their roles in collagen degradation and nociception, matrix-metalloproteinase (MMP-1) and neuronal expression of the neurotransmitter substance P were probed after gel failure. The amount of FLS did not alter (p > 0.3) the gel failure force, displacement, or stiffness. FLS doubled regional strains at both low (p < 0.01) and high (p = 0.01) concentrations. For high FLS, the collagen network showed more reorganization at failure (p < 0.01). Although total MMP-1 and neuronal substance P were the same regardless of FLS concentration before loading, protein expression of both increased after failure, but only in low FLS gels (p ≤ 0.02). The concentration-dependent effect of FLS on microstructure and cellular responses implies that capsule regions with different FLS densities experience variable microenvironments. This study presents a novel DRG-FLS co-culture collagen gel system that provides a platform for investigating the complex biomechanics and physiology of human joint capsules, and is the first relating DRG and FLS interactions between each other and their surrounding collagen network.

Neuropeptides: important regulators of joint homeostasis

PURPOSE

This review explores the mechanisms of joint pain with a special focus on the role of neuropeptides in pain transmission and their potential role in the progression of joint degeneration as seen in osteoarthritis.

METHODS

A literature search was performed on papers published between January 1990 and September 2017 using the Web of Science Core Collection, MEDLINE and Scopus databases.

RESULTS

What is seen in the subchondral bone and synovia is mirrored in the central nervous system (CNS). Substance P, calcitonin gene-related peptide, vasoactive intestinal peptide and neuropeptide Y are the major peptides involved both in the generation of pain as well as reducing pain post-joint trauma. The interplay between them and other neuropeptides and cytokines influence how noxious stimuli are transduced, transmitted and modulated for a final pain perception as part of a complex cascade of events. There is a close interaction between the different components in the joint that together cross-talk to adapt to load and catabolic factors during injury and inflammation.

CONCLUSION

The articular joint should be seen as an organ where local joint pain development and maintenance is influenced by interplay between the local transmitters in the joints as well as their dependence on the CNS. A slow-release cocktail of mixed antibodies targeted against neuropeptides and receptor blockers/stimulators involved in the events of early joint pain or any inflammatory joint disease is a future treatment target.

LEVEL OF EVIDENCE

V.

A Chitosan-Based Liposome Formulation Enhances the In Vitro Wound Healing Efficacy of Substance P Neuropeptide

Currently, there is considerable interest in developing innovative biodegradable nanoformulations for controlled administration of therapeutic proteins and peptides. Substance P (SP) is a neuropeptide of 11 amino acids that belongs to the tachykinins family and it plays an important role in wound healing. However, SP is easily degradable in vivo and has a very short half-life, so the use of chitosan-based nanocarriers could enhance its pharmaceutical properties. In light of the above, the aim of this work was to produce and characterize chitosan-coated liposomes loaded with SP (SP-CH-LP) as novel biomaterials with potential application in mucosal wound healing. The loaded system’s biophysical properties were characterized by dynamic light scattering with non-invasive back scattering (DLS-NIBS), mixed mode measurements and phase analysis light scattering (M3-PALS) and high performance liquid chromatography with ultraviolet/visible light detection (HPLC-UV/VIS). Then, the efficacy of the obtained nanoformulations was examined via proof-of-principle experiments using in vitro cell assays. These assays showed an increment on cell motility and proliferation after treatment with free and encapsulated neuropeptides. Additionally, the effect of SP on wound healing was enhanced by the entrapment on CH-LP. Overall, the amenability of chitosan-based nanomaterials to encapsulate peptides and proteins constitutes a promising approach towards potential novel therapies to treat difficult wounds.

Characterization of Substance P processing in mouse spinal cord S9 fractions using high-resolution Quadrupole-Orbitrap mass spectrometry

Tachykinins are a family of pronociceptive neuropeptides with a specific role in pain and inflammation. Several mechanisms regulate endogenous tachykinins and Substance P (SP) levels, including the differential expression of protachykinin mRNA and the controlled secretion of tachykinins from neurons. Proteolysis is suspected to regulate extracellular SP concentrations but few studies were conducted on the metabolism of proneuropeptides and neuropeptides. Here, we provide evidence that proteolysis controls SP levels in the spinal cord leading to the formation of active C-terminal fragments. Using high-resolution mass spectrometry, specific tachykinins fragments were characterized and quantified. The metabolic stability of β-Tachykinin_58-71 and SP were very short resulting in half-life of 5.7 and 3.5min respectively. Several C-terminal fragments were identified, including SP_3-11, SP_5-11 and SP_8-11, which conserve affinity for the Neurokinin 1 receptor. Interestingly, the metabolic stability of C-terminal fragments was significantly superior. Two specific Prolyl endopeptidase inhibitors were used and showed a significant reduction in the rate of formation of SP_3-11 and SP_5-11 providing strong evidence that Prolyl endopeptidase is involved into N-terminal processing of SP in the spinal cord.

The angiotensin converting enzyme inhibitor, captopril, prevents the hyperactivity and impulsivity of neurokinin-1 receptor gene 'knockout' mice: sex differences and implications for the treatment of attention deficit hyperactivity disorder

Mice lacking functional neurokinin-1 receptors (NK1R-/-) display behavioural abnormalities resembling attention deficit hyperactivity disorder (ADHD): locomotor hyperactivity, impulsivity and inattentiveness. The preferred ligand for NK1R, substance P, is metabolised by angiotensin converting enzyme (ACE), which forms part of the brain renin angiotensin system (BRAS). In view of evidence that the BRAS modulates locomotor activity and cognitive performance, we tested the effects of drugs that target the BRAS on these behaviours in NK1R-/- and wildtype mice. We first tested the effects of the ACE inhibitor, captopril, on locomotor activity. Because there are well-established sex differences in both ADHD and ACE activity, we compared the effects of captopril in both male and female mice. Locomotor hyperactivity was evident in male NK1R-/- mice, only, and this was abolished by treatment with captopril. By contrast, male wildtypes and females of both genotypes were unaffected by ACE inhibition. We then investigated the effects of angiotensin AT1 (losartan) and AT2 (PD 123319) receptor antagonists on the locomotor activity of male NK1R-/- and wildtype mice. Both antagonists increased the locomotor activity of NK1R-/- mice, but neither affected the wildtypes. Finally, we tested the effects of captopril on the performance of male NK1R-/- and wildtype mice in the 5-choice serial reaction-time task (5-CSRTT) and found that ACE inhibition prevented the impulsivity of NK1R-/- mice. These results indicate that certain behaviours, disrupted in ADHD, are influenced by an interaction between the BRAS and NK1R, and suggest that ACE inhibitors could provide a novel treatment for this disorder.

Specificity studies on Kallikrein-related peptidase 7 (KLK7) and effects of osmolytes and glycosaminoglycans on its peptidase activity

KLK7 substrate specificity was evaluated by families of fluorescence resonance energy transfer (FRET) peptides derived from Abz-KLFSSK-Q-EDDnp (Abz=ortho-aminobenzoic acid and Q-EDDnp=glutaminyl-N-[2,4-dinitrophenyl] ethylenediamine), by one bead-one peptide FRET peptide library in PEGA resin, and by the FRET peptide libraries Abz-GXX-Z-XX-Q-EDDnp (Z and X are fixed and random natural amino acids, respectively). KLK7 hydrolyzed preferentially F, Y or M, and its S1' and S2' subsites showed selectivity for hydrophilic amino acids, particularly R and K. This set of specificities was confirmed by the efficient kininogenase activity of KLK7 on Abz-MISLM(↓)KRPPGFSPF(↓)RSSRI-NH2 ((↓)indicates cleavage), hydrolysis of somatostatin and substance P and inhibition by kallistatin. The peptide Abz-NLY(↓)RVE-Q-EDDnp is the best synthetic substrate so far described for KLK7 [kcat/Km=455 (mMs)(-1)] that was designed from the KLK7 substrate specificity analysis. It is noteworthy that the NLYRVE sequence is present in human semaphorin 6B. KLK7 is activated by GAGs, inhibited by neutral salts, and activated by high concentration of kosmotropic salt. Pyroglutamic acid inhibited KLK7 (Ki=33mM) and is present in skin moisturizing factor (124mM). The KLK7 specificity described here and elsewhere reflects its participation in patho-physiological events in skin, the gastrointestinal tract and central nervous system, where KLK7 is significantly expressed.

Increasing substance P levels in serum and synovial tissues from patients with developmental dysplasia of the hip (DDH)

BACKGROUND

The tachykininergic neurotransmitters have been proved to be involved in the inflammatory progress and chronic pain in series of disease. The present study was undertaken to evaluate the levels of substance P (SP) and its receptors NK-1 receptor (NK-1R) in both serum and synovial tissues of hip joint from patients with different stages of DDH, and to detect the possible correlation of serum SP levels with pain sensation and dysfunction of the hip joint.

METHODS

SP levels in serum and synovial tissues from patients with DDH and DDH combined with osteoarthritis (DDH&OA) group were compared through immunohistochemistry (IHC), ELISA, and 2-step acetic acid extraction method respectively. Expression of NK-1R in synovial tissues was compared through IHC, quantitive Real-Time PCR (QRT-PCR) and Western-Blot. The severities of pain sensation and the functional activities of hip joint were assessed by Visual analogue scale (VAS) and Harris hip score (HHS). Correlations of serum SP levels with VAS, HHS and erythrocyte sedimentation rate (ESR) were evaluated respectively in these groups.

RESULTS

Significantly elevated serum SP levels were detected in group of DDH and DDH&OA compared to that in normal group. IHC, QRT-PCR as well as tissue Elisa showed that SP levels in synovial tissue of DDH&OA group is stronger than that in DDH group. Serum SP levels in each group have no gender differences. The enhanced SP levels in synovial tissue mainly came from the segregation of peripheral nerve endings. Serum SP correlated with VAS and HHS in patients with DDH&OA (Male + Female). Serum SP correlated with HHS in patients with DDH (Male). Serum SP levels also correlated with erythrocyte sedimentation rate (ESR) in patients with DDH&OA (Male + Female). Up-regulated expression of NK-1R was also observed in synovial tissue of patients with DDH&OA compared to patients with DDH, through western-blot, IHC, and QRT-PCR.

CONCLUSIONS

These findings indicated that the increasing SP levels in serum and synovial tissues, observed from patients with DDH to patients with DDH&OA, might associate with the loss of function and chronic pain sensation in hip joint. SP along with its receptors NK-1R might be involved in the progression of DDH into DDH&OA. In the future, inhibitors of SP as well as NK-1R may represent a novel pharmacotherapy target for pain relieving, inflammation alleviating and joint degeneration delaying for patients with DDH.