The impact of substance P signalling on the development of experimental staphylococcal sepsis and arthritis

Inflammation and Organ Injury the Role of Substance P and Its Receptors

Tightly controlled inflammation is an indispensable mechanism in the maintenance of cellular and organismal homeostasis in living organisms. However, aberrant inflammation is detrimental and has been suggested as a key contributor to organ injury with different etiologies. Substance P (SP) is a neuropeptide with a robust effect on inflammation. The proinflammatory effects of SP are achieved by activating its functional receptors, namely the neurokinin 1 receptor (NK1R) receptor and mas-related G protein-coupled receptors X member 2 (MRGPRX2) and its murine homolog MRGPRB2. Upon activation, the receptors further signal to several cellular signaling pathways involved in the onset, development, and progression of inflammation. Therefore, excessive SP-NK1R or SP-MRGPRX2/B2 signals have been implicated in the pathogenesis of inflammation-associated organ injury. In this review, we summarize our current knowledge of SP and its receptors and the emerging roles of the SP-NK1R system and the SP-MRGPRX2/B2 system in inflammation and injury in multiple organs resulting from different pathologies. We also briefly discuss the prospect of developing a therapeutic strategy for inflammatory organ injury by disrupting the proinflammatory actions of SP via pharmacological intervention.

Neurokinin-1 Receptor Deficiency Improves Survival in Murine Polymicrobial Sepsis Through Multiple Mechanisms in Aged Mice

OBJECTIVE

Substance P (SP) is a neuropeptide that contributes to a proinflammatory state by binding to the neurokinin 1 receptor (NK-1R). Limiting this interaction has been shown to attenuate the acute inflammation. Our hypothesis was that NK-1R activation would contribute to the morbidity and mortality of sepsis in a model using mice genetically deficient in the NK-1R.

METHODS

To investigate the role of the SP/NK-1R axis in a murine model of sepsis, cecal ligation and puncture (CLP) in NK-1R deficient and wild type (WT) aged mice was performed. Acute inflammation was assessed by measuring circulating cytokines and clinical parameters.

RESULTS

Deletion of the NK-1R results in improved survival following CLP (NK-1R knockout mice survival = 100% vs. WT = 14%). A reduction in the inflammatory cytokines interleukin (IL) 6, macrophage inflammatory peptide 2, and IL-1 receptor antagonist, improved hemodynamic parameters, and increased neutrophilia were present in the NK-1R-deficient mice after CLP compared with WT mice.

CONCLUSIONS

These data confirm the hypothesis that eliminating the SP/NK-1R interaction in a highly lethal murine model of sepsis leads to decreased morbidity and mortality through multiple mechanisms.

The Diverse Functional Roles of Elongation Factor Tu (EF-Tu) in Microbial Pathogenesis

Elongation factor thermal unstable Tu (EF-Tu) is a G protein that catalyzes the binding of aminoacyl-tRNA to the A-site of the ribosome inside living cells. Structural and biochemical studies have described the complex interactions needed to effect canonical function. However, EF-Tu has evolved the capacity to execute diverse functions on the extracellular surface of both eukaryote and prokaryote cells. EF-Tu can traffic to, and is retained on, cell surfaces where can interact with membrane receptors and with extracellular matrix on the surface of plant and animal cells. Our structural studies indicate that short linear motifs (SLiMs) in surface exposed, non-conserved regions of the molecule may play a key role in the moonlighting functions ascribed to this ancient, highly abundant protein. Here we explore the diverse moonlighting functions relating to pathogenesis of EF-Tu in bacteria and examine putative SLiMs on surface-exposed regions of the molecule.

Sustained Low Serum Substance P Levels in Non-Surviving Septic Patients

Previously, researchers found higher serum substance P (SP) concentrations in survivors of severe sepsis than in non-survivors at the time of severe sepsis diagnosis. The objectives of our current study were to determine whether there is an association between serum SP levels during the first week and sepsis mortality, sepsis severity, serum levels of tumor necrosis factor (TNF)-α and interleukin (IL)-10, and whether serum SP levels during the first week could be used as a biomarker of sepsis mortality. We determined serum concentration of SP, TNF-α, and IL-10 at days 1, 4, and 8. The end-point of the study was mortality at 30 days. We found that non-survivor (n = 104) compared to survivor patients (n = 206) showed lower serum SP levels at days 1, 4, and 8 (p < 0.001). Multiple logistic regression analyses showed an association between 30-day mortality and serum SP levels at days 1, 4, and 8 (p < 0.001) controlling for SOFA score, diabetes mellitus, age, and lactic acid levels. The most interesting findings of our study were that there is an association between serum SP levels during the first week and sepsis mortality, and that serum SP levels during the first week could be used as a biomarker of sepsis mortality.

Antagonism of the Neurokinin-1 Receptor Improves Survival in a Mouse Model of Sepsis by Decreasing Inflammation and Increasing Early Cardiovascular Function

OBJECTIVES

Sepsis remains a serious clinical problem despite intensive research efforts and numerous attempts to improve outcome by modifying the inflammatory response. Substance P, the principal ligand for the neurokinin-1 receptor, is a potent proinflammatory mediator that exacerbates inflammatory responses and cardiovascular variables in sepsis.

DESIGN

The current study examined whether inhibition of the neurokinin-1 receptor with a specific antagonist (CJ-12,255) would improve survival in the cecal ligation and puncture model of sepsis in adult female outbred mice.

SETTING

University basic science research laboratory.

MEASUREMENTS AND MAIN RESULTS

Neurokinin-1 receptor treatment at the initiation of sepsis improved survival in cecal ligation and puncture sepsis (neurokinin-1 receptor antagonist survival = 79% vs vehicle = 54%). Delaying therapy for as little as 8 hours postcecal ligation and puncture failed to provide a survival benefit. Neurokinin-1 receptor antagonist treatment did not prevent the sepsis-induced decrease in circulating WBCs, augment the early (6 hr postcecal ligation and puncture) recruitment of inflammatory cells to the peritoneum, or improve phagocytic cell killing of pathogens. However, the neurokinin-1 receptor antagonist significantly reduced both circulating and peritoneal cytokine concentrations. In addition, the cardiovascular variable, pulse distension (a surrogate for stroke volume) was improved in the neurokinin-1 receptor antagonist group during the first 6 hours of sepsis, and there was a significant reduction in loss of fluid into the intestine.

CONCLUSION

These data show that early activation of the neurokinin-1 receptor by substance P decreases sepsis survival through multiple mechanisms including depressing stroke volume, increasing fluid loss into the intestine, and increasing inflammatory cytokine production.

Serum Levels of Substance P and Mortality in Patients with a Severe Acute Ischemic Stroke

Substance P (SP), a member of tachykinin family, is involved in the inflammation of the central nervous system and in the appearance of cerebral edema. Higher serum levels of SP have been found in 18 patients with cerebral ischemia compared with healthy controls. The aim of our multi-center study was to analyze the possible association between serum levels of SP and mortality in ischemic stroke patients. We included patients with malignant middle cerebral artery infarction (MMCAI) and a Glasgow Coma Scale (GCS) lower than 9. Non-surviving patients at 30 days (n = 31) had higher serum concentrations of SP levels at diagnosis of severe MMCAI than survivors (n = 30) (p < 0.001). We found in multiple regression an association between serum concentrations of SP higher than 362 pg/mL and mortality at 30 days (Odds Ratio = 5.33; 95% confidence interval = 1.541-18.470; p = 0.008) after controlling for age and GCS. Thus, the major novel finding of our study was the association between serum levels of SP and mortality in patients suffering from severe acute ischemic stroke.

Serum Levels of Substance P and Mortality in Patients with a Severe Acute Ischemic Stroke

Substance P (SP), a member of tachykinin family, is involved in the inflammation of the central nervous system and in the appearance of cerebral edema. Higher serum levels of SP have been found in 18 patients with cerebral ischemia compared with healthy controls. The aim of our multi-center study was to analyze the possible association between serum levels of SP and mortality in ischemic stroke patients. We included patients with malignant middle cerebral artery infarction (MMCAI) and a Glasgow Coma Scale (GCS) lower than 9. Non-surviving patients at 30 days (n = 31) had higher serum concentrations of SP levels at diagnosis of severe MMCAI than survivors (n = 30) (p < 0.001). We found in multiple regression an association between serum concentrations of SP higher than 362 pg/mL and mortality at 30 days (Odds Ratio = 5.33; 95% confidence interval = 1.541-18.470; p = 0.008) after controlling for age and GCS. Thus, the major novel finding of our study was the association between serum levels of SP and mortality in patients suffering from severe acute ischemic stroke.

Mapping genetic determinants of host susceptibility to Pseudomonas aeruginosa lung infection in mice

Background

P. aeruginosa is one of the top three causes of opportunistic human bacterial infections. The remarkable variability in the clinical outcomes of this infection is thought to be associated with genetic predisposition. However, the genes underlying host susceptibility to P. aeruginosa infection are still largely unknown.

Results

As a step towards mapping these genes, we applied a genome wide linkage analysis approach to a mouse model. A large F2 intercross population, obtained by mating P. aeruginosa-resistant C3H/HeOuJ, and susceptible A/J mice, was used for quantitative trait locus (QTL) mapping. The F2 progenies were challenged with a P. aeruginosa clinical strain and monitored for the survival time up to 7 days post-infection, as a disease phenotype associated trait. Selected phenotypic extremes of the F2 distribution were genotyped with high-density single nucleotide polymorphic (SNP) markers, and subsequently QTL analysis was performed. A significant locus was mapped on chromosome 6 and was named P. aeruginosa infection resistance locus 1 (Pairl1). The most promising candidate genes, including Dok1, Tacr1, Cd207, Clec4f, Gp9, Gata2, Foxp1, are related to pathogen sensing, neutrophils and macrophages recruitment and inflammatory processes.

Conclusions

We propose a set of genes involved in the pathogenesis of P. aeruginosa infection that may be explored to complement human studies.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2676-4) contains supplementary material, which is available to authorized users.

Association between serum substance P levels and mortality in patients with severe sepsis

BACKGROUND

Substance P (SP) is a peptide of the tachykinins family involved in the inflammatory response. Circulating SP levels have been assessed in septic patients in 2 previous studies with a small number of subjects (61 and 42 patients, respectively), and there were no significant differences in SP levels at the moment of sepsis diagnosis between surviving and nonsurviving patients. The main goal of this study was to determine a possible relationship between serum SP levels and patient outcome in the largest cohort of severe septic patients analyzed so far.

METHODS

We performed an observational, prospective, multicenter study in 6 Spanish intensive care units. Serum SP levels were measured at the moment of severe sepsis diagnosis in 238 patients. The end point of the study was 30-day mortality.

RESULTS

We found that surviving septic patients (n = 153) showed higher serum SP levels than did nonsurvivors (n = 85). Multiple logistic regression analysis showed that serum SP levels higher than 350 pg/mL were associated with survival at 30 days (odds ratio, 0.43; 95% confidence interval, 0.24-0.77; P = .005) after controlling for serum lactic acid levels and Sepsis-related Organ Failure Assessment score.

CONCLUSIONS

The major new finding of our study was that serum SP levels were associated with mortality in severe septic patients.

Altered serum stress neuropeptide levels in critically ill individuals and associations with lymphocyte populations

OBJECTIVE

Potential physiological correlates of stress and the role of stress neuropeptides, other than those of the hypothalamic-pituitary-adrenal axis, in critical illness have not been addressed. We investigated: (a) serum levels of stress neuropeptides (ACTH, substance P (SP), neuropeptide Y (NPY), cortisol, prolactin) in critically ill individuals compared to matched controls, (b) associations with lymphocyte counts, (c) associations among stress neuropeptide levels, and (d) associations with perceived intensity of stress, critical illness severity and survival.

METHODS

Correlational design with repeated measures. Thirty-six critically ill patients were followed up for 14 days compared to 36 healthy matched controls. Stress was assessed by the ICUESS scale. Correlations, cross-sectional comparisons and multiple regression models were pursued.

RESULTS

For the first time, we report lower SP (Difference of means (DM) = 2928-3286 ng/ml, p < 0.001) and NPY (DM = 0.77-0.83 ng/ml, p < 0.0001) levels in critically ill individuals compared to controls. Cortisol levels were higher (DM = 140-173 ng/ml, p<0.0001) and lymphocyte population counts (p < 0.002) were lower in patients throughout the study. NPY levels associated with lymphocyte (r = 0.411-0.664, p < 0.04), T-lymphocyte (r = 0.403-0.781, p< 0.05), T-helper (r = 0.492-0.690, p < 0.03) and T-cytotoxic cell populations (r = 0.39-0.740, p < 0.03). On day 1, cortisol levels exhibited associations with lymphocyte (r = -0.452, p = 0.01), T-cell (r = -0.446, p = 0.02), T-helper (r = -0.428, p = 0.026) and T-cytotoxic cells ( r = -0.426, p = 0.027). ACTH levels associated with NK cell counts (r = 0.326-0.441, p < 0.05). Associations among stress neuropeptides levels were observed throughout (p < 0.05). ACTH levels associated with disease severity (r = 0.340-0.387, p < 0.005). A trend for an association between ACTH levels and intensity of stress was noted (r = 0.340, p = 0.057).

CONCLUSION

The significantly lowered NPY and SP levels and the associations with cortisol, ACTH and lymphocytes suggest that the role of these peptides in critical illness merit further investigation. Future studies need to address associations between these neuropeptides and functional immune cell responses and inflammatory markers in critical illness.

Neurokinin-1 receptor antagonists for chemotherapy-induced nausea and vomiting: a systematic review

BACKGROUND

The addition of neurokinin-1 receptor (NK1R) antagonists to antiemetic regimens has substantially reduced chemotherapy-induced nausea and vomiting (CINV). We sought to systematically review the overall impact of NK1R antagonists on CINV prevention.

METHODS

We systematically searched the MEDLINE, EMBASE, and CENTRAL databases, and meeting proceedings for randomized controlled trials (RCTs) that evaluated NK1R antagonists plus standard antiemetic therapy for CINV prevention. Complete response (CR) to therapy was defined as the absence of emesis and the absence of rescue therapy. The endpoints were defined as CR in the overall phase (during the first 120 hours of chemotherapy), CR in the acute phase (first 24 hours), and the delayed phase (24-120 hours) after chemotherapy, nausea, and toxicity. Subgroup analyses evaluated the type of NK1R antagonist used, the emetogenic potential of the chemotherapy regimen, and prolonged use of 5-HT3 (serotonin) receptor antagonists, a class of standard antiemetic agents. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using a random-effects model. Statistical tests for heterogeneity were one-sided; statistical tests for effect estimates and publication bias were two-sided.

RESULTS

Seventeen trials (8740 patients) were included in this analysis. NK1R antagonists increased the CR rate in the overall phase from 54% to 72% (OR = 0.51, 95% CI = 0.46 to 0.57, P < .001). CR and nausea were improved in all phases and subgroups. The expected side effects from NK1R antagonists did not statistically significantly differ from previous reports; however, this analysis suggests that the incidence of severe infection increased from 2% to 6% in the NK1R antagonist group (three RCTs with a total of 1480 patients; OR = 3.10; 95% CI = 1.69 to 5.67, P < .001).

CONCLUSIONS

NK1R antagonists increased CINV control in the acute, delayed, and overall phases. They are effective for both moderately and highly emetogenic chemotherapy regimens. Their use might be associated with increased infection rates; however, additional appraisal of specific data from RCTs is needed.

S100A4 deficiency is associated with efficient bacterial clearance and protects against joint destruction during Staphylococcal infection

BACKGROUND

Efficient host defense mechanisms are crucial for survival in sepsis and septic arthritis. S100 proteins are reported to have proinflammatory and bactericidal properties. The aim of this study was to investigate the role of S100A4 in staphylococcal arthritis.

METHODS

S100A4 knockout mice (S100A4KO) and wild-type counterparts (WT) were intravenously and intra-articularly challenged with Staphylococcus aureus strain LS-1. Clinical and morphological signs of arthritis and sepsis, phagocytosis, bone mineral density (BMD), and bone metabolism were then monitored in S100A4 and WT mice.

RESULTS

S100A4KO mice had a lower bacterial load in the kidneys than WT mice (P < .05) but developed more severe clinical signs of arthritis (P < .001) and had higher levels of interleukin 6 and L-selectin (P = .002). S100A4KO mice had fewer morphological signs of synovitis and cartilage/bone destruction following intra-articular instillation of bacteria. S100A4KO mice were protected from loss of BMD and had lower levels of RANKL, MMP3, and MMP9 (P < .05). S100A4 was not bactericidal in vitro.

CONCLUSIONS

In staphylococcal infection, S100A4 regulates bacterial clearance as well as systemic and local inflammatory responses.

Geranylgeranyltransferase type I (GGTase-I) deficiency hyperactivates macrophages and induces erosive arthritis in mice

RHO family proteins are important for the function of inflammatory cells. They are modified with a 20-carbon geranylgeranyl lipid in a process catalyzed by protein geranylgeranyltransferase type I (GGTase-I). Geranylgeranylation is viewed as essential for the membrane targeting and activity of RHO proteins. Consequently, inhibiting GGTase-I to interfere with RHO protein activity has been proposed as a strategy to treat inflammatory disorders. However, here we show that mice lacking GGTase-I in macrophages develop severe joint inflammation resembling erosive rheumatoid arthritis. The disease was initiated by the GGTase-I-deficient macrophages and was transplantable and reversible in bone marrow transplantation experiments. The cells accumulated high levels of active GTP-bound RAC1, CDC42, and RHOA, and RAC1 remained associated with the plasma membrane. Moreover, GGTase-I deficiency activated p38 and NF-κB and increased the production of proinflammatory cytokines. The results challenge the view that geranylgeranylation is essential for the activity and localization of RHO family proteins and suggest that reduced geranylgeranylation in macrophages can initiate erosive arthritis.

TGF-beta regulates T-cell neurokinin-1 receptor internalization and function

Substance P (SP) is a proinflammatory mediator implicated in inflammatory bowel disease (IBD) and other inflammatory states. SP acts by stimulating the neurokinin-1 receptor (NK-1R) on T lymphocytes and other cell types, and regulates these cells in a complex interplay with multiple cytokines. The mechanisms of interaction among these inflammatory mediators are not yet fully understood. Here, we demonstrate that function of the NK-1R, a member of the G protein-coupled receptor (GPCR) superfamily, is modulated by TGF-beta. The latter acts not on a GPCR but via serine-threonine kinase-class receptors. By flow confocal image analysis, we demonstrate that TGF-beta delays SP-induced NK-1R internalization on mucosal T cells isolated from a mouse model of IBD and on granuloma T cells in murine schistosomiasis. Furthermore, luciferase reporter-gene assays revealed that NK-1R stimulation activates the nuclear factor of activated T cell- and activator protein-1-dependent signaling pathways, which are known triggers of effector T-cell cytokine production. TGF-beta markedly increases SP-induced activation of these signaling cascades, suggesting that delayed NK-1R internalization results in enhanced signaling. Providing a link to amplified immune function, SP and TGF-beta, when applied in combination, trigger a strong release of the proinflammatory cytokines IFN-gamma and IL17 from intestinal inflammatory T cells, whereas either agonist alone shows no effect. These observations establish precedent that members of two distinct receptor superfamilies can interact via a previously unrecognized mechanism, and reveal a paradigm of GPCR transregulation that is relevant to IBD and possibly other disease processes.

The paradoxical role of the transient receptor potential vanilloid 1 receptor in inflammation

The transient potential receptor vanilloid 1 (TRPV1) receptor is a non-selective cation channel that is chemically activated by capsaicin, the pungent component of hot peppers. In addition, endogenous compounds, in particular the endogenous cannabinoid receptor activator, anandamide, have been demonstrated to activate TRPV1 in vivo. TRPV1 receptors are also activated by temperatures within the noxious range (>43 degrees C) and low pH (<pH 6.0). TRPV1 receptors are predominantly expressed in primary afferent fibres which are peptidergic sensory neurones, such as the thinly myelinated A-delta and unmyelinated C-fibres. TRPV1 receptors have also been demonstrated to be present in non-neuronal cells. Historically, TRPV1 has been considered as a pro-inflammatory receptor due to its key role in several conditions, including neuropathic pain, joint inflammation and inflammatory bowel disease, amongst others. However, the purpose of this review is to underline the emerging new evidence which demonstrate paradoxical, protective functions for this unique receptor in vivo. For example, in experimentally induced sepsis, TRPV1 null mice demonstrated elevated levels of pathological markers in comparison to wild-type mice. In addition to the pro-inflammatory and protective roles of TRPV1 in pathophysiological states, TRPV1 has also been shown to have important functions under normal physiological conditions, for example in urinary bladder function, thermoregulation and neurogenesis. The emerging functions of TRPV1 highlight the necessity for further research in light of increasing reports of potential TRPV1 antagonists undergoing pre-clinical experimentations.