Tachykinin Neuropeptide Research Articles

Brn3b regulates the formation of fear-related midbrain circuits and defensive responses to visual threat.

Defensive responses to visually threatening stimuli represent an essential fear-related survival instinct, widely detected across species. The neural circuitry mediating visually triggered defensive responses has been delineated in the midbrain. However, the molecular mechanisms regulating the development and function of these circuits remain unresolved. Here, we show that midbrain-specific deletion of the transcription factor Brn3b causes a loss of neurons projecting to the lateral posterior nucleus of the thalamus. Brn3b deletion also down-regulates the expression of the neuropeptide tachykinin 2 (Tac2). Furthermore, Brn3b mutant mice display impaired defensive freezing responses to visual threat precipitated by social isolation. This behavioral phenotype could be ameliorated by overexpressing Tac2, suggesting that Tac2 acts downstream of Brn3b in regulating defensive responses to threat. Together, our experiments identify specific genetic components critical for the functional organization of midbrain fear-related visual circuits. Similar mechanisms may contribute to the development and function of additional long-range brain circuits underlying fear-associated behavior.

Threat gates visual aversion via theta activity in Tachykinergic neurons

Animals must adapt sensory responses to an ever-changing environment for survival. Such sensory modulation is especially critical in a threatening situation, in which animals often promote aversive responses to, among others, visual stimuli. Recently, threatened Drosophila has been shown to exhibit a defensive internal state. Whether and how threatened Drosophila promotes visual aversion, however, remains elusive. Here we report that mechanical threats to Drosophila transiently gate aversion from an otherwise neutral visual object. We further identified the neuropeptide tachykinin, and a single cluster of neurons expressing it (“Tk-GAL42 ∩ Vglut neurons”), that are responsible for gating visual aversion. Calcium imaging analysis revealed that mechanical threats are encoded in Tk-GAL42 ∩ Vglut neurons as elevated activity. Remarkably, we also discovered that a visual object is encoded in Tk-GAL42 ∩ Vglut neurons as θ oscillation, which is causally linked to visual aversion. Our data reveal how a single cluster of neurons adapt organismal sensory response to a threatening situation through a neuropeptide and a combination of rate/temporal coding schemes.

Tachykinin Neuropeptides and Amyloid β (25-35) Assembly: Friend or Foe?

Amyloid β (Aβ) protein is responsible for Alzheimer's disease, and one of its important fragments, Aβ(25-35), is found in the brain and has been shown to be neurotoxic. Tachykinin neuropeptides, including Neuromedin K (NK), Kassinin, and Substance P, have been reported to reduce Aβ(25-35)'s toxicity in cells even though they share similar primary structures with Aβ(25-35). Here, we seek to understand the molecular mechanisms of how these peptides interact with Aβ(25-35) and to shed light on why some peptides with similar primary structures are toxic and others nontoxic. We use both experimental and computational methods, including ion mobility mass spectrometry and enhanced-sampling replica-exchange molecular dynamics simulations, to study the aggregation pathways of Aβ(25-35), NK, Kassinin, Substance P, and mixtures of the latter three with Aβ(25-35). NK and Substance P were observed to remove the higher-order oligomers (i.e., hexamers and dodecamers) of Aβ(25-35), which are related to its toxicity, although Substance P did so more slowly. In contrast, Kassinin was found to promote the formation of these higher-order oligomers. This result conflicts with what is expected and is elaborated on in the text. We also observe that even though they have significant structural homology with Aβ(25-35), NK, Kassinin, and Substance P do not form hexamers with a β-sheet structure like Aβ(25-35). The hexamer structure of Aβ(25-35) has been identified as a cylindrin, and this structure has been strongly correlated to toxic species. The reasons why the three tachykinin peptides behave so differently when mixed with Aβ(25-35) are discussed.

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.

Nociception and hypersensitivity involve distinct neurons and molecular transducers in Drosophila

Acute nociception is essential for survival by warning organisms against potential dangers, whereas tissue injury results in a nociceptive hypersensitivity state that is closely associated with debilitating disease conditions, such as chronic pain. Transient receptor potential (Trp) ion channels expressed in nociceptors detect noxious thermal and chemical stimuli to initiate acute nociception. The existing hypersensitivity model suggests that under tissue injury and inflammation, the same Trp channels in nociceptors are sensitized through transcriptional and posttranslational modulation, leading to nociceptive hypersensitivity. Unexpectedly and different from this model, we find that in Drosophila larvae, acute heat nociception and tissue injury-induced hypersensitivity involve distinct cellular and molecular mechanisms. Specifically, TrpA1-D in peripheral sensory neurons mediates acute heat nociception, whereas TrpA1-C in a cluster of larval brain neurons transduces the heat stimulus under the allodynia state. As a result, interfering with synaptic transmission of these brain neurons or genetic targeting of TrpA1-C blocks heat allodynia but not acute heat nociception. TrpA1-C and TrpA1-D are two splicing variants of TrpA1 channels and are coexpressed in these brain neurons. We further show that Gq-phospholipase C signaling, downstream of the proalgesic neuropeptide Tachykinin, differentially modulates these two TrpA1 isoforms in the brain neurons by selectively sensitizing heat responses of TrpA1-C but not TrpA1-D. Together, our studies provide evidence that nociception and noncaptive sensitization could be mediated by distinct sensory neurons and molecular sensors.

Neurokinin-1 Receptor (NK-1R) Antagonists: Potential Targets in the Treatment of Glioblastoma Multiforme.

The current standard of care in glioblastoma multiforme (GBM), as the most morbid brain tumor, is not adequate, despite substantial progress in cancer therapy. Among patients receiving current standard treatments, including surgery, irradiation, and chemotherapy, the overall survival (OS) period with GBM is less than one year. The high mortality frequency of GBM is due to its aggressive nature, including accelerated growth, deregulated apoptosis, and invasion into surrounding tissues. The understanding of the molecular pathogenesis of GBM is, therefore, crucial for identifying, designing, and repurposing potential agents in future therapeutic approaches. In recent decades, it has been apparent that several neurotransmitters, specifically substance P (SP), an undecapeptide in the family of neuropeptides tachykinins, are found in astrocytes. After binding to the neurokinin-1 receptor (NK-1R), the SP controls cancer cell growth, exerts antiapoptotic impacts, stimulates cell invasion/metastasis, and activates vascularization. Since SP/NK-1R signaling pathway is a growth driver in many cancers, this potential mechanism is proposed as an additional target for treating GBM. Following an evaluation of the function of both SP and its NK-1R inhibitors in neoplastic cells, we recommend a unique and promising approach for the treatment of patients with GBM.

A copper complex formed with neurokinin B: binding stoichiometry, redox properties, self-assembly and cytotoxicity.

The tachykinin neuropeptide of neurokinin B (NKB) is a copper-binding amyloid peptide with important roles in the regulation of physiological functions and pathophysiological processes in the central and peripheral nervous systems. In this work, the formation of a NKB-Cu2+ complex in a 1 : 1 stoichiometry was confirmed by mass spectrometry. The self-assembly of NKB and its mutant species was investigated by Thioflavin T (ThT) fluorescence assay and atomic force microscopy (AFM), and at the same time, the effect of Cu2+ on the aggregation of NKB was studied. As evidenced by cyclic voltammetry, the redox potential of NKB-Cu2+ was determined to be 0.77 V (vs. Ag/AgCl). It has been demonstrated that NKB at low concentrations exerts its neuroprotective function by inhibiting Cu2+-mediated reactive oxygen species (ROS) production in the presence of ascorbic acid (AA). In comparison with equivalent Cu2+, the peptide-Cu2+ aggregates aggravated the viability of PC-12 cells more seriously in the absence of AA. These results should be extremely valuable for understanding the NKB/Cu2+ interactions and the toxicity mechanism of Cu2+ associated with neurodegenerative diseases.

Restoration of Regulatory T-Cell Function in Dry Eye Disease by Antagonizing Substance P/Neurokinin-1 Receptor

Substance P (SP) is a tachykinin neuropeptide, implicated in the pathogenesis of various inflammatory conditions and a critical mediator in pain transmission. Recently, the role of SP was described in the pathogenesis of dry eye disease (DED) through its role in the maturation of antigen-presenting cells at the ocular surface after exposure to desiccating stress. However, the effect of SP on regulatory T cells (Tregs), which are functionally impaired in DED, remains unclear. This study examined the phenotypic and functional changes in Tregs in response to SP in DED. The invitro cultures of normal Tregs in the presence of SP led to a significant reduction in both Treg frequencies and their suppressive function, which was prevented by the addition of an SP receptor (neurokinin-1 receptor) antagonist. Furthermore, invivo treatment with the neurokinin-1 receptor antagonist in DED mice effectively restored Treg function, suppressed pathogenic T helper 17 response, and significantly ameliorated the disease. Our results show that a significant increase in SP levels promotes Treg dysfunction in DED, and blockade of SP effectively restores Treg function and suppresses DED severity.

The Role of the Medial Habenula Cholinergic System in Addiction and Emotion-Associated Behaviors.

The habenula is a complex nucleus composed of lateral and medial subnuclei, which connect between the limbic forebrain and midbrain. Over the past few years, the lateral habenula has received considerable attention because of its potential roles in cognition and in the pathogenesis of various psychiatric disorders. Unlike extensively studied lateral habenula, anatomically and histologically distinct medial habenula remains largely understudied. The medial habenula can be further subdivided into a dorsal region containing excitatory neurons that express the tachykinin neuropeptide substance P and a ventral region containing dense cholinergic neurons. Although the medial habenula is the source of one of the major cholinergic pathways in the brain, relatively few studies have been conducted to understand its roles. Recently, however, the medial habenula cholinergic system has attracted more attention because of its potential to provide therapeutic targets for the treatment of nicotine withdrawal symptoms, drug addiction, and various mood disorders. Here, we discuss the role of the medial habenula cholinergic system in brain function.

Sex differences in aggression: Differential roles of 5-HT2, neuropeptide F and tachykinin.

Despite the conserved function of aggression across taxa in obtaining critical resources such as food and mates, serotonin’s (5-HT) modulatory role on aggressive behavior appears to be largely inhibitory for vertebrates but stimulatory for invertebrates. However, critical gaps exist in our knowledge of invertebrates that need to be addressed before definitively stating opposing roles for 5-HT and aggression. Specifically, the role of 5-HT receptor subtypes are largely unknown, as is the potential interactive role of 5-HT with other neurochemical systems known to play a critical role in aggression. Similarly, the influence of these systems in driving sex differences in aggressive behavior of invertebrates is not well understood. Here, we investigated these questions by employing complementary approaches in a novel invertebrate model of aggression, the stalk-eyed fly. A combination of altered social conditions, pharmacological manipulation and 5-HT2 receptor knockdown by siRNA revealed an inhibitory role of this receptor subtype on aggression. Additionally, we provide evidence for 5-HT2’s involvement in regulating neuropeptide F activity, a suspected inhibitor of aggression. However, this function appears to be stage-specific, altering only the initiation stage of aggressive conflicts. Alternatively, pharmacologically increasing systemic concentrations of 5-HT significantly elevated the expression of the neuropeptide tachykinin, which did not affect contest initiation but instead promoted escalation via production of high intensity aggressive behaviors. Notably, these effects were limited solely to males, with female aggression and neuropeptide expression remaining unaltered by any manipulation that affected 5-HT. Together, these results demonstrate a more nuanced role for 5-HT in modulating aggression in invertebrates, revealing an important interactive role with neuropeptides that is more reminiscent of vertebrates. The sex-differences described here also provide valuable insight into the evolutionary contexts of this complex behavior.

Parasitoid Jewel Wasp Mounts Multipronged Neurochemical Attack to Hijack a Host Brain.

The parasitoid emerald jewel wasp Ampulex compressa induces a compliant state of hypokinesia in its host, the American cockroach Periplaneta americana through direct envenomation of the central nervous system (CNS). To elucidate the biochemical strategy underlying venom-induced hypokinesia, we subjected the venom apparatus and milked venom to RNAseq and proteomics analyses to construct a comprehensive "venome," consisting of 264 proteins. Abundant in the venome are enzymes endogenous to the host brain, including M13 family metalloproteases, phospholipases, adenosine deaminase, hyaluronidase, and neuropeptide precursors. The amphipathic, alpha-helical ampulexins are among the most abundant venom components. Also prominent are members of the Toll/NF-κB signaling pathway, including proteases Persephone, Snake, Easter, and the Toll receptor ligand Spätzle. We find evidence that venom components are processed following envenomation. The acidic (pH∼4) venom contains unprocessed neuropeptide tachykinin and corazonin precursors and is conspicuously devoid of the corresponding processed, biologically active peptides. Neutralization of venom leads to appearance of mature tachykinin and corazonin, suggesting that the wasp employs precursors as a prolonged time-release strategy within the host brain post-envenomation. Injection of fully processed tachykinin into host cephalic ganglia elicits short-term hypokinesia. Ion channel modifiers and cytolytic toxins are absent in A. compressa venom, which appears to hijack control of the host brain by introducing a "storm" of its own neurochemicals. Our findings deepen understanding of the chemical warfare underlying host-parasitoid interactions and in particular neuromodulatory mechanisms that enable manipulation of host behavior to suit the nutritional needs of opportunistic parasitoid progeny.

Characterization of a tachykinin signalling system in the bivalve mollusc Crassostrea gigas

Although tachykinin-like neuropeptides have been identified in molluscs more than two decades ago, knowledge on their function and signalling has so far remained largely elusive. We developed a cell-based assay to address the functionality of the tachykinin G-protein coupled receptor (Cragi-TKR) in the oyster Crassostrea gigas. The oyster tachykinin neuropeptides that are derived from the tachykinin precursor gene Cragi-TK activate the Cragi-TKR in nanomolar concentrations. Receptor activation is sensitive to Ala-substitution of critical Cragi-TK amino acid residues. The Cragi-TKR gene is expressed in a variety of tissues, albeit at higher levels in the visceral ganglia (VG) of the nervous system. Fluctuations of Cragi-TKR expression is in line with a role for TK signalling in C. gigas reproduction. The expression level of the Cragi-TK gene in the VG depends on the nutritional status of the oyster, suggesting a role for TK signalling in the complex regulation of feeding in C. gigas.

The Neuropeptide Tac2 Controls a Distributed Brain State Induced by Chronic Social Isolation Stress

Chronic social isolation causes severe psychological effects in humans, but their neural bases remain poorly understood. 2weeks (but not 24hr) of social isolation stress (SIS) caused multiple behavioral changes in mice and induced brain-wide upregulation of the neuropeptide tachykinin 2 (Tac2)/neurokinin B (NkB). Systemic administration of an Nk3R antagonist prevented virtually all of the behavioral effects of chronic SIS. Conversely, enhancing NkB expression and release phenocopied SIS in group-housed mice, promoting aggression and converting stimulus-locked defensive behaviors to persistent responses. Multiplexed analysis of Tac2/NkB function in multiple brain areas revealed dissociable, region-specific requirements for both the peptide and its receptor in different SIS-induced behavioral changes. Thus, Tac2 coordinates a pleiotropic brain state caused by SIS via a distributed mode of action. These data reveal the profound effects of prolonged social isolation on brain chemistry and function and suggest potential new therapeutic applications for Nk3R antagonists.

Neuropeptidergic Control of an Internal Brain State Produced by Prolonged Social Isolation Stress.

Prolonged periods of social isolation can generate an internal state that exerts profound effects on the brain and behavior. However, the neurobiological underpinnings of protracted social isolation have been relatively understudied. Here, we review recent literature implicating peptide neuromodulators in the establishment and maintenance of such internal states. More specifically, we describe an evolutionarily conserved role for the neuropeptide tachykinin in the control of social isolation-induced aggression and review recent data that elucidate the manner by which Tac2 controls the widespread effects of social isolation on behavior in mice. Last, we discuss potential roles for additional neuromodulators in controlling social isolation and a more general role for Tac2 in the response to other forms of stress.

Real-time near-infrared bioimaging of a receptor-targeted cytotoxic dendritic theranostic agent.

Efficient and site-specific delivery of anticancer drugs to tumors is important in the development of effective cancer chemotherapy. As an undecapeptide of the tachykinin neuropeptide family, the substance P (SP)/neurokinin-1 receptor (NK1R) system has been identified as a promising ligand-receptor pair in tumor-specific drug delivery. However, the rational design of suitable theranostic agents with high drug loading capacity and tumor targeting for cancer patients remains a great challenge. Herein, we report a dendritic strategy that utilizes the two amine functionalities of lysine to create branch points that allow conjugation of the anticancer drug 5-fluorouracil (5-FU) to the tumor-targeting ligand substance P, along with an additional near-infrared (NIR) squaraine dye, to construct a theranostic dendritic agent, P-FU 4. This cytotoxic theranostic agent, containing four carboxyl-modified 5-FU molecules, has several desirable advantages: i) the ability to self-assemble into nanoparticles; ii) enhanced cytotoxicity with high drug loading capacity (16%) and a specific receptor-targeted interaction with NK1R through the SP moiety; and iii) a high NIR squaraine fluorescence efficiency due to the specific dendron isolation, avoiding aggregation-mediated quenching. As demonstrated in this report, the cytotoxic activity of P-FU 4 is dose-dependent against the tested cancer cells. The improved drug loading capacity with dendritic branching distinctly enhanced cytotoxicity to tumor cells but had little effect on the viability of normal cells. P-FU 4 was preferentially taken up by tumor cells through a receptor-mediated interaction, which was monitored by effective NIR fluorescence with high tissue penetration. Studies using a mouse model revealed that P-FU 4 can significantly inhibit tumor progression, with a tumor-inhibition rate of 60.2%. The receptor-targeted cytotoxic dendritic theranostic agent is highly preferable to standard chemotherapeutic treatments and decreases the negative side effects of medications on healthy cells, which establishes its utility in drug delivery and cancer chemotherapy.

Endocytosis of the tachykinin neuropeptide, neurokinin B, in astrocytes and its role in cellular copper uptake

The tachykinin neuropeptide, neurokinin B (NKB), belongs to a family of peptides having diverse roles in the brain. NKB, along with several other tachykinins, has been identified as a copper-binding peptide, however the physiological relevance of the binding is unclear. Previously, NKB was shown to limit the ability of copper to enter astrocytes and disrupt calcium homeostasis and it was thought that the peptide was sequestering the metal extracellularly. Here we use a fluorescein-labelled NKB peptide (F-NKB) to show that NKB is not retained extracellularly, but is endocytosed within 10–20min after addition to the cell media. The endocytosis is not inhibited when NKB is delivered as a copper-complex, [CuII(F-NKB)2]. Endocytosis of NKB can increase intracellular copper. Comparison to cells cultured in copper-free buffer indicated that apo-NKB can facilitate uptake of copper found in normal culture media. To achieve this NKB must compete with a variety of copper proteins, and we show that NKB can successfully compete with copper-binding peptides derived from the prion protein, itself associated with Cu(II) and Zn(II) metabolism. We suggest a mechanism of receptor mediated endocytosis to account for the observations.

The neuropeptide tachykinin is essential for pheromone detection in a gustatory neural circuit.

Gustatory pheromones play an essential role in shaping the behavior of many organisms. However, little is known about the processing of taste pheromones in higher order brain centers. Here, we describe a male-specific gustatory circuit in Drosophila that underlies the detection of the anti-aphrodisiac pheromone (3R,11Z,19Z)-3-acetoxy-11,19-octacosadien-1-ol (CH503). Using behavioral analysis, genetic manipulation, and live calcium imaging, we show that Gr68a-expressing neurons on the forelegs of male flies exhibit a sexually dimorphic physiological response to the pheromone and relay information to the central brain via peptidergic neurons. The release of tachykinin from 8 to 10 cells within the subesophageal zone is required for the pheromone-triggered courtship suppression. Taken together, this work describes a neuropeptide-modulated central brain circuit that underlies the programmed behavioral response to a gustatory sex pheromone. These results will allow further examination of the molecular basis by which innate behaviors are modulated by gustatory cues and physiological state.

Therapeutic Potential of 17<i>β</i> Estradiol with Tachykinin Neuropeptide NKB and A<i>β</i>(25 - 35) on Na<sup>+</sup> - K<sup>+</sup> ATPase Activity in Aging Female Rat Brain

The Na+ - K+ ATPase is an enzyme responsible for the active transport of Na+ and K+ in most eukaryotic cells. The aim of the present study was to determine the effect of Tachykinin neuropeptide, Neurokinin B (NKB) and Amyloid beta fragment Aβ (25 - 35) on 17β estradiol (E2) treated aging female rat brain synaptosomes of different age groups, by assaying Na+ - K+ ATPase enzyme activity. An in vitro incubation of isolated synaptosomes with Aβ (25 - 35) showed toxic effects while NKB showed stimulating effect on the Na+ - K+ ATPase activity, and the combined NKB + Aβ (25 - 35) incubations showed a partial effect as compared to the Aβ (25 - 35) alone. To understand whether E2 affects the expression of Na+ - K+ ATPase molecules, we examined the expression of Na+ - K+ ATPase subunit α1 and β2 in E2 treated aging female rat brain synaptosomes. The enzyme was quantified by SDS PAGE in control and E2 treated rat brain. We observed that the expression of α1 and β2 Na+ - K+ ATPase molecules increased and reversed to a normal level in E2 treated synaptosomes. These results confirmed that E2 increased turnover of Na+ - K+ ATPase molecules in aging rat brain. The present findings also suggest a possible role of NKB with E2 in the age related changes in the brain.

The tachykinin peptide neurokinin B binds copper(I) and silver(I) and undergoes quasi-reversible electrochemistry: Towards a new function for the peptide in the brain

The tachykinin neuropeptide family, which includes substance P and neurokinin B, is involved in a wide array of biological functions. Among these is the ability to protect against the neurotoxic processes in Alzheimer’s Disease, but the mechanisms driving neuroprotection remain unclear. Dysregulation of metal ions, particularly copper, iron and zinc is a common feature of Alzheimer’s Disease, and other amyloidogenic disorders. Copper is known to be released from neurons and recent work has shown that some tachykinins can bind Cu(II) ions, and that neurokinin B can inhibit copper uptake into astrocytes. We have now examined whether neurokinin B is capable of binding Cu(I), which is predicted to be available in the synapse. Using a combination of spectroscopic techniques including cyclic voltammetry and magnetic resonance we show that neurokinin B can bind Cu(I) either directly from added CuCl or by reduction of Cu(II)-bound neurokinin B. The results showed that the Cu(I) binding site differs greatly to that of Cu(II) and involves thioether coordination via Met2 and Met10 and an imidazole nitrogen ligand from His3. The Cu(I) coordination is also different to the site adopted by Ag(I). During changes in oxidation state, copper remains bound to neurokinin B despite large changes to the inner coordination sphere. We predict that neurokinin B may be involved in synaptic copper homeostasis.

Serum level of substance P in patients with lung injuries due to sulfur mustard.

Background:Chronic bronchiolitis is the most important problems of chemical victims of mustard gas. Diverse studies suggest that substance P (SP) as a member of tachykinin neuropeptides, has a significant role in the neurogenic inflammation processes of the airways and lungs. We aimed to determine the serum level of SP in chemical victims of mustard gas and compare it with normal subjects.Materials and Methods:The chemical victims were divided into the 2 groups of 30:A group with mild to moderate pulmonary symptoms and other group with moderate to severe symptoms and compared with 3rd group as healthy controls. After preparing our samples and using the SP kit, final analysis was performed with enzyme-linked immunosorbent assay reader.Results:The Concentration of circulatory SP levels in the chemical patients was 2.86 ± 1.47 ng/ml and had not a significant difference with the control group (3.15 ± 1.03 ng/ml) (P > 0.05). The circulatory SP levels were 2.48 ± 0.92 ng/ml and 3.28 ± 1.73 ng/ml in patients with moderate to severe symptoms and mild to moderates (P < 0.05) respectively.Conclusion:The SP may have a role in pulmonary complications of mustard gas. The lower level of SP in the moderate to severe patients may be due to corticosteroid consumption in such severe cases. However, further studies are needed to clarify the roles and mechanism of SP in this setting.