The Concise Guide to PHARMACOLOGY 2023/24: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2023/24 is the sixth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of approximately 1800 drug targets, and about 6000 interactions with about 3900 ligands. There is an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (https://www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes almost 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.16177. G protein-coupled receptors are one of the six major pharmacological targets into which the Guide is divided, with the others being: ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2023, and supersedes data presented in the 2021/22, 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

THE CONCISE GUIDE TO PHARMACOLOGY 2021/22: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes over 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.15538. G protein-coupled receptors are one of the six major pharmacological targets into which the Guide is divided, with the others being: ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2021, and supersedes data presented in the 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

THE CONCISE GUIDE TO PHARMACOLOGY 2021/22: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2021/22 is the fifth in this series of biennial publications. The Concise Guide provides concise overviews, mostly in tabular format, of the key properties of nearly 1900 human drug targets with an emphasis on selective pharmacology (where available), plus links to the open access knowledgebase source of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. Although the Concise Guide constitutes over 500 pages, the material presented is substantially reduced compared to information and links presented on the website. It provides a permanent, citable, point-in-time record that will survive database updates. The full contents of this section can be found at http://onlinelibrary.wiley.com/doi/bph.15538. G protein-coupled receptors are one of the six major pharmacological targets into which the Guide is divided, with the others being: ion channels, nuclear hormone receptors, catalytic receptors, enzymes and transporters. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. The landscape format of the Concise Guide is designed to facilitate comparison of related targets from material contemporary to mid-2021, and supersedes data presented in the 2019/20, 2017/18, 2015/16 and 2013/14 Concise Guides and previous Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC-IUPHAR), therefore, providing official IUPHAR classification and nomenclature for human drug targets, where appropriate.

LITAF mediation of increased TNF-α secretion from inflamed colonic lamina propria macrophages

Dysregulation of TNF-α in lamina propria macrophages (LPM) is a feature of inflammatory bowel diseases (IBD). LPS-Induced-TNF-Alpha-Factor (LITAF) is a transcription factor that mediates TNF-α expression. To determine whether LITAF participates in the mediation of TNF-α expression in acutely inflamed colonic tissues, we first established the TNBS-induced colonic inflammation model in C57BL/6 mice. LPM were harvested from non-inflamed and inflamed colonic tissue and inflammatory parameters TNF-α and LITAF mRNA and protein levels were measured ex-vivo. LPM from TNBS-treated mice secreted significantly more TNF-α at basal state and in response to LPS than LPM from untreated mice (p<0.05). LITAF mRNA and protein levels were elevated in LPM from TNBS compared with untreated animals and LPS further increased LITAF protein levels in LPM from inflamed tissue (P<0.05). To further confirm the role of LITAF in acutely inflamed colonic tissues, TNBS-induced colonic inflammation was produced in LITAF macrophage specific knockout mice (LITAF mac -/- mice) and compared to wild type (WT) C57BL/6. Twenty four hours following TNBS administration, colonic tissue from LITAF mac -/- mice had less MPO activity and reduced colonic TNF-α mRNA then WT C57BL/6 mice (p<0.05). LPM harvested from LITAF mac -/- secreted significantly less TNF-α in response to LPS than wild type (WT) C57BL/6 (p<0.05). This study provides evidence that LITAF contributes to the regulation of TNF-α in LPM harvested following acute inflammation or LPS treatment paving the way for future work focusing on LITAF inhibitors in the treatment of TNF-α-mediated inflammatory conditions.

Substance P induces rapid and transient membrane blebbing in U373MG cells in a p21-activated kinase-dependent manner

U373MG astrocytoma cells endogenously express the full-length neurokinin 1 receptor (NK1R). Substance P (SP), the natural ligand for NK1R, triggers rapid and transient membrane blebbing and we report that these morphological changes have different dynamics and intracellular signaling as compared to the changes that we have previously described in HEK293-NK1R cells. In both cell lines, the SP-induced morphological changes are Gq-independent, and they require the Rho, Rho-associated coiled-coil kinase (ROCK) signaling pathway. Using confocal microscopy we have demonstrated that tubulin is phosphorylated subsequent to cell stimulation with SP and that tubulin accumulates inside the blebs. Colchicine, a tubulin polymerization inhibitor, blocked SP-induced blebbing in U373MG but not in HEK293-NK1R cells. Although p21-activated kinase (PAK) is expressed in both cell lines, SP induced rapid phosphorylation of PAK in U373MG, but failed to phosphorylate PAK in HEK293-NK1R cells. The cell-permeable Rho inhibitor C3 transferase inhibited SP-induced PAK phosphorylation, but the ROCK inhibitor Y27632 had no effect on PAK phosphorylation, suggesting that Rho activates PAK in a ROCK-independent manner. Our study demonstrates that SP triggers rapid changes in cell morphology mediated by distinct intracellular signaling mechanisms in U373MG versus HEK293-NK1R cells.

Substance P (SP)-neurokinin-1 receptor (NK-1R) alters adipose tissue responses to high-fat diet and insulin action

Peripheral administration of a specific neurokinin-1 receptor (NK-1R) antagonist to mice leads to reduced weight gain and circulating levels of insulin and leptin after high-fat diet (HFD). Here, we assessed the contribution of substance P (SP) and NK-1R in diet-induced obesity using NK-1R deficient [knockout (KO)] mice and extended our previous findings to show the effects of SP-NK-1R interactions on adipose tissue-associated insulin signaling and glucose metabolic responses. NK-1R KO and wild-type (WT) littermates were fed a HFD for 3 wk, and obesity-associated responses were determined. Compared with WT, NK-1 KO mice show reduced weight gain and circulating levels of leptin and insulin in response to HFD. Adiponectin receptor mRNA levels are higher in mesenteric fat and liver in NK-1 KO animals compared with WT, after HFD. Mesenteric fat from NK-1R KO mice fed with HFD has reduced stress-activated protein kinase/c-Jun N-terminal kinase and protein kinase C activation compared with WT mice. After glucose challenge, NK-1R KO mice remove glucose from the circulation more efficiently than WT and pair-fed controls, suggesting an additional peripheral effect of NK-1R-mediated signaling on glucose metabolism. Glucose uptake experiments in isolated rat adipocytes showed that SP directly inhibits insulin-mediated glucose uptake. Our results further establish a role for SP-NK-1R interactions in adipose tissue responses, specifically as they relate to obesity-associated pathologies such as glucose intolerance and insulin resistance. Our results highlight this pathway as an important therapeutic approach for type 2 diabetes.

Human mast cell degranulation and preformed TNF secretion require mitochondrial translocation to exocytosis sites: relevance to atopic dermatitis

BACKGROUND

Mast cells derive from hematopoietic cell precursors and participate in tissue allergic, immune, and inflammatory processes. They secrete many mediators, including preformed TNF, in response to allergic, neuropeptide, and environmental triggers. However, regulation of mast cell degranulation is not well understood.

OBJECTIVE

We investigated the role of mitochondrial dynamics in degranulation of human cultured mast cells.

METHODS

Human umbilical cord blood-derived mast cells (hCBMCs) and Laboratory of Allergic Diseases 2 (LAD2) mast cells were examined by confocal and differential interference contrast microscopy during activation by IgE/antigen and substance P (SP). Mast cells in control and atopic dermatitis (AD) skin were evaluated by transmission electron microscopy. LAD2 cells were pretreated with mitochondrial division inhibitor, a dynamin-related protein 1 (Drp1) inhibitor, and small interfering RNA for Drp1, which is necessary for mitochondrial fission and translocation. Calcineurin and Drp1 gene expression was analyzed in stimulated LAD2 cells and AD skin biopsies.

RESULTS

Stimulation of hCBMCs with IgE/antigen or LAD2 cells with SP leads to rapid (30 minutes) secretion of preformed TNF. Degranulation is accompanied by mitochondrial translocation from a perinuclear location to exocytosis sites. Extracellular calcium depletion prevents these effects, indicating calcium requirement. The calcium-dependent calcineurin and Drp1 are activated 30 minutes after SP stimulation. Reduction of Drp1 activity by mitochondrial division inhibitor and decrease of Drp1 expression using small interfering RNA inhibit mitochondrial translocation, degranulation, and TNF secretion. Mitochondrial translocation is also evident by transmission electron microscopy in skin mast cells from AD biopsies, in which gene expression of calcineurin, Drp1, and SP is higher than in normal skin.

CONCLUSION

Human mast cell degranulation requires mitochondrial dynamics, also implicated in AD.

Neurokinin-1 receptor: functional significance in the immune system in reference to selected infections and inflammation

The G protein-coupled receptor (GPCR), neurokinin-1 receptor (NK1R), and its preferred ligand, substance P (SP), are reviewed in relationship to the immune system and selected infections. NK1R and SP are ubiquitous throughout the animal kingdom. This important pathway has unique functions in numerous cells and tissues. The interaction of SP with its preferred receptor, NK1R, leads to the activation of nuclear factor-kappa B (NF-κB) and proinflammatory cytokines. NK1R has two isoforms, both a full-length and a truncated form. These isoforms have different functional significances and differ in cell signaling capability. The proinflammatory signals modulated by SP are important in bacterial, viral, fungal, and parasitic diseases, as well as in immune system function. The SP-NK1R system is a major class 1, rhodopsin-like GPCR ligand-receptor interaction.

Practical limitations of bioresorbable membranes in the prevention of intra-abdominal adhesions

INTRODUCTION

Intra-abdominal adhesions are a significant source of postoperative morbidity. Bioresorbable barriers composed of hyaluronic acid and carboxymethylcellulose (HA/CMC) reduce adhesion formation by physically separating injured or healing peritoneal surfaces. To assess whether the efficacy of a physical barrier can extend beyond the site of application, we evaluated the effectiveness of an HA/CMC barrier in preventing adhesions distal to the site of placement.

METHODS

Adhesions were induced in rats by creating peritoneal ischemic buttons on either side of a midline incision. An HA/CMC barrier (Seprafilm Genzyme) was intraoperatively placed either under the midline incision, unilaterally over half the ischemic buttons, or bilaterally over all ischemic buttons. Control buttons received no HA/CMC. On day 7 adhesions were scored. In similar experiments, peritoneal fluid was collected at 24 h to assess the effects of HA/CMC on tissue plasminogen activator activity.

RESULTS

Placement of HA/CMC under the midline incision did not reduce adhesion formation to distal ischemic buttons (72 +/- 7%) compared to controls (80 +/- 8%). Unilateral placement of HA/CMC significantly (p < 0.05) reduced adhesion formation to those ischemic buttons over which the barrier was applied (35 +/- 7%) compared to both contralateral (83 +/- 9%) and control (80 +/- 8%) ischemic buttons. The bilateral application of HA/CMC also significantly (p < 0.05) reduced adhesion formation to all ischemic buttons compared to controls (22 +/- 7% vs. 66 +/- 7%, respectively). HA/CMC did not affect peritoneal tPA activity.

CONCLUSIONS

Effective adhesion reduction by the physical barrier HA/CMC appears to be limited to the site of application in this rat model. Despite the presence of a bioresorbable membrane at predicted sites of adhesion formation in the peritoneal cavity, adhesions readily form to distal unprotected sites.

An FDA approved neurokinin-1 receptor antagonist is effective in reducing intraabdominal adhesions when administered intraperitoneally, but not orally

INTRODUCTION

Postoperative adhesions pose a continued healthcare problem. We previously demonstrated that intraperitoneal (i.p.) administration of a neurokinin-1 receptor antagonist (NK-1RA) at surgery reduces intraabdominal adhesions in rats. The NK-1RA aprepitant (Emend, Merck) is clinically approved for preventing postoperative nausea and vomiting; however, its effects on adhesion formation are unknown. Thus, we determined the effects of i.p. and oral administration of aprepitant on adhesion formation in a rat model.

METHODS

Adhesions were surgically induced in rats that were randomized to receive either one or five oral preoperative doses or a single intraoperative i.p. dose of aprepitant (50 mg/kg). Adhesions were scored at 7 days. In similar experiments using i.p. dosing, animals were sacrificed at 24 h and peritoneal fluid, and tissue were collected to assess fibrinolytic activity and tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) mRNA levels, respectively.

RESULTS

I.p. aprepitant reduced adhesion formation by 33% (p < 0.05) compared with controls while oral aprepitant had no effect. Compared to controls i.p. aprepitant reduced tPA activity by 55% (p < 0.05), increased PAI-1 mRNA levels by 140% (p < 0.05), and had no affect on tPA mRNA levels.

CONCLUSION

These data suggest that aprepitant maybe a useful pharmacologic agent for reducing adhesion formation clinically.

Insulin stimulates the cleavage and release of the extracellular domain of Klotho by ADAM10 and ADAM17

Cleavage and release (shedding) of membrane proteins is a critical regulatory step in many normal and pathological processes. Evidence suggests that the antiaging transmembrane protein Klotho (KL) is shed from the cell surface by proteolytic cleavage. In this study, we attempted to identify the enzymes responsible for the shedding of KL by treating KL-transfected COS-7 cells with a panel of proteinase inhibitors and measuring cleavage products by Western blot. We report that metalloproteinase inhibitors, including EDTA, EGTA, and TAPI-1, inhibit the shedding of KL, whereas insulin increases shedding. The effects of the inhibitors in KL-transfected COS-7 cells were repeated in studies on rat kidney slices ex vivo, which validates the use of COS-7 cells as our model system. Tissue inhibitor of metalloproteinase (Timp)-3 effectively inhibits KL cleavage, whereas Timp-1 and Timp-2 do not, a profile that indicates the involvement of members of the A Desintegrin and Metalloproteinase (ADAM) family. Cotransfection of KL with either ADAM10 or ADAM17 enhances KL cleavage, whereas cotransfection of KL with small interference RNAs specific to ADAM10 and ADAM17 inhibits KL secretion. These results indicate that KL shedding is mediated mainly by ADAM10 and ADAM17 in KL-transfected COS-7 cells. The effect of insulin is abolished when ADAM10 or ADAM17 are silenced. Furthermore, we demonstrate that the effect of insulin on KL shedding is inhibited by wortmannin, showing that insulin acts through a PI3K-dependent pathway. Insulin enhances KL shedding without increasing ADAM10 and ADAM17 mRNA and protein levels, suggesting that it acts by stimulating their proteolytic activities.

Functional consequences of alteration of N-linked glycosylation sites on the neurokinin 1 receptor

The neurokinin 1 receptor (NK1R), a G protein-coupled receptor involved in diverse functions including pain and inflammation, has two putative N-linked glycosylation sites, Asn-14 and Asn-18. We studied the role of N-linked glycosylation in the functioning of the NK1R by constructing three receptor mutants: two single mutants (Asn --> Gln-14 and Asn --> Gln-18) and a double mutant, lacking both glycosylation sites. Using a lentiviral transfection system, the mutants were stably transfected into NCM 460 cells, a nontransformed human colonic epithelial cell line. We observed that the magnitude of glycosylation as estimated by changes in gel migration depends on the number of glycosylation sites available, with the wild-type receptor containing the greatest amount of glycosylation. All mutant receptors were able to bind to substance P and neurokinin A ligand with similar affinities; however, the double mutant, nonglycosylated NK1R showed only half the B(max) of the wild-type NK1R. In terms of receptor function, the ablation of both N-linked glycosylation sites did not have a profound effect on the receptors' abilities to activate the MAP kinase families (p42/p44, JNK, and p38), but did affect SP-induced IL-8 secretion. All mutants were able to internalize, but the kinetics of internalization of the double mutant receptor was more rapid, when compared with wild-type NK1R. Therefore, glycosylation of NK1R may stabilize the receptor in the plasma membrane. These results contribute to the ongoing elucidation of the role of glycosylation in G protein-coupled receptors and the study of the neurokinin receptors in particular.

A critical role for the E3-ligase activity of c-Cbl in VEGFR-2-mediated PLCgamma1 activation and angiogenesis

Activation of phospholipase Cgamma1 (PLCgamma1) by vascular endothelial growth factor receptor-2 (VEGFR-2) in endothelial cells in part is responsible for angiogenesis in vivo. The cellular mechanisms exerting negative control over PLCgamma1 activation, however, remain unaddressed. Here by using in vitro and in vivo binding assays, we show that the Casitas B-lineage lymphoma (c-Cbl) E3 ubiquitin ligase constitutively associates with PLCgamma1 via its C-terminal domain and conditionally interacts with VEGFR-2 via the N-terminal/TKB domain. Site-directed mutagenesis of VEGFR-2 showed that full activation of c-Cbl requires its direct association with phospho-tyrosines 1052 and 1057 of VEGFR-2 via its TKB domain and indirect association with phospho-tyrosine 1173 of VEGFR-2 via PLCgamma1. The tertiary complex formation between VEGFR-2, PLCgamma1 and c-Cbl selectively promotes ubiquitylation and suppression of tyrosine phosphorylation of PLCgamma1 by a proteolysis-independent mechanism. Further analysis showed that association of c-Cbl with VEGFR-2 does not impact ubiquitylation, down-regulation, or tyrosine phosphorylation of VEGFR-2. Silencing of c-Cbl by siRNA revealed that endogenous c-Cbl plays an inhibitory role in angiogenesis. Our data demonstrate that corecruitment of c-Cbl and PLCgamma1 to VEGFR-2 serves as a mechanism to fine-tune the angiogenic signal relay of VEGFR-2.

A neurokinin 1 receptor antagonist decreases adhesion reformation after laparoscopic lysis of adhesions in a rat model of adhesion formation

BACKGROUND

Up to 94% of patients experience fibrous adhesions after abdominal surgery, and a significant number of these patients require a second operation for open or laparoscopic lysis of adhesions (LOA). The authors have previously shown that inhibition of the binding of tachykinin ligands to the neurokinin 1 receptor (NK-1R) using the neurokinin 1 receptor antagonist (NK-1RA) CJ-12,255 decreases primary adhesion formation and upregulates the peritoneal fibrinolytic system in a rat model. Whereas most studies have focused on the prevention of primary adhesions, few have addressed adhesion reformation after LOA. This study aimed to determine the effects of NK-1RA administration on adhesion reformation and peritoneal fibrinolytic activity after laparoscopic LOA.

METHODS

Adhesions were induced in 31 rats using our previously described ischemic button model. The rats underwent laparoscopy 7 days later, during which adhesions were scored and lysed followed by administration of the NK-1RA or saline. Then 7 days after LOA, 23 rats were killed and adhesions were scored. Eight rats also were killed 24 h after the LOA to obtain peritoneal tissue and fluid, which were analyzed for tissue plasminogen activator (tPA) mRNA expression and peritoneal fibrinolytic activity by reverse transcriptase-polymerase chain reaction (RT-PCR) and bioassay, respectively.

RESULTS

At laparoscopy, 79% +/- 3% of the buttons formed adhesions. In the saline-administered control animals, 42% +/- 3.2% of the buttons reformed adhesions after LOA (p < 0.05), whereas in the animals that received the NK-1RA, 18.2% +/- 3.5% of the buttons reformed adhesions (p < 0.05). As compared with control animals, NK-1RA administration increased tPA mRNA levels by 38% and fibrinolytic activity sixfold (p < 0.05; 7.0 +/- 2.1 U/ml vs 1.2 +/- 0.54 U/ml).

CONCLUSIONS

When administered during laparoscopic LOA, an NK-1RA significantly upregulates peritoneal fibrinolytic activity and decreases adhesion reformation.

The effectiveness of a single intraperitoneal infusion of a neurokinin-1 receptor antagonist in reducing postoperative adhesion formation is time dependent

BACKGROUND

Current methods to prevent intraabdominal adhesions are not uniformly effective. We recently showed in rats that a neurokinin-1 receptor (NK-1R) antagonist is capable of reducing adhesion formation. To determine the clinical feasibility of using an NK-1R antagonist to reduce adhesions, this study examined the time dependence for the effectiveness of NK-1R antagonist administration and its effects on wound healing.

METHODS

Adhesions were surgically induced in rats receiving a single intraperitoneal infusion of the NK-1R antagonist, CJ-12,255, during or 1, 5, 12, or 24 hours after surgery. Adhesion formation was assessed 7 days later. In a subset of animals, tissue plasminogen activator (tPA) activity, which is a measure of peritoneal fibrinolytic activity, was determined in peritoneal fluid 24 hours after surgery (48 hours for animals infused at 24 hours). The tPA activity was also determined in nonoperated animals 24 hours after peritoneal injection of the NK-1R antagonist. Colonic burst pressures were measured 7 days after creation of anastomoses in rats that were administered the antagonist at surgery.

RESULTS

The NK-1R antagonist significantly reduced (P=.003) intraabdominal adhesions when administered during or 1 hour after surgery, only moderately reduced (P=.08) adhesions when administered at 5 hours, and had no effect at 12 or 24 hours. Peritoneal tPA activity was significantly increased (P<.05) in peritoneal fluid 24 hours after administration of the NK-1R antagonist regardless of the surgical procedure. The NK-1R antagonist did not alter colonic anastomotic healing.

CONCLUSIONS

These data show that some of the events critical to adhesion formation occur within the first 5 hours following an abdominal operation in this model. The fact that the NK-1R antagonist does not impair colonic anastomotic healing enhances its usefulness as a therapeutic agent to inhibit adhesion formation.

Statins (HMG-CoA reductase inhibitors) decrease postoperative adhesions by increasing peritoneal fibrinolytic activity

OBJECTIVES

The aims of this study were to determine if statins reduce adhesion formation in vivo and to identify the mechanism of action in vitro.

BACKGROUND

: Intraperitoneal adhesions develop in up to 95% of patients following laparotomy. Adhesions are reduced by mechanisms that up-regulate fibrinolysis within the peritoneum. Statins promote fibrinolysis in the cardiovascular system and may play a role in the prevention of adhesions.

METHODS

Adhesions were induced in rats (n = 102) using our previously described ischemic button model. Rats received vehicle (controls), lovastatin (30 mg/kg), or atorvastatin (30 mg/kg) as a single intraperitoneal dose at the time of laparotomy. Animals were killed and adhesions were quantified at day 7. Peritoneal fluid and tissue were collected at day 1 to measure tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) by real-time PCR and ELISA. To assess the effects of statins on wound healing, burst pressures were measured in anastomoses of the colon. The effects of lovastatin on tPA and PAI-1 production were measured in vitro in human mesothelial cells (HMC) in the presence or absence of mevalonate (MVA), geranylgeranyl-pyrophosphate (GGPP) and farnesyl-pyrophosphate (FPP), all intermediates in the cholesterol pathway downstream of HMG-CoA. The effect of a Rho protein inhibitor, exoenzyme C3 transferase, on tPA production was also determined.

RESULTS

Lovastatin and atorvastatin reduced adhesion formation by 26% and 58%, respectively (P < 0.05), without affecting anastomotic burst pressure. At 24 hours, tPA mRNA levels in peritoneal tissue and tPA activity in peritoneal fluid from lovastatin-treated animals were increased by 57% and 379%, respectively (P < 0.05), while PAI-1 levels were unchanged. HMC incubated with either lovastatin or atorvastatin showed concentration-dependent increases in tPA production and decreases in PAI-1 production (P < 0.05). These lovastatin-induced changes in tPA and PAI-1 production were significantly reversed by the addition of MVA, GGPP, and FPP. The Rho protein inhibitor increased tPA production and rescued tPA production from the inhibitory effect of GGPP.

CONCLUSION

These data suggest that statins administered within the peritoneum can up-regulate local fibrinolysis, while the in vitro studies show that this effect may be mediated, in part, by intermediates of the cholesterol biosynthetic pathway that regulate Rho protein signaling.

Induction of colitis causes inflammatory responses in fat depots: evidence for substance P pathways in human mesenteric preadipocytes

Intracolonic administration of trinitrobenzene sulfonic acid in mice causes inflammation in the colon that is accompanied by increased expression of proinflammatory cytokines and of the substance P (SP), neurokinin 1 receptor (NK-1R) in the proximal mesenteric fat depot. We also investigated whether human mesenteric preadipocytes contain NK-1R and examined the functional consequences of exposure of these cells to SP as it relates to proinflammatory signaling. We found that human mesenteric preadipocytes express NK-1R both at the mRNA and protein levels. Exposure of human mesenteric preadipocytes to SP increased NK-1R mRNA and protein expression by 3-fold, and stimulated IL-8 mRNA expression and protein secretion. This effect was abolished when these cells were pretreated with the specific NK-1R antagonist CJ 012,255. Moreover, human mesenteric preadipocytes transfected with a luciferase promoter/reporter system containing the IL-8 promoter with a mutated NF-kappaB site lost their ability to respond to SP, indicating that SP-induced IL-8 expression is NF-kappaB-dependent. This report indicates that human mesenteric preadipocytes contain functional SP receptors that are linked to proinflammatory pathways, and that SP can directly increase NK-1R expression. We speculate that mesenteric fat depots may participate in intestinal inflammatory responses via SP-NK-1R-related pathways, as well as other systemic responses to the presence of an ongoing inflammation of the colon.

LPS induces the interaction of a transcription factor, LPS-induced TNF-alpha factor, and STAT6(B) with effects on multiple cytokines

TNF-alpha is a pivotal cytokine whose overproduction can be lethal. Previously, we identified a transcription factor, LPS-induced TNF-alpha factor (LITAF), that regulates TNF-alpha transcription. We now report the discovery and characterization of a regulatory cofactor that we call signal transducer and activator of transcription (STAT) 6(B) because of its considerable homology to STAT6 [here referred to as STAT6(A)]. The STAT6(B) gene expression was found to be activated by LPS. Furthermore, we show that cotransfection of STAT6(B) and LITAF induces an interaction between the two proteins, consequently forming a complex that subsequently translocates into the nucleus and up-regulates the transcription of cytokines. The effect of the complex on a panel of cytokines was tested. In addition, the specific role of LITAF in this complex was established with experiments, including RNA interference technology. Overall, these findings describe roles for LITAF, STAT6(B), and the LITAF-STAT6(B) complex in the regulation of inflammatory cytokines in response to LPS stimulation in mammalian cells.

A neurokinin 1 receptor antagonist decreases postoperative peritoneal adhesion formation and increases peritoneal fibrinolytic activity

Fibrous adhesions remain a major sequela of abdominal surgery. The proinflammatory peptide substance P (SP), known to participate in inflammatory events, may play a key role in adhesion formation. This hypothesis was tested by using an antagonist, CJ-12,255 (Pfizer), that blocks the binding of SP to the neurokinin 1 receptor (NK-1R). Adhesion formation was surgically induced in the peritoneum of rats receiving daily doses of the NK-1R antagonist (NK-1RA; 5.0 or 10.0 mg/kg per day) or saline. On postoperative day 7, both the low and high doses of NK-1RA significantly (P < 0.05) reduced adhesion formation by 45% and 53%, respectively, compared with controls. Subsequently, the effect of NK-1RA administration on peritoneal fibrinolytic activity was investigated to determine a potential mechanism for SP action in the peritoneum. Samples were collected from nonoperated controls and from animals 24 h postsurgery that were administered either NK-1RA or saline. Fibrinolytic activity in peritoneal fluid was assayed by zymography, and expression of tissue plasminogen activator (tPA) and plasminogen activator inhibitor 1, both regulators of fibrinolytic activity, was assessed in peritoneal tissue and fluid by RT-PCR and bioassay, respectively. NK-1RA administration led to a marked (P < 0.05) increase in tPA mRNA levels in peritoneal tissue compared with nonoperated and saline-administered animals. Likewise, NK-1RA administration significantly (P < 0.05) increased tPA in the peritoneal fluid. These data suggest that activation of the NK-1R promotes peritoneal adhesion formation by limiting fibrinolytic activity in the postoperative peritoneum, thus enabling fibrinous adhesions to persist.

A neurokinin 1 receptor antagonist reduces an ongoing ileal pouch inflammation and the response to a subsequent inflammatory stimulus

Ileal pouch-anal anastomosis (IPAA) is an excellent surgical option for patients with chronic ulcerative colitis (CUC) requiring colectomy; however, persistent episodes of ileal pouch inflammation, or pouchitis, may result in debilitating postoperative complications. Because considerable evidence implicates substance P (SP) as an inflammatory mediator of CUC, we investigated whether SP participates in the pathophysiology of pouchitis. With the use of a rat model of IPAA that we developed, we showed that ileal pouch MPO levels and neurokinin 1 receptor (NK-1R) protein expression by Western blot analysis were significantly elevated 28 days after IPAA surgery. In situ hybridization and immunohistochemistry showed that the increase in NK-1R protein expression was localized to the lamina propria and epithelia of pouch ileum. The intraperitoneal administration of the NK-1R antagonist (NK-1RA) CJ-12,255 for 4 days, starting on day 28, was effective in reducing MPO levels. Starting on day 28, animals with IPAA were given 5% dextran sulfate sodium (DSS) in their drinking water for 4 days, which caused histological and physical signs of clinical pouchitis concomitant with significant increases in ileal pouch MPO concentrations as well as NK-1R protein expression by Western blot analysis. In situ hybridization and immunohistochemistry showed that the increase in NK-1R protein expression was especially evident in crypt epithelia of pouch ileum. When the NK-1RA was administered 1 day before starting DSS and continued for the duration of DSS administration, the physical signs of clinical pouchitis and the rise in MPO were prevented. These data implicate SP in the pathophysiology of pouchitis and suggest that NK-1RA may be of therapeutic value in the management of clinical pouchitis.

Clinical and neuroinflammatory responses to meningoencephalitis in substance P receptor knockout mice

Human African trypanosomiasis, also known as sleeping sickness, affects the CNS at the late stage of the disease. Untreated the disease is invariably fatal, and melarsoprol, the only available and effective treatment for CNS disease, is associated in up to 10% of cases with a severe post-treatment reactive encephalopathy (PTRE), which can itself cause death. We used a reproducible mouse model of the PTRE to investigate the pathogenesis and treatment of this condition. Mice infected with Trypanosoma brucei brucei and treated subcuratively with diminazene aceturate develop a severe meningoencephalitis that closely resembles PTRE. We previously reported that substance P plays an important role in PTRE. We investigated the effect of disrupting the gene encoding for the NK1 receptor in mice on the clinical and neuroinflammatory response in this model. After induction of PTRE, NK1-/- mice showed a significant reduction in clinical impairment compared with NK1+/+ mice, but the severity of the neuroinflammatory response was significantly greater in NK1-/- mice. To explore the mechanisms of this dissociated phenotype, we treated infected NK1-/- mice with antagonists to NK2 and NK3 receptors, either singly or in combination. While none of these antagonist treatments altered the clinical score, combined treatment with the NK2 and NK3 antagonists significantly reduced the neuroinflammatory grading score in the NK1-/- mice. Thus, the clinical and neuroinflammatory responses to parasite invasion can be mediated by different pathways, and, importantly, the neuroinflammatory response is altered by alternative tachykinin receptor usage. These findings could be exploited to develop novel anti-inflammatory therapies in Human African trypanosomiasis by modulating the NK1 receptor as well as the parasite.

Neurokinin-1 receptor and substance P messenger RNA levels increase during intraabdominal adhesion formation

BACKGROUND

Intraabdominal peritoneal adhesions are a significant cause of postoperative morbidity and remain one of the major long-term complications associated with abdominal surgery. Adhesion formation at the molecular level involves a complex interaction of cytokines, growth factors, cell adhesion molecules, and neuropeptides, as well as many other factors secreted by cells proximate to the traumatized area. Limited studies exist which investigate the molecular processes involved in adhesion formation. Therefore, the aim of the present study was to determine the pattern of gene expression for substance P, the neurokinin-1 receptor, and downstream mediators of substance P action during the early stages of adhesion formation in the rat.

METHODS

Four ischemic buttons were created on one side of the peritoneum in male Wistar rats. Animals were sacrificed at 3, 6, and 12 h and 1, 3, 5, and 7 days following surgery. Peritoneal tissue from ischemic buttons and from the opposite sidewall was harvested for total RNA isolation. Semiquantitative RT-PCR was used to measure changes at the transcript level for the neurokinin-1 receptor, substance P, TGFbeta-1, and the cell adhesion molecules ICAM-1 and VCAM-1.

RESULTS

Messenger RNA levels for substance P, neurokinin-1 receptor, TGFbeta-1, ICAM-1, and VCAM-1 were significantly increased in peritoneal tissue taken from ischemic button sites (P < 0.05) when compared with controls. In the peritoneal tissues taken from the opposite sidewall, there was a significant (P < 0.05) early increase in substance P mRNA levels. TGF-beta1, neurokinin-1 receptor, and ICAM-1 mRNA levels were also significantly (P < 0.05) increased when compared to controls, while the mRNA levels for VCAM-1 did not change.

CONCLUSIONS

The increased levels of mRNA for substance P, the neurokinin-1 receptor, and the downstream mediators of substance P action, TGF-beta1, ICAM-1, and VCAM-1, in peritoneal tissue associated with intraabdominal adhesions support a role for substance P in adhesion formation.

Direct evidence for the interaction of neurokinin A with the tachykinin NK(1) receptor in tissue

Neurokinin A (NKA) is a tachykinin peptide that binds with high affinity to the tachykinin NK(2) receptor. Recent homologous binding studies, however, have shown that neurokinin A is also a high-affinity ligand for the tachykinin NK(1) receptor. In this report, we demonstrate that a photoreactive neurokinin A analogue specifically labels the NK(1) receptor in rat submandibular gland membranes and show via bioassay that neurokinin A is a potent stimulator of salivary secretion. Through the use of specific non-peptide antagonists in both photolabeling and functional assays, we unequivocally demonstrate that neurokinin A can specifically interact with the NK(1) receptor in vivo and elicit NK(1) receptor-mediated physiological responses.

Evidence for spatial proximity of two distinct receptor regions in the substance P (SP)*neurokinin-1 receptor (NK-1R) complex obtained by photolabeling the NK-1R with p-benzoylphenylalanine3-SP

Substance P (SP) belongs to the tachykinin family of bioactive peptides and exerts its many biological effects through functional interaction with its cell-surface, G protein-coupled neurokinin-1 receptor (NK-1R). Previous studies from our laboratory have shown that (125)I-Bolton-Hunter reagent-labeled p-benzoylphenylalanine(8)-SP (Bpa(8)SP) covalently attaches to Met(181), whereas (125)I-Bolton-Hunter reagent-labeled Bpa(4)SP covalently attaches to Met(174), both of which are located on the second extracellular loop (EC2) of the NK-1R. In this study, evidence has been obtained that at equilibrium, the photoreactive SP analogue (125)I-[D-Tyr(0)]Bpa(3)SP covalently labels residues in two distinct extracellular regions of the NK-1R. One site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on EC2 within a segment of the receptor extending from residues 173 to 177; a second site of (125)I-[D-Tyr(0)]Bpa(3)SP photoinsertion is located on the extracellular N terminus within a segment of the receptor extending from residues 11 to 21, a sequence that contains both potential sites for N-linked glycosylation. Since competition binding data presented in this study do not suggest the existence of multiple peptide.NK-1R complexes, it is reasonable to assume that the receptor sequences within EC2 and N terminus identified by peptide mapping are in close proximity in the equilibrium complex.

Further definition of the substance P (SP)/neurokinin-1 receptor complex. MET-174 is the site of photoinsertion p-benzoylphenylalanine4 SP

The covalent attachment site of a substance P (SP) analogue containing the photoreactive amino acid p-benzoyl-l-phenylalanine (Bpa) in position 8 of the C-terminal portion of the peptide was identified previously as Met-181 on the neurokinin-1 (NK-1) receptor. In this study, a second photoreactive SP analogue, Bpa(4)-SP, in which the Bpa residue is located in the N-terminal portion of the peptide, was used to define further the peptide-receptor interface. The NK-1 receptor expressed in Chinese hamster ovary cells was specifically and efficiently photolabeled with a radioiodinated derivative of Bpa(4)-SP. Fragmentation analysis of the photolabeled receptor restricted the site of photoincorporation of Bpa(4)-SP to an amino acid within the sequence Thr-173 to Arg-177 located on the N-terminal side of the E2 loop. To identify the specific amino acid in this sequence that serves as the covalent attachment site for Bpa(4)-SP, a small photolabeled receptor fragment was generated by chemical cleavage with cyanogen bromide. Matrix-assisted laser desorption/ionization time of flight mass spectrometric analysis of the purified fragment identified a single protonated molecular ion with a molecular mass of 1801.3 +/- 1.8, indicating that upon irradiation, the bound photoligand covalently attaches to the terminal methyl group of a methionine residue. This result, taken together with the results of the peptide mapping studies, establishes that the site of Bpa(4)-SP covalent attachment to the NK-1 receptor is Met-174.

Photoaffinity labeling of mutant neurokinin-1 receptors reveals additional structural features of the substance P/NK-1 receptor complex

Photoaffinity labeling, receptor site-directed mutagenesis, and high-resolution NMR spectroscopy have been combined to further define the molecular details of the binding of substance P (SP) to the rat neurokinin-1 (NK-1) receptor. Mutant NK-1 receptors were constructed by substituting Ala for Met174 and/or Met181: residues previously identified as the sites of covalent attachment of radioiodinated, photoreactive derivatives of SP containing p-benzoyl-L-phenylalanine (Bpa) in positions 4 and 8, respectively. Photoaffinity labeling of the M181A mutant using radioiodinated Bpa8-SP resulted in a marked reduction in photoincorporation efficiency compared to the wild-type receptor. In contrast, photoaffinity labeling of the M174A mutant using radioiodinated Bpa4-SP gave the unexpected result of an increase in the efficiency of photoincorporation compared to the wild-type receptor. Enzymatic and chemical fragmentation analysis of the photolabeled receptor mutants established that the sites of covalent attachment were not the substituted alanine, but rather the other methionine on the second extracellular (E2) loop sequence, that is not the primary site of attachment in the wild-type receptor. The results thus suggest a close spatial relationship between Met174 and Met181 on the NK-1 receptor. To evaluate this structural disposition, NMR analyses were performed on a synthetic peptide with a sequence corresponding to the entire E2 loop and segments of the adjoining transmembrane helices to anchor the peptide in the lipids used to mimic a membrane. The structural features of the E2 loop include a centrally located alpha-helix, extending from Pro175 to Glu183, as well as smaller alpha-helices at the termini, corresponding to the transmembrane regions. The two methionine residues are located on the same face of the central alpha-helix, approximately 11 A apart from each other, and are therefore consistent with the conclusions of the photoaffinity labeling results.

Isolation and characterization of substance P-containing dense core vesicles from rabbit optic nerve and termini

In neurons, neuropeptides and other synaptic components are transported down the axon to the synapse in vesicles using molecular motors of the kinesin family. In the synapse, these neuropeptides are found in dense core vesicles (DCVs), and, following calcium-mediated exocytosis, they interact with receptors on the target cell. We have developed a rapid, large-scale technique for purifying peptide-containing DCVs from specific nuclei in the central nervous system. By using differential velocity gradient and equilibrium gradient centrifugation, neuropeptide-containing DCVs can be separated by size and density from optic nerve (ON) and its termini, the lateral geniculate nuclei and the superior colliculi. Isolated DCVs contain neuropeptides (substance P and brain-derived neurotrophic factor), synaptic vesicle (SV) membrane proteins (SV2, synaptotagmins, synaptophysin, Rab3 and synaptobrevin), SV-associated proteins (alpha-synuclein), secretory markers for DCVs previously isolated (secretogranin II), and beta-amyloid precursor protein. By using electron microscopic techniques, DCV were also visualized and shown to be immunoreactive for neuropeptides, neurotrophins, and SV membrane proteins. Because of the interesting group of physiological and potentially pathophysiological proteins associated with these vesicles; this isolation procedure, applicable to other CNS nuclei, should represent an important research tool.

The common C-terminal sequences of substance P and neurokinin A contact the same region of the NK-1 receptor

Although neurokinin A (NKA), a tachykinin peptide with sequence homology to substance P (SP), is a weak competitor of radiolabeled SP binding to the NK-1 receptor (NK-1R), more recent direct binding studies using radiolabeled NKA have demonstrated an unexpected high-affinity interaction with this receptor. To document the site of interaction between NKA and the NK-1R, we have used a photoreactive analogue of NKA containing p-benzoyl-L-phenylalanine (Bpa) substituted in position 7 of the peptide. Peptide mapping studies of the receptor photolabeled by (125)I-iodohistidyl(1)-Bpa(7)NKA have established that the site of photoinsertion is located within a segment of the receptor extending from residues 178 to 190 (VVCMIEWPEHPNR). We have previously shown that (125)I-BH-Bpa(8)SP, a photoreactive analogue of SP, covalently attaches to M(181) within this same receptor sequence. Importantly, both of these peptides ((125)I-iodohistidyl(1)-Bpa(7)NKA and (125)I-BH-Bpa(8)SP) have the photoreactive amino acid in an equivalent position within the conserved tachykinin carboxyl-terminal tail. In this report, we also show that site-directed mutagenesis of M(181) to A(181) in the NK-1R results in a complete loss of photolabeling of both peptides to this receptor site, indicating that the equivalent position of SP and NKA, when bound to the NK-1R, contact the same residue.

Widespread expression in adult rat forebrain of mRNA encoding high-affinity neurotensin receptor

The peptides neurotensin (NT) and neuromedin N exert effects on neurons by means of a high-affinity NT receptor (NTRH) belonging to the superfamily of G-protein-coupled receptors. In the present study, we used in situ hybridization histochemistry with sensitive riboprobe methodology to investigate the distribution of NTRH mRNA in the forebrain of adult rats. Labeled cells were abundant in the hypothalamus, epithalamus, ventral thalamus, septum, amygdala, and pallidum, including many regions where NTRH mRNA had not been detected previously. In the hypothalamus, novel sites of NTRH mRNA expression included the arcuate, periventricular, paraventricular, supraoptic, medial preoptic, anterior, ventromedial, and posterior nuclei, as well as the lateral hypothalamic area. In the thalamus, novel sites of expression included the anterodorsal nucleus, lateral habenula, and zona incerta, where labeling was much more extensive than previously reported. Novel telencephalic sites of expression included most bed nuclei of the stria terminalis, most divisions of the amygdala, the main olfactory bulb, the endopiriform nucleus, the claustrum, many parts of retrohippocampal allocortex, and limited parts of most isocortical areas. Novel sites of expression were also observed in the midbrain and pons. Taking into account expected differences in the subcellular locations of receptor mRNA and protein, the regional distribution of NTRH mRNA agrees well with that of NTRH determined previously. Our results identify many novel sites of NTRH mRNA expression in adult brain and provide a basis for investigating involvement of NT and related peptides in regulating the activity of these diverse cells, whose phenotypes remain largely undetermined.

Substance P receptor expression in intestinal epithelium in clostridium difficile toxin A enteritis in rats

We previously reported that the inflammatory effects of Clostridium difficile toxin A on rat intestine can be significantly inhibited with a specific neurokinin-1 receptor (NK-1R) antagonist. In this study we investigated the localization and expression of NK-1R mRNA and protein in rat intestine by in situ hybridization, Northern blot analysis, and immunohistochemistry, respectively, after exposure to toxin A. Northern blot analysis showed increased mucosal levels of NK-1R mRNA starting 30 min after toxin A administration. In situ hybridization showed that toxin A increased NK-1R mRNA expression in intestinal epithelial cells after 30, 120, and 180 min. In rats pretreated with the NK-1R antagonist CP-96345 the increase in NK-1R mRNA levels after exposure to toxin A was inhibited, indicating that NK-1R upregulation is substance P (SP) dependent. One hour after exposure to toxin A many of the intestinal epithelial cells showed staining for NK-1R compared with controls. Specific 125I-SP binding to purified epithelial cell membranes obtained from ileum exposed to toxin A for 15 min was increased twofold over control and persisted for 4 h. This report provides evidence that NK-1R expression is increased in the intestinal epithelium shortly after exposure to toxin A and may be important in toxin A-induced inflammation.

Neuroimmune mechanisms of intestinal responses to stress. Role of corticotropin-releasing factor and neurotensin

Previous studies showed that exposure of experimental animals to immobilization stress increases colonic motility and that these effects are mediated by release of corticotropin-releasing factor (CRF), Studies from our laboratory showed that 30-min immobilization stress of rats caused several not previously described colonic responses to stress, including increased colonic mucin and prostaglandin E2 (PGE2) secretion, increased colonic mucosal levels of cyclooxygenase-2 (COX-2) mRNA, and degranulation of colonic mast cells. These stress-associated colonic changes were reproduced by intravenous or intracerebral injection of CRF in conscious, nonstressed rats. Furthermore, pretreatment of rats with the CRF antagonist alpha-helical CRF9-41, hexamethonium, or the mast cell stabilizer lodoxamide inhibited our observed colon responses to immobilization stress. Our results indicate that CRF released during immobilization stress increases colonic transit via a neuronal pathway and stimulates colonic mucin release via activation of neurons and colonic mast cells. These results provide support for an important role for CRF in stress-mediated colonic responses and a link between the nervous and the immune systems.

Two distinct populations of synaptic-like vesicles from rat brain

In nonneuronal cells, several plasma membrane proteins such as exofacial enzymes, receptors, and ion channels recycle between their intracellular compartment(s) and the cell surface via an endosomal pathway. In neurons, however, this pathway has not been extensively characterized. In particular, it remains unclear whether or not it is related to the recycling of small synaptic vesicles, the major pathway of membrane traffic in nerve terminals. To approach this problem, we purified and studied a vesicular fraction from rat brain synaptosomes. Two distinct populations of vesicles with different buoyant densities and sedimentation coefficients were detected in this fraction by sucrose gradient centrifugation and Western blot analysis of the individual proteins. Both populations contain proteins that are markers of synaptic vesicles, namely, SV2, synaptotagmin, synaptophysin, secretory carrier membrane proteins (SCAMPs), synaptobrevin, and rab3a. A striking difference between the two populations is the presence of arginine aminopeptidase activity (a previously suggested marker for the regulated endosomal recycling pathway) exclusively in the lighter less-dense vesicles. The same two vesicular populations were also detected in the preparation of clathrin-coated vesicles isolated from whole rat brain or purified synaptosomes after removal of their clathrin coats by incubation at pH 8.5. We conclude, therefore, that both types of vesicles recycle in synaptosomes via a clathrin-mediated pathway. These data present experimental evidence for biochemical heterogeneity of synaptic-like vesicles in rat brain.

A substance P (neurokinin-1) receptor mutant carboxyl-terminally truncated to resemble a naturally occurring receptor isoform displays enhanced responsiveness and resistance to desensitization

Two isoforms of the substance P (SP) receptor, differing in the length of the cytoplasmic carboxyl-terminus by approximately 8 kDa, have been detected previously in rat salivary glands and other tissues. The binding and functional properties of these two isoforms have been investigated using full-length (407 amino acids) and carboxyl-terminally truncated (324 amino acids) rat SP receptors transfected stably into Chinese hamster ovary cells. Both the full-length and the truncated receptor bound radiolabeled SP with a similar Kd ( approximately 0.1 nM). The average number of high affinity SP binding sites per cell was 1.0 x 10(5) and 0.3 x 10(5) for the full-length and the truncated SP receptor, respectively. In both cell lines, SP induced a rapid but transient increase in cytosolic calcium concentration ([Ca2+]i), which consisted of the release of Ca2+ from intracellular stores and the influx of extracellular Ca2+. Both components are dependent on phospholipase C activation. Although the full-length and the truncated receptor utilize the same calcium pathways, they differ in their EC50 values (0.28 nM for the full-length; 0.07 nM for the truncated). These differences in responsiveness may be related to the observed differences in receptor desensitization. The truncated receptor, in contrast to the full-length receptor, does not undergo rapid and long-lasting desensitization. Cells possessing the short isoform of the SP receptor would thus be expected to exhibit a prolonged responsiveness.

Increased substance P responses in dorsal root ganglia and intestinal macrophages during Clostridium difficile toxin A enteritis in rats

Previously we reported that pretreatment of rats with the substance P (SP) antagonist CP-96,345 inhibits the enterotoxic responses following administration of toxin A from Clostridium difficile into ileal loops, indicating that SP participates in the intestinal responses to this toxin. We now report that injection of toxin A into rat ileum causes a rapid increase in SP content in lumbar dorsal root ganglia (DRG) and mucosal scrapings 30-60 min after toxin A administration. Toxin A-mediated fluid secretion, mannitol permeability, and ileal histologic damage is significantly increased only after 2 hr. Toxin A also causes an increase in the abundance of SP mRNA in lumbar DRG and ileal mucosa as measured by reverse transcription-PCR. Lamina propria macrophages (LPMs) obtained from toxin A-injected loops release greater amounts of tumor necrosis factor alpha (TNFalpha) and SP as compared with LPMs isolated from buffer-injected loops (P < 0.01). Pretreatment of rats with the SP antagonist CP-96,345 inhibits toxin A-mediated TNFalpha release from isolated LPMs, whereas an inactive enantiomer (CP-96,344) of the SP antagonist has no effect. LPMs obtained from toxin A-injected ileal loops incubated in vitro with SP (10(-8) to 10(-9) M) show enhanced TNFalpha secretion, whereas LPMs isolated from buffer-injected loops do not respond to SP. In addition, LPMs obtained from toxin A-injected ileal loops incubated in vitro with CP-96,345 showed a diminished TNFalpha release. Our results indicate that activated LPMs secrete SP during toxin A enteritis that can lead to secretion of cytokines, suggesting an autocrine/paracrine regulation of cytokine secretion by SP from LPMs during intestinal inflammation.

A substance P antagonist, RP-67,580, ameliorates a mouse meningoencephalitic response to Trypanosoma brucei brucei

Mice infected with the protozoan parasite Trypanosoma brucei brucei and treated subcuratively with the trypanocidal drug diminazene aceturate develop an acute inflammatory meningoencephalitis with associated astrocytic proliferation. This reaction is very similar to that seen in the fatal posttreatment reactive encephalopathies that can occur in human African trypanosomiasis. The 11-amino acid neuropeptide substance P (SP) has recently been identified as a mediator in many inflammatory responses, and the development of potent, highly specific, nonpeptide SP antagonists has provided a new opportunity to investigate the possible involvement of SP in a variety of pathological conditions. We therefore postulated that SP may play a role in the development of the posttreatment inflammatory encephalopathy found in this experimental mouse model of African trypanosomiasis. In the present study RP-67,580, a SP antagonist that binds specifically to NK-1 receptors, was given intraperitoneally at a dose of 2 mg/kg twice daily to mice in which a severe meningoencephalitis had been produced. A significant reduction in both the severity of the inflammatory response (P = 0.0001) as well as the degree of astrocyte activation (P < 0.001) was found in the brains of these animals as compared with control mice that had not received RP-67,580. An inactive enantiomer of this SP antagonist, RP-68,651, had no effect on the central nervous system inflammatory reaction. We conclude from these findings that the neuropeptide SP plays a key role in the development of the severe central nervous system inflammatory response associated with African trypanosomiasis.

Role of substance P in blood pressure regulation in salt-dependent experimental hypertension

The participation of substance P in the pathogenesis of five models of experimental hypertension, ie, DOCA-salt, subtotal nephrectomy, one-kidney-one clip renovascular, two-kidney-one clip renovascular, and spontaneous hypertension, was evaluated via an acute infusion of a newly synthesized potent, specific nonpeptide antagonist of substance P at the NK-1 receptor, the agent CP 96,345. In conscious unrestrained rats, CP 96,345 induced significant and sustained increases in mean arterial pressure of DOCA-salt, subtotal nephrectomy, and one-kidney-one clip renovascular hypertensive rats but only small and nonsignificant changes in blood pressure of two-kidney-one clip renovascular and spontaneously hypertensive rats. CP 96,345 had no effect on the blood pressure of sham-treated controls and Wistar-Kyoto rats. This NK-1 receptor antagonist did not significantly affect the heart rate of any experimental model studied. The data suggest that endogenous substance P may act as a partial counterregulatory mechanism against vasoconstriction in models of salt-dependent hypertension.

A neurotensin antagonist, SR 48692, inhibits colonic responses to immobilization stress in rats

We previously reported that short-term immobilization stress of rats causes increased colonic mucin release, goblet cell depletion, prostaglandin E2 secretion, and colonic mast cell activation, as well as increased colonic motility. The purpose of this study was to investigate whether neurotensin (NT), a peptide expressed in both brain and digestive tract, participates in these responses. Rats were pretreated with SR 48692 (1 mg/kg, i.p.), an NT antagonist, 15 min before immobilization (30 min). The administration of the antagonist significantly inhibited stress-mediated secretion of colonic mucin, prostaglandin E2, and a product of rat mast cells, rat mast cell protease II (P < 0.05), but did not alter the increase in fecal pellet output caused by immobilization stress. Immobilization stress also resulted in a quantifiable decrease in the abundance of NT receptor mRNA in rat colon compared with that in colonic tissues from nonimmobilized rats as measured by densitometric analysis of in situ hybridization studies (P < 0.03). We conclude that the peptide NT is involved in colonic goblet cell release and mucosal mast cell activation after immobilization stress.