Blockade of mast cell histamine secretion in response to neurotensin by SR 48692, a nonpeptide antagonist of the neurotensin brain receptor

Between two storms, vasoactive peptides or bradykinin underlie severity of COVID-19?

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to be a world-wide pandemic with overwhelming socioeconomic impact. Since inflammation is one of the major causes of COVID-19 complications, the associated molecular mechanisms have been the focus of many studies to better understand this disease and develop improved treatments for patients contracting SARS-CoV-2. Among these, strong emphasis has been placed on pro-inflammatory cytokines, associating severity of COVID-19 with so-called "cytokine storm." More recently, peptide bradykinin, its dysregulated signaling or "bradykinin storm," has emerged as a primary mechanism to explain COVID-19-related complications. Unfortunately, this important development may not fully capture the main molecular players that underlie the disease severity. To this end, in this focused review, several lines of evidence are provided to suggest that in addition to bradykinin, two closely related vasoactive peptides, substance P and neurotensin, are also likely to drive microvascular permeability and inflammation, and be responsible for development of COVID-19 pathology. Furthermore, based on published experimental observations, it is postulated that in addition to ACE and neprilysin, peptidase neurolysin (Nln) is also likely to contribute to accumulation of bradykinin, substance P and neurotensin, and progression of the disease. In conclusion, it is proposed that "vasoactive peptide storm" may underlie severity of COVID-19 and that simultaneous inhibition of all three peptidergic systems could be therapeutically more advantageous rather than modulation of any single mechanism alone.

Neurolysin substrates bradykinin, neurotensin and substance P enhance brain microvascular permeability in a human in vitro model

Increased brain microvascular permeability and disruption of blood-brain barrier (BBB) function are among hallmarks of several acute neurodegenerative disorders, including stroke. Numerous studies suggest the involvement of bradykinin (BK), neurotensin (NT) and substance P (SP) in BBB impairment and oedema formation after stroke; however, there is paucity of data in regard to the direct effects of these peptides on the brain microvascular endothelial cells (BMECs) and BBB. The present study aimed to evaluate the direct effects of BK, NT and SP on the permeability of BBB in an in vitro model based on human induced pluripotent stem cell (iPSC)-derived BMECs. Our data indicate that all three peptides increase BBB permeability in a concentration-dependent manner in an in vitro model formed from two different iPSC lines (CTR90F and CTR65M) and widely used hCMEC/D3 human BMECs. The combination of BK, NT and SP at a sub-effective concentration also resulted in increased BBB permeability in the iPSC-derived model indicating potentiation of their action. Furthermore, we observed abrogation of BK, NT and SP effects with pretreatment of pharmacological blockers targeting their specific receptors. Additional mechanistic studies indicate that the short-term effects of these peptides are not mediated through alteration of tight-junction proteins claudin-5 and occludin, but likely involve redistribution of F-actin and secretion of vascular endothelial growth factor. This is the first experimental study to document the increased permeability of the BBB in response to direct action of NT in an in vitro model. In addition, our study confirms the expected but not well-documented, direct effect of SP on BBB permeability and adds to the well-recognised actions of BK on BBB. Lastly, we demonstrate that peptidase neurolysin can neutralise the effects of these peptides on BBB, suggesting potential therapeutic implications.

Improvement in blastocyst quality by neurotensin signaling via its receptors in bovine spermatozoa during in vitro fertilization

Previously, we reported that neurotensin (NT), which is expressed in the uterus and oviduct, enhanced bovine sperm capacitation and acrosome reactions. As NT mRNA expression in bovine oviducts increases dramatically in the follicular phase, we hypothesized that NT modulates fertilization and subsequent conception in cattle. The objective of this study was to evaluate the effect of NT on embryo development and blastocyst quality. The rate of embryo cleavage was significantly increased by the addition of NT to the fertilization medium. Furthermore, the total number of cells and numbers of cells in the inner cell mass of blastocysts were significantly increased by NT during in vitro fertilization (IVF). These results suggested that NT enhanced the efficiency of early bovine embryo development and blastocyst quality. The expression of NT receptors (NTRs) in sperm, testes, oocytes, and cumulus cells was evaluated to determine whether NT acted via NTRs in sperm alone or in both male and female reproductive cells during IVF. Immunocytochemistry and reverse transcription polymerase chain reaction revealed that NTR1 and NTR2 were expressed in sperm and testes, but not in oocytes and cumulus cells. We propose that NT selectively acts upon sperm via NTR1 and NTR2 during IVF to improve the cleavage rate and quality of blastocysts, which are important determinants of sperm quality for successful conception. This research supports our hypothesis that NT acts as a key modulator of fertilization and conception in cattle. Further studies are necessary to apply our findings to the industrial framework of bovine reproduction.

Neurotensin stimulates sortilin and mTOR in human microglia inhibitable by methoxyluteolin, a potential therapeutic target for autism

We had reported elevated serum levels of the peptide neurotensin (NT) in children with autism spectrum disorders (ASD). Here, we show that NT stimulates primary human microglia, the resident immune cells of the brain, and the immortalized cell line of human microglia-SV40. NT (10 nM) increases the gene expression and release (P < 0.001) of the proinflammatory cytokine IL-1β and chemokine (C-X-C motif) ligand 8 (CXCL8), chemokine (C-C motif) ligand 2 (CCL2), and CCL5 from human microglia. NT also stimulates proliferation (P < 0.05) of microglia-SV40. Microglia express only the receptor 3 (NTR3)/sortilin and not the NTR1 or NTR2. The use of siRNA to target sortilin reduces (P < 0.001) the NT-stimulated cytokine and chemokine gene expression and release from human microglia. Stimulation with NT (10 nM) increases the gene expression of sortilin (P < 0.0001) and causes the receptor to be translocated from the cytoplasm to the cell surface, and to be secreted extracellularly. Our findings also show increased levels of sortilin (P < 0.0001) in the serum from children with ASD (n = 36), compared with healthy controls (n = 20). NT stimulation of microglia-SV40 causes activation of the mammalian target of rapamycin (mTOR) signaling kinase, as shown by phosphorylation of its substrates and inhibition of these responses by drugs that prevent mTOR activation. NT-stimulated responses are inhibited by the flavonoid methoxyluteolin (0.1-1 μM). The data provide a link between sortilin and the pathological findings of microglia and inflammation of the brain in ASD. Thus, inhibition of this pathway using methoxyluteolin could provide an effective treatment of ASD.

Neurotensin enhances sperm capacitation and acrosome reaction in mice

Neurotensin (NT) has multiple functions, ranging from acting as a neurotransmitter to regulating intestinal movement. However, its function in reproductive physiology is unknown. Here, we confirmed the expression and localization of NT receptors (NTR1) in mouse epididymal spermatozoa and investigated the effect of NT on sperm function. Sperm protein tyrosine phosphorylation, one of the indices of sperm capacitation, was facilitated dose-dependently by NT administration. In addition, the acrosome reaction was promoted in capacitated spermatozoa, and addition of a selective antagonist of NTR1 and NTR2 blocked the induction. Furthermore, intracellular calcium mobilization by NT addition was observed. This showed that NT was an accelerator of sperm function via its functional receptors. The presence of NT was confirmed by immunohistochemistry and its localization was observed in epithelia of the uterus and oviduct isthmus and ampulla, which correspond to the fertilization route of spermatozoa. The NT mRNA level in ovulated cumulus cell was remarkably increased by treatment with human chorionic gonadotropin (hCG). Using an in vitro maturation model, we analyzed the effects of FSH, epidermal growth factor (EGF), estradiol, and progesterone in NT production in cumulus cells. We found that FSH and EGF upregulated NT release and mRNA expression. Both FSH- and EGF-induced upregulation were inhibited by U0126, an MAPK kinase inhibitor, indicating that FSH and EGF regulate NT expression via a MAPK-dependent pathway. This evidence suggests that NT can act as a promoter of sperm capacitation and the acrosome reaction in the female reproductive tract.

Cannabinoid CB1 Receptors Mediate the Gastroprotective Effect of Neurotensin

OBJECTIVES

Several lines of evidence indicate that neuropeptides exhibit protective properties against gastroduodenal ulcers. Neurotensin, a gut-brain neuropeptide, is implicated in a number of physiological processes in the central nervous system and peripheral tissues including gastrointestinal tract. In the present study, we aimed to investigate the gastroprotective potential of either peripherally or centrally administered neurotensin with a look at the role of the cannabinoid CB1 receptors which are located in brain areas implicated in the regulation of gastric functions.

MATERIALS AND METHODS

Gastric mucosal damage was induced by intragastric administration of acidified ethanol in male Wistar rats. One hour later, gastric lesions were evaluated macroscopically. In gastroprotection study, neurotensin was administered either intravenously (1.5, 3, and 5 µM/kg) or intracerebroventricularly (0.5, 1, and 2.5 nM/rat) 30 min before the ethanol challenge. In order to evaluate the involvement of central CB1 receptors in the gastroprotective effect of neurotensin, the CB1 receptor antagonist AM251 (5, 10, and 15 nM/rat) was given i.c.v. 30 min prior to the administration of neurotensin. The effects of AM251 on the intact stomach and ethanol-induced gastric lesions were also evaluated.

RESULTS

Acidified ethanol induced large areas of gastric lesions which were significantly reduced by the highest dose of neurotensin in i.v. or i.c.v. application. The gastroprotective effect of neurotensin was prevented by pretreatment with 15 nM/rat AM251. AM251 had no effect by itself.

CONCLUSION

Peripherally or centrally given neurotensin protects gastric mucosa against damage induced by acidified ethanol through the activation of central cannabinoid CB1 receptors.

The potential use of the neurotensin high affinity receptor 1 as a biomarker for cancer progression and as a component of personalized medicine in selective cancers

A growing challenge in medicine today, is the need to improve the suitability of drug treatments for cancer patients. In this field, biomarkers have become the "flags" to provide additional information in tumor biology. They are a relay between the patient and practitioner and consequently, aid in the diagnosis, providing information for prognosis, or in some cases predicting the response to specific therapies. In addition to being markers, these tumor "flags" can also be major participants in the process of carcinogenesis. Neurotensin receptor 1 (NTSR1) was recently identified as a prognosis marker in breast, lung, and head and neck squamous carcinomas. Neurotensin (NTS) was also shown to exert numerous oncogenic effects involved in tumor growth and metastatic spread. These effects were mostly mediated by NTSR1, making the NTS/NTSR1 complex an actor in cancer progression. In this review, we gather information on the oncogenic effects of the NTS/NTSR1 complex and its associated signaling pathways in order to illuminate its significant role in tumor progression and its potential as a biomarker and a therapeutic target in some tumors.

Advanced glycation end products (AGEs) activate mast cells

BACKGROUND AND PURPOSE

Advanced glycation endproducts (AGEs) represent one of the many types of chemical modifications that occur with age in long-lived proteins. AGEs also accumulate in pathologies such as diabetes, cardiovascular diseases, neurodegeneration and cancer. Mast cells are major effectors of acute inflammatory responses that also contribute to the progression of chronic diseases. Here we investigated interactions between AGEs and mast cells.

EXPERIMENTAL APPROACHES

Histamine secretion from AGEs-stimulated mast cells was measured. Involvement of a receptor for AGEs, RAGE, was assessed by PCR, immunostaining and use of inhibitors of RAGE. Production of reactive oxygen species (ROS) and cytokines was measured.

KEY RESULTS

Advanced glycation endproducts dose-dependently induced mast cell exocytosis with maximal effects being obtained within 20 s. RAGE mRNA was detected and intact cells were immunostained by a specific anti-RAGE monoclonal antibody. AGEs-induced exocytosis was inhibited by an anti-RAGE antibody and by low molecular weight heparin, a known RAGE antagonist. RAGE expression levels were unaltered after 3 h treatment with AGEs. AGE-RAGE signalling in mast cells involves Pertussis toxin-sensitive G(i)-proteins and intracellular Ca(2+) increases as pretreatment with Pertussis toxin, caffeine, 2-APB and BAPTA-AM inhibited AGE-induced exocytosis. AGEs also rapidly stimulated ROS production. After 6 h treatment with AGEs, the pattern of cytokine secretion was unaltered compared with controls.

CONCLUSIONS AND IMPLICATIONS

Advanced glycation endproducts activated mast cells and may contribute to a vicious cycle involving generation of ROS, increased formation of AGEs, activation of RAGE and to the increased low-grade inflammation typical of chronic diseases.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Effects of NT on gastrointestinal motility and secretion, and role in intestinal inflammation

It is well established that interactions of neuropeptides with several cell types at various parts of the intestine are critically involved in intestinal pathophysiology. Among them, neurotensin has been identified as an important mediator in the development and progress of several gastrointestinal functions and disease conditions, exerting its effects by interacting with specific receptors that exert direct and indirect effects on nerves, epithelial cells, and cells of the immune and inflammatory systems. This review summarizes our recent understanding on the participation of neurotensin in the physiology and pathophysiology of the small and large intestine, and discusses various mechanisms that could be involved in these actions.

Corticotropin-releasing hormone induces skin vascular permeability through a neurotensin-dependent process

Many skin disorders are associated with increased numbers of activated mast cells and are worsened by stress; however, the mechanism underlying these processes is not understood. Corticotropin-releasing hormone (CRH) is secreted under stress from the hypothalamus, but also in the skin, where it induces mast cell activation and vascular permeability. We investigated the effect of CRH in a number of animal models by using i.v. Evans blue extravasation as a marker of vascular permeability. Intradermal CRH is among the most potent peptides at 100 nM, its effect being nearly comparable to that of neurotensin (NT). Pretreatment of skin injection sites with the NT receptor antagonist SR48692 blocks CRH-induced vascular permeability, which is diminished in NT-/- mice, implying that NT is necessary for the effect of CRH. CRH and NT precursor mRNA are shown to be expressed in both dorsal root ganglia and skin, whereas the latter also expresses mRNA for prohormone convertase 5, an enzyme that cleaves pro-NT into its active form. We also show that the effect of both CRH and NT is absent in W/W(v) mast cell-deficient mice; however, only a fraction of skin mast cells express CRH receptors, as shown by FACS analysis of CRH receptor (CRHR) and c-kit double-positive disaggregated mouse skin mast cells. These findings suggest that CRH induces skin vascular permeability through NT acting on mast cells and that both peptides should be considered in the pathogenesis of skin disorders exacerbated by stress.

Neuropeptide neurotensin stimulates intestinal wound healing following chronic intestinal inflammation

Because neurotensin (NT) and its high-affinity receptor (NTR1) modulate immune responses, chloride secretion, and epithelial cell proliferation, we sought to investigate their role in the repair process that follows the development of mucosal injuries during a persistent inflammation. Colonic NT and NTR1, mRNA, and protein significantly increased only after dextran sodium sulfate (DSS)-induced inflammatory damage developed. Colitis-induced body weight loss, colonic myeloperoxidase activity, and histological damage were significantly enhanced by SR-48642 administration, a nonpeptide NTR1 antagonist, whereas continuous NT infusion ameliorated colitis outcome. To evaluate the NT and NTR1 role in tissue healing, mucosal inflammatory injury was established administering 3% DSS for 5 days. After DSS discontinuation, mice rapidly gained weight, ulcers were healed, and colonic NT, NTR1, and cyclooxygenase (COX)-2 mRNA levels were upregulated, whereas SR-48642 treatment caused a further body weight loss, ulcer enlargement, and a blunted colonic COX-2 mRNA upregulation. In a wound-healing model in vitro, NT-induced cell migration in the denuded area was inhibited by indomethacin but not by an antitransforming growth factor-beta neutralizing antibody. Furthermore, NT significantly increased COX-2 mRNA levels by 2.4-fold and stimulated PGE(2) release in HT-29 cells. These findings suggest that NT and NTR1 are part of the network activated after mucosal injuries and that NT stimulates epithelial restitution at least, in part, through a COX-2 dependent pathway.

Neurotensin stimulates interleukin-8 expression through modulation of I kappa B alpha phosphorylation and p65 transcriptional activity: involvement of protein kinase C alpha

Neurotensin (NT) is released in the gastrointestinal tract and participates in the pathophysiology of colonic inflammation. We have shown that NT mediates acute intestinal inflammation in vivo and stimulates nuclear factor-kappaB-dependent interleukin (IL)-8 expression in nontransformed human colonocytes in vitro. However, the exact mechanisms by which NT induces IL-8 expression have not been elucidated. In this study, we first show that NT stimulates IkappaBalpha phosphorylation and degradation and p65 phosphorylation and transcriptional activity. Inhibition of protein kinase C (PKC) activation significantly attenuates NT-induced IL-8 expression. This effect seems to be mediated through inhibition of IkappaBalpha phosphorylation and degradation and by p65 phosphorylation and transcriptional activity. We also show that intracellular calcium mobilization is necessary for NT-induced phosphorylation of IkappaBalpha and p65, suggesting that a conventional PKC is involved. Furthermore, transfection of a dominant-negative form of PKCalpha significantly reduces NT-induced IL-8 promoter activity. These results indicate that the conventional PKCalpha is an important mediator in the proinflammatory signaling pathway elicited by NT at the colonocyte level.

Neurotensin receptor-3/sortilin mediates neurotensin-induced cytokine/chemokine expression in a murine microglial cell line

We show that the type I neurotensin receptor-3 (also called sortilin) is the only known neurotensin receptor expressed in a murine microglial cell line and that its activation leads to phosphorylation of both extracellular signaling-regulated (Erk1/2) and Akt kinases. Using semiquantitative reverse-transcriptase (RT) PCR, we demonstrate that neurotensin induces gene expression of several cytokines/chemokines including macrophage inflammatory protein (MIP)-2, monocyte chemotactic protein (MCP)-1, interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. This induction is dependent on both phosphatidylinositol 3-kinase and mitogen-activated protein kinases pathways. We observe that the effect of neurotensin on cytokine/chemokine expression is inhibited by the neurotensin receptor-3 propeptide, a selective ligand of this receptor. These results demonstrate that the neurotensin receptor-3 is functional in microglial cells where it mediates the induction of chemokines/cytokines expression by neurotensin.

The anorectic effect of neurotensin is mediated via a histamine H1 receptor in mice

Neurotensin (NT), a tridecapeptide found in the mammalian brain and peripheral tissues, induces a decrease in food intake after central administration. In this investigation, we examine whether the histaminergic system is involved in NT-induced suppression of feeding. Intracerebroventricular injection of NT (0.1-1 nmol/mouse) led to dose-dependent inhibition of food intake in fasted ddY mice. The anorectic effect induced by NT (0.1 nmol/mouse) was ameliorated upon co-administration of pyrilamine (3 nmol/mouse), an antagonist for histomine H1 receptor. The NT-induced anorectic effect was partially ameliorated in H1 knockout mice. The findings suggest that the H1 receptor in part mediates the NT-induced suppression of food intake.

Involvement of mast cells in basal and neurotensin-induced intestinal absorption of taurocholate in rats

Neurotensin (NT), a hormone released from intestine by ingested fat, facilitates lipid digestion by stimulating pancreatic secretion and slowing the movement of chyme. In addition, NT can contract the gall bladder and enhance the enterohepatic circulation (EHC) of bile acids to promote micelle formation. Our recent finding that NT enhanced and an NT antagonist inhibited [(3)H]taurocholate ([(3)H]TC) absorption from proximal rat small intestine indicated a role for endogenous NT in the regulation of EHC. Here, we postulate the involvement of intestinal mast cells in the TC uptake process and in the stimulatory effect of NT. In anesthetized rats with the bile duct cannulated for bile collection, infusion of NT (10 pmol.kg(-1).min(-1)) enhanced the [(3)H]TC recovery rate from duodenojejunum by 2.2-fold. This response was abolished by pretreatment with mast cell stabilizers (cromoglycate, doxantrazole) and inhibitors of mast cell mediators (diphenhydramine, metergoline, zileuton). In contrast, mast cell degranulators (compound 48/80, substance P) and mast cell mediators (histamine, leukotriene C(4)) reproduced the effect of NT. N(G)-nitro-l-arginine methyl ester enhanced and l-arginine inhibited basal and NT-induced TC uptake, consistent with the known inhibitory effect of nitric oxide (NO) on mast cell reactivity. These results argue that basal and NT-stimulated TC uptake in rat jejunum are similarly dependent on mast cells, are largely mediated by release of mast cell mediators, and are subject to regulation by NO.

Endogenous neurotensin facilitates visceral nociception and is required for stress-induced antinociception in mice and rats

Central neurotensin (NT) administration can both facilitate and inhibit somatic and visceral nociception, depending on the dose and administration site. NT microinjection in the rostroventral medulla facilitates nociception at low doses, while NT antagonist microinjection can markedly attenuate nociception, supporting the hypothesis that endogenous NT facilitates nociception. However, higher doses of NT produce a mu-opioid receptor-independent analgesia, similar to that resulting from various intense stressors. Furthermore, intense stress results in increased NT expression in several hypothalamic nuclei that have been implicated in stress-induced antinociception (SIAN); however, there is little direct evidence that endogenous NT is required for SIAN. We have investigated the role of endogenous NT in both basal visceral nociception and SIAN using both NT knockout mice and pharmacological approaches in rats. Visceral nociception was monitored by measuring visceromotor responses during colorectal distension both prior to and following water avoidance stress. Visceral nociception was significantly attenuated in both NT knockout mice and rats pre-treated with the NT antagonist SR 48692. Disruption of NT signaling also blocked SIAN, revealing a novel stress-induced hyperalgesic response that was significantly greater in female than in male rats. NT was also required for acetic acid-induced hyperalgesia. These results indicate that endogenous NT normally facilitates visceral pain responses, is required for irritant-induced hyperalgesia, and plays a critical role in SIAN.

Histamine releasing peptide (HRP) has proinflammatory effects and is present at sites of inflammation

Albumin, the most abundant plasma protein, readily enters sites of inflammation during the period of increased vascular permeability. There it encounters proteases released from mast cells and invading leukocytes which earlier work has shown can act on albumin to liberate the peptide, histamine releasing peptide (HRP), first identified and named by its ability to stimulate histamine release from isolated mast cells. In this report we show that HRP releases histamine from cutaneous mast cells in vivo resulting in increased vascular permeability and persistent edema while in vitro, HRP promotes chemotaxis of leukocytes and enhances macrophage phagocytosis. Moreover, we show that the level of HRP is increased with the induction of an acute cutaneous inflammatory response in rats, that HRP is present at sites of acute and chronic inflammation in humans and that HRP is rapidly degraded by proteases thereby limiting its action to the area of its generation. We suggest that HRP is a pro-inflammatory peptide that helps amplify and perpetuate the inflammatory response. Inhibitors of inflammatory proteases or antagonists that block the action of peptides like HRP may, therefore, be useful in breaking the cycle of inflammation.

Catestatin (CgA344-364) stimulates rat mast cell release of histamine in a manner comparable to mastoparan and other cationic charged neuropeptides

Catestatin (bovine CgA(344-364)) is a cationic peptide, which besides reducing catecholamine secretion from chromaffin cells in vitro also acts a potent vasodilator in the rat in vivo. The alleged histamine releasing effect of catestatin was tested in vitro in rat mast cells. The most active domain of catestatin (bovine CgA(344-358): RSMRLSFRARGYGFR) caused concentration-dependent (0.01-5 microM) release of histamine from peritoneal and pleural mast cells. The potency and efficacy of catestatin was higher than for the wasp venom peptide, mastoparan. Only in the pleural cells was neurotensin (NT) more potent than catestatin, mastoparan and substance P (SP), consistent with a receptor-mediated histamine release by neurotensin. Amongst these cationic peptides, substance P was least effective. The acidic CgA peptide (WE-14, bovine CgA (324-337)) neither stimulated nor modulated histamine release by the cationic peptides. The catestatin and neurotensin evoked histamine release were suppressed by pertussis toxin (PTX), suggesting involvement of a G(i) subunit. Electron micrographs of rat pleural mast cells responding to catestatin revealed a concentration-dependent discharge of granular material. We propose that catestatin activates histamine release from rat mast cells by a mechanism analogous to that already established for mastoparan and other amphiphilic cationic neuropeptides (the peptidergic pathway) and distinct from the mechanism of inhibition of catecholamine release from chromaffin cells.

G protein-dependent activation of mast cell by peptides and basic secretagogues

Signaling pathways leading to exocytosis and arachidonate release from serosal mast cells by basic secretagogues, including cationic peptides, arise from the involvement of betagamma subunits from G(i2) and G(i3) GTP-binding proteins. The original concept that basic secretagogues directly interact with G proteins implicated the entry of secretagogues into mast cells. This has been demonstrated only for the neuropeptide substance P. Basic secretagogues might share a common mechanism of penetration with the newly described cell-penetrating peptides. The involvement of some membrane transporter or non-selective membrane receptor to basic secretagogues cannot be excluded.

Signal transduction pathways mediating neurotensin-stimulated interleukin-8 expression in human colonocytes

Neurotensin (NT), a neuropeptide released in the gastrointestinal tract in response to several stimuli, is involved in the pathophysiology of colonic inflammation. However, the molecular mechanism(s) mediating this proinflammatory response remains unclear. We found that NCM460, non-transformed human colonocytes, express a functional high affinity NT receptor that mediates NT-induced Erk activation. By using NCM460 cells stably transfected with NTR1, we show that NTR1 activation leads to interleukin (IL)-8 secretion that is mediated via both NF-kappaB- and Erk-dependent pathways. In addition, NT-stimulated NF-kappaB activation is dependent on intracellular calcium release. NT-stimulated Erk activity requires Ras activation because overexpression of the dominant negative Ras mutant Ras-17N almost completely inhibits the Erk activation. Furthermore, NT directly stimulates Ras-GTP formation as shown by a Ras-GTP pull-down assay. By using reporter gene constructs containing targeted substitutions in the IL-8 promoter, we show that the NF-kappaB, AP-1, and to a lesser degree the C/EBP sites in the IL-8 promoter region are required for IL-8 gene expression induced by NT. In summary, our results demonstrate that NT stimulates calcium-dependent NF-kappaB and Ras-dependent Erk pathways that mediate the release of IL-8 from non-transformed human colonocytes. We speculate that these NT-related proinflammatory pathways are important in the pathophysiology of colonic inflammation.

New agents for the medical treatment of interstitial cystitis

Interstitial cystitis (IC) is a painful, sterile, disorder of the urinary bladder characterised by urgency, frequency, nocturia and pain. IC occurs primarily in women but also in men with recent findings indicating that chronic, abacterial prostatitis may be a variant of this condition. The prevalence of IC has ranged from about 8 - 60 cases/100,000 female patients depending on the population evaluated. About 10% of patients have severe symptoms that are associated with Hunner's ulcers on bladder biopsy; the rest could be grouped in those with or without bladder inflammation. Symptoms of IC are exacerbated by stress, certain foods and ovulatory hormones. Many patients also experience allergies, irritable bowel syndrome (IBS) and migraines. There have been various reports indicating dysfunction of the bladder glycosaminoglycan (GAG) protective layer and many publications showing a high number of activated bladder mast cells. Increasing evidence suggests that neurogenic inflammation and/or neuropathic pain is a major component of IC pathophysiology. Approved treatments so far include intravesical administration of dimethylsulphoxide (DMSO) or oral pentosanpolysulphate (PPS). New treatments focus on the combined use of drugs that modulate bladder sensory nerve stimulation (neurolytic agents), inhibit neurogenic activation of mast cells, or provide urothelial cytoprotection, together with new drugs with anti-inflammatory activity.

Acute immobilization stress triggers skin mast cell degranulation via corticotropin releasing hormone, neurotensin, and substance P: A link to neurogenic skin disorders

Many skin disorders, such as atopic dermatitis and psoriasis, worsen during stress and are associated with increased numbers and activation of mast cells which release vasoactive, nociceptive, and proinflammatory mediators. Nontraumatic acute psychological stress by immobilization has been shown to induce mast cell degranulation in the rat dura and colon. Moreover, intradermal injection of corticotropin-releasing hormone (CRH) or its analogue urocortin (10(-5)-10(-7) M) induced skin mast cell degranulation and increased vascular permeability. Here, we investigated the effect of acute immobilization stress on skin mast cell degranulation by light microscopy and electron microscopy. Immobilization for 30 min resulted (P < 0.05) in degranulation of 40.7 +/- 9.1% of skin mast cells compared to 22.2 +/- 7.3% in controls killed by CO(2) or 17.8 +/- 2.4% in controls killed by pentobarbital. Pretreatment intraperitoneally (ip) with antiserum to CRH for 60 min prior to stress reduced (P < 0.05) skin mast cell degranulation to 21.0 +/- 3. 3%. Pretreatment with the neurotensin (NT) receptor antagonist SR48692 reduced (P < 0.05) mast cell degranulation to 12.5 +/- 3.4%, which was significantly (P < 0.05) below control levels. In animals treated neonatally with capsaicin to deplete their sensory neurons of their neuropeptides, such as substance P (SP), mast cell degranulation due to immobilization stress was reduced to about 15%. This is the first time that stress has been shown to trigger skin mast cell degranulation, an action not only dependent on CRH, but apparently also involving NT and SP. These findings may have implications for the pathophysiology and possible therapy of neuroinflammatory skin disorders such as atopic dermatitis, neurogenic pruritus, or psoriasis, which are induced or exacerbated by stress.

Neurotensin mediates rat bladder mast cell degranulation triggered by acute psychological stress

OBJECTIVES

An increased number of activated mast cells have been documented in interstitial cystitis (IC), a painful bladder disorder occurring primarily in women and exacerbated by stress. Mast cells in the bladder and in the intestine are often found in juxtaposition to neurons, where they are activated by neuropeptides and neurotransmitters as well as by acute psychological stress. This work was undertaken to investigate whether the neuropeptide neurotensin (NT) is involved in the activation of bladder mast cells by acute psychological stress.

METHODS

Male 300-g Sprague-Dawley rats were either kept on the bench in a quiet procedure room or stressed by confining them one at a time for 30 minutes in a clear Plexiglas immobilizer and then killed with carbon dioxide. The bladder was removed and fixed with 4% paraformaldehyde. Frozen sections were either stained with acidified toluidine blue or processed for NT immunocytochemical analysis. An immunosorbent assay was used to also measure NT in bladder homogenate before and after stress.

RESULTS

Bladder mast cell activation in control rats was 37.3 +/- 1.4%, as judged by extrusion of granule contents. Degranulation in stressed animals increased to 75.3 +/- 5.5% (P = 0.0003). Treatment of the animals neonatally with capsaicin decreased mast cell degranulation to 48.9 +/- 7.5% (P = 0.008), a 35.1% inhibition. Intraperitoneal administration of the nonpeptide NT receptor antagonist SR48692 sixty minutes before stress decreased bladder mast cell degranulation to 25.2 +/- 3.6% (P = 0.00007), a 66.5% inhibition. This value is 32.5% below control levels, indicating that NT is involved in basal mast cell degranulation. Stress also reduced the total bladder NT content.

CONCLUSIONS

The present results indicate that NT mediates the effect of acute, nontraumatic psychological stress on bladder mast cell degranulation. They further suggest that NT receptor antagonists may be useful in subpopulations of patients with IC in whom symptoms worsen under stress.

Neurotensin is a proinflammatory neuropeptide in colonic inflammation

The neuropeptide neurotensin mediates several intestinal functions, including chloride secretion, motility, and cellular growth. However, whether this peptide participates in intestinal inflammation is not known. Toxin A, an enterotoxin from Clostridium difficile, mediates pseudomembranous colitis in humans. In animal models, toxin A causes an acute inflammatory response characterized by activation of sensory neurons and intestinal nerves and immune cells of the lamina propria. Here we show that neurotensin and its receptor are elevated in the rat colonic mucosa following toxin A administration. Pretreatment of rats with the neurotensin receptor antagonist SR-48, 692 inhibits toxin A-induced changes in colonic secretion, mucosal permeability, and histologic damage. Exposure of colonic explants to toxin A or neurotensin causes mast cell degranulation, which is inhibited by SR-48,692. Because substance P was previously shown to mediate mast cell activation, we examined whether substance P is involved in neurotensin-induced mast cell degranulation. Our results show that neurotensin-induced mast cell degranulation in colonic explants is inhibited by the substance P (neurokinin-1) receptor antagonist CP-96,345, indicating that colonic mast activation in response to neurotensin involves release of substance P. We conclude that neurotensin plays a key role in the pathogenesis of C. difficile-induced colonic inflammation and mast cell activation.

Neurotensin stimulation of mast cell secretion is receptor-mediated, pertussis-toxin sensitive and requires activation of phospholipase C

Pretreatment of isolated rat serosal mast cells with U-73122, an aminosteroid inhibitor of phospholipase C, inhibited histamine secretion in response to neurotensin (NT). This inhibition reached a maximum after 1 h of pretreatment at 37 degrees C and was dependent upon the concentration of U-73122 (IC50 approximately 0.2 microM). The inactive analog, U-73343, had no effect on the secretory response to NT. Pretreatment of mast cells with U-73122 also blocked histamine secretion in response to substance P (SP), mastoparan (MP), compound 48/80, or amidated NT (NT-NH2). Stimulation of mast cells by NT was accompanied by a rise in the level of intracellular free calcium and a rapid (within seconds) increase in the level of inositol trisphosphate (IP3) which was inhibited by pretreatment of the cells with U-73122. Pretreatment of isolated mast cells with pertussis toxin (PTx) blocked histamine release in response to NT as well as to all peptides tested. PTx had no effect on histamine secretion elicited by anti-IgE stimulation of sensitized mast cells. Pretreatment of mast cells with SR 48692, a NT-receptor antagonist, had no effect on histamine release induced by MP. At a high concentration (100 nM) SR 48692 partially inhibited the response to NT-NH2. These results, together with our earlier findings with SR 48692, indicate that the signal transduction pathway in mast cells activated by NT requires a specific NT-receptor, the activation of phospholipase C, and the involvement of a PTx sensitive G protein. The peptides SP and MP, and compound 48/80, while also requiring the activation of PLC and a PTx sensitive G protein, are not inhibited by the NT-R antagonist, SR 48692, suggesting that they exert their actions either via a different mast cell receptor or via a receptor-independent mechanism.

SR142948A is a potent antagonist of the cardiovascular effects of neurotensin

The novel compound SR142948A was compared with SR48692 as an antagonist of neurotensin-induced cardiovascular effects both in vitro and in vivo. SR142948A inhibited [125I]-neurotensin binding [median inhibitory concentration (IC50) = 0.24 +/- 0.01 nM], neurotensin-induced cytosolic free Ca2+ increase (IC50 = 19 +/- 6 nM), and prostacyclin production in human umbilical vein endothelial cells (IC50 = 17 +/- 3 nM) at much lower concentrations than did SR48692 (respective IC50 values, 14 +/- 5, 41 +/- 16, and 86 +/- 16 nM). Oral administration of SR142948A (10 microg/kg) resulted in significant inhibition of neurotensin-induced blood pressure changes, whereas SR48692 was active only at 10-fold higher doses. Furthermore, SR142948A administered i.v. in microg/kg quantities in the rat was as active as mg/kg doses of SR48692 on neurotensin-induced increase in hematocrit. SR142948A injected intradermally also significantly inhibited neurotensin-induced plasma extravasation at concentrations as low as 10 pmol/site, whereas 1,000 pmol/site of SR48692 were necessary to reach a significant inhibition. These data show that SR142948A is a novel, extremely potent antagonist of neurotensin-induced cardiovascular responses both in vitro and in vivo. SR142948A and SR48692 constitute a pair of nonpeptide neurotensin antagonists of different potency, which may be used to probe for the implication of neurotensin receptors in physiologic or pathologic phenomena.

Effect of octreotide, a somatostatin analogue, on release of inflammatory mediators from isolated guinea pig bladder

OBJECTIVE

Somatostatin has been demonstrated to inhibit inflammation under certain circumstances. We hypothesized that in vivo treatment with octreotide, a long-acting analogue of somatostatin analogue, would diminish the capacity of inflammatory peptides to stimulate in vitro release of inflammatory mediators by the bladder.

METHODS

Female guinea pigs were injected with octreotide (20 mg./kg. i.m.) prior to euthanasia. Control guinea pigs received no treatment prior to euthanasia. Urinary bladders were removed and incubated with substance P (SP, 10 microM), neurokinin A (NKA, 10 microM), or bradykinin (BK, 10 microM) in the presence or absence of indomethacin (50 microM), and release of histamine, prostaglandins (PGE2 and PGF2 alpha), and leukotriene (LTB4) was determined.

RESULTS

Sensory peptides and BK induced time-dependent release of histamine and eicosanoids from isolated urinary bladder. Blockade of cyclooxygenase with indomethacin (50 microM) abolished peptide-induced prostaglandin release but enhanced LTB4 release. In vivo octreotide pretreatment decreased peptide-induced histamine release, had no effect on PGE2 or PGF2 alpha release, and LTB4 release. However, octreotide prevented the increase in LTB4 release in tissues incubated with indomethacin.

CONCLUSIONS

These results indicate that somatostatin has the capacity to suppress the release of histamine and prevents potentiation of LTB4 release by indomethacin by the guinea pig bladder in response to pro-inflammatory peptides, indicating that somatostatin may be useful in preventing or treating some forms of cystitis.

Neurotensin induces the release of prostacyclin from human umbilical vein endothelial cells in vitro and increases plasma prostacyclin levels in the rat

Human umbilical vein endothelial cells express high affinity neurotensin receptors which are coupled to phosphoinositide turnover and 45Ca2+ efflux (Schaeffer et al., 1995. J. Biol. Chem. 270, 3409-3413). In order to assess the physiological significance of neurotensin receptor activation in endothelial cells, we have compared the in vitro effect of neurotensin on prostacyclin release and cytosolic free calcium increase ([Ca2+]i) as determined by fura-2 fluorescence experiments to the in vivo effect of neurotensin on blood pressure and haematocrit. Neurotensin increased [Ca2+]i levels at low concentrations (EC50 = 4.2 +/- 0.2 nM, n = 3). At similar concentrations, neurotensin was also able to induce prostacyclin release from human umbilical vein endothelial cells (EC50 = 14 +/- 1 nM, n = 3) as determined by a 6-keto-prostaglandin F1 alpha enzyme immunoassay. The neurotensin (100 nM)-induced [Ca2+]i increase and prostacyclin release were inhibited by the specific non-peptide neurotensin receptor antagonist SR 48692 at similar concentrations (IC50 = 41 +/- 16 nM and 86 +/- 17 nM, respectively, n = 3), confirming that these responses were mediated by high affinity neurotensin receptors. Intravenous injection of neurotensin (1-4 nmol/kg i.v.) in the rat resulted in a drop of blood pressure and increased haematocrit, and nearly doubled the plasma levels of 6-keto-prostaglandin F1 alpha, the stable metabolite of prostacyclin. Whereas indomethacin (10 mg/kg i.v.) pretreatment significantly reduced the effect of neurotensin on blood pressure, it did not alter its effect on haematocrit. These results suggest that prostacyclin release plays a role in the hypotensive effects of neurotensin, but is not involved in its effects on haematocrit.

Antagonism by SR 48692 of mechanical responses to neurotensin in rat intestine

1. The effects of SR 48692 on neurotensin (NT)-induced mechanical responses were investigated in rat duodenum and proximal colon by use of isometric, isovolumic preparations. 2. SR 48692 inhibited the relaxant responses to NT in duodenal circular and longitudinal muscle. It also antagonized the NT-induced contractile effects in duodenal circular muscle and in proximal colon (both muscular layers). 3. From Schild analysis and pA2 value for SR 48692 was 8.2 in tissues where NT induced relaxant effects and 7.5 in tissues where NT induced contractile effects and the slope of the regression line was not significantly different from unity, indicating competitive antagonism. 4. SR 48692 did not antagonize the duodenal relaxant effect induced by noradrenaline and the contractile response to carbachol or substance P in duodenum and colon. 5. Our results demonstrate that SR 48692 selectively antagonizes the mechanical actions of NT in rat intestine and confirm the existence of specific NT receptors. Receptors that subserve a relaxant effect seem to be related, but not identical, to those that mediate contractile effects.