The effect of neuropeptide Y and peptide YY on electrogenic ion transport in rat intestinal epithelia

Synthetic G protein-coupled bile acid receptor agonists and bile acids act via basolateral receptors in ileal and colonic mucosa

BACKGROUND

The G protein-coupled bile acid (BA) receptor, GPBA (previously named TGR5), mediates BA gastrointestinal (GI) activities. Our aim was to elucidate the mucosal and motility responses to selective GPBA agonists compared with conjugated BA (eg, taurodeoxycholate, TDCA) in mouse and human colon.

METHODS

Ion transport responses to GPBA agonists or BAs were measured in mucosal preparations with intact submucous innervation, from C57Bl/6, PYY-/-, or GPBA-/- mice and compared with GPBA signaling in human colon. We also investigated the mechanisms underlying GPBA agonism in mucosae and on natural fecal pellet propulsion.

KEY RESULTS

GPBA agonist Merck V stimulated basolateral responses involving peptide YY (PYY), cholinergic, and 5-HT mechanisms in colonic mucosa. The PYY-mediated GPBA signal was glucose-sensitive. Luminal TDCA crossed the epithelial lining via the apical sodium-dependent BA transporter (ASBT) and its inhibitor, GSK2330672 significantly reduced luminal, but not basolateral TDCA activity. Merck V also slowed natural fecal pellet progression in wild-type and PYY-/- colons but not in GPBA-/- colon, while TDCA increased motility in wild-type colon. The antimotile GPBA effect was reversed by blockade of glucagon-like peptide 1 (GLP-1) receptors or nitric oxide synthase, indicating involvement of GLP-1 and nitric oxide.

CONCLUSIONS & INFERENCES

We conclude that several different targets within the lamina propria express GPBA, including L cells (that release PYY and GLP-1), enterochromaffin cells and neurons (that release 5-HT), and other enteric neurons. Furthermore, luminal-conjugated BAs require transport across the epithelium via ASBT in order to activate basolateral GPBA.

Calcimimetic acts on enteric neuronal CaSR to reverse cholera toxin-induced intestinal electrolyte secretion

Treatment of acute secretory diarrheal illnesses remains a global challenge. Enterotoxins produce secretion through direct epithelial action and indirectly by activating enteric nervous system (ENS). Using a microperfused colonic crypt technique, we have previously shown that R568, a calcimimetic that activates the calcium-sensing receptor (CaSR), can act on intestinal epithelium and reverse cholera toxin-induced fluid secretion. In the present study, using the Ussing chamber technique in conjunction with a tissue-specific knockout approach, we show that the effects of cholera toxin and CaSR agonists on electrolyte secretion by the intestine can also be attributed to opposing actions of the toxin and CaSR on the activity of the ENS. Our results suggest that targeting intestinal CaSR might represent a previously undescribed new approach for treating secretory diarrheal diseases and other conditions with ENS over-activation.

L-arginine promotes gut hormone release and reduces food intake in rodents

AIMS

To investigate the anorectic effect of L-arginine (L-Arg) in rodents.

METHODS

We investigated the effects of L-Arg on food intake, and the role of the anorectic gut hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), the G-protein-coupled receptor family C group 6 member A (GPRC6A) and the vagus nerve in mediating these effects in rodents.

RESULTS

Oral gavage of L-Arg reduced food intake in rodents, and chronically reduced cumulative food intake in diet-induced obese mice. Lack of the GPRC6A in mice and subdiaphragmatic vagal deafferentation in rats did not influence these anorectic effects. L-Arg stimulated GLP-1 and PYY release in vitro and in vivo. Pharmacological blockade of GLP-1 and PYY receptors did not influence the anorectic effect of L-Arg. L-Arg-mediated PYY release modulated net ion transport across the gut mucosa. Intracerebroventricular (i.c.v.) and intraperitoneal (i.p.) administration of L-Arg suppressed food intake in rats.

CONCLUSIONS

L-Arg reduced food intake and stimulated gut hormone release in rodents. The anorectic effect of L-Arg is unlikely to be mediated by GLP-1 and PYY, does not require GPRC6A signalling and is not mediated via the vagus. I.c.v. and i.p. administration of L-Arg suppressed food intake in rats, suggesting that L-Arg may act on the brain to influence food intake. Further work is required to determine the mechanisms by which L-Arg suppresses food intake and its utility in the treatment of obesity.

Selective FFA2 Agonism Appears to Act via Intestinal PYY to Reduce Transit and Food Intake but Does Not Improve Glucose Tolerance in Mouse Models

Free fatty acid receptor 2 (FFA2) is expressed on enteroendocrine L cells that release glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) when activated by short-chain fatty acids (SCFAs). Functionally GLP-1 and PYY inhibit gut transit, increase glucose tolerance, and suppress appetite; thus, FFA2 has therapeutic potential for type 2 diabetes and obesity. However, FFA2-selective agonists have not been characterized in vivo. Compound 1 (Cpd 1), a potent FFA2 agonist, was tested for its activity on the following: GLP-1 release, modulation of intestinal mucosal ion transport and transit in wild-type (WT) and FFA2(-/-) tissue, and food intake and glucose tolerance in lean and diet-induced obese (DIO) mice. Cpd 1 stimulated GLP-1 secretion in vivo, but this effect was only detected with dipeptidyl peptidase IV inhibition, while mucosal responses were PYY, not GLP-1, mediated. Gut transit was faster in FFA2(-/-) mice, while Cpd 1 slowed WT transit and reduced food intake and body weight in DIO mice. Cpd 1 decreased glucose tolerance and suppressed plasma insulin in lean and DIO mice, despite FFA2(-/-) mice displaying impaired glucose tolerance. These results suggest that FFA2 inhibits intestinal functions and suppresses food intake via PYY pathways, with limited GLP-1 contribution. Thus, FFA2 may be an effective therapeutic target for obesity but not for type 2 diabetes.

Tumor necrosis factor-neuropeptide Y cross talk regulates inflammation, epithelial barrier functions, and colonic motility

BACKGROUND

Neuro-immune interactions play a significant role in regulating the severity of inflammation. Our previous work demonstrated that neuropeptide Y (NPY) is upregulated in the enteric nervous system during murine colitis and that NPY knockout mice exhibit reduced inflammation. Here, we investigated if NPY expression during inflammation is induced by tumor necrosis factor (TNF), the main proinflammatory cytokine.

METHODS

Using primary enteric neurons and colon explant cultures from wild type and NPY knockout (NPY(-/-)) mice, we determined if NPY knockdown modulates TNF release and epithelial permeability. Further, we assessed if NPY expression is inducible by TNF in enteric neuronal cells and mouse model of experimental colitis, using the TNF inhibitors-etanercept (blocks transmembrane and soluble TNF) and XPro1595 (blocks soluble TNF only).

RESULTS

We found that enteric neurons express TNF receptors (TNFR1 and R2). Primary enteric neurons from NPY(-/-) mice produced less TNF compared with wild type. Further, TNF activated NPY promoter in enteric neurons through phospho-c-Jun. NPY(-/-) mice had decreased intestinal permeability. In vitro, NPY increased epithelial permeability through phosphatidyl inositol-3-kinase (PI3-K)-induced pore-forming claudin-2. TNF inhibitors attenuated NPY expression in vitro and in vivo. TNF inhibitor-treated colitic mice exhibited reduced NPY expression and inflammation, reduced oxidative stress, enhanced neuronal survival, and improved colonic motility. XPro1595 had more protective effects on neuronal survival and motility compared with etanercept.

CONCLUSIONS

We demonstrate a novel TNF-NPY cross talk that modulates inflammation, barrier functions, and colonic motility during inflammation. It is also suggested that selective blocking of soluble TNF may be a better therapeutic option than using anti-TNF antibodies.

Calcium-sensing receptor inhibits secretagogue-induced electrolyte secretion by intestine via the enteric nervous system

Bacterial toxins such as cholera toxin induce diarrhea by both direct epithelial cell generation of cyclic nucleotides as well as stimulation of the enteric nervous system (ENS). Agonists of the extracellular calcium-sensing receptor (CaSR) can reduce toxin-stimulated fluid secretion in ENS-absent colonic epithelial crypts by increasing phosphodiesterase-dependent cyclic-nucleotide degradation. Here we show that the CaSR is also highly expressed in tetrodotoxin (TTX)-sensitive neurons comprising the ENS, suggesting that CaSR agonists might also function through neuronal pathways. To test this hypothesis, rat colon segments containing intact ENS were isolated and mounted on Ussing chambers. Basal and cyclic nucleotide-stimulated electrolyte secretions were monitored by measuring changes in short-circuit current (I(sc)). CaSR was activated by R-568 and its effects were compared in the presence and absence of TTX. Consistent with active regulation of anion secretion by the ENS, a significant proportion of I(sc) in the proximal and distal colon was inhibited by serosal TTX, both at basal and under cyclic AMP-stimulated conditions. In the absence of TTX, activation of CaSR with R-568 significantly reduced basal I(sc) and cyclic AMP-stimulated I(sc); it also completely reversed the cAMP-stimulated secretory responses if the drug was applied after the forskolin stimulation. Such inhibitory effects of R-568 were either absent or significantly reduced when serosal TTX was present, suggesting that this agonist exerts its antisecretory effect on the intestine by inhibiting ENS. The present results suggest a new model for regulating intestinal fluid transport in which neuronal and nonneuronal secretagogue actions are modulated by the inhibitory effects of CaSR on the ENS. The ability of a CaSR agonist to reduce secretagogue-stimulated Cl(-) secretion might provide a new therapeutic approach for secretory and other ENS-mediated diarrheal conditions.

Endogenous peptide YY and neuropeptide Y inhibit colonic ion transport, contractility and transit differentially via Y₁ and Y₂ receptors

BACKGROUND AND PURPOSE

Peptide YY (PYY) and neuropeptide Y (NPY) activate Y receptors, targets under consideration as treatments for diarrhoea and other intestinal disorders. We investigated the gastrointestinal consequences of selective PYY or NPY ablation on mucosal ion transport, smooth muscle activity and transit using wild-type, single and double peptide knockout mice, comparing mucosal responses with those from human colon.

EXPERIMENTAL APPROACH

Mucosae were pretreated with a Y₁ (BIBO3304) or Y₂ (BIIE0246) receptor antagonist and changes in short-circuit current recorded. Colonic transit and colonic migrating motor complexes (CMMCs) were assessed in vitro and upper gastrointestinal and colonic transit measured in vivo.

KEY RESULTS

Y receptor antagonists revealed tonic Y₁ and Y₂ receptor-mediated antisecretory effects in human and wild-type mouse colon mucosae. In both, Y₁ tone was epithelial while Y₂ tone was neuronal. Y₁ tone was reduced 90% in PYY⁻/⁻ mucosa but unchanged in NPY⁻/⁻ tissue. Y₂ tone was partially reduced in NPY⁻/⁻ or PYY⁻/⁻ mucosae and abolished in tetrodotoxin-pretreated PYY⁻/⁻ tissue. Y₁ and Y₂ tone were absent in NPYPYY⁻/⁻ tissue. Colonic transit was inhibited by Y₁ blockade and increased by Y₂ antagonism indicating tonic Y₁ excitation and Y₂ inhibition respectively. Upper GI transit was increased in PYY⁻/⁻ mice only. Y₂ blockade reduced CMMC frequency in isolated mouse colon.

CONCLUSIONS AND IMPLICATIONS

Endogenous PYY and NPY induced significant mucosal antisecretory tone mediated by Y₁ and Y₂ receptors, via similar mechanisms in human and mouse colon mucosa. Both peptides contributed to tonic Y₂-receptor-mediated inhibition of colonic transit in vitro but only PYY attenuated upper GI transit.

Stimulation of apical Cl⁻/HCO₃⁻(OH⁻) exchanger, SLC26A3 by neuropeptide Y is lipid raft dependent

Neuropeptide Y (NPY), an important proabsorptive hormone of the gastrointestinal tract has been shown to inhibit chloride secretion and stimulate NaCl absorption. However, mechanisms underlying the proabsorptive effects of NPY are not fully understood. The present studies were designed to examine the direct effects of NPY on apical Cl⁻/HCO₃⁻(OH⁻) exchange activity and the underlying mechanisms involved utilizing Caco2 cells. Our results showed that NPY (100 nM, 30 min) significantly increased Cl⁻/HCO₃⁻(OH⁻) exchange activity (∼2-fold). Selective NPY/Y1 or Y2 receptor agonists mimicked the effects of NPY. NPY-mediated stimulation of Cl⁻/HCO₃⁻(OH⁻) exchange activity involved the ERK1/2 MAP kinase-dependent pathway. Cell surface biotinylation studies showed that NPY does not alter DRA (apical Cl⁻/HCO₃⁻(OH⁻) exchanger) surface expression, ruling out the involvement of membrane trafficking events. Interestingly, DRA was found to be predominantly expressed in the detergent-insoluble (DI) and low-density fractions (LDF) of human colonic apical membrane vesicles (AMVs) representing lipid rafts. Depletion of membrane cholesterol by methyl-β-cyclodextrin (MβCD, 10 mM, 1 h) remarkably decreased DRA expression in the DI fractions. Similar results were obtained in Triton-X 100-treated Caco2 plasma membranes. DRA association with lipid rafts in the DI and LDF fractions of Caco2 cells was significantly enhanced (∼45%) by NPY compared with control. MβCD significantly decreased Cl⁻/HCO₃⁻(OH⁻) exchange activity in Caco2 cells as measured by DIDS- or niflumic acid-sensitive ³⁶Cl⁻ uptake (∼50%). Our results demonstrate that NPY modulates Cl⁻/HCO₃⁻(OH⁻) exchange activity by enhancing the association of DRA with lipid rafts, thereby resulting in an increase in Cl⁻/HCO₃⁻(OH⁻) exchange activity. Our findings suggest that the alteration in the association of DRA with lipid rafts may contribute to the proabsorptive effects of NPY in the human intestine.

Peptide YY is critical for acylethanolamine receptor Gpr119-induced activation of gastrointestinal mucosal responses

Peptide YY (PYY) is released following food intake and regulates intestinal function and glucose homeostasis, but the mechanisms underpinning these processes are unclear. Enteroendocrine L cells contain PYY and express the acylethanolamine receptor, Gpr119. Here, we show that Gpr119 activation inhibited epithelial electrolyte secretion in human and mouse colon in a glucose-sensitive manner. Endogenous PYY selectively mediated these effects, since PYY(-/-) mice showed no Gpr119 response, but responses were observed in NPY(-/-) mice. Importantly, Gpr119 responses in wild-type (WT) mouse tissue and human colon were abolished by Y(1) receptor antagonism, but were not enhanced by dipeptidylpeptidase IV blockade, indicating that PYY processing to PYY(3-36) was not important. In addition, Gpr119 agonism reduced glycemic excursions after oral glucose delivery to WT mice but not PYY(-/-) mice. Taken together, these data demonstrate a previously unrecognized role of PYY in mediating intestinal Gpr119 activity and an associated function in controlling glucose tolerance.

Antisecretory effects of neuropeptide Y in the mouse colon are region-specific and are lost in DSS-induced colitis

Regulation of water movement in the gut is an important homeostatic event that is critical to normal intestinal function. We assessed the effect of neuropeptide Y (NPY) on epithelial ion transport in the normal and inflamed mouse colons. Colitis was induced by dextran sodium sulfate (DSS, 4% wt./vol.) administered in the drinking water for 5 days followed by 3 days of regular water. Segments of proximal and distal colons were excised and short-circuit current (I(SC)) was measured in Ussing chambers to assess net electrogenic active ion transport. NPY Y(1) receptor (Y(1)R) expression was measured by quantitative real-time PCR and immunohistochemistry. Challenge of distal colon from normal mice with NPY (10(-7)M) evoked a drop in I(SC) (51.4±9.1 μA/cm(2)), which was dependent on Cl(-) flux, was insensitive to neural blockade with tetrodotoxin and was mediated primarily through the Y(1)R. In contrast, the proximal colon was largely unresponsive to NPY, expressing ~ten-fold less Y(1)R mRNA compared to the distal colon. These findings confirm that specific regional regulation of ion transport occurs in the colon. Segments of proximal and distal colons from mice with DDS-induced colitis were virtually unresponsive to NPY, expressed less Y(1)R mRNA than tissues from control mice and displayed loss of Y(1)R protein expression in the colonic epithelium. This hypo-responsiveness to an antisecretory stimulus adds to the well-documented loss of responsiveness to pro-secretory agents during inflammation, attesting to a profound loss of control of active ion transport during enteric inflammatory disease.

Physiological activity of neuropeptide f on the hindgut of the blood-feeding hemipteran, Rhodnius prolixus

Current hypotheses propose that, in the invertebrates, neuropeptide F (NPF), the vertebrate NPY homologue, may be capable of regulating responses to diverse cues related to nutritional status and feeding. An investigation into the effects of Drosophila melanogaster NPF (DrmNPF) and Anopheles gambiae NPF (AngNPF) on hindgut physiology of Rhodnius prolixus Stal (Heimptera: Reduviidae) suggests a myoinhibitory role for these peptides and the R. prolixus native peptide. Extracts of the central nervous system of R. prolixus were processed and several HPLC-fractions revealed NPF-like activity within the nanomolar equivalent range when tested using the hindgut contraction assay. Although NPF has been shown to decrease epithelial membrane potential in Aedes aegypti larval midgut preparations, NPF does not appear to play a role in epithelial transport of potassium in the hindgut. While the function of NPF has yet to be established, NPF-like effects suggest multiple physiological roles for NPF among invertebrates.

A functional comparison of recombinant and native somatostatin sst2 receptor variants in epithelia

BACKGROUND AND PURPOSE

Somatostatin (SRIF-14) exerts broad spectrum antisecretory effects by activating the somatostatin 2 (sst(2)) receptor. The rat (r) sst(2) receptor exists in 'long' (sst(2a)) and 'short' (sst(2b)) forms that differ in their C termini, while a single human (h) sst(2a) exists. This study compares the characteristics of recombinant rsst(2a), rsst(2b) and hsst(2a) activation in human epithelia, and with native sst(2) responses in rat colon.

EXPERIMENTAL APPROACH

Epithelial layers of each clone or rat colon were placed in Ussing chambers and short-circuit current (I (SC)) measured in response to SRIF-14 and chosen analogues. The relative potencies and ability to cause desensitization to SRIF-14 were assessed, and the affinities of the sst(2) antagonist, D-Tyr(8) CYN154806 for hsst(2a), rsst(2a) and native rat colon sst(2) receptors were established.

KEY RESULTS

Basolateral SRIF-14 responses were transient in hsst(2a) and rsst(2a) epithelia, but prolonged in rsst(2b)-expressing cells. Activation of rsst(2a) resulted in significant desensitization to SRIF-14 and receptor phosphorylation, whereas the rsst(2b) receptor did neither. Sst(2)-preferred agonists (BIM23190C and BIM23027) reduced I (sc) with similar potency and both caused complete desensitization to SRIF-14. CYN154806 antagonized hsst(2a) and rsst(2a) receptors with pK (B) values of 7.9 and 7.8, respectively. In rat colon mucosa, CYN154806 blocked SRIF-14 responses with a pA (2) value of 8.2, and BIM23190C responses with a pK (B) of 8.4.

CONCLUSIONS AND IMPLICATIONS

SRIF-14 caused rapid rsst(2a) receptor phosphorylation and desensitization of epithelial antisecretory responses, neither of which occurred with the rsst(2b) receptor. These mechanisms are most likely to be a prerequisite for sensitivity to sst(2)-analogues with radiotherapeutic potential.

The pancreatic polypeptide family and the migrating motor complex of the rat: differential effects in the duodenum and jejunum

AIM

To investigate the effects of members of the pancreatic polypeptide family on migrating myoelectric complexes in rats in vivo.

METHODS

Rats were supplied with bipolar electrodes at 5 (duodenum), 15 and 25 cm (jejunum) distal to pylorus for electromyography. The natural ligands neuropeptide Y, pancreatic polypeptide, peptide YY1-36 and peptide YY3-36 were infused IV at doses of 0.5-400 pmol kg(-1) min(-1). The mechanisms of action were studied after pre-treatment with N(omega)-nitro-L-arginine (L-NNA) 1 mg kg(-1), guanethidine 3 mg kg(-1) and in bilaterally vagotomized animals.

RESULTS

PP inhibited myoelectrical activity dose-dependently in both the duodenum (ED50 5.8 pmol kg(-1) min(-1)) and jejunum (2.6 pmol kg(-1) min(-1)). PYY1-36 and PYY3-36 also had inhibitory effect in the jejunum (4.4 and 130 pmol kg(-1) min(-1), respectively). PYY1-36 had no significant effect in the duodenum, whereas PYY3-36 stimulated myoelectrical activity at the highest doses. NPY was without effect. In the jejunum neither L-NNA, guanethidine or vagotomy had any significant influence on the inhibitory effects of PP, PYY1-36 and PYY3-36. In the duodenum, the effect of PP was inhibited by guanethidine, but not L-NNA or vagotomy. The stimulatory effect of PYY3-36 in the duodenum was blocked by L-NNA and vagotomy, whereas guanethidine was without effect.

CONCLUSION

Peptides of the PP family modulate small bowel motility differentially. Whereas their general effect is inhibitory in the jejunum, the mixing duodenal compartment is stimulated by PYY3-36, suggested to reflect receptor distribution distinction in the gut. This implicates distribution of distinct receptors in the gut being activated by either peptide.

Peptide YY: a neuroendocrine neighbor of note

Endocrine cells, enteric neurons and enterocytes provide an integrated functional defense against luminal factors, including nutrients, microbes and toxins. Prominent among intrinsic mediators is peptide YY (PYY) which is present in approximately 50% of colorectal endocrine cells and neuropeptide Y (NPY), a neurotransmitter expressed in submucous and myenteric nerves. Both peptides and their long fragments (PYY(3-36) and NPY(3-36)) are potent, long-lasting anti-secretory agents in vitro and in vivo and, they provide significant Y receptor-mediated absorptive tone in human and mouse colon mucosa. The main function of the colon is to absorb 90% of approximately 2l of daily ileal effluent (in adult humans) and Y-absorptive tone can contribute significantly to this electrolyte absorption. Blockade or loss of this mucosal Y-absorptive tone (i.e. with Y(1) or Y(2) antagonists) leads to hypersecretion and potentially to diarrhea, so Y agonists are predicted to rescue absorption by mimicking endogenous neuroendocrine PYY or neuronal NPY.

Neuropeptide Y receptors; antisecretory control of intestinal epithelial function

This paper reviews the cellular localisation, mechanisms of release and intestinal absorptive actions of neuropeptide Y and its related peptides, peptide YY, pancreatic polypeptide and major fragments NPY(3-36) and PYY(3-36). While NPY is commonly found in inhibitory enteric neurons that can be interneurons, motor neurons or secretomotor-nonvasodilator in nature, its analogue, peptide YY in contrast, is located in neuroendocrine L-cells that predominate in the colorectal mucosa. Peptide YY is released from these cells when nutrients arrive in the small or large bowel, exerting paracrine as well as hormonal actions. Pancreatic polypeptide is found in relatively few, scattered intestinal endocrine cells, the majority of this peptide being produced by, and released from pancreatic islet F-cells in response to food intake. An introduction to the current pharmacology of this family of peptides is provided and the different types of neuropeptide Y (termed Y) receptors, their agonist preferences, antagonism, and preferred signalling pathways, are described. Our current understanding of specific Y receptor localisation within the intestine as determined by immunohistochemistry, is presented as a prelude to an assessment of functional studies that have monitored ion transport across isolated mucosal preparations. It is becoming clear that three Y receptor types are significant functionally in human colon, as well as particular rodent models (e.g. mouse) and these, namely the Y(1), Y(2) and Y(4) receptors, are discussed in detail. Their presence within the basolateral aspect of the epithelial layer (Y(1) and Y(4) receptors) or on enteric neurons (Y(1) and Y(2) receptors) and their activation by endogenous neuropeptide Y, peptide YY (Y(1) and Y(2) receptors) or pancreatic polypeptide (which prefers Y(4) receptors) results consistently in antisecretory/absorptive responses. The recent use of novel mouse knockouts has helped establish loss of specific intestinal functions including Y(1) and Y(2) receptor-mediated absorptive tone in colon mucosa. Progress in this field has been rapid recently, aided by the availability of selective antagonists and mutant mice lacking either one (e.g. Y(4)-/-, for which no antagonists exist at present) or more Y receptor types. It is therefore timely to review this work and present a rational basis for developing stable synthetic Y receptor agonists as novel anti-diarrhoeals.

Plasticity of the enteric nervous system during intestinal inflammation

Inflammation of the bowel causes structural and functional changes to the enteric nervous system (ENS). While morphological alterations to the ENS are evident in some inflammatory conditions, it appears that relatively subtle modifications to the neurophysiology of enteric microcircuits may play a role in gastrointestinal (GI) dysfunction. These include changes to the excitability and synaptic properties of enteric neurones. The response of the ENS to inflammation varies according to the site and type of inflammation, with the functional consequences depending on the nature of the inflammatory stimulus. It has become clear that inflammation at one site can produce changes that occur at remotes sites in the GI tract. Immunohistochemical data from patients with inflammatory bowel disease (IBD) and animal models indicate that inflammation alters the neurochemical content of some functional classes of enteric neurones. A growing body of evidence supports an active role for enteric glia in neuronal and neuroimmune communication in the GI tract, particularly during inflammation. In conclusion, plasticity of the ENS is a feature of intestinal inflammation. Elucidation of the mechanisms whereby inflammation alters enteric neural control of GI functions may lead to novel treatments for IBD.

Neuropeptide Y, ubiquitous and elusive

This paper reviews aspects of NPY research that were emerging in 1985, shortly after the isolation and characterization of the peptide. NPY had become known for its widespread distribution especially in the central and peripheral nervous systems, but also in the gastro-intestinal and respiratory tracts and in fibers innervating smooth muscle around blood vessels. Consistent with its distribution, it was determined that NPY is a potent vasoconstrictor, affects neuroendocrine systems and is involved in appetite regulation--areas of research still relevant today. Through advances in technology knowledge about NPY's role in these and newly discovered physiological functions has deepened considerably. Successful cloning of a series of NPY receptors has opened up new and complex research vistas. Lately, the creation of mice genetically modified for NPY as well as for several receptor subtypes has brought many puzzling observations--followed by questions yet to be answered.

Role of gastrointestinal hormones in the proliferation of normal and neoplastic tissues

Gastrointestinal (GI) hormones are chemical messengers that regulate the physiological functions of the intestine and pancreas, including secretion, motility, absorption, and digestion. In addition to these well-defined physiological effects, GI hormones can stimulate proliferation of the nonneoplastic intestinal mucosa and pancreas. Furthermore, in an analogous fashion to breast and prostate cancer, certain GI cancers possess receptors for GI hormones; growth can be altered by administration of these hormones or by blocking their respective receptors. The GI hormones that affect proliferation, either stimulatory or inhibitory, include gastrin, cholecystokinin, gastrin-releasing peptide, neurotensin, peptide YY, glucagon-like peptide-2, and somatostatin. The effects of these peptides on normal and neoplastic GI tissues will be described. Also, future perspectives and potential therapeutic implications will be discussed.

Functional consequences of neuropeptide Y Y 2 receptor knockout and Y2 antagonism in mouse and human colonic tissues

1 Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) differentially activate three Y receptors (Y(1), Y(2) and Y(4)) in mouse and human isolated colon. 2 The aim of this study was to characterise Y(2) receptor-mediated responses in colon mucosa and longitudinal smooth muscle preparations from wild type (Y(2)+/+) and knockout (Y(2)-/-) mice and to compare the former with human mucosal Y agonist responses. Inhibition of mucosal short-circuit current and increases in muscle tone were monitored in colonic tissues from Y(2)+/+ and Y(2)-/- mice+/-Y(1) ((R)-N-[[4-(aminocarbonylaminomethyl)phenyl)methyl]-N(2)-(diphenylacetyl)-argininamide-trifluoroacetate (BIBO3304) or Y(2) (S)-N(2)-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide (BIIE0246) antagonists. 3 Predictably, Y(2)-/- tissues were insensitive to Y(2)-preferred agonist PYY(3-36) (</=100 nM), but unexpectedly Y(4)-preferred PP responses were right-shifted probably as a consequence of elevated circulating PP levels, particularly in male Y(2)-/- mice (Sainsbury et al., 2002). 4 BIBO3304 and BIIE0246 elevated mucosal ion transport, indicating blockade of inhibitory mucosal tone in Y(2)+/+ tissue. While BIBO3304 effects were unchanged, those to BIIE0246 were absent in Y(2)-/- mucosae. Neither antagonist altered muscle tone; however, BIIE0246 blocked NPY and PYY(3-36) increases in Y(2)+/+ basal tone. BIBO3304 abolished residual Y(1)-mediated NPY responses in Y(2)-/- smooth muscle. 5 Tetrodotoxin significantly reduced BIIE0246 and PYY(3-36) effects in Y(2)+/+ mouse and human mucosae, but had no effect upon Y-agonist contractile responses, indicating that Y(2) receptors are located on submucosal, but not myenteric neurones. 6 Tonic activation of submucosal Y(2) receptors by endogenous NPY, PYY or PYY(3-36) could indirectly reduce mucosal ion transport in murine and human colon, while direct activation of Y(2) receptors on longitudinal muscle results in contraction.

Dual and selective antagonism of neurokinin NK(1) and NK(2) receptor-mediated responses in human colon mucosa

The neurokinin (NK) receptors, NK(1) and NK(2), which are activated by substance P (SP) and NKA, have been identified as potential therapeutic targets in irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). Here we have investigated the effects of a novel dual NK(1) and NK(2) receptor antagonist, namely DNK333 upon responses elicited by [Sar(9), Met(O(2))(11)]-SP (SMSP) and [betaAla(8)]-NKA(4-10) in isolated human colon mucosa mounted in Ussing chambers. A selective NK(1) receptor antagonist, SR140333 and NK(2) receptor antagonist, SR48968 have been tested for comparison. Additions of SMSP (100 nM) or [betaAla(8)]-NKA(4-10) (100 nM) increased basal short-circuit current and responses to both peptides were inhibited by DNK333, while SR140333 only inhibited SMSP and SR48968 blocked only [betaAla(8)]-NKA(4-10) responses. SR140333 did not attenuate [betaAla(8)]-NKA(4-10) effects and SR48968 had no effect upon SMSP responses. Carbachol (1 micro M) responses were not altered by any of the three NK antagonists. We conclude that activation of either NK(1) or NK(2) receptors can stimulate epithelial ion transport in human colon mucosa and that the novel dual antagonist, DNK333 may be of potential therapeutic interest in the treatment of IBD and IBS.

Neuropeptide Y, Y1, Y2 and Y4 receptors mediate Y agonist responses in isolated human colon mucosa

1. The aim of this study was to provide a pharmacological characterization of the Y receptor types responsible for neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) effects upon electrogenic ion transport in isolated human colonic mucosa. 2. Preparations of descending colon were voltage-clamped at 0 mV in Ussing chambers and changes in short-circuit current (I(sc)) continuously recorded. Basolateral PYY, NPY, human PP (hPP), PYY(3 - 36), [Leu(31), Pro(34)]PYY (Pro(34)PYY) and [Leu(31), Pro(34)]-NPY (Pro(34)NPY) all reduced basal I(sc) in untreated colon. Of all the Y agonists tested PYY(3 - 36) responses were most sensitive to tetrodotoxin (TTX) pretreatment, indicating that Y(2)-receptors are located on intrinsic neurones as well as epithelia in this tissue. 3. The EC(50) values for Pro(34)PYY, PYY(3 - 36) and hPP were 9.7 nM (4.0 - 23.5), 11.4 nM (7.6 - 17.0) and 14.5 nM (10.2 - 20.5) and response curves exhibited similar efficacies. The novel Y(5) agonist [Ala(31), Aib(32)]-NPY had no effect at 100 nM. 4. Y(1) receptor antagonists, BIBP3226 and BIBO3304 both increased basal I(sc) levels per se and inhibited subsequent PYY and Pro(34)PYY but not hPP or PYY(3 - 36) responses. The Y(2) antagonist, BIIE0246 also raised basal I(sc) levels and attenuated subsequent PYY(3 - 36) but not Pro(34)PYY or hPP responses. 5. We conclude that Y(1) and Y(2) receptor-mediated inhibitory tone exists in human colon mucosa. PYY and NPY exert their effects via both Y(1) and Y(2) receptors, but the insensitivity of hPP responses to either Y(1) or Y(2) antagonism, or to TTX, indicates that Y(4) receptors are involved and that they are predominantly post-junctional in human colon.

Peptide YY as a growth factor for intestinal epithelium

Peptide YY is an abundant distal gut hormone that may play a significant role in intestinal epithelial proliferation. Gut epithelial cells express specific receptors for PYY, PYY induces proliferation in intestinal cells in vivo and in vitro, and the Y1 receptor subtype couples to mitogenic signaling pathways. In addition to proposed physiologic effects on gut mucosal maintenance, PYY proliferative effects may be hypothesized to contribute to pathophysiologic consequences of stimulated growth.

Pancreatic polypeptide receptors: affinity, sodium sensitivity and stability of agonist binding

Cloned rat, human and guinea-pig Y4 pancreatic polypeptide (PP) receptors expressed in Chinese hamster ovary (CHO) cells, as well as the rabbit Y4-like PP receptor, show a selective sensitivity to Na+ over K+ ion in PP attachment, but little sensitivity to Na+ in dissociation of bound PP peptides. Agonist binding to Y4 receptors of intact CHO cells also shows much greater sensitivity to Na+ over K+, and a tenacious attachment of the bound agonist. Binding sensitivity to K+ is greatly enhanced upon receptor solubilization. Pancreatic polypeptide sites also show large sensitivity to modulators of Na+ transport such as N5-substituted amilorides and to RFamides, as different from Y1 or Y2 receptors. Thus, PP binding is modulated by cation-induced changes in site environment (with selectivity for Na+) and ultimately results in a blocking attachment. This would support receptor operation in the presence of ion gradients, as well as prolonged agonist-delimited signaling activity (which can include partial antagonism). Also, this could point to an evolutionary adaptation enabling small numbers of PP receptors to perform extensive metabolic tasks in response to low agonist signals.

The peptide YY-preferring receptor mediating inhibition of small intestinal secretion is a peripheral Y(2) receptor: pharmacological evidence and molecular cloning

A peptide YY (PYY)-preferring receptor [PYY > neuropeptide Y (NPY)] was previously characterized in rat small intestinal crypt cells, where it mediates inhibition of fluid secretion. Here, we investigated the possible status of this receptor as a peripheral Y(2) receptor in rats. Typical Y(2) agonists (PYY(3-36), NPY(3-36), NPY(13-36), C2-NPY) and very short PYY analogs (N-alpha-Ac-PYY(22-36) and N-alpha-Ac-PYY(25-36)) acting at the intestinal PYY receptor were tested for their ability to inhibit the binding of (125)I-PYY to membranes of rat intestinal crypt cells and of CHO cells stably transfected with the rat hippocampal Y(2) receptor cDNA. Similar PYY preference was observed and all analogs exhibited comparable high affinity in both binding assays. The same held true for the specific Y(2) antagonist BIIE0246 with a K(i) value of 6.5 and 9.0 nM, respectively. BIIE0246 completely abolished the inhibition of cAMP production by PYY in crypt cells and transfected CHO cells. Moreover, the antagonist 1) considerably reversed the PYY-induced reduction of short-circuit current in rat jejunum mucosa in Ussing chamber and 2) completely abolished the antisecretory action of PYY on vasoactive intestinal peptide (VIP)-induced fluid secretion in rat jejunum in vivo. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that Y(2) receptor transcripts were present in intestinal crypt cells (3 x 10(2) molecules/100 ng RNA(T)) with no expression in villus cells, in complete agreement with the exclusive binding of PYY in crypt cells. Finally, a full-length Y(2) receptor was cloned by RT-PCR from rat intestinal crypt cells and also from human small intestine. We conclude that the so-called PYY-preferring receptor mediating inhibition of intestinal secretion is a peripheral Y(2) receptor.

Neuropeptide Y inhibits the protein kinase C-stimulated Cl(-) secretion in the human colonic cell line HT29cl.19A cell line via multiple sites

Neuropeptide Y is known to exert inhibitory effects on ion secretion in the intestine by reducing the activity of adenylyl cyclase. In the human intestinal epithelial cell line HT29cl.19A, it has been previously shown that neuropeptide Y inhibits the electrophysiological phenomena related to Cl(-) secretion, when induced by elevation of cAMP via forskolin. Moreover, the secretion induced via elevation of intracellular calcium levels via muscarinic activation can be inhibited by neuropeptide Y. Part of these inhibitions appeared to be due to lowered calcium activity in the epithelial cells, thereby reducing the basolateral K(+) conductance. The phorbol ester 4-phorbol-12,13-dibutyrate (PDB) can induce secretion in this cell line via activation of protein kinase C as well; however, the effect of neuropeptide Y on this pathway has not yet been studied. In the present experiments, it is shown that neuropeptide Y inhibits the PDB-induced secretion at two sides: one located in the apical membrane and another in the basolateral membrane. It is shown that the latter effect can, at least partially, be explained via a direct effect of neuropeptide Y on the K(+) conductance. This was concluded from the observation that neuropeptide Y could also reduce basolateral K(+) conductance when intracellular calcium was dramatically increased by ionomycin. The observed inhibitory effects suggest that neuropeptide Y is a very powerful antisecretory peptide in human intestinal epithelial cells.

Multiple Y receptors mediate pancreatic polypeptide responses in mouse colon mucosa

A functional study has been performed to characterise the Y receptors responsible for NPY, PYY and PP-stimulated responses in mouse colonic mucosal preparations. Electrogenic ion secretion was stimulated with VIP following which NPY, PYY and PP analogues were, to varying degrees, inhibitory. PYY(3-36), hPP, Gln(23)hPP and rPP were effective but less potent than full length PYY, NPY or their Pro(34)-substituted analogues, while the Y(5) agonist Ala(31), Aib(32)hNPY was the least active peptide tested. The Y(1) antagonists, BIBP3226 and BIBO3304 virtually abolished Pro(34)PYY and PYY responses while PYY(3-36) responses were selectively inhibited by the Y(2) antagonist, BIIE0246. A combination of BIBO3304 and BIIE0246 also partially attenuated hPP responses, leaving residual effects that were most probably Y(4)-mediated. Thus we conclude that Y(1), Y(2) and Y(4) receptors attenuate ion secretion in mouse colon.

Constitutive neuropeptide Y Y(4) receptor expression in human colonic adenocarcinoma cell lines

1. Three human adenocarcinoma cell lines, Colony-24 (Col-24), Col-6 and Col-1 have been studied as confluent epithelial layers able to transport ions vectorially in response to basolateral vasoactive intestinal polypeptide (VIP) and pancreatic polypeptides (PP). 2. Different species PP stimulated responses in Col-24 with Y(4)-like pharmacology. Bovine (b)PP, human (h)PP and porcine (p)PP were equipotent (EC(50) values 3.0--5.0 nM) while rat (r)PP, avian (a)PP and [Leu(31), Pro(34)]PYY (Pro(34)PYY) were significantly less potent. PYY was inactive. The PP pharmacology in Col-1 was comparable with Col-24. However, Col-6 cells were different; pPP had an EC(50) intermediate (22.0 nM) between that of bPP (3.0 nM) and hPP (173.2 nM), with aPP and rPP being at least a further fold less potent. 3. Deamidation of Tyr(36) in bPP (by O-methylation or hydroxylation) or removal of the residue resulted in significant loss of activity in Col-24. 4. GR231118 (1 microM) had no PP-like effects. In Col-24 and Col-1, GR231118 significantly attenuated bPP (30 nM) or hPP (100 nM) responses, but it did not alter bPP responses in Col-6. BIBP3226 and GR231118 both inhibited Y(1)-mediated responses which were only present in Col-6. 5. RT--PCR analysis confirmed the presence of hY(4) receptor mRNA in Col-24 and Col-1 epithelia but a barely visible hY(4) product was observed in Col-6 and we suggest that an atypical Y(4) receptor is expressed in this cell line.

Neuropeptides in drug research

Neuropeptides have been a subject of considerable interest in the pharmaceutical industry over the last 20 years or more. Many drug discovery teams have contributed to our understanding of neuropeptide biology but no significant drugs that act selectively upon neuropeptide receptors have yet emerged from the clinic. There are, however, a plethora of clinically useful drugs that act at other classes of neurotransmitter and neuromodulator receptors, many of them discovered over the last 20 years. Nevertheless, we think that the future for the discovery of novel drugs acting at neuropeptide receptors looks bright for two reasons: (1) there has been a substantial increase in our understanding of the function of neuropeptides; and (2) high-throughput screening (HTS) against neuropeptide receptors has now begun to yield many interesting drug-like molecules, rather than peptides, that have the potential to become clinically useful drugs. The objective of this review is to summarise our current understanding of specific areas of neuropeptide biology and pharmacology in the CNS as well as the PNS. We will also speculate on where we think the new generation of neuropeptide agonists and antagonists could emerge from the clinic.

PYY preference is a common characteristic of neuropeptide Y receptors expressed in human, rat, and mouse gastrointestinal epithelia

This investigation describes the relative potencies of four peptide agonists, namely, peptide YY (PYY), [Leu31,Pro34]PYY (Pro34PYY), neuropeptide Y (NPY), and [Leu31,Pro34]NPY (Pro34NPY), as antisecretory agents in human, rat, and mouse gastrointestinal preparations. The inhibition of agonist responses by the Y1-receptor antagonist BIBP 3226 was also tested in each preparation. An unexpectedly pronounced preference for PYY and Pro34PYY was observed in functional studies of two human epithelial lines stably transfected with the rat Y1 receptor (Y1-7 and C1Y1-6). NPY and Pro34NPY were at least an order of magnitude less effective than PYY in these functional studies but were only marginally less potent in displacement binding studies using membrane preparations of the same clonal lines. The orders of agonist potency obtained in Y1-7 and C1Y1-6 epithelia were compared with those obtained from a single human colonic adenocarcinoma cell line (Colony-6, which constitutively expresses Y1 receptors) and also from mucosal preparations of rat and mouse descending colon. Similar peptide orders of potency were obtained in rat and mouse colonic mucosae and Colony-6 epithelia, all of which exhibited PYY preference (although less pronounced than with Y1-7 and C1Y1-6 epithelia) and significant sensitivity to the Y1 receptor antagonist, BIBP 3226. We have compared the pharmacology of these five mammalian epithelial preparations and provide cautionary evidence against the reliance upon agonist concentration-response relationships alone, in the characterization of NPY receptor types.Key words: Y receptors, neuropeptide Y, gastrointestinal epithelia, ion transport.

Neural mechanism of the antisecretory effect of peptide YY in the rat colon in vivo

The purpose of this work was to determine the mechanism of the antisecretory effect of peptide YY in the rat colon and whether this effect is physiological. In this prospect, doses of exogenous peptide YY producing physiological and supraphysiological plasma levels were intravenously infused in rats provided with colonic and jejunal ligated loops in vivo, under secretory stimulation by vasoactive intestinal peptide. Peptide YY decreased the secretory effect of VIP in a dose-related fashion. The effect of peptide YY was blocked or strongly decreased by tetrodotoxin, hexamethonium, idazoxan, haloperidol, and the sigma antagonist BMY 14, 802 in both the colon and jejunum. We conclude that peptide YY decreases water and electrolyte secretion in the colonic mucosa by a complex neural mechanism involving at least two neurons connected through a nicotinic synapse, alpha-2 adrenoceptors and sigma receptors, and that this effect can occur with physiological doses of peptide YY.

Peptide YY/neuropeptide Y Y1 receptor expression in the epithelium and mucosal nerves of the human colon

OBJECTIVES

Peptide YY is an abundant distal gut hormone which regulates secretion, motility, and possibly epithelial proliferation in the gut. Though messenger RNA for the peptide YY Y1 receptor subtype occurs in the basal colonic crypts of humans, peptide YY receptors themselves have not been clearly localized within the adult human gastrointestinal tract. Using an antiserum directed against the C-terminus of the Y1 receptor we determined the actual extent of Y1 receptor protein expression in the human colon in order to identify areas targeted for peptide YY effects and suggest additional physiological roles for PYY in the human gut.

RESULTS

Y1 receptor protein expression was seen throughout the colonic epithelium along its basolateral aspect. There was an unexpected dense distribution of Y1 receptor immunoreactivity in varicose fibers within the mucosa. Staining was also noted in nerve fibers of the muscularis mucosae, in the submucous and myenteric plexuses, and in nerves in the muscularis propria.

CONCLUSIONS

Widespread distribution of Y1 receptors in the colonic epithelium and mucosal nerve fibers suggests diverse regulatory roles for peptide YY in modulating epithelial function as well as secretomotor reflexes in response to lumenal peptide YY-release signals.

Effect of sorbin on electrolyte transport in rat and human intestine

Stimulating water absorption in the colon represents an important target to reduce stool output in secretory diarrhea. Recently, a 153-amino-acid peptide was isolated from porcine upper small intestine and purified, taking into account the increase of water absorption in guinea pig gallbladder. Accordingly, this peptide was named sorbin. The aim of the present study was to determine if the COOH-terminal heptapeptide of sorbin (C7-sorbin) participates in the regulation of electrolyte transport in the colon. Different regions (from duodenum to colon) of stripped intestinal mucosa from rats or humans were mounted in Ussing chambers to measure the changes in short-circuit current (DeltaIsc) and net 22Na and 36Cl fluxes (JNanet and JClnet) after serosal exposure of 10(-7) to 10(-3) M C7-sorbin. In fasted rat intestine, C7-sorbin (10(-4) M) induced an immediate reduction in Isc in the distal ileum and proximal and distal colon but not in the duodenum and jejunum. In the colon, Isc reduction and JNanet and JClnet stimulation were dose dependent (EC50 = 2 x 10(-5) M). At 10(-3) M, maximal effect was observed (DeltaIsc = -1.14 +/- 0.05, DeltaJNanet = +4.97 +/- 1.38, and DeltaJClnet = +9.25 +/- 1.44 microeq. h-1. cm-2). C7-sorbin (10(-3) M) inhibited the increase in Isc induced by a series of 10 secretory agents such as secretin, vasoactive intestinal peptide, PGE2, and serotonin. In HT-29-Cl19A cells, C7-sorbin induced an increase in Isc, with a maximal effect at 10(-3) M (DeltaIsc = 0.29 +/- 0.10 microeq. h-1. cm-2). In human intestine, a dose-dependent decrease in Isc was observed in right and sigmoid colons in basal and stimulated conditions (EC50 congruent with 10(-5) M; at 10(-4) M, DeltaIsc = -2.66 +/- 0.17 microeq. h-1. cm-2) but not in the jejunum. The results indicate that C7-sorbin stimulated NaCl neutral absorption and inhibited electrogenic Cl- in rat and human intestinal epithelia. In addition, the antisecretory effect was essentially observed in the distal part of both rat and human intestine and the magnitude of the proabsorptive effect was directly related to the magnitude of the previously induced secretion.

Antisecretory effect of peptide YY through neural receptors in the rat jejunum in vitro

Basal short circuit current (Isc) was measured in stripped rat jejunum after addition of neural antagonists and of peptide YY (PYY). Basal Isc was slightly (by 10-21%) but significantly inhibited by tetrodotoxin, hexamethonium, idazoxan, and the sigma antagonist BMY 14,802. PYY (10(-7) M) reduced basal Isc by approximately 54%. This inhibition was unchanged by hexamethonium but reduced by 44-68% in the presence of tetrodotoxin, idazoxan, haloperidol, BMY 14,802, and atropine. The Y2 agonist pYY(3-36) was more potent than the Y1 agonist (Leu31,Pro34)PYY. In conclusion, PYY reduces basal Isc in rat jejunum in part through a neural mechanism involving muscarinic receptors, alpha2 adrenoceptors, and sigma receptors and, in part, through a direct effect on enterocytes. The PYY effect seems mainly carried out through Y2-receptor activation.

Pharmacological profile of the rat intestinal crypt peptide YY receptor vs. the recombinant rat Y5 receptor

Peptide YY and neuropeptide Y have potent antisecretory effects in rat small intestine. Scatchard analysis of [125I]peptide YY binding revealed a 10-fold higher concentration of receptors in rat jejunal crypt cells than in villus cells and no detectable receptors in colonic epithelium. Reverse transcription polymerase chain reaction analysis of neuropeptide Y Y5 receptor mRNA indicated that they are mainly expressed in rat jejunal crypts with very few or no expression in villus cells and colon epithelium, respectively. In order to determine whether neuropeptide Y Y5 receptors could represent the intestinal crypt receptor for peptide YY and neuropeptide Y, the ability of peptide YY, neuropeptide Y, pancreatic polypeptide and analogues to inhibit [125I]peptide YY binding to membrane prepared from rat crypt cells and COS-7 cells (African green monkey kidney cells) transfected with the rat neuropeptide Y Y5 receptor cDNA was tested. It appeared that several analogues displayed different inhibition constants (Ki) in the two binding assays, more especially N-alpha-acetyl-peptide YY-(22-36) which was 1200 x more potent in the crypt cell binding assay than in the recombinant neuropeptide Y Y5 receptor binding assay. These data support that the intestinal crypt peptide YY receptor is not a Y5 receptor. reserved.

Structure-activity relationships with neuropeptide Y analogues: a comparison of human Y1-, Y2- and rat Y2-like systems

A structure-activity study utilising 36 synthetic Ala-analogues of the 36-residue oligopeptide neuropeptide Y (NPY) has been performed with mucosal preparations from the rat jejunum (Y2-like receptor) and compared with receptor displacement binding in the human neuroblastoma cell lines, SMS-KAN, (Y2-receptors) and SK-N-MC cells (Y1-receptors). Each amino acid of the natural sequence was replaced by L-alanine, and the four intrinsic alanine residues at position 12, 14, 18 and 23 were replaced by glycine. The purified peptides were characterized by electrospray mass spectrometry, analytical HPLC and amino acid analysis. Binding was investigated using membranes prepared from either SMS-KAN or SK-N-MC cells. The activity of each Ala-NPY analogue was assessed in mucosal preparations of rat jejunum, where NPY and PYY exert antisecretory responses which are Y2-like in pharmacology. Fourteen analogues with L-alanine replacements at position 3, 5, 8, 13, 20, 21, 22, 26, 27, 28, 29, 30, 34 and 36 were selected, none of which exhibited any antagonism of NPY responses. An order of agonist potency showed [Ala3] NPY and [Ala30] NPY equipotent with NPY, a 4-20-fold loss of activity with [Ala5] NPY, [Ala13] NPY, [Ala20] NPY, [Ala21] NPY and [Ala22] NPY; a 50-100-fold loss of activity, [Ala8] NPY, [Ala27] NPY, [Ala28] NPY and [Ala36] NPY, while [Ala34] NPY was inactive. This structure-activity relationship is similar to, but not the same as that observed in Y2-expressing SMS-KAN cells.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Neuropeptide Y inhibits ciliary beat frequency in human ciliated cells via nPKC, independently of PKA

The intracellular mechanisms whereby the inhibitory neurotransmitter neuropeptide Y (NPY) decreases ciliary beat frequency (CBF) were investigated in cultured human tracheal and bronchial ciliated cells. CBF was measured by nonstationary analysis laser light scattering. NPY at 1 and 10 microM decreased CBF from a baseline of 6.7 +/- 0.5 (n = 12) to 6.1 +/- 0.5 (P < 0.05) and 5.8 +/- 0.4 (P < 0.01) Hz, respectively. Prior application of PYX-1, an NPY antagonist, prevented the decreases of CBF induced by both doses of NPY. Two broad protein kinase C (PKC) kinase inhibitors, staurosporine and calphostin C, also abolished the NPY-induced decrease in CBF. The NPY-induced decrease in CBF was abolished by GF 109203X, a novel PKC (nPKC) isoform inhibitor, whereas this decrease in CBF was not attenuated by Gö-6976, a specific inhibitor of conventional PKC isoforms. Because pretreatment with NPY did not block the stimulation of CBF by forskolin and pretreatment with forskolin did not abolish the NPY-induced inhibition of CBF, this NPY receptor-mediated signal transduction mechanism appears to be independent of the adenylate cyclase-protein kinase A (PKA) pathway. Inhibition of Ca2+-ATPase by thapsigargin also prevented the suppression of CBF induced by subsequent application of NPY. These novel data indicate that, in cultured human epithelia, NPY decreases CBF below its basal level via the activation of an nPKC isoform and Ca2+-ATPase, independent of the activity of PKA. This is consistent with the proposition that NPY is an autonomic efferent inhibitory neurotransmitter regulating mucociliary transport.

Identification and distribution of mRNA encoding the Y1, Y2, Y4, and Y5 receptors for peptides of the PP-fold family in the rat intestine and colon

Peptide YY (PYY), neuropeptide Y (NPY) and pancreatic polypeptide (PP) are structurally related peptides which have potent antisecretory effects in small and/or large intestines. Receptors mediating these effects are still unknown with the exception of a PYY-preferring receptor expressed in small intestinal crypts. In the present study, expression of recently cloned Y1, Y2, and Y5 receptors which have similar affinity for PYY and NPY and Y4 receptors which have a high affinity for PP was investigated in gut by RT-PCR analysis. The data show that all Y receptors are expressed in small intestine and/or colon but with specific distributions. Y1 receptors are only expressed in nonepithelial colonic tissue, whereas Y2 and Y4 receptors are present in both epithelial and nonepithelial tissue of the small or large intestine. In contrast, Y5 receptor expression appears to be restricted to epithelial crypts of the small intestine and nonepithelial tissue of colon. Sequencing of PCR products showed 100% identity with the corresponding sequences of the cloned Y1, Y4, or Y5 receptors. The PCR product obtained with Y2 primers from rat crypt cells showed 84% identity with the cloned human Y2 receptor. These data indicate a wide distribution of Y receptors in small intestine and colon. They also suggest that Y1, Y2, Y4, and Y5 receptors may be responsible for still unexplained effects of PYY, NPY, or PP on secretion in small and large intestines.

Inhibitory effects of peptide YY on basal and VIP-stimulated short-circuit current in the rat jejunum: influence of technical conditions on observed results

The interaction of PYY and VIP was studied in stripped and intact rat jejunum preparations mounted in Ussing chambers. PYY decreased basal Isc in intact as well as in stripped jejunum. Stripping was necessary to evidence a stimulation of basal Isc by VIP. When PYY and VIP were administered at the same time in the serosal bath, their effects seemed additive; VIP stimulation took over when VIP was present in ten times larger amounts than PYY, while PYY inhibition predominated at isomolar concentrations (10(-7) M) of both peptides. However, when PYY was administered three to six minutes before isomolar amounts of VIP, the VIP stimulation developed without being notably hampered. At this time, however, the amount of radioimmunoassayable PYY in the serosal compartment represented still 60% of the added amount. In conclusion, the experimental conditions can significantly change the results: stripping the longitudinal muscle/myenteric plexus impairs the effect of PYY and VIP in a different fashion, while the timing and order of administration of the peptides may change the apparent interaction between VIP stimulation and PYY inhibition.

Immunocytochemical localization of the NPY/PYY Y1 receptor in enteric neurons, endothelial cells, and endocrine-like cells of the rat intestinal tract

Neuropeptide Y (NPY) and peptide YY (PYY) are structurally related peptides that are considered to mediate inhibitory actions on gastrointestinal motility, secretion, and blood flow. Several receptor subtypes for these peptides have been identified and the Y1, Y2, Y4/PP1, Y5, and Y5/PP2/Y2b receptors have been cloned. In this article we report the immunocytochemical localization of the Y1 receptor to myenteric and submucosal nerve cell bodies, endothelial cells, and scattered endocrine-like cells of rat intestinal tract. Moreover, double immunofluorescence demonstrates that subpopulations of the Y1 receptor-positive nerve cell bodies are immunopositive for NPY, vasoactive intestinal polypeptide, and nitric oxide synthase. In part, such co-localizations were made possible by use of peroxidase-mediated deposition of tyramide, which permitted use of antisera derived from the same species. Our observations suggest the existence of multiple neuronal, endothelial, and endocrine target sites for NPY and PYY and that some of the actions of these regulatory peptides can be mediated by vasoactive intestinal peptide and nitric oxide synthase.

Peptide YY selectively stimulates expression of the colonocytic phenotype

Peptide YY (PYY) is produced by colonic mucosal endocrine cells and modulates gastrointestinal endocrine activity through specific Y-receptors. The direct effects of PYY on intestinal mucosal growth and differentiation remain uncharacterized. The abundance of PYY in colonic mucosa suggests that PYY acts locally to maintain colonocytic differentiation. We tested this hypothesis in human Caco-2 intestinal epithelial cells, which express alkaline phosphatase (AP) and dipeptidyl dipeptidase (DP), brush-border enzymes differentially concentrated in large and small intestinal mucosa, respectively. The effects of PYY on enzyme specific activity were compared with those of pancreatic polypeptide, neuropeptide-Y, vasoactive intestinal peptide, pentagastrin, bombesin, and selective Y1- and Y2-receptor agonists. Brush-border enzyme activity was assessed by AP and DP specific activity in cell lysates quantitated spectrophotometrically following synthetic substrate digestion. PYY, neuropeptide-Y, pancreatic polypeptide, and vasoactive intestinal peptide (10(-7) mol/L) stimulated AP activity. PYY brought about the greatest increase (38.0%+/-11.0%, n=48). Only PYY decreased DP specific activity (7.9%+/-2.2%, n=48). The Y2-agonist but not the Y1-agonist mimicked these PYY effects (increasing AP 28.3%+/-3.5% and decreasing DP 10.4%+/-3.6%). These data suggest that PYY promotes differentiation toward a colonocytic phenotype in Caco-2 intestinal epithelial cells and that this effect may be mediated through the Y2-receptor subtype.

Peptide YY receptor distribution and subtype in the kidney: effect on renal hemodynamics and function in rats

This study characterizes the location and subtype of peptide YY (PYY) receptors in rat and rabbit kidney and the effect of PYY on renal function and renal hemodynamics in rats. Receptor autoradiography performed on kidney sections revealed a dense concentration of specific high-affinity binding sites [dissociation constant (Kd) = 0.7 +/- 0.1 nM] in the papilla of the rat, as well as cortical and papillary binding in the rabbit (papilla, Kd = 1.6 +/- 0.6 nM) and some medullary binding in both species. In the rat papilla, neuropeptide Y (NPY) and the Y1 agonist [Leu31,Pro34]NPY competed with PYY for binding (Kd = 1.1 +/- 0.4 nM and 1.6 +/- 0.5 nM, respectively), but NPY-(13-36) (Y2 agonist) and pancreatic polypeptide (PP, Y4 agonist) were without effect, demonstrating that the PYY receptor in the rat papilla is of the Y1 subtype. In the rabbit papilla, NPY and NPY-(13-36) competed with PYY (Kd = 0.5 +/- 0.1 and 3.1 +/- 0.6 nM, respectively), but [Leu31,Pro34]NPY and PP were without effect, evidence that the PYY receptor in the rabbit papilla is of the Y2 subtype. Infusion of PYY into rats (47 pmol x kg(-1) x min[-1]) increased mean arterial pressure (103 +/- 6 to 123 +/- 8 mmHg) and decreased renal plasma flow (13 +/- 1.8 to 8.4 +/- 2.1 ml/min) but produced no significant change in glomerular filtration rate or sodium excretion. Injection of PYY or angiotensin II directly into the renal artery caused a dose-related vasoconstriction, which was less intense but of longer duration for PYY than for angiotensin II. These results show that receptors for PYY are widely distributed in the kidney and that exogenously administered PYY causes renal vasoconstriction and may influence renal sodium excretion.

Neural modulation of the antisecretory effect of peptide YY in the rat jejunum

The endocrine and neural peptide, peptide YY, inhibits intestinal secretion of water and electrolytes in several animal species and in man. Peptide YY receptors have been evidenced on isolated rat jejunal crypt cells, but neural receptors are also likely to participate in the antisecretory effect of peptide YY in vivo. The aim of the present study was to investigate the mechanisms of the peptide YY effect on vasoactive intestinal peptide (VIP)-stimulated jejunal net water flux in the rat. Antagonist experiments using several drugs affecting neurally mediated processes were done for the purpose. A small peptide YY dose (10 pmol/kg) inhibited significantly (P < 0.005) the jejunal net water flux produced by 30 microg/kg per h of VIP. The inhibitory effect of peptide YY was suppressed, or strongly and significantly reduced, by tetrodotoxin, hexamethonium, lidocaine, idazoxan and BMY14,802 (51-(4-fluorophenyl)-4-(-4-(5-fluoro-2pyrimidinyl)-1-piperazinyl)- 1-butanol), whereas devazepide and L-NAME (L-omega-N-arginine methyl ester) had no effect. These results suggest that peptide YY inhibits VIP-stimulated jejunal net water flux in vivo through a neural mechanism implicating the participation of nicotinic synapses, alpha2-adrenoceptors and sigma receptors.

Antisecretory mechanisms of peptide YY in rat distal colon

Peptide YY (PYY) is a potent regulator of intestinal secretion. These studies investigated the role of Y1 and Y2 receptor subtypes in mediating the antisecretory effects of PYY on mucosa-submucosa preparations of rat distal colon. Addition of vasoactive intestinal peptide (VIP) to these tissues resulted in a 140 +/- 18% increase in basal short-circuit current (Isc) and the induction of Cl- secretion. VIP-stimulated increases in Isc were abolished by the addition of each of PYY, (Pro34)-PYY, a Y1 receptor-selective agonist, and PYY-(3-36), an endogenous Y2 receptor-selective ligand. However, when tissue neural transmission was blocked with tetrodotoxin, neither PYY nor its receptor subtype-selective analogs were able to inhibit VIP-stimulated increases in Isc. These results suggest that in the rat distal colon, the antisecretory actions of PYY are mediated through a combination of Y1 and Y2 receptor subtypes or through a novel receptor subtype that is unable to discriminate between (Pro34)-PYY and PYY-(3-36).

Intraluminal peptide YY induces colonic absorption in vivo

INTRODUCTION

Peptide YY (PYY) is a 36 amino acid hormone released into the circulation and lumen of the intestine after a meal. Previous studies have shown that exogenous administration of intravenous PYY stimulates water and electrolyte absorption in both the small and large intestines. The purpose of this study was to examine the effects of intraluminal administration of PYY on colonic absorption of electrolytes and water.

METHODS

Six conditioned 25-kg dogs had 20 cm of colonic Thiry-Vella fistulae surgically constructed under general anesthesia. After a two-week recovery period, the animals received intraluminal PYY at 600 pmol/kg/hour after a 90-minute steady-state basal period. The Thiry-Vella fistulae were perfused with an isotonic buffer solution containing [14C]polyethylene glycol as a volume marker. Ion and water transport were measured every 15 minutes.

RESULTS

On intraluminal infusion of PYY, increased absorption of water, sodium, and chloride was observed in the colon. A twofold increase in absorption rates occurred compared with basal rates lasting more than one hour after cessation of intraluminal PYY (N = 6; P < 0.05 vs. basal by analysis of variance).

CONCLUSION

PYY-secreting cells of the colon may contribute to the regulation of absorption after a meal. Exogenous administration of intraluminal PYY may also be a therapeutic treatment modality for malabsorption.

Several receptors mediate the antisecretory effect of peptide YY, neuropeptide Y, and pancreatic polypeptide on VIP-induced fluid secretion in the rat jejunum in vivo

Several Y receptor subtypes have been cloned and/or pharmacologically characterized that mediate the effects of the regulatory peptides peptide YY (PYY), neuropeptide Y (NPY), and pancreatic polypeptide (PP). These peptides possess antisecretory properties on the intestine. This effect can be blocked in vivo by neural antagonists, suggesting the intervention of neural receptors, although epithelial PYY-preferring receptors have been evidenced on jejunal crypt cells. The purpose of the present experiments was to compare the antisecretory properties in vivo of a series of PYY and NPY derivatives with various affinities for different Y receptor subtypes, in order to determine which subtypes were involved. A model of VIP-stimulated secretion by rat jejunal loops was used. The results were compared with the binding affinities for PYY-preferring receptors determined on rat jejunal crypt cell membranes. Full-length PYY(1-36) was about three times more potent than NPY(1-36), and 10 times more potent than PP in the low dose range. PP, however, had a low efficacy limited to about 50% inhibition of VIP effect. Both Y1 agonists ([Leu31, Pro34]PYY and [Leu31,Pro34]NPY), and Y2 agonists [C-terminal fragments ranging from PYY (3-36) and NPY(3-36) to PYY(22-36) to NPY(22-36)] displayed potent antisecretory properties. PYY derivatives and fragments were always more potent than their respective NPY counterparts. In contrast, Y1 derivatives and PP had very low affinity for the epithelial PYY receptor as measured in vitro by radioreceptor assay. These data suggest that the antisecretory effect of PYY/NPY/PP peptides in vivo involves the effects of several receptors: a Y2-like, PYY-preferring receptor identical to the epithelial receptor, a Y1-like receptor, and a third receptor with high affinity for PP.