Reversal by NPY, PYY and 3-36 molecular forms of NPY and PYY of intracisternal CRF-induced inhibition of gastric acid secretion in rats

Fecal microbiota transplantation for irritable bowel syndrome: An intervention for the 21st century

Irritable bowel syndrome (IBS) affects about 12% of the global population. Although IBS does not develop into a serious disease or increase mortality, it results in a considerable reduction in the quality of life. The etiology of IBS is not known, but the intestinal microbiota appears to play a pivotal role in its pathophysiology. There is no effective treatment for IBS, and so the applied treatments clinically focus on symptom relief. Fecal microbiota transplantation (FMT), an old Chinese treatment, has been applied to IBS patients in seven randomized controlled trials (RCTs). Positive effects on IBS symptoms in various degrees were obtained in four of these RCTs, while there was no effect in the remaining three. Across the seven RCTs there were marked differences in the selection processes for the donor and treated patients, the transplant dose, the route of administration, and the methods used to measure how the patients responded to FMT. The present frontier discusses these differences and proposes: (1) criteria for selecting an effective donor (superdonor); (2) selection criteria for patients that are suitable for FMT; (3) the optimal FMT dose; and (4) the route of transplant administration. FMT appears to be safe, with only mild, self-limiting side effects of abdominal pain, cramping, tenderness, diarrhea, and constipation. Although it is early to speculate about the mechanisms underlying the effects of FMT, the available data suggest that changes in the intestinal bacteria accompanied by changes in fermentation patterns and fermentation products (specifically short-chain fatty acids) play an important role in improving the IBS symptoms seen after FMT. FMT appears to be a promising treatment for IBS, but further studies are needed before it can be applied in everyday clinical practice.

Possible role of peptide YY (PYY) in the pathophysiology of irritable bowel syndrome (IBS)

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder of unknown aetiology for which there is no effective treatment. Although IBS does not increase mortality, it reduces the quality of life and is an economic burden to both the patients themselves and society as a whole. Peptide YY (PYY) is localized in endocrine cells located in the ileum, colon and rectum. The concentration of PYY and the density of PYY cells are decreased in both the colon and rectum but unchanged in the ileum of patients with IBS. The low density of PYY cells in the large intestine may be caused by a decreased number of stem cells and their progeny toward endocrine cells. PYY regulates the intestinal motility, secretion and absorption as well as visceral sensitivity via modulating serotonin release. An abnormality in PYY may therefore contribute to the intestinal dysmotility and visceral hypersensitivity seen in IBS patients. Diet management involving consuming a low-FODMAP diet restores the density of PYY cells in the large intestine and improves abdominal symptoms in patients with IBS. This review shows that diet management appears to be a valuable tool for correcting the PYY abnormalities in the large intestine of IBS patients in the clinic.

The role of the neuropeptide Y (NPY) family in the pathophysiology of inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD) includes three main disorders: ulcerative colitis, Crohn's disease, and microscopic colitis. The etiology of IBD is unknown and the current treatments are not completely satisfactory. Interactions between the gut neurohormones and the immune system are thought to play a pivot role in inflammation, especially in IBD. These neurohormones are believed to include members of the neuropeptide YY (NPY) family, which comprises NPY, peptide YY (PYY), and pancreatic polypeptide (PP). Understanding the role of these peptides may shed light on the pathophysiology of IBD and potentially yield an effective treatment tool. Intestinal NPY, PYY, and PP are abnormal in both patients with IBD and animal models of human IBD. The abnormality in NPY appears to be primarily caused by an interaction between immune cells and the NPY neurons in the enteric nervous system; the abnormalities in PYY and PP appear to be secondary to the changes caused by the abnormalities in other gut neurohormonal peptides/amines that occur during inflammation. NPY is the member of the NPY family that can be targeted in order to decrease the inflammation present in IBD.

Neuropeptide Y (NPY) cleaving enzymes: structural and functional homologues of dipeptidyl peptidase 4

N-terminal truncation of NPY has important physiological consequences, because the truncated peptides lose their capability to activate the Y1-receptor. The sources of N-terminally truncated NPY and related peptides are unknown and several proline specific peptidases may be involved. First, we therefore provide an overview on the peptidases, belonging to structural and functional homologues of dipeptidyl peptidase 4 (DP4) as well as aminopeptidase P (APP) and thus, represent potential candidates of NPY cleavage in vivo. Second, applying selective inhibitors against DP4, DP8/9 and DP2, respectively, the enzymatic distribution was analyzed in brain extracts from wild type and DP4 deficient F344 rat substrains and human plasma samples in activity studies as well as by matrix assisted laser desorption/ionisation-time of flight (MALDI-TOF)-mass spectrometry. Third, co-transfection of Cos-1 cells with Dpp4 and Npy followed by confocal lasermicroscopy illustrated that hNPY-dsRed1-N1 was transported in large dense core vesicles towards the membrane while rDP4-GFP-C1 was transported primarily in different vesicles thereby providing no clear evidence for co-localization of NPY and DP4. Nevertheless, the review and experimental results of activity and mass spectrometry studies support the notion that at least five peptidases (DP4, DP8, DP9, XPNPEP1, XPNPEP2) are potentially involved in NPY cleavage while the serine protease DP4 (CD26) could be the principal peptidase involved in the N-terminal truncation of NPY. However, DP8 and DP9 are also capable of cleaving NPY, whereas no cleavage could be demonstrated for DP2.

Excitatory stimulation of neurons in the arcuate nucleus initiates central CRF-dependent stimulation of colonic propulsion in rats

It is well established that autonomic control of digestive function is modulated by central autonomic neurotransmission. In this context it has been shown that digestive function can be modulated by exogenous neuropeptides microinjected into specific brain sides. Furthermore, there is considerable evidence suggesting that neurons projecting from the arcuate nucleus (ARC) to the PVN may be the source of endogenous neuropeptide release in the PVN. Neuronal projections from the ARC have been proposed to target corticotropin-releasing factor (CRF)-positive neurons in the PVN. Exogenous CRF in the PVN has been shown to modulate digestive function like gastric acid secretion and GI motility. Recently we have demonstrated that activation of ARC neurons inhibits gastric acid secretion via central CRF receptor dependent mechanisms. This poses the question whether neuronal activation of the ARC alters digestive function beside gastric acid secretion. In the present study we investigated whether CRF pathways in the ARC-PVN axis are involved in the modulation of colonic motility. First we examined the effect of an excitatory amino acid, kainate, microinjected into the ARC on colonic motility in anesthetized rats. Colonic motility was measured with a non-absorbable radioactive marker using the geometric center method. Kainate (120 pmol/rat) bilaterally microinjected into the ARC induced a significant stimulation of colonic propulsion. To assess the contribution of hypothalamic CRF to the effects of neuronal stimulation in the ARC on colonic motility we performed consecutive bilateral microinjections of an antagonist to CRF receptors into the PVN and the excitatory amino acid kainate into the ARC. Microinjection of the non-selective CRF receptor antagonist, astressin (100 ng), into the PVN abolished the stimulatory effect of neuronal activation in the ARC by kainate on colonic motor function. The data indicate that activation of neurons in the ARC stimulates colonic motility via CRF-receptor-mediated mechanism in the PVN and underlines the important role of the ARC-PVN circuit for the integrative CNS regulation of GI function.

Effects of PYY[3-36] in rodent models of diabetes and obesity

BACKGROUND

Peptide YY (PYY) is a 36 amino-acid peptide secreted from ileal L cells following meals. The cleaved subpeptide PYY[3-36] is biologically active and may constitute the majority of circulating PYY-like immunoreactivity. The peptide family that includes PYY, pancreatic peptide and neuropeptide Y is noted for its orexigenic effect following intracerebroventricular administration.

OBJECTIVE

To investigate the effects of peripheral (intraperitoneal and chronic subcutaneous) infusions of PYY[3-36] on food intake, body weight and glycemic indices.

DESIGN/RESULTS

Food intake was measured in normal mice and in several rodent models of obesity and type II diabetes. In marked contrast to the reported central orexigenic effects, in the present study, PYY[3-36] acutely inhibited food intake by up to 45%, with an ED(50) of 12.5 microg/kg in fasted female NIH/Swiss mice. A 4-week infusion reduced weight gain in female ob/ob mice, without affecting the cumulative food intake. In diet-induced obese male mice, PYY[3-36] infusion reduced cumulative food intake, weight gain and epididymal fat weight (as a fraction of carcass) with similar ED(50)'s (466, 297 and 201 microg/kg/day, respectively) and prevented a diet-induced increase in HbA1c. Infusion at 100 microg/kg/day for 8 weeks in male fa/fa rats reduced the weight gain (288+/-11 vs 326+/-12 g in saline-infused controls; P<0.05), similar to effects in a pair-fed group. In female ob/ob and db/db mice, there was no acute effect of PYY[3-36] on plasma glucose concentrations. In male diabetic fatty Zucker rats, PYY[3-36] infused for 4 weeks reduced HbA1c and fructosamine (ED(50)'s 30 and 44 microg/kg/day).

CONCLUSION

Peripheral PYY[3-36] administration reduced the food intake, body weight gain and glycemic indices in diverse rodent models of metabolic disease of both sexes. These findings justify further exploration of the potential physiologic and therapeutic roles of PYY[3-36].

Increased expression of the gene for the Y1 receptor of neuropeptide Y in the amygdala and paraventricular nucleus of Y1R/LacZ transgenic mice in response to restraint stress

A sustained increase in the brain concentrations of neuroactive steroids was previously shown to induce Y1 receptor gene expression in the amygdala of Y1R/LacZ transgenic mice which harbour a construct comprising the murine Y1 receptor gene promoter and the lacZ reporter gene. We now investigated the effects of restraint stress on both the cerebrocortical concentrations of neuroactive steroids and Y1 receptor gene expression in the amygdala and hypothalamic paraventricular nucleus (PVN) of Y1R/LacZ transgenic mice. The cerebrocortical concentrations of allopregnanolone and allotetrahydrodeoxycorticosterone were significantly increased immediately after a 1-h exposure to restraint stress and had returned to control values within 30 min. Expression of Y1R/LacZ was increased in the amygdala and PVN 6 h after restraint. The 5alpha-reductase inhibitor finasteride, that prevented the increase in neuroactive steroid concentrations, did not block that in transgene expression induced by 1-h restraint. Daily exposure to restraint for 10 days also increased the cerebrocortical concentrations of neuroactive steroids but failed to affect transgene expression. Acute but not repeated restraint thus increases Y1 receptor gene expression in the amygdala and PVN, suggesting that tolerance develops towards this stressor. The effect of acute restraint is not mediated by the increase in the brain concentrations of neuroactive steroids but may rather reflect a ligand-induced increase in Y1 receptor gene transcription. Data support a role of Y1 receptors in the behavioural and neuroendocrine responses to stress.

Stimulation of neurons in rat ARC inhibits gastric acid secretion via hypothalamic CRF1/2- and NPY-Y1 receptors

Neuropeptide Y (NPY) neuronal projections from the arcuate nucleus (ARC) have been proposed to target corticotropin-releasing factor (CRF)-positive neurons in the paraventricular nucleus (PVN) as part of the ARC-PVN axis. The existence of a positive feedback loop involving CRF receptors in the PVN has been suggested. Exogenous NPY and CRF in the PVN have been shown to inhibit gastric acid secretion. Recently, we have demonstrated that activation of ARC neurons inhibits gastric acid secretion via vagal pathways. To what extent NPY- and CRF-mediated mechanisms in the PVN contribute to the CNS modulation of gastric acid secretion is still an open question. In the present study, we performed consecutive bilateral microinjections of antagonists to NPY receptor subtypes Y1 and Y2 and to CRF1/2 receptors in the PVN and of the excitatory amino acid kainate in the ARC to assess the role of NPY- and CRF-mediated mechanisms in the kainate-induced effects on gastric acid secretion. Gastric acid secretion was measured at the basal condition and during pentagastrin (16 microg/kg body wt) stimulation. Microinjection of vehicle in the PVN and kainate in the ARC decreased gastric acid secretion. Microinjection of the specific NPY-Y1 receptor antagonist BIBP-3226 (200 pmol) and the nonspecific CRF1/2 antagonist astressin (30 pmol) in the PVN abolished the inhibitory effect of neuronal activation in the ARC by kainate on gastric acid secretion. The CRF antagonist astressin was more effective. Pretreatment with the NPY-Y2 receptor antagonist BIIE-0246 (120 pmol) in the PVN had no significant effect. Our results indicate that activation of neurons in the ARC inhibits gastric acid secretion via CRF1/2 and NPY-Y1 receptor-mediated pathways in the PVN.

Gastric protective effect of peripheral PYY through PYY preferring receptors in anesthetized rats

The influence of intravenous peptide YY (PYY) on the gastric injury induced by 45% ethanol was investigated in urethane-anesthetized rats. PYY (25, 75, 125, and 250 pmol x kg(-1) x h(-1)) significantly reduced gastric lesions by 36, 59, 40, and 38%, respectively. Antibody against ratPYY (2 mg/rat) injected intravenously completely prevented the gastroprotective effect of intravenous PYY (75 pmol x kg(-1) x h(-1)), whereas injected intracisternally (460 microg/20 microl), it significantly prevented intracisternal PYY (24 pmol/rat)-induced 58% reduction of ethanol lesions but not that induced by intravenous PYY. Vagotomy did not influence the gastroprotective effect of intravenous PYY. The Y(1)/"PYY-preferring" receptor agonist [Pro(34)]PYY (75 pmol x kg(-1) x h(-1) iv) significantly decreased ethanol-induced gastric lesions by 82%, whereas [Leu(31), Pro(34)]NPY, a Y(1)/Y(3) agonist, and PYY-(3-36), a Y(2) agonist, had no effect. These data indicate that PYY-infused intravenously at doses reported to mimic postprandial peak blood levels prevents ethanol-induced gastric injury through vagal independent pathways and PYY-preferring receptors.

Changes in expression of the neuropeptide Y Y1 receptor gene in the medial amygdala of transgenic mice during pregnancy and after delivery

Long-term administration of progesterone or allopregnanolone was previously shown to increase Y1 receptor gene expression in the medial amygdala of Y1R/LacZ transgenic mice, which harbor a construct comprising the murine Y1 receptor gene promoter and a lacZ reporter. We have now investigated the effects of physiological fluctuations in the cerebrocortical concentrations of neuroactive steroids during pregnancy on Y1R/LacZ transgene expression by quantitative histochemical analysis of beta-galactosidase activity. Cerebrocortical concentrations of progesterone and its metabolites allopregnanolone and allotetrahydrodeoxycorticosterone were increased on day 18 of pregnancy and had returned to control values 2 days after delivery. Transgene expression in the medial amygdala was also increased on day 18 of pregnancy and had returned to control values 2 days after delivery. Similar results were obtained after analysis of Y1R mRNA levels in the medial amygdala of pregnant mice by in situ hybridization. Administration of the 5alpha-reductase inhibitor finasteride to pregnant mice prevented both the increase in the cerebrocortical concentrations of neuroactive steroids as well as the increase in transgene expression. These data suggest that fluctuations in the brain concentrations of endogenous neuroactive steroids during pregnancy are associated with changes in Y1 receptor gene expression in the medial amygdala, further supporting a functional interaction between the GABAergic and NPY-Y1 receptor systems.

Neuropeptide Y blocks anxiogenic-like behavioral action of corticotropin-releasing factor in an operant conflict test and elevated plus maze

Central administration of neuropeptide Y (NPY) produces anxiolytic-like behavioral effects in rat models of anxiety. Because previous evidence has suggested a relationship between NPY and corticotropin-releasing factor (CRF) in the brain, we have focused on the interaction of these neuropeptide systems in emotional responsiveness to stressful stimuli. Intracerebroventricular administration of CRF produced a marked response suppression in an operant incremental shock conflict paradigm. NPY [(1 microg, intracerebroventricularly (i.c.v.)] significantly antagonized the response-suppressing effects of CRF (0.75 microg, i.c.v.) on punished responding in the conflict test at doses that produced little or no behavioral effect when administered alone. Central administration of the CRF antagonist [D-Phe(12), Nle(21,38),C(alpha) MeLeu(37)]CRF (D-Phe CRF(12-41)) alone did not alter punished or unpunished responding in the conflict test. However, pretreatment with the CRF antagonist before a subthreshold dose of NPY (1 microg, i.c.v.) produced a significant potentiation of the release of punished responding relative to NPY alone and untreated controls. NPY also antagonized the "anxiogenic-like" behavioral effects of CRF in the elevated plus maze. These findings support the hypothesis that NPY and CRF may reciprocally modulate an animal's behavioral response to stressful stimuli.

Modulation of innate immune functions by intracerebroventricularly applied neuropeptide Y: dose and time dependent effects

Centrally applied neuropeptide Y (NPY) interacts with the autonomic nervous system and the hypothalamo-pituitary-adrenal (HPA) axis activity. Since these physiological systems have been shown to modulate innate immune functions, the effects of intracerebroventricular (i.c.v.) NPY administration on leukocyte subsets in the blood, spleen and intravascular pool of the lung, blood granulocyte chemiluminescence response, and splenic natural killer (NK) cell-mediated lysis were studied in Lewis rats. Concentration-dependent NPY effects were tested at 15 min and 24 h post i.c.v. injection at dosages of 10(-6) M, 10(-9) M, and 10(-12) M. Time dependent effects were investigated at 15 min, 1 h and 24 h after i.c.v. administration of 10(-9) M NPY. Compared to saline controls, an increased number of granulocytes and NK cells in the blood, associated with a decreased granulocyte function and NK cytotoxicity was observed 15 min following NPY infusion. This initial immunosuppression was followed by long lasting stimulatory effects of NPY on the functional capacity of both cell populations when tested at 1 h and 24 h. The dosage of i.c.v. 10(-6) M NPY produced no changes, whilst 10(-9) M produced maximal, and 10(-12) M still significant effects. Results provide evidence that centrally applied NPY influences innate immunity in a dose and time dependent fashion. Cell mobilization from the vascular marginal pool is likely to be an underlying mechanism for the initial immunosuppression.

Neuropeptide Y stimulates bile secretion via Y1 receptor in the left dorsal vagal complex in rats

Neuropeptide Y (NPY) injected into the cerebrospinal fluid and the left dorsal vagal complex enhances bile acid-independent and bicarbonate-dependent bile secretion through vagal muscarinic pathways in animal models. NPY binds to and activates six different receptor subtypes, and NPY Y1 and Y2 receptors are distributed in the dorsal vagal complex. We sought to determine which NPY receptor subtypes are involved in central stimulation of bile secretion by examining the effect of microinjection of specific NPY receptor agonists into the dorsal vagal complex. The bile duct was cannulated in urethane-anesthetized and bile acid-compensated rats. After measuring basal secretion, NPY, peptide YY (PYY), [Leu31, Pro34]NPY, NPY(13-36), or NPY(3-36) was microinjected into the either right or left dorsal vagal complex and bile secretion was observed for 100 minutes. Hepatic branch vagotomy was performed 2 hours before the peptide injection. Microinjection of NPY and PYY (8 pmol) into the left dorsal vagal complex increased bile secretion. [Leu31, Pro34]NPY microinjected into the left dorsal vagal complex also dose-dependently (1-8 pmol) stimulated bile acid-independent and bicarbonate-dependent bile secretion. Microinjection of NPY(13-36) into the left dorsal vagal complex did not stimulate and NPY(3-36) dose-dependently inhibited bile secretion. Stimulation of bile secretion by [Leu31, Pro34]NPY was abolished by hepatic branch vagotomy. NPY acts in the left dorsal vagal complex to stimulate bile acid-independent and bicarbonate-dependent bile secretion via Y1 receptor subtype.

Cardiovascular actions of neuropeptide Y and social stress

The role of central neuropeptide Y (NPY) in the cardiovascular response to social stress was evaluated in freely moving rats using telemetry. In unstressed rats, intracerebroventricular (ICV) administration of NPY and the selective Y1 receptor agonist [Leu31, Pro34]-NPY decreased blood pressure and heart rate, while the selective Y2 agonist NPY13-36 transiently raised blood pressure. NPY and [Leu31, Pro34]-NPY blunted elevations in blood pressure and pulse rate following exposure to the resident-intruder procedure, an established social stress paradigm. In contrast, the Y2 agonist significantly augmented stress-induced pressor effects. These observations indicate that the hypotensive effects of ICV NPY appear to be mediated by the Y1 receptor subtype and the NPY receptor subtypes may mediate opposing cardiovascular actions in response to stressful stimuli.