Proadrenomedullin N-terminal 20 peptide (PAMP) inhibits food intake and gastric emptying in mice

Xenin delays gastric emptying rate and activates the brainstem in mice

Xenin, a 25-amino acid gastrointestinal peptide, inhibits feeding by acting through the central nervous system. Gastrointestinal hormones reduce food intake partly by activating the brainstem and inhibiting gastric emptying. Therefore, we hypothesized that xenin delays gastric emptying through the activation of the brainstem cells. To address this hypothesis, we examined the effect of intraperitoneal (i.p.) injection of xenin on gastric emptying rate and brainstem Fos expression in mice. Gastric emptying rate was reduced by about 93% in xenin-treated mice compared to saline-treated control mice. The i.p. xenin injection significantly increased Fos-immunoreactive cells in the nucleus of the solitary tract (NTS) of the brainstem, but not area postrema (AP) and dorsal motor nucleus of the vagus (DMV). These findings support the hypothesis that xenin-induced anorexia is at least partly due to delayed gastric emptying and the activation of the NTS cells.

Complement C5a stimulates food intake via a prostaglandin D(2)- and neuropeptide Y-dependent mechanism in mice

We have recently found that prostaglandin (PG) D(2) stimulates food intake via DP(1) receptor. Here we show that complement C5a stimulates food intake by activating the orexigenic PGD(2) system. C5a (30-100 pmol/mouse), after intracerebroventricular administration, stimulated food intake in non-food-deprived mice. The orexigenic activity of C5a was blocked by co-administration of a DP(1) receptor antagonist, BWA868C. Central administration of C5a elevated the hypothalamic mRNA expression of COX-2 but not COX-1, and the food intake stimulation of C5a was inhibited by pretreatment with a COX-2 inhibitor, celecoxib, suggesting that C5a activates COX-2 upstream of the PGD(2)-DP(1) system. The orexigenic activity of C5a was also inhibited by an antagonist for neuropeptide Y (NPY) Y(1) receptor, which was activated downstream of the PGD(2)-DP(1) system. These results suggest that C5a stimulates food intake via a PGD(2)- and NPY-dependent mechanism. C5a is the first example of orexigenic peptides acting through the PGD(2)-NPY system in the central nervous system.

Orally administered novokinin, an angiotensin AT2 receptor agonist, suppresses food intake via prostaglandin E2-dependent mechanism in mice

Novokinin (Arg-Pro-Leu-Lys-Pro-Trp), having affinity for the AT(2) receptor, is a potent vasorelaxing and hypotensive peptide designed based on the structure of ovokinin(2-7), a bioactive peptide derived from ovalbumin. Here we show that intracerebroventricularly (i.c.v.) administered novokinin dose-dependently suppresses food intake at a dose of 30-100 nmol/mouse in fasted conscious mice. Orally administered novokinin (30-100mg/kg) also suppressed food intake. Novokinin suppressed food intake in wild-type and AT(1) receptor-knockout mice but not in AT(2) receptor-knockout mice after i.c.v. or oral administration. Novokinin-induced anorexigenic activity after i.c.v. administration was blocked by indomethacin, a cyclooxygenase inhibitor, or ONO-AE3-208, an antagonist for EP(4) receptor for PGE(2). Taken together, novokinin may suppress food intake via activation of PGE(2)-EP(4), downstream of the AT(2) receptor.

Angiotensin II and III suppress food intake via angiotensin AT(2) receptor and prostaglandin EP(4) receptor in mice

Intracerebroventricularly administered angiotensin (Ang) II and III dose-dependently suppressed food intake in mice and their anorexigenic activities were inhibited by AT(2) receptor-selective antagonist. Ang II did not suppress food intake in AT(2) receptor-knockout mice, while it did significantly in wild-type and AT(1) receptor-knockout mice. The suppression of food intake in AT(1) receptor-knockout mice was smaller than that in wild-type. The anorexigenic activities of Ang II and III were also blocked by a selective antagonist for prostaglandin EP(4) receptor. Taken together, centrally administered Ang II and III may decrease food intake through AT(2) receptor with partial involvement of AT(1) receptor, followed by EP(4) receptor activation, which is a novel pathway regulating food intake.

Activation of prostaglandin E receptor EP4 subtype suppresses food intake in mice

Prostaglandin (PG) E2, a bioactive lipid produced in the brains of various mammals, decreases food intake after central administration. We examined which of four distinct subtypes of PGE2 receptors (EP1-EP4) mediated the anorexigenic action of PGE2 using highly selective ligands. PGE2 at a dose of 0.1-10 nmol/mouse decreased food intake after intracerebroventricular (i.c.v.) administration in a dose-dependent manner in fasted mice. A centrally administered EP4 agonist, ONO-AE1-329 at a dose of 1-10 nmol/mouse mimicked the anorexigenic action by PGE2. The anorexigenic action of PGE2 or EP4 agonist was ameliorated by EP4 antagonist ONO-AE3-208 at a dose of 10 nmol/mouse. Thus, activation of PGE2-EP4 signaling in the central nervous system suppresses food intake. The EP4 agonist at a dose of 10 nmol/mouse delayed gastric emptying and elevated blood glucose.

Arg-Ile-Tyr (RIY) derived from rapeseed protein decreases food intake and gastric emptying after oral administration in mice

We previously reported that a bioactive tripeptide Arg-Ile-Tyr (RIY), which has been isolated as an inhibitor for angiotensin I-converting enzyme from the subtilisin digest of rapeseed protein, decreased blood pressure. In this study, we also found that RIY dose-dependently decreased food intake at a dose of 150 mg/kg after oral administration in fasted ddY male mice. The anorexigenic action of RIY was blocked by a cholecystokinin-1 CCK1 receptor antagonist, lorglumide. RIY also decreased the gastric emptying rate at a dose of 150 mg/kg and the RIY-induced delay of gastric emptying was blocked by lorglumide. However, RIY had no affinity for CCK1 receptor. Taken together, RIY decreased food intake and gastric emptying by stimulating CCK release.

[Trp3, Arg5]-ghrelin(1-5) stimulates growth hormone secretion and food intake via growth hormone secretagogue (GHS) receptor

Ghrelin, a 28 amino acid peptide identified as an endogenous ligand for growth hormone secretagogue (GHS) receptor, stimulates food intake and growth hormone (GH) secretion. We designed low molecular weight peptides with affinity for the GHS receptor based on the primary structure of ghrelin. We found that [Trp3, Arg5]-ghrelin(1-5) (GSWFR), a novel pentapeptide composed of all L-amino acids, had affinity for the GHS receptor (IC50 = 10 microM). GSWFR stimulated GH secretion after intravenous or oral administration. Centrally administered GSWFR increased food intake in non-fasted mice. The orexigenic action of GSWFR was inhibited by a GHS receptor antagonist, [D-Lys3]-GH-releasing peptide-6, suggesting that GSWFR stimulated food intake through the GHS receptor. The orexigenic action of GSWFR was also inhibited by a neuropeptide Y (NPY) Y1 receptor antagonist, BIBO3304. These results suggest that the GSWFR-induced feeding is mediated by the NPY Y1 receptor.

NMR conformational analysis of proadrenomedullin N-terminal 20 peptide, a proangiogenic factor involved in tumor growth

The preferred conformation of Proadrenomedullin N-Terminal 20 Peptide (PAMP; ARLDVASEFRKKWNKWALSR-amide) has been determined using 1H and 13C two-dimensional nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. PAMP is a peptide that has various physiological functions, including its role as a proangiogenic factor in facilitating tumor growth and its inhibitory effect on catecholamine secretion at nicotinic receptors. The preferred conformation of PAMP was determined in a helix-inducing trifluoroethanol and water (TFE/H2O) solution, and in a membrane-mimetic sodium dodecylsulfate-d25 (SDS) micellar solution. The secondary structure consists of an alpha-helix for residues Arg2 to Arg20 in TFE/H2O solution and an alpha-helix for residues Arg2 to Ala17 in SDS solution. We postulate that the polar charged residues Arg2, Lys12, and Arg20 are responsible for the initial interaction of the peptide with the micelle, and that this is followed by the binding of the hydrophobic residues Leu3, Val5, Phe9, Trp13, and Trp16 to the micellar core. The three C-terminal amino acid residues adopt an extended structure in SDS, suggesting that they are important in receptor recognition and binding. This is supported by truncation studies done by Mahata et al. (Hypertension, 1998, Vol. 32, pp. 907-916), which show the importance of the C-terminal in physiological activity. Furthermore, Belloni et al. (Hypertension, 1999, Vol. 33, pp. 1185-1189), and Martinez et al. (Cancer Research, 2004, Vol. 64, pp. 6489-6494) suggested that the N-terminal was also important in PAMP activity. However, no differences in conformational preference of the N-terminal were observed between the two solvent systems.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

Albutensin A and complement C3a decrease food intake in mice

Albutensin A (Ala-Phe-Lys-Ala-Trp-Ala-Val-Ala-Arg) derived from serum albumin dose-dependently decreased food intake after intracerebroventricular (10-50 nmol/mouse) or peripheral (0.3-1.0 micromol/mouse) administration in fasted conscious ddY mice. Albutensin A delayed gastric emptying and elevated blood glucose levels. Although albutensin A showed low affinity for bombesin receptor, it decreased food intake in bombesin receptor knockout mice, indicating that its inhibitory effect on feeding was not mediated through bombesin receptor. Then, we investigated whether the albutensin A-induced decrease in food intake was mediated by complement C3a and C5a receptors, because albutensin A had affinities for these receptors. Des-Arg-albutensin A, lacking affinity for C3a and C5a receptors, did not inhibit food intake. We found for the first time that centrally administered C3a (10-100 pmol/mouse) by itself decreased food intake in fasted mice. In contrast, C5a increased food intake after central injection. Based on these results, we conclude that the inhibitory effect of albutensin A on food intake is mediated through the C3a receptor.

Novel actions of proadrenomedullin N-terminal 20 peptide (PAMP)

Poadrenomedullin N-terminal 20 peptide (PAMP) is a hypotensive peptide derived from the precursor of adrenomedullin. We identified novel actions of proadrenomedullin N-terminal 20 peptide (PAMP) on blood glucose, food intake and gastric emptying after exogenous administration. PAMP elevated blood glucose levels after central injection in fasted mice. PAMP had affinity for bombesin (BN) receptor and the hyperglycemic effect of PAMP was blocked by a BN antagonist, indicating that the elevation of blood glucose after central administration of PAMP was mediated by BN receptor. Centrally administered PAMP inhibited food intake and gastric emptying in fasted conscious mice. However, studies using a BN antagonist and BN receptor knockout mice suggested that the inhibitory effects of PAMP on feeding and gastric emptying were mediated not via BN receptor but via another receptor specific for PAMP. In the present review, we summarize these effects of PAMP and report other novel actions of PAMP on body temperature and oxygen consumption. In addition, the mechanism underlying the cardiovascular functions of PAMP is discussed.