Kousaku Ohinata

β-Lactotensin and neurotensin rapidly reduce serum cholesterol via NT2 receptor

Beta-lactotensin, a neurotensin NT2 agonist derived from beta-lactoglobulin, has hypocholesterolemic activity after administration for 2 days at a dose of 30 mg/kg (i.p.) or 100 mg/kg (p.o.) for 2 days in mice fed a high-cholesterol/cholic acid diet. The onset of hypocholesterolemic activity of beta-lactotensin was observed 90 min after a single i.p. or p.o. administration at the same dose as described above. Neurotensin also induced hypocholesterolemic activity 90 min after single i.p. administration at a dose of 2 microg per mouse but was ineffective after oral administration. The rapid onset of hypocholesterolemic activities of beta-lactotensin and neurotensin was blocked by levocabastine (50 microg/kg), an NT2 antagonist, and raclopride (0.5 mg/kg), a dopamine D2 antagonist.

Soymorphins, Novel μ Opioid Peptides Derived from Soy β-Conglycinin β-Subunit, Have Anxiolytic Activities

Based on the amino acid sequence YPFV found in the soy β-conglycinin β-subunit, which is common to an opioid peptide human β-casomorphin-4, peptides YPFVV, YPFVVN, and YPFVVNA were synthesized according to their primary structure. On guinea pig ileum (GPI) assay, they showed opioid activity (IC50 = 6.0, 9.2 and 13 μM respectively) more potent than human β-casomorphins, and were named soymorphins-5, -6, and -7, respectively. Their opioid activities on mouse vas deferens (MVD) assay were less potent than on GPI assay, suggesting that they are selective for the μ opioid receptor. Human β-casomorphin-4 and soymorphin-5 were released from the soy 7S fraction (β-conglycinin) by the action of gastrointestinal proteases. Soymorphins-5, -6, and -7 had anxiolytic activities after oral administration at doses of 10–30 mg/kg in the elevated plus-maze test in mice.

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.

Central prostaglandin D2 stimulates food intake via the neuropeptide Y system in mice

We found that prostaglandin (PG) D2, the most abundant PG in the central nervous system, stimulates food intake after intracerebroventricular administration in mice. The orexigenic effect of PGD2 was mimicked by a selective agonist for the DP1 receptor among two receptor subtypes for PGD2, and abolished by its antagonist. Central administration of an antagonist or antisense oligodeoxynucleotide for the DP1 receptor remarkably decreased food intake, body weight and fat mass. Hypothalamic mRNA levels of lipocalin‐type PGD synthase were up‐regulated after fasting. The orexigenic activity of PGD2 was also abolished by an antagonist for neuropeptide Y (NPY) Y1 receptor. Taken together, PGD2 may stimulate food intake through central DP1 receptor coupled to the NPY system.

Orally administered soymorphins, soy-derived opioid peptides, suppress feeding and intestinal transit via gut μ1-receptor coupled to 5-HT1A, D2, and GABAB systems

We previously reported that soymorphins, mu-opioid agonist peptides derived from soy beta-conglycinin beta-subunit, have anxiolytic-like activity. The aim of this study was to investigate the effects of soymorphins on food intake and gut motility, along with their mechanism. We found that soymorphins decreases food intake after oral administration in fasted mice. Orally administered soymorphins suppressed small intestinal transit at lower dose than that of anorexigenic activity. Suppression of food intake and small intestinal transit after oral administration of soymorphins was inhibited by naloxone or naloxonazine, antagonists of mu- or mu(1)-opioid receptor, respectively, after oral but not intraperitoneal administration. The inhibitory activities of small intestinal transit by soymorphins were also inhibited by WAY100135, raclopride, or saclofen, antagonists for serotonin 5-HT(1A), dopamine D(2), or GABA(B) receptor, respectively. We then examined the order of activation of 5-HT(1A), D(2), and GABA(B) receptors, using their agonists and antagonists. The inhibitory effect of 8-hydroxy-2-dipropylaminotetralin hydrobromide, a 5-HT(1A) agonist, after oral administration on small intestinal transit was blocked by raclopride or saclofen. Bromocriptine, a D(2) agonist-induced small intestinal transit suppression, was inhibited by saclofen, but not by WAY100135. Baclofen, a GABA(B) agonist-induced small intestinal transit suppression, was not blocked by WAY100135 or raclopride. These results suggest that 5-HT(1A) activation elicits D(2) followed by GABA(B) activations in small intestinal motility. We conclude that orally administered soymorphins suppress food intake and small intestinal transit via mu(1)-opioid receptor coupled to 5-HT(1A), D(2), and GABA(B) systems.

Proadrenomedullin N‐terminal 20 peptide (PAMP) elevates blood glucose levels via bombesin receptor in mice

We found a potent hyperglycemic effect of proadrenomedullin N‐terminal 20 peptide (PAMP) after intra‐third cerebroventricular administration at a dose of 10 nmol in fasted mice. PAMP has four homologous residues with bombesin (BN), a hyperglycemic peptide. PAMP showed affinity for gastrin‐releasing peptide preferring receptor (GRP‐R) and neuromedin B preferring receptor. The PAMP‐induced hyperglycemic effect was inhibited by [D‐Phe6, Leu‐NHEt13, des‐Met14]‐BN (6–14), GRP‐R specific antagonist, indicating that the hyperglycemic effect is mediated at least in part via GRP‐R. Furthermore, pretreatment of α‐adrenergic blocker inhibited the PAMP‐induced hyperglycemia and hyperglucagonemia, suggesting that the increase of glucagon secretion through α‐adrenergic activation is involved in this hyperglycemic effect of PAMP.

Zinc as an Appetite Stimulator - The Possible Role of Zinc in the Progression of Diseases Such as Cachexia and Sarcopenia

Zinc is required by humans and animals for many physiological functions, such as growth, immune function, and reproduction. Zinc deficiency induces a number of physiological problems, including anorexia, growth retardation, dermatitis, taste disorder, and hypogonadism. Although it is clear that zinc deficiency produces specific and profound anorexia in experimental animals, the connection between zinc deficiency and anorexia is less certain. We were the first to show that orally, but not intraperitoneally, administered zinc rapidly stimulates food intake through orexigenic peptides coupled to the afferent vagus nerve using rats during early-stage zinc deficiency without decreased zinc concentrations in plasma and tissues. We confirmed that a zinc-sufficient diet containing zinc chloride acutely stimulated food intake after short-term zinc deprivation. We also found that orally administered zinc sulfate increased the expression of NPY and orexin mRNA after administration. Using vagotomized rats, we tested whether the increase in food intake after oral administration of zinc was mediated by the vagus nerve. In sham-operated rats, the oral administration of zinc stimulated food intake, whereas zinc and saline administrations did not exhibit differing effects in vagotomized rats. We conclude that zinc stimulates food intake in short-term zinc-deficient rats through the afferent vagus nerve with subsequent effects on hypothalamic peptides associated with food intake regulation. In this review, we describe recent research investigating the roles of zinc as an appetite stimulator in food intake regulation, along with research about hypothalamus, ghrelin, leptin and zinc receptor, and clinical application about anorexia nervosa, cachexia and sarcopenia. The article also presents some promising patents on zinc.

Dipeptide Tyr-Leu (YL) exhibits anxiolytic-like activity after oral administration via activating serotonin 5-HT1A, dopamine D1 and GABAA receptors in mice.

We found that Tyr‐Leu (YL) dose‐dependently exhibits potent anxiolytic‐like activity (0.1–1 mg/kg, i.p.) comparable to diazepam in the elevated plus‐maze test in mice. YL was orally active (0.3–3 mg/kg). A retro‐sequence peptide or a mixture of Tyr and Leu was inactive. The anxiolytic‐like activity of YL was inhibited by antagonists for serotonin 5‐HT1A, dopamine D1 and GABAA receptors; however, YL had no affinity for them. We also determined the order of their activation is 5‐HT1A, D1 and GABAA receptors using selective agonists and antagonists. Taken together, YL may exhibit anxiolytic‐like activity via activation of 5‐HT1A, D1 and GABAA receptors.

Met-Arg-Trp derived from Rubisco lowers blood pressure via prostaglandin D2-dependent vasorelaxation in spontaneously hypertensive rats

Met-Arg-Trp (MRW) has been isolated as an inhibitor for angiotensin I-converting enzyme (ACE) from a pepsin-pancreatin digest of spinach ribulose bisphosphate carboxylase/oxygenase (Rubisco) (IC(50)=0.6 microM). It has been reported that hypotensive activity of ACE-inhibitory peptides derived from food proteins are weakened in spontaneously hypertensive rats older than 25 weeks (old SHR). However, MRW reduced blood pressure after oral administration at a dose of 5 mg/kg in old SHR as well as in younger SHR. MRW exhibited vasorelaxing activity above 1 microM in isolated mesenteric artery from adult and old SHR. The vasorelaxing activity of MRW was blocked by indomethacin and BW A868C, a cyclooxygenase inhibitor and an antagonist for DP(1) receptor, respectively. However, N(G)-nitro-L-arginine methyl ester, an inhibitor for nitric oxide synthase, had no effect on the relaxation. The hypotensive activity of MRW was also blocked by indomethacin and BW A868C, respectively, in adult and old SHR. Taken together, the vasorelaxing and hypotensive activities of MRW may be mediated by prostaglandin D(2) and the DP(1) receptor. These findings suggest that the hypotensive activity of MRW is mainly caused by vasorelaxation rather than by ACE-inhibition.

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.