Naohiko Ueno

Characterization of the effects of pancreatic polypeptide in the regulation of energy balance

BACKGROUND & AIMS Pancreatic polypeptide (PP) belongs to a family of peptides including neuropeptide Y and peptide YY. We examined the role of PP in the regulation of body weight as well as the therapeutic potential of PP. METHODS We measured food intake, gastric emptying, oxygen consumption, and gene expression of hypothalamic neuropeptides, gastric ghrelin, and adipocytokines in mice after administering PP intraperitoneally. Peptide gene expression was also examined in PP-overexpressing mice. Vagal and sympathetic nerve activities were recorded after intravenous administration in rats. Effects of repeated administrations of PP on energy balance and on glucose and lipid metabolism were examined in both ob/ob obese mice and fatty liver Shionogi (FLS)-ob/ob obese mice. RESULTS Peripherally administered PP induced negative energy balance by decreasing food intake and gastric emptying while increasing energy expenditure. The mechanism involved modification of expression of feeding-regulatory peptides (decrease in orexigenic neuropeptide Y, orexin, and ghrelin along with an increase in anorexigenic urocortin) and activity of the vagovagal or vagosympathetic reflex arc. PP reduced leptin in white adipose tissue and corticotropin-releasing factor gene expression. The expression of gastric ghrelin and hypothalamic orexin was decreased in PP-overexpressing mice. Repeated administrations of PP decreased body weight gain and ameliorated insulin resistance and hyperlipidemia in both ob/ob obese mice and FLS-ob/ob obese mice. Liver enzyme abnormalities in FLS-ob/ob obese mice were also ameliorated by PP. CONCLUSIONS These observations indicate that PP may influence food intake, energy metabolism, and the expression of hypothalamic peptides and gastric ghrelin.

Decreased food intake and body weight in pancreatic polypeptide-overexpressing mice

BACKGROUND & AIMS Pancreatic polypeptide (PP) is a 36-amino acid hormone produced by F cells within the pancreatic islets and the exocrine pancreas. The definitive function of PP in mammalian physiology remains to be determined. This study examined the effects of chronic overexpression of PP through the development of PP transgenic mice. METHODS PP transgenic mice were created by using mouse PP complementary DNA under the control of the cytomegalovirus immediate early enhancer-chicken beta-actin hybrid promoter (pCAGGS expression vector). RESULTS A unique line of transgenic mice was created that overexpresses PP in the pancreatic islets with low levels of expression in other tissues including the brain. Plasma PP concentrations were more than 20 times higher than those of control littermates. However, PP overproduction led to postnatal lethality in half of the pups because of markedly decreased milk intake. The remaining PP transgenic mice gained less weight with specifically reduced food intake and fat mass compared with controls, a result that was more evident in male than in female mice. The transgenic mice exhibited a reduced rate of gastric emptying of a solid meal but had normal oxygen consumption and fasting leptin levels. Immunoneutralization with anti-PP antiserum reversed the phenotypic changes of transgenic animals. CONCLUSIONS PP could be involved in feeding and body weight regulation partly through regulation of gastric emptying.

Urocortin reduces food intake and gastric emptying in lean and ob/ob obese mice☆☆☆

BACKGROUND & AIMS Gastric emptying plays an important role in regulating food intake. This study was designed to investigate whether intraperitoneally injected urocortin reduces gastric emptying, feeding, and body weight in lean and ob/ob obese mice. METHODS Food intake and body weight were measured after intraperitoneal injections of one of the following: urocortin, deamidated form of urocortin (urocortin OH), corticotropin-releasing factor (CRF), CRF6-33, cholecystokinin octapeptide (CCK-8), and leptin in 16-hour food-deprived animals. Gastric emptying was assessed 2, 4, or 8 hours after intraperitoneal injection. Repeated injections of urocortin were continued for 5 days in ob/ob mice. RESULTS Urocortin (0.003-3 nmol) dose-dependently and potently decreased food intake and body weight gain in lean mice. The ranking order of potency was urocortin > urocortin OH >/= CRF > CCK-8 > CRF6-33 > leptin. Gastric emptying was also potently reduced by urocortin with a similar ranking order of potency of urocortin > CRF > urocortin OH > CCK-8. Simultaneous administration of urocortin and CRF receptor antagonist, alpha-helical CRF9-41, blocked the effects of urocortin. Urocortin reduced food intake and body weight gain, as well as the rate of gastric emptying, in ob/ob mice, which was significantly faster than that of lean mice. Five daily injections of urocortin significantly lowered body weight and improved glycemic control in ob/ob mice. CONCLUSIONS The urocortin-induced decrease in food intake and body weight in lean and ob/ob mice is closely related to gastric emptying and opens new possibilities for the treatment of obesity.

Synergistic Effects of Y2 and Y4 Receptors on Adiposity and Bone Mass Revealed in Double Knockout Mice

ABSTRACT Neuropeptide Y regulates numerous physiological processes via at least five different Y receptors, but the specific roles of each receptor are still unclear. We previously demonstrated that Y2 receptor knockout results in a lean phenotype, increased cancellous bone volume, and an increase in plasma pancreatic polypeptide (PP), a ligand for Y4 receptors. PP-overexpressing mice are also known to have a lean phenotype. Deletion of the Y4 receptor also produced a lean phenotype and increased plasma PP levels. We therefore hypothesized that part of the Y2 phenotype results from increased PP action on Y4 receptors and tested this in PP transgenic Y4−/− and Y2−/− Y4−/− double knockout mice. Bone mass was not altered in Y4 knockout mice. Surprisingly, despite significant hyperphagia, Y2−/− Y4−/− mice retained a markedly lean phenotype, with reduced body weight, white adipose tissue mass, leptinemia, and insulinemia. Furthermore, bone volume was also increased threefold in Y2−/− Y4−/− mice, and this was associated with enhanced osteoblastic activity. These changes were more pronounced than those observed in Y2−/− mice, suggesting synergy between Y2 and Y4 receptor pathways. The lack of bone changes in PP transgenic mice suggests that PP alone is not responsible for the bone mass increases but might play a major role in the lean phenotype. However, a synergistic interaction between Y2 and Y4 pathways seems to regulate bone volume and adiposity and could have important implications for possible interventions in obesity and for anabolic treatment of osteoporotic bone loss.

Mouse pancreatic polypeptide modulates food intake, while not influencing anxiety in mice☆

This study was designed to investigate the effects of synthetic mouse pancreatic polypeptide (mPP) on feeding and anxiety in mice. The intracerebroventricular (i.c.v.) injection of mPP (0.003-3 nmol) dose-dependently increased food intake. A significant increase was observed 20 min after i.c.v. injection and continued for 4 h. The intraperitoneal (i.p.) injection of mPP (0.03-30 nmol) dose-dependently decreased food intake. A significant decrease was observed 20 min after i.p. injection and continued for 4 h. In the elevated plus maze test, the i.c.v. injection of mPP (0.003-3 nmol) did not affect anxiety behavior. These results suggest that mPP modulates food intake and the Y4 receptor in the brain may contribute to the regulation of feeding, whereas appearing not to influence anxiety in mice.

Neuropeptide Y produces anxiety via Y2-type receptors.

In the present study, the effects of intracerebroventricular (ICV) NPY, [Leu31, Pro34]NPY and NPY13-36 have been evaluated with respect to anxiety in mice in the elevated plus maze. NPY had opposing effects on behavior, depending on the doses used. NPY decreased the normal preference for the closed arms of the maze at 0.7 nmol, indicating an anxiolytic effect; however, at 7 pmol NPY further increased the preference for the closed arm, indicating an anxiogenic effect. [Leu31, Pro34]NPY, a Y1-type receptor agonist, significantly reduced the preference for the closed arms at 70 pmol. NPY13-36, a Y2-type receptor agonist, significantly intensified the preference at 20 pmol. It has been demonstrated that NPY produces not only an anxiolytic effect via Y1-type receptors, but also an anxiogenic effect via Y2-type receptors. The time course of these NPY actions are quite different and the anxiogenic effect was observed only shortly after ICV NPY injection.

A role for pancreatic polypeptide in feeding and body weight regulation

PP administration induces negative energy balance by suppressing food intake and gastric emptying while increasing energy expenditure in rodents. The mechanism of PP actions involves the changes in the expression of hypothalamic feeding-regulatory peptides and the activity of the vago-vagal and vago-sympathetic reflex arc. PP-overexpressing mice we developed exhibited the thin phenotype with decreased food intake and gastric emptying rate. Plasma cholecystokinin (CCK) concentrations were increased in the transgenic mice and CCK-1 receptor antagonist improved the anorexia of the animals. These results, together with the previous notion of PP as an anti-CCK hormone in pancreatic exocrine secretion and gallbladder contraction, indicate that PP-CCK interactions may be either antagonistic or synergistic and the transgenic mice may exhibit the mixed phenotype by overproduction of PP and CCK.

Endomorphins have orexigenic and anxiolytic activities in mice.

THIS study was designed to investigate the effects of endomorphin 1 and 2, recently identified μ-opioid receptor selective peptides, on food intake and anxiety in non-food-deprived mice. The intracerebroventricular (i.c.v.) injection of either endomorphin 1 or 2 (0.03–30 nmol) increased food intake in a dose-related manner. A significant increase was observed 20 min after i.c.v. injection of endomorphin 1 or 2 and continued for 4 h. In the elevated plus maze test, the i.c.v. injection of endomorphin 1 (30 nmol) significantly decreased the normal preference for the closed arms. These results suggest that endomorphin produces orexigenic and anxiolytic effects, and that the μ-opioid receptor contributes to the regulation of feeding and anxiety in mice.

Leptin transgene expression in the hypothalamus enforces euglycemia in diabetic, insulin-deficient nonobese Akita mice and leptin-deficient obese ob/ob mice.

We have tested the hypothesis that sustained leptin action in the hypothalamus alone can engender and maintain euglycemia in wild type mice and in two monogenic diabetic models, the insulin-deficient nonobese Akita mice and the hyperinsulinemic leptin-deficient obese, ob/ob mice. A single intracerebroventricular injection of recombinant adeno-associated virus vector encoding leptin (rAAV-lep) enhanced leptin transgene expression in the hypothalamus without any evidence of leptin leakage to the peripheral circulation, and promptly reinstated euglycemia that persisted along with severe insulinopenia in all three genotypes through the 7-week period of observation. A comparative evaluation of known etiologic factors of hyperglycemia showed that this long-term benefit on glucose homeostasis was not due to diminished energy consumption, weight and adiposity, but was conferred by at least two mechanisms operating simultaneously, enhanced glucose metabolism to meet the demand for the rAAV-lep induced increased non-shivering thermogenesis mediated by brown adipose tissue and insulin hypersensitivity. These findings endorse the hypothesis that increased leptin action locally in the hypothalamus can impose euglycemia independent of pancreatic insulin, and central leptin reinforcement may serve as a newer adjunct therapy to treat type 1 and type 2 diabetes.

Helicobacter pylori infection is associated with colon adenomatous polyps detected by high-resolution colonoscopy

Helicobacter pylori (H. pylori) is associated with the development of cancer in the stomach, but both positive and negative associations were reported with colorectal neoplasia. We sought to determine whether H. pylori is associated with colon neoplasia in Japanese population. We examined 332 patients who underwent routine high‐resolution total colonoscopy and serologic testing for IgG antibodies agonist H. pylori. Subjects who received cyclooxygenase‐2 inhibitors or previous eradication therapy and those with borderline titer levels were excluded from data analysis (n = 27). Seronegative control subjects were from the same study population to maximize the representativeness. There were no significant differences in age and gender between the 2 patient groups. A significant increase in the incidence of adenomatous polyps (p < 0.0001) and decrease in normal colonoscopic findings (p < 0.0005) were observed in seropositive patients than those seronegative. Our study indicates an etiological link of H. pylori infection to colorectal neoplasia and the need of routine colonoscopy in seropositive patients.