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Biomedical subjects

Akihiro Asakawa

Publications and source records attributed to Akihiro Asakawa.

At least 19 recordsLinked to original sources
PubMed2004

Ghrelin, appetite, and gastric motility: the emerging role of the stomach as an endocrine organ.

Recent progress in the field of energy homeostasis was triggered by the discovery of adipocyte hormone leptin and revealed a complex regulatory neuroendocrine network. A late addition is the novel stomach hormone ghrelin, which is an endogenous agonist at the growth hormone secretagogne receptor and is the motilin-related family of regulatory peptides. In addition to its ability to stimulate GH secretion and gastric motility, ghrelin stimulates appetite and induces a positive energy balance leading to body weight gain. Leptin and ghrelin are complementary, yet antagonistic, signals reflecting acute and chronic changes in energy balance, the effects of which are mediated by hypothalamic neuropeptides such as neuropeptide Y and agouti-related peptide. Endocrine and vagal afferent pathways are involved in these actions of ghrelin and leptin. Ghrelin is a novel neuroendocrine signal possessing a wide spectrum of biological activities that illustrates the importance of the stomach in providing input into the brain. Defective ghrelin signaling from the stomach could contribute to abnormalities in energy balance, growth, and associated gastrointestinal and neuroendocrine functions.

Aged↗
PubMed2004

Cancer anorexia-cachexia syndrome: cytokines and neuropeptides.

PURPOSE OF REVIEW: Cancer anorexia-cachexia syndrome is observed in 80% of patients in the advanced stages of cancer and is a strong independent risk factor for mortality. Numerous cytokines produced by tumor and immune cells, interacting with the neuropeptidergic system, mediate the cachectic effect of cancer. Since there is currently no effective pharmacological treatment and the anorexia-cachexia syndrome continues to be defined biochemically, we review the role of cytokines and neuropeptides in this process. RECENT FINDINGS: Currently data suggest that cancer anorexia-cachexia syndrome results from a multifactorial process involving many mediators, including hormones (e.g. leptin), neuropeptides (e.g. neuropeptide Y, melanocortin, melanin-concentrating hormone and orexin) and cytokines (e.g. interleukin 1, interleukin 6, tumor necrosis factor alpha and interferon gamma). It is likely that close interrelation among these mediators exists in the hypothalamus, decreasing food intake and leading to cachexia. SUMMARY: In the pathogenesis of cancer anorexia, cytokines play a pivotal role influencing the imbalance of orexigenic and anorexigenic circuits that regulate the homeostatic loop of body-weight regulation, leading to cachexia. Interfering pharmacologically with cytokine expression or neural transduction of cytokine signals can be an effective therapeutic strategy in anorectic patients before they develop cancer anorexia-cachexia syndrome.

Animals↗
PubMed2004

Development of pancreatic islets in pancreatic polypeptide-overexpressing mice.

Recently we produced pancreatic polypeptide transgenic (PPTG) mice and found that PP was overexpressed in pancreatic islets. The present study examines development of four islet hormones in PPTG mice at embryonic days (ED) 15, 17, and 19, and in adult animals. Adult PPTG mice showed massive aggregation of PP-positive cells and glucagon-positive cells seen at the central area of the islets. Confocal laser microscopic study showed that three islet hormones (insulin, glucagon and PP) were completely overlapped in islets of PPTG mice. Overlapping of somatostatin/glucagon and somatostatin/PP were also increased at the peripheral area of the islets in adult PPTG mice compared to wild-type mice. In prenatal development of pancreatic islets of PPTG mice, somatostatin/glucagon overlapping cells appeared at ED 15, two days earlier than in wild-type mice. Differentiation of these somatostatin/glucagon double-positive cells into single-positive cells was disturbed in the PPTG mice during perinatal to postnatal periods. Differentiation of glucagon/insulin-double positive cells into single-positive cells was disturbed remarkably in postnatal development of the islets of PPTG mice. The present results suggest that early and overexpression of PP may engender the early appearance of somatostatin producing cells; however, that may disturb differentiation of multihormonal immature endocrine cells into single hormonal mature endocrine cells.

Animals↗
PubMed2003

Ghrelin induces fasted motor activity of the gastrointestinal tract in conscious fed rats.

Ghrelin is a newly discovered orexigenic peptide originating from the stomach. However, its action in regulating the fed and fasted motor activity of the digestive tract is not fully understood. In the present study, we examined the effects of intracerebroventricular (I.C.V.) and intravenous (I.V.) injection of ghrelin on the physiological fed and fasted motor activities in the stomach and duodenum of freely moving conscious rats. I.C.V. and I.V. injection of ghrelin induced fasted motor activity in the duodenum in normal fed rats, while I.V. injection of ghrelin induced fasted motor activity in both the stomach and duodenum in vagotomized rats. The effects of I.C.V. and I.V. injected ghrelin were blocked by growth hormone secretagogue receptor (GHS-R) antagonist given by the same route and also blocked by immunoneutralization of neuropeptide Y (NPY) in the brain. The effects of I.V. injected ghrelin were not altered by I.C.V. injection of GHS-R antagonist in vagotomized rats. Injection of GHS-R antagonist blocked the fasted motor activity in both the stomach and duodenum in vagotomized rats but did not affect the fasted motor activity in normal rats. Low intragastric pH inhibited the effect of ghrelin. The present results indicate that ghrelin is involved in regulation of fasted motor activity in the stomach and duodenum. Peripheral ghrelin may induce the fasted motor activity by activating the NPY neurons in the brain, probably through ghrelin receptors on vagal afferent neurons. Once the brain mechanism is eliminated by truncal vagotomy, ghrelin might be primarily involved in the regulation of fasted motor activity through ghrelin receptors on the stomach and duodenum. The action of ghrelin to induce fasted motor activity is strongly affected by intragastric pH; low pH inhibits the action.

Animals↗
PubMed2003

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.

Animals↗
PubMed2003

Histologic diagnosis and management of hypothalamic tumors in children by the use of newly developed flexible neuroendoscopes.

Hypothalamic tumors are difficult to treat surgically, and chemotherapy and/or radiation are given based on the histology and the neuraxis staging of the tumors. We have developed flexible neuroendoscopes (Yamadori-type 8 and 9) which have excellent image quality and maneuverability as well as capabilities for biopsy and electrocoagulative debulking of the cystic tumors. We report the successful application of the neuroendoscopes to 10 children with hypothalamic tumors diagnosed with computed tomography or magnetic resonance imaging. Histologic diagnosis was obtained from all the patients. Cystic tumors were evacuated, hydrocephalus managed with endoscopic operations, and some benign tumors were removed totally. The relatively non-invasive approach reported here would represent a significant technical advance in the diagnosis and management of hypothalamic and other ventricular tumors.

Adolescent↗
PubMed2003

Intracerebroventricular administration of NPY stimulates resistin gene expression in mice.

Resistin is thought to cause insulin resistance and link obesity to type 2 diabetes mellitus. However, little is known about the effects of neuropeptide Y (NPY) on resistin gene expression in white adipose tissue (WAT). Resistin gene expression was determined by northern blot analysis in food-deprived mice after NPY administration. Administered NPY (1 nmol/mouse) significantly increased resistin mRNA expression in WAT by 72% compared with artificial cerebrospinal fluid treated controls. These observations indicate that NPY might have a role in regulating resistin gene expression in WAT and that the novel brain-fat axis might be involved in the pathogenesis of obesity and related diseases.

Adipose Tissue↗
PubMed2003

Acute intracerebroventricular administration of either carboxyl-terminal or amino-terminal fragments of agouti-related peptide produces a long-term decrease in energy expenditure in rats.

We investigated if agouti-related peptide (AgRP), an endogenous antagonist of melanocortin receptors (MC3-R and MC4-R), effects energy expenditure in rats. Fragments of the carboxyl-terminal, AgRP (83-132), and the amino-terminals, AgRP (25-51) and AgRP (54-82), were administered intracerebroventricularly (ICV). Food intake, body weight and fat weight changes were measured 5 and/or 24 h after a single ICV injection of the fragments. Oxygen consumption and colonic temperature were measured as indices of energy expenditure, during 3 and 24 h after the ICV injections, respectively. An oral glucose tolerance test was performed 24 h after ICV AgRP (83-132) injection. Binding experiments were performed in HEK-293 cells that over-expressed human MC4-R. AgRP (83-132), but not AgRP (25-51) nor AgRP (54-82), induced a potent and long-lasting increase in the cumulative food intake. Both the carboxyl-terminal and amino-terminal AgRP fragments significantly decreased oxygen consumption and colonic temperature. Despite the absence of hyperphagia and cross-reactivities with MC4-R, AgRP (25-51) and AgRP (54-82) significantly increased body weight and epididymal/mesenteric fat weight. AgRP (83-132) did not affect glucose and insulin responses to the oral glucose tolerance test. AgRP causes a potent and long-lasting decrease in energy expenditure; an effect that is exhibited by carboxyl-terminal fragments and amino-terminal fragments that lack antagonist activity at the MC receptors. This suggests that the amino-terminal region of AgRP plays a regulatory role in energy metabolism.

Agouti-Related Protein↗
PubMed2003

Helicobacter pylori cytotoxin: a novel ligand for receptor-like protein tyrosine phosphatase beta (review).

The impacts of toxins are generally observed as acute intoxications, whereas the environmental health effects of chronic exposure to mostly low levels of toxins are only poorly documented and are an emerging issue. Furthermore, toxins are potentially useful as tools to study the physiological role of particular channels or to determine structural features of channels that are important for their function. Recent studies suggest that vacuolating cytotoxin (VacA) is a novel ligand for receptor protein tyrosine phosphatase (RPTP) beta. VacA is a virulence factor of Helicobacter pylori that is involved in gastric ulceration and cancer in experimental animals and humans. VacA may represent the chronic exposure of A-B family of bacterial endotoxins and be a useful probe for RPTPbeta functions in the gastrointestinal system.

Bacterial Proteins↗
PubMed2002

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.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed2002

Roles of pancreatic polypeptide in regulation of food intake.

Pancreatic polypeptide (PP) is produced in pancreatic islets of Langerhans and released into the circulation after ingestion of a meal. Peripherally administered PP suppresses food intake and gastric emptying. On the other hand, central administration of PP elicits food intake and gastric emptying. Therefore, PP actions on food intake may be, in part, attributable to gastric emptying. PP transgenic mice exhibit decreases in both food intake and gastric emptying rate that were clearly reversed by anti-PP antiserum. PP is an anorexigenic signal in the periphery and an orexigenic signal in the central nervous system.

Animals↗
PubMed2002

Anticancer drugs that induce cancer-associated cachectic syndromes.

Cachexia--a wasting condition--seriously impairs the quality of life of patients with advanced cancer. Previous studies have shown that several inflammatory cytokines mediate the development of cancer-associated cachexia. Experimentally, cachexia-like symptoms can be induced in tumor-bearing mice and treatment of such mice with chemotherapeutic agents reverses cachexia as a result of its therapeutic action. Nonetheless, cancer chemotherapy occasionally induces anorexia as an adverse reaction. For example, treatment with antitubulin taxanes reduces body weight in tumor-bearing mice more than healthy mice, even when the agents significantly reduce tumor growth. However, the complex relationship between cancer cachexia and the effects of anticancer drugs remains to be elucidated. This review outlines what is known about the development of cachectic reactions, especially in tumor-bearing mice, that occur during treatment with anticancer agents and highlights the clinical relevance of the information.

Animals↗
PubMed2002

Effects of agouti-related protein, orexin and melanin-concentrating hormone on oxygen consumption in mice.

Neuropeptides in the hypothalamus play a pivotal role in the regulation of energy balance. Agouti-related protein (AGRP), orexin and melanin-concentrating hormone (MCH) have been identified in the hypothalamus as orexigenic peptides. This study was undertaken to investigate the effects of AGRP, orexin and MCH on oxygen consumption. Oxygen consumption was determined by an O2/CO2 metabolism measuring system at 22 degrees C. Mice were kept unrestrained in the chamber without food or water during the light cycle, and the oxygen consumption was measured for 2 h after intra-cerebroventricular (ICV) administration. ICV administered AGRP (1 nmol/mouse) significantly decreased oxygen consumption compared to ACSF-treated controls. Orexin (1 nmol/mouse) significantly increased oxygen consumption, while MCH (1 nmol/mouse) had no significant effect compared to ACSF-treated controls. These results suggest that AGRP, orexin and MCH might have different effects on energy expenditure, thereby regulating appetite and body weight.

Agouti-Related Protein↗
PubMedDate not supplied

Leptin treatment ameliorates anxiety in ob/ob obese mice.

We investigated whether or not administered leptin influences anxiety-like behavior in ob/ob mice. Repeated intraperitoneal administrations of leptin were continued for 5 days. Anxiety was assessed in the standard elevated plus maze. Body weight was measured daily. Repeated administrations of leptin significantly increased the percentage of the total number of entries in the open arms and the number of total entries. The body weight was significantly reduced by 13.2% after treatment. Leptin treatment ameliorated not only obesity but also anxiety in ob/ob mice. Our results indicate that the treatment of obesity may lead to the solution of psychological problems.

Animals↗