Leon Luong

PACAP intraperitoneal treatment suppresses appetite and food intake via PAC1 receptor in mice by inhibiting ghrelin and increasing GLP-1 and leptin.

Pituitary adenylate cyclase-activating peptide (PACAP) is expressed within the gastroenteric system, where it has profound physiological effects. PACAP was shown to regulate food intake and thermogenesis centrally; however, PACAP peripheral regulation of appetite and feeding behavior is unknown. Therefore, we studied PACAPs effect on appetite and food intake control by analyzing feeding behavior and metabolic hormones in PAC1-deficient (PAC1-/-) and age-matched wild-type (WT) mice intraperitoneally injected with PACAP1-38 or PACAP1-27 before the dark phase of feeding. Food intake and feeding behavior were analyzed using the BioDAQ system. Active ghrelin, glucagon-like peptide-1 (GLP-1), leptin, peptide YY, pancreatic polypeptide, and insulin were measured following PACAP1-38 administration in fasted WT mice. PACAP1-38/PACAP1-27 injected into WT mice significantly decreased in a dose-dependent manner cumulative food intake and reduced bout and meal feeding parameters. Conversely, PACAP1-38 injected into PAC1-/- mice failed to significantly change food intake. Importantly, PACAP1-38 reduced plasma levels of active ghrelin compared with vehicle in WT mice. In PAC1-/- mice, fasting levels of active ghrelin, GLP-1, insulin, and leptin and postprandial levels of active ghrelin and insulin were significantly altered compared with levels in WT mice. Therefore, PAC1 is a novel regulator of appetite/satiety. PACAP1-38/PACAP1-27 significantly reduced appetite and food intake through PAC1. In PAC1-/- mice, the regulation of anorexigenic/orexigenic hormones was abolished, whereas active ghrelin remained elevated even postprandially. PACAP significantly reduced active ghrelin in fasting conditions. These results establish a role for PACAP via PAC1 in the peripheral regulation of appetite/satiety and suggest future studies to explore a therapeutic use of PACAP or PAC1 agonists for obesity treatment.

PACAP Regulation of Gastrointestinal Function and Obesity

Pituitary adenylate cyclase activating polypeptide (PACAP) is a 27- or 38-amino acid peptide that is widely distributed in both the peripheral and central nervous systems. PACAP has been found to be expressed within the enteric nervous system and gastric mucosa and has profound physiological effects in the gastrointestinal tract. We have previously shown that PACAP regulates gastric acid secretion by activating its high affinity PAC1 receptors expressed on gastric enterochromaffin-like cells (ECL). However, the peripheral mechanisms involved in PACAP regulation of appetite and feeding are unknown. Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide abundantly expressed in the central nervous system as well as in the gastrointestinal tract, where it regulates different physiological functions. VIP inhibits gastric acid secretion via its VPAC1 receptors expressed on gastric D cells. VIP also regulates intestinal motility and VIP gene deletion results in the development of intestinal ileus. VIP is involved in the control of appetite/satiety, feeding behavior and in the secretion of some key regulatory metabolic hormones. VIP plays a very important role in the regulation of body weight and mass composition by significantly enhancing body weight and fat mass. Therefore, both PACAP and VIP neuropeptides could be crucial targets for the regulation of appetite/satiety, body phenotype and for the treatment of obesity.

Long-Term Intake of a High-Protein Diet Affects Body Phenotype, Metabolism, and Plasma Hormones in Mice

Background: High-protein diets (HPDs) recently have been used to obtain body weight and fat mass loss and expand muscle mass. Several studies have documented that HPDs reduce appetite and food intake.Objective: Our goal was to determine the long-term effects of an HPD on body weight, energy intake and expenditure, and metabolic hormones.Methods: Male C57BL/6 mice (8 wk old) were fed either an HPD (60% of energy as protein) or a control diet (CD; 20% of energy as protein) for 12 wk. Body composition and food intakes were determined, and plasma hormone concentrations were measured in mice after being fed and after overnight feed deprivation at several time points.Results: HPD mice had significantly lower body weight (in means ± SEMs; 25.73 ± 1.49 compared with 32.5 ± 1.31 g; P = 0.003) and fat mass (9.55% ± 1.24% compared with 15.78% ± 2.07%; P = 0.05) during the first 6 wk compared with CD mice, and higher lean mass throughout the study starting at week 2 (85.45% ± 2.25% compared with 75.29% ± 1.90%; P = 0.0001). Energy intake, total energy expenditure, and respiratory quotient were significantly lower in HPD compared with CD mice as shown by cumulative energy intake and eating rate. Water vapor was significantly higher in HPD mice during both dark and light phases. In HPD mice, concentrations of leptin [feed-deprived: 41.31 ± 11.60 compared with 3041 ± 683 pg/mL (P = 0.0004); postprandial: 112.5 ± 102.0 compared with 8273 ± 1415 pg/mL (P < 0.0001)] and glucagon-like peptide 1 (GLP-1) [feed-deprived: 5.664 ± 1.44 compared with 21.31 ± 1.26 pg/mL (P = <0.0001); postprandial: 6.54 ± 2.13 compared with 50.62 ± 11.93 pg/mL (P = 0.0037)] were significantly lower, whereas postprandial glucagon concentrations were higher than in CD-fed mice.Conclusions: In male mice, the 12-wk HPD resulted in short-term body weight and fat mass loss, but throughout the study preserved body lean mass and significantly reduced energy intake and expenditure as well as leptin and GLP-1 concentrations while elevating postprandial glucagon concentrations. This study suggests that long-term use of HPDs may be an effective strategy to decrease energy intake and expenditure and to maintain body lean mass.

Mo1986 Vasoactive Intestinal Peptide (VIP) Plays a Role in the Regulation of Orexigenic and Anorexigenic Hormones and Body Fat and Lean Mass Composition

Aim: To create HEK293 cells and murine ES cell lines that synthesize and release either GIP or the specific GIPR antagonist GIP(5-42). Methods: Using PCR, chimeric genes, consisting of the mouse growth hormone leader (mGH), the furin cleavage site, and either GIP or GIP(5-42), were generated and cloned into a lentiviral vector downstream of a constitutive promoter. After the generation of lentiviral pseudoparticles containing the chimeric genes, mGH-GIP and mGH-GIP(5-42), HEK 293 and ES cells were transduced with ~108 pseudoparticles. Pools of cells containing the co-expressed fluorescent marker ZsGreen were isolated using flow cytometry before supernates from cultured cells were collected, and a specific ELISA was employed to quantify GIP immunoreactivity. To assess GIP bioactivity in supernates, a specific bioassay consisting of reporter cells expressing GIPR and containing the LacZ gene under the control of a cAMP-responsive promoter was used. To demonstrate antagonist activity, peptides in supernates from HEK 293 cells containing mGH-GIP(5-42) were concentrated 50-fold using a C-18 reverse phase column before being mixed with 1010 M GIP and added to reporter cells. Results: HEK 293 cells containing mGH-GIP and mGH-GIP(5-42) expressed 8x10-4 and 10-4 pg/cell/h, respectively, while ES cells containing mGH-GIP and mGH-GIP(5-42) expressed 10-4 and 6x10-3 pg/cell/h, respectively. Supernates from HEK 293 and ES cells containing mGH-GIP were both shown to induce LacZ expression, demonstrating the presence of bioactive GIP. As expected, supernates from either HEK 293 cells or ES cells containing mGH-GIP(5-42) did not induce LacZ expression. However, after concentration, supernates from HEK 293 cells containing mGH-GIP(5-42) inhibited LacZ expression induced by 10-10 M GIP, indicating the presence of antagonist activity. Summary and Conclusion: The results of these studies demonstrate the successful engineering of HEK 293 and ES cells to express bioactive GIP and GIP(5-42). Although early in its development, engraftment of tissue derived fromGIP(5-42) expressing stem cells may provide a method for treating obesity.