Ghrelin-O-Acyltransferase und Dipeptidylpeptidase-4: zwei mögliche neue Targets für die Therapie der Adipositas

Introduction. In light of the rapidly increasing prevalence of obesity and lack of pharmacological treatment options, a better understanding of feeding regulation is needed. Ghrelin is the only known peripherally produced and centrally acting feeding stimulator, while ghrelin-O-acyltransferase (GOAT) is the only known ghrelin-activating enzyme. Animal studies regarding its role in feeding regulation are contradictory and few data is published on the occurrence of GOAT and function in humans. Dipeptidyl peptidase 4 (DPP4-) cleaves several peptides involved in the feeding regulation, mainly deactivating anorexigenic peptides. The regulation of DPP-4 by chronically altered body mass index (BMI) is unknown. Methods. In the first study, food intake, body weight and behavior of rats housed in the special cages of a new food intake monitoring device were measured. With this device, the microstructure of feeding after peripheral GOAT inhibition was analyzed (inhibitor: GO-CoA-Tat; doses: 32, 96 and 288 µg/kg; n=9-11/group). For the second study, GOAT was measured in human blood and its BMI-dependent expression was examined (groups by BMI: 50 kg/m², n=9/group). For the third study, blood samples of subjects with a range of BMI from 9 to 85 kg/m² (n=75) were taken and DPP-4 was measured. Results. In the first study, animals adapted rapidly within 2-3 days to the cages of the feeding monitoring system. GOAT inhibition led to dose-dependent reduction of food intake (effective dose: 96 µg/kg; -27% in 2nd hour vs. controls; p50 kg/m², n=9/Gruppe). Für die dritte Studie wurde Patienten (BMI-Spanne von 9 bis 85 kg/m², n=75) Blut entnommen und DPP-4 gemessen. Ergebnisse. In der ersten Studie zeigten die Tiere eine rasche Adaptation in 2-3 Tagen an die Spezialkäfige zur mikrostrukturellen Analyse der Nahrungsaufnahme. Eine GOAT-Hemmung führte zur dosisabhängigen Reduktion der Nahrungsaufnahme (effektive Dosis: 96 µg/kg; -27% in Stunde 2 vs. Kontrolltiere; p<0,05). Diese Reduktion wurde über eine verringerte Häufigkeit der Mahlzeiten (-15% vs. Kontrolltiere; p<0,05) bei gleichbleibender Mahlzeitgröße vermittelt und war mit niedrigeren Acyl-Ghrelin-Spiegeln assoziiert (-57% in Stunde 2 vs. Kontrolltiere; p<0,05). GOAT konnte auch im menschlichen Plasma nachgewiesen werden und war BMI-abhängig exprimiert, was sich in einer positiven Korrelation mit dem BMI widerspiegelte (r=0,71, p<0,001). In der dritten Studie war auch zirkulierende DPP-4 positiv mit dem BMI korreliert (r=0,34, p=0,004). Schlussfolgerung. Eine Methode zur Messung der Nahrungsaufnahme-Mikrostruktur, welche die genaue Charakterisierung nahrungsregulatorischer Peptide erlaubt, wurde für den Einsatz bei Ratten etabliert. Periphere GOAT-Inhibition bewirkte eine Reduktion der Nahrungsaufnahme über gesteigerte satiety (späterer Beginn der nächsten Mahlzeit). GOAT ist beim Menschen vorhanden und wird BMI-abhängig exprimiert. Möglicherweise trägt die veränderte Regulierung von GOAT bei Über- (mehr GOAT) bzw. Untergewicht (weniger GOAT) zur Erhaltung des Krankheitszustandes bei. Auch DPP-4 korreliert positiv mit dem BMI mit erhöhten Konzentrationen bei Adipositas. Da DPP-4 vor allem anorexigene Peptide deaktiviert, könnte sich auch dies ungünstig auf die Gewichtsregulation auswirken. Diese Ergebnisse könnten zu neuen medikamentösen Strategien der Adipositas-Therapie beitragen

Nesfatin-130−59 Injected Intracerebroventricularly Differentially Affects Food Intake Microstructure in Rats Under Normal Weight and Diet-Induced Obese Conditions

Nesfatin-1 is well-established to induce an anorexigenic effect. Recently, nesfatin-130−59, was identified as active core of full length nesfatin-11−82 in mice, while its role in rats remains unclear. Therefore, we investigated the effects of nesfatin-130−59 injected intracerebroventricularly (icv) on the food intake microstructure in rats. To assess whether the effect was also mediated peripherally we injected nesfatin-130−59 intraperitoneally (ip). Since obesity affects the signaling of various food intake-regulatory peptides we investigated the effects of nesfatin-130−59 under conditions of diet- induced obesity (DIO). Male Sprague–Dawley rats fed ad libitum with standard diet were icv cannulated and injected with vehicle (5 μl ddH2O) or nesfatin-130−59 at 0.37, 1.1, and 3.3 μg (0.1, 0.3, 0.9 nmol/rat) and the food intake microstructure assessed using a food intake monitoring system. Next, naïve rats were injected ip with vehicle (300 μl saline) or nesfatin-130−59 (8.1, 24.3, 72.9 nmol/kg). Lastly, rats were fed a high fat diet for 10 weeks and those developing DIO were icv cannulated. Nesfatin-1 (0.9 nmol/rat) or vehicle (5 μl ddH2O) was injected icv and the food intake microstructure assessed. In rats fed standard diet, nesfatin-130−59 caused a dose-dependent reduction of dark phase food intake reaching significance at 0.9 nmol/rat in the period of 4–8 h post injection (−29%) with the strongest reduction during the fifth hour (−75%), an effect detectable for 24 h (−12%, p < 0.05 vs. vehicle). The anorexigenic effect of nesfatin-130−59 was due to a reduction in meal size (−44%, p < 0.05), while meal frequency was not altered compared to vehicle. In contrast to icv injection, nesfatin-130−59 injected ip in up to 30-fold higher doses did not alter food intake. In DIO rats fed high fat diet, nesfatin-130−59 injected icv reduced food intake in the third hour post injection (−71%), an effect due to a reduced meal frequency (−27%, p < 0.05), while meal size was not altered. Taken together, nesfatin-130−59 is the active core of nesfatin-11−82 and acts centrally to reduce food intake in rats. The anorexigenic effect depends on the metabolic condition with increased satiation (reduction in meal size) under normal weight conditions, while in DIO rats satiety (reduction in meal frequency) is induced

The dopamine antagonist flupentixol does not alter ghrelin-induced food intake in rats

It has been shown that dopamine antagonists suppress the ghrelin-induced increased motivation to work for food. The aim of this study was to investigate the influence of the dopamine antagonist flupentixol on ghrelin-induced food intake. Ad libitum fed male Sprague-Dawley (SD) rats were injected intraperitoneally (ip) with vehicle plus vehicle, vehicle plus ghrelin (13. &mu;g/kg), 0.25. mg/kg or 0.5. mg/kg flupentixol plus ghrelin, or 0.25. mg/kg or 0.5 mg/kg flupentixol plus vehicle. In a second experiment, intracerebroventricularly (icv) cannulated rats received an ip injection of vehicle (0.15. M NaCl) or flupentixol (0.25. mg/kg) and 20. min later an icv injection of vehicle or ghrelin (1. &mu;g/rat). Both experiments were performed twice: first, rats were offered only standard chow, while in the second experiment they could choose between standard chow and a palatable/preferred chow. Cumulative light phase food intake was assessed for 7. h. Ip as well as icv injected ghrelin reliably increased intake of standard chow. Flupentixol did not affect ghrelin-induced intake of standard chow. Ip injected ghrelin failed to increase the intake of palatable chow, whereas icv injected ghrelin did. This effect was not blocked by ip flupentixol. In summary, ip administered ghrelin did not increase the intake of chow the rats preferred; whereas icv injected ghrelin further stimulated the intake of preferred chow suggesting a direct central mediation of this effect. Our results show that the dopamine antagonist flupentixol does not influence ghrelin-induced feeding in our choice paradigm