RESUMEN
Xenin-25, a peptide co-secreted with the incretin hormone glucose-dependent insulinotropic polypeptide (GIP), possesses promising therapeutic actions for obesity-diabetes. However, native xenin-25 is rapidly degraded by serum enzymes to yield the truncated metabolites: xenin 9-25, xenin 11-25, xenin 14-25 and xenin 18-25. This study has examined the biological activities of these fragment peptides. In vitro studies using BRIN-BD11 cells demonstrated that native xenin-25 and xenin 18-25 possessed significant (P<0.05 to P<0.001) insulin-releasing actions at 5.6 and 16.7 mM glucose, respectively, but not at 1.1â mM glucose. In addition, xenin 18-25 significantly (P<0.05) potentiated the insulin-releasing action of the stable GIP mimetic (D-Ala²)GIP. In contrast, xenin 9-25, xenin 11-25 and xenin 14-25 displayed neither insulinotropic nor GIP-potentiating actions. Moreover, xenin 9-25, xenin 11-25 and xenin 14-25 significantly (P<0.05 to P<0.001) inhibited xenin-25 (10â»6 M)-induced insulin release in vitro. I.p. administration of xenin-based peptides in combination with glucose to high fat-fed mice did not significantly affect the glycaemic excursion or glucose-induced insulin release compared with controls. However, when combined with (D-Ala²)GIP, all xenin peptides significantly (P<0.01 to P<0.001) reduced the overall glycaemic excursion, albeit to a similar extent as (D-Ala²)GIP alone. Xenin-25 and xenin 18-25 also imparted a potential synergistic effect on (D-Ala²)GIP-induced insulin release in high fat-fed mice. All xenin-based peptides lacked significant satiety effects in normal mice. These data demonstrate that the C-terminally derived fragment peptide of xenin-25, xenin 18-25, exhibits significant biological actions that could have therapeutic utility for obesity-diabetes.
Asunto(s)
Neurotensina/metabolismo , Neurotensina/farmacología , Fragmentos de Péptidos/metabolismo , Fragmentos de Péptidos/farmacología , Animales , Células Cultivadas , Dieta Alta en Grasa , Evaluación Preclínica de Medicamentos , Hipoglucemiantes/química , Hipoglucemiantes/metabolismo , Hipoglucemiantes/farmacología , Insulina/metabolismo , Secreción de Insulina , Masculino , Ratones , Neurotensina/química , Proteolisis , Saciedad/efectos de los fármacosRESUMEN
BACKGROUND: Rapid enzymatic degradation of the incretin hormone, glucose-dependent insulinotropic polypeptide (GIP), limits therapeutic use of the native peptide for diabetes. However, enzymatically stable analogues of GIP, such as (d-Ala(2))GIP, have been generated, but are still susceptible to renal filtration. METHODS: The present study examines the in vitro and in vivo biological actions of a novel, acylated GIP analogue, (d-Ala(2))GIP[Lys(37)PAL]. RESULTS: In BRIN-BD11 cells, (d-Ala(2))GIP[Lys(37)PAL] concentration-dependently stimulated (p<0.05 to p<0.001) insulin secretion at 5.6 and 16.7mM glucose. Intraperitoneal administration of (d-Ala(2))GIP[Lys(37)PAL] to normal mice 8h prior to a glucose load significantly reduced (p<0.05) the overall glycaemic excursion compared to controls, and increased (p<0.001) the insulinotropic response compared to (d-Ala(2))GIP and saline treated high fat control mice. Once daily administration of (d-Ala(2))GIP[Lys(37)PAL] for 21days in high fat fed mice did not affect energy intake, body weight or fat deposition. However, circulating blood glucose was significantly lower (p<0.05) accompanied by increased (p<0.05) insulin concentrations by day 21. In addition, (d-Ala(2))GIP[Lys(37)PAL] treatment significantly (p<0.01) reduced the overall glycaemic excursion and increased pancreatic insulin content (p<0.05) and the insulinotropic response (p<0.01) to an exogenous glucose challenge on day 21. Chronic treatment with (d-Ala(2))GIP[Lys(37)PAL] did not result in resistance to the metabolic effects of a bolus injection of native GIP. Finally, insulin sensitivity was significantly improved (p<0.001) in (d-Ala(2))GIP[Lys(37)PAL] treated mice compared to high fat controls. CONCLUSIONS: These data confirm that (d-Ala(2))GIP[Lys(37)PAL] is a stable, long-acting potent GIP agonist. GENERAL SIGNIFICANCE: (d-Ala(2))GIP[Lys(37)PAL] may be suitable for further evaluation and future clinical development.
Asunto(s)
Distribución de la Grasa Corporal , Diabetes Mellitus Experimental/tratamiento farmacológico , Polipéptido Inhibidor Gástrico/análogos & derivados , Polipéptido Inhibidor Gástrico/farmacología , Hipoglucemiantes/farmacología , Animales , Diabetes Mellitus Experimental/metabolismo , Polipéptido Inhibidor Gástrico/agonistas , Polipéptido Inhibidor Gástrico/síntesis química , Polipéptido Inhibidor Gástrico/química , Fármacos Gastrointestinales/síntesis química , Fármacos Gastrointestinales/química , Fármacos Gastrointestinales/farmacología , Glucosa/metabolismo , Hipoglucemiantes/síntesis química , Hipoglucemiantes/química , Insulina/metabolismo , Masculino , RatonesRESUMEN
Xenin-25, a K-cell derived peptide co-secreted with glucose-dependent insulinotropic polypeptide (GIP), has recently been shown to have glucose homeostatic actions and potentiate the insulinotropic effect of GIP. However, the biological actions of xenin-25 are brief due to rapid metabolism, yet little is known regarding enzymatic degradation of this peptide. Therefore, the present study has fully characterised the plasma enzymatic degradation products of xenin-25. We have also generated a novel acylated xenin-25 analogue, xenin-25(Lys(13)PAL), and evaluated its stability, biological action profile and therapeutic applicability compared to the native peptide. In contrast to xenin-25, xenin-25(Lys(13)PAL) was completely resistant to plasma enzyme degradation. Insulinotropic responses of xenin-25(Lys(13)PAL) in clonal beta-cells were similar to native xenin-25, moreover xenin-25(Lys(13)PAL) significantly (p<0.05 to p<0.001) potentiated the insulin releasing action of (D-Ala(2))GIP. When administered together with glucose to normal mice, the glycaemic excursion was significantly (p<0.05) less and overall insulin secretory effect significantly (p<0.05) greater for xenin-25(Lys(13)PAL) when compared to xenin-25 mice. Glucose-lowering and insulin releasing effects of both peptides was less prominent in high fat fed mice and ob/ob mice. However, xenin-25 significantly (p<0.05) augmented the glucose-lowering action of (D-Ala(2))GIP in both groups of mice. Similarly, xenin-25(Lys(13)PAL) potentiated (p<0.05) the gluco-regulatory effect of (D-Ala(2))GIP. Overall, these data indicate that palmitate-derivatised analogues of xenin-25 represent a novel class of GIP potentiator drugs for possible type 2 diabetes therapy.