Paule Sarah G, Nikolovski Biljana, Ludeman Justin, Gray Robyn E, Spiccia Leone, Zimmet Paul Z, Myers Mark A
Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
Peptides. 2009 Jun;30(6):1088-97. doi: 10.1016/j.peptides.2009.02.020. Epub 2009 Mar 20.
GHTD-amide is a tetrapeptide originally isolated from human urine that has hypoglycemic activity. Insulin occurs in secretory granules of beta cells as zinc-stabilized hexamers and must disperse to monomeric form in order to bind to its receptor. The aim of this study was to identify whether GHTD-amide and an analog called ISF402 (VHTD-amide) reduce blood glucose through enhancement of insulin activity by dispersing oligomers of insulin. Peptides containing the HTD-amide sequence and a free alpha-amino group were optimal at binding Zn(2+) and adopting secondary structure in the presence of Zn(2+). Binding was concentration dependent and resulted in a 1:1 Zn:peptide complex. In vitro the tetrapeptides dispersed hexameric insulin to dimers and monomers. GHTD-amide and ISF402 potentiated the activity of hexameric insulin when co-injected into insulin resistant Zucker rats. Injection of peptides with insulin caused reductions in blood glucose and C-peptide significantly larger than achieved with insulin alone, and serum insulin time profiles were also altered consistent with a reduced clearance or enhanced dispersal of the injected insulin. Insulin potentiation by ISF402 was reduced when lispro insulin, which does not form zinc-stabilized hexamers, was used in place of hexameric zinc insulin. In conclusion, GHTD-amide and ISF402 are zinc binding peptides that disperse hexameric insulin in vitro, and potentiate the activity of hexameric insulin more so than monomeric lispro insulin. These results suggest that dispersal of hexameric insulin through chelation of Zn(2+) contributes to the hypoglycemic activity of these tetrapeptides.
GHTD-酰胺是一种最初从人尿中分离出来的具有降血糖活性的四肽。胰岛素以锌稳定的六聚体形式存在于β细胞的分泌颗粒中，必须分散成单体形式才能与受体结合。本研究的目的是确定GHTD-酰胺和一种名为ISF402（VHTD-酰胺）的类似物是否通过分散胰岛素寡聚体来增强胰岛素活性从而降低血糖。含有HTD-酰胺序列和游离α-氨基的肽在结合Zn(2+)以及在Zn(2+)存在下形成二级结构方面表现最佳。结合呈浓度依赖性，形成1:1的锌:肽复合物。在体外，四肽将六聚体胰岛素分散为二聚体和单体。当共同注射到胰岛素抵抗的 Zucker 大鼠体内时，GHTD-酰胺和ISF402增强了六聚体胰岛素的活性。与胰岛素单独注射相比，将肽与胰岛素一起注射导致血糖和C肽的降低幅度显著更大，并且血清胰岛素时间曲线也发生了改变，这与注射胰岛素的清除率降低或分散增强一致。当使用不形成锌稳定六聚体的赖脯胰岛素代替六聚体锌胰岛素时，ISF402对胰岛素的增强作用减弱。总之，GHTD-酰胺和ISF402是锌结合肽，它们在体外可分散六聚体胰岛素，并且比单体赖脯胰岛素更能增强六聚体胰岛素的活性。这些结果表明，通过螯合Zn(2+)来分散六聚体胰岛素有助于这些四肽的降血糖活性。
