Berger H, Heinrich N, Albrecht E, Kertscher U, Oehlke J, Bienert M, Schäfer H, Baeger I, Mehlis B
Institute of Drug Research, Berlin, F.R.G.
Regul Pept. 1991 May 17;33(3):299-311. doi: 10.1016/0167-0115(91)90232-6.
There are two types of superactive agonists of gonadotropin-releasing hormone (GnRHa-I: (D-amino acid)6-GnRH and GnRHa-II: (D-amino acid)6-(desGly)10-GnRH- ethylamide) the high hormonal activity of which is understood to be due to their higher receptor affinity and their higher proteolytic stability as compared with the native GnRH sequence. Using the soluble fractions of various rat tissues in studies on the inactivation of GnRH peptides, we confirmed the higher proteolytic resistance of GnRHa-II, but not of D-Phe6-GnRH (GnRHa-I) and of another analog, D-Trp3-D-Phe6-GnRH, as compared with GnRH. The exact behaviour of the peptides during degradation was found to be dependent on the peptide concentrations used, showing the importance of using conditions as near to the physiological ones a possible. Towards the membrane fractions, however, the order of degradability was found to be GnRH much greater than D-Phe6-GnRH much greater than D-Trp3-D-Phe6-GnRH. The pharmacokinetic consequences of the different proteolytic degradabilities of the GnRH peptides, observed in rats, were a moderate increase in the biological half-life of D-Phe6-GnRH by 2.5-fold, as compared with GnRH, and a small increase in half-life of D-Trp3-D-Phe6-GnRH by 1.4-fold when compared with D-Phe6-GnRH. Whereas no intact GnRH was recovered in rat urine, small amounts of D-Phe6-GnRH (about 1% of dose) and high amounts of D-Trp3-D-Phe6-GnRH (25.5%) were excreted into urine. Combining the biochemical and pharmacokinetic data, it is concluded that proteolytic stability of GnRH analogs in pharmacological terms means stability towards membrane enzymes (pharmacologically-related stability) and that designing analogs with further increased proteolytic stability will be of only limited consequences with respect to their biological half-lives, the glomerular filtration rate of the kidney becoming the determining factor in the peptide clearance.
促性腺激素释放激素有两种超活性激动剂（GnRHa - I：（D - 氨基酸）6 - GnRH和GnRHa - II：（D - 氨基酸）6 - （去甘氨酸）10 - GnRH - 乙酰胺），据认为其高激素活性是由于与天然GnRH序列相比，它们具有更高的受体亲和力和更高的蛋白水解稳定性。在对GnRH肽失活的研究中，使用各种大鼠组织的可溶部分，我们证实了与GnRH相比，GnRHa - II具有更高的抗蛋白水解能力，但D - Phe6 - GnRH（GnRHa - I）和另一种类似物D - Trp3 - D - Phe6 - GnRH则不然。发现肽在降解过程中的具体行为取决于所使用的肽浓度，这表明尽可能使用接近生理条件的重要性。然而，对于膜部分，发现降解顺序为GnRH远大于D - Phe6 - GnRH远大于D - Trp3 - D - Phe6 - GnRH。在大鼠中观察到的GnRH肽不同蛋白水解降解性的药代动力学结果是，与GnRH相比，D - Phe6 - GnRH的生物半衰期适度增加了2.5倍，与D - Phe6 - GnRH相比，D - Trp3 - D - Phe6 - GnRH的半衰期小幅增加了1.4倍。虽然在大鼠尿液中未检测到完整的GnRH，但少量的D - Phe6 - GnRH（约占剂量的1%）和大量的D - Trp3 - D - Phe6 - GnRH（25.5%）被排泄到尿液中。综合生化和药代动力学数据，可以得出结论，从药理学角度来看，GnRH类似物的蛋白水解稳定性意味着对膜酶的稳定性（药理学相关稳定性），并且设计具有进一步提高的蛋白水解稳定性的类似物对于其生物半衰期的影响将非常有限，肾脏的肾小球滤过率成为肽清除的决定性因素。
