Chittchang Montakarn, Alur Hemant H, Mitra Ashim K, Johnston Thomas P
Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, MO 64110-2499, USA.
J Pharm Pharmacol. 2002 Mar;54(3):315-23. doi: 10.1211/0022357021778556.
Low oral bioavailability of therapeutic peptides and proteins generally results from their poor permeability through biological membranes and enzymatic degradation in the gastrointestinal tract. Since different secondary structures exhibit different physicochemical properties such as hydrophobicity, size and shape, changing the secondary structure of a therapeutic polypeptide may be another approach to increasing its membrane permeation. Poly(L-lysine) was used as a model polypeptide. The objectives of this study were to induce secondary structural changes in poly(L-lysine) and to determine the time course over which a given conformer was retained. In addition, the hydrophobicity of each secondary structure of poly(L-lysine) was assessed. The circular dichroism (CD) studies demonstrated that the conditions employed could successfully induce the desired secondary structural changes in poly(L-lysine). The alpha-helix conformer appeared to be more stable at 25 degrees C whereas the beta-sheet conformer could be preserved at 37 degrees C. On the other hand, the random coil conformer was retained at both temperatures. Significant losses of the alpha-helix and the beta-sheet conformers were observed when the pH was reduced. The change in ionic strength did not affect any of the conformers. The octanol/buffer partitioning studies indicated that the alpha-helix and the beta-sheet conformers exhibited significantly different (P < 0.05) hydrophobicities. In conclusion, variation of pH and temperature conditions can be used to induce secondary structural changes in poly(L-lysine). These changes are reversible when the stimuli are removed. The alpha-helix and the beta-sheet conformers of poly(L-lysine) are more lipophilic than the native random coil conformer. Thus, poly(L-lysine) may represent an ideal model polypeptide with which to further investigate the effects of secondary structure on membrane diffusion or permeation.
治疗性肽和蛋白质的口服生物利用度较低，这通常是由于它们通过生物膜的渗透性较差以及在胃肠道中发生酶降解所致。由于不同的二级结构表现出不同的物理化学性质，如疏水性、大小和形状，改变治疗性多肽的二级结构可能是提高其膜渗透性的另一种方法。聚（L-赖氨酸）被用作模型多肽。本研究的目的是诱导聚（L-赖氨酸）的二级结构变化，并确定给定构象体保持的时间进程。此外，还评估了聚（L-赖氨酸）每个二级结构的疏水性。圆二色性（CD）研究表明，所采用的条件能够成功地诱导聚（L-赖氨酸）产生所需的二级结构变化。α-螺旋构象体在25℃时似乎更稳定，而β-折叠构象体在37℃时可以保存。另一方面，无规卷曲构象体在两个温度下都能保持。当pH降低时，观察到α-螺旋和β-折叠构象体有显著损失。离子强度的变化对任何构象体都没有影响。正辛醇/缓冲液分配研究表明，α-螺旋和β-折叠构象体表现出显著不同（P<0.05）的疏水性。总之，pH和温度条件的变化可用于诱导聚（L-赖氨酸）的二级结构变化。当去除刺激因素时，这些变化是可逆的。聚（L-赖氨酸）的α-螺旋和β-折叠构象体比天然的无规卷曲构象体更具亲脂性。因此，聚（L-赖氨酸）可能是进一步研究二级结构对膜扩散或渗透影响的理想模型多肽。
