Schoenmakers R G, Stehouwer M C, Tukker J J
Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences, Faculty of Pharmacy, Universiteit Utrecht, The Netherlands.
Pharm Res. 1999 Jan;16(1):62-8. doi: 10.1023/a:1018866611555.
The objective of this study was to determine the influence of the peptide bond with emphasis on the carbonyl group on the interaction with and transport by the intestinal small-peptide carrier. Therefore enalapril, a known substrate for the small-peptide carrier, has been modified to an analogue with a reduced peptide bond, enamipril. The transport characteristics of both compounds have been determined.
The in vitro transport studies were performed using rat ileum in Ussing chambers. The transport of enalapril and enamipril were measured in a concentration range from 0.5-8 mM in both directions across the ileum. in the presence and absence of inhibitors. The interaction with the small-peptide carrier was studied by evaluating the ability of enalapril and its analogue enamipril to inhibit the transport rate of amoxycillin.
Enalapril shows, besides passive diffusion (P(m)3.06+/-0.14 . 10(-6)cm/s), saturable transport kinetics (Jmax = 16+/-5 nmol/h.cm2, Km = 1.86+/-0.64 mM) which can be inhibited with 10 mM cephalexin. The analogue with a reduced peptide bond does not show saturable transport from the mucosal to the serosal side, and cephalexin does not inhibit the flux of enamipril. However, the transport of enamipril from the serosal to mucosal side of the intestinal membrane is saturable and can be inhibited by 100 microM verapamil. Although enamipril is not a substrate for the small-peptide carrier in contrast to enalapril, both enalapril and enamipril are able to inhibit the active transport of amoxycillin with a K(i) of 0.41+/-0.24 mM and 0.24+/-0.12 mM respectively.
The reduction of the peptide bond of enalapril results in a compound, enamipril, which does not show polarized and saturable transport from the mucosal to the serosal side of the intestinal tissue. Also because the transport of enamipril cannot be inhibited by cephalexin, the analogue with the reduced peptide bond is no longer a substrate for the intestinal small-peptide carrier. Therefore, it can be concluded that the carbonyl group is an essential structural requirement for transport by the small-peptide carrier. In contrast, the interaction with the small-peptide carrier is still present, shown by the inhibition of the fluxes of amoxycillin. Reduction of the peptide bond of enalapril resulted in a new substrate for the P-glycoprotein efflux pump.
本研究的目的是确定肽键尤其是羰基对与肠道小肽载体相互作用及转运的影响。因此，将已知的小肽载体底物依那普利修饰为肽键减少的类似物依那普利拉。已测定了这两种化合物的转运特性。
使用Ussing槽中的大鼠回肠进行体外转运研究。在存在和不存在抑制剂的情况下，测定依那普利和依那普利拉在0.5 - 8 mM浓度范围内双向穿过回肠的转运情况。通过评估依那普利及其类似物依那普利拉抑制阿莫西林转运速率的能力来研究与小肽载体的相互作用。
依那普利除了被动扩散（P(m)3.06±0.14. 10(-6)cm/s）外，还表现出可饱和的转运动力学（Jmax = 16±5 nmol/h.cm2，Km = 1.86±0.64 mM），可被10 mM头孢氨苄抑制。肽键减少的类似物从黏膜向浆膜侧未表现出可饱和转运，头孢氨苄也不抑制依那普利拉的通量。然而，依那普利拉从肠道膜的浆膜侧向黏膜侧的转运是可饱和的，可被100 μM维拉帕米抑制。尽管与依那普利不同，依那普利拉不是小肽载体的底物，但依那普利和依那普利拉都能够抑制阿莫西林的主动转运，其抑制常数（K(i)）分别为0.41±0.24 mM和0.24±0.12 mM。
依那普利肽键的减少产生了一种化合物依那普利拉，它在肠道组织从黏膜向浆膜侧未表现出极化和可饱和转运。而且由于依那普利拉的转运不能被头孢氨苄抑制，肽键减少的类似物不再是肠道小肽载体的底物。因此，可以得出结论，羰基是小肽载体转运的必需结构要求。相反，与小肽载体的相互作用仍然存在，这通过对阿莫西林通量的抑制得以体现。依那普利肽键的减少产生了一种新的P - 糖蛋白外排泵底物。
