Sorensen M, Steenberg B, Knipp G T, Wang W, Steffansen B, Frokjaer S, Borchardt R T
Department of Pharmaceutics, Royal Danish School of Pharmacy, Copenhagen, Denmark.
Pharm Res. 1997 Oct;14(10):1341-8. doi: 10.1023/a:1012104301773.
To investigate the effects of the beta-turn structure of a peptide on its permeation via the paracellular and transcellular routes across cultured bovine brain microvessel endothelial cell (BBMEC) monolayers, an in vitro model of the blood-brain barrier (BBB).
The effective permeability coefficients (Peff) of the model peptides were determined across BBMEC monolayers. The dimensions of the aqueous pores in the tight junctions (TJs) of the BBMEC monolayers were determined using a series of hydrophilic permeants. This value and the molecular radius of each peptide were used to calculate the theoretical paracellular (PP*) and transcellular (PT*) permeability coefficients for each peptide.
A comparison of the theoretical PP* values with the observed Peff values was made for a series of model peptides. For the most hydrophobic peptides (Ac-PheProXaaIle-NH2 and Ac-PheProXaaIleVal-NH2; Xaa = Gly, Ile), it was concluded that the Gly-containing peptide of each pair more readily permeates BBMEC monolayers via the transcellular pathway than the Ile-containing analog. In addition, the Gly-containing peptides, which exhibit more beta-turn structure, were shown to be more lipophilic than the Ile-containing peptides as estimated by the log of their 1-octanol:HBSS partition coefficients (log Po/w). However, the three hydrophilic peptide pairs (Ac-TyrProXaaAspVal-NH2, Ac-TyrProXaaAsnVal-NH2, and Ac-TyrProXaaIleVal-NH2; Xaa = Gly, Ile) were found to permeate BBMEC monolayers predominantly via the paracellular pathway. No differences were observed in the Peff values of the hydrophilic peptides having higher beta-turn structures as compared to the peptides lacking these structural features. In addition, the Ile-containing peptides exhibited significantly higher log Po/w values than the Gly-containing hydrophilic peptides.
Hydrophobic peptides that exhibit significant beta-turn structure in solution are more lipophilic as measured by log Po/w, and more readily permeate BBMEC monolayers via the transcellular route than hydrophobic peptides that lack this type of solution structure. Similar secondary structural features in hydrophilic peptides do not appear to sufficiently alter the physicochemical properties of the peptides so as to alter their paracellular flux through BBMEC monolayers.
通过体外血脑屏障（BBB）模型，即培养的牛脑微血管内皮细胞（BBMEC）单层，研究肽的β-转角结构对其通过细胞旁和跨细胞途径渗透的影响。
测定模型肽在BBMEC单层上的有效渗透系数（Peff）。使用一系列亲水性渗透剂测定BBMEC单层紧密连接（TJ）中水孔的尺寸。该值和每种肽的分子半径用于计算每种肽的理论细胞旁（PP*）和跨细胞（PT*）渗透系数。
对一系列模型肽的理论PP*值与观察到的Peff值进行了比较。对于最疏水的肽（Ac-PheProXaaIle-NH2和Ac-PheProXaaIleVal-NH2；Xaa = Gly，Ile），得出结论：每对含Gly的肽比含Ile的类似物更易于通过跨细胞途径渗透BBMEC单层。此外，通过其1-辛醇：HBSS分配系数的对数（log Po/w）估计，具有更多β-转角结构的含Gly的肽比含Ile的肽更具亲脂性。然而，发现三对亲水性肽（Ac-TyrProXaaAspVal-NH2、Ac-TyrProXaaAsnVal-NH2和Ac-TyrProXaaIleVal-NH2；Xaa = Gly，Ile）主要通过细胞旁途径渗透BBMEC单层。与缺乏这些结构特征的肽相比，具有较高β-转角结构的亲水性肽的Peff值未观察到差异。此外，含Ile的肽的log Po/w值显著高于含Gly的亲水性肽。
通过log Po/w测量，在溶液中表现出显著β-转角结构的疏水肽更具亲脂性，并且比缺乏这种溶液结构的疏水肽更易于通过跨细胞途径渗透BBMEC单层。亲水性肽中类似的二级结构特征似乎没有充分改变肽的物理化学性质，从而改变其通过BBMEC单层的细胞旁通量。
