PDF(Pubmed)
Abstract：
The efflux ratio (ER), determined by Caco-2/MDCK assays, is the standard in vitro metric to establish qualitatively whether a compound is a substrate of an efflux transporter. However, others have also enabled the utilisation of this metric quantitatively by deriving a relationship that expresses the ER as a function of the intrinsic membrane permeability of the membrane (P0) as well as the permeability of carrier-mediated efflux (Ppgp). As of yet, Ppgp cannot be measured directly from transport experiments or otherwise, but the ER relationship provides easy access to this value if P0 is known. However, previous derivations of this relationship failed to consider the influence of additional transport resistances such as the aqueous boundary layers (ABLs) and the filter on which the monolayer is grown. Since single fluxes in either direction can be heavily affected by these experimental artefacts, it is crucial to consider the potential impact on the ER. We present a model that includes these factors and show both mathematically and experimentally that this simple ER relationship also holds for the more realistic scenario that does not neglect the ABLs/filter. Furthermore, we also show mathematically how paracellular transport affects the ER, and we experimentally confirm that paracellular dominance reduces the ER to unity and can mask potential efflux.
摘要：
外排比(ER)，通过Caco-2/MDCK测定法测定，是定性确定化合物是否是外排转运蛋白的底物的标准体外度量。然而,其他人也通过推导一种关系来定量地利用该指标，该关系将ER表达为膜的固有膜通透性（P0）以及载体介导的外排通透性（Ppgp）的函数。到目前为止，Ppgp不能直接从运输实验或其他方法中测量，但如果P0已知，ER关系提供了对此值的轻松访问。然而,这种关系的先前推导未能考虑其他传输阻力的影响，例如水性边界层（ABL）和在其上生长单层的过滤器。由于任一方向的单个通量都会受到这些实验伪影的严重影响，考虑对ER的潜在影响至关重要。我们提出了一个包含这些因素的模型，并在数学和实验上都表明，这种简单的ER关系也适用于不忽略ABL/过滤器的更现实的场景。此外，我们还在数学上展示了细胞旁运输如何影响ER，我们通过实验证实，细胞旁优势将ER降低到统一，并可以掩盖潜在的外排。
