Pala Laura, Senn Hans M, Caldwell Stuart T, Prime Tracy A, Warrington Stefan, Bright Thomas P, Prag Hiran A, Wilson Claire, Murphy Michael P, Hartley Richard C
School of Chemistry, University of Glasgow, Glasgow, United Kingdom.
MRC Mitochondrial Biology Unit, University of Cambridge, Cambridge, United Kingdom.
Front Chem. 2020 Sep 9;8:783. doi: 10.3389/fchem.2020.00783. eCollection 2020.
There is considerable interest in developing drugs and probes targeted to mitochondria in order to understand and treat the many pathologies associated with mitochondrial dysfunction. The large membrane potential, negative inside, across the mitochondrial inner membrane enables delivery of molecules conjugated to lipophilic phosphonium cations to the organelle. Due to their combination of charge and hydrophobicity, quaternary triarylphosphonium cations rapidly cross biological membranes without the requirement for a carrier. Their extent of uptake is determined by the magnitude of the mitochondrial membrane potential, as described by the Nernst equation. To further enhance this uptake here we explored whether incorporation of a carboxylic acid into a quaternary triarylphosphonium cation would enhance its mitochondrial uptake in response to both the membrane potential and the mitochondrial pH gradient (alkaline inside). Accumulation of arylpropionic acid derivatives depended on both the membrane potential and the pH gradient. However, acetic or benzoic derivatives did not accumulate, due to their lowered pK. Surprisingly, despite not being taken up by mitochondria, the phenylacetic or phenylbenzoic derivatives were not retained within mitochondria when generated within the mitochondrial matrix by hydrolysis of their cognate esters. Computational studies, supported by crystallography, showed that these molecules passed through the hydrophobic core of mitochondrial inner membrane as a neutral dimer. This finding extends our understanding of the mechanisms of membrane permeation of lipophilic cations and suggests future strategies to enhance drug and probe delivery to mitochondria.
为了理解和治疗与线粒体功能障碍相关的多种疾病，人们对开发靶向线粒体的药物和探针有着浓厚的兴趣。线粒体内膜两侧存在较大的膜电位，内膜内侧为负，这使得与亲脂性鏻阳离子共轭的分子能够被递送至该细胞器。由于其电荷与疏水性的结合，季铵化三芳基鏻阳离子无需载体即可快速穿过生物膜。其摄取程度由能斯特方程描述的线粒体膜电位大小决定。为了进一步增强这种摄取，我们在此探究将羧酸引入季铵化三芳基鏻阳离子是否会增强其在线粒体膜电位和线粒体pH梯度（内侧呈碱性）共同作用下的线粒体摄取。芳基丙酸衍生物的积累取决于膜电位和pH梯度。然而，乙酸或苯甲酸衍生物并未积累，因为它们的pK值降低。令人惊讶的是，尽管苯基乙酸或苯基苯甲酸衍生物未被线粒体摄取，但当它们在其同源酯在线粒体基质中水解产生时，也不会保留在线粒体内。晶体学支持的计算研究表明，这些分子以中性二聚体形式穿过线粒体内膜的疏水核心。这一发现扩展了我们对亲脂性阳离子膜渗透机制的理解，并提出了未来增强药物和探针递送至线粒体的策略。
