Porphyrin depth in lipid bilayers as determined by iodide and parallax fluorescence quenching methods and its effect on photosensitizing efficiency
Porphyrin depth in lipid bilayers as determined by iodide and parallax fluorescence quenching methods and its effect on photosensitizing efficiency
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DOI：
10.1529/biophysj.104.041434
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发表时间：
2004-08-01
影响因子：
3.4
通讯作者：
Ehrenberg, B
中科院分区：
文献类型：
--
作者：
Bronshtein, I;Afri, M;Ehrenberg, B
卟啉和其他四吡咯发色团的光敏作用在生物学和医学上用于杀死细胞。这种由光触发产生的单线态氧被用来消灭癌细胞，这一过程被称为“光动力疗法”（PDT）。大多数光敏剂是两亲性的，它们分裂成细胞脂质膜。它们对宿主细胞造成的光损伤主要局限于膜蛋白。这种光敏性损伤必须与单线态氧通过脂相的快速扩散和逃逸到水相的竞争中发生。在这篇文章中，我们展示了损伤的程度可以通过使用修饰的血卟啉和原卟啉来调节，它们在四吡咯环和锚定在脂质/水界面的羧酸基团之间具有不同长度的烷基间隔。因此，分子的生色团部分和单线态氧的产生点位于双分子层中较深的位置。用9,10-二甲基镧（单线态氧的荧光化学靶标）测定了光敏效率。通过两种荧光猝灭技术来评估敏化剂的垂直插入：来自水相的碘离子；通过自旋探针标记的磷脂，用视差法将其纳入双分子层。这些方法还表明，当膜处于液相时，温度对膜深度的影响很小。然而，当双分子层经历相变到固体凝胶相时，卟啉随着温度的降低而向水界面挤压。这些结果，连同之前在该杂志上发表的一篇文章，代表了一个独特的和先例的情况下，一个小分子在膜上的垂直位置对其膜活性有影响。
Photosensitization by porphyrins and other tetrapyrrole chromophores is used in biology and medicine to kill cells. This light-triggered generation of singlet oxygen is used to eradicate cancer cells in a process dubbed "photodynamic therapy,'' or PDT. Most photosensitizers are of amphiphilic character and they partition into cellular lipid membranes. The photodamage that they inflict to the host cell is mainly localized in membrane proteins. This photosensitized damage must occur in competition with the rapid diffusion of singlet oxygen through the lipid phase and its escape into the aqueous phase. In this article we show that the extent of damage can be modulated by employing modified hemato- and protoporphyrins, which have alkyl spacers of varying lengths between the tetrapyrrole ring and the carboxylate groups that are anchored at the lipid/water interface. The chromophore part of the molecule, and the point of generation of singlet oxygen, is thus located at a deeper position in the bilayer. The photosensitization efficiency was measured with 9,10-dimethylanthracene, a fluorescent chemical target for singlet oxygen. The vertical insertion of the sensitizers was assessed by two fluorescence-quenching techniques: by iodide ions that come from the aqueous phase; and by spin-probe-labeled phospholipids, that are incorporated into the bilayer, using the parallax method. These methods also show that temperature has a small effect on the depth when the membrane is in the liquid phase. However, when the bilayer undergoes a phase transition to the solid gel phase, the porphyrins are extruded toward the water interface as the temperature is lowered. These results, together with a previous publication in this journal, represent a unique and precedental case where the vertical location of a small molecule in a membrane has an effect on its membranal activity.