Bacellar Isabel O L, Oliveira Maria Cecilia, Dantas Lucas S, Costa Elierge B, Junqueira Helena C, Martins Waleska K, Durantini Andrés M, Cosa Gonzalo, Di Mascio Paolo, Wainwright Mark, Miotto Ronei, Cordeiro Rodrigo M, Miyamoto Sayuri, Baptista Mauricio S
Departamento de Bioquímica, Instituto de Química , Universidade de São Paulo , Avenida Prof. Lineu Prestes 748 , São Paulo , SP , Brazil , 05508-000.
Department of Chemistry and Center for Self-Assembled Chemical Structures CSACS/CRMAA , McGill University , 801 Sherbrook Street West , Montreal , QC , Canada , H3A 0B8.
J Am Chem Soc. 2018 Aug 1;140(30):9606-9615. doi: 10.1021/jacs.8b05014. Epub 2018 Jul 23.
Although the general mechanisms of lipid oxidation are known, the chemical steps through which photosensitizers and light permeabilize lipid membranes are still poorly understood. Herein we characterized the products of lipid photooxidation and their effects on lipid bilayers, also giving insight into their formation pathways. Our experimental system was designed to allow two phenothiazinium-based photosensitizers (methylene blue, MB, and DO15) to deliver the same amount of singlet oxygen molecules per second to 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine liposome membranes, but with a substantial difference in terms of the extent of direct physical contact with lipid double bonds; that is, DO15 has a 27-times higher colocalization with ω-9 lipid double bonds than MB. Under this condition, DO15 permeabilizes membranes at least 1 order of magnitude more efficiently than MB, a result that was also valid for liposomes made of polyunsaturated lipids. Quantification of reaction products uncovered a mixture of phospholipid hydroperoxides, alcohols, ketones, and aldehydes. Although both photosensitizers allowed the formation of hydroperoxides, the oxidized products that require direct reactions between photosensitizer and lipids were more prevalent in liposomes oxidized by DO15. Membrane permeabilization was always connected with the presence of lipid aldehydes, which cause a substantial decrease in the Gibbs free energy barrier for water permeation. Processes depending on direct contact between photosensitizers and lipids were revealed to be essential for the progress of lipid oxidation and consequently for aldehyde formation, providing a molecular-level explanation of why membrane binding correlates so well with the cell-killing efficiency of photosensitizers.
尽管脂质氧化的一般机制已为人所知，但光敏剂和光使脂质膜通透性增加的化学步骤仍知之甚少。在此，我们对脂质光氧化产物及其对脂质双层的影响进行了表征，同时也深入了解了它们的形成途径。我们设计了实验系统，使两种基于吩噻嗪鎓的光敏剂（亚甲蓝，MB，和DO15）每秒向1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱脂质体膜传递相同数量的单线态氧分子，但在与脂质双键的直接物理接触程度方面存在显著差异；也就是说，DO15与ω-9脂质双键的共定位比MB高27倍。在这种条件下，DO15使膜通透性增加的效率比MB至少高一个数量级，这一结果对由多不饱和脂质制成的脂质体也有效。反应产物的定量分析发现了磷脂氢过氧化物、醇、酮和醛的混合物。尽管两种光敏剂都能形成氢过氧化物，但需要光敏剂与脂质直接反应的氧化产物在被DO15氧化的脂质体中更为普遍。膜通透性增加总是与脂质醛的存在相关，脂质醛会导致水渗透的吉布斯自由能垒大幅降低。结果表明，依赖于光敏剂与脂质直接接触的过程对于脂质氧化的进行以及醛的形成至关重要，这从分子水平解释了为什么膜结合与光敏剂的细胞杀伤效率相关性如此之好。
