Table 1_Synergistic antibacterial photodynamic therapy of lysine-porphyrin conjugate and metal ions combination against Candida albicans and Mycobacterium tuberculosis.xlsx

IntroductionIn previous research, antibacterial photodynamic therapy using lysine-porphyrin conjugate LD4 effectively inactivated methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli; however, it exhibited limited activity against Candida albicans and Mycobacterium tuberculosis.
MethodsTo address this limitation, we developed a synergistic antibacterial strategy by combining LD4 with Cu2+ or Zn2+.
ResultsSynergy was confirmed via minimum inhibitory concentration and fractional inhibitory concentration index analyses, demonstrating 16- to 64-fold enhanced antibacterial efficacy compared to LD4 alone. Mechanistic studies revealed divergent pathways for LD4 + Cu2+ and LD4 + Zn2+: Zn2+ increased the reactive oxygen species yield and promoted LD4 uptake by pathogens, while LD4 + Cu2+ induced oxidative damage to cell walls and membranes in darkness, with light exposure exacerbating structural damage. Cytotoxicity assessments confirmed low toxicity, with >90% survival of normal cells at bactericidal concentrations. Fluorescence and infrared spectroscopy characterized metal-LD4 complexes, showing stabilization through interactions between amino and pyrrolic imino groups of LD4 and metal ions, which promoted non-radiative transitions and fluorescence quenching. Both combinations caused significant bacterial membrane disruption and growth suppression. Notably, cytotoxicity exhibited a biphasic dose-response linked to metal-LD4 complexation-dependent particle size changes.
DiscussionThis study elucidated the enhanced antimicrobial mechanisms and safety of LD4-metal ion combinations. The findings resolve the limitations of LD4 while providing a theoretical framework for developing novel therapies against fungal and mycobacterial infections.

引言 既往研究表明，采用赖氨酸-卟啉偶联物（lysine-porphyrin conjugate）LD4实施的抗菌光动力疗法，可有效灭活耐甲氧西林金黄色葡萄球菌、铜绿假单胞菌与大肠埃希菌；但该疗法对白色念珠菌及结核分枝杆菌的抗菌活性较为有限。
方法 为解决上述局限性，本研究开发了一种协同抗菌策略，将LD4分别与铜离子（Cu²+）或锌离子（Zn²+）联合使用。
结果 通过最低抑菌浓度（minimum inhibitory concentration, MIC）与分级抑菌浓度指数（fractional inhibitory concentration index, FICI）分析证实了协同效应，相较于单独使用LD4，联合疗法的抗菌效力提升了16至64倍。机制研究揭示了LD4与Cu²+、LD4与Zn²+联合使用的不同作用通路：Zn²+可提高活性氧（reactive oxygen species, ROS）的生成量，并促进病原体对LD4的摄取；而LD4与Cu²+联合可在黑暗环境下诱导细胞壁与细胞膜发生氧化损伤，光照暴露则会加剧结构损伤。细胞毒性评估结果显示该疗法毒性较低，在杀菌浓度下正常细胞存活率仍超过90%。通过荧光与红外光谱对金属-LD4复合物进行表征，发现LD4的氨基与吡咯亚氨基可与金属离子发生相互作用，从而稳定复合物，该过程可促进非辐射跃迁并引发荧光猝灭。两种联合疗法均可显著破坏细菌细胞膜并抑制细菌生长。值得注意的是，细胞毒性呈现双相剂量反应，这与金属-LD4络合依赖的粒径变化相关。
讨论 本研究阐明了LD4与金属离子联合疗法的增强型抗菌机制与安全性。本研究结果不仅解决了LD4单独使用的局限性，还为开发针对真菌与分枝杆菌感染的新型治疗手段提供了理论框架。