Related Experiment Videos
Potential Toxicity of Polymyxins in Human Lung Epithelial Cells
Maizbha U Ahmed1,2, Tony Velkov1, Yu-Wei Lin3
1Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia.
Abstract:
Inhaled polymyxins are of considerable utility in achieving optimal exposure in the respiratory tract for the treatment of lung infections caused by multidrug-resistant Gram-negative pathogens. Current inhaled polymyxin therapy is empirical, and often large doses are used that may lead to potential pulmonary adverse effects. This study aimed to investigate the effect of polymyxins on human lung epithelial (A549) cells. The viability of A549 cells was examined after treatment with polymyxins by flow cytometry. Activation of caspases 3, 8, and 9, expression of Fas ligand (FasL), loss of mitochondrial membrane potential, and mitochondrial oxidative stress induced by polymyxin B were evaluated. The concentration of polymyxin B required to induce 50% of maximal cell death was 1.74 mM (95% confidence interval, 1.60 to 1.90 mM). Colistin was at least 2-fold less toxic than polymyxin B, while colistimethate was nontoxic. With 2.0 mM polymyxin B, 30.6% ± 11.5% (mean ± standard deviation) of the cells were apoptotic at 8 h and this increased to 71.3% ± 3.72% at 24 h. Concentration- and time-dependent activation of caspases 3, 8, and 9 was evident, while the activation of caspase 9 was more dramatic. Furthermore, polymyxin B caused concentration- and time-dependent FasL expression, production of mitochondrial reactive oxygen species, and changes in mitochondrial membrane potential. This is the first study to demonstrate that both extrinsic death receptor and intrinsic mitochondrial pathways are involved in polymyxin-induced toxicity in A549 cells. This knowledge base is critical for the development of novel strategies for the safe and effective inhalation therapy of polymyxins against Gram-negative "superbugs."
Insights
Polymyxin B induces lung cell death through both extrinsic and intrinsic pathways, with colistin being less toxic. This research informs safer inhaled polymyxin therapies for multidrug-resistant infections.
Area of Science:
- Pharmacology
- Cell Biology
- Toxicology
Background:
- Inhaled polymyxins treat Gram-negative lung infections but may cause pulmonary adverse effects due to high doses.
- Current inhaled polymyxin dosing is empirical, necessitating research into toxicity mechanisms.
Purpose of the Study:
- To investigate the effects of polymyxins on human lung epithelial (A549) cells.
- To elucidate the cellular pathways involved in polymyxin-induced lung cell toxicity.
Main Methods:
- A549 cell viability was assessed using flow cytometry after polymyxin treatment.
- Caspase activation (3, 8, 9), Fas ligand (FasL) expression, mitochondrial membrane potential, and oxidative stress were evaluated.
Main Results:
- Polymyxin B induced concentration- and time-dependent apoptosis in A549 cells (50% cell death at 1.74 mM).
- Colistin exhibited lower toxicity than polymyxin B; colistimethate was non-toxic.
- Polymyxin B activated caspases (3, 8, 9), increased FasL expression, and induced mitochondrial dysfunction and oxidative stress.
Conclusions:
- Polymyxin B toxicity in lung cells involves both extrinsic (death receptor) and intrinsic (mitochondrial) pathways.
- Understanding these mechanisms is crucial for developing safer inhaled polymyxin therapies against resistant Gram-negative bacteria.