Potential Toxicity of Polymyxins in Human Lung Epithelial Cells

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% Ϯ 11.5% (mean Ϯ standard deviation) of the cells were apoptotic at 8 h and this increased to 71.3% Ϯ 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 polymyxininduced 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."

Antibiotic efficacy varies based on the infection model and treatment regimen for Pseudomonas aeruginosa

“…Thus, "early" treatment with TOB was effective in both the acute and chronic infection models, while the efficacy of COL differed in the two murine models. Toxicity and potential adverse effects of repeated doses may partly explain the results obtained in the chronic infection model for COL [25,26]. Our findings suggest that the results seen upon short-term treatment in mouse models of acute infection may not be predictive of the efficacy of the repeated treatment regimen followed in chronic infections.…”

The Effect of Modified Porcine Surfactant Alone or in Combination with Polymyxin B on Lung Homeostasis in LPS-Challenged and Mechanically Ventilated Adult Rats

“…Polymyxins are generally considered to be toxic [ 11 ]. As for the lungs, information on possible toxicity is limited to two studies in which PxB induced oxidative stress in alveolar epithelial cells and induced their apoptosis [ 15 , 17 ]. Nephrotoxicity induced by polymyxins may be the result of their extensive reabsorption by renal tubular cells mediated by the oligopeptide transporter PEPT2 [ 47 ].…”

“…Even topical lung administration may not be safer as indicated by recent in vitro studies. Recently, it was demonstrated that both extrinsic death receptors and intrinsic mitochondrial pathways are involved in polymyxin-induced lung toxicity [ 15 ], and intracellular localization of polymyxins in human alveolar epithelial cells A549 was identified [ 16 ]. PxB reduced viability and stimulated exocytosis in alveolar type II (ATII) cells isolated from rat lungs.…”

Polymyxin B-induced rhabdomyolysis

“…In this case, we hypothesized that the mechanism underlying rhabdomyolysis might be related to mitochondrial injury or neurotoxicity, based on several reports. [ 19 – 21 ] In rat models, polymyxin B assembles around the mitochondria and endoplasmic reticulum of renal tubular cells, leading to the activation of caspase –3, –8, and –9. [ 19 ] Another study about polymyxin B related nephrotoxicity demonstrated that polymyxin B damaged mitochondria by inducing their fragmentation, reducing membrane potential, and stimulating oxidative activities in kidney proximal tubular cells.…”

“…[ 20 ] Ahmed et al found that polymyxin B injured mitochondria in lung epithelial cells. [ 21 ] In terms of neurotoxicity, polymyxin B could potentially act on the presynaptic membrane of nerve cells and inhibit acetylcholine release, leading to dysfunction of nerve-muscle junction transmission. Long-term depolarization of neural cells caused by polymyxin B could induce calcium overload in muscle cells and cause cell death.…”