Cytotoxic interaction between amiodarone and desethylamiodarone in human peripheral lung epithelial cells

The potent and efficacious anti-dysrhythmic agent amiodarone (AM) can cause potentially life-threatening lung damage (amiodarone-induced pulmonary toxicity; AIPT), which is characterized by cell death in the lungs, followed by inflammation and fibrosis. AM’s major metabolite, desethylamiodarone (DEA), has a greater toxic potency than AM and it has been suggested that DEA may act synergistically with AM to cause lung toxicity. The objective of this study was to determine the type of cytotoxic interaction between AM and DEA in HPL1A human peripheral lung epithelial cells. Cytotoxicity was measured by lactate dehydrogenase release. AM and DEA caused concentration-dependent cytotoxicity in HPL1A cells. The concentration of drug causing 50% cell death (LC50) and the Hill slope factor, which represents steepness of the concentration–cell death curve, were significantly different between AM and DEA (12.4 μM and 1.98; 5.07 μM and 5.43, for AM and DEA, respectively) indicating that they may induce cytotoxicity through different mechanisms. A combined concentration of 7.13 μM AM plus DEA, equivalent to 41% of each compound’s individual LC50 value, resulted in 50% cell death. Isobolographic analysis revealed this effect to be additive, although the combined concentrations were only slightly higher than the concentrations that defined the threshold of synergy (threshold of synergy = 4.21 ± 1.98 μM AM plus 1.73 ± 1.05 μM DEA; experimental data point = 5.06 ± 0.47 μM AM plus 2.07 ± 0.47 μM DEA). The cytotoxic interaction between AM and DEA may be clinically relevant in the development of AIPT.