Incompatibility of silver nanoparticles with lactate dehydrogenase leakage assay for cellular viability test is attributed to protein binding and reactive oxygen species generation

A growing number of studies report that conventional cytotoxicity assays are incompatible with certain nanoparticles (NPs) due to artifacts caused by the distinctive characteristics of NPs. Lactate dehydrogenase (LDH) leakage assays have inadequately detected cytotoxicity of silver nanoparticles (AgNPs), leading to research into the underlying mechanism. When ECV304 endothelial-like umbilical cells were treated with citrate-capped AgNPs (cAgNPs) or bare AgNPs (bAgNPs), the plasma membrane was disrupted, but the LDH leakage assay failed to detect cytotoxicity, indicating interference with the assay by AgNPs. Both cAgNPs and bAgNPs inactivated LDH directly when treated to cell lysate as expected. AgNPs adsorbed LDH and thus LDH, together with AgNPs, was removed from assay reactants during sample preparation, with a resultant underestimation of LDH leakage from cells. cAgNPs, but not bAgNPs, generated reactive oxygen species (ROS), which were successfully scavenged by N-acetylcysteine or ascorbic acid. LDH inhibition by cAgNPs could be restored partially by simultaneous treatment with those antioxidants, suggesting the contribution of ROS to LDH inactivation. Additionally, the composition of the protein corona surrounding AgNPs was identified employing liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In sum, the LDH leakage assay, a conventional cell viability test method, should be employed with caution when assessing cytotoxicity of AgNPs.