In laboratory experiments, many electrophilic cytotoxic agents induce cell death accompanied by reactive oxygen species (ROS) production and/or by glutathione (GSH) depletion. Not surprisingly, millimolar concentrations of N-acetylcysteine (NAC), which is used as a universal ROS scavenger and precursor of GSH biosynthesis, inhibit ROS production, restore GSH levels, and prevent cell death. The protective effect of NAC is generally used as corroborative evidence that cell death induced by a studied cytotoxic agent is mediated by an oxidative stress-related mechanism. However, any simple interpretation of the results of the protective effects of NAC may be misleading because it is unable to interact with superoxide (O2•-), the most important biologically relevant ROS, and is a very weak scavenger of H2O2. In addition, NAC is used in concentrations that are unnecessarily high to stimulate GSH synthesis. Unfortunately, the possibility that NAC as a nucleophile can directly interact with cytotoxic electrophiles to form non-cytotoxic NAC-electrophile adduct is rarely considered, although it is a well-known protective mechanism that is much more common than expected. Overall, apropos the possible mechanism of the cytoprotective effect of NAC in vitro, it is appropriate to investigate whether there is a direct interaction between NAC and the cytotoxic electrophile to form a non-cytotoxic NAC-electrophilic adduct(s).

• Keywords
• N-acetylcysteine, N-acetylcysteine-electrophile adduct, electrophile, mechanism of protection, nucleophile,
• Publication type
• Journal Article MeSH
• Review MeSH

N-acetylcysteine (NAC), often used as an antioxidant-scavenging reactive oxygen species (ROS) in vitro, was recently shown to increase the cytotoxicity of other compounds through ROS-dependent and ROS-independent mechanisms. In this study, NAC itself was found to induce extensive ROS production in human leukemia HL-60 and U937 cells. The cytotoxicity depends on ROS-modulating enzyme expression. In HL-60 cells, NAC activated NOX2 to produce superoxide (O2•-). Its subsequent conversion into H2O2 by superoxide dismutase 1 and 3 (SOD1, SOD3) and production of ClO- from H2O2 by myeloperoxidase (MPO) was necessary for cell death induction. While the addition of extracellular SOD potentiated NAC-induced cell death, extracellular catalase (CAT) prevented cell death in HL-60 cells. The MPO inhibitor partially reduced the number of dying HL-60 cells. In U937 cells, the weak cytotoxicity of NAC is probably caused by lower expression of NOX2, SOD1, SOD3, and by the absence of MOP expression. However, even here, the addition of extracellular SOD induced cell death in U937 cells, and this effect could be reversed by extracellular CAT. NAC-induced cell death exhibited predominantly apoptotic features in both cell lines. Conclusions: NAC itself can induce extensive production of O2•- in HL-60 and U937 cell lines. The fate of the cells then depends on the expression of enzymes that control the formation and conversion of ROS: NOX, SOD, and MPO. The mode of cell death in response to NAC treatment bears apoptotic and apoptotic-like features in both cell lines.

• Keywords
• HL-60 cells, MPO, N-acetylcysteine, NOX, SOD, U937 cells, oxidative stress,
• MeSH
• Acetylcysteine pharmacology   MeSH
• HL-60 Cells MeSH
• Catalase genetics   MeSH
• Leukemia drug therapy   genetics   metabolism   MeSH
• Humans MeSH
• NADPH Oxidase 2 genetics   MeSH
• Oxidative Stress drug effects   MeSH
• Peroxidase genetics   MeSH
• Cell Proliferation drug effects   MeSH
• Reactive Oxygen Species metabolism   MeSH
• Gene Expression Regulation, Neoplastic drug effects   MeSH
• Gene Expression Profiling MeSH
• Superoxide Dismutase genetics   MeSH
• U937 Cells MeSH
• Cell Survival drug effects   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Acetylcysteine MeSH
• CYBB protein, human MeSH Browser
• Catalase MeSH
• MPO protein, human MeSH Browser
• NADPH Oxidase 2 MeSH
• Peroxidase MeSH
• Reactive Oxygen Species MeSH
• Superoxide Dismutase MeSH