Role of Downstream Metabolic Processing of Proinflammatory Fatty Acids by 5-Lipoxygenase in HL-60 Cell Apoptosis

Background: Proinflammatory eicosanoids formed from arachidonic acid (AA) by lipoxygenase (LO) and cyclooxygenase (COX) pathways have been shown to inhibit apoptosis in certain cell types. This study determined whether inhibition of LO and COX increased apoptosis in AA-treated HL-60 cells in vitro. Methods: HL-60 cells were incubated with 50 μmol/L AA and an enzyme inhibitor (1-10 μmol/L) for COX, LO, 12-LO, and 5-LO for 12 hours. Flow cytometry was used to assess viability, apoptosis, and necrosis. Apoptosis was further assessed using terminal dUTP nick end-labeling and DNA fragmentation. Results: The highest concentration of LO inhibitors, but not COX inhibitors, decreased viability and increased apoptosis and necrosis in the presence of exogenous AA. Conclusion: These results suggest that disruption of the metabolism of AA by LO, in particular 5-LO, decreases cell survival and increases apoptosis. Thus, downstream metabolic processing of AA by LO but not COX plays a critical role in the regulation of HL-60 cell apoptosis.