Chlorpyrifos induces apoptosis in human monocyte cell line U937

Ari Nakadai, Qing Li, Tomoyuki Kawada

Research output: Contribution to journalArticlepeer-review

69 Citations (Scopus)


In order to investigate chlorpyrifos-induced cell death and its underlying mechanism in human immune cells, a human monocyte like cell line (U937) was treated with chlorpyrifos at 4.45-570 μM for 0.5-24 h at 37 °C in a 5% CO2 incubator. We first found that chlorpyrifos induced cell death of U937 in a dose- and time-dependent manner, as shown by LDH and MTT assays and PI uptake. Then, we investigated if chlorpyrifos-induced cell death consisted of apoptosis, as determined by analysis of Annexin-V staining and the intracellular level of active caspase-3 by flow cytometry, and DNA fragmentation analysis. We found that chlorpyrifos induced apoptosis in U937 in a time- and dose-dependent manner, as shown by Annexin-V staining. DNA fragmentation was detected when cells were treated with 71 to 284 μM chlorpyrifos for 4 or 6 h. Chlorpyrifos also induced an increase of intracellular active caspase-3 in U937 cells in a dose-dependent manner, and a caspase-3 inhibitor, Z-DEVD-FMK, significantly inhibited the chlorpyrifos-induced apoptosis. These findings indicate that chlorpyrifos can induce apoptosis in U937 cells, and this effect is partially mediated by activation of intracellular caspase-3.

Original languageEnglish
Pages (from-to)202-209
Number of pages8
Issue number3
Publication statusPublished - 2006 Jul 25
Externally publishedYes


  • Annexin-V
  • Apoptosis
  • Caspase-3
  • Chlorpyrifos
  • DNA fragmentation
  • U937

ASJC Scopus subject areas

  • Toxicology


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