Terpinen-4-ol Induces Autophagic and Apoptotic Cell Death in Human Leukemic HL-60 Cells

Background: Terpinen-4-ol, a monoterpene, is found as the main component of essential oil extracts frommany plants. In this study apoptotic and autophagic types of cell death induced by terpinen-4-ol and associatedmechanisms were investigated in human leukemic HL-60 cells. Materials and
Methods: The cytotoxicity ofhuman leukemic U937 and HL-60 cells was determined by MTT assay. Cytochrome c release, expression of Bax,Bcl-2, Bcl-xl and cleaved Bid were determined by Western blotting. Cell morphology was examined under atransmission electron microscope. LC3-I/II, ATG5 and Beclin-1 levels were detected by immunoblotting.
Results:Terpinen-4-ol exhibited cytotoxicity to human leukemic HL-60 but not U937 cells. The apoptotic response toterpinen-4-ol in HL-60 cells was due to induction of cytochrome c release from mitochondria and cleavage of Bidprotein after the stimulation of caspase-8. There was a slightly decrease of Bcl-xl protein level. The characteristiccell morphology of autophagic cell death was demonstrated with multiple autophagosomes in the cytoplasm.At the molecular level, the results from Western blot analysis showed that terpinen-4-ol significantly inducedaccumulation of LC3-I/II, ATG5 and Beclin-1, regulatory proteins required for autophagy in mammalian cells.
Conclusions: Terpinen-4-ol induced-human leukemic HL-60 cell death was via both autophagy and apoptosis.