5E, 8Z, HZ, 14Z-eicosatetraenoic acid, a novel transisomer of arachidonic acid, causes G₁ phase arrest and induces apoptosis of HL-60 cells

Trans arachidonic acid isomers (trans-AA) constitute a new group of trans fatty acids (trans-FA) generated in vivo via endogenous cis-trans isomerization stimulated by the NO₂ radical. Because both NO₂ and trans-FA have been implicated as causative factors in cancer, we studied the effect of the trans-AA isomers on proliferation and viability of human promyelocytic (HL-60) cells. The four trans arachidonic (trans-AA) acid isomers synthesized by us have been presently tested with respect to their competence to affect the proliferation and viability of humal promyeolocytic HL-60 cells in culture. The data demonstrate that one of the isomers, 5,6-trans-AA, showed distinct activity by targeting cell progression through the cell cycle and inducing apoptosis. The effects were time- and concentration-dependent: the cytostatic effect of 5E-AA was observed at 10 μM following 72 h of treatment. This effect was manifested as a perturbation of cell progression through G ₁, phase, indicating the ′on′ activation of the G ₁, checkpoint as evidenced by the flow- and laser scanning-cytometry techniques. Apoptotic cells were identified by comparison of their morphology, DNA fragmentation, caspase activation and collapse of mitochondrial potential with control cells. These observations suggested that 5E-AA induced a mitochondrial pathway of apoptosis. There was no evidence of cell-cycle phase specificity in induction of apoptosis by 5E-AA, as the cells showing highly fragmented DNA or caspase-3 activation were distributed in all phases of the cycle. The data suggest that 5E-AA may have at least two targets: one that is cell-cycle specific and associated with the observed arrest in the G₁ phase and another, unrelated to the cell cycle, which is responsible for triggering apoptosis indiscriminately, regardless of cycle phase I.