OBJECTIVETo explore the effect of combined application of psoralen (PSO, an extract from psoralea) and ultraviolet A (UVA) for inducing the apoptosis of human leukemic cell line NB4 and its impact on the Fas/FasL gene expressions.

METHODSAccording to factorial design, changes of apoptosis rate and ultrastructure of NB4 cells, as well as the gene and protein expressions of Fas/FasL were observed after cells were treated with PSO in different concentrations and irradiated by UVA of 360 nm wavelength for different times, using flow cytometry, transmission electron microscopy and quantitative polymerase chain reaction (PCR), and the outcomes were treated with variable analysis.

RESULTS(1) After treatment of PSO in concentration of 10, 20, 40, 80 microg/mL combined with a 5-min exposure of UVA, the NB4 cells apoptosis rate induced were 26.57% +/- 0.42%, 30.67% +/- 0.11%, 34.90% +/- 0.30% and 24.63% +/- 0.38% respectively. The effects were dose- and time-dependent, and an interaction was shown between the two actors. (2) After being treated by PSO plus UVA, obvious ultrastructure changes with apoptosis characteristics were shown in NB4 cell under electron microscope. (3) PSO plus UVA showed up-regulatory effect on gene and protein expressions of Fas, and down-regulatory effect on gene and protein expressions of FasL in a dose- and time-dependent manner, with the interaction between the two actors in altering Fas gene expression, also in altering FasL gene and protein expressions.

CONCLUSIONCombined application of PSO and UVA can induce the apoptosis of NB4 cells, and the Fas/FasL system is one of the pathways for apoptosis inducing.