We have examined the antioxidant properties of structurally related flavones/isoflavones in 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated HL-60 cells. In the presence of 1.3% dimethyl sulfoxide in the medium for seven days, promyelocytic HL-60 cells were differentiated into neutrophil-like cells possessing phagocytic properties and the capacity to generate H2O2 on TPA stimulation. The effects of five selected flavones/isoflavones on the formation of H2O2 and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were examined in TPA-stimulated HL-60 cells. The results indicated that genistein was the most potent inhibitor of H2O2 production by TPA-stimulated HL-60 cells, followed by apigenin and daidzein, whereas prunectin and biochanin A exhibited no effect. This inhibitory effect correlates well with the scavenging capacity of H2O2 by these flavones/isoflavones in an in vitro system. The formation of 8-OHdG in cellular DNA of HL-60 cells was induced by TPA and further enhanced by the addition of FeCl2 to the medium. Most flavones/isoflavones significantly inhibited TPA + FeCl2-induced 8-OHdG formation in HL-60 cells, with genistein being the most potent quencher. The inhibition of H2O2 production and 8-OHdG formation by these structurally related flavones/isoflavones may contribute to their chemopreventive potentials against human cancers.
While much evidence indicates a high degree of spatial organization in the nucleus, the underlying molecular structures that support it remain poorly characterized. By extracting with high concentrations of RNase A in a modification of the sequential extraction protocol of Penman, we have identified a novel intranuclear network in the mouse lymphoma cell line, EL-4. Micrographs of embedment-free sections of extracted cells reveal anastomosing filaments of two different diameters: 3-5 nm and 8-10 nm. The 3-5-nm filaments are interconnected in many junctions and appear to blend smoothly into each other. The 8-10-nm fibers frequently split into two 3-5-nm filaments. Some 3-5-nm fibers appear to be connected at 90 degrees angles with the 8-10-nm fibers. All junctions are smooth with no apparent junction protein. Flow cytometric analysis of RNase A- (and DNase I-) extracted nuclear matrices indicates that they do not contain significant amounts of protein that react with anti-actin and anti-vimentin monoclonal antibodies. Extraction of EL-4 nuclear matrices with high salt does not reveal 8-10-nm core filaments described after similar treatment of tumor cell lines of cervical and mammary origin. The novel characteristics of the core filaments in EL-4 lymphoma cells may reflect cell-type specificity of the nuclear matrix.
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