ABSTRACT
<p><b>OBJECTIVE</b>1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is a potent inducer of differentiation in myeloid leukemia cells, but its clinical use is limited due to its hypercalcaemic effect and resistance. Carnosic acid is a plant-derived polyphenol food preservative with chemoprotective effects against carcinogens. Recent research has shown that carnosic acid potentiates the effects of 1,25(OH)2D3 on differentiation of human leukemia cells. This study examined the effects of 1,25(OH)2D3 in combination with carnosic acid on monocytic differentiation as well as intracellular reactive oxygen species (ROS) and Ca2+ levels in human leukemia HL-60 cells.</p><p><b>METHODS</b>HL-60 cells were randomly treated with 1 nmol/L 1,25(OH)2D3, 100 nmol/L 1,25(OH)2D3, 10 micromol/L carnosic acid, a combination of 1 nmol/L 1,25(OH)2D3 and 10 micromol/L carnosic acid or placebo. Cell growth was observed by MTT assay for 72 hrs at an interval of 24 hrs. Cells were harvested after 72 hrs of culture. Morphologic features of the cells were observed by microscopy. Flow cytometry was used to detect cell cycle, monocytic differentiation marker CD14 expression, and intracellular ROS and Ca2+ levels.</p><p><b>RESULTS</b>A combination of 1 nmol/L 1,25(OH)2D3 and 10 micromol/L carnosic acid resulted in greater proliferation inhibition (Ab: 0.56 0+/- 0.020 vs 1.482 +/- 0.327; P <0.01), mature monocytic features, G0 /G1 cell arrest, higher CD14 expression (57.62 +/- 0.817% vs 2.76 +/- 0.828%; P <0.01), lower intracellular ROS levels (52.67 +/- 10.76% vs 86.46 +/- 40.52%; P <0.01 and similar intracellular Ca2+ levels in HL-60 cells when compared with the placebo group. The ability of a combination of 1 nmol/L 1,25(OH)2D3 and 10 micromol/L carnosic acid to inhibit the proliferation and induce the differentiation of HL-60 cells was similar to that of 100 nmol/L 1,25(OH)2D3, while the intracellular Ca2+ level (115.64 +/- 17.74 nmol/L vs 185.75 +/- 27.38 nmol/L) was significantly lower than that in the 100 nmol/L 1,25(OH)2D3 group.</p><p><b>CONCLUSIONS</b>Low concentration of 1,25(OH)2D3 combined with 10 micromol/L carnosic acid can produce enhanced differentiation, proliferation inhibition and antioxidant effects of HL-60 cells. The combination of the two inducers dose not increases intracellular Ca2+ levels.</p>