Objective:To study the variation of nitric oxide and investigate its relationship with apoptosis in apoptotic K562 cells induced by simvastatin.Methods: K562 cells were exposed to 20 μmol/L concentrations of simvastatin at different times(24

48 and 72 h).Flow cytometry were performed to confirm cell apoptotic ratio.Colorimetric method was used to measure level of intracellular nitric oxide.Reverse transcription-polymerase chain reaction was used to detect the quantity of iNOS mRNA.The apotontic ratio of K562 cells treated with nitric oxide inhibitor and simvastatin were detected at different times.Results: K562 cells could undergo apoptosis after the treatment of 20μmol/L simvastatin for 24

48 and 72 h

and the apoptotic ratios were 6.1%±0.4%

14.2%±0.4%

30.7%±0.6%

respectively.Furthermore

the intracellular nitric oxide levels and iNOS mRNA of K562 cells in treated group were increased remarkably in contrast to the control group.The intracellular nitric oxide levels in the K562 cells of treated group were(0.3±0.1) mg/ml

(2.8±0.2) mg/ml

(3.8±0.4) mg/ml.The cell apoptotic ratios of treated group decreased by addition of nitric oxide inhibitor

as compared with the control group.Conclusion: K562 cells could be induced to apoptosis by simvastatin

the underlying mechanism of which might be related to regulation of increased intracellular nitric oxide levels.