RESUMO
AIM Inhibitors of xanthine oxidase (XOD) may be potentially useful for the treatment of gout or other XOD inducing diseases, so the inhibition on XOD activity of diterpenoid tanshinones such as cyptotanshinone (CT) and methylenetanshinone (MT) from Tanshen (Salvia miltiorrhiza Bge.) was studied. METHODS The formation rate of uric acid from xanthine was determined by measuring the absorbance increment at 290 nm (ΔA290 nm) in the reactive medium of xanthine/XOD when CT or MT was added. RESULTS It was found that CT and MT inhibited XOD activity. Dixon plots showed that the inhibition mode was competitive type. The Ki values of CT and MT were 17.8 μmol·L-1 and 25.9 μmol·L-1, respectively. Their inhibitory potencies positively correlated with their concentrations and the IC50 values of CT and MT were 70 and 67 μmol·L-1, respectively. The IC50 value of allopurinol, the positive control, was 60 μmol·L-1. CONCLUSION CT and MT have inhibitory effects on XOD activity and may be potentially useful for the treatment of gout or other XOD inducing diseases.