Inhibition of cyclooxygenase/lipoxygenase from human platelets by polyhydroxylated/methoxylated flavonoids isolated from medicinal plants

Various flavonoid derivatives were previously reported to possess the inhib itory activity on cyclooxygenase/lipoxygenase. And these properties of flav onoids might contribute to their antiinflammatory activity in vivo. In this study, several polyhydroxylated/methoxylated flavonoid derivatives such as oroxylin A, wogonin, skullcapflavone II, tectorigenin and iristectorigenin A were isolated from the medicinal plants. These compounds were evaluated for their inhibitory effects on cyclooxygenase/lipoxygenase from the homoge nate of human platelets in vitro. It was found that isoflavones including d aidzein and tectorigenin possessed the inhibitory activity on cyclooxygenas e, although the potency of inhibition was far less than that of indomethaci n. In addition, oroxylin A, baicalein and wogonin inhibited 12-lipoxygenase activity without affecting cyclooxygenase, which suggested that 5,6,7- or 5,7,8-trisubstitutions of A-ring of flavone gave favorable results. The IC5 0 values of oroxylin A and NDGA aginst 12-lipoxygenase were found to be 100 and 1.5 uM, respectively.