Cyclooxygenase-2 and 5-lipoxygenase pathways in diosgenin-induced apoptosis in HT-29 and HCT-116 colon cancer cells.

We studied the relationship between diosgenin-induced apoptosis and arachidonic acid metabolism in two cancer cell lines, the HT-29 and HCT-116. Diosgenin is a steroidal saponin known for its antiproliferative and pro-apoptotic effects on cancer cells. We focused our attention on two enzymes intervening in two different pathways of arachidonic metabolism: cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX). HT-29 and HCT-116 cells express 5-LOX but only HT-29 cells express COX-2 since HCT-116 are deficient. After 40 microM diosgenin treatment, we observed apoptosis hallmarks in both cell lines but HT-29 cells were more resistant with delayed apoptosis. In these cells, COX-2 expression and activity were increased and for the first time we showed that diosgenin also increased 5-LOX expression and enhanced leukotriene B4 production. Inhibition of 5-LOX by AA-861 significantly reduced apoptosis in both cell lines but COX-2 inhibition by NS-398 strongly sensitized HT-29 cells to diosgenin-induced apoptosis compared to HCT-116 cells. In this study, we showed the implication of COX-2 and 5-LOX in diosgenin-induced apoptosis but these results demonstrate how difficult it is to assess the correlation between the apoptotic signalling pathway of diosgenin and arachidonic acid metabolism with certitude.