The anti-apoptotic effects of nordihydroguaiaretic acid: Inhibition of cPLA2 activation during TNF-induced apoptosis arises from inhibition of calcium signaling

Nordihydroguaiaretic acid (NDGA) is a plant lignan produced by Larrea tridentata, the creosote bush of the American southwest. In this report we examine the mechanism underlying the ability of NDGA to inhibit TNF-induced apoptosis. Our results show that NDGA blocks many key indicators of apoptosis. Caspase cleavage, mitochondrial inactivation, externalization of phosphatidyl serine, and 51Cr-release were all blocked by low micromolar concentrations of NDGA. NDGA also inhibited the cPLA2-dependent release of 3H-arachidonic acid. We investigated this activity and found that NDGA prevented the rise in intracellular calcium necessary for the apoptotic activation of cPLA2. On the other hand, NDGA did not interfere with the TNF-induced phosphorylation of cPLA2, indicating that NDGA does not block all TNF-dependent signaling. Finally, we asked whether the anti-apoptotic effect of NDGA could be attributed to its anti-oxidant activity. Comparison with the effects of butylated hydroxyanisole (BHA) did not completely support this hypothesis. While BHA strongly inhibited caspase activation and partially blocked the release of 51Cr, it was unable to significantly block the calcium response or the release of 3H-arachidonic acid associated with TNF-induced apoptosis. The anti-oxidant activity of NDGA may, therefore, explain some but not all of its anti-apoptotic activity.