Inhibitors of arachidonic acid metabolism potentiate tumour necrosis factor-alpha-induced apoptosis in HL-60 cells

We investigated whether and how could various modulators of arachidonic aci d metabolism affect apoptosis induced by tumour necrosis factor-alpha (TNF- alpha) in human myeloid leukaemia HL-60 cells. These included arachinonyltr ifluoromethyl ketone (AACOCF(3); cytosolic phospholipase A(2) inhibitor), i ndomethacin (cyclooxygenase inhibitor), MK-886 (3-[1-(4-chlorobenzyl)-3-t-b utyl-thio-5-isopro-pylindol-2-yl]-2,2-dimethyl propanoic acid; 5-lipoxygena se-activating protein inhibitor), nordihydroguaiaretic acid (general lipoxy genase inhibitor), and arachidonic acid itself. Incubation of HL-60 cells w ith nordihydroguaiaretic acid resulted in apoptosis and it was characterise d by mitochondria membrane depolarisation, release of cytochrome c from mit ochondria into cytosol and activation of caspase-3. Indomethacin and nordih ydroguaiaretic acid synergistically potentiated TNF-alpha -induced apoptosi s, while arachidonic acid, AACOCF3 and MK-886 did not modulate its effects. Furthermore, indomethacin potentiated apoptosis in cells treated with a di fferentiating agent, all-trans retinoic acid, which induces resistance to T NF-alpha. However, the observed effects were probably not associated either with the cyclooxygenase- or lipoxygenase-dependent activities of indometha cin and nordihydroguaiaretic acid, respectively. Since indomethacin may rep ortedly activate peroxisome proliferator-activated receptors (PPARs), the e ffects of specific ligands of PPARs on apoptosis were studied as well. It w as found that selective PPARs ligands had no effects on TNF-alpha -induced apoptosis. The findings suggest that arachidonic acid metabolism does not p lay a key role in regulation of apoptosis induced by TNF-alpha in the prese nt model. Nevertheless, our data raise the possibility that indomethacin co uld potentially be used to improve the treatment of human myeloid leukaemia . (C) 2001 Elsevier Science B.V. All rights reserved.