Characterization and inhibition of 15-lipoxygenase in human monocytes: Comparison with soybean 15-lipoxygenase

These studies characterize a method to measure 15-lipoxygenase (15-LO) activity in human monocytes (HMC) exposed to interleukin-4 (IL-4) and compare the activity with that of soybean 15-LO. 15-LO activity was quantitated by measuring 15-[¹⁴C]hydroxyeicosa-5Z,8Z,11Z,13E-tetraenoic acid (15-HETE) production from the substrate [¹⁴C]arachidonic acid (AA) after high- performance liquid chromatographic or thin-layer chromatographic separation. 15-HETE production by HMC was significantly elevated after continuous exposure to a single dose (10 ng/ml) of IL-4 for 4 days, was maximal at 5 days, and remained elevated at 6 days. At 6 days 15-LO activity in IL-4- treated HMC was increased significantly (2.81 ± 0.70 fmol 15-HETE/cell) compared with background levels of 15-HETE in untreated HMC (0.098 ± 0.31 fmol 15-HETE/cell). 15-HETE production was linear in the range of 5 x 10⁴ to 7 x 10⁵ HMC/assay, from 2 to 160 μM AA, and during 5-10 min of incubation with AA. Ethyl 2-cyano-3-(3',4'-dihydroxyphenyl)propenoate (a caffeic acid analogue), N-methyl-4-benzyloxyphenyl acetohydroxamate (RG-6866), esculetin, and four novel lipoxygenase inhibitors, a phenylcyanomethylene analogue (RP- 27493) and three benzoxadiazine analogues (RP-64835, RP-65047, and RP- 65208), inhibited HMC 15-LO, with concentrations eliciting 50% of maximal inhibition (μM) of 0.21, 0.8, 6.3, 10, 22, 20, 6.3, 3, and 20 and 5.8, 5, 12, 1, 30, 0.8, 0.15, 0.05, and 2.8 for inhibition of soybean 15-LO, respectively. These data define conditions for optimal production of 15-HETE by IL-4-treated HMC. Known and novel lipoxygenase inhibitors inhibit IL-4- treated HMC 15-LO and soybean 15-LO, suggesting that IL-4-treated HMC provide an appropriate system to study human 15-LO activity.