(c) LC-MS identification of 15-LOX induced SAPE oxidation products in cell lysates. This oxidative PE death pathway may also represent a target for drug finding. < 0.05 WT+RSL3 cells (t-test). (c) WT and Acsl4 KO cells were treated with RSL3 (100 nM) for 2, 4, and 6 hrs before cell death analysis. Data are mean s.d., n=3. *< 0.05 ACSL4 KO+RSL3 (t-test). (d) Fluorescence reactions from Mito-FAP (reddish, upper panel) and ER-FAP (reddish, lower panel) LiperFluo (green, both panels, scale bars 5 m). (e) ACSL inhibitor, Triacsin C, suppresses ferroptosis in Pfa1 cells. AA (2.5 M,16 hrs); RSL3 (100 nM, 6 hrs); Triacsin C (2.5 M, 6 hrs). Data are mean s.d., n=3. *< 0.05 control (t-test). (f) Material of AA-CoA and AdA-CoA in WT and Acsl4 KO cells. Data are mean s.d., n=3. *< 0.05 WT cells (t-test). (g) Distribution of free and esterified PUFA-OOH in WT and Acsl4 KO Pfa1 cells treated with RSL3 (100 nM, 6 hrs). Measurements of reactive HIF-2a Translation Inhibitor oxygen varieties (ROS) and pro-oxidant activity towards non-lipidic fluorogenic substrates (e.g., a lipid ROS probe, C11-BODIPY 581/591, or linoleamide alkyne click-conjugated by cyclo-addition reaction with fluorescein azide) have been utilized mainly because surrogate steps for lipid peroxidation9. While fluorescence reactions HIF-2a Translation Inhibitor from these probes showed overall activation during ferroptosis, they could not reveal the direct production of lipid hydroperoxides. Both C11-BODIPY and LiperFluo can react with peroxyl radicals whereas LiperFluo (but not C11-BODIPY) interacts with (phospho)lipid hydroperoxides10. By contrast, LiperFluo fluorescence reliably reports intracellular sites of lipid hydroperoxide build up8. GPX4 reduces hydroperoxides of polyunsaturated fatty acids (PUFA-OOH) and phospholipids (PL-OOH)7. Esterification of PUFA into phospholipids requires acyl-CoA synthase catalyzed formation of PUFA-CoA. Specifically, ACSL4 catalyzes synthesis of long-chain polyunsaturated-CoAs having a preference for AA11, therefore facilitating their esterification into phospholipids12. While genetic ablation13 or inhibition of ACSL4 by Triacsin C were both effective in protecting against RSL3 induced cell death (Fig. 1e) we found out more robust LiperFluo fluorescence response from Acsl4 KO cells compared to WT cells (Fig. 1a, b). Because Acsl4 KO cells have decreased levels of polyunsaturated-acyl-CoAs (Fig. 1f), they likely accumulate free PUFA-OOH (rather than esterified PL-OOH) causing elevated LiperFluo fluorescence emission. To test this, we performed LC-MS/MS analysis of free PUFA-OOH and PL-OOH in WT Acsl4 KO cells. This was achieved by the use of platelet-activating element acetylhydrolase (PAF-AH), an enzyme specifically cleaving the oxidized PUFA residues from phospholipids14 to yield FA-OOH and lyso-phospholipids. Indeed, in Acsl4 KO cells, RSL3 induced mainly accumulation of free oxygenated PUFA (Fig. 1g) - in contrast to higher levels of esterified oxygenated AA and adrenic acid (AdA, C22:4) in WT cells (Fig. 1g). Assessments of the reaction rate constants for AA-OOH and purified PE-OOH with LiperFluo in ethanol showed that its reactivity towards free PUFA-OOH was slightly higher than with PL-OOH with the reaction rate constants of 1 1.60.1103M?1s?1 15 and 1.20.1103M?1s?1, respectively. Therefore higher material of free PUFA-OOH and their higher reactivity toward LiperFluo HIF-2a Translation Inhibitor both contributed to the strong fluorescence response to LiperFluo in Ascl4 KO cells. AA enhances ferroptotic response in RSL3-treated cells Suggesting that esterified oxygenated PUFA, act as the proximate executioners of ferroptotic death, we supplemented WT Rabbit Polyclonal to FCGR2A and Acsl4 KO cells with exogenous AA. This resulted in a 24% increase of ferroptosis in RSL3-treated WT cells and only a 13% increase of death in Acsl4 KO cells (Fig. 2a). Accordingly, LC-MS/MS analysis (after PAF-AH treatment) shown higher build up of esterified oxygenated AA in phospholipids of WT vs Acsl4 KO cells following RSL3 treatment (Fig. 1g). Additionally, we observed that supplementation with AA induced elongation activity resulting in the increased content material of AdA and its oxygenated forms (Fig. 2b, c). The amounts of oxygenated esterified AA and AdA were reduced RSL3-treated Acsl4 KO cells than in RSL3-treated WT cells (72.227.0 and 28.28.0 compared to 199.326.2 and 137.877.7 pmol/mol phospholipids, respectively, < 0.05 control, RSL3 (or Acsl4.