Defining mechanisms of toxicity for linoleic acid monoepoxides and diols in Sf-21 cells

Linoleic acid monoepoxides have been correlated with many pathological cond itions. Studies using insect cells derived from Spodoptera frugiperda (Sf-2 1 cells) have suggested that conversion of the epoxides to the diols is req uired for toxicity. However, more recent studies using rabbit renal proxima l tubules have suggested that linoleic acid monoepoxides are direct mitocho ndrial toxins. To better understand these discrepancies, we compared the to xicity of these linoleic acid metabolites in Sf-21 cells using mitochondria l respiration as an end point. Linoleic acid (100 muM) and 12,13-epoxy-9-oc tadecenoic acid (12,13-EOA, 100 muM) increased the rate of oligomycin-insen sitive respiration by approximately 3.5- and 3-fold, respectively, decrease d the rate of oligomycin-sensitive respiration by approximately 52 and 68%, respectively, and had no effect on the integrity of the electron transport chain. These effects were concentration-dependent, occurred within 1 min, and recovered to basal levels within 45 min. 12,13-Dihydroxy-9-octadecenoic acid (12,13-DHOA, 100 muM) had no effect on oligomycin-insensitive respira tion but decreased the rate of oligomycin-sensitive respiration and uncoupl ed respiration in a concentration-dependent manner. Approximately 79 and 68 % of oligomycin sensitive respiration and uncoupled respiration was inhibit ed by 12,13-DHOA (100 muM), respectively. These effects occurred within 1 m in and were not reversible in 6 h. Effects similar to those induced by 12,1 3-DHOA (100 muM) were observed using 12,13-EGA (100 muM) in Sf-21 cells exp ressing human soluble epoxide hydrolase. These data suggest that in this Sf -21 model linoleic acid and linoleic monoepoxides have transient uncoupling effects, whereas the primary mechanism of toxicity for linoleic acid diols in this model is inhibition of the electron transport chain.