Long-chain fatty acid (LCFA) oxidation has been shown to play an important role in interleukin-4 (IL-4)-mediated macrophage polarization (M(IL-4)). However, many of these conclusions are based on the inhibition of carnitine palmitoyltransferase-1 with high concentrations of etomoxir that far exceed what is required to inhibit enzyme activity (EC < 3 μM). We employ genetic and pharmacologic models to demonstrate that LCFA oxidation is largely dispensable for IL-4-driven polarization. Unexpectedly, high concentrations of etomoxir retained the ability to disrupt M(IL-4) polarization in the absence of Cpt1a or Cpt2 expression. Although excess etomoxir inhibits the adenine nucleotide translocase, oxidative phosphorylation is surprisingly dispensable for M(IL-4). Instead, the block in polarization was traced to depletion of intracellular free coenzyme A (CoA), likely resulting from conversion of the pro-drug etomoxir into active etomoxiryl CoA. These studies help explain the effect(s) of excess etomoxir on immune cells and reveal an unappreciated role for CoA metabolism in macrophage polarization.

Current perspective holds that the generation of secondary signaling mediators from nitrite (NO2−) requires acidification to nitrous acid (HNO2) or metal catalysis. Herein, the use of stable isotope-labeled NO2− and LC-MS/MS analysis of products revealed that NO2− also participates in fatty acid nitration and thiol S-nitrosation at neutral pH. These reactions occur in the absence of metal centers and are stimulated by nitric oxide (•NO) autoxidation via symmetrical dinitrogen trioxide (nitrous anhydride, symN2O3) formation. While theoretical models have predicted physiological symN2O3 formation, its generation is now demonstrated in aqueous reaction systems, cell models and in viv, with the concerted reactions of •NO and NO2− shown to be critical for symN2O3 formation. These results reveal new mechanisms underlying the NO2− propagation of •NO signaling and the regulation of both biomolecule function and signaling network activity via NO2−-dependent nitrosation and nitration reactions.

Conjugated linoleic acid (CLA) is a prime substrate for intra-gastric nitration giving rise to the formation of nitro-conjugated linoleic acid (NO2-CLA). Herein, NO2-CLA generation is demonstrated within the context of acute inflammatory responses both in vitro and in vivo. Macrophage activation resulted in dose- and time-dependent CLA nitration and also in the production of secondary electrophilic and non-electrophilic derivatives. Both exogenous NO2-CLA as well as that generated in situ, attenuated NF-κB-dependent gene expression, decreased pro-inflammatory cytokine production and up-regulated Nrf2-regulated proteins. Importantly, both CLA nitration and the corresponding downstream anti-inflammatory actions of NO2-CLA were recapitulated in a mouse peritonitis model where NO2-CLA administration decreased pro-inflammatory cytokines and inhibited leukocyte recruitment. Taken together, our results demonstrate that the formation of NO2-CLA has the potential to function as an adaptive response capable of not only modulating inflammation amplitude but also protecting neighboring tissues via the expression of Nrf2-dependent genes.