Comparative evaluation of itaconate and its derivatives reveals divergent inflammasome and type I interferon regulation in macrophages

Following activation, macrophages undergo extensive metabolic rewiring(1,)(2). Production of itaconate through the inducible enzyme IRG1 is a key hallmark of this process(3). Itaconate inhibits succinate dehydrogenase(4,5), has electrophilic properties(6) and is associated with a change in cytokine production(4). Here, we compare the metabolic, electrophilic and immunologic profiles of macrophages treated with unmodified itaconate and a panel of commonly used itaconate derivatives to examine its role. Using wild-type and Irg1(-/-) macrophages, we show that neither dimethyl itaconate, 4-octyl itaconate nor 4-monoethyl itaconate are converted to intracellular itaconate,while exogenous itaconic acid readily enters macrophages. We find that only dimethyl itaconate and 4-octyl itaconate induce a strong electrophilic stress response, in contrast to itaconate and 4-monoethyl itaconate. This correlates with their immunosuppressive phenotype: dimethyl itaconate and 4-octyl itaconate inhibited I kappa B zeta and pro-interleukin (IL)-1 beta induction, as well as IL-6, IL-10 and interferon-beta secretion, in an NRF2-independent manner. In contrast, itaconate treatment suppressed IL-1 beta secretion but not pro-IL-1 beta levels and, surprisingly, strongly enhanced lipopolysaccharide-induced interferon-beta secretion. Consistently, Irg1(-/-) macrophages produced lower levels of interferon and reduced transcriptional activation of this pathway. Our work establishes itaconate as an immunoregulatory, rather than strictly immunosuppressive, metabolite and highlights the importance of using unmodified itaconate in future studies.