In vivo itaconate tracing reveals degradation pathway and turnover kinetics

Itaconate is an immunomodulatory metabolite that alters mitochondrial metabolism and immune cell function. This organic acid is endogenously synthesized by tricarboxylic acid (TCA) metabolism downstream of TLR signalling. Itaconate-based treatment strategies are under investigation to mitigate numerous inflammatory conditions. However, little is known about the turnover rate of itaconate in circulation, the kinetics of its degradation and the broader consequences on metabolism. By combining mass spectrometry and in vivo 13C itaconate tracing in male mice, we demonstrate that itaconate is rapidly eliminated from plasma, excreted via urine and fuels TCA cycle metabolism specifically in the liver and kidneys. Our results further reveal that itaconate is converted into acetyl-CoA, mesaconate and citramalate. Itaconate administration also influences branched-chain amino acid metabolism and succinate levels, indicating a functional impact on succinate dehydrogenase and methylmalonyl-CoA mutase activity in male rats and mice. Our findings uncover a previously unknown aspect of itaconate metabolism, highlighting its rapid catabolism in vivo that contrasts findings in cultured cells. In this study, Willenbockel et al. trace circulating itaconate in vivo to gain insight into its fate and systemic metabolism.