Itaconate Serves as a Urinary Biomarker and an Inhibitor of Chronic Kidney Inflammation

Background: Inflammation plays a pivotal role in the pathogenesis of chronic kidney diseases (CKD), serving as a predominant pathological alteration and a key driving force. The identification of a noninvasive biomarker for renal inflammation holds significant implications for elevating the progression of CKD. Notably, the correlation between phenotypes and metabolite levels surpasses that observed for proteins and genes, highlighting the growing attention towards exploring metabolites as biomarkers for human diseases. Therefore, this study aims to investigate noninvasive metabolic biomarkers of renal inflammation. Methods: Metabonomics analysis was used to identify key differential metabolites in urine samples from CKD patients and healthy individuals. The correlation between urinary itaconate levels measured by LC-MS/MS and renal inflammation was investigated. Furthermore, the mechanism underlying the upregulation of itaconate was explored using single-cell sequencing, Western Blot, qRT-PCR, and ChIP assays. To explore the role of itaconate in the progression of CKD, IRG1 global knockout mice and macrophage specific IRG1 deletion mice were generated, and were subjected to bilateral ischemia reperfusion (bIRI) surgery. Results: Through metabonomics and LC-MS/MS analysis, we found that urinary itaconate was elevated in patients and mice with CKD, and positively correlated to renal inflammation and the decline of renal function. Mechanistically, the IL-1β signaling pathway activates the transcription factor AP-1, thereby upregulating the expression of IRG1, which encodes the enzyme responsible for catalyzing itaconate production through direct binding to its promoter in macrophages. Furthermore, renal cytokines and alternative M2 macrophages accumulation, as well as the development of renal fibrosis induced by bIRI were aggravated by global Irg1 knockout and macrophage specific Irg1 knockout. Conclusion: Our findings not only provide a noninvasive biomarker of chronic renal inflammation but also elucidate the role and mechanism of itaconate in CKD. Funding: Government Support – Non-U.S.