Systemic lupus erythematosus (SLE) is a multi-system autoimmune disease primarily affecting young to middle-aged women. Lupus nephritis (LN) may arise from the formation and deposition of immune complexes within the glomeruli of the kidneys. LN is a major cause of morbidity and mortality in SLE. A kidney biopsy which is an invasive procedure is currently the gold standard to confirm the diagnosis of LN and to establish histopathologic patterns as a guide for therapy. Undergoing a series of biopsies for monitoring disease progression and treatments is unlikely suitable for patients with LN. Thus, there is an urgent need for non-invasive alternative biomarkers that can facilitate LN class diagnosis. Such biomarkers will be very useful in guiding intervention strategies to mitigate or treat patients with LN. Urine samples were collected from two independent cohorts. Patients with LN were classified into proliferative (class III/IV) and membranous (class V) by kidney histopathology. Metabolomics was performed to identify potential metabolites, which could be specific for the classification of membranous LN. The ratio of picolinic acid (Pic) to tryptophan (Trp) ([Pic/Trp] ratio) was found to be a promising candidate for LN diagnostic and membranous classification. It has high potential as an alternative biomarker for the non-invasive diagnosis of LN

Krittima Anekthanakul, Siriphan Manocheewa, Kittiphan Chienwichai, Patcha Poungsombat, Suphitcha Limjiasahapong, Kwanjeera Wanichthanarak, Narumol Jariyasopit, Vivek Bhakta Mathema, Chutima Kuhakarn, Vichai Reutrakul, Jutarop Phetcharaburanin, Atikorn Panya, Natthaporn Phonsatta, Wonnop Visessanguan, Yotsawat Pomyen, Yongyut Sirivatanauksorn, Suchin Worawichawong, Nuankanya Sathirapongsasuti, Chagriya Kitiyakara, Sakda Khoomrung. “Predicting lupus membranous nephritis using reduced picolinic acid to tryptophan ratio as a urinary biomarker” iScience 2022, 24(11), 103355.