NPPA and multiple sclerosis: In a recent multinational cross-sectional study including 353 persons with multiple sclerosis and 111 healthy controls, targeted LC-MS/MS profiling of serum KP metabolites followed by exploratory factor analysis revealed two distinct KP metabolite patterns, an inflammation-driven neurotoxic profile (NeuroTox), characterized by higher neopterin, KYN/Trp ratio, 3-HK, QA and an increased QA/KA ratio, and a neuroprotective profile (NeuroPro), characterized by higher KYNA, quinaldic acid, XA and picolinic acid together with an inverse loading of the QA/KA ratio.