Abstract
Nitrated fatty acids are important anti-inflammatory and protective lipids formed in the gastric compartment, with conjugated linoleic acid (rumenic acid, RA, 9Z,11E-18:2) being the primary substrate for lipid nitration. The recently reported identification of nitrated rumelenic acid (NO(2)-RLA) in human urine has led to hypothesize that rumelenic acid (RLA, 9Z,11E,15Z-18:3) from dairy fat is responsible for the formation of NO(2)-RLA. To evaluate the source and mechanism of NO(2)-RLA formation, (15)N labeled standards of NO(2)-RLA were synthesized and characterized. Afterward, milk fat with different RA and RLA levels was administered to mice in the presence of nitrite, and the appearance of nitrated fatty acids in plasma and urine followed. We confirmed the formation of NO(2)-RLA and defined the main metabolites in plasma, urine, and tissues. In conclusion, RLA obtained from dairy products is the main substrate for forming this novel electrophilic lipid reported to be present in human urine.