Combined NMR and GC-MS analyses revealed dynamic metabolic changes associated with the carrageenan-induced rat pleurisy

Inflammation is closely associated with pathogenesis of various metabolic disorders, cardiovascular diseases, and cancers. To understand the systems responses to localized inflammation, we analyzed the dynamic metabolic changes in rat plasma and urine associated with the carrageenan-induced self-limiting pleurisy using NMR spectroscopy in conjunction with multivariate data analysis. Fatty acids in plasma were also analyzed using GC-FID/MS with the data from clinical chemistry and histopathology as complementary information. We found that in the acute phase of inflammation rats with pleurisy had significantly lower levels in serum albumin, fatty acids, and lipoproteins but higher globulin level and larger quantity of pleural exudate than controls. The carrageenan-induced inflammation was accompanied by significant metabolic alterations involving TCA cycle, glycolysis, biosyntheses of acute phase proteins, and metabolisms of amino acids, fatty acids, ketone bodies, and choline in acute phase. The resolution process of pleurisy was heterogeneous, and two subgroups were observed for the inflammatory rats at day-6 post treatment with different metabolic features together with the quantity of pleural exudate and weights of thymus and spleen. The metabolic differences between these subgroups were reflected in the levels of albumin and acute-phase proteins, the degree of returning to normality for multiple metabolic pathways including glycolysis, TCA cycle, gut microbiota functions, and metabolisms of lipids, choline and vitamin B₃. These findings provided some essential details for the dynamic metabolic changes associated with the carrageenan-induced self-limiting inflammation and demonstrated the combined NMR and GC-FID/MS analysis as a powerful approach for understanding biochemical aspects of inflammation.