In vivo metabolomic and lipidomic response of healthy humans to intravenous lipopolysaccharide challenge

Abstract

IntroductionAcute inflammation is a complex protective response to injury or infection. However, systemic hyperinflammatory states can lead to septic shock. Lipopolysaccharide (LPS) is a component of gram‐negative bacteria that is widely used for inducing inflammatory responses in animal models. However, many of the critical molecular networks involved in the LPS response in humans remain largely unknown.ObjectiveTo better characterize the molecular underpinnings of acute inflammation in humans through real‐time biochemical and network appraisals of in vivo challenge with LPS.MethodsHealthy men were intravenously injected with 0.6 ng/kg LPS at Pennsylvania State University. Plasma markers of inflammation (IL‐6, TNFα, and CRP) were measured prior to and 1, 2, 4, 8, 24, and 72 h post injection. Untargeted metabolomic and lipidomic profiling using liquid chromatography tandem mass spectrometry was conducted on the plasma from 10 men. Deuterated internal standards (SPLASH, Avanti Polar Lipids) were added to plasma to facilitate semi‐quantitative analysis of individual lipid molecular species. Statistics were performed in R (version 1.1.463) and Microsoft Excel (version 16.30).ResultsOf the 1847 metabolites reliably detected, 265 remained significant (FDR‐adjusted p < 0.05) after analysis. Of these metabolites, 197 increased, 51 decreased, and 17 both increased and decreased (depending on the point in the time course). Both metabolomics and lipidomics revealed that molecular species of lipid classes including phospholipids (PL), lyso‐PLs, sphingolipids (SL), diglycerides (DG), and triglycerides (TG) had largest number of metabolites altered after LPS challenge. Notably, levels of 50 lyso‐PLs including lyso‐phosphatidylcholine (PC) and lyso‐phosphatidylethanolamine (PE) molecular species were increased in plasma. Additionally, there were significant elevations in certain PL molecular species representing PC, PE, phosphatidylserine, and phosphatidylinositol. Levels of 29 molecular species of SL increased with the majority representing sphingomyelin and ceramide classes. Neutral lipids including DG and TG were also markedly elevated. Pathway analyses highlighted glycerophospholipid metabolism (p < 0.0001) and sphingolipid metabolism (p < 0.001) as highly significant. These data also suggest the activation of multiple lipases including phospholipase A2, phospholipase C and phospholipase D play a critical role in the inflammatory response induced by LPS.DiscussionIntravenous LPS injection profoundly alters lipid metabolism in healthy adult men. These data may facilitate the identification of biochemical lipid networks and the development of biomarkers associated with inflammatory health/disease status.Support or Funding InformationFunding source: NIH R01 AT008621