The outer monolayer of the outer membrane of Gram-negative bacteria consists of the lipid A component of lipopolysaccharide (LPS), a glucosamine-based saccharolipid that is assembled on the inner surface of the inner membrane. The first six enzymes of the lipid A pathway are required for bacterial growth and are excellent targets for the development of new antibiotics. Following assembly, the ABC transporter MsbA flips nascent LPS to the periplasmic side of the inner membrane, whereupon additional transport proteins direct it to the outer surface of the outer membrane. Depending on the bacterium, various covalent modifications of the lipid A moiety may occur during the transit of LPS to the outer membrane. These extra-cytoplasmic modification enzymes are therefore useful as reporters for monitoring LPS trafficking. Because of its conserved structure in diverse Gram-negative pathogens, lipid A is recognized as foreign by the TLR4/MD2 receptor of the mammalian innate immune system, resulting in rapid macrophage activation and robust cytokine production

Despite improvement in clinical management, allogeneic hematopoietic stem cell transplantation (HSCT) is still hampered by high morbidity and mortality rates, mainly due to graft versus host disease (GvHD). Recently, it has been demonstrated that the allogeneic immune response might be influenced by external factors such as tissues microenvironment or host microbiota. Here we used high throughput metabolomics to analyze two cohorts of genotypically HLA-identical related recipient and donor pairs. Metabolomic profiles markedly differ between recipients and donors. At the onset of acute GvHD, in addition to host-derived metabolites, we identify significant variation in microbiota-derived metabolites, especially in aryl hydrocarbon receptor (AhR) ligands, bile acids and plasmalogens. Altogether, our findings support that the allogeneic immune response during acute GvHD might be influenced by bile acids and by the decreased production of AhR ligands by microbiota that could limit indoleamine 2,3-dioxygenase induction and influence allogeneic T cell reactivity.

Context:The experimental paradigm of acute caloric restriction (CR) followed by refeeding (RF) can be used to study the homeostatic mechanisms that regulate energy homeostasis, which are relevant to understanding the adaptive response to weight loss.Objective:Metabolomics, the measurement of hundreds of small molecule metabolites, their precursors, derivatives, and degradation products, has emerged as a useful tool for the study of physiology and disease and was used here to study the metabolic response to acute CR.Participants, Design, and Setting:We used four ultra high-performance liquid chromatography-tandem mass spectrometry methods to characterize changes in carbohydrates, lipids, amino acids, and steroids in eight normal weight men at baseline, after 48 hours of CR (10% of energy requirements) and after 48 hours of ad libitum RF in a tightly controlled environment.Results:We identified a distinct metabolomic signature associated with acute CR characterized by the expected switch from carbohydrate to fat utilization with increased lipolysis and β-fatty acid oxidation. We found an increase in ω-fatty acid oxidation and levels of endocannabinoids, which are known to promote food intake. These changes were reversed with RF. Several plasmalogen phosphatidylethanolamines (endogenous antioxidants) significantly decreased with CR (all P ≤ 0.0007). Additionally, acute CR was associated with an increase in the branched chain amino acids (all P ≤ 1.4 × 10−7) and dehydroepiandrosterone sulfate (P = 0.0006).Conclusions:We identified a distinct metabolomic signature associated with acute CR. Further studies are needed to characterize the mechanisms that mediate these changes and their potential contribution to the adaptive response to dietary restriction.

Metabolism directs the severe acute inflammatory reaction of monocytes to guard homeostasis. This occurs by sequentially activating anabolic immune effector mechanisms, switching to immune deactivation mechanisms and then restoring immunometabolic homeostasis. Nuclear sirtuin 1 and mitochondrial pyruvate dehydrogenase kinase metabolically drive this dynamic and are druggable targets that promote immunometabolic resolution in septic mice and increase survival. We used unbiased metabolomics and a validated monocyte culture model of activation, deactivation, and partial resolution of acute inflammation to sequentially track metabolic rewiring. Increases in glycogenolysis, hexosamine, glycolysis, and pentose phosphate pathways were aligned with anabolic activation. Activation transitioned to combined lipid, protein, amino acid, and nucleotide catabolism during deactivation, and partially subsided during early resolution. Lipid metabolic rewiring signatures aligned with deactivation included elevated n-3 and n-6 polyunsaturated fatty acids and increased levels of fatty acid acylcarnitines. Increased methionine to homocysteine cycling increased levels of s-adenosylmethionine rate-limiting transmethylation mediator, and homocysteine and cysteine transsulfuration preceded increases in glutathione. Increased tryptophan catabolism led to elevated kynurenine and de novo biosynthesis of nicotinamide adenine dinucleotide from quinolinic acid. Increased branched-chain amino acid catabolism paralleled increases in succinyl-CoA. A rise in the Krebs cycle cis-aconitate-derived itaconate and succinate with decreased fumarate and acetyl-CoA levels occurred concomitant with deactivation and subsided during early resolution. The data suggest that rewiring of metabolic and mitochondrial bioenergetics by monocytes sequentially activates, deactivates, and resolves acute inflammation. K E Y W O R D Sanabolism,