Lipid IVA inhibits synthesis and release of tumor necrosis factor induced by lipopolysaccharide in human whole blood ex vivo.

Summary Tumor necrosis factor(TNF) released bylipopolysaccharide (LPS)-stimulated mononuclearphagocytesisa critical mediatorofsepsis .We examinedthecapacities ofrough mutant Salmonella typhimurium LPS (Rc)andLPS partialstructures lipidA, monophosphoryl lipidA (MPLA), lipidIVY,andlipidX toinduceproductionofTNF inwholeblood.Rc LPS (0.0001-10ng/ml) producedadose-dependent release ofTNF asdeterminedbycytotoxicity ofactinomycin D-sensitized L929 murinefibroblasts .LipidA, MPLA, lipidIVe,andlipidX exhibiteddecreasing capacities tostimulateproductionofTNF inwhole blood,respectively .Fractional dearylation ofLPS by incubationwithacyloxyacyl hydrolaseisolated from human leukocytesproducedareductionin thecapacityofLPS toinduceTNF release inwholeblood.Maximalenzymaticdearylation reduced activityofLPS by >100-fold. Coincubationwith lipidIVY inhibitedTNF releaseinducedby Rc LPS orlipidA, butnot byphorbolester .Incontrast, MPLA, lipidX,anddeacylated LPS failed toinhibitLPS-stimulated releaseofTNF .Correspondingtotheinhibition ofthereleaseofTNF protein,lipidIVn also inhibitedtheaccumulationofTNF mRNA inLPS-stimulatedmononuclearcells .Theseresults suggestthatlipidIVY may actasacompetitiveantagonistofLPS,perhapsatthereceptorlevel . G ram-negative bacterial infection inducesacomplexarray ofinflammatoryresponsesincludingfever, leuocytosis, and activation ofthecoagulation,complement,and kinin systems.Thesemanifestations ofGram-negativeinfection are primarily inducedby heat-stable endotminsreleased fromthe outermembrane ofGram-negativebacteria .LPS aretheprincipalbiologically activecomponent ofendotoxinsthathave acommon macromoleculararchitecture .Threemajordomains compriseLPS structure :an0-antigensidechaincomposed of repeatingoligosaccharides, a corepolysaccharide, and lipidA. Chemicaldegradationstudiesandbacterial mutantswith defective synthesisofLPS haveprovidedinsightsintobiosynthesis andstructure-function relationships ofLPS andits components.LipidA isthesmallestsubstructure ofLPS exhibitingallbiological activities (1).LipidA from common pathogensexhibitthesame generalfeatures, a0-1,6D-glucosaminedisaccharide backbone,withfourmoleequivalents of3-hydroxymyristate or3-hydroxylaurate inamideandester linkage,and two monophosphate groupsat1 and 4: Aryl residuesarelocatedatthe2,2,3,and3'positionson the disaccharides, and theR-3 hydroxylsubstitutes ofthearyl