Enzymatic deacylation of the lipid A moiety of Salmonella typhimurium lipopolysaccharides by human neutrophils

Regulation of amyloid A gene expression in cultured cells

Serum amyloid A (SAA) proteins are secreted by mammalian liver in response to inflammatory stimuli. Both transcriptional and posttranscriptional mechanisms have been shown to regulate the 2,000-fold increase in SAA mRNA after injection of endotoxin into mice. We report here the characterization of a cell line derived from mouse liver (BNL) in which the expression of SAA3 mRNA is regulated. In this model, SAA3 mRNA accumulated in response to conditioned medium from the mouse macrophage P388D1 cell line with kinetics similar to that seen in mouse liver (C. A. Lowell, R. S. Stearman, and J. F. Morrow, J. Biol. Chem. 261:8453-8461, 1986). In in vitro nuclear transcription assays, the SAA3 gene was transcribed equally in induced and uninduced cells. In addition, in steady-state RNA studies treatment with conditioned medium allowed the cells to rapidly accumulate SAA3 mRNA without an apparent change in half-life. These observations suggest that conditioned medium contains a factor(s) that acts directly on hepatocytes to regulate SAA3 mRNA processing.

Lipopolysaccharide priming of human neutrophils for an enhanced respiratory burst. Role of intracellular free calcium

Lipopolysaccharide (LPS) pretreatment "primes" neutrophils to release increased amounts of superoxide anion (O2-) when stimulated. We investigated the molecular basis of this enhanced activity. Comparison of kinetic parameters of the respiratory burst NADPH oxidase in unstimulated LPS-primed and control neutrophils disclosed a similar Km for NADPH and no difference was seen in the content of cytochrome b. Pertussis toxin, which inhibits some G proteins, did not prevent priming. Change in membrane potential (delta psi) was five-fold greater in LPS-primed cells and paralleled the increased O2- release. Cytofluorographic analysis indicated that the increased change in delta psi was due to the creation of a new population of active cells. Changes in the concentration of intracellular free Ca2+ ([Ca2+]i) are believed to antecede changes in delta psi. There was a consistent increment (67 +/- 8%, n = 12) in resting [Ca2+]i in cells preincubated with LPS compared with control. When stimulated, the peak [Ca2+]i was significantly higher in LPS-primed cells. Ca2+-dependent protein kinase C activity was unaltered in resting and FMLP-stimulated neutrophils preexposed to LPS. Addition to cells of the intracellular Ca2+ chelator MAPTAM before preincubation with LPS blocked the changes in [Ca2+]i and the enhanced respiratory burst that characterize LPS priming. The increased resting [Ca2+]i in LPS-primed cells may enhance stimulus-induced cellular activity by modifying a Ca2+-dependent step in signal transduction.

Structural requirements of lipid A for endotoxicity and other biological activities

For the past ten years, several groups were engaged in synthetic studies of lipid A, namely the lipid portion of bacterial lipopolysaccharides (LPS) that has been assumed to be the bioactive center of LPS, but has not been unanimously approved. Among them, Shiba, Kusumoto, and colleagues, Osaka, Japan have synthesized most energetically and successfully a variety of counterparts of lipid As, biosynthetic lipid A precursors, and their analogs. The endotoxic and related bioactivities of these synthetic compounds were studied by Japanese and German groups, including ours. In 1985, one of the compounds, having an acylation and phosphorylation pattern in beta(1-6)-D-glucosamine disaccharide which was proposed for Escherichia coli F515 lipid A was found to be exhibit full endotoxic and related bioactivities identical to those of the bacterial product. The study was extended by synthesis and examination of bioactivities of variously acylated D-glucosamine di- and monosaccharide phosphates, which correspond to structural components of lipid As, and their analogs or derivatives. Thus, structural requirements have been fairly well elucidated. In this article, first we will review the progress of synthetic and biological studies, with particular emphasis on chemical structure--bioactivities relationships of lipid As, and then we will discuss possible usefulness of some less or nontoxic lipid A-related synthetic compounds in clinical and preventive medicine.

Regulation of amyloid A gene expression in cultured cells

Serum amyloid A (SAA) proteins are secreted by mammalian liver in response to inflammatory stimuli. Both transcriptional and posttranscriptional mechanisms have been shown to regulate the 2,000-fold increase in SAA mRNA after injection of endotoxin into mice. We report here the characterization of a cell line derived from mouse liver (BNL) in which the expression of SAA3 mRNA is regulated. In this model, SAA3 mRNA accumulated in response to conditioned medium from the mouse macrophage P388D1 cell line with kinetics similar to that seen in mouse liver (C. A. Lowell, R. S. Stearman, and J. F. Morrow, J. Biol. Chem. 261:8453-8461, 1986). In in vitro nuclear transcription assays, the SAA3 gene was transcribed equally in induced and uninduced cells. In addition, in steady-state RNA studies treatment with conditioned medium allowed the cells to rapidly accumulate SAA3 mRNA without an apparent change in half-life. These observations suggest that conditioned medium contains a factor(s) that acts directly on hepatocytes to regulate SAA3 mRNA processing.

Modulation of granulocyte functions by bacterial exotoxin and endotoxins

The modulation of granulocyte functions by bacterial exotoxins (Streptolysin O, alveolysin, theta toxin) and endotoxins from salmonella and lipid A is described here. Incubation of polymorphonuclear granulocytes with thiol-activated toxins resulted in an increased leukotriene generation. Toxin-pretreated PMNs revealed an increased omega oxidation of LTB4, which may explain why toxin-stimulated cells release more LTC4 than LTB4. Furthermore, toxin-pretreated PMNs showed a decreased leukotriene generation on subsequent stimulation with the Ca-ionophore A 23187 or opsonized zymosan.

The immunogenicity and antigenicity of lipid A are influenced by its physicochemical state and environment

We investigated the immunogenicity and antigenicity of synthetic lipid A and partial structures thereof. Included in the study were compounds which varied in the position of phosphate (1-mono-, 4'-mono-, and 1,4'-bisphosphates) and in the acylation (type, number, and distribution of fatty acids) and, in the case of monosaccharide compounds, the nature of the backbone sugar (D-glucosamine, D-glucose, 3-amino-3-deoxy-D-glucose, and 2,3-diamino-2,3-dideoxy-D-glucose). With the aid of the passive-hemolysis and passive-hemolysis-inhibition assays and by absorption experiments, five distinct antibody specificities were detected in polyclonal rabbit antisera raised against sheep erythrocyte-coated lipid A and lipid A incorporated into the membrane of liposomes (liposome-incorporated immunogens). Three antibody specificities reacted with disaccharide antigens specific for a 1-mono-, 4'-mono-, and 1,4'-bisphosphorylated beta-1,6-linked D-glucosamine disaccharide. Two antibodies reacted with either 1- or 4-phosphates of acylated D-gluco-configured monosaccharides and exhibited no cross-reaction with each other. However, they cross-reacted with disaccharide antigens with phosphate groups in the appropriate positions. We found that the physicochemical state and the environment of lipid A modulated its immunoreactivity. The immunogenicity was best expressed by erythrocyte-coated and liposome-incorporated immunogens. The antigenicity of lipid A was also greatly influenced by its physical surroundings. The reaction pattern of the above antibodies was highly specific in the hemolysis assay and in absorption experiments (the antibody reacted with antigen embedded in a cell membrane), whereas some cross-reactivities were observed in inhibition studies (the antibody reacts with antigen in aqueous solution). By using liposome-incorporated antigens as inhibitors, nonspecific reactions were avoided and specific ones were enhanced. Thus the antibodies described above against lipid A recognize epitopes in the hydrophilic backbone, the exposure of which depends on the intrinsic physicochemical properties of lipid A on the one hand and the physical environment on the other.

Human monoclonal antibodies that recognize conserved epitopes in the core-lipid A region of lipopolysaccharides

Epstein-Barr virus (EBV)-transformed human B lymphocytes were fused with a murine-human heteromyeloma to produce stable hybrid cell lines that secreted human monoclonal antibodies (mAbs) of the IgM class that recognized conserved epitopes in the core-lipid A region of lipopolysaccharides (LPS). Three of the mAbs reacted with epitopes on the lipid A moiety, while a fourth recognized a determinant in the core oligosaccharide. The lipid A-specific mAbs cross-reacted with heterologous rough LPS and with lipid As released by acid hydrolysis of different intact (smooth) LPS. Carbohydrate groups in the O-side chain and core oligosaccharide of isolated, smooth LPS restricted antibody access to antigenic sites on lipid A. Yet, one lipid A-reactive mAb recognized its epitope on the surfaces of a variety of intact bacteria. These findings confirm the presence of highly conserved epitopes in the core-lipid A complex and prove the existence of human B cell clones with the potential for secreting high avidity IgM antibodies that react with these widely shared determinants. Such human mAbs might provide protective activity against disease caused by diverse gram-negative bacteria.

Deacylated lipopolysaccharide inhibits neutrophil adherence to endothelium induced by lipopolysaccharide in vitro

Selective deacylation of the nonhydroxylated fatty acids from S. typhimurium LPS by an acyloxyacyl hydrolase isolated from leukocytes reduces toxic activity of LPS in vivo. We examined the effect of deacylated LPS on neutrophil adherence to human umbilical vein endothelial cells (HUVE). Pretreatment of HUVE with LPS (13 ng/ml for 4 h) produced a marked increase in the adherence of subsequently added neutrophils. In contrast, there was no increase in the adherence of neutrophils to HUVE pretreated with deacylated LPS (up to 260 ng/ml for 4 h). Neutrophil adherence to HUVE pretreated with LPS decreased as the degree of LPS deacylation increased. Deacylated LPS was not only itself inactive, but it inhibited neutrophil-endothelial interactions induced by LPS. Neutrophil adherence to HUVE pretreated with LPS was inhibited by deacylated LPS in a dose-dependent manner. Complete inhibition of adherence was observed at a 20:1 ratio (wt/wt) of deacylated LPS to LPS. Significantly, inhibition of neutrophil adherence to HUVE pretreated with LPS was observed even when deacylated LPS was added to HUVE up to 60 min after LPS. Deacylated LPS, however, did not inhibit neutrophil adherence induced by pretreatment of HUVE with IL-1 or TNF-alpha. We conclude that enzymatic deacylation of the nonhydroxylated fatty acids of LPS abolishes the ability of LPS to induce surface expression of a neutrophil adherence promoting activity in HUVE. Furthermore, deacylated LPS inhibits neutrophil adherence to HUVE induced by LPS, perhaps by preventing the interaction of LPS with a specific cell-surface or intracellular target.

Dephosphorylation of the lipid A moiety of Escherichia coli lipopolysaccharide by mouse macrophages

An Escherichia coli deep rough lipopolysaccharide (LPS), biosynthetically labeled with 32PO4 and [3H]glucosamine, was used to study dephosphorylation of the lipid A moiety by murine macrophages. Over a 48-h incubation period, the macrophages removed approximately two-thirds of the 32P from [3H32P]LPS that was added to the culture medium. The LPS-derived phosphate was incorporated into cell components (e.g., phospholipids), as well as released from the cells. Cell lysates were also able to remove phosphate from [3H32P]LPS. The phosphatase activity was optimal at acidic pH and was greatly reduced by 10 mM sodium fluoride or heating at 80 degrees C. There was no evident difference in the LPS-dephosphorylating ability of macrophages from LPS-responsive and -hyporesponsive mice. The results indicate that murine macrophages dephosphorylate the lipid A moiety of deep rough E. coli LPS and raise the possibility that enzymatic dephosphorylation may modify LPS bioactivity.

Antibody- and complement-dependent cell injury assayed by 51Cr release from human peripheral blood mononuclear cells pretreated with lipopolysaccharide

Exposure of human peripheral blood mononuclear (MN) cells to deesterified (alkali-treated) lipopolysaccharide (LPS-OH) and then to 51Cr rendered the cells susceptible to 51Cr release in the presence of specific antibody and complement. The assay was optimized by using rough (Rb2 or Re) LPS. 51Cr release did not occur from cells preexposed to untreated or electrodialyzed LPS. Studies of isolated monocytes and lymphocytes revealed that the majority of the 51Cr released was derived from monocytes. The optimum concentration of LPS-OH was 10 micrograms/ml. Antiyersinia agglutinin-positive serum, but not a negative serum, obtained from patients with reactive yersinia arthritis caused 51Cr release from MN cells pretreated with yersinia LPS-OH. This implies that during yersinia infection antibodies are generated that can attack the cell membrane--LPS-OH complex. We conclude that the method provides a tool to demonstrate binding of LPS to MN cells in a manner that leads to cell injury in an immune host.

Detoxification of bacterial lipopolysaccharides (endotoxins) by a human neutrophil enzyme

Lipopolysaccharides in the cell walls of Gram-negative bacteria elicit toxic as well as potentially beneficial inflammatory responses in animals. It is now reported that tissue toxicity caused by lipopolysaccharides is preferentially reduced by an enzymatic activity in human neutrophils. Acyloxyacyl hydrolysis removes fatty acyl chains that are linked to the hydroxyl groups of 3-hydroxytetradecanoyl residues in the bioactive lipid A moiety of the lipopolysaccharides. Maximal acyloxyacyl hydrolysis reduced lipopolysaccharide tissue toxicity, as measured in the dermal Shwartzman reaction, by a factor of 100 or more. In contrast, the ability of the deacylated lipopolysaccharides to stimulate B lymphocytes to divide was decreased only by a factor of 12. It is suggested that during tissue invasion by Gram-negative bacteria acyloxyacyl hydrolysis may be a defense mechanism that reduces the toxicity of lipopolysaccharides while preserving some of their potentially beneficial inflammatory and immune stimuli.

In vitro deacylation of lipopolysaccharide of Salmonella minnesota by Acanthamoeba castellanii enzymes

Enzymatic deacylation of the lipopolysaccharide isolated from a Salmonella Rd mutant by a cell-free preparation from Acanthamoeba castellanii has been studied. The degradation was found to be dependent on the presence of a surface-active component (Triton X-100) in the reaction mixture. The lipid A part of the lipopolysaccharide was the primary target of the enzymes, which cleaved with high efficiency the ester-bound long-chain nonhydroxylated and 3-hydroxylated acyl residues, i.e. lauric, myristic, palmitic and 3-hydroxymyristic acid. The cell-free preparation also exhibited amidase activity cleaving about 50% of the amide-bound 3-hydroxymyristic acid residues. In addition the extract proved to possess phosphatase activity liberating ester-bound and glycosidically bound phosphate groups of lipid A. On the other hand, the glucosaminyl-beta 1,6-glucosamine disaccharide was not degraded and remained bound to the oligosaccharide part (heptose/3-deoxyoctulosonic acid) of the lipopolysaccharide.

Uptake and subcellular localization of bacterial lipopolysaccharide in the adrenal gland

For determination of the kinetics of uptake and subcellular localization of lipopolysaccharide (LPS) from LPS-high density lipoprotein (LPS-HDL) complexes in the adrenal gland, LPS-HDL complexes were isolated by immunoaffinity chromatography of 125I-Salmonella minnesota Re595 LPS that had been incubated with 20 mM EDTA-rabbit plasma. After intravenous injection of LPS-HDL complexes in rabbits, preferential uptake of the LPS was observed in the adrenal, so that by 5 hours, adrenal-tissue-bound LPS concentrations (determined by use of 131I-BSA blood marker) exceeded all other tissues examined, including liver and spleen, by at least three-fold. For determination of the subcellular localization of LPS, cholesterol-rich (lipid droplet) fractions and cholesterol-depleted fractions were obtained by ultracentrifugation of homogenates of adrenal tissue from rabbits killed at various times after injection of LPS-HDL complexes. As much as 40% of the adrenal-tissue-bound LPS was recovered in the cholesterol-rich fraction 2.5-24 hours after injection of LPS-HDL complexes. Electron-microscopic autoradiographic and immunocytochemical analysis of adrenal cortex of animals killed 5 hours after injection of LPS-HDL complexes demonstrated specific localization of LPS in lipid droplets. These data thus provide direct evidence for the uptake of LPS into the adrenal cortex of animals with intravascular LPS-HDL complexes and indicate that further study of the effect of LPS on adrenocortical function is warranted.

Excretion of radioactivity in faeces and urine of rats injected with 3H,14C-lipopolysaccharide

The route of excretion of lipopolysaccharide (LPS) and its possible degradation in vivo was studied in rats using biosynthetically radiolabelled LPS from Salmonella abortus equi, carrying 3H activity exclusively in fatty acids and 14C activity in fatty acids and sugars. Following intravenous injection of the above LPS in AS2 rats with or without anaesthesia, excretion of radioactivity occurred mainly in the faeces and to smaller extent in urine. The rate of excretion was slow, a large part of the radioactivity being still present in the liver after 14 days. In faeces the percent recovery of 3H (18%) was lower than that of 14C (32%) suggesting loss of tritium activity and thereby of fatty acids from the excreted LPS. A similar loss of tritium was also found in the material remaining in the liver and spleen 14 days after LPS administration. In urine the material recovered during 14 days (about 7% of injected) was different from the original LPS, 70% of 14C activity being dialysable and practically all 3H activity being volatile. Similar results were also obtained following administration of the LPS intraperitoneally under anaesthesia. However, when the LPS was administered intraperitoneally without anaesthesia, in the majority of the animals, 90% of 14C and 54% of 3H was excreted in faeces within 3 days, suggesting that both route of administration and use of anaesthesia during injection influence the subsequent rate of excretion of LPS.

Uptake and deacylation of bacterial lipopolysaccharides by macrophages from normal and endotoxin-hyporesponsive mice

Macrophages are thought to play a central role in the responses of animals to gram-negative bacterial lipopolysaccharides (LPS). Since nothing is known about the metabolism of LPS by these cells, we studied the uptake and deacylation of radiolabeled LPS by thioglycolate-elicited peritoneal macrophages from normal (C3H/HeN) and LPS-hyporesponsive (C3H/HeJ) mice. Macrophages from both kinds of mice took up and deacylated LPS that were added to the culture medium. Opsonization of the LPS with anti-LPS immunoglobulin G antibodies greatly increased LPS uptake; the opsonized LPS also underwent deacylation at rates that were directly related to the amount of cell-associated LPS. An analysis of the fatty acid composition of the cell-associated LPS indicated that the cells have one or more acyloxyacyl hydrolases that remove the non-hydroxylated fatty acids that are normally substituted to the hydroxyl groups of (glucosamine-linked) 3-hydroxytetradecanoate residues in lipid A; we also found evidence for deacylation of 3-hydroxytetradecanoate from the glucosamine backbone. LPS deacylation by macrophages from C3H/HeN and C3H/HeJ mice was qualitatively and quantitatively similar. Nonopsonized LPS are able to stimulate LPS-responsive cells; in these studies we established that animal cells can deacylate nonopsonized LPS, thus raising the possibility that LPS metabolism may play a role in modulating cellular stimulation.

Priming of neutrophils for enhanced release of oxygen metabolites by bacterial lipopolysaccharide. Evidence for increased activity of the superoxide-producing enzyme

We investigated the capacity of bacterial endotoxin (lipopolysaccharide, LPS) to modify the oxidative metabolic response to membrane stimulation of human neutrophils. Neutrophils were pretreated for 60 min with LPS, 10 ng/ml, then stimulated by exposure to fixed immune complexes, the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (FMLP), or phorbol myristate acetate. Release of superoxide anion (O-2) was up to 7-times greater in cells preincubated with LPS, depending upon the stimulus used. Consumption of oxygen and release of hydrogen peroxide (H2O2) were similarly increased, using FMLP as stimulus. The enhancement was accompanied by a reduction in lag time and an increase in the rate of the response, but the duration of the oxidative events was not changed. The molecular basis for the augmented oxidative response of LPS-pretreated cells was investigated. Preincubation with LPS at 0 degrees C prevented priming, but preincubation in the presence of cycloheximide or chelation of extracellular calcium ion did not. Neutrophils preincubated with LPS had slightly decreased numbers of binding sites and equivalent binding affinity for radiolabeled FMLP. Possible changes in the enzyme responsible for the oxidative burst were analyzed by studying NADPH-dependent generation of O-2 by particulate fractions from cells preincubated with LPS or buffer, then stimulated before cell disruption. The fraction prepared from LPS-pretreated neutrophils exhibited greater release of O-2 over a wide range of concentrations of NADPH. The calculated apparent Km for NADPH was equivalent in the two fractions, but the Vmax was increased 2.5-fold in the subcellular fraction from LPS-pretreated cells. These results suggest that LPS could increase neutrophil-mediated host defense or the tissue damage associated with endotoxemia by enhancing the generation of oxygen metabolites by neutrophils. These results also support the concept that the neutrophil is not an end-stage cell in regard to function or metabolic activity.

Generation of slow-reacting substance (leukotrienes) by endotoxin and lipid A from human polymorphonuclear granulocytes

Leukotrienes were released from human polymorphonuclear granulocytes on incubation with endotoxins and lipid A. The analysis was performed by their smooth muscle contracting properties, reversed phase high-pressure liquid chromatography and radioimmunoassay for leukotrienes C4 and D4. The active component of the lipopolysaccharides seems to be the lipid A portion.