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

Structural and biological characterisation of a novel tetra-acyl lipid A from Escherichia coli F515 lipopolysaccharide acting as endotoxin antagonist in human monocytes

We here report on the structural analysis of a novel tetra-acyl lipid A (LAtetra) isolated from Escherichia coli deep rough (Re)-mutant strain F515. In addition to the biologically active hexa-acyl E. coli-type lipid A (compound 506), this incompletely acylated lipid A was found to be also present in the native LPS. Its structure was studied without further derivatisation by chemical analysis, matrix-assisted laser desorption/ionization mass spectrometry, and one- and two-dimensional 1H- and 13C-NMR spectroscopy. It was found to be structurally distinct from the tetraacyl lipid A biosynthetic precursor Ia (compound 406) in lacking the primary ( R)-3-hydroxytetradecanoic acid 14:0(3-OH) in position 3′ ester-linked to the `non-reducing' glucosamine (GlcN II). The hydroxyl group at the ( R)-3-hydroxytetradecanoic acid attached to position 2′ of GlcN II was found to be substituted by dodecanoic acid (12:0), thus forming a dodecanoyloxytetradecanoyl residue 14:0[3- O(12:0)]. The acylation pattern at the `reducing' GlcN I was identical to that of compound 406 in having two primary ( R)-3-hydroxy tetradecanoic acid residues [14:0(3-OH)] attached to positions 3 (ester-linked) and 2 (amide-linked), respectively. In human mononuclear cells (hMNC) the new LAtetra antagonized LPS-induced release of interleukine-1 (IL-1), interleukine-6 (IL-6), and tumor necrosis factor (TNF) in a dose-dependant manner with identical antagonistic potency as compared with compound 406. Also like compound 406, it was found to be an agonist in murine macrophage-like J774.1 cells.

The Characteristics and Function of Bacterial Lipopolysaccharides and Their Endotoxic Potential in Humans

Cross-talk between enteral microbiota and human host is essential for the development and maintenance of the human gastrointestinal and systemic immune systems. The presence of lipopolysaccharides (LPS) lysed from the cell membrane of Gram-negative bacteria in the gut lumen is thought to promote the development of a balanced gut immune response whilst the entry of the same LPS into systemic circulation may lead to a deleterious pro-inflammatory systemic immune response. Recent data suggest that chronically low levels of circulating LPS may be associated with the development of metabolic diseases such as insulin resistance, type 2 diabetes, atherosclerosis and cardiovascular disease. This review focuses on the cross-talk between enteral commensal bacteria and the human immune system via LPS. We explain the structural characterisation of the LPS molecule and its function in the bacteria. We then examine how LPS is recognised by various elements of the human immune system and the signalling pathways that are activated by the structure of the LPS molecule and the effect of various concentrations. Further, we discuss the sequelae of this signalling in the gut-associated and systemic immune systems i.e. the neutralisation of LPS and the development of tolerance to LPS.

Dual labeling of lipopolysaccharides for SPECT-CT imaging and fluorescence microscopy

Lipopolysaccharides (LPS) or endotoxins are amphipathic, pro-inflammatory components of the outer membrane of Gram-negative bacteria. In the host, LPS can trigger a systemic inflammatory response syndrome. To bring insight into in vivo tissue distribution and cellular uptake of LPS, dual labeling was performed with a bimodal molecular probe designed for fluorescence and nuclear imaging. LPS were labeled with DOTA-Bodipy-NCS, and pro-inflammatory properties were controlled after each labeling step. LPS were then radiolabeled with (111)In and subsequently injected intravenously into wild-type, C57B16 mice, and their in vivo behavior was followed by single photon emission computed tomography coupled with X-ray computed tomography (SPECT-CT) and fluorescence microscopy. Time course of liver uptake of radiolabeled LPS ((111)In-DOTA-Bodipy-LPS) was visualized over a 24-h period in the whole animal by SPECT-CT. In complementary histological analyses with fluorescent microscopy, the bulk of injected (111)In-DOTA-Bodipy-LPS was found to localize early within the liver. Serum kinetics of unlabeled and DOTA-Bodipy-labeled LPS in mouse plasma were similar as ascertained by direct quantitation of β-hydroxymyristate, and DOTA-Bodipy-LPS was found to retain the potent, pro-inflammatory property of the unlabeled molecule as assessed by serum cytokine assays. It is concluded that the dual labeling process, involving the formation of covalent bonds between a DOTA-Bodipy-NCS probe and LPS molecules is relevant for imaging and kinetic analysis of LPS biodistribution, both in vivo and ex vivo. Data of the present study come in direct and visual support of a lipopolysaccharide transport through which pro-inflammatory LPS can be transported from the periphery to the liver for detoxification. The (111)In-DOTA-Bodipy-LPS probe arises here as a relevant tool to identify key components of LPS detoxification in vivo.

Parental dietary fat intake alters offspring microbiome and immunity

Mechanisms underlying modern increases in prevalence of human inflammatory diseases remain unclear. The hygiene hypothesis postulates that decreased microbial exposure has, in part, driven this immune dysregulation. However, dietary fatty acids also influence immunity, partially through modulation of responses to microbes. Prior reports have described the direct effects of high-fat diets on the gut microbiome and inflammation, and some have additionally shown metabolic consequences for offspring. Our study sought to expand on these previous observations to identify the effects of parental diet on offspring immunity using mouse models to provide insights into challenging aspects of human health. To test the hypothesis that parental dietary fat consumption during gestation and lactation influences offspring immunity, we compared pups of mice fed either a Western diet (WD) fatty acid profile or a standard low-fat diet. All pups were weaned onto the control diet to specifically test the effects of early developmental fat exposure on immune development. Pups from WD breeders were not obese or diabetic, but still had worse outcomes in models of infection, autoimmunity, and allergic sensitization. They had heightened colonic inflammatory responses, with increased circulating bacterial LPS and muted systemic LPS responsiveness. These deleterious impacts of the WD were associated with alterations of the offspring gut microbiome. These results indicate that parental fat consumption can leave a "lard legacy" impacting offspring immunity and suggest inheritable microbiota may contribute to the modern patterns of human health and disease.

Persistently active microbial molecules prolong innate immune tolerance in vivo

Measures that bolster the resolution phase of infectious diseases may offer new opportunities for improving outcome. Here we show that inactivation of microbial lipopolysaccharides (LPS) can be required for animals to recover from the innate immune tolerance that follows exposure to Gram-negative bacteria. When wildtype mice are exposed to small parenteral doses of LPS or Gram-negative bacteria, their macrophages become reprogrammed (tolerant) for a few days before they resume normal function. Mice that are unable to inactivate LPS, in contrast, remain tolerant for several months; during this time they respond sluggishly to Gram-negative bacterial challenge, with high mortality. We show here that prolonged macrophage reprogramming is maintained in vivo by the persistence of stimulatory LPS molecules within the cells' in vivo environment, where naïve cells can acquire LPS via cell-cell contact or from the extracellular fluid. The findings provide strong evidence that inactivation of a stimulatory microbial molecule can be required for animals to regain immune homeostasis following parenteral exposure to bacteria. Measures that disable microbial molecules might enhance resolution of tissue inflammation and help restore innate defenses in individuals recovering from many different infectious diseases.

We showed previously that mice lacking acyloxyacyl hydrolase (AOAH), the host enzyme that inactivates Gram-negative bacterial lipopolysaccharides (LPS), are unable to regain normal immune responsiveness for many weeks/months after they are exposed in vivo to a small amount of LPS or Gram-negative bacteria. The many possible explanations for slow recovery included long-lasting epigenetic changes in macrophages or other host cells, chronically stimulated cells that produce certain mediators, and persistent signaling by internalized LPS within macrophages. Using several in vivo techniques to study peritoneal macrophages, we found that none of these mechanisms was correct. Rather, prolonged recovery is caused by intact LPS that remains in the environment where macrophages live and can pass from one cell to another in vivo. This is the first evidence that the persistence of a bioactive microbial agonist, per se, can prevent resolution of inflammation in vivo. It also identifies the stimulatory microbial molecule as a realistic target for intervention – in further support, we found that providing recombinant AOAH can be partially preventive. In a larger sense, showing that chemical inactivation of one important microbial signaling molecule is required for full recovery should encourage efforts to find out whether disabling other microbial agonists (chitin, lipopeptides, flagella, others) also benefits infected animals.

The transport and inactivation kinetics of bacterial lipopolysaccharide influence its immunological potency in vivo

The extraordinary potency and pathological relevance of gram-negative bacterial LPSs have made them very popular experimental agonists, yet little is known about what happens to these stimulatory molecules within animal tissues. We tracked fluorescent and radiolabeled LPS from a s.c. inoculation site to its draining lymph nodes (DLN), blood, and liver. Although we found FITC-labeled LPS in DLN within minutes of injection, drainage of radiolabeled LPS continued for >6 wk. Within the DLN, most of the LPS was found in the subcapsular sinus or medulla, near or within lymphatic endothelial cells and CD169(+) macrophages. Whereas most of the LPS seemed to pass through the DLN without entering B cell follicles, by 24 h after injection a small amount of LPS was found in the paracortex. In wild-type mice, ≥70% of the injected radiolabeled LPS underwent inactivation by deacylation before it left the footpad; in animals that lacked acyloxyacyl hydrolase, the LPS-deacylating enzyme, prolonged drainage of fully acylated (active) LPS boosted polyclonal IgM and IgG3 Ab titers. LPS egress from a s.c. injection site thus occurred during many weeks and was mainly via lymphatic channels. Its immunological potency, as measured by its ability to stimulate polyclonal Ab production, was greatly influenced by the kinetics of both lymphatic drainage and enzymatic inactivation.

Host defense genes in asthma and sepsis and the role of the environment

PURPOSE OF REVIEW

There is growing evidence that innate immunity genes contribute to asthma pathogenesis. At the core of the innate immune response are ubiquitous, soluble fragments of bacterial lipopolysaccharide or endotoxin, and chronic exposure to domestic endotoxin has been shown to influence asthma severity. Asthmatic and atopic individuals are more sensitive to endotoxin than nonallergic individuals, suggesting a role for genetics in the innate immunity response, and the potential for gene-environment interactions. Variants in genes associated with classic innate immunity-related disorders, such as sepsis, may be unique candidates for asthma susceptibility.

RECENT FINDINGS

Candidate genes for asthma and allergic diseases co-associated with sepsis including innate immunity receptors and related molecules (CD14, TLR4 and AOAH) and novel genes such as MYLK provide good examples of pleitropic effects of innate immunity genes, where variants conferring risk to specific traits (i.e. sepsis) under one set of genetic and environmental circumstances confer a reduced risk in a different (but possibly related) clinical outcome (i.e. allergic asthma), and support the 'common variant/multiple disease' hypothesis.

SUMMARY

Collectively, these observations suggest a greater role for the innate immunity response in allergic asthma than previously assumed, and implicate host defense genes in disease pathology.

From infection to autoimmunity: a new model for induction of ANCA against the bactericidal/permeability increasing protein (BPI)

Antineutrophil cytoplasmic autoantibodies against the neutrophil granule bactericidal/permeability increasing protein (BPI-ANCA) have been found in diseases of different etiologies, such as cystic fibrosis, TAP deficiency or inflammatory bowel diseases. A common feature of these conditions is the chronic or profuse exposure of the host to Gram-negative bacteria and their endotoxin. BPI plays an important role in killing Gram-negative bacteria as well as neutralization and disposal of their endotoxin. During this interaction BPI can direct the delivery of complexes which contain endotoxin and bacterial outer membrane proteins to antigen presenting cells. Based on recent findings on how complexes of endotoxin and protein antigens need to be processed by dendritic cells in order to become presented on MHC class II molecules, a model can be proposed how Gram-negative bacterial infections can be linked to the generation of autoantibodies against BPI.

Quantitative aspects of lipopolysaccharide and cytokine requirements to generate nitric oxide in macrophages from LPS-hyporesponsive (Lps(d)) C3H/HeJ mice

Due to a gene defect (Lps(d)), C3H/HeJ mice are known to be hyporesponsive to the immunobiological potential of lipopolysaccharide (LPS). We studied dose requirements for LPS, IFN-gamma, and cytokines TNF-alpha and IL-10 to produce nitric oxide (NO) in peritoneal macrophages (Mphi) from these animals. In contrast to the Lps(n) C3H/HeN mice, high concentrations of LPS (up to 5 microg/mL) or IFN-gamma (up to 5 ng/mL) by themselves were unable to activate NO production in C3H/HeJ Mphi. The failure to produce NO could not be overcome by addition of L-arginine or tetrahydropterin. The high-output NO biosynthesis was dose-dependently stimulated by combined administration of varying concentrations of IFN-gamma (50-5000 pg/mL) and LPS (approximately 1 ng/mL) or to a lesser extent by IFN-gamma plus TNF-alpha or TNF-alpha/IL-10. Formation of NO in C3H/HeJ MCO triggered by high concentration of LPS (approximately 1 microg/mL) given together with IFN-gamma (0.2-5 ng/mL) reached the values typical for Lps(n) C3H/HeN mice. While Mphi from C3H/HeN mice secreted TNF-alpha, IL-10, and IL-10 upon contact with a low dose of LPS (1 ng/mL), C3H/HeJ Mphi required high concentration of LPS (5 microg/mL) to enhance the secretion of the cytokines. Yet, this dose remained ineffective to stimulate IFN-gamma in Mphi from C3H/HeJ mice. It can be presumed that one of the important factors influencing their deficient ability to form NO is a failure of Mphi to produce IFN-gamma upon LPS contact.

Evidence against a role for endotoxin in the hepatic encephalopathy of rats with thioacetamide-induced fulminant hepatic failure

BACKGROUND AND AIMS

Endotoxin has been proposed to participate in the development of hepatic encephalopathy. However, there is no published data concerning the effects of endotoxin neutralization on the degree of hepatic encephalopathy. The present study investigated the effect of chronic intraperitoneal injection of polymyxin B, a neutralizing antagonist of endotoxin, on hepatic encephalopathy in rats with thioacetamide (TAA)-induced fulminant hepatic failure.

METHODS

Male Sprague-Dawley rats weighing 300-350 g were used. Fulminant hepatic failure was induced by intraperitoneal injection of TAA (350 mg/kg/day) for 3 days. Two series of rats were designed to compare the effects of low dose (0.1 mg) or high dose (0.2 mg) intraperitoneal polymyxin B administration versus normal saline (NS) on hepatic encephalopathy. The injection was twice daily started from 2 days prior to TAA administration and lasted for 5 days. Severity of encephalopathy was assessed by the counts of motor activity in an Opto-Varimex animal activity meter. Plasma levels of endotoxin and tumor necrosis factor-alpha (an index of liver injury) were measured by Limulus assay and the ELISA method, respectively.

RESULTS

Neutralization of endotoxin by either low dose or high dose polymyxin B administration did not significantly alleviate the degree of hepatic encephalopathy, as represented by the counts of motor activities (P > 0.05). Plasma levels of endotoxin and tumor necrosis factor-alpha were comparable between rats treated with polymyxin B or NS (P > 0.05).

CONCLUSION

Our findings do not support the notion that endotoxin plays a major role in the pathogenesis of hepatic encephalopathy in rats with TAA-induced fulminant hepatic failure.

Lipoproteins, not lipopolysaccharide, are the key mediators of the proinflammatory response elicited by heat-killed Brucella abortus

Inflammation is a hallmark of brucellosis. Although Brucella abortus, one of the disease's etiologic agents, possesses cytokine-stimulatory properties, the mechanism by which this bacterium triggers a proinflammatory response is not known. We examined the mechanism whereby heat-killed B. abortus (HKBA), as well as its LPS, induces production of inflammatory cytokines in monocytes/macrophages. Polymyxin B, a specific inhibitor of LPS activity, did not inhibit the production of TNF-alpha- and IL-6-induced HKBA in the human monocytic cell line THP-1. HKBA induced the production of these cytokines in peritoneal macrophages of both C3H/HeJ and C3H/HeN mice, whereas B. abortus LPS only stimulated cells from C3H/HeN mice. Anti-TLR2 Ab, but not anti-TLR4 Ab, blocked HKBA-mediated TNF-alpha and IL-6 production in THP-1 cells. Because bacterial lipoproteins, a TLR2 ligand, have potent inherent stimulatory properties, we investigated the capacity of two B. abortus lipoproteins, outer membrane protein 19 (Omp19) and Omp16, to elicit a proinflammatory response. Lipidated (L)-Omp16 and L-Omp19, but not their unlipidated forms, induced the secretion of TNF-alpha, IL-6, IL-10, and IL-12 in a time- and dose-dependent fashion. Preincubation of THP-1 cells with anti-TLR2 Ab blocked L-Omp19-mediated TNF-alpha and IL-6 production. Together, these results entail a mechanism whereby B. abortus can stimulate cells from the innate immune system and induce cytokine-mediated inflammation in brucellosis. We submit that LPS is not the cause of inflammation in brucellosis; rather, lipoproteins of this organism trigger the production of proinflammatory cytokines, and TLR2 is involved in this process.

Identification of acyloxyacyl hydrolase, a lipopolysaccharide-detoxifying enzyme, in the murine urinary tract

Acyloxyacyl hydrolase (AOAH) is an unusual but highly conserved lipase, previously described only in myeloid cells, that removes secondary fatty acyl chains from bacterial lipopolysaccharides (LPS) and may also act on various glycero(phospho)lipids. Deacylation by AOAH greatly reduces the ability of LPS to stimulate cells via CD14-MD-2-Toll-like receptor 4. We report here that renal cortical tubule cells produce AOAH and secrete it into urine, where it can deacylate LPS. In vitro studies revealed that proximal tubule cells secrete pro-AOAH, which can be taken up by bladder cells and processed to the heterodimeric, more enzymatically active, mature form of AOAH. AOAH can then be used by the recipient cells to deacylate LPS. The enzyme produced by proximal tubule epithelium may thus be shared with downstream cells. In addition, mature AOAH is found in the urine. We suggest that cortical tubule cells may produce and secrete AOAH to limit inflammatory responses to gram-negative bacteria throughout the urinary tract.

Stimulus-dependent deacylation of bacterial lipopolysaccharide by dendritic cells

We describe here a previously unrecognized property of dendritic cells (DCs), the ability to deacylate the lipid A moiety of gram-negative bacterial LPSs. Both immature DCs of the XS52 cell line and bone marrow-derived DCs produce acyloxyacyl hydrolase, an enzyme that detoxifies LPS by selectively removing the secondary acyl chains from lipid A. Acyloxyacyl hydrolase expression decreased when DCs were incubated with IL-4, IL-1 beta, TNF alpha, and an agonistic CD40 antibody (maturation cocktail), and increased after treatment with LPS, CpG oligodeoxynucleotides, or a gram-positive bacterium (Micococcus luteus). Maturation cocktail treatment also diminished, whereas LPS treatment enhanced or maintained the cells' ability to kill Escherichia coli, deacylate LPS, and degrade bacterial protein. Enzymatic deacylation of LPS is an intrinsic, regulated mechanism by which DCs may modulate host responses to this potent bacterial agonist.

Scavenger-receptor-mediated endocytosis of lipopolysaccharide in Atlantic cod (Gadus morhua L.)

The mechanism of elimination of blood-borne Vibrio salmonicida lipopolysaccharide (LPS) from Atlantic cod (Gadus morhua L.) was studied. The anatomical distribution of LPS was determined using both morphological and radiotracing methods. Immunohistochemistry performed on tissue specimens after injection of LPS disclosed that the endocardial endothelial cells (EECs) represented the cellular site of uptake in heart. Co-injection of trace amounts of [125I]LPS together with excess amounts of formaldehyde-treated albumin (FSA), a ligand for the scavenger receptor, significantly inhibited the accumulation of the radiotracer in heart only. Studies on purified monolayer cultures of atrial EECs showed that fluorescein-labelled LPS was taken up in structures reminiscent of endosomal/lysosomal vesicles. Incubation of cultures with [125I]LPS together with excess amounts of FSA, fucoidan and dextran sulphate, molecules known to compete for endocytosis via the scavenger receptor, reduced uptake of the probe by 80 %. Mannan, a ligand for the mannose receptor, did not compete for uptake. Kinetic studies on the uptake and degradation of [125I]LPS in cultured atrial endocardial cells revealed no degradation after 48 h of culture. In conclusion, we have shown that the EECs of cod remove V. salmonicida LPS from the circulation by scavenger-receptor-mediated endocytosis.

Role of endogenous interleukin-1 receptor antagonist in regulating fever induced by localised inflammation in the rat

1. Interleukin (IL)-1 is a mediator of host defence responses to inflammation and injury, including fever, but its sites of synthesis and action have not been fully elucidated. The actions of IL-1 are antagonised by IL-1 receptor antagonist (IL-1ra). The present study tested the hypothesis that IL-1 and IL-1ra are produced locally at sites of peripheral inflammation in rats, and that endogenous IL-1ra acts to limit the fever resulting from the inflammation. 2. Injection of lipopolysaccharide (LPS; 100 microg kg-1) into a subcutaneous air pouch (I.PO.) of rats induced a significant increase in body temperature. Virtually all (approximately 85 %) of the injected LPS was recovered from the pouch between 1 and 8 h (when the experiment was terminated) after injection of LPS, but LPS was undetectable (< 50 pg ml-1) in plasma at any time. Concentrations of immunoreactive IL-1alpha and IL-1beta were increased significantly in the pouch at 1, 2, 3, 5 and 8 h after injection of LPS, corresponding with the rise in body temperature and the fever peak. The appearance of IL-1ra was delayed until 2 h. Thereafter, the concentrations of IL-1beta and IL-1ra increased in parallel with the development of fever, while the concentrations of IL-1alpha remained constant. IL-1ra, but not IL-1alpha or IL-1bet, was detected in significant quantities in the plasma of LPS-injected animals. 3. Treatment of rats with an anti-IL-1ra serum (2 ml, I.PO.) at the time of injection of LPS (10 or 100 microg kg-1, I.PO.) abolished the appearance of IL-1ra in the circulation. Although neutralisation of endogenous IL-1ra did not affect the maximum body temperature reached after injection of submaximum (10 microg kg-1, I.PO.) or maximum (100 microg kg-1, I.PO.) doses of LPS, the duration of the fever was significantly prolonged, and was associated with a 3- to 4-fold increase in immunoreactive IL-1beta concentrations in the pouch fluid, but not in the plasma, at the 8 h time point. 4. These data show that effects of local (I.PO.) injection of LPS are not due to its action in the circulation or at distant sites (such as at the blood-brain barrier). These data also show that locally produced IL-1ra, in response to injection (I.PO.) of LPS, inhibits the production and/or action of locally produced IL-1beta. The ability of IL-1ra to limit the duration, rather than the magnitude of the fever, is consistent with its delayed production, relative to IL-IL-1ra, therefore, appears to play a key role in the resolution of fever induced by localised inflammatory responses.

Deacylation of lipopolysaccharide in whole Escherichia coli during destruction by cellular and extracellular components of a rabbit peritoneal inflammatory exudate

Deacylation of purified lipopolysaccharides (LPS) markedly reduces its toxicity toward mammals. However, the biological significance of LPS deacylation during infection of the mammalian host is uncertain, particularly because the ability of acyloxyacyl hydrolase, the leukocyte enzyme that deacylates purified LPS, to attack LPS residing in the bacterial cell envelope has not been established. We recently showed that the cellular and extracellular components of a rabbit sterile inflammatory exudate are capable of extensive and selective removal of secondary acyl chains from purified LPS. We now report that LPS as a constituent of the bacterial envelope is also subject to deacylation in the same inflammatory setting. Using Escherichia coli LCD25, a strain that exclusively incorporates radiolabeled acetate into fatty acids, we quantitated LPS deacylation as the loss of radiolabeled secondary (laurate and myristate) and primary fatty acids (3-hydroxymyristate) from the LPS backbone. Isolated mononuclear cells and neutrophils removed 50% and 20-30%, respectively, of the secondary acyl chains of the LPS of ingested whole bacteria. When bacteria were killed extracellularly during incubation with ascitic fluid, no LPS deacylation occurred. In this setting, the addition of neutrophils had no effect, but addition of mononuclear cells resulted in removal of >40% of the secondary acyl chains by 20 h. Deacylation of LPS was always restricted to the secondary acyl chains. Thus, in an inflammatory exudate, primarily in mononuclear phagocytes, the LPS in whole bacteria undergoes substantial and selective acyloxyacyl hydrolase-like deacylation, both after phagocytosis of intact bacteria and after uptake of LPS shed from extracellularly killed bacteria. This study demonstrates for the first time that the destruction of Gram-negative bacteria by a mammalian host is not restricted to degradation of phospholipids, protein, and RNA, but also includes extensive deacylation of the envelope LPS.

Transport of bacterial lipopolysaccharide to the golgi apparatus

Addition of lipopolysaccharide (LPS) to cells in the form of LPS-soluble (s)CD14 complexes induces strong cellular responses. During this process, LPS is delivered from sCD14 to the plasma membrane, and the cell-associated LPS is then rapidly transported to an intracellular site. This transport appears to be important for certain cellular responses to LPS, as drugs that block transport also inhibit signaling and cells from LPS-hyporesponsive C3H/HeJ mice fail to exhibit this transport. To identify the intracellular destination of fluorescently labeled LPS after its delivery from sCD14 into cells, we have made simultaneous observations of different organelles using fluorescent vital dyes or probes. Endosomes, lysosomes, the endoplasmic reticulum, and the Golgi apparatus were labeled using Texas red (TR)-dextran, LysoTrackertrade mark Red DND-99, DiOC6(3), and boron dipyrromethane (BODIPY)-ceramide, respectively. After 30 min, LPS did not colocalize with endosomes, lysosomes, or endoplasmic reticulum in polymorphonuclear leukocytes, although some LPS-positive vesicles overlapped with the endosomal marker, fluorescent dextran. On the other hand, LPS did appear to colocalize with two markers of the Golgi apparatus, BODIPY-ceramide and TRITC (tetramethylrhodamine isothiocyanate)-labeled cholera toxin B subunit. We further confirmed the localization of LPS in the Golgi apparatus using an epithelial cell line, HeLa, which responds to LPS-sCD14 complexes in a CD14-dependent fashion: BODIPY-LPS was internalized and colocalized with fluorescently labeled Golgi apparatus probes in live HeLa cells. Morphological disruption of the Golgi apparatus in brefeldin A-treated HeLa cells caused intracellular redistribution of fluorescent LPS. These results are consistent with the Golgi apparatus being the primary delivery site of monomeric LPS.

Deacylation of purified lipopolysaccharides by cellular and extracellular components of a sterile rabbit peritoneal inflammatory exudate

The extent to which the mammalian host is capable of enzymatic degradation and detoxification of bacterial lipopolysaccharides (LPS) is still unknown. Partial deacylation of LPS by the enzyme acyloxyacyl hydrolase (AOAH) provides such a mechanism, but its participation in the disposal of LPS under physiological conditions has not been established. In this study, deacylation of isolated radiolabeled LPS by both cellular and extracellular components of a sterile inflammatory peritoneal exudate elicited in rabbits was examined ex vivo. AOAH-like activity, tested under artificial conditions (pH 5.4, 0.1% Triton X-100), was evident in all components of the exudate (mononuclear cells [MNC] > polymorphonuclear leukocytes [PMN] > inflammatory [ascitic] fluid [AF]). Under more physiological conditions, in a defined medium containing purified LPS-binding protein, the LPS-deacylating activity of MNC greatly exceeded that of PMN. In AF, MNC (but not PMN) also produced rapid and extensive CD14-dependent LPS deacylation. Under these conditions, almost all MNC-associated LPS underwent deacylation within 1 h, a rate greatly exceeding that previously found in any cell type. The remaining extracellular LPS was more slowly subject to CD14-independent deacylation in AF. Quantitative analysis showed a comparable release of laurate and myristate but no release of 3-hydroxymyristate, consistent with an AOAH-like activity. These findings suggest a major role for CD14(+) MNC and a secondary role for AF in the deacylation of cell-free LPS at extravascular inflammatory sites.

Lysosomal Accumulation and Recycling of Lipopolysaccharide to the Cell Surface of Murine Macrophages, an In Vitro and In Vivo Study

In this study, we detailed in a time-dependent manner the trafficking, the recycling, and the structural fate of Brucella abortus LPS in murine peritoneal macrophages by immunofluorescence, ELISA, and biochemical analyses. The intracellular pathway of B. abortus LPS, a nonclassical endotoxin, was investigated both in vivo after LPS injection in the peritoneal cavity of mice and in vitro after LPS incubation with macrophages. We also followed LPS trafficking after infection of macrophages with B. abortus strain 19. After binding to the cell surface and internalization, Brucella LPS is routed from early endosomes to lysosomes with unusual slow kinetics. It accumulates there for at least 24 h. Later, LPS leaves lysosomes and reaches the macrophage cell surface. This recycling pathway is also observed for LPS released by Brucella S19 following in vitro infection. Indeed, by 72 h postinfection, bacteria are degraded by macrophages and LPS is located inside lysosomes dispersed at the cell periphery. From 72 h onward, LPS is gradually detected at the plasma membrane. In each case, the LPS present at the cell surface is found in large clusters with the O-chain facing the extracellular medium. Both the antigenicity and heterogenicity of the O-chain moiety are preserved during the intracellular trafficking. We demonstrate that LPS is not cleared by macrophages either in vitro or in vivo after 3 mo, exposing its immunogenic moiety toward the extracellular medium.

Evidence against a role for endotoxin in the hyperdynamic circulation of rats with prehepatic portal hypertension

BACKGROUND/AIMS

Excessive formation of nitric oxide may mediate the generalized vasorelaxation and hyporesponsiveness to vasoconstrictors observed in portal hypertensive states. Endotoxin, released from the bowel and detoxified by the liver, could stimulate inducible nitric oxide synthase directly or indirectly via the cytokine cascade. This study investigated the effect of chronic intraperitoneal injection of polymyxin B, a neutralizing antagonist of endotoxin, on the hemodynamics of partially portal vein-ligated (PVL) rats.

METHODS

Concomitantly with endotoxin (600 EU) and dactinomycin (80 microg), polymyxin B (0.1 mg) or normal saline (N/S) was administered via an intraperitoneal route to male Sprague-Dawley rats. Twenty-four hours later, mean arterial pressure was determined. In PVL rats polymyxin B (0.1 mg in 5 cc N/S) or N/S was given intraperitoneally twice daily from 2 days prior to operation until 5 days (short-term) or 14 days (long-term) after the operation. Long-term polymyxin B- or N/S-treated sham-operated rats were included as controls. Hemodynamic studies with a thermodilution technique were performed at the end of treatment. Blood samples were collected from another series of PVL rats with long-term treatment to determine plasma levels of endotoxin and tumor necrosis factor-alpha. Plasma levels of endotoxin and tumor necrosis factor-alpha were measured by Limulus assay and the ELISA method, respectively.

RESULTS

With the dosage of 0.1 mg polymyxin B, hypotension in rats subjected to endotoxin and dactinomycin administration could be corrected (polymyxin B vs. placebo: 130.0+/-7.7 vs. 108.8+/-6.7 mm Hg, p<0.05). However, long-term or short-term treatment with the same dosage of polymyxin B failed to ameliorate the hyperdynamic circulation of PVL rats. In addition, long-term treatment with polymyxin B did not change systemic and portal hemodynamics in sham-operated rats. Plasma levels of endotoxin and tumor necrosis factor-alpha were comparable in PVL rats treated with long-term polymyxin B or N/S (p>0.05).

CONCLUSIONS

Our findings do not support the role of endotoxin in the hyperdynamic circulation of PVL rats.

Acyloxyacyl hydrolase activity of neutrophil leukocytes in normal early postpartum dairy cows and in cows with retained placenta

Acyloxyacyl hydrolase (AOAH) is an enzyme of bovine polymorphonuclear neutrophil leukocytes (PMN) that is capable of detoxifying endotoxin (25). The activity of AOAH in PMN isolated from the blood was investigated in dairy cows that expelled the fetal membranes normally (Group NFM) and in cows with retained fetal membranes (Group RFM) to obtain better insight into the role of the AOAH enzyme of neutrophils in endotoxin-related diseases, which occur frequently in dairy cows during the early postpartum period, especially in RFM cows. Twenty early postpartum dairy cows were used in the study: 13 NFM cows and 7 RFM cows. In the RFM cows, the percentage of PMN in blood (29+/-4%) was significantly (P<0.05) lower than in NFM cows (43+/-4%). The average AOAH activity in RFM cows (mean +/- SEM = 89+/-13 pmol fatty acid/10(7) PMN/h) was lower than in NFM cows (107+/-6 pmol fatty acid/10(7) PMN/h), but the difference in neutrophil AOAH activity between the 2 groups was not significant. There was also a higher percentage of immature neutrophils in isolated leukocyte suspensions from RFM cows (22+/-8%) than from NFM cows (15+/-4%), so that impairment of AOAH activity in early postpartum cows could be explained, in part, by immaturity of the neutrophils. These results suggest that the decreased AOAH activity of PMN could play a role in the pathogenesis of endotoxin-related diseases in dairy cows during the early postpartum period.

Reduction of acyloxyacyl hydrolase activity in circulating neutrophils from cows after parturition

Bovine neutrophils contain the enzyme acyloxyacyl hydrolase, which hydrolyzes the acyloxyacyl linkage of the two nonhydroxylated fatty acyl chains to two 3-hydroxy fatty acids in the highly conserved lipid A part of endotoxins with high specificity. This hydrolysis decreases the toxicity of lipid A, but the immunostimulatory capacity of endotoxins is largely maintained. In two trials, we studied the activity of acyloxyacyl hydrolase in neutrophils that had been isolated from the blood of 18 dairy cows around parturition. Between 10 and 26 d after parturition, the activity of acyloxyacyl hydrolase in neutrophils decreased approximately 20% below prepartum activity. At about 2 mo after parturition, acyloxyacyl hydrolase activity returned to prepartum values. Changes in acyloxyacyl hydrolase activity could not be attributed to changes in binding of lipopolysaccharides by the CD14 molecules on neutrophils or monocytes. We hypothesize that decreased acyloxyacyl hydrolase activity in neutrophils shortly after parturition is a factor that increases the susceptibility of dairy cows to coliform mastitis during early lactation.

CD14-Dependent Internalization of Bacterial Lipopolysaccharide (LPS) Is Strongly Influenced by LPS Aggregation But Not by Cellular Responses to LPS

We analyzed the impact of ligand aggregation and LPS-induced signaling on CD14-dependent LPS internalization kinetics in human monocytic THP-1 cells and murine macrophages. Using two independent methods, we found that the initial rate and extent of LPS internalization increased with LPS aggregate size. In the presence of LPS binding protein (LBP), large LPS aggregates were internalized extremely rapidly (70% of the cell-associated LPS was internalized in 1 min). Smaller LPS aggregates were internalized more slowly than the larger aggregates, and LPS monomers, complexed with soluble CD14 in the absence of LBP, were internalized very slowly after binding to membrane CD14 (5% of the cell-associated LPS was internalized in 1 min). In contrast, the initial aggregation state had little or no effect on the stimulatory potency of the LPS. Previous studies suggest that LPS-induced signal responses may influence the intracellular traffic and processing of LPS. We found that elicited peritoneal macrophages from LPS-responsive (C3H/HeN) and LPS-hyporesponsive (C3H/HeJ) mice internalized LPS with similar kinetics. In addition, pre-exposure of THP-1 cells to LPS had no effect on their ability to internalize subsequently added LPS, and pre-exposure of the cells to the LPS-specific inhibitor, LA-14-PP, inhibited stimulation of the cells without inhibiting LPS internalization. In these cells, LPS is thus internalized by a constitutive cellular mechanism(s) with kinetics that depend importantly upon the physical state in which the LPS is presented to the cell.

Mice genetically hyporesponsive to lipopolysaccharide (LPS) exhibit a defect in endocytic uptake of LPS and ceramide

We have recently shown that monomeric bacterial LPS is rapidly delivered from the plasma membrane to an intracellular site and that agents that block vesicular transport block responses of neutrophils to lipopolysaccharide (LPS) (Detmers, P.A., N. Thiéblemont, T. Vasselon, R. Pironkova, D.S. Miller, and S.D. Wright. 1996. J. Immunol. 157:5589-5596). To examine further the connection between intracellular transport of LPS and signaling, we observed internalization of fluorescently labeled LPS in cells from LPS-hyporesponsive (Lpsd) mice. Binding of fluorescent LPS from LPS-soluble CD14 (sCD14) complexes by peritoneal macrophages from Lpsd and control (Lpsn) mice was quantitatively similar, and confocal images obtained from these cells exhibited an identical appearance immediately after labeling. Incubation of labeled Lpsn macrophages at 37 degrees C caused movement of the fluorescence from the cell perimeter in one or two spots in the perinuclear region. However, in Lpsd cells the fluorescence remained dispersed, suggesting a defect in vesicular transport. LPS resembles ceramide, and Lpsd mice fail to respond to ceramide. As with LPS, we found that binding of fluorescent ceramide by Lpsd and Lpsn macrophages was quantitatively similar, and the label moved rapidly to one to two spots in the perinuclear region in Lpsn mice. However, in Lpsd macrophages the fluorescence remained dispersed. These results show that cells deficient in responses to LPS exhibit defective vesicular transport of LPS and ceramide and point to a role for vesicular transport in responses to these mediators.

Biliary secretion of endotoxin and pathogenesis of primary biliary cirrhosis

Previous studies suggested endotoxin, derived from the intestine through the portal blood to the liver, was predominantly metabolized by Kupffer cells. In the present study, fluorescent-labeled endotoxin injected into the rat portal vein was demonstrated not only in Kupffer cells but also in hepatocytes. Furthermore a great amount of labeled endotoxin was recovered in bile. In the livers of patients with primary biliary cirrhosis (PBC), immunohistochemistry demonstrated significant retention of endotoxin in the biliary epithelial cells, and treatment with ursodeoxycholic acid significantly reduced the retention in those cells. The study for detection of apoptosis demonstrated increased rates of apoptosis in hepatocytes and biliary epithelial cells in PBC liver, and the rate of apoptosis in biliary epithelial cells was significantly reduced after treatment with ursodeoxycholic acid. Immunohistochemistry in PBC liver demonstrated significant reduction of fluorescence intensity for a 7H6 antigen in biliary epithelial cells, indicating the increased paracellular permeability of bile ducts, because cellular immunolocalization of that antigen has been shown to be inversely correlated with the paracellular permeability of the tight junction. These results suggest that, in biliary epithelial cells, retention of endotoxin, increased apoptosis, and increased permeability of tight junctions may be involved in the pathogenesis of PBC.

Plasma interleukin-6 levels in patients with cirrhosis. Relationship to endotoxemia, tumor necrosis factor-alpha, and hyperdynamic circulation

BACKGROUND

Liver cirrhosis with portal hypertension is associated with hyperdynamic circulation characterized by generalized vasodilatation and increased cardiac output and regional blood flows. Patients with liver cirrhosis present with increased levels of interleukin-6 (IL-6), which may inhibit vascular smooth-muscle contraction. We investigated whether increased plasma IL-6 levels contribute to the pathogenesis of hyperdynamic circulation observed in cirrhotic patients and whether they are correlated with plasma tumor necrosis factor-alpha (TNF-alpha) and endotoxin concentrations.

METHODS

In 58 consecutive cirrhotic patients and 34 healthy subjects the plasma concentrations of TNF-alpha and IL-6 were measured with enzyme-linked immunosorbent assay, and endotoxin determinations with a limulus assay. In addition, 52 cirrhotic patients underwent a hemodynamic study using Swan-Ganz catheterization.

RESULTS

Plasma TNF-alpha, IL-6, and endotoxin levels were significantly higher in cirrhotic patients than in healthy subjects (7.3 +/- 0.2 versus 5.8 +/- 0.1 pg/ml, 6.4 +/ 0.8 versus 2.0 +/- 0.2 pg/ml, and 7.6 +/- 1.2 versus 2.8 +/- 0.3 pg/ml, respectively; p < 0.01). In cirrhotic patients the plasma levels of TNF-alpha IL-6, and endotoxin progressively increased in relation to the severity of liver dysfunction (graded by Pugh's classification). A significant correlation was observed between plasma TNF-alpha and IL-6 levels (r = 0.48, p < 0.001), whereas no correlation was observed between plasma endotoxin levels and plasma TNF-alpha and IL-6 levels. Plasma IL-6 levels correlated negatively with systemic vascular resistance in patients with cirrhosis (r = 0.5, p < 0.01).

CONCLUSIONS

Plasma IL-6 levels are increased in patients with cirrhosis. The severity of liver cirrhosis is an important factor for the occurrence of increased IL-6 levels. IL-6 may play a role in the hyperdynamic circulation observed in patients with cirrhosis.

Susceptibility of lipopolysaccharide-responsive and -hyporesponsive ItyS Mice to infection with rough mutants of Salmonella typhimurium

The R5 (chemotype Rb) but not the R10 (chemotype Rd) mutant of murine pathogen Salmonella typhimurium 395MS was extremely virulent in intraperitoneal infections of C57BL/10ScCr mice carrying the ityS and lpsD alleles. C57BL/6J (ityS lpsN) and C3H/HeJ (ityR lpsD) mice showed a much higher resistance to the R5 mutant. Further studies were performed with peritoneal macrophages in vitro in order to elucidate susceptibility in lipopolysaccharide (LPS)-hyporesponsive mice carrying ItyS. The intracellular killing capacity of the ItyS LpsD macrophages was lower than that of the ItyS LpsN macrophages for the R5 mutant and may partly explain the increased susceptibility of the ItyS LpsD mice. The deep rough mutant, R10, was rapidly killed intracellularly by the ItyS LpsD macrophages. Processing of the bacteria in macrophages that had phagocytosed R5 or R10 bacteria was followed for up to 18 days by endotoxin measurements (limulus assay) and immunostaining, with monoclonal antibodies to various parts of the LPS molecule being used. Only 0.1% or less of the macrophage-associated bacteria remained alive after 48 h of incubation, and none were alive on day 7. Although immunostaining showed that LPS was present in both the LpsD and LpsN macrophages during the whole incubation period of 18 days, endotoxin activity in the LpsD macrophages on day 7 was lower than that in the LpsN macrophages, indicating that qualitative modifications of the chemical composition or physical state of the LPS molecule occurred. The interleukin-6 response in the ItyS LpsD macrophages was delayed and of shorter duration compared with that in the ItyS LpsN macrophages. The results suggest that the difference between the LPS-hyporesponsive and -responsive ItyS mice in susceptibility to infection with the R5 mutant was due to the lower activation state of the LpsD macrophages during infection, leading to a lower intracellular bactericidal systems of the macrophages. A rapid killing of the bacterium should restrict the infection and may partly compensate for a diminished inflammatory response. The persistence of LPS within the cells is discussed.

Role of endotoxaemia in hyperdynamic circulation in rats with extrahepatic or intrahepatic portal hypertension

This study investigated the role of endotoxaemia in the development of hyperdynamic circulation observed in rats with extrahepatic (high collateralization) or intrahepatic (low collateralization) portal hypertension. Compared with sham-operated rats, decreased mean arterial pressure and systemic vascular resistance were detected on days 1, 4, and 14 following partial portal vein ligation. By day 1, the cardiac index of portal vein-ligated rats was similar to that of sham-operated rats and progressively increased, thereafter, reaching statistically higher values days 4 and 14. No differences in plasma endotoxin levels were found between portal vein-ligated and sham-operated rats throughout the observation period. Both carbon tetrachloride-induced cirrhotic rats with and without ascites had a higher cardiac index and lower systemic vascular resistance. Plasma endotoxin levels were higher in cirrhotic rats with ascites (8.6 +/- 2.0 pg/mL; P < 0.01) than those of control rats (2.2 +/- 0.3 pg/mL) and cirrhotic rats without ascites (2.4 +/- 0.6 pg/mL). These results suggest that factors other than endotoxaemia play a role in the development of hyperdynamic circulation observed in rats with extrahepatic portal hypertension and cirrhotic rats without ascites, but that endotoxaemia may contribute to the maintenance of hyperdynamic circulation found in cirrhotic rats with ascites. The severity of liver disease may be a more important factor than the presence of portosystemic shunting for the development of endotoxaemia in portal hypertensive states.

Role of hepatocytes in direct clearance of lipopolysaccharide in rats

BACKGROUND & AIMS

The liver is the clearance organ for lipopolysaccharide (LPS). The aim of this study was to investigate the biliary excretion of LPS using fluorescein isothiocyanate (FITC)-labeled LPS.

METHODS

After FITC-LPS was injected intravenously into rats, the cellular localization of fluorescence in the liver was examined and the biliary excretion of fluorescence was measured. The effects of gadolinium chloride, a blocker of Kupffer cells, and colchicine, an inhibitor of microtubules, on the biliary excretion of fluorescence was investigated, and bile was analyzed using high-performance liquid chromatography.

RESULTS

Laser scanning confocal microscopy showed that fluorescence was taken up by hepatocytes 5 minutes after injection of FITC-LPS into the portal vein. When FITC-LPS was injected into the portal vein, fluorescence was rapidly secreted into bile, peaking at 20 minutes, and 25.1% of the injected dose appeared in bile within 60 minutes. When the same dose of FITC-LPS was injected into the tail vein, 15.8% appeared in bile within 60 minutes. Chromatography showed that FITC-LPS was excreted into bile in an unchanged form over a period of 20 minutes after injection. Colchicine significantly reduced the biliary excretion of fluorescence, but gadolinium chloride had no effect.

CONCLUSIONS

LPS was directly and effectively processed by hepatocytes and secreted into the bile canalicular system via a microtubule-dependent vesicular pathway.

Enhancement of uptake of lipopolysaccharide in macrophages by the major outer membrane protein OmpA of gram-negative bacteria

Monoclonal antibodies (MAb) to lipopolysaccharide (LPS) and to the major outer membrane protein OmpA from Proteus mirabilis were generated and used to monitor the kinetics of uptake in macrophages of LPS as well as LPS bound to OmpA. Uptake was measured by a modified enzyme-linked immunosorbent assay (ELISA) in a microtiter culture system. The MAb were of various immunoglobulin G subclasses and showed strong reactivities with their antigens. Four hybridoma clones recognizing LPS and three recognizing OmpA from P. mirabilis 19 were selected for the present study on the basis of reactions in ELISA and Western blot (immunoblot) analyses. In the uptake assay, it was possible to differentiate between antigen on the cell surface and antigen which had been internalized. Uptake of LPS by macrophages was relatively rapid during the first 4 h of culture and then progressed more slowly over the remaining 24-h observation period. The level of detection of LPS in this assay system was in the nanogram range. When macrophages were pulsed with LPS for 30 min and subsequently washed to remove antigen not bound to the cells, the amount of LPS detectable on the macrophage surface decreased progressively for 3 h after the pulse, which indicated internalization of the antigen. Thereafter, LPS rose to an increased level on the cell surface. The rate of uptake of LPS was more rapid when it was in complex with OmpA. When the fate of OmpA was monitored in the same LPS-protein complexes by use of MAb to OmpA in a pulse experiment, the level of protein measured on the cell surface decreased after an initial rise, which again indicated internalization, but the protein did not reappear on the cell surface in a form detectable with the MAb. Compared with the LPS monitoring system, detection of OmpA associated with macrophages was weak, although the MAb to OmpA reacted strongly with the protein in the ELISA and Western blot analyses.

Prolonged expression of lipopolysaccharide (LPS)-induced inflammatory genes in whole blood requires continual exposure to LPS

Blood-borne lipopolysaccharide (LPS) is thought to be a major inducer of sepsis; however, it remains controversial whether an ongoing exposure to LPS is required to maintain the underlying systemic inflammatory response. To address this question, we have studied the expression of tumor necrosis factor alpha (TNF-alpha), interleukin 1-beta (IL-1 beta), and the procoagulant protein tissue factor induced by LPS ex vivo in whole human blood. The addition of a 1-ng/ml bolus of LPS to blood rapidly induced mRNA expression of all three genes. The mRNA levels peaked after 1 to 2 h, depending on the gene, and then declined to baseline after approximately 5 h. The decline in mRNA expression was not caused by a loss of responsiveness of the blood cells to LPS but rather correlated with the neutralization of LPS inflammatory activity by plasma components. Furthermore, administering a 1-ng/ml dose of LPS in six hourly aliquots of 167 pg/ml greatly prolonged the expression of mRNAs and induced a much greater release of TNF-alpha and IL-1 beta protein than did a single bolus. Dosing by repeated additions was more effective than a single bolus in inducing secretion of TNF-alpha and IL-1 beta at LPS levels of < or = 10 ng/ml, which corresponded to the LPS neutralization capacity of plasma. Finally, both mRNA expression and protein secretion induced by repeated administration of LPS were rapidly reversed by the addition of the LPS-neutralizing protein, bactericidal/permeability-increasing protein, even after several hours of stimulation. These results indicate that continuous or repeated exposure to LPS is required to maintain the expression of inflammatory genes and that the activated state is rapidly reversed with LPS neutralization.

Endotoxemia in patients with chronic liver diseases: relationship to severity of liver diseases, presence of esophageal varices, and hyperdynamic circulation

Plasma endotoxin levels were investigated using a quantitative Limulus assay in patients with chronic liver diseases and correlated with the severity of liver diseases, the presence of esophageal varices, and hemodynamic parameters. The plasma endotoxin levels were significantly higher in chronic hepatitis patients with acute exacerbation (10.1 +/- 1.3 pg/ml, n = 13, p < 0.05) and patients with cirrhosis (7.0 +/- 0.7 pg/ml, n = 126, p < 0.05) than in healthy subjects (2.9 +/- 0.2 pg/ml, n = 45). Chronic hepatitis patients (n = 30) had plasma endotoxin levels which were similar to those in healthy subjects (4.6 +/- 0.5 vs. 2.9 +/- 0.2 pg/ml, p > 0.05) but lower than those in chronic hepatitis patients with acute exacerbation (4.6 +/- 0.5 vs. 10.1 +/- 1.3 pg/ml, p < 0.05). Endotoxemia (plasma endotoxin level > 5.7 pg/ml) was found in 27%, 85% and 41% of patients with chronic hepatitis, chronic hepatitis with acute exacerbation, and cirrhosis, respectively. In patients with cirrhosis, the plasma endotoxin levels progressively increased in relation to the severity of liver dysfunction (Pugh's class A/B/C = 4.9 +/- 0.5/7.9 +/- 1.4/10.2 +/- 2.0 pg/ml, p < 0.05). In contrast, plasma endotoxin levels were comparable between patients with cirrhosis with and without esophageal varices (p > 0.05). Chronic hepatitis patients with acute exacerbation (no collaterization) had much higher plasma endotoxin levels than those in patients with cirrhosis and large varices (p < 0.05), whereas compensated patients with cirrhosis and large esophageal varices had plasma endotoxin levels similar to those seen in chronic hepatitis patients (no collaterization) (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Biosynthetic radiolabeling of bacterial lipopolysaccharide to high specific activity

We describe a method for producing radiolabeled lipopolysaccharide (LPS) by incorporating [3H]acetate into an aceEF, gltA strain of Escherichia coli K12. The LPS has substantially greater specific radioactivity (2 microCi per microgram LPS, or approximately 8 Ci/mmol) than has been reported previously for biosynthetically radiolabeled LPS. The 3H is incorporated into the fatty acyl chains of the lipid A moiety. LPS prepared by this method has several attractive features for biological studies, including native structure and bioactivity, long radioactive half-life, and high specific activity.

Induction of cationic amino acid transport activity in mouse peritoneal macrophages by lipopolysaccharide

The transport of cationic amino acids has been investigated in mouse peritoneal macrophages cultured in vitro. The transport activity for lysine was rather low in cells cultured for 1 h and increased slightly in cells cultured for 12 h. This increase varied with the serum lot used in the culture medium and was suppressed by polymyxin B, suggesting that the transport activity is induced by endotoxins in the serum. When the macrophages were cultured in the medium containing 1 ng/ml lipopolysaccharide, the transport activity for lysine increased by more than 10-fold. The transport activity for lysine induced by lipopolysaccharide has been characterized. Lysine was transported mainly by a Na(+)-independent, saturable system. The uptake of lysine was potently inhibited by extracellular cationic amino acids, but not by neutral amino acids tested. In addition, transport of lysine showed trans-stimulation. From these results, we have concluded that the transport activity for cationic amino acids is potently induced by lipopolysaccharide and that the characteristics of the induced activity is consistent with those of system y+.

How do animal phagocytes process bacterial lipopolysaccharides?

Phagocytic cells, the front-line defense against bacterial invasion, have enzymes that deacylate and dephosphorylate the toxic lipid A moiety of gram-negative bacterial lipopolysaccharide (LPS, also called endotoxin). These enzymes may detoxify LPS without destroying its immunogenicity or antigenicity--in fact, the polysaccharide region of LPS often resists degradation in vivo and retains its antigenic epitopes for long periods of time. The net result, detoxification of LPS with preservation of its immunogenic and antigenic properties, may prevent excessive inflammatory responses while promoting the development of antibacterial immunity.

Deacylation of endotoxin during natural cases of bovine mastitis

Acyloxyacyl hydrolase, a lysosomal enzyme that deacylates and thus detoxifies lipopolysaccharide (endotoxin) has been identified in bovine peripheral blood and milk neutrophils. Enzymatic activity increases on a per neutrophil basis during cases of experimental Escherichia coli mastitis. The objective of this study was to quantify acyloxyacyl hydrolase activity from milk neutrophils collected from mammary glands naturally infected with a variety of bacteria. Acyloxyacyl hydrolase activity was detectable in milk neutrophils isolated from cases of both Gram-negative and Gram-positive bacterial infections, with highest activities found in milk neutrophils from glands infected with organisms known to cause the most severe forms of mastitis. In addition, acyloxyacyl hydrolase activity was inhibited to varying degrees in mastitic milk by a nonprotein inhibitory substance. Nonenzymatic deacylation of endotoxin also occurred in mastitic milk, but to a lesser degree than enzymatic deacylation. Nonenzymatic deacylation of endotoxin was not found to occur in clinically normal milk. Severity of coliform mastitis in individual cows may be dependent in part on the interaction of endotoxin with milk neutrophil acyloxyacyl hydrolase activity, inhibition of acyloxyacyl hydrolase activity by an inhibitory substance, and the inherent ability of milk to deacylate endotoxin nonenzymatically.

Intracellular and extracellular enzymatic deacylation of bacterial endotoxin during localized inflammation induced by Escherichia coli

Acyloxyacyl hydrolase (AOAH), an enzyme that removes the secondary acyl chains of gram-negative bacterial lipid A (endotoxin), has been identified previously in human neutrophils and mouse macrophages. We report here that bovine leukocytes also contain AOAH activity. Although bovine AOAH deacylates bacterial lipopolysaccharide in a manner similar to human AOAH, it is active in vitro over a broader pH range, from 4.0 to 7.0. By using Escherichia coli infection of the bovine mammary gland as a model of localized gram-negative bacterial disease and associated tissue inflammation, AOAH activity per leukocyte increased. In addition, AOAH activity increased in the cell-free portion of infected mammary secretions. These data indicate that AOAH activity increases in leukocytes associated with inflammation induced by gram-negative bacteria and provide additional evidence of its potential involvement in the defense against the effects of bacterial endotoxin.

Bacterial lipopolysaccharides: structure, metabolism and mechanisms of action

Endotoxins (lipopolysaccharides, LPS) are biologically active substances present in the outer membrane of gram-negative bacteria. They induce a spectrum of biological effects which may be harmful or beneficiary for the host. Lipid A is the biologically active part of the LPS molecule. This was demonstrated using soluble forms of lipid A and more recently confirmed further by employing synthetic lipid A. LPS administered into experimental animals circulates as LPS/HDL complex and is cleared from the blood mainly into the liver and spleen. In the liver LPS undergoes partial deacylation however without a loss of toxic activity. Its excretion is effected mainly via the bile into the gut. The lethal toxicity and tolerance inducing properties of LPS are mediated by macrophages through tumor necrosis factor alpha (TNF alpha), which is probably the most important endogenous mediator of the lethal effects of LPS. The lethal toxicity of LPS may be completely inhibited by anti-TNF alpha antibodies.

Deacylation of bacterial lipopolysaccharide in rat hepatocytes in vitro

The possible role of liver parenchymal cells in the uptake and degradation of bacterial lipopolysaccharide (LPS) was investigated in vitro by employing radiolabelled LPS as substrate. Hepatocytes obtained from Wistar rats by collagenase treatment were found to take up LPS only when it was not linked to the polysaccharide of O-antigen. The amount of LPS taken up increased with time and after 48 h incubation it increased in a dose-dependent manner up to at least 30 micrograms. When incubated with LPS radiolabelled exclusively in the fatty-acid moiety, cultured hepatocytes released lipophilic materials into the culture medium. These were identified as beta-hydroxytetradecanoic acid and triglyceride, in the ratio of 7:I. These results indicate that the R-form of LPS which lacks the O-antigen polysaccharide is taken up and deacylated in hepatocytes, and the derived fatty acids are released into the culture medium either in the free form or after conversion to triglyceride.

Clearance of gut-derived endotoxins by the liver. Release and modification of 3H, 14C-lipopolysaccharide by isolated rat Kupffer cells

This paper describes experiments that were designed to study postuptake modification by isolated rat Kupffer cells of a 3H,14C-biosynthetically labeled endotoxin purified from Escherichia coli J5 as assessed by cesium chloride isopyknic density gradients and gel permeation chromatography. Pulse-chase experiments demonstrated that half as much of the endotoxin's lipid, relative to polysaccharide, was released by the cells. Density gradients revealed that native endotoxin equilibrated at a density of 1.412 g/ml, whereas endotoxin retained by Kupffer cells equilibrated at densities of 1.274 and 1.295 g/ml. Gel permeation chromatography indicated that endotoxin retained by Kupffer cells formed a larger micelle than either exocytosed or native endotoxin. Endotoxin exocytosed by Kupffer cells fractionated into two peaks, one with a smaller and one with a larger apparent micelle size than native endotoxin but both smaller than the retained lipopolysaccharide. Both systems indicated that the Kupffer cell modified endotoxin by enriching the lipid content of the molecule and shortening the length of the O-antigen. Thus, the Kuffer cell, in its mode of action on the endotoxin molecule, appears to play a prominent role in the initial phase of a biochemical process for endotoxin clearance and detoxification.

Uptake and modification of 125I-lipopolysaccharide by isolated rat Kupffer cells

While it is generally believed that hepatic clearance of lipopolysaccharide involves Kupffer cells, the mechanism involved has not been fully elucidated. This study assesses this phenomenon in terms of in vitro uptake and post-uptake modification experiments with an 125I-labeled Salmonella minnesota lipopolysaccharide. 125I-Lipopolysaccharide was added to Kupffer cells in suspension cultures under a variety of conditions. In vitro uptake of 125I-Lipopolysaccharide was not saturable up to concentrations of 33.33 micrograms per ml. Kinetics experiments performed at 16.67 micrograms per ml demonstrated that Kupffer cells were unsaturable after 60 min of incubation. The kinetics of uptake could be inhibited, however, by incubation in the presence of a 10-fold excess of unlabeled lipopolysaccharide, indicating that a component of the uptake process may be limited. Energy dependence in this process was demonstrated by incubation in the presence of 1 mM 2-deoxyglucose which inhibited 125I-lipopolysaccharide uptake by approximately 30%. Pretreatment with 7.5 x 10(-5) M colchicine had no effect on kinetics, implying no role for the cell cytoskeleton in lipopolysaccharide uptake. These results are inconsistent with a receptor-mediated process as previously suggested. Modification of internalized label has been demonstrated by changes in buoyant density in CsCl isopyknic density gradients following overnight incubation with Kupffer cells. These results indicate that Kupffer cells clear bacterial endotoxin in vitro and post-uptake degradation occurs within 20 hr of incubation.