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PubMed1992

Dibutyryl cyclic AMP attenuates lung responses induced by endotoxin in conscious sheep.

Dibutyryl cyclic AMP (DBcAMP) could inhibit the production of prostanoids and modulate the pulmonary vascular responses induced by endotoxin. Diffuse lung injury after endotoxemia in sheep is accompanied by the production of prostanoids and an increase in endothelial permeability. To determine whether exogenous DBcAMP could prevent the endotoxin responses, we measured pulmonary hemodynamics, gas exchange, and lung lymph responses to an intravenous infusion of Escherichia coli endotoxin (1.0 micrograms/kg over 30 min) in unanesthetized sheep in the presence and absence of DBcAMP (30 micrograms/kg/min) infused intravenously for 6 h beginning 1 h before endotoxin infusion or for 4.5 h after 30 min of treatment with endotoxin infusion. We also measured circulating leukocytes and lung lymph and plasma concentrations of thromboxane B2 (TXB2) and prostacyclin (6-keto-PGF1 alpha) metabolites by radioimmunoassay. DBcAMP infusion before endotoxin infusion decreased endotoxin-induced pulmonary hypertension and hypoxemia and markedly attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP after endotoxin only attenuated the increased lung lymph flow and lymph protein clearance. DBcAMP treatment both before and after endotoxin infusion blocked endotoxin-induced increases in lung lymph and plasma TXB2 and 6-keto-PGF1 alpha. DBcAMP did not affect the number of circulating leukocytes. Although DBcAMP alone did not affect the pulmonary and systemic hemodynamics and lung lymph balance, the potential that DBcAMP directly modulates the pulmonary vascular responses to endotoxin as a vasodilator could be expected. We conclude that DBcAMP infusion attenuates lung dysfunction caused by endotoxemia, possibly by preventing prostanoid release and modulating the pulmonary vascular responses.

6-Ketoprostaglandin F1 alpha↗

PubMed1990

Prolonged exposure of rat aorta to low levels of endotoxin in vitro results in impaired contractility. Association with vascular cytokine release.

Treatment of volunteers or animals with endotoxin in vivo results in reduced vascular reactivity to catecholamines. Endotoxin also causes liberation of the vasoactive cytokines interleukin-1 (IL-1) and tumor necrosis factor (TNF) from vascular smooth muscle and endothelial cells in culture. This study tested whether defects in contractility could be induced in isolated vascular tissue by prolonged exposure to endotoxin (1-100 ng/ml) in vitro, and whether IL-1 and TNF release by blood vessels is altered during the establishment of endotoxin induced contractile dysfunction. A concentration of endotoxin as low as 1 ng/ml suppressed contractions to norepinephrine (NE) and KCl; aortic sensitivity to NE also decreased. The presence of serum constituents or an intact endothelium were not necessary for endotoxin-induced vascular suppression. Aortas incubated with endotoxin liberated IL-1 and TNF in a dose-dependent fashion. The addition of dexamethasone or indomethacin during the incubations generally suppressed release of the cytokines and improved tissue reactivity to NE. The endotoxin-induced diminished vascular contraction and augmented IL-1 and TNF liberation required de novo protein synthesis; tissue incubated with endotoxin plus actinomycin D was completely shielded from the influence of endotoxin on vascular reactivity to NE. The association between endotoxin-induced vascular cytokine release and diminished contraction suggests a possible role for cytokines derived from the vasculature in the regulation of contractile function.

Animals↗

PubMed2000

Longitudinal study of dust and airborne endotoxin in the home.

To characterize the seasonal variability of endotoxin levels, we measured endotoxin in dust from the bed, bedroom floor, and kitchen floor in 20 homes, and in air from the bedroom in 15 of the homes. All homes were located in the greater Boston, Massachusetts, area and were sampled each month from April 1995 to June 1996. Outdoor air was collected at two locations. We found greater within-home than between-home variance for bedroom floor, kitchen floor, and airborne endotoxin. However, the reverse was true for bed dust endotoxin. Thus, studies using single measurements of dust endotoxin are most likely to reliably distinguish between homes if bed dust is sampled. Dust endotoxin levels were not significantly associated with airborne endotoxin. Airborne endotoxin was significantly (p = 0. 04) and positively associated with absolute humidity in a mixed-effect model adjusting for a random home effect and fixed effect of sampling month and home characteristics. This finding implies that indoor humidity may be an important factor controlling endotoxin exposure. We found a significant (p < 0.05) seasonal effect in kitchen floor dust (spring > fall) and bedroom airborne endotoxin (spring > winter), but not in the other indoor samples. We found significant seasonal pattern in outdoor airborne endotoxin (summer > winter).

Air Pollution, Indoor↗

PubMed2002

Bone-resorptive effects of endotoxin-contaminated high-density polyethylene particles spontaneously eliminated in vivo.

Wear particles commonly used for experiments may carry adherent endotoxin on their surfaces, which may be responsible for the observed effects. In this study, we attached titanium plates to the tibiae of 20 rats. After osseointegration, endotoxin-contaminated or uncontaminated high-density-polyethylene (HDPE) particles were applied. Contaminated specimens showed a dramatic resorption of bone after seven days but new bone filled the site again at 21 days. Uncontaminated specimens showed no resorption. In 18 rats we implanted intramuscularly discs of ultra-high-molecular-weight polyethylene (UHMWPE) with baseline or excess contamination of endotoxin. Excess endotoxin disappeared within 24 hours and the amount of endotoxin remained at baseline level (contamination from production). Uncontaminated titanium discs did not adsorb endotoxin in vivo. The endotoxin was measured by analytical chemistry. Locally-applied endotoxin stimulated bone resorption similarly to that in experiments with wear particles. Endotoxin on the surface of implants and particles appeared to be inactivated in situ. A clean implant surface did not adsorb endotoxin. Our results suggest that endotoxin adhering to orthopaedic implants is not a major cause for concern.

Animals↗

PubMed1993

The effects of inhalation of grain dust extract and endotoxin on upper and lower airways.

To characterize the short-term effects of grain dusts on pulmonary function, mucosal inflammation, and systemic responses, four women and three men inhaled nebulized corn and soybean dust extracts, endotoxin diluted with Hanks' balanced salt solution (HBSS), and HBSS. Subjects were volunteers recruited via newspaper advertisement and were required to be healthy, nonasthmatic, nonatopic never-smokers. The mean age was 26.9 years (range, 19 to 36 years). Using a randomized, double-blind, crossover design, each subject was challenged with each of the 4 substances with at least 10 days between challenges. Serial spirometry, peripheral blood leukocyte and differential cell counts, and 24-h postchallenge nasal lavages were performed. Extracts were produced by mixing 3 g of the corn or soybean dust with 30 ml HBSS followed by shaking for 60 min, centrifugation, then filter sterilization. The endotoxin solution was produced by mixing lyophilized Escherichia coli endotoxin (serotype 0111:B4) with HBSS to attain a final concentration of 7 mg/L, which was the same as the concentration of endotoxin in both grain dust solutions. The pH of all solutions and unmixed HBSS was adjusted to 5.8, which was the native pH of the soybean dust extract. Subjects were challenged with 0.08 ml/kg of each substance, resulting in a range of endotoxin doses of 30 to 60 micrograms, similar to that which a worker might inhale over the course of one workshift. The lowest mean percentage baseline FEV1 (+/- SD) after inhalation challenge was 99.2 +/- 2.1 for HBSS, and it was significantly lower for endotoxin (90.1 +/- 8.5, p = 0.03), corn dust extract (93.1 +/- 4.3, p = 0.02), and soybean dust extract (96.2 +/- 3.7, p = 0.03). In addition, a peripheral blood leukocytosis developed after exposure to all three endotoxin-containing solutions (p < 0.05), yet a lower peripheral blood lymphocyte count was found only after inhalation of corn dust extract (p = 0.02). Interestingly, this was associated with a higher nasal lavage lymphocyte count after inhalation of corn dust extract (p = 0.03). Neither the decrease in peripheral blood lymphocytes nor the increase in nasal lymphocytes were found after inhalation of soybean dust extract or endotoxin. Our results indicate that extracts of grain dusts have physiologic effects similar to endotoxin. However, in spite of the same endotoxin levels, the effects of corn dust extract appear to have different biologic activity than either soybean dust extract or endotoxin.

Administration, Inhalation↗

PubMed1995

Endotoxin administration decreases plasma insulin-like growth factor (IGF)-I and IGF-binding protein-2 in Angus x Hereford steers independent of changes in nutritional intake.

Endotoxemia and sepsis cause severe shifts in metabolism towards catabolic events. The objective of the research was to determine whether endotoxin administration changes plasma concentrations of IGF-I and IGF-binding protein-2 (IGFBP-2) in Angus x Hereford steers. In Experiment 1, mean feed intake in endotoxin-treated steers (n = 6) decreased 60% within the first 24 h after endotoxin and averaged, for the duration of the 96 h test period, an intake 35.5% lower than the mean ad libitum intake recorded prior to endotoxin. Plasma concentrations of IGF-I averaged 182 ng/ml in steers before endotoxin (E. coli, 055:B5, 0.2 micrograms/kg, i.v. bolus) and decreased an average of 24.2% at 24 to 96 h after endotoxin. In Experiment 2, a paired feeding strategy was used to determine whether the reduced feed intake was a significant factor in changing plasma concentrations of IGF-I and IGFBP-2 after endotoxin challenge. Steers were divided into endotoxin (0.2 micrograms/kg, i.v., n = 6) or control (saline, i.v., n = 3) treatments. Each of three endotoxin-treated steers was paired to a specific control. In this fashion, the adjusted feed intake of each endotoxin-treated steer was fed to it's paired control every 24 h through 96 h after endotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Nutritional Physiological Phenomena↗

PubMed1989

Role of tumour necrosis factor in the enhanced sensitivity of mice to endotoxin after exposure to lead.

Heavy metals administered to animals, at doses which appear relatively innoxious by themselves, enhance susceptibility to endotoxin. The mechanisms which underly this phenomenon are not yet fully understood. In this study we investigated the role of the cytokine Tumour Necrosis Factor (TNF), an important mediator of the effects of endotoxin, in this phenomenon. First it was studied whether lead enhances sensitivity of mice to endotoxin and to TNF. Lead appeared to enhance sensitivity to both endotoxin and TNF resulting in mortality of mice at low endotoxin and TNF doses. Next we studied the influence of lead on serum TNF levels after stimulation by endotoxin. Lead treated mice showed lower TNF blood levels two hours after injection of endotoxin and lead. Six and eight hours after injection TNF levels of lead treated mice were higher compared to those of mice injected with endotoxin only. In the last part of our investigation, we studied the influence of a monoclonal hamster anti TNF antibody on the effect of combined lead-endotoxin exposure. Administration of the antibody prevents lethality completely. Our data indicate that TNF plays a central role in the phenomenon of the enhanced susceptibility of animals to endotoxin after exposure to lead. The enhanced susceptibility to endotoxin is caused by an enhanced susceptibility to TNF and possibly by a prolonged exposure to a higher level of TNF.

Animals↗

PubMed1990

Endotoxin extends survival of adult mice in hyperoxia.

Research on endotoxin protection from oxygen toxicity is presently limited to the rat model since only rats have been protected by endotoxin. This study reports that endotoxin also extends survival of adult male mice in hyperoxia (greater than 99% oxygen at 1 ATA). Initially, 4-month-old male mice were treated with Boivin-extracted E. coli endotoxin and placed in hyperoxia. Zymosan-primed mice receiving 2 or 10 micrograms endotoxin, and unprimed mice receiving 10-40 micrograms endotoxin, showed moderate protection against hyperoxia; 11/15 Boivin-treated mice survived 120 hours exposure to hyperoxia with time-of-death in hyperoxia = 126.7 +/- 4.4 hours (mean +/- SEM, n = 15). This contrasts with untreated male mice; 0/4 survived 120 hours exposure to hyperoxia with mean survival = 103.5 +/- 3.5 hours. Mice receiving 20 or 60 micrograms Westphal-extracted endotoxin were not protected nor were older female mice receiving 20 micrograms Boivin-extracted endotoxin. This study suggests that age, sex, the extraction method used to obtain endotoxin, and possibly the time of year when endotoxin is administered, are important variables in allowing endotoxin to extend survival of mice in hyperoxia.

Analysis of Variance↗

PubMed1975

The role of granulocytes in the activation of intravascular coagulation and the precipitation of soluble fibrin by endotoxin.

This study examines the role of neutrophils (PMN) in the pathogenesis of endotoxin-induced microclot formation. It is intended to clarify whether granulocytes are involved in endotoxin-induced activation of intravascular coagulation (generation of soluble fibrin) and/or in endotoxin-induced precipitation of soluble fibrin. Precipitation of soluble fibrin was achieved by injection of endotoxin into ancrod-infused rabbits with circulating soluble fibrin (first model). Activation of intravascular coagulation was elicited by two intravenous injections of endotoxin into rabbits (second model). Seventy-two and ninety-six hours after injection of nitrogen mustard, leukopenic rabbits had PMN counts between 0 and 50 cells per mul. Neutropenia did not prevent the occurrence of glomerular microclots after infusion of ancrod and injection of endotoxin (first model). Neutropenia influenced neither the decrease in mean fibrinogen concentrations nor the drop in mean platelet counts after ancrod and endotoxin administration. In contrast to the first model, neutropenia prevented the occurrence of glomerular microclots and of circulating soluble fibrin after two injections of endotoxin (second model). It did not, however, protect rabbits from the decrease in mean platelet counts after endotoxin administration. These data indicate that granulocytes are involved in endotoxin-induced activation of intravascular coagulation and the production of soluble fibrin but are not essential to endotoxin-induced precipitation of soluble fibrin.

Animals↗

PubMed2003

A cell line assay system for predicting the response of human blood to endotoxin.

Some parenteral drugs augment the in vivo action of endotoxin. It is necessary to regulate the overall toxic action of contaminating endotoxin by developing a clinically relevant test method for the safety control of such drugs. Although the responses of human peripheral blood cells (hPBC) to endotoxins to produce tumour necrosis factor alpha (TNF-alpha), interleukin 6 (IL-6), and IL-1beta showed considerable variation depending on the endotoxin and also on the individuals used as sources of blood, the responses to each of the endotoxins evaluated relative to that to the Japanese reference standard endotoxin were found to be highly reproducible irrespective of the sources of hPBC. The evaluation procedure based on the relative responsiveness to various endotoxins was shown to be highly effective to detect differences in responsiveness among the endotoxin test, the pyrogen test, and the cytokine induction in hPBC. When eight human monocytoid cell lines were examined, only THP-1 and 28SC cells showed a significant dose-dependent IL-6 production. However, THP-1 failed to show consistency with hPBC in responses to the panel of endotoxins. 28SC cells showed appropriate consistency with hPBC not only in terms of respective responses to the endotoxins but also with regard to detection of the effect of human interferons to augment endotoxin to induce IL-6.

Animals↗

PubMed1989

Response of humans to gamma-irradiated reference Escherichia coli endotoxin.

This study assesses the effect of gamma-irradiation of endotoxin given intravenously to healthy human volunteers. The national reference standard endotoxin derived from E. coli was placed in aqueous medium in sterile-sealed ampoules and divided into four groups. One group received endotoxin with no radiation while the other three received endotoxin with gamma-irradiation at doses of 0.18, 0.36, or 1.08 Mrad. These doses of radiation cause characteristic alterations to the endotoxin molecule, primarily to the O-polysaccharide moiety. Each of the four different preparations of endotoxin was given intravenously to four volunteers at a concentration of 4 ng/kg. The responses for clinical symptoms, cortisol, and growth hormone were significantly and progressively reduced by increasing the irradiation to the endotoxin. Most strikingly, no clinical symptoms were noted with the endotoxin exposed to the highest dose of radiation (1.08 Mrad). Fever, vital signs, white blood cell count, and differential exhibited no statistically significant differences among the groups, but the kinetics of change were altered by increasing doses of gamma-irradiation. Irradiated endotoxin was significantly more effective in decreasing the platelet count than untreated endotoxin. The fever index correlated significantly with maximum temperature, change in temperature, white blood cell count index, mature neutrophil count index, and the cortisol index. Thus, there is dissociation of biological activities for endotoxin in humans due to molecular changes primarily in the O-polysaccharide moiety from exposure to gamma-irradiation.

Adult↗

PubMed1986

Synergistic toxicity of endotoxin and hemoglobin.

Stroma-free hemoglobin (SFH) is advocated as an oxygen-transporting resuscitation solution. Hemoglobin has been shown to enhance endotoxin lethality when given intraperitoneally. It is possible that SFH could interact with endotoxin when used as an oxygen-transporting resuscitation system for trauma victims with contaminating wounds. To assess the effects of these two agents when given intravascularly, rabbits were infused with SFH (1.75 gm/kg) or albumin (controls; 1.75 gm/kg) with and without endotoxin. Two doses of endotoxin were used. At 14.5 ng/kg of Salmonella enteritidis endotoxin, no effect was seen in the albumin group. However, 50% of the hemoglobin group died. At 14.5 micrograms/kg, the albumin group showed hematologic alterations, but all animals lived. All SFH-treated animals died at the higher endotoxin dose. SFH alone caused cardiac abnormalities (bradycardia in 100%, sinus arrhythmias in 30%, and ventricular arrhythmias in 20%), liver abnormalities (necrosis in 40% and 240% increase in alanine aminotransferase activity by 6 hours), and intravascular thrombi (30%). The only hemoglobin-induced abnormality that was more frequent in the presence of endotoxin was ventricular arrhythmias (up to 75% of animals). Thrombin times were approximately 20% larger in all SFH groups compared with the albumin groups. By 6 hours after infusion, endotoxin prolonged the thrombin time even further, despite the lack of fibrinogen consumption. This study shows that endotoxin and SFH exert synergistic toxicity when SFH is given in a clinically relevant dose for an oxygen-transporting resuscitation system. Only minute quantities of endotoxin are needed to produce this phenomenon. We hypothesize that this synergism is endotoxin enhancement of hemoglobin toxicity.

Animals↗

PubMed1985

Endotoxin-induced eicosanoid production by equine vascular endothelial cells and neutrophils.

Dispersed equine vascular endothelial cells grown in tissue culture, and freshly isolated neutrophils were used to determine direct effects of endotoxin on cyclooxygenase and lipoxygenase products. Endothelial cells (10(7)/ml) or neutrophils (2 X 10(6)/ml) were incubated with (a) buffer, (b) endotoxin (10 micrograms/ml), (c) endotoxin + flunixin meglumine (10 micrograms/ml), or (d) calcium ionophore, A23187 (10 micrograms/ml). Thromboxane (TxB2), prostacyclin (6-keto-PGF1 alpha), and leukotriene C4 (LTC4) were determined in the incubation fluid by radioimmunoassay. Thromboxane and prostacyclin levels increased in endothelial cells incubated with endotoxin. Treatment with flunixin meglumine prevented the endotoxin-induced release of these cyclooxygenase products to levels below those observed in control cells. Leukotriene production was increased in endothelial cells incubated with endotoxin plus flunixin meglumine. Endotoxin as well as endotoxin plus flunixin meglumine increased the production of prostacyclin and LTC4 by freshly isolated neutrophils. Cells exposed to endotoxin plus flunixin meglumine produced more LTC4 than cells exposed to endotoxin. The data revealed that endotoxin has a direct effect on arachidonic acid metabolism in endothelial cells and neutrophils. Flunixin meglumine reduced the level of cyclooxygenase products but increased the level of lipoxygenase products. Therefore, the well-established beneficial effects of cyclooxygenase inhibitors during endotoxemia may be improved even more if they are used in conjunction with lipoxygenase inhibitors or a combined cyclooxygenase-lipoxygenase inhibitor.

6-Ketoprostaglandin F1 alpha↗

PubMedDate not supplied

Role of endotoxin in L-arginine-induced relaxation of rat thoracic aorta mediated by muscle-derived nitric oxide.

The contribution of endotoxin to the L-arginine-induced relaxation of the endothelium-denuded rat thoracic aorta, which appears to be mediated by nitric oxide synthase in the vascular smooth muscle, was investigated. Special attention was paid to the time course of the phenomenon and its dependence on the concentration of endotoxin. In the absence of endotoxin, L-arginine induced scarcely any relaxation of the arteries. Treatment of the arteries with endotoxin initiated relaxation in response to 10 microM L-arginine with lag periods of 2-4 hours. The degree of relaxation increased on repeated applications of L-arginine, to reach a consistent level after several hours. Increase in the concentration of endotoxin shortened the lag period, enhanced the degree of relaxation and lowered the threshold concentration of L-arginine required to relax the arteries. In endotoxin-primed arteries, L-arginine, at concentrations necessary to induce relaxation, stimulated the cyclic GMP production. Prophylactic application of actinomycin D or dexamethasone, which inhibits the induction of nitric oxide synthase, prevented the induction by endotoxin of the L-arginine-induced relaxation and cyclic GMP formation. Polymyxin B, which inhibits the action of endotoxin, also prevented the development of the endotoxin-sensitized relaxation and the cyclic GMP formation induced by L-arginine. When the Krebs solution was prepared using deionized water, the amount of endotoxin in the reservoir was above the level required to initiate the L-arginine-induced relaxation and cyclic GMP formation. These results suggest that endotoxin triggered the time-dependent development of the L-arginine-induced relaxation by expressing nitric oxide synthase in the vascular smooth muscle.

Amino Acid Oxidoreductases↗

PubMed1994

The fate of intravenously injected endotoxin in normal rats and in rats with liver failure.

The elimination of endotoxin from the blood was studied in rats with D-galactosamine-induced liver failure and in normal controls after intravenous injection of various doses of endotoxin. Endotoxin was found to localize in liver tissue by immunohistochemical staining with factor C, which is derived from amebocyte lysate of the horseshoe crab and which reacts specifically with endotoxin. Before injection, the blood endotoxin concentrations were normal both in control rats and in rats with liver failure. The blood concentrations of endotoxin were significantly higher after intravenous injection of endotoxin in the D-galactosamine-induced liver failure group (p < 0.05) and decreased much more slowly (p < 0.05). Endotoxin concentrations were also significantly higher after in vitro incubation with plasma from rats with liver failure (p < 0.05). After intravenous injection of endotoxin (1 mg/kg), endothelial and Kupffer cells in the liver sinusoids were positively stained for endotoxin in the control group, but not stained or faintly stained in the liver failure group. Endotoxemia in liver failure thus results from reduced inactivation of endotoxin in plasma and from impaired hepatic clearance.

Animals↗

PubMed1993

[A quality control for the culture system using endotoxin assays in human in vitro fertilization and embryo transfer].

The purpose of this study is to investigate the effects of endotoxin on human in vitro fertilization and embryo transfers (IVF-ET) and to evaluate a quality control system for a culture medium using endotoxin assays. Before the final water purification (in an ultra-pure water system with a depyrogen filter) of the medium, the sources of water were pre-purified as follows; (I) distillation-->deionization x 2, (II) distillation-->ultra-pure water system or (III) reverse osmosis system. The limulus amebocyte lysate gelation tests (sensitivities of 0.03 and 0.25EU/ml) were used to detect endotoxin in the medium and in pre-purified water (pre-water). No pregnancies occurred in the endotoxin-positive medium (endotoxin > or = 0.03EU/ml). The endotoxin-negative medium resulted in a 33.3% pregnancy rate and 13.4% implantation rate. No statistical differences in the implantation rate were found among these methods of pre-purification (I: 12.5%, II: 13.4% and III: 20.0%). Endotoxin was detected in all the pre-water between 0.25 and 4.0EU/ml. The clinical pregnancy rate (36.6%) and the implantation rate (16.9%) in pre-water of endotoxin < 0.25EU/ml were significantly higher than those (10.5% and 5.5%) in pre-water of endotoxin > or = 0.25EU/ml (p < 0.05). We confirmed that a very low concentration of endotoxin disturbed a human embryo implantation. Endotoxin assays, not only in the media, but also in pre-water before final purification are useful as a quality control for the IVF-ET program.

Culture Media↗

PubMed1996

Endotoxin stimulates in vitro pituitary growth hormone release in eicosanoid-dependent manner.

OBJECTIVE: To investigate the signal transduction pathways by which endotoxin stimulates in vitro pituitary cell growth hormone (GH) release. ANIMALS: Pituitary cell cultures derived from 6 sheep. PROCEDURE: Signal transduction pathways involved in endotoxin-mediated GH release from sheep pituitary cell cultures were evaluated by the use of specific blockers of arachidonic acid and its metabolites, extracellular calcium, protein kinase C, and protein kinase A. Cell cultures were exposed to the specific blockers in the presence or absence of endotoxin (Escherichia coli O55:B5, 10 micrograms/ml) for 24 hours. In addition, effects of endotoxin on GH cell content and GH mRNA values were determined. RESULTS: Nordihydroquairetic acid (lipoxygenase blocker, 10 microM, 30 microM) and eicosatetraynoic acid (arachidonic acid competitor, 10 microM) decreased endotoxin-stimulated GH release. The calcium channel blocker verapamil (25 microM) decreased baseline and endotoxin-stimulated GH release. Phorbol myristate acetate-induced down-regulation of protein kinase C, indomethacin, or the protein kinase A blocker H89 did not alter endotoxin-stimulated GH release. Endotoxin increased GH mRNA values by 50.1 +/- 6.0%, but the cell content of GH was not affected. CONCLUSIONS: A direct effect of endotoxin on the pituitary gland to stimulate GH secretion was evident, an effect mediated predominantly by arachidonic acid and its metabolites through the lipoxygenase pathway. Endotoxin-stimulated GH release requires extracellular calcium and is associated with increased cell GH mRNA content. CLINICAL RELEVANCE: A better understanding of the signal transduction pathways involved in endotoxin-mediated effects will allow more appropriate therapeutic intervention in clinical cases of endotoxemia.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1999

Endotoxin down-regulates T cell activation by antigen-presenting liver sinusoidal endothelial cells.

Endotoxin is physiologically present in portal venous blood at concentrations of 100 pg/ml to 1 ng/ml. Clearance of endotoxin from portal blood occurs through sinusoidal lining cells, i.e., Kupffer cells, and liver sinusoidal endothelial cells (LSEC). We have recently shown that LSEC are fully efficient APCs. Here, we studied the influence of endotoxin on the accessory function of LSEC. Incubation of Ag-presenting LSEC with physiological concentrations of endotoxin lead to >/=80% reduction of the accessory function, measured by release of IFN-gamma from CD4+ T cells. In contrast, conventional APC populations rather showed an increase of the accessory function after endotoxin treatment. Inhibition of the accessory function in LSEC by endotoxin was not due to lack of soluble costimulatory signals, because neither supplemental IL-1beta, IL-2, IFN-gamma, or IL-12 could rescue the accessory function. Ag uptake was not influenced by endotoxin in LSEC. However, we found that endotoxin led to alkalinization of the endosomal/lysomal compartment specifically in LSEC but not in bone marrow macrophages, which indicated that Ag processing, i.e., proteolytic cleavage of protein Ags into peptide fragments, was affected by endotoxin. Furthermore, endotoxin treatment down-regulated surface expression of constitutively expressed MHC class II, CD80, and CD86. In conclusion, it is conceivable that endotoxin does not alter the clearance function of LSEC to remove gut-derived Ags from portal blood but specifically affects Ag processing and expression of the accessory molecules in these cells. Consequently, Ag-specific immune responses by CD4+ T cells are efficiently down-regulated in the hepatic microenvironment.

Animals↗