Hepatic and extrahepatic factors critical for liver injury during lipopolysaccharide exposure

Protease-activated receptors in health and disease

Proteases are signaling molecules that specifically control cellular functions by cleaving protease-activated receptors (PARs). The four known PARs are members of the large family of G protein-coupled receptors. These transmembrane receptors control most physiological and pathological processes and are the target of a large proportion of therapeutic drugs. Signaling proteases include enzymes from the circulation; from immune, inflammatory epithelial, and cancer cells; as well as from commensal and pathogenic bacteria. Advances in our understanding of the structure and function of PARs provide insights into how diverse proteases activate these receptors to regulate physiological and pathological processes in most tissues and organ systems. The realization that proteases and PARs are key mediators of disease, coupled with advances in understanding the atomic level structure of PARs and their mechanisms of signaling in subcellular microdomains, has spurred the development of antagonists, some of which have advanced to the clinic. Herein we review the discovery, structure, and function of this receptor system, highlight the contribution of PARs to homeostatic control, and discuss the potential of PAR antagonists for the treatment of major diseases.

Concurrent Inflammation Augments Antimalarial Drugs-Induced Liver Injury in Rats

Purpose: Accumulating evidence suggests that drug exposure during a modest inflammation induced by bacterial lipopolysaccharide (LPS) might increase the risk of drug-induced liver injury. The current investigation was designed to test if antimalarial drugs hepatotoxicity is augmented in LPS‑treated animals. Methods: Rats were pre-treated with LPS (100 µg/kg, i.p). Afterward, non-hepatotoxic doses of amodiaquine (25, 50 and 100 mg/kg, oral) and chloroquine (25, 50 and 100 mg/kg, oral) were administered. Results: Interestingly, liver injury was evident only in animals treated with both drug and LPS as estimated by pathological changes in serum biochemistry (ALT, AST, LDH, and TNF-α), and liver tissue (severe hepatitis, endotheliitis, and sinusoidal congestion). An increase in liver myeloperoxidase enzyme activity, lipid peroxidation, and protein carbonylation, along with tissue glutathione depletion were also detected in LPS and drug co-treated animals. Conclusion: Antimalarial drugs rendered hepatotoxic in animals undergoing a modest inflammation. These results indicate a synergistic liver injury from co-exposure to antimalarial drugs and inflammation.

Cocaine Hepatotoxicity and Its Potentiation by Lipopolysaccharide: Treatment and Gender Effects

This study was conducted to investigate the effect of a 7-day treatment as well as the influence of gender on cocaine hepatotoxicity (CH). Lipopolysaccharide (LPS) potentiation of CH was also investigated. Male and female CF-1 mice were orally administered 20 mg/kg body weight cocaine hydrochloride once daily for 7 days. Four hours after the last cocaine administration, the mice were administered 12 × 106 EU LPS (or equal volume of sterile saline) intraperitoneally. Plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were evaluated as indices of liver injury. Blood and liver glutathione (GSH), glutathione reductase (GRx), and catalase (CAT) activities were also determined to investigate the oxidation stress induced by the treatment. Plasma ALT and AST concentrations were elevated in all males receiving cocaine alone or cocaine + LPS. Furthermore, blood GSH and CAT were decreased and GRx activity was elevated in the same males. Histological analysis revealed a high degree of focal necrosis in the male cocaine group, and severe necrosis in the male cocaine + LPS group. Unlike males, females showed no effect of either cocaine alone or cocaine + LPS treatments. These results indicate that gender plays a significant role in CH and its potentiation by LPS and lengthening the administration by two treatments increased the severity of cocaine + LPS hepatotoxicity dramatically in male mice.

Influence of Gender on Cocaine Hepatotoxicity in CF-1 Mice

Gender is known to play a role in the bioavailability, metabolism, and lethality of many toxic substances. This study was conducted to investigate the influence of gender on cocaine hepatotoxicity (CH) and lipopolysaccharide (LPS) potentiation of CH. Male and female CF-1 mice were orally administered 20 mg/kg body weight cocaine hydrochloride once daily for 7 days. Four hours after the last cocaine administration, the mice were administered 12 × 106 EU LPS (or equal volume of sterile saline) intraperitoneally. Plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were evaluated as indices of liver injury. Blood and liver glutathione (GSH), glutathione reductase (GRx), and catalase (CAT) activities were also determined to investigate the extent of oxidative stress induced by the treatments. Serum ALT and AST concentrations were elevated in all males receiving cocaine alone or cocaine + LPS. Furthermore, blood GSH and CAT were decreased and GRx activity was elevated in these same animals. Histological analysis revealed a high degree of hepatic focal necrosis in the male cocaine group, and severe hemorrhagic necrosis in the male cocaine + LPS group. Unlike males, females showed no damage resulting from cocaine or cocaine + LPS exposure, whereas testosterone-supplemented ovariectomized females displayed histological and biochemical profiles statistically similar to males. The results demonstrate that the extent of CH or LPS-potentiated CH is influenced by gender and sex hormones, particularly testosterone.

Protective effects of propolis on female rats' histopathological, biochemical and genotoxic changes during LPS induced endotoxemia

In recent years, propolis has been the object of extensive research for its antibacterial, antioxidant, anti-inflammatory, and antitumoral activities. This study aims to determine the hepatoprotective efficiency of propolis on experimental endotoxemia in rats. In the current study, fifty adult Sprague Dawley rats (weighing 200-300 g) were randomly divided into five groups of ten rats each. Normal saline solution was administered to the rats in the control group, while in the second group LPS (30 mg/kg), in the third group propolis (250 mg/kg), in the fourth group first propolis and then LPS (30 mg/kg), and in the fifth group, first LPS (30 mg/kg) and then propolis were given. Six hours after the application, biochemical (MDA levels) and histopathological changes as well as global DNA methylation analysis in the liver tissue samples were determined, while in the blood tissue samples Genomic Template Stability (GTS, %) was evaluated using RAPD-PCR profiles. The results demonstrated that the administration of propolis could have a protective effect against changes of both genomic stability values and methylation profiles, and it minimized the increase in MDA and tissue damage caused by LPS. In conclusion, the application of propolis prior to LPS-induced endotoxemia has shown to reduce hepatic damage.

T-5224, a selective inhibitor of c-Fos/activator protein-1, attenuates lipopolysaccharide-induced liver injury in mice

The effect of T-5224, a selective inhibitor of c-Fos/activator protein (AP)-1, on lipopolysaccharide (LPS) induced liver injury was examined in mice. Administration of LPS (10 mg kg(-1), i.p.) markedly increased serum levels of tumor necrosis factor-alpha (TNFα), high mobility group box 1 (HMGB1), alanine aminotransferase/aspartate aminotransferase (ALT/AST), liver tissue levels of macrophage-inflammatory protein-1 alpha (MIP-1α) and monocyte chemoattractant protein-1 (MCP-1), as well as hepatic necrosis and inflammation, leading to 67 % lethality. Administration of T-5224 (300 mg kg(-1), p.o.) after intraperitoneal injection of LPS imparted appreciable protection against acute elevations in serum levels of TNFα, HMGB1, ALT/AST as well as in liver tissue levels of MIP-1α and MCP-1, and reduced the lethality (27 %). These data indicate that T-5224 ameliorates liver injury and improves survival through decreasing production of proinflammatory cytokines and chemokines in endotoxemic mice.

Downregulation effects of beta-elemene on the levels of plasma endotoxin, serum TNF-alpha, and hepatic CD14 expression in rats with liver fibrosis

It has been demonstrated that β-elemene could protect against carbon tetrachloride (CCl(4))-induced liver fibrosis in our laboratory work, and the aim of this paper is to reveal the protective mechanisms of β-elemene. The hepatic fibrosis experimental model was induced by the hypodermical injection of CCl(4) in Wistar male rats. β-elemene was intraperitoneally administered into rats for 8 weeks (0.1 mL/100 g bodyweight per day), and plasma endotoxin content was assayed by biochemistry. The serum TNF-α level was detected using radioactive immunity. CD14 expression in rat livers was measured by immunohistochemistry and Western blot. The results showed that β-elemene can downregulate the levels of plasma endotoxins, serum TNF-α, and hepatic CD14 expression in rats with liver fibrosis. β-elemene plays an important role in downregulating the lipopolysaccharide signal transduction pathway, a significant pathway in hepatic fibrosis development.

Tissue-engineered model for real-time monitoring of liver inflammation

Tissue-engineered in vitro models have the potential to be used for investigating inflammation in the complex microenvironment found in vivo. We have developed an in vitro model of hepatic tissue that facilitates real-time monitoring of endothelium activation in liver tissue. This was achieved by creating a layered coculture model in which hepatocytes were embedded in collagen gel and a reporter clone of endothelial cells, which synthesizes green fluorescent protein in response to nuclear factor-kappa B (NF-κB) activation, was overlaid on top of the gel. The efficacy of our approach was established by monitoring in real time the dynamics of NF-κB-regulated fluorescence in response to tumor necrosis factor α. Our studies revealed that endothelial cells in coculture with hepatocytes exhibited a similar NF-κB-mediated fluorescence to both pulse and step stimulation of lipopolysaccharide. By contrast, endothelial cells in monoculture displayed enhanced NF-κB-regulated fluorescence to step in comparison to pulse lipopolysaccharide stimulation. The NF-κB-mediated fluorescence correlated with endothelial cell expression of NF-κB-regulated genes such as intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and E-Selectin, as well as with leukocyte adhesion. These findings suggest that our model provides a powerful platform for investigating hepatic endothelium activation in real time.

Effect of polymyxin B-immobilized fiber hemoperfusion on respiratory impairment, hepatocellular dysfunction, and leucopenia in a neonatal sepsis model

PURPOSE

Sepsis and septic shock remain a major source of morbidity and mortality in neonates despite advances in antimicrobials and aggressive supportive care. Our aim was to study the effects of polymyxin-B direct hemoperfusion (PMX-DHP) therapy on sepsis-induced respiratory impairment, liver dysfunction and leucopenia in a neonatal cecal ligation and perforation (CLP) model.

METHODS

Fourteen anesthetized and mechanically ventilated 3-day-old piglets underwent CLP and an arteriovenous extracorporeal circuit from 3 h until 6 h post-CLP, with a PMX column in the PMX-DHP treated group (7 piglets). Changes in oxygen saturation, PCO(2), base excess, white blood cell (WBC) count, platelet count, hematocrit (Hct%), serum glutamate pyruvate transaminase (SGPT), and serum glutamic oxaloacetic transaminase were measured before CLP and at 1, 3 and 6 h after.

RESULTS

At 6 h, the PMX-DHP group showed lower Hct%, and SGPT in comparison to the control group, but higher oxygen saturation and WBC count. No effects on the platelet count were found. The survival times of the PMX-DHP group were longer than in control.

CONCLUSION

PMX-DHP therapy limited the respiratory impairment, liver dysfunction and leucopenia in a neonatal septic model, which resulted in an improvement of survival time.

Inflammatory stress and idiosyncratic hepatotoxicity: hints from animal models

Adverse drug reactions (ADRs) present a serious human health problem. They are major contributors to hospitalization and mortality throughout the world (Lazarou et al., 1998; Pirmohamed et al., 2004). A small fraction (less than 5%) of ADRs can be classified as "idiosyncratic." Idiosyncratic ADRs (IADRs) are caused by drugs with diverse pharmacological effects and occur at various times during drug therapy. Although IADRs affect a number of organs, liver toxicity occurs frequently and is the primary focus of this review. Because of the inconsistency of clinical data and the lack of experimental animal models, how IADRs arise is largely undefined. Generation of toxic drug metabolites and induction of specific immunity are frequently cited as causes of IADRs, but definitive evidence supporting either mechanism is lacking for most drugs. Among the more recent hypotheses for causation of IADRs is that inflammatory stress induced by exogenous or endogenous inflammagens is a susceptibility factor. In this review, we give a brief overview of idiosyncratic hepatotoxicity and the inflammatory response induced by bacterial lipopolysaccharide. We discuss the inflammatory stress hypothesis and use as examples two drugs that have caused IADRs in human patients: ranitidine and diclofenac. The review focuses on experimental animal models that support the inflammatory stress hypothesis and on the mechanisms of hepatotoxic response in these models. The need for design of epidemiological studies and the potential for implementation of inflammation interaction studies in preclinical toxicity screening are also discussed briefly.

Hepatoprotective effect of 3-alkynyl selenophene on acute liver injury induced by D-galactosamine and lipopolysaccharide

The aim of this study was to investigate the hepatoprotective effect of 3-alkynyl selenophene (compound a), a selenophene compound, on acute liver injury induced by D-galactosamine (D-GalN) and lipopolysaccharide (LPS) in rats. The animals received compound a (25 and 50 mg/kg; per oral, p.o.) in the first day of treatment. In the second day, the rats received D-GalN (500 mg/kg; intraperitoneal, i.p.) and LPS (50 microg/kg; intraperitoneal, i.p.). Twenty-four hours after D-GalN/LPS administration animals were euthanized to the biochemical and histological analysis. Compound a (25 and 50 mg/kg; p.o.) protected against the increase in aspartate aminotransferase (AST) activity induced by D-GalN/LPS. Compound a at 50 mg/kg protected against the increase in alanine aminotransferase (ALT) activity induced by D-GalN/LPS. The inhibition of delta-aminolevulinic dehydratase (delta-ALA-D) activity and the decrease of ascorbic acid levels caused by D-GalN/LPS were protected by compound a (25 and 50 mg/kg). Glutathione S-transferase (GST) and catalase activities were not altered in all groups. The histological data showed that sections of liver from D-GalN/LPS-treated rats presented massive hemorrhage, the presence of inflammatory cells and necrosis. Compound a attenuated D-GalN/LPS-induced hepatic histopathological alterations. Based on the results, we demonstrated the hepatoprotective effect of compound a on acute liver injury induced by D-GalN/LPS.

Differential effects of pyrrolidine dithiocarbamate on TNF-alpha-mediated liver injury in two different models of fulminant hepatitis

BACKGROUND/AIMS

Pyrrolidine dithiocarbamate (PDTC) is an inhibitor of nuclear factor kappa B (NF-kappaB) activation. The present study aimed to investigate the effects of PDTC on lipopolysaccharide (LPS)-induced liver injury in two different models of fulminant hepatitis.

METHODS

Mice infected with Bacillus Calmette Guerin (BCG) were challenged with LPS (0.2 mg/kg) to induce the model of inflammatory liver injury. Mice were injected with D-galactosamine (GalN, 600 mg/kg) and LPS (20 microg/kg) to induce the model of apoptotic liver injury. In the treatment groups, mice were pre-treated with PDTC (100 mg/kg), initiated 24 h prior to LPS.

RESULTS

PDTC pretreatment reduced the infiltration of inflammatory cells, inhibited NF-kappaB activation and the expression of tumor necrosis factor alpha (TNF-alpha), attenuated nitric oxide production, and alleviated hepatic glutathione depletion. Correspondingly, PDTC reduced serum alanine aminotransferase, improved hepatic necrosis, and prolonged the survival in the BCG/LPS model. Conversely, PDTC accelerated death and aggravated liver apoptosis in the GalN/LPS model, although it reduced nitric oxide production, attenuated glutathione depletion, and inhibited the expression of TNF-alpha in liver.

CONCLUSIONS

PDTC protects mice against BCG/LPS-induced inflammatory liver injury through the repression of NF-kappaB-mediated TNF-alpha release, while it seems to be detrimental in GalN/LPS-induced apoptotic liver damage.

Effects of thrombin inhibition with melagatran on renal hemodynamics and function and liver integrity during early endotoxemia

Sepsis is associated with an activation of the coagulation system and multiorgan failure. The aim of the study was to examine the effects of selective thrombin inhibition with melagatran on renal hemodynamics and function, and liver integrity, during early endotoxemia. Endotoxemia was induced in thiobutabarbital-anesthetized rats by an intravenous bolus dose of lipopolysaccharide (LPS; 6 mg/kg). Sham-Saline, LPS-Saline, and LPS-Melagatran study groups received isotonic saline or melagatran immediately before (0.75 micromol/kg iv) and continuously during (0.75 micromol.kg(-1).h(-1) iv) 4.5 h of endotoxemia. Kidney function, renal blood flow (RBF), and intrarenal cortical and outer medullary perfusion (OMLDF) measured by laser-Doppler flowmetry were analyzed throughout. Markers of liver injury and tumor necrosis factor (TNF)-alpha were measured in plasma after 4.5 h of endotoxemia. In addition, liver histology and gene expression were examined. Melagatran treatment prevented the decline in OMLDF observed in the LPS-Saline group (P < 0.05, LPS-Melagatran vs. LPS-Saline). However, melagatran did not ameliorate reductions in mean arterial pressure, RBF, renal cortical perfusion, and glomerular filtration rate or attenuate tubular dysfunctions during endotoxemia. Melagatran reduced the elevated plasma concentrations of aspartate aminotransferase (-34 +/- 11%, P < 0.05), alanine aminotransferase (-21 +/- 7%, P < 0.05), bilirubin (-44 +/- 9%, P < 0.05), and TNF-alpha (-32 +/- 14%, P < 0.05) in endotoxemia. Melagatran did not diminish histological abnormalities in the liver or the elevated hepatic gene expression of TNF-alpha, intercellular adhesion molecule-1, and inducible nitric oxide synthase in endotoxemic rats. In summary, thrombin inhibition with melagatran preserved renal OMLDF, attenuated liver dysfunction, and reduced plasma TNF-alpha levels during early endotoxemia.

Phagocytic and oxidative burst activity of neutrophils in the end stage of liver cirrhosis

AIM

To evaluate the phagocytic activity and neutrophil oxidative burst in liver cirrhosis.

METHODS

In 45 patients with advanced postalcoholic liver cirrhosis (aged 45+/-14 years) and in 25 healthy volunteers (aged 38+/-5 years), the percentage of phagocytizing cells after in vitro incubation with E. coli (Phagotest Kit), phagocytic activity (mean intensity of fluorescence, MIF) and the percentage of neutrophil oxidative burst (Bursttest Kit), and the level of free oxygen radical production (MIF of Rodamine 123) were analyzed by flow cytometry. The levels of soluble sICAM-1, sVCAM-1, sP-selectin, sE-selectin, sL-selectin, and TNF-alpha were determined in blood serum.

RESULTS

The percentage of E. coli phagocytizing neutrophils in liver cirrhosis patients was comparable to that in healthy subjects. MIF of neutrophil -- ingested E. coli was higher in patients with liver cirrhosis. The oxidative burst in E. coli phagocytizing neutrophils generated less amount of active oxygen compounds in liver cirrhosis patients (MIF of R123: 24.7+/-7.1 and 29.7+/-6.6 in healthy, P<0.01). Phorbol myristate acetate (PMA) -- stimulated neutrophilsproduced less reactive oxidants in liver cirrhosis patients than in healthy subjects (MIF of R123: 42.7+/-14.6 vs 50.2+/-13.3, P<0.01). A negative correlation was observed between oxidative burst MIF of PMA-stimulated neutrophils and ALT and AST levels (r -0.35, P<0.05; r-0.4, P<0.03). sVCAM-1, sICAM-1, sE-selectin concentrations correlated negatively with the oxygen free radical production (MIF of R123) in neutrophils after PMA stimulation in liver cirrhosis patients (r-0.45, P<0.05; r-0.41, P<0.05; r-0.39, P<0.05, respectively).

CONCLUSION

Neutrophil metabolic activity diminishes together with the intensification of liver failure. The metabolic potential of phagocytizing neutrophils is significantly lower in liver cirrhosis patients, which can be one of the causes of immune mechanism damage. The evaluation of oxygen metabolism of E. coli-stimulated neutrophils reveals that the amount of released oxygen metabolites is smaller in liver cirrhosis patients than in healthy subjects.

Protection of lethal toxicity of endotoxin by Salvia miltiorrhiza BUNGE is via reduction in tumor necrosis factor alpha release and liver injury

Lipopolysaccharide (LPS) has been implicated as one of the major cause of Gram-negative bacteria-induced sepsis that are life-threatening syndromes occurring in intensive care unit patients. Many natural products derived from medicinal plants may contain therapeutic values on protecting endotoxemia-induced sepsis by virtue their ability to modulate multiple pro-inflammatory cytokines. In the present study, we show that Salvia miltiorrhiza (SM) BUNGE or Danshen, used in treatment of various systemic and surgical infections in the hospitals of China, was able to block the lethal toxicity of LPS in mice via suppression of TNF-alpha release and protection on liver injury. The ability of SM to suppress LPS-induced TNF-alpha release is further confirmed by in vitro experiments conducted on human peripheral blood leukocytes (PBL) and the RAW 264.7 macrophage cell line. Immunophenotyping by flow cytometry shows improved T-helper cell (CD4) and T-suppressor cells (CD8) ratio in SM-treated PBL and splenocytes of LPS-challenged mice. The drop in plasma glutamate-pyruvate transaminase (GPT) induced by LPS provides evidence that SM can protect hepatic damage. The present study explains some known biological activities of SM, and supports the clinical application of SM in the prevention of inflammatory diseases induced by Gram-negative bacteria.

Hypocapnia attenuates mesenteric ischemia-reperfusion injury in a rat model

PURPOSE

Hypocapnia, a recognized complication of high frequency oscillation ventilation, has multiple adverse effects on lung and brain physiology in vivo, including potentiation of free radical injury. We hypothesized that hypocapnia would potentiate the effects of mesenteric ischemia-reperfusion on bowel, liver and lung injury.

METHODS

Anesthetized male Sprague-Dawley rats were ventilated with high frequency oscillation and were randomized to one of four groups, exposed to either mesenteric ischemia-reperfusion or sham surgery, and to either hypocapnia or normocapnia.

RESULTS

All animals survived the protocol. Ischemia-reperfusion caused significant histologic bowel injury. Bowel 8-isoprostane generation was greater in ischemia-reperfusion vs sham, but was attenuated by hypocapnia. Laser-Doppler flow studies of bowel perfusion confirmed that hypocapnia attenuated reperfusion following ischemia. Plasma alanine transaminase, reflecting overall hepatocellular injury, was not increased by ischemia-reperfusion but was increased by hypocapnia; however, hepatic isoprostane generation was increased by ischemia-reperfusion, and not by hypocapnia. Oxygenation was comparable in all groups, and compliance was impaired by ischemia-reperfusion but not by hypocapnia.

CONCLUSION

Hypocapnia, although directly injurious to the liver, attenuates ischemia-reperfusion induced lipid peroxidation in the bowel, possibly through attenuation of blood flow during reperfusion.

Plasma butyrylcholinesterase activity protects against cocaine hepatotoxicity in female mice

Oral cocaine administration results in hepatic necrosis, increased plasma transaminase concentration, and decreased antioxidative capability, which is potentiated by lipopolysaccharide (LPS) in male CF-1 mice. Females administered the same treatment regimen display none of the hepatotoxic effects seen in their male counterparts. This study was conducted to further dissect the mechanism responsible for this gender difference in cocaine hepatotoxicity (CH) and lipopolysaccharide potentiation of CH. Male and female CF-1 mice were orally administered 20 mg/kg cocaine hydrochloride once daily for 7 days. Four hours after the last cocaine administration the mice were administered 12 x 10(6) EU LPS intraperitoneally. The activity of plasma esterase (butyrylcholinesterase), the enzyme responsible for the major pathway of cocaine metabolism to nonhepatotoxic metabolites, was measured. Aminotransferase release and histological analysis were used to determine hepatotoxicity. The concentration of the hepatotoxic precursor norcocaine was measured in the plasma and liver. Regardless of treatment, males were shown to have only 30% of the plasma esterase activity displayed by females. In addition, administration of testosterone to ovariectomized females resulted in a 70% reduction in plasma esterase activity when compared with surgically unaltered females. Moreover, hepatic norcocaine was not detected in the plasma or liver of surgically unaltered female animals, while it was present in males and testosterone-supplemented ovariectomized females. These results indicate that plasma esterase activity is heavily influenced by sex hormones, predominantly testosterone, in CF-1 mice. Suppression of plasma esterase by testosterone correlates with decreased norcocaine production and is therefore responsible, in part, for the increased CH seen following oral administration with and without LPS exposure in male CF-1 mice.

Induction of a 72-kDa heat shock protein and protection against lipopolysaccharide-induced liver injury in cirrhotic rats

BACKGROUND AND AIM

A 70-kDa heat shock protein (stress-inducible HSP70, HSP72) has been reported to be a cytoprotectant in a variety of organs. It has been reported that HSP72 protected non-cirrhotic rats against endotoxemia. However, its cytoprotective effect against endotoxemia in cirrhotic rats has not yet been studied. In this study, we investigated the cytoprotective effect of HSP72 on lipopolysaccharide (LPS)-induced liver injury in carbon tetrachloride (CCl(4))-induced cirrhotic rats.

METHODS

Liver cirrhosis was produced by an 8-week intraperitoneal injection of CCl(4) in male Sprague-Dawley rats. Expression of HSP72 was investigated using western blot analysis. Cirrhotic rats were given an intraperitoneal injection of LPS (10 mg/kg) with or without hyperthermia (42.5 degrees C, 15 min) preconditioning. Liver injury was assessed biochemically (aspartate transaminase, alanine transaminase, bilirubin, lactate dehydrogenase, creatinine) and histologically. The plasma tumor necrosis factor (TNF)-alpha level was determined.

RESULTS

Hyperthermia preconditioning induced a 4-fold increase in HSP72 in the cirrhotic rat liver. Pre-induction of HSP72 prevented LPS-induced liver injury, as evaluated using serum biochemical parameters and histology with reduced TNF-alpha response.

CONCLUSION

These findings suggest that pre-induction of HSP72 may provide therapeutic strategies for Gram-negative sepsis-induced liver injury in liver cirrhosis.

Effect of intravenous endotoxin on blood cell profiles of broilers housed in cages and floor litter environments

Commercial broilers are constantly exposed to airborne microorganisms and endotoxin (lipopolysaccharide, LPS). It has been shown that microbial contamination of the air was higher in broiler houses using floor litter than in broiler houses using netting-type floors. The current study evaluated the effect of housing conditions on blood leukocyte profiles and tested the hypothesis that, when compared to broilers reared in clean stainless steel cages (Cage group), broilers raised on floor litter (Floor group) should experience a higher environmental challenge and have a desensitized immune system that may exhibit better tolerance/resistance to subsequent intravenous LPS challenge. Hematological parameters were evaluated prior to and following i.v. administration of 1 mg/kg BW Salmonella typhimurium LPS (dissolved at 1 mg/0.25 mL in PBS) or i.v. injection of 0.25 mL/kg BW PBS alone. The results showed that prior to LPS/PBS injection, broilers in the cage group had higher heterophil and monocyte concentrations, a higher B cell percentage within the lymphocyte population, and a higher heterophil to lymphocyte (H:L) ratio in the blood. The i.v. LPS injection resulted in 25% mortality in the cage group and 42% mortality in the floor group within 8 h post-injection. LPS reduced the concentrations of total white blood cells (WBC) and all differential WBC except eosinophils and increased thrombocyte concentrations within 1 h post-injection in both groups. All of these values returned to their respective pre-injection levels within 48 h post-injection in the surviving birds. The two groups exhibited similar overall hematological changes after LPS injection except that the cage group showed a higher H:L ratio at 8 h post-injection and a lower B-cell percentage within the lymphocyte population at 48 h post-injection when compared with the floor group. We concluded that the immune systems of broilers reared on floor litter were desensitized and exhibited less pronounced leukocyte responses to i.v. LPS when compared with those of broilers reared in clean stainless steel cages. However, such desensitization of the immune system did not help broilers survive subsequent i.v. LPS challenge.

The coagulation system contributes to synergistic liver injury from exposure to monocrotaline and bacterial lipopolysaccharide

Coexposure to a noninjurious dose of bacterial lipopolysaccharide (LPS; 7.4 x 106 EU/kg) and a nontoxic dose of the food-borne toxin monocrotaline (MCT; 100 mg/kg) leads to synergistic hepatotoxicity in Sprague-Dawley rats. Inflammatory factors, such as Kupffer cells (KCs), tumor necrosis factor-alpha (TNF)-alpha, and neutrophils (polymorphonuclear leukocytes; PMNs), are critical to the pathogenesis. Inasmuch as activation of the coagulation system and sinusoidal endothelial cell (SEC) injury precede hepatic parenchymal cell (HPC) injury, and since fibrin deposition occurs within liver lesions, the coagulation system might be a critical component of injury. In this study, this hypothesis is tested, and the interdependence of the coagulation system and inflammatory factors is explored. Administration of the anticoagulants heparin or warfarin to MCT/LPS-cotreated animals attenuated HPC and SEC injury. Morphometric analysis revealed that anticoagulant treatment significantly reduced the area of centrilobular and midzonal lesions. Heparin treatment also reduced fibrin deposition in these regions. Furthermore, anticoagulant treatment decreased hepatic PMN accumulation but did not affect plasma TNF-alpha concentration. Neither KC inactivation nor TNF-alpha depletion prevented activation of the coagulation system. PMN depletion, however, prevented coagulation system activation, suggesting that PMNs are needed for this response. These results provide evidence that the coagulation system and its interplay with PMNs are important in the pathogenesis of MCT/LPS-induced liver injury.

Thrombin and protease-activated receptor-1 agonists promote lipopolysaccharide-induced hepatocellular injury in perfused livers

Bacterial lipopolysaccharide (LPS) is a potent inflammatory agent capable of producing liver injury, the pathogenesis of which depends on numerous mediators, including thrombin. Previous studies showed that thrombin promotes LPS-induced liver injury independent of its ability to form fibrin clots. In isolated, buffer-perfused livers from LPS-treated rats, thrombin added to the perfusion buffer caused dose-dependent liver injury with an EC(50) value of 0.4 nM, consistent with activation by thrombin of a protease-activated receptor (PAR). Actions of thrombin at PARs can be mimicked by thrombin receptor-activating peptides (TRAPs). TRAPs for PAR-1 reproduced the injury caused by thrombin in isolated livers, suggesting that one mechanism by which thrombin promotes LPS-induced liver injury is by activating PAR-1. Immunocytochemistry demonstrated the presence of PAR-1 on sinusoidal endothelial cells and Kupffer cells but not on parenchymal cells or neutrophils. Previous studies showed that thrombin interacts with neutrophils in the genesis of liver injury after LPS treatment. To explore this interaction further, the influence of thrombin on mediators that modulate neutrophil function were evaluated. Inhibition of thrombin in LPS-treated rats prevented liver injury but did not prevent up-regulation of cytokine-induced neutrophil chemoattractant-1, macrophage inflammatory protein-2, or intercellular adhesion molecule-1. Thrombin inhibition did, however, prevent neutrophil (PMN) degranulation in vivo as measured by plasma elastase levels. In addition, elastase concentration was increased in the perfusion medium of livers isolated from LPS-treated rats and perfused with TRAPs. These results suggest that activation of PAR-1 after LPS exposure promotes PMN activation and hepatic parenchymal cell injury.

Lipopolysaccharides in liver injury: molecular mechanisms of Kupffer cell activation

Endogenous gut-derived bacterial lipopolysaccharides have been implicated as important cofactors in the pathogenesis of liver injury. However, the molecular mechanisms by which lipopolysaccharides exert their effect are not entirely clear. Recent studies have pointed to proinflammatory cytokines such as tumor necrosis factor-alpha as mediators of hepatocyte injury. Within the liver, Kupffer cells are major sources of proinflammatory cytokines that are produced in response to lipopolysaccharides. This review will focus on three important molecular components of the pathway by which lipopolysaccharides activate Kupffer cells: CD14, Toll-like receptor 4, and lipopolysaccharide binding protein. Within the liver, lipopolysaccharides bind to lipopolysaccharide binding protein, which then facilitates its transfer to membrane CD14 on the surface of Kupffer cells. Signaling of lipopolysaccharide through CD14 is mediated by the downstream receptor Toll-like receptor 4 and results in activation of Kupffer cells. The role played by these molecules in liver injury will be examined.