Kinetics of lipopolysaccharide clearance by Kupffer and parenchyma cells in perfused rat liver

Increased Liver Localization of Lipopolysaccharides in Human and Experimental NAFLD

BACKGROUND AND AIMS

Lipopolysaccharides (LPS) is increased in nonalcoholic fatty liver disease (NAFLD), but its relationship with liver inflammation is not defined.

APPROACH AND RESULTS

We studied Escherichia coli LPS in patients with biopsy-proven NAFLD, 25 simple steatosis (nonalcoholic fatty liver) and 25 nonalcoholic steatohepatitis (NASH), and in mice with diet-induced NASH. NASH patients had higher serum LPS and hepatocytes LPS localization than controls, which was correlated with serum zonulin and phosphorylated nuclear factor-κB expression. Toll-like receptor 4 positive (TLR4+ ) macrophages were higher in NASH than simple steatosis or controls and correlated with serum LPS. NASH biopsies showed a higher CD61+ platelets, and most of them were TLR4+ . TLR4+ platelets correlated with serum LPS values. In mice with NASH, LPS serum levels and LPS hepatocyte localization were increased compared with control mice and associated with nuclear factor-κB activation. Mice on aspirin developed lower fibrosis and extent compared with untreated ones. Treatment with TLR4 inhibitor resulted in lower liver inflammation in mice with NASH.

CONCLUSIONS

In NAFLD, Escherichia coli LPS may increase liver damage by inducing macrophage and platelet activation through the TLR4 pathway.

Drainage of inflammatory macromolecules from the brain to periphery targets the liver for macrophage infiltration

Many brain pathologies are associated with liver damage, but a direct link has long remained elusive. Here, we establish a new paradigm for interrogating brain-periphery interactions by leveraging zebrafish for its unparalleled access to the intact whole animal for in vivo analysis in real time after triggering focal brain inflammation. Using traceable lipopolysaccharides (LPS), we reveal that drainage of these inflammatory macromolecules from the brain led to a strikingly robust peripheral infiltration of macrophages into the liver independent of Kupffer cells. We further demonstrate that this macrophage recruitment requires signaling from the cytokine IL-34 and Toll-like receptor adaptor MyD88, and occurs in coordination with neutrophils. These results highlight the possibility for circulation of brain-derived substances to serve as a rapid mode of communication from brain to the liver. Understanding how the brain engages the periphery at times of danger may offer new perspectives for detecting and treating brain pathologies.

Non-amyloid liver involvement in familial Mediterranean fever: A systematic literature review

INTRODUCTION

Familial Mediterranean fever (FMF), the most frequent autoinflammatory disease, is caused by mutations in the MEFV gene. It is characterized by recurrent febrile attacks of polyserositis. Liver abnormalities may develop during its course, but they remain poorly defined.

OBJECTIVE

To describe liver involvement in FMF patients.

METHODS

A systematic search was conducted through PubMed/Medline and Embase from 1946 to January 2020. All articles describing children and adults with FMF and liver involvement were included. Patients with amyloidosis were excluded. The selected full-text articles were independently reviewed by three investigators.

RESULTS

Forty-three articles were identified, of which 20 articles with a total of 99 patients were included: 74 adults, 23 children and two patients of unknown age. Ten patients had cryptogenic cirrhosis, 48 had nonalcoholic fatty liver disease (NAFLD), four had Budd-Chiari syndrome (BCS), 12 had isolated hyperbilirubinaemia and 25 had elevated liver enzymes.

CONCLUSION

Despite a low prevalence of metabolic risk factors, FMF may be associated with NAFLD and cryptogenic cirrhosis as a consequence of chronic or recurrent inflammation. FMF patients should be regularly screened for liver injury. The latter may be prevented and treated by daily colchicine intake. The evidence was insufficient to establish an association with BCS, hyperbilirubinaemia or autoimmune hepatitis.

Hepatocyte Injury and Hepatic Stem Cell Niche in the Progression of Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease characterized by lipid accumulation in hepatocytes in the absence of excessive alcohol consumption. The global prevalence of NAFLD is constantly increasing. NAFLD is a disease spectrum comprising distinct stages with different prognoses. Non-alcoholic steatohepatitis (NASH) is a progressive condition, characterized by liver inflammation and hepatocyte ballooning, with or without fibrosis. The natural history of NAFLD is negatively influenced by NASH onset and by the progression towards advanced fibrosis. Pathogenetic mechanisms and cellular interactions leading to NASH and fibrosis involve hepatocytes, liver macrophages, myofibroblast cell subpopulations, and the resident progenitor cell niche. These cells are implied in the regenerative trajectories following liver injury, and impairment or perturbation of these mechanisms could lead to NASH and fibrosis. Recent evidence underlines the contribution of extra-hepatic organs/tissues (e.g., gut, adipose tissue) in influencing NASH development by interacting with hepatic cells through various molecular pathways. The present review aims to summarize the role of hepatic parenchymal and non-parenchymal cells, their mutual influence, and the possible interactions with extra-hepatic tissues and organs in the pathogenesis of NAFLD.

Disruption of the gut-liver axis in the pathogenesis of acute-on-chronic liver failure

Acute-on-chronic liver failure (ACLF) is characterized by organ failure mediated by acute decompensation of cirrhosis. Recent studies have highlighted the importance of the gut-liver axis (GLS) and its association with ACLF pathogenesis. In this review, we discuss the mechanisms related to the alteration of the GLA and their involvement in ACLF pathogenesis and suggest some possible therapeutic options that could modulate the GLA dysfunction. This knowledge may provide information useful for the design of therapeutic strategies for gut dysbiosis and its complications in ACLF.

CETP Lowers TLR4 Expression Which Attenuates the Inflammatory Response Induced by LPS and Polymicrobial Sepsis

Sepsis is a systemic inflammatory response to infection eliciting high mortality rate which is a serious health problem. Despite numerous studies seeking for therapeutic alternatives, the mechanisms involved in this disease remain elusive. In this study we evaluated the influence of cholesteryl ester transfer protein (CETP), a glycoprotein that promotes the transfer of lipids between lipoproteins, on the inflammatory response in mice. Human CETP transgenic mice were compared to control mice (wild type, WT) after polymicrobial sepsis induced by cecal ligation and puncture (CLP), aiming at investigating their survival rate and inflammatory profiles. Macrophages from the peritoneal cavity were stimulated with LPS in the presence or absence of recombinant CETP for phenotypic and functional studies. In comparison to WT mice, CETP mice showed higher survival rate, lower IL-6 plasma concentration, and decreased liver toll-like receptor 4 (TLR4) and acyloxyacyl hydrolase (AOAH) protein. Moreover, macrophages from WT mice to which recombinant human CETP was added decreased LPS uptake, TLR4 expression, NF-κB activation and IL-6 secretion. This raises the possibility for new therapeutic tools in sepsis while suggesting that lowering CETP by pharmacological inhibitors should be inconvenient in the context of sepsis and infectious diseases.

Immunohistochemical and histoplanimetrical study on the endothelial receptor involved in transportation of minute chylomicrons into subepithelial portal blood in intestinal villi of the rat jejunum

A portion of the minute chylomicrons less than 75 nm in diameter are transcytosed from the extravascular tissue into the subepithelial blood capillaries (sBC) in the villous apices of the rat jejunum. However, the details of the transportation mechanism have not been clarified. In this study, the endothelial receptor involved in the transportation of minute chylomicrons into the sBC’s lumina was immunohistochemically and histoplanimetrically examined in intestinal villi of the rat jejunum. Immunopositivity for very low density lipoprotein (VLDL) receptor was detected on the luminal and basal surfaces of the endothelial cells of sBC in approximately 68% of those apices of jejunal villi that possessed numerous chylomicrons in the lamina propria, while VLDL receptor was detected on the endothelial cells of sBC in only approximately 8% of intestinal villi that possessed few or no chylomicrons in the lamina propria. No immunopositivity for LDL receptor was detected in the sBC of all intestinal villi. These findings suggest that VLDL receptor is expressed by the endothelial cells of the sBC in conjunction with the filling of the lamina propria of jejunal villi with many chylomicrons produced by the villous columnar epithelial cells and that the VLDL receptor mediates the transportation of minute chylomicrons, maybe VLDL, into the subepithelial portal blood from the extravascular tissue of the rat jejunal villi.

Hepatic uptake and deacylation of the LPS in bloodborne LPS-lipoprotein complexes

Much evidence indicates that bacterial LPS (endotoxin) is removed from the bloodstream mainly by the liver, yet the hepatic uptake mechanisms remain uncertain and controversial. In plasma, LPS can be either 'free' (as aggregates, bacterial membrane fragments or loosely bound to albumin, CD14, or other proteins) or 'bound' (complexed with lipoproteins). Whereas most free LPS is taken up by Kupffer cells (KCs), lipoprotein-bound LPS has seemed to be cleared principally by hepatocytes. Here, we compared the liver's ability to take up and deacylate free LPS aggregates and the LPS in preformed LPS-high density lipoprotein (HDL) complexes. In mice examined from 1 h to 7 d after a small amount of fluorescent (FITC-)LPS was injected into a lateral tail vein, we found FITC-LPS almost entirely within, or adjacent to, KCs. As expected, FITC-LPS complexed with HDL (FITC-LPS-HDL) disappeared more slowly from the circulation and a smaller fraction of the injected dose of FITC-LPS was found in the liver. Unexpectedly, the FITC-LPS injected as FITC-LPS-HDL complexes was also found within sinusoids, adjacent to, or within, KCs. In other experiments, we found that both free and HDL-bound radiolabeled LPS underwent enzymatic deacylation by acyloxyacyl hydrolase (AOAH), the LPS-inactivating enzyme that is principally produced within the liver by KCs. Our observations suggest that KCs and AOAH play important roles in clearing and catabolizing both free LPS and the LPS in circulating LPS-HDL complexes.

Beta2-integrin-induced p38 MAPK activation is a key mediator in the CD14/TLR4/MD2-dependent uptake of lipopolysaccharide by hepatocytes

The liver is the main organ that clears circulating lipopolysaccharide (LPS), and hepatocytes are a major cell type involved in LPS uptake. Little is known about the mechanisms for LPS internalization in hepatocytes and what signaling pathways are involved. We show here that LPS uptake is initiated after formation of a multi-receptor complex within lipid rafts. We find that essential components for LPS uptake are CD14, TLR4, MD2, and the beta2-integrin CD11b/CD18. Activation of p38 MAPK is also essential for the initiation of LPS uptake, and interestingly, we show that this activation is not through TLR4 signaling by MyD88 but through activation of TIRAP via CD11b/CD18. However, TLR4/MD2 remain essential components at the cell surface as part of the LPS receptor complex. We therefore suggest novel roles for TLR4/MD2, CD11b/CD18, TIRAP, and p38 MAPK in LPS uptake by hepatocytes.

Familial Mediterranean fever and cryptogenic cirrhosis

Familial Mediterranean fever (FMF) is a febrile disease characterized by acute, spontaneously resolving episodes of fever and pain caused by serosal inflammation and associated with mutations in the FMF gene, MEFV. Prophylaxis is maintained with colchicine. To our knowledge, no study has yet shown an association between FMF and cirrhosis of the liver. We conducted the current study to describe cryptogenic cirrhosis in FMF and to examine the possible relationship between the 2 entities. Patients with chronic liver disease were retrospectively identified through a computer search of a registry of 6000 patients with FMF followed in the clinics of the National Center for FMF. Data pertaining to FMF phenotype and genotype and characteristics of the liver disease were abstracted from patients' charts. Cryptogenic cause of cirrhosis was determined by exclusion of known causes of liver disease. Nine patients with cryptogenic cirrhosis were identified, comprising 0.15% of the FMF patient population, a rate significantly higher than the rate of 0.015% of cirrhosis of all types expected in the total population of Israel (p < 0.000). Most patients had typical FMF, with a normal severity score distribution. The mean daily dose of colchicine was 1.4 +/- 0.4 mg, not different from the usual dose. All 7 patients who underwent mutation analysis had 2 mutations. Five of them were homozygous for M694V. Child-Pugh classification was determined in 6 patients at the time of cirrhosis diagnosis, and was classified as A in 4 of them. These findings suggest that MEFV may serve as a modifier gene in cryptogenic cirrhosis. Genetic analysis in patients with cryptogenic cirrhosis unrelated to FMF, particularly patients of a Mediterranean origin, may be warranted in future studies.

Mannose-binding lectin augments the uptake of lipid A, Staphylococcus aureus, and Escherichia coli by Kupffer cells through increased cell surface expression of scavenger receptor A

We investigated roles of scavenger receptor A (SR-A) and mannose-binding lectin (MBL) in the uptake of endotoxin and bacteria by Kupffer cells. When [3H]lipid A was injected into retro-orbital plexus of mice, significantly less accumulation of lipid A in the liver was observed in SR-A-deficient mice and wild-type mice coinjected with fucoidan or acetylated low-density lipoprotein, which are known ligands for SR-A. Isolated Kupffer cells were able to take up [3H]lipid A in a time-dependent manner. The amount of lipid A associated with nonadherent Kupffer cells derived from SR-A-deficient mice was reduced by approximately 80% when compared with wild-type cells, indicating an important role of SR-A in endotoxin uptake by Kupffer cells. The lipid A uptake by Kupffer cells was significantly enhanced in the presence of rMBL. Coincubation of fucoidan with [3H]lipid A significantly inhibited the basal and the MBL-stimulated uptake of lipid A by Kupffer cells. Preincubation of MBL with Kupffer cells also increased the uptake of lipid A. These results indicate that MBL augments the SR-A-mediated uptake of lipid A by Kupffer cells. Consistently, the exposure of MBL to Kupffer cells increased cell surface SR-A expression. The phagocytosis of Staphylococcus aureus and Escherichia coli by Kupffer cells was also enhanced by preincubation of MBL with the cells. In addition, MBL bound to lipid A, LPS, and S. aureus, and precipitated S. aureus. This study demonstrates important roles of SR-A and MBL in the uptake of endotoxin and bacteria by Kupffer cells.

Effects of lactitol on intestinal microflora and plasma endotoxin in patients with chronic viral hepatitis

OBJECTIVES

To investigate the effects of lactitol on intestinal flora and the levels of plasma endotoxin in patients with chronic viral hepatitis.

METHODS

Sixty patients with chronic viral hepatitis and gut-derived endotoxemia were randomly divided into two groups: lactitol group (n=30) and control group (n=30). Patients in the control group received standard medical treatment for 3 weeks, while patients in the lactitol group received lactitol orally in addition to the standard medical treatment. Fecal flora and plasma endotoxin were measured before and after the treatment.

RESULTS

In the lactitol group, the numbers of Bifidobacterium and Lactobacillus per gram of wet feces were significantly increased (p<0.01) and Clostridium perfringens count was decreased markedly (p<0.001). The levels of plasma endotoxin decreased after the treatment from 72.89 ng/L to 33.33 ng/L in the lactitol group and from 66.00 ng/L to 51.07 ng/L in the control group, but the plasma endotoxin levels in the lactitol group decreased far more than in the control group (p<0.01).

CONCLUSIONS

Lactitol can decrease the levels of plasma endotoxin more effectively than standard medical treatment in patients with chronic viral hepatitis through improving intestinal microflora.

Binding of LPS and LPS--LDL complexes to rat hepatocytes

We studied binding of 3H-LPS toxin and LPS complexes with serum 125I-LDL to primary culture of rat hepatocytes. Receptor binding of LPS and LDL--LPS complex was 50 and 77% of the total, respectively. Scatchard plot was linear in both cases. LDL and LDL--LPS complexes were inessential for LPS binding, while LDL--LPS binding was appreciably suppressed by LPS (-30%) and LDL (-65%).

TLR-4 regulates CD8+ T cell trapping in the liver

Mammalian TLRs are understood primarily as an activating system for innate and adaptive immunity, but have also been implicated in sensing cellular damage and in promoting intestinal integrity. In this study we show that TLR-4 also controls the in vivo distribution of activated CD8+ T cells. The liver is a site for trapping and apoptosis of activated CD8+ T cells during systemic immune responses, but the reason for this is unknown. In this study we tested the hypothesis that the liver's constant exposure to endotoxin, derived from commensal bacteria in the gut, acts via TLR-4 to promote activated T cell adhesion. In the absence of TLR-4, the liver was compromised in its ability to sequester activated CD8+ T cells, and there was an inverse correlation between the frequency of activated CD8+ T cells trapped in the liver and their frequency in the circulating pool. Thus, in the absence of any inflammation, TLR-4 ligands play a significant role in the ability of the liver to trap activated CD8+ T cells. This provides a new perspective on the regulation of immune responses by TLR-4 under basal conditions.

Liver in sepsis and systemic inflammatory response syndrome

In patients with sepsis and SIRS, the liver has two opposing roles: a source of inflammatory mediators and a target organ for the effects of the inflammatory mediators. The liver is pivotal in modulating the systemic response to severe infection, because it contains the largest mass of macrophages (Kupffer cells) in the body; these macrophages can clear the endotoxin and bacteria that initiate the systemic inflammatory response. This article summarizes the functional changes that take place in the liver during sepsis and systemic inflammatory response syndrome and discusses the cellular and molecular mechanisms that underlie clinical outcomes.