Expression and regulation of intercellular adhesion molecule-1 (ICAM-1) in organotypic cultures of rat liver tissue

The gut–liver axis in sepsis: interaction mechanisms and therapeutic potential

Sepsis is a potentially fatal condition caused by dysregulation of the body's immune response to an infection. Sepsis-induced liver injury is considered a strong independent prognosticator of death in the critical care unit, and there is anatomic and accumulating epidemiologic evidence that demonstrates intimate cross talk between the gut and the liver. Intestinal barrier disruption and gut microbiota dysbiosis during sepsis result in translocation of intestinal pathogen-associated molecular patterns and damage-associated molecular patterns into the liver and systemic circulation. The liver is essential for regulating immune defense during systemic infections via mechanisms such as bacterial clearance, lipopolysaccharide detoxification, cytokine and acute-phase protein release, and inflammation metabolic regulation. When an inappropriate immune response or overwhelming inflammation occurs in the liver, the impaired capacity for pathogen clearance and hepatic metabolic disturbance can result in further impairment of the intestinal barrier and increased disruption of the composition and diversity of the gut microbiota. Therefore, interaction between the gut and liver is a potential therapeutic target. This review outlines the intimate gut–liver cross talk (gut–liver axis) in sepsis.

Prominent Receptors of Liver Sinusoidal Endothelial Cells in Liver Homeostasis and Disease

Liver sinusoidal endothelial cells (LSECs) are the most abundant non-parenchymal cells lining the sinusoidal capillaries of the hepatic system. LSECs are characterized with numerous fenestrae and lack basement membrane as well as a diaphragm. These unique morphological characteristics of LSECs makes them the most permeable endothelial cells of the mammalian vasculature and aid in regulating flow of macromolecules and small lipid-based structures between sinusoidal blood and parenchymal cells. LSECs have a very high endocytic capacity aided by scavenger receptors (SR), such as SR-A, SR-B (SR-B1 and CD-36), SR-E (Lox-1 and mannose receptors), and SR-H (Stabilins). Other high-affinity receptors for mediating endocytosis include the FcγRIIb, which assist in the antibody-mediated removal of immune complexes. Complemented with intense lysosomal activity, LSECs play a vital role in the uptake and degradation of many blood borne waste macromolecules and small (<280 nm) colloids. Currently, seven Toll-like receptors have been investigated in LSECs, which are involved in the recognition and clearance of pathogen-associated molecular pattern (PAMPs) as well as damage associated molecular pattern (DAMP). Along with other SRs, LSECs play an essential role in maintaining lipid homeostasis with the low-density lipoprotein receptor-related protein-1 (LRP-1), in juxtaposition with hepatocytes. LSECs co-express two surface lectins called L-Specific Intercellular adhesion molecule-3 Grabbing Non-integrin Receptor (L-SIGN) and liver sinusoidal endothelial cell lectin (LSECtin). LSECs also express several adhesion molecules which are involved in the recruitment of leukocytes at the site of inflammation. Here, we review these cell surface receptors as well as other components expressed by LSECs and their functions in the maintenance of liver homeostasis. We further discuss receptor expression and activity and dysregulation associated with the initiation and progression of many liver diseases, such as hepatocellular carcinoma, liver fibrosis, and cirrhosis, alcoholic and non-alcoholic fatty liver diseases and pseudocapillarization with aging.

Role of liver ICAM-1 in metastasis

Intercellular adhesion molecule (ICAM)-1, is a transmembrane glycoprotein of the immunoglobulin (Ig)-like superfamily, consisting of five extracellular Ig-like domains, a transmembrane domain and a short cytoplasmic tail. ICAM-1 is expressed in various cell types, including endothelial cells and leukocytes, and is involved in several physiological processes. Furthermore, it has additionally been reported to be expressed in various cancer cells, including melanoma, colorectal cancer and lymphoma. The majority of studies to date have focused on the expression of the ICAM-1 on the surface of tumor cells, without research into ICAM-1 expression at sites of metastasis. Cancer cells frequently metastasize to the liver, due to its unique physiology and specialized liver sinusoid capillary network. Liver sinusoidal endothelial cells constitutively express ICAM-1, which is upregulated under inflammatory conditions. Furthermore, liver ICAM-1 may be important during the development of liver metastasis. Therefore, it is necessary to improve the understanding of the mechanisms mediated by this adhesion molecule in order to develop host-directed anticancer therapies.

Autocrine vascular endothelial growth factor signaling promotes cell proliferation and modulates sorafenib treatment efficacy in hepatocellular carcinoma

Tumor cells express vascular endothelial growth factor (VEGF) that can activate VEGF receptors (VEGFRs) on or within tumor cells to promote growth in an angiogenesis-independent fashion; however, this autocrine VEGF pathway has not been reported in hepatocellular carcinoma (HCC). Sorafenib, an angiogenic inhibitor, is the only drug approved for use in advanced HCC patients. Yet the treatment efficacy is diverse and the mechanism behind it remains undetermined. Our aims were to study the molecular mechanisms underlying autocrine VEGF signaling in HCC cells and evaluate the critical role of autocrine VEGF signaling on sorafenib treatment efficacy. By immunohistochemistry, we found robust nuclear and cytoplasmic staining for active, phosphorylated VEGF receptor 1 (pVEGFR1) and phosphorylated VEGF receptor 2 (pVEGFR2), and by western blotting we found that membrane VEGFR1 and VEGFR2 increased in HCC tissues. We showed that autocrine VEGF promoted phosphorylation of VEGFR1 and VEGFR2 and internalization of pVEGFR2 in HCC cells, which was both pro-proliferative through a protein lipase C-extracellular kinase pathway and self-sustaining through increasing VEGF, VEGFR1, and VEGFR2 mRNA expressions. In high VEGFR1/2-expressing HepG2 cells, sorafenib treatment inhibited cell proliferation, reduced VEGFR2 mRNA expression in vitro, and delayed xenograft tumor growth in vivo. These results were not found in low VEGFR1/2-expressing Hep3B cells. In an advanced HCC population on sorafenib treatment for postoperative recurrence, we found that the absence of VEGFR1 or VEGFR2 expression in resected tumor tissues before sorafenib treatment was associated with poorer overall survival.

CONCLUSION

Autocrine VEGF signaling directly promotes HCC cell proliferation and affects the sorafenib treatment outcome in vitro and in vivo, which may enable better stratification for clinical treatment decisions.

Focal adhesion kinase (FAK) gene amplification and its clinical implications in gastric cancer

Focal adhesion kinase, a nonreceptor tyrosine kinase, is known to be associated with tumor progression in various tumors. Because the clinical implications of focal adhesion kinase overexpression in gastric cancer have been inconsistent, we extended previous studies and evaluated focal adhesion kinase gene amplification as well as its protein expression. Immunohistochemical tissue array analysis showed that focal adhesion kinase immunoreactivity was present in both the cytoplasm and membrane of gastric cancer cells. Diffuse immunoreactivity of focal adhesion kinase protein in cytoplasm or membrane was found in 240 (54%) or 263 (59%) of 444 surgical samples, respectively, and positively correlated with tumor size, depth of tumor infiltration, nodal metastasis, distant metastasis, lymphatic invasion, and venous invasion (P < .001). Regarding focal adhesion kinase gene amplification, fluorescence in situ hybridization analysis showed focal adhesion kinase gene amplification in 34 (8.9%) of 384 gastric cancer specimens, whereas there was no amplification in any case of atrophy, intestinal metaplasia, or adenoma/dysplasia. Focal adhesion kinase gene amplification was positively associated with age (P = .012), tumor size (P = .007), nodal metastasis (P = .021), distant metastasis (P = .029), lymphatic invasion (P = .006), venous invasion (P = .032), and perineural invasion (P = .023). Focal adhesion kinase protein expression and gene amplification were positively correlated with each other, and each of them was found to be an independent poor prognostic factor (P < .01). In conclusion, our results showed that either focal adhesion kinase protein expression or focal adhesion kinase gene amplification was significantly correlated with cancer progression and poor prognosis in gastric cancer. Thus, focal adhesion kinase gene amplification could supplement its protein expression for the diagnosis and treatment of gastric cancer.

Liver fibrosis in vitro: Cell culture models and precision-cut liver slices

Chronic liver injury of various etiologies can cause liver fibrosis, which is characterized by the progressive accumulation of connective tissue in the liver. As no effective treatment for liver fibrosis is available yet, extensive research is ongoing to further study the mechanisms underlying the development of disease- or toxicity-induced liver fibrosis and to identify potential pro- or anti-fibrotic properties of compounds. This review gives an overview of the in vitro methods that are currently available for this purpose. The first focus is on cell culture models, since the majority of in vitro research uses these systems. Both primary cells and cell lines as well as the use of different culture matrices and co-culture models are discussed. Second, the use of precision-cut liver slices, which recently came into attention as in vitro model for the study of fibrosis, is discussed. The overview clearly shows that continuous optimization and adaptation have extended the potential of in vitro models for liver fibrosis during the past years. By combining the use of the different cell and tissue culture models, the mechanisms underlying multicellular fibrosis development can be studied in vitro and potential pro- or anti-fibrotic properties of compounds can be identified both on single liver cell types and in human liver tissue.

Downregulation of cytokine release by heat preconditioning of livers used for transplantation in rats

We evaluated the changes in the levels of released cytokines following heat preconditioning of the livers used in rat liver transplantation. The donor rats in the heat preconditioning (HP) group were subjected to heat preconditioning 48 h before graft harvesting. The liver isografts were preserved in Euro-Collins solution for 8 h, and then transplanted orthotopically. The one-week survival rate of the HP group was significantly better than that of the control (C) group. The serum levels of interleukin-6 and interleukin-10 were significantly lower in the HP group than in the C group. Histological staining revealed that the stagnation of red blood cells and infiltration of neutrocytes were reduced in the HP group. The expression of intercellular adhesion molecule-1 was decreased around the central vein in the HP group, as revealed by immunohistochemistry. These results indicate that heat preconditioning downregulates cytokine release and reduces the frequency of microcirculation disorders.

Functional analysis of mouse hepatocytes differing in DNA content: volume, receptor expression, and effect of IFNgamma

Polyploidy and binuclearity are characteristics of the mammalian liver. Increasing polyploidisation occurs with age and after administration of various drugs and chemicals. This study was designed to examine the function of ploidy by addressing several questions: (1) Does the increase in size of polyploid hepatocytes have any physiological function by altering surface receptor expression such as intercellular adhesion molecule-1 (ICAM-1, CD54) or IFNgammaR? and (2) Do polyploid cells respond differently to inflammatory cytokines such as interferon gamma (IFNgamma)? We have developed a method to accurately measure the volume of live isolated hepatocytes using confocal microscopy and image analysis. Using flow cytometry, we have shown that the expression of ICAM-1 increases with increasing DNA content and IFNgammaR is not detectable on isolated mouse hepatocytes. Diploid (2n), tetraploid (4n) and octoploid (8n) hepatocytes were found to be equally susceptible to IFNgamma-induced apoptosis in vitro. Although the function of polyploidy remains unanswered, we have described some of the characteristics of polyploidy in isolated hepatocytes and in vitro.

Luteolin reduces lipopolysaccharide-induced lethal toxicity and expression of proinflammatory molecules in mice

Luteolin is a flavonoid that has been shown to reduce proinflammatory molecule expression in vitro. In the present study, we have tested the ability of luteolin to inhibit lipopolysaccharide (LPS)- induced lethal toxicity and proinflammatory molecule expression in vivo. Mice receiving LPS (Salmonella enteriditis LPS, 32 mg/kg, intraperitoneally) exhibited high mortality with only 4.1% of the animals surviving seven days after the LPS challenge. On the contrary, mice that had received luteolin (0.2 mg/kg, intraperitoneally) before LPS showed an increased survival rate with 48% remaining alive on Day 7. To investigate the mechanism by which luteolin affords protection against LPS toxicity we measured intercellular adhesion molecule-1 (ICAM-1) and tumor necrosis factor-alpha (TNF-alpha) production in response to LPS in the presence or absence of luteolin pretreatment. Treatment of animals with LPS increased serum TNF-alpha levels in a time-dependent manner. The increase in peak serum TNF-alpha levels was sensitive to luteolin pretreatment. Luteolin pretreatment also reduced LPS-stimulated ICAM-1 expression in the liver and abolished leukocyte infiltration in the liver and lung. We conclude that luteolin protects against LPS-induced lethal toxicity, possibly by inhibiting proinflammatory molecule (TNF-alpha, ICAM-1) expression in vivo and reducing leukocyte infiltration in tissues.

Integrin up-regulation in chronic liver disease: relationship with inflammation and fibrosis in chronic hepatitis C

In 94 patients with chronic hepatitis C, the pattern of integrin expression was correlated with firstly, the histological activity index, necro-inflammatory grade, and stage of fibrosis; secondly, the expression of inflammatory markers including ICAM-1; and thirdly, the extent and intensity of laminin deposition in the perisinusoidal matrix. Immunohistochemical results were evaluated according to a semi-quantitative scoring system or by image analysis. Increased beta1 expression was observed in 88.2% of cases. The expression of alpha1 and alpha5 was increased in 55% and 58.5% of cases, respectively. alpha6 chain was detected in 78.7% of cases. There were no statistically significant differences in integrin expression level according to Knodell's score, inflammatory grade, or stage of fibrosis. ICAM-1 expression was higher in patients with high scores for beta1 expression, but the differences were not statistically significant. There were significantly more patients with high scores for beta1 expression among those with continuous perisinusoidal deposition of laminin. Moreover, a close statistical correlation was observed between alpha6 induction and perisinusoidal laminin deposition (p<0.001). The results suggest that integrin up-regulation in chronic hepatitis C is more closely related to the fibrotic process than to the inflammatory lesions. This reinforces the idea that integrin induction in chronic liver disease is part of a coordinated process involved in the progression of liver fibrosis.

Spheroids: relation between tumour and endothelial cells

It has recently been established that the microenvironment plays a major role in many physiological and pathological events. Indeed cell-cell and cell-extracellular matrix contacts are necessary for much cellular function such as differentiation, proliferation, cell death, apoptosis and angiogenesis. For growth, proliferating tumour cells need to be fed by nutrients and oxygen brought by new vessels. In this context, scientists seek a new model that allows for the investigation of both angiogenesis and the influence of the microenvironment on this phenomenon. The purpose of this paper is to review the literature on the relation between tumour and endothelial cells grown as spheroids, a technique that allows us to study in three-dimensions the influence of cell contact on this growth. For the purpose of clarification, this review has recategorised the different studies on spheroids into three classes: (1) spheroids grown in vitro and then reimplanted in animals to follow endothelial cell infiltration; (2) spheroids grown in vitro and then cultured on endothelial cell monolayers; (3) tumours grown in vitro such as organotypic culture. This review attempts to demonstrate that spheroid cell cultures are useful for studying the relation between tumour and endothelial cells and to analyse physiological phenomena such as wound healing, extravasation and intravasation.