Dynamics of cellular plasticity in non-alcoholic steatohepatitis (NASH)

Non-alcoholic steatohepatitis (NASH) is a pathogenic stage of the broader non-alcoholic fatty liver disease (NAFLD). Histological presentation of NASH includes hepatocyte ballooning, macrophage polarization, ductular reaction, and hepatic stellate cell (HSCs) activation. At a cellular level, a heterogenous population of cells such as hepatocytes, macrophages, cholangiocytes, and HSCs undergo dramatic intra-cellular changes in response to extracellular triggers, which are termed "cellular plasticity. This dynamic switch in the cellular structure and function of hepatic parenchymal and non-parenchymal cells and their crosstalk culminates in the perpetuation of inflammation and fibrosis in NASH. This review presents an overview of our current understanding of cellular plasticity in NASH and its molecular mechanisms, along with possible targeting to develop cell-specific NASH therapies.

Phenotypic characterization of liver tissue heterogeneity through a next-generation 3D single-cell atlas

Three-dimensional (3D) geometrical models are potent tools for quantifying complex tissue features and exploring structure-function relationships. However, these models are generally incomplete due to experimental limitations in acquiring multiple (> 4) fluorescent channels in thick tissue sections simultaneously. Indeed, predictive geometrical and functional models of the liver have been restricted to few tissue and cellular components, excluding important cellular populations such as hepatic stellate cells (HSCs) and Kupffer cells (KCs). Here, we combined deep-tissue immunostaining, multiphoton microscopy, deep-learning techniques, and 3D image processing to computationally expand the number of simultaneously reconstructed tissue structures. We then generated a spatial single-cell atlas of hepatic architecture (Hep3D), including all main tissue and cellular components at different stages of post-natal development in mice. We used Hep3D to quantitatively study 1) hepatic morphodynamics from early post-natal development to adulthood, and 2) the effect on the liver's overall structure when changing the hepatic environment after removing KCs. In addition to a complete description of bile canaliculi and sinusoidal network remodeling, our analysis uncovered unexpected spatiotemporal patterns of non-parenchymal cells and hepatocytes differing in size, number of nuclei, and DNA content. Surprisingly, we found that the specific depletion of KCs results in morphological changes in hepatocytes and HSCs. These findings reveal novel characteristics of liver heterogeneity and have important implications for both the structural organization of liver tissue and its function. Our next-gen 3D single-cell atlas is a powerful tool to understand liver tissue architecture, opening up avenues for in-depth investigations into tissue structure across both normal and pathological conditions.

Role of Macrophages in Liver Fibrosis

Liver fibrosis, which ultimately leads to liver cirrhosis and hepatocellular carcinoma, is a major health burden worldwide. The progression of liver fibrosis is the result of the wound-healing response of liver to repeated injury. Hepatic macrophages are cells with high heterogeneity and plasticity and include tissue-resident macrophages termed Kupffer cells, and recruited macrophages derived from circulating monocytes, spleen and peritoneal cavity. Studies have shown that hepatic macrophages play roles in the initiation and progression of liver fibrosis by releasing inflammatory cytokines/chemokines and pro-fibrogenic factors. Furthermore, the development of liver fibrosis has been shown to be reversible. Hepatic macrophages have been shown to alternately regulate both the regression and turnover of liver fibrosis by changing their phenotypes during the dynamic progression of liver fibrosis. In this review, we summarize the role of hepatic macrophages in the progression and regression of liver fibrosis.

Novel phenotypical and functional sub-classification of liver macrophages highlights changes in population dynamics in experimental mouse models

Liver macrophages are critical components of systemic immune system defense mechanisms. F4/80high Kupffer cells (KCs) are the predominant liver-resident macrophages and the first immune cells to contact pathogens entering the liver. F4/80low monocyte-derived macrophages (MoMφs) are essential macrophages that modulate liver immune functions. Here we report a novel method of identifying subpopulations of these two populations using traditional flow cytometry and examine each subpopulation for its putative roles in the pathogenesis of an experimental non-alcoholic steatohepatitis model. Using male C57BL/6 mice, we isolated and analyzed liver non-parenchymal cells by flow cytometry. We identified F4/80high and F4/80low macrophage populations and characterized subpopulations using uniform manifold approximation and projection. We identified three subpopulations in F4/80high macrophages: CD163(+) KCs, CD163(-) KCs, and liver capsular macrophages. CD163(+) KCs had higher phagocytic and bactericidal activities and more complex cellular structures than CD163(-) KCs. We also identified four subpopulations of F4/80low MoMφs based on Ly6C and MHC class II expression: infiltrating monocytes, pro-inflammatory MoMφs, Ly6C(-) monocytes, and conventional dendritic cells. CCR2 knock-out mice expressed lower levels of these monocyte-derived cells, and the count varied by subpopulation. In high-fat- and cholesterol-diet-fed mice, only one subpopulation, pro-inflammatory MoMφs, significantly increased in count. This indicates that changes to this subpopulation is the first step in the progression to non-alcoholic steatohepatitis. The community can use our novel subpopulation and gating strategy to better understand complex immunological mechanisms in various liver disorders through detailed analysis of these subpopulations.

Kupffer cells prevent pancreatic ductal adenocarcinoma metastasis to the liver in mice

Although macrophages contribute to cancer cell dissemination, immune evasion, and metastatic outgrowth, they have also been reported to coordinate tumor-specific immune responses. We therefore hypothesized that macrophage polarization could be modulated therapeutically to prevent metastasis. Here, we show that macrophages respond to β-glucan (odetiglucan) treatment by inhibiting liver metastasis. β-glucan activated liver-resident macrophages (Kupffer cells), suppressed cancer cell proliferation, and invoked productive T cell-mediated responses against liver metastasis in pancreatic cancer mouse models. Although excluded from metastatic lesions, Kupffer cells were critical for the anti-metastatic activity of β-glucan, which also required T cells. Furthermore, β-glucan drove T cell activation and macrophage re-polarization in liver metastases in mice and humans and sensitized metastatic lesions to anti-PD1 therapy. These findings demonstrate the significance of macrophage function in metastasis and identify Kupffer cells as a potential therapeutic target against pancreatic cancer metastasis to the liver.

PM2.5 exposure aggravates acute liver injury by creating an inflammatory microenvironment through Kupffer cell

AIM

This work aimed to investigate the impact of PM2.5 exposure on acute liver injury METHODS: C57BL/6 mice were used to examine the hepatic histopathological changes in PM2.5-exposed mice, as well as in CCl4-mediated acute liver injury mice after long-term exposure to PM2.5. During in vitro experiments, Kupffer cells were detected for M1 polarization level after treating with PM2.5, and the activation level of NLRP3 inflammasomes were assessed.

RESULTS

According to our findings, PM2.5 can induce M1 polarization of Kupffer cells in the liver to create an inflammatory microenvironment. Long-term exposure to PM2.5 can aggravate acute liver injury in mice. Treatment with MCC950, an NLRP3 inhibitor, can inhibit the effect of PM2.5. As demonstrated by in vitro analysis, PM2.5 can promote M1 polarization of Kupffer cells.

CONCLUSION

As suggested by our results, long-term exposure to PM2.5 can create an inflammatory microenvironment to aggravate mouse acute liver injury. The effect is related to NLRP3-mediated M1 polarization in Kupffer cells.

Major roles of kupffer cells and macrophages in NAFLD development

Non-alcoholic fatty liver disease (NAFLD) is an important public health problem with growing numbers of NAFLD patients worldwide. Pathological conditions are different in each stage of NAFLD due to various factors. Preclinical and clinical studies provide evidence for a crucial role of immune cells in NAFLD progression. Liver-resident macrophages, kupffer cells (KCs), and monocytes-derived macrophages are the key cell types involved in the progression of NAFLD, non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma (HCC). Their unique polarization contributes to the progression of NAFLD. KCs are phagocytes with self-renewal abilities and play a role in regulating and maintaining homeostasis. Upon liver damage, KCs are activated and colonized at the site of the damaged tissue. The secretion of inflammatory cytokines and chemokines by KCs play a pivotal role in initiating NAFLD pathogenesis. This review briefly describes the role of immune cells in the immune system in NAFLD, and focuses on the pathological role and molecular pathways of KCs and recruited macrophages. In addition, the relationship between macrophages and insulin resistance is described. Finally, the latest therapeutics that target KCs and macrophages are summarized for the prevention and treatment of NAFLD.

[The Role and Significance of Hepatic Environmental Cells in Tumor Metastatic Colonization to Liver]

Metastasis, a main cause of death in tumor patients, is a complicated process that involves multiple steps, presenting a major clinical challenge. Tumor cells break the physical boundaries of a primary tumor, intravasate into the lumina of blood vessels, travel around through blood circulation, extravasate into distant organs, colonize the host organs, and eventually develop into the foci of metastatic cancer. The metastasis of tumor cells exhibits organ-tropism, i.e., tumor cells preferentially spread to specific organs. Liver is a common site for metastasis. The pattern of metastasis in uveal melanoma, colorectal carcinoma, and pancreatic ductal adenocarcinoma shows organ-tropism for liver. The anatomical structure of liver determines its hemodynamic characteristics, e.g., low pressure and slow blood flow, which tend to facilitate the stasis and colonization of tumor cells in the liver. Besides the hemodynamic features, the metastatic colonization of liver depends largely on the interaction between tumor cells and the hepatic microenvironment (especially liver-resident cellular components). Resident cells of the hepatic microenvironment include hepatocytes, liver sinusoidal endothelial cells (LSECs), hepatic stellate cells (HSCs), Kupffer cells (KCs), etc. Herein, we discussed the role and significance of liver-resident cells in the metastatic colonization of tumor in the liver.

Kupffer Cells Contested as Early Drivers in the Pathogenesis of Primary Sclerosing Cholangitis

Primary sclerosing cholangitis (PSC) is an idiopathic chronic immune-mediated cholestatic liver disease characterized by fibro-inflammatory bile duct strictures, progressive hepatobiliary fibrosis, and gut-liver axis disruption. The pathophysiology of PSC remains insufficiently characterized, which hampers the development of effective therapies. Hepatic macrophages (MFs) are implicated in PSC pathogenesis, but the exact role of Kupffer cells (KCs) is unclear. Using the latest markers to discriminate resident KCs (ResKCs) from their monocyte-derived counterparts (MoKCs), and two models for intrahepatic and extrahepatic cholestasis, respectively, this study shows that CLEC4F⁺TIM4⁺ ResKCs are depleted after chronic cholestatic liver injury, whereas infiltrating CLEC4F⁺TIM4^- MoKCs are already enriched during the acute phase. Transcriptional profiling of hepatic MF subsets during early cholestatic injury indicates that ResKCs are indeed activated and that MoKCs express even higher levels of pro-inflammatory and proliferative markers compared with ResKCs. Conditional depletion of KCs, by using Clec4f^DTR transgenic mice, before and during early cholestasis induction had no effect, however, on the composition of the hepatic myeloid cell pool following injury progression and did not affect disease outcomes. Taken together, these results provide new insights on the heterogeneity of the MF pool during experimental PSC and evidence that depletion of resident and activated KCs during sclerosing cholangitis does not affect disease outcome in mice.

An Eye on Kupffer Cells: Development, Phenotype and the Macrophage Niche

Macrophages are key participants in the maintenance of tissue homeostasis under normal and pathological conditions, and implement a rich diversity of functions. The largest population of resident tissue macrophages is found in the liver. Hepatic macrophages, termed Kupffer cells, are involved in the regulation of multiple liver functionalities. Specific differentiation profiles and functional activities of tissue macrophages have been attributed to the shaping role of the so-called tissue niche microenvironments. The fundamental macrophage niche concept was lately shaken by a flood of new data, leading to a revision and substantial update of the concept, which constitutes the main focus of this review. The macrophage community discusses contemporary evidence on the developmental origins of resident macrophages, notably Kupffer cells and the issues of heterogeneity of the hepatic macrophage populations, as well as the roles of proliferation, cell death and migration processes in the maintenance of macrophage populations of the liver. Special consideration is given to interactions of Kupffer cells with other local cell lineages, including Ito cells, sinusoidal endothelium and hepatocytes, which participate in the maintenance of their phenotypical and functional identity.

Clodronate-nintedanib-loaded exosome-liposome hybridization enhances the liver fibrosis therapy by inhibiting Kupffer cell activity

Liver fibrosis therapy remains limited due to the inefficiency of drug delivery and inflammation induced by Kupffer cells. In this study, an exosome-liposome hybrid drug delivery system (LIEV) was developed to increase the efficacy of clodronate (CLD)-inhibition of Kupffer cells and to effectively deliver nintedanib (NIN) to liver fibroblasts to ensure enhanced anti-fibrosis therapy. CLD and NIN co-loaded LIEV (CLD/NIN@LIEV) exerted non-specific inhibition of phagocytosis by Kupffer cells, reduced inflammatory cytokines, and showed homologous homing properties mediated by fibroblast-derived exosomes, thereby achieving superior antifibrotic effects in a CCl4-induced fibrosis mouse model by inhibiting the proliferation of fibroblasts. Furthermore, the inhibited Kupffer cells regenerated within 10 days after dosage withdrawal. Unlike carrier-free NIN treatment, CLD/NIN@LIEV induced a marked decrease in liver enzymes, indicating improved safety and anti-fibrosis efficacy. These results indicate its great potential for treatment with the combined anti-fibrosis agent and Kupffer cell inhibition strategies to enhance the liver fibrosis therapy.

Macrophages as key regulators of liver health and disease

Macrophages are a heterogeneous population of innate immune cells and key cellular components of the liver. Hepatic macrophages consist of embryologically-derived resident Kupffer cells (KC), recruited monocyte-derived macrophages (MDM) and capsular macrophages. Both the diversity and plasticity of hepatic macrophage subsets explain their different functions in the maintenance of hepatic homeostasis and in injury processes in acute and chronic liver diseases. In this review, we assess the evidence for macrophage involvement in regulating both liver health and injury responses in liver diseases including acute liver injury (ALI), chronic liver disease (CLD) (including liver fibrosis) and hepatocellular carcinoma (HCC). In healthy livers, KC display critical functions such as phagocytosis, danger signal recognition, cytokine release, antigen processing and the ability to orchestrate immune responses and maintain immunological tolerance. However, in most liver diseases there is a striking hepatic MDM expansion, which orchestrate both disease progression and regression. Single-cell approaches have transformed our understanding of liver macrophage heterogeneity, dynamics, and functions in both human samples and preclinical models. We will further discuss the new insights provided by these approaches and how they are enabling high-fidelity work to specifically identify pathogenic macrophage subpopulations. Given the important role of macrophages in regulating injury responses in a broad range of settings, there is now a huge interest in developing new therapeutic strategies aimed at targeting macrophages. Therefore, we also review the current approaches being used to modulate macrophage function in liver diseases and discuss the therapeutic potential of targeting macrophage subpopulations as a novel treatment strategy for patients with liver disorders.

Pyrroloquinoline quinone (PQQ) alleviated sepsis-induced acute liver injury, inflammation, oxidative stress and cell apoptosis by downregulating CUL3 expression

PQQ has anti-inflammatory and anti-oxidant effects. PQQ can relieve high glucose-induced renal cell damage by suppressing Keap1 expression. Keap1 can interact with CUL3. Upregulation of CUL3 facilitates the apoptosis of LPS-induced podocytes. Based on knowledge above, this current work was designed to explore the role of PQQ in sepsis and determine the molecular function of CUL3 in the pathogenesis of sepsis. Rats received CLP surgery to establish sepsis models in vivo. Kupffer cells were pretreated with PQQ (10, 50 and 100 nmol/L) for 2 h and then treated with 100 ng/mL LPS for 24 h, simulating sepsis-induced acute liver injury in vitro. H&E staining was performed to evaluate liver injury of SD rats. Levels of inflammatory factors and oxidative stress markers were detected to assess inflammatory response and oxidative stress. Moreover, TUNEL staining, flow cytometric analysis and western blot were applied to determine cell apoptosis. It was confirmed that PQQ treatment relieved acute liver injury, inflammatory and oxidative stress damage and apoptosis of liver tissue cells in sepsis rats. In addition, PQQ therapy could alleviate inflammation, oxidative stress and apoptosis in LPS-induced Kupffer cells. Notably, LPS stimulation enhanced CUL3 expression and PQQ repressed CUL3 expression in Kupffer cells suffered from LPS. Overall, CUL3 overexpression weakened the remission effects of PQQ on LPS-induced inflammatory and oxidative damage and apoptosis of Kupffer cells. Mechanistically, PQQ treatment may mitigate sepsis-induced acute liver injury through downregulating CUL3 expression.

TCF4 enhances hepatic metastasis of colorectal cancer by regulating tumor-associated macrophage via CCL2/CCR2 signaling

Colorectal cancer (CRC) liver metastasis is a significant clinical problem for which better therapies are urgently needed. Tumor-associated macrophage, a major cell population in the tumor microenvironment, is a known contributor to primary cancer progression and cancer metastasis. Here, we found TAM recruitment and M2 polarization were increased in the hepatic metastatic lesion compared with the primary site of human CRC tissues. Moreover, Pearson correlation analysis showed that TAM recruitment and polarization were closely correlated with the elevated TCF4 expression in the metastatic site. To investigate the role of TCF4 in CRC liver metastasis, we generated a syngeneic mouse model using MC38 cells splenic injection. Results from in vivo experiments and mouse models revealed that TCF4 deficiency in MC38 cells does not affect their proliferation and invasion; however, it reduces TAM infiltration and M2 polarization in the metastasis site. Further studies indicated that these effects are mediated by the TCF4 regulated CCL2 and CCR2 expression. TCF4 or CCL2 silencing in the tumor cells prevent CRC liver metastasis in the mouse model. Altogether, these findings suggest that the TCF4-CCL2-CCR2 axis plays an essential role in CRC liver metastasis by enhancing TAMs recruitment and M2 polarization.

Liver Injury and the Macrophage Issue: Molecular and Mechanistic Facts and Their Clinical Relevance

The liver is an essential immunological organ due to its gatekeeper position to bypassing antigens from the intestinal blood flow and microbial products from the intestinal commensals. The tissue-resident liver macrophages, termed Kupffer cells, represent key phagocytes that closely interact with local parenchymal, interstitial and other immunological cells in the liver to maintain homeostasis and tolerance against harmless antigens. Upon liver injury, the pool of hepatic macrophages expands dramatically by infiltrating bone marrow-/monocyte-derived macrophages. The interplay of the injured microenvironment and altered macrophage pool skews the subsequent course of liver injuries. It may range from complete recovery to chronic inflammation, fibrosis, cirrhosis and eventually hepatocellular cancer. This review summarizes current knowledge on the classification and role of hepatic macrophages in the healthy and injured liver.

GeromiRs Are Downregulated in the Tumor Microenvironment during Colon Cancer Colonization of the Liver in a Murine Metastasis Model

Cancer is a phenomenon broadly related to ageing in various ways such as cell cycle deregulation, metabolic defects or telomerases dysfunction as principal processes. Although the tumor cell is the main actor in cancer progression, it is not the only element of the disease. Cells and the matrix surrounding the tumor, called the tumor microenvironment (TME), play key roles in cancer progression. Phenotypic changes of the TME are indispensable for disease progression and a few of these transformations are produced by epigenetic changes including miRNA dysregulation. In this study, we found that a specific group of miRNAs in the liver TME produced by colon cancer called geromiRs, which are miRNAs related to the ageing process, are significantly downregulated. The three principal cell types involved in the liver TME, namely, liver sinusoidal endothelial cells, hepatic stellate (Ito) cells and Kupffer cells, were isolated from a murine hepatic metastasis model, and the miRNA and gene expression profiles were studied. From the 115 geromiRs and their associated hallmarks of aging, which we compiled from the literature, 75 were represented in the used microarrays, 26 out of them were downregulated in the TME cells during colon cancer colonization of the liver, and none of them were upregulated. The histone modification hallmark of the downregulated geromiRs is significantly enriched with the geromiRs miR-15a, miR-16, miR-26a, miR-29a, miR-29b and miR-29c. We built a network of all of the geromiRs downregulated in the TME cells and their gene targets from the MirTarBase database, and we analyzed the expression of these geromiR gene targets in the TME. We found that Cercam and Spsb4, identified as prognostic markers in a few cancer types, are associated with downregulated geromiRs and are upregulated in the TME cells.

Kupffer cell-targeting strategy for the protection of hepatic ischemia/reperfusion injury

The aim of this study is to evaluate the effect of rare earth upconversion nanoparticles (UCNs) on hepatic ischemia reperfusion injury (IRI) and explore its possible mechanism. Hepatic IRI seriously affects the prognosis of patients undergoing liver surgery. Liver-resident Kupffer cells have been reported to promote IRI. Nanomedicines are known to be effective in the treatment of liver diseases, however, Kupffer cell-targeting nanomedicines for the treatment of IRI are yet to be developed. As potential bioimaging nanomaterials, UCNs have been found to specifically deplete Kupffer cells, but the underlying mechanism is unknown. In this study, we found that UCNs specifically depleted Kupffer cells by pyroptosis, while the co-administration of the caspase-1 inhibitor VX-765 rescued the UCN-induced Kupffer cell pyroptosis in mice. Furthermore, the pre-depletion of Kupffer cells by the UCNs significantly suppressed the release of inflammatory cytokines and effectively improved hepatic IRI. The rescue of the pyroptosis of the Kupffer cells by VX-765 abrogated the protective effect of UCNs on the liver. These results suggest that UCNs are highly promising for the development of Kupffer cell-targeting nanomedicines for intraoperative liver protection.

Amygdalin inhibits TGFβ1-induced activation of hepatic stellate cells (HSCs) in vitro and CCl4-induced hepatic fibrosis in rats in vivo

The activation of hepatic stellate cells (HSCs) has been considered one of the major events in hepatic fibrosis. Amygdalin has been used to treat cancers and alleviate pain; however, its role and mechanism in HSC activation and hepatic fibrosis remain unclear. In the present study, transforming growth factor-beta 1 (TGF-β1) stimulated the activation of HSCs, as indicated by significantly increased alpha-smooth muscle actin (α-SMA), desmin, collagen I, and tissue inhibitor of metalloproteinase-1 (TIMP-1) protein levels. Amygdalin treatment dramatically suppressed TGF-β1-induced HSC proliferation and activation. Moreover, amygdalin treatment also reduced the TGF-β1-induced secretion of cytokines, including tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), platelet-derived growth factor (PDGF), and chemokine (C-C motif) ligand 2 (CCL2), as well as the phosphorylation of Smad2, Smad3, and p65. In the CCl4-stimulated liver fibrosis rat model, amygdalin treatment improved liver fibrosis and liver damage by reducing focal necrosis, collagen fiber accumulation, and the protein levels of α-SMA, desmin, collagen I, and TIMP-1 in hepatic tissue samples and reducing serum alanine transaminase (ALT) and aspartate transaminase (AST) levels. In conclusion, we demonstrated the suppressive effects of amygdalin in TGF-β1-induced HSC activation through modulating proliferation, fibrogenesis, and inflammation signaling in vitro and the antifibrotic effects of amygdalin in CCl4-stimulated hepatic fibrosis in rats in vivo.

High prevalence of hepatic steatosis and vascular thrombosis in COVID-19: A systematic review and meta-analysis of autopsy data

BACKGROUND

Coronavirus disease 2019 (COVID-19) disease can frequently affect the liver. Data on hepatic histopathological findings in COVID-19 is scarce.

AIM

To characterize hepatic pathological findings in patients with COVID-19.

METHODS

We conducted a systematic review with meta-analysis registered on PROSPERO (CRD42020192813), following PRISMA guidelines. Eligible trials were those including patients of any age and COVID-19 diagnosis based on a molecular test. Histopathological reports from deceased COVID-19 patients undergoing autopsy or liver biopsy were reviewed. Articles including less than ten patients were excluded. Proportions were pooled using random-effects models. Q statistic and I² were used to assess heterogeneity and levels of evidence, respectively.

RESULTS

We identified 18 studies from 7 countries; all were case reports and case series from autopsies. All the patients were over 15 years old, and 67.2% were male. We performed a meta-analysis of 5 studies, including 116 patients. Pooled prevalence estimates of liver histopathological findings were hepatic steatosis 55.1% [95% confidence interval (CI): 46.2-63.8], congestion of hepatic sinuses 34.7% (95%CI: 7.9-68.4), vascular thrombosis 29.4% (95%CI: 0.4-87.2), fibrosis 20.5% (95%CI: 0.6-57.9), Kupffer cell hyperplasia 13.5% (95%CI: 0.6-54.3), portal inflammation 13.2% (95%CI: 0.1-48.8), and lobular inflammation 11.6% (95%CI: 0.3-35.7). We also identified the presence of venous outflow obstruction, phlebosclerosis of the portal vein, herniated portal vein, periportal abnormal vessels, hemophagocytosis, and necrosis.

CONCLUSION

We found a high prevalence of hepatic steatosis and vascular thrombosis as major histological liver features. Other frequent findings included portal and lobular inflammation and Kupffer cell hyperplasia or proliferation. Further studies are needed to establish the mechanisms and implications of these findings.

Characterization of hepatic macrophages and evaluation of inflammatory response in heme oxygenase-1 deficient mice exposed to scAAV9 vectors

Adeno-associated viral (AAV) vectors are characterised by low immunogenicity, although humoral and cellular responses may be triggered upon infection. Following systemic administration high levels of vector particles accumulate within the liver. Kupffer cells (KCs) are liver resident macrophages and an important part of the liver innate immune system. Decreased functional activity of KCs can contribute to exaggerated inflammatory response upon antigen exposure. Heme oxygenase-1 (HO-1) deficiency is associated with considerably reduced numbers of KCs. In this study we aimed to investigate the inflammatory responses in liver and to characterise two populations of hepatic macrophages in adult wild type (WT) and HO-1 knockout (KO) mice following systemic administration of one or two doses (separated by 3 months) of self-complementary (sc)AAV9 vectors. At steady state, the livers of HO-1 KO mice contained significantly higher numbers of monocyte-derived macrophages (MDMs), but significantly less KCs than their WT littermates. Three days after re-administration of scAAV9 we observed increased mRNA level of monocyte chemoattractant protein-1 (Mcp-1) in the livers of both WT and HO-1 KO mice, but the protein level and the macrophage infiltration were not affected. Three days after the 1^st and 3 days after the 2^nd vector dose the numbers of AAV genomes in the liver were comparable between both genotypes indicating similar transduction efficiency, but the percentage of transgene-expressing MDMs and KCs was higher in WT than in HO-1 KO mice. In the primary culture, KCs were able to internalize AAV9 particles without induction of TLR9-mediated immune responses, but no transgene expression was observed. In conclusion, in vivo and in vitro cultured KCs have different susceptibility to scAAV9 vectors. Regardless of the presence or absence of HO-1 and initial numbers of KCs in the liver, scAAV9 exhibits a low potential to stimulate inflammatory response at the analysed time points.

Myeloid-specific IRE1alpha deletion reduces tumour development in a diabetic, non-alcoholic steatohepatitis-induced hepatocellular carcinoma mouse model

BACKGROUND AND AIMS

Obesity, diabetes and associated non-alcoholic steatohepatitis (NASH) are rising risk factors for hepatocellular carcinoma (HCC). Macrophages are important immune cells involved in inflammation and tumour development. Macrophage inositol-requiring enzyme 1 alpha (IRE1α), an ER-stress protein, has been shown to be involved in macrophage cytokine production, and myeloid-specific IRE1α knock-out (myeloid IRE1α-KO) mice showed reduced weight gain during high-fat diet feeding. However, the effect of myeloid IRE1α on NASH and subsequent HCC development has not been examined. Here, we characterized the transcriptional profile of the hepatic macrophage population in a diabetes-NASH-HCC mouse model, and investigated the effect of myeloid-specific IRE1α deletion on the phenotype of hepatic macrophage subsets and experimental NASH-HCC development.

METHODS

Mice with non-functional myeloid IRE1α were created by crossing Ire1a floxed mice with Lysm-Cre mice. Two-day old myeloid IRE1α-KO and wild type (WT) mice were subcutaneously injected with streptozotocin (STZ), and male mice were fed a high-fat, -sucrose, -cholesterol diet (Western diet, WD) from the age of 4 weeks until 21 weeks. Control myeloid IRE1α-KO and WT mice received a PBS injection and were fed a matched control diet. These mice were evaluated for obesity, diabetes, NASH and HCC. The hepatic macrophage population was evaluated by flow cytometry and RNA sequencing on FACS-isolated macrophage subsets.

RESULTS

STZ-injection and WD feeding resulted in an impaired glucose tolerance, advanced NASH with fibrosis, and HCC development. Myeloid IRE1α-KO STZ mice showed lower fasting glucose levels at the start of WD feeding, and an improved glucose tolerance and attenuated HCC development after 17 weeks of WD feeding despite a similar degree of liver steatosis and inflammation compared to WT mice. Transcriptomic analysis of WT liver Kupffer cells, macrophages and monocytes revealed phenotypical changes in those cell subsets during NASH-HCC development. Isolated liver Kupffer cells and macrophages from mice with a myeloid IRE1α deletion showed downregulated pathways involved in immune system activation and metabolic pathways (only in Kupffer cells), whereas pathways involved in cell division and metabolism were upregulated in monocytes. These transcriptional differences were attenuated during NASH-HCC development.

CONCLUSION

Our results show that myeloid-specific IRE1α deletion results in an altered transcriptional profile of hepatic macrophages and dampens diabetes-induced NASH-HCC development, possibly by attenuated diabetes induction.

Association of novel markers of liver disease with neonatal liver disease in premature baboons, Papio sp

Parenteral Nutrition (PN) Associated Liver Disease (PNALD) affects up to 60% of neonates; however, techniques for diagnosing and monitoring disease progression remain limited. The neonatal baboon model may provide a unique opportunity to identify serologic markers associated with this disease. The purpose of this study was to investigate if Hyaluronic Acid (HA), TIMP metallopeptidase inhibitor 1 (TIMP1), Amino-terminal Propeptide of Type-III Collagen (PIIINP) and Enhanced Liver Fibrosis (ELF) score associate with histological liver disease in neonatal baboons exposed to PN. Preterm baboons delivered via c-section at 67% gestation received PN for 14 days with or without Intralipid (PRT+IL, PRT-IL, respectively) or were sacrificed after birth (PRTCTR). Term baboons were sacrificed after birth (TERMCTR) or survived 14 days (TERM+14d). Serum HA, TIMP1, and PIIINP concentrations were measured by ELISA. A blinded pathologist assigned liver histological scores following necropsy. HA increased 9.1-fold, TIMP1 increased 2.2-fold, and ELF score increased 1.4-fold in PRT-IL compared to PRTCTR. ALT, AST, and GGT were within normal limits and did not vary between groups. A trend towards increased fibrosis was found in PRT-IL baboons. Microvesicular hepatocyte steatosis and Kupffer cell hypertrophy were elevated in PRT-IL vs PRTCTR. HA and TIMP1 were significantly elevated in preterm baboons with early histological findings of liver disease evidenced by hepatic steatosis, Kupffer cell hypertrophy and a trend towards fibrosis whereas traditional markers of liver disease remained normal. These novel markers could potentially be utilized for monitoring early hepatic injury in neonates.

Liver Tropism in Cancer: The Hepatic Metastatic Niche

The liver is the largest organ in the human body and is prone for cancer metastasis. Although the metastatic pattern can differ depending on the cancer type, the liver is the organ to which cancer cells most frequently metastasize for the majority of prevalent malignancies. The liver is unique in several aspects: the vascular structure is highly permeable and has unparalleled dual blood connectivity, and the hepatic tissue microenvironment presents a natural soil for the seeding of disseminated tumor cells. Although 70% of the liver is composed of the parenchymal hepatocytes, the remaining 30% is composed of nonparenchymal cells including Kupffer cells, liver sinusoidal endothelial cells, and hepatic stellate cells. Recent discoveries show that both the parenchymal and the nonparenchymal cells can modulate each step of the hepatic metastatic cascade, including the initial seeding and colonization as well as the decision to undergo dormancy versus outgrowth. Thus, a better understanding of the molecular mechanisms orchestrating the formation of a hospitable hepatic metastatic niche and the identification of the drivers supporting this process is critical for the development of better therapies to stop or at least decrease liver metastasis. The focus of this perspective is on the bidirectional interactions between the disseminated cancer cells and the unique hepatic metastatic niche.

Dual TBK1/IKKɛ inhibitor amlexanox attenuates the severity of hepatotoxin-induced liver fibrosis and biliary fibrosis in mice

Although numerous studies have suggested that canonical IκB kinases (IKK) play a key role in the progression of liver fibrosis, the role of non-canonical IKKε and TANK-binding kinase 1 (TBK1) on the development and progression of liver fibrosis remains unclear. To demonstrate such issue, repeated injection of CCl4 was used to induce hepatotoxin-mediated chronic liver injury and biliary fibrosis was induced by 0.1% diethoxycarbonyl-1, 4-dihydrocollidine diet feeding for 4 weeks. Mice were orally administered with amlexanox (25, 50, and 100 mg/kg) during experimental period. Significantly increased levels of TBK1 and IKKε were observed in fibrotic livers or hepatic stellate cells (HSCs) isolated from fibrotic livers. Interestingly, amlexanox treatment significantly inhibited the phosphorylation of TBK1 and IKKε accompanied by reduced liver injury as confirmed by histopathologic analysis, decreased serum biochemical levels and fibro-inflammatory responses. Additionally, treatment of amlexanox promoted the fibrosis resolution. In accordance with these findings, amlexanox treatment suppressed HSC activation and its related fibrogenic responses by partially inhibiting signal transducer and activator of transcription 3. Furthermore, amlexanox decreased the activation and inflammatory responses in Kupffer cells. Collectively, we found that inhibition of the TBK1 and IKKε by amlexanox is a promising therapeutic strategy to cure liver fibrosis.

Sensitivity of Kupffer cells and liver sinusoidal endothelial cells to ricin toxin and ricin toxin-Ab complexes

Ricin toxin is a plant-derived, ribosome-inactivating protein that is rapidly cleared from circulation by Kupffer cells (KCs) and liver sinusoidal endothelial cells (LSECs)-with fatal consequences. Rather than being inactivated, ricin evades normal degradative pathways and kills both KCs and LSECs with remarkable efficiency. Uptake of ricin by these 2 specialized cell types in the liver occurs by 2 parallel routes: a "lactose-sensitive" pathway mediated by ricin's galactose/N-acetylgalactosamine-specific lectin subunit (RTB), and a "mannose-sensitive" pathway mediated by the mannose receptor (MR; CD206) or other C-type lectins capable of recognizing the mannose-side chains displayed on ricin's A (RTA) and B subunits. In this report, we investigated the capacity of a collection of ricin-specific mouse MAb and camelid single-domain (VH H) antibodies to protect KCs and LSECs from ricin-induced killing. In the case of KCs, individual MAbs against RTA or RTB afforded near complete protection against ricin in ex vivo and in vivo challenge studies. In contrast, individual MAbs or VH Hs afforded little (<40%) or even no protection to LSECs against ricin-induced death. Complete protection of LSECs was only achieved with MAb or VH H cocktails, with the most effective mixtures targeting RTA and RTB simultaneously. Although the exact mechanisms of protection of LSECs remain unknown, evidence indicates that the Ab cocktails exert their effects on the mannose-sensitive uptake pathway without the need for Fcγ receptor involvement. In addition to advancing our understanding of how toxins and small immune complexes are processed by KCs and LSECs, our study has important implications for the development of Ab-based therapies designed to prevent or treat ricin exposure should the toxin be weaponized.

Mesenchymal stem cells attenuate sepsis-induced liver injury via inhibiting M1 polarization of Kupffer cells

Sepsis is a leading cause of death in intensive care units that can result in acute hepatic damage. Animal experiments and clinical trials have shown that mesenchymal stem cell (MSC) therapy has some beneficial in several liver diseases. However, the protective effects of MSC therapy on sepsis-induced hepatic damage and associated mechanisms are not completely understood. The aim of the present study was to investigate the effects of MSCs on sepsis-induced liver injury and underlying mechanisms. A rat model of sepsis-induced liver injury was established by cecal ligation and puncture, and serum alanine aminotransferase and aspartate transaminase activities as well as liver histological changes were measured. Inflammatory cytokines, Kupffer cell M1 phenotype markers, and associated signal molecules were also determined in septic rats and in lipopolysaccharide (LPS)-treated Kupffer cells. Our results showed that injection of MSCs attenuated sepsis-induced liver injury. Treatment with MSCs inhibited activation of Kupffer cells towards M1 phenotype, attenuated TNF-α and IL-6 expression, and promoted IL-4 and IL-10 expression in septic rats and LPS-treated Kupffer cells. Furthermore, MSCs also inhibited the nuclear translocation of nuclear factor-kappa B in LPS-challenged Kupffer cells and the liver of septic rats. These results indicated that MSCs attenuated sepsis-induced liver injury through suppressing M1 polarization of Kupffer cells.

Activated Macrophages of Monocytic Origin Predominantly Express Proinflammatory Cytokine Genes, Whereas Kupffer Cells Predominantly Express Anti-Inflammatory Cytokine Genes

In the central nervous system and in the liver, the macrophage populations are represented exclusively by descendants of the hematopoietic progenitor cells of the yolk sac. The reasons for such differential distribution of macrophages are not fully understood. We found that, as can be judged by corresponding changes in the expression of CD86 and CD163 markers, the transient macrophages of monocytic lineage are more sensitive to activating stimuli. The two macrophage populations have distinct patterns of gene expression, which is particularly noticeable for M1- and M2-associated genes. For instance, Kupffer cells more readily develop and longer maintain the elevated expression levels of Il4, Il10, and Il13 upon the activation; by contrast, the macrophages of monocytic lineage express Il1b, Il12a, and Tnfα upon the activation. The obtained results allow us to conclude that the in vitro activated Kupffer cells of the liver are committed to M2 phenotype, whereas the in vitro activated monocyte-derived macrophages show a typical M1 behavior. These observations are likely to reflect the situation in the in vivo microenvironments.

Trichloroethene metabolite dichloroacetyl chloride induces apoptosis and compromises phagocytosis in Kupffer Cells: Activation of inflammasome and MAPKs

Exposure to trichloroethene (TCE), an occupational and ubiquitous environmental contaminant, is associated with the development of several autoimmune diseases, including autoimmune hepatitis (AIH). However, mechanisms contributing to TCE-mediated AIH are not known. Earlier, we have shown that dichloroacetyl chloride (DCAC), one of the reactive metabolites of TCE with strong acylating capability, can elicit an autoimmune response at much lower dose than TCE in female MRL+/+ mice. Furthermore, Kupffer cells (KCs), the liver resident macrophages, are crucial for hepatic homeostasis, but can also participate in the immunopathogenesis of AIH. However, contribution of KCs in TCE-mediated AIH and the underlying mechanisms are not understood. We hypothesized that increased apoptosis and delayed clearance of apoptotic bodies, due to compromised KC function, will result in the breakdown of self-tolerance, autoimmunity, and ultimately AIH. Therefore, using an in vitro model of immortalized mouse KCs, we investigated the contribution of DCAC in TCE-mediated AIH. KCs were treated with different concentrations of DCAC and apoptosis was measured by Annexin V and PI staining. Also, the impact of DCAC on phagocytic potential of KCs was evaluated. Furthermore, markers of inflammasome (NLRP3 and caspase1) were analyzed by real-time PCR and Western blot analysis. DCAC treatment resulted in significantly increased early and late-stage apoptosis, accompanied with inflammasome activation (NLRP3 increases). DCAC treatment resulted in decreased phagocytic function of KCs in a dose-dependent manner, with reduced MFG-E8 levels (phagocytotic function). Furthermore, DCAC exposure led to induction of phos-ERK and phos-AKT signaling. These findings suggest that DCAC induces apoptosis and inflammasome activation, while compromising the phagocytic function of KCs. Our data support that increased apoptosis and impaired KC function by DCAC could be contributory to TCE-mediated AIH.

Modulation of Chemokine- and Adhesion-Molecule Gene Expression and Recruitment of Neutrophil Granulocytes in Rat and Mouse Liver after a Single Gadolinium Chloride or Zymosan Treatment

Kupffer cells are professional phagocytes of the liver clearing bacteria from portal blood. Their clearance capacity, however, can be overwhelmed, transforming them into critical mediators of hepatic-injury. We investigated the consequences of selective Kupffer cell-overload by intraperitoneally administering pyrogen-free gadolinium chloride (GdCl₃) or Zymosan into rats and into endotoxin-resistant mice (C3H/HeJ). The number of myeloperoxidase-positive (MPO⁺) cells increased at 3 h mainly around the portal vessel after both GdCl₃ and Zymosan treatment. Simultaneously, GdCl₃ administration reduced detectability of ED-1⁺ (but not ED-2) cells near the portal vessel. Serum chemokine (C-X-C motif) ligand 1 (CXCL-1), CXCL-2 and chemokine (C-C motif) ligand 2 (CCL-2) showed a peak at 3 h after both treatment regimens although at a higher extent after Zymosan administration. Accordingly, CXCL-1, CXCL-5 and CCL-2 gene expression in the liver was up-regulated after GdCl₃ treatment at 3 h. After Zymosan administration a significant up-regulation of CXCL-1, CXCL-2, CXCL-10, CCL-2, CCL-3 and CCL-20 gene expression in liver at 3 h was observed. After Zymosan administration intracellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) gene expression was up-regulated in rat liver tissue. In C3H/HeJ mice both treatment regimens up-regulated CCL-2 and ICAM-1 gene expression after 3 h and down-regulated platelet endothelial cell adhesion molecule 1 (PECAM-1) gene expression. In conclusion, phagocytosis overload of Kupffer cells causes induction of several CXC, CC-chemokines, upregulation of "positive" adhesion molecule gene expression, down-regulation of the "negative" adhesion molecule PECAM-1 and a recruitment of neutrophil granulocytes in the portal area of the liver of treated rats and mice mainly in close contact to the liver macrophages.

RAMP1 in Kupffer cells is a critical regulator in immune-mediated hepatitis

The significance of the relationship between the nervous and immune systems with respect to disease course is increasingly apparent. Immune cells in the liver and spleen are responsible for the development of acute liver injury, yet the regulatory mechanisms of the interactions remain elusive. Calcitonin gene-related peptide (CGRP), which is released from the sensory nervous system, regulates innate immune activation via receptor activity-modifying protein 1 (RAMP1), a subunit of the CGRP receptor. Here, we show that RAMP1 in Kupffer cells (KCs) plays a critical role in the etiology of immune-mediated hepatitis. RAMP1-deficient mice with concanavalin A (ConA)-mediated hepatitis, characterized by severe liver injury accompanied by infiltration of immune cells and increased secretion of pro-inflammatory cytokines by KCs and splenic T cells, showed poor survival. Removing KCs ameliorated liver damage, while depleting T cells or splenectomy led to partial amelioration. Adoptive transfer of splenic T cells from RAMP1-deficient mice led to a modest increase in liver injury. Co-culture of KCs with splenic T cells led to increased cytokine expression by both cells in a RAMP1-dependent manner. Thus, immune-mediated hepatitis develops via crosstalk between immune cells. RAMP1 in KCs is a key regulator of immune responses.

The surreptitious survival of the emerging pathogen Staphylococcus lugdunensis within macrophages as an immune evasion strategy

Staphylococcus lugdunensis is a commensal bacterium that can cause serious infection suggesting an ability to circumvent aspects of host immunity. We demonstrate here that macrophages fail to kill ingested S. lugdunensis and the bacteria persist for extended periods, without replicating, within mature LAMP-1-positive phagolysosomes. Phagocytosed S. lugdunensis also do not intoxicate host cells in contrast to Staphylococcus aureus. Optimal survival of S. lugdunensis requires O-acetylated peptidoglycan because an oatA mutant, which is more sensitive to killing by lysozyme than wild type, survived to a lesser extent in macrophages. In vitro models of macrophage infection reveal that viable intracellular S. lugdunensis bacteria can be made to grow by pharmacologic perturbation of phagosome function or by phagocyte intoxication by S. aureus toxins. Remarkably, replicating S. lugdunensis is not constrained by LAMP-1 and phosphatidylserine-positive endomembranes, which is distinct from S. aureus that replicates within phagolysosomes. In vivo, S. lugdunensis can also reside in the murine Kupffer cell where the bacteria persist without replicating and require oatA to resist killing in vivo. The intracellular environment of the macrophage represents a niche where S. lugdunensis can exist while protected from extracellular immune factors and may serve as a reservoir from which these bacteria could disseminate.

Abrogation of GH action in Kupffer cells results in increased hepatic CD36 expression and exaggerated nonalcoholic fatty liver disease

OBJECTIVE

To investigate the effects of GH signaling on Kupffer cells and the resulting changes in lipid homeostasis and their underlying mechanism(s) in the livers of diet-induced obese (DIO) mice.

DESIGN

Male macrophage specific-growth hormone receptor knockout mice (MacGHR KO) and their litter mate controls were fed a high fat diet containing 60% calories from fat for 26 weeks. Lipid content and lipid profiles in the liver and circulation were analyzed. Expression levels of CD36 in the liver were quantified by RT-PCR and Western Blot.

RESULTS

Increased hepatic lipid content and abundance of long-chain unsaturated fatty acids were observed in the liver of MacGHR KO mice. These findings were associated with increased steady state levels of CD36 mRNA and protein in MacGHR KO mice when compared with their litter mate controls.

CONCLUSION

GH action in Kupffer cells is required for maintaining hepatic lipid homeostasis, in part via regulation of hepatic CD36 expression.

Kahweol Ameliorates the Liver Inflammation through the Inhibition of NF-κB and STAT3 Activation in Primary Kupffer Cells and Primary Hepatocytes

Gut derived bacterial endotoxins, such as lipopolysaccharide (LPS), are involved in one of the important mechanisms that lead to inflammation associated with various liver diseases, including nonalcoholic fatty liver disease and alcoholic liver disease. Kahweol is a coffee-specific diterpene present in coffee bean and exhibits anti-angiogenic and anti-inflammatory activities. However, to date, the effect of kahweol on liver inflammation remains unknown. In this study, we examined whether kahweol exhibits a protective effect by inhibiting liver inflammation in primary Kupffer cells and primary hepatocytes cultures as well as their co-cultures. Kahweol decreased the LPS-induced production of interleukin 1 alpha, interleukin 1 beta, interleukin 6, and tumor necrosis factor alpha. The inhibitory effect of kahweol on the liver inflammation was associated with the down regulation of LPS-stimulated phospho-nuclear factor kappa B and -signal transducer and activator of transcription 3 expression. These results suggest that kahweol might be a novel potent agent to treat liver inflammation induced by LPS.

The process of liver fibrosis in chronic hepatitis C - histological and immunohistochemical study

Liver fibrosis is one of the most serious histopathological (HP) lesions that, together with the inflammatory process and the hepatocyte lesions, determine the change of the liver architecture, having as a clinical result the onset of liver failure phenomena. Hepatitis C virus represents one of the most frequent conditions leading to the onset of liver fibrosis and favors the progression of the disease towards hepatocellular carcinoma. We evaluated the HP and immunohistochemical (IHC) aspects on fragments of liver biopsies taken from 104 patients diagnosed with chronic hepatitis C and altered capacity of work. In our study, we observed a growth of the portal (Kiernan) spaces by the presence of a chronic inflammatory infiltrate, the presence of collagen fibers and conjunctive matrix. The density and dimensions of collagen fibers were correlated with the severity of the liver disease, in the severe forms being highlighted porto-portal and porto-central fibrous bridges. The IHC examinations highlighted the change of the phenotype of perisinusoidal dendritic cells, the growth of the myofibroblast cells in the portal spaces, the growth of the macrophage number in the inflammatory infiltrate and of the Kupffer cells in the liver parenchyma.

Oxidative and ER stress-dependent ASK1 activation in steatotic hepatocytes and Kupffer cells sensitizes mice fatty liver to ischemia/reperfusion injury

Steatosis intensifies hepatic ischemia/reperfusion (I/R) injury increasing hepatocyte damage and hepatic inflammation. This study evaluates if this process is associated to a differential response of steatotic hepatocytes (HP) and Kupffer cells (KC) to I/R injury and investigates the molecular mechanisms involved. Control or steatotic (treated with 50 μmol palmitic acid, PA) mouse HP or KC were exposed to hypoxia/reoxygenation (H/R). C57BL/6 mice fed 9 week with control or High Fat diet underwent to partial hepatic IR. PA increased H/R damage of HP and further activated the ASK1-JNK axis stimulated by ER stress during H/R. PA also induced the production of oxidant species (OS), and OS prevention nullified the capacity of PA to increase H/R damage and ASK1/JNK stimulation. ASK1 inhibition prevented JNK activation and entirely protected HP damage. In KC, PA directly activated ER stress, ASK1 and p38 MAPK and increased H/R damage. However, in contrast to HP, ASK1 inhibition further increased H/R damage by preventing p38 MAPK activation. In mice liver, steatosis induced the expression of activated ASK1 in only KC, whereas I/R exposure of steatotic liver activated ASK1 expression also in HP. "In vivo", ASK1 inhibition prevented ASK1, JNK and p38 MAPK activation and protected I/R damage and expression of inflammatory markers.

CONCLUSIONS

Lipids-induced ASK1 stimulation differentially affects HP and KC by promoting cytotoxic or protective signals. ASK1 increases H/R damage of HP by stimulating JNK and protects KC activating p38MAPK. These data support the potentiality of the therapeutic employment of ASK1 inhibitors that can antagonize the damaging effects of I/R upon fatty liver surgery by the contextual reduction of HP death and of KC-mediated reactions.

Inactivation of Kupffer Cells by Selenizing Astragalus Polysaccharides Prevents CCl4-Induced Hepatocellular Necrosis in the Male Wistar Rat

Selenizing astragalus polysaccharides-3 (sAPS₃) was prepared by nitric acid-sodium selenite method. The effects of sAPS₃ on carbon tetrachloride (CCl₄) induced hepatocellular necrosis, and its underlying mechanisms were studied in male Wistar rats. Hepatic damage was induced by intraperitoneal injection of CCl₄ twice a week, for 3 weeks. Meanwhile, the rats in addition to CCl₄ were also exposed to sodium selenite (SS), astragalus polysaccharides (APS), SS + APS or sAPS₃, in parallel by oral gavage once a day for 3 weeks. At the end of 3 weeks, blood and liver tissue were taken. Serum was collected to test the levels of alanine aminotransferase, aspartate aminotransferase and antioxidant status parameters. Liver tissue was collected for histopathological examination and determination of messenger RNA (mRNA) expression levels of CD68, TNF-α, IL-1β and ATG7 followed by the measurements of CD68, IL-1β and LC3II by immunohistochemistry assay (IHC), or TNF-α by immunofluorescence assay (IFA). The results showed that sAPS₃ effectively ameliorated CCl₄ induced hepatocellular necrosis and inflammation and significantly decreased the levels of aspartate aminotransferase, alanine aminotransferase, malondialdehyde and the expression levels of Kupffer cells (KCs)-specific biomarker CD68 and proinflammatory cytokines produced by activated KCs such as IL-1β and TNF-α (P < 0.01). While increasing the levels of total antioxidant capacity, glutathione, glutathione peroxidase and superoxide dismutase (P < 0.05) and reduced the expression levels of a key regulator of autophagy in KCs ATG7 or LC3II (P < 0.05). These findings indicate that sAPS₃ could ameliorate CCl₄-induced hepatocellular necrosis by inactivation of Kupffer cells and its activity may be superior to the application of selenium, APS or combination of selenium with APS.

Inhibition of nitric oxide production reverses diabetes-induced Kupffer cell activation and Klebsiella pneumonia liver translocation

Klebsiella pneumoniae (KP) is the most common pathogen of pyogenic liver abscess in East and Southeast Asia and diabetes mellitus (DM) is a major risk factor. The effect and mechanism of diabetes on KP liver abscess was examined in streptozotocin-induced diabetic mice and Akita mice (C57BL/6J-Ins2^Akita). KP translocation to liver and plasma alaine transaminase levels were increased and liver clearance of KP was decreased in DM mice. Diabetic mice exhibited overgrowth of Enterococcus as well as E.coli and decreased lactobacilli/bifidas growth in intestine, increased intestinal iNOS protein and nitrite levels in portal vein, and increased IL-1β and TNF-α expression of Kupffer cells. Fructooligosaccharides (FOS) or dead L. salivarius (dLac) supplementation reversed diabetes-induced enteric dysbiosis, NO levels in portal vein, and KP translocation to liver. L-NAME treatment decreased intestinal iNOS protein expression as well as Kupffer cell activation and increased liver clearance of KP in DM mice. Dead E.coli (2×10⁸ CFU/ml) feeding for one week induced iNOS and TLR4 expression of intestine in germ-free (GF) mice. Dead bacteria feeding induced IL-1β and TNF-α expression of Kupffer cells in GF mice but not in GF TLR4^-/- mice. In conclusion, balance of intestinal microflora is important for preventing intestinal iNOS expression, Kupffer cell activation, and KP liver translocation in diabetes. Reversal of diabetes-induced enteric dysbiosis with FOS or dead L. salivarius decreases diabetes-induced intestinal iNOS expression and KP liver translocation. Diabetes induces Kupffer cell activation and KP liver translocation through enteric dysbiosis and nitric oxide production.

Zinc oxide nanoparticles hepatotoxicity: Histological and histochemical study

Zinc oxide nanoparticles (ZnO NPs) are widely used in industry and cosmetic products with promising investment in medical diagnosis and treatment. However, these particles may reveal a high potential risk for human health with no information about hepatotoxicity that might be associated with their exposure. The present work was carried out to investigate the histological and histochemical alterations induced in the hepatic tissues by naked 35nm ZnO NPs. Male Wistar albino rats were exposed to ZnO NPs at a daily dose of 2mg/kg for 21days. Liver biopsies from all rats under study were subjected to histopathological examinations. In comparison with the control rats, the following histological and histochemical alterations were demonstrated in the hepatic tissues of rats exposed to ZnO NPs: sinusoidal dilatation, Kupffer cells hyperplasia, lobular and portal triads inflammatory cells infiltration, necrosis, hydropic degeneration, hepatocytes apoptosis, anisokaryosis, karyolysis, nuclear membrane irregularity, glycogen content depletion and hemosidrosis. The findings of the present work might indicate that ZnO NPs have potential oxidative stress in the hepatic tissues that may affect the function of the liver. More work is needed to elucidate the toxicity and pathogenesis of zinc oxide nanoparticles on the vital organs.

Liver inflammation and fibrosis

Chronic liver inflammation leads to fibrosis and cirrhosis, which is the 12th leading cause of death in the United States. Hepatocyte steatosis is a component of metabolic syndrome and insulin resistance. Hepatic steatosis may be benign or progress to hepatocyte injury and the initiation of inflammation, which activates immune cells. While Kupffer cells are the resident macrophage in the liver, inflammatory cells such as infiltrating macrophages, T lymphocytes, neutrophils, and DCs all contribute to liver inflammation. The inflammatory cells activate hepatic stellate cells, which are the major source of myofibroblasts in the liver. Here we review the initiation of inflammation in the liver, the liver inflammatory cells, and their crosstalk with myofibroblasts.

Myeloid DLL4 Does Not Contribute to the Pathogenesis of Non-Alcoholic Steatohepatitis in Ldlr-/- Mice

Non-alcoholic steatohepatitis (NASH) is characterized by liver steatosis and inflammation. Currently, the underlying mechanisms leading to hepatic inflammation are not fully understood and consequently, therapeutic options are poor. Non-alcoholic steatohepatitis (NASH) and atherosclerosis share the same etiology whereby macrophages play a key role in disease progression. Macrophage function can be modulated via activation of receptor-ligand binding of Notch signaling. Relevantly, global inhibition of Notch ligand Delta-Like Ligand-4 (DLL4) attenuates atherosclerosis by altering the macrophage-mediated inflammatory response. However, the specific contribution of macrophage DLL4 to hepatic inflammation is currently unknown. We hypothesized that myeloid DLL4 deficiency in low-density lipoprotein receptor knock-out (Ldlr^-/-) mice reduces hepatic inflammation. Irradiated Ldlr^-/- mice were transplanted (tp) with bone marrow from wild type (Wt) or DLL4^f/fLysMCre^+/0 (DLL4^del) mice and fed either chow or high fat, high cholesterol (HFC) diet for 11 weeks. Additionally, gene expression was assessed in bone marrow-derived macrophages (BMDM) of DLL4^f/fLysMCre^WT and DLL4^f/fLysMCre^+/0 mice. In contrast to our hypothesis, inflammation was not decreased in HFC-fed DLL4^del-transplanted mice. In line, in vitro, there was no difference in the expression of inflammatory genes between DLL4-deficient and wildtype bone marrow-derived macrophages. These results suggest that myeloid DLL4 deficiency does not contribute to hepatic inflammation in vivo. Since, macrophage-DLL4 expression in our model was not completely suppressed, it can’t be totally excluded that complete DLL4 deletion in macrophages might lead to different results. Nevertheless, the contribution of non-myeloid Kupffer cells to notch signaling with regard to the pathogenesis of steatohepatitis is unknown and as such it is possible that, DLL4 on Kupffer cells promote the pathogenesis of steatohepatitis.

Kupffer Cells Undergo Fundamental Changes during the Development of Experimental NASH and Are Critical in Initiating Liver Damage and Inflammation

Non-alcoholic fatty liver disease has become the leading liver disease in North America and is associated with the progressive inflammatory liver disease non-alcoholic steatohepatitis (NASH). Considerable effort has been made to understand the role of resident and recruited macrophage populations in NASH however numerous questions remain. Our goal was to characterize the dynamic changes in liver macrophages during the initiation of NASH in a murine model. Using the methionine-choline deficient diet we found that liver-resident macrophages, Kupffer cells were lost early in disease onset followed by a robust infiltration of Ly-6C⁺ monocyte-derived macrophages that retained a dynamic phenotype. Genetic profiling revealed distinct patterns of inflammatory gene expression between macrophage subsets. Only early depletion of liver macrophages using liposomal clodronate prevented the development of NASH in mice suggesting that Kupffer cells are critical for the orchestration of inflammation during experimental NASH. Increased understanding of these dynamics may allow us to target potentially harmful populations whilst promoting anti-inflammatory or restorative populations to ultimately guide the development of effective treatment strategies.

Critical Role of Kupffer Cell CD89 Expression in Experimental IgA Nephropathy

Although IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide, its etiology remains only partly understood. It is clear that the pathogenesis of IgAN involves the formation of macromolecular IgA1 complexes and increased levels of serum IgA1 and IgA1-immune complexes(IC), due to defective IgA1 clearance. Previous studies suggest that the blood and tissue myeloid cell-expressed IgA Fc receptor (FcαR/CD89) mediates IgA-IC clearance and its dysfunction, via decreased activity or excessive levels of soluble FcαR/sCD89 induces IgAN. Such a mechanism requires robust stimulation of IgAN levels via forced expression of CD89. In the absence of unequivocal evidence supporting such a mechanism to date, we attempted to test the extent of CD89-evoked IgAN by generating a transgenic mouse strain expressing human CD89 under the control of murine CD14 promotor. No deposition of IgA-CD89 complexes or glomerulonephritis was detected, however. Further studies showed that elimination of murine IgA was mediated by Kupffer cells. In patients, however, CD89/IgA complexes were detected, and injection of patient IgA induced IgAN-like features in CD89 Tg mice. In transgenic mice, IgAN pathogenesis involves impaired clearance of abnormal IgA via CD89, primarily by the Kupffer cells. Conditional IgAN progression in CD89 transgenic mice thus reveals important aspects of IgAN pathogenesis.

Liver metastases: Microenvironments and ex-vivo models

The liver is a highly metastasis-permissive organ, tumor seeding of which usually portends mortality. Its unique and diverse architectural and cellular composition enable the liver to undertake numerous specialized functions, however, this distinctive biology, notably its hemodynamic features and unique microenvironment, renders the liver intrinsically hospitable to disseminated tumor cells. The particular focus for this perspective is the bidirectional interactions between the disseminated tumor cells and the unique resident cell populations of the liver; notably, parenchymal hepatocytes and non-parenchymal liver sinusoidal endothelial, Kupffer, and hepatic stellate cells. Understanding the early steps in the metastatic seeding, including the decision to undergo dormancy versus outgrowth, has been difficult to study in 2D culture systems and animals due to numerous limitations. In response, tissue-engineered biomimetic systems have emerged. At the cutting-edge of these developments are ex vivo 'microphysiological systems' (MPS) which are cellular constructs designed to faithfully recapitulate the structure and function of a human organ or organ regions on a milli- to micro-scale level and can be made all human to maintain species-specific interactions. Hepatic MPSs are particularly attractive for studying metastases as in addition to the liver being a main site of metastatic seeding, it is also the principal site of drug metabolism and therapy-limiting toxicities. Thus, using these hepatic MPSs will enable not only an enhanced understanding of the fundamental aspects of metastasis but also allow for therapeutic agents to be fully studied for efficacy while also monitoring pharmacologic aspects and predicting toxicities. The review discusses some of the hepatic MPS models currently available and although only one MPS has been validated to relevantly modeling metastasis, it is anticipated that the adaptation of the other hepatic models to include tumors will not be long in coming.

Evaluation of Cytotoxicity and Hypoxic Effect of Nitroimidazole Embedded Nanoparticles

Adenylate cyclase is a key intracellular enzyme involved in energy imbalance leading to tumor hypoxia and cytotoxicity. In this study, adenylate cyclase activities in isolated hepatocytes and Kupffer cells were compared in the presence of several metabolic stimulators. In cultured hepatocyte cells, adenylate cyclase was stimulated by guanylyl imidotriphosphate (GITP), guanosine triphosphate (GTP), progesterone and nitroimidazole embedded nanoparticle (NNP) effectors, while prostaglandin E2 and F2α were used as effectors in cultured Kupffer cells. The results showed that NNPs decreased adenylate cyclase specific activity in a dose-dependent manner after preincubation of hepatocytes with NNPs. The NNPs stimulated adenylate cyclase activities in hepatocytes were evaluated based on measurement of cyclic adenosine monophosphate (cAMP). The stimulatory effects of NNPs on adenylate cyclase were independent of the presence of GTP and may have been due to a direct effect on the catalytic subunit of adenylate cyclase. In addition, basal cAMP generation in hepatocyte cells was efficiently suppressed by the NNPs. In conclusion, NNPs exerted direct effects on the catalytic subunit of the adenylate cyclase system, and adenylate cyclase was hormone sensitive in liver cells.

Hepatic non-parenchymal cells: Master regulators of alcoholic liver disease?

Chronic alcohol consumption is one of the most common causes of the progression of alcoholic liver disease (ALD). In the past, alcohol-mediated hepatocyte injury was assumed to be a significantly major cause of ALD. However, a huge number of recent and brilliant studies have demonstrated that hepatic non-parenchymal cells including Kupffer cells, hepatic stellate cells, liver sinusoidal endothelial cells and diverse types of lymphocytes play crucial roles in the pathogenesis of ALD by producing inflammatory mediators such as cytokines, oxidative stress, microRNA, and lipid-originated metabolites (retinoic acid and endocannabinoids) or by directly interacting with parenchymal cells (hepatocytes). Therefore, understanding the comprehensive roles of hepatic non-parenchymal cells during the development of ALD will provide new integrative directions for the treatment of ALD. This review will address the roles of non-parenchymal cells in alcoholic steatosis, inflammation, and liver fibrosis and might help us to discover possible therapeutic targets and treatments involving modulating the non-parenchymal cells in ALD.

Activation of Kupffer Cells Is Associated with a Specific Dysbiosis Induced by Fructose or High Fat Diet in Mice

The increase consumption of fructose in diet is associated with liver inflammation. As a specific fructan substrate, fructose may modify the gut microbiota which is involved in obesity-induced liver disease. Here, we aimed to assess whether fructose-induced liver damage was associated with a specific dysbiosis, especially in mice fed a high fat diet (HFD). To this end, four groups of mice were fed with normal and HFD added or not with fructose. Body weight and glucose sensitivity, liver inflammation, dysbiosis and the phenotype of Kupffer cells were determined after 16 weeks of diet. Food intake was increased in the two groups of mice fed with the HFD. Mice fed with HFD and fructose showed a higher infiltration of lymphocytes into the liver and a lower inflammatory profile of Kupffer cells than mice fed with the HFD without fructose. The dysbiosis associated with diets showed that fructose specifically prevented the decrease of Mouse intestinal bacteria in HFD fed mice and increased Erysipelotrichi in mice fed with fructose, independently of the amount of fat. In conclusion, fructose, used as a sweetener, induced a dysbiosis which is different in presence of fat in the diet. Consequently, the activation of Kupffer cells involved in mice model of HFD-induced liver inflammation was not observed in an HFD/fructose combined diet. These data highlight that the complexity of diet composition could highly impact the development of liver lesions during obesity. Specific dysbiosis associated with the diet could explain that the progressions of liver damage are different.

Inhibition of sphingosine kinase 1 ameliorates acute liver failure by reducing high-mobility group box 1 cytoplasmic translocation in liver cells

AIM: To determine the therapeutic potential of sphingosine kinase 1 (Sphk1) inhibition and its underlying mechanism in a well-characterized mouse model of D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced acute liver failure (ALF).

METHODS: Balb/c mice were randomly assigned to different groups, with ALF induced by intraperitoneal injection of D-GaIN (600 mg/kg) and LPS (10 μg/kg). The Kaplan-Meier method was used for survival analysis. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels at different time points within one week were determined using a multi-parametric analyzer. Serum high-mobility group box 1 (HMGB1), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, IL-10, and sphingosine-1-phosphate were detected by enzyme-linked immunosorbent assay. Hepatic morphological changes at 36 h after acute liver injury induction were assessed by hematoxylin and eosin staining. HMGB1 expression in hepatocytes and cytoplasmic translocation were detected by immunohistochemistry. Expression of Sphk1 in liver tissue and peripheral blood mononuclear cells (PBMCs) was analyzed by Western blot.

RESULTS: The expression of Sphk1 in liver tissue and PBMCs was upregulated in GalN/LPS-induced ALF. Upregulated Sphk1 expression in liver tissue was mainly caused by Kupffer cells, the resident macrophages of the liver. The survival rates of mice in the N,N-dimethylsphingosine (DMS, a specific inhibitor of SphK1) treatment group were significantly higher than that of the control group (P < 0.001). DMS treatment significantly decreased the levels of serum ALT and AST at 6, 12, and 24 h compared with that of the control group (P < 0.01 for all). Serum HMGB1 levels at 6, 12, and 24 h, as well as serum TNF-α, IL-6, and IL-1β levels at 12 h, were significantly lower in the DMS treatment group than in the control group (P < 0.01 for all). Furthermore, hepatic inflammation, necrosis, and HMGB1 cytoplasm translocation in liver cells were significantly decreased in the DMS treatment group compared to the control group (43.72% ± 5.51% vs 3.57% ± 0.83%, χ² = 12.81, P < 0.01).

CONCLUSION: Inhibition of SphK1 ameliorates ALF by reducing HMGB1 cytoplasmic translocation in liver cells, and so might be a potential therapeutic strategy for this disease.

Inflammation drives thrombosis after Salmonella infection via CLEC-2 on platelets

Thrombosis is a common, life-threatening consequence of systemic infection; however, the underlying mechanisms that drive the formation of infection-associated thrombi are poorly understood. Here, using a mouse model of systemic Salmonella Typhimurium infection, we determined that inflammation in tissues triggers thrombosis within vessels via ligation of C-type lectin-like receptor-2 (CLEC-2) on platelets by podoplanin exposed to the vasculature following breaching of the vessel wall. During infection, mice developed thrombi that persisted for weeks within the liver. Bacteria triggered but did not maintain this process, as thrombosis peaked at times when bacteremia was absent and bacteria in tissues were reduced by more than 90% from their peak levels. Thrombus development was triggered by an innate, TLR4-dependent inflammatory cascade that was independent of classical glycoprotein VI-mediated (GPVI-mediated) platelet activation. After infection, IFN-γ release enhanced the number of podoplanin-expressing monocytes and Kupffer cells in the hepatic parenchyma and perivascular sites and absence of TLR4, IFN-γ, or depletion of monocytic-lineage cells or CLEC-2 on platelets markedly inhibited the process. Together, our data indicate that infection-driven thrombosis follows local inflammation and upregulation of podoplanin and platelet activation. The identification of this pathway offers potential therapeutic opportunities to control the devastating consequences of infection-driven thrombosis without increasing the risk of bleeding.

Hepatic histological alterations and biochemical changes induced by sildenafil overdoses

Sildenafil is used for the treatment of erectile dysfunction and is helping millions of men around the world to achieve and maintain a long lasting erection. Fifty healthy male rabbits (Oryctolagus cuniculus) were used in the present study and exposed daily to sildenafil (0, 1, 3, 6, 9 mg/kg) for 5 days per week for 7 weeks to investigate the biochemical changes and alterations in the hepatic tissues induced by this drug overdosing. In comparison with respective control rabbits, sildenafil overdoses elevated significantly (p-value<0.05, ANOVA test) alanine aminotransferase (ALT), aspartate aminotransferase (AST), testosterone, follicular stimulating hormone and total protein, while creatinine and urea were lowered with no significant alteration was observed in uric acid and luteinizing hormone concentration. Also sildenafil provoked hepatocytes nuclear alterations, necrosis, hydropic degeneration, bile duct hyperplasia, Kupffer cells hyperplasia, inflammatory cells infiltration, hepatic vessels congestion and evident partial depletion of glycogen content. The results show that subchronic exposure to sildenafil overdoses exhibits significant biochemical and alterations in the hepatic tissues that might affect the functions of the liver and other vital organs.

Tobacco and e-cigarette products initiate Kupffer cell inflammatory responses

Kupffer cells are liver resident macrophages that are responsible for screening and clearing blood of pathogens and foreign particles. It has recently been shown that Kupffer cells interact with platelets, through an adhesion based mechanism, to aid in pathogen clearance and then these platelets re-enter the general systemic circulation. Thus, a mechanism has been identified that relates liver inflammation to possible changes in the systemic circulation. However, the role that Kupffer cells play in cardiovascular disease initiation/progression has not been elucidated. Thus, our objective was to determine whether or not Kupffer cells are responsive to a classical cardiovascular risk factor and if these changes can be transmitted into the general systemic circulation. If Kupffer cells initiate inflammatory responses after exposure to classical cardiovascular risk factors, then this provides a potential alternative/synergistic pathway for cardiovascular disease initiation. We aimed to elucidate the prevalence of this potential pathway. We hypothesized that Kupffer cells would initiate a robust inflammatory response after exposure to tobacco cigarette or e-cigarette products and that the inflammatory response would have the potential to antagonize other salient cells for cardiovascular disease progression. To test this, Kupffer cells were incubated with tobacco smoke extracts, e-cigarette vapor extracts or pure nicotine. Complement deposition onto Kupffer cells, Kupffer cell complement receptor expression, oxidative stress production, cytokine release and viability and density were assessed after the exposure. We observed a robust inflammatory response, oxidative stress production and cytokine release after Kupffer cells were exposed to tobacco or e-cigarette extracts. We also observed a marginal decrease in cell viability coupled with a significant decrease in cell density. In general, this was not a function of the extract formulation (e.g. tobacco vs. e-cigarette products or the formulation of the cigarette product). These results indicate that Kupffer cells are responsive to classical cardiovascular risk factors and that an inflammatory response is initiated that may pass into the general systemic circulation.