Tumor necrosis factor stimulates DNA synthesis in the liver of intact rats

GSK3β/NF-κB -dependent transcriptional regulation of homeostatic hepatocyte Tnf production

Maintenance of hepatocyte homeostasis plays an important role in mediating the pathogenesis of many diseases. A growing body of literature has established a critical role played by tumor necrosis factor-α (TNFα) in maintaining hepatocyte homeostasis; however, the transcriptional mechanisms underlying constitutive Tnf expression are unknown. Whole liver fractions and primary hepatocytes from adult control C57BL/6 mice and the murine hepatocyte cell line AML12 were assessed for constitutive Tnf expression. Impacts of glycogen synthase kinase-3 β (GSK3β) and nuclear factor κB (NF-κB) inhibition on constitutive Tnf expression were assessed in AML12 cells. Finally, AML12 cell proliferation following GSK3β and NF-κB inhibition was evaluated. Constitutive Tnf gene expression is present in whole liver, primary hepatocytes, and cultured AML12 hepatocytes. Cytokine-induced Tnf gene expression is regulated by NF-κB activation. Pharmacological inhibition of GSK3β resulted in a time- and dose-dependent inhibition of Tnf gene expression. GSK3β inhibition decreased nuclear levels of the NF-κB subunits p65 and p50. We determined that NF-κB transcription factor subunit p65 binds to consensus sequence elements present in the murine TNFα promoter and inhibition of GSK3β decreases binding and subsequent Tnf expression. Finally, AML12 cell growth was significantly reduced following GSK3β and NF-κB inhibition. These results demonstrate that GSK3β and NF-κB are essential for mediating Tnf expression and constitutive hepatocyte cell growth. These findings add to a growing body of literature on TNFα mediated hepatocyte homeostasis and identify novel molecular mechanisms involved in mediating response to various disease states in the liver.NEW & NOTEWORTHY Maintenance of hepatocyte homeostasis plays an important role in controlling the pathogenesis of many diseases. Our findings add to a growing body of literature on tumor necrosis factor-α (TNFα)-mediated hepatocyte homeostasis and identify novel molecular mechanisms involved in regulating this response.

Antitumour necrosis factor-α agents and development of new-onset cirrhosis or non-alcoholic fatty liver disease: a retrospective cohort

Objective

Elevated tumour necrosis factor (TNF)-α has been implicated in the progression of liver fibrosis and pathogenesis of non-alcoholic fatty liver disease (NAFLD). We aim to investigate the impact of anti-TNF-α agents on the development of cirrhosis and NAFLD.

Design

This retrospective cohort study used a US claims database between 1 January 2010 and 31 December 2016. We identified adult patients with ankylosing spondylitis, inflammatory bowel disease, psoriatic arthritis or rheumatoid arthritis. Anti-TNF-α agents of interest included adalimumab, certolizumab, etanercept, golimumab and infliximab. The primary composite outcome was the development of new-onset cirrhosis, NAFLD or non-alcoholic steatohepatitis (NASH). The secondary outcomes were the development of (1) cirrhosis and (2) NAFLD or NASH. Propensity score for anti-TNF-α agent use was generated by logistic regression. Cox proportional hazard models adjusting for the propensity score were used with regard to time-varying anti-TNF-α agent exposure.

Results

This study included 226 555 incident patients with immune-related diseases. During the median 1.5 years follow-up, there was an increased hazard with anti-TNF-α agent use in regard to liver outcomes (composite outcome HR: 1.47, 95% CI 1.27 to 1.70; cirrhosis HR 1.47, 95% CI 0.96 to 2.23; NAFLD or NASH HR 1.53, 95% CI 1.32 to 1.77). The composite outcome hazard was increased for each immune-related disease (HR 1.25–1.90).

Conclusion

In the short term, we did not observe a beneficial effect of anti-TNF-α agent use for development of cirrhosis, NAFLD or NASH in patients with immune-related diseases.

Exploration of the Transcriptional Landscape of ALPPS Reveals the Pathways of Accelerated Liver Regeneration

Background and Aims: ALPPS (associating liver partition and portal vein ligation for staged hepatectomy), a novel 2-staged hepatectomy, dramatically accelerates liver regeneration and thus enables extensive liver tumor resection. The signaling networks underlying the ALPPS-induced accelerated regeneration process are largely unknown.

Methods: We performed transcriptome profiling (TP) of liver tissue obtained from a mouse model of ALPPS, standard hepatectomy (68% model), and additional control surgeries (sham, PVL and Tx). We also performed TP using human liver biopsies (n = 5) taken from the occluded lobe and the future liver remnant (FLR) during the first step of ALPPS surgery (4–5 h apart). We used Oncofinder computational tools, which covers 378 ISPs, for unsupervised, unbiased quantification of ISP activity.

Results: Gene expression cluster analysis revealed an ALPPS specific signature: the IGF1R Signaling Pathway (Cell survival), the ILK Pathway (Induced cell proliferation), and the IL-10 Pathway (Stability determination) were significantly enriched, whereas the activity of the Interferon Pathway (Transcription) was reduced (p < 0.05). Further, the PAK- and ILK-associated ISPs were activated at an earlier time point, reflecting significant acceleration of liver regeneration (p < 0.001). These pathways, which were also recovered in human liver biopsies, control cell growth and proliferation, inflammatory response, and hypoxia-related processes.

Conclusions: ALPPS is not a straightforward addition of portal vein ligation (PVL) plus transection—it is more. The early stages of normal and accelerated liver regeneration are clearly discernible by a significantly increased and earlier activation of a small number of signaling pathways. Compounds mimicking these responses may help to improve the ALPPS method and further reduce the hospitalization time of the patient.

Future liver remnant growth after various portal vein embolization regimens: a quantitative comparison

Purpose: To compare the efficacy of right portal vein embolization using ethylene vinyl alcohol (EVOH-PVE) compared to other embolic agents and surgical right portal vein ligation (PVL).Material and methods: Patients with right sided liver malignancies scheduled for extensive surgery and receiving induction of liver hypertrophy via right portal vein embolization/ligature between 2010-2016 were retrospectively evaluated. Treatments included were ethylene vinyl alcohol copolymer (Onyx®, EVOH-PVE), ethiodized oil (Lipiodol^®, Lipiodol/PVA-PVE), polyvinyl alcohol (PVA-PVE) or surgical ligature (PVL). Liver segments S2/3 were used to assess hypertrophy. Primary outcome was future liver remnant growth in ml/day.Results: Forty-one patients were included (EVOH-PVE n = 11; Lipiodol/PVA-PVE n = 10; PVA-PVE n = 8; PVL n = 12), the majority presenting with cholangiocarcinoma and colorectal metastases (n = 11; n = 27). Pre-interventional liver volumes were comparable (p = .095). Liver hypertrophy was successfully induced in all but one patient receiving Lipiodol/PVA-PVE. Liver segment S2/3 growth was largest for EVOH-PVE (5.38 ml/d) followed by PVA-PVE (2.5 ml/d), with significantly higher growth rates than PVL (1.24 ml/d; p < .001; p = .007). No significant difference was evident for Lipiodol/PVA-PVE (1.43 ml/d, p = .809).Conclusions: Portal vein embolization using EVOH demonstrates fastest S2/3 growth rates compared to other embolic agents and PVL, potentially due to its permanent portal vein embolization and induction of hepatic inflammation.

Portal Vein Embolization Utilizing N-Butyl Cyanoacrylate for Contralateral Lobe Hypertrophy Prior to Liver Resection: A Systematic Review and Meta-Analysis

PURPOSE

To evaluate the safety and effectiveness of n-butyl cyanoacrylate (NBCA) for portal vein embolization (PVE) when used to induce contralateral future liver remnant (FLR) hypertrophy in patients undergoing planned hepatic resection for hepatic malignancy.

MATERIALS AND METHODS

The PubMed database (including articles indexed by MEDLINE) was searched for articles published from 1970 to 2018 describing patients treated with PVE utilizing NBCA to induce hypertrophy of the FLR prior to contralateral hepatic lobe resection. Demographic data, embolization technique, complications of embolization, resultant FLR hypertrophy, and surgical outcomes were obtained when available. A meta-analysis was performed to determine the cumulative relative hypertrophy rate of the FLR following PVE with NBCA.

RESULTS

The literature search yielded 18 relevant articles. Six hundred and seven patients (383 men, 220 women; mean age 60.7 years) with procedures describing PVE utilizing NBCA were reviewed. The most common underlying hepatic malignancies were colorectal metastases (n = 348), followed by cholangiocarcinomas (n = 92), and hepatocellular carcinomas (n = 89). Technical success was reportedly achieved in 603/607 patients, for a success rate of 99.3%. Fixed effects meta-analysis of the relative hypertrophy rate of the FLR among studies resulted in an aggregate rate of 49.4 ± 1.3%. Of the patients who underwent attempted PVE, 461/607 (75.9%) eventually underwent surgical resection. Major complications following PVE occurred in 19 patients (3.13%), while minor complications following PVE occurred in 38 patients (6.26%).

CONCLUSIONS

PVE utilizing NBCA to induce hypertrophy of the FLR prior to contralateral lobe resection in the setting of hepatic malignancy is safe and effective.

LEVEL OF EVIDENCE

Level IIa-Systematic review of cohort studies.

Dicer-dependent production of microRNA221 in hepatocytes inhibits p27 and is required for liver regeneration in mice

Dicer processes microRNAs (miRs) into active forms in a wide variety of tissues, including the liver. To determine the role of Dicer in liver regeneration, we performed a series of in vivo and in vitro studies in a murine 2/3 hepatectomy model. Dicer was downregulated after 2/3 hepatectomy, and loss of Dicer inhibited liver regeneration associated with decreased cyclin A2 and miR-221, as well as increased levels of the cell cycle inhibitor p27. In vitro, miR-221 inhibited p27 production in primary hepatocytes and increased hepatocyte proliferation. Specific reconstitution of miR-221 in hepatocyte-specific Dicer-null mice inhibited p27 and restored liver regeneration. In wild type mice, targeted inhibition of miR-221 using a cholesterol-conjugated miR-221 inhibited hepatocyte proliferation after 2/3 hepatectomy. These results identify Dicer production of miR-221 as an essential component of a miRNA-dependent mechanism for suppression of p27 that controls the rate of hepatocyte proliferation after partial hepatectomy.NEW & NOTEWORTHY Our findings demonstrate a direct role for microRNAs in controlling the rate of liver regeneration after injury. By deleting Dicer, an enzyme responsible for processing microRNAs into mature forms, we determined miR-221 is a critical microRNA in the physiological process of restoration of liver mass after injury. miR-221 suppresses p27, releasing its inhibitory effects on hepatocyte proliferation. Pharmaceuticals based on miR-221 may be useful to modulate hepatocyte proliferation in the setting of liver injury.

Administration of multipotent mesenchymal stromal cells restores liver regeneration and improves liver function in obese mice with hepatic steatosis after partial hepatectomy

Background

The liver has the remarkable capacity to regenerate in order to compensate for lost or damaged hepatic tissue. However, pre-existing pathological abnormalities, such as hepatic steatosis (HS), inhibits the endogenous regenerative process, becoming an obstacle for liver surgery and living donor transplantation.

Recent evidence indicates that multipotent mesenchymal stromal cells (MSCs) administration can improve hepatic function and increase the potential for liver regeneration in patients with liver damage. Since HS is the most common form of chronic hepatic illness, in this study we evaluated the role of MSCs in liver regeneration in an animal model of severe HS with impaired liver regeneration.

Methods

C57BL/6 mice were fed with a regular diet (normal mice) or with a high-fat diet (obese mice) to induce HS. After 30 weeks of diet exposure, 70% hepatectomy (Hpx) was performed and normal and obese mice were divided into two groups that received 5 × 10⁵ MSCs or vehicle via the tail vein immediately after Hpx.

Results

We confirmed a significant inhibition of hepatic regeneration when liver steatosis was present, while the hepatic regenerative response was promoted by infusion of MSCs. Specifically, MSC administration improved the hepatocyte proliferative response, PCNA-labeling index, DNA synthesis, liver function, and also reduced the number of apoptotic hepatocytes.

These effects may be associated to the paracrine secretion of trophic factors by MSCs and the hepatic upregulation of key cytokines and growth factors relevant for cell proliferation, which ultimately improves the survival rate of the mice.

Conclusions

MSCs represent a promising therapeutic strategy to improve liver regeneration in patients with HS as well as for increasing the number of donor organs available for transplantation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0469-y) contains supplementary material, which is available to authorized users.

SOCS2 Balances Metabolic and Restorative Requirements during Liver Regeneration

After significant injury, the liver must maintain homeostasis during the regenerative process. We hypothesized the existence of mechanisms to limit hepatocyte proliferation after injury to maintain metabolic and synthetic function. A screen for candidates revealed suppressor of cytokine signaling 2 (SOCS2), an inhibitor of growth hormone (GH) signaling, was strongly induced after partial hepatectomy. Using genetic deletion and administration of various factors we investigated the role of SOCS2 during liver regeneration. SOCS2 preserves liver function by restraining the first round of hepatocyte proliferation after partial hepatectomy by preventing increases in growth hormone receptor (GHR) via ubiquitination, suppressing GH pathway activity. At later times, SOCS2 enhances hepatocyte proliferation by modulating a decrease in serum insulin-like growth factor 1 (IGF-1) that allows GH release from the pituitary. SOCS2, therefore, plays a dual role in modulating the rate of hepatocyte proliferation. In particular, this is the first demonstration of an endogenous mechanism to limit hepatocyte proliferation after injury.

Liver regeneration following experimental major hepatectomy with choledochojejunostomy

BACKGROUND

Surgical treatment for perihilar cholangiocarcinoma frequently involves hepatectomy and extrahepatic bile duct resection with a choledochojejunostomy (CJ). Cholangitis owing to bilioenteric anastomosis is a common complication. The impact of CJ or regurgitating cholangitis on the liver regeneration process after major hepatectomy is unknown.

METHODS

Rats underwent 70 per cent hepatectomy (Hx group) or hepatectomy with CJ (Hx + CJ group). The intrahepatic inflammatory response, hepatic regeneration rate, and expression of regeneration-associated genes in the liver and blood were compared between these two groups.

RESULTS

Levels of hepatobiliary markers in the blood were significantly higher 4 and 7 days after operation in the Hx + CJ group than the Hx group. Intrahepatic expression of inflammation-associated genes, such as interleukin 6 and tumour necrosis factor α, was also significantly higher in the Hx + CJ group on days 4 and 7. A progressive periportal inflammatory response was identified in the Hx + CJ group by histological examination. The hepatic regeneration rate was significantly lower in the Hx + CJ group than in the Hx group on day 2 (mean(s.d.) 14·2(6·3) versus 21·4(2·6) per cent; P = 0·013) and day 4 (32·4(5·3) versus 41·3(4·4) per cent; P = 0·004). Gene expression levels of hepatic regeneration-promoting factors such as hepatocyte growth factor were significantly lower in the Hx + CJ group than the Hx group on day 1.

CONCLUSION

CJ perturbs early liver regeneration after hepatectomy. An excessive inflammatory response in the liver and suppression of liver regeneration-associated factors may play a role. Surgical relevance Patients with perihilar cholangiocarcinoma may need major hepatectomy with extrahepatic bile duct resection and choledochojejunostomy. This carries a substantial risk of postoperative complications including liver failure. A rat model of partial hepatectomy with choledochojejunostomy was established. The molecular mechanisms underlying liver regeneration, and perturbation of this process by duodenobiliary reflux via the choledochojejunostomy, are described. The results give insight into the pathophysiological events following major hepatectomy with extrahepatic bile duct resection and choledochojejunostomy. This may help to develop a treatment strategy to reduce postoperative liver failure.

Nonalcoholic Steatohepatitis: Involvement of the Telomerase and Proinflammatory Mediators

Nonalcoholic steatohepatitis or NASH is an excessive accumulation of fat in hepatocytes accompanied by inflammation and hepatic injury. Proinflammatory molecules such as IL-17, CCL20, S100A8, S100A9, and S100A8/A9 have been shown to be implicated in many types of cancer. Telomerase activity has been found to be associated with chronic inflammation and cancer. NASH can progress to fibrosis then cirrhosis and finally to hepatocellular carcinoma (HCC). Our objective is to try to find a relation between inflammation and the progression of NASH into HCC. We found that there was a significant elevation in the telomerase activity, detected by real-time PCR, between NASH and fibrotic NASH in the liver biopsies of patients. The expression of S100A8, S100A9, S100A8/A9, CCL20, and IL-17, detected by ELISA, is significantly increased in NASH patients with fibrosis in comparison with controls. But, in NASH patients, S100A9, S100A8/A9, and IL-17 only are significantly elevated in comparison with controls. The same, on the mRNA level, expression of IL-17, detected by RT-PCR, is significantly elevated in NASH patients in comparison with controls. Therefore, there is a direct link between the expression of IL-17, CCL20, telomerase, S100A8, and S100A9 in the fibrotic condition and the progression towards cancer.

Lysophosphatidic acid alters the expression profiles of angiogenic factors, cytokines, and chemokines in mouse liver sinusoidal endothelial cells

BACKGROUND AND AIMS

Lysophosphatidic acid (LPA) is a multi-function glycerophospholipid. LPA affects the proliferation of hepatocytes and stellate cells in vitro, and in a partial hepatectomy induced liver regeneration model, the circulating LPA levels and LPA receptor (LPAR) expression levels in liver tissue are significantly changed. Liver sinusoidal endothelial cells (Lsecs) play an important role during liver regeneration. However, the effects of LPA on Lsecs are not well known. Thus, we investigated the effects of LPA on the expression profiles of angiogenic factors, cytokines, and chemokines in Lsecs.

METHODS

Mouse Lsecs were isolated using CD31-coated magnetic beads. The mRNA expression levels of LPAR's and other target genes were determined by quantitative RT-PCR. The protein levels of angiogenesis factors, cytokines, and chemokines were determined using protein arrays and enzyme immunoassay (EIA). Critical LPAR related signal transduction was verified by using an appropriate chemical inhibitor.

RESULTS

LPAR1 and LPAR3 mRNA's were expressed in mouse LPA-treated Lsecs. Treating Lsecs with a physiological level of LPA significantly enhanced the protein levels of angiogenesis related proteins (cyr61 and TIMP-1), cytokines (C5/C5a, M-CSF, and SDF-1), and chemokines (MCP-5, gp130, CCL28, and CXCL16). The LPAR1 and LPAR3 antagonist ki16425 significantly inhibited the LPA-enhanced expression of cyr61, TIMP-1, SDF-1, MCP-5, gp130, CCL28, and CXCL16, but not that of C5/C5a or M-CSF. LPA-induced C5/C5a and M-CSF expression may have been through an indirect regulation mechanism.

CONCLUSION

LPA regulated the expression profiles of angiogenic factors, cytokines, and chemokines in Lsecs that was mediated via LPAR1 and LPAR3 signaling. Most of the factors that were enhanced by LPA have been found to play critical roles during liver regeneration. Thus, these results may prove useful for manipulating LPA effects on liver regeneration.

BMP4 is a novel paracrine inhibitor of liver regeneration

Transforming growth factor (TGF)-β family members exert strong effects on restoration of liver mass after injury. Bone morphogenetic proteins (BMPs) are members of the TGF-β family and are found in the liver, suggesting that these proteins may play a role in liver regeneration. We examined BMP signaling in the liver during hepatectomy. We found that BMP4 is constitutively expressed in the peribiliary stroma and endothelial cells of the liver and that expression is decreased after hepatectomy. Mice driven to maintain BMP4 expression in the liver display inhibited hepatocyte proliferation and restoration of liver mass after hepatectomy, suggesting that reduced BMP4 is necessary for normal regeneration. Consistent with this finding, hepatocyte-specific deletion of the BMP receptor activin receptor-like kinase 3 (Alk3) enhances regeneration and reduces phosphorylation of SMAD1/5/8, a transducer of BMP signaling. In contrast to experiments in wild-type mice, maintaining BMP4 levels has no effect on liver regeneration in hepatocyte-specific Alk3 null mice, providing evidence that BMP4 signals through Alk3 to inhibit liver regeneration. Consistent with these findings, the BMP4 antagonist Noggin enhances regeneration. Furthermore, high-dose BMP4 inhibits proliferation of primary hepatocytes and HepG2 cells in culture. These findings elucidate a new, potentially clinically relevant paradigm in which a constitutively expressed paracrine inhibitory factor plays a critical role in liver regeneration.

The use of fish oil lipid emulsion in the treatment of intestinal failure associated liver disease (IFALD)

Since 2004, fish oil based lipid emulsions have been used in the treatment of intestinal failure associated liver disease, with a noticeable impact on decreasing the incidence of morbidity and mortality of this often fatal condition. With this new therapy, however, different approaches have emerged as well as concerns about potential risks with using fish oil as a monotherapy. This review will discuss the experience to date with this lipid emulsion along with the rational for its use, controversies and concerns.

Molecular mechanisms of liver injury and hepatocarcinogenesis: focusing on the role of stress-activated MAPK

Hepatocellular carcinoma (HCC) is the third most common cause of cancer mortality. Short-term prognosis of patients with HCC has improved recently due to advances in early diagnosis and treatment, but long-term prognosis is still unsatisfactory. Therefore, obtaining a further understanding of the molecular carcinogenic mechanisms and the unique pathogenic biology of HCC is important. The most characteristic process in hepatocarcinogenesis is underlying chronic liver injury, which leads to repeated cycles of hepatocyte death, inflammation, and compensatory proliferation and subsequently provides a mitogenic and mutagenic environment leading to the development of HCC. Recent in vivo studies have shown that the stress-activated mitogen-activated protein kinase (MAPK) cascade converging on c-Jun NH(2)-terminal kinase (JNK) and p38 plays a central role in these processes, and it has attracted considerable attention as a therapeutic target. However, JNK and p38 have complex functions and a wide range of cellular effects. In addition, crosstalk with each other and the nuclear factor-kappaB pathway further complicate these functions. A full understanding is essential to bring these observations into clinical settings. In this paper, we discuss the latest findings regarding the mechanisms of liver injury and hepatocarcinogenesis focusing on the role of the stress-activated MAPK pathway.

Adipose tissue-derived mesenchymal stem cell transplantation promotes hepatic regeneration after hepatic ischemia-reperfusion and subsequent hepatectomy in rats

BACKGROUND

Adipose tissue-derived mesenchymal stem cells (ADSCs) are an attractive source for regenerative medicine because they are easily accessible through minimally invasive methods. We investigated the efficacy of ADSC transplantation on outcome after hepatic ischemia-reperfusion and subsequent hepatectomy in rats.

METHODS

ADSCs were isolated from subcutaneous adipose tissue of rats. After clamping the hepatoduodenal ligament for 15 min, the rats were subjected to a 70% partial hepatectomy. After releasing the clamp, 2 × 10(6) ADSCs per rat were injected through the penile vein. Phosphate buffered saline was injected as a control. The parameters of hepatic regeneration, such as hepatic regeneration rate, mitotic index, and anti-proliferating cell nuclear antigen levels, were examined. Furthermore, the expression of hepatic regeneration-associated proteins and genes in the regenerating liver was determined.

RESULTS

The hepatic regeneration rate 2 d after hepatectomy was significantly greater in the ADSC transplanted group compared with the sham group. Mitotic index, anti-proliferating cell nuclear antigen levels, and other regeneration-associated proteins in the liver were significantly higher in the ADSC transplanted group than the sham group on 1 d after hepatectomy. A number of hepatic regeneration-associated genes also were significantly upregulated in the ADSC transplanted group.

CONCLUSIONS

These results indicate that ADSC transplantation may provide beneficial effects in the process of liver regeneration after hepatic ischemia-reperfusion and subsequent hepatectomy.

Mmp23b promotes liver development and hepatocyte proliferation through the tumor necrosis factor pathway in zebrafish

The matrix metalloproteinase (MMP) family of proteins degrades extracellular matrix (ECM) components as well as processes cytokines and growth factors. MMPs are involved in regulating ECM homeostasis in both normal physiology and disease pathophysiology. Here we report the critical roles of mmp23b in normal zebrafish liver development. Mmp23b was initially identified as a gene linked to the genomic locus of an enhancer trap transgenic zebrafish line in which green fluorescent protein (GFP) expression was restricted to the developing liver. Follow-up analysis of mmp23b messenger RNA (mRNA) expression confirmed its liver-specific expression pattern. Morpholino knockdown of mmp23b resulted in defective hepatocyte proliferation, causing a reduction in liver size while maintaining relatively normal pancreas and gut development. Genetically, we showed that mmp23b functions through the tumor necrosis factor (TNF) signaling pathway. Antisense knockdown of tnfa or tnfb in zebrafish caused similar reductions of liver size, whereas overexpression of tnfa or tnfb rescued liver defects in mmp23b morphants but not vice versa. Biochemically, MMP23B, the human ortholog of Mmp23b, directly interacts with TNF and mediates its release from the cell membrane in a cell culture system. Because mmp23b/MMP23B is highly conserved, our findings in zebrafish warrant further investigation of its role in regulating liver development in mammals.

Tob1 is a constitutively expressed repressor of liver regeneration

How proliferative and inhibitory signals integrate to control liver regeneration remains poorly understood. A screen for antiproliferative factors repressed after liver injury identified transducer of ErbB2.1 (Tob1), a member of the PC3/BTG1 family of mito-inhibitory molecules as a target for further evaluation. Tob1 protein decreases after 2/3 hepatectomy in mice secondary to posttranscriptional mechanisms. Deletion of Tob1 increases hepatocyte proliferation and accelerates restoration of liver mass after hepatectomy. Down-regulation of Tob1 is required for normal liver regeneration, and Tob1 controls hepatocyte proliferation in a dose-dependent fashion. Tob1 associates directly with both Caf1 and cyclin-dependent kinase (Cdk) 1 and modulates Cdk1 kinase activity. In addition, Tob1 has significant effects on the transcription of critical cell cycle components, including E2F target genes and genes involved in p53 signaling. We provide direct evidence that levels of an inhibitory factor control the rate of liver regeneration, and we identify Tob1 as a crucial check point molecule that modulates the expression and activity of cell cycle proteins.

Gene expression profiling and network analysis reveals lipid and steroid metabolism to be the most favored by TNFalpha in HepG2 cells

Background

The proinflammatory cytokine, TNFα, is a crucial mediator of the pathogenesis of several diseases, more so in cases involving the liver wherein it is critical in maintaining liver homeostasis since it is a major determiner of hepatocyte life and death. Gene expression profiling serves as an appropriate strategy to unravel the underlying signatures to envisage such varied responses and considering this, gene transcription profiling was examined in control and TNFα treated HepG2 cells.

Methods and Findings

Microarray experiments between control and TNFα treated HepG2 cells indicated that TNFα could significantly alter the expression profiling of 140 genes; among those up-regulated, several GO (Gene Ontology) terms related to lipid and fat metabolism were significantly (p<0.01) overrepresented indicating a global preference of fat metabolism within the hepatocyte and those within the down-regulated dataset included genes involved in several aspects of the immune response like immunoglobulin receptor activity and IgE binding thereby indicating a compromise in the immune defense mechanism(s). Conserved transcription factor binding sites were identified in identically clustered genes within a common GO term and SREBP-1 and FOXJ2 depicted increased occupation of their respective binding elements in the presence of TNFα. The interacting network of “lipid metabolism, small molecule biochemistry” was derived to be significantly overrepresented that correlated well with the top canonical pathway of “biosynthesis of steroids”.

Conclusions

TNFα alters the transcriptome profiling within HepG2 cells with an interesting catalog of genes being affected and those involved in lipid and steroid metabolism to be the most favored. This study represents a composite analysis of the effects of TNFα in HepG2 cells that encompasses the altered transcriptome profiling, the functional analysis of the up- and down- regulated genes and the identification of conserved transcription factor binding sites. These could possibly determine TNFα mediated alterations mainly the phenotypes of hepatic steatosis and fatty liver associated with several hepatic pathological states.

Cholera toxin-sensitive GTP-binding protein-coupled activation of augmenter of liver regeneration (ALR) receptor and its function in rat kupffer cells

Mitogenic effect of augmenter of liver regeneration (ALR), a protein produced and released by hepatocytes, on hepatocytes in vivo but not in vitro suggests that the effect is mediated by nonparenchymal cells. Since mediators produced by Kupffer cells are implicated in hepatic regeneration, we investigated receptor for ALR and its functions in rat Kupffer cells. Kupffer cells were isolated from rat liver by enzymatic digestion and centrifugal elutriation. Radioligand ([(125)I] ALR) receptor binding, ALR-induced GTP/G-protein association, and nitric oxide (NO), tumor necrosis factor (TNF)-alpha, and interleukin-6 (IL-6) synthesis were determined. High-affinity receptor for ALR, belonging to the G-protein family, with K(d) of 1.25 +/- 0.18 nM and B(max) of 0.26 +/- 0.02 fmol/microg DNA was identified. ALR stimulated NO, TNF-alpha, and IL-6 synthesis via cholera toxin-sensitive G-protein, as well as p38-MAPK activity and nuclear translocation of NFkappaB. While inhibitor of NFkappaB (MG132) inhibited ALR-induced NO synthesis, MG132 and p38-MAPK inhibitor (SB203580) abrogated ALR-induced TNF-alpha and IL-6 synthesis. ALR also prevented the release of mediator(s) from Kupffer cells that cause inhibition of DNA synthesis in hepatocytes. Administration of ALR to 40% partially hepatectomized rats increased expression of TNF-alpha, IL-6, and inducible nitric oxide synthase (iNOS) and caused augmentation of hepatic regeneration. These results demonstrate specific G-protein coupled binding of ALR and its function in Kupffer cells and suggest that mediators produced by ALR-stimulated Kupffer cells may elicit physiologically important effects on hepatocytes.

Redox regulation of tumor necrosis factor signaling

Tumor necrosis factor-alpha (TNF) is a key cytokine that has been shown to play important physiologic (e.g., inflammation) and pathophysiologic (e.g., various liver pathologies) roles. In liver and other tissues, TNF treatment results in the simultaneous activation of an apoptotic pathway (i.e., TRADD, RIP, JNK) and a survival pathway mediated by NF-kappaB transcription of survival genes (i.e., GADD45beta, Mn-SOD, cFLIP). The cellular response (e.g., proliferation versus apoptosis) to TNF is determined by the balance between the apoptotic signaling pathway and the NF-kappaB survival pathway stimulated by TNF. Reactive oxygen species (ROS) are important modulators of signaling pathways and can regulate both apoptotic signaling and NF-kappaB transcription triggered by TNF. ROS are important in mediating the sustained activation of JNK, to help mediate apoptosis after TNF treatment. In some cells, ROS are second messengers that mediate apoptosis after TNF stimulation. Conversely, ROS can cause redox modifications that inhibit NF-kappaB activation, which can lead to cell death triggered by TNF. Consequently, the redox status of cells can determine the biologic response that TNF will induce in cells. In many liver pathologies, ROS generated extrinsically (e.g., inflammation) or intrinsically (i.e., drugs, toxins) may act in concert with TNF to promote hepatocyte death and liver injury through redox inhibition of NF-kappaB.

Does the simultaneous tumor necrosis factor receptor 2, tumor necrosis factor promoter gene polymorphism represent a higher risk for alcoholic liver disease?

BACKGROUND AND AIM

Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine that seems to play a crucial role in the pathogenesis of alcoholic liver disease (ALD). TNF-alpha exerts its effects by binding to specific receptors (TNFR); the polymorphism of TNFRII T587G has been associated with increased TNF apoptotic response and its presence may increase the risk to develop liver disease. The aim of this study was to evaluate the prevalence of the TNF-alpha G238A promoter and TNFRII polymorphisms, individually or simultaneously, in ALD.

METHODS

TNF-alpha G238A and TNFRII T587G polymorphisms were studied in 103 unrelated patients with ALD (biopsy confirmed or clinical evidence) and in 76 heavy drinkers without liver disease (NLD). Single nucleotide polymorphism gene was detected by a polymerase chain reaction-restriction fragment length polymorphisms method. All patients had, at least, a 5 year history of alcohol consumption greater than 80 g/day.

RESULTS

TNF-alpha G238A allele frequency was similar in both groups. TNFRII T587G allele frequency was slightly higher in the ALD group than in the NLD group (21 vs. 18%, P=NS). TNF-alpha G238A and TNFRII T587G were simultaneously present in six ALD patients and in none of NLD patients (P=0.04).

CONCLUSION

Although individually there was no association between TNFRII T587G or TNF-alpha G238A polymorphisms and ALD, this study suggests that the presence of both polymorphisms may enhance the susceptibility for ALD. TNF-alpha G238A may increase TNF-alpha production, which when associated with TNFRII T587G, can further exacerbate TNF-alpha response leading to a greater risk of ALD.

Effect of non-essential amino acid glycine administration on the liver regeneration of partially hepatectomized rats with hepatic ischemia/reperfusion injury

BACKGROUND & AIMS

Liver regeneration after partial hepatectomy or transplantation is a critical problem to affect prognosis. Ischemia/reperfusion (I/R) is an unavoidable process during liver resection or transplantation. The aim of this study was to investigate the effect of glycine on the regeneration of the remnant liver with I/R injury after partial hepatectomy.

METHODS

Partially hepatectomized rat with liver I/R injury was prepared by a two-thirds partial hepatectomy following 30 min of total hepatic ischemia. Glycine (5% in water) was orally administered to rats for 3 days as drinking water before the surgery.

RESULTS

Mortality rate in partially hepatectomized rats with severe hepatic I/R injury was so high compared to that in the rats with partial hepatectomy alone. However, when glycine was given to the partially hepatectomized rats with hepatic I/R injury, the survival rate, the recovery rate of the remnant liver weight, and the liver injury were obviously improved. On the other hand, when glycine-treated rats underwent partial hepatectomy without hepatic I/R, the recovery rate of the remnant liver weight was decreased as compared with that of the rats with partial hepatectomy alone. In these settings, glycine administration prevented the elevation of serum TNF-alpha levels and liver TNF-alpha mRNA expression.

CONCLUSIONS

Glycine improved the regeneration of the remnant liver with severe I/R injury after partial hepatectomy. This improvement may be at least partly due to the amelioration of the hepatic I/R injury by glycine. Glycine seems to be clinically beneficial to the prognosis of patients with liver resection.

Hepatic c-fos expression is independent of oxidative stress and inflammation induced by acute cadmium exposure in rats

AIM

To investigate the relationships between c-fos expression and oxidative stress or inflammation in the liver induced by acute cadmium (Cd) exposure.

METHODS

Sixty male Sprague-Dawley rats were randomly assigned to 1 of 6 groups, 10 rats in each group. They were intragastrically pretreated with distilled water, distilled water, vitamin E (50 mg/100 g body weight), 25, 50 and 75% Sagittaria sagittifolia (SS) extract (2 ml/100 g weight) once a day for 10 consecutive days. Twenty-four hours after the last feeding, all animals were intraperitoneally administered CdCl(2) (20 micromol/kg body weight) except for the control group which was given distilled water. Twenty-four hours after intoxication, the glutathione (GSH) and malondialdehyde (MDA) contents and gene expression of tumor necrosis factor-alpha (TNF-alpha) and c-fos were measured in the livers.

RESULTS

Acute Cd exposure significantly increased MDA levels, decreased GSH levels and upregulated the gene expression of TNF-alpha and c-fos in the liver. Vitamin E and middle and high doses of SS were able to inhibit the MDA level, but only middle and high doses of SS enhanced the GSH level and inhibited the upregulation of TNF-alpha gene expression. However, neither vitamin E nor SSwas able to inhibit the upregulation of c-fos gene expression in the liver.

CONCLUSION

Our data suggested that c-fos induction is independent of oxidative stress or inflammation in the liver during the process of acute Cd exposure in rats.

Mechanisms of hepatic regeneration following portal vein embolization and partial hepatectomy: a review

BACKGROUND

Portal vein embolization (PVE) improves outcome following major hepatectomy, and basic studies have presented evidence related to the mechanisms responsible for hepatic regeneration. Hemodynamic changes following PVE are similar to, but slightly different from, those of partial hepatectomy (PH) because arterial flow to the embolized lobe is preserved. However, the process of hepatic regeneration is essentially the same after both PVE and PH. A number of mediators are involved in PVE or PH-induced hepatic regeneration. These include inflammatory cytokines, vasoregulators, growth factors, eicosanoids, and various hormones. These mediators activate a complex network of signal transduction that promotes hepatic regeneration. A variety of conditions have been shown to modulate the function of these mediators and inhibit regeneration. These include biliary obstruction, diabetes, chronic ethanol consumption, malnutrition, gender, aging, and infection.

CONCLUSION

Optimizing these factors, where possible, before PVE or PH, is essential to maximize hypertrophy of the liver. A fuller understanding of hepatic physiology and pathophysiology following PVE or PH may lead to greater functional capacity of the remaining liver and extend the indications for hepatectomy in patients who require large liver volume resection.

Hepatic tumor necrosis factor signaling and nuclear factor-kappaB: effects on liver homeostasis and beyond

The proinflammatory cytokine TNF has a pivotal role in liver pathophysiology because it holds the capacity to induce both hepatocyte cell death and hepatocyte proliferation. This dual effect of TNF on hepatocytes reflects its ability to induce both nuclear factor kappaB (NF-kappaB)-dependent gene expression and cell death. Multiple studies have demonstrated the crucial role of the transcription factor NF-kappaB in the decision between life and death of a hepatocyte. Massive hepatocyte apoptosis preceding embryonic lethality in NF-kappaB-deficient mice constituted the first indication of an essential antiapoptotic function of NF-kappaB in the liver. Although many studies confirmed this crucial cytoprotective role of NF-kappaB in adult liver, a number of genetic studies recently obtained conflicting results on the exact role of NF-kappaB in different mouse models of TNF hepatotoxicity, demonstrating that caution should be taken when interpreting studies using different NF-kappaB-deficient mice in distinct models of liver injury. Recent reports showing a role for hepatic NF-kappaB activation in the proliferation of malignant cells during hepatocarcinogenesis, and in the progression of fatty liver diseases to insulin resistance and type 2 diabetes mellitus demonstrate that NF-kappaB can also have more detrimental effects in the liver. Moreover, its role in the development of the metabolic syndrome emphasizes that hepatic NF-kappaB activation might also have adverse effects on the endocrine system. Therefore, understanding the regulation of hepatic TNF signaling and NF-kappaB activation is of critical therapeutic importance. In this review, we summarize how studies on the role of NF-kappaB in different mouse models of liver pathologies have contributed to this understanding.

TNF-alpha modulates hepatic Na+-K+ ATPase activity via PGE2 and EP2 receptors

The effect of TNF-alpha on liver Na(+)-K(+) ATPase was studied in Sprague-Dawley rats and in HepG2 cells. TNF-alpha was injected intraperitoneally to rats and 4h later the liver was isolated and the activity and protein expression of hepatic Na(+)-K(+) ATPase studied. The cytokine caused a significant down-regulation of the ATPase and a decrease in its activity. This effect disappeared in presence of indomethacin, an inhibitor of COX enzymes, and PGE2 injected to the animals imitated the effect of TNF-alpha. The observed in vivo effects of TNF and PGE2 on the pump appeared again when HepG2 cells were treated with the cytokine or the prostaglandin. The application of different agonist and antagonist to EP receptors showed that the effect of PGE2 is mediated via EP2 receptors. It was concluded that TNF-alpha induces in hepatocytes, PGE2 production which in turn reduces the activity and protein expression of the Na(+)-K(+) ATPase by activating EP2 receptors.

Mechanism of impaired hepatic regeneration in cholestatic liver

The regenerative capacity of the liver is an important factor following liver surgery. The dramatic change in portal venous flow, due to either portal vein embolization or partial hepatectomy, induces a rapid change in liver volume. In response to these stresses, hepatocytes are primed, through the release of inflammatory cytokines, to increase the expression of immediate early genes and increase the activation of transcriptional factors. The primed hepatocytes then respond to growth factors, including hepatocyte growth factor, epidermal growth factor, and transforming growth factor-alpha. Several pathologic conditions have been shown to inhibit hepatic regeneration. These include diabetes mellitus, malnutrition, aging, infection, chronic ethanol consumption, and biliary obstruction. Impaired hepatic regeneration in the setting of biliary obstruction is an especially serious problem because it can be a major determinant in not considering surgical treatment. The mechanism responsible for impaired hepatic regeneration in patients with biliary obstruction includes decreased portal venous flow, attenuated production of liver proliferation-associated factors, an increased rate of apoptosis, and lack of enterohepatic circulation. Restoring these factors may lead to an improvement in regeneration in a cholestatic liver following portal vein embolization or partial hepatectomy. This review article summarizes the current understanding of the mechanism of hepatic regeneration, with particular emphasis on that in the cholestatic liver.

Thalidomide-induced severe hepatotoxicity

Thalidomide is a relatively safe and efficacious form of therapy in the treatment of advanced, refractory multiple myeloma. Hepatotoxicity is listed as an extremely rare adverse effect associated with its use. We describe a 76-year-old woman with multiple myeloma who was treated with dexamethasone and thalidomide. By week 6 of therapy, she had developed acute increases in her aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels to more than 50 times the upper limit of normal. Her liver function test results had been within the normal ranges before and immediately after the start of therapy, and the patient had no known history of underlying liver disease. A liver biopsy specimen demonstrated evidence of acute injury with chronic changes of underlying steatosis and bridging fibrosis due to previously undiagnosed nonalcoholic steatohepatitis. Immediately after discontinuing thalidomide, her liver function test results began trending downward. Seven days later, her AST and ALT levels had improved to 86 and 165 U/L, respectively. This case and a limited number of other reports demonstrate severe hepatotoxicity as a rare but potentially serious adverse effect of thalidomide therapy. With the expanding use of thalidomide as a therapeutic agent, clinicians must recognize severe hepatotoxicity as a potential complication. Whether patients with preexisting liver disease are at increased risk when receiving thalidomide remains to be seen.

Inhibition of matrix metalloproteinases increases PPAR-alpha and IL-6 and prevents dietary-induced hepatic steatosis and injury in a murine model

Steatosis is a prominent feature of nonalcoholic fatty liver disease and a potential promoter of inflammation. Injury leading to cirrhosis is partly mediated by dysregulation of matrix protein turnover. Matrix metalloproteinase (MMP) inhibitors protect mice from lethal TNF-alpha induced liver injury. We hypothesized that Marimastat, a broad-spectrum MMP and TNF-alpha converting enzyme (TACE) inhibitor, might modulate this injury through interruption of inflammatory pathways. Triglyceride and phospholipid levels (liver, serum) and fatty acid profiles were used to assess essential fatty acid status and de novo lipogenesis as mechanisms for hepatic steatosis. Mice receiving a fat-free, high-carbohydrate diet (HCD) for 19 days developed severe fatty liver infiltration, demonstrated by histology, magnetic resonance spectroscopy, and elevated liver function tests. Animals receiving HCD plus Marimastat (HCD+MAR) were comparable to control animals. Increased tissue levels of peroxisome proliferator activated receptor-alpha (PPAR-alpha), higher levels of serum IL-6, and decreased levels of serum TNF-alpha receptor II were also seen in the HCD+MAR group compared with HCD-only. In addition, there was increased phosphorylation, and likely activation, of PPAR-alpha in the HCD+MAR group. PPAR-alpha is a transcription factor involved in beta-oxidation of fatty acids, and IL-6 is a hepatoprotective cytokine. Liver triglyceride levels were higher and serum triglyceride and phospholipid levels lower with HCD-only but improved with Marimastat treatment. HCD-only and HCD+MAR groups were essential fatty acid deficient and had elevated rates of de novo lipogenesis. We therefore conclude that Marimastat reduces liver triglyceride accumulation by increasing fat oxidation and/or liver clearance of triglycerides. This may be related to increased expression and activation of PPAR-alpha or IL-6, respectively.

Biphasic activation of liver regeneration-associated signals in an early stage after portal vein branch ligation

At an early stage in liver regeneration, a variety of factors including transcriptional factors, proinflammatory cytokines, and proto-oncogenes are activated or expressed. However, these responses are affected by surgical stress in the conventional portal vein branch ligation model (PVL). We sought to determine the net activation of early regeneration-associated signals after PVL using a newly developed non-surgical stress PVL model. Male Wistar rats were assigned into two groups, a stress-PVL (sPVL) model with laparotomy and portal vein branch ligation, and a non-stress-PVL (nsPVL) one subjected to portal vein branch ligation 1 week after laparotomy in which the effects of surgical stress were subsided. The activation of transcriptional factors and expression of immediate early genes were analyzed at an early time point (within 24 h) by Western blotting and RT-PCR, respectively. A monophasic upregulation of nuclear factor-kappaB (NF-kappaB) and phosphorylated-signal transducer and activator of transcription 3 (p-STAT3) peaked at 3h after sPVL was observed. In contrast, the expression pattern of these factors was biphasic (first peak at 0.5-1 h, second peak at 3-6 h) in nsPVL group. The expression pattern of immediate early genes showed a similar trend between sPVL and nsPVL. cDNA array analysis for the non-ligated lobe at 2 h after PVL revealed a much higher gene activation in sPVL than in nsPVL. These results indicate that previously observed activation pattern of regeneration-associated signals after PVL is significantly affected by the effect of laparotomy and our results using nsPVL model may more accurately represent liver regeneration-associated signal pattern.

Proinflammatory cytokine production in liver regeneration is Myd88-dependent, but independent of Cd14, Tlr2, and Tlr4

TNF and IL-6 are considered to be important to the initiation or priming phase of liver regeneration. However, the signaling pathways that lead to the production of these cytokines after partial hepatectomy (PH) have not been identified. Enteric-derived LPS appears to be important to liver regeneration, possibly by stimulating proinflammatory cytokine production after surgery. To determine whether LPS signaling pathways are involved in the regulation of the proinflammatory cytokines TNF and IL-6 during the priming phase of liver regeneration, we performed PH on mice lacking the TLRs Tlr4 and Tlr2, the LPS coreceptor, Cd14, and Myd88, an adapter protein involved in most TLR and IL-1R pathways. In MyD88 knockout (KO) mice after PH, both liver Tnf mRNA and circulating IL-6 levels were severely depressed compared with heterozygous or wild-type mice. Activation of STAT-3 and three STAT-3 responsive genes, Socs3, Cd14, and serum amyloid A2 were also blocked. In contrast, Tlr4, Tlr2, and Cd14 KO mice showed no deficits in the production of IL-6. Surprisingly, none of these KO mice showed any delay in hepatocyte replication. These data indicate that the LPS receptor TLR4, as well as TLR2 and CD14, do not play roles in regulating cytokine production or DNA replication after PH. In contrast, MyD88-dependent pathways appear to be responsible for TNF, IL-6, and their downstream signaling pathways.

Non-parenchymal liver cells support the growth advantage in the first stages of hepatocarcinogenesis

Hepatocellular carcinoma almost always arises in chronically inflamed livers. We developed a culture model to study the role of non-parenchymal cells (NPCs) for inflammation-driven hepatocarcinogenesis. Rats were treated with the carcinogen N-nitrosomorpholine, which induced initiated hepatocytes expressing the marker placental glutathione-S-transferase (GSTp). After 21 days two preparations of hepatocytes were made: (i) conventional ones (Hep-conv) containing NPCs and (ii) hepatocytes purified of NPCs (Hep-pur). Initiated hepatocytes, being positive for GSTp (GSTp-pos) were present in both preparations and were cultured along with normal hepatocytes, being negative for GSTp (GSTp-neg). Under any culture condition DNA synthesis was approximately 4-fold higher in GSTp-pos than in GSTp-neg hepatocytes demonstrating the inherent growth advantage of the first stages of hepatocarcinogenesis. Hepatocytes showed approximately 3-fold lower rates of DNA synthesis in Hep-pur than in Hep-conv, which was elevated above Hep-conv levels by addition of NPC or NPC-supernatant. Pretreatment of NPCs with proinflammatory lipopolysaccharide (LPS) further increased DNA synthesis. Thus, NPCs release soluble growth stimulators. Next we investigated the effect of specific cytokines produced by NPCs. Tumour necrosis factor alpha and interleukin 6 barely altered DNA synthesis, whereas hepatocyte growth factor (HGF), keratinocyte growth factor (KGF) and the heparin-binding epidermal growth factor-like growth factor (HB-EGF) were potent inducers of DNA replication in both, GSTp-neg and GSTp-pos cells. In conclusion, DNA synthesis of hepatocytes is increased by factors released from NPCs, an effect augmented by LPS-stimulation. NPC-derived cytokines, such as KGF, HGF and HB-EGF, stimulate DNA synthesis preferentially in initiated hepatocytes, presumably resulting in tumour promotion. Similar mechanisms may contribute to carcinogenesis in human inflammatory liver diseases.

Normal liver regeneration and liver cell apoptosis after partial hepatectomy in tumor necrosis factor-alpha-deficient mice

AIMS/BACKGROUND

Tumor necrosis factor-alpha (TNF-alpha) is known as a proinflammatory cytokine that has been implicated as a contributing factor in a number of disease processes. TNF-alpha also influences liver repair following hepatotoxic damage, and regeneration following partial hepatectomy (PH). The aim of this study was to assess the mechanism by which TNF-alpha influences liver cell apoptosis and regeneration following PH in TNF-alpha-deficient (TNF-alpha(-/-)) mice.

METHODS

PH was performed in wild mice and TNF-alpha(-/-) mice.

RESULTS

In both groups, serum alanine aminotransferase and serum total bilirubin levels comparably peaked at 6 and 48 h after PH, respectively. No differences were observed in hepatocyte proliferation, as determined by mitotic and the proliferating cell nuclear antigen labeling indices, between TNF-alpha(+/+) and TNF-alpha(-/-) mice. Few terminal deoxynucleotidyl transferase nick end-labeling-positive hepatocytes were seen in either type of mice. Nuclear factor-kappa B DNA binding activity in the remaining liver of TNF-alpha(-/-) mice after PH was similar to that of control mice. Ribonuclease protection assay showed that transforming growth factor beta1 mRNA was up-regulated comparably in the livers of the two groups, and that other cytokines were hardly seen in either. Interleukin-6/ signal transducer and activator of transcription-3-dependent pathway was not affected in TNF-alpha(-/-) mice.

CONCLUSIONS

These findings suggest that TNF-alpha has little influence on liver regeneration and liver cell apoptosis after PH in mice.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.

TNF alpha-induced Ras activation due to ethanol promotes hepatocyte proliferation independently of liver injury in the mouse

Tumor necrosis factor alpha (TNFalpha) has been shown to be both proapoptotic and mitogenic for hepatocytes and necessary for alcohol-induced liver injury. Ras, a known proto-oncogene, is very important in the regulation of cellular responses to TNFalpha. Therefore, the purpose of this study was to investigate the role of Ras in alcohol-induced pathogenesis. Male C57Bl/6 mice were fed ethanol or high-fat control diet via intragastric cannulation for 4 weeks. Ras activity was increased significantly after 4 weeks of ethanol and correlated with an increase in pathologic features. However, in mice deficient in the receptor-type 1 for TNFalpha (TNFR1(-/-)), ethanol-induced liver injury and the increase in Ras activity were significantly blunted compared with wild-type mice. Furthermore, it was demonstrated that H-, K-, and R-Ras isoforms were increased after ethanol exposure in wild-type mice. In TNFR1(-/-) mice, R-Ras activity remained elevated by ethanol, whereas H-Ras and K-Ras activity was blunted significantly under these conditions. Interestingly, hepatocellular proliferation, which was elevated approximately fivefold after 4 weeks of chronic ethanol in wild-type mice, was also blunted in TNFR1(-/-) mice given ethanol. Inhibition of Ras with adenovirus containing a dominant-negative Ras had no effect on ethanol-induced liver injury, but significantly blunted ethanol-induced hepatocyte proliferation by more than 50%. Overexpression of mitochondrial superoxide dismutase using recombinant adenovirus blunted lipid peroxidation and attenuated hepatic injury resulting from ethanol, but had no effect on Ras activation and hepatocyte proliferation caused by ethanol. In conclusion, these data support the hypotheses that hepatocellular oxidative stress leads to cell death and that TNFalpha-induced Ras activation is important in hepatic proliferation in response to ethanol-induced liver injury.

Relationship between apoptosis, tumour necrosis factor, and cell proliferation in chronic cholestasis

BACKGROUND

Target of the immune response in chronic autoimmune cholestasis, is the bile duct epithelium. Lymphocytic infiltration and apoptosis have both been suggested to mediate the destruction of hepatocytes and biliary epithelium in primary biliary cirrhosis.

AIMS

To further address this issue in two cholestatic liver diseases characterized by an autoimmune pathogenesis and, furthermore, evaluate the relationship between apoptosis and both tumour necrosis factor alpha and cell proliferation.

METHODS

Liver tissue specimens from 16 patients with primary biliary cirrhosis, 15 with primary sclerosing cholangitis, and 16 with chronic hepatitis C (controls) were evaluated. DNA-fragmentation of apoptotic cells was ascertained by the TdT-mediated deoxyuridine triphosphate nick-end labelling method. Tumour necrosis factor alpha expression and cell proliferation (Ki-67 antigen) were assayed by immunohistochemistry.

RESULTS

Hepatocytes with DNA fragmentation were observed in 75% of patients with primary biliary cirrhosis, in 66.6% with primary sclerosing cholangitis, and in 43.7% with chronic hepatitis C. Biliocytes showed apoptosis in only 3 cases of primary biliary cirrhosis. Biliocytes showed a strong cytoplasmic expression in 4 cases (1 primary biliary cirrhosis, 2 primary sclerosing cholangitis and 1 chronic hepatitis C). A few intralobular and portal inflammatory mononuclear cells expressing tumour necrosis factor alpha were observed in 62.5% of patients with primary biliary cirrhosis, 46.1% with primary sclerosing cholangitis, and 56.2% with hepatitis C virus chronic hepatitis. The amount of intraportal mononuclear cells expressing Ki-67 antigen was significantly higher in primary biliary cirrhosis specimens than in primary sclerosing cholangitis (p<0.001) or hepatitis C virus-related chronic hepatitis (p<0.03). No correlation was found within the 3 groups of patients between the Ki-67 histological score and the severity of liver disease. Moreover, no relationship was found between TdT-mediated deoxyuridine triphosphate nick-end labelling and either tumour necrosis factor alpha or Ki-67 staining.

CONCLUSIONS

Apoptosis is a phenomenon which frequently involves hepatocytes in chronic autoimmune cholestasis. This process is apparently parallel, but unrelated to cell proliferation. Cell proliferation mainly involves mononuclear cells in portal tracts of primary biliary cirrhosis specimens. The finding of tumour necrosis factor alpha expression in biliocytes deserves further study to establish whether this cytokine is involved in triggering bile duct lesions.

Inhibition of DNA synthesis in cultured hepatocytes by endotoxin-conditioned medium of activated stellate cells is transforming growth factor-beta and nitric oxide-independent

Activated hepatic stellate cells play a major role in the pathophysiology of chronic liver disease. They can influence the metabolism of hepatocytes by producing a variety of cytokines and growth factors. Upon stimulation with endotoxin, stellate cells also synthesize nitric oxide (NO), a potent mediator of growth of several cell types including hepatocytes. We investigated the effect of serum-free medium conditioned by activated stellate cells in the absence and presence of endotoxin on NO and DNA synthesis in hepatocytes. Stellate cells and hepatocytes were isolated by enzymatic digestion of the liver. Stellate cells were cultured for 10 days after which the majority exhibited alpha-smooth muscle actin (a marker for activated cells); hepatocytes were used after overnight culture. While the medium conditioned by stellate cells in the absence of endotoxin stimulated DNA synthesis in hepatocytes, medium conditioned in its presence inhibited this process in an endotoxin concentration-dependent manner (10 - 1000 ng ml(-1)). Endotoxin-conditioned stellate cell medium also stimulated NO synthesis in hepatocytes; the effect was consistent with increased protein and mRNA expression of inducible NO synthase (iNOS). However, inhibition of DNA synthesis in hepatocytes caused by endotoxin-conditioned stellate cell medium was unaffected by the NOS inhibitor, L-N(G)-monomethylarginine (L-NMMA), guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and neutralizing antibodies for TGF-beta, IL-1beta, IL-6 and TNF-alpha. These results indicate that factors other than these cytokines produced by activated stellate cells upon stimulation with endotoxin or by hepatocytes challenged with endotoxin-conditioned stellate cell medium inhibit DNA synthesis in hepatocytes.

The effect of a tumour necrosis factor antibody on the regenerative response after partial hepatectomy in rats

In this study we investigated the effect of tumour necrosis factor (TNF) on the regenerative response after partial hepatectomy. Adult male rats were injected intravenously with an antibody to TNF immediately after partial hepatectomy. Animals were sacrificed at 0, 24, 48, 72 and 96 h postoperatively. Hepatic thymidine kinase (TK) activity, liver weight to body weight (LW/BW) ratio, and mitotic index (MI) were used as indices of hepatic regeneration. The rats treated with TNF-Ab had significantly lower levels of TK activity in the liver at 24 h postoperatively compared to the saline treated animals. Furthermore the peak hepatic TK activity was delayed to 48 h in the rats treated with TNF-Ab. The mitotic indices and LW/BW ratios in the TNF-Ab- and saline-treated animals were similar. These data suggest that TNF potentiates the regenerative response after partial hepatectomy.

Gadolinium chloride-induced hepatocyte proliferation is prevented by antibodies to tumor necrosis factor alpha

Gadolinium chloride (GdCl(3)) destroys large Kupffer cells and has been used extensively in mechanistic studies in a number of disease and toxicity processes; however, it cannot be used to study hepatocyte turnover since it increases cell proliferation itself. The mechanism by which GdCl(3) activates cell turnover in liver is unknown, but several possibilities exist. Here it was demonstrated that a direct mitogenic action on hepatocytes is unlikely since GdCl(3) did not stimulate the growth of primary rat hepatocyte in vitro. Therefore, it was hypothesized that GdCl(3) acts indirectly through mitogenic cytokines of nonparenchymal cell origin. Antibodies to tumor necrosis factor alpha (TNFalpha) were used to evaluate if TNFalpha is causally responsible for GdCl(3)-induced cell proliferation. GdCl(3) treatment of rats in vivo increased hepatocyte replication 5-fold in 24 h and 3-fold in 48 h. Pretreatment with specific anti-TNFalpha antibodies completely prevented these effects. However, when antibody treatment was delayed until 24 h after GdCl(3), increased cell proliferation was not prevented, suggesting that TNFalpha production during the first 24 h after treatment is responsible for activation of a signaling cascade involving other mitogens that sustain hepatocyte replication at 48 h. Twenty-four hours after treatment with GdCl(3), TNFalpha mRNA transcripts were increased 2-fold over control, an effect that was prevented by pretreatment with anti-TNFalpha antibody. NFkappaB, which is known to be involved in TNFalpha transcription, was activated by GdCl(3) about 4.5-fold over control 8 h after treatment in vivo, an increase not observed when antibodies to TNFalpha were present. When GdCl(3) was added to macrophages in culture, TNFalpha was nearly doubled 4 h after treatment. Additionally, conditioned media harvested from macrophages treated with GdCl(3) for 2 to 8 h stimulated the growth of HepG2 cells in culture about 2-fold, while antibodies to TNFalpha completely prevented this effect. Taken together, these data are consistent with the hypothesis that TNFalpha released from Kupffer cells at early time points prior to their destruction is causally responsible for triggering a cascade of events responsible for GdCl(3)-induced cell proliferation.

TNF-alpha regulates transforming growth factor-alpha expression in regenerating murine liver and isolated hepatocytes

TNF-alpha is a pleotropic proinflammatory cytokine that has been implicated as a contributing factor in a number of disease processes, primarily through its ability to induce the expression of inflammatory and cytotoxic mediators. TNF-alpha is also involved in cell growth accompanying the healing process in multiple organ systems and influences liver repair following hepatotoxic damage or regeneration following partial hepatectomy. In this respect, TNF-alpha is a known mitogen for hepatocytes. In this paper we describe a novel role for TNF-alpha in the modulation of expression of TGF-alpha, the latter being a complete hepatocyte mitogen. TNF-alpha directly up-regulates TGF-alpha mRNA by up to 7-fold in isolated mouse hepatocytes, whereas neutralization of TNF-alpha significantly decreased liver mRNA and protein expression of TGF-alpha following chemical-induced hepatotoxicity. That TNF-alpha directly stimulated TGF-alpha was suggested by the inability of either anti-IL-6 Abs or cycloheximide to inhibit TNF-alpha-induced TGF-alpha expression in hepatocytes. However, in the presence of anti-TGF-alpha neutralizing Abs, the mitogenic activity of TNF-alpha is abrogated. Using cells transfected with the TGF-alpha promoter, and an RNA polymerase inhibitor, it was shown that TNF-alpha modulates TGF-alpha expression through both pre- and posttranscriptional events. Taken together, these data suggest that TNF-alpha participates in liver repair and regeneration, in part, by directly inducing the expression of TGF-alpha.

Corn oil rapidly activates nuclear factor-kappaB in hepatic Kupffer cells by oxidant-dependent mechanisms

N-6 polyunsaturated fatty acids (N-6 PUFAs), major constituents of corn oil and natural ligands for peroxisome proliferator-activated receptors, increase the rate of growth of established tumors. It has been proposed that chemical peroxisome proliferators increase hepatocyte proliferation by mechanisms involving activation of nuclear factor-kappaB (NF-kappaB) and production of low levels of tumor necrosis factor alpha (TNFalpha) by Kupffer cells; however, how N-6 PUFAs are involved in increased cell proliferation in liver is not well understood. Here, the hypothesis that N-6 PUFAs increase production of mitogens by activation of Kupffer cell NF-kappaB was tested. A single dose of corn oil (2 ml/kg, i.g.), but not olive oil or medium-chain triglycerides (saturated fat), caused an approximately 3-fold increase in hepatocyte proliferation. Similarly, when activity of NF-kappaB in whole rat liver or isolated hepatocytes and Kupffer cells was measured at various time intervals for up to 36 h, only corn oil activated NF-kappaB. Corn oil increased NF-kappaB activity approximately 3-fold 1-2 h after treatment exclusively in the Kupffer cell fraction. In contrast, increases were small and only occurred after approximately 8 h in hepatocytes. The activation of NF-kappaB at 2 h and increases in cell proliferation at 24 h due to corn oil were prevented almost completely when rats were pretreated for 4 days with either dietary glycine (5% w/w), an agent that inactivates Kupffer cells, or the NADPH oxidase inhibitor, diphenyleneiodonium (s.c., 1 mg/kg/day). Furthermore, arachidonic acid (100 microM) activated superoxide production approximately 4-fold when added to isolated Kupffer cells in vitro. This phenomenon was not observed with oleic or linoleic acids. Interestingly, a single dose of corn oil increased TNFalpha mRNA nearly 2-fold 8 h after treatment. It is concluded that corn oil rapidly activates NF-kappaB in Kupffer cells via oxidant-dependent mechanisms. This triggers production of low levels of TNFalpha which is mitogenic in liver and promotes growth of hepatocytes.

Effects of deletion variant of hepatocyte growth factor on reduced-size liver transplantation in rats

BACKGROUND

The deletion variant of hepatocyte growth factor (dHGF) exerts mitogenic and antifibrotic effects. The purpose of this study was to evaluate the effect of dHGF on rats that had undergone syngeneic or allogeneic reduced-size (60%) orthotopic liver transplantation (ROLT).

METHODS

Starting immediately after the syngeneic (Lewis to Lewis) and allogeneic (Lewis to Brown Norway) ROLT, 500 microg/kg dHGF was administered i.v. twice a day until the day the rats were killed. Its effect on hepatic graft weight, regeneration, and biochemical parameters was evaluated.

RESULTS

dHGF promoted restoration of the liver volume and liver regeneration as well as protein synthesis in the rats that underwent syngeneic ROLT. In the rats that underwent allogeneic ROLT, dHGF reduced the level of serum cytosolic enzymes related to acute cellular rejection, but a significant improvement in liver regeneration and protein synthesis was not seen. When tacrolimus was administered to prevent rejection of the allogeneic grafts, the beneficial effect of dHGF was apparent, and was as beneficial as in syngeneic ROLT.

CONCLUSIONS

Administering dHGF after liver transplantation augments the regeneration and functional recovery of partial liver grafts and reduces hepatocyte injury in acute cellular rejection.

After portal branch ligation in rat, nuclear factor kappaB, interleukin-6, signal transducers and activators of transcription 3, c-fos, c-myc, and c-jun are similarly induced in the ligated and nonligated lobes

Several studies have emphasized the involvement of transcription factors, cytokines, and proto-oncogenes in initiating the regenerative process after partial hepatectomy. To assess whether these events do specifically occur in a cellular system undergoing regeneration, we studied the induction of nuclear factor kappaB (NFkappaB), interleukin-6 (IL-6), signal transducers and activators of transcription 3 (Stat3), c-fos, c-myc, c-jun, after portal branch ligation (PBL), which produces atrophy of the deprived lobes (70% of the liver parenchyma), whereas the perfused lobes undergo compensatory regeneration. Nuclear extracts and total RNA were prepared from control livers as well as from atrophying and regenerating lobes at 0.5, 1, 2, 5, and 8 after PBL. NFkappaB and Stat3 induction were studied by electrophoretic mobility shift assays and Western blotting. IL-6 and proto-oncogenes expressions were assessed by reverse transcription polymerase chain reaction and Northern blotting, respectively. Assays were also performed after a sham operation. NFkappaB and Stat3 protein expression and DNA binding were rapidly and similarly induced in nuclear extracts from the atrophying and regenerating lobes. IL-6 was elevated in both lobes from 1 to 8 hours after PBL as well as c-fos, c-myc, and c-jun during the first 2 hours. IL-6 and Stat3 but not NFkappaB were also elevated after a sham operation. These findings suggest that the cellular and molecular changes occurring early in a regenerating liver are nonspecific, possibly stress-induced, cellular responses. They do not indicate the future evolution towards atrophy or regeneration.