Clinical implications of advances in the basic science of liver repair and regeneration

Rapid liver self-recovery: A challenge for rat models of tissue damage

Animal models, mainly murine, stay as a fundamental resource in diverse research pursuits, notably contributing to significant strides in discovering novel treatments for therapeutic applications. Preclinical assays must consider the existence of self-recovery mechanisms in the murine species to achieve a well-designed control group. This study focuses on unveiling the innate rapid regenerative capacity of rat liver by utilizing the thioacetamide-induced sub-chronic liver injury model. Employing histopathological, biochemical, and molecular liver function tests, we assessed the recovery of liver tissue functionality. Moreover, animals were housed with voluntary running wheels and locomotory activity was recorded and employed as an indirect index of overall animal recuperation. Remarkably, basal locomotory activity reestablished to normal levels only two weeks post-thioacetamide exposure. Our results raise vital considerations about the importance of temporal synchronicity in comparative assays to validate the real action of treatments, emphasizing the role of the rapid rat liver endogenous self-recovery.

Metabolic reprogramming in Nrf2-driven proliferation of normal rat hepatocytes

BACKGROUND AND AIMS

Cancer cells reprogram their metabolic pathways to support bioenergetic and biosynthetic needs and to maintain their redox balance. In several human tumors, the Keap1-Nrf2 system controls proliferation and metabolic reprogramming by regulating the pentose phosphate pathway (PPP). However, whether this metabolic reprogramming also occurs in normal proliferating cells is unclear.

APPROACH AND RESULTS

To define the metabolic phenotype in normal proliferating hepatocytes, we induced cell proliferation in the liver by 3 distinct stimuli: liver regeneration by partial hepatectomy and hepatic hyperplasia induced by 2 direct mitogens: lead nitrate (LN) or triiodothyronine. Following LN treatment, well-established features of cancer metabolic reprogramming, including enhanced glycolysis, oxidative PPP, nucleic acid synthesis, NAD + /NADH synthesis, and altered amino acid content, as well as downregulated oxidative phosphorylation, occurred in normal proliferating hepatocytes displaying Nrf2 activation. Genetic deletion of Nrf2 blunted LN-induced PPP activation and suppressed hepatocyte proliferation. Moreover, Nrf2 activation and following metabolic reprogramming did not occur when hepatocyte proliferation was induced by partial hepatectomy or triiodothyronine.

CONCLUSIONS

Many metabolic changes in cancer cells are shared by proliferating normal hepatocytes in response to a hostile environment. Nrf2 activation is essential for bridging metabolic changes with crucial components of cancer metabolic reprogramming, including the activation of oxidative PPP. Our study demonstrates that matured hepatocytes exposed to LN undergo cancer-like metabolic reprogramming and offers a rapid and useful in vivo model to study the molecular alterations underpinning the differences/similarities of metabolic changes in normal and neoplastic hepatocytes.

Canonical Thyroid Hormone Receptor β Action Stimulates Hepatocyte Proliferation in Male Mice

CONTEXT

3,5,3'-L-triiodothyronine (T3) is a potent inducer of hepatocyte proliferation via the Wnt/β-catenin signaling pathway. Previous studies suggested the involvement of rapid noncanonical thyroid hormone receptor (TR) β signaling, directly activating hepatic Wnt/β-catenin signaling independent from TRβ DNA binding. However, the mechanism by which T3 increases Wnt/β-catenin signaling in hepatocytes has not yet been determined.

OBJECTIVE

We aimed to determine whether DNA binding of TRβ is required for stimulation of hepatocyte proliferation by T3.

METHODS

Wild-type (WT) mice, TRβ knockout mice (TRβ KO), and TRβ mutant mice with either specifically abrogated DNA binding (TRβ GS) or abrogated direct phosphatidylinositol 3 kinase activation (TRβ 147F) were treated with T3 for 6 hours or 7 days. Hepatocyte proliferation was assessed by Kiel-67 (Ki67) staining and apoptosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. Activation of β-catenin signaling was measured in primary murine hepatocytes. Gene expression was analyzed by microarray, gene set enrichment analysis (GSEA), and quantitative reverse transcription polymerase chain reaction.

RESULTS

T3 induced hepatocyte proliferation with an increased number of Ki67-positive cells in WT and TRβ 147F mice (9.2% ± 6.5% and 10.1% ± 2.9%, respectively) compared to TRβ KO and TRβ GS mice (1.2% ± 1.1% and 1.5% ± 0.9%, respectively). Microarray analysis and GSEA showed that genes of the Wnt/β-catenin pathway-among them, Fzd8 (frizzled receptor 8) and Ctnnb1 (β-catenin)-were positively enriched only in T3-treated WT and TRβ 147F mice while B-cell translocation gene anti-proliferation factor 2 was repressed. Consequently, expression of Ccnd1 (CyclinD1) was induced.

CONCLUSIONS

Instead of directly activating Wnt signaling, T3 and TRβ induce key genes of the Wnt/β-catenin pathway, ultimately stimulating hepatocyte proliferation via CyclinD1. Thus, canonical transcriptional TRβ action is necessary for T3-mediated stimulation of hepatocyte proliferation.

Nrf2 in Neoplastic and Non-Neoplastic Liver Diseases

Simple Summary

Although the Keap1-Nrf2 pathway represents a powerful cell defense mechanism against a variety of toxic insults, its role in acute or chronic liver damage and tumor development is not completely understood. This review addresses how Nrf2 is involved in liver pathophysiology and critically discusses the contrasting results emerging from the literature. The aim of the present report is to stimulate further investigation on the role of Nrf2 that could lead to define the best strategies to therapeutically target this pathway.

Abstract

Activation of the Keap1/Nrf2 pathway, the most important cell defense signal, triggered to neutralize the harmful effects of electrophilic and oxidative stress, plays a crucial role in cell survival. Therefore, its ability to attenuate acute and chronic liver damage, where oxidative stress represents the key player, is not surprising. On the other hand, while Nrf2 promotes proliferation in cancer cells, its role in non-neoplastic hepatocytes is a matter of debate. Another topic of uncertainty concerns the nature of the mechanisms of Nrf2 activation in hepatocarcinogenesis. Indeed, it remains unclear what is the main mechanism behind the sustained activation of the Keap1/Nrf2 pathway in hepatocarcinogenesis. This raises doubts about the best strategies to therapeutically target this pathway. In this review, we will analyze and discuss our present knowledge concerning the role of Nrf2 in hepatic physiology and pathology, including hepatocellular carcinoma. In particular, we will critically examine and discuss some findings originating from animal models that raise questions that still need to be adequately answered.

Potential role of two novel agonists of thyroid hormone receptor-β on liver regeneration

OBJECTIVES

Although the hepatomitogenic activity of triiodothyronine (T3) is well established, the wide range of harmful effects exerted by this hormone precludes its use in liver regenerative therapy. Selective agonists of the beta isoform of thyroid hormone receptor (TRβ) do not exhibit T3-induced cardiotoxicity and show a good safety profile in patients with NASH. The aim of this study was to investigate whether two novel TRβ agonists, the prodrug TG68 and the active compound IS25 could stimulate hepatocyte proliferation without T3/TRα-dependent side effects.

METHODS

Rats were treated with three different doses (12.5, 25 and 50 μg/100 g body weight) for one week. Hepatocyte proliferation, liver injury and serum biochemical parameters were measured by immunohistochemistry, qRT-PCR and Western blot.

RESULTS

Both drugs increased hepatocyte proliferation as assessed by bromodeoxyuridine incorporation (from 14% to 28% vs 5% of controls) and mitotic activity. Enhanced proliferation occurred in the absence of significant signs of liver injury as shown by lack of increased serum transaminase levels or of apoptosis. No cardiac or renal hypertrophy typically associated with treatment with T3 was observed. Importantly, no proliferation of pancreatic acinar cells, such as that seen after administration of T3 or the TRβ agonist GC1 was detected following either TG68 or IS25, demonstrating the hepato-specificity of these novel TRβ agonists.

CONCLUSIONS

The present study shows that TG68 and IS25 induce massive hepatocyte proliferation without overt toxicity. Hence, these agents may have a significant clinical application for regenerative therapies in liver transplantation or other surgical settings.

Therapeutic implication of platelets in liver regeneration -hopes and hues

Mounting evidence highlights platelet involvement in liver regeneration via interaction with liver cells, growth factors release, and signaling contributions. Existing research suggests a compelling biological rationale for utilizing platelet biology, with the goal of improving liver function and accelerating its regenerative potential. Despite its expanding application in several clinical areas, the contribution of the platelet and its therapeutic implementation in liver regeneration so far has not yet fulfilled the initial high expectations. Areas covered: This review scrutinizes the progress, current updates, and discusses how recent understanding - particularly in the clinical implications of platelet-based therapy - may enable strategies to introduce and harness the therapeutic potential of the platelet during liver regeneration. Expert commentary: Several clinical and translational studies have facilitated a platform for the development of platelet-based therapy to enhance liver regeneration. While some of these therapies are effective to augment liver regeneration, the others have had some detrimental outcomes. The existing evidence represents a challenge for future projects that are focused on directly incorporating platelet-based therapies to induce liver regeneration.

The ileal FGF15/19 to hepatic FGFR4 axis regulates liver regeneration after partial hepatectomy in mice

Fibroblast growth factor (FGF) has been considered to modulate liver regeneration (LR) after partial hepatectomy (PH) at the tissue level. Previous studies have demonstrated that FGF15 and FGF19 induce the activation of its receptor, FGF receptor 4 (FGFR4), which can promote hepatocellular carcinoma progression and regulate liver lipid metabolism. In this study, we aimed to explore the role of the ileal FGF15/19- hepatic FGFR4 axis in the LR after PH. Male C57BL/6 mice aged 8-12 weeks were partially hepatectomized and assessed for expression of ileal FGF15/19 to hepatic FGFR4 signaling. We used recombinant human FGF19 protein and a small interfering RNA (siRNA) of FGFR4 to regulate expression of the FGF15/19-FGFR4 axis in vitro and in vivo. The proliferation and cell cycle of hepatocytes, the expression levels of FGF15/19-FGFR4 downstream molecules, liver recovery, and lipid metabolism were assessed. We found that both ileal and serum FGF15 expression were upregulated and hepatic FGFR4 was activated after PH in mice. FGF15/19 promoted cell cycle progression, enhanced proliferation, and reduced hepatic lipid accumulation of hepatocytes both in vitro and in vivo. Furthermore, the proliferative effect and lipid regulatory properties of FGF15/19 were dependent on FGFR4 in hepatocytes. In addition, ileal FGF15/19-hepatic FGFR4 transduction during hepatocyte proliferation was regulated by extracellular regulated protein kinase (ERK) 1/2. In conclusion, the ileal FGF15/19 to hepatic FGFR4 axis is activated and promotes LR after PH in mice, supporting the potential of ileal FGF15/19 to hepatic FGFR4 axis-targeted therapy to enhance LR after PH.

GC-1: A Thyromimetic With Multiple Therapeutic Applications in Liver Disease

Thyroid hormones (THs), namely, 3,5,3'-triiodo-l-thyronine (T3) and 3,5,3',5'-tetraiodo-l-thyronine (thyroxine or T4), influence a variety of physiological processes that have important implications in fetal development, metabolism, cell growth, and proliferation. While THs elicit several beneficial effects on lipid metabolism and improve myocardial contractility, these therapeutically desirable effects are associated to a thyrotoxic state that severely limits the possible use of THs as therapeutic agents. Therefore, several efforts have been made to develop T3 analogs that could retain the beneficial actions (triglyceride, cholesterol, obesity, and body mass lowering) without the adverse TH-dependent side effects. This goal was achieved by the synthesis of TRβ-selective agonists. In this review, we summarize the current knowledge on the effects of one of the best characterized TH analogs, the TRβ1-selective thyromimetic, GC-1. In particular, we review some of the effects of GC-1 on different liver disorders, with reference to its possible clinical application. A brief comment on the possible therapeutic use of GC-1 in extrahepatic disorders is also included.

Thyroid Hormone Receptor-β Agonist GC-1 Inhibits Met-β-Catenin-Driven Hepatocellular Cancer

The thyromimetic agent GC-1 induces hepatocyte proliferation via Wnt/β-catenin signaling and may promote regeneration in both acute and chronic liver insufficiencies. However, β-catenin activation due to mutations in CTNNB1 is seen in a subset of hepatocellular carcinomas (HCC). Thus, it is critical to address any effect of GC-1 on HCC growth and development before its use can be advocated to stimulate regeneration in chronic liver diseases. In this study, we first examined the effect of GC-1 on β-catenin-T cell factor 4 activity in HCC cell lines harboring wild-type or mutated-CTNNB1. Next, we assessed the effect of GC-1 on HCC in FVB mice generated by hydrodynamic tail vein injection of hMet-S45Y-β-catenin, using the sleeping beauty transposon-transposase. Four weeks following injection, mice were fed 5 mg/kg GC-1 or basal diet for 10 or 21 days. GC-1 treatment showed no effect on β-catenin-T cell factor 4 activity in HCC cells, irrespective of CTNNB1 mutations. Treatment with GC-1 for 10 or 21 days led to a significant reduction in tumor burden, associated with decreased tumor cell proliferation and dramatic decreases in phospho-(p-)Met (Y1234/1235), p-extracellular signal-related kinase, and p-STAT3 without affecting β-catenin and its downstream targets. GC-1 exerts a notable antitumoral effect on hMet-S45Y-β-catenin HCC by inactivating Met signaling. GC-1 does not promote β-catenin activation in HCC. Thus, GC-1 may be safe for use in inducing regeneration during chronic hepatic insufficiency.

Thyroid Hormone Receptor β Agonist Induces β-Catenin-Dependent Hepatocyte Proliferation in Mice: Implications in Hepatic Regeneration

Triiodothyronine (T3) induces hepatocyte proliferation in rodents. Recent work has shown molecular mechanism for T3's mitogenic effect to be through activation of β-catenin signaling. Since systemic side effects of T3 may preclude its clinical use, and hepatocytes mostly express T3 hormone receptor β (TRβ), we investigated if selective TRβ agonists like GC-1 may also have β-catenin-dependent hepatocyte mitogenic effects. Here we studied the effect of GC-1 and T3 in conditional knockouts of various Wnt pathway components. We also assessed any regenerative advantage of T3 or GC-1 when given prior to partial hepatectomy in mice. Mice administered GC-1 showed increased pSer675-β-catenin, cyclin D1, BrdU incorporation, and PCNA. No abnormalities in liver function tests were noted. GC-1-injected liver-specific β-catenin knockouts (β-catenin LKO) showed decreased proliferation when compared to wild-type littermates. To address if Wnt signaling was required for T3- or GC-1-mediated hepatocyte proliferation, we used LRP5-6-LKO, which lacks the two redundant Wnt coreceptors. Surprisingly, decreased hepatocyte proliferation was also evident in LRP5-6-LKO in response to T3 and GC-1, despite increased pSer675-β-catenin. Further, increased levels of active β-catenin (hypophosphorylated at Ser33, Ser37, and Thr41) were evident after T3 and GC-1 treatment. Finally, mice pretreated with T3 or GC-1 for 7 days followed by partial hepatectomy showed a significant increase in hepatocyte proliferation both at the time (T0) and 24 h after surgery. In conclusion, like T3, TRβ-selective agonists induce hepatocyte proliferation through β-catenin activation via both PKA- and Wnt-dependent mechanisms and confer a regenerative advantage following surgical resection. Hence, these agents may be useful regenerative therapies in liver transplantation or other surgical settings.

Mesenchymal stem cells from the human umbilical cord ameliorate fulminant hepatic failure and increase survival in mice

BACKGROUND

Cell therapy has been promising for various diseases. We investigated whether transplantation of human umbilical cord mesenchymal stem cells (hUCMSCs) has any therapeutic effects on D-galactosamine/lipopolysaccharide (GalN/LPS)-induced fulminant hepatic failure in mice.

METHODS

hUCMSCs isolated from human umbilical cord were cultured and transplanted via the tail vein into severe combined immune deficiency mice with GalN/LPS-induced fulminant hepatic failure. After transplantation, the localization and differentiation of hUCMSCs in the injured livers were investigated by immunohistochemical and genetic analyses. The recovery of the injured livers was evaluated histologically. The survival rate of experimental animals was analyzed by the Kaplan-Meier method and log-rank test.

RESULTS

hUCMSCs expressed high levels of CD29, CD73, CD13, CD105 and CD90, but did not express CD31, CD79b, CD133, CD34, and CD45. Cultured hUCMSCs displayed adipogenic and osteogenic differentiation potential. Hematoxylin and eosin staining revealed that transplantation of hUCMSCs reduced hepatic necrosis and promoted liver regeneration. Transplantation of hUCMSCs prolonged the survival rate of mice with fulminant hepatic failure. Polymerase chain reaction for human alu sequences showed the presence of human cells in mouse livers. Positive staining for human albumin, human alpha-fetoprotein and human cytokeratin 18 suggested the formation of hUCMSCs-derived hepatocyte-like cells in vivo.

CONCLUSIONS

hUCMSC was a potential candidate for stem cell based therapies. After transplantation, hUCMSCs partially repaired hepatic damage induced by GalN/LPS in mice. hUCMSCs engrafted into the injured liver and differentiated into hepatocyte-like cells.

Hepatic regenerative medicine: exploiting the liver's will to live

This Guest Editorial introduces this month's special Liver Pathobiology Theme Issue, a series of reviews that encompass the discipline of hepatic regenerative medicine.

Mechanisms and consequences of injury and repair in older organ transplants

Donor organ scarcity remains a significant clinical challenge in transplantation. Older organs, increasingly utilized to meet the growing demand for donor organs, have been linked to inferior transplant outcomes. Susceptibility to organ injury, reduced repair capacity, and increased immunogenicity are interrelated and impacted by physiological and pathological aging processes. Insights into the underlying mechanisms are needed to develop age-specific interventional strategies with regards to organ preservation, immunosuppression, and allocation. In this overview, we summarize current knowledge of injury and repair mechanisms and the effects of aging relevant to transplantation.

Tri-iodothyronine induces hepatocyte proliferation by protein kinase A-dependent β-catenin activation in rodents

Thyroid hormone (T3), like many other ligands of the steroid/thyroid hormone nuclear receptor superfamily, is a strong inducer of liver cell proliferation in rats and mice. However, the molecular basis of its mitogenic activity, which is currently unknown, must be elucidated if its use in hepatic regenerative medicine is to be considered. F-344 rats or C57BL/6 mice were fed a diet containing T3 for 2-7 days. In rats, administration of T3 led to an increased cytoplasmic stabilization and nuclear translocation of β-catenin in pericentral hepatocytes with a concomitant increase in cyclin-D1 expression. T3 administration to wild-type (WT) mice resulted in increased hepatocyte proliferation; however, no mitogenic response in hepatocytes to T3 was evident in the hepatocyte-specific β-catenin knockout mice (KO). In fact, T3 induced β-catenin-TCF4 reporter activity both in vitro and in vivo. Livers from T3-treated mice demonstrated no changes in Ctnnb1 expression, activity of glycogen synthase kinase-3β, known to phosphorylate and eventually promote β-catenin degradation, or E-cadherin-β-catenin association. However, T3 treatment increased β-catenin phosphorylation at Ser675, an event downstream of protein kinase A (PKA). Administration of PKA inhibitor during T3 treatment of mice and rats as well as in cell culture abrogated Ser675-β-catenin and simultaneously decreased cyclin-D1 expression to block hepatocyte proliferation.

CONCLUSION

We have identified T3-induced hepatocyte mitogenic response to be mediated by PKA-dependent β-catenin activation. Thus, T3 may be of therapeutic relevance to stimulate β-catenin signaling to in turn induce regeneration in selected cases of hepatic insufficiency.

Sustained endoplasmic reticulum stress inhibits hepatocyte proliferation via downregulation of c-Met expression

The molecular mechanisms of impaired liver regeneration in several liver diseases remain poorly understood. Endoplasmic reticulum (ER) stress has been observed in a variety of liver diseases. The aims of this study were to explore the impacts of ER stress on hepatocyte growth factor (HGF)-induced proliferation and c-Met expression in human hepatocyte L02 cells. Human hepatocyte L02 cells were incubated with thapsigargin (TG) to induce ER stress. 4-Phenylbutyric acid (PBA) was used to rescue ER stress. Activation of glucose-regulated protein 78, phosphorylation of PKR-like ER kinase and eukaryotic translation initiation factor-2α, and the expression of c-Met were determined by western blotting. The expression of c-Met mRNA was observed by reverse transcription polymerase chain reaction. L02 cell proliferation was determined by the MTS assay. L02 cell proliferation was significantly impaired in TG-treated L02 cells from 24 to 48 h, while PBA partly restored the proliferation of L02 cells. In addition, TG treatment significantly decreased the sensitivity of L02 cells to HGF-induced proliferation. PBA partly resumed the sensitivity of L02 cells to HGF-induced proliferation. The expression of c-Met protein in L02 cells was downregulated from 6 h after TG treatment, and PBA partly restored c-Met expression inhibited by TG. The expression of c-Met mRNA was also significantly downregulated from 24 to 48 h after TG treatment. Our results strongly suggest that sustained ER stress inhibits hepatocyte proliferation via downregulation of both c-Met mRNA and protein expression in human hepatocyte L02 cells.

Hepatoprotective effect of polyphenols rich methanolic extract of Amorphophallus commutatus var. wayanadensis against CCl4 induced hepatic injury in swiss albino mice

The present study is to evaluate the hepatoprotective and antioxidant activity of methanolic extract of Amorphophallus commutatus var. wayanadensis against carbon tetrachloride induced hepatotoxicity in mice models. Hepatic injury was induced by injecting 0.2% CCl4 in olive oil intra peritoneally on 15th day of drug administration. Hepatoprotective activity was evaluated by estimating the levels of serum markers like alanine aminotransferase (ALT) and aspartate aminotransferase (AST), alkaline phosphatase (ALP), bilirubin and histopathological studies. Antioxidant potential of the extract was estimated by measuring the levels of antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferase (GST), glutathione peroxidase (GPx) and total reduced glutathione in the liver samples. Histopathological and biochemical results elicited the methanolic extract of A. commutatus has significant hepatoprotective activity comparable to the standard silymarin. The extract also showed dose dependent increase of antioxidant enzymes in CCl4 induced hepatotoxicity models. The methanolic extract of A. commutatus showed significant hepatoprotective and antioxidant activity which might be attributed due to the polyphenolic compounds present in the extract.

Role and regulation of β-catenin signaling during physiological liver growth

Wnt/β-catenin signaling plays key roles not only during development but also in adult tissue homeostasis. This is also evident in liver biology where many temporal roles of β-catenin have been identified during hepatic development, where, in hepatic progenitors or hepatoblasts, it is a key determinant of proliferation and eventually differentiation to mature hepatocytes, while also playing an important role in bile duct homeostasis. β-Catenin signaling cascade is mostly quiescent in hepatocytes in an adult liver except in the centrizonal region of a hepatic lobule. This small rim of hepatocytes around the central vein show constitutive β-catenin activation that in turn regulates expression of genes whose products play an important role in ammonia and xenobiotic metabolism. Intriguingly, β-catenin can also undergo activation in hepatocytes after acute liver loss secondary to surgical or toxicant insult. Such activation of this progrowth protein is observed as nuclear translocation of β-catenin and formation of its complex with the T-cell factor (TCF) family of transcription factors. Expression of cyclin-D1, a key inducer of transition from the G1 to S phase of cell cycle, is regulated by β-catenin-TCF complex. Thus, β-catenin activation is absolutely critical in the normal regeneration process of the liver as shown by studies in several models across various species. In the current review, the temporal role and regulation of β-catenin in liver development, metabolic zonation in a basal adult liver, and during the liver regeneration process will be discussed. In addition, the probability of therapeutically regulating β-catenin activity as a possible future treatment strategy for liver insufficiency will also be discussed.

Carbamazepine promotes liver regeneration and survival in mice

BACKGROUND & AIMS

Carbamazepine (CBZ), a widely used anticonvulsant and mood stabilizer, activates multiple proliferative and pro-survival pathways. Here, we hypothesize that CBZ may promote hepatocellular proliferation and ameliorate liver regeneration.

METHODS

C57BL6/J mice were orally administered CBZ or vehicle and underwent a 70% partial hepatectomy (PHx), 85% PHx or treatment with carbon tetrachloride (CCl4). Liver regeneration was determined by liver to body weight ratio, hepatocyte proliferation markers, and activation of intracellular signalling pathways.

RESULTS

Two to 5days after the 70% PHx, the liver to body weight ratio was significantly higher in the CBZ-treated mice than in the vehicle-treated mice. CBZ treatment upregulated the number of proliferative hepatocytes following PHx or CCl4 treatment, as assessed by intrahepatic Ki-67 staining, BrdU uptake, and PCNA protein expression. PHx surgery induced the expression of several cyclins and activated Akt/mTOR signalling pathways, all of which were enhanced by CBZ treatment. The administration of the mTOR inhibitor temsirolimus abrogated the hepato-proliferative effect of CBZ. CBZ treatment significantly improved the survival rate of the mice that underwent lethal 85% massive hepatectomy.

CONCLUSIONS

CBZ demonstrated a novel hepato-proliferative effect through the activation of the mTOR signalling pathway in hepatectomised mice. CBZ has the potential to be a therapeutic option for facilitating efficient liver regeneration in patients subjected to liver surgery.

Novel single nucleotide polymorphisms in interleukin 6 affect tacrolimus metabolism in liver transplant patients

BACKGROUND

Tacrolimus is the first-line immunosuppressant after organ transplantation. It is mainly metabolized by cytochrome P450, family 3, subfamily A (CYP3A) enzymes, but there are large individual differences in metabolism. Interleukin 6 (IL6) has been shown to cause a pan-suppression of mRNA levels of ten major CYP enzymes in human hepatocyte cultures. IL6 has been shown to provide hepatoprotection in various models of liver injury. Rs1800796 is a locus in the IL6 gene promoter region which regulates cytokine production. We speculated that IL6 rs1800796 polymorphisms may lead to individual differences in tacrolimus metabolism by affecting CYP3A enzymes levels and liver function after liver transplantation.

METHODOLOGY/PRINCIPAL FINDINGS

Ninety-six liver transplant patients receiving tacrolimus were enrolled in the study. Two single nucleotide polymorphisms (SNP), CYP3A5 rs776746 and IL6 rs1800796, were genotyped in both donors and recipients. The effects of SNPs on tacrolimus concentration/dose (C/D ratio) at four weeks after transplantation were studied, as well as the effects of donor IL6 rs1800796 polymorphisms on liver function. Both donor and recipient CYP3A5 rs776746 allele A showed association with lower C/D ratios, while donor IL6 rs1800796 allele G showed an association with higher C/D ratios. Donor CYP3A5 rs776746 allele A, IL6 rs1800796 allele C, and recipient CYP3A5 rs776746 allele A were associated with fast tacrolimus metabolism. With increasing numbers of these alleles, patients were found to have increasingly lower tacrolimus C/D ratios at time points after transplantation. Donor IL6 rs1800796 allele G carriers showed an association with higher glutamic-pyruvic transaminase (GPT) levels.

CONCLUSIONS

Combined analysis of donor CYP3A5 rs776746, IL6 rs1800796, and recipient CYP3A5 rs776746 polymorphisms may distinguish tacrolimus metabolism better than CYP3A5 rs776746 alone. IL6 may lead to individual differences in tacrolimus metabolism mainly by affecting liver function.

Gliotoxin-induced changes in rat liver regeneration after partial hepatectomy

BACKGROUND

Hepatic non-parenchymal cells (NPCs), encompassing hepatic stellate cells (HSCs), macrophages and endothelial cells, synthesize new hepatocyte growth factor (HGF) during liver regeneration (LR), and also play an important function in matrix production at the end of regeneration.

AIMS

The aim of this study was to determine whether ablating NPCs either during hepatocyte proliferation or during matrix resynthesis will have any effect on LR.

METHODS

Rats were injected with either gliotoxin (which induces NPC apoptosis) or vehicle control at various stages during partial hepatectomy (PH). NPCs and hepatocytes were also treated in vitro with gliotoxin.

RESULTS

Proliferating cells were abundant in control livers 24 h after PH, while in gliotoxin-treated rats, mitosis was absent, apoptotic NPCs were apparent and HGF was decreased. In vitro studies demonstrated a > 50% decrease in cell viability in NPC cultures, while hepatocyte viability and proliferation were unaffected. Chronic elimination of NPCs over a period of 5 days after PH led to increased desmin-positive HSCs and fewer alpha smooth muscle actin-expressing HSCs. Finally, there was continued proliferation of hepatocytes and decreased collagen I and TGF-β when HSCs, the matrix-producing NPCs, were ablated during later stages of LR.

CONCLUSIONS

Ablation of NPCs at early time points after PH interferes with liver regeneration, while their ablation at late stages causes impairment in the termination of LR, demonstrating a time-dependent regulatory role of NPCs in the regenerative process.

Down-regulation of microRNA-26a promotes mouse hepatocyte proliferation during liver regeneration

Background

Inadequate liver regeneration (LR) is still an unsolved problem in major liver resection and small-for-size syndrome post-living donor liver transplantation. A number of microRNAs have been shown to play important roles in cell proliferation. Herein, we investigated the role of miR-26a as a pivotal regulator of hepatocyte proliferation in LR.

Methodology/Principal Findings

Adult male C57BL/6J mice, undergoing 70% partial hepatectomy (PH), were treated with Ad5-anti-miR-26a-LUC or Ad5-miR-26a-LUC or Ad5-LUC vector via portal vein. The animals were subjected to in vivo bioluminescence imaging. Serum and liver samples were collected to test liver function, calculate liver-to-body weight ratio (LBWR), document hepatocyte proliferation (Ki-67 staining), and investigate potential targeted gene expression of miR-26a by quantitative real-time PCR and Western blot. The miR-26a level declined during LR after 70% PH. Down-regulation of miR-26a by anti-miR-26a expression led to enhanced proliferation of hepatocytes, and both LBWR and hepatocyte proliferation (Ki-67⁺ cells %) showed an increased tendency, while liver damage, indicated by aspartate aminotransferase (AST), alanine aminotransferase (ALT) and total bilirubin (T-Bil), was reduced. Furthermore, CCND2 and CCNE2, as possible targeted genes of miR-26a, were up-regulated. In addition, miR-26a over-expression showed converse results.

Conclusions/Significance

MiR-26a plays crucial role in regulating the proliferative phase of LR, probably by repressing expressions of cell cycle proteins CCND2 and CCNE2. The current study reveals a novel miRNA-mediated regulation pattern during the proliferative phase of LR.

Cell therapies for liver diseases

Cell therapies, which include bioartificial liver support and hepatocyte transplantation, have emerged as potential treatments for a variety of liver diseases. Acute liver failure, acute-on-chronic liver failure, and inherited metabolic liver diseases are examples of liver diseases that have been successfully treated with cell therapies at centers around the world. Cell therapies also have the potential to be widely applied to other liver diseases, including noninherited liver diseases and liver cancer, and to improve the success of liver transplantation. Here we briefly summarize current concepts of cell therapy for liver diseases.

Hierarchies of transcriptional regulation during liver regeneration

The remarkable capacity of the liver to regenerate after severe injury or disease has excited interest for centuries. The goal of harnessing this process in treatment of liver disease, and the appreciation of the parallels between regeneration and tumor development in the liver, remain a major driver for research in this area. Studies of liver regeneration as a model system offer a view of intricate and precisely timed regulatory pathways that drive the process toward completion. Successful regeneration of the liver mass demands a hierarchal and well-controlled balance between proliferative and metabolic functions, which is orchestrated by signaling and regulation of transcription factors. Control and regulation of these cascades of transcriptional activities, necessary for induction, renewal, and cessation of liver growth, are the focus of this chapter.

Hepatoprotective effects of lychee (Litchi chinensis Sonn.): a combination of antioxidant and anti-apoptotic activities

AIM OF THE STUDY

Gimjeng and Chakapat lychee (Litchi chinensis Sonn.) were evaluated for hepatoprotective activity on CCl(4)-induced hepatotoxicity in rats.

MATERIALS AND METHODS

Fruit pulp extracts of the lychees were examined for vitamin C, phenolic contents, anti-lipid peroxidation activity and hepatoprotective effect. Male Wistar albino rats were intraperitoneally injected (ip) with CCl(4) (2 ml/kg), then were orally administered (po) with silymarin (100mg/kg), and Gimjeng or Chakapat extracts (100 and 500 mg/kg). After ten days, the rats were sacrificed and their livers were examined histopathologically and immunohistochemically. Their serum glutamate-pyruvate transaminase, glutamate-oxalate transaminase, and alkaline phosphatase activities were analyzed. Apoptotic activity of the livers was assessed quantitatively.

RESULTS

The Gimjeng and Chakapat extracts showed the contents of vitamin C (1.2±0.6 and 4.3±0.1mg/100g) and phenolics like trans-cinnamic acid and pelargonidin-3-O-glucoside (9.80±0.21 and 19.56±0.4 mg GAE/g extract, respectively), and trolox equivalent antioxidant capacity (TEAC) values (11.64 and 9.09 g/mg trolox), respectively. The Gimjeng as compared to the Chakapat demonstrated a better antioxidant activity as revealed by anti-lipid peroxidation activity with the TEAC values. Administration of CCl(4) in rats elevated the serum GPT, GOT, and ALP level whereas silymarin, Gimjeng and Chakapat extracts prevented these increases significantly. Significant decrease of apoptotic cells together with restoration of morphological changes confirmed the hepatoprotective effect in the CCl(4)-induced rats pretreated with the extracts.

CONCLUSION

Antioxidant properties of the Gimjeng and Chakapat lychees as evidenced by the vitamin C and phenolic compounds, anti-lipid peroxidation and anti-apoptosis could explain the hepatoprotective effects in CCl(4)-induced hepatotoxicity.

Carbon monoxide enhances early liver regeneration in mice after hepatectomy

Hepatocyte proliferation early after liver resection is critical in restoring liver mass and preserving function as the liver regenerates. Carbon monoxide (CO) generated by heme oxygenase-1 (HO-1) strongly influences cellular proliferation and both HO-1 and CO are accepted hepatoprotective molecules. Mice lacking functional HO-1 were unable to mount an appropriate regenerative response following partial hepatectomy (PHTx) compared to wildtype controls. We therefore hypothesized that exogenous administration of CO at low, nontoxic concentrations would modulate hepatocyte (HC) proliferation and liver regeneration. Animals treated with a low concentration of CO 1 hour prior to 70% hepatectomy demonstrated enhanced expression of hepatocyte growth factor (HGF) in the liver compared to controls that correlated with a more rapid onset of HC proliferation as measured by phospho-histone3 staining, increased expression of cyclins D1 and E, phosphorylated retinoblastoma, and decreased expression of the mitotic inhibitor p21. PHTx also increased activation of the HGF receptor c-Met, which was detected more then 9 hours earlier in the livers of CO-treated mice. Blockade of c-Met resulted in abrogation of the CO effects on HC proliferation. Corresponding with increased HC proliferation, treatment with CO maintained liver function with normal prothrombin times versus a 2-fold prolongation in controls. In a lethal 85% PHTx, CO-treated mice showed a greater survival rate compared to controls. In vitro, CO increased HGF expression in hepatic stellate cells, but not HC, and when cocultured together led to increased HC proliferation. In summary, we demonstrate that administration of exogenous CO enhances rapid and early HC proliferation and, importantly, preserves function following PHTx. Taken together, CO may offer a viable therapeutic option to facilitate rapid recovery following PHTx.

Fulminant hepatic failure: when to transplant

Fulminant hepatic failure is a life-threatening condition that can lead to rapid deterioration and death if timely treatment is not instituted. Many patients recover with supportive care. Patients with deteriorating signs and laboratory parameters require prompt assessment and listing for liver transplantation. Outcome following transplantation is a function of severity of illness before transplantation, timeliness of liver transplantation and graft quality and function. With appropriate immunosuppression and close follow-up most patients can lead near normal lives following liver transplantation.

The challenges of liver transplantation for hepatocellular carcinoma on cirrhosis

Hepatocellular carcinoma (HCC) is a major cause of cancer mortality worldwide and liver transplantation (LT) has potentials to improve survival for patients with HCC. However, expansion of indications beyond Milan Criteria (MC) and use of bridging/downstaging procedures to convert intermediate-advanced stages of HCC within MC limits are counterbalanced by graft shortage and increasing use of marginal donors, partially limited by the use of donor-division protocols applied to the cadaveric and living-donor settings. Several challenges in technique, indications, pre-LT treatments and prioritization policies of patients on the waiting list have to be precised through prospective investigations that have to include individualization of prognosis, biological variables and pathology surrogates as stratification criteria. Also, liver resection has to be rejuvenated in the general algorithm of HCC treatment in the light of salvage transplantation strategies, while benefit of LT for HCC should be determined through newly designed composite scores that are able to capture both efficiency and equity endpoints. Innovative treatments such as radioembolization for HCC associated with portal vein thrombosis and molecular targeted compounds are likely to influence future strategies. Accepting this challenge has been part of the history of LT and will endure so also for the future.