Nutritional modulation of liver regeneration by carbohydrates, lipids, and amino acids: a review

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside promotes liver regeneration after partial hepatectomy in mice: The potential involvement of PPARα-mediated fatty acid metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

2,3,5,4'-tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG) is the principal bioactive compound contained in Polygonum multiflorum Thunb. (PMT), which is traditionally recorded to possess tonic and anti-aging efficacy.

AIM OF THE STUDY

To identify the TSG-provided promotion on liver regeneration (LR) following partial hepatectomy (PHx) in mice and to explicate its involved mechanism.

MATERIALS AND METHODS

The promotion of TSG on LR was evaluated by hematoxylin and eosin (H&E), 5-bromodeoxyuridinc (BrdU) and Ki-67 staining, and measuring the level of proliferating cell nuclear antigen (PCNA) and Cyclin D1 in mice with PHx at different time points. Gene Expression Omnibus (GEO, GSE15239) database and the label-free quantitative proteomics from liver of mice at 24 h after PHx were integrated to identify potential involved critical proteins, which were verified by Western-blot, Real-time polymerase chain reaction (RT-PCR), molecular docking and luciferase activity assay. Primary hepatocytes isolated from mice were used to investigate the TSG-provided promotion on proliferation in vitro.

RESULTS

TSG (20 mg/kg) promoted LR in mice after PHx. Results from RNA expression data from clinical samples and proteomic analysis from liver tissues indicated that peroxisome proliferator-activated receptor α (PPARα)-mediated fatty acid metabolism pathway were crucially associated with the TSG-provided promotion on LR. TSG enhanced the nuclear translocation of PPARα and the mRNA expression of a series of PPARα-regulated downstream genes. In addition, TSG lowered hepatic triglyceride (TG) and non-esterified fatty acid (NEFA) amounts and increased hepatic adenosine triphosphate (ATP) level in mice after PHx. TSG up-regulated the transcriptional activity of PPARα in vitro. Next results displayed that TSG promoted cell proliferation as well as ATP level in mice primary hepatocytes, which were abolished when PPARα was suppressed. Meanwhile, the cell viability was also elevated in mice primary hepatocytes treated with ATP.

CONCLUSION

Activating PPARα-mediated fatty acid β-oxidation (FAO) pathway led to the production of ATP, which contributed to the TSG-provided promotion on LR after PHx in mice.

Integrated analysis of lncRNA/circRNA-miRNA-mRNA in the proliferative phase of liver regeneration in mice with liver fibrosis

BACKGROUND

Non-coding RNAs play important roles in liver regeneration; however, their functions and mechanisms of action in the regeneration of fibrotic liver have not been elucidated. We aimed to clarify the expression patterns and regulatory functions of lncRNAs, circRNAs, miRNAs, and mRNAs in the proliferative phase of fibrotic liver regeneration.

METHODS

Based on a mouse model of liver fibrosis with 70% hepatectomy, whole-transcriptome profiling was performed using high-throughput sequencing on samples collected at 0, 12, 24, 48, and 72 h after hepatectomy. Hub genes were selected by weighted gene co-expression network analysis and subjected to enrichment analysis. Integrated analysis was performed to reveal the interactions of differentially expressed (DE) lncRNAs, circRNAs, miRNAs, and mRNAs, and to construct lncRNA-mRNA cis- and trans-regulatory networks and lncRNA/circRNA-miRNA-mRNA ceRNA regulatory networks. Real-Time quantitative PCR was used to validate part of the ceRNA network.

RESULTS

A total of 1,329 lncRNAs, 48 circRNAs, 167 miRNAs, and 6,458 mRNAs were differentially expressed, including 812 hub genes. Based on these DE RNAs, we examined several mechanisms of ncRNA regulatory networks, including lncRNA cis and trans interactions, circRNA parental genes, and ceRNA pathways. We constructed a cis-regulatory core network consisting of 64 lncRNA-mRNA pairs (53 DE lncRNAs and 58 hub genes), a trans-regulatory core network consisting of 103 lncRNA-mRNA pairs (18 DE lncRNAs and 85 hub genes), a lncRNA-miRNA-mRNA ceRNA core regulatory network (20 DE lncRNAs, 12 DE miRNAs, and 33 mRNAs), and a circRNA-miRNA-mRNA ceRNA core regulatory network (5 DE circRNAs, 5 DE miRNAs, and 39 mRNAs).

CONCLUSIONS

These results reveal the expression patterns of lncRNAs, circRNAs, miRNAs, and mRNAs in the proliferative phase of fibrotic liver regeneration, as well as core regulatory networks of mRNAs and non-coding RNAs underlying liver regeneration. The findings provide insights into molecular mechanisms that may be useful in developing new therapeutic approaches to ameliorate diseases that are characterized by liver fibrosis, which would be beneficial for the prevention of liver failure and treatment of liver cancer.

The pharmacology and mechanisms of traditional Chinese medicine in promoting liver regeneration: A new therapeutic option

BACKGROUND

The liver is renowned for its remarkable regenerative capacity to restore its structure, size and function after various types of liver injury. However, in patients with end-stage liver disease, the regenerative capacity is inhibited and liver transplantation is the only option. Considering the limitations of liver transplantation, promoting liver regeneration is suggested as a new therapeutic strategy for liver disease. Traditional Chinese medicine (TCM) has a long history of preventing and treating various liver diseases, and some of them have been proven to be effective in promoting liver regeneration, suggesting the therapeutic potential in liver diseases.

PURPOSE

This review aims to summarize the molecular mechanisms of liver regeneration and the pro-regenerative activity and mechanism of TCM formulas, extracts and active ingredients.

METHODS

We conducted a systematic search in PubMed, Web of Science and the Cochrane Library databases using "TCM", "liver regeneration" or their synonyms as keywords, and classified and summarized the retrieved literature. The PRISMA guidelines were followed.

RESULTS

Forty-one research articles met the themes of this review and previous critical studies were also reviewed to provide essential background information. Current evidences indicate that various TCM formulas, extracts and active ingredients have the effect on stimulating liver regeneration through modulating JAK/STAT, Hippo, PI3K/Akt and other signaling pathways. Besides, the mechanisms of liver regeneration, the limitation of existing studies and the application prospect of TCM to promote liver regeneration are also outlined and discussed in this review.

CONCLUSION

This review supports TCM as new potential therapeutic options for promoting liver regeneration and repair of the failing liver, although extensive pharmacokinetic and toxicological studies, as well as elaborate clinical trials, are still needed to demonstrate safety and efficacy.

PARK7 deficiency inhibits fatty acid β-oxidation via PTEN to delay liver regeneration after hepatectomy

Background & aims

Transient regeneration–associated steatosis (TRAS) is a process of temporary hepatic lipid accumulation and is essential for liver regeneration by providing energy generated from fatty acid β‐oxidation, but the regulatory mechanism underlying TRAS remains unknown. Parkinsonism‐associated deglycase (Park7)/Dj1 is an important regulator involved in various liver diseases. In nonalcoholic fatty liver diseased mice, induced by a high‐fat diet, Park7 deficiency improves hepatic steatosis, but its role in liver regeneration remains unknown

Methods

Park7 knockout (Park7^−/−), hepatocyte‐specific Park7 knockout (Park7^△hep) and hepatocyte‐specific Park7‐Pten double knockout mice were subjected to 2/3 partial hepatectomy (PHx)

Results

Increased PARK7 expression was observed in the regenerating liver of mice at 36 and 48 h after PHx. Park7^−/− and Park7^△hep mice showed delayed liver regeneration and enhanced TRAS after PHx. PPARa, a key regulator of β‐oxidation, and carnitine palmitoyltransferase 1a (CPT1a), a rate‐limiting enzyme of β‐oxidation, had substantially decreased expression in the regenerating liver of Park7^△hep mice. Increased phosphatase and tensin homolog (PTEN) expression was observed in the liver of Park7^△hep mice, which might contribute to delayed liver regeneration in these mice because genomic depletion or pharmacological inhibition of PTEN restored the delayed liver regeneration by reversing the downregulation of PPARa and CPT1a and in turn accelerating the utilization of TRAS in the regenerating liver of Park7^△hep mice

Conclusion

Park7/Dj1 is a novel regulator of PTEN‐dependent fatty acid β‐oxidation, and increasing Park7 expression might be a promising strategy to promote liver regeneration.

Grain-Based Dietary Background Impairs Restoration of Blood Flow and Skeletal Muscle During Hindlimb Ischemia in Comparison With Low-Fat and High-Fat Diets

Background: Among vascular pathologies associated with obesity, peripheral artery disease (PAD) occupies the important position. In clinical practice, nutritional interventions are recommended for patients with PAD. In this work, we investigated how the different dietary backgrounds affect the regeneration rate of ischemic hindlimb in mice.

Methods: Male C57BL/6J mice were housed on three types of diet: low-fat (LFD), high-fat (HFD), and grain-based diet (GBD) for 13 weeks. Metabolic parameters including FBG level, ITT, and GTT were evaluated. The blood flow was assessed by laser Doppler scanning on 7, 14, and 21 days after hindlimb ischemia. Necrotic area of m.tibialis, macrophage infiltration, and angiogenesis/arteriogenesis were evaluated by histology. Glucose uptake in recovered skeletal muscle was analyzed using [3H]-2-deoxyglucose, and GLUT1 and GLUT4 expression were assessed by Western blotting.

Results: In our work, we developed three experimental groups with different metabolic parameters: LFD with normal glucose metabolism, GBD with mild hyperglycemia, and HFD with impaired glucose tolerance. GBD-fed mice had a tendency to increase necrosis of m. tibialis and significantly higher macrophage infiltration than LFD and HFD groups. Moreover, GBD-fed mice had a trend to decreased blood flow recovery and significantly impaired arteriogenesis. Recovered skeletal muscle of GBD-fed mice had lower glucose uptake and decreased level of GLUT4 expression.

Conclusion: Thus, we conclude that dietary background and metabolic status determine the rate of post-ischemic regeneration including angiogenesis, skeletal muscle recovery and metabolic activity. The most effective regeneration is supported by LFD, while the lowest rate of regeneration occurs on GBD.

Metabolic hallmarks of liver regeneration

Despite the crucial role of cell metabolism in biological processes, particularly cell division, metabolic aspects of liver regeneration are not well defined. Better understanding of the metabolic activity governing division of liver cells will provide powerful insights into mechanisms of physiological and pathological liver regeneration. Recent studies have provided evidence that metabolic response to liver failure might be a proximal signal to initiate cell proliferation in liver regeneration. In this review, we highlight how lipids, carbohydrates, and proteins dynamically change and orchestrate liver regeneration. In addition, we discuss translational studies in which metabolic intervention has been used to treat chronic liver diseases (CLDs).

Role of Dietary Nutritional Treatment on Hepatic and Intestinal Damage in Transplantation with Steatotic and Non-Steatotic Liver Grafts from Brain Dead Donors

Herein, we investigate whether: (1) the administration of glucose or a lipid emulsion is useful in liver transplantation (LT) using steatotic (induced genetically or nutritionally) or non-steatotic livers from donors after brain death (DBDs); and (2) any such benefits are due to reductions in intestinal damage and consequently to gut microbiota preservation. In recipients from DBDs, we show increased hepatic damage and failure in the maintenance of ATP, glycogen, phospholipid and growth factor (HGF, IGF1 and VEGFA) levels, compared to recipients from non-DBDs. In recipients of non-steatotic grafts from DBDs, the administration of glucose or lipids did not protect against hepatic damage. This was associated with unchanged ATP, glycogen, phospholipid and growth factor levels. However, the administration of lipids in steatotic grafts from DBDs protected against damage and ATP and glycogen drop and increased phospholipid levels. This was associated with increases in growth factors. In all recipients from DBDs, intestinal inflammation and damage (evaluated by LPS, vascular permeability, mucosal damage, TLR4, TNF, IL1, IL-10, MPO, MDA and edema formation) was not shown. In such cases, potential changes in gut microbiota would not be relevant since neither inflammation nor damage was evidenced in the intestine following LT in any of the groups evaluated. In conclusion, lipid treatment is the preferable nutritional support to protect against hepatic damage in steatotic LT from DBDs; the benefits were independent of alterations in the recipient intestine.

The role of skeletal muscle in the pathogenesis of altered concentrations of branched-chain amino acids (valine, leucine, and isoleucine) in liver cirrhosis, diabetes, and other diseases

The article shows that skeletal muscle plays a dominant role in the catabolism of branched-chain amino acids (BCAAs; valine, leucine, and isoleucine) and the pathogenesis of their decreased concentrations in liver cirrhosis, increased concentrations in diabetes, and nonspecific alterations in disorders with signs of systemic inflammatory response syndrome (SIRS), such as burn injury and sepsis. The main role of skeletal muscle in BCAA catabolism is due to its mass and high activity of BCAA aminotransferase, which is absent in the liver. Decreased BCAA levels in liver cirrhosis are due to increased use of the BCAA as a donor of amino group to alpha-ketoglutarate for synthesis of glutamate, which in muscles acts as a substrate for ammonia detoxification to glutamine. Increased BCAA levels in diabetes are due to alterations in glycolysis, citric acid cycle, and fatty acid oxidation. Decreased glycolysis and citric cycle activity impair BCAA transamination to branched-chain keto acids (BCKAs) due to decreased supply of amino group acceptors (alpha-ketoglutarate, pyruvate, and oxaloacetate); increased fatty acid oxidation inhibits flux of BCKA through BCKA dehydrogenase due to increased supply of NADH and acyl-CoAs. Alterations in BCAA levels in disorders with SIRS are inconsistent due to contradictory effects of SIRS on muscles. Specifically, increased proteolysis and insulin resistance tend to increase BCAA levels, whereas activation of BCKA dehydrogenase and glutamine synthesis tend to decrease BCAA levels. The studies are needed to elucidate the role of alterations in BCAA metabolism and the effects of BCAA supplementation on the outcomes of specific diseases.

Altered metabolism by autophagy defection affect liver regeneration

Autophagy is the primary intracellular catabolic process for degrading and recycling long-lived proteins and damaged organelles, which maintains cellular homeostasis. Autophagy has key roles in development and differentiation. By using the mouse with liver specific knockout of autophagy related gene 5 (Atg5), a gene essential for autophagy, we investigated the possible role of autophagy in liver regeneration after 70% partial hepatectomy (PHx). Ablation of autophagy significantly impaired mouse liver regeneration, and this impairment was associated with reduced hepatocellular proliferation rate, down-regulated expression of cyclins and tumor suppressors, and increased hepatocellular apoptosis via the intrinsic apoptotic pathway. Ablation of autophagy does not affect IL-6 and TNF-α response after PHx, but the altered hepatic and systemic metabolic responses were observed in these mice, including reduced ATP and hepatic free fatty acid levels in the liver tissue, increased glucose level in the serum. Autophagy is required to promote hepatocellular proliferation by maintaining normal hepatic and systemic metabolism and suppress hepatocellular apoptosis in liver regeneration.

PDK4-Deficiency Reprograms Intrahepatic Glucose and Lipid Metabolism to Facilitate Liver Regeneration in Mice

Liver regeneration requires intrahepatic and extrahepatic metabolic reprogramming to meet the high hepatic bioenergy demand for liver cell repopulation. This study aims to elucidate how pyruvate dehydrogenase kinase 4 (PDK4), a critical regulator of glucose and lipid metabolism, coordinates metabolic regulation with efficient liver growth. We found that hepatic Pdk4 expression was elevated after two-thirds partial hepatectomy (PHx). In Pdk4 ^-/- PHx mice, the liver/body weight ratio was more rapidly restored, accompanied by more aggressive hepatic DNA replication; however, Pdk4 ^-/- mice developed more severe hypoglycemia. In Pdk4 ^-/- PHx livers, the pro-regenerative insulin signaling was potentiated, as demonstrated by early peaking of the phosphorylation of insulin receptor, more remarkable induction of the insulin receptor substrate proteins, IRS1 and IRS2, and more striking activation of Akt. The hepatic up-regulation of CD36 contributed to the enhanced transient regeneration-associated steatosis in Pdk4 ^-/- PHx mice. Notably, CD36 overexpression in mice promoted the recovery of liver/body weight ratio and elevated intrahepatic adenosine triphosphate after PHx. CD36 expression was transcriptionally suppressed by FOXO1 (forkhead box protein O1), which was stabilized and translocated to the nucleus following AMPK (adenosine monophosphate-activated protein kinase) activation. PHx remarkably induced AMPK activation, which became incompetent to respond in Pdk4 ^-/- livers. Moreover, we defined that PDK4-regulated AMPK activation directly depended on intracellular adenosine monophosphate in vitro and in regenerative livers. Conclusion: PDK4 inhibition reprograms glucose and lipid metabolism to promote liver regeneration by enhancing hepatic insulin/Akt signaling and activating an AMPK/FOXO1/CD36 regulatory axis of lipid. These findings may lead to potential therapeutic strategies to prevent hepatic insufficiency and liver failure.

Amino acid-induced regulation of hepatocyte growth: possible role of Drosha

In an adult healthy liver, hepatocytes are in a quiescent stage unless a physical injury, such as ablation, or a toxic attack occur. Indeed, to maintain their crucial organismal homeostatic role, the damaged or remaining hepatocytes will start proliferating to restore their functional mass. One of the limiting conditions for cell proliferation is amino-acid availability, necessary both for the synthesis of proteins important for cell growth and division, and for the activation of the mTOR pathway, known for its considerable role in the regulation of cell proliferation. The overarching aim of our present work was to investigate the role of amino acids in the regulation of the switch between quiescence and growth of adult hepatocytes. To do so we used non-confluent primary adult rat hepatocytes as a model of partially ablated liver. We discovered that the absence of amino acids induces in primary rat hepatocytes the entrance in a quiescence state together with an increase in Drosha protein, which does not involve the mTOR pathway. Conversely, Drosha knockdown allows the hepatocytes, quiescent after amino-acid deprivation, to proliferate again. Further, hepatocyte proliferation appears to be independent of miRNAs, the canonical downstream partners of Drosha. Taken together, our observations reveal an intriguing non-canonical action of Drosha in the control of growth regulation of adult hepatocytes responding to a nutritional strain, and they may help to design novel preventive and/or therapeutic approaches for hepatic failure.

Coordinated cytochrome P450 expression in mouse liver and intestine under different dietary conditions during liver regeneration after partial hepatectomy

Liver resection is performed to remove tumors in patients with liver cancer, but the procedure's suitability depends on the regenerative ability of the liver. It is important to consider the effects of exogenous factors, such as diets, on liver regeneration for the recovery of function. The evaluation of drug metabolism during liver regeneration is also necessary because liver dysfunction is generally observed after the operation. Here, we investigated the influence of a purified diet (AIN-93G) on liver regeneration and changes in the mRNA expression of several cytochrome P450 (CYP) isoforms in the liver and small intestine using a two-thirds partial hepatectomy (PH) mouse model fed with a standard diet (MF) and a purified diet. Liver regeneration was significantly delayed in the purified diet group relative to that in the standard diet group. The liver Cyp2c55 and Cyp3a11 expression was increased at 3 day after PH especially in the purified diet group. Bile acid may partly cause the differences in liver regeneration and CYP expression between two types of diets. On the other hand, Cyp3a13 expression in the small intestine was transiently increased at day 1 after PH in both diet groups. The findings suggest that compensatory induction of the CYP expression occurred in the small intestine after attenuation of drug metabolism potential in the liver. The present results highlight the importance of the relationship between liver regeneration, drug metabolism, and exogenous factors for the effective treatment, including surgery and medication, in patients after liver resection or transplantation.

Hepatic stress associated with pathologies characterized by disturbed glucose production

The liver is an organ with many facets, including a role in energy production and metabolic balance, detoxification and extraordinary capacity of regeneration. Hepatic glucose production plays a crucial role in the maintenance of normal glucose levels in the organism i.e. between 0.7 to 1.1 g/l. The loss of this function leads to a rare genetic metabolic disease named glycogen storage disease type I (GSDI), characterized by severe hypoglycemia during short fasts. On the contrary, type 2 diabetes is characterized by chronic hyperglycemia, partly due to an overproduction of glucose by the liver. Indeed, diabetes is characterized by increased uptake/production of glucose by hepatocytes, leading to the activation of de novo lipogenesis and the development of a non-alcoholic fatty liver disease. In GSDI, the accumulation of glucose-6 phosphate, which cannot be hydrolyzed into glucose, leads to an increase of glycogen stores and the development of hepatic steatosis. Thus, in these pathologies, hepatocytes are subjected to cellular stress mainly induced by glucotoxicity and lipotoxicity. In this review, we have compared hepatic cellular stress induced in type 2 diabetes and GSDI, especially oxidative stress, autophagy deregulation, and ER-stress. In addition, both GSDI and diabetic patients are prone to the development of hepatocellular adenomas (HCA) that occur on a fatty liver in the absence of cirrhosis. These HCA can further acquire malignant traits and transform into hepatocellular carcinoma. This process of tumorigenesis highlights the importance of an optimal metabolic control in both GSDI and diabetic patients in order to prevent, or at least to restrain, tumorigenic activity during disturbed glucose metabolism pathologies.

Liver-specific Repin1 deficiency impairs transient hepatic steatosis in liver regeneration

Transient hepatic steatosis upon liver resection supposes functional relationships between lipid metabolism and liver regeneration. Repin1 has been suggested as candidate gene for obesity and dyslipidemia by regulating key genes of lipid metabolism and lipid storage. Herein, we characterized the regenerative potential of mice with a hepatic deletion of Repin1 (LRep1−/−) after partial hepatectomy (PH) in order to determine the functional significance of Repin1 in liver regeneration. Lipid dynamics and the regenerative response were analyzed at various time points after PH. Hepatic Repin1 deficiency causes a significantly decreased transient hepatic lipid accumulation. Defects in lipid uptake, as analyzed by decreased expression of the fatty acid transporter Cd36 and Fatp5, may contribute to attenuated and shifted lipid accumulation, accompanied by altered extent and chronological sequence of liver cell proliferation in LRep1−/− mice. In vitro steatosis experiments with primary hepatocytes also revealed attenuated lipid accumulation and occurrence of smaller lipid droplets in Repin1-deficient cells, while no direct effect on proliferation in HepG2 cells was observed. Based on these results, we propose that hepatocellular Repin1 might be of functional significance for early accumulation of lipids in hepatocytes after PH, facilitating efficient progression of liver regeneration.

Foie gras and liver regeneration: a fat dilemma

The liver has a unique ability of regenerating after injuries or partial loss of its mass. The mechanisms responsible for liver regeneration - mostly occurring when the hepatic tissue is damaged or functionally compromised by metabolic stress - have been studied in considerable detail over the last few decades, because this phenomenon has both basic-biology and clinical relevance. More specifically, recent interest has been focusing on the widespread occurrence of abnormal nutritional habits in the Western world that result in an increased prevalence of non-alcoholic fatty liver disease (NAFLD). NAFLD is closely associated with insulin resistance and dyslipidemia, and it represents a major clinical challenge. The disease may progress to steatohepatitis with persistent inflammation and progressive liver damage, both of which will compromise regeneration under conditions of partial hepatectomy in surgical oncology or in liver transplantation procedures. Here, we analyze the impact of ER stress and SIRT1 in lipid metabolism and in fatty liver pathology, and their consequences on liver regeneration. Moreover, we discuss the fine interplay between ER stress and SIRT1 functioning when contextualized to liver regeneration. An improved understanding of the cellular and molecular intricacies contributing to liver regeneration could be of great clinical relevance in areas as diverse as obesity, metabolic syndrome and type 2 diabetes, as well as oncology and transplantation.

Glucagon-like peptide-1 analogues exenatide and liraglutide exert inhibitory effect on the early phase of liver regeneration after partial hepatectomy in rats

Glucagon-like peptide-1 (GLP-1) is an incretin known for proliferative and antiapoptotic effects on various tissues. Exenatide and Liraglutide are GLP-1 analogues used in clinical practice as antidiabetic drugs. Since GLP-1 and its analogues exert significant effect on liver metabolism and since changes in intermediary metabolism play an important role in the process of liver regeneration, we decided to determine the effect of Exenatide and Liraglutide on the early phase of liver regeneration and selected metabolic parameters in a model of 2/3 partial hepatectomy (PHx) in rats. Animals were submitted either to PHx or laparotomy and received 3 doses of either GLP-1 analogues (Exenatide - 42 microg/kg b.w., Liraglutide - 0.75 mg/kg b.w.) or saline intraperitoneally. We analyzed body and liver weight, liver bromodeoxyuridine incorporation, liver content of DNA, triacylglycerols and cholesterol and biochemical serum parameters. Bromodeoxyuridine labeling was significantly lower in hepatectomized rats receiving either type of GLP-1 analogues when compared to hepatectomized controls. This effect was more pronounced in the Liraglutide group compared to Exenatide (p<0.001). In addition, liver DNA content was lower in hepatectomized rats receiving Liraglutide than in hepatectomized control rats (p<0.001). In conclusion, GLP-1 analogues Exenatide and Liraglutide significantly inhibited an early phase of liver regeneration after PHx in rats. This inhibitory effect was more pronounced in rats receiving Liraglutide.

Liver Regeneration Is Impaired in Mice with Acute Exposure to a Very Low Carbohydrate Diet

BACKGROUND

The metabolic response to hepatic insufficiency has been implicated in the regulators of normal liver regeneration. Modulation of nutritional factors has been demonstrated to affect liver regeneration. Diets containing very low carbohydrate and high fat levels cause a unique metabolic state, the effect of which on liver regeneration is unknown.

METHODS

Mice were placed on standard mice chow (ND) or a very low carbohydrate diet (VLCD) after 70% partial hepatectomy (PH). After 48 h, mice on VLCD were placed back to ND. The serum metabolic profiles, hepatic lipid content, and gene expression profile were examined. The dynamics of liver regeneration were detected at timed points. Activation of signaling pathways was examined.

RESULTS

VLCD feeding caused hypoglycemia and elevation of serum β-hydroxybutyrate and free fatty acids in mice after PH. It increased hepatic triglyceride contents, enhanced fatty acid oxidation, and reduced lipid synthesis. Mice on VLCD exhibited diminished hepatocellular mitotic frequency, a reduced BrdU incorporation and liver mass regeneration ratio, and delayed expression of PCNA. Expressions of IL-6 and TNFα in liver and serum were downregulated. Meanwhile, phosphorylation of STAT3, Erk, and AKT was delayed compared with controls.

CONCLUSIONS

VLCD feeding delayed liver regeneration, probably because of the suppression of TNFα-IL-6-STAT3 signaling and delayed activation of Erk and AKT induced by the unique metabolic effects of this diet.

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.

Microbiota and bile acid profiles in retinoic acid-primed mice that exhibit accelerated liver regeneration

Background & Aims

All-trans Retinoic acid (RA) regulates hepatic lipid and bile acid homeostasis. Similar to bile acid (BA), RA accelerates partial hepatectomy (PHx)-induced liver regeneration. Because there is a bidirectional regulatory relationship between gut microbiota and BA synthesis, we examined the effect of RA in altering the gut microbial population and BA composition and established their relationship with hepatic biological processes during the active phases of liver regeneration.

Methods

C57BL/6 mice were treated with RA orally followed by 2/3 PHx. The roles of RA in shifting gut microbiota and BA profiles as well as hepatocyte metabolism and proliferation were studied.

Results

RA-primed mice exhibited accelerated hepatocyte proliferation revealed by higher numbers of Ki67-positive cells compared to untreated mice. Firmicutes and Bacteroidetes phyla dominated the gut microbial community (>85%) in both control and RA-primed mice after PHx. RA reduced the ratio of Firmicutes to Bacteroidetes, which was associated with a lean phenotype. Consistently, RA-primed mice lacked transient lipid accumulation normally found in regenerating livers. In addition, RA altered BA homeostasis and shifted BA profiles by increasing the ratio of hydrophilic to hydrophobic BAs in regenerating livers. Accordingly, metabolic regulators fibroblast growth factor 21, Sirtuin1, and their downstream targets AMPK and ERK1/2 were more robustly activated in RA-primed than unprimed regenerating livers.

Conclusions

Priming mice with RA resulted in a lean microbiota composition and hydrophilic BA profiles, which were associated with facilitated metabolism and enhanced cell proliferation.

Impact of Perioperative Phosphorus and Glucose Levels on Liver Regeneration and Long-term Outcomes after Major Liver Resection

INTRODUCTION

The impact of phosphorus as well as glycemic alterations on liver regeneration has not been directly examined. We sought to determine the impact of phosphorus and glucose on liver regeneration after major hepatectomy.

METHODS

Early and late liver regeneration index was defined as the relative increase of liver volume (RLV) within 2[(RLV2m-RLVp)/RLVp] and 7 months[(RLV7m-RLVp)/RLVp] following surgery. The association of perioperative metabolic factors, liver regeneration, and outcomes was assessed.

RESULTS

On postoperative day 2, 50 (52.6 %) patients had a low phosphorus level (≤2.4 mg/dl), while 45 (47.4 %) had a normal/high phosphorus level (>2.4 mg/dl). Despite comparable clinicopathologic characteristics (all P > 0.05) and RLV/TLV at surgery (P = 0.84), regeneration index within 2 months was lower in the normal/high phosphorus group (P = 0.01) with these patients having increased risk for postoperative liver failure (P = 0.01). The inhibition of liver regeneration persisted at 7 months (P = 0.007) and was associated with a worse survival (P = 0.02). Preoperative hypoglycemia was associated only with a lower early regeneration index (P = 0.02).

CONCLUSIONS

Normal/high phosphorus was associated with inhibition of early and late liver regeneration, as well as with an increased risk of liver failure and worse long-term outcomes. Immediate preoperative hypoglycemia was associated with a lower early volumetric gain. Metabolic factors may represent early indicators of liver failure that could identify patients at increased risk for worse outcomes.

Preexposure to Olive Oil Polyphenols Extract Increases Oxidative Load and Improves Liver Mass Restoration after Hepatectomy in Mice via Stress-Sensitive Genes

Polyphenols can act as oxidants in some conditions, inducing redox-sensitive genes. We investigated the effect of preexposure to the olive oil polyphenols extract (PFE) on time-dependent changes in the hepatic oxidative state in a model of liver regeneration—a process in which oxidative stress associated with the metabolic overload accounts for the early events that contribute to the onset of liver self-repair. Liver regeneration was induced by one-third hepatectomy in mice. Prior to hepatectomy, mice were intraperitoneally given either PFE (50 mg/kg body weight) or saline for seven consecutive days, while respective controls received vehicle alone. Redox state-regulating enzymes and thiol proteins along with the mRNA levels of Nrf2 gene and its targets γ-glutamylcysteine synthetase and heme oxygenase-1 were determined at different time intervals after hepatectomy. The liver mass restoration was calculated to assess hepatic regeneration. The resulting data demonstrate the effectiveness of preexposure to PFE in stimulating liver regeneration in a model of a small tissue loss which may be ascribed to the transient increase in oxidant load during the first hours after hepatectomy and associated induction of stress response gene-profiles under the control of Nrf2.

The effects of glucose and lipids in steatotic and non-steatotic livers in conditions of partial hepatectomy under ischaemia-reperfusion

BACKGROUND

Steatosis is a risk factor in partial hepatectomy (PH) under ischaemia-reperfusion (I/R), which is commonly applied in clinical practice to reduce bleeding. Nutritional support strategies, as well as the role of peripheral adipose tissue as energy source for liver regeneration, remain poorly investigated.

AIMS

To investigate whether the administration of either glucose or a lipid emulsion could protect steatotic and non-steatotic livers against damage and regenerative failure in an experimental model of PH under I/R. The relevance of peripheral adipose tissue in liver regeneration following surgery is studied.

METHODS

Steatotic and non-steatotic rat livers were subjected to surgery and the effects of either glucose or lipid treatment on damage and regeneration, and part of the underlying mechanisms, were investigated.

RESULTS

In non-steatotic livers, treatment with lipids or glucose provided the same protection against damage, regeneration failure and ATP drop. Adipose tissue was not required to regenerate non-steatotic livers. In the presence of hepatic steatosis, lipid treatment, but not glucose, protected against damage and regenerative failure by induction of cell cycle, maintenance of ATP levels and elevation of sphingosine-1-phosphate/ceramide ratio and phospholipid levels. Peripheral adipose tissue was required for regenerating the steatotic liver but it was not used as an energy source.

CONCLUSION

Lipid treatment in non-steatotic livers provides the same protection as that afforded by glucose in conditions of PH under I/R, whereas the treatment with lipids is preferable to reduce the injurious effects of liver surgery in the presence of steatosis.

Glutamine and ornithine alpha-ketoglutarate supplementation on malate dehydrogenases expression in hepatectomized rats

PURPOSE

To evaluate the relative gene expression (RGE) of cytosolic (MDH1) and mitochondrial (MDH2) malate dehydrogenases enzymes in partially hepatectomized rats after glutamine (GLN) or ornithine alpha-ketoglutarate (OKG) suplementation.

METHODS

One-hundred and eight male Wistar rats were randomly distributed into six groups (n=18): CCaL, GLNL and OKGL and fed calcium caseinate (CCa), GLN and OKG, 0.5 g/Kg by gavage, 30 minutes before laparotomy. CCaH, GLNH and OKGH groups were likewise fed 30 minutes before 70% partial hepatectomy. Blood and liver samples were collected three, seven and 14 days after laparotomy/hepatectomy for quantification of MDH1/MDH2 enzymes using the real-time polymerase chain reaction (PCR) methodology. Relative enzymes expression was calculated by the 2-(ΔΔC)T method using the threshold cycle (CT) value for normalization.

RESULTS

MDH1/MDH2 RGE was not different in hepatectomized rats treated with OKG compared to rats treated with CCa. However, MDH1/MDH2 RGE was greater on days 3 (321:1/26.48:1) and 7 (2.12:1/2.48:1) while MDH2 RGE was greater on day 14 (7.79:1) in hepatectomized rats treated with GLN compared to control animals.

CONCLUSION

Glutamine has beneficial effects in liver regeneration in rats by promoting an up-regulation of the MDH1 and MDH2 relative gene expression.

Acute ethanol preexposure promotes liver regeneration after partial hepatectomy in mice by activating ALDH2

It is known that chronic ethanol significantly impairs liver regeneration. However, the effect of acute ethanol exposure on liver regeneration remains largely unknown. To address this question, C57Bl6/J mice were exposed to acute ethanol (6 g/kg intragastrically) for 3 days, and partial hepatectomy (PHx) was performed 24 h after the last dose. Surprisingly, acute ethanol preexposure promoted liver regeneration. This effect of ethanol did not correlate with changes in expression of cell cycle regulatory genes (e.g., cyclin D1, p21, and p27) but did correlate with protection against the effect of PHx on indices of impaired lipid and carbohydrate metabolism. Ethanol preexposure protected against inhibition of the oxidant-sensitive mitochondrial enzyme, aconitase. The activity of aldehyde dehydrogenase 2 (ALDH2) was significantly increased by ethanol preexposure. The effect of ethanol was blocked by inhibiting (Daidzin) and was mimicked by activating (Alda-1) ALDH2. Lipid peroxides are also substrates for ALDH2; indeed, alcohol preexposure blunted the increase in lipid peroxidation (4OH-nonenal adducts) caused by PHx. Taken together, these data suggest that acute preoperative ethanol exposure "preconditions" the liver to respond more rapidly to regenerate after PHx by activating mitochondrial ALDH2, which prevents oxidative stress in this compartment.

Elucidating the metabolic regulation of liver regeneration

The regenerative capability of liver is well known, and the mechanisms that regulate liver regeneration are extensively studied. Such analyses have defined general principles that govern the hepatic regenerative response and implicated specific extracellular and intracellular signals as regulated during and essential for normal liver regeneration. Nevertheless, the most proximal events that stimulate liver regeneration and the distal signals that terminate this process remain incompletely understood. Recent data suggest that the metabolic response to hepatic insufficiency might be the proximal signal that initiates regenerative hepatocellular proliferation. This review provides an overview of the data in support of a metabolic model of liver regeneration and reflects on the clinical implications and areas for further study suggested by these findings.

To divide or not to divide: revisiting liver regeneration

The liver has a remarkable capacity to regenerate. Even with surgical removal (partial hepatectomy) of 70% of liver mass, the remnant tissue grows to recover the original mass and functions. Liver regeneration after partial hepatectomy has been studied extensively since the 19th century, establishing the long-standing model that hepatocytes, which account for most of the liver weight, proliferate to recover the original mass of the liver. The basis of this model is the fact that almost all hepatocytes undergo S phase, as shown by the incorporation of radioactive nucleotides during liver regeneration. However, DNA replication does not necessarily indicate the execution of cell division, and a possible change in hepatocyte size is not considered in the model. In addition, as 15-30% of hepatocytes in adult liver are binuclear, the difference in nuclear number may affect the mode of cell division during regeneration. Thus, the traditional model seems to be oversimplified. Recently, we developed new techniques to investigate the process of liver regeneration, and revealed interesting features of hepatocytes. In this review, we first provide a historical overview of how the widely accepted model of liver regeneration was established and then discuss some overlooked observations together with our recent findings. Finally, we describe the revised model and perspectives on liver regeneration research.

Parenteral solution of nutritional hepatotrophic factors improves regeneration in thioacetamide-induced cirrhotic livers after partial hepatectomy

Liver resection is a suitable option for the treatment of certain hepatic conditions, particularly hepatocarcinomas, in patients with cirrhosis. However, this disease impairs liver regeneration, which increases the risk of liver failure and postoperative death. Supportive treatments for regeneration of the remaining liver may be useful for the recovery of these patients. We demonstrated that nutritional hepatotrophic factors (NHF) is an effective regenerative stimulus for cirrhotic livers in rats subjected to partial hepatectomy (PH). The rats with thioacetamide-induced cirrhosis were subjected to PH, and they were divided into 2 groups. One group received intraperitoneal administration of NHF, and the other group received saline solution. After 12 days, biometric data, collagen content, hepatocyte regeneration (proliferation cell nuclear antigen immunochemistry), and profibrotic gene expression (Collagen-α1, matrix metalloproteinase 2, tissue inhibitor of metalloproteinase 1, and transforming growth factor beta 1) were assessed. The results indicated that the rats treated with NHF after PH had an increased liver size, a reduced amount of collagen, and a higher hepatocyte proliferation index compared with the rats that underwent PH alone. In addition, collagen-α1 gene expression was decreased in the NHF-treated rats. Thus, postoperative improvement in the liver morphology following NHF treatment may cause a significant decrease in the risk of liver failure and mortality after hepatic resection.

Branched-chain amino acid-enriched nutrients improve nutritional and metabolic abnormalities in the early post-transplant period after living donor liver transplantation

BACKGROUND/PURPOSE

Malnutrition and metabolic disorder of patients undergoing living donor liver transplantation (LDLT) can affect post-transplant prognosis. The aim of this study was to establish whether perioperative usage of branched-chain amino-acid (BCAA)-enriched nutrients improve metabolic abnormalities of patients undergoing LDLT.

METHODS

We designed a randomized pilot study (UMIN registration number; 000004323). Twenty-five consecutive adult elective LDLT recipients were enroled and divided into two groups: the BCAA group (BCAA-enriched nutrients, n = 12) and the control group (standard diet, n = 13). Metabolic and nutritional parameters, including BCAA-to-tyrosine ratio (BTR), retinol binding protein (RBP), and prealbumin were regularly measured from 1 week before to 4 weeks after LDLT. Non-protein respiratory quotient (npRQ) was measured before and 4 weeks after LDLT.

RESULTS

BTR and RBP improved considerably in the BCAA group compared with the controls. npRQ significantly increased from 1 week before LDLT to 4 weeks after LDLT in the BCAA group (0.77 ± 0.05 to 0.84 ± 0.06, P = 0.002), but not in the control group (0.78 ± 0.04 to 0.81 ± 0.05).

CONCLUSIONS

Supplementation with BCAA-enriched nutrients might improve persistent nutritional and metabolic disorders associated with end-stage liver disease in the early post-transplant period, and consequently shorten the post-transplant catabolic phase after LDLT. A larger multicenter trial is needed to confirm these findings.

Signals and cells involved in regulating liver regeneration

Liver regeneration is a complex phenomenon aimed at maintaining a constant liver mass in the event of injury resulting in loss of hepatic parenchyma. Partial hepatectomy is followed by a series of events involving multiple signaling pathways controlled by mitogenic growth factors (HGF, EGF) and their receptors (MET and EGFR). In addition multiple cytokines and other signaling molecules contribute to the orchestration of a signal which drives hepatocytes into DNA synthesis. The other cell types of the liver receive and transmit to hepatocytes complex signals so that, in the end of the regenerative process, complete hepatic tissue is assembled and regeneration is terminated at the proper time and at the right liver size. If hepatocytes fail to participate in this process, the biliary compartment is mobilized to generate populations of progenitor cells which transdifferentiate into hepatocytes and restore liver size.

Parenteral nutrition in liver resection

Albeit a very large number of experiments have assessed the impact of various substrates on liver regeneration after partial hepatectomy, a limited number of clinical studies have evaluated artificial nutrition in liver resection patients. This is a peculiar topic because many patients do not need artificial nutrition, while several patients need it because of malnutrition and/or prolonged inability to feeding caused by complications. The optimal nutritional regimen to support liver regeneration, within other postoperative problems or complications, is not yet exactly defined. This short review addresses relevant aspects and potential developments in the issue of postoperative parenteral nutrition after liver resection.

Functional Relationships between Lipid Metabolism and Liver Regeneration

The regenerative capacity of the liver is well known, and the mechanisms that regulate this process have been extensively studied using experimental model systems including surgical resection and hepatotoxin exposure. The response to primary mitogens has also been used to investigate the regulation of hepatocellular proliferation. Such analyses have identified many specific cytokines and growth factors, intracellular signaling events, and transcription factors that are regulated during and necessary for normal liver regeneration. Nevertheless, the nature and identities of the most proximal events that initiate hepatic regeneration as well as those distal signals that terminate this process remain unknown. Here, we review the data implicating acute alterations in lipid metabolism as important determinants of experimental liver regeneration and propose a novel metabolic model of regeneration based on these data. We also discuss the association between chronic hepatic steatosis and impaired regeneration in animal models and humans and consider important areas for future research.

S6 kinase 1 is required for rapamycin-sensitive liver proliferation after mouse hepatectomy

Rapamycin is an antibiotic inhibiting eukaryotic cell growth and proliferation by acting on target of rapamycin (TOR) kinase. Mammalian TOR (mTOR) is thought to work through 2 independent complexes to regulate cell size and cell replication, and these 2 complexes show differential sensitivity to rapamycin. Here we combine functional genetics and pharmacological treatments to analyze rapamycin-sensitive mTOR substrates that are involved in cell proliferation and tissue regeneration after partial hepatectomy in mice. After hepatectomy, hepatocytes proliferated rapidly, correlating with increased S6 kinase phosphorylation, while treatment with rapamycin derivatives impaired regeneration and blocked S6 kinase activation. In addition, genetic deletion of S6 kinase 1 (S6K1) caused a delay in S phase entry in hepatocytes after hepatectomy. The proliferative defect of S6K1-deficient hepatocytes was cell autonomous, as it was also observed in primary cultures and hepatic overexpression of S6K1-rescued proliferation. We found that S6K1 controlled steady-state levels of cyclin D1 (Ccnd1) mRNA in liver, and cyclin D1 expression was required to promote hepatocyte cell cycle. Notably, in vivo overexpression of cyclin D1 was sufficient to restore the proliferative capacity of S6K-null livers. The identification of an S6K1-dependent mechanism participating in cell proliferation in vivo may be relevant for cancer cells displaying high mTOR complex 1 activity and cyclin D1 accumulation.

Modelo de suplementação nutricional com fatores hepatotróficos aumenta proliferação celular em fígado de ratos sadios

Foram avaliados dois protocolos de administração, em ratos sadios, de uma solução de fatores hepatotróficos (FH), composta por aminoácidos, vitaminas, sais minerais, glicose, insulina, glucagon e triiodotironina (T3). A solução foi administrada durante 10 dias, 40mg/kg/dia, i.p., em duas, grupo 2xFH (n=15), ou três doses, grupo 3xFH (n=15), diárias. Foram observados os efeitos na proliferação celular dos hepatócitos, na angiogênese e na matriz extracelular hepática, assim como as possíveis reações adversas. Os animais dos grupos 2xFH e 3xFH apresentaram aumento da massa hepática de 30,1% e 22,5%, respectivamente, em relação ao grupo-controle (CT; n=15). O índice de proliferação hepatocelular foi maior nos grupos 2xFH (1,4%) e 3xFH (1,2%) em relação ao grupo CT (0,53%), e a densitometria relativa do fator de crescimento do endotélio vascular pelo imunoblot não revelou diferença estatística entre os três grupos. Nos grupos 2xFH e 3xFH, houve redução do colágeno intersticial em relação ao grupo CT. A solução de FH estimulou o crescimento hepático e reduziu o volume de colágeno perissinusoidal. A administração em três doses diárias resultou em mortalidade de 26,7%, possivelmente pelo excessivo estresse da manipulação e pela menor adaptação fisiológica dos ratos, o que não ocorreu nos grupos 2xFH e CT. Para esse tipo de abordagem em ratos, o procedimento experimental mais apropriado, seguro, com melhor chance de adaptação dos animais e com resultados significativos é a aplicação dos FH em duas doses diárias.

The effect of high-fat diet on the sphingolipid pathway of signal transduction in regenerating rat liver

Liver regeneration after partial hepatectomy (PH) is achieved by intense cells proliferation. Sphingosine-1-phosphate stimulates proliferation but ceramide and sphingosine induce apoptosis. The aim of the study was to investigate the influence of high-fat diet (HFD) on the sphingolipid metabolism during the first 24h of liver regeneration in rats. Rats were fed HFD or standard diet for 7 days prior to the PH. The content of sphingolipids and the activity of sphingomyelinases (n and aSMase), ceramidases (n and aCDase) and sphingosine kinase (SPHK) were measured. It has been found that HFD increased the activity of aSMase and nCDase at 4th hour after PH. The content of ceramide and sphingosine decreased in HFD group at each time point. This was accompanied by elevated content of sphingosine-1-phosphate and sphinganine-1-phosphate. Decrease in SPHK activity in cytosol after partial hepatectomy was inversely correlated (r=-0.7538) with increase in S1P, which suggest translocation of SPHK to plasma membrane. Shingosine-1-phosphate to ceramide ratio was higher in rats fed HFD. It is concluded that HFD stimulates the pro-mitotic action of the sphingolipid signaling in regenerating rat liver.

Hepatotrophic factors reduce hepatic fibrosis in rats

CONTEXT: Hepatic fibrosis occurs in response to several aggressive agents and is a predisposing factor in cirrhosis. Hepatotrophic factors were shown to stimulate liver growth and to restore the histological architecture of the liver. They also cause an improvement in liver function and accelerate the reversion of fibrosis before it progresses to cirrhosis. OBJECTIVE: To test the effects of hepatic fibrosis solution composed by amino acids, vitamins, glucose, insulin, glucagon and triiodothyronine on hepatic fibrosis in rats. METHODS: Fibrosis was induced in rats by gastric administration of dimethylnitrosamine (10 mg/kg) for 5 weeks. After liver biopsy, the rats received either hepatotrophic factors solution (40 mg/kg/day) or saline solution for 10 days by intraperitoneal injection. Blood samples and liver fragments were collected for hepatic function analysis, standard histopathology evaluation, and morphometric collagen quantification. RESULTS: Rats in the hepatotrophic factors group showed a decrease of the histopathological components of fibrosis and an increase of their hepatic mass (12.2%). There was no development of neoplasic lesions in both groups. Compared with the saline group, the hepatotrophic factors group also had a decrease of blood levels of hepatic-lesion markers (AST, ALT) and a decrease of collagen content in the portal spaces (31.6%) and perisinusoidal spaces (42.3%), as well as around the hepatic terminal vein (57.7%). Thus, hepatotrophic factors administration in the portal blood promoted a regenerative hepatic response, with an overall reduction of the volumetric density of collagen, improved hepatic function, and a general improvement in the histopathological aspects of fibrosis. CONCLUSION: Taken together, these results suggest the potential therapeutic use of this hepatotrophic factors solution to treat chronic liver diseases.

Three targets of branched-chain amino acid supplementation in the treatment of liver disease

The article explains the pathogenesis of disturbances in branched-chain amino acid (BCAA; valine, leucine, and isoleucine) and protein metabolism in various forms of hepatic injury and it is suggested that the main cause of decrease in plasma BCAA concentration in liver cirrhosis is hyperammonemia. Three possible targets of BCAA supplementation in hepatic disease are suggested: (1) hepatic encephalopathy, (2) liver regeneration, and (3) hepatic cachexia. The BCAA may ameliorate hepatic encephalopathy by promoting ammonia detoxification, correction of the plasma amino acid imbalance, and by reduced brain influx of aromatic amino acids. The influence of BCAA supplementation on hepatic encephalopathy could be more effective in chronic hepatic injury with hyperammonemia and low concentrations of BCAA in blood than in acute hepatic illness, where hyperaminoacidemia frequently develops. The favorable effect of BCAA on liver regeneration and nutritional state of the body is related to their stimulatory effect on protein synthesis, secretion of hepatocyte growth factor, glutamine production and inhibitory effect on proteolysis. Presumably the beneficial effect of BCAA on hepatic cachexia is significant in compensated liver disease with decreased plasma BCAA concentrations, whereas it is less pronounced in hepatic diseases with inflammatory complications and enhanced protein turnover. It is concluded that specific benefits associated with BCAA supplementation depend significantly on the type of liver disease and on the presence of inflammatory reaction. An important task for clinical research is to identify groups of patients for whom BCAA treatment can significantly improve the health-related quality of life and the prognosis of hepatic disease.

p21 is required for dextrose-mediated inhibition of mouse liver regeneration

The inhibitory effect of dextrose supplementation on liver regeneration was first described more than 4 decades ago. Nevertheless, the molecular mechanisms responsible for this observation have not been elucidated. We investigated these mechanisms using the partial hepatectomy model in mice given standard or 10% dextrose (D10)-supplemented drinking water. The results showed that D10-treated mice exhibited significantly reduced hepatic regeneration compared with controls, as assessed by hepatocellular bromodeoxyuridine (BrdU) incorporation and mitotic frequency. D10 supplementation did not suppress activation of hepatocyte growth factor (HGF), induction of transforming growth factor alpha (TGF-alpha) expression, or tumor necrosis factor alpha-interleukin-6 cytokine signaling, p42/44 extracellular signal-regulated kinase (ERK) activation, immediate early gene expression, or expression of CCAAT/enhancer binding protein beta (C/EBPbeta), but did augment expression of the mito-inhibitory factors C/EBPalpha, p21(Waf1/Cip1), and p27(Kip1). In addition, forkhead box M1 (FoxM1) expression, which is required for normal liver regeneration, was suppressed by D10 treatment. Finally, D10 did not suppress either FoxM1 expression or hepatocellular proliferation in p21 null mice subjected to partial hepatectomy, establishing the functional significance of these events in mediating the effects of D10 on liver regeneration.

CONCLUSION

These data show that the inhibitory effect of dextrose supplementation on liver regeneration is associated with increased expression of C/EBPalpha, p21, and p27, and decreased expression of FoxM1, and that D10-mediated inhibition of liver regeneration is abrogated in p21-deficient animals. Our observations are consistent with a model in which hepatic sufficiency is defined by homeostasis between the energy-generating capacity of the liver and the energy demands of the body mass, with liver regeneration initiated when the functional liver mass is no longer sufficient to meet such demand.

Differential expression of the genes involved in amino acids and nitrogen metabolisms during liver regeneration of mice

AIM

Liver regeneration is a highly coordinated response to hepatic injury or resection that is controlled by the body's overall requirement for liver function. The level of circulating amino acids in blood increases after acute liver injury and administration of amino acid mixtures induces hepatic DNA replication. These findings suggest a close connection between amino acid metabolism and hepatic proliferation. However, the underlying molecular mechanisms have not been completely elucidated. Here, we applied a cDNA micro-array technique to analyze expression profiles of the genes associated with nitrogen and amino acid metabolism during liver regeneration in mice following treatment with CCl(4).

METHODS

Seventy-nine genes were identified for their significantly altered expression patterns at different stages of liver damage and regeneration.

RESULTS

We observed that the numbers of down-regulated genes were remarkably higher than that of up-regulated genes at 1.5 days following carbon tetrachloride administration when hepatic DNA replication was most active, indicating the existence of a counter balance between cell proliferation and liver metabolism functions.

CONCLUSIONS

Our results suggest that suppression of amino acids metabolism after acute liver injury results in the accumulation of amino acids in plasma that serves as a driving force for liver regeneration.

Caloric intake and liver dysfunction in critically ill patients

PURPOSE OF REVIEW

Despite increasing evidence that critically ill patients have lower energy requirements than expected, most guidelines continue to recommend elevated caloric requirements in these patients, particularly in septic patients. This practice leads to liver dysfunction when artificial nutrition is employed and worsens the prognosis of these patients. This review is focused on recent developments in the pathogenesis of artificial nutrition associated liver dysfunction in critically ill patients.

RECENT FINDINGS

The liver plays a pivotal role in managing nutritional substrates, and it is involved in the inflammatory response to injury and sepsis. The landmark phenomenon is insulin resistance and changes in the metabolic fates of glucose and fat. Glucose and lipids can act as toxics synergistically with inflammation to induce liver dysfunction. There are experimental evidences that insulin resistance in critically ill patients can share the same biochemical mechanisms and metabolic fates involved in insulin resistance of type 2 diabetes mellitus and metabolic syndrome. Furthermore, steatosis is also a common feature in both clinical pictures

SUMMARY

The pathogenesis of artificial nutrition associated with liver dysfunction is related to overfeeding and sepsis with a pathophysiology, similar to metabolic syndrome and type 2 diabetes. Changing nutritional strategies and adding new drugs will prevent, in part, liver dysfunction in these patients.

O estresse oxidativo na regeneração hepática em ratos

OBJETIVO: Investigar o estresse oxidativo durante a regeneração hepática em ratos submetidos à hepatectomia (HP) e, ao mesmo tempo, avaliar a função hepática enquanto em regeneração. MÉTODO: 36 ratos Wistar machos jovens foram aleatoriamente distribuídos em dois grupos de 18 animais: submetidos somente à laparotomia (controle, Grupo G1) e parcialmente hepatectomizados (experimento, Grupo G2). Nos tempos 36h (T1), 168h (T2) e 336h (T3) pós-HP, GSH foi medida no plasma e no tecido hepático, enquanto Gli e BT foram aquilatados no sangue. A massa do fígado residual foi utilizada para estimar a evolução da regeneração hepática. RESULTADOS: Houve diferença estatisticamente significativa no crescimento dos lobos residuais nos grupos controle e experimento. GSH hepático e plasmático se mostraram significantemente maior nos animais parcialmente hepatectomizados.,em todos os tempos. Hiperglicemia estatisticamente significativa ocorreu nos ratos pós-HP nos tempos T2 e T3. A BT não apresentou qualquer alteração entre os grupos. CONCLUSÃO: Durante a regeneração hepática pós-HP em ratos há um aumento do estresse oxidativo e o fígado residual permanece apto na manutenção da homeostase orgânica.

Liver regeneration is suppressed in small-for-size liver grafts after transplantation: involvement of c-Jun N-terminal kinase, cyclin D1, and defective energy supply

BACKGROUND

Small-for-size liver grafts have decreased survival compared to full-size grafts. This study investigated mechanisms of suppression of liver regeneration in small-for-size grafts.

METHODS

Rat liver explants were reduced in size to 50% and implanted into recipients of different body weights, resulting in graft weight/standard liver weights of approximately 50% (half-size) and approximately 25% (quarter-size).

RESULTS

Hepatic cellular 5-bromo-2'-deoxyuridine (BrdU) incorporation increased from 0.2% after sham operation to 2%, 18%, and 1.2% in full-size, half-size, and quarter-size grafts, respectively. Graft weight did not increase in full- and quarter-size grafts but increased 40% in half-size grafts. By contrast, apoptosis remained low (< or =0.7%) and stem cells did not increase in all conditions. Phospho-c-Jun increased 27-fold in half-size grafts but only sevenfold in quarter-size grafts. Activating protein-1 activation increased 14-fold in half-size grafts but only fivefold in quarter-size grafts. Cyclin D1 (CyD1), which was barely detectable in full- and quarter-size grafts, increased 8.3-fold in half-size grafts. Adenosine 5'-triphosphate (ATP) per gram tissue decreased 70% in quarter-size grafts. Treatment of quarter-size grafts with radical scavenging C. sinenesis polyphenols (20 microg/ml) increased BrdU labeling and weight gain to 35% and 56%, respectively, reversed inhibition of CyD1 expression, c-Jun phosphorylation, and AP-1 activation in quarter-size grafts compared to half-size grafts, and restored ATP levels to 75%.

CONCLUSIONS

Liver regeneration is stimulated in half-size grafts but suppressed in quarter-size grafts. Defective liver regeneration in small grafts is associated with an inhibition of the c-Jun N-terminal kinase/c-Jun and CyD1 pathways and compromised energy production.

Proteomic analysis of the transition from quiescent to proliferating stages in rat liver hepatectomy model

The 70% (or 2/3) partial hepatectomy (PHx) rat liver model provides an effective medium for study of the transition and regulation of hepatocytes from quiescent to proliferating phase. Although the gene expression pattern has come under intense scrutiny, a differential proteomic study could help to reveal the mechanism of how the process is initiated and regulated. The proteomic changes were analyzed in two groups, 7 h after 70% PHx test group and sham-operation control group, by two-dimensional gel electrophoresis with 907 +/- 33 and 910 +/- 64 spots on gels, respectively. Twelve down-regulated spots and twenty-six up-regulated spots were recognized using ImageMaster software and were identified by matrix-assisted laser desorption/ionization-mass spectrometry-quadrupole time of flight mass spectrometry and/or tandem mass spectrometry reconfirmation. Some of the differential proteins were associated with stress defense, lipid metabolism, and macromolecular biosynthesis while the others were shown to be involved in regulating transcript factors associated with liver regeneration. A "proteomic model" for liver regeneration was suggested based on our data and related scientific literature to interpret the differential proteome pattern that reflected the transition of cells from quiescent to proliferating state, including but not limited to the rat liver after 70% PHx.

Prometheus' challenge: molecular, cellular and systemic aspects of liver regeneration

The fascinating aspect of the liver is the capacity to regenerate after injury or resection. A variety of genes, cytokines, growth factors, and cells are involved in liver regeneration. The exact mechanism of regeneration and the interaction between cells and cytokines are not fully understood. There seems to exist a sequence of stages that result in liver regeneration, while at the same time inhibitors control the size of the regenerated liver. It has been proven that hepatocyte growth factor, transforming growth factor, epidermal growth factor, tumor necrosis factor-alpha, interleukins -1 and -6 are the main growth and promoter factors secreted after hepatic injury, partial hepatectomy and after a sequence of different and complex reactions to activate transcription factors, mainly nuclear factor kappaB and signal transduction and activator of transcription-3, affects specific genes to promote liver regeneration. Unraveling the complex processes of liver regeneration may provide novel strategies in the management of patients with end-stage liver disease. In particular, inducing liver regeneration should reduce morbidity for the donor and increase faster recovery for the liver transplantation recipient.

Amino acids regulate hepatocyte proliferation through modulation of cyclin D1 expression

The mechanisms by which amino acids regulate the cell cycle are not well characterized. In this study, we examined the control of hepatocyte proliferation by amino acids and protein intake. In short-term culture, hepatocytes demonstrated normal entry into S phase and cell cycle protein expression in the absence of essential amino acids. However, deprivation of a set of nonessential amino acids (NEAA) potently inhibited cell cycle progression and selectively down-regulated the expression of proliferation-control proteins. Notably, NEAA withdrawal after the mitogen restriction point still inhibited entry into S phase, suggesting that these amino acids regulate a distinct checkpoint. Cyclin D1, an important mediator of hepatocyte proliferation, was markedly inhibited at the transcriptional level by NEAA deprivation, and transfection with cyclin D1 (but not cyclin E) overcame the cell cycle arrest. As previously shown, protein-deprived mice demonstrated impaired hepatocyte proliferation in vivo after 70% partial hepatectomy. The expression of cyclin D1 and downstream cell cycle proteins after partial hepatectomy was inhibited in these mice. Transfection with cyclin D1 in vivo triggered hepatocyte DNA synthesis and the expression of S phase proteins in the absence of dietary protein. Cyclin D1 also induced global protein synthesis in NEAA-deprived hepatocytes and promoted liver growth in vivo in the setting of protein deprivation. These results indicate that cyclin D1 is a key target of amino acid signaling in hepatocytes.

Effect of nutritional state of brain-dead organ donor on transplantation

OBJECTIVE

We describe the effect of the metabolic and nutritional modifications caused by severe illness or injury in brain-dead organ donors on transplant organ function. Malnutrition is frequently found in brain-dead organ donors and nutrients may interfere with different organ functions.

METHODS

Literature was obtained from MEDLINE using the key words organ donation, brain death, transplantation, nutrition, fish oil, amino acids.

RESULTS

In the liver, infusion of large quantities of dextrose can restore glycogen reserves but may induce hyperglycemia and a hyperosmolar hepatic state. Feeding improves protein synthesis in hepatocytes, and fat (fish oil) administration in particular increases the hepatic energy and adenosine triphosphate content. Amino acids have a significant effect on regenerating hepatic tissue when given with fat and glucose. In the heart, free fatty acids administered during reperfusion improve cardiac functional recovery, and administration of propofol, a general anesthetic agent enriched with fatty acids, have protective effects on ischemia-and-reperfusion injury. Glutamine also can induce graft protection during ischemia-and-reperfusion injury. Renal function is improved by fish oil supplementation. In addition, effective renal plasma flow, glomerular filtration rate, and renal blood flow are increased, apparently by a reduction in thromboxane B2 production. Glycine or alanine can protect renal tubules from stress injury.

CONCLUSION

Nutrition plays an important role in the modulation of organ function after transplantation.

Expression of suppressors of cytokine signaling during liver regeneration

The cytokines TNF and IL-6 play a critical role early in liver regeneration following partial hepatectomy (PH). Since IL-6 activates signal transducers and activators of transcription (STATs), we examined whether the suppressors of cytokine signaling (SOCS) may be involved in terminating IL-6 signaling. We show here that SOCS-3 mRNA is induced 40-fold 2 hours after surgery. SOCS-2 and CIS mRNA are only weakly induced, and SOCS-1 is not detectable. SOCS-3 induction after PH is transient and correlates with a decrease in STAT-3 DNA binding and a loss of tyrosine 705 phosphorylation. This response is markedly reduced in IL-6 knockout (KO) mice. TNF injection induces SOCS-3 mRNA in wild-type mice (albeit weakly compared with the increase observed after PH) but not in TNF receptor 1 or IL-6 KO mice. In contrast, IL-6 injection induces SOCS-3 in these animals, demonstrating a requirement for IL-6 in SOCS-3 induction. IL-6 injection into wild-type mice also induces SOCS-1, -2, and CIS mRNA, in addition to SOCS-3. Together, these results suggest that SOCS-3 may be a key component in downregulating STAT-3 signaling after PH and that SOCS-3 mRNA levels in the regenerating liver are regulated by IL-6.