Purification and physical-chemical characterization of hepatic stimulator substance

Augmenter of liver regeneration: Essential for growth and beyond

Liver regeneration is a well-orchestrated process that is triggered by tissue loss due to trauma or surgical resection and by hepatocellular death induced by toxins or viral infections. Due to the central role of the liver for body homeostasis, intensive research was conducted to identify factors that might contribute to hepatic growth and regeneration. Using a model of partial hepatectomy several factors including cytokines and growth factors that regulate this process were discovered. Among them, a protein was identified to specifically support liver regeneration and therefore was named ALR (Augmenter of Liver Regeneration). ALR protein is encoded by GFER (growth factor erv1-like) gene and can be regulated by various stimuli. ALR is expressed in different tissues in three isoforms which are associated with multiple functions: The long forms of ALR were found in the inner-mitochondrial space (IMS) and the cytosol. Mitochondrial ALR (23 kDa) was shown to cooperate with Mia40 to insure adequate protein folding during import into IMS. On the other hand short form ALR, located mainly in the cytosol, was attributed with anti-apoptotic and anti-oxidative properties as well as its inflammation and metabolism modulating effects. Although a considerable amount of work has been devoted to summarizing the knowledge on ALR, an investigation of ALR expression in different organs (location, subcellular localization) as well as delineation between the isoforms and function of ALR is still missing. This review provides a comprehensive evaluation of ALR structure and expression of different ALR isoforms. Furthermore, we highlight the functional role of endogenously expressed and exogenously applied ALR, as well as an analysis of the clinical importance of ALR, with emphasis on liver disease and in vivo models, as well as the consequences of mutations in the GFER gene.

Lack of hepatic stimulator substance expression promotes hepatocellular carcinoma metastasis partly through ERK-activated epithelial-mesenchymal transition

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies due to its high frequency of metastasis via the epithelial-mesenchymal transition (EMT) pathway. Hepatic stimulator substance (HSS) can protect hepatocytes from injury and promote liver growth. Recent studies indicated that HSS expression is increased in HCC tissues; however, whether HSS expression is potentially associated with HCC metastasis, particularly through the EMT pathway, remains largely unknown. In this study, the relationship between HSS expression and HCC metastasis was investigated in clinical samples of HCC. Meanwhile, the regulation of HCC metastasis and EMT progression by HSS were also analyzed in both in vitro and in vivo models. The results showed that the expression of 23 kDa HSS was significantly decreased among HCC tissues with angioinvasion. A decrease in HSS predicted poor prognosis with a lower survival rate. Furthermore, the growth of xenograft tumors after inoculating MHCC97H-HSS-shRNA (HCC) cells into nude mice was notably accelerated compared to those inoculated with HSS-expressing cells. Further analysis revealed that knockdown of HSS expression in both MHCC97H and HepG2 cells could enhance the migration of these HCC cells. Concurrently, interference of HSS expression by shRNA promoted conversion of morphologically epithelial-like HCC cells into mesenchymal-like cells, together with downregulations of epithelial markers (such as E-cadherin and zonula occludens-1) and upregulation of mesenchymal-like makers (such as α-SMA, β-catenin, and fibronectin). Furthermore, it was demonstrated that, as well as promoting EMT, HSS-shRNA induced the phosphorylation of extracellular signal-regulated kinase (ERK) and elevated the expression of the EMT-related transcription factor Snail. Specific inhibition of HSS-shRNA-induced ERK phosphorylation by PD98059 attenuated HCC cell migration in a dose-dependent manner. In conclusion, we demonstrated that downregulation of HSS expression contributes to HCC metastasis partially through the ERK-activated EMT pathway.

Augmenter of liver regeneration potentiates doxorubicin anticancer efficacy by reducing the expression of ABCB1 and ABCG2 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is highly chemoresistant and therefore challenges both physicians and patients. Augmenter of liver regeneration (ALR), previously also known as 'hepatic stimulator substance', is reported to inhibit the epithelial-mesenchymal transition (EMT) in HCC, one of the frequent events that occur in cancer metastasis, suggesting that ALR is involved in HCC. In this study, we report for the first time that the transfection of ALR enhances the antitumor effect of chemotherapy with doxorubicin, a typical anticancer drug, on HCC in vitro and in vivo. The efflux of doxorubicin from ALR-transfected HCC cells is efficiently suppressed. This implies the intracellular retention of doxorubicin in tumor cells, which is at least partly attributable to the effective inhibition of ABCB1 and ABCG2 transporter expression in ALR-expressing cells. The downregulation of ALR expression by short hairpin RNA diminishes the antitumor effect of ALR. We further demonstrate that ALR inhibits the AKT/Snail signaling pathway, resulting in the downregulation of ABCB1 and ABCG2 expression. In conclusion, our results suggest that ALR is a potential chemotherapeutic agent against HCC.

[Possible use of the growing liver biological set for hepatic recovery after toxic damage (an experimental study)]

The lack of acceptable pharmacological approaches for restoration of the injured liver is associated with complex of mechanisms involved in hepatic regeneration and with difficulty of the target selection. The aim of this research was to study the hepatoprotective function of the extract from both the growing and regenerating liver containing a natural set of factors crucial for the hepatic restoration. Extracts from both regenerating liver of rats after 70% hepatic resection and the growing liver of neonatal pigs were obtained using own original technique. The set of resultant extracts was named as the hepatic regeneration set (HRS). HRS fractionation was carried out using the Toyopearl HW-50S sorbent. The efficiency of HRS and its fractions was estimated using a model of the mouse liver thioacetamide injury and monitoring hepatic enzyme activity in blood serum. The activities of AST and ALT in intact animals were 50 U/l and 80 U/l, respectively; after thioacetamide administration they increased to 2059±212 U/l and 4280±440 E/l, respectively (p<0.05). Treatment of injured animals with HRS from the rat regenerating liver resulted in a significant decrease of transaminase activities to 924±148 U/l (AST; p<0.05) and 1633±308 U/l (ALT; p<0.05). A similar effect was observed after treatment with HRS from the neonatal pig liver: the AST decreased to 937±138 U/l (p<0.05), while ALT activity decreased to 1710±237 U/l (p<0.05). HRs fractionation resulted in identification two active fractions characterized by much higher (8-29) hepatotropic effect that that of the whole extract. These fractions contained peptide/protein components with the range of molecular mass of 3-60 kDa (fraction 1) and 3-25 kDa (fraction 2a). Fraction 1 also contained some polynucleotides in fraction 1. Subsequent studies of these fractions exceeding the hepatotropic effect of original HRS is clearly needed to identify their individual components by immunochromatography methods, ELISA, MRM mass spectrometry and quantitative PCR.

Alleviation of Ischemia-Reperfusion Injury in Liver Steatosis by Augmenter of Liver Regeneration Is Attributed to Antioxidation and Preservation of Mitochondria

BACKGROUND

Fatty liver is one of the major impediments to liver surgery and liver transplantation because steatotic hepatocytes are more susceptible to ischemia-reperfusion injury (IRI). In this study, the effects of augmenter of liver regeneration (ALR) on hepatic IRI in steatotic mice were investigated.

METHODS

In vivo, liver steatosis of mice was induced by feeding a methionine-choline-deficient diet for 2 weeks. Three days before hepatic partial warm IRI, mice were transfected with the ALR-containing adenovirus. In an in vitro study, the protective effect of ALR on steatotic HepG2 cells was analyzed after hypoxia/reoxygenation (HR) treatment.

RESULTS

The transfection of the ALR gene into steatotic mice attenuated liver injury, inhibiting hepatic oxidative stress, increasing antioxidation capacities, promoting liver regeneration, and consequently suppressing cell apoptosis/death. Furthermore, resistance to HR injury was notably increased in ALR-transfected cells compared with the vector-transfected cells. The HR-induced rise in the mitochondrial reactive oxygen species was reduced, and cellular antioxidant activities were enhanced. The ALR transfection prevented cells from apoptosis, which can be attributed to the preservation of the mitochondrial membrane potential, enhancement of oxygen consumption rate and production of adenosine triphosphate.

CONCLUSIONS

ALR protects steatotic hepatocytes from IRI by attenuating oxidative stress and mitochondrial dysfunction, as well as improving antioxidant effect. ALR may be used as a potential therapeutic agent when performing surgery and transplantation of steatotic liver.

A New Member of the TBC1D15 Family from Chiloscyllium plagiosum: Rab GTPase-Activating Protein Based on Rab7 as a Substrate

APSL (active peptide from shark liver) is a hepatic stimulator cytokine from the liver of Chiloscyllium. It can effectively protect islet cells and improve complications in mice with alloxan-induced diabetes. Here, we demonstrate that the APSL sequence is present in the N-terminus of novel TBC (Tre-2, Bub2 and Cdc16) domain family, member 15 (TBC1D15) from Chiloscylliumplagiosum. This shark TBC1D15 gene, which contains an ORF of 2088 bp, was identified from a cDNA library of regenerating shark liver. Bioinformatic analysis showed that the gene is highly homologous to TBC1D15 genes from other species. Moreover, the N-terminus of shark TBC1D15 contains a motif of unknown function (DUF3548), which encompasses the APSL fragment. Rab-GAP activity analysis showed that shark TBC1D15 is a new member of the TBC1D15 family. These results demonstrated that shark TBC1D15 possesses Rab-GAP activity using Rab7 as a substrate, which is a common property of the TBC1D15 family. The involvement of APSL at the N-terminus of TBC1D15 also demonstrates that this protein might be involved in insulin signaling and may be associated with the development of type 2 diabetes. The current findings pave the way for further functional and clinical studies of these proteins from marine sources.

Involvement of hepatic stimulator substance in the regulation of hepatoblast maturation into hepatocytes in vitro

Hepatic stimulator substance (HSS), also known as augmenter of liver regeneration (ALR), acts as a hepatotrophic growth factor to promote liver regeneration after liver damage or partial hepatectomy. However, the expression and function of HSS during liver development in mammals remain largely unknown. In this work, the hepatoblasts were isolated from mice at embryonic day 13.5 (E13.5), and HSS expression and its role during hepatoblast maturation were investigated. The results showed that HSS expression was enhanced in the hepatoblasts compared with mouse primary hepatocytes. HSS expression (23 kDa) was significantly decreased if the hepatoblast maturation was induced by a combination of oncostatin M (OSM), dexamethasone (DEX), and hepatocyte growth factor (HGF). We also found that knockdown of HSS expression (mainly 23-kDa isoform) by siRNA promoted hepatoblast maturation and also activated the signal transducer and activator of transcription 3 (STAT3) phosphorylation levels. However, if STAT3 activity was blocked by a small-molecule inhibitor Stattic, then hepatocyte maturation could be abolished, suggesting that STAT3 was most likely a potential molecule responsible for HSS signaling. In summary, our results demonstrated for the first time that HSS might be an active factor participating in the regulation of liver development and hepatocyte maturation.

Anti-diabetic effects of CTB-APSL fusion protein in type 2 diabetic mice

To determine whether cholera toxin B subunit and active peptide from shark liver (CTB-APSL) fusion protein plays a role in treatment of type 2 diabetic mice, the CTB-APSL gene was cloned and expressed in silkworm (Bombyx mori) baculovirus expression vector system (BEVS), then the fusion protein was orally administrated at a dose of 100 mg/kg for five weeks in diabetic mice. The results demonstrated that the oral administration of CTB-APSL fusion protein can effectively reduce the levels of both fasting blood glucose (FBG) and glycosylated hemoglobin (GHb), promote insulin secretion and improve insulin resistance, significantly improve lipid metabolism, reduce triglycerides (TG), total cholesterol (TC) and low density lipoprotein (LDL) levels and increase high density lipoprotein (HDL) levels, as well as effectively improve the inflammatory response of type 2 diabetic mice through the reduction of the levels of inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Histopathology shows that the fusion protein can significantly repair damaged pancreatic tissue in type 2 diabetic mice, significantly improve hepatic steatosis and hepatic cell cloudy swelling, reduce the content of lipid droplets in type 2 diabetic mice, effectively inhibit renal interstitial inflammatory cells invasion and improve renal tubular epithelial cell nucleus pyknosis, thus providing an experimental basis for the development of a new type of oral therapy for type 2 diabetes.

Adenoviral gene transfer of hepatic stimulator substance confers resistance against hepatic ischemia-reperfusion injury by improving mitochondrial function

Hepatic stimulator substance (HSS) has been suggested to protect liver cells from various toxins. However, the precise role of HSS in hepatic ischemia-reperfusion (I/R) injury remains unknown. This study aims to elucidate whether overexpression of HSS could attenuate hepatic ischemia-reperfusion injury and its possible mechanisms. Both in vivo hepatic I/R injury in mice and in vitro hypoxia-reoxygenation (H/R) in a cell model were used to evaluate the effect of HSS protection after adenoviral gene transfer. Moreover, a possible mitochondrial mechanism of HSS protection was investigated. Efficient transfer of the HSS gene into liver inhibited hepatic I/R injury in mice, as evidenced by improvement in liver function tests, the preservation of hepatic morphology, and a reduction in hepatocyte apoptosis. HSS overexpression also inhibited H/R-induced cell death, as detected by cell viability and cell apoptosis assays. The underlying mechanism of this hepatic protection might involve the attenuation of mitochondrial dysfunction and mitochondrial-dependent cell apoptosis, as shown by the good preservation of mitochondrial ultrastructure, mitochondrial membrane potential, and the inhibition of cytochrome c leakage and caspase activity. Moreover, the suppression of H/R-induced mitochondrial ROS production and the maintenance of mitochondrial respiratory chain complex activities may participate in this mechanism. This new function of HSS expands the possibility of its application for the prevention of I/R injury, such as hepatic resection and liver transplantation in clinical practice.

Hepatopoietin Cn reduces ethanol-induced hepatoxicity via sphingosine kinase 1 and sphingosine 1-phosphate receptors

The hepatic growth factor hepatopoietin Cn (HPPCn) prevents liver injury induced by carbon tetrachloride in rats. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid produced by sphingosine kinase (SphK). S1P and S1P receptors (S1PRs) are involved in liver fibrogenesis and oxidative injury. This work sought to understand the mechanism by which SphK/S1P/S1PRs are involved in the protective effects of HPPCn on ethanol-induced liver injury and fibrosis. Transgenic mice with liver-specific overexpression of HPPCn (HPPCn(liver) (+/+)) were generated. Two ethanol feeding protocols were used to assess the protective effect of HPPCn on acute and chronic liver injury in mice. Specific inhibitors of S1PR1, S1PR2 and S1PR3 and siRNA were used to examine the roles of S1PRs in hepatic stellate cell (HSC) activation and hepatocyte apoptosis. Increased HPPCn expression in transgenic mice attenuated fibrosis induced by ethanol and carbon tetrachloride (CCl4). Treatment with recombinant human HPPCn prevented human hepatocyte apoptosis and HSC activation. JTE-013 or S1PR2-siRNA attenuated the effect of HPPCn on HSC activation induced by tumour necrosis factor-α (TNF-α). Consistent with the effect of N,N-dimethylsphingosine (DMS), suramin or S1PR3-siRNA treatment blocked HPPCn-induced Erk1/2 phosphorylation in human hepatocytes. This study demonstrated that HPPCn attenuated oxidative injury and fibrosis induced by ethanol feeding and that the SphK1/S1P/S1PRs signalling pathway contributes to the protective effect of HPPCn on hepatocyte apoptosis and HSC activation.

A shark liver gene-derived active peptide expressed in the silkworm, Bombyx mori: preliminary studies for oral administration of the recombinant protein

Active peptide from shark liver (APSL) is a cytokine from Chiloscyllium plagiosum that can stimulate liver regeneration and protects the pancreas. To study the effect of orally administered recombinant APSL (rAPSL) on an animal model of type 2 diabetes mellitus, the APSL gene was cloned, and APSL was expressed in Bombyx mori N cells (BmN cells), silkworm larvae and silkworm pupae using the silkworm baculovirus expression vector system (BEVS). It was demonstrated that rAPSL was able to significantly reduce the blood glucose level in mice with type 2 diabetes induced by streptozotocin. The analysis of paraffin sections of mouse pancreatic tissues revealed that rAPSL could effectively protect mouse islets from streptozotocin-induced lesions. Compared with the powder prepared from normal silkworm pupae, the powder prepared from pupae expressing rAPSL exhibited greater protective effects, and these results suggest that rAPSL has potential uses as an oral drug for the treatment of diabetes mellitus in the future.

Augmenter of liver regeneration

'Augmenter of liver regeneration' (ALR) (also known as hepatic stimulatory substance or hepatopoietin) was originally found to promote growth of hepatocytes in the regenerating or injured liver. ALR is expressed ubiquitously in all organs, and exclusively in hepatocytes in the liver. ALR, a survival factor for hepatocytes, exhibits significant homology with ERV1 (essential for respiration and viability) protein that is essential for the survival of the yeast, Saccharomyces cerevisiae. ALR comprises 198 to 205 amino acids (approximately 22 kDa), but is post-translationally modified to three high molecular weight species (approximately 38 to 42 kDa) found in hepatocytes. ALR is present in mitochondria, cytosol, endoplasmic reticulum, and nucleus. Mitochondrial ALR may be involved in oxidative phosphorylation, but also functions as sulfhydryl oxidase and cytochrome c reductase, and causes Fe/S maturation of proteins. ALR, secreted by hepatocytes, stimulates synthesis of TNF-α, IL-6, and nitric oxide in Kupffer cells via a G-protein coupled receptor. While the 22 kDa rat recombinant ALR does not stimulate DNA synthesis in hepatocytes, the short form (15 kDa) of human recombinant ALR was reported to be equipotent as or even stronger than TGF-α or HGF as a mitogen for hepatocytes. Altered serum ALR levels in certain pathological conditions suggest that it may be a diagnostic marker for liver injury/disease. Although ALR appears to have multiple functions, the knowledge of its role in various organs, including the liver, is extremely inadequate, and it is not known whether different ALR species have distinct functions. Future research should provide better understanding of the expression and functions of this enigmatic molecule.

Increased hepatic apoptosis in high-fat diet-induced NASH in rats may be associated with downregulation of hepatic stimulator substance

The mechanisms of progression from fatty liver to steatohepatitis and cirrhosis are not well elucidated. Hepatocellular apoptosis could be one of the key factors in the pathogenesis of non-alcoholic steatohepatitis (NASH). Hepatic stimulator substance (HSS) protects liver cells from various toxins. We previously reported that HSS is critically important for the survival of hepatocytes due to its mitochondrial association. This study aims to investigate the relationship between HSS and hepatocellular apoptosis in vivo models of high-fat diet-induced NASH and in vitro models of palmitic acid-induced hepatocyte injury. Sprague-Dawley rats were fed a high-fat diet for 8, 12 and 16 weeks. Hepatic histological lesions, liver function and apoptosis were examined. HSS expression, in association with caspase-3 and cytochrome c leakage, which are both indicators of cell apoptosis, was measured. Results showed that a high-fat diet altered liver function and histology in a manner resembling NASH. Hepatic protein and mRNA HSS expression was decreased as NASH progressed. Meanwhile, cell apoptosis increased as result of caspase-3 activation and cytochrome c release, indicating that HSS might be involved in NASH pathogenesis. Furthermore, in palmitic acid-induced hepatic cell damage, over-expression of HSS decreased cells apoptosis. In contrast, repression of HSS expression by siRNA increased cell apoptosis. In conclusion, these data imply that cell apoptosis contributes to the pathogenesis of NASH, during which HSS expression is downregulated. Increasing HSS expression in hepatocytes may forestall cell apoptosis as result of fatty acid insult.

Construction and characterization of a cDNA library from shark regenerated hepatic tissue

Sharks are a type of fish with a full cartilaginous skeleton and have big livers. To better understand liver regeneration in sharks and screening for the important genes participated in disease-defense, in this study, a cDNA library of regenerated liver tissues of shark, Chiloscyllium plagiosum, was constructed. A total of 2103 expressed sequence tags (ESTs), which represents 997 unique genes, were sequenced. Among these genes, 434 (43.53%) of them showed significant similarity (E-values < 10⁻⁵) to the sequences in NCBI Nt database, 685 (68.71%) of these unique genes showed significant similarity (E-values < 10⁻⁵) to the sequences in NCBI Nr database, and 662 (66.40%) of these unique genes showed significant similarity (E-values < 10⁻⁵) to the Swiss-Prot database. Preliminary analysis of unique genes according to COG database showed that unigenes were further grouped into 21 functional categories including inorganic ion transport and metabolism, energy production and conversion, posttranslational modification, protein turnover and chaperones, general function prediction only, translation, and ribosomal structure and biogenesis. Several possible candidate genes involved in liver regeneration were selected to analyze their expression with relative quantification real-time PCR. This study may contribute to our better understanding of the molecular mechanism of regeneration in shark liver. Furthermore, the EST cataloguing and profiling of shark will be also benefited to the functional genomic research in this marine species.

Hepatopoietin Cn suppresses apoptosis of human hepatocellular carcinoma cells by up-regulating myeloid cell leukemia-1

AIM: To investigate the role of hepatopoietin Cn (HPPCn) in apoptosis of hepatocellular carcinoma (HCC) cells and its mechanism.

METHODS: Two human HCC cell lines, SMMC7721 and HepG2, were used in this study. Immunostaining, Western blotting and enzyme linked immunosorbent assay were conducted to identify the expression of HPPCn and the existence of an autocrine loop of HPPCn/HPPCn receptor in SMMC7721 and HepG2. Apoptotic cells were detected using fluorescein isothiocyanate (FITC)-conjugated Annexin V and propidium iodide.

RESULTS: The HPPCn was highly expressed in human HCC cells and secreted into culture medium (CM). FITC-labeled recombinant human protein (rhHPPCn) could specifically bind to its receptor on HepaG2 cells. Treatment with 400 ng/mL rhHPPCn dramatically increased the viability of HCC-derived cells from 48.1% and 36.9% to 85.6% and 88.4%, respectively (P < 0.05). HPPCn silenced by small-interfering RNA reduced the expression and secretion of HPPCn and increased the apoptosis induced by trichostatin A. Additionally, HPPCn could up-regulate the expression of myeloid cell leukemia-1 (Mcl-1) in HCC cells via mitogen-activated protein kinase (MAPK) and sphingosine kinase-1.

CONCLUSION: HPPCn is a novel hepatic growth factor that can be secreted to CM and suppresses apoptosis of HCC cells by up-regulating Mcl-1 expression.

Down-regulation of hepatic nuclear factor 4alpha on expression of human hepatic stimulator substance via its action on the proximal promoter in HepG2 cells

hHSS (human hepatic stimulator substance) stimulates hepatocyte growth. To understand the mechanism controlling hHSS expression, we analysed the proximal promoter activity and identified two regulatory regions (-212/-192 and -152/-132) that were important for transcription in HepG2 cells. Using the luciferase reporter assay, gel-shift experiments and ChIP (chromatin immunoprecipitation), we found that the transcription factors HNF4alpha (hepatocyte nuclear factor 4alpha) and Sp1 (stimulating protein-1) were essential for hHSS promoter activity and could directly bind to regions -209/-204 and -152/-145 respectively. We also confirmed that activation and repression of hHSS transcription induced by Sp1 and HNF4alpha resulted from binding of these factors to these two cis-elements respectively. Overexpression of HNF4alpha led to a dramatic repression of the promoter activity and, in contrast, the activity was markedly elevated by overexpression of Sp1. Furthermore, overexpression of HNF4alpha1, one of the HNF4alpha isoforms, resulted in a dramatic suppression of the promoter activity. Moreover, repression of HNF4alpha expression by siRNA (small interfering RNA) remarkably enhanced the hHSS mRNA level. It has been reported previously that expression of HNF4alpha is functionally regulated by dexamethasone. To further confirm the transcriptional control of HNF4alpha on hHSS, we tested the effect of dexamethasone on hHSS transcription in HepG2 cells. In the present study we have demonstrated that the expression of the hHSS gene was down-regulated at the transcriptional level by dexamethasone in HepG2 cells. A deletion and decoy assay revealed that binding of HNF4alpha to nucleotides -209/-204 was responsible for the suppression of hHSS promoter activity by dexamethasone. Increases in the HNF4alpha-binding activity and expression were simultaneously observed in an electrophoretic mobility-shift assay and Western blot analysis. These results suggested that Sp1 activates hHSS basal expression, but HNF4alpha inhibits hHSS gene expression.

Isolation and functional identification of a novel human hepatic growth factor: hepatopoietin Cn

Hepatic stimulating substance (HSS) was first isolated from weanling rat liver in 1975 and found to stimulate hepatic DNA synthesis both in vitro and in vivo. Since then, mammalian and human HSS have been investigated for their potential to treat hepatic diseases. However, the essential nature in composition and structure of HSS remain puzzling because HSS has not been completely purified. Heating, ethanol precipitation, and ion-exchange chromatographies had been carried out to isolate the protein with specific stimulating activity from newborn calf liver, and [(3)H]thymidine deoxyribose (TdR)/bromodeoxyuridine (BrdU) incorporation and carboxyfluorescein diacetate succinimidyl ester (CFSE)-based proliferation assay to determine the bioactivity in vitro and in vivo. We report the purification of a novel 30-kDa protein from a crude extract of calf liver HSS. This protein is a member of the leucine-rich acidic nuclear protein family (LANP) and has been named hepatopoietin Cn (HPPCn). Studies of partially hepatectomized (PH) mice show that levels of HPPCn messenger RNA (mRNA) increase after liver injury. Furthermore, the recombinant human protein (rhHPPCn) was shown to stimulate hepatic DNA synthesis and activate signaling pathways involved in hepatocyte proliferation in vitro and in vivo.

CONCLUSION

HPPCn is a novel hepatic growth factor that plays a role in liver regeneration.

Effect of heat and pH denaturation on the structure and conformation of recombinant human hepatic stimulator substance

Hepatic stimulator substance (HSS) is a novel liver-specific growth-promoting factor. Although HSS has been successfully crystallized, several properties of this protein have yet to be determined. This study shows that recombinant human HSS (rhHSS) is a dimer with a molecular mass of 31 kDa, the protein is weakly acidic and has an isoelectric point (pI) of 4.50. RhHSS was able to protect hepatoma cells from H2O2-induced apoptosis and to stimulate cell growth. The recombinant protein was thermostable up to 80 degrees C and resistant to changes in pH, as determined by synchronous fluorescence and far-UV circular dichroism (CD). Within the range of pH 4.0-10.0, rhHSS assumed a folded conformation identical to the secondary structure of the original, native protein and a native-like far-UV CD spectrum. Denatured rhHSS could be partly reconstituted with respect to its structure, but not its activity. Thus, rhHSS is a structurally stable protein insensitive to thermal and acid-alkaline denaturation.

Transfection of hepatic stimulator substance gene desensitizes hepatoma cells to H2O2-induced cell apoptosis via preservation of mitochondria

Hepatic stimulator substance (HSS) protects liver cells from various toxins. However, the mechanism by which HSS protects hepatocytes remains unclear. In this study, we report that the HSS gene, after transfection into BEL-7402 hepatocma cells, is stably expressed in the mitochondria. Hydrogen peroxide (H(2)O(2))-induced cell apoptosis in the HSS-transfected cells is reduced, as shown by morphologic analysis. In the HSS-transfected cells, disruption of mitochondrial transmembrane potential (MTP) and cytochrome c leakage are reduced. The anti-apoptotic gene Bcl-2 is also highly expressed. In addition, ATP levels in the HSS-transfected cells are maintained. In conclusion, in hepatoma cells, HSS gene expression protects cells against H(2)O(2) injury, and this effect is likely to be associated with preservation of mitochondria.

Identification of human hepatic stimulator substance gene promoter and demonstration of dual regulation of AP1/AP4 cis-acting element in different cell lines

Human hepatic stimulator substance (hHSS) is a newly identified growth-promoting factor in the liver. HSS is capable of stimulating hepatic regeneration in partial hepatectomized rats, thus, promoting growth of hepatic tumor cells. To understand and elucidate the transcriptional regulation of hHSS gene, the 4890bp of 5'-flanking region of the gene have been isolated and sequenced. The transcriptional start site, located at 248nt upstream from the ATG starting codon, was identified by 5'-rapid amplification cDNA end (5'-RACE). The classical promoter sequences, such as TATA box or GAATT were not identified in the promoter region, instead a GC-rich segment was formed (>70%) by expanding to a longer than 400bp, and immediately upstream from the ATG start codon. The transient transfection assays, using promoter deletion constructs, showed that hHSS promoter was efficiently capable in driving the reporter expression not only in HepG2 cells, but also in Cos7 cells. A region spanning nucleotides in the range of -447 to -358bp revealed a negative regulation on promoter activity in HepG2 cells, but with positive regulation in Cos7 and Hela cells. The promoter activity was obviously influenced by AP1/AP4 (-375/-369nt) mutation in these three cell lines. EMSAs showed that the site was recognized by AP1 in HepG2 cell, and only by an AP4 protein in Cos7 cells. The c-Jun bound to the promoter was further verified by supershift in HepG2 cells and human liver tissue. Chromatin immuno-precipitation (ChIP) demonstrated that there was a direct association of c-Jun with hHSS promoter in HepG2 cells. The c-Jun strongly suppressed hHSS promoter activity in transient expression analyses in HepG2 cells. Mutations in the AP1 binding sites rescued suppression caused by c-Jun, suggesting this was a direct regulation of the hHSS promoter. In contrast, there was no significant effect in c-Jun over-expressed Cos7 and Hela cells. The tissue-specific function of c-Jun in hHSS promoter activity may in part help explain the differences in biology function of hHSS between liver and non-liver cells.

Augmenter of liver regeneration promotes hepatocyte proliferation induced by Kupffer cells

AIM

To observe the effects of augmenter of liver regeneration (ALR) on Kupffer cells and to determine whether ALR promotes hepatocyte proliferation induced by Kupffer cells.

METHODS

Kupffer cells and hepatocytes were cultured in vitro and various concentrations of recombinant rat ALR (rrALR) were added. 3H-thymidine, BrdU and 3H-leucine incorporation was determined in cultured Kupffer cells and hepatocytes, in hepatocytes conditioned by Kupffer cells, and in associated medium. rrALR was labeled by iodination and used to determine its binding activity by Scatchard analysis in Kupffer cells and primarily cultured rat hepatocytes.

RESULTS

rrALR stimulated DNA replication in Kupffer cells and protein synthesis both in cells and in medium in a non-concentration-dependent manner. The effect was significant at the concentration of 1 microg/L ALR. However, rrALR had no effect on primarily cultured hepatocytes, when hepatocytes were cultured with the Kupffer cell medium conditioned by ALR, DNA replication and protein synthesis in hepatocytes increased significantly at the concentration of 1 microg/L ALR. When the ALR concentration was increased, its effect on hepatocyte proliferation decreased to the basal level. Scatchard analysis indicated the presence of a single class of high affinity receptors with a dissociation constant (Kd) of 0.883 nmol/L and a maximum binding capacity (Bmax) of 126.1 pmol/g protein in the rat Kupffer cells.

CONCLUSION

ALR can promote hepatocyte proliferation induced by Kupffer cells, which is associated with the concentration of ALR, suggesting that Kupffer cells play a dual role in liver regeneration.

Hepatoprotective effect of fetal tissue cytosol and its thermostable fraction in rats with carbon tetrachloride-induced hepatitis

Pretreatment of rats with cytosol of fetal tissue or its thermostable fraction prevented death of animals from CCl4 intoxication, decreased serum transaminase activities and level of TBA-reactive products, and normalized the prooxidant/antioxidant balance in the liver. The effect of cytosol was more pronounced than that of its thermostable fraction.

Repression of Cytochrome P450 Activity in Human Hepatocytes in Vitro by a Novel Hepatotrophic Factor, Augmenter of Liver Regeneration

Pathological disorders of the liver were shown to be associated with an impairment of hepatic drug metabolism mediated in part by growth factors. Augmenter of liver regeneration (ALR) is a novel liver-specific hepatotrophic growth factor, whereas its action on cytochrome P450 (P450) metabolism is completely unknown. Application of ALR to primary human hepatocytes in vitro reduced P450 isoenzyme activities (1A2 and 2A6) in a dose-dependent manner. Time-course analysis revealed that the maximal inhibitory effect was reached after 24 to 72 h of exposure with 50 nM ALR. The reduction of basal activities upon ALR treatment was 35% for CYP1A2, 56% for CYP2A6, 18% for CYP2B6, and 45% for CYP2E1. Additionally, after induction of P450 with specific inducers, ALR revealed an inhibitory effect on the isoenzyme activities (CYP1A2, 41%; CYP2B6, 35%). Investigations of protein and mRNA expression of basal and induced CYP1A2 and CYP3A4 after ALR treatment by Western blotting and real-time reverse transcriptase-polymerase chain reaction, respectively, suggest a regulation on the transcriptional level. Furthermore, ALR treatment increased nuclear factor kB activity and reduced constitutive androstane receptor but not pregnane X receptor or aryl hydrocarbon receptor expression. In contrast, ALR revealed no effects on phase II reactions (glutathione/oxidized glutathione, UDP-glucuronyltransferase conjugation). Our results indicate that ALR, as a member of hepatotrophic factors, down-regulates basal and induced P450 in human liver and therefore cross-links growth signals to regulation of hepatic metabolism. These findings further imply a possible role of ALR in drug interactions during impaired hepatic function, whereas liver regeneration is triggered.

Expression of augmenter of liver regeneration (ALR) in human liver cirrhosis and carcinoma

AIMS

To determine the expression of a protein termed augmenter of liver regeneration (ALR), recently found to have a specific and beneficial effect on the process of liver regeneration in normal and diseased human liver.

METHODS AND RESULTS

ALR expression in normal and cirrhotic human livers with various underlying diseases as well as in tissue samples of hepatocellular carcinoma (HCC) and cholangiocellular carcinoma (CCC) was analysed by immunohistochemistry and quantitative reverse transciptase-polymerase chain reaction (RT-PCR). Expression analysis of ALR in total liver protein extracts by Western blotting showed mainly dimeric ALR protein. Immunohistochemically, cytosolic and perinuclear immunosignals were found in hepatocytes and cholangiocytes in normal, cirrhotic or cancerous liver tissue and only weak signals in some endothelial cells in normal livers. Quantitative mRNA analysis revealed significantly increased ALR expression in cirrhosis compared with normal liver tissue. In HCC and CCC ALR mRNA expression was also significantly enhanced compared with normal liver tissue, but expression levels did not differ from the matching non-neoplastic tissue in the same patient.

CONCLUSIONS

The findings suggest an important role for ALR in hepatocellular regeneration in liver cirrhosis as well as in hepatocarcinogenesis and therefore its potential value in the clinical diagnosis of hepatic cirrhosis and cancer.

Effects of shark hepatic stimulator substance on the function and antioxidant capacity of liver mitochondria in an animal model of acute liver injury

This study was carried out to investigate whether shark hepatic stimulator substance (HSS) can prevent acute liver injury and affect mitochondrial function and antioxidant defenses in a rat model of thioacetamide (TAA)-induced liver injury. The acute liver injury was induced by two intraperitoneal injections of TAA (400 mg/kg) in a 24 h interval. In the TAA plus shark HSS group, rats were treated with shark HSS (80 mg/kg) 1 h prior to each TAA injection. In this group, serum liver enzyme activities were significantly lower than those in the TAA group. The mitochondrial respiratory control ratio was improved, and the mitochondrial respiratory enzyme activities were increased in the TAA plus shark HSS group. The mitochondrial antioxidant enzyme activities and glutathione level were higher in the TAA plus shark HSS group than in the TAA group. These results suggest that the protective effect of shark HSS against TAA-induced acute liver injury may be a result of the restoration of the mitochondrial respiratory function and antioxidant defenses and decreased oxygen stress.

Hepatic stimulator substance administration ameliorates liver regeneration in an animal model of fulminant hepatic failure and encephalopathy

AIMS/BACKGROUND

Hepatic stimulator substance (HSS) is a liver-specific growth factor implicated in hepatocellular proliferation and hepatoprotection in models of acute liver injury. In the present study, we examined the effect of exogenous HSS administration on liver proliferating capacity and survival outcome in an experimental animal model of fulminant hepatic failure (FHF) and encephalopathy, induced by repeated injections of thioacetamide (TAA) in rats.

METHODS

Fulminant hepatic failure was induced in adult male Wistar rats by three consecutive intraperitoneal injections of TAA (400 mg/kg of body weight), at 24 h time intervals. The animals received intraperitoneally either a saline solution or HSS (50 mg protein/kg of body weight), 2 h after the second and third TAA injections. The animals were killed at 6, 12 and 18 h post the last injection of TAA.

RESULTS

Levels of liver enzymes and urea in serum, blood ammonia values, liver histology, stage of hepatic encephalopathy and survival were statistically significantly improved in TAA-intoxicated and HSS-treated rats compared to TAA-intoxicated and saline-treated ones. Furthermore, HSS ameliorated liver regenerative indices--DNA biosynthesis, thymidine kinase activity and hepatocyte mitotic activity--in a statistically significant manner.

CONCLUSIONS

Our data suggest the beneficial effect of HSS administration in this animal model of FHF and encephalopathy, supporting evidence for a possible use of HSS as supportive therapy, by increasing hepatocellular proliferation, in management of FHF.

[The protective effect of hepatocyte growth-promoting factor (pHGF) against carbon tetrachloride-induced acute liver injury in rats. II. Protective effects on cell membrane injury]

To examine the protective effects of hepatocyte growth-promoting factor (pHGF) against carbon tetrachloride (CCl4) -induced acute liver injury in rats, the pathological changes were observed by light and electron microcopy, and the serum GOT and GPT levels were measured. Acute liver injury was produced by the injection of CCl4 (2ml/kg BW) in two groups of animals, of which one received pHGF (300 microg/kg BW) via the tail vein after 4 hrs. In the group treated with CCl4 alone, serum GOT and GPT were significantly elevated (1280+/-228 and 187+/-73 IU/l, respectively) 6 hrs after injection, indicating the induction of liver injury by CCl4. They reached a peak (3836+/-654 and 1022+/-230 IU/l, respectively) at 48 hrs and declined thereafter, but did not completely recover after 72 hrs. PAS-negative cells were observed around the central veins after 6 hrs and most of the hepatocytes were PAS-negative at 12 hrs. PAS-positive cells began to appear and increased in number after 24 hrs. There were scarcely any PAS-negative cells remaining in the lobules after 72 hrs. In the group treated with CCl4 followed by pHGF, serum GOT and GPT levels were significantly lower than in the CCl4-treated group, and abundant PAS-positive hepatocytes were observed. Also, all hepatocytes were PAS-positive (as in normal liver) after 72 hrs. Administration of pHGF resulted in a decrease in the ultrastructural changes in rats with CCl4-induced liver injury such as vacuolation, cisternae formation and dilatation of the rough endoplasmic reticulum. These results suggest that pHGF acts to stabilize cell membranes, thereby providing protection against CCl4-induced hepatic injury.

Hepatic stimulator substance activity in the liver of thioacetamide-intoxicated rats

AIMS/BACKGROUND

Hepatic stimulator substance (HSS) is a known hepatic growth factor which appears to be organ-specific but species non-specific. We have recently shown that the administration of HSS enhanced hepatocyte proliferation occurring due to thioacetamide (TAA)-induced liver injury in rats (Theocharis SE, et al., Scand J Gastroenterol 1998; 33: 656-63). In the present study, we examined the activity of the endogenously produced HSS in the liver of TAA administered rats during injury and regeneration.

METHODS

TAA at a dose of 300 mg/kg of body weight was injected intraperitoneally in male Wistar rats. The animals were sacrificed at 0, 12, 24, 36, 48, 60 and 72 h after TAA administration. The rate of tritiated thymidine incorporation into hepatic DNA, the enzymatic activity of liver thymidine kinase and the assessment of mitotic index in hepatocytes were used to estimate liver regeneration. HSS extract was obtained from the livers of TAA-treated rats, sacrificed at the above mentioned time points. This HSS extract was injected in 34% partially hepatectomized rats, to assess its activity. The ability of the injected HSS extract to increase hepatocellular proliferation over that normally occurring 24 h following 34% partial hepatectomy was used to express the activity of HSS by determining the above mentioned indices of liver regeneration.

RESULTS

The administration of TAA caused severe hepatic injury recognized histopathologically as well as by the increased activities of serum hepatic enzymes aspartate and alanine aminotrasferases. The hepatic injury, which peaked at 24 and 36 h post-TAA treatment (p<0.001), was followed by hepatocyte proliferation, presenting peaks at 48 and 60 h (p<0.001). The activity of the endogenously produced HSS from livers of TAA-treated rats increased at 36 h after TAA administration as well as being highly expressed at 48 and 60 h thus coinciding with the peak of hepatocyte proliferation. At other time points, HSS activity was decreased.

CONCLUSIONS

The observed variations of HSS activity in rat liver suggest active participation of this growth factor in hepatocyte replication which follows toxin-induced liver injury as a repair mechanism process.

Growth induction of hepatic stimulator substance in hepatocytes through its regulation on EGF receptors

The cytosolic liver-specific growth factor-hepatic stimulator substance (HSS) has been shown to be able to amplify the rat hepatocyte proliferation responded to EGF. In order to get more insight into the mechanism, the regulatory effect of HSS on EGF-receptor (EGF-R) and the receptor phosphorylation at molecular level was studied. HSS partially purified from weanling rat liver was given to cultured hepatocytes and its influence on EGF-R specific binding and internalization as well as mRNA expression were investigated. The results showed that preincubation of hepatocytes with HSS could lead to an increase in [125I]-EGF binding to its receptors and inhibit EGF-induced receptor down-regulation. Furthermore, the over-expression of EGF-R mRNA stimulated by HSS was seen during 2-12 h after the incubation. Additionally, it was demonstrated with human hepatoma SMMC-7721 cells in Western blot that the EGF-R expression and the receptor autophosphorylation were increased with dose/time-dependency after HSS treatment. These results strongly suggest that the mechanism of HSS action on hepatocyte growth might be related to its modulation on EGF-R and receptor-mediated signaling transduction.

The current status of primary hepatocyte culture

Recently, there have been significant advances toward the development of culture conditions that promote proliferation of primary rodent hepatocytes. There are two major methods for the multiplication of hepatocytes in vitro: one is the use of nicotinamide, the other is the use of a nutrient-rich medium. In the medium containing a high concentration of nicotinamide and a growth factor, primary hepatocytes can proliferate well. In this culture condition small mononucleate cells, which are named small hepatocytes, appear and form colonies. Small hepatocytes have a high potential to proliferate while maintaining hepatic characteristics, and can differentiate into mature ones. On the other hand, combining the nutrient-rich medium with 2% DMSO, the proliferated hepatocytes can recover the hepatic differentiated functions and maintain them for a long time. In this review I describe the culture conditions for the proliferation and differentiation of primary hepatocytes and discuss the small hepatocytes, especially their roles in liver growth.

Liver regeneration

Liver regeneration after the loss of hepatic tissue is a fundamental parameter of liver response to injury. Recognized as a phenomenon from mythological times, it is now defined as an orchestrated response induced by specific external stimuli and involving sequential changes in gene expression, growth factor production, and morphologic structure. Many growth factors and cytokines, most notably hepatocyte growth factor, epidermal growth factor, transforming growth factor-alpha, interleukin-6, tumor necrosis factor-alpha, insulin, and norepinephrine, appear to play important roles in this process. This review attempts to integrate the findings of the last three decades and looks toward clues as to the nature of the causes that trigger this fascinating organ and cellular response.

Hepatic stimulator substance administration enhances regenerative capacity of hepatocytes in cadmium-pretreated partially hepatectomized rats

The liver is of central importance in the metabolism of essential and toxic metals such as cadmium (Cd). Cd pretreatment suppressed the regenerative capacity of hepatocytes, which normally occurs 24 hr after partial hepatectomy, due to the inhibition of the activity of the enzyme thymidine kinase. The effect of hepatic stimulator substance (HSS) administration (10, 20, and 40 mg protein/kg body weight) on hepatocyte proliferation was investigated in Cd-pretreated partially hepatectomized rats. HSS administration partly restored the suppressed hepatocyte DNA biosynthesis in Cd-pretreated partially hepatectomized rats. The hepatocyte mitotic activity and the percentage of proliferating cell nuclear antigen-positive nuclei were in accordance with the liver proliferative status. The administration of HSS did not affect in a statistically significant manner the activity of the enzyme thymidine kinase in Cd-pretreated partially hepatectomized rats. It is suggested that the administration of HSS ameliorates the diminished hepatocyte regenerative response to partial hepatectomy in this model of acute liver injury, due to Cd intoxication.

Comitogenic effects of vasoactive intestinal polypeptide on rat hepatocytes

The primary mitogens such as epidermal growth factor and transforming growth factor-alpha are known to stimulate DNA synthesis in primary cultures of adult rat hepatocytes. Vasoactive intestinal polypeptide (VIP) was found to amplify DNA synthesis induced by the primary mitogens and thus acted as a comitogen. The comitogenic effect of VIP was specific for the culture medium, suggesting that minor components in the medium were required for hepatocytes to fully respond to VIP. Glutamic acid is probably one of these minor components, although other components present in the nutrient-rich medium were also necessary for the full comitogenic effect. Other comitogens such as insulin, vasopressin, and angiotensin II interacted additively with low concentrations of VIP. The comitogenic effect of VIP was also found in hepatocytes cultured from regenerating rat liver after a partial hepatectomy. In the regenerating hepatocyte cultures, VIP can act as a mitogen even in the absence of the primary mitogen EGF. VIP mRNA was found in several organs including brain, intestine, and liver, and its expression was slightly induced in liver 24 h after a partial hepatectomy. These results suggest that VIP can act as a hepatic comitogen and may play a role in liver cell proliferation.

Liver regeneration following partial hepatectomy and stimulation by hepatic stimulatory substance in cirrhotic and non-cirrhotic rats

The effects of hepatic stimulatory substance (HSS) on cirrhotic and non-cirrhotic rats were studied after 70% partial hepatectomy. Liver cirrhosis was produced by weekly intragastric infusion of chloroform for 12-16 weeks. The HSS was prepared by extraction from the livers of weanling mice. Rats in the experimental group were injected with 5 ml HSS after 70% partial hepatectomy, and those in the control group received normal saline. The results showed that the 3H-thymidine incorporation was higher in the HSS group 24 h after partial hepatectomy in both cirrhotic and non-cirrhotic rats, and persistently higher in the non-cirrhotic rats at 48 h. Total DNA was significantly higher in the HSS group of non-cirrhotic rats 24 and 48 h after partial hepatectomy. The restituted liver volume and weight was significantly higher in non-cirrhotic rats 48 h after partial hepatectomy, while there was no significant difference between the HSS and the control groups in the cirrhotic rats. The HSS induced significant effects on 3H-thymidine incorporation in the non-cirrhotic liver, resulting in increasing liver weight, volume and total DNA 48 h after partial hepatectomy. In cirrhotic rats, the 3H-thymidine incorporation was higher in the HSS group at 24 h after partial hepatectomy, though not showing any increase at 48 h, but the regeneration of liver weight, volume and total DNA at 48 h showed no difference between the HSS group and the control group.

Effects of growth factors on the enzymes of purine metabolism in culture of regenerating rat liver cells

Hepatocytes are affected by many cytokines and growth factors during liver regeneration. In regenerating rat liver cells cultures, liver cell growth factor (LCGF), hepatic stimulator substance (HSS), interleukin-1 beta (IL-1 beta), as well as their combination, were tested for their ability to activate the enzymes involved in purine metabolism. The enzymes tested were 5' nucleotidase, AMP deaminase, adenosine deaminase and xanthine oxidase. The cytokines alone or in combination, activated 5' nucleotidase and adenosine deaminase. Activity of AMP deaminase was stimulated by IL-1 beta associated with LCGF, HSS and IL-1 beta. Xanthine oxidase was stimulated by IL-1 beta but not with HSS and LCGF. Associated with IL-1 beta these two substances decreased its activity. A novel approach to the understanding of the mechanisms involved in the regulation of purine metabolism during liver regeneration, is proposed.

Effects of albumin-bilirubin complexes with syngeneic or allogeneic albumin on DNA and protein synthesis in liver and spleen of partially hepatectomized rats

The effects of non-covalently bound complexes of allogeneic or syngeneic albumin with bilirubin and of albumin alone on DNA and protein synthesis in rat liver and spleen cells after partial hepatectomy were studied. The assay procedure was based on different intravenous doses of these compounds in rats after partial hepatectomy. The allogeneic albumin-bilirubin complex (at protein doses of 0.9 and 90 micrograms/100 g body weight) stimulated DNA and protein synthesis in liver cells irrespective of the dose. At a dose of 0.9 micrograms the syngeneic albumin-bilirubin complex enhanced DNA synthesis insignificantly and produced no effect on protein synthesis, while at a dose of 90 micrograms, both DNA and protein synthesis were considerably increased. Allogeneic or syngeneic albumin at the above doses stimulated only protein, not DNA, synthesis in the liver, while the highest stimulation was at 90 micrograms allogeneic albumin. It was found also that partial hepatectomy decreased DNA and protein synthesis in spleen cells. Albumin-bilirubin complex with allogeneic or syngeneic albumin and albumin alone either significantly enhanced DNA and protein synthesis in the spleen, compared to controls, or only restored synthesis to control levels. Thus DNA and protein synthesis in the regenerating liver and spleen was significantly enhanced after the injection of small doses of the albumin-bilirubin complex, indicating the existence of small amounts of a similar endogenous complex in the blood stream.

Effects of human neonatal serum on DNA synthesis in suckling and adult rat hepatocytes in primary culture

The effect of human neonatal serum on DNA synthesis in suckling and adult rat hepatocytes in primary culture was investigated to characterize growth regulating factors of the liver in neonates and to confirm whether the stimulatory factor is human hepatocyte growth factor (hHGF). Neonatal serum stimulated DNA synthesis of both adult and suckling rat hepatocytes. The stimulatory effect was dose-dependent up to 20% in volume. The molecular weight of the stimulatory substance in neonatal serum was between 12,500 and 25,000, as estimated by gel filtration. Its activity was stable after heating at 56 degrees C for 20 min, but was lost after heating at 90 degrees C for 30 s, and easily passed through S- or heparin-Sepharose columns. The concentration of hHGF quantified by ELISA was too low to stimulate DNA synthesis in vitro. Biological and biochemical properties of the growth stimulatory activity in neonatal serum differed from that of hHGF. The presence of other growth factors in human neonatal serum for suckling and adult hepatocytes was suggested.

Suppressing effects of human fetal cell extract on micronuclei induced by cyclophosphamide in mice

The genotoxicity of human fetal cell extract (HFCE) and its effect on the frequency of micronucleated polychromatic erythrocytes (PCE-MNF) in mice induced by cyclophosphamide (CP) were studied. Statistically significant differences were not found between the control group and each group treated with HFCE (0.3, 3, 30 mg/kg bw). CP (200 mg/kg bw) induced a marked increase in MNF (P < 0.01). Administered together with CP, HFCE suppressed the increase of MNF induced by CP. The reduction effect is dependent on the dose of HFCE. At doses of 3 and 30 mg/kg bw HFCE, MNF decreased markedly (P < 0.05 and < 0.01, respectively). It showed that HFCE did not induce micronucleus formation, while it could suppress the micronucleus formation induced by CP in mice. The results suggested that HFCE might be antimutagenic and have potential value in clinical application.

Cloning and sequence analysis of the rat augmenter of liver regeneration (ALR) gene: expression of biologically active recombinant ALR and demonstration of tissue distribution

A full-length cDNA clone encoding a purified augmenter of liver regeneration (ALR) factor prepared from the cytosol of weanling rat livers was isolated. The 1.2-kb cDNA included a 299-bp 5' untranslated region, a 375-bp coding region, and a 550-bp 3' untranslated region. It encoded a protein consisting of 125 amino acids. The molecular weight of ALR calculated from the cDNA was 15,081, which is consistent with the size estimated by SDS/PAGE under reducing conditions. The molecular weight of the purified native ALR estimated by SDS/PAGE under nonreducing conditions was approximately 30,000; thus ALR apparently has a homodimeric structure. The recombinant ALR produced by expression of the cDNA in COS cells was tested in vivo in the canine Eck fistula model and found to have potency equivalent to the purified native ALR. The 125-aa sequence deduced from the rat ALR cDNA shows 50% homology to the amino acid sequence of the gene for oxidative phosphorylation and vegetative growth in the yeast Saccharomyces cerevisiae.

Characterization of human hepatocyte lines derived from normal liver tissue

Four separate continuous lines of human hepatocytes (HH01, HH02, HH09, HH25) were developed from normal liver tissue by subjecting cocultures of human hepatocytes with rat liver epithelial cells in a highly enriched medium to frequent subculturing. The addition of conditioned medium from either the human hepatoma line Hep G2 or one of these stable human hepatocyte lines (HH09) appeared to facilitate establishment of line HH25. These human hepatocyte lines have been in continuous culture for 2 to 5 yr and consist of approximately 95% human cells by analysis of cell surface antigens. Cytogenetic analysis also confirmed the human origin of these cells and showed clonal origin with abnormal ploidy. Cells in these human hepatocyte lines retain morphological features of hepatocytes by both light and electron microscopy. They also retain glucose-6-phosphatase activity and secrete proteins characteristic of hepatocytes, such as albumin, alpha-fetoprotein and transferrin. After incubation with 13 mumol/L dibenz(a,h) anthracene for 24 hr, each line had detectable activity of aryl hydrocarbon hydroxylase, ethoxyresorufin O-deethylase and methoxyresorufin O-demethylase. Thus, these human hepatocyte lines retain important differentiated characteristics of hepatocytes. Derived from normal liver tissue, they appear to be immortalized. They provide a new model system for studying human hepatocellular drug metabolism. These lines may also be useful for studying the regulation of synthesis of albumin, alpha-fetoprotein and other proteins in human hepatocytes, determining the effects of cytokines and growth factors and designing systems to effect gene transfer into human hepatocytes for the purpose of gene therapy.

Studies on the biological characterization and mitogenic interactions between hepatic stimulator substance and acidic fibroblast growth factor

During liver regeneration, hepatic stimulator substance (HSS) and acidic fibroblast growth factor (FGF-1) are produced in the liver. These growth factors may be involved in liver growth control but an understanding of their regulatory interactions is limited. To further characterize the mitogenic activity of HSS, we compared its effects with FGF-1 in cells of hepatocyte, non-parenchymal liver epithelial and non-hepatic lineages. Our studies with these cell types demonstrated differences in the mitogenic specificities of HSS and FGF-1. Whereas exposure of primary hepatocytes to epidermal growth factor and HSS synergistically increased DNA synthesis, simultaneous exposure to HSS and FGF-1 resulted in no such effect. Receptor-binding assays showed that HSS did not compete with FGF-1 in binding to FGF-1 receptors on rat primary hepatocytes. Additional immunoblot analysis demonstrated no cross-reactivity between FGF-1 antibodies and HSS. Distinct mitogenic and immunologic properties of HSS and FGF-1 should facilitate further analysis of liver regeneration and hepatic oncogenesis.