Screening for candidate hepatic growth factors by selective portal infusion after canine Eck's fistula

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

Hepatopoietin Cn (HPPCn) Generates Protective Effects on Acute Liver Injury

Objective: To observe the protective role of hapatopoietin Cn (HPPcn) on acute liver injury.

Methods: Six hours after 10 mmol/L CCl₄, 150 mmol/L ethanol, or 0.6 mmol/L H₂O₂ treatment, SMMC7721 human hepatoma cells were incubated with 10, 100, or 200 ng/ml recombinant human HPPCn protein (rhHPPCn) for an additional 24 h. The cell survival rate was analyzed using the CCK-8 assay. The CCl₄-induced apoptosis of SMMC7721 cells was detected by flow cytometry. Then, the levels of glutamic oxaloacetic transaminase (GOT), glutamic-pyruvic transaminase (GPT), malondialdehyde (MDA), lactate dehydrogenase (LDH), glutathione peroxidase (GSH-PX), and superoxide dismutase (SOD) in SMMC7721 cell lysates and cell culture supernatant were detected. SMMC7721 cells were treated with different concentrations of rhHPPCn (0, 10, and 100 ng/ml). The cell proliferation indexes (BrdU incorporation and PCNA expression) were detected by immunohistochemistry (IHC). An acute liver injury mouse model was established by a one-time intraperitoneal injection of 20% CCl₄ at a volume of 5 ml/kg body weight. One hour after CCl₄ injection, 1.25 or 2.5 mg rhHPPCn/12 h/kg body weight was injected via the tail vein. The serum levels of GOT and GPT were detected at different time points. Pathological changes in the liver were evaluated. PCNA expression levels were observed by IHC.

Results: rhHPPCn increased the survival rate of SMMC7721 cells and inhibited chemical toxicity-induced cell apoptosis. The levels of GOT, GPT, MDA, and LDH in the cell supernatant were significantly reduced, while GSH-PX and SOD were significantly increased after rhHPPCn treatment in the CCl₄-treated SMMC7721 cells. BrdU incorporation and PCNA expression increased in a concentration-dependent manner, indicating that rhHPPCn promotes cell proliferation. The results showed that rhHPPCn significantly reduced the serum levels of GOT and GPT in CCl₄-induced acute liver injury mice. rhHPPCn alleviated the tissue damage and increased PCNA expression, indicating the promotion of proliferation after acute injury.

Conclusion: rhHPPCn protects hepatocytes from chemical toxins by promoting proliferation and inhibiting apoptosis in vivo and in vitro. Our study provides new insights for the clinical treatment of acute liver injury.

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.

Decreased expression of the augmenter of liver regeneration results in increased apoptosis and oxidative damage in human-derived glioma cells

The mammalian growth factor erv1-like (GFER) gene encodes a sulfhydryl oxidase enzyme, named Augmenter of Liver Regeneration (ALR). Recently it has been demonstrated that ALR supports cell proliferation acting as an anti-apoptotic factor. This effect is determined by ALR ability to support the anti-apoptotic gene expression and to preserve cellular normoxic conditions. We recently demonstrated that the addition of recombinant ALR (rALR) in the culture medium of H₂O₂-treated neuroblastoma cells reduces the lethal effects induced by the hydrogen peroxide. Similar data have been reported in the regenerating liver tissue from partially hepatectomized rats treated with rALR. The purpose of the present study was to evaluate the effect of the GFER inhibition, via the degradation of the complementary mRNA by the specific siRNA, on the behaviour of the apoptosis (apoptotic gene and caspase expression and apoptotic cell number) and of the oxidative stress-induced parameters (reactive oxygen species (ROS), clusterin expression and mitochondrial integrity) in T98G glioma cells. The results revealed a reduction of (i) ALR, (ii) clusterin and (iii) bcl-2 and an increase of (iv) caspase-9, activated caspase-3, ROS, apoptotic cell number and mitochondrial degeneration. These data confirm the anti-apoptotic role of ALR and its anti-oxidative properties, and shed some light on the molecular pathways through which ALR modulates its biological effects.

Facilitation of Survival in a Rat Fulminant Hepatic Failure Model by Combination Therapy Using Recombinant G-CSF and Tacrolimus

The mortality rate of fulminant hepatic failure (FHF) is high because of retarded liver regeneration. Recombinant human granulocyte colony-stimulating factor (rHuG-CSF) and tacrolimus are known to be immunosuppressive and supportive to liver regeneration. We investigated the effects of their combination therapy in a rat FHF model with a 68% partial hepatectomy and 24% liver necrosis. All rats without drug pretreatment died within 55 h. The median time was prolonged from 37 to 52 h by rHuG-CSF (250 microg/kg/day s.c. on days -5 to 0) and to 46 h by tacrolimus (0.5 mg/kg/day i.m. on days -2 to 0). Notably, the combination therapy facilitated DNA biosynthesis and survival prolongation, with a median of 77 h. The interferon-gamma (IFN-gamma) protein levels and natural killer cell (NK) activity in the liver were low at 12 h, and no further inhibition was detected by any treatment. Tacrolimus significantly upregulated the mRNA levels of insulin receptors and transforming growth factor-alpha (TGF-alpha), whereas rHuG-CSF did not. Regarding tissue remodeling-related factors, rHuG-CSF upregulated mRNA levels of vascular endothelial growth factor (VEGF) and matrix metalloproteinase- 9 (MMP-9), whereas tacrolimus did not. The combination treatment upregulated protein levels of both insulin receptors and VEGF. These results suggest that tacrolimus improves the hepatocyte replication and rHuG-CSF contributes to tissue reconstitution, and this combination therapy directly facilitates liver regeneration in the FHF model.

Histological organization in hepatocyte organoid cultures

Hepatocytes and other cellular elements isolated by collagenase perfusion of the liver and maintained in defined culture conditions undergo a series of complex changes, including apoptosis and cell proliferation, to reconstruct tissue with specific architecture. Cultures in collagen-coated pleated surface roller bottles, with hepatocyte growth medium medium and in the presence of hepatocyte growth factor (HGF) and epidermal growth factor (EGF), form characteristic and reproducible tissue architecture composed of a superficial layer of biliary epithelial cells, an intermediate layer of connective tissue and hepatocytes, and a basal layer of endothelial cells. Dexamethasone, EGF, and HGF are required for the complete histological organization. Analysis of the structures formed demonstrates that the receptor tyrosine kinase ligands HGF and EGF are required for the presence, growth, and phenotypic maturation of the biliary epithelium on the surface of the cultures and for the formation of connective tissue in the cultures. Dexamethasone, in the presence of HGF and EGF, was required for the phenotypic maturation of hepatocytes. The results demonstrate the role of these molecules for the formation and phenotypic maturation of specific histological elements of the liver and suggest roles for these signaling molecules in the formation and structure of the in vivo hepatic architecture.

FK506 promotes liver regeneration by suppressing natural killer cell activity

We examined the mechanism of promotion of liver regeneration by tacrolimus hydrate (FK506), a potent immunosuppressant, after partial hepatectomy. The administration of FK506 significantly increased the bromodeoxyuridine (BrdU) labelling index at 36 and 48 h after 70% hepatectomy compared with the placebo group. Using the same model, we examined the effect of FK506 on the expression of hepatocyte growth factor (HGF) and transforming growth factor-beta 1 (TGF-beta 1) and found no changes in HGF and TGF-beta 1 mRNA expression in the liver or in the HGF protein concentration in plasma. We found that pretreatment with FK506 markedly reduced the activity and number of liver-resident natural killer (NK) cells at the time of partial hepatectomy. Our observations suggest that the promotion of liver regeneration by FK506 may be attributable to a reduction in the number of liver-resident NK cells and to inhibition of their activity.

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.

Effect on the canine Eck fistula liver of intraportal TGF-beta alone or with hepatic growth factors

Transforming growth factor-beta canceled the hepatocyte proliferation caused by transforming growth factor-alpha when the two substances were mixed and administered through a disconnected central portal vein branch after creation of an Eck fistula. In contrast, transforming growth factor-beta had no antidotal action on the stimulatory effects of insulin or full test doses of insulinlike factor-2, hepatocyte growth factor, epidermal growth factor or triiodothymanine. A minor antidotal effect on hepatic stimulatory substance activity could be detected, but only with hepatic stimulatory substance was given in doses smaller than those known to cause maximum stimulatory response. These results suggest a highly specific pharmacological and physiological interaction between transforming growth factor-alpha and transforming growth factor-beta in the modulation of liver growth control.