Liver-specific growth factors

Mass Transfer Limitations to the Performance of Membrane Bioartificial Liver Support Devices

A number of membrane bioartificial devices have been proposed for liver support. However, their design does not yet ensure the successful treatment of acute liver insufficiency. In this paper, the Author reviews the limitations of the mass transport phenomena to the performance of a membrane bioartificial liver support device. First of all the requirements that an optimal membrane bioartificial liver support device has to meet for the therapy to be effective are presented. On these grounds, the issues that are still to be addressed to optimize the performance of such devices are discussed: particular attention is devoted to the mass transport phenomena in each region of the membrane bioartificial device. Finally, the main transport features of the membrane bioartificial liver support devices proposed so far are illustrated and examined.

Collagen Gel Immobilisation Provides a Suitable Cell Matrix for Long Term Human Hepatocyte Cultures in Hybrid Reactors

An easy to apply culture technique is presented that protects a monolayer configuration of liver cells within an extracellular matrix. The Immobilising Gel (IG)-Technique not only preserves hepatocyte morphology and supports a variety of differentiated cell functions over long term periods, but also offers higher resistance of IG-culture systems against shear forces of fluids in a hybrid reactor device, as compared to other culture techniques. Human hepatocyte cultures in IG-Technique: DNA-normalised levels for the total production of cholinesterase, albumin, urea and lactate remained high throughout the investigational period (50 days). Glutamic-Pyruvic-Transaminase (GPT) release decreased after peak values during early culture adaptation. Electron Microscopic (EM) findings after the shear forces experiment revealed undisturbed subcellular structures and a preserved intercellular morphology, including bile canaliculi and desmosomes. We conclude that the IG-technique is of considerable advantage as compared to other culture systems, especially in the field of dynamic applications, e.g. hybrid reactors for artificial organ development.

Granulocyte colony-stimulating factor impairs liver regeneration in mice through the up-regulation of interleukin-1beta

BACKGROUND/AIMS

Stem cell induction via granulocyte colony-stimulating factor (G-CSF) administration is utilized in the treatment of various diseases. Therefore, we examined the effect of G-CSF administration to a liver fibrosis model induced by dimethylnitrosamine (DMN).

METHODS

ICR mice were subcutaneously injected with either G-CSF (150microg/kg) or saline at days 0, 3, 7 and 10. Subacute liver injury was established by intraperitoneal injection of DMN (10mg/kg) on three consecutive days of each week.

RESULTS

G-CSF administration significantly decreased the survival rate of mice treated with DMN. There was no difference in the degree of liver injury or fibrosis between either group of mice. However, assessment by proliferating cell nuclear antigen (PCNA) revealed that the G-CSF-treated mice experienced a greater degree of inhibition of liver cell proliferation than the control mice. Interleukin-1beta (IL-1beta) mRNA expression increased in the livers of G-CSF-treated mice. PCNA staining and analysis of cell cycle-related proteins also revealed that passive immunization with anti-IL-1beta-neutralizing antibody improved the impaired hepatocellular regeneration and resulted in an improved survival rate of mice treated with G-CSF and DMN.

CONCLUSIONS

G-CSF administration suppressed liver cell proliferation through the up-regulation of IL-1beta expression in DMN-induced liver injury.

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.

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.

Effect of hepatic stimulator substance administration on tissue regeneration due to thioacetamide-induced liver injury in rats

BACKGROUND

Hepatic stimulator substance (HSS) is a known hepatic growth factor that appears to be organ-specific but species-nonspecific. In the present study we investigated the effect of HSS administration in a rat model of liver injury and regeneration induced by thioacetamide (TAA) injection.

METHODS

TAA (300 mg/kg body weight) was injected intraperitoneally in male Wistar rats (group I). HSS (50 mg protein/kg body weight) was administered intraperitoneally either at 24 h (group II) or at 36 h (group III) after TAA treatment. The animals were killed at different time points after TAA injection, and the rate of tritiated thymidine incorporation into hepatic DNA, the activity of the enzyme thymidine kinase in liver, and the assessment of the mitotic index in hepatocytes were used to estimate liver regeneration.

RESULTS

The administration of TAA caused severe hepatic injury recognized histopathologically and by increased activities of the serum hepatic enzymes aspartate and alanine aminotransferases. The hepatic injury, which peaked at 24 h and 36 h after TAA injection, was followed by a regenerative process of hepatocytes which presented peaks after 48 h and 60 h (group I). The regenerative process of hepatocytes remained unaffected when HSS was administered 24 h after the injection of TAA (group II). In the case of HSS administration 36 h after the injection of TAA (group III) the examined indices of hepatocyte proliferation were statistically significantly increased at 48 h (P < 0.001), compared with those observed in group I.

CONCLUSIONS

The administration of HSS enhanced the hepatocyte proliferative capacity, induced by TAA treatment, depending on the time of its administration.

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.

Immunohistochemical analysis of retinoblastoma gene product (pRB) expression in malignant and non-malignant liver diseases

The retinoblastoma gene product is a nuclear phosphoprotein that undergoes cell cycle-dependent changes in its phosphorylation status. To analyze the expression of retinoblastoma gene product in the process of liver regeneration and the initiation of hepatocellular carcinoma, we studied immunohistochemically the expression of retinoblastoma gene product and DNA polymerase alpha (DPA) in 33 patients with various liver diseases. Only a few hepatocytes positive for retinoblastoma gene product were found in undamaged, nonregenerating liver tissues, whereas many hepatocytes positive for retinoblastoma gene product were detected in specimens of regenerating liver obtained from patients with acute or chronic liver diseases. Similarities were found between distribution patterns of hepatocytes positive for retinoblastoma gene product and those of hepatocytes positive for DPA, and a highly significant positive correlation was found between the number of hepatocyte nuclei stained for retinoblastoma gene product per 1000 nuclei examined (R-LI) and the number of hepatocyte nuclei stained for DPA per 1000 nuclei examined (D-LI) in tissues obtained from patients with nonmalignant liver disease. Hepatocellular carcinoma cells positive for DPA were detected in the 14 hepatocellular carcinoma specimens tested. In ten of these specimens, hepatocellular carcinoma cells positive for retinoblastoma gene product were found but not in the other four. For all hepatocellular carcinoma specimens, R-LI was proportional to D-LI. Thus in both nonmalignant and malignant liver, retinoblastoma gene product increased in proportion to proliferation of hepatocytes or hepatocellular carcinoma cells.

Concurrent changes in sinusoidal expression of laminin and affinity of hepatocytes to laminin during rat liver regeneration

Distribution of fibronectin, laminin, and collagens type I, III, IV, and V in the lobular regions of regenerating rat liver was studied by indirect immunofluorescence. Little or no laminin was detected in sham-operated controls throughout the experimental period, while it was detected in sinusoids of regenerating liver as early as 6 h after partial hepatectomy (PH). After reaching a maximum at 24 h, it decreased and was barely detectable 6 days after PH. Changes in the other extracellular matrix (ECM) proteins were evident 3 days after PH, but not earlier than 24 h. Hepatocytes isolated from regenerating rat livers were tested in a short term assay for attachment to the substrates coated with the ECM proteins. The attachment of hepatocytes to laminin substrates increased 12 h after PH, reached a maximum at 24 h, and decreased to the control level 6 days after PH, while that of the control remained constant. The attachment to fibronectin substrates was not different between regenerating livers and controls at any time point. The attachment to collagen did not change earlier than 24 h after PH, but increased slightly 3 days after PH. Primary rat hepatocytes cultured on the substrates coated with the ECM proteins were determined for replicative DNA synthesis in response to epidermal growth factor. Both in normal liver and in regenerating liver 24 h after PH, laminin was one of the most effective substrates in supporting the responsiveness of hepatocytes to the growth stimulus. Taken together, these results suggest the importance of hepatocyte-laminin interaction during the early stage of liver regeneration possibly in growth stimulation of hepatocytes and/or maintenance of hepatocyte-specific functions.

Structural and functional aspects of regeneration of human liver

Regeneration of human liver was long suspected to occur. It was proven in animals 100 years ago but could not be demonstrated in man until liver biopsy and modern hepatic tests became available. Structural changes in the regenerating liver mainly concern the arrangement of liver cell plates and the size and appearance of hepatocytic nuclei. A return to normalcy in test results depends on the factors responsible for regeneration since various test results change at different rates. Mass, estimated by imaging procedures, is restored parallel with the return of function. Shape is not restored but the pressure of neighboring organs and structures molds the growing remnant so that it almost resembles the original. Factors regulating regeneration in man are beginning to be recognized as they have been in animals. The hope is that regeneration can be accelerated or that cells can be transplanted to replace those lost.

Protooncogenes and growth factors associated with normal and abnormal liver growth

Hepatocyte replication during liver regeneration depends on extrinsic (circulating) and intrinsic (intrahepatic) factors. Two important growth factors produced in the regenerating liver are discussed, TGF alpha, an autocrine, stimulatory growth factor, and TGF beta, a paracrine inhibitory factor. The balance between the activities of these factors is likely to play an important role in regulating hepatocyte proliferation. The expression of some protooncogenes occurs sequentially during the first few hours after partial hepatectomy and is a marker for the entry of hepatocytes into the cell cycle (proliferative competence). As hepatocytes become competent to proliferate, they respond to TGF alpha and other growth factors and enter a proliferative phase. It is possible that TGF beta 1 serves as a stop signal for liver regeneration but the mechanisms by which TGF beta inhibits hepatocyte DNA synthesis are still unknown.

Induction of hepatocyte mitosis in intact adult rat by interleukin-1 alpha and interleukin-6

In the adult rat the liver is normally quiescent, but it proliferates rapidly in response to partial hepatectomy (PH). A hepatectomized rat is subjected to stress by the operation. We have examined the effects of acute phase cytokines. To investigate the mediation of hepatocyte growth, recombinant human interleukin-1 alpha (IL-1) and interleukin-6 (IL-6) were injected into male rats. Administration of IL-1 or IL-6 followed by NH4Cl and glucagon could induce hepatocyte mitosis 30 h after the first injection. This activity was lost when interleukins were exposed to 90 degrees C for 30 minutes. NH4Cl augmented the effects of IL-1 and IL-6. These results suggest that the IL-1 and IL-6 are important mediators of liver regeneration after PH. We present a hypothesis for the triggering mechanism of hepatocyte proliferation.

Serum changes the response of cultured Morris hepatoma 7777 cells to autocrine growth factors

The addition of calf serum to culture medium alters the biological response of Morris hepatoma 7777 (MH) cells to autocrine growth factors isolated from conditioned medium of the investigated cells. Acetic acid (AA) extract obtained from conditioned medium of MH cells showed a change in anchorage-independent growth-regulatory activity from stimulation (serum-free) to inhibition (10% calf serum). Two protein fractions of apparent molecular weight 15 and 7.5 kDa isolated from AA-extract by Bio-Gel P-60 filtration also changed their growth-regulatory activity after supplementation of culture medium with calf serum. The contradictory effect of autocrine regulators estimated in soft agar using the 3H-thymidine (3H-TdR) incorporation test and colony formation assay gave generally comparable results, except in the case of the 15-kDa fraction. The most active 7.5-kDa fraction stimulated 3H-TdR incorporation and colony formation in serum-free medium up to about 300 and 500% respectively, while in the presence of 10% calf serum inhibition of about 20 and 50% has been observed. Our results suggest that the fraction contains an autocrine growth factor(s), whose activity is inverted in the presence of serum.

Transient induction of c-jun during hepatic regeneration

The cellular oncogene c-jun is transiently expressed in cultured cells stimulated to proliferate but has not been identified in normal liver. Because partial hepatectomy results in coordinated cell proliferation in the remaining liver, we investigated c-jun expression after partial hepatectomy in mice. Northern analysis of whole liver mRNA demonstrated a transient increased expression of c-jun within half an hour of the operation. The related gene junB increased only 50%, whereas c-jun expression increased 13-fold compared with sham-operated controls. To determine the cell of origin of the c-jun transcript, both in situ hybridization and Northern analysis of mRNAs from parenchymal and nonparenchymal cell fractions were performed 2 hr after partial hepatectomy. C-jun expression was found in both cell populations. To investigate the mechanism of increased c-jun expression, cycloheximide was given to some animals preoperatively. C-jun induction occurred with cycloheximide alone, but partial hepatectomy further increased c-jun expression, indicating that new protein synthesis was not required for this effect. Furthermore, run-on transcriptional assay demonstrated a twofold increase in c-jun expression. Thus c-jun expression increases after hepatectomy by transcriptional and posttranscriptional mechanisms. Because the extracellular matrix-degrading enzyme transin, which bears the recognition site for jun/AP-1, showed sustained induction after hepatectomy, we speculate that an important function of c-jun expression could be the remodeling of extracellular matrices to accommodate cell proliferation.