The characterization and partial purification of hepatocyte proliferation factor

Insights into the role of interleukin-6 in the induction of hepatic injury after trauma-hemorrhagic shock

Although systemic interleukin-6 (IL-6) level is elevated, hepatocellular function is impaired and liver injury occurs after trauma-hemorrhage (T-H), it remains unknown whether a causal relationship exists between elevated IL-6 levels and liver injury after T-H. We hypothesized that IL-6 is causative in the development of hepatic dysfunction and injury after T-H. To examine this, adult male Sprague-Dawley rats underwent a 5-cm midline laparotomy and were subjected to hemorrhagic shock (blood pressure = 35 mmHg for ∼90 min), followed by resuscitation (Ringer lactate, 4 times the shed blood volume). At 2, 5, and 24 h thereafter, blood samples were collected and the liver isolated and perfused for 60 min. Portal inflow pressure was measured, and perfusate samples were collected to measure IL-6, alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) levels. A significant positive correlation between plasma levels of IL-6 and ALT and perfusate levels of IL-6 and LDH levels was observed. In a second series of experiments, rats were treated with immunoglobulin G (IgG) or antibodies against rat IL-6 (anti-IL-6) at the onset of resuscitation. At 5 h after resuscitation, anti-IL-6 treatment attenuated the T-H induced increases in plasma ALT and thromboxane B2 (a thromboxane A2 metabolite) levels, and bile flow was normalized to sham levels. Perfusion of livers from normal rats with IL-6 did not alter portal pressure; however, perfusion of a stable thromboxane A2 analog dose dependently increased portal pressure. Thus IL-6 plays a significant role in the induction of hepatic dysfunction and liver injury after T-H that appears to be in part mediated by increased thromboxane A2 levels.

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.

Beneficial effect of hepatic stimulatory substances on the survival of intrasplenically transplanted hepatocytes

Intrasplenic hepatocyte transplantation has been demonstrated to have a tentative role in treating experimental liver disease, but methods for promoting the rapid proliferation of intrasplenic hepatocytes are still quite limited. In this study, hepatic stimulatory substances (HSS) obtained from regenerating porcine livers were injected directly into the subcutaneously translocated spleens of recipient rats that had received intrasplenic hepatocyte transplantation. The clusters of intrasplenic hepatocytes contained more than 100 cells, and formed cord structures at 2 wk after transplantation, and the hepatocytes still survived at 6 wk in the HSS-treated rats. In contrast, the clusters contained less than 10 hepatocytes at 2 wk after transplantation, and no surviving hepatocytes was observed at 4 and 6 wk in control rats. Additionally, marked proliferation of bile ductular-like structures appeared around the clusters of surviving hepatocytes in the splenic red pulp of the HSS-treated rats, but were not found in control rats at 4 and 6 wk after transplantation.

Effect of pancreaticobiliary diversion on liver regeneration

To ascertain whether the increase in cholecystokinin (CCK) level associated with pancreaticobiliary diversion has a cytoproliferative effect on the liver similar to that on the pancreas, we studied three groups of rats: group I (n = 19) had a pancreaticobiliary diversion and 4 weeks later a 70% liver resection, group II (n = 13) had a liver resection only, and group III (n = 6) underwent a sham liver operation. Tissue samples were taken from the liver and pancreas 48 h after the liver operation. Liver regeneration was evaluated on the basis of continuous incorporation of tritiated thymidine into hepatocytes, liver weight, and DNA content. For confirmation of the increase in CCK levels the effects on the pancreas was studied by measuring wet weight, total protein, and total DNA content. The results showed trophic effects on the pancreas, as expected, but no effects whatsoever on liver regeneration. CCK does not seem to have any role in the regulation of liver regeneration.

Factors controlling pancreatic islet neogenesis

We have established a model in which cellophane wrapping induces reiteration of the normal ontogeny of beta-cell differentiation from ductal tissue. The secretion of insulin is physiologic and coordinated to the needs of the animal. Streptozotocin-induced diabetes in hamsters can be "cured" at least half the time. There appears to be activation of growth factor(s) within the pancreas, acting in an autocrine, paracrine, or juxtacrine manner to induce ductal cell proliferation and differentiation into functioning beta cells. Given the results of our studies to date, it does not seem premature to envisage new approaches to the treatment of diabetes mellitus. Identification of the factor(s) regulating islet-cell proliferation and differentiation in our model may permit islets to be grown in culture. This concept could be extended to induce endocrine cell differentiation in vitro as well. Furthermore, islet-cell growth factors could be used to provide "trophic support" to islet transplants as a means of maintaining graft viability. There may also be greater scope for gene therapy when the growth factor(s) have been isolated, purified, sequenced, and cloned.

Availability of energy substrates during liver regeneration in malnourished rats

A retarded liver regeneration rate during malnutrition has previously been reported. To explore the mechanisms, some energy substrates were studied during liver regeneration and malnutrition. Forty-one rats were allocated to one of three groups (G): GI were normally nourished rats, which were partially hepatectomized; GII were semistarved rats, which were partially hepatectomized; and GIII were normally nourished rats, which were sham-operated. Biopsy specimens were taken from the liver at the time of partial hepatectomy and when they were killed after 48 h of regeneration. The samples were analysed for adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), glycogen, lactate, and pyruvate, and energy charge potential (ECP) was calculated. ATP, ECP, and glycogen levels were decreased in the malnourished group before the resection. After 48 h of regeneration all values were unchanged in the normally nourished group, whereas ATP, ADP, and ECP were increased in the malnourished group compared with the initial values. The lactate/pyruvate quotient was increased in malnourished rats compared with normal rats. The results suggest that the energy supply is not a limiting factor for the reduced regeneration rate seen in malnourished animals.

Hepatocyte growth inhibitory factor derived from HTLV-I(+) T cell lines: effect on the epidermal growth factor-dependent proliferation of rat hepatocytes

A human T cell leukemia virus-I infected T cell line, ATL-2, produces an interleukin-2 receptor inducing factor, adult T cell leukemia (ATL)-derived factor (ADF). In the conditioned medium (CM) of ATL-2, we found an inhibitory activity on the epidermal growth factor (EGF)-dependent proliferation of primary cultured rat hepatocytes, measured by cell number and [3H]thymidine incorporation. ATL-2 CM dose-dependently inhibited hepatocyte proliferation. This activity was fractionated by gel filtration at a molecular size of 15,000 to 40,000 and was tentatively called hepatocyte growth inhibitory factor (HGI). Further fractionation with the ion-exchange column indicated that HGI was separable from ADF. Nevertheless, there was a positive correlation between HGI and ADF production, because the HGI activity was also detected in the CM of another ADF producer cell line (HUT102), while no significant HGI activity was detected in the CM of low ADF producer cell lines, ED and MOLT4.

Human hepatic regenerative stimulator substance: partial purification and biological characterization of hepatic stimulator substance from human fetal liver cells

Current support or replacement therapies for fulminant acute hepatic failure are frequently very disappointing. In this study, human hepatic stimulator substance--a liver-specific growth factor--was partially purified from human fetal liver cells and characterized by its biological effects. Almost 70-fold protein content was purified with an approximately 80-fold increase in specific growth stimulator activity. Human hepatic stimulator substance proved to be heat-stable, protease-sensitive, organ-specific and species-nonspecific. Human hepatic stimulator substance produced a two- to threefold increase of 3H-thymidine incorporation into hepatic DNA when injected intraperitoneally into growing weanling mice (nonhepatectomized) or regenerating rats (34% hepatectomy). The effects of hHSS in reversing the lethality of D-galactosamine (1.6 gm/kg body weight)-induced hepatic necrosis in rats were further evaluated. A survival rate of 4% (n = 24), 41% (n = 12, p less than 0.05), 33% (n = 12, p less than 0.05), 31% (n = 13, p less than 0.05) and 18% (n = 11, p greater than 0.05) was observed when the rats were injected with 4 ml of saline intraperitoneally, 4 ml of human intact fetal hepatocytes (2.4 x 10(8] intraperitoneally, 4 ml of human hepatic stimulator substance intraperitoneally, 2 ml of twofold concentrated human hepatic stimulator substance intravenously and 1 ml of fourfold human hepatic stimulator substance intramuscularly, respectively, 20 hr after poisoning.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatocyte regeneration after partial hepatectomy occurs even under severely thrombocytopenic conditions in the rat

In order to investigate the role of blood platelets in regenerative proliferation of hepatocytes in vivo, partial hepatectomy was carried out under conditions of severe thrombocytopenia achieved by X-irradiation and the time-dependent degree of hepatocyte regeneration was measured as labeling index (LI) after 3H-thymidine injection. LI values reached a maximum 36 h after hepatectomy performed 7 days subsequent to a whole-body irradiation of 7.5 Gy, although the maximum rate was found to be only about one-third of that found in unirradiated control rats. At this time point, the number of peripheral blood platelets was decreased to about 2% of that of unirradiated controls and bone marrow megakaryocytes were virtually undetectable. A decrease of LI, similar to that found for the whole-body irradiation in degree, was also observed after local irradiation of the liver with the same dose but without an apparent decrease in platelets. When whole-body irradiation was performed with the liver shielded, under which conditions the numbers of blood platelets decreased to about 8% of the control levels, almost no decrease in LI was found. The results thus suggest that the observed inhibition of hepatocyte regeneration was directly due to liver irradiation and that depletion of blood platelets itself does not interfere with the regeneration process, providing evidence against a dominant role of the platelets in the regeneration as proposed by other authors.

Response of cultured hepatocytes to a hepatomitogen after initiation by conditioned medium or other factors

Injection of a substantially purified hepatomitogen into recipient rats that had 40% of their liver removed resulted in a significant stimulation of hepatic DNA synthesis as determined by the labeling index and the mitotic index. Normal or sham-operated rats did not respond to the injection of the mitogen. The extraction and partial purification of this hepatomitogen have previously been reported (A. Francavilla et al., Cancer Res., 47:5600-5605, 1987). Addition of the factor to an epithelial-like liver-derived cell line in culture (clone 9) or to a hepatoma cell line (HTC-SR) resulted in a dose-dependent stimulation of DNA synthesis. Hepatocytes in primary culture, on the other hand, were not stimulated by the addition of the factor. However, when the mitogen was added to hepatocytes in primary culture, together with conditioned medium, obtained from the responsive cell lines, a significant stimulation of DNA synthesis could be demonstrated in hepatocytes in culture. The stimulation was dose dependent with respect to the mitogen, was abolished by 10 mM hydroxyurea, and was independent of epidermal growth factor. The conditioned medium could be replaced by a protein factor extracted from the two cell lines as previously reported (P. Ove et al., J. Cell. Physiol., 131: 165-174, 1987). It appears that a cofactor is provided by the conditioned medium or by the cell extract, enabling the hepatomitogen to act on hepatocytes in primary culture.

Altered responsiveness of metastatic versus non-metastatic fibroblasts to heparin-binding growth factors

Cells may become more metastatic partially by gaining growth factor autonomy. This hypothesis was examined by investigating the effects on DNA synthesis of a novel hepatic heparin-binding growth factor (HBGF), and of the well-characterized HBGF, basic fibroblast growth factor (bFGF), using cells of varying metastatic potential. Cells were rendered metastatic by transfection of parental 10T 1/2 fibroblasts with the T24-H-ras oncogene. Both HBGFs stimulated DNA synthesis 2.0-11.1 fold in 10T 1/2 cells in the presence of alpha-minimal essential medium containing 10% fetal bovine serum. In contrast, cells of intermediate metastatic potential or of high metastatic potential, were inhibited approximately 2-fold by the hepatic HBGF, and did not respond to bFGF in alpha-minimal essential medium plus 10% fetal bovine serum. This lack of stimulation was converted to an enhancement of DNA synthesis in the absence of serum when using metastatic but not non-metastatic cells. This is the first demonstration that metastatic cells have a significantly altered responsiveness to these growth factors as compared to non-metastatic parental cells, and indicates that these modifications may play a role in a mechanism of tumor progression.

Extraction and partial purification of a hepatic stimulatory substance in rats, mice, and dogs

A factor has been isolated from weanling rat liver which stimulates in vivo hepatic DNA synthesis in a dose dependent manner when injected into 40% hepatectomized rats. The factor has been partially purified by successive steps, involving ethanol precipitation, ultrafiltration through an Amicon PM 30 membrane, and finally fast protein liquid chromatography, resulting in a 38,000-fold increase in specific activity over that in the original cytosol. The factor contains a few bands in the molecular weight range of 14,000-50,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Active fractions from fast protein liquid chromatography (F150), when injected into 40% hepatectomized rats, increased hepatic DNA synthesis 3-fold over the background stimulation due to the hepatectomy. The response was dose dependent over a range from 1.76 micrograms to 6.8 micrograms per 200-g (body weight) rat. Mitotic and labeling indexes confirmed that F150 stimulates both replicative DNA synthesis and cell proliferation. The factor is heat and neuraminidase resistant, trypsin sensitive, organ specific, but not species specific.