Modulation of functional activities in cultured rat hepatocytes

Effect of growth hormone on alcohol dehydrogenase activity in hepatocyte culture

The effect of growth hormone on the activity of alcohol dehydrogenase was determined in hepatocyte culture from normal and hypophysectomized male rats. Alcohol dehydrogenase activity was highest in hepatocytes harvested from hypophysectomized rats. The enzyme activity remained stable in hepatocytes harvested from normal rats during 2 to 6 days of culture but declined steadily in hepatocytes cultured from hypophysectomized rats. The combination of growth hormone (1 microgram per ml) and corticosterone (1 microM) increased alcohol dehydrogenase activity in hepatocytes from normal rats, while neither hormone alone had an effect. Corticosterone (1 microM) prevented the decline of the enzyme activity in hepatocytes from hypophysectomized rats, and the combination of growth hormone (1 microgram per ml) and corticosterone (1 microM) resulted in a further increase in enzyme activity. The increases in alcohol dehydrogenase, due to the exposure of the hepatocytes to the combination of growth hormone and corticosterone, were associated with increases in the rate of ethanol elimination. These observations indicate that growth hormone enhances liver alcohol dehydrogenase activity and ethanol elimination, and that this effect is dependent on the permissive influence of corticosterone.

Essential fatty acid uptake and esterification in primary culture of rat hepatocytes

Primary cultures of adult rat hepatocytes were used to compare the uptake and esterification of essential polyunsaturated fatty acids (18:2, 20:3 and 20:4 of the n-6 series) with those of palmitic and oleic acids. The uptake of unesterified fatty acids was linearly related to the free fatty acid/albumin molar ratio for 14 h and did not depend on the unbound free fatty acid level. Whatever the initial free fatty acid/albumin molar ratio, it dropped to 0.5 +/- 0.1 mM after 14 h, thus showing that hepatocytes have a high capacity for clearing free fatty acids from the medium at high free fatty acid/albumin molar ratios. The free fatty acid uptake become saturable when the free fatty acid and albumin concentrations were raised and the free fatty acid/albumin ratio remained constant. This strongly suggests that albumin-hepatocyte interaction mediates free fatty acid uptake. This uptake was identical whatever the fatty acid tested and did not depend on the relative amounts of fatty acids when they were added simultaneously. Triacylglycerol accumulation and synthesis, monitored by labelled fatty acids, were related to the free fatty acid/albumin molar ratio and exhibited no specificity for the series of fatty acids tested. Triacylglycerols were enriched in all the fatty acids tested by up to 60%, and fatty acid incorporation into diacylglycerols and triacylglycerols reflected the free fatty acid composition of the medium. By contrast, neither the level nor the synthesis of phospholipids varied with free fatty acid/albumin, but the rate of phospholipid turnover depended on the fatty acids tested. Accumulation of these acids was smaller in phospholipids than in triacylglycerols. When linoleic and arachidonic acids were added together, phospholipids (especially phosphatidylethanolamine and phosphatidylinositol) were more enriched in arachidonic acid than triacylglycerols. This might be due to the specificity for fatty acid of the enzymes involved in phospholipid metabolism.

Long-term biosynthesis of complement component C3 and alpha-1 acid glycoprotein by adult rat hepatocytes in a co-culture system with an epithelial liver cell-type

We used a system of co-culture of adult rat hepatocytes with another epithelial cell type from rat liver to study the synthesis of two acute-phase reactants, alpha-1 acid glycoprotein (alpha 1AGP) and the third component of complement (C3), and we have obtained long-term secretion of these two proteins. After a period of adaptation corresponding to the first 2-4 days of the co-culture, hepatocytes secreted C3 and alpha 1AGP for at least 2 weeks at a mean level higher than that observed in the first days of a pure culture of hepatocytes. When pulse-chase analysis was performed on day 6 of co-culture, kinetics of synthesis of alpha 1AGP and C3 were the same as those observed on day 1 of a conventional culture of pure hepatocytes. Furthermore, intracellular and extracellular alpha 1AGP had Mr values respectively of 39,000 and of 42,000-52,000, identical with those observed in pure cultures of hepatocytes. Similarly, the molecular size and subunit structures of C3 were the same in co-culture and in cultures, indicating an identical processing of this protein. C3 produced in co-culture was also haemolytically active. Therefore, the system of adult hepatocytes co-cultured with this liver epithelial cell provides a physiological system in vitro which permits long-term synthesis of the two acute-phase reactants C3 and alpha 1AGP. This model opens the possibility to study the modulation of the synthesis of these two proteins during a long period by inflammatory agents or by hormones.

Cell types involved in collagen and fibronectin production in normal and fibrotic human liver

Three collagen types (I, III and IV) and fibronectin were localized in normal and alcoholic human liver by light and electron microscopy using the indirect immunoperoxidase technique. In normal liver, most of the bundles of collagen fibers stained for type pro-III collagen while only a few reacted for type I. Basement membranes stained for type IV collagen which formed discontinuous discrete deposits in sinusoids. Only fibronectin appeared as an almost continuous layer in the space of Disse. At the intracellular level, hepatocytes were found to contain little type I collagen and large amounts of fibronectin. Fat-storing cells strongly stained for type IV collagen and expressed low amounts of types I and III collagen and fibronectin. Endothelial cells contained low amounts of all the components. Alcoholic livers were studied at three stages: steatosis, fibrosis and cirrhosis. Qualitative and quantitative differences were observed in extracellular and intracellular distributions of matrix proteins. Increased amounts of all components were usually found in fibrotic and cirrhotic livers compared to normal liver. In two fibrotic livers which contained numerous bundles of collagen in the sinusoids, fat-storing cells stained more intensely for type III collagen. In a cryptogenic fibrotic liver, abundant type IV collagen was observed in hepatocytes. These results suggest that hepatocytes, fat-storing cells and endothelial cells are engaged in production of extracellular matrix components in normal human liver. In fibrosis, hepatocytes which normally did not synthesize types III and IV collagen may produce these collagens.

Two types of growth inhibitor in rat platelets for primary cultured rat hepatocytes

Rat platelets contain two types of growth inhibitor of adult rat hepatocytes in primary culture. One, named platelet derived growth inhibitor (PDGI)-alpha, is a heat- and acid-labile protein with a molecular weight of over 200 KD that is not released on thrombin treatment. The other, named PDGI-beta, is a heat- and acid-stable factor with a molecular weight of 24 KD that is released by thrombin. Both PDGI-alpha and -beta were inactivated by treatment with dithiothreitol. They both caused dose-dependent inhibition of DNA synthesis stimulated by insulin plus epidermal growth factor. These inhibitions were closely correlated with marked decrease in the labeling index. Neither PDGI-alpha nor -beta had a cytotoxic effect as judged by phase-contrast microscopic examination of the cells nor inhibition of protein synthesis. The properties of PDGI-beta suggest that it may be identical with transforming growth factor-beta. These results indicate that rat platelets contain not only a growth factor (HGF), but also growth inhibitors that affect adult rat hepatocytes.

Inhibitory effect of transforming growth factor-beta on DNA synthesis of adult rat hepatocytes in primary culture

A transforming growth factor-beta (TGF-beta) found in platelets strongly inhibited DNA synthesis of adult rat hepatocytes in primary culture stimulated by insulin plus EGF or by hepatocyte growth factor (HGF) from rat platelets, but not the syntheses of secretory and intracellular proteins by the cells. TGF-beta had no cytotoxic effect, as judged by phase-contrast microscopic examination of the cell morphology. The inhibition of DNA synthesis by TGF-beta was correlated with marked decrease in the labeling index. TGF-beta did not inhibit growth of hepatoma cell line. These findings indicate that TGF-beta is a strong growth inhibitor of adult rat hepatocytes and may block their shift from the G1 phase to the S phase. The physiological role of TGF-beta in inhibiting growth of adult hepatocytes during liver regeneration is discussed.

Effects of dexamethasone on albumin and collagen gene expression in primary cultures of adult rat hepatocytes

To further our studies on collagen gene expression, we have evaluated the molecular basis for the finding that steroids decrease collagen synthesis in cultured hepatocytes. We studied the effects of dexamethasone on primary cultures of adult rat hepatocytes grown on tissue culture plastic in either serum-supplemented medium or a serum-free hormonally defined medium. Cells were plated and allowed to attach for 24 hr in a mixture of serum-supplemented medium + hormonally defined medium. Cultures were then fed every 24 hr for 4 days under 1 of 4 conditions: serum-supplemented medium, serum-supplemented medium + dexamethasone, hormonally defined medium or hormonally defined medium + dexamethasone. On the fifth day, RNA was extracted. Dexamethasone did not affect the amount of RNA isolated; nor did it influence the quantitative translation of the mRNA in the rabbit reticulocyte lysate mRNA-dependent system. Employing hybridization analysis, dexamethasone resulted in increased albumin mRNA content in hepatocytes grown in serum-supplemented medium but had no affect on hormonally defined medium, and decreased type I in collagen mRNA content in cells grown in either serum-supplemented medium or hormonally defined medium. In cells cultured in hormonally defined medium, the beta-actin and procollagen mRNA levels were lower than those in serum-supplemented medium, but albumin mRNA levels were higher, and in fact equivalent to those in vivo. beta-Actin mRNA levels were not affected by dexamethasone in either serum-supplemented medium or hormonally defined medium.(ABSTRACT TRUNCATED AT 250 WORDS)

The acute-phase response of cultured rat hepatocytes. System characterization and the effect of human cytokines

Hepatocytes were isolated from adult livers and cultured for periods of up to 5 days as monolayers at an initial density of 10(6) cells/10cm2 in Williams E medium containing insulin, dexamethasone and 5% foetal-calf serum. The daily production of 11 plasma proteins was measured by electroimmunoassay and compared with the concentrations of the same proteins in the plasma of normal rats and of those with experimental inflammation. Hepatocytes from normal rats synthesized proteins in relative amounts which were similar to the relative proportions of the same proteins in the plasma of turpentine-injected animals. The pattern changed only slowly during 5 days in culture, but it did so profoundly either when the medium was devoid of dexamethasone or when human cytokines (from endotoxin-stimulated monocytes or unstimulated human squamous-carcinoma cell line COLO-16) were added. The cytokines consistently increased the synthesis of alpha 2-macroglobulin and fibrinogen and depressed that of albumin; variable increases in the synthesis of alpha 1-acute-phase globulin, alpha 1-acid glycoprotein, haptoglobin and alpha 1-proteinase inhibitor, and variable decreases in transferrin synthesis, were seen, whereas the synthesis of antithrombin III, alpha 1-macroglobulin and prothrombin remained virtually unaffected. The cytokine effects on protein synthesis required the presence of dexamethasone. The hepatocyte-stimulating activity derived from monocytes chromatographed on Sephadex G-100 corresponding to 30 000 Da, as opposed to the lymphocyte-activating factor, which was eluted as a molecule of approx. 15 000 Da. This suggests that both activities probably reside with distinct molecular species in the preparations of human cytokines.

Lack of coordination between glucose-6-phosphatase and gamma glutamyltranspeptidase activities in rat hepatocytes maintained in primary culture

Glucose-6-phosphatase activity decreases whereas gamma glutamyltranspeptidase activity increases during hepatocarcinogenesis and the maintenance of hepatocytes in primary culture. This report describes the effect of culture conditions that are known to preserve hepatic glucose-6-phosphatase activity on gamma glutamyltranspeptidase activity. The results indicate that the regulation of glucose-6-phosphatase and gamma glutamyltranspeptidase activities is not coordinated in primary cultures of hepatocytes.

Modulation of human fetal hepatocyte survival and differentiation by interactions with a rat liver epithelial cell line

Fetal human hepatocytes were isolated by collagenase digestion of liver fragments and cultured either alone or mixed with rat liver epithelial cells. Whereas they did not survive more than 2-3 weeks and showed rapid morphologic and functional alterations in conventional culture, fetal hepatocytes survived and retained or reverted to a globular morphology for several weeks and showed active albumin secretion for at least 13 days when cultured with rat liver cells. Increased levels of secreted albumin correlated with deposition of an insoluble extracellular material containing fibronectin and type III collagen located principally between the two cell types and around parenchymal cells. These observations show that fetal human hepatocytes are able to interact in vitro with another epithelial liver cell type obtained from a divergent species and that these cell-cell interactions influence both hepatocyte survival and expression of albumin.

Long-term co-cultures of adult human hepatocytes with rat liver epithelial cells: modulation of albumin secretion and accumulation of extracellular material

High yields of viable human hepatocytes were obtained by enzymatic perfusion of the left hepatic lobe of kidney donors and cultured alone or with an epithelial cell line derived from rat liver. In conventional cultures, human hepatocytes did not survive more than 2 to 3 weeks and by Day 8 decreased their ability to secrete albumin. When co-cultured, they survived for more than 2 months and secreted high levels of albumin even in a serum-free medium. This long-term survival appeared to correlate with production of an extracellular material which is rich in Type III collagen. In vitro phenotypic alterations of parenchymal cells were reversed by addition of rat liver cells and were characterized by recovery of cuboidal morphology, increased albumin secretion and a shift from Type I to Type III collagen deposition. Rat liver epithelial cells could not be replaced by nonhepatic epithelial cells. These observations suggest that when adult human hepatocytes are maintained in a culture which closely resembles their in vivo environment, they are capable of continuing to actively express specific cell functions.

Long term production of acute-phase proteins by adult rat hepatocytes co-cultured with another liver cell type in serum-free medium

Three acute-phase proteins, haptoglobin, alpha 2-macroglobulin and hemopexin, as well as albumin, have been measured daily in the hydrocortisone-supplemented serum-free medium of pure and mixed cultures of adult rat hepatocytes for 5 and 20 days respectively. Whereas plasma protein production rapidly declined in pure culture, it remained relatively stable when hepatocytes were co-cultured with rat liver epithelial cells. In the latter cultures, an early stimulation of albumin and alpha 2-macroglobulin secretion was observed. In addition, four other plasma proteins, fibrinogen, alpha 1-acute-phase protein, alpha 1-acid glycoprotein and alpha 1-antitrypsin were shown by immunodiffusion to still be produced by day 20 of co-culture. These results suggest that hepatocyte co-cultures represent a suitable model for studying the mechanism which controls synthesis of plasma proteins, including acute-phase proteins by liver cells.