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

Regulation of angiotensinogen gene expression in a human hepatoma cell line

Angiotensinogen is the precursor of biologically active peptide angiotensin II and its synthesis is increased in the liver during acute inflammation. We have used radiolabeled human angiotensinogen cDNA to study the effect of hepatocyte stimulating factor (HSF), a protein synthesized in differentiating monocytes which increases the synthesis of various hepatic proteins during inflammation, on angiotensinogen mRNA levels in human hepatoma cells (HepG2). Our results indicate that angiotensinogen mRNA is present in human hepatoma (HepG2) cells and its levels are decreased when treated with hepatocyte stimulating factor. Although dexamethasone elevated angiotensinogen mRNA levels, HSF reduced this increase. These results suggest that a factor other than HSF may be involved in elevating the angiotensinogen mRNA levels in the liver during inflammation.

Interferon beta 2/B-cell stimulatory factor type 2 shares identity with monocyte-derived hepatocyte-stimulating factor and regulates the major acute phase protein response in liver cells

One of the oldest and most preserved of the homeostatic responses of the body to injury is the acute phase protein response associated with inflammation. The liver responds to hormone-like mediators by the increased synthesis of a series of plasma proteins called acute phase reactants. In these studies, we examined the relationship of hepatocyte-stimulating factor derived from peripheral blood monocytes to interferon beta 2 (IFN-beta 2), which has been cloned. Antibodies raised against fibroblast-derived IFN-beta having neutralizing activity against both IFN-beta 1 and -beta 2 inhibited the major hepatocyte-stimulating activity derived from monocytes. Fibroblast-derived mediator elicited the identical stimulated response in human HepG2 cells and primary rat hepatocytes as the monocyte cytokine. Finally, recombinant-derived human B-cell stimulatory factor type 2 (IFN-beta 2) from Escherichia coli induced the synthesis of all major acute phase proteins studied in human hepatoma HepG2 and primary rat hepatocyte cultures. These data demonstrate that monocyte-derived hepatocyte-stimulating factor and IFN-beta 2 share immunological and functional identity and that IFN-beta 2, also known as B-cell stimulatory factor and hybridoma plasmacytoma growth factor, has the hepatocyte as a major physiologic target and thereby is essential in controlling the hepatic acute phase response.

Recombinant human B cell stimulatory factor 2 (BSF-2/IFN-beta 2) regulates beta-fibrinogen and albumin mRNA levels in Fao-9 cells

Conditioned medium from human monocytes contains a partially characterized hepatocyte-stimulating factor that simultaneously elevates the mRNA levels of the acute-phase protein beta-fibrinogen and decreases albumin mRNA in rat hepatoma cells. We demonstrate that recombinant human B-cell stimulatory factor 2, which is identical to interferon-beta 2/26 kDa protein and interleukin-HP1, exhibits the same activity as hepatocyte-stimulating factor. Furthermore, a specific antibody against B-cell stimulatory factor 2 was able to inhibit hepatocyte-stimulating factor in conditioned medium from human monocytes. Our data show that hepatocyte-stimulating factor and B-cell stimulatory factor 2 are functionally and immunologically related proteins.

Synthesis of hemopexin and cysteine protease inhibitor is coordinately regulated by HSF-II and interferon-beta 2 in rat hepatoma cells

Rat hepatoma (H-35) cells respond to hepatocyte-stimulating factors by increased expression of major acute phase plasma proteins. The synthesis of hemopexin is stimulated 10-fold by either hepatocyte-stimulating factor-II of human squamous carcinoma cells or hepatocyte-stimulating factor/interferon-beta 2 of activated human blood monocytes. The hormone specificity, time course and dose-dependence of hemopexin regulation is closely correlated with that of cysteine protease inhibitor. The coordinate expression of hemopexin and other type II acute phase proteins suggests the existence of common molecular regulatory mechanisms.

Restoration of the LPS responsive phenotype in C3H/HeJ macrophage hybrids: LPS regulation of hepatocyte-stimulating factor production

The fusion of thioglycollate-elicited peritoneal macrophages from lipopolysaccharide (LPS) non-responsive C3H/HeJ mice to an HPRT-negative variant of the murine macrophage cell line P388D1 has resulted in the derivation of a series of macrophage hybrids. Following exposure to LPS, these hybrids now produce the cytokine hepatocyte-stimulating factor (HSF) which induces the synthesis of the acute-phase reactant alpha 2-macroglobulin in primary rat hepatocyte cultures. The concentration of extracellular HSF was dependent upon both the duration and amount of LPS, with optimal HSF being detected after 72 hr incubation with 10 micrograms/ml of LPS. Parallel LPS-stimulated cultures treated with 10(-6)M dexamethasone did not secrete detectable amounts of HSF. Both the molecular weight (29,000 MW), and the fact that HSF activity was not inhibited by an antiserum directed against murine interleukin-1 alpha (IL-1 alpha), suggests that HSF and IL-1 are distinct cytokines. Therefore, macrophage hybrids have been derived which have acquired the LPS-responsive phenotype and which synthesize the cytokine HSF following LPS stimulation. This phenotype appears stable since similar results have been observed with these hybrids after in vitro culture for over 8 months.

Discrimination of hepatocyte-stimulating activity from human recombinant tumor necrosis factor alpha

The involvement of tumor necrosis factor alpha (TNF alpha) in the regulation of acute-phase protein synthesis is currently under discussion. In this study the effect of human recombinant TNF alpha on the regulation of the 4 acute-phase proteins alpha 2-macroglobulin, albumin, alpha 1-proteinase inhibitor and alpha 1-acute-phase globulin was investigated in rat hepatocyte primary cultures. No changes in synthesis of any of the 4 proteins were observed. However, an acute-phase response similar to that in vivo could be generated by conditioned media from human monocytes containing natural TNF alpha. This response remained unchanged after neutralizing TNF alpha activity by the addition of a specific antibody to TNF alpha. It is concluded that the hepatocyte-stimulating activity synthesized by human monocytes is different from TNF alpha.

Comparison of the acute phase response of cultured Morris hepatoma 7777 cells and of rat hepatocytes

Isolated Morris hepatoma cells (line 7777) or adult rat hepatocytes were cultured for 3 days and daily production of four plasma proteins was estimated in the cell media by rocket immunoelectrophoresis with monospecific antisera. Addition of cytokines from rat peritoneal macrophages to cultured hepatocytes or hepatoma cells augmented accumulation in the medium of two positive acute phase proteins: fibrinogen (FIB) and cysteine proteinase inhibitor (CPI). At the same time synthesis of alpha-fetoprotein (AFP) was inhibited in hepatoma cells but remained undetectable in hepatocytes. Rat macrophage cytokines typically depressed synthesis of albumin (ALB) in cultured rat hepatocytes but increased production of this protein by hepatoma cells.

The inflammation mediators interleukin 1 and hepatocyte-stimulating factor are differently regulated in human monocytes

Human peripheral monocytes can be induced by bacterial lipopolysaccharide to produce the inflammatory mediators interleukin 1 (IL 1) and hepatocyte-stimulating (HS) activity. IL1 and HS activities were separated by gel permeation chromatography. It is also shown that the two monokines are differently regulated. Evidence for this stems from the finding that monocytes cultured for 24 h lose their ability to produce IL1 in response to lipopolysaccharide, while synthesis of HS activity remains essentially unaffected.

Isolation of hepatocyte stimulating factor from human monocytes

Hepatocyte stimulating factor is a monocyte derived protein which regulates hepatic plasma protein synthesis. Human hepatocyte stimulating factor was purified to apparent homogeneity from adherent peripheral blood monocytes by using ion exchange, gel permeation and reversed phase chromatography. Electrophoretic analysis showed that it has a Mr of 28,000 daltons and an isoelectric point of 5.4. Biological assays specific for hepatocyte stimulating factor and interleukin-1 showed that they are distinct and have independent biological effects.

Kupffer cells and their function

The intention of this review is to stress new information regarding the quite versatile functions of Kupffer cells. Although their main function is phagocytosis and defence of the liver against bacteria, endotoxaemia and viral infections, they also fulfil other important roles. They will phagocytose and partially degrade bacterial antigens before handing them on to the hepatocytes for excretion into the bile. They handle LDL lipoproteins, whilst the HDL proceed directly into the hepatocytes. They produce lymphokine mediators that direct protein synthesis by the hepatocytes. Also they normally produce prostaglandins that are cyto-protective for the hepatocytes. Conversely, if they are required to attack infected hepatocytes or cancer cells, then they switch to the production of leukotrienes. Thus they function as specialised macrophages, and it is not surprising that other "activated macrophages" have to be recruited into the liver to support them in inflammatory reactions.

Influence of branched-chain amino acids and branched-chain keto acids on protein synthesis in isolated hepatocytes

We investigated the effects of the branched-chain amino acids--valine, leucine and isoleucine--or their keto analogs, the branched-chain keto acids--alpha-ketoisovaleric acid, alpha-ketoisocaproic acid and alpha-keto-beta-methylvaleric acid--on protein synthesis and secretion by monolayers of rabbit hepatocytes incubated with [35S] methionine in pulse-chase and steady-state experiments. The branched-chain amino acids (2.0 mM or 1.0 mM), in the presence or absence of insulin (2 X 10(-4) IU per dish) and in both types of experiments, reduced the trichloroacetic acid-precipitable 35S-protein secreted into the medium. The branched-chain keto acids (2.0 mM or 1.0 mM) had a stimulatory effect on secreted trichloroacetic acid-precipitable 35S-protein which was observed only by the pulse-chase technique in the presence of insulin. Immunoaffinity chromatography of medium demonstrated a slight inhibition by branched-chain amino acids and a slight stimulation by branched-chain keto acids on secretion of 35S-albumin and no effect of either treatment on secretion of 35S-fibrinogen. ELISA analysis of total (i.e., 35S-labeled and unlabeled) secreted albumin revealed an inhibitory effect of the branched-chain amino acids in both pulse-chase and steady-state experiments, and a small stimulatory effect, in steady-state experiments, of the branched-chain keto acids; both effects were insulin-dependent. Total secreted fibrinogen, under steady-state conditions, was increased by the branched-chain keto acids in the presence of insulin, while transferrin production was unaffected by any treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the effect of inflammation on the acute phase response using rat liver slices

Liver slices from control and inflamed rats were incubated in McCoy's medium and incorporation of [3H]leucine into liver and medium proteins and into albumin and alpha 1-acid glycoprotein was monitored over 48 hr. The release of the new acute phase reactant, sialyltransferase was also monitored in this system. Earlier observations in which liver slices were incubated for 6 hr showed that increased leucine incorporation into liver and medium proteins and alpha 1-acid glycoprotein, coupled with decreased incorporation into albumin, correlated with the acute phase response of these proteins. Increased incorporation of leucine into these proteins was found following 48 hr incubation in McCoy's medium showing that slices were able to express the changes characteristic of the acute phase response over this longer time period of incubation. Sialyltransferase was released into medium in a linear fashion up to 15 hr and continued to increase for 30 hr in this system; there was a substantial increase in release of enzyme activity from slices from inflamed rats when compared to controls. Monokine-conditioned medium prepared from peritoneal exudate cells isolated from rats at various times after lipopolysaccharide administration was used to induce the acute phase response by intraperitoneal injection. Slices were prepared from these rats and sialyltransferase release from slices was monitored. Monokines prepared from peritoneal exudate cells isolated from rats at about 30 hr were most effective in stimulating sialyltransferase release from liver slices.

Purified interleukin-1 (IL-1) from human monocytes stimulates acute-phase protein synthesis by rodent hepatocytes in vitro

A universal component of inflammation is the increased synthesis of a series of plasma proteins (acute-phase proteins) by the liver. The postulated messenger of acute-phase protein induction is released by leucocytes at the site of inflammation and has been shown to co-purify with endogenous pyrogen or lymphocyte-activating factor. Interleukin-1, molecular weight 17,000, pI 6 X 8-7 X 2, was purified to homogeneity from adherent human blood monocytes by a combination of affinity chromatography, gel filtration and isoelectric focusing. We examined the direct effect of pure IL-1 on the induction of acute-phase protein synthesis in vitro using rat and mouse hepatocytes. IL-1 caused significant increased synthesis of alpha 1-acid glycoprotein and smaller increases in the synthesis of other acute-phase proteins, and significant decreased synthesis of albumin. The pattern of induction of acute-phase proteins differs from that seen with a separate 30,000 molecular weight hepatocyte-stimulating factor from human monocytes described previously. We conclude that human IL-1 is one of the mediators responsible for the acute-phase protein response of the liver in inflammation and can directly cause stimulation of specific gene expression in normal hepatocytes.

Localization of DNA sequences involved in dexamethasone-dependent expression of the rat alpha 1-acid glycoprotein gene

Synthesis of rat alpha 1-acid glycoprotein (AGP), one of the major inflammation-induced plasma proteins, is positively regulated by dexamethasone. To define the dexamethasone-responsive genetic element, we isolated and tested AGP gene sequences for the ability to confer glucocorticoid induction to the bacterial chloramphenicol acetyltransferase (CAT) gene in L cells. A 141-base-pair region of the AGP gene, including 120 base pairs of DNA upstream from the start site of transcription and 21 base pairs of the 5' untranslated region, was sufficient for maximal CAT gene induction by dexamethasone. To localize more precisely the AGP glucocorticoid-responsive element, parts of this 141-base-pair region were inserted 5' to either an AGP promoter-CAT gene or a human triosephosphate isomerase promoter-CAT gene, both of which lacked a response to the steroid. The AGP gene region between 120 and 42 base pairs upstream from the start site of transcription was found to mediate maximal dexamethasone induction of CAT enzyme levels. This result was unexpected because this region does not contain sequence homologies to known glucocorticoid receptor-binding sites and those AGP gene regions that lay further upstream and were homologous to other glucocorticoid receptor-binding sites were inactive in the CAT assay. The fact that the AGP gene region mediating dexamethasone regulation was distinct from the transcribed region indicates that glucocorticoids increase AGP gene expression primarily at the transcriptional rather than the posttranscriptional level.

The acute phase response to inflammation: the role of monokines in changes in liver glycoproteins and enzymes of glycoprotein metabolism

The role of monocyte derived factors in the acute phase response to inflammation is discussed. The kinetics of response of alpha 1-acid glycoprotein, sialyltransferase and albumin to a rat monokine preparation is described. There was an increase in synthesis of alpha 1-acid glycoprotein and sialyltransferase and a decrease in albumin synthesis following administration. However, the kinetics of response of sialyltransferase to the monokine was much slower than was found for the other two proteins. The possibility that sialyltransferase responds to a different monokine compared to the other acute phase proteins is discussed.

Changes in plasma albumin concentration, synthesis rate, and mRNA level during acute inflammation

Induction of acute inflammation in rats by the subcutaneous injection of turpentine resulted in a marked fall in the concentration of albumin in plasma. This fall, which reached a minimum of 45% of the control level at 36 h after injection of the inflammatory agent, occurred in the presence of no significant change in the concentration of total protein in plasma. It was accompanied by a corresponding decline in the relative abundance of albumin mRNA in liver, which reached a minimum of 25% of the control level at 36 h after initiation of the inflammatory response. Perfused livers from 36-h postinjection rats exhibited albumin secretion rates that were reduced to 38% of control values. In contrast, release of total secretory proteins, secretion of nonalbumin plasma proteins, and synthesis of nonexported proteins by perfused livers were elevated to 166, 266, and 117% of the control values, respectively, as a result of the inflammatory response. These results demonstrate that acute inflammation causes a relative reduction in hepatic albumin mRNA, which leads to a corresponding decrease in albumin synthesis and secretion by liver and a fall in the concentration of albumin in plasma. The concentration of total protein in plasma is maintained during acute inflammation in part by increased synthesis and secretion by liver of nonalbumin plasma proteins, e.g. the acute-phase reactants.

Stimulation of muscle protein degradation by murine and human epidermal cytokines: relationship to thermal injury

Accelerated muscle proteolysis is a characteristic of systemic reaction following trauma, sepsis, or extensive thermal injury. The factors involved in this accelerated muscle breakdown have not been fully described. However, recently leukocytic pyrogen or interleukin 1 (IL-1) have been implicated in the induction of muscle protein degradation in septicemia or trauma. The epidermal cytokine epidermal cell-derived thymocyte activating factor (ETAF) is biochemically and functionally similar to IL-1. Injury to skin can augment ETAF activity. Using a murine model, we found that thermal injury can significantly enhance ETAF/IL-1 activity in a dose-dependent fashion. In addition, ETAF can cause net muscle protein breakdown in vitro. Thus, increased amounts of ETAF produced by thermally injured skin may contribute to the accelerated muscle breakdown in extensive thermal injury.

Effect of hepatocyte-stimulating factor and glucocorticoids on plasma fibronectin levels

We evaluated the effects of hepatocyte-stimulating factor (HSF) and a glucocorticoid (dexamethasone) on changes in the levels, in vivo and in vitro, of plasma fibronectin (Fn), a glycoprotein that is synthesized and secreted by hepatocytes. In turpentine-treated chickens, plasma levels of Fn, which peaked at 48 h (whereas fibrinogen levels were maximum at 72 h) rose 200-250% over basal levels, whereas albumin levels decreased by 20-40%. Corticosterone levels in serum samples taken between 5 and 48 h after injection revealed a 124% increase in hormone levels at 24 h in turpentine-treated chickens. We also showed that circulating HSF levels were maximal 8 to 12 h after injection and that HSF activity, as assessed by molecular-exclusion chromatography, was eluted in the 30-45 kDa range. Addition of either serum-derived HSF or dexamethasone (2 nM) to chick hepatocyte cultures resulted in a 130-150% increase in secreted Fn as well as in fibrinogen. When HSF and dexamethasone were added together, a 360-489% increase in the secreted levels of both proteins was found. Chicken mononuclear phagocytic cells treated with lipopolysaccharide secreted an HSF activity that was eluted in two peaks, a minor peak at approximately 70 kDa and a major peak in the 25-40 kDa range. Addition of mononuclear-cell-derived HSF resulted in a greater increase in Fn levels than did the addition of serum HSF. These findings indicate that Fn, like fibrinogen, is an acute-phase protein, the production of which, at least in chickens, is stimulated by HSF and glucocorticoids in an additive manner.

Monocyte-conditioned medium, interleukin-1, and tumor necrosis factor stimulate the acute phase response in human hepatoma cells in vitro

Human hepatoma cells mimic the acute phase response after treatment with monocyte-conditioned medium. Levels of secreted fibrinogen, alpha-1 acid glycoprotein, C-reactive protein, haptoglobin, and the third component of complement were elevated compared with control levels after 48 h of incubation with conditioned supernatant medium from an enriched fraction of normal peripheral monocytes. Albumin levels declined and alpha-1 antitrypsin remained unchanged. Levels of specific mRNA were measured by hybridization to slot blots and Northern blots and changed in correspondence with protein alterations. Interleukin-1 and tumor necrosis factor stimulated the third component of complement, but did not elevate any other member of the acute phase group and were therefore only partially active in this system. The identification of an in vitro model of the human acute phase response will permit analysis of the molecular basis for coordinate regulation of this group of facultative genes.

Localization of DNA sequences involved in dexamethasone-dependent expression of the rat alpha 1-acid glycoprotein gene

Synthesis of rat alpha 1-acid glycoprotein (AGP), one of the major inflammation-induced plasma proteins, is positively regulated by dexamethasone. To define the dexamethasone-responsive genetic element, we isolated and tested AGP gene sequences for the ability to confer glucocorticoid induction to the bacterial chloramphenicol acetyltransferase (CAT) gene in L cells. A 141-base-pair region of the AGP gene, including 120 base pairs of DNA upstream from the start site of transcription and 21 base pairs of the 5' untranslated region, was sufficient for maximal CAT gene induction by dexamethasone. To localize more precisely the AGP glucocorticoid-responsive element, parts of this 141-base-pair region were inserted 5' to either an AGP promoter-CAT gene or a human triosephosphate isomerase promoter-CAT gene, both of which lacked a response to the steroid. The AGP gene region between 120 and 42 base pairs upstream from the start site of transcription was found to mediate maximal dexamethasone induction of CAT enzyme levels. This result was unexpected because this region does not contain sequence homologies to known glucocorticoid receptor-binding sites and those AGP gene regions that lay further upstream and were homologous to other glucocorticoid receptor-binding sites were inactive in the CAT assay. The fact that the AGP gene region mediating dexamethasone regulation was distinct from the transcribed region indicates that glucocorticoids increase AGP gene expression primarily at the transcriptional rather than the posttranscriptional level.

The effects of endotoxaemia on protein metabolism in skeletal muscle and liver of fed and fasted rats

The response of muscle and liver protein metabolism to either a single or three successive daily injections of an endotoxin (Escherichia coli lipopolysaccharide, serotype 0127 B8; 1 mg/ml, 0.3 mg/100 g body wt.) was studied in vivo in the fed rat, and at 24 and 30 h after endotoxin treatment during fasting. In the fed rats there was a catabolic response in muscle, owing to a 60-100% increase in muscle protein degradation rate, and a 52% fall in the synthesis rate. Although there was a 20% decrease in food intake, the decrease in protein synthesis was to some extent independent of this, since rats treated with endotoxin and fasted also showed a lower rate of muscle protein synthesis, which was in excess of the decrease caused by fasting alone. The mechanism of this decreased protein synthesis involved decreased translational activity, since in both fed and fasted rats there was a decreased rate of synthesis per unit of RNA. This occurred despite the fact that insulin concentrations were either maintained or increased, in the fasted rats, to those observed in fed rats. In the liver total protein mass was increased in the fed rats by 16% at 24 h, and the fractional synthesis rate at that time was increased by 35%. In rats fasted after endotoxin treatment the liver protein mass was not decreased as it was in the control fasted rats, and the fractional synthesis rate was increased by 22%. In both cases the increased synthesis rate reflected an elevated hepatic RNA concentration. The extent of this increase in hepatic protein synthesis was sufficient at one point to compensate for the fall in estimated muscle protein synthesis, so that the sum total in the two tissues was maintained.

Studies on the effect of the hepatocyte-stimulating factor on galactose-beta 1----4-N-acetylglucosamine alpha 2----6-sialyltransferase in cultured hepatocytes

Rat hepatic Gal beta 1----4GlcNAc alpha 2----6 sialyltransferase is released into the blood at elevated levels following an inflammatory challenge: this is a typical response of the group of plasma proteins known as acute-phase reactants. In the present study, primary cultures of liver parenchymal cells are used to demonstrate that the same hepatic cell type that produces plasma proteins such as fibrinogen also produces and releases sialyltransferase. Hepatic production of sialyltransferase is stimulated by a major regulator of hepatic acute-phase reactant production, the hepatocyte-stimulating factor (HSF), while another monokine, interleukin-1, does not affect hepatocyte sialyltransferase production. The maximum increase in sialyltransferase occurs 48 h after exposure to HSF which is considerably later than the fibrinogen response. The sialyltransferase that is stimulated by HSF is the Gal beta 1----4GlcNAc alpha 2----6 isozyme.

Regulation of major acute-phase plasma proteins by hepatocyte-stimulating factors of human squamous carcinoma cells

Human squamous carcinoma (COLO-16) cells release factors which specifically stimulate the synthesis of major acute-phase plasma proteins in human and rodent hepatic cells. Anion exchange, hydroxyapatite, lectin, and gel chromatography of conditioned medium of COLO-16 cells result in separation into three distinct forms of hepatocyte-stimulating factors (designated HSF-I, HSF-II, and HSF-III) with apparent molecular weights of 30,000, 50,000 and 70,000, respectively. None of the preparations contains detectable amounts of thymocyte-stimulating activity. Each of the three HSF forms stimulates the accumulation of mRNA for alpha 1-antichymotrypsin in the human hepatoma cell line, HepG2. When the same factors were added to primary cultures of adult rat hepatocytes, the expression of the same set of plasma proteins was modulated as by nonfractionated medium. The hormonally induced accumulation of mRNA for acute phase proteins is qualitatively comparable to that occurring in the liver of inflamed rats. Unlike in human cells, in rat liver cells dexamethasone acts additively and synergistically with HSFs. The only functional difference between the three HSF forms lies in the level of maximal stimulation. HSF-I represents the predominant form produced by normal human keratinocytes and closely resembles in molecular size and isoelectric point the activity produced by activated peripheral blood monocytes while the larger molecular weight forms are more prevalent in human as well as mouse squamous carcinoma cells. The observation that HSFs from different sources elicit essentially the same pleiotropic response in hepatic cells led to the hypothesis that the species-specific reaction of adult liver cells to inflammatory stimuli is pre-programmed and that the function of any HSF is to trigger and tune the execution of this fixed cellular process.

Murine interleukin 1 stimulates alpha 2-macroglobulin synthesis in rat hepatocyte primary cultures

In rat hepatocyte primary cultures recombinant interleukin 1 was found to stimulate alpha 2-macroglobulin synthesis, whereas albumin synthesis was decreased. Although recent experiments gave evidence that a hepatocyte-stimulating factor distinct from interleukin 1 must exist, we conclude that interleukin 1 exerts a direct effect on hepatocytes by inducing acute-phase protein synthesis.

Cytokines regulating acute inflammation and synthesis of acute phase proteins

The acute phase response to injury includes metabolic alterations, such as fever, leucocytosis, enhanced uptake of some metals and amino acids by liver, and changes in the synthesis of certain plasma proteins. Many of these effects can be elicited either in vivo or in tissue culture by monocyte- and keratinocyte-derived cytokine interleukin 1 (IL-1), which had earlier been variably termed leucocytic endogenous mediator, lymphocyte activating factor, or endogenous pyrogen. Although recombinant murine IL-1 was shown to induce hepatic synthesis of acute phase proteins other authors demonstrated that hepatocyte stimulating factor (HSF) is distinct from IL-1. Possible relationships between HSF und IL-1 and the molecular mechanisms of action of these cytokines on the synthesis of acute phase proteins are briefly discussed.

Studies of monokines as mediators of the acute phase response: effects on sialyltransferase, albumin, alpha 1-acid glycoprotein and beta-N-acetylhexosaminidase

Rat peritoneal leukocytes (PEC) were fractionated on Percoll gradients to prepare populations of monocytes/lymphocytes and polymorphonuclear leukocytes; adherent (monocyte enriched) and non-adherent (lymphocytes/polymorphonuclear leukocytes) cells were also isolated from PEC. Cytokines were prepared from PEC and subfractions and injected into rats to induce the acute phase reactants serum alpha 1-acid glycoprotein and sialyltransferase; negative acute phase parameters serum albumin and liver hexosaminidase were also assayed. Monocyte derived cytokines (monokines) mimicked the acute phase response of all four parameters in vivo. The sialyltransferase isoenzyme that responded to monokine was identified as the Gal beta 1----4GlcNAc alpha 2----6 isoenzyme.

A simple bioassay for monocyte-derived hepatocyte stimulating factor: increased synthesis of alpha 2-macroglobulin and reduced synthesis of albumin by cultured rat hepatocytes

Cytokines released from monocytes upon stimulation by lipopolysaccharide cause a number of cells to undergo proliferative and synthetic changes. At least one of these cytokines affects hepatocytes in vivo causing increased synthesis of a series of acute-phase proteins. We have established an in vitro micro-assay for hepatocyte stimulating factor (HSF) using primary cultures of normal rat hepatocytes. Measurement of increased synthesis of alpha 2-macroglobulin and decreased synthesis of albumin caused by exogenously added factor constitute a sensitive parameter for quantifying HSF. For comparing various cytokines preparations, we have defined a unit of HSF activity in terms of a stimulation index. We have used this assay to follow some preliminary attempts to isolate the factors responsible for stimulation of synthesis of acute-phase reactant by the liver.