Dexamethasone regulation of alpha 1-acid glycoprotein and other acute phase reactants in rat liver and hepatoma cells

alpha1-Acid glycoprotein production in rat dorsal air pouch in response to inflammatory stimuli, dexamethasone and honey bee venom

This study shows the rapid and differential production of the 40-43 kDa and the 70-90 kDa alpha1-acid glycoprotein (AGP) fucosylated glycoforms after treatment of the dorsal air pouch with bacterial lipopolysaccharide (LPS), HgCl(2) or Freund's complete adjuvant (FCA). The 40-43 kDa and the 70-90 kDa AGP production is peaked 1-3 h post-LPS treatment. We observed that the responses to LPS and FCA are similar in that both AGP isoforms are induced whereas they differ in that the FCA exhibits a 6 h lag period. The response to HgCl(2,) however, exhibits the specific biphasic induction only of the 40-43 kDa AGP. The serum 40-43 kDa AGP glycoform gradually increases in response to all of the above stimulants and peaks by 24 h post- treatment. The increase of the 70-90 kDa AGP levels in the air pouch occurs in association with the accumulation of polymorphonuclear (PMN) cells while dexamethasone (DEX) increases only the 40-43 kDa AGP production in the absence of PMN accumulation. Macrophage-monocyte lineage cells forming the air pouch lining tissue may potentially be the cells that secrete the 40-43 kDa AGP while polymorphonuclear cells that infiltrate the air pouch secrete the 70-90 kDa AGP. The 40-43 kDa and 70-90 kDa AGP production induced by LPS in the air pouch precedes that of interleukin-1 (IL-1) or interleukin-6 (IL-6) while the 40-43 kDa AGP glycoform potentially increases IL-6 production by air pouch PMN exudate cells. These significant differences suggest a local pro-inflammatory role of AGP. Honeybee venom suppressed arthritis development and exhibited differential local or systemic regulation of AGP in serum vs. air pouch exudate or synovial fluid. This study with the air pouch model of facsimile synovium tissue suggests that local alpha1-acid glycoprotein (AGP) production may contribute to pro-inflammatory and anti-inflammatory activities during the local acute phase response or during chronic inflammatory stress as in arthritis.

The acute phase response in the rodent

In the rodent, the general response to acute inflammation and tissue damage is characterized by a complex rearrangement in the pattern of concentrations of proteins in the plasma leading to an increase in the sedimentation rate of erythrocytes, an increase in leukocyte concentration in the bloodstream, and a decrease in the hematocrit. Body temperature changes only slightly or not at all. The reasons for the change in plasma concentrations of proteins are changes in their rates of synthesis in the liver. Degradation of plasma proteins is not affected. The details of the acute phase response evolved in the interaction of species with their environment. Therefore, it is not surprising to find differences in the details of the acute phase response among species. For example, alpha 2-macroglobulin is a strongly positive acute phase reactant in the rat, but not in the mouse; C-reactive protein is a strongly positive acute phase protein in the mouse, but is not found in the rat. An inducible acute phase cysteine proteinase inhibitor system, which has evolved from a primordial kininogen gene, has been observed so far only in the rat. The changes in the synthesis rates of acute phase proteins during inflammation are closely reflected by corresponding changes in intracellular mRNA levels. In the liver, the capacity to induce the acute phase pattern of synthesis and secretion of plasma proteins probably develops around birth. Changes in mRNA levels are brought about by changes in transcription rates or by changes in mRNA stability. Kinetics of mRNA changes during the acute phase response differ for individual proteins. The main signal compound for eliciting the acute phase response in liver seems to be interleukin-6/interferon-beta 2/hepatocyte stimulating factor, whereas interleukin-1 leads to typical acute phase changes in mRNA levels only for alpha 1-acid glycoprotein, albumin, and transthyretin. Plasma protein genes are expressed in various extrahepatic tissues, such as the choroid plexus, the yolk sac, the placenta, the seminal vesicles, and other sites. All these tissues are involved in maintaining protein homeostasis in associated extracellular compartments by synthesis and secretion of proteins. Synthesis and secretion of plasma proteins in paracompartmental organs other than the liver is not influenced by the acute phase stimuli.

Monitoring the effects of drug treatment in rat models of disease by serum protein analysis

In this review we list from literature investigations on rat serum proteins using electrophoretic techniques in connection with drug testing. From our own research work, we provide annotated two-dimensional maps of rat serum proteins under control and experimental conditions. Emphasis is on species-specific components and on the effects of acute and chronic inflammation. We discuss our project of structural proteomics on rat serum as a minimally invasive approach to pharmacological investigation, and we outline a typical experimental plan for drug testing according to the above guidelines. We then report in detail on the results of our trials of anti-inflammatory drugs on adjuvant arthritis, an animal model of disease resembling in many aspects human rheumatoid arthritis. We demonstrate a correlation between biochemical parameters and therapeutic findings and outline the advantages of the chosen methodological approach, which proved also sensitive in revealing "side effects" of the test drugs. In an appendix we describe our experimental protocol when performing two-dimensional electrophoresis of rat serum.

Negative regulation of human fibrinogen gene expression by peroxisome proliferator-activated receptor alpha agonists via inhibition of CCAAT box/enhancer-binding protein beta

Fibrinogen is a coagulation factor and an acute phase reactant up-regulated by inflammatory cytokines, such as interleukin 6 (IL-6). Elevated plasma fibrinogen levels are associated with coronary heart diseases. Fibrates are clinically used hypolipidemic drugs that act via the nuclear receptor peroxisome proliferator-activated receptor alpha (PPAR alpha). In addition, most fibrates also reduce plasma fibrinogen levels, but the molecular mechanism is unknown. In this study, we demonstrate that fibrates decrease basal and IL-6-stimulated expression of the human fibrinogen-beta gene in human primary hepatocytes and hepatoma HepG2 cells. Fibrates diminish basal and IL-6-induced fibrinogen-beta promoter activity, and this effect is enhanced in the presence of co-transfected PPAR alpha. Site-directed mutagenesis experiments demonstrate that PPAR alpha activators decrease human fibrinogen-beta promoter activity via the CCAAT box/enhancer-binding protein (C/EBP) response element. Co-transfection of the transcriptional intermediary factor glucocorticoid receptor-interacting protein 1/transcriptional intermediary factor 2 (GRIP1/TIF2) enhances fibrinogen-beta gene transcription and alleviates the repressive effect of PPAR alpha. Co-immunoprecipitation experiments demonstrate that PPAR alpha and GRIP1/TIF2 physically interact in vivo in human liver. These data demonstrate that PPAR alpha agonists repress human fibrinogen gene expression by interference with the C/EBP beta pathway through titration of the coactivator GRIP1/TIF2. We observed that the anti-inflammatory action of PPAR alpha is not restricted to fibrinogen but also applies to other acute phase genes containing a C/EBP response element; it also occurs under conditions in which the stimulating action of IL-6 is potentiated by dexamethasone. These findings identify a novel molecular mechanism of negative gene regulation by PPAR alpha and reveal the direct implication of PPAR alpha in the modulation of the inflammatory gene response in the liver.

Alpha-1-acid glycoprotein

Alpha-1-acid glycoprotein (AGP) or orosomucoid (ORM) is a 41-43-kDa glycoprotein with a pI of 2.8-3.8. The peptide moiety is a single chain of 183 amino acids (human) or 187 amino acids (rat) with two and one disulfide bridges in humans and rats,respectively. The carbohydrate content represents 45% of the molecular weight attached in the form of five to six highly sialylated complex-type-N-linked glycans. AGP is one of the major acute phase proteins in humans, rats, mice and other species. As most acute phase proteins, its serum concentration increases in response to systemic tissue injury, inflammation or infection, and these changes in serum protein concentrations have been correlated with increases in hepatic synthesis. Expression of the AGP gene is controlled by a combination of the major regulatory mediators, i.e. glucocorticoids and a cytokine network involving mainly interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF alpha), interleukin-6 and IL-6 related cytokines. It is now well established that the acute phase response may take place in extra-hepatic cell types, and may be regulated by inflammatory mediators as observed in hepatocytes. The biological function of AGP remains unknown; however,a number of activities of possible physiological significance, such as various immunomodulating effects, have been described. AGP also has the ability to bind and to carry numerous basic and neutral lipophilic drugs from endogenous (steroid hormones) and exogenous origin; one to seven binding sites have been described. AGP can also bind acidic drugs such as phenobarbital. The immunomodulatory as well as the binding activities of AGP have been shown to be mostly dependent on carbohydrate composition. Finally, the use of AGP transgenic animals enabled to address in vivo, functionality of responsive elements and tissue specificity, as well as the effects of drugs that bind to AGP and will be an useful tool to determine the physiological role of AGP.

Stress-induced enhancement of skin immune function: A role for gamma interferon

Contrary to the widespread belief that stress is necessarily immunosuppressive, recent studies have shown that, under certain conditions, stress can induce a significant enhancement of a skin cell-mediated immune response [delayed-type hypersensitivity (DTH) or contact hypersensitivity]. Adrenal stress hormones and a stress-induced trafficking of leukocytes from the blood to the skin have been identified as systemic mediators of this immunoenhancement. Because gamma interferon (IFNgamma) is an important cytokine mediator of DTH, the studies described here were designed to examine its role as a local mediator of the stress-induced enhancement of skin DTH. The effect of acute stress on skin DTH was examined in wild-type and IFNgamma receptor-deficient (IFNgammaR-/-) mice that had previously been sensitized with 2,4-dinitro-1-fluorobenzene. Acutely stressed wild-type mice showed a significantly larger DTH response than nonstressed mice. In contrast, IFNgammaR-/- mice failed to show a stress-induced enhancement of skin DTH. Immunoneutralization of IFNgamma in wild-type mice significantly reduced the stress-induced enhancement of skin DTH. In addition, an inflammatory response induced by direct IFNgamma administration to the skin was significantly enhanced by acute stress. Our results suggest that IFNgamma is an important local mediator of a stress-induced enhancement of skin DTH. These studies are clinically relevant because, depending on the nature of the antigen, DTH reactions mediate numerous protective (e.g., resistance to viral, bacterial, parasitic, and fungal infections) or pathological (e.g., autoimmune reactions and contact sensitivity reactions such as that to poison ivy) immune responses.

The stressful condition as a nutritionally dependent adaptive dichotomy

The injured body manifests a cascade of cytokine-induced metabolic events aimed at developing defense mechanisms and tissue repair. Rising concentrations of counterregulatory hormones work in concert with cytokines to generate overall insulin and insulin-like growth factor 1 (IGF-1), postreceptor resistance and energy requirements grounded on lipid dependency. Salient features are self-sustained hypercortisolemia persisting as long as cytokines are oversecreted and down-regulation of the hypothalamo-pituitary-thyroid axis stabilized at low basal levels. Inhibition of thyroxine 5'-deiodinating activity (5'-DA) accounts for the depressed T3 values associated with the sparing of both N and energy-consuming processes. Both the liver and damaged territories adapt to stressful signals along up-regulated pathways disconnected from the central and peripheral control systems. Cytokines stimulate liver 5'-DA and suppress the synthesis of transthyretin (TTR), causing the drop of retinol-binding protein (RBP) and the leakage of increased amounts of T4 and retinol in free form. TTR and RBP thus work as prohormonal reservoirs of precursor molecules which need to be converted into bioactive derivatives (T3 and retinoic acids) to reach transcriptional efficiency. The converting steps (5'-DA and cellular retinol-binding protein-I) are activated by T4 and retinol, themselves operating as limiting factors of positive feedback loops. Healthy adults with normal macrophage functioning and liver parenchymal integrity, who submitted to a stress of medium severity, are characterized by TTR-RBP plasma levels reduced by half and an estimated ten-fold increase in free ligand disposal to target cells during the days ensuing injury. This transient hyperthyroid and hyperretinoid climate creates a second defense line strengthening and fine-tuning the effects primarily initiated by cytokines. The suicidal behavior of thyroxine-binding globulin (TBG), corticosteroid-binding globulin (CBG), and IGFBP-3 allows the occurrence of peak endocrine and mitogenic influences at the site of inflammation. The production rate of TTR by the liver is the main determinant of both the hepatic release and blood transport of holoRBP, which explains why poor nutritional status concomitantly impairs thyroid- and retinoid-dependent acute-phase responses, hindering the stressed body to appropriately face the survival crisis. The prognostic significance of low TT4 blood levels may be assigned to the exhaustion of extrathyroidal hormonal pools normally stored in liver and plasma but markedly shrunken in protein-depleted states. These data offer new insights into the mechanisms whereby preexisting malnutrition and stressful complications are interrelated, emphasizing the pivotal role played by TTR in that context.

In vitro effects of Clostridium difficile toxins on hepatocytes

BACKGROUND

Clostridium difficile infections are associated with development of the systemic inflammatory response, including the production of hepatic acute phase proteins. Lipopolysaccharide (LPS) directly stimulates the production of at least one of these proteins, a 23-kDa acute phase protein (the LPS-induced protein, or LIP) by murine hepatocytes in vitro. The aim of the present study was to determine if C. difficile toxins also stimulated the synthesis of this protein in vitro.

METHODS

Cultured murine hepatocytes were treated for 24 h with various concentrations of C. difficile culture extract or purified toxins A and B in the presence or absence of dexamethasone or interleukin-1 (IL-1) receptor antagonist (IL-1 RA). The cells were then metabolically radiolabeled with [35S]methionine. Secretory proteins were identified using electrophoresis and autoradiography, and their synthesis was quantitated by image analysis of the autoradiograms.

RESULTS

The C. difficile culture extract, at dilutions as low as 1:200,000, significantly stimulated LIP synthesis in vitro. Toxins A and B, at concentrations as low as 1.6 and 0.02 pg/ml, respectively, also induced production of this protein. Dexamethasone further augmented C. difficile toxin-stimulated synthesis of LIP, but IL-1 RA inhibited the effects of these toxins on the synthesis of this protein. Only minimal quantities of IL-1 were found in culture supernatants following treatment with the toxins.

CONCLUSIONS

C. difficile toxins A and B, at very low concentrations, stimulate hepatocyte acute phase protein synthesis. Even though IL-1 RA inhibits this process, it does not appear that local production of IL-1 mediates the action of these toxins.

Coactivator TIF1beta interacts with transcription factor C/EBPbeta and glucocorticoid receptor to induce alpha1-acid glycoprotein gene expression

The transcription of the alpha1-acid glycoprotein gene is induced by inflammatory cytokines and glucocorticoids. C/EBPbeta is a major transcription factor involved in the induction of the agp gene by some cytokines. In this report, we have identified a novel transcriptional intermediary factor, TIF1beta, which could enhance the transcription of the agp gene by the glucocorticoid receptor (GR) and C/EBPbeta. TIF1beta belongs to a subgroup of RING (really interesting new gene) finger proteins that contain a RING finger preceding two B box-type fingers and a putative coiled-coil domain (RBCC domain). Immunoprecipitation experiments showed that the interaction between GR and TIF1beta is ligand independent. The overexpression of the TIF1beta gene enhances GR-regulated expression in a ligand- and glucocorticoid-responsive element (GRE)-dependent manner. TIF1beta can also augment C/EBPbeta-mediated activity on wild-type and GRE-mutated agp genes, but this augmentation is diminished when all three C/EBPbeta-binding elements are mutated. Functional and biochemical characterizations indicated that the bZIP domain of C/EBPbeta and the RBCC domain, plant homeodomain finger, and bromodomain of TIF1beta are crucial for the interactions of these proteins. Taken together, these results suggest that TIF1beta serves as a converging mediator of signal transduction pathways of glucocorticoids and some inflammatory cytokines.

Effect of fentanyl on morphine levels in the brain in rats receiving intracerebroventricular injection of TNF-alpha

Fentanyl citrate analgesia attenuates the excess nitrogen excretion in the urine and glucose production induced by trauma. On the other hand, intracerebroventricular injection of morphine stimulates excretion of stress hormones, such as catecholamines and corticosterone. Furthermore, morphine levels in the brain are increased during fasting and sepsis. The aims of this study were to determine whether intracerebroventricular injection of tumor necrosis factor-alpha (TNF-alpha) elevates morphine levels in the rat brain and whether prophylactic administration of fentanyl blocks metabolic responses induced by intracerebroventricular injection of TNF-alpha because of a reduction of morphine levels in the brain. Morphine levels in the brain were increased from 648 to 1,134 fmol/g at 30 min after intracerebroventricular injection of TNF-alpha (P < 0.05 vs. control). This increase was associated with an increase in stress hormones (corticosterone: 416.1 +/- 69.1 ng/ml, P < 0.05 vs. control; epinephrine: 3,778.3 +/- 681.3 pg/ml, P < 0.01 vs. control) and an enhancement of proteolysis (254.2 +/- 45.7 micromol Leu . kg-1 . h-1, P < 0.01 vs. control) and glucose production (7.5 +/- 0. 7 mg . kg-1 . min-1, P < 0.05 vs. control). Fentanyl reduced morphine levels in the brain to 624 fmol/g (not significant vs. control), resulting in a reduction of stress hormone levels in the plasma and blunted metabolic responses. In conclusion, prophylactic administration of fentanyl prevented an increase in morphine levels in the brain induced by intracerebroventricular injection of TNF-alpha, leading to a reduction in stress hormone levels and subsequent metabolic responses.

Adrenalectomy and dexamethasone treatment alter the patterns of basal and acute phase response-induced expression of acute phase protein genes in rat liver

Hormonal requirements for full hepatic expression of alpha2-macroglobulin (alpha2M), alpha1-acid glycoprotein (AGP), haptoglobin (Hp) and gamma-fibrinogen (Fb) were assessed at the level of mRNA. Prior to exposure to turpentine-induced inflammation, rats were either depleted of glucocorticoids by adrenalectomy or supplemented with an excess of dexamethasone. Adrenalectomy alone did not affect the basal level of acute phase protein (APP) expression except for alpha2M mRNA, the level of which was enhanced. In contrast, dexamethasone treatment alone promoted full induction of alpha2M, significant, but not maximal increase of AGP and Hp mRNAs and suppression of Fb. In adrenalectomized rats, acute phase (AP)-cytokines, released in response to inflammation, promoted full expression of Fb and Hp and increased the level of AGP mRNA whereas alpha2M mRNA remained at the basal level. Inflammation in dexamethasone pretreated rats elicited changes which, in comparison to mRNA values for dexamethasone unpretreated inflamed rats, were seen as overexpression of alpha2M, full expression of AGP and incomplete expression of Hp, whereas Fb mRNA remained at the basal level. These data suggest that glucocorticoids are the principal inducers of alpha2M and AP-cytokines of Fb. For full induction of AGP, additive actions of glucocorticoids and AP-cytokines are required whereas expression of Hp is predominantly controlled by AP-cytokines.

The response of hepatic acute phase proteins during experimental pulmonary tuberculosis

A mouse model of pulmonary tuberculosis induced by the intratracheal instillation of live and virulent mycobacteria strain H37-Rv was used to study the relationship of the histopathological changes with the kinetics of local production and circulating levels of interleukin 6 (IL-6) and the gene expression of acute phase proteins (APP) in the liver. The histopathological studies showed a mononuclear inflammatory infiltrate located in the perivascular, peribronchial, and interstitial areas, with granulomas which started to form 2 weeks after the infection. Numerous IL-6 immunostained activated macrophages were observed in the inflammatory infiltrate, particularly in the interstitial-intralveolar compartment and granulomas, coexisting with a high IL-6 mRNA concentration determined by reverse transcription polimerase chain reaction in lung homogenates, particularly at day 21 of infection. Two peaks of IL-6 demonstrated by ELISA in lung homogenates and sera were observed at day 3 and 21 of infection, being higher on the latter. The hepatic APP mRNA transcription (alpha1-acid glycoprotein, fibrinogen, complement factor 4) analyzed by Northern blot showed a rapid and high increase at day one postinfection, which rapidly decreased and showed another second peak at day 21, when granulomas reached full maturity and the maximal production of IL-6 was observed. At the same time the liver mRNA concentrations of the negative APP albumin showed a substantial decrease. From 1 to 4 months after M. tuberculosis intratracheal instillation, histopathological changes of more severity (pneumonia, necrosis) and chronicity (interstitial fibrosis) were seen, as well as small groups of IL-6 immunostained macrophages in the pneumonic areas, granulomas and perivascular compartments, in coexistence with low IL-6 expression. During this advanced stage of the disease a high mRNA concentration of alpha1-acid glycoprotein and fibrinogen associated with low expression of the albumin gene in the liver continued. Thus, it seems that the time course of hepatic APP genetic expression in experimental pulmonary tuberculosis is related to the production of IL-6 and relevant histopathological changes, particularly the formation of granuloma.

Proteins of rat serum: I. Establishing a reference two-dimensional electrophoresis map by immunodetection and microbore high performance liquid chromatography-electrospray mass spectrometry

In the present investigation, we have identified 56 major spots, or spot rows, corresponding to 22 proteins, in the 2-DE pattern of adult male rats. This was done mainly by applying two complementary techniques, namely immunoblotting and high performance liquid chromatography-mass spectrometry (HPLC-MS) peptide mapping. Glycoproteins were characterized by affinity blotting with six lectins. We have also detailed how rat serum differs from human serum in two main respects: (i) relative abundance of individual proteins, which amounts in some cases to a complete absence in either sample, and (ii) varying molecular parameters for homologous proteins. It was thus possible to establish a first-generation reference map of rat serum proteins, which can be accessed through http://weber.u.washington.edu/ruedilab/aebersold++ +.html. We hope the present database will be a useful reference for the evaluation of changes in serum protein distribution in the course of pharmacological and toxicological studies. The recognition of species-specific proteins appears of special relevance in this respect.

Induction of a subgroup of acute phase protein genes in mouse liver by hyperthermia

We have demonstrated that two members of the acute phase reactant family of positively regulated genes, alpha 1-acid glycoprotein (AGP-1 and AGP-2) and C-reactive protein (CRP) are induced by hyperthermia, while two others, the serum amyloid A (SAA) and alpha 1-antitrypsin (AT) genes, are not. Albumin (ALB), a negative acute phase reactant gene, is also induced by hyperthermia. The AGP-1, AGP-2, and CRP genes require glucocorticoids, but not IL-6, IL-1 beta or TNF alpha in response to hyperthermia. As with LPS, the C/EBP beta mRNA levels increased, while the C/EBP alpha mRNA levels decreased in response to LPS. In contrast to the LPS response, C/EBP delta was unchanged. Protein pool levels and DNA-binding activities of the 35 and 20 kDa C/EBP beta isoforms increase, whereas protein pool levels of the 42 kDa C/EBP alpha decrease and the 30kDa remained high. These studies suggest that the synthesis of specific C/EBP alpha and C/EBP beta isoforms is induced by hyperthermia, and that the regulation of the AGP-1 and AGP-2 genes during heat stress may involve one of these isoforms. The difference between the responses to hyperthermia and LPS is that the former, may not involve the participation of cytokines. Furthermore, since cis-acting heat shock elements (HSE) are located in the promoter regions of the ALB, CRP, and C/EBP beta genes, these regulatory sequences may be involved in the in vivo activation of these genes by hyperthermia.

The heat-stable enterotoxin-guanylin receptor is expressed in rat hepatocytes and in a rat hepatoma (H-35) cell line

BACKGROUND/AIMS

Guanylyl cyclase C (GC-C) is an intestinal transmembrane receptor which binds both guanylin, an endogenous ligand, and Escherichia coli heat-stable enterotoxin (STa) resulting in 5'-cyclic guanosine monophosphate (cGMP) accumulation and chloride secretion. In the adult rat, there is a high basal level of GC-C expression in the intestine, but not in the liver. Increased expression of GC-C in the rat liver has been demonstrated during the perinatal period as well as with liver regeneration and during an acute phase response. The aim of this study was to identify and utilize cell culture models to further characterize the expression of GC-C in the liver.

METHODS

STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression by Northern analysis were determined in primary cultures of rat hepatocytes and H-35 cells, a rat hepatoma cell line, following treatment with dexamethasone and/or interleukin-6 (IL-6).

RESULTS

In rat hepatocytes treated with the combination of dexamethasone and IL-6, there was an increase in STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression as compared to untreated cells. In H-35 cells treated with dexamethasone alone, there was an increase in STa binding, STa-stimulated cGMP accumulation, and GC-C RNA expression as compared to untreated cells.

CONCLUSION

Primary cultures of rat hepatocytes and H-35 cells can be utilized to further study upregulation of GC-C in the hepatocyte. The expression of this receptor in hepatocytes, combined with the recent demonstration of circulating guanylin, is consistent with a functional role for GC-C in the liver.

Role of glucocorticoid in the upregulation of type I interleukin-1 receptor mRNA expression in hepatocytes of endotoxin-administrated mice

The interleukin-1 (IL-1) signal is transduced through type I IL-1 receptor (IL-1RI). We have recently reported that lipopolysaccharide (LPS) upregulated IL-1RI mRNA expression in mouse liver in vivo and that IL-1 and IL-6 directly upregulated IL-1RI mRNA expression in primary cultured mouse hepatocytes. Glucocorticoid (GC) has been reported to increase IL-1 binding to the cell surface and the expression level of IL-1R mRNA in a variety of cell types. As serum GC level is elevated in an inflammatory response, we evaluated the role of GC in LPS-induced upregulation of IL-1RI mRNA in the mouse liver. When LPS was administered to adrenalectomized (ADX) mice, IL-1RI mRNA was upregulated at a level comparable to those of untreated or sham-operated mice. A high dose of dexamethasone (Dex), however, caused upregulation of the mRNA. When primary cultured mouse hepatocytes were treated with Dex, only a weak upregulation of IL-1RI mRNA was observed. However, Dex in combination with IL-1 or IL-6 markedly enhanced the IL-1RI mRNA expression. A marked upregulation of the mRNA was also induced by treatment with a combination of IL-1 and IL-6 in the absence of Dex, reflecting the observation in ADX mice. These results suggest that the upregulation of IL-1RI mRNA in response to LPS is induced by the interaction of IL-1 and IL-6 and that GC augments their effect.

Effects of cytokine antagonists on the hepatic acute-phase response

Endotoxin-induced hepatic acute-phase protein synthesis has been thought to be primarily regulated through cytokines such as interleukin-1 (IL-1) and interleukin-6 (IL-6). Previously, it was found that a 23-kDa murine acute-phase protein, the lipopolysaccharide (LPS)-induced protein (LIP), was synthesized following treatment of hepatocytes in vitro with LPS. Since this protein was also induced by IL-1 and IL-6, the present studies were undertaken to determine if the effect of endotoxin was mediated through these cytokines. Primary cultures of murine hepatocytes were treated with LPS, IL-1, IL-6, or an LPS-stimulated macrophage supernatant in the presence or absence of the IL-1 receptor antagonist (IL-1 RA) and/or an anti-IL-6 antibody. The cells were then radiolabeled with [35S]methionine. LIP was detected by electrophoresis and autoradiography of the secreted proteins. In vitro, IL-1 RA completely inhibited the stimulation of LIP synthesis elicited by IL-1 and the macrophage supernatant, but did not affect LPS-stimulated synthesis of this protein. The anti-IL-6 antibody inhibited IL-6-triggered synthesis of LIP, but had no effect on LPS-stimulated synthesis. Hepatocytes isolated from mice treated in vivo with both IL-1 RA and LPS synthesized LIP to the same degree as hepatocytes isolated from mice treated with LPS alone. LPS-stimulated synthesis of LIP in vitro does not require IL-1 or IL-6 as an obligatory intermediate. These results are consistent with the hypothesis that endotoxin can directly stimulate hepatocyte acute-phase protein synthesis in the absence of cytokines.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

An apparent autocrine mechanism amplifies the dexamethasone- and retinoic acid-induced expression of mouse lipocalin-encoding gene 24p3

We have isolated, sequenced and characterized the mouse 24p3 gene. The 24p3 protein is a member of the lipocalin family comprising secreted transporters of hydrophobic ligands. The 24p3 cDNA had been initially isolated during a search for genes overexpressed during a SV40-induced mitotic reaction [Hraba-Renevey et al., Oncogene 4 (1989) 601-608]. 24p3 comprises six exons, five introns and 793 bp of 5' regulatory region. The transcription start point (tsp) was identified by primer extension. Putative regulatory elements, including a TATA-like box and two glucocorticoid responsive core elements (GRE), have been mapped in the 5'-flanking region. Based on this observation, we examined the effect of a glucocorticoid (dexamethasone, Dex) on 24p3 expression. Dex induced the expression of 24p3 dramatically in the absence of de novo protein synthesis. This activation was further amplified by an apparent autocrine mechanism. Similar results were obtained with retinoic acid. Using the cat reporter gene system, we have shown that the 5'-flanking region of 24p3 confers Dex inducibility. Furthermore, we have identified a 43-bp region of the 24p3 promoter required for the Dex responsiveness. The biological implications are discussed in light of these results.

Effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression in primary cultures of normal rat hepatocytes

While the effects of insulin, dexamethasone and cytokines on alpha 1-acid glycoprotein gene expression have been investigated in various hepatoma cell lines, the individual and combined effects of these components on the expression of this gene have been rarely studied in cultured normal rat hepatocytes. In this cell model, we have shown that mRNA levels of alpha 1-acid glycoprotein were not decreased at least during the first 24 h of culture under basal conditions. During these short-term cultures, the expression of alpha 1-acid glycoprotein in normal hepatocytes showed a high degree of responsiveness to dexamethasone alone (20-fold increase) and to dexamethasone associated with various cytokines (interleukin-1 beta, interleukin-6 and tumor necrosis factor alpha) with a 40 to 100-fold increase depending on the cytokine. Insulin alone did not modify alpha 1-acid glycoprotein mRNA; however, this hormone exerted a positive effect (about 50% increase) in the presence of dexamethasone or dexamethasone with cytokines. These results indicate that the regulation of alpha 1-acid glycoprotein in cultured normal rat hepatocytes presents major differences when compared to reported observations in rat hepatoma cell lines.

Differential regulation of the cytochrome P450 3A1 gene transcription by dexamethasone in immature and adult rat liver

We have previously shown that the in vivo induction of cytochrome P450 3A1 by dexamethasone occurs through a sharp and early transcriptional activation in the immature rat liver that is drastically impaired in adults [Telhada, M. B., Pereira, T. M. & Lechner, M. C. (1992) Arch. Biochem. Biophys. 298, 714-725]. In the present study we investigate the relative importance of cytochrome P450 3A1 gene transcription on the adaptive response to the synthetic glucocorticoid dexamethasone, by measuring the time-course run-on transcription rate and concomitant mRNA accumulation in the male rat liver at two different ontological developmental stages. The primary (direct) or secondary (dependent on protein neo-synthesis) nature of the in vivo inductive response to dexamethasone and to pregnenolone 16 alpha-carbonitrile, is further investigated by inhibiting translation by cycloheximide pretreatment. The induction of cytochrome P450 3A1 gene transcription by the anti-glucocorticoid pregnenolone 16 alpha-carbonitrile is demonstrated to occur through a secondary mechanism, requiring ongoing protein biosynthesis, regardless of the developmental stage of the animals. Conversely, a significant developmentally controlled change is observed in the inductive response of the cytochrome P450 3A1 gene to dexamethasone, characterized by a markedly delayed transcriptional activation in the adult rat liver (90 day old) as compared to the immature rat liver (21 day old). This is consistent with the net primary response of the cytochrome P450 3A1 gene to dexamethasone demonstrated in this study to occur in the immature rat liver and almost lost at the adult stage, when protein neo-synthesis becomes essential for the inductive response. Our results demonstrate (a) a difference in the mechanisms underlying induction of the cytochrome P450 3A1 gene by the glucocorticoid agonist dexamethasone and by the antagonist pregnenolone 16 alpha-carbonitrile, and (b) an important change in the mechanisms of the inductive response to dexamethasone, associated with the immature/adult liver phenotype transition. This indicates the participation of specific labile transcription factors in the induction of cytochrome P450 3A1 gene by the synthetic glucocorticoids.

Transcriptional activation of the alpha-1 acid glycoprotein gene by YY1 is mediated by its functional interaction with a negative transcription factor

Regulation of alpha-1 acid glycoprotein (AGP) gene expression involves both positive and negative transcription factors. We have previously identified two dominant factors: positive and negative transcription factors, AGP/EBP and factor B, respectively, involved in the transcription of AGP and other acute-phase response genes. In this report, we present evidence showing that the transcription of the AGP gene is positively regulated by a transcription factor, YY1. The activation of AGP gene by YY1 is mediated by a negative element B in the AGP promoter region. YY1 can also activate the B motif linked to a heterologous promoter. However, YY1 does not bind directly to the B motif per se. Rather, our data suggest that the activation of AGP gene by YY1 may be mediated by its functional interaction with factor B, which recognizes the B motif.

Characterization of a novel transcription complex required for glucocorticoid regulation of the rat alpha-1-acid glycoprotein gene

The liver alpha-1-acid glycoprotein (AGP) gene promoter contains several positive cis-acting sequences that are involved in the hormone regulation of its expression. We have characterized a new functionally important sequence located at -155 to -143 upstream from the glucocorticoid regulatory element (GRE, -120 to -105). At least three nuclear proteins bind to this sequence (CTGTGGGAACAG), called the upstream regulatory element (URE). One of these proteins, AGP nuclear factor 4 (ANF-4), is the major component of the DNA-protein complex we detected in footprint and electrophoresis mobility shift assay (EMSA) experiments using rat liver, HTC(JZ-1) rat hepatoma cell extracts and affinity-purified proteins. Another is C/EBP beta, which also binds to three elements downstream from the GRE. The third protein is shown to have a molecular weight of 102 kD. Deletions and site-directed mutagenesis demonstrated that this complex of proteins is involved in the positive hormonal regulation of AGP gene transcription. Binding experiments revealed that ANF-4 and C/EBP beta binding sites are partially overlapping and require the palindromic structure of the URE for high-affinity binding. Southwestern (DNA-protein blot analysis) and cross-linking experiments with nuclear extracts from rat liver and HTC(JZ-1) rat hepatoma cells, revealed two identical constitutive binding activities with molecular masses of 66 and 102 kD. We concluded that this transcription complex is composed of three distinct proteins, ANF-4, C/EBP beta, and a 102-kD protein, and that they play an important role for the hormone regulation of AGP.

Changes in the glycoforms of rat alpha-1-acid glycoprotein during experimental polyarthritis

We analyzed the carbohydrate moiety of purified alpha-1-acid glycoprotein (AGP) from Lewis adult male rats that were healthy (AGPh) or had experimental polyarthritis (AGPi). Sodium dodecyl sulfate polyacrylamide gel electrophoresis before and after N-glycanase treatment showed that AGPi had a slightly lower molecular mass (43 kDa vs. 45 kDa for AGPh) due to a lesser carbohydrate content. Carbohydrate analysis of purified AGP showed a slight decrease in the sialyl and galactosyl molar ratio in polyarthritis. However, the same difference in AGPh and AGPi (i.e. 0.6 residue) between the sialyl and galactosyl molar ratio indicated more than one sialyl residue per complex-type branch. Affinity for concanavalin A (ConA) of the whole glycoprotein and released oligosaccharides showed a progression during polyarthritis towards more reactive glycoforms or more ConA-bound oligosaccharides. Anion-exchange HPLC of the ConA-fractionated oligosaccharides corroborated the decreased sialylation in polyarthritis. Taken together, these results suggest a fall in branched and sialylated oligosaccharides during experimental polyarthritis. These structural changes might be related to an increase in Gal beta 1-4GlcNAc alpha 2-6 sialyltransferase activity described elsewhere in inflammatory states.

Modulation of alpha 1-acid glycoprotein (AGP) gene induction following honey bee venom administration to adjuvant arthritic (AA) rats; possible role of AGP on AA development

Honey bee venom (HBV) administration to adjuvant arthritic (AA) rats resulted in a significant suppression of arthritis and in suppression of the hepatic acute phase alpha 1-acid glycoprotein (AGP) gene induction at the early stages of disease development. AGP administration in AA rats resulted in acceleration of arthritis development and in increase of severity and duration of the disease. IL-1, IL-6, tumour necrosis factor (TNF) and glucocorticoids alone are not responsible for the HBV-mediated AGP gene down-regulation. These results indicate that AGP gene expression in AA and HBV-treated AA rats involves the interaction of several factors, and that AGP plays a role for AA development in rats.

Myocardial injury: the acute phase response and lipoprotein metabolism

Myocardial infarction and other types of tissue injury generate changes in plasma proteins known as the acute phase response. Variations in lipid and lipoprotein levels after acute myocardial infarction are manifest within 24 to 48 h after the onset of chest pain. Maximal postinfarction reductions in total cholesterol occur at days 4 to 5 with levels 47% below baseline; low and high density lipoprotein cholesterol fractions decrease to their nadir on day 7 to concentrations that are 48% and 32% below baseline, respectively. Triglyceride levels increase after acute myocardial infarction to a maximal level that is 58% above baseline on day 7. These alterations in lipid and lipoprotein levels generally stabilize by 2 months after the acute event. Screening for dyslipidemias in survivors of myocardial infarction requires clinical decision-making based on accurate and reliable measurements. The clinician must be familiar with characteristic changes in acute phase lipids and lipoproteins to ensure that patients receive appropriate, potentially life-saving therapy.

The differential induction of alpha 1-acid glycoprotein and serum amyloid A genes by heavy metals

We have investigated the differential regulation of the mouse (Balb/c) acute phase reactants, alpha 1-acid glycoprotein and serum amyloid A by heavy metals (Hg, Cd, Pb, Cu, Ni and Zn). Mice have two distinct alpha 1-acid glycoprotein mRNAs encoded by alpha 1-acid glycoprotein gene-1, (AGP-1) and alpha 1-acid glycoprotein gene-2 (AGP-2) and 3 distinct serum amyloid A mRNAs encoded by serum amyloid A gene-1, (SAA-1), serum amyloid A gene-2 (SAA-2) and serum amyloid A gene-3 (SAA-3). Using specific oligonucleotides as probes we have demonstrated that the AGP-1 and AGP-2 genes, and the SAA-1 and SAA-2 genes are differentially induced by heavy metals in the liver. At the peak of induction, AGP-2 mRNA is 80-100-fold higher than the AGP-1 mRNA level; the SAA-1 mRNA level is approx. 40-fold higher than SAA-2, and SAA-3 mRNA is not detected. A similar differential pattern of expression is observed in bacterial lipopolysaccharide mediated inductions. However, low levels of SAA-3 are also seen in this treatment. Adrenalectomy has no effect on the inductions by heavy metals of AGP-2 and the SAAs, indicating that the glucocorticoid receptor pathway may not function in this regulation. However, AGP-1 induction is significantly delayed, indicating that glucocorticoid may be essential for a rapid response to Hg. The liver is the major site of heavy metal induction of AGP and SAA genes; Hg induces AGP-1 and 2, and SAA-1 and 2 only in the liver. Our studies clearly show that the AGP and SAA genes belong to a subgroup of acute-phase reactants that respond to heavy metals. CRP is another member of this family. Furthermore, our data suggest that the mechanism is not directly mediated by glucocorticoid or cytokine induction pathways.

Sialyltransferase: a novel acute-phase reactant

1. Proteins that are released into the circulation in elevated amounts in injured mammals are referred to as acute-phase reactants. Most are liver synthesized glycoproteins of the secretable type. However, Gal-beta(1-->4)-GlcNAc-alpha(2-->6)-sialyltransferase (EC 2.4.99.1) is a novel acute-phase reactant since it is a Golgi membrane-bound enzyme rather than a secretable glycoprotein. 2. The role of glucocorticoids and cytokines in the control of synthesis and expression of acute-phase glycoproteins, including sialyltransferase, is discussed. 3. The acute-phase behaviour of Gal-beta(1-->4)-GlcNAc-alpha(2-->6)-sialyltransferase is dependent on the release of the enzyme from the Golgi in the acute-phase state. The mechanism of release of a catalytically active form of the enzyme is described.

Regulation of IL-6 and the hepatic IL-6 receptor in acute inflammation in vivo

The serum levels of interleukin 6 (IL-6) and the expression (mRNA) of the 80 kDa IL-6 receptor (IL-6R) were examined in three different models of acute inflammation. Rats were treated with either Freund's complete adjuvant (FA) via intraperitoneal injection, LPS via intravenous injection, or turpentine via subcutaneous injection. Using bio- and specific immunoassays, rat serum levels of IL-6, corticosterone, and acute phase proteins were quantified. LPS treatment induced the quickest and greatest serum IL-6 response (> 100 ng/ml within 3 h). In comparison, sera from turpentine and FA-treated rats contained much lower levels of IL-6 activity (< 10 ng/ml). Serum corticosterone levels increased by 3 h after injection in all three models, and equivalent raised serum levels of acute phase proteins were detected within 12-24 h. The expression of IL-6 receptor mRNA in hepatocytes increased markedly as early as 3 h after treatment and message levels began to decline by 6-12 h in all three models. To analyze the individual effects of raised corticosterone and IL-6 on the expression of hepatic IL-6R mRNA, rats were injected with either dexamethasone (Dex) or purified recombinant rat IL-6 (rIL-6) via intraperitoneal injection. Rats injected with rIL-6 showed highly induced IL-6R mRNA levels as early as 1 h after injection, and Dex-injected rats showed a significant but less dramatic rise in IL-6R message levels. Dex- or rIL-6-injected rats demonstrated a distinct profile of acute phase protein response different from that seen in the three experimental models. Regulation of IL-6R gene expression in the liver in vivo depends on a complex interaction between the hepatocyte and a combination of cytokines and other hormones.

Alpha 2u-globulin is the only member of the lipocalin protein superfamily that binds to hyaline droplet inducing agents

The rate-limiting step in chemically induced, male rat-specific hyaline droplet nephropathy is the reversible binding of a xenobiotic to alpha 2u-globulin. In this study, equilibrium saturation binding experiments were conducted to evaluate the in vitro binding of d-limonene-1,2-oxide (dLO) and 2,4,4-trimethyl-2-pentanol (TMP-OH) to alpha 2u-globulin and members of the alpha 2u-globulin protein superfamily. Both dLO and TMP-OH bound to alpha 2u-globulin, with Scatchard analysis yielding dissociation constants of 5.6 and 6.4 x 10(-7) M, respectively. The Bmax for binding (nmol bound/mg protein) was 50.7 and 61.1 for dLO and TMP-OH, respectively, yielding a molar ratio of approximately 1 for both ligands. The ability of dLO and TMP-OH to bind to human-derived alpha 1-acid glycoprotein, rat-derived retinol-binding protein, human protein-1, and bovine beta-lactoglobulin was also studied. These superfamily proteins are generally abundant in plasma, are freely filtered across the glomerulus, and can bind a wide range of ligands. However, neither dLO nor TMP-OH bound to any of the superfamily proteins. In contrast, under identical experimental conditions, alpha 1-acid glycoprotein did bind progesterone (Kd = 10(-6) M), whereas both beta-lactoglobulin and retinol-binding protein bound retinol (Kd = 10(-8) M for both proteins). These results indicate that, under conditions where alpha 2u-globulin superfamily proteins bind to established ligands, the proteins do not interact with hyaline droplet inducing agents. Thus, the interaction between male rat-specific nephrotoxicants and alpha 2u-globulin is unique to this protein. More importantly, these results provide direct evidence that the presence of the alpha 2u-globulin superfamily proteins does not predispose humans to develop hyaline droplet nephropathy and renal cancer from this class of chemicals.

The expression of liver acute-phase protein genes during rat development and in response to inflammation of the dam

The hepatic expression of albumin (Al) and plasma acute phase protein genes (APP) was examined during the development of rat liver and in response to inflammation of the dam. Throughout the 10- to 20-day gestation period the level of alpha 2-macroglobulin (alpha 2M) mRNA in fetal liver exceeded twice that of the adult liver. The concentrations of the other APP and Al mRNAs were 10-30% of those of the adult liver between days 10 and 13 of gestation, then increased to values which ranged from 40% for haptoglobin (Hp) to 80% for Al and alpha 1-acid glycoprotein (AGP) mRNAs on day 19 of gestation. The transition of fetuses to an extrauterine environment was followed by a temporary overexpression of the Hp gene and an increase of the fibrinogen (Fb), AGP and thiostatin (TST) mRNAs to adult levels. Fetal liver responded to inflammation of the mother by a transcriptional induction of all of the investigated APP genes, except for the Fb gene whose level of expression remained unchanged. The pattern of individual APP genes expression in maternal and fetal livers was similar and characteristic for the acute phase reaction.

Modification of inflammatory processes by phenobarbital in rats

Enzyme-inducing drugs such as phenobarbital (PB) increase serum concentrations of an acute-phase protein, alpha 1-acid glycoprotein (AGP), in man, dogs, and rats via an unknown mechanism. We studied the effects of PB on components of an acute inflammatory reaction in rats in order to determine if PB acts only on this biological marker of inflammation or is capable of altering the clinical course of inflammatory processes. Local carrageenan injection induces a similar time-dependent plantar edema and increases serum AGP levels in Sprague-Dawley (SD) and Dark Agouti (DA) rats. Pretreatment with PB for seven days modified neither parameter in SD rats while plantar edema was aggravated and serum AGP levels were increased in DA rats. The sedative-hypnotic properties of PB were not involved, since a single administration of this drug had no action in DA rats. On the other hand, chronic PB administration reduced the severity of an autoimmune disease, type II collagen-induced arthritis, in DA rats. These data indicate that PB, a potent inducer a cytochrome P-450-dependent enzymes, modifies the course of the inflammatory process. Preliminary results with macrophage transfer experiments suggest that this response to PB could be mediated by stimulated macrophages.

Insulin modulation of acute-phase protein production in a human hepatoma cell line

Insulin is widely used as a growth factor in hepatocyte culture but its effect on the production of acute-phase proteins has not been studied. By measuring four positive (fibrinogen, alpha 1-antitrypsin, alpha 1-acid glycoprotein, and alpha 1-antichymotrypsin) and four negative (albumin, prealbumin, transferrin, and retinol binding protein) acute-phase proteins produced by the Hep G2 hepatoma cell line, we have shown that insulin is an important modulator of acute-phase protein production. Our data show that insulin is able to inhibit the synthesis of prealbumin, transferrin, and fibrinogen. The results also show a complex interaction between insulin, interleukin 6, and glucocorticoids because insulin is able to inhibit the dexamethasone induction of alpha 1-antichymotrypsin, and in the presence of interleukin 6, dexamethasone is able to regulate the production of fibrinogen and prealbumin. The regulatory role of insulin in fibrinogen production was confirmed by pulse chase labeling followed by immunoprecipitation and fluorography.

Stimulation of CRP secretion in HepG2 cells: cooperative effect of dexamethasone and interleukin 6

This report described the capability of the human. human acute phase reactant, C-reactive protein (CRP). Its secretion is stimulated by interleukin 6 (IL-6) in a dose-dependent fashion and can further be positively modulated by dexamethasone. The way in which this glucocorticoid influences the CRP response depends on its time of application. Incubation of HepG2 cells simultaneously with IL-6 and dexamethasone increases the magnitude of CRP release significantly above that seen with IL-6 alone. After preincubation with dexamethasone, the kinetics of CRP release, induced by IL-6, are increased and approach that observed in the case of alpha 1-acid glycoprotein (alpha 1-AGP) without dexamethasone pretreatment. Conditions for optimal secretion of CRP were determined.

Differential expression of the mouse alpha 1-acid glycoprotein genes (AGP-1 and AGP-2) during inflammation and aging

In this study we investigated the expression of the Balb/c mouse alpha 1-acid glycoprotein genes. Mice, like humans, have two distinct alpha 1-acid glycoprotein mRNAs. As in humans and rats, mouse alpha 1-acid glycoprotein is a strong acute-phase reactant and its expression can be induced by acute-phase stimulatory agents such as bacterial lipopolysaccharides. Southern analysis and partial sequencing of different alpha 1-acid glycoprotein genomic clones indicated the existence of three distinct alpha 1-acid glycoprotein genes in the Balb/c genome. Using oligonucleotide hybridization, we showed that two of the three genes were expressed while the third gene was either not expressed or expressed at extremely low levels. The mRNA levels for the two expressed genes, alpha 1-acid glycoprotein-1 and alpha 1-acid glycoprotein-2, were both induced during the acute-phase response. However, alpha 1-acid glycoprotein-2 mRNA was present in at least 10-fold higher levels in both induced and uninduced mice. There were also differences in the developmental patterns of the two mRNAs in that the constitutive alpha 1-acid glycoprotein-1 mRNA levels increased 20-fold between 2 and 7 months, while alpha 1-acid glycoprotein-2 mRNA pools remained constant. During the acute-phase response in aged animals, there was an increase in the time required for both mRNAs to respond, and the maximum induced level of both mRNAs decreased. These studies set the stage for future experiments to determine the mechanisms by which the different alpha 1-acid glycoprotein genes are regulated during the acute-phase response and how aging affects these regulatory processes.

Quantification of acute phase proteins in rat serum and in the supernatants of a cultured rat hepatoma cell line and cultured primary hepatocytes by an enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay (ELISA) has been developed to measure acute phase reactants (APRs) in rat serum. Rat APRs of alpha 2-macroglobulin, alpha 1-acid glycoprotein (AGP), haptoglobin (Hp), haemopexin (Hpx), cysteine protease inhibitor (CPI), albumin (Alb) and transferrin (Tf) were purified from the plasma of turpentine treated rats. Fab' fragments from each IgG fraction were labelled with horseradish peroxidase (POD) by the maleimide method and the assay was performed using a sandwich technique. This ELISA procedure was able to measure nanogram quantities of rat serum APRs.

Radial immunodiffusion assay for rat alpha 1-acid glycoprotein

alpha 1-Acid glycoprotein (AGP) is an "acute phase protein" whose expression is altered in several human pathologies. Using antiserum from New Zealand white rabbits, a radial immunodiffusion assay for measuring AGP levels in rat plasma was developed operating in the range of 50-2500 micrograms/ml with high specificity. Standard curves were constructed (precipitin ring diameter 2 vs. micrograms/ml AGP) yielding highly linear plots (r = .98). The plasma concentration of AGP in spontaneously hypertensive (SHR) rats was double that of the normotensive Kyoto-Wistar (WKY) rats (208 +/- 10 vs. 118 +/- 5 micrograms/ml). AGP induction by turpentine resulted in a 14- and 26-fold increase in AGP levels in SHR and WKY rats, respectively. Induction of AGP by dexamethasone injection was examined in the SHR and WKY rat strains resulting in a 5- and 12-fold increase in AGP levels, respectively. AGP concentration in whole brain of rats was determined to be 12.7 +/- 1.8 micrograms/g. AGP concentrations in SHR and WKY liver were also determined to be 159 +/- 3 and 148 +/- 5 micrograms/g liver tissue.

Acute-phase response of human hepatocytes: regulation of acute-phase protein synthesis by interleukin-6

Human hepatocytes in primary culture were used as a model system to investigate the mechanism(s) involved in the induction of the acute-phase response in human liver. Hepatocytes were incubated with increasing amounts of recombinant human interleukin-1 beta, recombinant interleukin-6 and tumor necrosis factor-alpha. Synthesis of C-reactive protein was studied at the mRNA and protein levels. Only recombinant interleukin-6 was capable of inducing C-reactive protein-mRNA and C-reactive protein-protein synthesis. Also, fibrinogen and alpha-1-antitrypsin synthesis measured by immunoprecipitation with specific antisera increased in a dose-dependent, time-dependent manner, whereas albumin synthesis decreased to about 50% of controls. Maximal effects were observed at 100 to 300 units of recombinant interleukin-6/ml culture medium after 20 hr of incubation. Although the synthetic glucocorticoid dexamethasone slightly modulated the effect of recombinant interleukin-6, it was not an absolute requirement for the induction of acute-phase protein synthesis in human hepatocytes. In pulse-chase experiments it was shown that the time course of the disappearance of the acute-phase proteins from the cells and their appearance in the medium is not influenced by recombinant interleukin-6. This finding suggests that recombinant interleukin-6 exerts its regulatory effect on acute-phase protein synthesis at the pretranslational level.