IL-1 receptor antagonist (IL-1Ra) does not inhibit the production of C-reactive protein or serum amyloid A protein by human primary hepatocytes. Differential regulation in normal and tumour cells

The Complex Role of C-Reactive Protein in Systemic Lupus Erythematosus

C-reactive protein (CRP) is well-known as a sensitive albeit unspecific biomarker of inflammation. In most rheumatic conditions, the level of this evolutionarily highly conserved pattern recognition molecule conveys reliable information regarding the degree of ongoing inflammation, driven mainly by interleukin-6. However, the underlying causes of increased CRP levels are numerous, including both infections and malignancies. In addition, low to moderate increases in CRP predict subsequent cardiovascular events, often occurring years later, in patients with angina and in healthy individuals. However, autoimmune diseases characterized by the Type I interferon gene signature (e.g., systemic lupus erythematosus, primary Sjögren’s syndrome and inflammatory myopathies) represent exceptions to the general rule that the concentrations of CRP correlate with the extent and severity of inflammation. In fact, adequate levels of CRP can be beneficial in autoimmune conditions, in that they contribute to efficient clearance of cell remnants and immune complexes through complement activation/modulation, opsonization and phagocytosis. Furthermore, emerging data indicate that CRP constitutes an autoantigen in systemic lupus erythematosus. At the same time, the increased risks of cardiovascular and cerebrovascular diseases in patients diagnosed with systemic lupus erythematosus and rheumatoid arthritis are well-established, with significant impacts on quality of life, accrual of organ damage, and premature mortality. This review describes CRP-mediated biological effects and the regulation of CRP release in relation to aspects of cardiovascular disease and mechanisms of autoimmunity, with particular focus on systemic lupus erythematosus.

Mast Cell Cytokines IL-1, IL-33, and IL-36 Mediate Skin Inflammation in Psoriasis: A Novel Therapeutic Approach with the Anti-Inflammatory Cytokines IL-37, IL-38, and IL-1Ra

Psoriasis (PS) is a skin disease with autoimmune features mediated by immune cells, which typically presents inflammatory erythematous plaques, and is associated with many comorbidities. PS exhibits excessive keratinocyte proliferation, and a high number of immune cells, including macrophages, neutrophils, Th1 and Th17 lymphocytes, and mast cells (MCs). MCs are of hematopoietic origin, derived from bone marrow cells, which migrate, mature, and reside in vascularized tissues. They can be activated by antigen-provoking overexpression of proinflammatory cytokines, and release a number of mediators including interleukin (IL)-1 and IL-33. IL-1, released by activated keratinocytes and MCs, stimulates skin macrophages to release IL-36—a powerful proinflammatory IL-1 family member. IL-36 mediates both innate and adaptive immunity, including chronic proinflammatory diseases such as psoriasis. Suppression of IL-36 could result in a dramatic improvement in the treatment of psoriasis. IL-36 is inhibited by IL-36Ra, which binds to IL-36 receptor ligands, but suppression can also occur by binding IL-38 to the IL-36 receptor (IL-36R). IL-38 specifically binds only to IL-36R, and inhibits human mononuclear cells stimulated with IL-36 in vitro, sharing the effect with IL-36Ra. Here, we report that inflammation in psoriasis is mediated by IL-1 generated by MCs—a process that activates macrophages to secrete proinflammatory IL-36 inhibited by IL-38. IL-37 belongs to the IL-1 family, and broadly suppresses innate inflammation via IL-1 inhibition. IL-37, in murine models of inflammatory arthritis, causes the suppression of joint inflammation through the inhibition of IL-1. Therefore, it is pertinent to think that IL-37 can play an inhibitory role in inflammatory psoriasis. In this article, we confirm that IL-38 and IL-37 cytokines emerge as inhibitors of inflammation in psoriasis, and hold promise as an innovative therapeutic tool.

Serum amyloid A stimulates cultured endothelial cells to migrate and proliferate: inhibition by the multikinase inhibitor BIBF1120

In the present study, we tested whether serum amyloid A (SAA) protein, an established biomarker of inflammation, also plays a role in stimulating neovascularization. To evaluate this possibility, human carotid artery endothelial (HCtAE) cells were cultured and cellular migration and the proinflammatory and/or thrombotic activity of SAA (0, 1 or 10 μg/mL) on vascular endothelial cells was verified by determining gene regulation relative to control (in the absence of SAA). Exposure of HCtAE cells to SAA increased expression of the transcription factor nuclear factor-κB (NFKB), tumour necrosis factor (TNF) and pro-coagulative tissue factor (F3), and stimulated phosphorylation of the P65 subunit of the NFKB complex. Enhanced production of TNF and NFKB was paralleled by increased vascular endothelial growth factor (VEGF) mRNA and protein expression, as demonstrated by quantitative polymerase chain reaction, western blotting and ELISA. Administration of 10 μg/mL SAA enhanced endothelial cell migration (1.6-fold vs control), stimulated regrowth of HCtAE cells after mechanical injury (~1.2-fold vs control) and increased endothelial tube formation relative to control after 6 h. The SAA-mediated enhancement of endothelial cell migration, proliferation and tube formation were markedly inhibited by pretreatment of HCtAE cells with the multi-angiokinase receptor inhibitor BIBF1120 (100 nmol/L), although SAA-stimulated gene responses for F3 and NFKB were unaffected by 100 nmol/L BIBF1120 pretreatment. Overall, BIBF1120 inhibited the pro-angiogenic activity of SAA on vascular endothelial cells in this experimental model of inflammation.

GH activity and markers of inflammation: a crossover study in healthy volunteers treated with GH and a GH receptor antagonist

INTRODUCTION

The GH/IGF1 axis may modulate inflammatory processes. However, the relationship seems complicated as both pro- and anti-inflammatory effects have been demonstrated.

METHODS/DESIGN

Twelve healthy volunteers (mean age 36, range 27-49 years) were treated in random order with increasing doses of GH for 3 weeks (first week 0.01  mg/kg per day, second week 0.02  mg/kg per day, and third week 0.03  mg/kg per day) or a GH receptor antagonist (pegvisomant; first week 10  mg/day and last two weeks 15  mg/day), separated by 8 weeks of washout. Circulating levels of the pro-inflammatory cytokines tumor necrosis factor α (TNFα (TNFA)), interleukin 6 (IL6), and IL1β (IL1B) and the acute phase proteins (APPs) C-reactive protein (CRP), haptoglobin, orosomucoid, YKL40 (CHI3L1), and fibrinogen were measured.

RESULTS

During GH treatment, IGF1 (median 131 (Inter-quartile range (IQR) 112-166) vs 390 (322-524) μg/l, P=0.002) increased together with TNFα (0.87 (0.74-1.48) vs 1.27 (0.80-1.69) ng/l, P=0.003), IL6 (1.00 (0.83-1.55) vs 1.35 (0.80-4.28) ng/l, P=0.045), and fibrinogen (9.2 (8.8-9.6) vs 11.1 (9.4-12.4) μM, P=0.002). By contrast, orosomucoid decreased (18.0 (15.5-24.3) vs 15.0 (15.0-17.0) μM, P=0.018). CRP, YKL40, and haptoglobin were unchanged. During pegvisomant treatment, IGF1 decreased (139 (117-171) vs 91 (78-114) ng/ml, P=0.005). Orosomucoid (21.0 (16.3-23.8) vs 22.0 (17.0-29.3) μM, P=0.036) and CRP (1.00 (0.62-1.77) vs 1.43 (0.71-3.29) mg/l, P=0.074) increased without an increase in pro-inflammatory cytokines.

CONCLUSIONS

GH/IGF1 action appears to modulate the initial stage of the inflammatory response as well as downstream processes elucidated by levels of APPs. The data suggest a complicated relationship not allowing any simple conclusions as to whether GH/IGF1 actions have mainly pro- or anti-inflammatory effects in vivo.

Interleukin-8 producing hepatocellular carcinoma with pyrexia

We discuss a patient who had poorly differentiated HCC with pyrexia and high CRP in laboratory data, which are not commonly observed in the usual HCC. A 50-year-old man with a history of liver dysfunction was admitted with a chief complaint of a prolonged fever and general fatigue. Preoperative diagnosis was HCC with portal vein tumor thrombus. Posterior segmentectomy of the liver and thrombectomy was performed. Rapid tumor recurrence occurred after surgery, and he died 79 days after the operation. Immunohistochemical stain of HCC in this patient revealed the production of proinflammatory cytokine, interleukin-8 (IL-8). IL-8 production may have contributed to the high fever, high inflammatory reaction, and poor prognosis in this case.

Impaired counter-regulation of interleukin-1 by the soluble IL-1 receptor type II in patients with chronic liver disease

OBJECTIVE

To assess the production of the endogenous IL-1 modulators IL-1 receptor antagonist (IL-1Ra), type I and II soluble IL-1 receptors (IL-1sRI and II) in patients with chronic liver disease (CLD).

MATERIAL AND METHODS

Plasma levels of IL-1beta (IL-1beta) and IL-1 modulators were assessed in 126 CLD patients and 39 healthy controls. IL-1sRII was also measured in the supernatants of primary hepatocyte cultures.

RESULTS

Plasma IL-1sRI and IL-1Ra levels were significantly higher in cirrhotic CLD patients than in non-cirrhotic CLD patients and in controls. Levels did not depend on the etiology of CLD. Likewise, plasma IL-1beta levels were elevated in CLD patients compared with those in controls. In contrast, IL-1sRII levels did not differ between CLD patients and controls. Cultures of human primary hepatocytes showed that IL-1sRII is induced by IL-1beta, but not IL-6.

CONCLUSIONS

In cirrhotic CLD patients elevated plasma IL-1beta is not counteracted by endogenous levels of IL-1sRII, whereas high IL-1sRI is expected to neutralize the naturally occurring antagonist IL-1Ra, resulting in a dysregulation of the IL-1 system that might enhance pro-inflammatory activity of IL-1.

Serum amyloid A: an acute-phase protein involved in tumour pathogenesis

The synthesis of acute-phase protein serum amyloid A (SAA) is largely regulated by inflammation- associated cytokines and a high concentration of circulating SAA may represent an ideal marker for acute and chronic inflammatory diseases. However, SAA is also synthesized in extrahepatic tissues, e.g. human carcinoma metastases and cancer cell lines. An increasing body of in vitro data supports the concept of involvement of SAA in carcinogenesis and neoplastic diseases. Accumulating evidence suggests that SAA might be included in a group of biomarkers to detect a pattern of physiological events that reflect the growth of malignancy and host response. This review is meant to provide a broad overview of the many ways that SAA could contribute to tumour development, and accelerate tumour progression and metastasis, and to gain a better understanding of this acute-phase reactant as a possible link between chronic inflammation and neoplasia.

Serum amyloid A, procalcitonin, tumor necrosis factor-alpha, and interleukin-1beta levels in neonatal late-onset sepsis

Background. Sepsis is an important cause of mortality in newborns. However, a single reliable marker is not available for the diagnosis of neonatal late-onset sepsis (NLS). The aim of this study is to evaluate the value of serum amyloid A (SAA) and procalcitonin (PCT) in the diagnosis and follow-up of NLS. Methods. 36 septic and healthy newborns were included in the study. However, SAA, PCT, TNF-α, IL-1β, and CRP were serially measured on days 0, 4, and 8 in the patients and once in the controls. Töllner's sepsis score (TSS) was calculated for each patient. Results. CRP, PCT, and TNF-α levels in septic neonates at each study day were significantly higher than in the controls (P = .001). SAA and IL-1β levels did not differ from healthy neonates. The sensitivity and specificity were 86.8% and 97.2% for PCT, 83.3% and 80.6% for TNF-α, 75% and 44.4% for SAA on day 0. Conclusion. Present study suggests that CRP seems to be the most helpful indicator and PCT and TNF-α may be useful markers for the early diagnosis of NLS. However, SAA, IL-1β, and TSS are not reliable markers for the diagnosis and follow-up of NLS.

Activation of NF-κB by IL-1β blocks IL-6-induced sustained STAT3 activation and STAT3-dependent gene expression of the human γ-fibrinogen gene

Despite the essential role of the fibrinogen gamma-chain as a blood clotting factor, the fibrinogen gamma-chain contains a number of interaction sites to recruit other factors such as leukocytes important for prevention of pathogen entry and propagation of the repair process. Interleukin-6 (IL-6) is known as the major inducer of gamma-fibrinogen synthesis in hepatocytes, whereas IL-1beta has been shown to act as a potent inhibitor of gamma-fibrinogen expression. Studies on the rat fibrinogen gamma-chain promoter suggest that nuclear factor (NF)-kappaB replaces the signal transducer and activator of transcription (STAT) 3 from binding to overlapping NF-kappaB/STAT3 binding sites within the 5' regulatory region of the rat gamma-chain gene promoter. However, despite its physiological relevance, the underlying mechanism responsible for the inhibitory effect of IL-1beta in humans is still not understood and apparently more complex. In contrast to the mechanism described for the rat gene our results indicate that IL-1beta suppresses the IL-6-induced activation of the human gamma-fibrinogen gene particularly by blocking the late phase STAT3-tyrosine phosphorylation NF-kappaB-dependently but independent from de novo protein synthesis. Consequently, blocking NF-kappaB activation restores specifically late phase STAT3 activation as well as the induction of the human gamma-fibrinogen gene. In contrast, specifically early STAT3 activation could be restored by a block of the p38 mitogen-activated protein kinase (p38(MAPK)) pathway. In summary, our results indicate that expression of the gamma-fibrinogen gene is mainly controlled by the strength of late phase STAT3 activation, which in turn is negatively regulated by the extent of IL-1beta-mediated NF-kappaB activity.

The impact of preoperative serum C-reactive protein on the prognosis of patients with hepatocellular carcinoma

BACKGROUND

The authors evaluated the significance of the preoperative serum C-reactive protein (CRP) level as a prognostic indicator in patients with hepatocellular carcinoma (HCC).

METHODS

One hundred forty-one patients who underwent curative resection for HCC were reviewed retrospectively. Clinicopathologic variables were compared between patients with serum CRP levels >/= 1.0 mg/dL (n = 22 patients; the CRP-positive group) and patients with serum CRP levels < 1.0 mg/dL (n = 119 patients; the CRP-negative group). Univariate and multivariate analyses were conducted to identify factors that affected survival and disease recurrence.

RESULTS

There was a significant correlation between the preoperative serum CRP level and tumor size. Invasion to the portal vein in the CRP-positive group was significantly more frequent than that in the CRP-negative group. Even after they underwent curative resection, 75.3% of patients in the CRP-positive group experienced recurrence within 1 year. The overall survival and recurrence-free survival rates in the CRP-positive group were significantly lower compared with the rates in the CRP-negative group. On multivariate analysis, the preoperative serum CRP level was selected as one of the unfavorable indicators regarding survival and recurrence. When CRP levels, albumin levels, and platelet counts that were available before surgery were scored as a combined index, the total score demonstrated a good stratification value for survival after hepatic resection.

CONCLUSIONS

The current results showed that the preoperative serum CRP level is an independent and significant indicator predictive of poor prognosis and early recurrence in patients with HCC. The new CRP-based scoring system offers reliable information for predicting survival.

IL-6 plays a critical role in the synergistic induction of human serum amyloid A (SAA) gene when stimulated with proinflammatory cytokines as analyzed with an SAA isoform real-time quantitative RT-PCR assay system

Serum amyloid A (SAA) is known to be a precursor of amyloid A (AA) protein in AA (secondary) amyloidosis and SAA1 to be mainly involved in AA amyloidosis. We established an SAA isoform real-time quantitative RT-PCR assay and found that beta-2 microglobulin is more stable as an internal control than GAPDH and beta-actin for our system. Either IL-6 and IL-1beta or IL-6 and TNFalpha, but not IL-1beta and TNFalpha, induced the synergistic induction of SAA1 and SAA2 genes. Anti-IL-6 receptor monoclonal antibody completely inhibited the synergistic induction of SAA1 and SAA2 during triple stimulation with IL-6, IL-1beta, and TNFalpha, but, IL-1 receptor antagonist or anti-TNFalpha monoclonal antibody was only partially inhibited in HepG2, Hep3B, and PLC/PRF/5 cells. Although the SAA1 promoter has no STAT3 consensus sequence, the JAK2 inhibitor-AG490 reduced SAA1 gene expression to 30%, suggesting the involvement of STAT3. We were able to demonstrate that IL-6 plays a critical role in the synergistic induction of human SAA gene when stimulated with proinflammatory cytokines.

Inflammation, thrombosis and atherosclerosis: results of the Glostrup study

Inflammation and thrombosis are important mechanisms in cardiovascular disease, as illustrated by the consistent association between inflammatory and hemostatic variables and the risk of cardiovascular events in epidemiological studies. However, the relationship between plasma concentrations of inflammatory and hemostatic markers and the severity of atherosclerosis is not yet well studied. We have evaluated 325 men and 370 women of 60 years, participating in the Danish Glostrup study. We diagnosed atherosclerosis by ultrasonographic measurement of intima-media thickness (IMT) of the right carotid artery and the assessment of plaque occurrence. Plasma samples were analyzed for the concentration of C-reactive protein (CRP), fibrinogen, d-dimer, plasminogen activator inhibitor type-1 (PAI-1) antigen and activity, tissue-type plasminogen activator (t-PA) antigen and activity, factor VII (FVII) antigen, FVII coagulant activity (FVII:C) and activated FVII (FVIIa). DNA variations were determined for fibrinogen, PAI-1, t-PA, FVII, factor XIII and methylene tetrahydrofolate reductase (MTHFR). Subjects with high IMT (upper 10% of distribution, n = 63) had higher CRP levels [2.2 mg L-1 (SE 0.3)] than subjects with IMT in the lowest tertile (n = 217) [1.7 mg L-1 (SE 0.1), P = 0.04], whereas there was no association between the hemostatic variables and IMT. There was an association between fibrinogen and d-dimer concentrations and number of plaques (P < 0.01), whereas there were no associations between CRP and the other hemostatic variables and the number of plaques. Genetic variation in the t-PA and MTHFR gene was associated with IMT. In conclusion, in the Glostrup population study, thrombosis and inflammation are associated with the severity of atherosclerosis, as reflected by IMT and plaque occurrence.

Transcriptional regulation of serum amyloid A1 gene expression in human aortic smooth muscle cells involves CCAAT/enhancer binding proteins (C/EBP) and is distinct from HepG2 cells

Regulation of acute-phase serum amyloid A (A-SAA) synthesis by proinflammatory cytokines and steroid hormones in human aortic smooth muscle cells (HASMCs) is distinct from that in HepG2 cells. To study the cis- and trans-activating promoter element involved in the SAA1 gene expression by HASMCs and HepG2 cells, we constructed plasmid vectors for luciferase reporter gene assay with varying lengths of SAA1 upstream regulatory region (up to 1431 bp), and examined their response to proinflammatory cytokines and/or steroid hormones. The corresponding vectors with the SAA4 upstream regulatory region served as controls. The presence of proposed transcriptional regulatory factors binding to these regions was confirmed immunohistochemically. The sequences of 1478 and 1836 bp of the SAA1 and SAA4 5'-flanking regions were determined, respectively. SAA1 promoter transcription in cultured HASMCs was upregulated not by proinflammatory cytokines, but rather by glucocorticoids. This differed from HepG2 cells, in which SAA1 promoter transcription was upregulated synergistically by proinflammatory cytokines and glucocorticoids. The promoter activity of a series of truncated SAA1 promoter constructs measured using the reporter gene assay showed that the 5'-region from -252 to -175, containing a consensus site for CCAAT/enhancer binding proteins alpha,beta (C/EBPalpha,beta), was essential for SAA1 induction in HASMCs. In HepG2 cells, the 5'-region from -119 to -79, containing a nuclear factor kappa-B (NFkappaB) consensus sequence, was essential for the induction. The functional significance of the C/EBP site as indicated by the immunohistochemical result was that in HASMCs anti-C/EBPbeta reactivity was shifted from the cytoplasm to the nuclei. We have, therefore, demonstrated that the region containing the C/EBPalpha,beta consensus binding site between the bases -252 and -175 is important for the glucocorticoid-induced SAA1 gene expression in HASMCs but not in HepG2 cells.

Indicators of acute pain and fly avoidance behaviors in Holstein calves following tail-docking

Previous work showed that the banding process of docking minimally affected mature cows' behavior and physiology, but cutting off the necrotic tail increased haptoglobin. Additionally the docked cows had more flies on the rear legs and exhibited more fly avoidance behaviors. Because many producers dock young calves while they are in hutches where fly problems are more pronounced, we investigated changes in behavior and physiology of young calves following docking by banding. Twenty calves (3 to 5 wk of age) were assigned to a docked or control group, at each of two locations (Indiana and Wisconsin). After applying a band to dock the tail, calves were tested every 15 min for sensitivity to heat below the band at the Indiana location. Calf behavior was recorded for 2 h postbanding and analyzed continuously for that period. After 3 wk, tails were removed and then 1 wk later, fly counts and fly avoidance behaviors were observed at both locations. Tails were sensitive to heat below the banding site, for 60 to 120 min postbanding (mean 87 min). Banded calves were more active than control calves during the 2 h following banding. Percentage of time spent lying was greater for control calves, and the percentage of time spent walking was greater for docked than control calves. More importantly, movements of the head to touch the tail were increased for banded calves (eight-fold more movements). Fly avoidance behaviors directed toward the rear of the calf were evident at noon or in the afternoon. Ear twitches were more frequent for the docked calves and less frequent in the morning for all calves. Licking was more frequent for the docked calves at 1200 and 1600 h. Tail swings were most frequent at 1200 and more frequent for control calves. Two acute phase proteins, haptoglobin and alpha1 acid-glycoprotein, were not different at any time. In this study, calves that were banded at 3-wk-of-age showed behaviors indicative of discomfort for 2 h, were attacked by more flies, and showed increased fly avoidance behaviors when docked.

Tail-docking alters fly numbers, fly-avoidance behaviors, and cleanliness, but not physiological measures

Tail docking is an animal well-being issue not only regarding the docking procedures but also because of concerns during fly season. To address the latter question, we selected eight cows that had been tail-docked in a previous experiment and eight nondocked cows matched by stage of lactation. Physiological, immunological, and behavioral measures were used to evaluate the well being of those cows housed in a tie-stall barn during fly season for 5 consecutive days. Behavior was observed for 5-min interval instantaneous scan samples for 1 h each at 0800, 1200, and 1600 h. Flies were counted before behavior observations. Blood samples were taken daily for plasma and leukocyte separation. Cows were scored on d 5 for cleanliness on a five-point scale. Docked cows were cleaner, but fly counts of docked cows were greater for total fly counts and rear leg counts. However, counts were not different on front legs. Time of day was significant, so each time of day was analyzed separately. Docked cows were observed to exhibit fewer tail swings at 0800 h, but docked cows tended to ruminate more at that time. Docked cows tended to stand less at the 1200 h observation. Total fly-avoidance behaviors were greater for all cows at the 1600-h observation. Only tail swings tended to be more frequent with docked cows, but foot stomps occurred only in the docked cows. Lymphocyte phenotypes, acute-phase proteins, and immunoglobulin concentrations did not differ. In conclusion, although docked cows were cleaner, as the fly numbers increase throughout the day, fly-avoidance behaviors also increased and foot stomping appeared as an alternative method for fly avoidance by docked cows.

Role of serum C-reactive protein as a marker of hepatocellular carcinoma in patients with cirrhosis

BACKGROUND

The usefulness of C-reactive protein (CRP) as a tumour marker in patients with hepatocellular carcinoma (HCC) is controversial. The purpose of this study was to determine whether CRP estimation could be used to identify patients with HCC among those with cirrhosis.

METHODS

Serum levels of CRP and alpha-fetoprotein (AFP) were investigated in 122 previously untreated patients with cirrhosis and HCC. Another 76 patients with cirrhosis alone were also investigated as controls.

RESULTS

Of the subjects tested, 47.5% of patients with HCC and 39.5% of controls had elevated CRP values (> 6 microg/mL). Although using elevated CRP and/or AFP (> 20 ng/mL) as a criterion showed a significant difference between controls and patients with multiple nodular, massive, or diffuse type HCC (all P < 0.005), the clinical application of this criterion was limited because of low specificity (58%) and accuracy (all < 73%). By using receiver-operating characteristic curves no valuable threshold value of CRP was found to discriminate various types of HCC, except for distinguishing the diffuse type from controls. The CRP value of 12 microg/mL could be used as the cut-off value to differentiate diffuse-type HCC from controls (sensitivity 82.4%, specificity 82%, accuracy 82.1%, P<0.005).

CONCLUSIONS

Serum CRP is not a good marker for HCC. However, very high values of CRP in patients with cirrhosis may suggest the presence of a diffuse-type HCC.

Apolipoprotein serum amyloid A down-regulates smooth-muscle cell lipid biosynthesis

The addition of acute-phase apolipoprotein serum amyloid A (SAA) to cultured aortic smooth-muscle cells caused a decrease in the incorporation of [(14)C]acetate into lipids. Optimal inhibition of lipid biosynthesis was achieved with 2 microM SAA, and the effect was maintained for up to 1 week when SAA was included in the culture medium. Lipid extracts were subjected to TLC and it was determined that the SAA-induced decrease in [(14)C]acetate incorporation into lipids was attributable to decreases in cholesterol, phospholipid and triglyceride levels. The accumulated mass of cholesterol and phospholipid in SAA-treated cultures was significantly less than that of controls, with no change in the accumulated protein. Moreover, SAA had no effect on either protein synthesis or DNA synthesis, suggesting that SAA specifically alters lipid synthesis. By using a peptide corresponding to the cholesterol-binding domain of acute-phase SAA (amino acids 1-18), it was shown that this region of the molecule was as effective as the full-length protein in decreasing lipid synthesis and the accumulation of cholesterol and phospholipid. The implications of these findings for atherosclerosis and Alzheimer's disease are discussed.

Serum amyloid A, the major vertebrate acute-phase reactant

The serum amyloid A (SAA) family comprises a number of differentially expressed apolipoproteins, acute-phase SAAs (A-SAAs) and constitutive SAAs (C-SAAs). A-SAAs are major acute-phase reactants, the in vivo concentrations of which increase by as much as 1000-fold during inflammation. A-SAA mRNAs or proteins have been identified in all vertebrates investigated to date and are highly conserved. In contrast, C-SAAs are induced minimally, if at all, during the acute-phase response and have only been found in human and mouse. Although the liver is the primary site of synthesis of both A-SAA and C-SAA, extrahepatic production has been reported for most family members in most of the mammalian species studied. In vitro, the dramatic induction of A-SAA mRNA in response to pro-inflammatory stimuli is due largely to the synergistic effects of cytokine signaling pathways, principally those of the interleukin-1 and interleukin-6 type cytokines. This induction can be enhanced by glucocorticoids. Studies of the A-SAA promoters in several mammalian species have identified a range of transcription factors that are variously involved in defining both cytokine responsiveness and cell specificity. These include NF-kappaB, C/EBP, YY1, AP-2, SAF and Sp1. A-SAA is also post-transcriptionally regulated. Although the precise role of A-SAA in host defense during inflammation has not been defined, many potential clinically important functions have been proposed for individual SAA family members. These include involvement in lipid metabolism/transport, induction of extracellular-matrix-degrading enzymes, and chemotactic recruitment of inflammatory cells to sites of inflammation. A-SAA is potentially involved in the pathogenesis of several chronic inflammatory diseases: it is the precursor of the amyloid A protein deposited in amyloid A amyloidosis, and it has also been implicated in the pathogenesis of atheroscelerosis and rheumatoid arthritis.

Interleukin-4 (IL-4) and IL-13 Enhance the Effect of IL-1β on Production of IL-1 Receptor Antagonist by Human Primary Hepatocytes and Hepatoma HepG2 Cells: Differential Effect on C-Reactive Protein Production

Interleukin-1 receptor antagonist (IL-1Ra) is produced by hepatocytes with characteristics of an acute-phase protein. To examine the role of IL-4 and IL-13 in production of IL-1Ra, human primary hepatocytes and HepG2 human hepatoma cells were cultured in the presence of IL-4 or IL-13 in combination with IL-1β and/or IL-6. The results indicated that both IL-4 and IL-13 amplified the stimulatory effect of IL-1β on production of IL-1Ra protein and messenger RNA (mRNA) by both human primary hepatocytes and HepG2 cells. IL-1Ra refers to three different peptides, one secreted (sIL-1Ra) and two intracellular (icIL-1RaI and icIL-1RaII), derived from the same gene. sIL-1Ra and icIL-1RaI are the products of two different mRNA, whereas icIL-1RaII is synthesized by alternative translation initiation mainly from sIL-1Ra mRNA. Our results show that both sIL-1Ra and icIL-1RaII, but not icIL-1RaI, are produced by HepG2 cells and human hepatocytes. Transient transfection experiments as well as mRNA stability studies indicated that IL-4 stimulated sIL-1Ra production primarly at the level of transcription. Gel retardation assays showed that IL-4 induced the formation of a STAT6-DNA complex with a STAT6 binding element within the sIL-1Ra promoter, but had no effect on IL-1–induced NF-κB binding activity. In contrast to IL-1Ra, production of C-reactive protein by human primary hepatocytes was stimulated by IL-6 and decreased by the addition of IL-4.

Interleukin-4 (IL-4) and IL-13 Enhance the Effect of IL-1β on Production of IL-1 Receptor Antagonist by Human Primary Hepatocytes and Hepatoma HepG2 Cells: Differential Effect on C-Reactive Protein Production

Interleukin-1 receptor antagonist (IL-1Ra) is produced by hepatocytes with characteristics of an acute-phase protein. To examine the role of IL-4 and IL-13 in production of IL-1Ra, human primary hepatocytes and HepG2 human hepatoma cells were cultured in the presence of IL-4 or IL-13 in combination with IL-1β and/or IL-6. The results indicated that both IL-4 and IL-13 amplified the stimulatory effect of IL-1β on production of IL-1Ra protein and messenger RNA (mRNA) by both human primary hepatocytes and HepG2 cells. IL-1Ra refers to three different peptides, one secreted (sIL-1Ra) and two intracellular (icIL-1RaI and icIL-1RaII), derived from the same gene. sIL-1Ra and icIL-1RaI are the products of two different mRNA, whereas icIL-1RaII is synthesized by alternative translation initiation mainly from sIL-1Ra mRNA. Our results show that both sIL-1Ra and icIL-1RaII, but not icIL-1RaI, are produced by HepG2 cells and human hepatocytes. Transient transfection experiments as well as mRNA stability studies indicated that IL-4 stimulated sIL-1Ra production primarly at the level of transcription. Gel retardation assays showed that IL-4 induced the formation of a STAT6-DNA complex with a STAT6 binding element within the sIL-1Ra promoter, but had no effect on IL-1–induced NF-κB binding activity. In contrast to IL-1Ra, production of C-reactive protein by human primary hepatocytes was stimulated by IL-6 and decreased by the addition of IL-4.

Regulation of serum amyloid A protein expression during the acute-phase response

The acute-phase (AP) serum amyloid A proteins (A-SAA) are multifunctional apolipoproteins which are involved in cholesterol transport and metabolism, and in modulating numerous immunological responses during inflammation and the AP response to infection, trauma or stress. During the AP response the hepatic biosynthesis of A-SAA is up-regulated by pro-inflammatory cytokines, and circulating concentrations can increase by up to 1000-fold. Chronically elevated A-SAA concentrations are a prerequisite for the pathogenesis of secondary amyloidosis, a progressive and fatal disease characterized by the deposition in major organs of insoluble plaques composed principally of proteolytically cleaved A-SAA, and may also contribute to physiological processes that lead to atherosclerosis. There is therefore a requirement for both positive and negative control mechanisms that permit the rapid induction of A-SAA expression until it has fulfilled its host-protective function(s) and subsequently ensure that its expression can be rapidly returned to baseline. These mechanisms include modulation of promoter activity involving, for example, the inducer nuclear factor kappaB (NF-kappaB) and its inhibitor IkappaB, up-regulatory transcription factors of the nuclear factor for interleukin-6 (NF-IL6) family and transcriptional repressors such as yin and yang 1 (YY1). Post-transcriptional modulation involving changes in mRNA stability and translation efficiency permit further up- and down-regulatory control of A-SAA protein synthesis to be achieved. In the later stages of the AP response, A-SAA expression is effectively down-regulated via the increased production of cytokine antagonists such as the interleukin-1 receptor antagonist (IL-1Ra) and of soluble cytokine receptors, resulting in less signal transduction driven by pro-inflammatory cytokines.

Testosterone and IL-6 Requirements for Human C-Reactive Protein Gene Expression in Transgenic Mice

In vitro, IL-6 is the main inducer of the human C-reactive protein (CRP) gene, and IL-1 and steroids can enhance this effect. However, in mice, IL-6 is necessary but not sufficient for induction of the human CRP transgene, and testosterone is required for its constitutive expression by males. To examine the relative contributions of testosterone and IL-6 in the regulation of CRP gene expression, we produced CRP-transgenic (CRPtg), IL-6-deficient (IL-6−/−) mice. Male CRPtg/IL-6−/− mice expressed CRP constitutively, but CRP levels were not increased after injection of LPS. However, acute-phase CRP levels were attained after injection of IL-6. In contrast, female CRPtg/IL-6−/− mice did not express CRP constitutively or after administration of LPS, IL-6, IL-1, or IL-6 plus IL-1. Like males, testosterone-treated CRPtg/IL-6−/− females expressed CRP constitutively, and their transgene responded to injection of IL-6. The endogenous acute-phase protein serum amyloid P (SAP) was expressed constitutively equally by male and female IL-6−/− mice, responded minimally to LPS, and did not respond to either IL-6 or IL-1 alone. Acute-phase levels of SAP were induced in IL-6−/− mice by injection of IL-6 together with IL-1 or LPS. We conclude that in vivo, both constitutive and IL-6-dependent acute-phase expression of the CRP transgene require testosterone. In contrast, testosterone is not required for expression of the SAP gene, which requires IL-1 plus IL-6 for acute-phase induction.

Mice Lacking Both Granulocyte Colony-Stimulating Factor (CSF) and Granulocyte-Macrophage CSF Have Impaired Reproductive Capacity, Perturbed Neonatal Granulopoiesis, Lung Disease, Amyloidosis, and Reduced Long-Term Survival

Mice lacking granulocyte colony-stimulating factor (G-CSF) are neutropenic with reduced hematopoietic progenitors in the bone marrow and spleen, whereas those lacking granulocyte-macrophage colony-stimulating factor (GM-CSF) have impaired pulmonary homeostasis and increased splenic hematopoietic progenitors, but unimpaired steady-state hematopoiesis. These contrasting phenotypes establish unique roles for these factors in vivo, but do not exclude the existence of additional redundant functions. To investigate this issue, we generated animals lacking both G-CSF and GM-CSF. In the process of characterizing the phenotype of these animals, we further analyzed G-CSF– and GM-CSF–deficient mice, expanding the recognized spectrum of defects in both. G-CSF–deficient animals have a marked predisposition to spontaneous infections, a reduced long-term survival, and a high incidence of reactive type AA amyloidosis. GM-CSF–deficient mice have a modest impairment of reproductive capacity, a propensity to develop lung and soft-tissue infections, and a similarly reduced survival as in G-CSF–deficient animals. The phenotype of mice lacking both G-CSF and GM-CSF was additive to the features of the constituent genotypes, with three novel additional features: a greater degree of neutropenia among newborn mice than in those lacking G-CSF alone, an increased neonatal mortality rate, and a dominant influence of the lack of G-CSF on splenic hematopoiesis resulting in significantly reduced numbers of splenic progenitors. In contrast to newborn animals, adult mice lacking both G-CSF and GM-CSF exhibited similar neutrophil levels as G-CSF–deficient animals. These findings demonstrate that the additional lack of GM-CSF in G-CSF–deficient animals further impairs steady-state granulopoiesis in vivo selectively during the early postnatal period, expand the recognized roles of both G-CSF and GM-CSF in vivo, and emphasize the utility of studying multiply deficient mouse strains in the investigation of functional redundancy.

Interleukin 1 receptor antagonist (IL-1Ra) is an acute-phase protein

Interleukin 1 receptor antagonist (IL-1Ra) levels are elevated in the blood of patients with a variety of infectious, immune, or traumatic conditions. To examine whether IL1Ra is produced by liver cells with characteristics resembling an acute-phase protein, human primary hepatocytes isolated from liver biopsies and HepG2 hepatoma cells were stimulated with IL-1beta, IL-6, and TNFalpha. IL-1Ra was present in the supernatants of both cells, with production significantly enhanced by IL-1beta, and by the combination of IL-1beta and IL-6. The term IL-1Ra refers to two different proteins encoded by the same gene, but generated by alternative splicing of two different first exons. One isoform is secreted (17-kD sIL-1Ra), and the other isoform remains in the cytoplasm (18-kD icIL-1Ra). By Western blot analysis, the supernatants of human hepatoma (HepG2) cells contained only sIL-1Ra, whereas the lysates contained a novel smaller molecular mass isoform of 16 kD. RT-PCR and ribonuclease protection assay with RNA from HepG2 cells showed that only sIL-1Ra mRNA was expressed, and confirmed the inducing effect of IL-1beta and IL-6. Transfection studies were performed using constructs containing the promoters of either sIL-1Ra or icIL-1Ra coupled to the luciferase reporter gene. The sIL-1Ra promoter was active in HepG2 cells stimulated by IL-1beta and/or IL-6, whereas the icIL-1Ra promoter was inactive. Mutation of binding sites for transcription factors NF-kappaB and/or C/EBP within the proximal sIL-1Ra promoter led to significant decreases in response to IL-1beta and IL-6 in comparison to the wild-type promoter. Electromobility gel shift assays confirmed the presence of NF-kappaB and C/EBP binding sites within the sIL-1Ra promoter, and indicated a significant increase in the binding activities of nuclear proteins from HepG2 cells treated with IL-1beta and IL-6. In summary, sIL-1Ra, but not icIL-1Ra, is produced by hepatocytes, and is regulated by proinflammatory cytokines as an acute-phase protein. In addition, NF-kappaB and C/EBP family members are likely to play important roles in the full expression of IL-1Ra by hepatocytes during inflammatory conditions.

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.

Cytokines and the hepatic acute phase response

The acute phase response is an orchestrated response to tissue injury, infection or inflammation. A prominent feature of this response is the induction of acute phase proteins, which are involved in the restoration of homeostasis. Cytokines are important mediators of the acute phase response. Uncontrolled and prolonged action of cytokines is potentially harmful, therefore mechanisms exist which limit the activity of cytokines; these include soluble cytokine receptors and receptor antagonists. The cytokine signal is transmitted into the cell via membrane-bound receptors. Different intracellular signalling pathways are activated by different cytokine-receptor interactions. Eventually, cytokine-inducible transcription factors interact with their response elements in the promotor region of acute phase genes and transcription is induced. Systemic inflammation results in a systemic acute phase response. However, local inflammatory or injurious processes in the liver may also induce an acute phase response, for example after partial hepatectomy and during hepatic fibrosis. The acute phase proteins induced in these conditions probably act to limit proteolytic and/or fibrogenic activity and tissue damage. The possible function of the acute phase protein alpha 2-macroglobulin in hepatic fibrosis is discussed in some detail.