Rapid clearance of serum amyloid A from high-density lipoproteins

Serum Amyloid A Stimulates Vascular and Renal Dysfunction in Apolipoprotein E-Deficient Mice Fed a Normal Chow Diet

Elevated serum amyloid A (SAA) levels may promote endothelial dysfunction, which is linked to cardiovascular and renal pathologies. We investigated the effect of SAA on vascular and renal function in apolipoprotein E-deficient (ApoE^−/−) mice. Male ApoE^−/− mice received vehicle (control), low-level lipopolysaccharide (LPS), or recombinant human SAA by i.p. injection every third day for 2 weeks. Heart, aorta and kidney were harvested between 3 days and 18 weeks after treatment. SAA administration increased vascular cell adhesion molecule (VCAM)-1 expression and circulating monocyte chemotactic protein (MCP)-1 and decreased aortic cyclic guanosine monophosphate (cGMP), consistent with SAA inhibiting nitric oxide bioactivity. In addition, binding of labeled leukocytes to excised aorta increased as monitored using an ex vivo leukocyte adhesion assay. Renal injury was evident 4 weeks after commencement of SAA treatment, manifesting as increased plasma urea, urinary protein, oxidized lipids, urinary kidney injury molecule (KIM)-1 and multiple cytokines and chemokines in kidney tissue, relative to controls. Phosphorylation of nuclear-factor-kappa-beta (NFκB-p-P65), tissue factor (TF), and macrophage recruitment increased in kidneys from ApoE^−/− mice 4 weeks after SAA treatment, confirming that SAA elicited a pro-inflammatory and pro-thrombotic phenotype. These data indicate that SAA impairs endothelial and renal function in ApoE^−/− mice in the absence of a high-fat diet.

Impact of individual acute phase serum amyloid A isoforms on HDL metabolism in mice

The acute phase (AP) reactant serum amyloid A (SAA), an HDL apolipoprotein, exhibits pro-inflammatory activities, but its physiological function(s) are poorly understood. Functional differences between SAA1.1 and SAA2.1, the two major SAA isoforms, are unclear. Mice deficient in either isoform were used to investigate plasma isoform effects on HDL structure, composition, and apolipoprotein catabolism. Lack of either isoform did not affect the size of HDL, normally enlarged in the AP, and did not significantly change HDL composition. Plasma clearance rates of HDL apolipoproteins were determined using native HDL particles. The fractional clearance rates (FCRs) of apoA-I, apoA-II, and SAA were distinct, indicating that HDL is not cleared as intact particles. The FCRs of SAA1.1 and SAA2.1 in AP mice were similar, suggesting that the selective deposition of SAA1.1 in amyloid plaques is not associated with a difference in the rates of plasma clearance of the isoforms. Although the clearance rate of SAA was reduced in the absence of the HDL receptor, scavenger receptor class B type I (SR-BI), it remained significantly faster compared with that of apoA-I and apoA-II, indicating a relatively minor role of SR-BI in SAA's rapid clearance. These studies enhance our understanding of SAA metabolism and SAA's effects on AP-HDL composition and catabolism.

Identification of potential serum biomarkers for Wilms tumor after excluding confounding effects of common systemic inflammatory factors

Wilms tumor is the most common pediatric tumor of the kidney. Previous studies have identified several serum biomarkers for Wilms tumor; however, they lack sufficient specificity and may not adequately distinguish Wilms tumor from confounding conditions. To date, no specific protein biomarker has been confirmed for this pediatric tumor. To identify novel serum biomarkers for Wilms tumor, we used proteomic technologies to perform protein profiling of serum samples from pre-surgery and post-surgery patients with Wilms tumor and healthy controls. Some common systemic inflammatory factors were included to control for systemic inflammation. By comparing protein peaks among the three groups of sera, we identified two peaks (11,526 and 4,756 Da) showing significant differential expression not only between pre-surgery and control sera but also between pre-surgery and post-surgery sera. These two peaks were identified as serum amyloid A1 (SAA1) and apolipoprotein C-III (APO C-III). Western blot analysis confirmed that both proteins were expressed at higher levels in pre-surgery sera than in post-surgery and control sera. Using the method of leave-1-out for cross detection, we demonstrate that detection of these two candidate biomarkers had high sensitivity and specificity in discriminating pre-surgery sera from post-surgery and normal control sera. Taken together, these findings suggest that SAA1 and APO C-III are two potential biomarkers for Wilms tumor.

Serum amyloid A as a marker and mediator of acute coronary syndromes

Inflammation promotes acute coronary syndromes and ensuing clinical complications. An emerging downstream marker of inflammation is serum amyloid A (SAA). Elevated plasma SAA levels predict increased cardiovascular risk and portend worse prognosis in patients with acute coronary artery disease (CAD). The pathophysiological role of SAA remains enigmatic. SAA plays a role in host defense, but it might also be atherogenic. SAA affects cholesterol transport, contributes to endothelial dysfunction, promotes thrombosis, evokes recruitment of inflammatory cells, activates neutrophils and suppresses neutrophil apoptosis, key events underlying acute coronary syndromes. These results provide a potential link between SAA and CAD and suggest that reducing SAA levels and/or opposing the actions of SAA may have beneficial effects in patients with acute CAD.

Serum amyloid A protein in acute myocardial infarction

Tissue injury including myocardial infarction leads to a variety of changes in plasma proteins commonly referred to as "the acute phase response". In this report the concentrations of serum amyloid A protein (SAA) were measured serially in 6 patients with myocardial infarction and 4 with angina. SAA was found to be increased in all patients with infarction, but in no patients with angina. Significantly increased SAA levels were detected 12 hours after the peak level of creatine kinase, and the concentrations of SAA seemed to correlate to the amount of damaged tissue. The SAA-response was both faster and more extensive than the response of C-reactive protein (CRP), but the correlation between SAA and CRP was very good.

Aberrant expression of serum amyloid A in head and neck squamous cell carcinoma

Serum amyloid A (SAA) is an acute-phase reactant, the blood level of which is often elevated in response to some types of neoplasia. Here, we investigated expression of the gene SAA1 and the protein SAA in head and neck squamous cell carcinoma (HNSCC) and normal oral mucosal tissues as well as blood SAA levels in HNSCC patients. Also, we investigated the effects of inhibiting signal transducer and activator of transcription 3 (STAT3) signaling on SAA1 expression in the HNSCC cell line SAS. Serum SAA levels in HNSCC patients were significantly higher than those in healthy volunteers. In addition, real-time quantitative reverse transcription-polymerase chain reaction analysis revealed a significantly higher SAA1 expression level in HNSCC than in normal mucosa (P < 0.0001). Furthermore, Western blot and immunohistochemical analyzes revealed that high expression of SAA in carcinomas was detected predominantly in tumor cells, but not in normal mucosal tissues. An inhibitor of STAT3 activation, AG490, significantly reduced SAA1 expression in SAS cells. These data demonstrated that SAA was up-regulated in HNSCC through the Janus kinase-STAT3 pathway.

Serum amyloid A induces CCL2 production via formyl peptide receptor-like 1-mediated signaling in human monocytes

Although the presence of an elevated level of serum amyloid A (SAA) has been regarded as a cardiovascular risk factor, the role of SAA on the progress of atherosclerosis has not been fully elucidated. In the present study, we investigated the effect of SAA on the production of CCL2, an important mediator of monocyte recruitment, and the mechanism underlying the action of SAA in human monocytes. The stimulation of human monocytes with SAA elicited CCL2 production in a concentration-dependent manner. The production of CCL2 by SAA was found to be mediated by the activation of NF-kappaB. Moreover, the signaling events induced by SAA included the activation of ERK and the induction of cyclooxygenase-2, which were required for the production of CCL2. Moreover, SAA-induced CCL2 induction was inhibited by a formyl peptide receptor-like 1 (FPRL1) antagonist. We also found that the stimulation of FPRL1-expressing RBL-2H3 cells induced CCL2 mRNA accumulation, but the vector-expressing RBL-2H3 cells combined with SAA did not. Taken together, our findings suggest that SAA stimulates CCL2 production and, thus, contributes to atherosclerosis. Moreover, FPRL1 was found to be engaged in SAA-induced CCL2 induction, and cyclooxygenase-2 induction was found to be essential for SAA-induced CCL2 expression. These results suggest that SAA and FPRL1 offer a developmental starting point for the treatment of atherosclerosis.

Opposing regulation of neutrophil apoptosis through the formyl peptide receptor-like 1/lipoxin A4 receptor: implications for resolution of inflammation

Neutrophils have a central role in innate immunity, and their programmed cell death and removal are critical to the optimal expression as well as to efficient resolution of inflammation. Human neutrophils express the pleiotropic receptor formyl peptide receptor-like 1/lipoxin A4 (LXA(4)) receptor that binds a variety of ligands, including the acute-phase reactant serum amyloid A (SAA), the anti-inflammatory lipids LXA(4) and aspirin-triggered 15-epi-LXA(4) (ATL), and the glucocorticoid-inducible protein annexin 1. In addition to regulation of neutrophil activation and recruitment, these ligands have a profound influence on neutrophil survival and apoptosis with contrasting actions, mediating aggravation or resolution of the inflammatory response. Thus, annexin 1 accelerates, whereas SAA rescues human neutrophils from constitutive apoptosis by preventing mitochondrial dysfunction and subsequent activation of caspase-3. Furthermore, ATL overcomes the antiapoptosis signal from SAA and redirects neutrophils to caspase-mediated cell death. We review recent developments about the molecular basis of these actions and suggest a novel mechanism by which aspirin promotes resolution of acute inflammation and tissue injury.

Serum proteome analysis for profiling protein markers associated with carcinogenesis and lymph node metastasis in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC), one of the most common cancers in population with Chinese or Asian progeny, poses a serious health problem for southern China. It is unfortunate that most NPC victims have had lymph node metastasis (LNM) when first diagnosed. We believe that the 2D based serum proteome analysis can be useful in discovering new biomarkers that may aid in the diagnosis and therapy of NPC patients. To filter the tumor specific antigen markers of NPC, sera from 42 healthy volunteers, 27 non-LNM NPC patients and 37 LNM NPC patients were selected for screening study using 2D combined with MS. Pretreatment strategy, including sonication, albumin and immunoglobulin G (IgG) depletion, was adopted for screening differentially expressed proteins of low abundance in serum. By 2D image analysis and MALDI-TOF-MS identification, twenty-three protein spots were differentially expressed. Three of them were further validated in the sera using enzyme-linked immunosorbent assay (ELISA). Our research demonstrates that HSP70, sICAM-1 and SAA, confirmed with ELISA at sera and immunohistochemistry, are potential NPC metastasis-specific serum biomarkers which may be of great underlying significance in clinical detection and management of NPC.

Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Elevated plasma levels of the acute-phase reactant serum amyloid A (SAA) have been used as a marker and predictor of inflammatory diseases. SAA regulates leukocyte activation; however, it is not known whether it also modulates neutrophil apoptosis, which is critical to the optimal expression and resolution of inflammation. Culture of human neutrophils with SAA (0.1-20 microg/ml) markedly prolonged neutrophil longevity by delaying constitutive apoptosis. SAA evoked concurrent activation of the ERK and PI3K/Akt signaling pathways, leading to phosphorylation of BAD at Ser(112) and Ser(136), respectively, and to prevention of collapse of mitochondrial transmembrane potential, cytochrome c release, and caspase-3 activation. These actions were abrogated by pharmacological inhibition of the formyl peptide receptor, ERK or PI3K. Furthermore, aspirin-triggered 15-epi-lipoxin A(4) (15-epi-LXA(4)) and its stable analog 15-epi-16-p-fluorophenoxy-LXA(4), which binds to the same receptor as SAA, effectively overrode the antiapoptosis signal from SAA even when neutrophils were treated with 15-epi-LXA(4) at either 1 or 4 h postculture with SAA. 15-Epi-LXA(4) itself did not affect neutrophil survival and apoptosis. Our results indicate that SAA at clinically relevant concentrations promotes neutrophil survival by suppressing the apoptotic machinery, an effect that can be opposed by 15-epi-LXA(4). The opposing actions of SAA and aspirin-triggered 15-epi-LXA(4) may contribute to the local regulation of exacerbation and resolution of inflammation, respectively.

Distinctive serum protein profiles involving abundant proteins in lung cancer patients based upon antibody microarray analysis

Background

Cancer serum protein profiling by mass spectrometry has uncovered mass profiles that are potentially diagnostic for several common types of cancer. However, direct mass spectrometric profiling has a limited dynamic range and difficulties in providing the identification of the distinctive proteins. We hypothesized that distinctive profiles may result from the differential expression of relatively abundant serum proteins associated with the host response.

Methods

Eighty-four antibodies, targeting a wide range of serum proteins, were spotted onto nitrocellulose-coated microscope slides. The abundances of the corresponding proteins were measured in 80 serum samples, from 24 newly diagnosed subjects with lung cancer, 24 healthy controls, and 32 subjects with chronic obstructive pulmonary disease (COPD). Two-color rolling-circle amplification was used to measure protein abundance.

Results

Seven of the 84 antibodies gave a significant difference (p < 0.01) for the lung cancer patients as compared to healthy controls, as well as compared to COPD patients. Proteins that exhibited higher abundances in the lung cancer samples relative to the control samples included C-reactive protein (CRP; a 13.3 fold increase), serum amyloid A (SAA; a 2.0 fold increase), mucin 1 and α-1-antitrypsin (1.4 fold increases). The increased expression levels of CRP and SAA were validated by Western blot analysis. Leave-one-out cross-validation was used to construct Diagonal Linear Discriminant Analysis (DLDA) classifiers. At a cutoff where all 56 of the non-tumor samples were correctly classified, 15/24 lung tumor patient sera were correctly classified.

Conclusion

Our results suggest that a distinctive serum protein profile involving abundant proteins may be observed in lung cancer patients relative to healthy subjects or patients with chronic disease and may have utility as part of strategies for detecting lung cancer.

Identification of Serum Amyloid A Protein As a Potentially Useful Biomarker to Monitor Relapse of Nasopharyngeal Cancer by Serum Proteomic Profiling

PURPOSE

Nasopharyngeal cancer (NPC) is a common cancer in Hong Kong, and relapse can occur frequently. Using protein chip profiling analysis, we aimed to identify serum biomarkers that were useful in the diagnosis of relapse in NPC.

EXPERIMENTAL DESIGN

Profiling analysis was performed on 704 sera collected from 42 NPC patients, 39 lung cancer patients, 30 patients with the benign metabolic disorder thyrotoxicosis (TX), and 35 normal individuals (NM). Protein profile in each NPC patient during clinical follow up was correlated with the relapse status.

RESULTS

Profiling analysis identified two biomarkers with molecular masses of 11.6 and 11.8 kDa, which were significantly elevated in 22 of 31 (71%) and 21 of 31 (68%) NPC patients, respectively, at the time of relapse (RP) as compared with 11 patients in complete remission (CR; RP versus CR, P = 0.009), 30 TX (RP versus TX, P < 0.001), or 35 NM (RP versus NM, P < 0.001). The markers were also elevated in 16 of 39 (41%) lung cancer patients at initial diagnosis. By tryptic digestion, followed by tandem mass spectrometry fragmentation, the markers were identified as two isoforms of serum amyloid A (SAA) protein. Monitoring the patients longitudinally for SAA level both by protein chip and immunoassay showed a dramatic SAA increase, which correlated with relapse and a drastic fall correlated with response to salvage chemotherapy. Serum SAA findings were compared with those of serum Epstein-Barr virus DNA in three relapsed patients showing a similar correlation with relapse and chemo-response.

CONCLUSIONS

SAA could be a useful biomarker to monitor relapse of NPC.

Serum amyloid A induces IL-8 secretion through a G protein-coupled receptor, FPRL1/LXA4R

Host response to injury and infection is accompanied by a rapid rise in the blood of acute-phase proteins such as serum amyloid A (SAA). Although SAA has been used as a marker for inflammatory diseases, its role in the modulation of inflammation and immunity has not been defined. Human neutrophils respond to SAA with secretion of the proinflammatory cytokines interleukin 8 (IL-8) and, to a lesser extent, tumor necrosis factor alpha (TNF-alpha). The induction of IL-8 secretion by SAA involves both transcription and translation and correlates with activation of nuclear factor kappaB (NF-kappaB). The proximal signaling events induced by SAA include mobilization of intracellular Ca(2+) and activation of the mitogen-activated protein kinases ERK1/2 and p38, both required for the induced IL-8 secretion. Pertussis toxin effectively blocks SAA-induced IL-8 secretion indicating involvement of a Gi-coupled receptor. Overexpression of FPRL1/LXA4R in HeLa cells results in a significant increase of the expression of NF-kappaB and IL-8 luciferase reporters by SAA, and an antibody against the N-terminal domain of FPRL1/LXA4R inhibits IL-8 secretion. Lipoxin A4, which binds to FPRL1/LXA4R specifically, decreases SAA-induced IL-8 secretion significantly. Collectively, these results indicate that the cytokine-like property of SAA is manifested through activation of the Gi-coupled FPRL1/LXA4R, which has been known to mediate the anti-inflammatory effects of lipoxin A4. The ability of FPRL1/LXA4R to mediate 2 drastically different and opposite functions suggests that it plays a role in the modulation of inflammatory and immune responses.

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.

New insights into the biology of the acute phase response

Innate or natural immunity is a highly conserved defense mechanism against infection found in all multicellular organisms. The acute phase response is the set of immediate inflammatory responses initiated by pattern recognition molecules. These germ cell-encoded proteins recognize microbial pathogens based on shared molecular structures and induce host responses that localize the spread of infection and enhance systemic resistance to infection. Innate immunity also influences the initiation and type of adaptive immune response by regulating T cell costimulatory activity and antigen presentation by antigen presenting cells and by influencing mediator production, which affects lymphocyte function and trafficking. Acute phase protein concentrations rapidly increase after infection, and their production is controlled primarily by IL-6- and IL-1-type cytokines. The acute phase proteins provide enhanced protection against microorganisms and modify inflammatory responses by effects on cell trafficking and mediator release. For example, serum amyloid A has potent leukocyte activating functions including induction of chemotaxis, enhancement of leukocyte adhesion to endothelial cells, and increased phagocytosis. The constellation of inflammatory responses seen after endotoxin administration to humans represents an in vivo model of the acute phase response. Studies with inflammatory modifying agents, such as soluble dimeric TNF receptor and IL-10, show that these responses are not dependent on a single mediator but result from multiple overlapping inflammatory pathways. Understanding the factors that initiate and alter the magnitude and duration of the acute phase response represents an important step in the development of new therapies for infectious and inflammatory diseases.

Catabolism of lipid-free recombinant apolipoprotein serum amyloid A by mouse macrophages in vitro results in removal of the amyloid fibril-forming amino terminus

Serum amyloid A fibrils are formed when the normally rapid catabolism of the acute-phase reactant apolipoprotein serum amyloid A (apoSAA) is incomplete; thus amyloidosis may be viewed as a condition of dysregulated proteolysis. There is evidence that apoSAA is dissociated from plasma high-density lipoprotein (HDL) prior to fibril formation. The objective of this study was to investigate degradation of lipid-free apoSAA by tissue macrophages derived from amyloid-susceptible CBA/J mice in vitro. Peritoneal macrophages derived from untreated (normal) mice converted apoSAA (12 kDa) to a single 4 kDa C-terminal peptide while splenic macrophages converted apoSAA to 10, 7 and 4 kDa C-terminal peptides and a 4 kDa peptide that lacked the C- and N-terminal regions. Similar patterns of proteolysis occurred when peritoneal and splenic macrophages from amyloidotic CBA/J mice were used. Conditioned medium prepared from peritoneal, but not splenic macrophages, degraded apoSAA. Specific sites of cleavage indicated activity of cathepsin G- and elastase-like neutral proteases. The data indicate that lipid-free apoSAA can be degraded by secreted or cell-associated neutral proteases that are generated by macrophages to yield peptides that lack fibrillogenic potential.

Differential plasma clearance of murine acute-phase serum amyloid A proteins SAA1 and SAA2

Serum amyloid A (SAA) proteins SAA1 and SAA2 are prominent acute-phase reactants which circulate in association with the high-density-lipoprotein (HDL) fraction of plasma. Plasma levels of SAA1 and SAA2 increase dramatically, by as much as 1000-fold, within 24 h of tissue injury and then rapidly decrease with cessation of the inflammatory stimulus, suggesting that SAA clearance and/or catabolism is important to the re-establishment of homoeostasis. In this context, aberrant SAA catabolism has long been considered a potential factor in the pathogenesis of reactive amyloidosis. To initiate studies aimed at understanding the differential regulation of SAA metabolism, we have produced 35S-labelled murine SAA1 and SAA2 in Escherichia coli, bound them individually to HDL, and then compared the plasma-clearance characteristics of SAA1 and SAA2 under normal and acute-phase conditions. When bound to normal HDL, SAA2 [half-life (t1/2) = 30 min] was cleared significantly faster than SAA1 (t1/2 = 75 min). Clearance of SAA1 and SAA2 was significantly slower when each was bound to acute-phase HDL as opposed to normal HDL, when clearance rates were determined in acute-phase mice versus normal mice, and when normal HDL was remodelled to contain both recombinant isotypes rather than just one of the isotypes. Thus it appears that an increased amount of SAA on HDL, or possibly the combined presence of both isotypes on HDL, is associated with a prolongation in the plasma half-life of SAA.

Serum amyloid A (SAA): an acute phase protein and apolipoprotein

Serum amyloid A (SAA) proteins comprise a family of apolipoproteins coded for by at least three genes with allelic variation and a high degree of homology between species. The synthesis of certain members of the family is greatly increased in inflammation. However, SAA is not often used as an acute-phase marker despite being at least as sensitive as C-reactive protein. SAA proteins can be considered as apolipoproteins since they associate with plasma lipoproteins mainly within the high density range, perhaps through amphipathic alpha-helical structure. It is not known why certain subjects expressing SAA develop secondary systemic amyloidosis. There is still no specific function attributed to SAA; however, a popular hypothesis suggests that SAA may modulate metabolism of high density lipoproteins (HDL). This may impede the protective function of HDL against the development of atherosclerosis. The potential significance of the association between SAA and lipoproteins needs further evaluation.

A functional characterization of macrophage alterations in casein-treated B6C3F1 mice

We have previously reported that subcutaneous injection of casein, a potent inducer of the immunomodulatory acute phases reactant, serum amyloid A (SAA) protein, produces a marked suppression of humoral responses that require macrophage accessory cell cooperativity in the B6C3F1 mouse. The objective of these studies was to further characterize the immunological changes produced by casein treatment. It was observed that the inhibition of the sRBC IgM AFC response which accompanies casein treatment is dose related to the amount of casein introduced subcutaneously to the mouse. These studies, as well as those previously reported by several laboratories including our own have demonstrated that spleen cells isolated from casein-treated mice also exhibit markedly suppressed humoral responses in vitro. However, casein added directly to naive spleen cell cultures at concentrations significantly higher than those which would be found in the lymphoid tissues of the intact animal have no direct inhibitory effect on the sRBC IgM AFC response, suggesting that casein alone does not exert a direct immunosuppressive effect. Kinetics of recovery studies indicate that the casein-induced immunosuppression is readily reversible. Humoral responses are fully recovered within 3 days, once subcutaneous injections of casein are terminated. In vitro measurements of IL-1 secretion following stimulation of splenic macrophages, isolated from casein treated mice, with lipopolysaccharide indicate no significant effect on the capacity of these cells to produce this cytokine. Direct addition of recombinant IL-1 or interferon-gamma to spleen cell cultures isolated from casein-treated mice also was found to be incapable of reversing the inhibited IgM AFC response. Taken together, these studies strongly suggest that the accessory cell dysfunction associated with macrophages from casein-treated mice is not due to the inability of these cells to secrete IL-1 and indicate that the dysfunction cannot be reversed by IL-1 or interferon-gamma. Casein treatment was also found to markedly inhibit DTH, a cell-mediated immune response requiring macrophage accessory cell function. interestingly, the DTH responses were only affected by casein when it was administered post-sensitization with antigen (sRBC) but prior to antigen challenge. When casein was administered prior to sensitization with antigen, which is analogous to the treatment schedule that was found to suppress the sRBC antibody response, no effect was observed on DTH.

Serum amyloid A protein in very low density--and high density lipoproteins during the course of acute myocardial infarction

In a preceding paper we reported on the detection and characterization of human serum amyloid A protein (SAA) in very low density lipoproteins (VLDL) and high density lipoproteins (HDL) of patients after acute myocardial infarction. Here we describe the time course of the occurrence of SAA in VLDL and HDL in the postinfarction period. SAA reached its maximum in VLDL and HDL approximately 53 h after the acute event. At the peak of the acute-phase response, SAA comprised as much as 38% of the total apoproteins of VLDL and HDL. SAA appeared at the same points in time and with nearly the same concentrations in VLDL and HDL. We conclude that SAA is not exchanged in plasma between lipoproteins of different densities and that this protein is secreted on its own by hepatocytes and not as a part of an already constituted lipoprotein particle.

Acute-phase protein synthesis in human hepatoma cells: differential regulation of serum amyloid A (SAA) and haptoglobin by interleukin-1 and interleukin-6

Interleukin-6 (IL-6, BSF-2 or IFN-beta 2) is thought to be the major regulator of the acute-phase protein response that follows tissue injury and inflammation, with interleukin-1 (IL-1), tumour necrosis factor and more recently, LIF or HSF III, slightly stimulatory on only certain acute phase proteins. The synthesis of the major acute-phase protein SAA, originally described as being synthesized in response to IL-1, has been claimed recently to be mainly under IL-6 regulation. Our results show that in the human hepatoma cell line HuH-7, IL-1 is the major stimulating cytokine increasing SAA synthesis by a factor in excess of 100-fold. We also show that under most conditions interleukin-6 and tumour necrosis factor stimulate additively in combination with IL-1. Isoelectric focusing has demonstrated that SAA1 and SAA2 alpha are expressed but not SAA2 beta. The HuH-7 cell line is IL-6 responsive since haptoglobin is stimulated mainly by IL-6.

Purification and characterization of hamster serum amyloid A protein (SAA) by cholesteryl hemisuccinate affinity chromatography

High-density lipoprotein (HDL) apolipoprotein was separated from hamster serum by cholesteryl hemisuccinate affinity chromatography (CHAC) in comparison with the density-gradient ultracentrifugation (DGUC). The apolipoprotein recovery from serum by CHAC was 70% and by DGUC 80%. This disadvantage is compensated for by the ease of purification by CHAC, a method particularly suited for the processing of large amounts of serum. From the acute-phase HDL CHAC fraction, apo SAA was isolated by gel filtration. Using isoelectrofocusing, two-dimensional gel electrophoresis, and titration curve, four isotypes of hamster apo SAA were identified and characterized. In the acute-phase serum, one of the isotypes was predominant (apo SAA1). In serum of amyloidotic animals, the relative contribution of apo SAA1 was considerably lower, suggesting selective removal of the latter during amyloidogenesis and possibly its deposition in hamster AA amyloid. Furthermore, the affinity chromatography method was modified with gradient elution of affinity-bound material. By this method HDL apolipoprotein was separated into three subclasses. Apo SAA was shown to associate with two different subclasses. In acute-phase serum most of the apo SAA1 was found in the subclass with the lowest affinity for the cholesteryl beads, whereas the latter was depressed in amyloidotic serum, suggesting that the amyloidogenicity of a particular apo SAA isotype is determined by its cholesteryl-binding properties.

Evidence for qualitative abnormalities in high-density lipoproteins from myeloma patients: the presence of amyloid A protein could explain HDL modifications

HDL apolipoproteins (apo) from normal subjects and patients with multiple myeloma were studied by isoelectric focusing (IEF) and by two-dimensional gel electrophoresis. Qualitative abnormalities were detected in myeloma HDL apolipoproteins. We observed two new bands not previously described in this disease. As determined by IEF and two-dimensional gel electrophoresis, the relative molecular weight of these two proteins was 12,600, with pI = 6.04 and 6.36, respectively. They correspond to two isoforms of serum amyloid A protein (SAA), as confirmed by western blot assay against specific antiserum to SAA. The high sensitivity of this assay revealed also other SAA isoforms. Our data are consistent with the hypothesis that major apolipoproteins of normal HDL, apo A-I and apo A-II, could be displaced by SAA isoproteins in myeloma HDL. This could lead structural changes in HDL.

Dyslipoproteinemia in pediatric systemic lupus erythematosus

Patients with systemic lupus erythematosus are at increased risk for premature atherosclerosis. We examined one possible etiologic factor, dyslipoproteinemia, both before and after corticosteroid therapy. We identified 2 distinct patterns of dyslipoproteinemia. One is attributable to active disease; the other is attributable, in part, to corticosteroid therapy. The dyslipoproteinemia of active disease consists of depressed high density lipoprotein cholesterol and apoprotein A-I with elevated very low density lipoprotein cholesterol and triglyceride, while the dyslipoproteinemia after corticosteroid therapy consists of increased total cholesterol, very low density lipoprotein cholesterol, and triglyceride. The possible pathophysiologic mechanisms responsible for these patterns, as well as the possible roles in premature atherosclerosis seen in systemic lupus erythematosus patients, are discussed.

Neutrophil association and degradation of normal and acute-phase high-density lipoprotein 3

The interaction of normal and acute-phase high-density lipoproteins of the subclass 3 (N-HDL3 and AP-HDL3) with human neutrophils and the accompanying degradation of HDL3 apolipoproteins have been studied in vitro. The chemical composition of normal and acute-phase HDL3 was similar except that serum amyloid A protein (apo-SAA) was a major apolipoprotein in AP-HDL3 (approx. 30% of total apolipoproteins). 125I-labelled AP-HDL3 was degraded 5-10 times faster than 125I-labelled N-HDL3 during incubation with neutrophils or neutrophil-conditioned medium. Apo-SAA, like apolipoprotein A-II (apo-A-II), was more susceptible than apolipoprotein A-I (apo-A-I) to the action of proteases released from the cells. The amounts of cell-associated AP-HDL3 apolipoproteins at saturation were up to 2.8 times greater than N-HDL3 apolipoproteins; while apo-A-I was the major cell-associated apolipoprotein when N-HDL3 was bound, apo-SAA constituted 80% of the apolipoproteins bound in the case of AP-HDL3. The associated intact apo-SAA was mostly surface-bound as it was accessible to the action of exogenous trypsin. alpha 1-Antitrypsin-resistant (alpha 1-AT-resistant) cellular degradation of AP-HDL3 apolipoproteins also occurred; experiments in which pulse-chase labelling was performed or lysosomotropic agents were used indicated that insignificant intracellular degradation occurred which points to the involvement of cell-surface proteases in this degradation.

Dyslipoproteinemia in systemic lupus erythematosus. Effect of corticosteroids

The increased incidence of atherosclerotic coronary artery disease in patients with systemic lupus erythematosus (SLE) may be due to a dyslipoproteinemia caused by corticosteroid administration. To determine whether lipoprotein lipid levels are abnormal in SLE and the relation of lipoprotein levels to corticosteroid use, lipid and apolipoprotein levels were measured in 46 female patients with SLE and 30 matched control subjects. The patients with SLE had higher levels of plasma triglyceride (134 versus 73 mg/dl; p less than 0.001), cholesterol (201 versus 168 mg/dl; p less than 0.001), and low-density lipoprotein cholesterol (121 versus 94 mg/dl; p less than 0.001) than control subjects. The levels of high-density lipoprotein cholesterol, high-density lipoprotein subfraction 3 cholesterol, and apolipoprotein Al were similar in the two groups, but high-density lipoprotein subfraction 2 cholesterol was lower in the patients with SLE (10.2 versus 18.2 mg/dl; p less than 0.001). When patients with SLE treated with prednisone (n = 32) were compared to patients with SLE not treated with prednisone (n = 14), the former had higher triglyceride (158 versus 87 mg/dl; p less than 0.001), cholesterol (214 versus 170 mg/dl; p less than 0.001), and low-density lipoprotein cholesterol (130 versus 103 mg/dl; p less than 0.001) levels. The patients with SLE not treated with prednisone had lipid levels similar to those in control subjects except that high-density lipoprotein cholesterol was lower (49.7 versus 59.0 mg/dl; p less than 0.05). The daily prednisone dosage in the treated patients with SLE correlated with levels of cholesterol (r = 0.38, p less than 0.02), high-density lipoprotein cholesterol (r = 0.40, p less than 0.02), and high-density lipoprotein subfraction 3 cholesterol (r = 0.47, p less than 0.01). Thus, female patients with SLE have a dyslipoproteinemia of the type that would place them at an increased risk for coronary artery disease. Corticosteroids, used in the treatment of SLE, seem to play a role in the pathogenesis of the observed lipoprotein abnormalities.