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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.

Although the SAA1 and SAA2 protein isoforms (A-SAA) of the serum amyloid A (SAA) family of acute phase reactants have been found in a number of extrahepatic tissues; the site of synthesis of extrahepatic SAA remains to be clarified. To investigate site(s) of synthesis of the SAA protein localized to atherosclerotic plaque, expression of the SAA1 and SAA2 genes by cultured human aortic smooth muscle cells (HASMC) was investigated. A-SAA protein isoforms were detectable by immunoblot analysis in the culture medium of HASMC. Both A-SAA and C-SAA (SAA4) mRNA isoforms were constitutively expressed by HASMC, but not, however, by the human umbilical vein endothelial cells. Expression of A-SAA mRNA by HASMC was upregulated by corticoid hormones including dexamethasone (Dex), corticosterone, hydrocortisone, and aldosterone, but not by the cytokines interleukin (IL)-1, IL-6, and tumour necrosis factor (TNF)-alpha alone. Dex stimulation of A-SAA mRNA was time and dose dependent from 6 to 48 h. The threshold concentration for upregulation of A-SAA mRNA in HASMC by Dex was between 0.1 and 1 nM. IL-1, known to upregulate extrahepatic A-SAA gene expression in other cell systems only slightly, if at all, upregulated Dex-induced A-SAA expression by HASMC. Thus, it is possible that some of the A-SAA protein in the vascular wall (atherosclerotic plaques) can originate from smooth muscle cells. In consideration of recent reports that A-SAA modulates the inflammatory process and lipid synthesis, A-SAA can potentially serve as a physiological regulator of smooth muscle cell homeostasis within that, in a disease state, participates in the formation of atherosclerotic plaques.

The composition of high-density lipoprotein (HDL) changes during inflammation; however, potential changes of HDL function during inflammation and the effects of acute phase proteins that are either on the HDL particles or in the serum have not been clarified. The concentrations of C-reactive protein (CRP), serum amyloid A protein (apoSAA) isoforms, lipids and apolipoproteins, and the activities of lecithin-cholesterol acyltransferase (LCAT) and paraoxonase (PON) were measured before and after laparoscopic cholecystectomy, in 12 patients with cholecystolithiasis to clarify the function of acute-phase HDL and the relationship between acute-phase proteins and HDL functions. Both acute-phase apoSAA (A-apoSAA) and CRP increased, reached their maximum levels 3-6 days after the operation, and then returned to preoperative levels after 2 weeks. In contrast, apolipoproteins and LCAT decreased reciprocally, reached their minimum levels 3-6 days after the operation, and returned to preoperative levels after 2 weeks. However, PON decreased 3-6 days after the operation, and remained low even after 2 weeks. At the nadir the mean activities of LCAT and PON were 56 and 76% of the preoperative levels, respectively. HDL-cholesterol or constitutive apoSAA did not change significantly. LCAT has been reported to be involved in reverse-cholesterol transport and PON to be preventive for lipid peroxidation of low-density lipoprotein in vitro. Thus, during the acute phase of inflammation, HDL may be altered to an atherogenic state due to a decrease in LCAT and PON activities. Therefore, this longitudinal analysis was carried out to determine whether HDL function is modified in a single episode of inflammation and thus may contribute to the occurrence of atherosclerotic disease in patients with chronic or recurrent acute inflammation.

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.

Serum amyloid A apolipoproteins (apoSAA) appear to compromise the ability of high density lipoprotein to protect against atherosclerosis and it is of interest to determine whether aortic smooth muscle cells can contribute to local pools of apoSAA in the presence of cytokines that are known to stimulate acute phase apoSAA (A-apoSAA) synthesis in the liver. In this study, the regulation of A-apoSAA synthesis was monitored in cultured neonatal rabbit aortic smooth muscle cells. Constitutive apoSAA3 gene expression was minimal, and only detectable by amplification of the mRNA by reverse transcriptase-polymerase chain reaction. ApoSAA3 gene expression and protein synthesis were stimulated by IL-1 alpha; as little as 0.01 ng/ml of IL-1 alpha stimulated an increase in steady state levels of apoSAA3 mRNA. Interestingly, IL-6 (which is required in addition to IL-1 alpha for the optimal synthesis of A-apoSAA by human hepatoma cells) had little if any effect on apoSAA3 synthesis by the smooth muscle cells. In a time course, it was shown that the stimulation of apoSAA3 mRNA levels was apparent by 1-2 h after the addition of cytokine, and that levels remained elevated in the presence of the cytokine for at least 48 h. Immunoprecipitation using an antiserum directed against apoSAA3 revealed that IL-1 alpha stimulated the synthesis and secretion of apoSAA3 protein in a manner that was consistent with apoSAA3 mRNA expression. The implications of these findings in atherogenesis are discussed.

Degradation of serum amyloid A (apoSAA) by resident peritoneal cells (RPCS) and conditioned medium (CDM), prepared with RPCS, from amyloid-susceptible CBA/J mice, amyloid-resistant CE/J mice and their amyloid-resistant CBA/J x CE/J F1 progeny was investigated in vitro. Serum amyloid A was derived from murine acute phase (AP) plasma and associated with high density lipoprotein (HDL). Degradation of apoSAA by RPCS and CDM from CBA/J mice was complete while degradation by RPCS and CDM from CE/J mice did not occur. Degradation of apoSAA by RPCS and CDM from CBA/J x CE/J F1 hybrid mice was indistinguishable from that by RPCS and CDM from the CBA/J parent. Intermediate fragments were not detected with either RPCS or CDM from CBA/J mice or CBA/J x CE/J F1 hybrid mice. Degradation of apoSAA was inhibited by phenylmethanylsulfonyl fluoride (PMSF) indicating that the enzyme, secreted into the fluid phase, was a serine esterase. Unlike apoSAA, HDL-associated apoA-1 remained intact. It was thus concluded that while selective degradation of HDL-associated apoSAA (apoSAA-HDL) by RPCS from the CBA/J and CE/J mice was significantly different, the genetic study did not support the hypothesis that there was direct linkage between impaired degradation of apoSAA-HDL in the CE/J mouse strain and protection against amyloid fibril formation. As amyloid resistance in CBA/J x CE/J F1 hybrid mice is not attributable to failure to express the amyloidogenic isoform apoSAA2, the study supports the original hypothesis that amyloid resistance may be linked to expression of apoSAAcej.

Two hundred and seventy-seven patients with a broad spectrum of neoplastic diseases, including 10 classes of solid tumours and three classes of haematologic malignancies, were retrospectively surveyed, and from the same sample of plasma or serum their concentrations of serum amyloid A (SAA), serum amyloid P component (SAP), C-reactive protein (CRP), and carcinoembryonic antigen (CEA) were measured. SAA levels varied from 105 ng/ml to 105,000 ng/ml, and mean SAA levels were higher in patients with metastatic tumours than in those with limited disease (P less than 0.001). Similarly, CRP levels varied from less than 8 micrograms/ml to 328 micrograms/ml and were significantly higher in the metastatic disease category. In contrast, SAP levels varied from 32 micrograms/ml to 120 micrograms/ml and showed no difference in patients with limited or metastatic disease, although an overall slight elevation was present. CEA levels were available in 150 patients and were significantly higher in patients with advanced lung or breast cancer than in patients with limited disease. The correlation between mean SAA and CRP levels was significant (r = 0.74, P less than 0.001), suggesting that SAA originates as an acute-phase protein rather than as a tumour cell product. However, the consistent elevation of SAA in all tumour types and the more marked elevation in metastatic disease may make its measurement useful in malignancy.