Serum amyloid A to monitor cancer dissemination

Control of the acute-phase serum amyloid A and C-reactive protein response: comparison of total replacement of the hip and knee

The acute-phase serum protein response induced by arthroplasty of the knee was compared with that induced by arthroplasty of the hip in patients with rheumatoid arthritis (RA). Total replacement of the knee (n = 13) caused a markedly greater serum amyloid A protein (SAA) (P less than 0.001) and C-reactive protein (CRP) (P less than 0.001) elevation that did total replacement of the hip (n = 13). This effect was not merely due to the use of tourniquet in the knee arthroplasties, since synovectomy of the knee, matched for the duration of the use of tourniquet, induced an SAA response that was significantly lower (P less than 0.001) than that caused by replacement of the knee; the SAA response after knee synovectomy was similar to that after hip arthroplasty. The kinetics and magnitude of the SAA response in patients with reactive amyloidosis were similar to those found in RA patients without amyloidosis. The results show that replacement of the knee is a stronger stimulator of SAA and CRP elevation than replacement of the hip. Thus, total replacement of the knee, possibly due to the performance of the arthroplasty under ischaemic conditions, appears to be more traumatic to the organism than total replacement of the hip.

Acute-phase proteins or tumour markers: the role of SAA, SAP, CRP and CEA as indicators of metastasis in a broad spectrum of neoplastic diseases

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.

Reactive (secondary) amyloidosis and its pathogenesis

Recent advances in amyloid research have broadened our understanding of amyloidogenesis in connection with chronic inflammatory and infectious conditions. Experimental and clinical studies have clarified many of the mechanisms of induction, synthesis and regulation of the amyloid-related serum component SAA and have shed light on the enzymatic processes involved in the cleavage of SAA and degradation of fibrillar AA protein. The current pathogenetic model emphasizes the dynamic character of amyloid disease.

Comparison of serum amyloid A protein and C-reactive protein concentrations in cancer and non-malignant disease

Serum amyloid A (SAA) concentrations correlate well with C-reactive protein (CRP) concentrations. However, SAA is sometimes raised in disease when CRP is normal. This appears to occur more often in certain diseases such as rheumatoid arthritis, primary biliary cirrhosis and chronic active hepatitis. SAA concentrations did not distinguish between cancer with and without metastases as previously indicated, although mean concentrations were higher in more advanced tumours. Despite the higher sensitivity of SAA over CRP in the inflammatory response, SAA has little advantage over CRP in the assessment of malignant disease.

Amyloid A fibril degrading activity in serum in liver disease--relation to serum acute phase and other protein levels

Human serum contains amyloid A degrading activity. This activity is decreased in patients with reactive systemic amyloidosis. To study the specificity of this finding, we evaluated the effect of liver disease per se on the amyloid degrading activity in serum as well as its relation to serum amyloid A (SAA), the putative precursor of amyloid A fibrils, and other serum protein levels in alcoholic and non-alcoholic non-malignant liver diseases without signs of amyloidosis. The amyloid A-degrading activity was significantly decreased in liver cirrhosis. The lowest activity was seen in patients with advanced cirrhosis. There was a positive correlation between the degradative activity and indices of hepato-cellular synthetic function (serum albumin, r = 0.77; serum prealbumin, r = 0.65). Most of the patients with liver disease had a detectable SAA level; 77% had a level higher than 5 mg/l (compared to 12% among blood donors). However, the SAA increase was generally only slight, e.g. in alcoholic liver cirrhosis the median SAA level was 15 mg/l. The results show that liver dysfunction per se decreases amyloid A-degrading activity in serum. A reduced activity cannot therefore be regarded as specific for reactive amyloidosis. Since reactive amyloidosis is extremely rare in liver cirrhosis, it seems obvious that a reduced amyloid degrading activity alone, in the absence of a markedly elevated SAA level, does not predispose, at least in patients with liver disease, to amyloidosis.

Quantitative radial immunodiffusion assay for serum amyloid A protein

A radial immunodiffusion assay for serum amyloid A protein (SAA) using a commercially available antiserum is described. Serum is applied untreated to 1% agarose gels prepared in 0.02 M barbitone buffer, pH 8.6, containing 40 g/l polyethylene glycol 6000. Incubation is carried out overnight at 37 degrees C. The assay combines the advantages of simplicity, rapidity, specificity and stability, and avoids the hazards associated with the previously described radioimmunoassays. The method has sufficient sensitivity to measure SAA in the majority (99%) of normal subjects, and confirms the behaviour of SAA as a very sensitive acute phase reactant in inflammatory disease. The method is ideally suited to the rapid processing of a large number of samples.

Mechanism of reduced amyloid-A-degrading activity in serum of patients with secondary amyloidosis

Human serum contains amyloid-A-degrading (AADP) activity. This activity is reduced in amyloidosis associated with rheumatoid arthritis. Since AADP co-migrates with albumin on agarose-gel electrophoresis, the relationship between these serum factors was studied in patients with amyloidosis and patients with amyloidosis and patients with altered albumin synthesis and/or distribution. AADP activity correlated positively with albumin levels in patients with rheumatoid arthritis complicated by amyloidosis. A weaker association was noted between serum activity and prealbumin levels. The AADP activity in patients with rheumatoid arthritis without signs of amyloidosis and patients with liver cirrhosis was also positively associated with serum albumin level. During the acute-phase reaction after surgery serum AADP activity fell in parallel with serum albumin level. Purified albumin preparations displayed AADP activity. The results show that serum albumin level reflects AADP activity. It is suggested that the development of hypoalbuminaemia in patients with amyloidosis may give rise to a vicious circle which leads to an accelerated reduction in AADP activity and accelerated amyloidogenesis.