Serum amyloid A polymorphism in a subject with a naturally occurring inflammatory response

Massive vascular AA-amyloidosis: a histologically and biochemically distinctive subtype of reactive systemic amyloidosis

Amyloid protein AA consists of several subspecies which mainly arise through proteolytic cleavage at various sites of the precursor, serum protein AA. The most common protein AA subspecies (the protein AA prototype) contains 76 amino-acid residues. In previous studies we have shown that distinctive patterns of amyloid infiltration occur in AA-amyloidosis. The amyloid in different patterns of infiltration seems to consist of distinctive protein AA subspecies. In the present study we have analysed protein AA in three patients with a form of AA-amyloidosis with heavy vascular infiltration and show that the amyloid fibrils contain two groups of protein AA subspecies. One, quantitatively predominating, group contains large subspecies of up to 94 amino-acid residues and a second group of protein AA-molecules contains around 50 amino-acid residues. The AA molecules lack the N-terminal arginine residue. It is concluded that AA-amyloidosis with massive vascular infiltration is a distinctive subform with typical clinical and histological appearance and with fibrils containing characteristic protein AA subspecies.

The pathogenesis of reactive systemic amyloidosis

The diagnosis of amyloidosis is based on the presence of extracellular tissue deposits of proteinaceous material that demonstrate a characteristic green color when stained with Congo red and viewed under polarized light. Several different proteins are amyloidogenic but, in domestic animals, spontaneously occurring systemic amyloidosis is reactive in nature and characterized by the presence of amyloid protein AA. This type of systemic amyloidosis may occur secondary to chronic inflammatory or neoplastic disease, but in many instances no predisposing disease is found. A sustained increase in the serum concentration of serum amyloid A protein (SAA) is necessary but not sufficient for the development of reactive amyloidosis. Other inherited and acquired host-related factors are likely to be important in the development of reactive amyloidosis because this condition develops in few patients with chronic inflammatory disease. The tissue tropism of amyloid deposits varies with the amyloid protein itself and species affected. The consequences of amyloidosis for the host depend upon the tissues involved and the response of these tissues to the presence of the amyloid deposits. In domestic animals, reactive systemic amyloidosis is nephropathic, leading to end-stage renal disease, and the clinical presentation is that of uremia.

Serum amyloid A and high density lipoproteins during the acute phase response

Serum amyloid A and high density lipoprotein (HDL) interrelationships were evaluated in 11 normal men during an acute phase response induced by the inflammatory steroid etiocholanolone. Compared with baseline, HDL-cholesterol levels were significantly elevated at 30 h but not at 50 h (P less than 0.05) after etiocholanolone. A-apoprotein concentrations were unchanged at 30 h but were reduced at 54 h (P less than 0.01). Four subjects were sampled every 6-8 h for 5 days. Two men had peak SAA concentrations of 30 and 33 mg dl-1. Their A-apoprotein levels declined as SAA rose and remained low even after SAA levels had returned to baseline. High density lipoprotein cholesterol levels did not fall, however, when SAA was increasing, and fell only after SAA levels declined. No changes in HDL-cholesterol or protein were observed in two subjects whose peak SAA concentrations were 10 and 12 mg dl-1. These observations suggest that a threshold level of acute phase response is required before HDL reductions occur. Column chromatography of SAA-rich plasma did not demonstrate the presence of either SAA or A-apoproteins that were unassociated with lipoproteins. Serum amyloid A, moreover, demonstrated little capacity to displace A-proteins from HDL at SAA concentrations typically observed during the acute phase response. We infer from these studies that SAA may substitute for the A-apoproteins and temporarily maintain HDL-cholesterol levels; but that low HDL levels during the acute phase response are likely due to reduced A-protein synthesis rather than displacement by SAA.

Serum amyloid A protein, apolipoprotein A-I, and apolipoprotein B during the course of acute myocardial infarction

Serum amyloid A protein (SAA), apolipoprotein A-I (apoA-I), apolipoprotein B (apoB) concentrations, and creatine kinase (CK)-MB isoenzyme activity were serially measured in 10 patients during the course of acute myocardial infarction. Pronounced increases in SAA concentrations were observed in all patients during infarction. The highest SAA values were observed, on average, 67 hours after the onset of chest pain. After infarction both apoA-I and apoB concentrations decreased. The reduction in apoA-I concentration 67 to 72 hours after the onset of chest pain was (31%) (p less than 0.01) and the reduction in apoB concentration 55 to 60 hours after the onset of pain was (34%) (p less than 0.01). Negative correlations were found between the concentrations of SAA and apoproteins A-I and B; this inverse relation was stronger between SAA and apoB than between SAA and apo-AI.

Purification of serum amyloid A and other high density apolipoproteins by hydrophobic interaction chromatography

A chromatographic procedure is described for the purification of apolipoprotein components of high density lipoprotein from serum. Hydrophobic interaction chromatography (HIC) using phenyl- or octyl-Sepharose was used to purify the high density lipoprotein (HDL)-associated acute phase reactant serum amyloid A (SAA). The purification of SAA is described in detail and it is shown how the main components of normal HDL, apolipoproteins AI and AII (Apo-AI, Apo-AII), can also be purified. Serum was applied at a low salt concentration and apolipoproteins were eluted with a gradient into 4 M guanidine hydrochloride, 30% ethanediol, and 10 mM NaOH. This method was also used to partially purify the low density lipoprotein component apolipoprotein B. Apolipoproteins are purified free from lipid in one rapid chromatographic procedure rather than several ultracentrifugation steps and delipidation with organic solvents. The apolipoproteins from HIC chromatography are already partially separated and can be purified to homogeneity using conventional chromatographic methods under dissociating conditions.

Human high-density lipoprotein associated amyloid A protein. Structural characteristics, relation to apo A-I and A-II concentrations, and plasma clearance kinetics in the rat

Five amyloid related low-molecular-weight apoproteins were isolated and characterized from the plasma high-density lipoprotein fraction of a patient with glomerulonephritis caused by basement membrane antibodies. Amino acid and carbohydrate analyses of apoSAA subfractions showed that they were non-glycosylated polypeptides rich in aspartic acid, glycine, glutamic acid, glutamine, and arginine. The apo SAA subtype pattern was similar to that described in some other pathological conditions. Following injections of the isolated SAA-rich high density lipoprotein fraction into rat circulation, similar disappearance curves were obtained for apoSAA and apo A-I.

Degradation of amyloid A and serum amyloid A by red blood cell haemolysate in patients with familial mediterranean fever

Enzymatic activity for the degradation of serum amyloid A (SAA) and amyloid A (AA) was detected in erythrolysates of normal subjects and patients with familial mediterranean fever. A significant difference between the activity of normal subjects and patients was not found. Serum inhibited the SAA (but not the AA) haemolysate proteolytic activity. Interindividual variation in the susceptibility of SAA to degradation by RBC haemolysates was shown. The original digestible fraction of SAA became gradually resistant to proteolytic cleavage over a 9 month period while the susceptibility of AA to degradation remained unchanged in this time period. These findings suggest that enzymatic degradation of SAA depends on the source of SAA, as well as inhibitory activity in serum.

Trauma, high density lipoproteins, and serum amyloid protein A

Several apoproteins not readily detectable in normal serum lipoproteins were found in markedly increased amounts in the lipoprotein density interval 1.125-1.21 g/ml (HDL3) of serum obtained from victims of severe trauma. Following electrophoretic separations, they were shown to be isotypes of the acute-phase protein serum amyloid A (SAA) by immunoreaction with antiserum to the structurally related tissue amyloid protein A (AA). The two principal apoSAA isotypes in the HDL3 of trauma patients appear to be identical to the two principal isotypes (apoSAA1 and apoSAA2) previously isolated from the HDL3 of pooled serum representing an unselected patient population. Concentrations of apolipoproteins A-I and A-II in the HDL3 of the trauma patients were significantly lower than in the HDL3 of normal serum. Evidence is presented that several recently described 'new' families of HDL apoproteins, all of an acute-phase nature, are SAA apoproteins, which are emerging as sensitive indicators of tissue damage.

Acute phase proteins with special reference to C-reactive protein and related proteins (pentaxins) and serum amyloid A protein

The acute phase response among plasma proteins is a normal response to tissue injury and is therefore a fundamental aspect of many diverse disease processes. It probably usually has a beneficial net function in limiting damage and promoting repair but in some circumstances it may have pathological consequences. Sustained high levels of acute phase proteins and especially SAA are associated with the development of amyloidosis in some individuals. Increased concentrations of CRP may, by activating the complement system, contribute to inflammation and enhance tissue damage. Failure of the normal or appropriate CRP response may also possibly have deleterious effects. SAA is a polymorphic protein which is normally present only in trace amounts but which, during the acute phase response, becomes one of the major apolipoproteins associated with high-density lipoprotein particles. The function of apoSAA is not known but it must have considerable physiological significance apart from its role as the putative precursor of amyloid A protein fibrils. CRP and SAP have been very stably conserved throughout vertebrate evolution and homologous proteins are apparently present even in vertebrates. This strongly suggests that they have important functions although these have not yet been precisely delineated. The main role of CRP may be to provide for enhanced clearance of inappropriate materials from the plasma whether these are of extrinsic origin, such as microorganisms and their products, or the autologous products of cell damage and death. The interaction between aggregated CRP and plasma low-density lipoprotein may play a significant part in the normal function of CRP and may also have a role in lipoprotein metabolism, clearance, and deposition. SAP is a normal tissue protein as well as being a plasma protein. Aggregated SAP selectively binds fibronectin and this may represent an aspect of the normal function of SAP. The deposition of SAP in amyloid is evidently not a normal function but it is not known whether this deposition is involved in the pathogenesis of amyloid or whether it is merely an epiphenomenon. In any case immunohistochemical staining for SAP is useful in the diagnosis of amyloid, in investigation of glomerulonephritis, and in studying disorders of elastic tissue. Regardless of its physiological or pathophysiological functions, the assay of serum CRP is a valuable aid to clinical management in a number of different situations and in different diseases provided results are interpreted in the light of full clinical information.(ABSTRACT TRUNCATED AT 400 WORDS)