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.