Search

The plasma proteins α1 microglobulin (α1-m) and bikunin are synthesized in the liver as a common precursor which is cleaved just before secretion. Half of plasma α1-m is covalently linked to fibronectin and α1-inhibitor-3, and more than 95% of bikunin is part of pre-α-inhibitor, inter-α-inhibitor and related large molecules. Both α1-m and bikunin have been shown to be involved in inflammation, but the regulation of their synthesis is not clear. The authors have measured the plasma and urinary concentrations of α1-m and bikunin as well as their hepatic mRNA levels in rats during the development of collagen-induced arthritis. Also, the plasma concentrations of acknowledged acute-phase proteins were measured. The results suggested a biphasic inflammatory reaction: an early response after 1 week, represented by an elevated fibronectin level; and a late response after 3 weeks, represented by elevated α1-acid glycoprotein and decreased albumin and α1 -inhibitor-3 levels. The α1-m-bikunin mRNA content in liver was slightly reduced after I week and elevated after 3 weeks, but the total concentrations of free and bound α1-m and bikunin in plasma were unchanged. The free bikunin fraction as well as the fibronectin/α1-m complex in plasma, however, were elevated after 1 week. Urinary bikunin levels were also elevated after 1 week, whereas urinary α1-m levels remained unchanged. The results thus suggest that free bikunin in plasma is increased and excreted in the urine at an early stage during the development of collagen-induced arthritis. Later, when the synthesis rate of α1-m-bikunin is elevated. both proteins are most likely directed to other locations in the body. [ABSTRACT FROM AUTHOR]