Plasma bikunin: Half-life and tissue uptake

Abstract

Bikunin is a chondroitin sulfate-containing plasma protein synthesized in the liver. In vitro, it has been shown to inhibit proteases and to have additional activities, but its biological function is still unclear. Here we have studied the dynamics of plasma bikunin in rats and mice. A half-life of 7 +/- 2 min was obtained from the time course of the decrease of the plasma level of bikunin following hepatectomy. Clearance experiments with intravenously injected radiolabeled bikunin with or without the chondroitin sulfate chain showed that the polysaccharide had little influence on the elimination rate of the protein. The uptake of bikunin by different tissues was studied using bikunin labeled with the residualizing agent 125I-tyramine cellobiose; 60 min after intravenous injection, 49% of the radioactivity was recovered in the kidneys and 6-11% in the liver, bones, skin, intestine and skeletal muscle. The uptake in the liver was analyzed by intravenous injection of radiolabeled bikunin followed by collagenase perfusion and dispersion of the liver cells. These experiments indicated that bikunin is first trapped extracellularly within the liver before being internalized by the cells.

Development of a method for urine bikunin/urinary trypsin inhibitor (UTI) quantitation and structural characterization: Application to type 1 and type 2 diabetes

“…Besides its proteinase inhibitory activities, for example, toward plasmin during tumor cell invasion and metastasis , bikunin plays additional roles, such as inhibition of interleukin (IL)‐8 gene expression induced by lipopolysaccharide , smooth muscle contraction , neutrophil release of elastase , mast cell release of histamine , and urolithiasis , as well as stabilization of lysosomal membranes . Free bikunin is rapidly cleared from circulation by both tissue uptake and renal excretion and it is found in urine as the urinary trypsin inhibitor (UTI). UTI levels are usually low in healthy individuals but they increase up to tenfold in both acute and chronic inflammatory diseases .…”

Levels of Urinary Trypsin Inhibitor and Structure of Its Chondroitin Sulphate Moiety in Type 1 and Type 2 Diabetes

“…The polypeptide portion consists of 147 amino acid residues folded in two Kunitz-type domains (7 kDa each) containing three disulphide bonds, a connecting peptide as well as N- and C-terminal moieties of 10–25 amino acid residues each [ 4 ]. The molecular mass of the whole proteoglycan is about 25-26 kDa, being the protein core, the CS moiety, and the oligosaccharide chains 16 kDa, 7 kDa, and 2 kDa, respectively, as reported by various studies and confirmed by ultracentrifugation methods [ 1 , 3 – 5 ]. However, because of CS chain extended conformation, bikunin behaves like a globular protein of about 67 kDa by gel filtration and has an apparent molecular mass of 35–45 kDa by SDS-PAGE [ 6 ].…”

“…Urinary trypsin inhibitor (UTI) is a small proteoglycan (PG), with inhibitory activity against serine proteases, resulting from excretion of plasma bikunin into urine [ 1 ]. Despite that UTI was purified in 1955 for the first time [ 2 ] and several studies on its structure and levels have been performed since the 1950s, its biological function has not been fully understood yet [ 3 ]. It is composed of a protein moiety, a low-sulphated chondroitin sulphate (CS) chain, O-linked to the serine 10, as well as an oligosaccharide, N-linked to the asparagine 45 of the protein moiety ( Figure 1 ).…”

Electrospray ionization Fourier transform mass spectrometric analysis of intact bikunin glycosaminoglycan from normal human plasma

“…It has been shown that a significant proportion of bikunin is secreted in a free form, i.e. lacking the HC polypeptides [18, 30], and rapidly cleared through renal filtration [14, 30]. Thus, it is possible that bikunin PG that escapes assembly into multi-chain bikunin proteins and the urinary bikunin PG represent the same biosynthetic product [41].…”

“…In plasma, free bikunin is released from the multi-chain proteins as a result of increased serine protease activity in response to inflammation [14, 17] and quickly passes into urine. An average half-life of free bikunin in plasma is approximately 10 min [14, 18]. Elevated concentrations of bikunin in plasma and urine are associated with the acute-phase inflammatory response [14, 17]; and the increased chain length and decreased sulfation of its GAG component have been observed in patients with different inflammatory syndromes [19, 20].…”