Origin of plasma α₂HS-glycoprotein and its accumulation in bone

Abstract

WE have shown previously that a glycoprotein constituent of calcified cortical bone matrix is immunochemically identical to a component of blood plasma^1,2. In bone and dentine this specific α-glycoprotein is concentrated in amounts relative to plasma albumin but is not present at greater concentrations than in plasma in various other tissues. This material, although mainly present in extra-vascular sites in bone, could originate from the plasma because it represents a substantial proportion of the radioactivity in bone tissue 12 d after injection of ¹⁴C-total plasma glycoprotein¹. Rabbit bone α-glycoprotein is analogous to human α₂HS-glycoprotein^3,4, which is located in mineralising areas in normal human bone matrix⁵. To our knowledge direct conclusive proof of the tissue origin of the plasma α₂HS-glycoprotein is lacking although most of the serum glycoproteins seem to be synthesised by the liver^6,7. Nevertheless, its increased concentration in calcified tissues suggests that its presence in plasma could be a result of synthesis and release by bone tissue. We now report that the α₂HS-glycoprotein is synthesised by the liver and a proportion is subsequently accumulated in bone tissue.