Metabolism of glycosylated human salivary amylase: in vivo plasma clearance by rat hepatic endothelial cells and in vitro receptor mediated pinocytosis by rat macrophages

J Leukoc Biol. 1984 Sep;36(3):307-20. doi: 10.1002/jlb.36.3.307.

Abstract

Salivary-type amylase normally comprises about 60% of the amylase activity in human serum, but only a small fraction is a glycosylated isoenzyme (amylase A). In contrast, 1/3 of amylase in human saliva is glycosylated. Since glycosylation can affect circulatory clearance, we studied the clearance of amylase A in rats and its uptake by rat alveolar macrophages. Following intravenous injection, 125I-labeled amylase A disappeared rapidly from plasma (t 1/2 = 9 min) and accumulated in the liver. Simultaneous injection of mannose-albumin slowed its clearance to a rate comparable to that of 125I-labeled nonglycosylated salivary amylase (t 1/2 = 45 min). In contrast, galactose-albumin had no effect. Electron microscope autoradiography of the liver following injection of 125I-labeled amylase A revealed a localization of grains over the hepatic endothelial cells. In vitro studies indicated that amylase A is taken up by alveolar macrophages via receptor-mediated pinocytosis. Uptake was linear over time, saturable, and inhibited by mannan and mannose-albumin, but not by galactose-albumin. We conclude that amylase A, which is a naturally occurring human glycoprotein with at most three terminal L-fucose residues per molecule, is recognized in rats by a mannose receptor located on hepatic endothelial cells. We speculate that this receptor, by rapidly clearing circulating amylase A, may be responsible for the low level of amylase A in human serum.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amylases / metabolism*
  • Animals
  • Autoradiography
  • Biological Transport
  • Endothelium / metabolism
  • Female
  • Humans
  • Iodine Radioisotopes
  • Kinetics
  • Lectins, C-Type*
  • Liver / metabolism*
  • Liver / ultrastructure
  • Macrophages / metabolism*
  • Male
  • Mannose Receptor
  • Mannose-Binding Lectins*
  • Microscopy, Electron
  • Pinocytosis*
  • Rats
  • Rats, Inbred Strains
  • Receptors, Cell Surface*
  • Receptors, Immunologic / metabolism*
  • Saliva / enzymology*

Substances

  • Iodine Radioisotopes
  • Lectins, C-Type
  • Mannose Receptor
  • Mannose-Binding Lectins
  • Receptors, Cell Surface
  • Receptors, Immunologic
  • Amylases