Although serum concentrations of ascorbic acid seldom exceed 150 mu mo
l/L, mature neutrophils and mononuclear phagocytes accumulate millimol
ar concentrations of vitamin C. Relatively little is known about the m
echanisms regulating this process. The colony-stimulating factors (CSF
s), which are central modulators of the production, maturation, and fu
nction of human granulocytes and mononuclear phagocytes, are known to
stimulate increased glucose uptake in target cells. We show here that
vitamin C uptake in neutrophils, monocytes, and a neutrophilic HL-60 c
ell line is enhanced by the CSFs. Hexose uptake studies and competitio
n analyses showed that dehydroascorbic acid is taken up by these cells
through facilitative glucose transporters. Human monocytes were found
to have a greater capacity to take up dehydroascorbic acid than neutr
ophils, related to more facilitative glucose transporters on the monoc
yte cell membrane. Ascorbic acid was not transported by these myeloid
cells, indicating that they do not express a sodium-ascorbate cotransp
orter. Granulocyte (G)- and granulocyte-macrophage colony-stimulating
factor (GM-CSF) stimulated increased uptake of vitamin C in human neut
rophils, monocytes, and HL-60 neutrophils. In HL-60 neutrophils, GM-CS
F increased both the transport of dehydroascorbic acid and the intrace
llular accumulation of ascorbic acid. The increase in transport was re
lated to a decrease in Km for transport of dehydroascorbic acid withou
t a change in Vmax, Increased ascorbic acid accumulation was a seconda
ry effect of increased transport. Triggering the neutrophils with the
peptide fMetLeuPhe led to enhanced vitamin C uptake by increasing the
oxidation of ascorbic acid to the transportable moiety dehydroascorbic
acid, and this effect was increased by priming the cells with GM-CSF.
Thus, the CSFs act at least at two distinct functional loci to increa
se cellular vitamin C uptake: conversion of ascorbic acid to dehydroas
corbic acid by enhanced oxidation in the pericellular milieu and incre
ased transport of DHA through the facilitative glucose transporters at
the cell membrane, These results link the regulated uptake of vitamin
C in human host defense cells to the action of CSFs. (C) 1998 by The
American Society of Hematology.