Rn. Watts et Dr. Richardson, Nitrogen monoxide (NO) and glucose - Unexpected links between energy metabolism and NO-mediated iron mobilization from cells, J BIOL CHEM, 276(7), 2001, pp. 4724-4732
Nitrogen monoxide (NO) affects cellular iron metabolism due to its high aff
inity for this metal ion. Indeed, NO has been shown to increase the mRNA bi
nding activity of the iron-regulatory protein 1, which is a major regulator
of iron homeostasis, Recently, we have shown that NO generators increase F
e-59 efflux from cells pre-labeled with Fe-59-transferrin (Wardrop, S. L.,
Watts, R. N., and Richardson, D. R. (2000) Biochemistry 39, 2748-2758), The
mechanism involved in this process remains unknown, and in this investigat
ion we demonstrate that it is potentiated upon adding D-glucose (D-Glc) to
the reincubation medium. In D-Glc-free or D-Glc-containing media, 5.6 and 1
6.5% of cellular 59Fe was released, respectively, in the presence of S-nitr
osoglutathione. This difference in 59Fe release was observed with a variety
of NO generators and cell types and was not due to a change in cell viabil
ity. Kinetic studies showed that D-Glc had no effect on the rate of NO prod
uction by NO generators. Moreover, only the metabolizable monosaccharides D
-Glc and D-mannose could stimulate NO-mediated Fe-59 mobilization, whereas
other sugars not easily metabolized by fibroblasts had no effect. Hence, me
tabolism of the monosaccharides was essential to increase NO-mediated Fe-59
release. Incubation of cells with the citric acid cycle intermediates, cit
rate and pyruvate, did not enhance NO-mediated Fe-59 release. Significantly
, preincubation with the GSH-depleting agents, L-buthionine-[S,R]-sulfoximi
ne or diethyl maleate, prevented NO-mediated Fe-59 mobilization, This effec
t was reversed by incubating cells with N-acetyl-L-cysteine that reconstitu
tes GSH. These results indicate that GSH levels are essential for NO-mediat
ed Fe-59 efflux. Hence, D-Glc metabolism via the hexose monophosphate shunt
resulting in the generation of GSH may be essential for NO-mediated Fe-59
release. These results have important implications for intracellular signal
ing by NO and also NO-mediated cytotoxicity of activated macrophages that i
s due, in part, to iron release from tumor target cells.