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Nitric oxide reduces nontransferrin‐bound iron transport in HepG2 cells
Author(s) -
Barisani Donatella,
Cairo Gaetano,
Ginelli Enrico,
Marozzi Anna,
Conte Dario
Publication year - 1999
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.510290205
Subject(s) - snap , sodium nitroprusside , transferrin receptor , chemistry , ferritin , nitric oxide , transferrin , messenger rna , intracellular , receptor , biochemistry , microbiology and biotechnology , biology , gene , computer graphics (images) , organic chemistry , computer science
Nitric oxide (NO) donors S‐nitroso‐N‐acetylpenicillamine (SNAP) and sodium nitroprusside (SNP) modulate iron regulatory protein (IRP) activity and may, therefore, affect iron uptake through transferrin receptor expression. However, iron also enters the cell as nontransferrin‐bound iron (NTBI), and the aim of this study was to evaluate the effects of NO donors on NTBI transport in HepG2 cells, a model of liver physiology. Incubation with SNP and SNAP led to a time‐ and concentration‐dependent reduction in Fe 3+ and Fe 2+ uptake, thus indicating an effect on the transporter rather than on the reductase. In terms of Fe 2+ uptake, no variations in the Michaelis‐Menten constant ( K m ) and a reduction in maximum uptake ( V max ) (50, 33, and 16.6 fmol/μg protein/min in control, SNP‐, and SNAP‐treated cells, respectively) were detected, which suggested a decrease in the number of putative NTBI transport protein(s). Gel shift assays showed that IRP activity was reduced by SNP and slightly increased by SNAP. Northern blot analysis of transferrin receptor messenger RNA (mRNA) levels showed variations similar to those observed for IRPs, but both NO donors increased L‐ferritin mRNA levels and had no effect on the stimulator of Fe transport (SFT) mRNA. In conclusion, NO donors significantly reduce NTBI transport in HepG2 cells, an effect that seems to be IRP and SFT independent. Moreover, the reduction in NTBI uptake after NO treatment suggests that this form of iron may play a minor role in the increased hepatic iron stores observed in inflammation or that other liver cells are more involved in this pathological condition.