The Kupffer cells and the intrahepatic iron-metabolism pathway

Background and Aims: The liver plays a central role in regulation of iron metabolism. The hepatocyte synthesizes and secretes hepcidin (hepc), a central regulator of cellular iron uptake and of intestinal iron absorption. Hepc gene expression is upregulated by acute phase mediators, mainly IL–6 synthesized during inflammatory processes. Kupffer cells (KCs) may be induced to synthesize and secrete acute phase cytokines e.g. by treatment with endotoxin. Involvement of KCs in hepatic response after iron administration has been excluded by previous treatment of animals with gadolinium chloride (GD). We analysed the influence of GD on hepc and other iron related proteins gene expression in vivo and in vitro.

Material and Methods: Animals were sacrificed at different time points after intravenous injection of GD and liver was taken and snap frozen in liquid nitrogen. KCs were isolated from normal and GD treated livers. RNA was analysed by northern blot and quantitative real time PCR. Serum was used to measure transaminases, cytokine, hepc and iron level.

Results: GD treatment induced a reduction of ED1 positivity in liver parenchyma but no damage was detectable in liver sections. GD administration induced a 5 fold upregulation of hepc and a contemporary inhibition of Hjv gene expression (0.29 fold by 12h) in the liver. The other proteins behave as follow, besides the induction of hepc, a strong upregulation of TfR–1 gene expression (15 fold by 12h) was observed, while hephaestin gene expression reached the peak by 48h (7 fold). IL–6, IFN-γ, TNF-α were not detectable under the present conditions. While GD treated hepatocytes showed a downregulation of hepc expression, KCs treated with 10µg/ml GD showed a 4 fold upregulation of the same gene by 24h. In serum of GD treated animals iron and hepc concentration was transiently but significantly reduced.

Conclusion: GD treatment induces in vivo and in vitro changes of hepc gene expression and of other proteins involved in hepatic iron metabolism. These changes seemed to be not mediated by IL–6, TNF-α, IL–1β and by IFN-γ. KCs were not inactivated by GD-treatment. The effect of hepc seems to be mediated by the TfR–1, which was upregulated reaching the maximum by 12h.