Pathways underlying iron accumulation in human nonalcoholic fatty liver disease

BACKGROUND: Mild iron overload is frequently observed in nonalcoholic fatty liver disease (NAFLD). OBJECTIVE: We aimed to study putative pathways underlying iron accumulation in NAFLD. DESIGN: Hepatic and duodenal expression of critical iron molecules in NAFLD patients with (n = 32) and without (n = 29) iron overload, hereditary hemochromatosis (n = 10), and controls (n = 20) were investigated. Phlebotomy treatment was performed in 14 NAFLD patients. RESULTS: The hepatic expressions of the iron-export protein ferroportin-1 (FP-1) and of the iron-sensing molecule hemojuvelin (HJV) were significantly lower in NAFLD patients. The mRNA expression of the iron-regulatory peptide hepcidin was increased in NAFLD patients with iron overload, which was paralleled by low duodenal FP-1 expression. Hepatic mRNA and serum protein concentrations of tumor necrosis factor-alpha (TNF-alpha) were increased in NAFLD patients and were inversely correlated with both liver FP-1 and HJV mRNA and positively associated with body mass index and hepatic hepcidin mRNA. Accordingly, TNF-alpha inhibited the FP-1 and HJV mRNA formation in HepG2 cells. Phlebotomy treatment of NALFD patients reduced serum ferritin, transferrin saturation, and TNF-alpha concentrations and improved liver function tests. CONCLUSIONS: Iron accumulation in NAFLD may result from an impaired iron export due to down-regulation of FP1 and ineffective hepatic iron sensing, as indicated by low HJV expression. TNF-alpha appears to play a role in exerting these regulatory changes. Increased hepcidin formation in iron-overloaded NAFLD patients, however, results in decreased duodenal FP-1 expression, whereas a reduction in liver FP-1 may perpetuate hepatic iron retention. Phlebotomy offers a safe and efficient therapy for these metabolic disturbances.