Hemochromatosis gene (HFE) mutations may exacerbate chronic liver diseases through increased iron accumulation and subsequent oxidative stress.1 Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in North America and much of the developed world; children and possibly as many as one third of all U.S. adults are affected.2 A number of previous studies, especially those conducted in predominantly Caucasian populations, reported that HFE mutations were enriched among NAFLD patients, compared to controls, suggesting these genotypes may confer increased risk of NAFLD.3-8 However, these studies have been limited by inadequate power, small sample size, lack of standardized pathology, and lack of data on iron distribution. A recent meta-analysis of 1,727 NAFLD Caucasian cases and 4,275 controls concluded that HFE mutations were not more prevalent among NAFLD than non-NAFLD subjects.9 Several studies have found that HFE mutations are associated with higher hepatic and/or serum iron indices in nonalcoholic steatohepatitis (NASH) patients.4-8, 12, 14 Some studies have also examined the relationship between the presence of HFE mutations and severity of fibrosis in NASH.3-14 However, carriage of HFE mutations has not been identified as an independent risk factor for advanced fibrosis among patients with NAFLD or NASH in the majority of reports.6, 9-14
We have recently reported that more than one third of US patients enrolled in the Nonalcoholic Steatohepatitis Clinical Research Network (NASH CRN) had stainable hepatic iron on liver biopsy in one of the following three histologic patterns: hepatocellular only (HC; 7.4%), reticuloendothelial system cells only (RES; 10.7%), or a mixed HC/RES pattern (16.3%).15 In addition, RES iron was associated with advanced histologic features, including a higher mean NAFLD activity score (NAS). By contrast, an HC-only pattern of iron deposition was associated with milder histologic and clinical features, compared to the other groups, and the mixed HC/RES iron group had intermediate histologic severity. We proposed that the pattern of hepatic iron deposits in NAFLD is the result of differential expression of the body iron-regulatory hormone (hepcidin) by genetic factors and inflammatory signals.15
Hepcidin regulates iron absorption and recycling by binding to and initiating internalization and degradation of the sole cellular iron exporter, ferroportin, thus down-regulating iron efflux from the enterocyte, macrophage, and hepatocyte.16 Elevated body iron stores or plasma transferrin levels result in hepcidin up-regulation through the SMAD/bone morphogenetic protein (BMP)/hemojuvelin (HJV) pathway17 or through the HFE/transferrin receptor (TFR)1/TFR2 complex, respectively.18-20 Hemochromatosis patients with mutations in the HFE, HJV, and TFR2 genes have been shown to have inappropriately low urinary hepcidin levels, allowing unregulated iron absorption, resulting in hepatic iron loading in the classic hemochromatosis parenchymal HC pattern.21, 22 Thus, HC iron deposition in NAFLD, similar to that observed hemochromatosis, could be associated with decreased circulating hepcidin levels resulting from carriage of hemochromatosis mutations, such as HFE, HJV, TFR2 or other iron-regulatory genes, such as those involved in the SMAD/BMP pathway.
The aim of this study was to investigate the relationship between the two common HFE mutations, serum hepcidin levels, hepatic iron deposition, and histologic features of NASH in the large, well-characterized NASH CRN cohort.