Pathology of hepatic iron overload

Acquired iron overload associated with antitransferrin monoclonal immunoglobulin: a case report

We describe a patient with an unusual combination of hypersideremia (700 microg/dL), hypertransferrinemia (570 mg/dL), hyperferritinemia (800 microg/L), and monoclonal gammopathy of undetermined significance (MGUS), in which the monoclonal immunoglobulin showed specific transferrin-binding activity. Liver histology revealed hepatic iron overload, prominent in periportal hepatocytes, suggesting intestinal iron hyperabsorption. We demonstrate that low urinary hepcidin, likely due to impaired iron delivery to erythroid cells via the transferrin cycle pathway over time, may be the mechanism for iron loading. We suggest that MGUS associated with monoclonal antibodies with antitransferrin activity should be added to the list of acquired causes of hemochromatosis.

Regulation of the divalent metal ion transporter DMT1 and iron homeostasis by a ubiquitin-dependent mechanism involving Ndfips and WWP2

Many ion channels and transporters are regulated by ubiquitination mediated by the Nedd4 family of HECT-type ubiquitin ligases (E3s). These E3s commonly interact with substrates via their WW domains that bind to specific motifs in target proteins. However, not all potential targets of these E3s contain WW-binding motifs. Therefore, accessory proteins may mediate the interaction between Nedd4 family members and their targets. Here we report that the divalent metal ion transporter DMT1, the primary nonheme iron transporter in mammals, is regulated by ubiquitination mediated by the Nedd4 family member WWP2. DMT1 interacts with 2 WW domain-interacting proteins, Ndfip1 and Ndfip2, previously proposed to have roles in protein trafficking. This promotes DMT1 ubiquitination and degradation by WWP2. Consistent with these observations, Ndfip1−/− mice show increased DMT1 activity and a concomitant increase in hepatic iron deposition, indicating an essential function of Ndfip1 in iron homeostasis. This novel mechanism of regulating iron homeostasis suggests that Ndfips and WWP2 may contribute to diseases involving aberrant iron transport.

Hereditary hemochromatosis in the post-HFE era

Following the discovery of the HFE gene in 1996 and its linkage to the iron overload disorder hereditary hemochromatosis (HH) there have been profound developments in our understanding of the pathogenesis of the biochemical and clinical manifestations of a number of iron overload disorders. This article provides an update of recent developments and key issues relating to iron homeostasis and inherited disorders of iron overload, with emphasis on HFE-related HH, and is based on the content of the American Association for the Study of Liver Diseases Single-Topic Conference entitled "Hemochromatosis: What has Happened After HFE?" which was held at the Emory Convention Center in Atlanta, September 7-9, 2007.

Revaluation of clinical and histological criteria for diagnosis of dysmetabolic iron overload syndrome

AIM: To re-evaluate the diagnostic criteria of insulin resistance hepatic iron overload based on clinical, biochemical and histopathological findings.

METHODS: We studied 81 patients with hepatic iron overload not explained by known genetic and acquired causes. The metabolic syndrome (MS) was defined according to ATPIII criteria. Iron overload was assessed by liver biopsy. Liver histology was evaluated by Ishak’s score and iron accumulation by Deugnier’s score; steatosis was diagnosed when present in ≥ 5% of hepatocytes.

RESULTS: According to transferrin saturation levels, we observed significant differences in the amount of hepatic iron overload and iron distribution, as well as the number of metabolic abnormalities. Using Receiving Operating Curve analysis, we found that the presence of two components of the MS differentiated two groups with a statistically significant different hepatic iron overload (P < 0.0001). Patients with ≥ 2 metabolic alterations and steatosis had lower amount of hepatic iron, lower transferrin saturation and higher sinusoidal iron than patients with < 2 MS components and absence of steatosis.

CONCLUSION: In our patients, the presence of ≥ 2 alterations of the MS and hepatic steatosis was associated with a moderate form of iron overload with a prevalent sinusoidal distribution and a normal transferrin saturation, suggesting the existence of a peculiar pathogenetic mechanism of iron accumulation. These patients may have the typical dysmetabolic iron overload syndrome. By contrast, patients with transferrin saturation ≥ 60% had more severe iron overload, few or no metabolic abnormalities and a hemochromatosis-like pattern of iron overload.

[Genetic iron overloads and hepatic insulin-resistance iron overload syndrome: an update]

Hepcidin inhibits intestinal absorption of iron through internalisation of ferroportin. Its discovery helps to better understand the genetic iron overloads. The insulin resistance-hepatic iron overload (IR-HIO)--also coined as the dysmetabolic iron overload syndrome--is a common cause or iron overload. This article is a review about genetic iron overloads and IR-HIO. Type 1 haemochromatosis C282Y +/+ accounts for 95% of the haemochromatosis. Hepatic fibrosis may develop if serum ferritin is higher than 1000 microg/l but can be partially reversible with phlebotomies. Juvenile haemochromatosis (type 2) and type 3 haemochromatosis (mutation of the transferrin receptor 2) are very uncommon. Several mutations of the ferroportin gene can cause usually mild iron overload of autosomal dominant inheritance. Aceruleoplasminemia is an uncommon disorder involving cerebral iron overload. The causes and consequences of the IR-HIO are unknown. Treatment of IR-HIO is focused on metabolic syndrome and phlebotomies are questionable because the overload is moderate and intestinal absorption of iron seems to be low. MRI (or other non invasive methods) is needed to truly assess iron overload because serum ferritin overestimates it in metabolic syndrome. Several points have to be elucidated: how HFE interferes with hepcidin in type 1 haemochromatosis; the causes of variability of iron overload; the benefits of populations screening; the advantage of phlebotomies in IR-HIO; the use of new oral iron chelators.

Iron and the liver: update 2008

The cross-talk which has taken place in recent years between clinicians and scientists has resulted in a greater understanding of iron metabolism with the discovery of new iron-related genes including the hepcidin gene which plays a critical role in regulating systemic iron homeostasis. Consequently, the distinction between (a) genetic iron-overload disorders including haemochromatosis related to mutations in the HFE, hemojuvelin, transferrin receptor 2 and hepcidin genes and (b) non-haemochromatotic conditions related to mutations in the ferroportin, ceruloplasmin, transferrin and di-metal transporter 1 genes, and (c) acquired iron-overload syndromes has become easier. However, major challenges still remain which include our understanding of the regulation of hepcidin production, the identification of environmental and genetic modifiers of iron burden and organ damage in iron-overload syndromes, especially HFE haemochromatosis, indications regarding the new oral chelator, deferasirox, and the development of new therapeutic tools interacting with the regulation of iron metabolism.

Current approach to hemochromatosis

Iron overload diseases of genetic origin are an ever changing world, due to major advances in genetics and molecular biology. Five major categories are now established: HFE-related or type1 hemochromatosis, frequently found in Caucasians, and four rarer diseases which are type 2 (A and B) hemochromatosis (juvenile hemochromatosis), type 3 hemochromatosis (transferrin receptor 2 hemochromatosis), type 4 (A and B) hemochromatosis (ferroportin disease), and a(hypo)ceruloplasminemia. Increased duodenal iron absorption and enhanced macrophagic iron recycling, both due to an impairment of hepcidin synthesis, account for the development of cellular excess in types 1, 2, 3, and 4B hemochromatosis whereas decreased cellular iron egress is involved in the main form of type 4A) hemochromatosis and in aceruloplasminemia. Non-transferrin bound iron plays an important role in cellular iron excess and damage. The combination of magnetic resonance imaging (for diagnosing visceral iron overload) and of genetic testing has drastically reduced the need for liver biopsy. Phlebotomies remain an essential therapeutic tool but the improved understanding of the intimate mechanisms underlying these diseases paves the road for innovative therapeutic approaches.