African iron overload

Iron overload is common in rural sub-Saharan African populations that have the custom of drinking a traditional fermented beverage with high iron content. As with both excessive alcohol exposure and HFE hemochromatosis, hepatic portal fibrosis and micronodular cirrhosis are prominent sequelae of African iron overload. Two observations are therefore important in characterizing iron overload in Africa. First, the hepatic iron concentrations associated with African iron overload often far exceed those seen in alcoholic liver disease and histologic changes of alcohol effect are almost always absent. Second, the pattern of iron accumulation in African dietary iron is prominent in both macrophages and hepatic parenchymal cells; this pattern is in contrast to HFE homochromatosis, which is marked by predominantly parenchymal iron-loading. For a long time, it was thought that African iron overload was purely dietary in nature, that increased iron and alcohol in the diet could fully explain markedly elevated tissue iron levels sometimes seen with this condition. Recent studies of pedigrees suggest that, in addition to high dietary iron content, a genetic defect may also be implicated in iron overload in Africans. These studies indicate that the possible defect is different from mutations in the HFE gene frequently found in Caucasians with iron overload, but the putative gene has not been identified. Recent studies also indicate that non-HFE iron overload occurs in African-Americans, but the prevalence and possible genetic basis is yet to be determined.     

Dietary iron overload in the African and hepatocellular carcinoma.

Dietary iron overload occurs commonly in parts of sub-Saharan Africa. It results from the consumption of large volumes of traditional beer that is home-brewed in iron pots or drums and consequently has a high iron content. The liver becomes iron overloaded and may develop portal fibrosis or, less often, cirrhosis. A genetic predisposition to the condition has been suggested, but no putative gene has yet been identified. Although originally believed not to cause hepatocellular carcinoma, recent case-control studies have shown African Blacks with dietary iron overload to be at increased risk for the tumour and a causal association has been confirmed in an animal model. The mechanisms of iron-induced malignant transformation are yet to be fully characterised, but the close association between cirrhosis and hepatocellular carcinoma in patients with hereditary haemochromatosis and the lesser association in those with dietary iron overload, suggests that chronic necroinflammatory hepatic disease contributes to the malignant transformation. Increased hepatic iron may, however, also be directly carcinogenic. Probable mechanisms include the generation of reactive oxygen intermediates and the resultant chronic oxidative stress that damages hepatocytes and proteins, causes lipid peroxidation, and induces strand breaks, DNA unwinding, and mutations in tumour-suppressor genes and critical DNA repair genes.     

Iron overload in urban Africans in the 1990s

BACKGROUND: In a previously described model, heterozygotes for an African iron loading locus develop iron overload only when dietary iron is high, but homozygotes may do so with normal dietary iron. If an iron loading gene is common, then homozygotes with iron overload will be found even in an urban population where traditional beer, the source of iron, is uncommon. AIMS: To determine whether iron overload and the C282Y mutation characteristic of hereditary haemochromatosis are readily identifiable in an urban African population. METHODS: Histological assessment, hepatocellular iron grading, and dry weight non-haem iron concentration were determined in post mortem tissue from liver, spleen, heart, lungs, and skin. DNA of subjects with elevated hepatic iron indexes was analysed for the C282Y mutation. Iron concentrations in other tissues were compared. RESULTS: A moderate increase (>30 micromol/g) in hepatic iron concentrations was found in 31 subjects (23%; 95% confidence interval 15.9 to 30.1%), and they were considerably elevated (>180 micromol/g) in seven subjects (5.2%; 95% confidence interval 1.5 to 8.9%). Appreciably elevated hepatic iron concentrations were associated with heavy iron deposition in both hepatocytes and macrophages, and either portal fibrosis or cirrhosis. All were negative for the C282Y mutation. Very high concentrations were uncommon in subjects dying in hospital. Concentrations of iron in spleen, heart, lung, and skin were significantly higher in subjects with elevated hepatic iron. CONCLUSIONS: Iron overload is readily identified among urban Africans and is associated with hepatic damage and iron loading of several tissues. The condition is unrelated to the genetic mutation found in hereditary haemochromatosis.     

Non-transferrin-bound iron and hepatic dysfunction in African dietary iron overload

BACKGROUND: Circulating iron is normally bound to transferrin. Non-transferrin-bound iron (NTBI) has been described in most forms of iron overload, but has not been studied in African dietary iron overload. This abnormal iron fraction is probably toxic, but this has not been demonstrated. METHODS: High-pressure liquid chromatography was used to assay serum NTBI in 25 black African subjects with iron overload documented by liver biopsy and in 170 relatives and neighbours. Levels of NTBI were correlated with indirect measures of iron status and conventional liver function tests. RESULTS: Non-transferrin-bound iron (> 2 micromol/L) was present in 43 people, 22 of patients of whom underwent liver biopsy and 21 relatives and neighbours. All but four of these had evidence of iron overload on the basis of either liver biopsy or elevated transferrin and serum ferritin concentrations. Among all 195 subjects, the presence of NTBI in serum was independently related to elevations in alanine and aspartate aminotransferase activity and bilirubin concentration. This relationship between serum NTBI and hepatic dysfunction was confirmed in the subgroup of 25 subjects with iron overload documented by liver biopsy. Non-transferrin-bound iron correlated significantly with elevations in alanine and aspartate aminotransferase activities after adjustment for hepatic iron grades, inflammation and diet. CONCLUSIONS: Non-transferrin-bound iron was found to be commonly present in African patients with dietary iron overload and to correlate with transferrin saturation and serum ferritin concentration. The independent relationship between NTBI and elevated liver function tests suggests that it may be part of a pathway leading to hepatic injury.     

Glucose abnormalities in non‐alcoholic fatty liver disease and chronic hepatitis C virus infection: the role of iron overload

Non‐alcoholic fatty liver disease (NAFLD) and chronic hepatitis C virus (HCV) infection are major causes of liver disease frequently described in outpatient patients with glucose abnormalities. Hyperferritinemia, which suggests that iron overload plays a decisive role in the pathophysiology of insulin resistance and hyperglycemia, is a common finding in both disorders. However, the role of the hepatic iron deposition differs from one to the other. In NAFLD, a moderate liver iron accumulation has been observed and molecular mechanisms, including the downregulation of the liver iron exporter ferroportin‐1, have been described. Iron overload will enhance intrahepatic oxidative stress that promotes hepatic fibrosis, interfere with insulin signalling at various levels and may hamper hepatic insulin extraction. Therefore, liver fibrosis, hyperglycemia and hyperinsulinemia will lead to increased levels of insulin resistance and the development of glucose abnormalities. Furthermore, iron depletion by phlebotomy removes liver iron content and reduces serum glucose and insulin resistance in NAFLD patients. Therefore, it seems that iron overload participates in those glucose abnormalities associated with NAFLD. Concerning chronic HCV infection, it has been classically assumed that iron overload contributes to insulin resistance associated with virus infection. However, recent evidence argues against the presence of iron overload in these patients and points to inflammation associated with diabetes as the main contributor to the elevated ferritin levels. Therefore, glucose abnormalities, and specially type 2 diabetes, should be taken into account when evaluating serum ferritin levels in patients with HCV infection. Copyright © 2009 John Wiley & Sons, Ltd.     

The interactions between iron and copper in genetic iron overload syndromes and primary copper toxicoses in Japan

Iron and copper are trace elements essential for health, and iron metabolism is tightly regulated by cuproproteins. Clarification of the interactions between iron and copper may provide a better understanding of the pathophysiology and treatment strategy for hemochromatosis, Wilson disease, and related disorders. The hepcidin/ferroportin system was used to classify genetic iron overload syndromes in Japan, and ceruloplasmin and ATP7B were introduced for subtyping Wilson disease into the severe hepatic and classical forms. Interactions between iron and copper were reviewed in these genetic diseases. Iron overload syndromes were classified into pre‐hepatic iron loading anemia and aceruloplasminemia, hepatic hemochromatosis, and post‐hepatic ferroportin disease. The ATP7B‐classical form with hypoceruloplasminemia has primary hepatopathy and late extra‐hepatic complications, while the severe hepatic form is free from ATP7B mutation and hypoceruloplasminemia, and silently progresses to liver failure. A large amount of iron and trace copper co‐exist in hepatocellular dense bodies of all iron overload syndromes. Cuproprotein induction to stabilize excess iron should be differentiated from copper retention in Wilson disease. The classical form of Wilson disease associated with suppressed hepacidin25 secretion may be double‐loaded with copper and iron, and transformed to an iron disease after long‐term copper chelation. Iron disease may not be complicated with the severe hepatic form with normal ferroxidase activity. Hepatocellular dense bodies of iron overload syndromes may be loaded with a large amount of iron and trace copper, while the classical Wilson disease may be double‐loaded with copper and iron.     

Iron overload disease: recent findings

Iron overload diseases are due to a progressive increase in total body iron stores that leads to deposition of iron in parenchymal organs and to subsequent damage to these organs. The commonest inherited form of iron overload is hereditary hemochromatosis (HH), an autosomal recessive disorder affecting the white population. Although in the western world and in northern Europe the majority of cases of HH are associated with an HFE gene mutation (C282Y and H63D), there are families with a familial iron overload disorder in whom neither the C282Y nor the H63D mutations were found. Recently, other forms of HH that are not related to HFE, but are due to mutations in genes coding iron transport proteins (ferroportin-1, TfR2, hepcidin) have been described. The clinical presentation of the disorder is highly variable, depending on the severity of iron overload. In fact, the inappropriate absorption and deposition of dietary iron may result in the development of hepatic and non-hepatic end-organ injury, leading to liver cirrhosis, hepatocellular carcinoma, diabetes, arthritis, skin pigmentation and cardiac diseases. HH and its sequelae are preventable with an early diagnosis and treatment. Patients with evidence of iron overload, a family history of HH or other risk factors should be screened by genotype testing for the HFE mutation. Nowadays, HH is recognized as being a complex genetic disease with probable significant environmental and genetic modifying factors, such as hepatitis C virus infection and alcohol abuse, and it has been shown that HFE mutations represent an independent risk factor for fibrosis and cirrhosis in chronic hepatitis C.     

Iron overload in Africans and African-Americans and a common mutation in the SCL40A1 (ferroportin 1) gene

The product of the SLC40A1 gene, ferroportin 1, is a main iron export protein. Pathogenic mutations in ferroportin 1 lead to an autosomal dominant hereditary iron overload syndrome characterized by high serum ferritin concentration, normal transferrin saturation, iron accumulation predominantly in macrophages, and marginal anemia. Iron overload occurs in both the African and the African-American populations, but a possible genetic basis has not been established. We analyzed the ferroportin 1 gene in 19 unrelated patients from southern Africa (N = 15) and the United States (N = 4) presenting with primary iron overload. We found a new c. 744 C-->T (Q248H) mutation in the SLC40A1 gene in 4 of these patients (3 Africans and 1 African-American). Among 22 first degree family members, 10 of whom were Q248H heterozygotes, the mutation was associated with a trend to higher serum ferritin to amino aspartate transferase ratios (means of 14.8 versus 4.3 microg/U; P = 0.1) and lower hemoglobin concentrations (means of 11.8 versus 13.2 g/dL; P = 0.1). The ratio corrects serum ferritin concentration for alcohol-induced hepatocellular damage. We also found heterozygosity for the Q248H mutation in 7 of 51 (14%) southern African community control participants selected because they had a serum ferritin concentration below 400 microg/L and in 5 of 100 (5%) anonymous African-Americans, but we did not find the change in 300 Caucasians with normal iron status and 25 Caucasians with non-HFE iron overload. The hemoglobin concentration was significantly lower in the African community controls with the Q248H mutation than in those without it. We conclude that the Q248H mutation is a common polymorphism in the ferroportin 1 gene in African populations that may be associated with mild anemia and a tendency to iron loading.     

Role of hepatic iron in non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) includes a spectrum of clinical entities ranging from simple steatosis to non-alcoholic steatohepatitis (NASH) with possible evolution to cirrhosis and hepatocellular carcinoma. Iron is considered a putative element that interacts with oxygen radicals in inducing liver damage and fibrosis. The role of hepatic iron in the progression of NASH remains controversial, but in some patients, iron may have a role in the pathogenesis of NASH. Though genetic factors, insulin resistance, dysregulation of iron-regulatory molecules, erythrophagocytosis by Kupffer cells may be responsible for hepatic iron accumulation in NASH, exact mechanisms involved in iron overload remain to be clarified. Iron reduction therapy such as phlebotomy or dietary iron restriction may be promising in patients with NASH/NAFLD to reduce insulin resistance as well as serum transaminase activities.     

Dose-related effects of dietary iron supplementation in producing hepatic iron overload in rats

The influence of varying the level of supplemental dietary iron on the development of hepatic iron overload was examined in rats. Two days after giving birth, Porton rats were fed a diet supplemented with 0, 0.5, 1 or 2% carbonyl iron, to institute dietary iron supplementation to the young via breast milk. After weaning, the offspring continued to receive the assigned diet until 32 weeks of age. Liver biopsies were taken from some rats at 8, 16 and 24 weeks of age and from all rats at 32 weeks of age, for assessment of iron overload. For both male and female rats, hepatic iron content was increased in a dose-related manner by feeding supplemented diet. Hepatic iron content of male rats tended to reach a plateau after 8–16 weeks of supplementation, while that of female rats continued to rise throughout the experimental period, such that the hepatic iron content of female rats was 2.8-fold that of similarly treated males at 32 weeks of age. Iron supplementation was associated with only moderate retardation of growth. By choosing an appropriate level of iron supplementation, good (grade III-IV) hepatic iron loading can be achieved with minimal adverse effects on the animals’ overall health.     

Hepcidin biology and therapeutic applications

The hepatic peptide hormone hepcidin regulates plasma iron concentrations and tissue iron distribution by inhibiting dietary iron absorption and mobilization of iron from stores in macrophages and hepatocytes. Dysregulation of hepcidin production underlies many iron disorders. Deficient production of hepcidin causes systemic iron overload in hereditary hemochromatosis and iron-loading anemias, such as β-thalassemia, whereas hepcidin excess contributes to the development of anemia in inflammatory disorders and chronic kidney disease, and may cause erythropoietin resistance. The Scientific Program on Iron and Heme session at the 51st ASH annual meeting discussed recent advances in understanding hepcidin biology and explored the potential for hepcidin therapeutic applications. The session included three 30-min presentations.     

Iron Metabolism in Nonalcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) is a common worldwide clinical and major public health problem affecting both adults and children in developed nations. Increased hepatic iron stores are observed in about one-third of adult NAFLD patients. Iron deposition may occur in parenchymal and/or non-parenchymal cells of the reticuloendothelial system (RES). Similar patterns of iron deposition have been associated with increased severity of other chronic liver diseases including HCV infection and dysmetabolic iron overload, suggesting there may be a common mechanism for hepatic iron deposition in these diseases. In NAFLD, iron may potentiate the onset and progression of disease by increasing oxidative stress and altering insulin signaling and lipid metabolism. The impact of iron in these processes may depend upon the sub-cellular location of iron deposition in hepatocytes or RES cells. Iron depletion therapy has shown efficacy at reducing serum aminotransferase levels and improving insulin sensitivity in subjects with NAFLD.     

Ferroportin (Q248H) mutations in African families with dietary iron overload

BACKGROUND: Dietary iron overload found in sub-Saharan Africa might be caused by an interaction between dietary iron and an iron-loading gene. Caucasian people with ferroportin gene mutations have iron overload histologically similar to that found in African patients with iron overload. Ferroportin is also implicated in the hypoferremic response to inflammation. The prevalence of the ferroportin Q248H mutation, unique to African people, and its association with dietary iron overload, mean cell volume (MCV) and C-reactive protein (CRP) were examined in 19 southern African families. METHODS: Polymerase chain reaction (PCR) and restriction enzyme digestion were used to identify the Q248H mutation. Statistical analysis was carried out to correlate the presence of the mutation with markers of iron overload and inflammation. RESULTS: We identified three (1.4%) Q248H homozygotes and 53 (24.1%) heterozygotes in the families examined in the present study. There was no increased prevalence of the mutation in index subjects or their families. Logistic regression showed significantly higher serum ferritin concentrations with the mutation. The mean cell volume (MCV) was significantly lower, and the serum CRP significantly higher in subjects who carried the mutation. CONCLUSIONS: The present study of 19 families with African iron overload failed to show evidence that the ferroportin (Q248H) mutation is responsible for the condition. Logistic regression, correcting for factors influencing iron status, did show increased ferritin levels in individuals with the mutation. The strong association with low MCV suggests the possibility that the ferroportin (Q248H) mutation might interfere with iron supply, whereas the elevated serum CRP might indicate that the ferroportin mutation influences the inflammatory response in African populations.     

Iron overload in hematopoietic cell transplantation

Iron overload, primarily related to RBC transfusions, is a relatively common complication in hematopoietic cell transplant (HCT) recipients. Iron overload increases the risk of infections, veno-occlusive disease and hepatic dysfunction post transplant. Elevated pretransplant ferritin levels have been reported to increase the risk of nonrelapse mortality following HCT and might influence the risk of acute and chronic GVHD. Serum ferritin is sensitive but not specific for iron overload and is a poor predictor of body iron burden. Estimation of hepatic iron content with a liver biopsy or magnetic resonance imaging should be considered prior to initiating therapy for post transplant iron overload. A subgroup of transplant survivors with mild iron overload and no end-organ damage may not need therapy. Phlebotomy is the treatment of choice with iron-chelation therapy reserved for patients not eligible for phlebotomy. Natural history, evolution and treatment of iron overload in transplant survivors have not been adequately investigated and more studies are needed to determine its impact on short-term and long-term morbidity and mortality.     

Iron status and cellular immune competence

There is increasing evidence that both iron overload and iron deficiency are associated with significant abnormalities of immune function. In diseases associated with iron overload there is increased susceptibility to both infection and neoplasia. The precise mechanisms are still being unravelled but iron overload has been shown to impair antigen-specific immune responses and to reduce the number of functional helper precursor cells. Similarly, iron in vitro in concentrations reported to be present in the serum of patients with iron overload impairs the generation of cytotoxic T-cells, enhances suppressor T-cell activity and reduces the proliferative capacity of helper T-cells. The predominant tumor seen in iron overload is primary hepatocellular carcinoma; however other aetiological factors appear to be involved in addition to iron overload, especially hepatic cirrhosis. Nevertheless, primary liver cancer occurs much more frequently in hemochromatosis than in other forms of cirrhosis. Iron deficiency is associated with an altered response to infection but the relationship is again a complex one. The cellular mechanisms involved have yet to be clearly defined, although impaired T and B cell function have been demonstrated.     

Iron in nonhemochromatotic liver disorders

Iron is essential for cellular functions, but in excessive amounts it is toxic to cells. The harmful effects are related to increased oxidative stress and production of reactive oxygen species causing oxidative damage to lipids, proteins, and nucleic acids. Heavy iron overload as occurs in primary and secondary hemochromatosis can cause fibrosis of various parenchymal organs such as the liver, heart, and pancreas. Lesser degrees of hepatic iron deposition are also associated with, and seem to be risk factors for, certain nonhemochromatotic liver diseases. Porphyria cutanea tarda is associated with hepatic iron overload and responds to iron-reduction therapy. Other recent evidence indicates that the prevalence of HFE gene mutations is increased in chronic viral hepatitis and that patients with chronic hepatitis C harboring especially the C282Y mutation are more likely to suffer from advanced hepatic fibrosis or cirrhosis and to do so at younger ages. In this article we review selected nonhemochromatotic disorders in which iron can play an important comorbid role.     

Iron toxicity and chelation therapy

Iron is an essential mineral for normal cellular physiology, but an excess can result in cell injury. Iron in low-molecular-weight forms may play a catalytic role in the initiation of free radical reactions. The resulting oxyradicals have the potential to damage cellular lipids, nucleic acids, proteins, and carbohydrates; the result is wide-ranging impairment in cellular function and integrity. The rate of free radical production must overwhelm the cytoprotective defenses of cells before injury occurs. There is substantial evidence that iron overload in experimental animals can result in oxidative damage to lipids in vivo, once the concentration of iron exceeds a threshold level. In the liver, this lipid peroxidation is associated with impairment of membrane-dependent functions of mitochondria and lysosomes. Iron overload impairs hepatic mitochondrial respiration primarily through a decrease in cytochrome C oxidase activity, and hepatocellular calcium homeostasis may be compromised through damage to mitochondrial and microsomal calcium sequestration. DNA has also been reported to be a target of iron-induced damage, and this may have consequences in regard to malignant transformation. Mitochondrial respiratory enzymes and plasma membrane enzymes such as sodium-potassium-adenosine triphosphatase (Na(+) + K(+)-ATPase) may be key targets of damage by non-transferrin-bound iron in cardiac myocytes. Levels of some antioxidants are decreased during iron overload, a finding suggestive of ongoing oxidative stress. Reduced cellular levels of ATP, lysosomal fragility, impaired cellular calcium homeostasis, and damage to DNA all may contribute to cellular injury in iron overload. Evidence is accumulating that free-radical production is increased in patients with iron overload. Iron-loaded patients have elevated plasma levels of thiobarbituric acid reactants and increased hepatic levels of aldehyde-protein adducts, indicating lipid peroxidation. Hepatic DNA of iron-loaded patients shows evidence of damage, including mutations of the tumor suppressor gene p53. Although phlebotomy therapy is effective in removing excess iron in hereditary hemochromatosis, chelation therapy is required in the treatment of many patients who have combined secondary and transfusional iron overload due to disorders in erythropoiesis. In patients with beta-thalassemia who undergo regular transfusions, deferoxamine treatment has been shown to be effective in preventing iron-induced tissue injury and in prolonging life expectancy. The use of the oral chelator deferiprone remains controversial, and work is continuing on the development of new orally effective iron chelators.     

Association between Alcoholism and Increased Hepatic Iron Stores

Although alcoholic liver disease is often associated with some increase in hepatic iron stores, it is now established that when gross iron overload is present, this is due to genetic hemochromatosis. Furthermore, there appears to be a critical iron concentration necessary for the induction of hepatic fibrosis. Lipid peroxidation induced by ethanol and/or iron would appear to play a major role in hepatic damage in both humans and experimental animals. Although the exact mechanism(s) of induction of lipid peroxidation by ethanol and iron remains to be elucidated, both toxins can exert a synergistic effect upon hepatic lipid peroxidation. Iron overload has also been shown to stimulate directly hepatocyte and hepatic procollagen mRNA expression, which is further stimulated by ethanol. The observed synergism between iron and alcohol with respect to both hepatic lipid peroxidation and collagen biosynthesis offers a possible explanation of the apparent early onset of fibrosis and cirrhosis in patients with iron overload who have an excessive alcohol intake.     

Australian guidelines for the assessment of iron overload and iron chelation in transfusion-dependent thalassaemia major, sickle cell disease and other congenital anaemias

Iron overload is the most important cause of mortality in patients with thalassaemia major. Iron chelation is therefore a critical issue in the management of these patients and others with transfusion-dependent haemoglobinopathies and congenital anaemias. In recent years, significant developments have been made in the assessment of iron overload, including the use of magnetic resonance imaging for measuring liver and cardiac iron. Advances in the modalities available for iron chelation, with the advent of oral iron chelators including deferiprone and deferasirox in addition to parenteral desferrioxamine, have expanded treatment options. A group of Australian haematologists has convened to formulate guidelines for managing iron overload on the basis of available evidence, and to describe best consensus practice as undertaken in major Australian Haemoglobinopathy units. The results of their discussions are described in this article, with the aim of providing guidance in the management of iron overload in these patients.     

Hepatocellular carcinoma and African iron overload.

Both hepatocellular carcinoma (HCC) and iron overload are important health problems in Africa. Chronic hepatitis B virus (HBV) infection is recognised as a major risk factor for HCC, but iron overload in Africans has not been considered in pathogenesis. Up to half the patients with HCC in Africa do not have any recognised risk factors such as preceding chronic HBV infection, and other risk factors remain unidentified. HCC is an important complication of HLA-linked haemochromatosis, an iron loading disorder found in Europeans. It is proposed that African iron overload might also be a risk factor for HCC.