Association of pulmonary tuberculosis with increased dietary iron

To determine whether increased dietary iron could be a risk factor for active tuberculosis, dietary iron history and human immunodeficiency virus (HIV) status were studied in 98 patients with pulmonary tuberculosis and in 98 control subjects from rural Zimbabwe. Exposure to high levels of dietary iron in the form of traditional beer is associated with increased iron stores in rural Africans. HIV seropositivity was associated with a 17.3-fold increase in the estimated odds of developing active tuberculosis (95% confidence interval [95% CI], 7.4-40.6; P<.001), and increased dietary iron was associated with a 3.5-fold increase (95% CI, 1.4-8.9; P=.009). Among patients treated for tuberculosis, HIV seropositivity was associated with a 3.8-fold increase in the estimated hazard ratio of death (95% CI, 1.0-13.8; P=.046), and increased dietary iron was associated with a 1.3-fold increase (95% CI, 0.4-6.4; P=.2). These findings are consistent with the hypothesis that elevated dietary iron may increase the risk of active pulmonary tuberculosis.

Distinct iron-sulfur cluster assembly complexes exist in the cytosol and mitochondria of human cells

Iron-sulfur (Fe-S) clusters are cofactors found in many proteins that have important redox, catalytic or regulatory functions. In mammalian cells, almost all known Fe-S proteins are found in the mitochondria, but at least one is found in the cytosol. Here we report cloning of the human homologs to IscU and NifU, iron-binding proteins that play a critical role in Fe-S cluster assembly in bacteria. In human cells, alternative splicing of a common pre-mRNA results in synthesis of two proteins that differ at the N-terminus and localize either to the cytosol (IscU1) or to the mitochondria (IscU2). Biochemical analyses demonstrate that IscU proteins specifically associate with IscS, a cysteine desulfurase that is proposed to sequester inorganic sulfur for Fe-S cluster assembly. Protein complexes containing IscU and IscS can be found in the mitochondria as well as in the cytosol, implying that Fe-S cluster assembly takes place in multiple subcellular compartments in mammalian cells. The possible roles of the IscU proteins in mammalian cells and the potential implications of compartmentalization of Fe-S cluster assembly are discussed.

A traditional beverage prevents iron deficiency in African women of child bearing age

OBJECTIVE

To determine if a traditional item in the diet might be useful in preventing iron deficiency in African women of child-bearing age.

DESIGN

In a prospective study, the iron status of women who did and did not drink traditional beer high in iron and folic acid, was compared. Iron status was determined by a combination of haemoglobin, serum ferritin and transferrin saturation.

SETTING

The study was conducted amongst rural villagers in the Murehwa and Zaka districts of Zimbabwe and in Mpumalanga Province, South Africa.

SUBJECTS

112 women aged between 12 and 50 y from a population of 425 rural people participating in on-going family genetic studies.

RESULTS

Women who consumed traditional beer had significantly higher serum ferritin concentrations and transferrin saturations compared to non-drinkers (P = 0.0001 and 0.03 respectively). Iron deficiency anaemia was not present in drinkers but the prevalence in non-drinkers was 13%. Forty seven percent of the non-drinkers and only 14% of the drinkers had evidence of iron deficiency (P = 0.002). Six (21%) of the drinkers and none of the non-drinkers had evidence of iron overload (transferrin saturation > 55% and serum ferritin > 400 ug/l).

CONCLUSION

We conclude that the consumption of traditional beer, rich in iron, protects women against iron deficiency. While the use of an alcoholic beverage is not ideal, our findings suggest that indigenous cultural practices might be successfully employed or adapted for promoting iron nutrition.

Is there a link between African iron overload and the described mutations of the hereditary haemochromatosis gene?

Over 80%, of Caucasian patients with hereditary haemochromatosis are homozygotes for a C282Y mutation in the HFE gene on chromosome 6. Recent evidence suggests that a genetic factor may also be involved in the pathogenesis of African iron overload, although the locus has not been described. PCR analysis of DNA from 25 southern Africans, identified by segregation analysis as having a high probability of carrying the putative African iron-loading gene, failed to identify any subjects with the C282Y mutation. The possible genetic defect in African iron overload appears to be different from that described in most cases of hereditary haemochromatosis in Caucasians.

Evidence of genetic transmission in African iron overload

Iron overload in Africa was previously regarded as purely due to excessive iron in traditional beer, but we recently found evidence that transferrin saturation and unsaturated iron binding capacity may be influenced by an interaction between dietary iron content and a gene distinct from any HLA-linked locus. To determine if serum ferritin follows a genetic pattern and to confirm our previous observations, we studied an additional 351 Zimbabweans and South Africans from 45 families ranging in size from two to 54 members. Iron status was characterized with repeated morning measurements of serum ferritin, transferrin saturation, and unsaturated iron binding capacity after supplementation with vitamin C. For each measure of iron status, segregation analysis was consistent with an interaction between a postulated iron-loading gene and dietary iron content (P < .01). In the most likely model, transferrin saturation is 75% and serum ferritin is 985 micrograms/L in a 40-year-old male heterozygote with an estimated beer consumption of 10,000 L, whereas the saturation is 36% and serum ferritin is 233 micrograms/L in an unaffected individual with identical age, sex, and beer consumption. This segregation analysis provides further evidence for a genetic influence on iron overload in Africans.

African iron overload and hepatocellular carcinoma (HA-7-0-080)

Although HLA-linked hemochromatosis greatly increases the risk for hepatocellular carcinoma in people of European ancestry, iron overload in Africa is not thought to be etiologically related to this malignancy. To determine if African iron overload may be associated with hepatocellular carcinoma, we reviewed 320 consecutive diagnostic liver biopsies processed at the University of Zimbabwe from 1992 to 1994 and we selected for analysis 215 biopsies from adults that were suitable for the histological assessment of hepatocellular iron. Subjects were stratified according to hepatocellular iron grades of 0-2+ (normal levels to mild siderosis; n = 183) and grades of 3+ and 4+ (distinctly elevated levels consistent with iron overload; n = 32). Thirty-six subjects had hepatocellular carcinoma. Logistic regression modeling revealed a significant association between iron overload and hepatocellular carcinoma after adjustment for age, sex and and the presence of portal fibrosis or cirrhosis (p = 0.041). The odds of hepatocellular carcinoma in subjects with iron overload was 3.1 (95% confidence interval of 1.05-9.4) times that of subjects without iron overload. While we could not test for exposure to viral hepatitis or to aflatoxins in this study, our findings suggest that iron overload may be a risk factor for hepatocellular carcinoma in Africa.

Hepatitis C virus in Zimbabwe

BACKGROUND

Hepatitis B is a common cause of chronic liver disease in Zimbabwe but other viral infections are also important. The prevalence of viral hepatitis C has not been previously described in healthy rural Zimbabwean adults.

OBJECTIVES

To determine the prevalence of seropositivity to hepatitis C in rural healthy adults in Zimbabwe, and to determine if there is evidence of active liver disease in subjects who are seropositive.

STUDY DESIGN

Cross sectional descriptive study.

SETTING

Rural communities around different parts of Zimbabwe, as part of a larger study into the prevalence and genetic pattern of iron overload.

SUBJECTS

An initial 150 rural Zimbabweans over the age of 12 years.

MAIN OUTCOME MEASURES

Presence of the following serological markers: hepatitis B surface antigen; antibodies to hepatitis C, B surface and B core antigens; hepatic enzymes and iron status determined on the basis of serum ferritin and transferrin saturation.

RESULTS

11 (7.7%) of the subjects were positive for antibodies to hepatitis C and they had significant elevations in hepatic enzymes and serum iron levels suggesting substantial hepatocellular damage. Twenty (14.1%) of the subjects were positive for hepatitis B surface antigen, but they did not have significant elevations in hepatic enzymes or indirect measures of iron status.

CONCLUSION

Seropositivity for hepatitis C is common and is approximately half the prevalence of hepatitis B chronic carrier status. Chronic hepatitis C may be more damaging to the liver than chronic hepatitis B and, therefore, may be an important cause of liver disease in rural Zimbabwe.

Traditional beer consumption and the iron status of spouse pairs from a rural community in Zimbabwe

To examine the relationship between dietary iron exposure through the consumption of traditional beer and the presence of iron overload in black Africans not related by birth, we studied 28 husband and wife pairs from a rural Zimbabwean community. Lifetime traditional beer consumption was estimated by questioning subjects and iron status was assessed by repeated measurements of serum ferritin and transferrin saturation in subjects who were fasting and had received vitamin C supplementation. Each of the 56 study subjects had an estimated lifetime traditional beer consumption >1,000 L. The mean +/- standard deviation (SD) concentration of iron in the supernatants of nine samples of traditional beer from the community was 46 +/- 10 mg/L. Four of 28 men (14.3%) and no women had the combination of an elevated serum ferritin and a transferrin saturation >70%, suggestive of substantial iron overload. Significant correlations were not found between the iron status of the husbands and their wives or between dietary iron exposure and iron stores. Our findings suggest that dietary iron exposure may not fully explain the development of iron overload in Africans and are consistent with the hypothesis that an iron-loading gene may also be implicated in pathogenesis.

Regulation of iron metabolism in eukaryotes

Iron metabolism is regulated in cells to ensure that iron supplies are adequate and nontoxic. The expression of iron metabolism is regulated primarily by posttranscriptional mechanisms. Ferritin, eALAS, SDHb of Drosophila, and mammalian mitochondrial aconitase are translationally regulated. The TfR is regulated at the level of mRNA stability. Iron regulatory proteins are regulated either by assembly or by disassembly of an iron-sulfur cluster (IRP1) or by rapid degradation in the presence of iron (IRP2). The list of targets for IRP-mediated regulation is growing longer, and a range of possibilities for versatile regulation exists, as each IRP can bind to unique targets that differ from the consensus IRE. The reactivity of iron with oxygen and the creation of toxic by-products may be the evolutionary stimulus that produced this system of tight posttranscriptional gene regulation.

Transcriptional regulation by iron of the gene for the transferrin receptor

Treatment of K562 cells with desferrioxamine, a permeable iron chelator, led to an increase in the number of transferrin receptors. Increasing intracellular iron levels by treatment of cells with either human diferric transferrin or hemin lowered the level of the transferrin receptors. By using a cDNA clone of the human transferrin receptor, we showed that the changes in the levels of the receptor by iron were accompanied by alterations in the levels of the mRNA for the receptor. The rapidity of these changes indicated that the mRNA had a very short half-life. By using an in vitro transcriptional assay with isolated nuclei, we obtained evidence that this regulation occurred at the transcriptional level.

Hemin, chelatable iron, and the regulation of transferrin receptor biosynthesis

We have examined the mechanism by which hemin regulates the expression of the human transferrin receptor. Previous work led to the suggestion that the regulatory signal is provided by heme (Ward J. H., Jordan, I., Kushner, J. P., and Kaplan, J. (1984) J. Biol. Chem. 259, 13235-13240). We demonstrated that hemin regulates the expression of the receptor via alterations in the rate of receptor biosynthesis. However, this effect can be completely abolished by addition of desferrioxamine, an intracellular iron chelator. Competition curves demonstrate that desferrioxamine and hemin affect the same intracellular iron pool. Since the chelator cannot remove iron from heme, we propose that hemin acts simply by delivering iron to a chelatable iron pool and that levels of chelatable iron provide the regulatory signal for expression of the transferrin receptor gene.

Aspiration of the asymptomatic metatarsophalangeal joint in gout patients and hyperuricemic controls

Asymptomatic metatarsophalangeal joints were aspirated in a group of patients with gout, in 2 control groups with hyperuricemia, and in 1 normouricemic control group. Extracellular urate crystals were present in 70% of gout patients, in 1 of 19 patients with asymptomatic hyperuricemia, and in 2 of 9 patients with renal failure and hyperuricemia but no history of joint disease. Crystals were not found in the 10 normouricemic patients who had other types of arthritis. The presence of crystals in the subjects with gout was not correlated with a history of podagra, duration of gout, presence of tophi, or degree of control of hyperuricemia. Though crystals were found on rare occasions in joint fluid of asymptomatic hyperuricemic subjects, the presence of these crystals in asymptomatic joints was more common in subjects with gout.