Serum ferritin concentration is affected by ferroportin Q248H mutation in Africans

The Role of Gene Variants in the Iron Metabolism of Anemic Adolescent Girls

Background and objectives Iron deficiency anemia (IDA) and the role of genetic variants in determining the iron status in adolescent girls are not yet well-understood. This study aims to investigate the association of the rs602662, rs1049296, rs1805051, rs855791, rs224589, and rs11568350 genes with IDA and iron bio-status parameters. Methods This study consisted of 132 patients (IDA group) and 110 healthy controls. The genotype was analyzed through polymerase chain reaction-restriction fragment length polymorphism. Results No differences were noted in the distribution of genotype and allele frequency single nucleotide polymorphism between the IDA and control group. In the IDA group, the GA carriers of rs602662 had a higher hemoglobin concentration (P=0.02) and packed cell volume (P=0.007), whereas transferrin saturation was increased in AA (P=0.02). The genetic variants rs1049296, rs1805051, rs224589, and rs855791 had a non-statistical significance on hematological parameters. Both the GT and TT carriers of the rs11568350 gene showed a low hemoglobin concentration (P=0.02 and <0.001) and mean corpuscular hemoglobin in GT carrier (P=0.01), whereas the TT risk of this gene showed a decreased packed cell volume (P=0.01). In the control patients, no association was observed with serum iron and hematological parameters. Conclusion Of these genetic variants, the GG and GA genotype frequency in rs602662 and the GG, GT, and TT in rs11568350 were associated with low iron status in anemic patients compared to the control patients.

Similar Ferroportin Q248H polymorphism prevalence in patients with Plasmodium falciparum malaria and control subjects in the low-endemic setting of Botswana

INTRODUCTION

Recent evidence suggests that ferroportin (FPN) Q248H may confer a survival advantage against malaria by reducing erythrocytic intracellular iron in Africans. We investigated if FPN Q248H mutation, that is prevalent in Batswana, is a factor in limiting the susceptibility to Plasmodium falciparum malaria.

METHODS

264 archived dried blood spot samples (183 P. falciparum malaria cases and 81 controls, matched for geographical region and season for equal exposure) were genotyped. Human and P. falciparum DNA was extracted using Chelex-100 resin and P. falciparum molecular confirmation performed. Ferroportin Q248H mutation was identified by restriction fragment length polymorphism. The prevalence of the FPN Q248H mutation and allele frequency and the accompanying 95% confidence interval were calculated. A qPCR method was employed to estimate P. falciparum parasitaemia. Association between FPN and malaria susceptibility was tested using Pearson Chi-square test and Mood's median test was used to compare P. falciparum parasitaemias according to FPN Q248H mutation.

RESULTS

All samples were successfully genotyped. The FPN Q248H allele frequency was 0.08 (95% CI: 0.05-0.11) in cases and 0.08 (95% CI: 0.02-0.14) in controls, consistent with Hardy-Weinberg equilibrium. The prevalence of FPN Q248H phenotype was comparable in patients with P. falciparum malaria and in un-infected individuals, 16.4% (95% CI: 11.0-21.8) vs 14.8% (95% CI: 7.1-22.5), P = 0.746. In addition, no association of presence of FPN Q248H with reduced parasitaemia was recorded, P = 0.837.

CONCLUSION

In this small study, FPN Q248H polymorphism prevalence was comparable between patients with P. falciparum malaria and control subjects in the low-endemic setting of Botswana.

Ethnic Differences in Iron Status

Iron is unique among all minerals in that humans have no regulatable excretory pathway to eliminate excess iron after it is absorbed. Iron deficiency anemia occurs when absorbed iron is not sufficient to meet body iron demands, whereas iron overload and subsequent deposition of iron in key organs occur when absorbed iron exceeds body iron demands. Over time, iron accumulation in the body can increase risk of chronic diseases, including cirrhosis, diabetes, and heart failure. To date, only ∼30% of the interindividual variability in iron absorption can be captured by iron status biomarkers or iron regulatory hormones. Much of the regulation of iron absorption may be under genetic control, but these pathways have yet to be fully elucidated. Genome-wide and candidate gene association studies have identified several genetic variants that are associated with variations in iron status, but the majority of these data were generated in European populations. The purpose of this review is to summarize genetic variants that have been associated with alterations in iron status and to highlight the influence of ethnicity on the risk of iron deficiency or overload. Using extant data in the literature, linear mixed-effects models were constructed to explore ethnic differences in iron status biomarkers. This approach found that East Asians had significantly higher concentrations of iron status indicators (serum ferritin, transferrin saturation, and hemoglobin) than Europeans, African Americans, or South Asians. African Americans exhibited significantly lower hemoglobin concentrations compared with other ethnic groups. Further studies of the genetic basis for ethnic differences in iron metabolism and on how it affects disease susceptibility among different ethnic groups are needed to inform population-specific recommendations and personalized nutrition interventions for iron-related disorders.

The ferroportin Q248H mutation protects from anemia, but not malaria or bacteremia

Iron acquisition is critical for life. Ferroportin (FPN) exports iron from mature erythrocytes, and deletion of the Fpn gene results in hemolytic anemia and increased fatality in malaria-infected mice. The FPN Q248H mutation (glutamine to histidine at position 248) renders FPN partially resistant to hepcidin-induced degradation and was associated with protection from malaria in human studies of limited size. Using data from cohorts including over 18,000 African children, we show that the Q248H mutation is associated with modest protection against anemia, hemolysis, and iron deficiency, but we found little evidence of protection against severe malaria or bacteremia. We additionally observed no excess Plasmodium growth in Q248H erythrocytes ex vivo, nor evidence of selection driven by malaria exposure, suggesting that the Q248H mutation does not protect from malaria and is unlikely to deprive malaria parasites of iron essential for their growth.

A simple colorimetric assay for measuring fructosamine 3 kinase activity

BACKGROUND

Fructosamine 3 kinase (FN3K) is a deglycating enzyme, which may play a key role in reducing diabetes-induced organ damage by removing bound glucose from glycated proteins. We wanted to develop a simple colorimetric method for assaying FN3K activity in human body fluids.

METHODS

Glycated bovine serum albumin (BSA) was obtained by glycation with a 10% glucose solution at 37 °C. After 72 h, glycated BSA was dialyzed against phosphate buffered saline (0.1 mol/L, pH 7.4). The dialyzed solution (containing ±1000 µmol/L fructosamine) was used as an FN3K substrate. In the assay, 300 µL of substrate was incubated with 50 µL of serum and 100 µL of MgCl2 (0.7 mmol/L)/ATP (3.2 mmol/L). The fructosamine concentration was determined at the start and after incubation (120 min, 25 °C). The decrease in fructosamine concentration over time is a measure for the FN3K activity (1 U corresponding to 1 µmol/min). Concomitantly, the FN3K SNP rs1056534 and the ferroportin SNP rs1156350 were genotyped.

RESULTS

Within-assay CV was 6.0%. Reference values for FN3K activity in serum were 14.2±1.6 U/L (n=143). Reference values for FN3K were neither age- nor sex-dependent. The various FN3K SNP rs1056534 genotypes showed no significant differences in serum FN3K activity. In diabetics (n=191), values (14.0±2.2 U/L) were comparable to those of the controls. FN3K activity in erythrocytes was significantly higher (170.3±7.6 U/L). The intra-erythrocytic FN3K activity makes the results prone to hemolysis. FN3K activity depended on the ferroportin Q248H genotypes, with the highest value for the wild type genotype. Neither transferrin saturation nor ferritin were confounders for the FN3K activity. FN3K activity was significantly (p<0.0001) correlated with HbA1c values, although the correlation between FN3K and HbA1c was weak.

CONCLUSIONS

The simple colorimetric method allows determining FN3K activity in human serum. The assay may be useful for studying the impact of deglycation processes in diabetes mellitus.

Whole blood Fe isotopic signature in a sub-Saharan African population

The Fe isotopic composition of an individual's whole blood has recently been shown to be an interesting clinical indicator of Fe status.

The association between fructosamine-3 kinase 900C/G polymorphism, transferrin polymorphism and human herpesvirus-8 infection in diabetics living in South Kivu

Prevalences of human herpesvirus-8 (HHV-8) infection and diabetes mellitus are very common in certain parts of Africa, containing iron-rich soils. We hypothesized that some genetic factors could have a link with susceptibility to HHV-8 infection. We focused on ferroportin Q248H mutation (rs11568350), transferrin (TF) polymorphism and fructosamine-3 kinase (FN3K) 900C/G polymorphism (rs1056534). The study population consisted of 210 type 2 diabetic adults and 125 healthy controls recruited in Bukavu (South Kivu). In the whole study population (diabetics+healthy controls), ferroportin Q248H mutation was detected in 47 subjects (14.0%) with 43 heterozygotes and 4 homozygotes. TF phenotype frequencies were 88.1% (CC), 10.4% (CD) and 1.5% (BC). Genotype frequencies of FN3K 900C/G polymorphism were respectively 9,3% (CC), 43.3% (GC) and 47.4% (GG). Prevalence of HHV8-infection in the study population was 77.3%. HHV-8 infection rate and HHV-8 IgG antibody titer were significantly higher in diabetics then in controls (p<0.0001). Significant differences were observed in HHV-8 infection rate and in HHV-8 IgG antibody titer according to FN3K rs1056534 (p<0.05 and p<0.05, respectively) and TF polymorphism (p<0.05 and p=0.005, respectively). No significant differences in HHV-8 infection rate and in HHV-8 IgG antibody titer were observed in the ferroportin Q248H mutation carriers (rs11568350) in comparison with ferroportin wild type. In a multiple regression analysis, FN3K rs1056534, TF polymorphism and presence of diabetes mellitus were predictors for HHV-8 infection. In contrast to these findings, ferroportin Q248H mutation (rs11568350) did not influence the susceptibility for an HHV-8 infection in sub-Saharan Africans.

Ironing out Ferroportin

Maintaining physiologic iron concentrations in tissues is critical for metabolism and host defense. Iron absorption in the duodenum, recycling of iron from senescent erythrocytes, and iron mobilization from storage in macrophages and hepatocytes constitute the major iron flows into plasma for distribution to tissues, predominantly for erythropoiesis. All iron transfer to plasma occurs through the iron exporter ferroportin. The concentration of functional membrane-associated ferroportin is controlled by its ligand, the iron-regulatory hormone hepcidin, and fine-tuned by regulatory mechanisms serving iron homeostasis, oxygen utilization, host defense, and erythropoiesis. Fundamental questions about the structure and biology of ferroportin remain to be answered.