FANCD2 monoubiquitination and activation by hexavalent chromium [Cr(VI)] exposure: Activation is not required for repair of Cr(VI)-induced DSBs

Fanconi anemia (FA) is a rare autosomal recessive disorder characterized by congenital abnormalities, progressive bone marrow failure, and cancer susceptibility. FA cells are hypersensitive to DNA crosslinking agents. FA is a genetically heterogeneous disease with at least 11 complementation groups. The eight cloned FA proteins interact in a common pathway with established DNA-damage-response proteins, including BRCA1 and ATM. Six FA proteins (A, C, E, F, G, and L) regulate the monoubiquitination of FANCD2 after DNA damage by crosslinking agents, which targets FANCD2 to BRCA1 nuclear foci containing BRCA2 (FANCD1) and RAD51. Some forms of hexavalent chromium [Cr(VI)] are implicated as respiratory carcinogens and induce several types of DNA lesions, including DNA interstrand crosslinks. We have shown that FA-A fibroblasts are hypersensitive to both Cr(VI)-induced apoptosis and clonogenic lethality. Here we show that Cr(VI) treatment induced monoubiquitination of FANCD2 in normal human fibroblasts, providing the first molecular evidence of Cr(VI)-induced activation of the FA pathway. FA-A fibroblasts demonstrated no FANCD2 monoubiquitination, in keeping with the requirement of FA-A for this modification. We also found that Cr(VI) treatment induced significantly more S-phase-dependent DNA double strand breaks (DSBs), as measured by γ-H2AX expression, in FA-A fibroblasts compared to normal cells. However, and notably, DSBs were repaired equally in both normal and FA-A fibroblasts during recovery from Cr(VI) treatment. While previous research on FA has defined the genetic causes of this disease, it is critical in terms of individual risk assessment to address how cells from FA patients respond to genotoxic insult.     

Asymptomatic Helicobacter pylori infection and iron deficiency are not associated with decreased growth among Alaska Native children aged 7-11 years

Introduction: Alaska Native children have high Helicobacter pylori infection and iron deficiency prevalences, and their average height‐for‐age is lower than US reference populations. During a clinical trial to determine the impact of H. pylori treatment on iron deficiency, we evaluated the effects of H. pylori infection and treatment on growth. Materials and Methods: We measured height and weight for children aged 7–11 years in western Alaska using village‐based measuring devices. H. pylori infection was determined by urea breath test and iron deficiency using serum ferritin. Children with H. pylori infection and iron deficiency entered the treatment phase and received iron alone or iron plus triple therapy for H. pylori. Follow‐up evaluations occurred at 2, 8, and 14 months. We evaluated the association between baseline H. pylori infection and growth; among children in the treatment phase, we also assessed the effect of H. pylori resolution on growth. Results: At baseline, 566 (87.1%) of 650 children were infected with H. pylori. Neither height and weight, nor body mass index differed by H. pylori infection status. Of 189 children in the treatment phase, 20 (10.6%) were uninfected at all three follow‐up periods, and 54 (28.6%) were uninfected for one or two periods. Compared with continuously infected children, children in these two groups had little evidence of improvements in any of the measured growth outcomes. Conclusions: H. pylori infection is not related to growth among Alaska Native children aged 7–11 years. Growth deficiency should not be considered an indication for H. pylori therapy.     

Volume,pH, and ion-content regulation in human red cells: Analysis of transient behavior with an integrated model

Summary A basic mathematical model of human red cells is presented which integrates the charge and nonideal osmotic behavior of hemoglobin and of other impermeant cell solutes with the ion transport properties of the red cell membrane. The computing strategy was designed to predict the behavior of all measurable variables in time in ways that optimize comparison with experimentally determined behavior. The need and applications of such a model are illustrated in three separate examples covering different areas of experimentation in the physiology and pathophysiology of red cells.     

Molecular spectra of HPRT deletion mutations in circulating T-lymphocytes in Fanconi anemia patients

The principal cellular feature of Fanconi anemia (FA), an inherited cancer prone disorder, is a high level of chromosomal breakage, amplified after treatment with crosslinking agents. Three of the eight genes involved in FA have been cloned: FANCA, FANCC and FANCG. However, their biological functions remain unknown. We previously observed an excessive production of deletions at the HPRT locus in FA lymphoblasts belonging to the relatively rare complementation group D(1) and an increased frequency of glycophorin A (GPA) variants in erythrocytes derived from FA patients (2). In thi study, we examined the molecular nature of 31 HPRT mutations formed in vivo in circulating T-lymphocytes isolated from 9 FA male patients. The results show that in all FA patients investigated the deletions are by far the most prevalent mutational event in contrast to age matched healthy donors, in which point mutations predominate. The complementation group in the FA patients examined in the present study has not yet been defined. However, knowing that mutations in the FANCA and FANCC gene are found to be involved in at least 70% of the FA patients, it can be expected that the excessive production of deletions is a general feature of the FA phenotype. In addition, the spectrum of HPRT deletions observed in FA patients differs from that of healthy children: there is a high frequency of 3'-terminal deletions and a strikingly low proportion of V(D)J mediated events. Based on previous findings, a decreased fidelity of coding V(D)J joint formation (3) and an inaccurate repair of specific DNA double strand breaks via Non-Homologous End Joining (4), we propose that FA genes play a role in the control of the fidelity of rejoining of specific DNA ends. Such a defect may explain several basic features of FA, such as chromosomal instability and deletion pronenness.     

Genetic Adaptation Controlled by Methylations and Acetylations at the Nuclear and Cytosolic Levels: A Hypothetical Model

Metabolic sensors related to the maturation of metabolism seem to control a process of generic adaptation involving the silencing of genes and the expression of their copies more adapted to environmental changes. Nuclear methylases and histone deacetylases control the gene silencing process. Nuclear methylases compete with cytosolic methylases for the same methyl donnors, this will favor the expression of unmethylated more adapted gene copies, when cytosotic methylases take over. Methylated cytosolic compounds may then represent an index of this adaptation. If a more adapted gene copy is mutated, the regulatory ligand of the gene product that does not find its target may induce a reexpression of the silenced gene. The hypothetical model proposed considers that gene silencing and expression of a more adequate copy involves a nonspecific gene silencer switch that depends on the histone status; the silencer switch is counteracted by the ligand of the adapted gene copy product acting like an inducer.     

Current knowledge of iron metabolism

Iron plays many roles in human physiology. In this article, we summarize the basic and current knowledge of this essential micronutrient on human metabolism.     

Distribution patterns of trace metals and of lipid peroxidation in plasma and erythrocytes of rat exposed to aluminum

Significant decreases of the hematocrit, hemoglobin, and plasma iron levels were observed in rats receiving daily intraperitoneal injections of aluminum at a dose of 27 mg Al/kg body wt for 3 wk, as compared to untreated controls. The activity of alkaline phosphatase was also significantly lower in the treated animals as a result of the accumulation of aluminum in the liver (p<0.05). Following aluminum administration, the plasma concentrations of aluminum and copper were also significantly increased, whereas the plasma zinc levels and oxidative stress measured through thiobarbituric acid reaction products showed nonsignificant differences between the two groups (p>0.05). The erythrocyte concentrations of aluminum, copper, zinc, and iron and of superoxide dismutase activity were found to be significantly higher in the study group as compared to controls. The treated animals also showed evidence of higher oxidative stress in comparison to controls. These results suggest that erythrocyte aluminum accumulation could result in abnormal trace element homeostasis and increasing oxidative stress, which might be a mechanism of aluminum-induced anemia.     

Helicobacter pylori‐Associated Chronic Gastritis and Unexplained Iron Deficiency Anemia: a Reliable Association?

Background and aim. About 35% of iron deficiency anemia cases remain unexplained after a gastrointestinal evaluation. An association between Helicobacter pylori and iron malabsorption has been suggested. The aim of this study was to determine whether H. pylori‐associated chronic gastritis is linked to unexplained iron deficiency anemia in adults. Methods. From 1996 to 2001, we identified 105 patients with unexplained iron deficiency anemia after upper endoscopy, colonoscopy, small bowel radiographic examination and duodenal biopsies. Two biopsies were obtained from the gastric antrum and two from the corpus of each patient. Gastritis status was described according to the Sydney System and H. pylori infection was assessed by an immunohistochemical test on biopsy specimens. This group was compared to a control group matched for sex and age. Results. There were 76 women and 29 men (mean age 57.4 ± 21.4 years) examined in the study. A H. pylori‐associated chronic gastritis was identified in 63 cases (60%) vs. 45 cases (43%) cases in the control group (p < .01). Atrophic gastritis was significantly associated with iron deficiency anemia compared with the control group [16 (15%) vs. 6 (6%); p < .03]. In the unexplained iron deficiency anemia group, (1) patients with chronic gastritis were significantly younger (52 ± 22 vs. 64 ± 20 years; p < .005), and (2) chronic gastritis was not linked to sex [sex ratio (male/female): 0.5 vs. 0.34, p = .34]. The prevalence of H. pylori infection was similar between premenopausal and postmenopausal women [28 (27%) vs. 26 (25%); p = .7] with iron deficiency anemia. Conclusion. H. pylori infection and chronic gastritis, especially atrophic gastritis, are significantly associated with unexplained iron deficiency anemia. Relationships between H. pylori‐associated chronic gastritis and unexplained iron deficiency anemia should be considered.