Rogerio Meneghini

Iron Homeostasis, Oxidative Stress, and DNA Damage

Cellular DNA damage under prooxidant conditions has been shown to be mediated by iron. In fact, iron is an important element in the establishment of a prooxidant status in the cell. It is discussed that there exists a mutual dependence between iron metabolism and oxidative stress. Changes in the former by means of genetic manipulation bring about modification in the redox status as judge by oxidative damage in DNA. On the other hand, the induction of a cellular prooxidative condition activates the protein IRP (iron regulatory protein) in a way that renders the cell more able to take up iron. The possible implications of these results is discussed in the light of recent findings reported in the literature on hydrogen peroxide as a signaling species for cell proliferation. The question of DNA strand break formation under prooxidant conditions is reviewed from the viewpoint of which agent is more important: an oxidant generated by Fenton type reaction or Ca2+-activated nucleases. The presence of iron in the nucleus is reviewed. Results have been produced indicating that the larger concentration of this metal in the nucleus, as compared to the cytosol, seems to be explained by an iron-type P-ATPase. There is no explanation, presently, for iron presence in the nucleus, but it certainly imposes a prooxidant trend that needs to be counterbalanced in some way, and evidence is reviewed that nuclear metallothionein plays a role in this regard.

In vivo formation of single-strand breaks in DNA by hydrogen peroxide is mediated by the Haber-Weiss reaction

Phenanthroline and bipyridine, strong chelators of iron, protect DNA from single-strand break formation by H2O2 in human fibroblasts. This fact strongly supports the concept that these DNA single-strand breaks are produced by hydroxyl radicals generated by a Fenton-like reaction between intracellular Fe2+ and H2O2: H2O2 + Fe2+----Fe3+ + OH- + OH: Corroborating this idea is the fact that thiourea, an effective OH radical scavenger, prevents the formation of DNA single-strand breaks by H2O2 in nuclei from human fibroblasts. The copper chelator diethyldithiocarbamate, a strong inhibitor of superoxide dismutase, greatly enhances the in vivo production of DNA single-strand breaks by H2O in fibroblasts. This supports the idea that Fe3+ is reduced to Fe2+ by superoxide ion: O divided by 2 + Fe3+----O2 + Fe2+; and therefore that the sum of this reaction and the Fenton reaction, namely the so-called Haber-Weiss reaction, H2O2 + O divided by 2----O2 + OH- + OH; represents the mode whereby OH radical is produced from H2O2 in the cell. EDTA completely protects DNA from single-strand break formation in nuclei. The chelator therefore removes iron from the chromatin, and although the Fe-EDTA complex formed is capable of reacting with H2O2, the OH radical generated under these conditions is not close enough to hit DNA. Therefore iron complexed to chromatin functions as catalyst for the Haber-Weiss reaction in vivo, similarly to the role played by Fe-chelates in vitro.

Is there science beyond English? Initiatives to increase the quality and visibility of non-English publications might help to break down language barriers in scientific communication.

Of the past 25 winners of the Nobel Prize in Literature, only 9 wrote their masterpieces in English; the remaining 16 laureates wrote in other native languages. Many of their works were eventually translated into English, which was probably necessary for international recognition and the attention of the Swedish Nobel Prize committee. The translators faced the arduous task of transferring the splendour of the original text into a different semantic, syntactic and sometimes cultural context to make it appeal to a wider audience. ![][1] Most Nobel laureates in Physics, Chemistry, and Physiology or Medicine do not face the challenge of translating their works into another language before gaining recognition. Many speak English as their first language and even non‐native English speakers usually publish their discoveries in English. Furthermore, given that English is the lingua franca of science, the international community—including the Nobel Prize committees at the Royal Swedish Academy of Sciences and the Karolinska Institute—do not have to wait for a translation. The situation is reminiscent of the ancient and medieval worlds, when scholars could communicate only in Latin until great historical literates, such as Dante Alighieri, William Shakespeare and Martin Luther, promoted the use of the Italian, English and German languages, respectively, by writing in their native languages. > Any scientist must therefore master English—at least to some extent—to obtain international recognition and to access relevant publications In fact, English has become the modern lingua franca in a world that is economically, scientifically and culturally largely dominated by Anglo‐American countries. Any scientist must therefore master English—at least to some extent—to obtain international recognition and to access relevant publications. But although this makes communication between scientists much easier, it also creates problems for non‐English‐speaking countries. Even if their scientists are able to read English publications, to reap the societal benefits they must … [1]: /embed/graphic-1.gif

Iron is the intracellular metal involved in the production of DNA damage by oxygen radicals

The metal chelators 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline (neocuproine) showed distinct abilities to prevent hydroxyl radical formation from hydrogen peroxide and Cu+ or F2(2+) (Fenton reaction) as determined by electron spin resonance. o-Phenanthroline prevented both Fe- and Cu-mediated Fenton reactions whereas neocuproine only prevented the Cu-mediated Fenton reaction. Because only 1,10-phenanthroline but not neocuproine prevented DNA strand-break formation in hydrogen peroxide-treated mammalian fibroblasts it appears that the Fe-mediated, as compared to the Cu-mediated, intranuclear Fenton reaction is responsible for DNA damage.

Protection of mammalian cells by o-phenanthroline from lethal and DNA-damaging effects produced by active oxygen species

Active oxygen species are suspected as being a cause of the cellular damage that occurs at the site of inflammation. Phagocytic cells accumulate at these sites and produce superoxide ion, hydrogen peroxide and hydroxyl radical. The ultimate killing species, the cellular target and the mechanism whereby the lethal injury is produced are unknown. We exposed mouse fibroblasts to xanthine oxidase and acetaldehyde, a system which mimics the membrane of phagocytic cells in terms of production of oxygen species. We observed that the generation of these species produced DNA strand breaks and cellular death. The metal chelator o-phenanthroline completely abolished the former effect, and at the same time it effectively protected the cells from lethal injuries. Because complexing iron o-phenanthroline prevents the formation of hydroxyl radical by the Fendon reaction (Fe(II) + H2O2----Fe(III) + OH- + OH.), it is proposed that most of the cell death and DNA damage are brought about by OH radical, produced from other species by iron-mediated reactions.

Correlation between cytotoxic effect of hydrogen peroxide and the yield of DNA strand breaks in cells of different species

The rate of loss of reproductive capacity produced by hydrogen peroxide was shown to be 6-times faster for human fibroblasts than for Chinese hamster fibroblasts. Mouse fibroblasts exhibited an intermediate response. The explanation for that does not lie in the different capacities of these cells to destroy H2O2. The kinetics of repair of single-strand breaks although slightly different for the three cell lines also does not provide a full explanation for the different sensitivity. What was shown to correlate well with the killing effect was the yield of strand breaks produced by H2O2 in the DNA of cells from the three species. A similar H2O2 concentration produced 5-10-times more strand breaks in human DNA than in hamster DNA and 2-4-times more than in mouse DNA. This ratio holds for different cell lines from human and hamster and thus seems to be species-specific. Based on our previous findings we propose that this difference may lie in the amount of chromatin-bound iron and the level of superoxide ion in these cells.

Iron and its sensitive balance in the cell

Iron is vital in life because it is an important component of molecules that undergoes redox reactions or transport oxygen. However, the existence of two stable and inter-convertible forms of iron, iron(III) and iron(II), makes possible one electron being transferred to or captured from other species to form radicals. In particular, superoxide and hydroxyl radicals may be formed in these reactions, both with capacity of attacking other molecules. DNA is one important target and a vast literature exists showing that attack of hydroxyl radical to DNA leads to cell death cellular necrosis, apoptosis, mutation and malignant transformation. Therefore, a fine balance must exist at various levels of an organism to maintain iron concentration in a narrow range, above and below which deleterious effects of distinct nature occur. This review will deal with the formation of oxygen reactive species in iron participating reactions, defenses in the organism against these species, the different mechanisms of iron homeostasis and iron deficiency and iron overload related diseases.

Action of hydrogen peroxide on human fibroblast in culture.

Abstract— Human fibroblasts in culture lose the capacity of proliferating when exposed to hydrogen peroxide in the concentration range of 1 to 10 μM. The toxicity of H2O2 to xeroderma pigmentosum cells (XP12RO). defective in excision repair of lesions produced by UV‐irradiation, was about twice as high as to cells proficient in excision repair (VA13). This compound produces single‐strand breaks in intracellular DNA but not in purified DNA. These breaks are in situ physical discontinuities rather than alkali‐labile bonds, and their generation occurs at the same extent at 4°C and 37° indicating that they are not produced by an endonuclease. The results favor the hypothesis that H2O2 reacts in the cell producing a radical species which brings about the formation of DNA single‐strand breaks. These breaks are effectively repaired by both XP12RO and VA13 fibroblasts. The possible reason for the lethality of H2O2 is discussed.

Articles by Latin American Authors in Prestigious Journals Have Fewer Citations

Background The journal Impact factor (IF) is generally accepted to be a good measurement of the relevance/quality of articles that a journal publishes. In spite of an, apparently, homogenous peer-review process for a given journal, we hypothesize that the country affiliation of authors from developing Latin American (LA) countries affects the IF of a journal detrimentally. Methodology/Principal Findings Seven prestigious international journals, one multidisciplinary journal and six serving specific branches of science, were examined in terms of their IF in the Web of Science. Two subsets of each journal were then selected to evaluate the influence of authors affiliation on the IF. They comprised contributions (i) with authorship from four Latin American (LA) countries (Argentina, Brazil, Chile and Mexico) and (ii) with authorship from five developed countries (England, France, Germany, Japan and USA). Both subsets were further subdivided into two groups: articles with authorship from one country only and collaborative articles with authorship from other countries. Articles from the five developed countries had IF close to the overall IF of the journals and the influence of collaboration on this value was minor. In the case of LA articles the effect of collaboration (virtually all with developed countries) was significant. The IFs for non-collaborative articles averaged 66% of the overall IF of the journals whereas the articles in collaboration raised the IFs to values close to the overall IF. Conclusion/Significance The study shows a significantly lower IF in the group of the subsets of non-collaborative LA articles and thus that country affiliation of authors from non-developed LA countries does affect the IF of a journal detrimentally. There are no data to indicate whether the lower IFs of LA articles were due to their inherent inferior quality/relevance or psycho-social trend towards under-citation of articles from these countries. However, further study is required since there are foreseeable consequences of this trend as it may stimulate strategies by editors to turn down articles that tend to be under-cited.

Iron-mediated induction of sister-chromatid exchanges by hydrogen peroxide and superoxide anion

When Chinese hamster fibroblasts were exposed to hydrogen peroxide or to a system consisting of xanthine oxidase and hypoxanthine, which generates superoxide anion plus hydrogen peroxide, sister-chromatid exchanges (SCEs) were formed in a dose-dependent manner. When the iron-complexing agent o-phenanthroline was present in the medium, however, the production of these SCEs was completely inhibited. This fact indicates that the Fenton reaction: Fe2+ + H2O2----OH0 + OH- + Fe3+ is responsible for the production of SCEs. When O2- and H2O2 were generated inside the cell by incubation with menadione, the production of SCE was prevented by co-incubation with copper diisopropylsalicylate, a superoxide dismutase mimetic agent. The most likely role of O2- is as a reducing agent of Fe3+: O2- + Fe3+----Fe2+ + O2, so that the sum of this and the Fenton reaction, i.e., the iron-catalyzed Haber-Weiss reaction, provides an explanation for the active oxygen species-induced SCE: H2O2 + O2(-)----OH- + OH0 + O2. According to this view, the OH radical thus produced is the agent which ultimately causes SCE. These results are discussed in comparison with other mechanisms previously proposed for induction of SCE by active oxygen species.