Decreased superoxide dismutase activity of erythrocytes and leukocytes in Fanconi's anemia

From clinical description, to in vitro and animal studies, and backward to patients: oxidative stress and mitochondrial dysfunction in Fanconi anemia

Fanconi anemia (FA) is a rare genetic disease associated with deficiencies in DNA repair pathways. A body of literature points to a pro-oxidant state in FA patients, along with evidence for oxidative stress (OS) in the FA phenotype reported by in vitro, molecular, and animal studies. A highlight arises from the detection of mitochondrial dysfunction (MDF) in FA cell lines of complementation groups A, C, D2, and G. As yet lacking, in vivo studies should focus on FA-associated MDF, which may help in the understanding of the mitochondrial basis of OS detected in cells and body fluids from FA patients. Beyond the in vitro and animal databases, the available analytical devices may prompt the direct observation of metabolic and mitochondrial alterations in FA patients. These studies should evaluate a set of MDF-related endpoints, to be related to OS endpoints. The working hypothesis is raised that, parallel to OS, nitrosative stress might be another, so far unexplored, hallmark of the FA phenotype. The expected results may shed light on the FA pathogenesis and might provide grounds for pilot chemoprevention trials using mitochondrial nutrients.

Influence of catalase on the radiosensitivity of Fanconi anemia lymphocytes in vitro

Fanconi anemia (FA) is a genetic disease characterized by progressive pancytopenia and cancer susceptibil?ity. The clinical and cellular phenotypes of Fanconi anemia are associated with a set of redox abnormalities, indicating that FA is an oxidative stress-related disorder. Fanconi anemia cells are highly sensitive to DNA clastogen agents, but their response to ionizing radiation is still unclear. The aim of this study was to evaluate the in vitro radiosensitivity of Fanconi anemia homozygotes and heterozygotes, and to assess the contribution of catalase and superoxide dismutase (SOD) to the overall radiobiological response of the cells. The incidence of radiation-induced lymphocyte micronuclei was used as the indicator of radiation sensitivity in vitro, whereas the activity of antioxidant enzymes was determined in erythrocytes. Patients with FA exhibited a two-fold decrease in catalase activity, accompanied by lowered activity of SOD, and increased incidence of baseline micronuclei. In the entire group of patients (with one exception), a reduced yield of radiation-induced micronuclei in lymphocytes was observed, and this was categorized as a radioresistant response. A mild radioresistant in vitro response was also observed in carrier-mothers, accompanied by reduced activity of catalase. The radiosensitivity of carrier-fathers was normal. The results of this study suggest that reduced activity of catalase is an important contributor to the radiobiological response of cells.

L'anémie de Fanconi : aspects cellulaires et moléculaires

Fanconi anemia (FA) is a recessive human cancer prone syndrome featuring bone marrow failure, developmental abnormalities and hypersensitivity to DNA crosslinking agents exposure. 11 among 12 FA gene have been isolated. The biochemical functions of the FANC proteins remain poorly understood. Anyhow, to cope with DNA crosslinks a cell needs a functional FANC pathway. Moreover, the FANC proteins appear to be involved in cell protection against oxidative damage and in the control of TNF-alpha activity. In this review, we describe the current understanding of the FANC pathway and we present how it may be integrated in the complex networks of proteins involved in maintaining the cellular homeostasis.

Fanconi anemia revisited: old ideas and new advances

This review summarizes both historical and more recent data on the clinical, cellular and genetic features of Fanconi anemia (FA), a rare autosomal recessive disorder. FA patients are characterized by pancytopenia, congenital malformations, growth delay and an increased susceptibility to the development of malignancies, particularly acute myelogenous leukemia. FA cells show chromosomal fragility, slow growth and increased sensitivity to DNA crosslinking agents. FA can be caused by defects in any one of at least four genes. Two general hypotheses have been proposed to explain the underlying defect: loss of a DNA repair function or of a step in the defense toward oxygen toxicity. After many attempts to clone the FA genes, the first one, that defective in group C, has been cloned by complementation of the increased sensitivity of FA(C) cells to mitomycin C and diepoxybutane. This gene (FACC) codes for a novel protein and is ubiquitously expressed. Mutations in various FA(C) patients that cause loss of function have been identified. The review concludes by suggesting directions for future research in FA.

Reactive oxygen species, chromosome mutation, and cancer: possible role of clastogenic factors in carcinogenesis

Superoxide radicals may induce genotoxic effects by indirect action mechanisms, implicating the formation of more long-lived, secondary clastogenic material called chromosome breakage factors or clastogenic factors (CF). CF are produced via the intermediacy of superoxide, and stimulate further superoxide production by competent cells. This results in a selfsustaining and longlasting process of clastogenesis, which may exceed the DNA repair system and ultimately lead to cancer. An increased cancer risk is indeed observed in conditions accompanied by CF formation. These include irradiated persons, asbestos workers, patients with chronic inflammatory diseases, HIV-infected persons, and the congenital breakage syndromes ataxia telangiectasia, Bloom's syndrome, and Fanconi's anemia. Because reactive oxygen species (ROS) are implicated in CF formation and CF action, antioxidants may be protective as anticlastogens and consequently as anticarcinogens. In persons at high risk because of their occupation, life style or place of residence, the presence of CF may represent an indication for chemoprevention of cancer by antioxidants. CF can be useful as biochemical markers and intermediate endpoints for the evaluation of promising drugs. They are therefore not only of interest as a mechanism by which ROS may exert genotoxic effects, but also have practical implications.

A trial of recombinant human superoxide dismutase in patients with Fanconi anaemia

Fanconi anaemia (FA) is a rare genetic disorder that predisposes to the development of aplastic anaemia and neoplasia. The pathophysiologic hallmark of FA is increased susceptibility to chromosomal breakage. Superoxide metabolism has also been shown to be involved in the cellular pathophysiology of FA. Human SOD (rh-SOD), an enzyme which dismutates superoxide, has recently been cloned and expressed in yeast. We treated four FA patients with a 2-week infusion of rh-SOD (25 mg/kg d daily) to determine whether rh-SOD had any effect on haemopoietic progenitor cell growth or on the abnormal cellular phenotype. We found that lymphocyte chromosomal aberrations induced by diepoxybutane were decreased during rh-SOD treatment in two patients and that bone marrow progenitors were increased in one patient.

Tumor necrosis factor-alpha overproduction in Fanconi's anemia

Various in vitro studies and clinical observations suggest that Fanconi's anemia (FA) patients are unable to detoxify adequately superoxide anions (O2-) released by activated phagocytes. Recent studies have shown that certain lymphokines such as tumor necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) can significantly enhance O2- production by phagocytic cells. To ascertain lymphokine production in FA patients, we measured TNF-alpha and IFN-gamma production in vivo and in vitro. TNF-alpha was detected in the plasma of 16 of 18 FA patients with concentrations ranging from 6 to 131 pg/ml (mean 31 pg/ml). TNF-alpha was detected in only one of 25 control (healthy donor) plasma, and the level was very low (7 pg/ml). IFN-gamma levels in normal and patient plasma were negligible. Spontaneous and phytohemagglutinin (PHA)-induced production of IFN-gamma and TNF-alpha by cultured peripheral blood mononuclear cells did not differ significantly between FA patients and normal controls. The significance of overproduction of TNF-alpha in vivo in the pathophysiology of FA is discussed.

Partial correction of chromosome instability in Fanconi anemia by desferrioxamine

The action of the iron chelator desferrioxamine (DFO) on the cytogenetic pattern of cultured lymphocytes from Fanconi anemia (FA) patients was investigated. The addition of 10(-4) M DFO throughout the culture time resulted in a 50% reduction of the spontaneous chromosome breakage of FA cells. In addition, the clastogenic action of diepoxybutane on FA lymphocytes was also partly counteracted by DFO. The above findings support the assumption that one of the mechanisms involved in the pathogenesis of FA might be an impaired capacity of the cells from such patients to remove active oxygen species. The relationship between intraleukocyte chelatable iron pool and free radical formation in FA subjects is discussed.

Decreased superoxide dismutase-2 activity in a patient with ring chromosome 6

Manganese superoxide dismutase (SOD-2) activity was measured in erythrocytes and leukocytes of a patient with ring chromosome 6. Compared to normal control individuals, SOD-2 activity in leukocytes of the patient was lower, whereas cuprozinc SOD (SOD-1) activity was normal. These findings suggest the cause of decreased enzyme activity is the effect of the ring form on production of the enzyme or inherent instability of ring chromosomes.

Antioxidant status of Fanconi anemia fibroblasts

Several observations in the recent literature have indicated that Fanconi anemia (FA) cells may be primarily deficient in the detoxification of activated oxygen species. To evaluate the antioxidant status of FA fibroblasts, we measured Mn-containing superoxide dismutase (Mn-SOD), CuZn-containing superoxide dismutase (CuZn-SOD), catalase, and glutathione peroxidase activities, as well as cellular glutathione contents and total nonenzymatic antioxidant potential in FA and control fibroblasts at multiple time points during a single passage. All parameters exhibited a characteristic pattern of changes during a period of 19 days following trypsinization. Unlike FA erythrocytes, which are known to be deficient in CuZn-SOD, FA fibroblasts exhibited normal CuZn-SOD activities. Also, the nonenzymatic "antioxidant potential" as well as glutathione levels were similar in FA and control fibroblasts. However, Mn-SOD, catalase, and glutathione peroxidase activities were consistently higher in FA fibroblasts. We hypothesize that the elevation of these enzyme activities might reflect a cellular "prooxidant" state in FA resulting from an increased formation of endogenous oxidizing molecular species that trigger enhanced synthesis of certain enzymatic antioxidant defenses.

Cytogenetics of Mendelian mutations associated with cancer proneness

About 5% of Mendelian mutations displaying neoplastic tendencies are associated with chromosomal aberrations. The best established examples are retinoblastoma and del(13)(q14) and aniridia-Wilms' tumor and del(11)(p13). Evidence suggests that both mutations behave as dominant traits in the individual and as recessive traits in the cells. DNA analysis indicates that tumorigenesis arises from homozygosisty for the mutant allele at these loci, as a consequence of mitotic nondisjunction or from a mitotic recombination event. An additional argument for this conclusion is provided by the demonstration of duplication of 11p15 in some patients with the Beckwith-Wiedemann syndrome, which is complicated often by Wilms' tumor and other embryonal tumors. Data obtained with molecular probes have shown that also rhabdomyosarcoma and hepatoblastoma arise by homozygosity for a mutant allele at a locus on 11p, suggesting ontogenic relatedness of these tumor types. Additional examples of Mendelian mutations associated with chromosome deletions and neoplasia include Langer-Giedion syndrome with multiple exostoses and del(8)(q24.1), multiple endocrine neoplasia and del(20)(p12.2). While the presence of specific chromosome changes in subjects with high susceptibility to neoplasia does pinpoint the location of DNA sequences involved in the predisposition to certain types of cancers, selected Mendelian mutations associated with chromosome instability and cancer proneness may elucidate biological principles of cell proliferation and transformation. However, our current knowledge of mechanisms resulting in increased frequency of chromosome breakage and cancer susceptibility in ataxia-teleangiectasia, Fanconi's anemia, Bloom's syndrome, and similar conditions are still very incomplete.

Fanconi anemia, dyskeratosis congenita, and WT syndrome

The association of congenital anomalies and pancytopenia is encountered in several clinical syndromes. Among these, Fanconi anemia is by far the most prevalent, and consequently best known. As a result, other similar conditions, such as dyskeratosis congenita and particularly WT syndrome, are often mistaken for Fanconi anemia. However, at a closer look, the type of congenital anomalies, the mode of inheritance, cytogenic and other laboratory findings allow clear differentiation between these 3 syndromes.