Diepoxybutane cytotoxicity on mouse germ cells is enhanced by in vivo glutathione depletion: a flow cytometric approach

Fanconi anemia (FA) and crosslinker sensitivity: Re-appraising the origins of FA definition

The commonly accepted definition of Fanconi anemia (FA) relying on DNA repair deficiency is submitted to a critical review starting from the early reports pointing to mitomycin C bioactivation and to the toxicity mechanisms of diepoxybutane and a group of nitrogen mustards causing DNA crosslinks in FA cells. A critical analysis of the literature prompts revisiting the FA phenotype and crosslinker sensitivity in terms of an oxidative stress (OS) background, redox-related anomalies of FA (FANC) proteins, and mitochondrial dysfunction. This re-appraisal of FA basic defect might lead to innovative approaches both in elucidating FA phenotypes and in clinical management.

Intake of anthocyanidins pelargonidin and cyanidin reduces genotoxic stress in mice induced by diepoxybutane, urethane and endogenous nitrosation

Pelargonidin (PEL) and cyanidin (CYN) are among the six most abundant anthocyanidins which provide red, blue and purple colors to fruits and vegetables. Health benefits associated with intake of anthocyanins have been attributed mainly to antioxidant activity of these color pigments. The aim of our present study was to assess in mice the impact of PEL and CYN intake on genotoxic stress induced by DNA damaging environmental toxicants. These anthocyanidins were administered by gavage to mice before exposure to genotoxic carcinogens diepoxybutane (DEB) and urethane (URE). In addition, the inhibitory effect of PEL and CYN on endogenous nitrosation was evaluated by using a model nitrosation reaction mixture consisting of methyl urea (MU)+sodium nitrite (SN) which reacts in the stomach to form the carcinogenic methyl nitrosourea (MNU). All the test doses of PEL (2.5-20 mg/kg) and CYN (1-4 mg/kg) significantly reduced the genotoxicity of DEB. A dose-related increase was observed for antigenotoxicity of PEL against URE. The lowest test-dose of CYN showed maximum protection against URE. Co-administration of PEL/CYN with the nitrosation reaction mixture led to reduction in genotoxicity. CYN was more effective as an inhibitor of endogenous nitrosation. Combination of PEL with ascorbic acid (AA) enhanced the antinitrosating effect when compared to that with each phytochemical alone. The results of our present study indicate that common anthocyanidins PEL and CYN can play a major role in reducing genotoxic stress induced by environmental toxicants.

Improvement of genetic stability in lymphocytes from Fanconi anemia patients through the combined effect of α-lipoic acid and N-acetylcysteine

Fanconi Anemia (FA) is a rare genetic disorder, characterized by progressive bone marrow failure and increased predisposition to cancer. Despite being highly heterogeneous, all FA patients are hypersensitive to alkylating agents, in particular to 1,2:3,4-diepoxybutane (DEB), and to oxidative damage. Recent studies point to defective mitochondria in FA cells, which is closely related with increased production of reactive oxygen species (ROS) and concomitant depletion of antioxidant defenses, of which glutathione is a well-known biomarker.The objective of the present work is to evaluate the putative protective effect of α-lipoic acid (α-LA), a mitochondrial protective agent, and N-acetylcysteine (NAC), a direct antioxidant and a known precursor for glutathione synthesis, in spontaneous and DEB-induced chromosome instability (CI) in lymphocyte cultures from FA patients.For that purpose, lymphocyte cultures from 15 FA patients and 24 healthy controls were pre-treated with 20 μM α-LA, 500 μM NAC and α-LA plus NAC at the same concentrations, and some of them were exposed to DEB (0.05 μg/ml). A hundred metaphases per treatment were scored to estimate the relative frequency of spontaneous and DEB-induced chromosome breakage.The obtained results revealed that a cocktail of α-LA and NAC can drastically improve the genetic stability in FA lymphocytes in vitro, decreasing CI by 60% and 80% in cultures from FA patients and FA mosaic/chimera patients, respectively. These results suggest that the studied cocktail can be used as a prophylactic approach to delay progressive clinical symptoms in FA patients caused by CI, which can culminate in the delay of the progressive bone marrow failure and early cancer development.

Sperm DNA integrity assessment: a new tool in diagnosis and treatment of fertility

Infertility affects 15% of all couples. Although male infertility factors with reduced semen quality are contributing to about half of all involuntary childlessness, the value of standard semen parameters in prediction of fertility in vivo and choice of proper method for assisted reproduction is limited. In the search for better markers of male fertility, during the last 10 years, assessment of sperm DNA integrity has emerged as a strong new biomarker of semen quality that may have the potential to discriminate between infertile and fertile men. Sperm DNA Fragmentation Index (DFI) as assessed by the flow cytometric Sperm Chromatin Structure Assay (SCSA) can be used for evaluation of sperm chromatin integrity. The biological background for abnormal DFI is not completely known, but clinical data show that DFI above 30% is associated with very low chance for achieving pregnancy in natural way or by insemination, but not in vitro. Already when the DFI is above 20%, the chance of natural pregnancy may be reduced, despite other sperm parameters being normal. Thus this method may explain a significant proportion of cases of unexplained infertility and can be beneficial in counselling involuntary childless couples need of in vitro fertilisation.

Protective effect of acetyl-l-carnitine and α-lipoic acid against the acute toxicity of diepoxybutane to human lymphocytes

The biotransformation and oxidative stress may contribute to 1,2:3,4-diepoxybutane (DEB)-induced toxicity to human lymphocytes of Fanconi Anemia (FA) patients. Thus, the identification of putative inhibitors of bioactivation, as well as the determination of the protective role of oxidant defenses, on DEB-induced toxicity, can help to understand what is failing in FA cells. In the present work we studied the contribution of several biochemical pathways for DEB-induced acute toxicity in human lymphocyte suspensions, by using inhibitors of epoxide hydrolases, inhibitors of protective enzymes as glutathione S-transferase and catalase, the depletion of glutathione (GSH), and the inhibition of protein synthesis; and a variety of putative protective compounds, including antioxidants, and mitochondrial protective agents. The present study reports two novel findings: (i) it was clearly evidenced, for the first time, that the acute exposure of freshly isolated human lymphocytes to DEB results in severe GSH depletion and loss of ATP, followed by cell death; (ii) acetyl-l-carnitine elicits a significant protective effect on DEB induced toxicity, which was potentiated by α-lipoic acid. Collectively, these findings contribute to increase our knowledge of DEB-induce toxicity and will be very useful when applied in studies with lymphocytes from FA patients, in order to find out a protective agent against spontaneous and DEB-induced chromosome instability.

Sperm chromatin structure assay (SCSA): a tool in diagnosis and treatment of infertility

Diagnosis of male infertility has mainly been based on the World Health Organization (WHO) manual-based semen parameter's concentration, motility and morphology. It has, however, become apparent that none of these parameters are reliable markers for evaluation of the fertility potential of a couple. A search for better markers has led to an increased focus on sperm chromatin integrity testing in fertility work-up and assisted reproductive techniques. During the last couple of decades, numerous sperm DNA integrity tests have been developed. These are claimed to be characterized by a lower intraindividual variation, less intralaboratory and interlaboratory variation and thus less subjective than the conventional sperm analysis. However, not all the sperm chromatin integrity tests have yet been shown to be of clinical value. So far, the test that has been found to have the most stable clinical threshold values in relation to fertility is the sperm chromatin structure assay (SCSA), a flow cytometric test that measures the susceptibility of sperm DNA to acid-induced DNA denaturation in situ. Sperm DNA fragmentation as measured by SCSA has shown to be an independent predictor of successful pregnancy in first pregnancy planners as well as in couples undergoing intrauterine insemination, and can be used as a tool in investigation, counseling and treatment of involuntary childlessness. More conflicting data exist regarding the role of sperm DNA fragmentation in relation to fertilization, pre-embryo development and pregnancy outcome in in vitro fertilization and intracytoplasmic sperm injection (ICSI).

Male reproductive and behavior toxicity in rats after subchronic exposure to organic extracts from Jialing River of Chongqing, China

BACKGROUND

More than 100 species of organic chemicals have been detected in Jialing River of Chongqing City. Most of them are endocrine-disrupting chemicals (EDCs), which can disrupt the functions of the reproductive and nervous systems.

METHODS

Organic extracts (OE) were obtained by solid extraction from the Jialing River, and administrated to rats by gavage every other day for 13 weeks at doses of 2, 12, and 72 L/kg bw/d. Sperm abnormity was analyzed by microscopy and flow cytometry. The Morris water maze task was employed to investigate the behaviors of space probing. Activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) content were measured to detect the peroxidation response in hippocampus and testis.

RESULTS

Animals in the 72-L/kg group showed significant degeneration of germ cells in the seminiferous tubule. Sperm abnormality of the 72-L/kg group was significantly higher than that of the solvent control group. The testis oxidative stress in the 72-L/kg group was severer than that of the other groups. The hippocampus neuron cells in the 72-L/kg group showed cellular edema and remarkable cell enlargement. The hippocampus oxidative stress in the 72-L/kg group was severer and the Morris water maze performance in this group showed longer latency time and swimming distance in the probing platform than the other groups.

CONCLUSIONS

OE caused pathological damage and peroxidation response to testis and hippocampus and disrupted spermatogenesis and behavior of space probing.

Effects of PCB99 and PCB153 exposure on spermatogenesis in young adult C57BL6 mice

This study examined the effects of acute exposure to PCB99 (2,2',4,4',5-pentachlorobiphenyl), and PCB153 (2,2',4,4'5,5'-hexachlorobiphenyl), on spermatogenesis in 8-week-old C57BL6 mice. The mice were randomly allocated to PCB99 and PCB153 and a single dose of respectively 10 and 100 mg/kg was given by oral gavage. During the 6-week experiment, six mice per treatment group were sacrificed weekly, body weights were recorded and samples with respect to the male reproductive system were collected until further analysis. None of the treatments, showed changes in body weight or reproductive endpoints. Flow cytometric analysis revealed spermatogenesis to be unaffected. However, PCB99 and PCB153 showed a significant increase in Leydig cell apoptosis. The results from the present study indicate that the male reproductive system is relatively refractory to PCB99 and PCB153 at levels exceeding those of wildlife and humans, when exposed during adult life. However, the finding of apoptotic Leydig cells merits further investigation.

Fanconi anaemia proteins: major roles in cell protection against oxidative damage

Fanconi anaemia (FA) is a cancer-prone genetic disorder that is characterised by cytogenetic instability and redox abnormalities. Although rare subtypes of FA (B, D1 and D2) have been implicated in DNA repair through links with BRCA1 and BRCA2, such a role has yet to be demonstrated for gene products of the common subtypes. Instead, these products have been strongly implicated in xenobiotic metabolism and redox homeostasis through interactions of FANCC with cytochrome P-450 reductase and with glutathione S-transferase, and of FANCG with cytochrome P-450 2E1, as well as redox-dependent signalling through an interaction between FANCA and Akt kinase. We hypothesise that FA proteins act directly (via FANCC and FANCG) and indirectly (via FANCA, BRCA2 and FANCD2) with the machinery of cellular defence to modulate oxidative stress. The latter interactions may co-ordinate the link between the response to DNA damage and oxidative stress parameters (3, 6-12).

Redox-modulated xenobiotic action and ROS formation: a mirror or a window?

A number of xenobiotics require redox reactions to form the reactive intermediates involved in the ultimate toxic events (e.g., adduct formation). The same mechanisms lead to the formation of reactive oxygen species (ROS), which can themselves exert direct toxicity including, e.g., DNA oxidative damage or glutathione depletion. The occurence of both mechanistic features in xenobiotic activation and toxicity may raise some difficulties in ascertaining the respective roles of reactive intermediates versus ROS-related mechnisms. An example is provided by the toxicity mechanisms of mitomycin C (MMC) and diepoxybutane (DEB), which are commonly referred to as 'cross-linkers'. Their toxic actions, however, are well-known to be modulated via redox parameters, such as oxygen tension, antioxidants levels, or thioredoxin overexpression. The diagnostic assessment of Fanconi's anaemia (FA) relies on MMC and DEB sensitivity, which is usually referred to as 'cross-linker sensitivity'; thus the redox-dependent toxicities of MMC and DEB may have direct implications for the definition of FA phenotype. Another major aspect in ROS formation relies on the extensive evidence pointing to the requirement for oxidative, as well as nitrosative activities in triggering a number of key events in cell division and differentiation, and in early embryogenesis. In turn, antioxidants that may prevent ROS-associated cellular damage in adult cells may prove to exert adverse or fatal outcomes when administered in early life stages. The overall information available on xenobiotic redox biotransformation and on the physiopathological roles of ROS points to the need of addressing ad hoc studies that should take into account the multiplicity of mechanistic events involved.

Penicillin productivity and glutathione-dependent detoxification of phenylacetic and phenoxyacetic acids in Penicillium chrysogenum

Both toxicity and penicillin productivity of the hydroxylated derivatives of phenylacetic acid (PA) and phenoxyacetic acid (POA) were highly dependent on the position of hydroxylation on the aromatic ring in Penicillium chrysogenum. Hydroxylation at position 2 diminished penicillin production but the compounds retained most of their toxicity. On the other hand, hydroxylation at position 4 resulted in barely toxic derivatives with still significant penicillin productivity. 3-Hydroxy-PA was a weak side-chain precursor with considerably reduced toxicity. The activity of the glutathione-dependent detoxification pathway correlated well with the toxicity of the compounds but there was no correlation between acidity, toxicity and penicillin productivity.

Human sperm immobilizing activity of aminophenyl arsenic acid and its N-substituted quinazoline, pyrimidine, and purine derivatives: protective effect of glutathione

We examined the potential toxicity of pentavalent organic arsenicals for human sperm. We used computer-assisted sperm analysis to examine the effects of three aminophenyl arsenicals and their nine N-substituted quinazoline, pyrimidine, and purine derivatives on human sperm motility and kinematics in human semen and medium. Among the arsenicals examined, (aminophenylazo)-phenyl arsonic acid and its N-substituted pyrimidine derivative PHI-370 (2-methylthio-4-[(4'-aminophenylazo)-phenylarsonic acid] pyrimidine) exhibited rapid sperm immobilizing activity in medium with EC(50) values of 77 and 82 microM, respectively, and t(1/2) of < 3 min. Molecular modeling analysis indicated that sperm-immobilizing organic arsenicals exhibit high dipole moments (>7 Debyes). Sperm immobilizing activity of these arsenicals was completely abrogated in the presence of seminal plasma. Furthermore, coincubation of motile sperm with PHI-370 in the presence of reduced glutathione (GSH) resulted in dose-dependent protection of sperm motility and sperm motion parameters. Coincubation of the arsenical with GSH at a molar ratio of 1:20 resulted in 95% retention of sperm progressive motility. The mean values of the other sperm movement characteristics also showed > 90% protection. These observations suggest that the rapid sperm immobilizing activity of these pentavalent arsenicals may be as a result of direct binding of the arsenical with the sperm thiol components essential for sperm motility as well as induction of oxidative damage by disruption of sperm cell's antioxidant system. Sodium arsanilate and its N-substituted pyrimidine derivative, PHI-370, are useful probes to further evaluate the mechanism of pentavalent arsanilate-induced human sperm dysfunction.

Reduction of diepoxybutane-induced sister chromatid exchanges by glutathione peroxidase and erythrocytes in transgenic Big Blue mouse and rat fibroblasts

We have investigated the effect of glutathione peroxidase (GSH-Px) and mammalian erythrocytes (RBCs) on spontaneous and diepoxybutane (DEB)-induced sister chromatid exchange (SCE) in primary Big Blue(R) mouse (BBM1) and Big Blue(R) rat (BBR1) fibroblasts. DEB is the putative carcinogenic metabolite of 1,3-butadiene (BD) for which inhalation exposure yields a high rate of malignancies in mice but not in rats. BD is metabolized differently in mice and rats, producing much higher levels of DEB in mice than in rats, which may partly explain the different carcinogenic responses. However, other factors may contribute to the observed differences in the rodent carcinogenic response to BD. DEB is a highly reactive compound. Upon epoxide hydrolysis, DEB can covalently bind to DNA bases. Likewise, DEB generates reactive oxygen species that, in turn, can either damage DNA or produce H(2)O(2). Reduced glutathione (GSH) is known to play a role in the metabolism and detoxification of DEB; and GSH is reduced by GSH-Px in the presence of H(2)O(2). GSH-Px is a constitutive enzyme that is found at high concentrations in mammalian RBCs. Therefore, we were interested in examining the role of RBCs and GSH-Px on DEB-induced SCE in rat and mouse cells for detection of possible differences in the species response. Transgenic BBM1 and BBR1 fibroblasts were treated with either 0, 2 or 4 microM DEB plus 0, 2 or 20 units of GSH-Px with and without 2x10(8) species-specific RBCs. DEB effectively induced SCEs in both rat and mouse cells. The relative induction of SCEs in both cell types was comparable. Both GSH-Px and RBCs alone and in combination were effective in significantly reducing DEB-induced SCEs in both mouse and rat fibroblasts, although there was more variability in the SCE response in rat cells. The present study suggests that GSH-Px may be important in the detoxification of DEB-induced DNA damage that results in the formation of SCEs.