Modulation of mitomycin C-induced sister chromatid exchanges and cell cycle delay by buthionine sulfoximine and reduced glutathione in mouse bone marrow cells in vivo

Two Aldehyde Clearance Systems Are Essential to Prevent Lethal Formaldehyde Accumulation in Mice and Humans

Reactive aldehydes arise as by-products of metabolism and are normally cleared by multiple families of enzymes. We find that mice lacking two aldehyde detoxifying enzymes, mitochondrial ALDH2 and cytoplasmic ADH5, have greatly shortened lifespans and develop leukemia. Hematopoiesis is disrupted profoundly, with a reduction of hematopoietic stem cells and common lymphoid progenitors causing a severely depleted acquired immune system. We show that formaldehyde is a common substrate of ALDH2 and ADH5 and establish methods to quantify elevated blood formaldehyde and formaldehyde-DNA adducts in tissues. Bone-marrow-derived progenitors actively engage DNA repair but also imprint a formaldehyde-driven mutation signature similar to aging-associated human cancer mutation signatures. Furthermore, we identify analogous genetic defects in children causing a previously uncharacterized inherited bone marrow failure and pre-leukemic syndrome. Endogenous formaldehyde clearance alone is therefore critical for hematopoiesis and in limiting mutagenesis in somatic tissues.

Alcohol and endogenous aldehydes damage chromosomes and mutate stem cells

Haematopoietic stem cells renew blood. Accumulation of DNA damage in these cells promotes their decline, while misrepair of this damage initiates malignancies. Here we describe the features and mutational landscape of DNA damage caused by acetaldehyde, an endogenous and alcohol-derived metabolite. This damage results in DNA double-stranded breaks that, despite stimulating recombination repair, also cause chromosome rearrangements. We combined transplantation of single haematopoietic stem cells with whole-genome sequencing to show that this damage occurs in stem cells, leading to deletions and rearrangements that are indicative of microhomology-mediated end-joining repair. Moreover, deletion of p53 completely rescues the survival of aldehyde-stressed and mutated haematopoietic stem cells, but does not change the pattern or the intensity of genome instability within individual stem cells. These findings characterize the mutation of the stem-cell genome by an alcohol-derived and endogenous source of DNA damage. Furthermore, we identify how the choice of DNA-repair pathway and a stringent p53 response limit the transmission of aldehyde-induced mutations in stem cells.

In vitro cytogenetic effects of Andrographis paniculata (kalmegh) on arsenic

In vitro effects of arsenic in human peripheral lymphocytes (HPL) at three different doses - 3.6x10(-4), 1.4 x 10(-3) and 0.72 x 10(-3) microM for 24h before harvesting on sister chromatid exchanges (SCE), Cell cycle proliferative index/replicative index (CCPI/RI), %M(1), %M(2) and %M(3), population doubling time (PDT) and average generation time (AGT) were examined. Andrographis paniculata (commonly referred to as 'kalmegh') has been used for centuries in traditional Indian and Chinese herbal medicine as a safe, natural folk remedy for assorted health concerns. In the present study, kalmegh (0.01 microg/7ml culture media) was used along with the highest dose of arsenic; the results showed that arsenic induced increase in these genotoxic endpoints were fairly diminished by kalmegh. In addition, mutagenic in vitro effect of ethyl methanesulphonate (EMS) was used as a positive control in this study. It is thus concluded from this study that Andrographis has a protective role in arsenic toxicity.

Influence of glutathione on the induction of chromosome aberrations, delay in cell cycle kinetics and cell cycle regulator proteins in irradiated mouse bone marrow cells

PURPOSE

Reduced glutathione (GSH) is an endogenous thiol and has long been thought to affect the sensitivity of cells to radiation. The aim was to see the influence of GSH on: (i) the production of all types of radiation-induced chromosome aberrations (CA), and (ii) the radiation-induced delay in cell cycle and the levels of cell cycle regulator proteins.

MATERIALS AND METHODS

Cell cycle kinetics were determined by scoring the mitotic index (MI). CA and MI were scored in gamma-irradiated buthionine sulfoximine (BSO) (10 h) or GSH (1 h) pretreated and untreated mouse bone marrow cells (BMC). The expression of p53 and p21 proteins after 2 and 6 h of irradiation and for the B-cell lymphoma 2 (Bcl-2) associated X-protein (Bax) after 24 h of irradiation with or without BSO or GSH treatment was analyzed by immunoblotting.

RESULTS

Radiation delays mouse BMC in their passage through the cell cycle and induces CA. Exogenous addition of GSH protected CA uniformly at lower doses of radiation but differentially at higher doses, whereas GSH-depletion by BSO increased the frequency of radiation-induced CA. Both GSH and BSO-pretreated cells reduced the delay in cell kinetics after irradiation. Levels of both p53 and p21 were enhanced after irradiation to BSO-pretreated cells. However, in GSH-pretreated cells the level of these proteins was reduced.

CONCLUSION

Data indicate that the induction of CA and delay in cell kinetics by radiation may not always be interlinked and that the level of endogenous GSH exerts its influence on these parameters. Both GSH and BSO pretreatment reduce delays in cell kinetics of irradiated cells which may die apoptotically, since they have either a higher frequency of exchange aberrations or CA, respectively.

Genotoxic effects in human lymphocytes exposed to arsenic and vitamin A

Arsenic is a ubiquitous trace element and a well-established human carcinogen. In search for an 'antidote' to this global poison, this work was undertaken to study the probable beneficial effect of vitamin A upon arsenic induced genotoxicity. Peripheral blood lymphocyte culture was carried out to study the effects of arsenic at three different dose levels (0.5, 1 and 2 microg) for 24 h prior to harvesting. In addition, mutagenic in vitro effect of ethyl methanesulphonate was studied as a positive control. Genotoxic variables presented here are sister chromatid exchanges (SCE), cell cycle proliferative index/replicative index (CCPI/RI), average generation time (AGT) and population doubling time (PDT). Inevitably, arsenic treatment showed dose-dependent augmentation in the incidences of SCE and CCPI/RI together with AGT and PDT. However, vitamin A supplemented arsenic cultures demonstrated remarkable resurgence in the described genotoxic parameters. This data shows that vitamin A might be a useful interventional treatment in arsenic poisoning.

Influence of endogenous glutathione level on X-ray induced cell cycle delay in human lymphocytes

Here, induction of chromosomal aberration after X-irradiation and the pattern of cell cycle kinetics have been investigated in human lymphocytes, after exogenous addition of reduced glutathione or by depleting levels of reduced glutathione endogenously. Involvement of cell cycle regulator proteins such as p53 and p21 has been investigated to elucidate their role in induction of delay in cell cycle progression after irradiation.

Interaction of radiation- and bleomycin-induced lesions and influence of glutathione level on the interaction

Radiation-induced exchange aberrations are thought to arise as a consequence of misrejoining of free ends of DNA double strand breaks (dsbs). In quiescent mammalian cells this process of misrejoining is prevalently taken up by the non-homologous end joining (NHEJ) process. In order to investigate the role of glutathione (GSH) in DNA dsb rejoining, the interaction of the lesions induced by bleomycin (Blem) and by radiation was studied since the lesions caused by both have similar and apparent rapid rates of repair. Endogenous GSH was depleted by buthionine sulfoximine (BSO) and chromosome aberrations (CAs) of human lymphocytes were scored from first cycle metaphases. Gamma radiation was administered 2 h after Blem treatment in combined studies. In the case of BSO, the treatment was given 3 h before Blem treatment. The BSO-treated samples showed higher sensitivity to radiation than BSO-untreated ones. Combined treatment of Blem and radiation induced higher frequency of CAs, in particular the exchange aberrations and interstitial deletions. However, such increased frequency of exchange aberrations was reduced drastically and the frequency of terminal deletions was increased significantly when combined treatment was given to BSO-pretreated cells. The consistent level of Ku70 protein in all the treated samples, with undetectable level of Rad51 in the G0-lymphocytes indicates the involvement of NHEJ pathway in misrejoining of DNA dsbs. It may be hypothesized that reduction in the frequency of exchange aberrations as induced by Blem + radiation combined treatment in BSO-treated samples could be because of reduced NHEJ pathway.

Genotoxic effect of raw betel-nut extract in relation to endogenous glutathione levels and its mechanism of action in mammalian cells

The mutagenic and carcinogenic potency of betel-nut components is well established. This study was undertaken to determine the genotoxic potency of an aqueous extract of raw betel nut (AEBN) in relation to the endogenous glutathione (GSH) level in mouse bone marrow cells (BMC) and human peripheral blood lymphocytes (PBLs), and to find out whether arecoline (ARC), an alkaloid of betel nut, could generate reactive oxygen species (ROS) in these cells. It was observed that AEBN has genotoxic properties, which is further enhanced by depletion of endogenous GSH levels. However, the degree of enhancement varies with the type of parameter and cell system studied. The present data indicate that the generation of ROS by ARC could partially contribute to the induction of chromosomal aberrations (CAs), since the frequency of ARC-induced CAs was reduced either by post-treatment with superoxide dismutase (SOD) or in anoxic conditions. However, the induction of sister chromatid exchanges (SCEs) probably involves p53-dependent changes in cell proliferation and allowing some repair of DNA damage. The extent of damage for each parameter was higher when the mice were exposed to AEBN for 30 days than 5 days. Longer exposure showed higher level of p53 expression in mouse BMC, which could block the damaged cells from proliferation and allow the cells to repair the DNA damage.

Fenvalerate-induced chromosome aberrations and sister chromatid exchanges in the bone marrow cells of mice in vivo

Fenvalerate, a synthetic pyrethroid insecticide, is commonly used in agriculture and other domestic applications due to its high insecticidal activity and low mammalian-, avian- and phyto-toxicities. However, the genotoxic effect of fenvalerate is highly equivocal. In the present study the genotoxic effects of fenvalerate was evaluated using structural chromosome aberration (CA) and sister chromatid exchange (SCE) assays in mice. Out of the three doses (5, 10 and 20 mg/kg) tested, statistically significant increase in CA was found following intra peritoneal (i.p.) treatment of 2 0 mg/kg of fenvalerate for 24 h (P<0.01) and 48 h (P<0.05) only. Neither the acute doses of 5 and 10 mg/kg, nor the sub-acute dose (5x4 mg/kg) of fenvalerate could induce any significant effect. All the three acute doses induced significant increase in the frequency of SCEs (P<0.01) in the bone marrow cells, which showed a significant dose-response correlation (r=0.9541, P<0.05). With certain reservations to possible impurities, from the present findings technical grade fenvalerate may be considered as a weak clastogen and a potent inducer of SCEs in mice.

Antiproliferative and cytotoxic effect of a novel organotin compound on mammalian cells both in vitro and in vivo

Organotin compounds are organometallic compounds showing various toxicological properties. Several organotin compounds also showed an antineoplastic effect. However, their relative mutagenic potential is not well established. In this study Et(2)SnCl(2).L [L=N-(2-pyridylmethylene)-4-toluidine] (OTC) has been subjected to investigation for its cytotoxic effect in mouse bone marrow cells (BMCs) and human peripheral blood lymphocyte cells (HPBLs). The Sn [bond] N bond in OTC is 2.46A which is greater than 2.39A and therefore, a better formation of tin-DNA complex can be expected. The present data indicate that OTC induced significant delay in cell kinetics and sister chromatid exchanges (SCEs) in both BMCs and HPBLs, whereas, induction of chromosome aberrations was found only in HPBLs. The presence of buthionine sulfoximine (BSO) modulated cellular sensitivity towards OTC in both cell systems. It may be inferred that the OTC could bind on DNA more easily owing to its structural advantage and this may explain the induction of DNA damage and the delay in cell proliferation. Since the cytotoxic effect of OTC is more in glutathione depleted cells, the concentration of OTC may be reduced to get an antitumour effect in GSH-depleted cells and thus minimizes its toxic side effect.