DNA-damaging disinfection byproducts: alkylation mechanism of mutagenic mucohalic acids

Base-Modified Nucleosides: Etheno Derivatives

This review presents synthesis and chemistry of nucleoside analogs, possessing an additional fused, heterocyclic ring of the "etheno" type, such as 1,N(6)-ethenoadenosine, 1,N(4)-ethenocytidine, 1,N(2)-ethenoguanosine, and other related derivatives. Formation of ethenonucleosides, in the presence of α-halocarbonyl reagents and their mechanism, stability, and degradation, reactions of substitution and transglycosylation, as well as their application in the nucleoside synthesis, have been described. Some of the discussed compounds may be applied as chemotherapeutic agents in antiviral and anticancer treatment, acting as pro-nucleosides of already known, biologically active nucleoside analogs.

Assessment of genotoxicity in gonads, liver and gills of zebrafish (Danio rerio) by use of the comet assay and micronucleus test after in vivo exposure to methyl methanesulfonate

Since generative tissues are a link between the generations, the detection of genetic damage in testis and ovary of fish is conductive to elucidating the relationship between genotoxicity and impairment of reproduction. In the current study, exposure of zebrafish to methyl methanesulfonate over two weeks caused concentration dependent genotoxic effects in gonads, liver and gills using the alkaline comet assay. Likewise, the micronucleus frequency was elevated in all of these organs. Thus, the comet assay and the micronucleus test proved appropriate for the detection of genotoxicity in primary male and female gonad cells and histological sections of the gonads from zebrafish, respectively.

Reproductive and genotoxic effects in zebrafish after chronic exposure to methyl methanesulfonate in a multigeneration study

There is still controversy whether adverse effects by genotoxic anthropogenic pollutants are linked to the decline of fish populations. Further investigations into the relationship between genotoxic stress and detrimental effects on development and reproduction in fish are required. For this end, zebrafish (F0 generation) were exposed in vivo to the alkylating model genotoxin methyl methanesulfonate (MMS) from fertilization to the age of 1 year. F0 fish were mated over 6 months to check for reproductive capacities. F1 fish grew up without exposure in order to allow for regeneration. Mortality of F0 fish depended on MMS concentrations. In MMS-exposed F0 fish, times of first spawning were delayed and fertility was reduced. Using the alkaline comet assay and the micronucleus test, significant genotoxic effects were found in the livers, gills and gonads of either sex in the F0 generation. No detrimental effects on growth were found. In F1 fish with parental exposure, teratogenic effects were increased, and larval survival was reduced. However, fertility capacities of the non-exposed F1 generation had recovered. Development and survival rates further recovered in the F2 generation. Anthropogenic genotoxicants may thus play a considerable role in the decline of wild fish populations.

Differential responses of sexual and asexual Artemia to genotoxicity by a reference mutagen: Is the comet assay a reliable predictor of population level responses?

The impact of chronic genotoxicity to natural populations is always questioned due to their reproductive surplus. We used a comet assay to quantify primary DNA damage after exposure to a reference mutagen ethyl methane sulfonate in two species of crustacean with different reproductive strategies (sexual Artemia franciscana and asexual Artemia parthenogenetica). We then assessed whether this predicted individual performance and population growth rate over three generations. Artemia were exposed to different chronic concentrations (0.78mM, 1.01mM, 1.24mM and 1.48mM) of ethyl methane sulfonate from instar 1 onwards for 3 h, 24 h, 7 days, 14 days and 21 days and percentage tail DNA values were used for comparisons between species. The percentage tail DNA values showed consistently elevated values up to 7 days and showed a reduction from 14 days onwards in A. franciscana. Whilst in A. parthenogenetica such a reduction was evident on 21 days assessment. The values of percentage tail DNA after 21 days were compared with population level fitness parameters, growth, survival, fecundity and population growth rate to know whether primary DNA damage as measured by comet assay is a reliable biomarker. Substantial increase in tail DNA values was associated with substantial reductions in all the fitness parameters in the parental generation of A. franciscana and parental, F1 and F2 generations of A. parthenogenetica. So comet results were more predictive in asexual species over generations. These results pointed to the importance of predicting biomarker responses from multigenerational consequences considering life history traits and reproductive strategies in ecological risk assessments.

DNA damage by genotoxic hydroxyhalofuranones: an in silico approach to MX

MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone), a disinfection byproduct present in chlorinated drinking water, is one of the most potent mutagens known. Whereas its genotoxic effects are well documented, the mechanism by which MX exerts such an intense biological effect is still unclear. To gain further insight into both the general reactivity of hydroxyhalofuranones, and especially as regards their genotoxicity, here we report an in silico study of the aqueous reactivity of MX and two less powerful analogues (MXY, in general): (3-chloro-4-(chloromethyl)-5-hydroxy-2(5H)-furanone -CMCF- and 3-chloro-4-(methyl)-5-hydroxy-2(5H)-furanone -MCF-). The following aspects were investigated: (i) the acid dissociation and isomerization equilibria of MXY, i.e. the species distribution among the possible isomers; (ii) the one-electron reduction potential of MXY; (iii) the guanosine and adenosine alkylation mechanism by MXY, which leads to covalent-DNA adducts; and (iv) the redox properties of the adducts. No significant differences were observed between MCF, CMCF, and MX, with a single exception: the unimolecular carbon-chlorine cleavage of some MX-nucleotide adducts may afford highly oxidative intermediates, which could be able to remove an electron from contiguous nucleotides directly, especially guanosine. This reaction would provide a pathway for the hypothesized ability of some hydroxyhalofuranones to oxidize DNA.