Proceedings: Differential induction of chromosome aberrations in mammalian cell lines.

Mutagenesis was studied in repair- and recombination-deficient strains of Haemophilus influenzae after treatment with N-nitrosocarbaryl (NC). Three different strains of H. influenzae carrying mutations affecting excision-repair of UV-induced pyrimidine dimers exhibited normal repair of premutational lesions (as detected by decreased mutation yield resulting from post-treatment DNA synthesis delay) and normal nonreplicative mutation fixation. This indicates that neither of these phenomena are caused by the same repair mechanism that removes UV-induced pyrimidine dimers from the DNA.The recombination-deficient mutant rec1 is apparently deficient in the replication-dependent mode of NC-induced mutation fixation. This conclusion is based on the following results: (1) NC-induced mutagenesis is lower in the rec1 strain than in rec⁺ cells. (2) Repair of premutational lesions (which depends on the existence of replication-dependent mutation fixation for its detection) was not detected in the rec1 strain. (3) When nonreplicative mutation fixation and final mutation frequency were measured in the same experiment, about $\text{1}\text{4}$ to $\text{1}\text{3}$ of the final mutation yield could be accounted for by nonreplicative mutation fixation in the rec⁺ strain, whereas all of the mutation could be accounted for in the rec1 strain by the nonreplicative mutation fixation. (4) When mutation fixation in strain dna9 rec1 was followed at the permissive (36°) and nonpermissive (41°) temperatures, it became apparent that in the rec1 strain replication-dependent mutation fixation occurs at early times, but these newly fixed mutations are unstable and disappear at later times, leaving only the mutations fixed by the nonreplicative process.The rec1 strain exhibits normal repair of NC-induced single-strand breaks or alkali-labile bonds in the DNA labeled before treatment, but is slow in joining discontinuities present in DNA synthesized after treatment. The results are consistent with the idea that in NC-treated H. influenzae cells the replication-dependent mode of mutation fixation occurs by error-prone joining of interruptions present in the DNA synthesized after treatment. The possibility still exists, however, that during DNA replication mispairing occurs opposite certain alkylation-induced lesions and that mutations arising during replication of strain rec1 later disappear as a result of degradation of newly synthesized DNA, which is excessive in this strain.     

The measurement of chemically-induced DNA repair synthesis in human cells by BND-cellulose chromatography.

Repair synthesis in human cells in tissue culture can be readily separated from semi-conservative DNA synthesis with the aid of a benzoylated naphthoylated DEAE cellulose (BND-cellulose) column. Cells are incubated with a radioactive DNA precursor during treatment with a repair-inducing agent. An inhibitor of semi-conservative DNA synthesis (hydroxyurea) is added to slow the progression of the DNA growing point. The cells are lysed and after treatment with ribonuclease and pronase the lysates are sheared and passed through a BND-cellulose column. Native DNA is eluted with I M NaCl. Any increase in radioactivity in the native DNA is due to repair synthesis and the specific repair activity (nucleotides inserted per mug of DNA) can be determined from radioactivity and absorbancy measurements. Repair can also be measured in the region of the DNA growing point by fractionation of the material eluted from BND-cellulose with 50% formamide. Repair was not detected in N-acetoxy-2-acetylaminofluorene (AAAF)-treated lymphoblasts derived from an individual with xeroderma pigmentosum although methyl methanesulfonate (MMS)-induced repair was observed in these cells.     

Mutagenicity of organophosphorus compounds in bacteria and drosophila

140 Organophosphorus compounds (OP's) have been tested for mutagenic activity in bacteria, principally by using two specially constructed sets of tester strains of the bacteria Salmonella typhimurium and Escherichia coli. It was found that 20% gave positive mutagenic responses and that this group of chemicals produce base substitutions rather than frame-shift mutations. In most cases the DNA repair genes exrA⁺ and recA⁺ were for mutagenic activity.Seven compounds were further tested in Drosophila melanogaster for the ability to induce recessive lethal mutations. In some of these cases the doses administered to the flies had to be very low due to the highly toxic nature of the compounds. To overcome this problem, the accumulation of recessive lethal mutations was measured in populations which were continually exposed to the compounds over a period of some 18 months. During this time the populations developed increased resistance to the compound and so the dose administered could gradually be increased. Six of the compounds were mutagenic.Of the compounds tested in both systems, those showing mutagenic activity in bacteria were also mutaganic in Drosophila, those mutagenic in bacteria were not mutagenic in Drosophila.     

New organic bases from amazonian Banisteriopsis caapi

Three new bases were isolated from Banisteriopsis caapi; they are harmine N-oxide, harmic acid methyl ester (methyl 7-methoxy-β-carboline 1-carboxylate) and harmalinic acid (7-methoxy-3,4-dihydro-β-carboline 1-carboxylic acid).     

Métabolisme du chloro-2 (p-chlorophényl)-3 propionate de méthyle et problème de sélectivité

The product of hydrolysis of the active principle of the herbicide Bidisine® is degraded in at least two different ways. One way gives p-chlorobenzoic acid. The other, more important one, gives a conjugate with l-cysteine, which is further oxidized. The ability to oxidize the conjugate provided a means of distinguishing between susceptible and resistant plant species.     

Caffeine toxicity in drosophila strains having different MMS sensitivities.

Larvae of Drosophila melanogaster were fed with caffeine, and the induced lethality was recorded using two different methods. With a wild-type strain a whole dose-response curve was obtained. The two sexes were equally sensitive. Four genetically different strains, showing different MMS sensitivities, were tested with two caffeine doses. The strains differed significantly in their caffeine sensitivity, but there existed no correlation between MMS and caffeine sensitivity.     

Influence of systems biology response and environmental exposure level on between-subject variability in breath and blood biomarkers

To explain the underlying causes of apparently stochastic disease, current research is focusing on systems biology approaches wherein individual genetic makeup and specific ‘gene–environment’ interactions are considered. This is an extraordinarily complex task because both the environmental exposure profiles and the specific genetic susceptibilities presumably have large variance components. In this article, the focus is on the initial steps along the path to disease outcome namely environmental uptake, biologically available dose, and preclinical effect. The general approach is to articulate a conceptual model and identify biomarker measurements that could populate the model with hard data. Between-subject variance components from different exposure studies are used to estimate the source and magnitude of the variability of biomarker measurements. The intent is to determine the relative effects of different biological media (breath or blood), environmental compounds and their metabolites, different concentration levels, and levels of environmental exposure control. Examples are drawn from three distinct exposure biomarker studies performed by the US Environmental Protection Agency that studied aliphatic and aromatic hydrocarbons, trichloroethylene and methyl tertiary butyl ether. All results are based on empirical biomarker measurements of breath and blood from human subjects; biological specimens were collected under appropriate Institutional Review Board protocols with informed consent of the subjects. The ultimate goal of this work is to develop a framework for eventually assessing the total susceptibility ranges along the toxicological pathway from exposure to effect. The investigation showed that exposures are a greater contributor to biomarker variance than are internal biological parameters.     

A protective effect of caffeine on drosophila larvae treated with methyl methanesulfonate.

Lethality induced in larval populations of Drosophila melanogaster was recorded after treatment with (1) caffeine, (2) MMS or (3) caffeine plus MMS. The mixture of caffeine plus MMS was less toxic than expected from the effects observed after treatment with either substance individually. It is postulated that in the combined treatment the caffeine, by inhibiting semiconservative DNA replication, allows for some additional time for repair of alkylated DNA by a repair pathway which is not sensitive to caffeine, possibly excision repair.