Gamma-ray induced double-strand breaks in DNA resulting from randomly-inflicted single-strand breaks: temporal local denaturation, a new radiation phenomenon?

The induction of single- and double-strand breaks in DNA by γ-rays has been measured. The maximum number of nucleotide paris (a) between two independently induced single-strand breaks in opposite strands of the DNA which cannot prevent the occurrence of a double-strand break was found to amount to about 16. This value did not differ significantly for the four types of bacteriophage DNA investigated (T4, T7 and PM2 DNA, and replicative form DNA of phage phiX174) and was the same in 10-2 M phosphate buffer containing 0, 0.5 or 1 M NaCl. In 10-3 M phosphate buffer (a) was 34 nucleotide pairs. Evidence is presented that the relatively large value of (a) has to be ascribed at least partly to a temporal local denaturation accompanying the induction of a single-strand scission. A contribution of base damage that labilizes the DNA-helix, between two single-strand breaks to the high value of (a) can not be excluded. Chemicals/CAS: Cobalt Radioisotopes; DNA, Circular; DNA, Single-Stranded; DNA, Vira

The induction of gamma-endonuclease susceptible sites by ??-rays in CHO cells and their cellular repair are not affected by the presence of thiol compounds during irradiation

Chemicals/CAS: endonuclease, 9055-11-2; DNA, 9007-49-2; Endonucleases, EC 3.1.-; Sulfhydryl Compound

An immunochemical assay to detect DNA damage in bovine sperm

An immunochemical assay has been developed to detect oxidative damage in bovine sperm DNA. Sperm DNA contains a large amount of oxidative damage as a result of exposure to exogenous agents, but damage also can caused by normal metabolic processes and the absence of DNA repair in the later stages of spermatogenesis. A freeze-thaw procedure performed on extended bovine sperm in straws did not induce additional DNA damage immediately after thawing compared with nonfrozen extended sperm. The data suggest that the amount of oxidative damage correlated to the percentage of artificially inseminated cows returning to service within 56 days postinsemination, because a number of sires with high sperm concentrations had a large variation in fertility after artificial insemination. These observations have led to the conclusion that by measuring DNA damage in thawed sperm, one might predict the fertility of bulls with high semen concentration

Intravenous toxicokinetics of sulfur mustard and its DNA-adducts in the hairless guinea pig and marmoset

ln order to provide a quantitative basis for pretreatment and therapy of intoxications with sulfur mustard the toxicokinetics of this agent as well as its major DNA-adducts are being studied in male hairless guinea pigs for the intravenous, respiratory and percutaneous routes. A highly sensitive method for bioanalysis of the intact agent in blood and tissues was developed, involving gas chromatography with automated thermodesorption injection and mass-spectrometric detection. Deuterated sulfur mustard is used as the internal standard. The absolute detection limit is 700 fg for sulfur mustard, which corresponds with a detection limit in blood of ca. 5 pg/ml. DNA-adducts are measured via the previously developed immuno-slot-blot method, using antibodies directed against the adduct of sulfur mustard to guanine. The intravenous 96-h LD50 of sulfur mustard in the hairless guinea pig was determined and appeared to be 8.2 mg/kg. The intravenous toxicokinetics of this dose in the hairless guinea pig are characterized by a very rapid distribution phase and a very slow elimination phase. A rapid adduct formation occurs in blood and lung, and subsequently in other organs. The adduct levels in lung were remarkably high. A considerable repair of the adducts is observed within 6 h. However, at 2 days after administration of sulfur mustard adducts are still detectable in most of the organs studied. The intravenous toxicokinetics of sulfur mustard were also studied in the marmoset at a dose corresponding with 1 LD50 in the hairless guinea pig. The results obtained sofar will be discussed

Immunochemical detection of sulfur mustard adducts with keratins in the stratum corneum of human skin

As part of a program to develop methods for diagnosis of exposure to chemical warfare agents, we developed immunochemical methods for detection of adducts of sulfur mustard to keratin in human skin. Three partial sequences of keratins containing glutamine or asparagine adducted with a 2-hydroxyethylthioethyl group at the ω-amide function were synthesized and used as antigens for raising antibodies. After immunization, monoclonal antibodies were obtained with affinity for keratin isolated from human callus exposed to 50 μM sulfur mustard. These antibodies showed binding to the stratum corneum of human skin exposed to low levels of sulfur mustard, as evidenced by immunofluorescence microscopy. This approach opens the way for development of a detection kit that can be applied directly to the skin. To the best of our knowledge, this is the first example of immunochemical detection of adduct formation of toxic chemicals with skin proteins. A similar approach can be followed for skin exposure to environmental pollutants