Amount Of DNA Repair Research Articles

ENERGETICS OF DNA REPAIR: EFFECTS OF TEMPERATURE ON DNA REPAIR IN UV‐IRRADIATED PERIPHERAL BLOOD LEUCOCYTES FROM CHRONIC MYELOID LEUKEMIC PATIENTS*

Abstract— The effects of different temperatures(34–43°C) were studied on the repair of UV‐induced (254‐nm) DNA damage and its energetics in peripheral blood leucocytes of chronic myeloid leukaemic patients. DNA repair was measured by the unscheduled DNA synthesis (UDS) technique. Cellular energy supply was modulated by inhibitors of oxidative phosphorylation (antimycin‐A) and glycolysis (2‐deoxy‐D‐glucose). It was observed that there is an increase in the amount of DNA repair with increasing temperatures up to 40°C and a fall thereafter. Longer periods of heat treatment (4 h) beyond 40°C were observed to further decrease the DNA repair. Increasing temperatures were observed to have no significant effect on the parameters of energy metabolism. Further, the activation energy of DNA repair was calculated as 92 ± 46 kJ/mol (22 ± 11 kcal/mol), which did not alter significantly even in the presence of inhibitors of energy metabolism.

Effects of pretreatment with inducers of hepatic mixed function oxidases on DNA repair elicited by various compounds in hepatocytes from adult and neonatal rats

Studies were conducted to assess the effects of inducers of hepatic mixed function oxidases on DNA repair responses to 13 different genotoxic agents in hepatocytes from adult male mice. Phenobarbital pretreatment increased DNA repair elicited by diethylnitrosamine but had no effect on responses to the other compounds. Pretreatment with p,p'-dichlorodiphenyltrichlorethane, 3-methyl-cholanthrene or beta-naphthoflavone induced the DNA repair responses to a variety of activation-dependent carcinogens. DNA repair responses to the direct-acting alkylating agents methyl methanesulfonate and N-methyl-N'-nitro-N-nitrosoguanidine were not increased by any of the pretreatments, which indicated that the pretreatment-related enhancement of responses to the other compounds was due to induction of their metabolic activation. Taken together, the findings suggest that Aroclor, or other pretreatments, may increase the sensitivity of the hepatocyte DNA repair assay for detecting the genotoxicity of certain compounds; however, the potential benefit may be limited due to specific features of the assay. In contrast, Aroclor pretreatment did not produce any enhancement of in vivo DNA repair elicited by dimethylnitrosamine, diethylnitrosamine, o-aminoazotoluene, 2-acetylaminofluorene, 3-methylcholanthrene or aflatoxin B1, and thus does not appear to be useful for improving the sensitivity of the in vivo/in vitro assay. Whereas the amount of DNA repair produced by dimethylnitrosamine was not increased by classical inducers of liver microsomal enzymes, pretreatment with pyrazole greatly augmented in vitro and in vivo DNA repair responses to dimethylnitrosamine; responses to diethylnitrosamine were increased to a lesser degree by pyrazole pretreatment. The effects of lactational exposure to enzyme inducing agents on DNA repair in neonatal hepatocytes was also investigated.

Selective inhibition of replicative and repair DNA synthesis in mouse colon following administration of 1,2-dimethylhydrazine.

Early alterations in normal semiconservative and repair DNA synthesis were determined in gastrointestinal tissues of HalCR mice following administration of the colon carcinogen 1,2-dimethylhydrazine (DMH). Following DMH injections of 60 and 200 mg/kg, normal DNA synthesis was rapidly inhibited in all tissues. The greatest depressions were observed in the descending colon, followed closely by the ascending colon. DNA repair was estimated by measuring unscheduled DNA synthesis. No repair was observable in the descending or ascending colon. The esophagus, forestomach, jejunum, and ileum demonstrated significant amounts of DNA repair, while the duodenum and gastric stomach displayed nominal or insignificant amounts of repair. Repair DNA synthesis was inhibited by simultaneous administration of caffeine and DMH. The degree of inhibition of normal replicative DNA synthesis and the amount of repair DNA synthesis in response to DMH treatment correlate closely with the incidence of DMH-induced tumors. Most tumors occur in the descending colon, followed by the ascending colon, and only a few in the duodenum and gastric stomach area. Neoplasms are rarely found in the remainder of the gastrointestinal system.

Measurement of ‘unscheduled’ DNA synthesis in HeLa cells by liquid scintillation counting after carcinogen treatment

HeLa cells, conditioned in an arginine-deficient medium to reduce DNA S-phase synthesis, were treated with one of four ultimate carcinogens (MNNG, BrMBA, N-acetoxy AAF and EMS) and one precarcinogen, AFB1. All treated cells preferentially incorporated [3H] thymidine as a result of DNA repair monitored by liquid scintillation counting of the extracted DNA. The cells showed some capacity to activate AFB1, but repair synthesis was much increased if a rat liver mixed function oxidase preparation was also present. At equimolar concentrations the various carcinogens stimulated different amounts of DNA repair; this variation was not proportional to the carcinogenic potency of the chemicals tested. Reasons for this are discussed as is the use of this technique as a screen for chemical carcinogens.