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Biomedical subjects

G Ahnström

Publications and source records attributed to G Ahnström.

15 recordsLinked to original sources
PubMed1992

On the bioactivation and genotoxic action of fluoranthene.

Fluoranthene (FA) was studied with respect to possible mechanisms of its high mutagenicity but low carcinogenicity, in comparison with the corresponding properties of benzo[a]pyrene (BaP), and with regard to the synergism of these two compounds shown by van Duuren and Goldschmidt (J Natl Cancer Inst 56, 1976, 1237). FA and BaP activated by S9 from Aroclor 1254 (PCB)-treated rats induce HPRT mutations in CHO cells with about equal effectiveness at the same exposure doses, which also lead to the same frequencies of repairable DNA adducts, enzyme-induced strand breaks being used as an indirect measure of adducts to DNA. FA was also shown to be an efficient inducer of SCE in human peripheral lymphocytes cocultivated with PCB-treated HepG2 cells or with liver cells from PCB-pretreated rats. For the induction of SCE, FA and BaP were shown to act additively. From metabolic studies with liver microsomes from C57Bl/6 mice it is concluded that, whereas BaP induces the metabolism of BaP to the mutagenic epoxide, neither BaP nor FA is able to induce the metabolism of FA. In mutation experiments with V79 cells (XEM2) constitutive for P450 IA1 activity, BaP 7,8-diol but not FA 2,3-diol provokes a high frequency of HPRT mutations. In cells constitutive for P450 IA2 enzymatic activity FA and BaP are but weakly mutagenic and practically nonmutagenic, respectively. Due to the additivity of the genotoxic effects of FA and BaP, induction of an error-prone condition by the latter compound seems to be excluded.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The filter does not act as a DNA size discriminator in the neutral filter elution technique.

Various types of filters were used with the neutral filter elution technique. No significant differences in elution rate or curve shapes were found. Therefore we assume that the release of DNA fragments from the DNA gel formed by lysis of cells is the rate-determining event in elution and not the rate of migration through the filter. We suggest that the filter only serves as a support for the DNA gel.

Cells, Cultured↗
PubMed1991

Exposure of pancreatic islets to different alkylating agents decreases mitochondrial DNA content but only streptozotocin induces long-lasting functional impairment of B-cells.

Pancreatic B-cells exposed in vivo or in vitro to streptozotocin (SZ), the N-nitrosourea derivative of glucosamide, present a long-lasting impairment in the production and release of insulin while other cell functions are better preserved. This functional impairment is associated with a defective mitochondrial function. To further study the mechanisms behind SZ actions, mouse pancreatic islets were exposed in vitro to SZ (1.5 mM) or to different concentrations of methyl methanesulfonate (MMS; 2, 4 and 6 mM). The effect of the aglucone moiety of SZ, nitroso-N-methylurea (NMU; 2, 4 and 6 mM) was also tested. Islets were either studied immediately after exposure to the drugs (day 0) or after six days in culture following toxin treatment (day 6). On day 0 the islets showed a decrease in the NAD + NADH content, decreased glucose oxidation rates and an impaired insulin release in response to glucose. Six days after exposure to SZ there was still impaired glucose oxidation and insulin release, and decreased islet insulin mRNA and insulin content, but the NAD + NADH content was again similar to the control group. On the other hand, islets which survived for 6 days in culture following exposure to either MMS or NMU were able to regain normal B-cell function. The mouse islets exposed to SZ, NMU and MMS showed on day 6 a 30-40% decrease in the content of the mitochondrial DNA encoded cytochrome b mRNA and a 60-70% decrease in total mitochondrial DNA, as evaluated by dot and Southern blot analysis. Only SZ decreased the insulin mRNA content whereas both MMS and NMU decreased the glucagon mRNA content. As a whole, the data obtained indicate that SZ, NMU and MMS induce damage to the mitochondrial genome, and this may contribute to the B-cell dysfunction observed after SZ treatment. It is conceivable that the glucose moiety of SZ may direct the methylation to other intracellular sites besides the mitochondrial DNA, thus explaining the different functional responses of islets following exposure to SZ and NMU.

Adenine↗
PubMed1991

DNA-bound proteins contribute much more than soluble intracellular compounds to the intrinsic protection against radiation-induced DNA strand breaks in human cells.

To assess the role of soluble intracellular compounds and DNA-bound proteins in the intrinsic protection against radiation-induced DNA strand breaks, the alkaline unwinding technique was applied to cellular, nuclear, and nucleoid monolayers. It was found that, when the soluble intracellular compounds were removed from human fibroblasts by permeabilization (nuclear monolayers) and irradiated in a phosphate buffer containing 150 mM monovalent cations (Na+ and K+) and 0.8 mM MgCl2, the frequency of radiation-induced DNA strand breaks increased twofold. Removal of both soluble intracellular compounds and DNA-bound proteins from the cells by a pretreatment with 2 M NaCl (nucleoid monolayers) resulted in a 100-fold increase in the frequency of strand-break induction by gamma radiation. Expressed as percentage of total intrinsic protection against radiation-induced DNA strand breaks, DNA-bound protein contributed 99% compared to 1% by soluble intracellular compounds. Using a different experimental approach it was found that the radioprotective capacity of soluble intracellular compounds was equivalent to about 5 mM dimethyl sulfoxide (DMSO) and DNA-bound proteins to about 70 mM DMSO. It is concluded that DNA-bound proteins play a much greater role than soluble intracellular compounds in the intrinsic protection against radiation-induced DNA strand breaks in cultured human cells.

Cells, Cultured↗
PubMed1989

Inhibition of DNA strand break rejoining in ultraviolet-irradiated human cells: comparison of aphidicolin and cytosine arabinoside.

When ultraviolet-irradiated mammalian cells are incubated in the presence of aphidicolin or cytosine arabinoside (ara C) DNA breaks accumulate. When the inhibitors are removed before a steady-state level of breaks has been reached, breaks accumulated in the presence of aphidicolin are rapidly sealed while breaks in ara-C-treated cells continue to increase. This suggests that the active metabolite of ara C, ara CTP, cannot, in contrast to aphidicolin, be easily washed out of cells.

Aphidicolin↗
PubMed1988

Effects of 3-aminobenzamide on the rejoining of DNA-strand breaks in mammalian cells exposed to methyl methanesulphonate; role of poly(ADP-ribose) polymerase.

The effect of 3-aminobenzamide (3AB), an inhibitor of poly(ADP-ribose) polymerase, on DNA-repair processes has been investigated after treating V79 hamster cells with methyl methanesulphonate (MMS). Repair activity was observed as changes in DNA-strand break levels. MMS induces transient strand breaks, the level of which slowly decreases with time. Addition of 3AB leads to a rapid increase in the number of breaks. The level of breaks increases linearly with time until it suddenly levels off. Increasing the concentration of 3AB does not change the slope of this curve, but the steady-state level of breaks increases. The incision-rejoining kinetics indicates that 3AB induces a delay in the strand-break rejoining process. In the absence of 3AB the breaks have a lifetime of 1-2 min and this is increased by a factor of 5 in the presence of 5 mM 3AB.

Animals↗
PubMed1988

Techniques to measure DNA single-strand breaks in cells: a review.

Alkaline sucrose sedimentation was for a number of years the standard procedure for the measurement of single-strand breaks. Some years ago a number of new techniques with improved sensitivity were introduced. The following techniques are presented and discussed: alkaline unwinding, alkaline filter elution, nucleoid sedimentation, viscoelastometry, microelectrophoresis of single cells, DNA precipitation, pulse field gel electrophoresis, fluctuation spectroscopy and nick translation.

DNA Damage↗
PubMed1979

Single-strand breaks in DNA during repair of UV-induced damage in normal human and xeroderma pigmentosum cells as determined by alkaline DNA unwinding and hydroxylapatite chromatography: effects of hydroxyurea, 5-fluorodeoxyuridine and 1-beta-D-arabinofuranosylcytosine on the kinetics of repair.

A simple and sensitive technique for detection of strand breaks in DNA has been further developed. The method has been used to follow UV-induced excision-repair in human fibroblasts. It has been possible to study the kinetics of enzymic reactions in intact cells, in which strand breaks in DNA are produced and sealed again. Hydroxyurea, 5-fluorodeoxyuridine and 1-beta-D-arabinofuranosylcytosine, potent inhibitors of DNA synthesis, drastically increased the number of breaks observed during the repair process. This was probably due to a decreased polymerase activity, which will cause the strand breaks formed by endonuclease to remain open longer. The initial rate of strand-break formation did not seem to be influenced by hydroxyurea or araC, and was about 4000 breaks per minute in a diploid genome, at a dose of 20 J/m2. After 5--30 min, depending on the dose of UV, the number of breaks reached a maximum and started to decrease again. Hydroxyurea decreased the rate of polymerization in the sites under repair. However, there was no concomitant reduction of repair-induced incorporation of [3H]thymidine and no reduction of the excision of pyrimidine dimers. It therefore seems that the action of the polymerase was not a rate-limiting event, but rather an earlier step. It is likely that the endonucleolytic activity determined the rate of repair. As a consequence, the endonuclease and polymerase cannot be bound in a permanent complex. Under certain assumptions, the time for repair of a site, i.e. the time from incision to final ligase sealing, can be estimated as between 3 and 10 min. Essentially no breaks were produced in Xeroderma pigmentosum cells belonging to complementation group A, and there was no enhancement by hydroxyurea. Cells from the variant type of Xeroderma pigmentosum behaved like normal cells in this respect.

Cell Line↗
PubMed1978

Extensive and equivalent repair in both radiation-resistant and radiation-sensitive E. coli determined by a DNA-unwinding technique.

The extent of strand breakage and repair in irradiated E. coli B/r and Bs-1 was studied using a DNA-unwinding technique in denaturing conditions of weak alkali. Although these two strains show widely different responses to the lethal effects of ionizing radiation, they both have an equal capacity to repair radiation-induced breaks in DNA. Oxygen enhancement ratios for the killing of B/r and Bs-1 were respectively 4 and 2; but after repair in non-nutrient or nutrient post-irradiation conditions, the oxygen enhancement values for the residual strand breaks were always the same for the two strains. The equal abilities of E. coli B/r and E. coli Bs-1 to remove the strand breaks measured by this weak-alkali technique leads us to suggest that some other type of damage to either DNA or another macromolecule may play a major role in determining whether or not the cells survive to proliferate.

DNA, Bacterial↗