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Biomedical subjects

B A Bridges

Publications and source records attributed to B A Bridges.

At least 127 records · Page 7Linked to original sources
PubMed1979

Mutation induction and killing of Escherichia coli by DNA adducts and crosslinks: a photobiological study with 8-methoxypsoralen.

Low doses of 350 nm radiation (NUV) in the presence of 8-methoxypsoralen (8-MOP) induce predominantly mono-adducts in bacterial DNA. Further exposure to NUV in the absence of 8-MOP converts a proportion of these mono-adducts to interstrand cross-links. Using this approach the relative effects of adducts and cross-links on bacteria with different repair capacities was studied. Escherichia coli WP100 uvrA recA, believed to be totally deficient in the ability to repair 8-MOP plus NUV damage to DNA, was inactivated on average by a single photon event occurring with a quantum efficiency of about 0.03. We conclude that the inactivating lesion is probably a single mono-adduct. E. coli WP2 uvrA, deficient in excision endonuclease activity, may be inactivated by a very small number of cross-links, probably one. These conclusions are consistent with present knowledge of the repair capabilities of these bacteria. Conversion of mono-adducts to cross-links in WP2 uvrA (which occurs with a quantum efficiency of around 0.3) greatly increases lethality but results in a reduction of the induced mutation frequency presumably because cross-links are (almost) invariably lethal. In the repair-proficient strain WP2 both adducts and cross-links can be repaired but the latter are more likely than the former to lead to either death or mutation.

Cross-Linking Reagents↗
PubMed1979

Methodology for the testing of food dyes for genotoxic activity: experiments with red 2G (C.I. 18050).

A methodology for investigating genotoxicity of food colours using the fluctuation and DNA-repair assays with bacteria is described. In addition, a liquid repair test, developed to permit incorporation of microsomes and the quantitative estimation of cell viability, has been characterised with a number of positive control agents. Results obtained in these systems suggest that the food colour Red 2G induces repairable DNA damage and base-substitution mutation, but only in the presence of a rat-liver microsomal preparation. The significance of the data in the light of other toxicological information is discussed.

Amaranth Dye↗
PubMed1979

Inactivation of Escherichia coli by near-ultraviolet light and 8-methoxypsoralen: different responses of strains B/r and K-12.

A series of Escherichia coli K-12 AB1157 strains with normal and defective deoxyribonucleic acid repair capacity were more resistant to treatment with 8-methoxypsoralen (8-MOP) and near-ultraviolet light (NUV) than a comparable series of strains from the B/r WP2 family although sensitivities to 254-nm ultraviolet light were closely similar. The difference was most marked with strains deficient in both excision and postreplication repair (uvrA recA). The hypothesis that the internal level of 8-MOP was lower in K-12 than B/r uvrA recA derivatives was ruled out on the basis of fluorometric determinations of 8-MOP content and the similar inactivation curves for phage T3 treated intracellularly within the two strains. The demonstration of liquid holding recovery with AB2480 but not WP100 (both recA uvrA strains) and the somewhat greater resistance of the former strain to inactivation by captan revealed the presence in the K-12 strain of a deoxyribonucleic acid repair system independent of the recA(+) and uvrA(+) genes. The presence of this repair system did not, however, affect the survival of T3 phage treated with 8-MOP plus NUV and probably has a relatively small effect on survival of AB2480 under normal conditions. Experiments in which 8-MOP monoadducts were converted to cross-links by a second NUV exposure in the absence of 8-MOP indicated that the level of potentially cross-linkable monoadducts immediately after 8-MOP + NUV is about eightfold lower in K-12-than in B/r-derived strains. It is therefore suggested that the photoproduct yield in the former is well below that in the latter. In agreement with this is the observation that, during the first 10 min after treatment, deoxyribonucleic acid synthesis was just over five times more sensitive to inhibition by 8-MOP plus NUV in WP100 than in AB2480. We assume that 8-MOP in K-12 bacteria is hindered in some way from adsorbing to cellular (though not to phage T3) deoxyribonucleic acid. Consistent with this, 8-MOP has been shown to act as an inhibitor of a component of repair of 254-nm ultraviolet light damage in WP2 but not in AB1157.

Captan↗
PubMed1977

Frameshift mutagenesis in bacteria by 8-methoxypsoralen (methoxalen) in the dark.

We confirm that 8-methoxypsoralen (8-MOP) in the dark induces frameshift mutations in both Escherichia coli and Salmonella typhimurium when present in adequate concentration under growth conditions. The dose response is sigmoidal with a threshold or quasi-threshold at concentrations below about 10 microgram/ml. Frameshift mutagenesis by 8-MOP in the dark is unaffected by mutations at the uvrA or uvrB genes, in contrast to base pair substitution mutagenesis by 8-MOP plus near UV light. RecA (but not recB) bacteria are hypersensitive to the growth-inhibiting action of 8-MOP in the dark and are not detectably mutagenized. The characteristics of 8-MOP dark mutagenesis are consistent with the chemical interacting in a non-covalent manner with DNA and affecting the rate of occurrence of base deletions or insertions during DNA replication. The question of extrapolation of the genetic effect of 8-MOP to man is discussed.

Darkness↗
PubMed1977

Mutagen screening by a simplified bacterial fluctuation test: use of microsomal preparations and whole liver cells for metabolic activation.

We describe the use of a simplified bacterial fluctuation test to detect induced mutation, either incorporating liver microsomal or whole liver cell preparations. We have evaluated both types of test using three agents. The fluctuation assay seems somewhat slower, simpler and more sensitive than a conventional plating test with microsomes. A whole cell preparation appears marginally more effective than a microsomal fraction for metabolic activation of 9,10-dimethyl-1,2-benzanthracene, but rather less effective for benz(a)pyrene and 2-acetamidofluorene. Ultimately the usefulness of activation by whole cells may depend upon whether the method can give a correlation with carcinogenicity that is more quantitative than microsome methods and better reflects organ and species specificity.

2-Acetylaminofluorene↗
PubMed1977

Mutagenic DNA repair in escherichia coli. V. Mutation frequency decline and error-free post-replication repair in an excision-proficient strain.

Mutation frequency decline (MFD) is an irreversible loss of newly-induced suppressor mutations occurring in excision-proficient Escherichia coli during a short period of incubation in minimal medium before plating on broth- or Casamino acids-enriched selective agar. It is known that MFD of UV-induced mutations may occur before DNA containing pre-mutagenic lesions is replicated, but we conclude that MFD can also occur after the damaged DNA has been replicated on the basis of the following evidence. (1) Mutation fixation in rich medium (i.e., loss of susceptibility to mutation frequency decline) with ethyl methanesulphonate mutagenesis begins immediately, whereas with UV it is delayed for 20--30 min. (2) The delay in mutation fixation after UV can be explained neither by inhibition of DNA replication nor by a delay in the appearance of error-prone repair activity in the irradiated population. (3) MFD at later times after UV irradiation is more rapid and is less strongly inhibited by caffeine than is MFD immediately after irradiation. (4) Excision is virtually complete 20 min after 3 J m-2 UV but at that time virtually all mutations are still susceptible to MFD. We have presented evidence elsewhere that in bacteria there is an alternative error-free excision-dependent type of post-replication repair of potentially mutagenic daughter strand gaps. We suggest that this process is inhibited at tRNA loci in the presence of nutrient broth or Casamino acids, possibly because of a broth-dependent change in the structure of the single-stranded region including the tRNA locus.

DNA Repair↗
PubMed1977

Cell division in Escherichia coli BS-12 is hypersensitive to deoxyribonucleic acid damage by ultraviolet light.

Escherichia coli BS-12 uvrA lon is hypersensitive to ultraviolet light. On minimal agar plates at densities in excess of about 10(7) bacteria per plate, as few as one or two photoreversible pyrimidine dimers in the entire genome are sufficient to cause inhibition of cell division. Most of the resulting filaments are unable to divide or form a viable colony. Inhibition of cell division appears to be a rapid consequence of replication of deoxyribonucleic acid containing a pyrimidine dimer. Photoreversibility of the inhibition of cell division persists indefinitely, indicating that the continued presence of the pyrimidine dimers (or the continued generation of daughter strand gaps) is necessary to maintain the division-inhibited state. In view of the kinetics for the production of filamentation by ultraviolet light and the extremely low average inducing fluence (0.03 J/m2), it is concluded that the initiating signal is not the same as that causing other inducible phenomena such as prophage induction or Weigle reactivation.

Bacterial Proteins↗
PubMed1977

DNA repair.

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Aging↗
PubMed1976

Short term screening tests for carcinogens.

There are now short term tests with a high predictive value for mammalian carcinogens. Many of them are based on the ability to detect damage to DNA in bacteria or mammalian cells after metabolic activation by microsomal enzymes. Their introduction will enable provisional safety assessments to be made for the many thousands of industrial and environmental chemicals for which long-term animal testing cannot at present be considered.

Animals↗