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Biomedical subjects

John C Sutherland

Publications and source records attributed to John C Sutherland.

10 recordsLinked to original sources
PubMed2006

Repair dependent radiation survival: a stochastic model with Euler gamma function solutions.

The probability of survival of cells or viruses exposed to various forms of radiation is expressed as a function of the probability that a given cell will receive a certain number of lethal damages, the average probability that each such damage is repairable, and an upper bound on the repair capacity of each cell. All lethal damages are presumed induced as a linear function of dose. The probability of survival is found to be the product of a single exponential, which reflects inactivation by unrepairable lethal damages and dominates at low doses, and an Euler gamma function, which reflects inactivation due to repairable damages formed in excess of the upper bound on repair capacity. Computational procedures obtain stochastic parameters from published survival data for the inactivation of bacterial, yeast and mammalian cells exposed to ionizing or ultraviolet radiation, including split-dose experiments. The survival of cells exposed to photodynamic therapy is analysed assuming that lethal damages cannot be repaired, but more than one may be required for inactivation.

Cell Survival↗
PubMed2006

DNA damage quantitation by alkaline gel electrophoresis.

Quantifying DNA lesions provides a powerful way to assess the level of endogenous damage or the damage level induced by radiation, chemical or other agents, as well as the ability of cells to repair such damages. Quantitative gel electrophoresis of experimental DNAs along with DNA length standards, imaging the resulting dispersed DNA and calculating the population average length allows accurate measurement of lesion frequencies. Number average length analysis provides high sensitivity and does not require any specific distribution of lesions within the DNA molecules. These methods are readily applicable to strand breaks and ultraviolet radiation induced pyrimidine dimers, but can also be used-with appropriate modifications-for ionizing radiation-induced lesions such as oxidized bases and abasic sites.

Animals↗
PubMed2003

Quantifying clustered DNA damage induction and repair by gel electrophoresis, electronic imaging and number average length analysis.

Assessing DNA damage induction, repair and consequences of such damages requires measurement of specific DNA lesions by methods that are independent of biological responses to such lesions. Lesions affecting one DNA strand (altered bases, abasic sites, single strand breaks (SSB)) as well as damages affecting both strands (clustered damages, double strand breaks) can be quantified by direct measurement of DNA using gel electrophoresis, gel imaging and number average length analysis. Damage frequencies as low as a few sites per gigabase pair (10(9)bp) can be quantified by this approach in about 50ng of non-radioactive DNA, and single molecule methods may allow such measurements in DNA from single cells. This review presents the theoretical basis, biochemical requirements and practical aspects of this approach, and shows examples of their applications in identification and quantitation of complex clustered damages.

Animals↗
PubMed2003

Evaluation of number average length analysis in quantifying double strand breaks in genomic DNAs.

Double strand breaks in DNA can be quantified down to very low frequencies (a few per Gigabase pair) in nanogram quantities of nonradioactive, genomic DNA by dispersing the DNAs on electrophoretic gels, digitizing them by quantitative electronic imaging, and calculating the DNA lengths by number average length analysis. No specific distribution of damages is required for number average length analysis. To test the validity of this approach, we used DNA populations of known absolute lengths and break frequencies as experimental DNAs and calculated the number average lengths and double strand break levels. Experimental DNAs and length standards were dispersed using pulsed field electrophoretic modes (unidirectional pulsed field, contour clamped homogeneous field, or transverse alternating field) appropriate for their size range, stained with ethidium, destained, and a quantitative electronic image obtained. A dispersion curve was constructed from the migration-mobility relationships of the length standard DNAs, and the number average lengths of the experimental DNAs were calculated. The calculated DNA lengths agreed well with the actual lengths. Furthermore, the double strand break frequencies calculated through number average length analysis of DNAs dispersed by these pulsed field gel modes and digitized by quantitative electronic imaging were in excellent agreement with the actual values for populations of DNA over the size range of approximately 4 kbp to approximately 3 Mbp. The use of this approach in quantifying DNA damages is illustrated for double strand breaks and damage clusters (e.g., OxyPurine clusters recognized by Escherichia coli Fpg protein) induced in T7 DNA by ionizing radiation.

Bacteriophage T7↗
PubMed2003

Quantifying double-strand breaks and clustered damages in DNA by single-molecule laser fluorescence sizing.

Fluorescence from a single DNA molecule passing through a laser beam is proportional to the size (contour length) of the molecule, and molecules of different sizes can be counted with equal efficiencies. Single-molecule fluorescence can thus determine the average length of the molecules in a sample and hence the frequency of double-strand breaks induced by various treatments. Ionizing radiation-induced frank double-strand breaks can thus be quantified by single-molecule sizing. Moreover, multiple classes of clustered damages involving damaged bases and abasic sites, alone or in combination with frank single-strand breaks, can be quantified by converting them to double-strand breaks by chemical or enzymatic treatments. For a given size range of DNA molecules, single-molecule sizing is as or more sensitive than gel electrophoresis, and requires several orders-of-magnitude less DNA to determine damage levels.

Bacteriophage T7↗
PubMed2002

Repair of cyclobutyl pyrimidine dimers in human skin: variability among normal humans in nucleotide excision and in photorepair.

BACKGROUND/AIMS: Photoreactivation (PR) of cyclobutyl pyrimidine dimers (CPD) in human skin remains controversial. Recently Whitmore et al. (1) reported negative results of experiments using two photorepair light (PRL) sources on UV-irradiated skin of volunteers. However, their PRL sources induced substantial levels of dimers in skin, suggesting that the additional dimers formed could have obscured PR. We met a similar problem of dimer induction by a PRL source. We designed and validated a PRL source of sufficient intensity to catalyse PR, but that did not induce CPD, and used it to measure photorepair in human skin. METHODS AND RESULTS: Using a solar simulator filtered with three types of UV-filters, we found significant dimer formation in skin, quantified by number average length analysis using electrophoretic gels of isolated skin DNA. To prevent scattered UV from reaching the skin, we interposed shields between the filters and skin, and showed that the UV-filtered/shielded solar simulator system did not induce damage in isolated DNA or in human skin. We exposed skin of seven healthy human volunteers to 302 nm radiation, then to the improved PRL source (control skin areas were kept in the dark for measurement of excision repair). CONCLUSIONS: Using a high intensity PRL source that did not induce dimers in skin, we found that three of seven subjects carried out rapid photorepair of dimers; two carried out moderate or slow dimer photorepair, and three did not show detectable photorepair. Excision repair was similarly variable in these volunteers. Subjects with slower excision repair showed rapid photorepair, whereas those with rapid excision generally showed little or no photoreactivation.

DNA Repair↗
PubMed2002

Clustered DNA damages induced in human hematopoietic cells by low doses of ionizing radiation.

Ionizing radiation induces clusters of DNA damages--oxidized bases, abasic sites and strand breaks--on opposing strands within a few helical turns. Such damages have been postulated to be difficult to repair, as are double strand breaks (one type of cluster). We have shown that low doses of low and high linear energy transfer (LET) radiation induce such damage clusters in human cells. In human cells, DSB are about 30% of the total of complex damages, and the levels of DSBs and oxidized pyrimidine clusters are similar. The dose responses for cluster induction in cells can be described by a linear relationship, implying that even low doses of ionizing radiation can produce clustered damages. Studies are in progress to determine whether clusters can be produced by mechanisms other than ionizing radiation, as well as the levels of various cluster types formed by low and high LET radiation.

Cell Line↗
PubMed2002

Biological effects of polychromatic light.

Predicting the effects of polychromatic light on biological systems is a central goal of environmental photobiology. If the dose-response function for a process is a linear function of the light incident on a system at each wavelength within the spectrum, the effect of a polychromatic spectrum is obtained by integrating the product of the cross section for the reaction at each wavelength and the spectral irradiance at that wavelength over both wavelength and time. This procedure cannot be used, however, if the dose-response functions for an effect are not linear functions of photon dose. Although many photochemical reactions are linear within the biologically relevant range of doses, many biological end points are not. I describe procedures for calculating the effects of polychromatic irradiations on systems that exhibit certain classes of dose-response functions, including power law responses typical of mutation induction and exponential dose-responses typical of cell survival. I also present an approach to predict the effects of polychromatic spectra on systems in which the ultraviolet components form pyrimidine dimers, and the longer-wavelength ultraviolet and visible components remove them by photoreactivation, thus generating complex dose-response functions for these coupled light-driven reactions.

DNA Damage↗
PubMed2002

Clustered DNA damages induced by x rays in human cells.

Although DNA DSBs are known to be important in producing the damaging effects of ionizing radiation in cells, bistranded clustered DNA damages-two or more oxidized bases, abasic sites or strand breaks on opposing DNA strands within a few helical turns-are postulated to be difficult to repair and thus to be critical radiation-induced lesions. Gamma rays can induce clustered damages in DNA in solution, and high-energy iron ions produce DSBs and oxidized pyrimidine clusters in human cells, but it was not known whether sparsely ionizing radiation can produce clustered damages in mammalian cells. We show here that X rays induce abasic clusters, oxidized pyrimidine clusters, and oxidized purine clusters in DNA in human cells. Non-DSB clustered damages comprise about 70% of the complex lesions produced in cells. The relative levels of specific cluster classes depend on the environment of the DNA.

Cell Line↗