The long-term objective of this project is to determine the mechanisms by which ionizing radiation, through direct effects, alters the primary structure of DNA. Damage due to direct effects accounts for 20-30% of the total damage to DNA for low LET radiations. At high LET, it increases to 80% of the damage. The accumulation of unrepaired damage in DNA is a critical variable in determining the risks due to long-term exposures to low doses of radiation, risks such as induction of cancer or leukemia. Achievement of the stated objective will be a major benefit in risk assessment and disease treatment.
The specific aims work toward the long-term goal by examining free radical processes initiated in DNA by direct ionization.
These aims are: (1) to determine the relative electron trapping efficiencies of the DNA bases and the spatial distribution of the electron adducts, (2) likewise, to determine the sites and distribution of electron loss, (3) to determine the yields of these initial free radical products as a function of chemical environment and molecular structure, working toward a chromatin environment, and (4) to follow the free radical reactions, qualitatively and quantitatively, that connect the initial free radical products with more stable end products. The approach is to use electron spin resonance (ESR) and electron nuclear double resonance (ENDOR) spectroscopies to study DNA constituents, deoxyoligonucleotides, deoxypolynucleotides, and DNA. These materials are studied in the form of powders, crystals, and frozen glasses. By X-irradiating at low temperatures, 4K, the initial free radical products are stabilized; controlled warming makes it possible to observe the sequence of free radical reactions that lead to more stable end products. The main thrust will involve experiments that characterize each of the one-electron reduced bases and then use these characteristics to determine the sites of electron attachment in complementary deoxyoligonucleotides of known base sequence and known conformation. Experiments that follow will apply this approach to oxidized instead of reduced bases. The deoxyoligonucleotides will be studied as solutes dissolved in 12 M LiCl glasses. Single crystal ESR/ENDOR will be used to assist in free radical characterization and in identifying the critical variables governing free radical yield. Powder ESR will be used in extending the information obtained from crystals and glasses to DNA polymers.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Method to Extend Research in Time (MERIT) Award (R37)
Project #
4R37CA032546-20
Application #
2088351
Study Section
Special Emphasis Panel (NSS)
Project Start
1982-02-01
Project End
1998-01-31
Budget Start
1995-02-28
Budget End
1996-01-31
Support Year
20
Fiscal Year
1995
Total Cost
Indirect Cost
Name
University of Rochester
Department
Physiology
Type
Schools of Dentistry
DUNS #
208469486
City
Rochester
State
NY
Country
United States
Zip Code
14627
Roginskaya, Marina; Mohseni, Reza; Moore, Terence J et al. (2014) Identification of the C4'-oxidized abasic site as the most abundant 2-deoxyribose lesion in radiation-damaged DNA using a novel HPLC-based approach. Radiat Res 181:131-7
Milano, M T; Bernhard, W A (1999) The influence of packing on free radical yields in solid-state DNA: film compared to lyophilized frozen solution. Radiat Res 152:196-201
Milano, M T; Bernhard, W A (1999) The effect of packing and conformation on free radical yields in films of variably hydrated DNA. Radiat Res 151:39-49
Milano, M T; Hu, G G; Williams, L D et al. (1998) Migration of electrons and holes in crystalline d(CGATCG)-anthracycline complexes X-irradiated at 4 K. Radiat Res 150:101-14
Mroczka, N E; Mercer, K R; Bernhard, W A (1997) The effects of lattice water on free radical yields in X-irradiated crystalline pyrimidines and purines: a low-temperature electron paramagnetic resonance investigation. Radiat Res 147:560-8
Mroczka, N E; Bernhard, W A (1995) Electron paramagnetic resonance investigation of X-irradiated poly(U), poly(A) and poly(A):poly(U): influence of hydration, packing and conformation on radical yield at 4 K. Radiat Res 144:251-7
Barnes, J P; Bernhard, W A (1995) The distribution of electron trapping in DNA: one-electron-reduced oligodeoxynucleotides of adenine and thymine. Radiat Res 143:85-92
Bernhard, W A; Mroczka, N; Barnes, J (1994) Combination is the dominant free radical process initiated in DNA by ionizing radiation: an overview based on solid-state EPR studies. Int J Radiat Biol 66:491-7
Stegelmeier, B L; Gillett, N A; Hahn, F F et al. (1994) Expression of transforming growth factor alpha and epidermal growth factor receptor in rat lung neoplasms induced by plutonium-239. Radiat Res 140:191-8
Mroczka, N; Bernhard, W A (1993) Hydration effects on free radical yields in DNA X-irradiated at 4 K. Radiat Res 135:155-9

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