1. BIOLOGICAL EFFECTS OF IONIZING RADIATION AT MOLECULES AND CELLS

2. The stage of action of ionizing radiation Physical stage The transfer of kinetic energy from ionizing radiation to atoms or molecules leads to excitation and ionization of these atoms or molecules 10 – 16 – 10 – 15 seconds Physic-chemical stage The displace of absorbed energy of ionizing radiation into molecules and between them. Formation of free radicals 10 – 14 – 10 – 11 seconds Chemical stage Reactions between free radicals, reactions between free radicals and intact molecules. Formation of molecules with abnormal structure and function 10 – 6 – 10 – 3 seconds Biological stage Formation of injures on all levels – from cellular structures to organism and population. Development of processes of biological damage and reparative processes Seconds – years

3. Effect of radiation on atom and molecules

4. Effects of ionizing radiation at atomic level Ionization Excitation

5. Mechananisms of damage at molecular level

6. Direct action of ionizing radiation Ionizing radiation + RH R - + H + OH I R – C = NH imidol (enol) O II R – C = NH 2 amide (ketol)   Tautomeric shifts Bond breaks

7. e-e- X ray  ray P+P+ O H H OH - H+H+ HoHo OH o Indirect action of ionizing radiation

8. Radiolysis of H 2 O molecule Shared electron H-O-H  H + + OH - (ionization) H-O-H  H 0 + OH 0 (free radicals)

9. Reaction of H 2 O molecule r adiolysis Н 2 О + h  Н 2 О + + е - Н 2 О + h  Н 2 О *  Н о + НО о Н 2 О + е -  е - гидр  Н о + НО - Н 2 О + е -  Н 2 О *  Н о + ОН о Н 2 О  Н + + ОН о е - + Н +  Н о Н 2 О + + ОН -  Н 2 О + ОН о Н 2 О + + Н 2 О  Н 3 О + + ОН о Н 3 О + + е -  Н 2 О + Н о

10. Effects of oxygen on free radical formation Oxygen can modify the reaction by enabling creation of other free radical species with greater stability and longer lifetimes H 0 + O 2  HO 2 0 (hydroperoxy free radical) R 0 + O 2  RO 2 0 (organic peroxy free radical)

11. Reactions with free radicals H 0 + OH 0  H 2 O H 0 + H 0  H 2 OH 0 + OH 0  H 2 O 2 RH + OH 0  R 0 + H 2 O RH + H 0  R 0 + H 2 R 0 + OH  ROH R 0 + H  RH R 0 + O 2  ROO 0 ROO 0 + RH  ROOH + R 0

12. Lifetimes of free radicals 3nm Because short life of simple free radicals (10 -10 sec), only those formed in water column of 2-3 nm around DNA are able to participate in indirect effect HoHo OH o HoHo HO 2 o RO 2 o

13. Relation between linear energy transfer (LET) and type of action Direct action is predominant with high LET radiation, e.g. alpha particles and neutrons Indirect action is predominant with low LET radiation, e.g. X and gamma rays

14. Effect of radiation on biological molecules

15. Biochemical reactions with ionizing radiation DNA is primary target for cell damage from ionizing radiation

16. Radiation induced DNA damage

17. The most important types of radiation induced lesions in DNA Single-strand breaks 500-1000 per 1 Gy Double strand breaks 40-50 per 1 Gy Base damage: 1000-2000 per 1 Gy

18. Mechanisms of base excision and nucleotide excision repair

19. Mechanism of s DNA repair Mechanism of single-strand breaks DNA repair 1 Endonuclease 2 DNA polymerase 4 DNA ligase 5 3 Exonuclease

20. DNA restoration failure Unrejoined DNA double strand breaks Incorrect repair of DNA damage Cytotoxic effectMutations

21. Radiation induced membrane damage

22. Effect of radiation on cells

23. Types of cellular damage Interphase cell death Changes of metabolism & function Mitotic cell death Norma repair Mutation

24. Cell cycle

25. Radiosensitivity of cell in cell cycle Relative survivability of cells irradiated in different phases of the cell cycle: synchronised cells in late G 2 and in mitosis (M) showed greatest sensitivity to cell killing M G 1 S G 2 M

26. NORMALIRRADIATED Mitotic death

27. The most ‘radiosensitive’ cells are  actively proliferating (dividing) at the time of exposure  undifferentiated (non-specialized in structure and function) Bergonié and Tribondeaus’ ‘law’ (1906)

28. Interphase death Why are peripheral blood lymphocytes highly sensitive to radiation, although well differentiated?

29.  Pyknosis: The nucleus becomes contracted, spheroidal, and filled with condensed chromatin.  Karyolysis: The nucleus swells and loses its chromatin.  Protoplasmic Coagulation: Irreversible gelatin formation occurs in both the cytoplasm and nucleus.  Karyorrhexis: The nucleus becomes fragmented and scattered throughout the cell.  Cytolysis: Cells swell until they burst and then slowly disappear.  Apoptosis: Programmed cell death, usually be fragmentation Morphological forms of cell death

30.  Block of Mitotic Cycle: Mitosis may be delayed or inhibited following radiation exposure.  Disruptions in Cell Growth: Cell growth may also be retarded, usually after a latent period.  Permeability Changes: Irradiated cells may show both increased and decreased permeability.  Changes in Cell Motility: The motility of a cell may be decreased following irradiation. Changes of cell metabolism and function

31. Radiation induced chromosome damage Chromosomes

32. Radiation induced chromosomal aberrations

33.  Vegetative Cells: these cells, comprising differentiated functional cells of a large variety of tissues, are generally the most radiosensitive.  Differentiating Cells: these cells are somewhat less sensitive to radiation; they are relatively short ‑ lived and include the first generation produced by division of the vegetative mitotic cells.  Totally Differentiated Cells: these cells are relatively radioresistant; they normally have relatively long lifespans and do not undergo regular or periodic division in the adult stage, except under abnormal conditions such as following damage to or destruction of a large number of their own kind.  Fixed Nonreplicating Cells: these cells are most radioresistant; they are highly differentiated morphologically and highly specialized in function. Relative cellular radiosensitivity

34. Summary of lection Cells going through the division phase (M and S) are generally the most sensitive to ionizing radiation. Exceptions: lymphocytes and some bone marrow stem cells, which exhibit interphase death Cells going through the division phase (M and S) are generally the most sensitive to ionizing radiation. Exceptions: lymphocytes and some bone marrow stem cells, which exhibit interphase death Bone marrow consists of progenitor and stem cells, the most radiosensitive cells in the human body and the most important in controlling infection Bone marrow consists of progenitor and stem cells, the most radiosensitive cells in the human body and the most important in controlling infection

35. Lecture is ended THANKS FOR ATTENTION In lecture materials of the International Atomic Energy Agency (IAEA), kindly given by doctor Elena Buglova, were used