BIOLOGICAL EFFECTS OF IONIZING RADIATION AT MOLECUL ES AND C ELL S

1. BIOLOGICAL EFFECTS OF IONIZING RADIATIONAT MOLECULES AND CELLS

2. The stage of action of ionizing radiation

3. Effect of radiation on atom and molecules

4. Effects of ionizing radiation at atomic level Ionization Excitation

5. Mechananisms of damageat molecular level

6. Direct actionof ionizing radiation Ionizing radiation + RH R- + H+ Bond breaks   O II R – C = NH2 amide (ketol) Tautomeric shifts OH I R – C = NH imidol (enol)

7. Indirect actionof ionizing radiation OH- H e- O H+ Xray  ray H Ho P+ OHo

8. Radiolysis of H2O molecule Shared electron Shared electron H-O-H  H+ + OH- (ionization) H-O-H  H0 + OH0 (free radicals)

9. Reaction of H2O molecule radiolysis Н2О + h Н2О+ + е- Н2О + h Н2О*  Но + НОо Н2О + е-  е-гидр  Но + НО- Н2О + е-  Н2О*  Но + ОНо Н2О  Н+ + ОНо е- + Н+  Но Н2О+ + ОН-  Н2О + ОНо Н2О+ + Н2О  Н3О+ + ОНо Н3О+ + е-  Н2О + Но

10. Effects of oxygen on free radical formation Oxygencan modify the reaction by enabling creation of other free radical species with greater stability and longer lifetimes H0 + O2  HO20(hydroperoxy free radical) R0+ O2 RO20(organic peroxy free radical)

11. Reactions with free radicals H0 + OH0 H2O H0 +H0  H2 OH0 +OH0  H2O2 RH + OH0 R0 + H2O RH + H0 R0+ H2 R0 + OH  ROH R0 + H  RH R0 + O2 ROO0 ROO0 + RH  ROOH + R0

12. Lifetimes of free radicals HO2o RO2o Ho OHo 3nm OHo Ho Because short life of simple free radicals (10-10sec), only those formed in water column of 2-3 nm around DNA are able to participate in indirect effect

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 Base damage: 1000-2000 per 1 Gy Single-strand breaks 500-1000 per 1 Gy Double strand breaks 40-50 per 1 Gy

18. Mechanisms of base excision and nucleotide excision repair

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

20. DNA restoration failure Unrejoined DNA double strand breaks Incorrect repair ofDNA damage Cytotoxic effect Mutations

21. Radiation induced membrane damage

22. Effect of radiation on cells

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

24. Cell cycle

25. Radiosensitivity of cell in cell cycle M G1 S G2M Relative survivability of cells irradiated in different phases of the cell cycle:synchronised cellsin late G2 and in mitosis (M)showed greatest sensitivity to cell killing

26. Mitotic death NORMAL IRRADIATED

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

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

29. Morphological forms of cell death • 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

30. Changes of cell metabolism and function • 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.

31. Radiation induced chromosome damage Chromosomes

32. Radiation induced chromosomal aberrations

33. Relative cellular radiosensitivity • 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.

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 • 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 EnergyAgency (IAEA), kindly given by doctor Elena Buglova, were used