Non-Targeted effects of Radiation: Implications for Low Dose Exposures

1. Non-Targeted effects of Radiation:Implications for Low Dose Exposures John B. Little Center for Radiation Sciences and Environmental Health Harvard School of Public Health

4. Potential risks at doses < 100 mSv • So Called Dirty Bombs • Scatter from Radiation Therapy • Diagnostic X-rays: CT Scans

5. August 1, 2010 by Walt Bogdanich

6. Factors that May Modify Radiation Effects at doses <0.1Gy 1. Gene Expression - Differs after high vs. low dose irradiation 2. Adaptive Response 3. “Non-Targeted” Effects of Radiation - Radiation-Induced Genomic Instability - Bystander Effect: cell to cell communication 4. Differences in Radiosensitivity among Individuals

7. TRADITIONAL THINKING Biological effects of radiation occur in irradiated cells as a consequence of the DNA damage they incur.

8. IMPLICATIONS • Biological effects occur in irradiated cells. • Radiation traversal through the nucleus of the cell is a prerequisite to produce a biological response. • DNA is the target molecule in the cell.

9. EVIDENCE FOR NON-DNA TARGETED EFFECTS OF RADIATION • Radiation-induced genomic instability. • Bystander effects. • Genetic effects produced by cytoplasmic irradiation.

10. RADIATION-INDUCED GENOMIC INSTABILITY • Radiation enhances the rate at which biological effects, including elevated frequencies of mutations and chromosomal aberrations, arise in the descendants of irradiated cells.

11. X X X X X X X X X X X X X X X • DIRECT RADIATION INDUCED MUTATIONS • Rare low frequency event • Predicts linear dose-response relationship

12. X X X X X X X • RADIATION INDUCED GENOMIC INSTABILITY • mutations arise in the descendents of irradiated cells • high frequency event • saturates at low doses • ?threshold phenomenon

13. RADIATION-INDUCED GENOMIC INSTABILITY • Genetic effects, such as mutations and chromosomal aberrations, arise in the distant progeny of irradiated cells. • Induction of such instability is a high frequency event. Saturates at low doses. • The induced mutations are different from those arising in directly irradiated cells.

14. BYSTANDER EFFECT • In a mixed population of irradiated and non-irradiated cells, biological effects arise in those cells that receive no radiation exposure (“bystander cells”)

15. Radiation-Induced Bystander Effect in Cell Cultures Irradiated by Very Low Fluences of -Particles Sister Chromatid exchanges Gene Expression Mutations Chromosomal Aberrations a

16. Sister Chromatid Exchanges Induced by Exposure to Very Low Fluences of -particles 0.15 0.10 Induced SCE per Chromosome 0.05 0.00 0 1.2 2.4 3.6 4.8 Mean Dose (mGy) 0 0.005 0.01 0.02 Tracks / nucleus Nagasawa and Little 1992

17. In situ Immunofluorescence detection of p21WAF1 expression in a-irradiated human cell cultures

18. . . C C 0.13 cGy . P21waf1 expression in confluent AG1522 cell cultures exposed to low fluence -particles:Extent of propagation of the bystander effect

19. BYSTANDER EFFECT • How are damage signals transmitted from irradiated to non-irradiated cells?

20. DIRECT CELL TO CELL COMMUNICATION • Connexin43 mediated Gap-Junction intercellular communication • For intercellular communication, the “gap junction” is one of the most widespread mechanisms, being found in most animal tissues and perhaps all animal species.

21. 0 cGy/Lindane 0.3 cGy 0.3 cGy/Lindane p21WAF1 expression in -particle irradiated cell cultures in the presence or absence of Lindane Azzam and Little, 2001

22. competent cells deficient cells 0 cGy 0.3 cGy 0 cGy 0.3cGy p21WAF1 expression in gap junction communication competent or deficient cells

23. Gene Expression by cDNA Microarray Analysis In -particle Irradiated Human Fibroblast Cultures 1 cGy Connexin-43

24. Regulation of Gene Expression in a-Irradiated Human Fibroblast Cultures • GenBankGeneFold • Symbol • HSCGJP Connexin43 5 • D79205 Ribosomal protein L39 4.5 • HUMPRP Prion protein 3.1 • HSU09953 Ribosomal protein L9 3.1 • D49817 Phosphofructokinase 2.9 • HSVPAM92 Proton ATPase subunit 2.8 • HSRPL31 Ribosomal protein L31 2.6 • HSL21PROT Ribosomal protein L21 2.6 • HUMTHYB4 Thymosin beta-4 2.6 • S45630 Alpha B-crystallin 2.5 • HSU14968 Ribosomal protein L27a 2.4 • HSRPRNA Ribosomal protein 2.4 • HSU54778 14-3-3-epsilon 2.4

25. 0 .16 .6 3 10 cGy cx43 -tubulin CONNEXIN43 is up-regulatedin -irradiated Cell Cultures Western: 0 . 16 .6 3 10 cGy cx43 -tubulin

26. gamma-rays Control Gamma radiation up-regulates expression of Connexin43

27. 1.DAMAGE SIGNALS ARE TRANSMITTED FROM IRRADIATED TO NON-IRRADIATED CELLS VIA GAP JUNCTION COMMUNICATION 2. RADIATION CAN ACTUALLY ENHANCE INTERCELLULAR COMMUNICATION 3. THESE EFFECTS MAY OCCUR AND SATURATE AT LOW DOSES, LEADING TO NON-LINEARITY OF THE DOSE RESPONSE RELATIONSHIP.

28. Non-Targeted Effects May Influence Non-linearity at Low Doses • Radiation Induced Genomic Instability • ? Threshold phenomenon at low doses • Saturates at 100-200 mSv • Occurs in in vivo systems • Bystander Effect • High LET particulate Radiation (radon exposure) • Non-homogeneous distribution of radionuclides • Importance for x-ray exposure under investigation

30. a-particle induced HPRT mutations (high doses)

31. Mutations induced by low-dose a-irradiation