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Radiological Science in the Context of Radiological Terrorism Basics of Ionizing Radiation Effects Charles R. Geard Center for Radiological Research Columbia University 1 Radiation and Life In the context of this conference αparticles are important only when radioactive material is inhaled or ingested. β-rays – only when ingested or skin X- and γ-rays – external radiation Neutrons – nuclear explosion Quantities and Units Dose – Measured Physical Quantity Old unit – rad New unit – Gray (Gy) 1 Gy = 100 rad 2 Quantities and Units Equivalent Dose – Calculated Quantity The same dose of different radiations does not produce the same biological effect. Equivalent dose = dose x radiation weighting factor (WR). WR = 20 for α-particles and some neutrons. Old unit – rem New unit – Sievert (Sv) 1 Sv = 100 rem Quantities and Units Effective Dose – Calculated Quantity Different organs vary in radiosensitivity; e.g., thyroid, breast and colon are more sensitive than extremities. Old unit – rem New unit – Sievert (Sv) 1 Sv = 100 rem 3 Doses to the U.S. Population Exposure to Natural Radiation 4 Radiation Exposure Due to Human Activity Average Effective Dose in U.S. (3.6 mSv/yr) 5 Ionizing Radiation(s) Able to ionize atoms – i.e., knock an electron out of orbit. Able to break chemical bonds and disrupt the large molecules that living things are made of. Ionizing Radiation The biological effect results, not from the total energy absorbed, but from the energy of the individual charged particle or photons of γ-rays. 6 Total Body Irradiation Mass = 70 kgm. LD/50/60 = 4 Gy. Energy absorbed = 70 x 4 = 280 Joules = 280 = 67 calories. 4.18 Drinking Hot Coffee Excess temperature (°C) = 60° - 37° = 23° Volume of coffee consumed to equal the energy in the LD/50/60 = 67 = 3 ml = 1 sip 23 7 Chain of Events Time Scale incident x-ray photon ↓ fast electron ↓ ion radical ↓ chemical changes due to the breakage of bonds ↓ biological effects 10-15 sec ↓ -5 10 sec ↓ days, years or generations RADIATION BIODOSIMETRY Dose Predictive Assays How much radiation has a person/cell received? Center for High-Throughput Minimally-Invasive Radiation Biodosimetry Radiation Dose Home Land Security – Dirty Bombs! Biological Response 8 BIOLOGICAL RESPONSES TO IONIZING RADIATION Cell Death Apoptosis Gene Mutation Chromosomal Aberrations Micronuclei A N D ! e g a m a D Changes in Levels of Specific Gene Products Others……… Direct and Indirect Action 9 DNA – Double Strand Break Biological Effects of Radiation Cell Killing – division of damaged chromosomes – Relevant to radiotherapy. – Cause of some effects on the embryo & fetus at low doses, and to adults at high doses. Mutation in Germ Cells - altered chromosomes – Hereditary consequences expressed in later generations. Carcinogenesis or Leukemogenesis – Chromosomal changes and/or mutations in dividing somatic cells. 10 Cell Killing Conventional Radiology – Doses too small to cause discernible cell killing (<10 cGy). Radiological event – Doses sufficient to cause erythema and possibly necrosis need to be greater than 1 Gy (e.g. an atomic bomb). Cellular consequences of radiation exposure Cell cycle arrest (cells stop dividing) • Temporary or permanent • Changes in gene products DNA repairNo change AlterationsViable or lethal Cell Death • Apoptosis or necrosis 11 Damaged Chromosome Reproduction Errors Dicentric Chromosome in a Peripheral Lymphocyte 12 Chromosome Translocation in Chronic Myeloid Leukemia 13 Complex inter-chromosomal translocation multiplex FISH Combined FITC SPECTRUM O TEXAS RED Cy5 DEAC 14 Radiation and Cell Damage Radiation breaks chromosomes. DNA breaks repair or mis-repair. Mis-repaired chromosomes can lead to abnormal cell division Cells die and are removed when they attempt to divide – micronuclei and nucleoplasmic bridges Carcinogenic change only expresses in dividing cells – translocations and small deletions Until then cells are present and can function. Radiation Dose Dose Response Biological Response Larger the Dose – Greater the Biological Response 15 Radiation Biodosimetry Irradiation of human peripheral blood lymphocytes • Separate lymphocytes from whole blood • Split culture: process for micronucleated cells, DNA damage foci, gene expression • Harvest RNA after 24 hours, compare on microarray • Follow-up of induced genes • ALL ENDPOINTS • Reproducibility in multiple donors • Time-course of response • Dose-response relationship 16 Aberrations per Cell Based on DNA Damage 17 γ-H2AX foci per cell γ-H2AX foci • Radiation causes gene expression changes • Gene expression changes underlie many cellular responses • We can now study changes in gene expression across the whole genome • Gene expression profiles may soon provide useful information for biodosimetry 18 Stress Signaling Pathways cytokine receptors ionizing radiation cell surface cera cytokines and bystander signals mide activation PKC Protein modifications plasma membrane NFκB MAPK (p38, JNK) c-Abl caspases DNA-PK Gene expression changes (Functional Genomics) ATM p53 DNA DNA damage ionizing radiation Altered cellular function nucleus Relative Expression Gene induction in PBL persists at least two days 24 hours post-irradiation 8 48 hours post-irradiation 8 DDB2 6 4 CDKN1A 6 XPC 4 2 DDB2 CDKN1A XPC 2 0 0 50 100 150 200 Dose (cGy) 0 0 50 100 150 200 Dose (cGy) Amundson et al., (2000) Radiation Research, 154 (3): 342-346 19 Developing gene expression for biodosimetry Blood sample Array Profile Integrated profiling cassette Dose Assessment - triage Informatic Analysis Compare Profile To Database Radiation biodosimetry in the event of population radiation exposure. Requirements: Speed Accuracy Longevity DNA damage and cytogenetic assays DNA based foci Chromosomal domain alterations Micronuclei and nucleoplasmic bridges Chromosomal aberrations 20 21