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Vol.12, Nos.1-2   February 2002

Understanding Health Risks from Low Doses of Ionizing Radiation

The Low Dose Radiation Research Program (http://lowdose.tricity.wsu.edu/) supports basic research to help characterize risk from exposure to low levels of ionizing radiation. This program is possible because of scientific advances in both genomics and technology over the past 10 years. Recognizing the importance of using these new and exciting tools and techniques, Congress requested in 1998 that DOE initiate a 10-year basic research program to support science that will underpin future risk-assessment standards and guidelines.

Epidemiological and toxicological research has long been used to characterize health responses by populations and individuals to high radiation doses and to set exposure standards that protect the public and the workforce. Standards for low radiation doses are determined from the number of cancers observed after high dose exposure. Models extrapolate this number to predict unmeasurable and unvalidated cancers following low radiation doses.

Recent advances, however, allow direct measurements of biological changes in cells and molecules after environmentally relevant radiation exposures. Such capabilities will enable regulators and policymakers to develop radiation-exposure standards based on a strong scientific and mechanistic foundation rather than on extrapolation.

One new tool is microbeam technology, which is being used to expose individual cells or cell parts—the nucleus, cytoplasm, or their specific regions—to a wide range of radiation energies (from heavy ions to electrons) and doses (including the ultimate low dose, a single ion).

New genomic technologies and data now allow scientists to measure the biological effects of radiation at the level of individual genes. This capability will enable the identification of genes critical for cancer development and the determination of their activities during radiation-induced carcinogenesis. The magnitude and spectrum of gene-expression changes hold important clues for understanding the mechanisms of radiation-induced cancer. Expression changes induced by high radiation doses in a specific subset of 10,000 to 15,000 genes can be compared quickly with those induced by low doses.

Biological effects also are being studied using new proteomics approaches. These techniques evaluate the types, activities, and configuration of proteins produced in cells in response to both high and low doses of radiation.

Some important questions to be addressed with these tools include the following: Are the cellular effects induced by different radiation doses identical at the molecular level, varying only quantitatively in proportion to dose? Do cells recognize changes induced by low radiation doses the same way they recognize changes induced by high doses? Do cells, tissues, and whole organisms each respond in a qualitatively similar wayto different levels of radiation?

What biological mechanisms are responsible for the bystander effect, in which unirradiated neighbors of exposed cells can exhibit biological responses as if they too had been irradiated? Similarly, what mechanisms lead to other phenomena such as the adaptive response and genomic instability?

Using emerging biological data to provide answers to these questions and help predict health risks is itself a difficult but crucial challenge requiring the development of appropriate mathematical models. The scientific foundation built upon these new data will be critical in adequately and appropriately protecting people from radiation and in making the most effective use of the nation’s resources.

Program funding was $18.5 million for FY2001. The programs home page includes solicitations for new research, frequently asked questions, and project descriptions.

Antone Brooks, Washington State University Tricities (tbrooks@tricity.swu.edu) and David Thomassen, DOE (david.thomassen@science.doe.gov)

FYI: Ionizing radiation has enough energy to remove one or more electrons from atoms it encounters, creating charged particles (ions) inside living cells. These ions can damage key substances in cells, including DNA, and can lead to cancer or other defects. People may be exposed to radiation through their occupations; such medical procedures as X rays and radiotracers; and natural background radiation from cosmic rays, radon, radium, and other radioactive materials.

The electronic form of the newsletter may be cited in the following style:
Human Genome Program, U.S. Department of Energy, Human Genome News (v12n1-2).

Human Genome Project 1990–2003

The Human Genome Project (HGP) was an international 13-year effort, 1990 to 2003. Primary goals were to discover the complete set of human genes and make them accessible for further biological study, and determine the complete sequence of DNA bases in the human genome. See Timeline for more HGP history.

Human Genome News

Published from 1989 until 2002, this newsletter facilitated HGP communication, helped prevent duplication of research effort, and informed persons interested in genome research.