Technology Solutions
An array of possibilities for evaluating environmental health New technologies emerging from the the scientists interviewed for this rapidly developing field of genomics article agreed. could revolutionize the study of how The new technologies being used pollutants impact human health. Beby environmental health scientists are cause the costs of using these technola byproduct of the efforts to characogies are decreasing steadily, a growing terize the entire sequence of DNA in number of researchers are exploring humans and other organisms. A numtheir applications for environmental ber of entrepreneurial high-tech comhealth, although some important ispanies, including Affymetrix, Gene sues still need to be addressed. Logic, and Incyte, now offer a variety of DNA data sets on silicon chips or Genomics technologies are already microscope slides, which have come being used for toxicology, the study of to be called microarrays. how poisons injure people and animals. Researchers involved with key aspects of environmental epidemiology, the study of how exposure to pollutants and chemicals can cause disease, plan to begin using these technologies in the next year. By elucidating what is happening at the cellular level, many scientists believe that these technologies may provide valuable insight into some of the thorniest problems associated Mass manufacturing of gene array chips is allowing with studying how pollutants for environmental health applications. impact people animals and ecosvstems said David Dix Microarrays are used extensively by bioloeist in the ReproducuVe Toxicolthe pharmaceutical industry for drug oev Division of EPA's National Health discovery and for assessing the potenand Environmental Effects Research tial toxicity of novel compounds, acLaboratory (NHEERD cording to Katherine Call, head of molecular genomics for Aventis Historically, toxicologists and epiCambridge Genomics Center, a drug demiologists have struggled to exdiscovery firm in Cambridge, MA. trapolate from the high doses used More recendy, government researchin the lab to the low levels of polluers have begun developing their own tion to which people are actually microarrays for public use (Environ. exposed. Evaluating data from Sci. Technoll 2000, 34 4(1), 244r-245). chronic exposures and dealing with the groups of everyday chemicals to The key assumption behind efwhich people are routinely subjected forts to apply technologies like miare also major challenges for envicroarrays to environmental health is ronmental health scientists. The new that exposure to environmental technology holds promise for all agents like pollutants can affect huthese complicated endeavors, and it mans and other organisms at the cellular level, causing mutations in day provide a means of an organism's DNA that may result proving that exposure to one particin cancer or immune dysfunction, ular chemical is of disease 2 9 6 A • JULY 1, 2000 /ENVIRONMENTAL SCIENCE & TECHNOLOGY /NEWS
explained Cynthia Afshari, codirector of the Microarray Center run by the National Institute of Environmental Health Sciences (NIEHS). To use these techniques, researchers isolate messenger RNA (mRNA), the genetic material involved in creating proteins, from cell cultures or tissues from humans or animals. To compare how exposure to a pollutant may change gene expression, they harvest mRNA from tissue or cell samples that have been exposed to the pollutant as well as mRNA from an untreated control population. By generating the DNA associated with that mRNA and applying it to the miCIO 3XT3V researchers can compare the gene expression caused by the two samples by looking for DNA matches Thus far, the most welldeveloped environmental application of these microarray techniques is in the area of toxicology. Researchers at NIEHS have already used microarrays to identify a new gene associated with exposure to the dioxin TCDD (2,3,7,8-tetrachlorotheir use p-dioxin), and they are currently using the techniques to study the genetic changes associated with chronic exposure to arsenic Afshari said At NHEERL, EPA researchers have created microarrays containing DNA from genes linked to endocrine-disrupting chemicals, male fertility genes, and "stress" genes like the cytochrome P450s, which are activated in response to a wide range of toxic exposures, Dix said. "Arrays have the potential for assisting with dose and species extrapolation and for identifying sensitive subpopulations," he explained. Dix is using the arrays to evaluate the chemical byproducts generated when water is disinfected with chlorine. Some of these byproducts, like bromochloroacetic acid, can be toxic to mammalian sperm, he explained. © 2000 American Chemical Society
To tease out the safe levels of the chemical in drinking water, researchers are comparing gene expression patterns at the lowest dose of bromochloroacetic acid shown to reduce fertility with the highest dose of the disinfection byproduct that does not affect fertility in mice and rats. If the altered gene expression patterns prove to be similar at these two dose points, it may indicate that séne expression is a faster and more sensitive indicator of adverse effect on fertility than the traditional method of mating mice and counting fetuses Dix said. The researchers are also investigating whether they can link altered gene expression patterns to individual susceptibilities Microarrays hold promise in the field of transitional epidemiology, which focuses on the period between when someone is exposed to a potentially harmful chemical and when it is apparent mat they have a disease. At the University of Vermont's medical school in Burlington, VT, scientists are planning to use microarrays to study the placentas of low-birthweight babies whose mothers were exposed to serious air pollution in the Czech Republic, said Richard Albertini, a professor of medicine at the University of Vermont's Genetic Toxicology Laboratory The Vermont researchers will evaluate gene expression in the placentas to see how it correlates with exposure to air pollution and the baby's health, he explained. The data might help reveal whether the exposure ultimately results in disease, he said. It is possible that the data could also enable researchers to find a biomarker (a consistent change in gene expression) that can serve as surrogate for the detailed information that researchers traditionally collect to show exposure, Albertini said. "There's even a hope that we could use die biomarker responses that we get in people in occupational settings, when we know the exposure, as endpoints to check out physiologically based toxicokinetic models derived from animals," Albertini said. "Humans could, in that sense, be better integrated into toxicology. Rather than standing by itself, molecular epidemiology could actually overlap with toxicology," he said. The first use of microarrays in a traditional epidemiological study is slated to take place later this year, ac-
cording to Paolo Boffetta, chief of the Environmental Cancer Epidemiology unit at die International Agency for Research on Cancer (IARC) in Lyon, France. IARC scientists are building "home-made" arrays to study cancers of the lung, head, neck, and kidney in Central Eastern Europe, he explained. After the arrays are completed, which Boffetta predicts will be by October the scientists plan to use them to evaluate the gene expression changes associated with human exposure to asbestrie*
And for all of the promise of microarrays, there are still some crucial issues to be worked out. For example, humans are extremely genetically diverse, but the challenge of accurately representing that diversity is an issue tiiat has yet to be addressed by me companies offering human DNA arrays said Seymour Garte of the toxicology division of the Environmental and Occupational Healtii Sciences Institute at the Robert Wood Johnson Medical School of Piscatawav NJ Scientists do not even know whetiier analyzing the same Derson's RNAfivetimes will alwavs nroduce the same result hp nninted out
polycyclic aromatic hvdrocarbons in the workDlace; heaw metals such as chromium arsenic and nickel; and some organic chemicals and solvents like frirhloropthvlpne and Once such issues are Boffetta said that his ironed out, data from Microarrays can be used to microarrays may be used researchers had used manual methods for gaug evaluate toxic chemicals in regulatory decisions, like dioxins. ing gene expression in Dix predicts. The Interprevious studies, but the national Life Sciences size of the population they intend to Institute, U.S. EPA, NIEHS, and the study in Central Eastern Europe— U.S. Food and Drug Administration approximately 11,000 subjects— are already collaborating to develop made it necessary to embrace faster guidelines for using microarrays for techniques like microarrays. The reassessing drug toxicology. Dix believes searchers already know which geries that mis could pave die way for using they want to home in on for each of the technology for environmental the cancers, and a major goal of the health toxicology. In two or three research will be to identify "high-risk years how to use data from microargenotypes" and if they match rays will be a high-profile issue in risk expectations Boffetta said. assessment he speculated. "We know that some carcinogens In the meantime, scientists like cause cancer, but only with a certain Boffetta and Albertini say that they degree of probability," Boffetta said. expect to find ways to validate the "By looking at different types of canutility of the arrays for use in epidecer and the expression of different miology and reduce die incidence of genes and which genes are mutated, potential problems like false posiwe might be able to find much more tives. They are also hoping to beef specific associations with environup some of the associated "bioinformental exposures." matics" tools needed to make sense of microarray data. The scientists interviewed for this article agreed diat one of die advan"Eventually, I would hope mat we tages of microarrays was their ability could substitute molecular endpoints to show the action of more man one for diseases, so you don't have to wait gene at a time. But to use microarrays for cancer outcomes or birth defects, effectively, Albertini stressed, it is crubut rather you can monitor people cial to choose die right tissue to study. witii a biomarker," Albertini said. He Easily obtainable material like red and foresees a day when genetic biomarkwhite blood cells may not provide iners might be monitored in the same formation on gene expression in tissues way as cholesterol and hormone levels from important organs like die liver, are currently watched by die medical lung, and pancreas, he cautioned. community. —KELLYN S. BETTS JULY 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 9 7 A
