By Kelly A. Reynolds, MSPH, PhD
Genetic profiling
New, high-throughput technologies in the molecular sciences paved the way for an explosion in genetic profiling and disease diagnostics. DNA testing has become a big business, where personal genomic profiles are used to trace family history, profile one’s ancestry and connect long-lost relatives. An emerging field of science, known as -omics research, uses complete genetic or molecular profiles of people that can reveal historical information and predict future health outcomes.
Most of us are familiar with heritable genetic traits, passed down from our parents or grandparents, such as similarities in our physical appearance or disorders, like diabetes or certain types of cancer that “run in the family.” Genomics, however, can be used to define environmental influences on current or future health outcomes. Specifically, the field of epigenetics refers to external modifications to DNA that either promote or prevent gene expression (e.g., the act of genes turning on or off). Exposure to certain chemicals, stress and even heat can cause changes in epigenetic regulations. Diet, exercise and smoking can also affect gene expression. Depending on the function of the gene, turning it on or off could be beneficial or harmful. Further, these environmentally induced changes could then be transmissible from parents to their offspring.
Environmental impacts on gene function
Essentially, epigenetics is the study of how your environment and behaviors can change the way your genes work. These changes continue to occur over a lifetime and just as scientists have mapped the entire human genome, we are beginning to map patterns of expression in specific genes that are linked to environmental hazard exposures and/or behaviors. Table 1 lists common types of epigenetic changes.
Some epigenetic changes are reversible. For example, DNA methylation patterns in specific gene sites, known as the AHRR gene, are predictive of smoking exposures.1The differences are more dramatic in heavy and long-term smokers. After quitting smoking, however, DNA methylation of the AHRR gene increases over time and in some cases, can fully recover to the levels of non-smokers in less than a year. Understanding how genes are turned off and on could lead to the discovery of targeted treatments to prevent or cure diseases. These targeted treatments might be tailored to the specific individual as in the emerging field of precision medicine.
The arsenic example
Arsenic is a federally regulated contaminant in drinking water that comes from both natural and industrial sources. According to the World Health Organization, millions of people around the world are exposed to dangerous levels of arsenic in drinking water, including residents in Argentina, Bangladesh, Chile, China, India, Mexico and the US. The agency has, in fact, listed arsenic as one of the 10 chemicals of major health concern and estimates that at least 140 million people in 50 countries have been drinking arsenic contaminated water above the maximum guidance value of 10 µg/L.2
Chronic exposure to arsenic through ingestion is known to cause a variety of respiratory conditions, including lung cancer. When children are exposed to arsenic early in life, DNA-directed functions are altered, leading to a chain of events that impair lung function. These impairments can affect life quality and quantity. Concerns are evident even before birth as data is now showing that children exposed to arsenic while in the womb also present with impaired lung function.3 Lung disease is only one adverse health outcome. Lower birth weight, increased infant mortality and neurological and intellectual impairment have also been traced to arsenic exposures during pregnancy. The adverse outcomes are traced back to specific genes that promote inflammation and a cascade of events later in life.
In a recent study, researchers identified proteins in humans that were associated with arsenic exposures in drinking water and a higher probability of lung cancer.4 This study supported previous research where humans and mice that consumed water with low levels of arsenic (concentrations ranging from 10-50 µg/L) exhibited modifications in the gene expression of proteins related to wound repair in the respiratory tract.5 Prior to the use of -omics research, health effects were evaluated in populations with high-dose exposures and outcomes were extrapolated to low-dose scenarios. The ability to directly monitor biomarkers and protein functions at the cellular level have increased our sensitivity in detecting adverse health outcomes with the more common low-concentration exposures.
Patterns of change
Patterns of epigenetic changes can be found that indicate specific hazard exposures. Genetic markers of exposure to drinking water contaminants have been identified for other water pollutants, including DBPs and tricholoroethylene (TCE). More studies are needed comparing gene expression profiles in populations exposed to carcinogens in water – or perhaps profiling persons with and without POU water treatment devices. It is feasible that in the future we will be able to run whole genome profiles to routinely determine current exposures and risks. Such information can be used to make more informed decisions about the need for improved water treatment options.
References
- McCartney DL, Stevenson AJ, Hillary RF, et al. Epigenetic signatures of starting and stopping smoking [Internet]. EBioMedicine 2018; 37:214–220[cited 2021 Apr 12] Available from: https://pubmed.ncbi.nlm.nih.gov/30389506/
- World Health Organization: Arsenic [Internet]. 2018; [cited 2018 Dec 10] Available from: http://www.who.int/en/news-room/fact-sheets/detail/arsenic
- Gonzalez-Cortes T, Recio-Vega R, Lantz RC, et al. DNA methylation of extracellular matrix remodeling genes in children exposed to arsenic. Toxicol Appl Pharmacol 2017; 329:140–147
- Vega-Millán CB, Dévora-Figueroa AG, Burgess JL, et al. Inflammation biomarkers associated with arsenic exposure by drinking water and respiratory outcomes in indigenous children from three Yaqui villages in southern Sonora, México. Environ Sci Pollut Res 2021;
- Olsen CE, Liguori AE, Zong Y, et al. Arsenic upregulates MMP-9 and inhibits wound repair in human airway epithelial cells [Internet]. Am J Physiol Cell Mol Physiol 2008; 295:L293–L302 [cited 2021 Apr 12] Available from: https://www.physiology.org/doi/10.1152/aj-plung.00134.2007
About the author
Dr. Kelly A. Reynolds is a University of Arizona Professor at the College of Public Health; Chair of Community, Environment and Policy; Program Director of Environmental Health Sciences and Director of Environment, Exposure Science and Risk Assessment Center (ESRAC). She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at [email protected]