Alzheimer's disease is a progressive brain disease that eventually strips sufferers of their ability to remember, communicate and live independently. By 2050, it is projected to affect nearly 14 million Americans and their families, with an economic cost of one trillion dollars - more than the estimated combined total for treating heart disease and cancer.
Where there's smoke
Mouse modelsFor the laboratory studies, we exposed female mice with Alzheimer genes to nano-sized air pollution for 15 weeks. The air particle collection technology, invented by our colleague Constantinos Sioutas from USC's Viterbi School of Engineering, collects air particles from the edge of USC's campus as a representative air sample from urban areas. The experimental data showed that mice systematically exposed to this particulate matter accumulated larger deposits of proteins called beta-amyloid in their brains. In humans, beta-amyloid is considered as a pathological driver of neurodegeneration and is a major target of therapeutic interventions to prevent the onset of Alzheimer's or slow its progress. Similar to our epidemiologic observation in older women, these effects were stronger for APOE4 female mice, which are predisposed to Alzheimer's disease.
Future studiesOur future studies will look at whether these findings also apply to men, and whether any drugs under development may provide protection against air pollution exposure. More work is also needed to confirm a causal relationship and to understand how air pollution enters and harms the brain. Brain aging from exposure to air pollution may start at development, so we also want to look at early life exposure to air pollution in relation to Alzheimer's disease. We already know that obesity and diabetes are Alzheimer's risk factors. We also know that children who live closer to freeways tend to be more obese, an effect that is compounded if adults in the household are smokers. Based on existing mouse models, one would predict that developmental exposure to air pollution could increase risk for Alzheimer's disease. This is an important piece of the scientific puzzle that we'd like to better understand.
Air pollution, public health and policiesAir pollution knows no borders. This gives our study global implications that should be taken seriously by policymakers and public health officials. The Clean Air Act requires the Environmental Protection Agency to develop National Ambient Air Quality Standards that provide an adequate margin of safety to protect sensitive populations, such as children and the elderly. In 2012 the EPA tightened the U.S. standard for PM2.5. Nonetheless, in 2015 nearly 24 million people lived in counties that still had unhealthful year-round levels of particle pollution, and over 41 million lived in counties that experienced short-term pollution spikes.Recent studies have shown that the prevalence of dementia in the United States declined between 2000 and 2012. However, we don't know whether this trend is connected to air pollution regulations, or if exposures to lower levels of PM2.5 in recent years still pose some degree of long-term threat to older Americans, especially those at risk for dementia. If long-term PM2.5 exposure indeed increases the risk for dementia, this would imply that public health organizations are underestimating the already large disease burden and health care costs associated with air pollution. For instance, the World Health Organization's latest assessment of the global burden of disease caused by PM2.5 does not include dementia. Air pollution levels are much higher in India, China and many other developing nations than U.S. levels.
Similarly, EPA has estimated that the Clean Air Act will provide almost US$2 trillion in benefits between 1990 and 2020, much of it from reduced deaths and illnesses. If there is a connection between particulate pollution and dementia, the Clean Air Act may be providing even larger benefits than EPA's estimate. The U.S. National Plan to Address Alzheimer's Disease, which was mandated by legislation enacted in 2011, aims to prevent or effectively treat Alzheimer's disease by 2025. We believe any measures that undermine EPA's operation or loosen clear air regulations will have unintended consequences that will make it challenging to meet this goal.Caleb Finch, University Professor, Leonard Davis School of Gerontology, University of Southern California and Jiu-Chiuan Chen, Associate Professor of Preventive Medicine, University of Southern California This article was originally published on The Conversation. Read the original article.