x-ray lung cancer
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African Americans and Latinos who smoke can develop specific epigenetic changes putting them particularly at risk for cancer says research that comes from one of the largest multiethnic studies yet of smoking’s influence on cancer risk.

Researchers from the Keck School of Medicine analyzed the link between smoking and DNA methylation. The study included data from 2,728 people across six distinct racial and ethnic groups. Researchers found 408 DNA methylation markers (CpG sites) related to smoking, including two that differed depending on race or ethnicity.

Their results were published in the American Journal of Human Genetics.

One site on the gene CYTH1 only showed changes in African American people who smoked; another site on MYO1G was more strongly linked with epigenetic changes in Latinos who smoked, compared to other racial and ethnic groups. Those genes performed functions that relate to cancer progression and other disease processes.

“We know that smoking affects people differently based on their race and ethnicity, but identifying epigenetic signatures of smoking would help us better predict risk for smoking-related diseases,” said Brian Huang, PhD, an assistant professor in the department of population and public health sciences at the Keck School of Medicine of USC and first author of the new study.

These researchers quantified smoking by calculating participants’ total nicotine equivalents (TNEs), a biological measure of nicotine uptake that measures levels of nicotine and several other metabolites of cigarette smoke with a urine sample. That enabled a more accurate calculation of smoking dose compared to much of the existing research, which relies on self-reported measures.

“This study gives us some additional information about the mechanism by which smoking can affect health, and how that could differ across various populations,” Huang said. “Ultimately, that can lead to better prediction, early detection and treatment for smoking-related conditions.”

The research team used data from the Multiethnic Cohort Study, a collaboration between USC and the University of Hawaii that includes African Americans, European Americans, Japanese Americans, Latinos and Native Hawaiians. Using biological samples from 1,994 participants, the researchers determined each person’s smoking dose (by measuring TNEs), as well as the levels of DNA methylation at CpG sites across the genome (through an epigenome-wide association study, or EWAS).

Across the epigenome, smoking was linked to DNA methylation at 408 sites. That total includes 45 new sites that were not identified in previous studies that relied on self-reports of smoking behavior.

“This gives us an indication that TNEs can provide more information beyond what we already know from self-reported measures of smoking,” Huang said.

To further confirm their findings, Huang and his team collected TNE and DNA methylation data from two other groups of participants: 340 people in the Singapore Chinese Health Study and 394 people in the Southern Community Cohort Study. The researchers identified many of the same CpG sites found in the Multiethnic Cohort Study, including the sites most strongly associated with TNEs. That provides evidence that the strongest epigenetic markers of smoking are consistent across multiple racial and ethnic groups, Huang said.

In their next study, the researchers will conduct an EWAS of DNA methylation and lung cancer risk: How do epigenetic changes increase a person’s risk for lung cancer?

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