With just a sample of human hair, scientists can now detect the presence of a chemical, derived from a person’s diet, that can cause DNA mutations. This was just one of several biomarker stories presented by Robert Turesky, Ph.D., at the NIEHS Keystone Science Lecture Seminar Series. Turesky spoke July 31 on “Novel Approaches to Assess Exposures to Hazardous Chemicals in the Diet.”
Turesky, an analytical chemist at the University of Minnesota, uses highly sensitive mass spectrometry equipment to detect hazardous chemicals in biological samples.
“His work is at the interface of exposure assessment and biological response, applying new technologies to understand the impact of environmental exposures on health outcomes,” said David Balshaw, Ph.D., who hosted Turesky’s seminar. Balshaw leads the NIEHS Exposure, Response, and Technology Branch.
Turesky focused on two dietary chemicals that have been linked to increased risk of cancer in humans — a compound called PhIP, which is formed when meat is cooked at high temperatures and allows certain chemicals naturally occurring in the meat to react with each other; and aristolochic acid, which comes from the herb Aristolochia clematitis.
Hair reveals meat consumption
When PhIP is metabolized, it reacts with DNA to form a type of damage called a DNA adduct. PhIP-DNA adducts are important because they may cause mutations and can lead to the onset of cancer. “Some DNA adducts can persist for years following exposure,” Turesky said.
Dissatisfied with estimates of exposure to PhIP that were based on questionnaires about how often a person ate certain foods, Turesky began analyzing hair. He showed that PhIP, which sticks to the pigment melanin, was easily detected in hair from omnivores but could barely be detected in hair from vegetarians.
In a follow-up study, Turesky and colleagues concluded that levels of PhIP in hair may be used as a biomarker of dietary exposure in studies of disease risk. Exposure to PhIP has been associated with an increased risk of colon cancer and, more recently, prostate cancer.
The International Agency for Research on Cancer characterized PhIP as possibly carcinogenic to humans. The National Toxicology Program’s Report on Carcinogens lists the compound as reasonably anticipated to be a human carcinogen.
Global footprints of a dietary carcinogen
The cause of a kidney disease particular to the Balkans was a mystery until a group of researchers, including Turesky, showed that exposure to aristolochic acid was the culprit. Aristolochic acid found its way into the food supply through bread contaminated with Aristolochia clematitis, a weed accidentally harvested along with wheat grown in the area.
Endemic (Balkan) nephropathy (EN) involves chronic kidney failure and is strongly associated with cancer of the upper urinary tract. The DNA sequence of p53, an important tumor suppressor gene, from individuals who had EN showed a distinct and unusual mutational pattern.
Turesky was able to identify the aristolochic acid-DNA adducts using mass spectrometry techniques that proved these adducts were responsible for the mutational pattern. This key finding linked epidemiological observations to molecular data and to adverse health outcomes.
That work with Arthur Grollman, M.D., from Stony Brook University, and international collaborators also laid the foundation for the rapid identification of DNA adducts of aristolochic acid in traditional Chinese medicine as a primary agent in carcinomas of the upper urinary tract in Taiwan.
Taking DNA adduct detection to a new level
Detecting biomarkers using mass spectrometry works best with fluids or fresh frozen tissue, Turesky said. However, specimens such as tumors are usually available to researchers only in a form known as formalin-fixed paraffin embedded samples, which limits analytical analysis.
Turesky developed a way to reverse the effects of formalin so that these samples can now be analyzed by mass spectrometry to detect DNA adducts and other biomarkers. Although this approach opens up what Turesky called a treasure trove of samples from around the world, he said there remains an unmet need to monitor biomarkers over time.
Bessette EE, Yasa I, Dunbar D, Wilkens LR, Le MarchandL, Turesky RJ. 2009. Biomonitoring of carcinogenic heterocyclic aromatic amines in hair: a validation study. Chem Res Toxicol 22(8):1454–1463.
Le Marchand L, Yonemori K, White KK, Franke AA, Wilkens LR, Turesky RJ. 2016. Dose validation of PhIP in hair level as a biomarker of heterocyclic aromatic amines exposure: a feeding study. Carcinogenesis 37(7):685–691.
Grollman AP, Shibutani S, Moriya M, Miller F, Wu L, Moll U, Suzuki N, Fernandes A, Rosenquist T, Medverec Z, Jakovina K, Brdar B, Slade N, Turesky RJ, Goodenough AK, Rieger R, Vukelic M, Jelakovic B. 2007. Aristolochic acid and the etiology of endemic (Balkan) nephropathy. Proc Natl Acad Sci U S A 104(29):12129–12134.
Chen CH, Dickman KG, Moriya M, Zavadil J, Sidorenko VS, Edwards KL, Gnatenko DV, Wu L, Turesky RJ, Wu XR, Pu YS, Grollman AP. 2012. Aristolochic acid-associated urothelial cancer in Taiwan. Proc Natl Acad Sci U S A 109(21):8241–8246.
(Stephanie Smith-Roe, Ph.D., is a toxicologist in the National Toxicology Program Genetic Toxicology Group.)