Why is tobacco exposure relevant to health?
Tobacco product exposure is so ubiquitous and its effects are so wide-ranging that it is nearly imperative to assess it in studies of health outcomes. Cigarette smoking harms nearly every organ of the body and reduces the health of smokers. In particular, smoking increases the risk for coronary heart disease, stroke, and multiple types of cancer.
Exposure to secondhand tobacco smoke is a cause of lung cancer, decreased lung function, lower respiratory illnesses, middle ear disease, asthma and other respiratory symptoms, and persistent adverse effects on lung function.
In addition, many adolescents may already be smokers, smokeless tobacco users, or e-cigarette users, and may be addicted to nicotine and subjected to chronic exposures to tobacco toxicants and carcinogens, thus increasing their risk for the multiple diseases associated with tobacco use.
What types of questions can be answered?
One can determine whether there is current exposure to secondhand tobacco smoke (for periods ranging from hours to 1-2 weeks after exposure). For current users of tobacco products, the type of product (combusted vs. non-combusted) can be determined. Users of e-cigarettes can also be specifically identified (by the ratio of nicotine metabolites to carcinogenic tobacco-specific nitrosamines (TSNAs) such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolites, or the ratio of nicotine metabolites to cyanoethyl mercapturic acid) in cases where nicotine replacement therapy has not been used. A panel of carcinogen and toxicant metabolites arising from tobacco products can be quantified in biospecimens to determine the nature of complex tobacco product exposures. DNA adducts of some tobacco smoke chemicals can be quantified in DNA from oral cells, leukocytes or formalin fixed tissue. Environmental samples can also be analyzed for compounds indicative of tobacco exposure, such as nicotine.
How can tobacco exposure be measured?
- Analytes: Nicotine and its metabolites, tobacco-specific nitrosamines and their metabolites, polycyclic aromatic hydrocarbon metabolites, metabolites of volatile organic compounds, metals, certain DNA adducts, and biomarkers of oxidative damage and inflammation can be measured. Tobacco-specific nitrosamine metabolites are specific to tobacco products; nicotine and its metabolites are also relatively specific but could also come from nicotine replacement therapy products or e-cigarettes. Metabolites of volatile organic compounds are consistently higher in active smokers than in non-smokers. Certain DNA adducts may be elevated in smokers, but there are competing environmental, endogenous, and dietary sources. For secondhand smoke exposure, metabolites of nicotine and tobacco-specific nitrosamines, measured in urine, are the most useful.
- Methods: A variety of methods that couple liquid chromatography with mass spectrometry are most commonly used. All methods require preliminary purification steps that remove interfering substances.
- Types of biospecimens: Urine, serum, plasma, saliva, oral cells, and toenails are used. Urine is generally the preferred biospecimen because the absolute amounts of the analytes are generally higher in urine samples than in the other types of specimens. Because analytes measured in urine vary in concentration, they are typically corrected for urine dilution. DNA adducts can be measured in DNA from leukocytes, oral cells or formalin-fixed tissues.
- Types of environmental samples: Dust is the most common medium analyzed, but silicone wristbands are increasingly being used to evaluate nicotine in secondhand and thirdhand tobacco smoke exposure.
How does HHEAR ensure the quality of its analyses?
All assays are well validated with respect to accuracy and precision. All assays have embedded positive and negative controls. The positive controls are used to check assay accuracy within each set of samples. The negative controls are generally water blanks or urine samples from non-exposed nonsmokers. These can be used to eliminate the possibility of cross contamination with tobacco-specific compounds, which can be a problem, particularly for measurements of nicotine.
What sample quality and quantity are necessary?
This is highly dependent on the assay to be run, but in general, a few milliliters of urine, serum, or plasma, about 10 micrograms of DNA or one gram of dust are required. Most of the analytes are quite stable, so multiple freeze-thaw cycles should not be a problem. The exception is nicotine itself, which can be lost or inadvertently introduced during multiple manipulations.
Benowitz NL, Bernert JT, Foulds J, Hecht SS, Jacob P III, Jarvis M, Joseph A, Oncken C, Piper M. Biochemical verification of tobacco use and abstinence. Nicotine Tob. Res.2019, in press.
Centers for Disease Control and Prevention. Smoking and Tobacco Use Factsheet: Health Effects of Cigarette Smoking.
Hecht SS, Yuan J-M, Hatsukami DK. Applying tobacco carcinogen and toxicant biomarkers in product regulation and cancer prevention. Chemical Research in Toxicology. 2010;23:1001-1008.
Hecht SS, Stepanov I, Carmella SG. Exposure and metabolic activation biomarkers of carcinogenic tobacco-specific nitrosamines. Accounts Chem. Res. 2016,49:106-114.