A, Calculation of MOE for a potential carcinogenic or genotoxic chemical or food additive.1,2 An MOE greater than 10 000 is applied by the US Food and Drug Administration (FDA) and other regulators as threshold for mitigation of potential carcinogenic activity of food additives.2 B, Comparison of the pulegone predicted MOE from tobacco products use (e-cigarette liquids for vape tanks and vape mod devices, smokeless tobacco, and menthol cigarette) to the FDA’s calculated MOE for pulegone from food intake. The MOEs within each tobacco product were also compared based on amount of tobacco product consumed. The MOEs for menthol cigarette use were calculated from the upper and lower level of pulegone range detected in 23 top-marketed brands (estimated to contain 0.037-0.290 μg/g of pulegone).5
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Jabba SV, Jordt S. Risk Analysis for the Carcinogen Pulegone in Mint- and Menthol-Flavored e-Cigarettes and Smokeless Tobacco Products. JAMA Intern Med. 2019;179(12):1721–1723. doi:10.1001/jamainternmed.2019.3649
Pulegone, a constituent of oil extracts prepared from mint plants, including peppermint, spearmint and pennyroyal, is a carcinogen that causes hepatic carcinomas, pulmonary metaplasia, and other neoplasms on oral administration in rodents.1 In 2018, the US Food and Drug Administration (FDA) banned synthetic pulegone as a food additive.2 Studies by the Centers for Disease Control and Prevention (CDC) detected substantial amounts of pulegone in mint- and menthol-flavored e-cigarette liquids and smokeless tobacco products marketed in the United States.3,4 The tobacco industry has minimized pulegone levels in cigarette flavorings because of toxicity concerns. Mint- and menthol-flavored e-cigarettes may be exempt from proposed federal regulations; therefore, the health risk associated with pulegone in these products should be considered.
To assess the risk associated with pulegone, we calculated the margin of exposure (MOE) by dividing the FDA-provided no-observed adverse effect level (NOAEL) of pulegone at which no treatment-related tumors were reported in animal studies (13.39 mg/kg of body weight/d)1,2 by the mean human exposure from mint- and menthol-flavored e-cigarette or smokeless tobacco products analyzed in the CDC studies.3,4 The MOE is the measure used by the FDA and other regulatory agencies for cancer risk assessment of food additives.2 Cancer risk is inversely proportional to the MOE, with values of 10 000 or below requiring mitigation strategies.2 We compared the risk associated with pulegone content in top-marketed brands of combustible menthol cigarettes to mint- and menthol-flavored e-cigarettes (5 e-liquids, 3 brands) and smokeless tobacco (1 brand).3-5 Based on daily use, we considered a light user to consume 5 mL of e-liquid, half a pack of cigarettes, or 10 g of smokeless tobacco; a moderate user to consume 10 mL of e-liquid, 1 pack of cigarettes, or 20 g of smokeless tobacco; and a heavy user to consume 20 mL of e-liquid, 2 packs of cigarettes, or 30 g of smokeless tobacco. This study was exempt from Duke University School of Medicine institutional review board approval following tenets of the Principal Investigator Checklists as not involving human participants.
For the e-liquid with the highest pulegone concentration, MOEs were between 1298 and 3084 for 5-mL daily consumption and between 325 and 771 for 20-mL daily consumption (Table and Figure), below the safety threshold of 10 000. Depending on consumption rates, MOEs for the e-liquids ranged between 325 and 6012; for a pulegone-containing smokeless tobacco they ranged between 549 and 1646.
Daily pulegone exposure from e-cigarettes compared with menthol cigarette use (estimated to contain 0.037-0.290 μg/g of pulegone)5 was higher across all user groups (ranging from 44-1608 times higher). Compared with menthol cigarettes, estimated pulegone intake from smokeless tobacco was 168 to 1319 times higher in light users and 126 to 990 times higher in heavy users.
Our analysis suggests that users of mint- and menthol-flavored e-cigarettes and smokeless tobacco are exposed to pulegone levels higher than the FDA considers unacceptable for intake of synthetic pulegone in food, and higher than in smokers of combustible menthol cigarettes.2,5
Inhalation toxicity data for pulegone are not available. Although carcinogenic or systemic risks associated with pulegone may vary by exposure route (inhalation or ingestion), extrapolation of MOEs derived from oral toxicity studies to inhalation exposure is a common practice among regulatory agencies, with inhalation exposure accepted to increase risk by 2-fold or higher.6 To limit complexity, we did not use extrapolations in this analysis. However, if we had applied the oral-to-inhalation extrapolation factor of 2 to the MOE calculations for pulegone, the MOEs for the e-liquids would have been reduced by half, resulting in exposures even further from the MOE safety threshold of 10 000.
Limitations of this study include consideration of only 5 e-liquids and 1 smokeless tobacco product for which analytical data were published, and following the FDA’s risk assessment procedures, which are based on animal data. Although pulegone is toxic in humans, it is unknown if users of combustible tobacco products, smokeless tobacco, or e-cigarettes absorb and metabolize the quantities associated with production of a carcinogenic effect. Nevertheless, the MOEs for all the products we analyzed are below the accepted MOE threshold of 10 000 for carcinogens. Our findings appear to establish health risks associated with pulegone intake and concerns that the FDA should address before suggesting mint- and menthol-flavored e-cigarettes and smokeless tobacco products as alternatives for people who use combustible tobacco products.
Accepted for Publication: June 28, 2019.
Corresponding Author: Sven-Eric Jordt, PhD, Department of Anesthesiology, Duke University School of Medicine, 3 Genome Ct, Durham, NC 27710 (firstname.lastname@example.org).
Published Online: September 16, 2019. doi:10.1001/jamainternmed.2019.3649
Author Contributions: Drs Jabba and Jordt had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Jordt.
Acquisition, analysis, or interpretation of data: Both authors.
Drafting of the manuscript: Both authors.
Critical revision of the manuscript for important intellectual content: Both authors.
Obtained funding: Jordt.
Administrative, technical, or material support: Jabba.
Conflict of Interest Disclosures: Dr Jordt reported grants from NIDA and grants from NIEHS during the conduct of the study; personal fees from Hydra Biosciences LLC, personal fees from Sanofi, and nonfinancial support from GSK Pharmaceuticals outside the submitted work. No other disclosures were reported.
Funding/Support: This work was supported by a grant from the National Institute of Environmental Health Sciences (NIEHS) (R01ES029435 to Dr Jordt).
Role of the Funder/Sponsor: The NIEHS had no role in the preparation or interpretation of the data; review or approval of the manuscript; nor in the decision to submit the manuscript for publication. The content is solely the responsibility of the authors and does not necessarily represent the views of the funding agencies.
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