6-methyl Nicotine in Electronic Cigarettes: Chemical Analysis and Toxicological Properties
Jordt, SE; Caceres, A; Silinski, P; Jabba, SV
Published in: American Journal of Respiratory and Critical Care Medicine
RATIONALE: The tobacco industry is known for constantly probing FDA's regulatory limits. In 2023, an e-cigarette product was introduced that, instead of nicotine, delivers a nicotine analogue, 6-methyl nicotine (6MN), claimed to be outside of FDA's regulatory authority. Pre-clinical studies demonstrated that 6MN is more potent than nicotine, raising concerns about increased addictiveness and toxicity. We aimed to identify additional e-cigarette products containing 6MN, chemically analyze their 6MN contents for risk assessment, and test the toxicological properties of 6MN in bronchial epithelial cells. METHODS: Industry reports, patent and trademark database were searched for 6MN products. Identified trademarks were used to search for new US-marketed e-cigarette products. High resolution liquid chromatography-mass spectrometry (LCMS) was used to detect and quantify potential nicotine analogues, using defined standards. Toxicological properties of 6MN were compared with nicotine's effects in BEAS-2B human bronchial epithelial cells using the Live-dead assay, qPCR of pro-inflammatory transcripts and analysis of oxidative metabolism. RESULTS: Additional trademarks for 6MN were identified, including “Imotine”, “Nixotine”, “NoNic” and “SFN” (Substitute For Nicotine). Between July – October 2024, four new product brands advertised to contain 6MN were identified, including three disposable e-cigarette brands, and one refill liquid brand. Concentrations of 6MN measured in e-liquids diverged widely from concentrations listed on product labels. One product line exclusively contained nicotinamide, marketed as an alternative nicotine analogue. 6MN was more effective than nicotine at inducing cell death of BEAS-2B cells, and induced transcription of NADPH oxidase subunit genes. 6MN also reduced oxygen consumption and other metabolic health parameters at lower concentrations than nicotine. CONCLUSION: The number of US-marketed 6MN-containing e-cigarette brands and model varieties is increasing, suggesting confidence in the strategy to use nicotine analogues to bypass federal and state regulations that restrict tobacco product flavors. Electronic cigarette products containing 6MN have highly variable 6MN contents, suggesting irregular production processes. Actual contents diverge strongly from label information, raising concerns about adverse effects and addictiveness. 6MN is more potent than nicotine at eliciting toxicological effects in human bronchoepithelial cells, calling for follow up in vivo and clinical studies. Nicotine analogues should be urgently addressed by lawmakers and regulators, and FDA should be granted the authority to regulate products containing them as tobacco products.
