Production of 3-Cyanopyridine upon Vaping Nicotinamide and Evaluation of the Toxicological Effects of Individual and Combined Exposures via Isobologram-Based Analysis

Nicotine has been used in e-cigarettes for many years; however, recently, nicotine analogs have risen in popularity. E-cigarettes containing nicotine analogs such as nicotinamide and 6-methylnicotine are currently sold without regulatory oversight. They are marketed as safer alternatives to nicotine-containing products, although there is little or no scientific evidence to support this claim. This study investigated the nicotine analog, nicotinamide (NA), along with its major degradant, 3-cyanopyridine (3CP), which is produced when NA is vaped. Upon heating and aerosolization, both chemicals are present in the exposure dose. Dose-response curves are created for relative concentrations of NA and 3CP, and an isobologram is formed to investigate their mixture effects. NA is toxic at concentrations greater than 2637 ppm; however, 3CP is harmful in concentrations as low as 0.0001 ppm. The most significant finding is that the isobologram indicates that the mixture effects are synergistic, where a decrease in viability can be seen in minimal doses of 3CP (i.e., 0.000001 ppm) and 1350 ppm of NA. The interaction index was calculated for each point, and all values were less than 1, indicating a statistically synergistic biological response. The study highlights how such small levels of 3CP can play a large role in inducing toxic responses of a presumed safe chemical (i.e., nicotinamide or niacinamide, a form of vitamin B3 (niacin)). These results indicate that chemical and biochemical reactions, as well as interactions between e-cigarette aerosol components, including nicotine analogs, warrant further investigation.