The ratio of propylene glycol to glycerol modulates nicotine taste and reward: more glycerol, more reward

Abstract

Background Propylene glycol (PG) and glycerol (Gly) are odorless tobacco product constituents that act as solvents in electronic cigarette e-liquids and as humectants in oral nicotine products. Little is known about how PG/Gly ratio may affect nicotine’s sensory and rewarding properties. To address this gap, we utilized the taste reactivity test and four-bottle choice test to investigate the impact of PG/Gly ratio on nicotine’s taste and reward. Methods A taste reactivity test was performed using young adult rats that received oral infusions of water, nicotine (10 μg/mL) and various PG/Gly ratios in the absence and presence of nicotine via intraoral catheters. Facial responses to each infusion were video recorded and the ingestive and aversive taste responses to each solution were scored and analyzed. In a separate cohort of rats, a four-bottle choice test was utilized to assess preference for various PG/Gly ratios with or without nicotine. Results Young adult rats exhibited higher aversive reactions to PG100/Gly0 alone. Higher Gly content (PG0/Gly100 with nicotine) increased ingestive responses compared to nicotine alone. Higher Gly content (PG20/Gly80 with nicotine and PG0/Gly100 with nicotine) decreased aversive reactions compared to nicotine alone. Young adult rats also displayed greater preference for PG0/Gly100 alone and PG0/Gly100 with nicotine compared to vehicle water and nicotine, respectively. Conclusion Overall, nicotine’s ingestive and aversive taste was altered by PG and Gly depending on the ratio. Specifically, higher Gly enhanced nicotine’s hedonic value and reduced nicotine’s aversive properties in both sexes. Higher Gly content was also preferred during the four-bottle choice test alone and in the presence of nicotine. Together, our results suggests that PG/Gly ratio, particularly high Gly content, influences nicotine’s abuse liability.