E-Cigarette Aerosol Elevates Cardiovascular Oxidative Stress In Mice With Aldehyde Dehydrogenase 2 Deficiency

Introduction: E-cigarette aerosol contains reactive aldehydes including acetaldehyde, formaldehyde, and acrolein when e-cigarette is heated. Approximately 560 million people worldwide cannot efficiently metabolize aldehydes present in e-cigarette aerosol, due to a genetic deficiency in aldehyde dehydrogenase 2 enzyme (ALDH2), known as ALDH2*2. Little is known how aldehyde exposure from e-cigarettes, coupled with genetic differences in aldehyde metabolism, affects cardiovascular oxidative stress both at a physiological and cellular level. Hypothesis: E-cigarette aerosol exposure will elevate heart rate and cellular oxidative stress more substantially in ALDH2*2 knock-in mice versus wild type ALDH2 mice. Methods: To measure aldehyde levels, e-cigarette Juul aerosols were collected and quantified by selective ion flow gas mass spectrometry. Further, age-matched male wild type and homozygous ALDH2*2 mice (8-10 weeks old, ~25g) were implanted with EKG telemeters. After surgical recovery, mice were paired by genotype (one wild type ALDH2 and one ALDH2*2 mice) and exposed to either Juul aerosol or room air 4 sessions per day for 10 days. For each session, 7 puffs/min were drawn for the first two minutes (a total of 14 puffs), and the whole body exposure to Juul aerosol lasted 7 minutes, continued with 23 minutes smoking-free intervals in each session. Mice EKG waveforms were recorded daily. After 10 days of exposure, heart homogenates were subjected to biochemical assays including lipid peroxidation, 4-HNE protein adduct formation, and protein carbonylation. Results: Quantification of reactive aldehyde levels in e-cigarettes revealed that Juul aerosol contained acetaldehyde (5.3±0.32 ppm), formaldehyde (0.20±0.02 ppm), and acrolein (0.09±0.01 ppm). When exposed to Juul aerosol, ALDH2*2 mice showed a maximal increase in heart rate unlike ALDH2 wild type mice (774.6±29.5 bpm versus 678.9±32.8 bpm respectively, * p <0.01, n=8) at day 6. Furthermore, heart homogenates from ALDH2*2 mice demonstrated exacerbated oxidative stress, including higher level of 4-HNE adducts (1.5-fold), protein carbonyls (1.5-fold) and lipid peroxides (2-fold) relative to hearts from wild type ALDH2 mice, when both genotype mice were exposed to Juul e-cigarette aerosol (n=4/group). Conclusions: These findings indicate e-cigarette aerosols contain reactive aldehydes, primarily acetaldehyde. A deficiency in reactive aldehyde metabolism by having an ALDH2*2 deficiency may contribute to increases in heart rate and oxidative stress within the cardiovascular system while smoking e-cigarettes.