Metabolic monitoring and cage activity in mice exposed to 7‐months of electronic cigarette vapor

Abstract

IntroductionNicotine is a known central nervous system stimulant that increases heart rate and metabolism. E‐cigarettes (E‐cig) are a new and highly effective nicotine delivery device, that include a vast array of flavorings and chemical by‐products that are likely to have deleterious consequences. Currently there is very little known about the long‐term effects of E‐cig vapor exposure, particularly in the context of whole body metabolism. We hypothesize that metabolic cage activity will be increased in mice chronically exposed to E‐cig vapor.MethodsC57BL/6 female mice were randomly assigned to 3R4F reference cigarette (N=13), cappuccino flavored E‐vapor (18 mg/ml nicotine, N=12), or filtered air (N=13) exposed groups. Animals were exposed 4 h/day, 5 d/w for 7 months. Whole body metabolic gas exchange and cage activity was measured after the 7‐month exposure using a home‐cage chronic laboratory animal monitoring system (Oxymax CLAMS, Columbus Instruments). Food and water were administered ad libitum.ResultsOxygen consumption (VO2) at night was significantly increased in E‐cig and 3R4F by 21% and 17%, respectively (p<0.05) compared to air exposed mice. However, VO2 was not significantly different between groups during the day. Carbon dioxide production (VCO2) at night was also increased in E‐cig and 3R4F by 19% (for both groups, p<0.05) compared to air, and also not significantly different during the day. Respiratory exchange ratio (RER) was not different between any of the groups at night or day, however indirect calorimetric assessment of heat production (kcal/hr) was significantly greater in E‐cig mice by 16% and 18% compared to 3R4F and air, respectively (p<0.05), at night. Heat, during the day, also tended to be greater in E‐cig mice by 12% and 11% compared to 3R4F and air, respectively (p=0.068). Spontaneous cage activity at night tended to be greater in E‐cig mice (p=0.06) compared to 3R4F and air groups, but no difference in cage activity occurred during the day.ConclusionExposure to E‐cigs increased VO2, VCO2 and heat production, which corresponded to greater cage activity, in measurements made at night (the animal's period of greatest cage activity), but not during the day (the period of least cage activity). Similar to E‐cigs, 3R4F reference cigarettes also increased VO2 and VCO2, but not heat production, at night. These data suggest chronic E‐cig exposure can increase basal metabolic and cage activity in mice.Support or Funding InformationNIH P20GM103434 (West Virginia IDeA Network for Biomedical Research Excellence) and the Marshall‐WVU Health Initiative Award