Sex‐Dependent Effects of Nicotine on the Gut Microbiome

Abstract

Nicotine is the addictive substance found in cigarettes and e‐cigarettes; however, nicotine's effect on many physiological processes has not been clearly delineated. A limited number of studies have investigated the impact of nicotine on the gut microbiome and most studies used oral administration instead of inhalation. During the last decade, the gut microbiome has been shown to influence host homeostasis, and its disruption (dysbiosis) has been associated with disease pathogenesis. This study aimed to determine if inhaled nicotine alters the gut microbiome and if an animal's sex can influence those changes. In this study, female (n=8 air and n=10 nicotine) and male (n=10 air and n=10 nicotine) C57BL6/J mice were exposed to air (control) or nicotine vapor (daily, 12 hours on/12 hour off) for 13 weeks. Serum cotinine, a measure of nicotine intake, was comparable to that observed in human smokers; interestingly, male mice had significantly higher levels than female mice. Body weight was significantly lower following nicotine vapor exposure in both male and female mice. A fecal sample was collected from each mouse at the time of sacrifice, followed by DNA isolation and 16S rRNA gene sequencing analysis of gut microbes. Differences in alpha and beta diversity were analyzed using Shannon and Bray‐Curtis statistics, respectively. Alpha diversity measures the diversity within a community, while beta diversity measures the pairwise similarity of communities. Nicotine significantly reduced alpha diversity in female mice but not male mice. In contrast, nicotine significantly altered community structure in both male and female mice producing clearly distinct clusters based on the Bray‐Curtis beta diversity metric. In addition, sex‐specific differences were observed in both alpha and beta diversity with air inhalation. In conclusion, we found that nicotine inhalation reduces the gut microbiome's bacterial diversity in a sex‐specific manner. Reduced diversity of the gut microbiome may contribute to nicotine's negative health impact.