On 2016 Jun 22, Zvi Herzig commented:

The authors mistakenly exclude the possibility that increased gene suppression in e-cigarette users relates to nicotine:

Based on the similar serum cotinine levels in cigarette smokers and e-cigarette users, it does not appear that the overall difference in number and level of gene expression changes is dependent on nicotine.

However, unlike smoking, e-cigarette use frequently entails nasal exhalation (as online videos on the subject can demonstrate). It is already known that nicotine alone affects gene expression Zhang S, 2001, Bavarva JH, 2013. Nasal mucosae of e-cigarette users are exposed to much more nicotine, hence the increased gene suppression.

The health effects of nicotine exposure alone can be established from long-term human studies of snus and NRT use Murray RP, 1996, Lee PN, 2013, Royal College of Physicians, 2016.

On 2016 Jun 22, Zvi Herzig commented:

The authors mistakenly exclude the possibility that increased gene suppression in e-cigarette users relates to nicotine:

Based on the similar serum cotinine levels in cigarette smokers and e-cigarette users, it does not appear that the overall difference in number and level of gene expression changes is dependent on nicotine.

However, unlike smoking, e-cigarette use frequently entails nasal exhalation (as online videos on the subject can demonstrate). It is already known that nicotine alone affects gene expression Zhang S, 2001, Bavarva JH, 2013. Nasal mucosae of e-cigarette users are exposed to much more nicotine, hence the increased gene suppression.

The health effects of nicotine exposure alone can be established from long-term human studies of snus and NRT use Murray RP, 1996, Lee PN, 2013, Royal College of Physicians, 2016.