In a later study, the authors also noted the decreased expression of Bax and caspase-8 in human small airway epithelial cells exposed to THC, which they suggest could have accounted for the previously observed suppression in Fas-mediated apoptosis ( Sarafian et al., 2005). Although apoptotic pathways were not significantly perturbed following TSC exposure in our present study, Sarafian

et al. and other investigators of tobacco smoke effects have found this to be a commonly disrupted pathway (Jorgensen et al., 2004, Nordskog et al., 2003, Sarafian et al., 2001 and Yauk et al., 2011). It is suspected that the gene expression fold change cutoff of 2 used LY294002 nmr in the present study likely prevented a number of apoptotic genes from being included in the analyses. Cursory analyses with a cutoff of 1.5 shows apoptotic pathways as being significant for TSC exposure as well (data not shown). It is important to note that the marijuana used for this study was obtained from a contracted supplier that provides marijuana for therapeutic use in Canada. It is grown under strictly controlled and documented conditions. Although this study has only examined smoke condensate from a single lot of marijuana, the quality control measures would be expected to minimise differences between marijuana harvests. The TSC used in this study was generated from cigarettes containing Virginia

flue-cured tobacco, VEGFR inhibitor the type of tobacco typically contained in Canadian cigarettes. This is distinct from the mixed tobacco blends (i.e., Virginia, Burley and Oriental) typically found in American cigarettes. Our Erastin cell line earlier toxicogenomic examination of TSC from three Canadian cigarette brands containing either Virginia flue-cured or mixed tobacco blends failed to show any appreciable brand-driven differences in gene expression

profiles elicited by in vitro exposures (Yauk et al., 2011). Therefore, we contend that the similarities and difference between MSC and TSC noted in this study can be cautiously extended to other types of tobacco. Nevertheless, it should also be noted that some toxicogenomic studies have shown that cigarette brand (e.g. full flavor vs. low-tar) can have a significant effect on gene expression signatures elicited by in vitro CSC exposures (Lu et al., 2007 and Pickett et al., 2010), and moreover, many aspects of cigarette design (e.g., rod length, filter presence and type, ventilation, packing density, additives, paper type) and smoking method (e.g., ISO, intense) have been shown to influence the composition and toxicological activity of TSC (Adam et al., 2010, O‘Connor and Hurley, 2008 and Rickert et al., 2007). Our work supports the findings of previous studies, which associate TSC exposure with the expression of genes involved in xenobiotic metabolism, oxidative stress, inflammation, and DNA damage response (i.e., cell cycle arrest, protein unfolding, and transcription regulation).