, 2004)]. Moreover, the concentration response patterns support the assertion of initial metabolic responses (e.g., CHIR-99021 mouse Nqo1, Cyp1a1, Cyp1b1), followed by responses to toxic insult (e.g., Hmox1) and secondary metabolism (e.g., Gsta5). Similar concentration response trends were noted in our previous toxicogenomics analysis of three different TSCs ( Yauk et al., 2011). Although very few studies have been conducted with marijuana smoke, Roth et al. (2001) demonstrated the induction of cytochrome P450 genes following exposure

of Hepa-1 cells to marijuana tar extracts. Furthermore, the authors showed that tar from marijuana cigarettes tends to be more effective than tar from tobacco at inducing Cyp1a1 gene expression. Since the cannabinoids present in marijuana are capable of acting through the aryl hydrocarbon receptor to induce cytochrome P450 enzymes ( Yamaori et al., 2010), and Cyp1a1 is known to bioactivate procarcinogens such as PAHs ( Bartsch et al., 1992), questions have been raised about the role of cannabinoids in augmenting the carcinogenic risk posed by marijuana smoke. The question becomes increasingly complex as the cannabinoids THC, CBD and CBN have also been shown to competitively inhibit Cyp1a1, potentially decreasing the production of carcinogens and curtailing negative consequences ( Roth et al., 2001). In the present study, PCI 32765 however, substantial

differences in the expression profiles of cytochrome P450 genes between the two smoke types were not observed. The expression of Cyp1a1 following exposure to MSC was comparable to that following TSC exposure, and the microarray results were supported by RT-PCR ( Table 5). One of the differences in the xenobiotic metabolism responses for the two condensate types is that Hsp90 and Rras2 were only up-regulated following MSC exposure. Despite these findings, Hsp90 has been previously observed to be induced following cigarette G protein-coupled receptor kinase smoke exposure ( Bosio et al., 2002 and Pinot et al., 1997), and mutations in genes from the Ras family are known to

be associated with cigarette-induced cancers ( Ahrendt et al., 2001). The IPA Canonical Pathway most significantly affected by exposure to TSC was the NRF2-Mediated Oxidative Stress Response Pathway. In this pathway, the transcription factor Nrf2 is phosphorylated following exposure to reactive oxygen, and translocates to the nucleus where it binds to antioxidant response elements ( Kensler et al., 2007). It then activates the expression of detoxification and antioxidant genes that protect the cell against oxidative damage. Of the 192 genes in this pathway, 6–18 genes were perturbed by TSC at the various time points in a concentration-dependent manner. The largest expression changes and number of genes were associated with the 6 h time point. Nrf2-regulated antioxidant genes have been shown to play an important role in protection against the toxic effects of tobacco smoke. Iizuka et al.