The gene expression results we obtained were compared with the enzyme activity data obtained for the tested CYPs (CYP1A1/1B1, CYP1A2, CYP2A6/2A13 and

CYP2E1). When BEAS-2B cells were pre-incubated with TCDD, CYP1A1/1B1 activity showed a statistically significant increase compared to non-treated cultures (Fig. 3A). This concurs with the gene up-regulation described earlier. TCDD-induced BEAS-2B cells showed an activity of 0.2 RLU/mg/min while HBEC cultures have been reported to show find more an enzyme activity level between 4.3 and 7.3 RLU/mg protein/min (Newland et al., 2011). No activity was observed in BEAS-2B cells for the other three CYPs analyzed (CYP2E1, CYP2A6/2A13 and CYP1A2) which confirms the findings from our gene expression analysis. Previous studies have also reported no detectable CYP1A2 activity in BEAS-2B cells and lung microsomes (Van Vleet et al., 2002 and Shimada et al., 1992), however, CYP1A2 activity could be induced by

environmental factors and specific CYP1A2 gene polymorphisms increasing lung cancer risk as recently reviewed (Pavanello see more et al., 2012). The activity related to CYP2A and CYP2E1 has not been previously reported in BEAS-2B cells, but has been detected in human lung (Hukkanen et al., 2002). Newland et al. also reported that HBEC cultures from three Cyclic nucleotide phosphodiesterase different donors showed a CYP2A6/2A13 activity between 0.15 and 1.33 pmol/mg/min (Newland et al., 2011) a similar study by Runge and colleagues showed that CYP2E1 activity in HBEC (0.6 pmol/mg/min),

however substantial inter-individual variability was reported as only two out of the four donors showed CYP2E1 activity (Runge et al., 2001). Overall, the relative enzyme activity level in BEAS-2B cells appears limited compared with normal tissue. For instance, immunobloting of human lung microsomes have been used to detect CYP1A1, 1B1, 2A6, 2B6, 2C9, 2D6, 2E1, 2F1 and 3A4/5 in normal airway tissue (Hukkanen et al., 2002 and Bernauer et al., 2006). In HBEC, these CYPs have been reported to show both gene expression and enzyme activity, however, high interindividual variability between different donors was also noted (Runge et al., 2001, Newland et al., 2011, Anttila et al., 2011 and Castell et al., 2005). The lack of gene expression for the majority of metabolizing enzyme-encoding genes tested, with or without induction by TCDD, and the lack of activity for three out of the four selected P450 enzymes indicates that BEAS-2B cells might not be suitable to study the toxicity of some inhaled pro-toxicants without an external source of metabolic activation (S9 fractions, microsomes, co-cultures or in vitro liver-like cell lines amongst others) ( Brandon et al., 2003).