, 2009). The assertion regarding the relative severity

of oxidative stress induced by MSC and TSC is supported by published results from other studies. In a previous study, Sarafian et al. examined reactive oxygen species (ROS) production and reduced glutathione (GSH) levels as indicators of oxidative damage following exposure to marijuana smoke (Sarafian et al., 1999). They showed that exposure of human endothelial cells to marijuana smoke resulted in an 80% increase in ROS over control levels, and these levels were as much as three times higher than those resulting from tobacco smoke. Moreover, intracellular glutathione levels following marijuana exposure were lower than for tobacco, and were reduced by 81% Epacadostat in vitro relative to controls. The authors argued that the products Ruxolitinib in vitro produced by the pyrolysis of the cannabinoids were likely responsible for the oxidative damage. The same authors also conducted preliminary studies with cultured lung alveolar macrophages from non-smokers and marijuana smokers, and found that marijuana smokers had lower levels of GSH than non-smokers, suggesting a decrease in GSH dependent oxidative defenses in habitual marijuana smokers.

M phase pathways, including the Mitotic Roles of Polo-like Kinase and G2/M DNA Damage Checkpoint Regulation pathways, were significantly perturbed in TSC exposed cells. At the highest concentration, TSC affects Ccnb1, Cdk1, Plk1, Plk2, Plk3, Prc1, Gadd45, Cdc20 and Mdm2 expression at the 6 h time point and Ccnb1, Cdk1, Plk1, Prc1, Gadd45, Ccnb2, Ppp2r2b and Top2a at the 6 + 4 h time point. Some of these

genes (e.g., Gadd45, Cdc20, Prc1, Top2a, Mdm2) are p53 responsive genes which could indicate a DNA damage response regulated by p53 ( Amundson et al., 1998 and Spurgers et al., 2006). The genes in these pathways are involved in checkpoint regulation Teicoplanin and, by providing time for DNA repair, they prevent cells with DNA damage from entering mitosis. Similar genes have also been found to be down-regulated in a study by Nordskog et al. ( Nordskog et al., 2003). Following exposure of primary cultures of human aorticendothelial cells to cigarette smoke condensate, they noted the down-regulation of cell cycle genes including Top2a, Ccnb1, Ccna, and Cdkn3. In contrast to TSC exposed cells, the above M phase pathways were not significantly perturbed in the marijuana exposed cells. Rather, the Cell Cycle Regulation by BTG Family Proteins Pathway was significantly disrupted, particularly for cells exposed to the highest MSC concentrations. The BTG proteins act as growth arrest genes and prevent G1 to S phase transition by inhibiting Ccnd1 and maintaining a quiescent state (Rouault et al., 1996).