ORLANDO, FL USA (UroToday.com) - Cellular oxidative stress (COS), post BCG treatment, plays a central role in mediating direct effect of BCG on urothelial carcinoma (UC) cells. Recent novel findings show that BCG acts as an H2O2 generator and provide insight into the genesis of BCG-induced COS. To date, the net impact of BCG exposure on specific contributors to COS remains poorly defined. The research group reports the results of experiments designed to assess the broad impact of BCG on inducers and regulators of COS, as well as downstream “targets” of COS.
Global profiling of reactive oxygen (ROS) and nitrogen species (RNS) was carried out in two human UC cell lines (253J, T24) using fluorescent probes for H2O2, nitric oxide (NO), and superoxides at various time points post BCG exposure. Enzymatic regulators of COS, superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) activities were measured at 6h post BCG exposure. Downstream targets of COS, DNA damage, and lipid peroxidation were determined by measuring 8-hydroxydeoxyguanosine (OHdG) and 4-hydroxynonenal (HNE) adduct, respectively.
The study showed an increase in cellular H2O2 (post BCG treatment) as early as 3h (p ≤ 0.05) and a sustained increase till 12h (p ≤ 0.005). H2O2 levels did not change significantly 24h onwards (p = 0.32). NO levels increased significantly at 6h (p ≤ 0.05) but not at 3h (p = 0.2) or 9h (p = 0.14) onwards. Superoxide levels showed significant increase at 6h (p ≤ 0.05) but reduced levels at 24h (p ≤ 0.05). Post BCG exposure, SOD and GPx activities were significantly higher at 6h (p ≤ 0.05), while catalase activity did not show any significant change (p = 0.5) in both cell lines. BCG treatment significantly increased lipid peroxidation (p ≤ 0.001) and DNA damage (p ≤ 0.05) in UC cells after 72h. Addition of iNOS inhibitor 1400W nullified the increase in NO, lipid peroxidation, and DNA damage.
The research group concludes that exposure of UC cells to BCG initiates a temporally complex COS response in the treated cells. Early production of H2O2 post BCG treatment suggests that H2O2 acts to initiate a primary wave of oxidative stress. Continued production of H2O2 leads to induction of NO and superoxide as a second wave of COS which leads to lipid peroxidation and DNA damage. NO has been shown to play a direct role in the induction of intracellular signaling, gene expression, and phenotypic changes including cellular necrosis and release of HMGB1. COS appears to play a central role in mediating the direct effects of BCG on UC cell biology. In conclusion COS is a candidate for targeted manipulation with the intent of increasing the efficacy of BCG.
Presented by Gopitkumar Shah, MD at the American Urological Association (AUA) Annual Meeting - May 16 - 21, 2014 - Orlando, Florida USA
Milwaukee, WI USA
Written by Achim Lusch, MD, University of California (Irvine), and medical writer for UroToday.com