Date of Award


Degree Type


Degree Name

Master of Science


Pharmacology and Toxicology


Dr. Jack R. Bend

Second Advisor

Dr. Subrata Chakrabarti

Third Advisor

Dr. David Freeman


Unconjugated bilirubin (UCB) is the final oxidation product of heme catabolism and can act as a prooxidant. Elevated concentrations of UCB is highly toxic to neonates and the mechanism(s) of toxicity remain(s) unknown. Several differences were recognized when previous work completed on murine Hepa 1c1c7 cells was compared to their human counterpart, the HepG2 cell line. The reason for the resistance of HepG2 cells to UCB-mediated apoptosis, compared to Hepa 1c1c7 cells is related either to the differences in the generation of ROS, the effectiveness of the GSH∕GSSG antioxidant system or the distribution of UCB. Different amounts of ROS were produced in the two cell lines when exposed to UCB, and modulators of GSH content (EtGSH, DEM and/or BSO) over time. Caspase-3 activation did not occur in HepG2 cells treated with UCB or UCB and DEM. Spectrophotometric analysis of UCB revealed that only small amounts of UCB entered HepG2 cells. In addition, there were differences in MAPK phosphorylation (p38 MAPK, SAPK/JNK and ERK1∕2) between the cell lines following treatment with H2O2 or UCB, when assayed by western blot These results allow us to conclude that Hepa 1c1c7 cells and HepG2 cells have altered sensitivities to ROS formation, MAPK phosphorylation and apoptosis upon exposure to equimolar concentrations of UCB.



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