| Superoxide radical, O2·-, is produced in mitochondria during normal aerobic metabolism. High levels are known to induce cell damage and cause cell death. However, cells contain large amount of antioxidant enzymes, which provide a defense system, to prevent and repair the damage caused by reactive oxygen species, ROS. Manganese-containing superoxide dismutase, MnSOD, and glutathione peroxidase, GPX, (with glutathione GSH) are primary antioxidant enzymes that convert O2·- to H2O2 and finally to water. The HARV bioreactor that was used provides a low shear environment as culturing system. The low shear stress condition in the vessel inevitably produces heterogeneity that subsequently causes the cell growth to be oxygen diffusion limited.; Therefore, both ROS and the HARV environment affects cell growth. However, analyzing both effects requires a multiscale approach. As a first step, research presented in this thesis takes aim at understanding the mitochondrial H 2O2 level corresponding to various levels of antioxidant enzymes, as well as the distributions of dissolved O2 and CO 2 within the HARV in response to different oxygen consumption rates over time.; Mathematical kinetic models were constructed to test the sensitivity of reaction rate constants and levels of antioxidant enzymes such as MnSOD, GPX, and GSH in combating oxidative stress following the antioxidant biochemical pathway of interest. Computer simulations were performed to study the corresponding H2O2 level to those perturbing factors. To study the distribution of dissolved O2 and CO2 within the vessel, computational fluid dynamic CFD software, Fluent(TM), was employed to solve the three dimensional transient mass transport equations and to simulate the transport of dissolved gases in the HARV under different oxygen consumption rate models.; Mathematical models show that mitochondrial level of H2O 2 depends on the combination of both MnSOD level and the rate of O 2·- production. Time constant of H 2O2 removal is found to be inversely proportional to the product of GPX and GSH levels. Short time CFD simulations show that a low O2 region exists near the radial center of the HARV. Both mathematical and CFD models built provide the necessary bases for more extensive studies of the oxidative stress in cells growing in bioreactors. |
