Role of polyamines in the protection of cells from reactive oxygen species.

摘要

Polyamines are positively charged macromolecules that are closely associated with negatively charged macromolecules including DNA, proteins, and phospholipids. Polyamines are required for cellular growth and differentiation of all cells however the roles they play in these processes is not well characterized. As a result of the importance of polyamines in tumorigenesis, the biosynthetic pathway has been targeted in the fields of chemoprevention and chemotherapy. Both the chemopreventive potential of inhibitors of the polyamine biosynthetic pathway, specifically α-difluoromethylornithine (DFMO), and the chemotherapeutic potential of polyamine analogues are currently being investigated in Phase II trials.; Previous investigations, mostly in cell free systems, have supported that polyamines protect DNA and phospholipids from exposure to reactive oxygen species (ROS). The purpose of this study was to investigate the role that the individual polyamines, Spd and Spm, play in protecting cells from ROS. In these studies, Spm deficient (Gy11) fibroblast cells exhibited similar sensitivities as normal (N6) cells to exposure to a variety of ROS. These data support the hypothesis that total polyamine levels, not Spm alone, are important in determining sensitivity to ROS. Spm deficient Gy11 cells exhibit substantial enhanced sensitivity to gamma irradiation and to H₂O ₂ as compared to N6 cells. These data demonstrate that at low intracellular polyamine concentrations, the role of Spm is not replaceable by Spd in protecting against gamma irradiation and H₂O₂ induced oxidative stress. Incubation with either Spd or Spm restored both cell types to normal levels of sensitivity to both H₂O₂ and gamma irradiation induced growth inhibition, supporting that Spm and Spd have equal roles in cytoprotection at physiological concentrations. Depletion of both glutathione (GSH) and endogenous polyamines in Gy11 and N6 cells resulted in increased sensitivity to H₂O₂ as compared to GSH depletion alone.; The results of the current investigations provide strong evidence that the polyamines Spm and Spd are essential in protecting cells from exposure to oxidative stress. These data suggest that although polyamines can lead to tumorigenesis at high concentrations through the augmentation of promotion, low levels may lead to elevated oxidative stress that could result in cellular damage, potentially leading to increased initiation.