Human ceruloplasmin exhibited different antioxidant effects according to the electron donors in a metal-catalyzed oxidation system. Purified ceruloplasmin did not play a significant role in the protection of DNA strand breaks in the ascorbate/Fe 3+ /O P system. However, when ascorbates were replaced with a thiol-reducing equivalent such as dithiothreitol, DNA strand breaks were significantly prevented by the same amount of ceruloplasmin. Ceruloplasmin did not catalyze the decomposition of H P O P in the absence of reduced glutathione. On the contrary, ceruloplasmin showed a potent peroxidase ability to destroy H P O P in the presence of reduced glutathione.In conclusion, the removal of H P O P by human ceruloplasmin is not simply stoichiometric but thiol-dependent.z 1998 Federation of European Biochemical Societies.

An increment of thioredoxin-1 (TRX) is observed in many human primary cancers and appears to contribute to an increase of cell growth and a resistance to chemotherapy. On the contrary, when TRX was overexpressed in the HT-1080 fibrosarcoma cells, the cell growth was retarded and chromosomal polyploidy and cellular senescence were induced. TRX-overexpression made HT-1080 cells resistant to an oxidative stress caused by H 2 O 2 or paraquat. But these cells were significantly sensitive to ionizing radiation, showing an abrogation of the G 2 checkpoint. Their DNA contents were twice of the controls and they expressed typical senescence markers. Their expression levels of p53 and cyclin-dependent kinase inhibitors (CDKI) were about 2-3-fold higher than the control. Nevertheless, cyclin D1 and D3, which are negatively regulated by CDKIs, were also increased. Overall, in HT-1080 cells the TRX-overexpression created a state of cellular senescence caused by a simultaneous stimulation of the mitogen-activated pathways and an inhibition of the cyclin-dependent kinases, which is known as a hypermitogenic arrest.

In previous studies, polyamine depletion by DFMO (alpha-difluoromethylornithine)-treatment reduced H(2)O(2)-induced apoptotic cell death by reduction of ferric ion uptake. In the present study, we analyzed the reduction of radiation-induced cell death by polyamine depletion. Exposure of HT29 cells to radiation induced severe cell death, but when cells were pretreated with DFMO, a specific inhibitor of polyamine biosynthesis, radiation-induced cell death was reduced to 50-60% of control. Cell cycle analysis showed that, in these cells, the time to reach the G(2)/M phase arrest was delayed for 20-24 h compared to the control cells, at which stage the fate of cells exposed to ionizing radiation is determined. DFMO-treated cells also showed a low level of thioredoxin, which is a high-level determinant of the cellular fate. To investigate the relationship between the G(2)/M phase arrest and the reduction of thioredoxin caused by polyamine depletion, we also analyzed thioredoxin-antisensed (asTRX) HT29 cells as for DFMO-treated cells. In asTRX-transfected cells, the gamma-irradiation-induced G(2)/M phase arrest was also significantly delayed and radiation-induced cell death was profoundly reduced, as in the DFMO-treated cells. Both sets of cells showed a decrease of cyclin D1 and an increment of HSP25, which are involved in radiation-induced cell cycle progress. Overall, these results suggest that polyamines are essential for normal cell death of HT29 cells triggered by gamma-radiation and that this is partially mediated by the regulation of thioredoxin expression.

Metabolism of lactate dehydrogenase (EC 1.1.1.27, LDH) was studied to identify the function of LDH-C. Tissues of LDH liver-specific Ldh-C expressed Carassius auratus and eye-specific Ldh-C expressed Lepomis macrochirus after starvation were studied. LDH activity in liver tissue from C. auratus was increased after starvation. And LDH specific activity (units/mg) and LDH/CS were increased in tissues. It means the anaerobic metabolism was taking place in C. auratus after starvation. LDH B4 isozyme was decreased in skeletal muscle and increased in heart tissue. LDH C4 isozymes those showed in eye and brain tissues were identified as liver-specific C4 isozymes and disappeared after starvation. And C hybrid in eye, A4 isozyme in brain, and both C hybrid and C4 isozyme in liver tissue were increased, respectively. In L. macrochirus, the level of variation of LDH activities was low but greatly increased especially in eye tissue and LDH A4 and AC hybrid were increased in brain tissue. The LDH activities in tissues from C. auratus and L. macrochirus remained 30.30-18.64% and 25-18.75%, respectively, as a result of the inhibition by 10 mM of pyruvate. The Km PYR values of LDH in C. auratus were increased. As a result, LDH liver-specific C4 isozyme was expressed in liver, brain and eye tissues during starvation. It seems metabolism of lactate was predominant in brain tissue. After starvation, the liver-specific LDH-C was affected more than eye-specific LDH-C.

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