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Objectives: Our aim was to perform a comprehensive analysis of the antioxidant capacity of transitional cell carcinoma (TCC) of urinary bladder and discern the role of enzymes associated with glutathione (GSH) in maintaining high GSH levels in these tumours. Because the redox-sensitive protein glutathione S-transferase P1 (GSTP1) might provide an important link between high antioxidant capacity and inhibition of apoptotic pathways, we also explored how the redox state in tumour cells interacts with the expression of GSTP1., Methods: We examined spectrophotometrically the specific activities of GSH-replenishing enzymes involved in GSH synthesis (gamma-glutamylcysteine synthetase, gamma-GCS), GSH regeneration (glutathione reductase, GR), and antioxidant protection (glutathione peroxidase, GPX; superoxide dismutase, SOD) in the cytosolic fraction of tumours and the surrounding normal tissue of 30 TCC patients. GSTP1-1 expression was also analyzed., Results: We found a significant increase in the activity of both GSH-replenishing and antioxidant enzymes as well as enhanced GSTP1-1 expression in tumours in comparison with adjacent normal uroepithelium. Mean gamma-GCS and GR activities in tumours were about 4- and 2-fold higher, respectively, than in corresponding normal tissue. Expression of GSTP1 correlated significantly with GSH level and gamma-GCS and GR activities. GPX and SOD activities in TCC were also markedly increased., Conclusions: Enhanced GSH-replenishing pathways account for increased GSH levels in TCC. Upregulated GPX and SOD also contribute to high antioxidant potential in TCC. Under such conditions, expression of redox-sensitive GSTP1 protein is upregulated.