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Chronic inflammation is
a significant risk factor for the development of urinary bladder cancer.
We showed previously that inflammation induced by killed Escherichia coli
strikingly enhanced N-methyl-N-nitrosourea (MNU)-initiated rat bladder carcinogenesis.
We also demonstrated a marked increase in several cytokines, including TNF-
alpha , in aspirates from bladders treated with killed E. coli. In the present
investigation, we tested the hypothesis that TNF- alpha released during
inflammation was causally related to the development of bladder cancer.
Using growth in soft agar and tumorigenicity in athymic nude mice as indices
of transformation, we examined the effect of TNF- alpha on the enhancement
of H2O2-initiated transformation of MYP3 cells; MYP3 is an anchorage-dependent
nontumorigenic rat urothelial cell line. We have already demonstrated that
H2O2 is a potent transforming agent which is released during the inflammatory
process. MYP3 cells pretreated with H2O2 were exposed to TNF-alpha (0 to
100 ng/ml) for 1 week in monolayer culture and were then subjected to growth
in soft agar. A marked increase in the number of colonies was observed in
the cells that were first treated with H2O2 and subsequently exposed to
TNF-alpha, as compared with the untreated control (p < 0.001). In addition,
treatment with TNF-alpha alone caused colony formation and was associated
with a 6.5- to 8.7-fold increase in intracellular H2O2 (p < 0.001). Addition
of an antioxidant, alpha-tocopherol, resulted in a significant reduction
in the number of colonies induced by TNF-alpha (p < 0.001). The transformants
induced by TNF-alpha have acquired the potential of anchorage-independent
growth and tumorigenicity in athymic nude mice. Our results suggest that
TNF-alpha-induced transformation in urothelial cells is due to induction
of H2O2, and that this may be one of the mechanisms involved in the carcinogenesis
in vivo associated with chronic urinary tract infection. |
