To study the early alterations in
carcinogenesis, we determined apoptosis and proliferation in rat
mucin depleted foci (
MDF), precancerous lesions in the colon under basal conditions and 24 h
after treatment with
1,2-dimethylhydrazine (
DMH), which induces apoptosis in the colon. Spontaneous apoptosis in
MDF was higher than in normal mucosa (Apoptotic Index was 1.61 ± 0.30 and 0.21 ± 0.02 in
MDF and normal mucosa, respectively, mean ± SE, p < 0.05).
DMH (30 and 75 mg/kg) increased apoptosis in both normal mucosa and
MDF (up to 20 times higher compared to basal levels in normal mucosa, but only two times in
MDF).
MDF had a higher and deregulated pattern of proliferation along the crypt compared to normal mucosa. After
DMH, proliferation in normal mucosa was significantly depressed, but it did not vary in
MDF. Survivin-Birc5 regulating apoptosis and proliferation was significantly over-expressed (RT-qPCR and immunohistochemistry experiments) in
MDF vs. normal mucosa, but did not vary in response to
DMH. The expression of the
pro-apoptotic protein Bak did not vary in normal mucosa and
MDF. Since
inflammation is present in
MDF, which may hamper apoptosis, we studied the effect of pre-treatment with
aspirin (600 ppm in the diet for 10 days). No significant effects of
aspirin were observed. In conclusion,
MDF had a higher spontaneous apoptosis and proliferation coupled with a reduced response to apoptotic stimuli from cytotoxic compounds.
Survivin over-expression in
MDF indicates that this is an early event in colon
carcinogenesis and suggests that down-regulation of
Survivin may represent a strategy for
cancer prevention.