Estradiol and progesterone regulate proliferation and apoptosis in colon cancer.

Epidemiological studies describe estrogens as protectors in the development of colon cancer in postmenopausal women treated with hormone replacement therapy. However, the role of progesterone in colon cancer has been minimally studied and the results are controversial. For the above, the objective of this work was to determine the hormonal regulation exerted by natural ovarian steroids on proliferation and apoptosis in an experimental model of colon cancer in ovariectomized rats treated with 17-beta estradiol and progesterone. Sprague-Dawley rats were exposed to the carcinogen 1,2-dimethylhydrazine to induce colon tumors. Thirty days later, the rats were ovariectomized and treated with estradiol (60 µg/kg), progesterone (10 mg/kg), estradiol plus progesterone (60 µg/kg and 10 mg/kg) or vehicle. We observed no significant differences in colon cancer incidence and tumor multiplicity between the groups. Nevertheless, we observed a decrease in PCNA expression and a greater number of apoptotic index, higher expression of caspase 3, cleaved PARP and cleaved caspase 8 in tumors, confirming the activation of the extrinsic pathway of apoptosis by the combined treatment. In addition, we observed a higher expression of estrogen receptor beta in these tumors. We conclude that the action of both hormones, estradiol and progesterone, is necessary to reduce proliferation and increase apoptosis in colon tumors, probably through estrogen receptor beta activation.

Experimental hypothyroidism increases apoptosis in dimethylbenzanthracene-induced mammary tumors.

Epidemiological and in vitro data have not provided conclusive evidence concerning the involvement of thyroid hormones (THs) on mammary carcinogenesis. We used an in vivo model to assess the relationship between THs, adipose tissue and breast cancer development. Female Sprague­Dawley rats were treated with a dose of 7,12-dimethylbenz(a)anthracene (15 mg/rat) at 55 days of age and were then divided into four experimental groups: hypothyroid rats (HypoT, 0.01% 6-N-propyl-2-thiouracil in drinking water), untreated control (EUT); hyperthyroid rats (HyperT, 0.25 mg/kg/day T4 s.c.) and vehicle-treated control rats. The latency of tumor appearance and the incidence and progression of tumors were determined. At sacrifice, blood samples were collected for hormone determinations and samples of tumor and mammary glands were obtained for immunohistological studies. HypoT rats had retarded growth and an increase in mammary fat. The latency was longer (p<0.0001), the incidence rate was lower (p<0.05) and tumor growth was slower in HypoT rats compared to EUT and HyperT rats. Mitotic index and PCNA immunostaining were similar in all groups. HypoT rats showed increased apoptosis (p<0.05) as evaluated by the apoptotic index and TUNEL staining. No differences in serum prolactin and progesterone were observed. However, circulating estradiol (E2) was significantly lower in HypoT and HyperT rats. Serum leptin levels were reduced in HypoT rats even though the abdominal fat mass was similar in all groups. To note, the leptin level was higher in HypoT rats that developed mammary tumors than the level in non-tumoral HypoT rats. In conclusion, hypothyroidism altered animal growth, breast morphology, body composition, leptin secretion and serum E2 enhancing apoptosis and, consequently, retarding mammary carcinogenesis in rats.