Beneficial effects of aromatase inhibitors on endometriotic lesions in an animal model

BILOTAS M; MERESMAN GF; STELLA I; SUELDO C; BARAÑAO RI

New Orleans, USA

Congreso; 62nd Annual meeting of the American Society for Reproductive Medicine; 2006

Objective: Endometriosis (EDT) is considered to be an estrogen-dependent disease and recent studies have shown that patients with EDT have high levels of aromatase P450 expression in the eutopic and ectopic endometrial tissue. Aromatase inhibitors are currently used in postmenopausal women to treat breast cancer. The objective of this study was to evaluate the effect of aromatase inhibitors (Letrozole and Anastrozole) on the implantation, proliferation and apoptosis of ectopic endometrial tissue “in vivo”, in an animal model. Design: We employed an experimental model of EDT in which we induced endometriotic lesions by implanting fragments of one autologous uterine horn in the mesothelium of Balb/c mice. After 28 days of treatment with aromatase inhibitors (beginning on day 1 post- induction of EDT) lesions were measured, and proliferation and apoptosis were assessed in histological samples. Materials and Methods:  For the experiments we employed 51 two months old female Balb/c mice, that were divided in three groups: Control (n=19), Anastrozole (n=16) and Letrozole (n=16).  All animals had surgery performed to induce the formation of endometriotic lesions, followed by treatment that started the following day. The treatment consisted of a daily s.c. injection of either Anastrozole (10 mg/day), Letrozole (10 mg/day) or saline (control). After 28 days of treatment the animals were sacrificed and the endometriotic lesions were counted and their size measured. Subsequently, the lesions were removed for further pathological evaluation. Histological samples of the lesions were used to evaluate cell proliferation and apoptosis. Cell proliferation was quantified by immunohistochemistry using a polyclonal anti-PCNA antibody and the percentage of apoptotic cells was quantified by means of the TUNEL technique. Statistical analysis was done by the non-parametric Kruskal-Wallis ANOVA test, followed by Dunn’s multiple comparisons test. Results: The percentage of animals that developed EDT and the number of lesions per animal were similar in all groups. On the other hand, the size of the endometriotic lesions was significantly smaller in the Anastrozole group (p< 0.05 vs. control) and in the Letrozole group (p<0.001 vs. control).  We found that both Letrozole and Anastrozole treatments produced a significant decrease in cell proliferation in the lesions, (p<0.01 and p<0.001 vs. control respectively). In addition, the assessment of apoptosis showed a significant increase in apoptosis both after Anastrozole (p<0.05 vs. control) and Letrozole (p<0.01 vs. control) treatments. Conclusions: The treatment of endometriosis with aromatase inhibitors in this animal model did not prevent the establishment of the lesions but significantly diminished the size of the lesions. Also, aromatase inhibitors inhibited cell proliferation in the EDT lesions and increased apoptosis levels. These data support further investigation on the use of aromatase inhibitors as treatment for EDT. Support: This study was supported by Grant PIP 02092 from the National Research Council of Argentina (CONICET)