Studies on over-expression of aromatase in leiomyoma of the uterus and its application for conservative management

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In the this study we characterized in detail the expression of aromatase P450 in leiomyomas to determine the physiological and pathological role of in situ estrogen in the growth advantage of leiomyomas.1) We demonstrated over-expression of aromatase P450 in leiomyoma tissues in comparison to the surrounding myometrium by three different and complementary methods: The levels of aromatase P45O transcripts were quantitated by quantitative competitive RT-PCR The amount of protein was semi-quantitated by Western blot analysis using microsomal fractions of leiomyoma tissues. Enzyme activity was measured by tritiated water-releasing assay using microsomal fractions.2) To identify a cell type that express aromatase P450 in leiomyoma tissues, immunohistochemical analysis was performed on the tissue samples and the leiomyoma cells that were released and cultured from the fresh leiomyoma tissues. Strong immunoreactivity was localized in the cytoplasm of leiomyoma cells.3) To determine whether endogenous aromatase P450 plays a role in the growth promotion of leiomyoma cells, we evaluated the cell W growth of leiomyoma cells treated with various concentration o of estrogens as well as androgens using a WST-1 assay and thymidine incorporation assay. We confirmed mat leiomyoma cells per se synthesize estrogen, which promotes their growth via an autocrine/intracrine mechanism.4) The expression of aromatase P450 in leiomyoma tissues was profoundly suppressed by preoperative gonadotrophin releasing hormone (GnRH) agonist therapy. In vitro experiment indicated that GnRH agonist acted directly on the leiomyoma cells to reduce the expression of aromatase. This direct inhibitory action of GnRH agonist on in situ aromatase seems to contributes to the rapid regression of leiomyoma during GnRH agonist therapy.