Inhibition of in Situ Expression of Aromatase P450 in Leiomyoma of the Uterus by Leuprorelin Acetate

Abstract

We have shown that in situ estrogen synthesized in leiomyoma of the uterus plays a possible role in the promotion of leiomyoma cell growth via an autocrine/paracrine mechanism. In the present study, we demonstrated that leuprorelin acetate, a GnRH agonist widely used for treatment of uterine leiomyoma by down-regulation of pituitary-ovarian function, suppressed the expression of aromatase P450 (an estrogen synthetase) in leiomyoma cells. Given the role of in situ estrogen in leiomyoma cell growth, the inhibition of in situ estrogen synthesis may play a role in GnRH agonist-induced rapid regression of leiomyomas. Quantitative RT-PCR revealed that in women receiving no medication uterine leiomyomas express aromatase P450 mRNA at levels 20 times higher than that in the surrounding myometrium. Leuprorelin acetate treatment (1.88 mg every 4 wk, sc injection) for 12-24 wk reduced the expression of aromatase P450 mRNA in leiomyoma tissue as well as in the myometrium, to approximately one tenth of that in the myometrium of untreated women. Suppression of aromatase P450 expression was also demonstrated by Western blot analysis and aromatase activity assay of microsomal fractions prepared from leiomyomas. On the other hand, no differences in the levels of activity and mRNA of aromatase P450 were observed between leiomyoma cells obtained from women treated with and without leuprorelin acetate injections when cells were cultured ex vivo and stimulated by various combinations of stimulants such as dexamethasone + IL-1beta. The addition of various concentrations of E2 did not affect the aromatase activity of leiomyoma cells, suggesting that deprivation of circulating (ovarian) estrogen is not a cause of decreased expression of aromatase during leuprorelin acetate therapy. On the other hand, 8-d treatment with leuprorelin acetate (100 nmol/liter) reduced dexamethasone + IL-1beta-induced activity and a mRNA level of aromatase by 28% and 42%, respectively. These results indicated that leuprorelin acetate inhibits the expression of aromatase P450 in leiomyoma cells, which contributes to the rapid regression of leiomyoma during leuprorelin acetate therapy.

The aromatase expression in myomas and myometriums of women in reproduction and perimenopausal age.

“…The only suggestion which can be put forward as to the mechanisms maintaining aromatase overexpression reflects the fact that no significant differences have been noted in aromatase expression between myoma cells and ex vivo cultured myometrial cells. When myoma cells become isolated from tissue and placed in a culture, aromatase expression decreases by 5-20% as compared to the values noted in the tissue [10,18,22]. In an ex vivo culture both basal and induced levels of expression are identical in myoma cells and in myometrium originating from the same uterus.…”

“…Some of the genes are stimulated by estrogen and manifest expression level normal for myometrium in conditions of hypoestrogenism, induced by GnRH agonists. Although treatment with GnRH agonists decreases also expression of aromatase in myomas, the estrogen-linked control does not seem to be related to aromatase since treatment with estradiol does not affect aromatase expression level in cultures of myoma cells [18]. The only suggestion which can be put forward as to the mechanisms maintaining aromatase overexpression reflects the fact that no significant differences have been noted in aromatase expression between myoma cells and ex vivo cultured myometrial cells.…”

“…The exogenous estrogen, produced by smooth muscle myomas, probably promotes growth in an autocrine or intracrine manner [11]. Production of estrogen in smooth muscle myomas is inhibited by treatment with GnRH agonist in situ [18] and in vivo [19] due to inhibition of aromatase activity. Shozu et al [20] found that size of smooth muscle myoma was directly related to expression of aromatase mRNA in various smooth muscle myomas within the same uterus.…”

“…Such a conversion takes place mainly in peripheral tissues but, as proven by results of studies on expression of aromatase gene, local synthesis of androgens occurs also in endometrial adenocarcinoma even if the amount of the hormone produced there is not sufficient to increase estrogen pool in the peripheral blood. Even if no direct proof is available for the role of estrogen in in situ growth of myoma cells, the experiment with use of a circulating androstenedione as a substrate showed that myoma cells are capable of synthesizing sufficient amounts of estrogens to promote their own growth [18].…”

“…Since blood androstenedione levels (5-10 nmol/l) in women at early menopause continue to persist close to K M value for aromatase, significant amounts of estrogen can be synthesized in situ taking advantage of plasma androstenedione [11]. Thus, estrogen produced in situ may prevent abrupt regression of myoma cells due to the complete disappearance of the ovarian estrogen [18]. In fact, most of myomas demonstrate no perceptible traits of regression in the course of the first 6 months of natural menopause despite the abrupt decrease in plasma estradiol concentration and the regression is clearly slower in women treated with GnRH agonists.…”