Endometrial Metabolism of 17β-Estradiol during the Window of Implantation in Women with Recurrent Implantation Failure

Abstract

Objectives: Alterations in 17β-estradiol metabolism are known to potentially impair endometrial receptivity. Previous pioneering studies have investigated the role of endometrial steroid metabolism by determining steroid hormone levels and steroid-metabolizing enzyme activity in endometrial biopsies of patients undergoing IVF. The activity of oxidative and reductive 17β-hydroxysteroid dehydrogenases (17β-HSDs), which catalyze the interconversion between estrone and 17β-estradiol, was found to be similar between IVF patients who - after fresh embryo transfer in the cycle following endometrial biopsy - did and did not become pregnant. However, inhibition of the reductive enzyme 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1), the most prominent 17β-HSD type in 17β-estradiol formation, was found to differ between groups. The primary objective of this study was to determine oxidative and reductive 17β-HSD enzyme activity in the endometrium of two well-defined groups: IVF patients with recurrent implantation failure (RIF) and control patients.

Design: This is a prospective observational study of IVF patients with RIF (n = 52) and controls (n = 25). Patients undergoing treatment because of pre-implantation genetic testing, a severe male factor, or bilateral tubal pathology were recruited as controls since these conditions did not suggest an endometrial contribution to infertility.

Participants/materials, setting, methods: Endometrial biopsies were obtained 5-8 days after a positive urine ovulation test in a natural cycle using a Pipelle catheter. Activity of oxidative and reductive enzymes, inhibition of 17β-HSD1, 5, 7, and 12, and immunostaining of 17β-HSD7 were performed. The formation of 17β-estradiol by reduction of estrone (reductive enzymes), formation of estrone by oxidation of 17β-estradiol (oxidative enzymes), and inhibition of specific 17β-HSD enzymes were determined using high-performance liquid chromatography. Formalin-fixed paraffin-embedded tissue was used for immunostaining. The Student's t test and Mann-Whitney U test were used for statistical analysis. Multivariate analysis was used to determine the influence of confounders.

Results: No differences were found in activity of oxidative and reductive 17β-HSD enzymes in RIF patients and controls. Combined inhibition of 17β-HSD5, 7, and 12 was significantly lower in the RIF group compared to controls (p = 0.04). Inhibition of 17β-HSD1 and 17β-HSD7 combined was also significantly lower (more production of 17β-estradiol remained) in the RIF group compared to controls (p < 0.01). However, solely inhibiting 17β-HSD1 or 17β-HSD7 showed no significant difference between groups. Immunostaining revealed the expression of 17β-HSD7 in all endometrial samples.

Limitations: Results should be interpreted carefully due to possible cycle-to-cycle variation, challenges to translate in vitro findings to biological conditions, and the heterogeneous etiology of RIF.

Conclusions: Differences in formation of 17β-estradiol in the presence of two specific inhibitors of 17β-HSD1 and 7 between RIF patients and controls were found. Although 17β-HSD1, expressed at the fetal-maternal interface, has been associated with fertility, the potential role of 17β-HSD7 in human implantation has not been previously described. The observed differences between patients with RIF and controls warrant future research on the role of this main enzyme and its lesser-known 17β-HSD type in endometrial receptivity and implantation.

Keywords: 17β-Estradiol; Endometrium; Implantation; In vitro fertilization; Intracrinology.

Fig. 1.

Schematic simplified representation of the conversion of estrone to 17β-estradiol and vice versa by 17β-HSD in the endometrium. The enzymes 17β-HSD1, 5, 7, and 12 have common catalytic reductive enzyme activity (reduction of estrone into 17β-estradiol). The oxidative enzyme 17β-HSD2 catalyzes the oxidation of 17β-estradiol to estrone. Subsequently, 17β-estradiol binds to the ER leading to estrogen-sensitive gene expression. HSD, hydroxysteroid dehydrogenase; ER, estrogen receptor.

Fig. 2.

Activity of reductive (a) and oxidative (b) 17β-HSD enzymes and activity ratio (c) of the reductive and oxidative 17β-HSD enzymes. The conversion of estrone to 17β-estradiol (a), conversion of 17β-estradiol to estrone (b), and the activity ratio of reductive and oxidative 17β-HSDs (c) were similar in the RIF (n = 52) and control (n = 25) group. Box plots show the 25th and 75th percentile within the median, and whiskers indicate 1.5 times the interquartile range.

Fig. 3.

Inhibition of the 17β-HSD1 and 17β-HSD5, 7, and 12 enzyme activity (%) in the control (n = 25) and RIF (n = 52) group. The difference in inhibition of 17β-HSD5, 7, and 12 between the control (n = 25) and RIF (n = 52) group was significant. *p < 0.05.

Fig. 4.

Inhibition of the 17β-HSD1 and 7 in the RIF (n = 31) versus control (n = 24) group. The difference in inhibition was significant. *p < 0.05.

Fig. 5.

Representative example of microscopic immunohistochemical 17β-HSD7 staining in RIF patients and control subjects. Upper left: control subject, ×40 magnification. Upper right: RIF patient, ×40 magnification. Lower left: control subject, ×100 magnification. Lower right: RIF patient, ×100 magnification. Scale bar is given for reference. Glands, stroma, lumen, luminal epithelium, and glandular epithelium are indicated.