The long-term actions of etonogestrel and levonorgestrel on decidualized and non-decidualized endometrium in a mouse model mimic some effects of progestogen-only contraceptives in women

Abstract

Breakthrough bleeding (BTB), a major side effect of long-acting progestogen (p)-only contraceptives in women, is the main reason for discontinuation of their use. To understand the mechanisms of BTB, a mouse model of endometrial breakdown and repair was adapted to evaluate the effects of long-term progestogens on the endometrium. Appropriately prepared mice received either an etonogestrel (ENG)-or levonorgestrel (LNG)-releasing subdermal implant. Forty eight hours after decidualization was induced in one uterine horn the majority of tissues were highly decidualized, designated 0 day (0d). Uteri were collected subsequently at 5-day intervals (to 45d) and both decidualized and non-decidualized horns were analysed for morphological changes, leukocyte infiltration and matrix metalloproteinase expression (MMP). In decidualized horns, large blood vessels (BV) developed and disturbance of tissue integrity was observed at 5d with substantial stromal breakdown by 10d, progressing until 25d when re-epithelialization was initiated. By 45d, the tissue was restored to its pre-decidualized state but with considerable tortuosity of the luminal epithelium. Tissue remodelling was not apparent in the non-decidualized horns before 35d, when hyperproliferation of the luminal epithelium resulted in tortuosity. Changes in morphology were similar with the two progestogens, but occurred more rapidly with LNG. Apart from macrophages, few leukocytes were present in non-decidualized horns but large infiltrates of neutrophils and uterine natural killer cells (uNK) were associated with tissue breakdown in decidualized tissue, many of these cells were MMP9-positive. MMP7 was primarily associated with tissue repair. Therefore, this model mimics some of the changes observed in endometria of women using p-only contraceptives and provides an opportunity for functional studies.

Stimulation of epithelial repair is a likely mechanism for the action of mifepristone in reducing duration of bleeding in users of progestogen-only contraceptives

“…We also show that while some proliferation occurs within the decidua, most is seen within the basal region below the area of tissue breakdown as well as in the repairing luminal epithelium and glands. As previously described, PR are present in scattered cells throughout the decidua in non-treated control endometrium but are up-regulated during endometrial breakdown (Morison et al 2007). However, after mifepristone treatment, PR are highly expressed in cells in the basal region of the breaking down and repairing tissue although not in the repairing or fully repaired epithelium.…”

“…Morphology of cross-sections of endometrium was assessed 12, 18, 24 and 48 h after mifepristone treatment and compared with that of untreated (control; no mifepristone) animals at 0 and 48 h. Control animals at 0 h had a highly decidualized endometrium containing many blood vessels and a closure of the lumen as described previously (Morison et al 2007; Fig. 1).…”

“…In this study, we used a previously described mouse model of long-term ENG exposure (Morison et al 2007) in functional studies to elucidate potential mechanisms underlying the successful use of mifepristone as a treatment for BTB in women. The results show that, in most mice, complete endometrial breakdown and repair occurs within 48 h of mifepristone administration with rapid restoration of an intact luminal epithelium.…”

“…Examination of endometrial morphology showed that large blood vessels developed and subsequently tissue integrity was reduced in the decidualized uterine horn: this was followed by tissue breakdown and eventual repair (Morison et al 2007). This model thus provides an opportunity for functional studies to examine the mechanisms of action of treatment modalities for the bleeding.…”

“…We administered a single dose of mifepristone at a time of endometrial instability to the mouse model for long-term ENG exposure (Morison et al 2007), and examined the endometrium at a number of time points following treatment to determine morphological changes, including epithelial repair, along with alterations in cellular proliferation markers and steroid receptor expression. The data suggest that mifepristone acts by exacerbating the endometrial fragility sufficiently to stimulate repair mechanisms, particularly restoration of an intact luminal epithelium.…”