Three-dimensional structure micelles of heparin-poloxamer improve the therapeutic effect of 17β-estradiol on endometrial regeneration for intrauterine adhesions in a rat model.

Intrauterine adhesions (IUA) frequently occur after infectious or mechanical injury to the endometrium, which may lead to infertility and/or pregnancy complications. There are few effective treatments due to the complex function of endometrium and shortage of native materials. 17β-estradiol (E2 ) is commonly used as an ancillary treatment in IUA patients, but it is limited by its poor solubility in aqueous solutions and low concentrations at the injured sites. In this research, a mini-endometrial curette was used to injure the rat's endometrium to form an IUA model. 17β-estradiol was encapsulated into the micelles of heparin-poloxamer and a thermosensitive hydrogel (E2 -HP hydrogel) was formed. This sustained releasing system was applied to restore the structure and function of the injured uterus. E2 -HP hydrogel was constructed and relevant characteristics including gelation temperature and micromorphology were evaluated. Sustained release of 17β-estradiol from HP hydrogel was performed both in vitro and in vivo. Ultrasonography measurement and pathologic characteristics on the IUA rats were performed to evaluate the therapeutic effect of E2 -HP hydrogel. Endoplasmic reticulum (ER) stress-related apoptosis was analyzed to explore the possible mechanisms in IUA recovery. E2 -HP hydrogel showed a prolonged release of E2 at the targeting region and more effective endometrium regeneration in IUA rats. Significant improvements in both gland numbers and fibrosis area were observed in the E2 -HP hydrogel group. We also demonstrated that E2 -HP hydrogel in the recovery of IUA was closely related to the suppression of ER stress signals via the activation of downstream signals, PI3K/Akt and ERK1/2. HP hydrogel might be an effective approach to deliver E2 into the injured endometrium. Therapeutic strategies targeting ER stress using E2 -HP hydrogel might be a promising solution for the treatment of women with intrauterine adhesions.