Surgical Induction of Endometriosis in Rhesus Macaques, Macaca mulatta.

Objective: Endometriosis is a disorder where endometrium-like tissues form lesions at ectopic sites outside of the uterus. Spontaneous endometriosis occurs only in women and menstruating nonhuman primates (NHPs). Progress on new therapies for endometriosis has been slow due to limited physiologically relevant animal models for preclinical studies of the disease. Inducing endometriosis in the baboon by inoculating the abdominal cavity with endometrial currettings is currently the most physiologically relevant model for in vivo studies of the disease. However, research in the baboon is limited by the cost and housing constraints associated with large NHPs. In contrast, macaques are the preferred NHP in many research institutes and the pharmaceutical industry, but the development of a reliable method of inducing endometriosis has been elusive. Anatomical restrictions in the macaque cervix prevent endometrial curettage to collect menstrual endometrium for inducing disease as is done in the baboon. Our goal was to develop a reliable and reproducible method for inducing endometriosis in macaques. Methods: Adult ovariectomized rhesus macaques (n=3) with no history of endometriosis were treated sequentially with estradiol and progesterone to induce artificial menstrual cycles. On day 2 of the menstrual phase of the first cycle, the animals underwent laparoscopic surgery during which a 20 cm, 14 gauge needle attached to a 3 cc syringe was passed percutaneously through the myometrium of the uterine fundus into the endometrial space. Menstrual debris was collected and immediately seeded into the intraperitoneal cavity. The animals were allowed to recover from surgery for one menstrual cycle and the procedure was repeated for two additional cycles (totaling three inoculations over three cycles). Prior to inoculations, animals underwent exploratory laparoscopy and the presence of endometriotic lesions was recorded. Lesions were collected in the proliferative phase of the fourth cycle. Results: Inoculations with menstrual debris created endometriosis in all three animals. Laparoscopic evaluation revealed that one animal developed Stage III disease with extensive lesions in the uterine cul-de-sac after the second inoculation. The other two animals developed Stage I-II disease after three inoculations. Immunohistochemistry of the lesions revealed endometrium-like glands and stroma, with abundant proliferating cells and strong staining for estrogen receptor-1 and progesterone receptor. Conclusion: Laparoscopic collection and immediate seeding of menstrual endometrium can reliably induce endometriosis in the rhesus macaque. Induced, early stage endometriosis in macaques parallels development of the disease in women and provides a stable animal model for in vivo studies. The accessibility and reproducibility of this animal model presents a valuable resource for future preclinical studies. Supported by P51 RR00163.