Quantification of endometriotic lesions in a murine model by fluorimetric and morphometric analyses

Development of a domestic animal model for endometriosis: Surgical induction in the dog, pigs, and sheep

Background:

Endometriosis affects one in ten women of reproductive age but it is diagnosed at advanced stages. Our objective was to develop a domestic animal model that would permit sequential assessment of endometriotic changes.

Materials and methods:

Surgical transplantation of endometrial tissue and fat (n = 4 grafts/tissue/animal) was done in dogs (n = 5), pigs (n = 4), and sheep (n = 5). Autologous grafts were sutured to the visceral (urinary bladder in dogs and pigs and uterus in sheep) and parietal peritoneum. Sham surgeries were performed (dogs and sheep n = 5 and pigs n = 3) by placing fat grafts alone. Plasma estrogen and progesterone concentration was performed prior to surgery and weekly following surgery until euthanasia. Animals were euthanized between 80 and 110 days after surgery. Gross and histopathologic features of endometriotic lesions were recorded.

Results:

A variety of lesions from transplanted endometrial grafts included endometriotic cysts, vesicles, solid lesions, or absence of lesions. The proportion of cysts was greater (p < 0.01) in dogs (18/20 grafts) than in pigs (5/16) and sheep (5/20). The area of endometriotic lesions at the time of euthanasia was greater than at the time of surgery in dogs (0.89 ± 0.11 cm2 vs 0.50 ± 0.09 cm2; p < 0.05), whereas, the size of lesions decreased (p < 0.05) by half or more in pigs and sheep. In dogs, endometrial cysts were characterized by simple cuboidal/columnar epithelium, endometrial glands, stromal tissue with hemorrhage and/or hemosiderin-laden macrophages, and smooth muscle cells.

Conclusion:

The development of endometriotic cysts was apparent in dogs than in sheep and pigs. Therefore, dog is a better domestic animal model for endometriosis.

Induction of Endometriosis in Nude Mice by Transplantation of Human Peritoneal Endometriotic Tissue

Purpose

Ectopic endometrial tissue is biochemically and functionally distinct from eutopic endometrium, including differences in receptivity to steroids and invasive potential. For this reason, using ectopic endometrial tissue to induce endometriosis in animal models may be of interest to understand better the pathogenesis of this disease. The aim of this study was to evaluate the potential of human pelvic endometriotic lesions (specifically red lesions) to implant into the peritoneal cavity of nude mice.

Methods

Human peritoneal endometriotic tissue (red lesions) was injected into the pelvic cavity of nude mice. The mice were euthanized after 5 or 14 days, lesions were recovered, and histological analysis was performed. Proliferative activity and neoangiogenesis of lesions were assessed after Ki67 and CD34 immunohistological staining, respectively.

Results

After 5 and 14 days, endometriotic tissue was found to have implanted onto intact mesothelium and reorganized into structured glands and stroma, forming endometriosis-like lesions. These lesions showed considerable proliferative activity and effective neoangiogenesis.

Conclusion

This model represents a promising tool to study in vivo implantation of human ectopic endometrium, which is dissimilar to eutopic endometrium. Moreover, this study shows that glands and stroma detached from red endometriotic lesions are able to implant in other peritoneal sites, as in a metastatic process.

Relevant human tissue resources and laboratory models for use in endometriosis research

Endometriosis is characterized by the growth of endometrium‐like tissue outside the uterus, most commonly on the pelvic peritoneum and ovaries. Although it may be asymptomatic in some women, in others it can cause debilitating pain, infertility or other symptoms including fatigue. Current research is directed both at understanding the complex etiology and pathophysiology of the disorder and at the development of new nonsurgical approaches to therapy that lack the unwanted side effects of current medical management. Tools for endometriosis research fall into two broad categories; patient‐derived tissues, and fluids (and cells isolated from these sources) or models based on the use of cells or animals. In this review, we discuss the literature that has reported data from the use of these tools in endometriosis research and we highlight the strengths and weaknesses of each. Although many different models are reported in the literature, hypothesis‐driven research will only be facilitated with careful experimental design and selection of the most appropriate human tissue from patients with and without endometriosis and combinations of physiologically relevant in vitro and in vivo laboratory models.

Induction of peritoneal endometriosis in nude mice with use of human immortalized endometriosis epithelial and stromal cells: a potential experimental tool to study molecular pathogenesis of endometriosis in humans

OBJECTIVE

To determine whether a mixed population of immortalized human endometriosis epithelial and stromal cells is able to induce peritoneal endometriosis in nude mice.

DESIGN

Prospective experimental study. Human immortalized endometriosis epithelial and stromal cells were xenografted into ovariectomized nude mice. Macroscopically, the number of induced endometriosis-like lesions and their color were determined. Microscopically, histomorphology of endometriosis glands and their structure were analyzed, and comparisons were made with tissue from spontaneous endometriosis in women.

SETTING

College of Veterinary Medicine and Biomedical Sciences, Texas A&M University.

ANIMALS

Seven ovariectomized nude mice.

INTERVENTION(S)

Minimal invasive procedures were performed to administer estrogen pellets and transplant immortalized human endometriosis epithelial and stromal cells into nude mice.

MAIN OUTCOME MEASURE(S)

Peritoneal endometriosis-like lesions induced in nude mice were characterized and compared with spontaneous peritoneal endometriosis in women.

RESULT(S)

Xenografts of human immortalized endometriosis epithelial and stromal cells into the peritoneal cavity of the recipient nude mice are able to proliferate, attach, invade, reorganize, and establish peritoneal endometriosis. Endometriosis glands at different stages of growth were present in induced endometriosis-like lesions. Proliferating cell nuclear antigen, metalloproteinase 2, estrogen receptor-alpha, cyclooxygenase-2, and prostaglandin E(2) receptors EP2 and EP4 proteins were expressed in both endometriosis glandular epithelial and stromal cells of the induced endometriosis-like lesions.

CONCLUSION(S)

This xenograft model could be used as a potential experimental tool to understand the molecular and cellular aspects of the pathogenesis of endometriosis in humans.

Agents blocking the nuclear factor-kappaB pathway are effective inhibitors of endometriosis in an in vivo experimental model

BACKGROUND

In vitro studies suggest that the transcription factor nuclear factor-kappa B (NF-kappaB) is implicated in the transduction of proinflammatory signals in endometriosis. The aim of this study was to investigate the involvement of NF-kappaB and the processes regulated by NF-kappaB in the initial development of endometriotic lesionsin vivo.

METHODS

Endometriosis was induced in nude mice by intraperitoneal injection of fluorescent-labeled menstrual endometrium. Two NF-kappaB inhibitors (BAY 11-7085 and SN-50) were injected intraperitoneally on days 0, 2 and 4 after endometriosis induction, and endometriotic lesions were recovered on day 5. Number, mass, fluorimetry and surface (morphometry) of endometriotic lesions were quantified. NF-kappaB activation, intercellular adhesion molecule (ICAM)-1 expression, cell proliferation and apoptosis were evaluated by immunohistochemical analyses and the TUNEL method.

RESULTS

Both NF-kappaB inhibitors induced a significant reduction in lesion development compared to control mice. NF-kappaB activation and ICAM-1 expression of endometriotic lesions were significantly reduced in treated mice, and cell proliferation was significantly reduced in BAY 11-7085-treated mice. Both inhibitors produced a significant increase in apoptosis of endometriotic lesions, as assessed by active caspase-3 immunostaining and the TUNEL method.

CONCLUSION

This study demonstrates, for the first time, that the NF-kappaB pathway is implicated in the development of endometriotic lesions in vivo and that NF-kappaB inhibition reduces ICAM-1 expression and cell proliferation, but increases apoptosis of endometriotic lesions, diminishing the initial development of endometriosis in an animal model.

In vitro and in vivo approaches to study angiogenesis in the pathophysiology and therapy of endometriosis

Endometriosis represents one of the most common gynaecological disorders. According to the implantation theory, angiogenesis is a major prerequisite for the initiation and progression of the disease. Thus, during the last decade, many studies have focused on the mechanisms regulating angiogenesis in endometriotic lesions. For this purpose, sophisticated in vitro and in vivo approaches have been established, which are highlighted in this review. Enzyme-linked immunosorbent assays demonstrate the imbalance of pro- and anti-angiogenic growth factors in isolated peritoneal fluid from endometriosis patients. Histological, immunohistochemical and gene expression analyses of endometriotic tissue provide detailed information on the angio-architecture of endometriotic lesions and the different growth factor expression by various cell populations. Moreover, cell culture systems are useful tools for the identification of hormonal and immunological factors involved in the angiogenic process. Finally, sophisticated in vivo models, such as rodent models of peritoneal endometriosis as well as the chorioallantoic membrane assay and the dorsal skinfold chamber, allow for the detailed analysis of blood vessel development in ectopic endometrium and the efficacy of angiogenesis inhibitors. The findings resulting from all these approaches will help to provide better insights into the pathophysiology of endometriosis and to establish new anti-angiogenic treatment strategies for the future.

Iron overload enhances epithelial cell proliferation in endometriotic lesions induced in a murine model

BACKGROUND

Iron deposits are characteristic of endometriotic lesions, and pelvic iron concentrations are higher in endometriosis patients than in women without endometriosis. In this study, the effect of iron overload and iron chelation on the development of endometriosis in a murine model was investigated.

METHODS

Human menstrual endometrium was injected i.p. into nude mice, either alone (controls) or supplemented with erythrocytes or desferrioxamine (DFO), an iron chelator. After 5 days, the iron load of endometriosis-like lesions and peritoneal macrophages and fluid was evaluated. Lesions were quantified by immunohistochemical morphometry, and their proliferative activity was assessed.

RESULTS

Injection of erythrocytes into the pelvic cavity caused iron overload in lesions (P < 0.025) and peritoneal macrophages (P < 0.01) and fluid (P < 0.05), whereas DFO effectively reduced iron status in lesions (P < 0.05) and macrophages (P < 0.01) compared with controls. No difference was observed in the number or surface area of lesions between the three groups. Erythrocytes increased (P < 0.05) and DFO significantly decreased (P < 0.01) the proliferative activity of lesions.

CONCLUSIONS

Iron overload does not appear to affect lesion establishment but may contribute to the further growth of endometriosis by promoting cell proliferation of lesions. Iron chelator treatment could therefore be beneficial in endometriosis to prevent iron overload in the pelvic cavity and decrease cellular proliferation of lesions.