Immunological aspects of surgically induced experimental endometriosis: variation in response to therapy

Animal Models in Endometriosis Research

The initiation of endometriosis in women is difficult to investigate, because there is usually a delay of several years from the onset of lesion development to the clinical diagnosis. Animal models of endometriosis, on the other hand, provide an important contribution to the investigation of the disease pathogenesis and the efficacy of therapeutic intervention strategies.

Increased cell proliferation in experimentally induced endometriosis in rabbits

OBJECTIVE

To characterize the pattern of cell proliferation and apoptosis of eutopic and ectopic endometrium in rabbits after endometrium implantation for the experimental induction of endometriosis.

DESIGN

Animal experimental study.

SETTING

Sector of experimental surgery.

ANIMAL(S)

Twenty-female New Zealand rabbits.

INTERVENTION(S)

All animals underwent laparotomy for endometriosis induction by resection of one uterine horn, isolation of the endometrium, and fixation of tissue segment to the pelvic peritoneum. Two groups of 10 animals were sacrificed 4 and 8 weeks after endometriosis induction. The lesion was excised together with the opposite uterine horn for endometrial gland and stroma determination.

MAIN OUTCOME MEASURE(S)

Cell proliferation and apoptosis were determined in the eutopic and ectopic endometrium, and the cell proliferation index (CPI) and apoptotic index (AI) were calculated as the number of labeled cells per 1,000 cells. The tissue homeostasis index was the CPI/AI ratio. Glands and stroma were analyzed separately.

RESULT(S)

The CPI for ectopic tissue was increased compared with eutopic tissue, but there was no difference in the ectopic lesions between 4 and 8 weeks of induction. Considering only the AI, eutopic and ectopic endometrium did not differ after 4 weeks, but differed significantly in glandular tissue after 8 weeks. The tissue homeostasis index revealed cell proliferation in these tissues, with a CPI/AI more than 1.

CONCLUSION(S)

Ectopic lesions seem to have a higher CPI than eutopic endometrium, with uncontrolled tissue growth occurring in induced endometriotic lesions.

Animal models in endometriosis research

Endometriosis is a common gynaecological disease, defined as the presence of endometrial tissue outside the uterus, causing pelvic pain and subfertility in approximately 10% of women of reproductive age. Current therapies lead to pain relief, however, do not address the causes and entail severe side effects. Still little is known about the pathogenic processes leading to the development and maintenance of endometriosis. Because endometriosis occurs spontaneously only in humans and some non-human primates, animal models of induced endometriosis have been developed and are of high value for the evaluation of pathophysiological mechanisms underlying the development of this disease. These experimental models include the autotransplantation of uterine fragments into the peritoneal cavity of rodents and non-human primates or the heterotransplantation of human endometrial or endometriotic tissue to immunodeficient mice or onto the chicken chorioallantoic membrane (CAM). This review describes the animal models for endometriosis and assesses their different potentials and limitations in regard to endometriosis research, with the aim of developing novel non-invasive diagnostic tools and improved strategies for the treatment of endometriosis in women.

An improved mouse model for endometriosis allows noninvasive assessment of lesion implantation and development

OBJECTIVE

To test whether fragments of human endometrium transduced with the green fluorescent protein (GFP) cDNA and transplanted into nude mice can be noninvasively visualized.

DESIGN

A murine experimental model for human endometriosis.

SETTING

A biotechnology company.

ANIMAL(S)

Ovariectomized nude mice.

INTERVENTION(S)

Whole fragments of human endometrium were transduced in vitro by adenoviral infection with the GFP cDNA before transplantation into nude mice. Animals were noninvasively and repeatedly imaged before lesion collection.

MAIN OUTCOME MEASURE(S)

Fluorescence of GFP-expressing human endometrial fragments was evaluated before transplantation into animals. Development of endometriotic lesions was monitored through direct visualization of fluorescent tissue in the living animal or through conventional dissection.

RESULT(S)

GFP gene transfer into whole endometrial fragments can be performed, and a high proportion of cells express the reporter gene. Fluorescent endometrial fragments implant in nude mice and form endometriotic-like lesions, which can be directly visualized through the skin of living mice using a simple imaging device.

CONCLUSION(S)

This improved mouse model allows noninvasive and dynamic studies of lesion implantation and development to be conducted. In addition to helping better understand the pathophysiology of the disease, this model represents a valuable preclinical tool for testing the efficacy of new drugs targeting endometriosis, which should ultimately accelerate their development phase.

Was Sampson wrong?

OBJECTIVE

Sampson's theory of reflux menstruation suggests that endometriosis is one form of a condition known as an autotransplant. This study seeks to characterize autotransplants as they are described in the literature and to determine whether endometriosis resembles an autotransplant.

DESIGN

Literature review of published studies containing the following types of information: [1] characterization of the histologic features, immunohistochemistry, or structural function of autotransplants; and [2] comparisons of endometriosis with endometrium.

MAIN OUTCOME MEASURE(S)

Characteristics of multiple types of autotransplants were noted. Similarity or dissimilarity of endometriosis and endometrium was tabulated to judge qualitatively whether the bulk of the evidence supports the notion that endometriosis is an autotransplant.

RESULT(S)

Autotransplants remain very similar or identical to eutopic tissues of origin, regardless of the length of time following autotransplantation. Endometriosis differs in many profound and fundamental ways from eutopic endometrium, including clonality of origin, enzymatic activity, protein expression, and histologic and morphologic characteristics. A minority of studies has found similarities between endometriosis and eutopic endometrium.

CONCLUSION(S)

Endometriosis is dissimilar to eutopic endometrium and therefore lacks characteristics of an autotransplant. Sampson's theory of origin of endometriosis is not supported by the results of this study. Studies of experimental endometriosis that have not used menstrual endometrium may be misleading.

Leukocyte subpopulation changes in rats with autotransplanted endometrium and the effect of danazol

PROBLEM

This study examines immune cell populations in rats with autotransplanted endometrium and determines the effect of danazol on leukocyte subsets.

METHODS

As an experimental model of endometriosis, an autologous endometrial segment was implanted in the rat peritoneum. We used flow cytometry to analyze lymphocyte subsets in the peripheral blood (PB) and peritoneal fluid (PF) of the following groups of rats: no treatment, sham operation, endometrial implantation, endometrial implantation treated with danazol, and normal rats treated with danazol.

RESULTS

The natural killer (NK) cell population was decreased in both the PB and PF of rats with autotransplanted endometrium. Moreover, NK cells increased in a dose-dependent manner following danazol administration. Surgery itself increased the number of peritoneal macrophages as compared with the untreated group. This elevation was suppressed partially by endometrium-implantation and was attenuated by subsequent administration of danazol in a dose-dependent fashion.

CONCLUSIONS

These data suggest that ectopic endometrial cells may release immunosuppressive factors. This is the first documentation that rats with autotransplanted endometrium show the same immunologic changes as humans with endometriosis, and establishes the utility of this model for the study of endometriosis.

Receptor concentrations for estradiol and progesterone in surgically induced endometriosis in the rat

In order to obtain more detailed information about the validity of the rat as an endometriotic experimental model, endometriosis was surgically induced in 48 female Wistar rats, and the estrogen (ERc) and progesterone (PRc) receptor concentrations present in experimental endometriosis and endometrium were compared in the four estrous phases (n = 12). Lower values of ERc were found in endometriosis than in endometrium (proestrus, 156.27 +/- 24.09 vs. 195.27 +/- 32.13 pmol/g tissue, P < 0.05; estrus, 302.33 +/- 45.16 vs. 335.67 +/- 44.82 pmol/g tissue, P < 0.05; metestrus, 166.60 +/- 26.09 vs. 193.30 +/- 22.04 pmol/g tissue, P < 0.05; diestrus, 130.27 +/- 20.58 vs. 135.81 +/- 16.25 pmol/g tissue, P > 0.05; Student's t-test). As in the case of ERc, lower PRc were observed in endometriotic than in endometrial tissues (proestrus, (proestrus, 137.83 +/- 22.64 vs. 176.54 +/- 21.78 pmol/g tissue, P < 0.05; estrus, 242.10 +/- 34.78 vs. 286.20 +/- 31.74 pmol/g tissue, P < 0.05; metestrus, 194.36 +/- 35.08 vs. 224.73 +/- 20.21 pmol/g tissue, P < 0.05; diestrus, 147.72 +/- 26.21 vs. 147.33 +/- 22.65 pmol/g tissue, P > 0.05; Student's t-test). Similar ERc/PRc ratios were found for both the endometriotic and the endometrial tissues (proestrus, 1.14 +/- 0.07 vs. 1.08 +/- 0.09, P > 0.05; estrus, 1.29 +/- 0.19 vs. 1.21 +/- 0.18, P > 0.05; metestrus, 0.87 +/- 0.14 vs. 0.89 +/- 0.11 P > 0.05; diestrus, diestrus, 0.89 +/- 0.06 vs. 0.92 +/- 0.06, P > 0.05; Student's t-test, NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Markers for endometriosis

Screening for endometriosis is subject to general rules. The two most important conditions, i.e. the disorder should be well-defined and serious, and there must be an effective way to treat or prevent it through screening, are not satisfied for endometriosis. Given the lack of understanding of the pathogenesis of this disease and the disreputable evidence of treatment effectiveness, other criteria for worthwhile screening programmes, such as prevalence, cost effectiveness and screening test performance, cannot be evaluated. Markers may be applied in the diagnostic process in the individual patient, although it should be realized that the best results will be obtained in patients with advanced disease, in whom routine pelvic examination will establish the diagnosis on purely clinical grounds anyway. The development of appropriate tissue markers may in the future shed more light on the intricate mechanisms involved in the pathogenesis of endometriosis.

Experimentally induced endometriosis in rats: effect on fertility and the effects of pregnancy and lactation on the ectopic endometrial tissue

OBJECTIVE

To investigate the repercussion of experimentally induced endometriosis on the fertility of Wistar rats and the effects of pregnancy and lactation on endometrial ectopic implants.

DESIGN

Eight-five animals were used for the experiment. Experimental endometriosis was induced in 44 and the remaining 41 were sham-operated (control group). After evaluating the growth of the implants in a second laparotomy, all the animals were mated until finding sperm in vaginal smears. In third and fourth laparotomies during pregnancy and lactation, pregnancy rate was determined, and the implants were re-evaluated, being resected for histological study. Serum estradiol (E2) and progesterone (P) levels were also measured.

RESULTS

The pregnancy rate in animals with endometriosis was 65.7% versus 100% in control group. No statistical differences in days of gestation and number of pups were found between the two groups. Ectopic implants underwent a significant regression during lactation period. Serum E2 and P levels and histological features sustained these findings.

CONCLUSION

Experimentally induced endometriosis diminishes pregnancy rate in rats. It is not pregnancy, but the anestrus condition created by lactation that exerts a beneficial effect on experimentally induced endometriosis in rats.

Endometrial antibodies in serum and peritoneal fluid of infertile patients with and without endometriosis

Passive hemagglutination assay was used to evaluate endometrial antibodies in serum and peritoneal fluid of 37 patients with endometriosis and 54 patients without endometriosis. The results showed that the concentration of antibody titers in serum and peritoneal fluid was significantly higher for endometriosis than control patients. The severity of endometriosis has no effect on antibody concentration. Furthermore, the concentration of endometrial antibody titers was significantly higher in serum than peritoneal fluid of patients with endometriosis. These results suggest that serum endometrial antibody assay is specific and valuable for the diagnosis and progress of endometriosis.