Is there added value in inducing endometriosis in baboons by laparotomic peritoneal grafting of uterine tissue obtained after hysterotomy?

Abstract

Endometriosis, defined as the growth of endometrium (EM) outside the uterus, can be diagnosed by pelvic laparoscopy, detecting variable phenotypes (such as peritoneal, ovarian endometriotic cysts, adhesions, or deeply infiltrative disease) in various stages (minimal, mild, moderate, or severe). Endometriosis is associated with infertility, pelvic pain, and reduced quality of life (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). The lack of a reliable, noninvasive method for the early detection of endometriosis makes it impossible to study the early development of the disease in women and often results in delayed diagnosis. It is ethically impossible to study the spontaneous evolution of endometriosis in women or to do prospective studies in women controlling for the pelvic condition (endometriosis, normal pelvis, or other pelvic pathology) and for symptoms (pain, subfertility, combined pain and subfertility, or no symptoms).Rodent models for endometriosis research have advantages such as low cost, ease of handling, and the possibility of genetic manipulation using knockout mice and transgenic mice, but the preclinical relevance of these models has been contested because of the wide gap between rodents and humans with respect to phylogenetics, reproductive anatomy and physiology, lack of menstruation, lack of peritoneal fluid, and lack of spontaneous endometriosis. The questionable unphysiologic induction of endometriosis by uterine square autotransplantation leads to major adhesion formation and unphysiologic “endometriotic lesions” that have a limited phenotype when compared with the spontaneous endometriosis found in women or in nonhuman primates (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar).Nonhuman primates represent the most relevant animal models in endometriosis research in view of their similarity to humans with respect to phylogenetics, reproductive anatomy and physiology, the presence of spontaneous endometriosis, and the possibility of induced endometriosis that is macroscopically and microscopically similar to the spontaneous condition. Among nonhuman primates, baboons represent the best documented and validated model for endometriosis research (81 papers according to a PubMed search based on the key words “endometriosis” and “baboon” on December 18, 2012). Baboons offer the following advantages: [1] noninvasive cycle monitoring based on perineal change; [2] continuous nonseasonal breeding; [3] relatively large size and strength (female adult size: 10–15 kg); [4] spontaneous presence of the peritoneal fluid important for the pathogenesis of endometriosis; [5] cross-reactivity of antibodies and DNA/RNA analytical methods between baboons and humans; [6] vaginal transcervical uterine access allowing EM biopsy, embryo transfer, preimplantation embryo flushing, and hysteroscopy; [7] spontaneous retrograde menstruation important for the pathogenesis of endometriosis; [8] minimal to severe spontaneous endometriosis, allowing the study of spontaneous evolution; [9] development of endometriosis within 25 days after intraperitoneal seeding of menstrual EM, allowing the study of in vivo EM-peritoneal interaction, implantation, invasion, and neuroangiogenesis, of cause-effect relationships in endometriosis, of new drugs for treatment or prevention of endometriosis, and of general and reproductive safety of new antiendometriosis drugs; [10] endometriosis-associated infertility studies controlled for the presence of endometriosis (laparoscopy assessment), ovulation (monitoring of the perineal cycle), sexual activity (observation of timed intercourse with male baboon and postictal tests), and male factors (males of proven fertility with a normal sperm analysis); and [11] endometriosis-associated pain studies (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar).In this issue of Fertility and Sterility, Donnez et al. (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) claim to have published the first experimental model of nodular endometriosis in baboons after laparotomic autografting of partial uterine grafts that contain endometrium (EM) + junctional zone (JZ), or total uterine thickness grafts that contain EM + JZ + myometrium (MM), obtained after hysterotomy, to the iliac fossae or anterior rectal wall, respectively. This claim can be challenged: white endometriotic nodules were reported to contribute to the progression of endometriosis in studies documenting the evolution of spontaneous or induced peritoneal endometriosis in baboons 16 years ago (see Tables 3 and 4 in D'Hooghe et al. 1996) (3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar). Furthermore, endometriotic nodules with associated dense adhesions were also reported to occur after induction of peritoneal endometriosis using laparoscopic intrapelvic injection of menstrual endometrium obtained during the first 2 days of menstruation (see Fig. 1B in D'Hooghe et al. 2006) (5D'Hooghe T.M. Nugent N. Cuneo S. Chai D.C. Deer F. Debrock S. et al.Recombinant human TNFRSF1A (r-hTBP-1) inhibits the development of endometriosis in baboons: a prospective, randomized, placebo- and drug-controlled study.Biol Reprod. 2006; 74: 131-136Crossref PubMed Scopus (108) Google Scholar) (see Fig. 3A in D'Hooghe 1995) (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). Finally, the occurrence of extensive spontaneous endometriosis leading to lethal bowel obstruction, strongly suggestive of invasive spontaneous bowel endometriosis, has been previously reported in both baboons and rhesus monkeys (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar).The technique chosen for induction of endometriotic nodules by Donnez et al. (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) was similar to the invasive methods used in rodents, including laparotomy, bilateral salpingo-oophorectomy, hysterotomy, endometrial/myometrial excision, and surgical peritoneal grafting using Vicryl sutures in four different pelvic areas: the pouch of Douglas (EM only), the anterior rectum (total uterine thickness biopsy only), the peritoneum right vesical fossa (deep MM only), and the left and right iliac fossa (EM and JZ only). As in rodents, this technique was associated with adhesion development in 57% of baboons and in 68% to 86% of the lesions induced by grafting EM + JZ or full thickness EM + MM biopsies (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar).The investigators' interpretation that EM + JZ grafts or total uterine thickness grafts represent deep nodular endometriosis (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) is debatable. In our opinion, both types of grafts contained EM, JZ, and a variable amount of MM, as it appears macroscopically impossible to completely dissect JZ from MM. The formation of dense adhesions related to these grafts can be caused by laparotomy, hysterotomy, and peritoneal graft suturing, with subsequent microscopic invasion of the rectum (full thickness EM + MM sutured to the anterior rectal wall) or sigmoid (EM + JZ sutured to the left iliac fossa), especially if the EM part of the graft was sutured in a way that allowed direct or close contact with the rectal or sigmoid serosa.In our interpretation, the differences observed in volume, surface area, and glandular density between the four groups (EM, EM + JZ, full thickness uterine biopsy, and outer MM biopsy) after surgical grafting simply represent the basal differences between these grafts before surgical grafting. Indeed, although the investigators have reported that all grafts had a surface area of ±10 mm, the volume of the grafts used for induction was not mentioned (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), but appeared to be very different between the grafts, according to their Supplemental Figure 1 (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar): Volume of total uterine thickness grafts > Outer myometrial grafts > EM + JZ grafts > EM grafts. Therefore, the main conclusion of the article was that autografting these four types of tissues is feasible (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), which is not new and has been demonstrated many times in rodent models of endometriosis.Although the take rate of EM was 100% after 1 month (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), the data for the EM group were only presented for 5 of 9 baboons after 5 to 6 months, and no data were provided for 4 of the 18 EM + JZ grafts after 6 to 7 months (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). The phenotype of the lesions observed after surgical grafting of EM (only brownish lesions macroscopically resembling hemosiderin deposits) was limited when compared with the variable spectrum of red, white, orange, and brown-black lesions that may be observed in spontaneous endometriosis occurring in humans or baboons, or in peritoneal endometriosis induced after pelvic seeding of menstrual endometrium in baboons (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar, 3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar, 4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). It is also unclear how the outcome was influenced by the menstrual cycle phase at induction (not mentioned in their article) or afterward, as induction was followed by hormone replacement therapy with 2 mg/day of estradiol-valerianate (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), a dose commonly used for humans but could be considered to be relatively high for adult female baboons weighing 10 to 15 kg. In terms of statistical analysis, we believe that Kruskal-Wallis tests should have been used instead of Mann-Whitney tests (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) to allow the comparison of nonparametrically distributed data between the four groups.The question arises as to why the investigators did not use laparoscopic intrapelvic injection of transcervically obtained menstrual endometrium (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar), a technique developed by our group more than 17 years ago in collaboration with the scientists at the same research center (Institute of Primate Research, Nairobi, Kenya) where their published study was performed (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). In all parous and in many nulligravid baboons, transcervical uterine access via vaginal speculum allows uterine curettage or endometrial biopsy to harvest EM tissue, which can be used for intrapelvic seeding (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar, 3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar, 4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). If routine uterine access via a vaginal speculum is difficult, combined abdominal-cervical manipulation (the Chai technique) allows transvaginal uterine access in nearly all cases (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar).Alternatively, endometrial biopsy is also possible by transabdominal insertion of a Novak curette through the uterine fundus under direct laparoscopic control (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). Since 1995, several investigators evaluating the pathogenesis of endometriosis or assessing the prevention or treatment of endometriosis have used laparoscopic pelvic injection of menstrual endometrium in baboons and confirmed it to be valid for the induction of peritoneal endometriosis (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). A total of 45 papers using or discussing this technique have been published (out of the 81 papers identified in a PubMed search including key words “baboon” and “endometriosis” on December 18, 2012).Because the extent of induced peritoneal endometriosis is positively correlated with the weight of the endometrium used for induction (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar), we hypothesize that intrapelvic injection of the total amount of menstrual endometrium, obtained by transcervical or laparoscopic transfundal uterine curettage, can lead to a more physiologic and preclinically more relevant development of endometriotic nodules, dense adhesions, and deeply infiltrative endometriosis, when compared with the method proposed in the article in this issue of Fertility and Sterility (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). Endometriosis, defined as the growth of endometrium (EM) outside the uterus, can be diagnosed by pelvic laparoscopy, detecting variable phenotypes (such as peritoneal, ovarian endometriotic cysts, adhesions, or deeply infiltrative disease) in various stages (minimal, mild, moderate, or severe). Endometriosis is associated with infertility, pelvic pain, and reduced quality of life (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). The lack of a reliable, noninvasive method for the early detection of endometriosis makes it impossible to study the early development of the disease in women and often results in delayed diagnosis. It is ethically impossible to study the spontaneous evolution of endometriosis in women or to do prospective studies in women controlling for the pelvic condition (endometriosis, normal pelvis, or other pelvic pathology) and for symptoms (pain, subfertility, combined pain and subfertility, or no symptoms). Rodent models for endometriosis research have advantages such as low cost, ease of handling, and the possibility of genetic manipulation using knockout mice and transgenic mice, but the preclinical relevance of these models has been contested because of the wide gap between rodents and humans with respect to phylogenetics, reproductive anatomy and physiology, lack of menstruation, lack of peritoneal fluid, and lack of spontaneous endometriosis. The questionable unphysiologic induction of endometriosis by uterine square autotransplantation leads to major adhesion formation and unphysiologic “endometriotic lesions” that have a limited phenotype when compared with the spontaneous endometriosis found in women or in nonhuman primates (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). Nonhuman primates represent the most relevant animal models in endometriosis research in view of their similarity to humans with respect to phylogenetics, reproductive anatomy and physiology, the presence of spontaneous endometriosis, and the possibility of induced endometriosis that is macroscopically and microscopically similar to the spontaneous condition. Among nonhuman primates, baboons represent the best documented and validated model for endometriosis research (81 papers according to a PubMed search based on the key words “endometriosis” and “baboon” on December 18, 2012). Baboons offer the following advantages: [1] noninvasive cycle monitoring based on perineal change; [2] continuous nonseasonal breeding; [3] relatively large size and strength (female adult size: 10–15 kg); [4] spontaneous presence of the peritoneal fluid important for the pathogenesis of endometriosis; [5] cross-reactivity of antibodies and DNA/RNA analytical methods between baboons and humans; [6] vaginal transcervical uterine access allowing EM biopsy, embryo transfer, preimplantation embryo flushing, and hysteroscopy; [7] spontaneous retrograde menstruation important for the pathogenesis of endometriosis; [8] minimal to severe spontaneous endometriosis, allowing the study of spontaneous evolution; [9] development of endometriosis within 25 days after intraperitoneal seeding of menstrual EM, allowing the study of in vivo EM-peritoneal interaction, implantation, invasion, and neuroangiogenesis, of cause-effect relationships in endometriosis, of new drugs for treatment or prevention of endometriosis, and of general and reproductive safety of new antiendometriosis drugs; [10] endometriosis-associated infertility studies controlled for the presence of endometriosis (laparoscopy assessment), ovulation (monitoring of the perineal cycle), sexual activity (observation of timed intercourse with male baboon and postictal tests), and male factors (males of proven fertility with a normal sperm analysis); and [11] endometriosis-associated pain studies (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). In this issue of Fertility and Sterility, Donnez et al. (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) claim to have published the first experimental model of nodular endometriosis in baboons after laparotomic autografting of partial uterine grafts that contain endometrium (EM) + junctional zone (JZ), or total uterine thickness grafts that contain EM + JZ + myometrium (MM), obtained after hysterotomy, to the iliac fossae or anterior rectal wall, respectively. This claim can be challenged: white endometriotic nodules were reported to contribute to the progression of endometriosis in studies documenting the evolution of spontaneous or induced peritoneal endometriosis in baboons 16 years ago (see Tables 3 and 4 in D'Hooghe et al. 1996) (3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar). Furthermore, endometriotic nodules with associated dense adhesions were also reported to occur after induction of peritoneal endometriosis using laparoscopic intrapelvic injection of menstrual endometrium obtained during the first 2 days of menstruation (see Fig. 1B in D'Hooghe et al. 2006) (5D'Hooghe T.M. Nugent N. Cuneo S. Chai D.C. Deer F. Debrock S. et al.Recombinant human TNFRSF1A (r-hTBP-1) inhibits the development of endometriosis in baboons: a prospective, randomized, placebo- and drug-controlled study.Biol Reprod. 2006; 74: 131-136Crossref PubMed Scopus (108) Google Scholar) (see Fig. 3A in D'Hooghe 1995) (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). Finally, the occurrence of extensive spontaneous endometriosis leading to lethal bowel obstruction, strongly suggestive of invasive spontaneous bowel endometriosis, has been previously reported in both baboons and rhesus monkeys (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). The technique chosen for induction of endometriotic nodules by Donnez et al. (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) was similar to the invasive methods used in rodents, including laparotomy, bilateral salpingo-oophorectomy, hysterotomy, endometrial/myometrial excision, and surgical peritoneal grafting using Vicryl sutures in four different pelvic areas: the pouch of Douglas (EM only), the anterior rectum (total uterine thickness biopsy only), the peritoneum right vesical fossa (deep MM only), and the left and right iliac fossa (EM and JZ only). As in rodents, this technique was associated with adhesion development in 57% of baboons and in 68% to 86% of the lesions induced by grafting EM + JZ or full thickness EM + MM biopsies (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). The investigators' interpretation that EM + JZ grafts or total uterine thickness grafts represent deep nodular endometriosis (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) is debatable. In our opinion, both types of grafts contained EM, JZ, and a variable amount of MM, as it appears macroscopically impossible to completely dissect JZ from MM. The formation of dense adhesions related to these grafts can be caused by laparotomy, hysterotomy, and peritoneal graft suturing, with subsequent microscopic invasion of the rectum (full thickness EM + MM sutured to the anterior rectal wall) or sigmoid (EM + JZ sutured to the left iliac fossa), especially if the EM part of the graft was sutured in a way that allowed direct or close contact with the rectal or sigmoid serosa. In our interpretation, the differences observed in volume, surface area, and glandular density between the four groups (EM, EM + JZ, full thickness uterine biopsy, and outer MM biopsy) after surgical grafting simply represent the basal differences between these grafts before surgical grafting. Indeed, although the investigators have reported that all grafts had a surface area of ±10 mm, the volume of the grafts used for induction was not mentioned (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), but appeared to be very different between the grafts, according to their Supplemental Figure 1 (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar): Volume of total uterine thickness grafts > Outer myometrial grafts > EM + JZ grafts > EM grafts. Therefore, the main conclusion of the article was that autografting these four types of tissues is feasible (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), which is not new and has been demonstrated many times in rodent models of endometriosis. Although the take rate of EM was 100% after 1 month (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), the data for the EM group were only presented for 5 of 9 baboons after 5 to 6 months, and no data were provided for 4 of the 18 EM + JZ grafts after 6 to 7 months (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). The phenotype of the lesions observed after surgical grafting of EM (only brownish lesions macroscopically resembling hemosiderin deposits) was limited when compared with the variable spectrum of red, white, orange, and brown-black lesions that may be observed in spontaneous endometriosis occurring in humans or baboons, or in peritoneal endometriosis induced after pelvic seeding of menstrual endometrium in baboons (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar, 3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar, 4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). It is also unclear how the outcome was influenced by the menstrual cycle phase at induction (not mentioned in their article) or afterward, as induction was followed by hormone replacement therapy with 2 mg/day of estradiol-valerianate (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar), a dose commonly used for humans but could be considered to be relatively high for adult female baboons weighing 10 to 15 kg. In terms of statistical analysis, we believe that Kruskal-Wallis tests should have been used instead of Mann-Whitney tests (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) to allow the comparison of nonparametrically distributed data between the four groups. The question arises as to why the investigators did not use laparoscopic intrapelvic injection of transcervically obtained menstrual endometrium (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar), a technique developed by our group more than 17 years ago in collaboration with the scientists at the same research center (Institute of Primate Research, Nairobi, Kenya) where their published study was performed (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). In all parous and in many nulligravid baboons, transcervical uterine access via vaginal speculum allows uterine curettage or endometrial biopsy to harvest EM tissue, which can be used for intrapelvic seeding (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar, 3D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. Koninckx P.R. Serial laparoscopies over 30 months show that endometriosis is a progressive disease in captive baboons (Papio Anubis, Papio cynocephalus).Fertil Steril. 1996; 65: 645-649PubMed Google Scholar, 4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar). If routine uterine access via a vaginal speculum is difficult, combined abdominal-cervical manipulation (the Chai technique) allows transvaginal uterine access in nearly all cases (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). Alternatively, endometrial biopsy is also possible by transabdominal insertion of a Novak curette through the uterine fundus under direct laparoscopic control (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). Since 1995, several investigators evaluating the pathogenesis of endometriosis or assessing the prevention or treatment of endometriosis have used laparoscopic pelvic injection of menstrual endometrium in baboons and confirmed it to be valid for the induction of peritoneal endometriosis (1D'Hooghe T.M. Kyama C.M. Chai D. Fassbender A. Vodolazkaia A. Bokor A. Mwenda J.M. Nonhuman primate models for translational research in endometriosis.Reprod Sci. 2009; 16: 152-161Crossref PubMed Scopus (95) Google Scholar). A total of 45 papers using or discussing this technique have been published (out of the 81 papers identified in a PubMed search including key words “baboon” and “endometriosis” on December 18, 2012). Because the extent of induced peritoneal endometriosis is positively correlated with the weight of the endometrium used for induction (4D'Hooghe T.M. Bambra C.S. Raeymaekers B.M. De Jonge I. Lauweryns J.M. Koninckx P.R. Intrapelvic injection of menstrual endometrium causes endometriosis in baboons (Papio cynocephalus, Papio Anubis).Am J Obstet Gynecol. 1995; 173: 125-134Abstract Full Text PDF PubMed Scopus (140) Google Scholar), we hypothesize that intrapelvic injection of the total amount of menstrual endometrium, obtained by transcervical or laparoscopic transfundal uterine curettage, can lead to a more physiologic and preclinically more relevant development of endometriotic nodules, dense adhesions, and deeply infiltrative endometriosis, when compared with the method proposed in the article in this issue of Fertility and Sterility (2Donnez O. Van Langendonckt A. Defrère S. Colette S. Van Kerk O. Dehoux J.P. Squifflet J. Donnez J. Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesions.Fertil Steril. 2013; 99: 783-789Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). Induction of endometriotic nodules in an experimental baboon model mimicking human deep nodular lesionsFertility and SterilityVol. 99Issue 3PreviewTo establish an experimental model for the study of deep nodular endometriosis. Full-Text PDF