Levator ani muscle and connective tissue changes associated with pelvic organ prolapse, parity, and aging in the squirrel monkey: a histologic study

Current practice in animal models for pelvic floor dysfunction

INTRODUCTION AND HYPOTHESIS

The objective was to explore the current practice of using animal models for female pelvic floor dysfunction (PFD).

METHODS

By applying PFD and animal models as the keywords, we made a computerized search using PubMed, Ovid-Medline and Ovid-Embase from 2000 to 2022. The publications on the construction and application of animal models for PFD were included, and the results are presented in narrative text.

RESULTS

Studies on PFD primarily use rodents, large quadrupeds, and nonhuman primates (NHPs). NHPs are closest to humans in anatomy and biomechanics of the pelvic floor, followed by large quadrupeds and rodents. Rodents are more suitable for studying molecular mechanism, histopathology of PFD, and mesh immune rejection. Large quadrupeds are adaptable to the study of pelvic floor biomechanics and the development of new surgical instruments for PFD. NHPs are suitable for studying the occurrence and pathogenesis of pelvic organ prolapse. Among modeling methods, violent destruction of pelvic floor muscles, regulation of hormone levels, and denervation were used to simulate the occurrence of PFD. Gene knockout can be used to study both the pathogenesis of PFD and the efficacy of treatments. Other methods such as abdominal wall defect, vaginal defect, and in vitro organ bath system are more frequently used to observe wound healing after surgery and to verify the efficacy of treatments.

CONCLUSIONS

The rat is currently the most applicable animal type for numerous modeling methods. Vaginal dilation is the most widely used modeling method for research on the pathogenesis, pathological changes, and treatment of PFD.

RECTAL PROLAPSE IN THE SULAWESI CRESTED BLACK MACAQUE (MACACA NIGRA): MORBIDITY, MORTALITY, AND RISK FACTORS

Empirical data suggest that rectal prolapse (RP) is common in captive Sulawesi crested black macaques (Macaca nigra) in Europe, resulting in the euthanasia of animals that experience repeat occurrences. However, the prevalence, etiology, and risk factors of RP remain unidentified. The aims of this retrospective study were to assess the morbidity and mortality of RP, to provide an overview of management practices, and to identify risk factors for RP in this species. A questionnaire was sent to all European Ex situ Programme institutions that housed M. nigra between 01 January 2014 and 31 December 2020. Zoological Information Management System medical records and the studbook were used to obtain additional information. The questionnaire had a response rate of 65%, accounting for 204 animals. Of these animals, 25 (12.3%) suffered from at least one RP event during the study period and recurrence was noted in 72%. The majority of prolapses reverted naturally, but 28% of afflicted animals were euthanized for this ailment. Institutions with M. nigra with high frequencies of diarrhea (P= 0.035), those that provided diets of ≥90% vegetables and high-fiber pellet (P < 0.001), and those with more male than female M. nigra (P < 0.001) had increased odds of RP. Institutions that provided fruits daily (P < 0.002) had reduced odds of having RP cases. Although correlation of RP with diet was identified, confounding cannot be excluded, and a detailed dietary analysis needs to take place before altering feeding practices. Acute stressors and detection of protozoa in fecal samples were common findings before an RP event. Demographic analysis indicated that aged females, young males, and subordinate individuals were most affected by this condition. Where tested during an RP intervention, animals had low serum levels of vitamin D. Pedigree analysis hinted at genetic predisposition in this species and requires further investigation.

Female squirrel monkeys as models for research on women's pelvic floor disorders

Animal models enable research on biological phenomena with controlled interventions not possible or ethical in patients. Among species used as experimental models, squirrel monkeys (Saimiri genus) are phylogenetically related to humans and are relatively easily managed in captivity. Quadrupedal locomotion of squirrel monkeys resembles most other quadrupedal primates in that they utilize a diagonal sequence/diagonal couplets gait when walking on small branches. However, to assume a bipedal locomotion, the human pelvis has undergone evolutionary changes. Therefore, the pelvic bone morphology is not that similar between the female squirrel monkey and woman, but pelvic floor support structures and impacts of fetal size and malpresentation are similar. Thus, this review explores the pelvic floor support structural characteristics of female squirrel monkeys, especially in relation to childbirth to demonstrate similarities to humans.

Research Relevant Conditions and Pathology in Nonhuman Primates

Biomedical research involving animal models continues to provide important insights into disease pathogenesis and treatment of diseases that impact human health. In particular, nonhuman primates (NHPs) have been used extensively in translational research due to their phylogenetic proximity to humans and similarities to disease pathogenesis and treatment responses as assessed in clinical trials. Microscopic changes in tissues remain a significant endpoint in studies involving these models. Spontaneous, expected (ie, incidental or background) histopathologic changes are commonly encountered and influenced by species, genetic variations, age, and geographical origin of animals, including exposure to infectious or parasitic agents. Often, the background findings confound study-related changes, because numbers of NHPs used in research are limited by animal welfare and other considerations. Moreover, background findings in NHPs can be exacerbated by experimental conditions such as treatment with xenobiotics (eg, infectious morphological changes related to immunosuppressive therapy). This review and summary of research-relevant conditions and pathology in rhesus and cynomolgus macaques, baboons, African green monkeys, common marmosets, tamarins, and squirrel and owl monkeys aims to improve the interpretation and validity of NHP studies.

Animal models for pelvic organ prolapse: systematic review

INTRODUCTION AND HYPOTHESIS

We aimed to summarize the knowledge on the pathogenesis of pelvic organ prolapse (POP) generated in animal models.

METHODS

We searched MEDLINE, Embase, Cochrane and the Web of Science to establish what animal models are used in the study of suggested risk factors for the development of POP, including pregnancy, labor, delivery, parity, aging and menopause. Lack of methodologic uniformity precluded meta-analysis; hence, results are presented as a narrative review.

RESULTS

A total of 7426 studies were identified, of which 51 were included in the analysis. Pregnancy has a measurable and consistent effect across species. In rats, simulated vaginal delivery induces structural changes in the pelvic floor, without complete recovery of the vaginal muscular layer and its microvasculature, though it does not induce POP. In sheep, first vaginal delivery has a measurable effect on vaginal compliance; measured effects of additional deliveries are inconsistent. Squirrel monkeys can develop POP. Denervation of their levator ani muscle facilitates this process in animals that delivered vaginally. The models used do not develop spontaneous menopause, so it is induced by ovariectomy. Effects of menopause depend on the age at ovariectomy and the interval to measurement. In several species menopause is associated with an increase in collagen content in the longer term. In rodents there were no measurable effects of age apart of elastin changes. We found no usable data for other species.

CONCLUSION

In several species there are measurable effects of pregnancy, delivery and iatrogenic menopause. Squirrel monkeys can develop spontaneous prolapse.

Platelet rich plasma as a minimally invasive approach to uterine prolapse

Pelvic organ prolapse (POP) is a major health problem that affects many women with potentially severe physical and psychological impact as well as impact on their daily activities, and quality of life. Several surgical techniques have been proposed for the treatment of POP. The FDA has published documents that refer to concerns about the use of synthetic meshes for the treatment of prolapse, in view of the severe complications that may occur. These led to hesitancy in use of these meshes and partial increase in use of other biological grafts such as allografts and xenografts. Although there seems to be an increasing tendency to use grafts in pelvic floor reconstructive procedures due to lower risks of erosion than synthetic meshes, there are inconclusive data to support the routine use of biological grafts in pelvic organ prolapse treatment. In light of these observations new strategies are needed for the treatment of prolapse. Platelet rich plasma (PRP) is extremely rich in growth factors and cytokines, which regulate tissue reconstruction and has been previously used in orthopaedics and plastic surgery. To date, however, it has never been used in urogynaecology and there is no evidence to support or oppose its use in women who suffer from POP, due to uterine ligament defects. PRP is a relatively inexpensive biological material and easily produced directly from patients' blood and is, thus, superior to synthetic materials in terms of potential adverse effects such as foreign body reaction. In the present article we summarize the existing evidence, which supports the conduct of animal experimental and clinical studies to elucidate the potential role of PRP in treating POP by restoring the anatomy and function of ligament support.

Pelvic reconstruction improves pelvic floor strength in pelvic organ prolapse patients

OBJECTIVE

To evaluate pelvic floor muscle strength after the modified pelvic reconstruction procedure for pelvic organ prolapse (POP).

MATERIALS AND METHODS

Patients were assigned to two groups consisting of 37 patients diagnosed with POP and undergoing modified pelvic reconstruction (reconstruction group), and 30 patients admitted to our hospital during the same period for other surgical indications (control group). Vaginal palpation of pelvic floor muscle strength was performed according to the modified Oxford grading system before operating on the two groups and again in the 3(rd) month following surgery for the reconstruction group. A comparative study was performed to evaluate the differences between the two groups and the improvement of pelvic floor muscle strength in the reconstruction group.

RESULTS

The pelvic floor muscle strength was significantly improved postoperatively when compared with preoperative results in the reconstruction group (t = -17.478, p < 0.001). However, pre- and postoperative muscle strength in the reconstruction group was significantly lower relative to the control group, respectively (χ(2) = 63.293, p < 0.001; χ(2) = 31.550, p < 0.001).

CONCLUSION

The modified pelvic reconstruction procedure could improve pelvic floor muscle strength in POP patients, which remains lower when compared with the normal population. Pelvic floor muscle strength should be included in the assessment of surgical outcomes in POP.

Randomized trial of cesarean vs vaginal delivery for effects on the pelvic floor in squirrel monkeys

BACKGROUND

Vaginal delivery is a risk factor in pelvic floor disorders. We previously described changes in the pelvic floor associated with pregnancy and parturition in the squirrel monkey, a species with a humanlike pattern of spontaneous age- and parity-associated pelvic organ prolapse.

OBJECTIVE

The potential to prevent or diminish these changes with scheduled cesarean delivery (CD) has not been evaluated. In a randomized, controlled trial, we compared female squirrel monkeys undergoing spontaneous vaginal delivery with those undergoing scheduled primary CD for pelvic floor muscle volumes, muscle contrast changes, and dynamic effects on bladder neck position.

STUDY DESIGN

Levator ani, obturator internus, and coccygeus (COC) muscle volumes and contrast uptake were assessed by magnetic resonance imaging in 20 nulliparous females examined prior to pregnancy, a few days after delivery, and 3 months postpartum. The position of bladder neck relative to bony reference line also was assessed with abdominal pressure using dynamic magnetic resonance imaging.

RESULTS

Baseline measurements of 10 females randomly assigned to scheduled primary CD were not different from those of 10 females assigned to spontaneous vaginal delivery. Levator ani and obturator internus muscle volumes did not differ between groups, while volumes were reduced (P < .05) in the observation immediately after pregnancy. The COC muscles increased (P < .05) immediately after delivery for females in the spontaneous vaginal delivery group, but not for females in the scheduled CD group. Position of the bladder neck descended (P < .05) by 3 months postpartum in both groups.

CONCLUSION

Scheduled CD diminishes changes in COC muscle volume and contrast reported to be associated with spontaneous vaginal delivery in squirrel monkeys. However, pelvic support of the bladder was not protected by this intervention suggesting that effects of pregnancy and delivery are not uniformly prevented by this procedure.

Comparison of pelvic muscle architecture between humans and commonly used laboratory species

INTRODUCTION AND HYPOTHESIS

Pelvic floor muscles (PFM) are deleteriously affected by vaginal birth, which contributes to the development of pelvic floor disorders. To mechanistically link these events, experiments using animal models are required, as access to human PFM tissue is challenging. In choosing an animal model, a comparative study of PFM design is necessary, since gross anatomy alone is insufficient to guide the selection.

METHODS

Human PFM architecture was measured using micromechanical dissection and then compared with mouse (n = 10), rat (n = 10), and rabbit (n = 10) using the Architectural Difference Index (ADI) (parameterizing a combined measure of sarcomere length-to-optimal-sarcomere ratio, fiber-to-muscle-length ratio, and fraction of total PFM mass and physiological cross-sectional area (PCSA) contributed by each muscle). Coccygeus (C), iliocaudalis (IC), and pubocaudalis (PC) were harvested and subjected to architectural measurements. Parameters within species were compared using repeated measures analysis of variance (ANOVA) with post hoc Tukey's tests. The scaling relationships of PFM across species were quantified using least-squares regression of log-10-transformed variables.

RESULTS

Based on the ADI, rat was found to be the most similar to humans (ADI = 2.5), followed by mouse (ADI = 3.3). When animals' body mass was regressed against muscle mass, muscle length, fiber length, and PCSA scaling coefficients showed a negative allometric relationship or smaller increase than predicted by geometric scaling.

CONCLUSION

In terms of muscle design among commonly used laboratory animals, rat best approximates the human PFM, followed by mouse. Negative allometric scaling of PFM architectural parameters is likely due to the multifaceted function of these muscles.

Fiber type characterization of striated muscles related to micturition in female rabbits

Pelvic and perineal striated muscles are relevant for reproduction and micturition in female mammals. Damage to these muscles is associated with pelvic organ prolapse and stress urinary incontinence. The fiber type composition of skeletal muscle influences the susceptibility for damage and/or regeneration. The aim of the present study was to determine the fiber type composition of a perineal muscle, the bulbospongiosus, and a pelvic muscle, the pubococcygeus. Both muscles were harvested from adult female rabbits (8-10 months old). NADH-TR (nicotinamide adenine dinucleotide tetrazolium reductase) histochemistry was undertaken to identify oxidative and glycolytic muscle fibers. Alkaline (pH 9.4) ATP-ase (actomyosin adenosine triphosphatase) histochemistry was used to classify type I, type IIb or type IIa/IId muscle fibers. Results showed that the content of glycolytic fibers in the bulbospongiosus muscle was higher than that of oxidative fibers. Meanwhile, the opposite was true for the pubococcygeus. In the bulbospongiosus muscle, the content of type IIb muscle fibers was higher than that of type I, but was similar to that of type IIa/IId. In contrast, the content of each fiber type was similar in the pubococcygeus muscle. The relative proportion of fibers in bulbospongiosus and pubococcygeus muscles is consistent with their function during voiding and storage phases of micturition.

Animal models of female pelvic organ prolapse: lessons learned

Pelvic organ prolapse is a vaginal protrusion of female pelvic organs. It has high prevalence worldwide and represents a great burden to the economy. The pathophysiology of pelvic organ prolapse is multifactorial and includes genetic predisposition, aberrant connective tissue, obesity, advancing age, vaginal delivery and other risk factors. Owing to the long course prior to patients becoming symptomatic and ethical questions surrounding human studies, animal models are necessary and useful. These models can mimic different human characteristics - histological, anatomical or hormonal, but none present all of the characteristics at the same time. Major animal models include knockout mice, rats, sheep, rabbits and nonhuman primates. In this article we discuss different animal models and their utility for investigating the natural progression of pelvic organ prolapse pathophysiology and novel treatment approaches.

Urogynecological effects of menopause

The menopause signifies a period after significant hormonal change that affects all estrogen-sensitive tissues. This change may result in symptoms affecting any part of the urogenital system. These changes can significantly affect women's health and quality of life. The menopause is associated with lower urinary tract symptoms, vulvovaginal symptoms and pelvic organ prolapse. In this article, we have aimed to describe the symptomatology along with pathophysiology of the effects of menopause on urogynecological problems affecting women's health. Other factors apart from menopause add to these symptoms, like parity, mode of delivery, obesity, smoking and poor psychological health.

The improvement of pelvic floor muscle function in POP patients after the Prolift procedure: results from surface electromyography

INTRODUCTION AND HYPOTHESIS

Patients with pelvic organ prolapse (POP) have lower pelvic floor muscle (PFM) function. We hypothesized that pelvic reconstructive surgery could improve PFM function and strength.

METHODS

The controlled, nonrandomized study recruited 37 POP patients in the Prolift group and 30 non-POP patients in the control group. Two urogynecologists performed the Prolift procedure. One experienced physiotherapist who was blinded to the grouping conducted the surface electromyography (SEMG) evaluation using an intravaginal probe. The patient was considered objectively cured if she had stage 0 or I according to the Pelvic Organ Prolapse Quantification system (POP-Q) at the 3rd month postoperatively. Two types of contractions, namely maximum voluntary contraction (MVC) and short, fast contractions (SFC) in 6 s were performed at each SEMG measurement. The SEMG data were collected once in the control group on admission and twice in the Prolift group (on admission and at the 3rd month postoperatively). The t test, Mann-Whitney U test, and Wilcoxon test were used for statistical analysis.

RESULTS

A total of 36 POP patients were cured by the Prolift procedure. At the 3-month follow-up, the voltage and duration of MVC as well as the numbers and voltage of SFC increased significantly in the Prolift group. These variables were lower in POP patients compared to women without POP.

CONCLUSIONS

The restoration of pelvic anatomy may account for the improved PFM function with increased electrical activity in POP patients verified by SEMG. Evaluation of PFM function may be used as a clinical tool in the overall assessment of pelvic reconstructive surgeries.

Expression and significance of lysyl oxidase-like 1 and fibulin-5 in the cardinal ligament tissue of patients with pelvic floor dysfunction

Pelvic organ prolapse (POP) is a disabling disorder in women characterized by a loss of pelvic floor support, leading to the herniation of the uterus into or through the vagina. POP is a complex problem that likely involves multiple mechanisms with limited therapies available, and is associated with defects in connective tissue including elastic fibers. This study was designed to investigate the expression of fibulin-5 and lysyl oxidase-like 1 (LOXL1) in the cardinal ligament in samples taken from the POP group compared to the non-POP group. Specimens were obtained during abdominal hysterectomy from the cardinal ligament of 53 women with POP and 25 age- and parity- matched women with non-POP among post-menopausal women with benign gynecologic pathology. Protein expression was evaluated using the immunohistochemical staining method. For statistical analyses, chi-square test and Spearman's correlation were used with the statistical package SPSS13.0 system. Our results showed that both fibulin-5 and LOXL1 expressions were decreased in the cardinal ligament in the POP group compared to the non-POP group (P < 0.05). The expression of fibulin-5 and LOXL1 were correlated closely with the stage of POP, accompanied by stress urinary incontinence and frequency of vaginal delivery (P < 0.05), but had no relationship with post-menopausal state (P > 0.05). The expression of fibulin-5 was positively associated with LOXL1 in POP (P < 0.05). We conclude that changes in fibulin-5 and LOXL1 expression may play a role in the development of POP.

Alterations in pelvic floor muscles and pelvic organ support by pregnancy and vaginal delivery in squirrel monkeys

INTRODUCTION AND HYPOTHESIS

The objective of this study was to measure the effects of pregnancy and parturition on pelvic floor muscles and pelvic organ support.

METHODS

Levator ani, obturator internus, and coccygeus (COC) muscle volumes and contrast uptake were assessed by MRI of seven females prior to pregnancy, 3 days, and 4 months postpartum. Bladder neck and cervix position were measured dynamically with abdominal squeezing.

RESULTS

The sides of three paired muscles were similar (p > 0.66). COC volumes were greater (p < 0.004) after parturition than before pregnancy or after recovery. COC contrast uptake increased (p < 0.02) immediately after delivery. Bladder neck position both in the relaxed state and abdominal pressure descended (p < 0.04) after delivery and descended further (p < 0.001) after recovery. Cervical position in the relaxed state before delivery was higher (p < 0.001) than postpartum but was unchanged (p = 0.50) with abdominal pressure relative to delivery.

CONCLUSION

In squirrel monkeys, coccygeus muscles demonstrate the greatest change related to parturition, and parturition-related bladder neck descent seems permanent.

Levator ani denervation and reinnervation 6 months after childbirth

OBJECTIVE

The objective of the study was to assess the prevalence of levator ani denervation and reinnervation 6 months after the first delivery.

STUDY DESIGN

Ninety-six primigravida women underwent quantitative electromyography of the levator ani during the third trimester and twice postpartum. A 95% confidence interval for normal function was created using interference pattern analysis. Fifty-seven who completed the study are presented in this secondary data analysis. Postpartum muscle sites outside the normal range were considered abnormal. Obstetric and demographic characteristics were assessed.

RESULTS

Of 57 subjects, 70% had no denervation. Of the 30% with denervation at 6 weeks, 35% recovered by 6 months. Obstetric or maternal characteristics were not predictive of denervation or reinnervation, except subjects with persistent denervation tended toward lower body mass index (BMI) independent of mode of delivery.

CONCLUSION

Nearly one-third of women have levator ani denervation after first delivery, but many recover by 6 months. Denervation is not clearly associated with mode of delivery, but higher maternal BMI may be protective.

Uterosacral ligament smooth muscle cell apoptosis is increased in women with uterine prolapse

PURPOSE

The purpose of this study was to compare the smooth muscle content and apoptosis of the uterosacral ligament in women with and without uterine prolapse.

STUDY DESIGN

Uterosacral ligaments were sampled in women with (n = 9) or without (n = 9) uterine prolapse undergoing hysterectomy. Smooth muscle of the uterosacral ligament was identified by immunohistochemistry. Digital image analysis was used to determine the fractional area of smooth muscle in the histologic cross sections. Apoptosis was assessed by terminal deoxynucelotidyl-transferase-mediated dUTP nick-end-labeling method.

RESULTS

The fractional area of nonvascular smooth muscle in the uterosacral ligament of women with uterine prolapse was significantly decreased compared to women without prolapse (0.32 +/- 0.12 vs. 0.42 +/- 0.03, P = .02) and the apoptotic index was significantly higher compared to women without prolapse (0.20 +/- 0.06 vs. 0.08 +/- 0.04, P < .01).

CONCLUSION

The fraction of smooth muscle in the uterosacral ligaments is significantly decreased, and the rate of apoptosis is higher in women with uterine prolapse compared to women without prolapse.

Effect of vaginal distention on elastic fiber synthesis and matrix degradation in the vaginal wall: potential role in the pathogenesis of pelvic organ prolapse

Matrix metalloprotease (MMP) activity is increased in the postpartum vagina of wild-type (WT) animals. This degradative activity is also accompanied by a burst in elastic fiber synthesis and assembly. The mechanisms that precipitate these changes are unclear. The goals of this study were to determine how vaginal distention (such as in parturition) affects elastic fiber homeostasis in the vaginal wall and the potential significance of these changes in the pathogenesis of pelvic organ prolapse. Vaginal distention with a balloon simulating parturition resulted in increased MMP-2 and MMP-9 activity in the vaginal wall of nonpregnant and pregnant animals. This was accompanied by visible fragmented and disrupted elastic fibers in the vaginal wall. In nonpregnant animals, the abundant amounts of tropoelastin and fibulin-5 in the vagina were not increased further by distention. In contrast, in pregnant animals, the suppressed levels of both proteins were increased 3-fold after vaginal distention. Distention performed in fibulin-5-deficient (Fbln5(-/-)) mice with defective elastic fiber synthesis and assembly induced accelerated pelvic organ prolapse, which never recovered. We conclude that, in pregnant mice, vaginal distention results in increased protease activity in the vaginal wall but also increased synthesis of proteins important for elastic fiber assembly. Distention may thereby contribute to the burst of elastic fiber synthesis in the postpartum vagina. The finding that distention results in accelerated pelvic organ prolapse in Fbln5(-/-) animals, but not in WT, indicates that elastic fiber synthesis is crucial for recovery of the vaginal wall from distention-induced increases in vaginal protease activity.

Effects of bilateral levator ani nerve injury on pelvic support in the female squirrel monkey

OBJECTIVE

To determine whether experimental denervation of the levator ani (LA) and its subsequent atrophy contribute to the development of pelvic organ prolapse in the squirrel monkey.

STUDY DESIGN

Thirty-seven female monkeys were evaluated including 7 that underwent bilateral LA neurectomy (bLAN), 17 nulliparous monkeys without prolapse, 7 parous monkeys without prolapse, and 6 parous monkeys with prolapse. Magnetic resonance imaging was used to calculate LA muscle volumes and obtain measurements of the position of bladder and cervix. Repeat observations in bLAN females occurred at different times in relation to parturition.

RESULTS

LA volumes were reduced in bLAN monkeys (P = .02). Bladder (P = .03) and cervix (P = .04) positions varied between groups, with nulliparous females having the most cephalad positions and females with prolapse having the most caudal positions. Bladder descent was observed in a subset of 4 bLAN females that experienced vaginal parturition (P = .04) and correlated with external findings of vaginal prolapse.

CONCLUSION

Bilateral transection of the LA nerve results in atrophy of denervated LA muscles but not a loss of pelvic support in nulliparous monkeys, suggesting that connective tissue components compensate for weakened pelvic floor muscles. LA denervation may accelerate the onset of vaginal prolapse subsequent to parturition.