Systematic Review of Animal Models Used in Research of Origins and Treatments of Fecal Incontinence

Effects of testosterone treatment on anal sphincter damage repair in ovariectomized rats

BACKGROUND

Fecal incontinence (FI) generally occurs with anal sphincter damage caused by vaginal delivery in women, obvious FI can develop in the postmenopausal stage. This pelvic floor dysfunction has no rational medical therapeutic options. We investigated the effect of testosterone treatment on the anal sphincter structure, serum thiol/disulfide levels, uterine tissue, and body composition in female rats in an experimental menopause-FI model.

METHODS

The animal experiments were performed between September and November 2020 at Experimental Animal Application and Research Center, Afyon Kocatepe University, Afyonkarahisar, Turkey. Thirty-two female rats were divided into four groups: sham, saline, 10 mg/kg testosterone undecanoate, 100 mg/kg testosterone undecanoate. Except for the sham group, all the other groups underwent ovariectomy (OVE) to create a menopause model. Two weeks after this procedure, the FI model was created under general anesthesia in all rat groups. At the end of the experiment, the rats were placed under general anesthesia, weighed, and euthanized after recording the data. The anal sphincter region and uterine tissue samples were collected for histopathological examinations, and blood samples were collected for total testosterone and thiol/disulfide homeostasis analyses.

RESULTS

An increase in anal sphincter muscles and connective tissue thickness was observed in the testosterone-administered groups (p = 0.001). No difference was detected between the groups in the total thiol, native thiol, and disulfide balance (p = 0.087, p = 0.604, p = 0.092). The testosterone-treated groups did not have severe uterine epithelial degradation, hyperemia, or increased endometrial thickness (p = 0.186, p = 0.222, p = 0.630). The body weight of all rats increased (p < 0.05), but the omental weight did not increase (p = 0.061).

DISCUSSION

Testosterone treatment increased the anal sphincter muscle and connective tissue thickness without causing any oxidative stress and did not result in a pathological change in the uterine tissue and body fat composition.

Differentiation of Adipose-Derived Stem Cells into Smooth Muscle Cells in an Internal Anal Sphincter-Targeting Anal Incontinence Rat Model

OBJECTIVE

Studies on development of an anal incontinence (AI) model targeting smooth muscle cells (SMCs) of the internal anal sphincter (IAS) have not been reported. The differentiation of implanted human adipose-derived stem cells (hADScs) into SMCs in an IAS-targeting AI model has also not been demonstrated. We aimed to develop an IAS-targeting AI animal model and to determine the differentiation of hADScs into SMCs in an established model.

MATERIALS AND METHODS

The IAS-targeting AI model was developed by inducing cryoinjury at the inner side of the muscular layer via posterior intersphincteric dissection in Sprague-Dawley rats. Dil-stained hADScs were implanted at the IAS injury site. Multiple markers for SMCs were used to confirm molecular changes before and after cell implantation. Analyses were performed using H&E, immunofluorescence, Masson's trichrome staining, and quantitative RT-PCR.

RESULTS

Impaired smooth muscle layers accompanying other intact layers were identified in the cryoinjury group. Specific SMC markers, including SM22α, calponin, caldesmon, SMMHC, smoothelin, and SDF-1 were significantly decreased in the cryoinjured group compared with levels in the control group. However, CoL1A1 was increased significantly in the cryoinjured group. In the hADSc-treated group, higher levels of SMMHC, smoothelin, SM22α, and α-SMA were observed at two weeks after implantation than at one week after implantation. Cell tracking revealed that Dil-stained cells were located at the site of augmented SMCs.

CONCLUSIONS

This study first demonstrated that implanted hADSc restored impaired SMCs at the injury site, showing stem cell fate corresponding to the established IAS-specific AI model.

A systematic review of translation and experimental studies on internal anal sphincter for fecal incontinence

The complexity in the molecular mechanism of the internal anal sphincter (IAS) limits preclinical or clinical outcomes of fecal incontinence (FI) treatment. So far, there are no systematic reviews of IAS translation and experimental studies that have been reported. This systematic review aims to provide a comprehensive understanding of IAS critical role in FI. Previous studies revealed the key pathway for basal tone and relaxation of IAS in different properties as follows; calcium, Rho-associated, coiled-coil containing serine/threonine kinase, aging-associated IAS dysfunction, oxidative stress, renin-angiotensin-aldosterone, cyclooxygenase, and inhibitory neurotransmitters. Previous studies have reported improved functional outcomes of cellular treatment for regeneration of dysfunctional IAS, using various stem cells, but did not demonstrate the interrelationship between those results and basal tone or relaxation-related molecular pathway of IAS. Furthermore, these results have lower specificity for IAS-incontinence due to the included external anal sphincter or nerve injury regardless of the cell type. An acellular approach using bioengineered IAS showed a physiologic response of basal tone and relaxation response similar to human IAS. However, in both cellular and acellular approaches, the lack of human IAS data still hampers clinical application. Therefore, the IAS regeneration presents more challenges and warrants more advances.