Experimental model of anal fistula in rats

A Preclinical Validation of Iron Oxide Nanoparticles for Treatment of Perianal Fistulizing Crohn's Disease

Fistulizing anoperineal lesions are severe complications of Crohn's disease (CD) that affect quality of life with a long-term risk of anal sphincter destruction, incontinence, permanent stoma, and anal cancer. Despite several surgical procedures, they relapse in about two-thirds of patients, mandating innovative treatments. Ultrasmall particles of iron oxide (USPIO) have been described to achieve in vivo rapid healing of deep wounds in the skin and liver of rats thanks to their nanobridging capability that could be adapted to fistula treatment. Our main purpose was to highlight preclinical data with USPIO for the treatment of perianal fistulizing CD. Twenty male Sprague Dawley rats with severe 2,4,6-trinitrobenzenesulfonic acid solution (TNBS)-induced proctitis were operated to generate two perianal fistulas per rat. At day 35, two inflammatory fistulas were obtained per rat and perineal magnetic resonance imaging (MRI) was performed. After a baseline MRI, a fistula tract was randomly drawn and topically treated either with saline or with USPIO for 1 min (n = 17 for each). The rats underwent a perineal MRI on postoperative days (POD) 1, 4, and 7 and were sacrificed for pathological examination. The primary outcome was the filling or closure of the fistula tract, including the external or internal openings. USPIO treatment allowed the closure and/or filling of all the treated fistulas from its application until POD 7 in comparison with the control fistulas (23%). The treatment with USPIO was safe, permanently closed the fistula along its entire length, including internal and external orifices, and paved new avenues for the treatment of perianal fistulizing Crohn's disease.

Establishment of a novel experimental model of infected anal fistula in rat

Refractory Crohn's-like enterocutaneous fistula indicates the aggressive manifestation and lead to poor prognosis of patients. The development of multidisciplinary strategies for fistula administration largely subjects to the deficiency of animal model for disease remodeling and the underlying pathogenic mechanism. For the purpose, infected anal fistula model was conducted by BLV single-core electrolytic aluminum combined with dextran sodium sulfate. Notably, the inflammatory granulation tissue and inflammatory cell infiltration in the perianal tissue were arised on day 7 of the model by utilizing the Hematoxylin–eosin staining. With the aid of magnetic resonance imaging and signals of high-brightness. We intuitively observed the thickening and edema appeared in the fistula wall, which collectively suggested the formation of a fistula in the perianal area of the rat. Distinguish from the current models of anal fistula modeling including the body surface of fistula, backside of fistula and drainage wire of fistula, our model revealed multifaceted advantages such as quicker generation, higher modeling rate, preferable stability, better consistency, cost-effective, and in particular, more convenient to mimic clinical manifestations of anal fistula.

EFFICACY OF LOW-LEVEL LASER THERAPY ON FISTULA-IN-ANO TREATMENT

Background:

Treating anal fistulae is still a great challenge due to the possibility of fecal incontinence after surgery and that the use of laser has been gaining space in medicine, including as an inducing method of healing.

Aim:

To evaluate the efficacy of low-level laser therapy on fistula-in-ano treatment in rats.

Methods:

Fifteen male Wistar rats weighing approximately 250-300g were used, which were subjected to the anal fistula induction procedure and after 30 days were distributed into two groups: control group (CG, n=5) and laser group (LG, n=10) observed for another 30 days. In the CG no treatment was performed and, in the LG, low-level laser therapy was applied in fistulous tracts daily. The closure of the fistulous tract, the area of the remaining tract, the inflammatory infiltrate and vascular congestion were evaluated.

Results:

There was no complete closure of the tract in any of the animals. The mean area of the remaining tract was 847.2 µm² in the CG and 248.5 µm² in the LG (p=0.001). The mean inflammatory infiltrate score was 2.4 in the CG and 1.3 in the LG (p=0.0285), while in the evaluation of vascular congestion, 1.6 was observed in the CG and 0.6 in the LG (p=0.031).

Conclusions:

Low-level laser therapy was able to reduce the area of the fistulous tracts as well as decrease the inflammatory process and local vascular congestion.

Effectiveness of the Aloe Vera extract in the treatment of fistula-in-ano

Rationale Considering that anal fistulae are still challenging regarding their treatment due to the risk of fecal incontinence in the most complex cases and the increasing use of phytotherapeutic drugs such as Aloe Vera in medicine, even with proven healing effectiveness, there is interest in researching this drug in the treatment of anal fistulae.

Objective To evaluate the efficacy ofAloe Vera extract in the treatment of anal fistulae in rats.

Method Thirty male Wistar rats weighing 250–300 g were submitted to anal fistula and after 30 days were divided into three groups: Control Group (GCo) (n = 5), Carbopol Group (GCa) (n = 5), and Aloe Vera Group (GAV) (n = 10). In the GCo no treatment was performed, while in the others a daily infusion of 0.3 mL of solution (Carbopol only in GCa and Carbopol plus Aloe Vera extract in the GAV) was performed through the external orifice of the fistula for 30 days. Afterwards, euthanasia was performed and specimens were removed for histological study. It was evaluated the closure of the fistulous tract, the area of the remaining tract, the inflammatory infiltrate and the degree of vascular congestion. The results were submitted to statistical treatment by Kruskall–Wallis test, considering p < 0.05.

Results There was no complete closure of the fistulous tract in any of the animals. The mean area of the remaining tract was 847.2 μm in the GCo, 565.6 μm in the GCa and 377.8 μm in the GAV (p < 0.05). The mean of the inflammatory infiltrate score was 2.4 in the GCo, 2.4 in the GCa and 2.3 in the GAV (p > 0.05), while in the evaluation of vascular congestion, we observed a mean of 1.6 in the GCo, 1.4 in GCa and 1.1 in GAV (p < 0.05).

Conclusion The extract of Aloe vera was able to reduce the lumen of the fistulous tract and reduce the degree of vascular congestion; however, it did not allow the complete closure of the fistulous tract nor diminished the inflammatory process.

Treatment of rats anal fistula with glycerin Aloe barbadensis Miller extract

Rationale There is a need for a low cost treatment for complex anal fistulas that can heal without causing fecal incontinence, with room for the study of herbal medicines.

Objective To evaluate the effect of the glycerin Aloe barbadensis Miller extract in the treatment of anal fistula in rats.

Method Thirty Wistar rats underwent peritoneal anesthesia with ketamine and Xylasine, followed by transfixation of the anal sphincter with a steel wire, which remained for 30 days to develop the anal fistula. After this period, the steel wire was removed and three groups with 10 animals were formed: A (control), without treatment; B (seton), in which a cotton seton was introduced; C (therapeutic seton), in which a cotton thread was introduced as a seton, and Aloe barbadensis Miller extract was daily dripped in the seton; after 30 days, the setons of groups B and C were removed, and after two weeks without a seton euthanasia and removal of specimens was conducted, and the fistula closure and the inflammatory process were analyzed.

Results Fistula persistence was observed in all animals in Group A, six in Group B and three in Group C (p = 0.015). The mean local inflammation levels were 0.9 in Group A; 0.8 in Group B, and 0 in Group C (p = 0.015).

Conclusion The use of a seton soaked in a glycerin Aloe barbadensis Miller extract was effective in the healing of anal fistulas in rats, in addition to causing less inflammatory process than the non-phytotherapeutic seton.

Preclinical Model of Perianal Fistulizing Crohn's Disease

BACKGROUND

Fistulizing anoperineal lesions (FAPLs) are common and severe complications of Crohn's disease (CD), exposing patients to the risk of anal sphincter alteration and permanent stoma. Due to the limited efficacy of current treatments, identifying new local therapies is mandatory. However, testing new treatments is currently limited because no relevant preclinical model of Crohn's-like FAPL is available. Thus, a reliable and reproducible experimental model of FAPLs is needed to assess new therapeutic strategies.

METHODS

Twenty-one rats received a rectal enema of 2,4,6-trinitrobenzensulfonic acid (TNBS) to induce proctitis. Seven days later, a transsphincteric fistula tract was created with a surgical thread, instilled with TNBS twice a week until its removal at day 7 (group 1), day 14 (group 2), or day 28 (group 3). In each rat, pelvic MRI was performed just before and 7 days after thread removal. Rats were sacrificed 7 days after thread removal for pathological assessment of the fistula tract.

RESULTS

The optimal preclinical model was obtained in group 3. In this group, 7 days after thread removal, all animals (9 of 9) had a persistent fistula tract visible on MRI with T2-hypersignal (normalized T2 signal intensity: 2.36 ± 0.39 arbitrary units [a.u.] [2.08-2.81]) and elevation of the apparent diffusion coefficient (1.33 ± 0.16 10-3 millimeter squared per seconds [1.18-1.49]). The pathological examination of the fistula tract revealed acute and chronic inflammation, granulations, fibrosis, epithelialization, and proctitis in the adjacent rectum.

CONCLUSIONS

This reproducible preclinical model could be used to assess the effectiveness of innovative treatments in perianal fistulizing CD.

Treatment of anal fistula with Baccharis dracunculifolia extract. Experimental study in rats

OBJECTIVE

to evaluate the efficacy of Baccharis dracunculifolia extract in the treatment of anal fistulas in rats.

METHODS

twenty male Wistar rats were submitted to anal fistula and, after 30 days, were divided into three groups: Control Group, with five animals; Carbopol Group, with five animals; and Baccharis dracunculifolia Group, with ten animals. In the Control Group, no treatment was performed. In the Carbopol Group, a daily infusion of Carbopol was performed for 30 days. In the Baccharis dracunculifolia Group, a daily infusion of Carbopol plus Baccharis dracunculifolia extract was performed for 30 days. Specimens were taken for histological analysis after euthanasia.

RESULTS

there was no complete closure of the fistulous tract in any of the animals. The mean area of the remaining tract was of 847.2µm2, 565.6µm2 and 372.7µm2, in the Control Group, Carbopol Group, and Baccharis dracunculifolia Group, respectively, (p=0.001). The mean of the inflammatory process score was of 2.4, 2.4, and 2.1, in the Control Group, Carbopol Group, and Baccharis dracunculifolia Group, respectively, (p=0.285), while the mean values of vascular congestion were of 1.6, 1.4, and 1.1, in the Control Group, Carbopol Group, and Baccharis dracunculifolia Group, respectively, (p=0.031).

CONCLUSION

Baccharis dracunculifolia extract was able to reduce the lumen of the fistulous tracts and the degree of vascular congestion, without, however, reducing the local inflammatory process or totally closing the fistulous tracts.

PRIMARY SPHINCTEROPLASTY COMPARING TWO DIFFERENT STITCHES IN ANAL FISTULA TREATMENT: EXPERIMENTAL STUDY IN RATS

BACKGROUND

Anal fistula is by definition the communication between the rectum or anal canal with the perineal region, which may be epithelialized and has cryptoglandular origin in 90% of cases. There are a large number of techniques for successfully treating trans-sphincteric fistulas of 20-50%, including primary sphincteroplasty, but it is not clear whether the material used would influence the outcome.

AIM

To analyze the efficacy of polydioxanone and polypropylene wire in primary post-fistulotomy sphincteroplasty in the treatment of trans-sphincteric fistulas in rats.

METHODS

Thirty Wistar rats had transfixation of the anal sphincter with steel wire, which remained for 30 days for the development of the anal fistula. After this period, it was removed and four groups were formed: A (control) without treatment; B (fistulotomy) submitted to such procedure and curettage only; C (polidioxanone) in which sphincteroplasty was performed after fistulotomy with polydioxanone wire; D (polypropylene) submitted to the same treatment as group C, but with polypropylene wire. After 30 days, euthanasia and removal of the specimens were performed for qualitative histopathological analysis, measurement of the area between the muscular cables edges and evaluation of the degree of local fibrosis.

RESULTS

There was persistence of the anal fistula in all animals of group A. There were no significant differences between groups B, C and D regarding the distance of the muscular cables (p=0.078) and the degree of fibrosis caused by the different treatments (p=0.373).

CONCLUSIONS

There was no difference between polydioxanone and polypropylene wires in post-fistulotomy primary sphincteroplasty, and this technique was not superior to simple fistulotomy in relation to the distance of the muscular cables nor did it present differences in relation to the degree of local fibrosis.

Review article: pathogenesis of Crohn's perianal fistula-understanding factors impacting on success and failure of treatment strategies

BACKGROUND

Evidence from groups who have studied fistula aetiology and extrapolation from interventional studies supports a multifactorial hypothesis of Crohn's perianal fistula, with several pathophysiological elements that may contribute to fistula formation, persistence and resistance to treatment.

AIM

An evidence synthesis of current understanding of pathophysiological factors underlying Crohn's perianal fistula is presented, exploring the fundamental reasons why some treatments succeed and others fail, as a means of focussing clinical knowledge on improving treatment of Crohn's perianal fistula.

METHODS

Evidence to support this review was gathered via the Pubmed database. Studies discussing pathophysiological factors underpinning perianal fistula, particularly in Crohn's disease, were reviewed and cross-referenced for additional reports.

RESULTS

Pathophysiological factors that impact on success or failure of interventions for Crohn's perianal fistulae include the high-pressure zone, obliterating the dead space, disconnecting the track from the anus, removing epithelialisation, eradicating sepsis and by-products of bacterial colonisation, correcting abnormalities in wound repair and removing the pro-inflammatory environment which allows fistula persistence. Most current interventions for Crohn's perianal fistulae tend to focus on a single, or at best two, aspects of the pathophysiology of Crohn's anal fistulae; as a result, failure to heal fully is common.

CONCLUSIONS

For an intervention or combination of interventions to succeed, multiple factors must be addressed. We hypothesise that correct, timely and complete attention to all of these factors in a multimodal approach represents a new direction that may enable the creation of an effective treatment algorithm for Crohn's anal fistula.

Experimental porcine model of complex fistula-in-ano

AIM

To establish and evaluate an experimental porcine model of fistula-in-ano.

METHODS

Twelve healthy pigs were randomly divided into two groups. Under general anesthesia, the experimental group underwent rubber band ligation surgery, and the control group underwent an artificial damage technique. Clinical magnetic resonance imaging (MRI) and histopathological evaluation were performed on the 38^th d and 48^th d after surgery in both groups, respectively.

RESULTS

There were no significant differences between the experimental group and the control group in general characteristics such as body weight, gender, and the number of fistula (P > 0.05). In the experimental group, 15 fistulas were confirmed clinically, 13 complex fistulas were confirmed by MRI, and 11 complex fistulas were confirmed by histopathology. The success rate in the porcine complex fistula model establishment was 83.33%. Among the 18 fistulas in the control group, 5 fistulas were confirmed clinically, 4 complex fistulas were confirmed by MRI, and 3 fistulas were confirmed by histopathology. The success rate in the porcine fistula model establishment was 27.78%. Thus, the success rate of the rubber band ligation group was significantly higher than the control group (P < 0.05).

CONCLUSION

Rubber band ligation is a stable and reliable method to establish complex fistula-in-ano models. Large animal models of complex anal fistulas can be used for the diagnosis and treatment of anal fistulas.