Rat model of anal sphincter injury and two approaches for stem cell administration

AIM To establish a rat model of anal sphincter injury and test different systems to provide stem cells to injured area.METHODS Adipose-derived stem cells(ASCs) were isolated from BDIX rats and were transfected with green fluorescent protein(GFP) for cell tracking. Biosutures(sutures covered with ASCs) were prepared with 1.5 × 10~6 GFPASCs, and solutions of 10~6 GFP-ASCs in normal saline were prepared for injection. Anorectal normal anatomy was studied on Wistar and BDIX female rats. Then, we designed an anal sphincter injury model consisting of a 1-cm extra-mucosal miotomy beginning at the anal verge in the anterior middle line. The sphincter lesion was confirmed with conventional histology(hematoxylin and eosin) and immunofluorescence with 4', 6-diamidino-2-phenylindole(commonly known as DAPI), GFP and α-actin. Functional effect was assessed with basal anal manometry, prior to and after injury. After sphincter damage, 36 BDIX rats were randomized to three groups for:(1) Cell injection without repair;(2) biosuture repair; and(3) conventional suture repair and cell injection. Functional and safety studies were conducted on all the animals. Rats were sacrificed after 1, 4 or 7 d. Then, histological and immunofluorescence studies were performed on the surgical area.RESULTS With the described protocol, biosutures had been covered with at least 820000-860000 ASCs, with 100% viability. Our studies demonstrated that some ASCs remained adhered after suture passage through the muscle. Morphological assessment showed that the rat anal anatomy is comparable with human anatomy; two sphincters are present, but the external sphincter is poorly developed. Anal sphincter pressure data showed spontaneous, consistent, rhythmic anal contractions, taking the form of "plateaus" with multiple twitches(peaks) in each pressure wave. These basal contractions were very heterogeneous; their frequency was 0.91-4.17 per min(mean 1.6980, SD 0.57698), their mean duration was 26.67 s and mean number of peaks was 12.53. Our morphological assessment revealed that with the aforementioned surgical procedure, both sphincters were completely sectioned. In manometry, the described activity disappeared and was replaced by a gentle oscillation of basal line, without a recognizable pattern. Surprisingly, these findings appeared irrespective of injury repair or not. ASCs survived in this potentially septic area for 7 d, at least. We were able to identify them in 84% of animals, mainly in the muscular section area or in the tissue between the muscular endings. ASCs formed a kind of "conglomerate" in rats treated with injections, while in the biosuture group, they wrapped the suture. ASCs were also able to migrate to the damaged zone. No relevant adverse events or mortality could be related to the stem cells in our study. We also did not find unexpected tissue growths. CONCLUSION The proposed procedure produces a consistent sphincter lesion. Biosutures and injections are suitable for cell delivery. ASCs survive and are completely safe in this clinical setting.

Omentum facilitates liver regeneration

AIM:To investigate the mechanism of liver regeneration induced by fusing the omentum to a small traumatic injury created in the liver. We studied three groups of rats. In one group the rats were omentectomized; in another group the omentum was left in situ and was not activated,and in the third group the omentum was activated by polydextran particles. METHODS:We pre-activated the omentum by injecting polydextran particles and then made a small wedge wound in the rat liver to allow the omentum to fuse to the wound. We monitored the regeneration of the liver by determining the ratio of liver weight/body weight,by histological evaluation (including immune staining for cytokeratin-19,an oval cell marker),and by testing for developmental gene activation using reverse transcription polymerase chain reaction (RT-PCR). RESULTS:There was no liver regeneration in the omentectomized rats,nor was there significant regeneration when the omentum was not activated,even though in this instance the omentum had fusedwith the liver. In contrast,the liver in the rats with the activated omentum expanded to a size 50% greater than the original,and there was histologically an interlying tissue between the wounded liver and the activated omentum in which bile ducts,containing cytokeratin-19 positive oval cells,extended from the wound edge. In this interlying tissue,oval cells were abundant and appeared to proliferate to form new liver tissue. In rats pre-treated with drugs that inhibited hepatocyte growth,liver proliferation was ongoing,indicating that regeneration of the liver was the result of oval cell expansion. CONCLUSION:Activated omentum facilitates liver regeneration following injury by a mechanism that depends largely on oval cell proliferation.

Autologous tissue patch rich in stem cells created in the subcutaneous tissue

AIM:To investigate whether we could create natural autologous tissue patches in the subcutaneous space for organ repair. METHODS: We implanted the following three types of inert foreign bodies in the subcutaneous tissue of rats to produce autologous tissue patches of different geometries:(1) a large-sized polyvinyl tube(L = 25 mm,internal diameter = 7 mm) sealed at both ends by heat application for obtaining a large flat piece of tissue patch for organ repair;(2) a fine polyvinyl tubing(L = 25 mm,internal diameter = 3 mm) for creating cylindrically shaped grafts for vascular or nerve repair; and(3) a slurry of polydextran particle gel for inducing a bladder-like tissue. Implantation of inert materials was carried out by making a small incision on one or either side of the thoracic-lumbar region of rats. Subcutaneous pockets were created by blunt dissection around the incision into which the inert bodies were inserted(1 or 2 per rat). The incisions were closed with silk sutures,and the animals were allowed to recover. In case of the polydextran gel slurry 5 m L of the slurry was injected in the subcutaneous space using an 18 gauge needle. After implanting the foreign bodies a newly regenerated encapsulating tissue developed around the foreign bodies. The tissues were harvested after 4-42 d of implantation and studied by gross examination,histology,and histochemistry for organization,vascularity,and presence of mesenchymal stem cells(MSCs)(CD271+CD34+ cells). RESULTS: Implanting a large cylindrically shaped polyvinyl tube resulted in a large flat sheet of tissue that could be tailored to a specific size and shape for use as a tissue patch for repairing large organs. Implanting a smaller sized polyvinyl tube yielded a cylindrical tissue that could be useful for repairing nerves and blood vessels. This type of patch could be obtained in different lengths by varying the length of the implanted tube. Implanting a suspension of inert polydextran suspension gave rise to a bladder-like tissue that could be potentially used for repairing heart valves. Histologically,the three different types of tissue patches generated were organized similarly,consisting of three layers,increasing in thickness until day 14. The inner layer in contact with the inert material was avascular; a middle layer that was highly vascular and filled with matrix,and an outer layer consisting of loose connective tissue. MSCs identified as CD271+CD34+ cells were present in the medial layer and around major blood vessels at day 4 but absent at later time points. The early-harvested tissues,endowed with MSCs,could be used for tissue repair,while the later-harvested tissues,being less vascular but thicker and tougher,could be used as filler tissue for cosmetic purposes. CONCLUSION: An autologous,vascularized tissue patch of desired shape and size can be created in the subcutaneous space by implanting different types of inert bodies.