The SIS stands out among several types of grafts due to its capacity to repair the bladder and other urinary tract tissues . The neobladder formed from the SIS, however, differs histologically from the normal bladder as regards the organization and amount of soft muscle fibers, disposed in a disorganized way and in a lower quantity in the SIS neobladder. Besides that, the bladder would become permanently contracted if repaired only with biomaterials, because the bladder’s capacity to contract and relax depends on the normal muscle layer [1, 10].
Because of this, HSMC obtained from cadaveric tissues can be an alternative to improving the quality of the repair tissue, since HSMC have the same characteristics of the autologous cells and a reduced immunogenic potential when expanded in vitro[11–13]. In addition, although the autologous cells still the first option on cell therapies, the amount of cells obtained is very limited, especially if we take into consideration the age of the patient . Another disadvantage is the possibility of collecting and cultivating neoplastic cells [8, 14].
The standardization of the cell culture in this work was essential for the results obtained, amongst which the satisfactory macroscopic reparation of the bladder. However, in spite of the good quality of the reparation tissue at the outer face of the bladder, the intraluminal face of the animals from the CG was characterized, sometimes, by the presence of opaque, irregular and eroded tissue, with the presence of uroliths adhered to its surface. The inferior quality of the reparation tissue on the animals from the CG, comparing to the TG, may be related to the naked lay of the SIS that may predispose to the precipitation and aggregation of the dissolved urine salts. The presence of these salts by itself would result in an increased inflammatory process and formation of uroliths . The inflammatory process would result also in a higher influx of fibroblasts and deposition of collagenous tissue, consequently forming lower quality reparation tissue with wide fibrosis areas .
Such findings match the histopathological alterations, characterized by the higher amount of urothelial coating failures in the samples from the CG animals when compared to the TG. This may result from the fact that the muscle cells are important for the maintenance of the structural integrity and organization of the cell graft [2, 16]. Grafts that are not seeded with muscle cells present epithelization failures, because although the epithelium has a high regenerative capacity, the muscle cells by yet unknown mechanisms modulate cell proliferation . Perhaps the production of cytokines and other specific metabolites by the muscle cells can provide answers to this issue, but additional studies will be needed.
Additionally, the insufficient revascularization of the graft and the acute inflammation could also have contributed to the unsatisfying results of the histopathological evaluation of the animals from the CG. As mentioned above, the inflammatory cells are responsible for liberating cytokines and other bioactive molecules that could lead to a higher collagen fiber deposition, hindering the restocking of the graft by the muscle cells [17, 18].
Thus, the cell coating would waterproof the graft, limiting the toxic effects of the urine on it and, consequently, decrease the inflammatory response [2, 14]. According to Zhang et al. (2005), such protective function is assigned only to the implanted cells over the intraluminal face of the graft. In this work, however, the HSMC have been seeded over the extraluminal face, which could help to the hypothesis that the muscle cells would participate in the organization and migration of other cells like the urothelial ones.
A cycle is, therefore, created, wherein the muscle cells seeded above the SIS contribute to the epithelization process which, in turn, contributes to muscle fibers deposition in the graft.
The absence of adequate urothelial coating would also justify the main alterations verified on the clinical, laboratorial and abdominal ultrasonographic evaluations, such as the presence of cystitis and urolithiasis. As mentioned previously, the presence of crystals and cell debris, dissolved in a higher quantity in the urine due to the surgical trauma, allied to the anatomical conformation of the female urethra, could result on the crust of the SIS, which would therefore result in an infection and urolithiasis [2, 19]. The HSMC would form a protective barrier avoiding the crystals from dissolving in the urine precipitates among the collagen fibers of the graft, consequently contributing to the absence of cystitis and urolithiasis in the animals from the TG [2, 20].
Besides that, the higher amount of collagen fibers in the acellular SIS would result in a lower capacity of bladder contractibility, thus resulting in a higher quantity of residual urine, which could also have predisposed an infection of the urinary tract in the animals from the CG .