Leukocyte inflammatory response in a rat urinary bladder regeneration model using porcine small intestinal submucosa scaffold.

Small intestinal submucosa (SIS) is a biodegradable scaffold that supports bladder regeneration after partial cystectomy. We sought to define the inflammatory response present in a rat bladder augmentation model using distal ileal SIS. Fifteen Sprague-Dawley rats underwent hemi-cystectomy followed by anastomosis of a bladder patch of SIS. Bladders were excised after days 2, 7, 14, 28, and 56. Tissue regeneration was evaluated by standard hematoxylin and eosin. Immunohistochemical staining was used to quantify neutrophils, macrophages, eosinophils, and mast cells. Total cell counts per unit area were compared between native and graft portions of the bladder for each cell type across the entire time course. Statistical analyses were conducted with the Wilcoxon Rank-Sum and Kruskal-Wallis tests. All tests were two-sided with significance set at p < 0.05. These inflammatory responses evolved consistently across all bladders over time. Neutrophil and eosinophil numbers were highest at day 2 and decreased over the 56-day period. In contrast, macrophage and mast cell numbers were low at days 2, 7, and 14; peaked at day 28; and decreased once again at day 56. Cell counts at native and graft sites were equivalent for all cell types, except neutrophils, which were more commonly found in the graft (124 vs. 24 cells/mm(2), p = 0.009). Thus, the inflammatory processes change over time during SIS-mediated bladder regeneration. Similar cell densities are present between the native and SIS portions of the bladder, but neutrophils predominate in the graft areas.

Temporal differentiation and maturation of regenerated rat urothelium.

OBJECTIVE: To determine if porcine small intestinal submucosa (SIS)-regenerated urothelium expresses markers of urothelial differentiation, uroplakin and zona occludens-1 (ZO-1), and whether their expression correlates with the histological appearance of the urothelium. MATERIALS AND METHODS: In all, 15 rats underwent partial cystectomy and bladder replacement with SIS. Regenerated bladders were harvested at either 2, 7, 14, 28, or 56 days after SIS grafting. Histological examination with haematoxylin and eosin staining was conducted to assess tissue regeneration. Immunohistochemistry was performed with uroplakin and ZO-1 antibodies. RESULTS: By 14 days after SIS grafting, the urothelial layer was completely confluent over the SIS. Expression of uroplakin and ZO-1, evident at 2 days after SIS grafting, progressed from a cytoplasmic pattern of expression to a mature pattern of cytoplasmic and membrane expression by 56 days after SIS grafting. CONCLUSION: In vivo tissue regeneration produces histologically and phenotypically mature urothelium within 2 weeks of SIS implantation. Regeneration of functional urothelium is probably essential for the subsequent development of the remaining bladder.