Well-Preserved Urinary Bladder Anatomy in Rats After Minimally Invasive Surgery

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Background: The setup of experimental protocols able to preserve the anatomical integrity also in terms of organ microarchitecture is mandatory to ensure result translatability. Also, the maintenance of structural integrity perfectly aligns with the refinement implementation aiming to reduce procedure severity, a key issue in animal studies deemed compulsory from both ethical and legal standpoints. Here we report a detailed description of all peri-operative and post-operative care and clinical evaluation in a surgical rat model to test the efficacy of a catheter functionalized by a peptide coating with antimicrobial and antibiofilm properties, whose efficacy was previously tested in vitro. Methods: We used male and female adult Fischer 344 rats (tot n = 44, n = 22 each sex), which were divided into four experimental groups. Each animal underwent refined surgery for the implantation of a functionalized or standard catheter, depending on the group, and was observed for 7 and 14 days. The surgical refinement strategy was based on the placement of the catheter into the bladder lumen rather than in the urethra. Still in the refinement perspective, ultrasound examination of the bladder was conducted to confirm the in situ position of the medical device at an intermediate time point, 4 or 10 days post-surgery depending on the group, while, at the same time, but also at days 0, 7, or 14 post-surgery, an ultrasound-guided cystocentesis was performed to collect sterile urine. The imaging approach was used in place of metabolic cages to minimize distress to the animals and to ensure reliable and unbiased scientific outcomes. Hematological and biochemical parameters were monitored along the preclinical trial; namely, blood sampling was performed at the beginning (day 0) and at the end of the trial (day 7 or 14 post-surgery depending on the group). Results: Clinical scores and biochemical analyses of all animals did not reveal signs of distress or disease. At the endpoints, histological analyses of urinary bladder displayed a well-preserved anatomical structure of the organ without significant signs of inflammatory infiltration into the urothelium. Conclusions: Our model represents a refined strategy to achieve the scientific goals required by the preclinical setting related to catheter-associated urinary tract infections. In particular, it ensures the preservation of bladder morphology and urothelium microarchitecture, maintaining an adequate level of animal health and welfare while monitoring the onset of urinary tract infections through the sterile collection of urine in long-lasting experiments.