The Effects and Mechanisms of the Rapamycin-eluting Stent in Urethral Stricture Prevention in Rabbits

Rapamycin was shown to reduce transforming growth factor β1 (TGF-β1) expression, inhibit the Mammalian target of rapamycin function, and prevent TGF-β1-induced pulmonary fibrosis. Rapamycin-eluting stents (RES) were successfully used to prevent coronary artery restenosis. Urethral stricture is one of the most challenging problems in urology. Thus, combining the pharmacological effects of rapamycin and the mechanical support of the stent on the urethra may prevent urethral stricture formation. However, the use of RES for urethral stricture treatment has not been studied.To observe the effects of RES in urethral stricture in a rabbit model.Animal experimentation.Twenty adult male New Zealand rabbits were randomly divided into control, urethral stricture model, bare-metal stent, and RES groups. The rabbits in the control group underwent urethroscopy alone without electrocoagulation. The rabbit model of urethral stricture was established by electrocoagulation using a self-made electrocoagulation device under direct vision using ureteroscopy. After model establishment, the rabbits in the bare-metal stent and RES groups received stent placement by ureteroscopy. On day 30, retrograde urethrography was performed to assess urethral stricture formation, ureteroscopy to remove the stents, and histological examinations to assess the degree of fibrosis. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis were used to evaluate the expression levels of TGF-β1, Smad3, and matrix metalloproteinase 1 (MMP1).Urethral stricture formation was seen in the model group, whereas not in the bare-metal stent group. The bare-metal stents did not displace but were difficult to remove. In the RES group, RES was dislodged in itself at postoperative day 27 in one rabbit, whereas successfully removed by ureteroscopy in the remaining four rabbits, and urethral stricture formation was not seen on retrograde urethrography after stent removal. Histological examination revealed a large number of dense fibroblasts and blue-stained collagen fibers in the bare-metal stent group, whereas the number of fibroblasts and collagen fibers under the mucosa was reduced in the RES group. RT-qPCR and Western blot analyses showed that the messenger ribonucleic acid (mRNA) and protein expression of TGF-β1and Smad3 was significantly decreased, and mRNA and protein expression of MMP1 was significantly increased in the RES group than that in the model ((P < 0.001) and bare-metal stent groups (P < 0.001).RES can effectively prevent electrocoagulation-induced urethral stricture in rabbits. The mechanism may be related to the effect of rapamycin on inhibiting TGF-β1 and Smad3 expression and promoting MMP1 expression in urethral tissues.