In colorectal cancers with peritoneal involvement, HIPEC is applied as a treatment in suitable patients(Anon n.d.), (Schneebaum et al. 1996). It has been shown that HIPEC application increases colorectal anastomotic leaks(López-López et al. 2019). There are few studies in the literature showing that sildenafil application increases the strength of colon anastomosis(Cakir et al. 2015; Hasanoğlu Adnan et al. 2007; Uzun et al. 2008).
Anastomotic leak after HIPEC is a clinically important condition. In a study, rectal anastomotic leak was observed in 9 (22%) of 41 patients who did not undergo diverting ileostomy, and the mortality rate within 90 days was 7.1%(Whealon et al. 2017). In another study, the rate of enteric fistula and leak was found to be 10.5%(Piso et al. 2019). Because of this situation, increasing the anastomotic strength and reducing the possibility of leak without an invasive procedure such as protective ileostomy are important in terms of clinical improvement and overall cost in these patients. Oral and topical agents are being tried to prevent anastomotic leak. As an example, studies have shown that platelet-rich plasma applied topically to the anastomosis in rats treated with 5-fluorouracil and HIPEC strengthens tissue healing(Gorur et al. 2020), (Buk et al. 2020). It was determined that anastomosis strength increased by showing that burst pressure, hydroxyproline levels and histopathologically increased collagen formation. Sildenafil was used similarly in our study. In the rat model, the physical resistance and histopathology of the anastomosis, which is assumed to be weakened by HIPEC and the possibility of leak, changed with sildenafil application, were examined.
There were no drug-related side effects or immune reactions throughout the study. In the study, there were 2 deaths in the study and control groups and 1 death in the sham group. New subjects were added to the study to complete the number instead of subjects who died. One rat from the control group died on the 3rd postoperative day. In the sham group, death was observed in 2 rats on the postoperative 1st day and in 1 rat on the 2nd postoperative day. Intraoperative deaths were thought to be due to anesthesia-related complications, and postoperative deaths were thought to be due to sepsis. The limited number of rats used was the limitation of our study, since the minimal number of rats recommended by the power analysis result was used in our study.
In our study, there was no significant difference between the sildenafil group and the control group in terms of intra-abdominal adhesion. There was a significant difference between the Sham group and both groups. It has been shown in the literature that intraperitoneal chemotherapy causes adhesion(Jacquet P. Sugarbaker PH 1995). The difference with the Sham group is also in line with these results. In a study conducted in the rat anastomosis model in 2008, it was observed that intra-abdominal adhesions were significantly less in rats administered intraperitoneal sildenafil in the exploration performed on the 7th postoperative day(Ayten et al. 2008). Contrary to oral administration in our study, intraperitoneal administration was performed. Although the dose of 8 mg/kg sildenafil given intraperitoneally during the operation was less than the daily dose of 10 mg/kg sildefanil given in our study, it was thought that it may have provided a higher effect in terms of bioavailability.
Burst pressure measurement could not be applied effectively in 5 rats in the sildenafil group and 4 rats in the control group. Anastomotic leak occurred in 9 rats that underwent HIPEC. In rats that could be measured, there was no difference between the sildenafil group and the control group. In various publications in the literature, it has been seen that sildenafil has positive effects in terms of anastomotic burst pressure(Ayten et al. 2008; Hasanoğlu Adnan et al. 2007). The reason why no difference was observed in our study is that the negative effect of HIPEC on anastomosis outweighs the effect of sildenafil. There was no significant difference in burst pressure between the sham group and sildenafil and control groups. Since the rats whose burst pressure could not be measured could not be included in the statistical analysis, it was thought that there was no significant result. Apart from these, a meaningful result can be found in the study by using a larger sample of burst pressure measurement.
When the inflammatory granuloma and granulation tissue formation were examined, a significant difference was observed between the sham group, sildenafil and control groups in terms of the presence of inflammatory cells, and a more intense inflammatory response was observed in rats treated with HIPEC. In terms of neovascularization, a significant difference was observed between the sham group and the control group, while a statistically insignificant difference was observed with the sildenafil group. There was a significant difference between the sildenafil group and the control group in terms of fibroblastic proliferation and fibrosis formation. In a study conducted in canine open wounds in 2002, it was stated that fibroblastic proliferation increased with the effect of sildenafil and accelerated wound healing with this feature(Taş et al. 2003). Although sildenafil has been shown to reduce pulmonary fibrosis, it accelerates wound healing by increasing epithelial fibrosis during wound healing (David A. Zisman and Marvin Schwarz 2010).
In our study, no significant difference was observed between the sildenafil group and the other groups in terms of neutrophil and lymphocyte infiltration for anastomotic inflammatory infiltration. While there was a significant difference between the sildenafil group and the control group in terms of histiocytes, a significant difference was observed between the sildenafil group and both groups in terms of giant cells. Giant cells and histiocytes have an important role in the granulation that occurs during wound healing. Consequently, sildenafil is expected to increase granulation.
In the meta-analysis of studies on anastomosis resistance, positive effects of many agents on anastomosis were observed. In addition, agents whose effectiveness has been proven in many studies have not been proven to have a significant effect(Øines et al. 2014), (Karahasanoğlu T, Altınlı E, and Hamzaoğlu İ 1998), (Moran et al. 2007), (Dauser et al. 2020), (Sümer et al. 2011). In our study, it was shown that sildenafil increased fibrosis and granulation. However, there was no difference in burst pressure and adhesion, and histological differences were not of clinical importance as in the agents used in other studies.
Study Limitations
In the study, a prominent limitation is the lack of compatibility between the animal model and the human model. When extrapolating chemotherapy dosages from humas to rodents, an appropriate dosage cannot be established. Additionally, the limited similarity in wound healing between rodents and humans restricts the applicability of findings. Beyond these concerns, the animal sampling may not be sufficient for producing statistically meaningful results.