The effects of oxidative DNA damage and mutations in the p53 protein on cells of the colonic mucosa with and without the fecal stream: an experimental study in rats

SHP-2 phosphatase contributes to KRAS-driven intestinal oncogenesis but prevents colitis-associated cancer development

A major risk factor of developing colorectal cancer (CRC) is the presence of chronic inflammation in the colon. In order to understand how inflammation contributes to CRC development, the present study focused on SHP-2, a tyrosine phosphatase encoded by PTPN11 gene in which polymorphisms have been shown to be markers of colitis susceptibility. Conversely, gain-of-function mutations in PTPN11 gene (E76 residue) have been found in certain sporadic CRC. Results shown herein demonstrate that SHP-2 expression was markedly increased in sporadic human adenomas but not in advanced colorectal tumors. SHP-2 silencing inhibited proliferative, invasive and tumoral properties of both intestinal epithelial cells (IECs) transformed by oncogenic KRAS and of human CRC cells. IEC-specific expression of a SHP-2^E76K activated mutant in mice was not sufficient to induce tumorigenesis but markedly promoted tumor growth under the Apc^Min/+ background. Conversely, mice with a conditional deletion of SHP-2 in IECs developed colitis-associated adenocarcinomas with age, associated with sustained activation of Wnt/β-catenin, NFκB and STAT3 signalings in the colonic mucosae. Moreover, SHP-2 epithelial deficiency considerably increased tumor load in Apc^Min/+ mice, shifting tumor incidence toward the colon. Overall, these results reveal that SHP-2 can exert opposing functions in the large intestine: it can promote or inhibit tumorigenesis depending of the inflammatory context.

Current overview of colitis-associated colorectal cancer

Colitis-associated colorectal cancer (CACRC) constitutes a severe complication of inflammatory bowel diseases (IBD) and occurs in more than one third of IBD patients. In this short review we focus on the mechanisms underlying CACRC pathogenesis, and discuss the approaches for prevention and therapy in CACRC.

Relationship between the severity of diversion colitis and the composition of colonic bacteria: a prospective study

Background/Aims

Diversion colitis is the inflammation of the excluded segment of the colon in patients undergoing ostomy. It has been suggested that a change in colonic flora may lead to colitis; however, direct evidence for this disease progression is lacking. The aim of this study was to evaluate the relationship between the severity of diversion colitis and the composition of colonic bacteria.

Methods

We used culture methods and polymerase chain reaction to analyze the colonic microflora of patients who underwent rectal cancer resection with or without diversion ileostomy. In the diversion group, we also evaluated the severity of colonoscopic and pathologic colitis before reversal.

Results

This study enrolled 48 patients: 26 in the diversion group and 22 in the control group. Significant differences were observed between the two groups in the levels of Staphylococcus (p=0.038), Enterococcus (p<0.001), Klebsiella (p<0.001), Pseudomonas (p=0.015), Lactobacillus (p=0.038), presence of anaerobes (p=0.019), and Bifidobacterium (p<0.001). A significant correlation between the severity of colitis and bacterial composition was only observed for Bifidobacterium (p=0.005, correlation coefficient=-0.531).

Conclusions

The colonic microflora differed significantly between the diversion and control groups. Bifidobacterium was negatively correlated with the severity of diversion colitis.

5-aminosalicylic acid (5-ASA) can reduce levels of oxidative DNA damage in cells of colonic mucosa with and without fecal stream

BACKGROUND

No studies have evaluated the effectiveness of 5-ASA against oxidative DNA damage in experimental models of diversion colitis.

AIM

To evaluate the effects of 5-ASA against oxidative DNA damage in an experimental model of diversion colitis.

METHODS

Twenty-six Wistar rats were divided into two groups corresponding to sacrifice at 2 or 4 weeks after fecal diversion of the left colon by means of proximal colostomy and distal mucosa fistula. Each group was divided into two subgroups according to intervention in excluded colon performed with 0.9% saline solution or 5-ASA. Level of oxidative DNA damage was determined by comet assay in cells obtained from segments with and without fecal stream before and after H2O2 challenge. For statistical analysis, was used one-way analysis of variance (ANOVA), adopting a 5% significance level (P<0.05).

RESULTS

Levels of DNA damage were always higher in colon segments without fecal stream, regardless of the intervention solution employed. DNA damage in colon segments with and without fecal stream in animals irrigated with 5-ASA was lower when compared with those treated with saline solution, regardless of time of irrigation. These levels remained lower after intervention with 5-ASA, even after H2O2 challenge.

CONCLUSIONS

Enema with 5-ASA reduces oxidative DNA damage in epithelial cells of colon segments without fecal stream, even after H2O2 challenge, confirming the effects of 5-ASA against DNA damage by oxygen free radicals.

Avaliação dos níveis de peroxidação lipídica em células da mucosa cólica após aplicação de enemas com peróxido de hidrogênio: estudo experimental em ratos

A aplicação de clisteres contendo peróxido de hidrogênio (H2O2) determina o aparecimento de quadros graves de colite, algumas vezes de evolução fatal. É possível que a colite induzida por H2O2 possa ocorrer pela quebra da barreira funcional do epitélio cólico por estresse oxidativo. Objetivo: Avaliar os níveis de peroxidação lipídica em células da mucosa cólica após instilação de H2O2 no reto excluso de trânsito fecal. Método: Vinte seis ratos Wistar machos foram submetidos a colostomia proximal terminal no cólon descendente e fístula mucosa distal. Os animais foram randomizados em dois grupos segundo o sacrifício ter sido realizado duas ou quatro semanas após a derivação intestinal. Cada grupo experimental foi dividido e dois subgrupos segundo aplicação de clisteres, em dias alternados, contendo solução fisiológica a 0,9% ou H2O2 a 3%. O diagnóstico de colite foi estabelecido por estudo histopatológico e os níveis de dano oxidativo tecidual pela dosagem de malondialdeído por espectrofotometria. Os resultados foram analisados com os testes de Mann-Whitney e Kruskal-Wallis, estabelecendo-se nível de significância de 5% (p<0,05). Resultados: Os níveis de malondialdeído nos irrigados com SF nos cólons com e sem trânsito fecal após duas e quatro semanas de irrigação foram de: 0,05 ± 0,006; 0,06 ± 0,006 e 0,05 ± 0,03, 0,08 ± 0,02, respectivamente. Os níveis de malondialdeído nos irrigados com H2O2, nos cólons com e sem trânsito, após duas e quatro semanas de irrigação foram de 0,070 ± 0,006; 0,077 ± 0,01 e 0,052 ± 0,01, 0,08 ± 0,04, respectivamente. Após duas semanas os níveis de malondialdeído foram maiores nos animais irrigados com H2O2 em relação ao grupo controle (p= 0,007 e p= 0,01, respectivamente). Após quatro semanas não houve diferenças significantes Não ocorreu variação nos níveis de malondialdeído com o decorrer tempo de irrigação. Conclusão: Clisteres com H2O2, podem determinar o aparecimento de colite por ocasionarem estresse oxidativo nas células epiteliais da mucosa intestinal.