The Interactions Between Structural Change Of Intestinal Microbiota And Development Of Colorectal Adenoma

Background Colorectal cancer(CRC)is cancer that starts in the colon or rectum.The morbidity and mortality of CRC is rising rapidly in China or throughout the world with the change of healthy lifestyles and aging population problems.CRC development is a multistep process that begins when normal epithelium forms aberrant crypts and further advances into stages of early and late adenomatous polyps,carcinoma in situ,invasive carcinoma and metastasis,most frequently as a result of mutations in numerous genetic changes.Colorectal adenoma(CRA)is the most frequent precancerous lesion and the adenoma detection rate is increasing with the implementation of screening colonoscopy programs.The gastrointestinal tract holds a complex community of microorganisms,which are essential for maintaining homeostasis.The intestinal microbiota participates in a number of human physiological activities and has an important influence on nutritional and immunological processes,regulation of intestinal epithelial barrier in a dynamic balance.There is growing evidence that dysbiosis of the gut microbiota is associated with fatty liver disease,obesity,diabetes and inflammatory bowel disease(IBD)by using next-generation sequencing(NGS),also known as high-throughput sequencing and multivariate statistics in microecology,studies have shown that the change of structure or number of intestinal flora is closely related to the occurrence of colorectal cancer development.But the intestinal flora in the colon specific pathogenesis is still unclear.To elucidate the adaptive alteration of the intestinal microbiota in different stage of colorectal cancer from a dynamic perspective will aid us in understanding the pathogenesis of colorectal cancer,providing further understanding of the biodiversity of intestinal flora and pathogenesis.Objective To investigate the taxonomic richness,diversity of gut microbiota in patients with adenoma and to determine the bacterial profile of adenomatous tissues and adjacent tissues versus normal tissues,helping elucidating the role of gut microorganisms in precancerous lesions in colon and rectum.Methods Adenomatous tissues and adjacent tissues with 31 patients versus normal tissues with 20 healthy controls were collected through colonoscopy.the total bacterial genomic DNA were extracted.The sequence of V3-V4 hypervariable region in bacterial 16SrRNA gene was amplified by polymerase chain reaction.Electrophoresis was used to purify the PCR products.Mixing DNA products after quantitation were sequenced on an Illumina MiSeq platform.Results Alpha diversity estimations revealed higher microbiota diversity and richness indices in samples from patients with adenomas than that of healthy controls(P<0.01).Mucosal microbiota of colorectal adenomas was structurally segregated from that of normal tissues as shown by both principal component analysis and cluster tree analyses.At the phylum level,a large decrease in Firmicutes with concomitant relative expansion of Proteobacteria was observed in patients with adenomas and a corresponding decrease in the Firmicutes/Bacteroidetes ratio(P<0.01).Abundance of eight phyla was significantly different.At the genus level,Lactococcus and Pseudomonas were enriched in preneoplastic tissue whereas Enterococcus,Bacillus,and Solibacillus were reduced(P<0.01).These findings are novel.We also found microbiota structure was similar between low grade colon intraepithelial neoplasia and high grade intraepithelial neoplasia,Escherichia-Shigella showed a rising trend in high grade intraepithelial neoplasia but no significant difference was detected(P>0.05).We compared adenoma biopsy samples with their adjacent non-adenoma samples from the same patient.However,there were no significant abundance differences across any of the sampled tissues and the overall microbial structures of precancerous and adjacent tissues were similar(P>0.05).Conclusion In conclusion,we have indicated that microbiome structural dysbiosis of gut microbiota likely leads to a changing pro-oncogenic microenvironment.Application of high-throughput sequencing on gut microbiota for the surveillance of colorectal tumor with different stages may contribute to screen for colorectal cancers.Early-stage cancer detection and intervention provides an important value in preventing colorectal tumor development.