The Study Of The Correlation Between The Gut Microbiota Dysbiosis And Colorectal Cancer

Colcorectal cancer(CRC)is the third most common cancer worldwide.In addition,it is also the second and the third leading cause of cancer deaths in western world and China,respectively.There were many potential risk factors associated with CRC,such as unhealthy lifestyle,smoking et al.Basically,CRC can be classified into two categories:hereditary and sporadic CRC according to its etiology.Hereditary CRC responsible for less than 5%,while sporadic CRC accounts for more than 95%of total CRC.It is estimated that more than 80%of sporadic CRC derived from colorectal adenomas.However,up to date,its etiology is still unclear.Recent study showed that gut microbiota probably involved in the development of CRC.The human colon contains up to 1014 bacteria,its total amount more than ten times of human cells.Therefore,the human microbiome was also been called "the second human genome" which covered more than 500-1000 species.They coevolved with human and the relative balance of gut microbiome is important in the maintenance of human health.These bacteria colonized in human gut,shaped the gut systemic immune system and promote the host metabolism.In recent years,a increasing evidence showed that the dysbiosis of gut microbiota was associated with several diseases,such as CRC.It was revealed that the gut microbiota structure of the patients with colorectal cancer and colorectal adenomas is altered.We have compared the structure differences of the gut microbiota between the patients with colorectal cancer and the healthy people by pyrosequencing in our lab.On the basis of this experiment,the changes of Fusobacterium and butyrate-producing bacteria in the intestinal tract of patients with colorectal adenomas and colorectal cancer were studied in this study.In this study,fecal samples were collected from CRC(n=20),adenomas patients(n=12)and healthy subjects(n=20).Firstly,we optimized the genome DNA extraction protocol from fecal samples.Then the Fusobacterium,Eubacterium rectale,Faecalibacterium prausnitzii and the total number of fecal bacteria were quantified using real-time PCR.The discrepancy of copy number of 16S rRNA gene indicated the dysbiosis of target bacteria in fecal samples.Results showed that the abundance of Fusobacterium was significantly higher in colorectal cancer patients than that in healthy subjects(P=0.000)and colorectal adenomas patients(P=0.013),and it was significantly higher in colorectal cancer patients than that in colorectal adenomas patients(P=0.002).F.prausnitzii was significantly lower in colorectal adenomas patients compared to healthy subjects(P=0.033).The total bacteria count was significantly lower in the colorectal adenomas samples than that in the healthy samples(P=0.002).While,there was no significantly difference of E.rectal between the three kinds of samples.The abundance of butyrate-producing bacterium,F.prausnitzii was decreased in the feces of colorectal adenomas patients.However,Fusobacterium was increased in the feces of colorectal adenomas and colorectal cancer patients.These shifts in the colonic bacterial population may potentially contribute to the development of colorectal cancer.Based on the previous study in our lab,the abundance of Fusobacterium genus were enriched in adenomas and CRC patients.In this study,we proved the positive detection rate in three groups of subjects and further investigate the species level by sequencing the 16S rRNA gene colon library.Results showed that Fusobacterium can be detected in assayed subjects and the positive rate were 10.0%,66.7%and 90.0%in healthy,adenomas and CRC group,respectively.And a significant difference were found between three assayed groups of subjects.The phylogenetic tree showed that F.nucleatum presented in adenomas and CRC fecal samples,while F.varium were found in all three groups of subjects.This results indicated that F.nucleatum probably involved in the development of CRC,while F.varium is a kind of commensal bacteria present in human gut.The significant difference of the positive rate of Fusobacterium in fecal samples of the three groups of subjects showed that it may be used as a potential biomarker for the early diagnose of CRC.