Systematic Evaluation of Clinical, Nutritional, and Fecal Microbial Factors for Their Association With Colorectal Polyps

Abstract

Introduction: The identification of risk factors for precursor lesions of colorectal cancer (CRC) holds great promise in the context of prevention. With this study, we aimed to identify patient characteristics associated with colorectal polyps (CPs) and polyp features of potential malignant progression. Furthermore, a potential association with gut microbiota in this context was investigated.

Methods: In this single-center study, a total of 162 patients with CPs and 91 control patients were included. Multiple variables including information on lifestyle, diet, serum parameters, and gut microbiota, analyzed by 16S-rRNA gene amplicon sequencing and functional imputations (Picrust2), were related to different aspects of CPs.

Results: We observed that elevated serum alkaline phosphatase (AP) levels were significantly associated with the presence of high-grade dysplastic polyps. This association was further seen for patients with CRC. Thereby, AP correlated with other parameters of liver function. We did not observe significant changes in the gut microbiota between patients with CP and their respective controls. However, a trend toward a lower alpha-diversity was seen in patients with CRC. Interestingly, AP was identified as a possible clinical effect modifier of stool sample beta diversity.

Discussion: We show for the first time an increased AP in premalignant CP. Furthermore, AP showed a significant influence on the microbial composition of the intestine. Relatively elevated liver enzymes, especially AP, may contribute to the detection of precancerous dysplastic or neoplastic changes in colorectal lesions. The association between elevated AP, premalignant CP, and the microbiome merits further study.

Graphical abstract

Figure 1.

Recruitment infrastructure, cohort demographics, and analyses. (a) Overview of the study's infrastructure and recruitment process, (b) patient cohorts and biomaterial availability, and (c) overview of the respective comparisons in the study. In total, 162 patients had at least 1 CP. Six comparisons were performed (#I–#VI) covering detection of polyps, comparison of conventional adenomas vs serrated lesions and risk signs. CP, colorectal polyp; CRC, colorectal carcinoma; HPL, hyperplastic polyp; SSL, sessile serrated lesion; TA, tubular adenoma; TSA, traditional serrated adenoma; TVA, tubulovillous adenoma.

Figure 2.

Clinical covariates related to risk factors of malignant progression in colorectal polyps. (a) Association of the presence of Association of the presence of adenoma with HGD feature or CRC (x-axis) with serum AP levels (y-axis). Hypothesis testing was performed using a 2-tailed Mann-Whitney U test. (b) Comparisons of P values derived from univariate assessment (grey) vs multivariate modeling (blue) for alkaline phosphatase levels. (c) Pairwise Spearman rank correlation between alkaline phosphatase levels and the indicated numeric covariates. (d) Association of the presence of HGD or CRC (x-axis) with serum alkaline phosphatase levels (y-axis). (e) Association of the indicated patient groups (x-axis) with serum alkaline phosphatase levels (y-axis). Hypothesis testing was performed using a 2-tailed Mann-Whitney U test with post hoc adjustment of P values using the Benjamini-Hochberg method. In boxplots, the box ranges from Q1 (the first quartile) to Q3 (the third quartile) of the distribution and the range represents the IQR. The median is indicated by a dashed line across the box. The “whiskers” on box plots extend from Q1 and Q3 to 1.5 the IQR. **FDR ≤0.01; *FDR ≤0.05; ns not significant. ALT, alanine aminotransferase; AP, alkaline phosphatase; AST, aspartate aminotransferase; CRC, colorectal carcinoma; FDR, false discovery rate; GGT, gamma-glutamyl transferase; HGD, high-grade dysplasia; HPL, hyperplastic polyps; IQR, interquartile range; LDH, serum lactate dehydrogenase.

Figure 3.

Microbial properties of the study population. (a) Relative abundances of phyla across control individuals and patients with polyp. Samples are ordered according to increasing relative abundances of Firmicutes. (b) Alpha diversity of the fecal microbiota in the whole cohort. Richness (left; 114 ± 34) and Shannon effective number of species (right; 49 ± 21). (c) Phylogenetic distance tree calculated from generalized Unifrac distances for all microbial stool samples. Stacked barplots show taxonomic distribution on the phylum level. Inner label shows the presence of the indicated polyp features. (d) Explained variations in fecal microbiota composition by covariates. All variables shown had a significant influence (P ≤ 0.05), displayed as proportions of explained variations based on R2. (e) Association of the indicated patient groups (x-axis) with species richness (y-axis). Hypothesis testing was performed using a 2-tailed Mann-Whitney U test with post hoc adjustment of P values using the Benjamini-Hochberg method. In boxplots, the box ranges from Q1 (the first quartile) to Q3 (the third quartile) of the distribution and the range represents the IQR. The median is indicated by a dashed line across the box. The “whiskers” on box plots extend from Q1 and Q3 to 1.5 the IQR. **FDR ≤0.01; *FDR ≤0.05; ns, not significant. ALT, alanine aminotransferase; AP, alkaline phosphatase; CRC, colorectal carcinoma; DM, diabetes mellitus; FDR, false discovery rate; HDL, high-density lipoprotein; HTN, hypertension; HPL, hyperplastic polyp; IQR, interquartile range.