Abstract
BACKGROUND: Microbial metabolism of lignans from high-fiber plant foods produces bioactive enterolignans, such as enterolactone (ENL) and enterodiol (END). Enterolignan exposure influences cellular pathways important to cancer risk and is associated with reduced colon tumorigenesis in animal models and lower colorectal cancer risk in humans. OBJECTIVES: The aim of this study was to test the effects of a flaxseed lignan supplement (50 mg secoisolariciresinol diglucoside/d) compared with placebo on host gene expression in colon biopsies and exfoliated colonocyte RNA in feces and fecal microbial community composition, and to compare responses in relation to ENL excretion. METHODS: We conducted a 2-period randomized, crossover intervention in 42 healthy men and women (20-45 y). We used RNA-seq to measure differentially expressed (DE) genes in colonic mucosa and fecal exfoliated cells through the use of edgeR and functional analysis with Ingenuity Pathway Analysis. We used 16S ribosomal RNA gene (V1-V3) analysis to characterize the fecal microbiome, and measured END and ENL in 24-h urine samples by gas chromatography-mass spectrometry. RESULTS: We detected 32 DE genes (false discovery rate <0.05) in the exfoliome, but none in the mucosal biopsies, in response to 60 d of lignan supplement compared with placebo. Statistically significant associations were detected between ENL excretion and fecal microbiome measured at baseline and at the end of the intervention periods. Further, we detected DE genes in colonic mucosa and exfoliome between low- and high-ENL excreters. Analysis of biopsy samples indicated that several anti-inflammatory upstream regulators, including transforming growth factor β and interleukin 10 receptor, were suppressed in low-ENL excreters. Complementary analyses in exfoliated cells also suggested that low-ENL excreters may be predisposed to proinflammatory cellular events due to upregulation of nuclear transcription factor κB and NOS2, and an inhibition of the peroxisome proliferator-activated receptor γ network. CONCLUSIONS: These results suggest that ENL or other activities of the associated gut microbial consortia may modulate response to a dietary lignan intervention. This has important implications for dietary recommendations and chemoprevention strategies.
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Key Points
Colorectal cancer (CRC) is the third most common cause of cancer-related deaths in men and women in North America. Experimental evidence suggests that enterolignans possess a variety of biological activities, including antioxidant, antitumor, weak estrogenic, and antiestrogenic properties, and modulate enzymes involved in steroid hormone metabolism. The primary aim of this human mechanistic study was to evaluate, in healthy individuals, the effects of a flaxseed lignan extract on gene expression in colonic mucosa and exfoliated cells in stool. A randomized, crossover intervention study to test the effect of dietary lignans compared with placebo on mRNA expression, and to evaluate the modifying effect of gut microbial community on ENL production and the host response was used. The noninvasive exfoliated transcriptome (exfoliome) and tissue level transcriptome were also compared in paired samples as a secondary aim. The study detected modest differences in colonic gene expression and the exfoliome in response to the supplement. However, significant contributions of the gut microbiome to production of the enterolignan ENL during the lignan intervention, and substantial differences in colonic and exfoliome gene expression between low- and high-ENL excreters was found. Future studies that incorporate microbial pathway analysis estimated from measures of microbial functional genes (i.e., metatranscriptomics) may capture more robustly the polymicrobial contribution to the ENL phenotype. The finding that metabolic and inflammatory pathways in colonic mucosa and exfoliated cells differed between the low and high-ENL excreters suggests that ENL or other activities of the associated gut microbial consortia are modulators of response to a dietary lignan intervention. This has important implications for personalized dietary recommendations and chemoprevention strategies (i.e., not all individuals will experience sufficient exposure to ENL as a result of plant lignan consumption so as to elicit a beneficial, cancer-preventive response).