Increasingly, the gut microbiome is implicated in the etiology of cancer, not only as an infectious agent, but also by altering exposure to dietary compounds that influence disease risk. While the composition and metabolism of the gut microbiome is influenced by diet, the gut microbiome can also modify dietary exposures in ways that are beneficial or detrimental to the human host. The colonic bacteria metabolize macronutrients, either as specialists or in consortia of bacteria, in a variety of diverse metabolic pathways. Microbial metabolites of diet can also be epigenetic activators of gene expression that may influence cancer risk in humans. Epigenetic involves heritable changes in gene expression via post translational and post transcriptional modifications. Microbial metabolites can influence epigenetics by altering the pool of compounds used for modification or by directly inhibiting enzymes involved in epigenetic pathways. Colonic epithelium is immediately exposed to these metabolites, although some metabolites are also found in systemic circulation. In this review, we discuss the role of the gut microbiome in dietary metabolism and how microbial metabolites may influence gene expression linked to colon cancer risk.

BackgroundPeriodontal infections are hypothesized to increase the risk of adverse systemic outcomes through inflammatory mechanisms. The magnitude of effect, if any, of anti-infective periodontal treatment on systemic inflammation is unknown, as are the patient populations most likely to benefit. We conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) to test the hypothesis that anti-infective periodontal treatment reduces systemic c-reactive protein (CRP).Methods and FindingsMEDLINE, EMBASE, CENTRAL and CINAHL databases were searched using sensitivity-enhancing search terms. Eligible RCTs enrolled patients with periodontal infection, compared a clearly defined anti-infective periodontal intervention (experimental group) to an “inactive control” (no periodontal intervention) or to an “active control” (lower treatment intensity than the experimental group). Mean differences in final CRP values at the earliest post-treatment time point (typically 1-3 months) between experimental and control groups were analyzed using random-effects regression. Among 2,753 possible studies 20 were selected, which included 2,561 randomized patients(median=57). Baseline CRP values were >3.0 mg/L in 40% of trials. Among studies with a control group receiving no treatment, the mean difference in CRP final values among experimental treatment vs. control groups was -0.37 mg/L [95%CI=-0.64, -0.11], (P=0.005), favoring experimental treatment. Trials for which the experimental group received antibiotics had stronger effects (P for interaction=0.03) and the mean difference in CRP final values among experimental treatment vs. control was -0.75 mg/L [95%CI=-1.17,-0.33]. No treatment effect was observed among studies using an active treatment comparator. Treatment effects were stronger for studies that included patients with co-morbidities vs. studies that included “systemically healthy” patients, although the interaction was not significant (P=0.48).ConclusionsAnti-infective periodontal treatment results in short-term modest reductions in systemic CRP.

Background Trimethylamine N-oxide (TMAO), a compound derived from diet and metabolism by the gut microbiome, has been associated with several chronic diseases, although the mechanisms of action are not well understood and few human studies have investigated microbes involved in its production. Objectives Our study aims were 1) to investigate associations of TMAO and its precursors (choline, carnitine, and betaine) with inflammatory and cardiometabolic risk biomarkers; and 2) to identify fecal microbiome profiles associated with TMAO. Methods We conducted a cross-sectional analysis using data collected from 1653 participants (826 men and 827 women, aged 60–77 y) in the Multiethnic Cohort Study. Plasma concentrations of TMAO and its precursors were measured by LC-tandem MS. We also analyzed fasting blood for markers of inflammation, glucose and insulin, cholesterol, and triglycerides (TGs), and further measured blood pressure. Fecal microbiome composition was evaluated by sequencing the 16S ribosomal RNA gene V1–V3 region. Associations of TMAO and its precursors with disease risk biomarkers were assessed by multivariable linear regression, whereas associations between TMAO and the fecal microbiome were assessed by permutational multivariate ANOVA and hurdle regression models using the negative binomial distribution. Results Median (IQR) concentration of plasma TMAO was 3.05 μmol/L (2.10–4.60 μmol/L). Higher concentrations of TMAO and carnitine, and lower concentrations of betaine, were associated with greater insulin resistance (all P < 0.02). Choline was associated with higher systolic blood pressure, TGs, lipopolysaccharide-binding protein, and lower HDL cholesterol (P ranging from <0.001 to 0.03), reflecting an adverse cardiometabolic risk profile. TMAO was associated with abundance of 13 genera (false discovery rate < 0.05), including Prevotella, Mitsuokella, Fusobacterium, Desulfovibrio, and bacteria belonging to the families Ruminococcaceae and Lachnospiraceae, as well as the methanogen Methanobrevibacter smithii. Conclusions Plasma TMAO concentrations were associated with a number of trimethylamine-producing bacterial taxa, and, along with its precursors, may contribute to inflammatory and cardiometabolic risk pathways.