Caffeic acid ameliorates colitis in association with increased Akkermansia population in the gut microbiota of mice

Potential and active functions in the gut microbiota of a healthy human cohort

BACKGROUND

The study of the gut microbiota (GM) is rapidly moving towards its functional characterization by means of shotgun meta-omics. In this context, there is still no consensus on which microbial functions are consistently and constitutively expressed in the human gut in physiological conditions. Here, we selected a cohort of 15 healthy subjects from a native and highly monitored Sardinian population and analyzed their GMs using shotgun metaproteomics, with the aim of investigating GM functions actually expressed in a healthy human population. In addition, shotgun metagenomics was employed to reveal GM functional potential and to compare metagenome and metaproteome profiles in a combined taxonomic and functional fashion.

RESULTS

Metagenomic and metaproteomic data concerning the taxonomic structure of the GM under study were globally comparable. On the contrary, a considerable divergence between genetic potential and functional activity of the human healthy GM was observed, with the metaproteome displaying a higher plasticity, compared to the lower inter-individual variability of metagenome profiles. The taxon-specific contribution to functional activities and metabolic tasks was also examined, giving insights into the peculiar role of several GM members in carbohydrate metabolism (including polysaccharide degradation, glycan transport, glycolysis, and short-chain fatty acid production). Noteworthy, Firmicutes-driven butyrogenesis (mainly due to Faecalibacterium spp.) was shown to be the metabolic activity with the highest expression rate and the lowest inter-individual variability in the study cohort, in line with the previously reported importance of the biosynthesis of this microbial product for the gut homeostasis.

CONCLUSIONS

Our results provide detailed and taxon-specific information regarding functions and pathways actively working in a healthy GM. The reported discrepancy between expressed functions and functional potential suggests that caution should be used before drawing functional conclusions from metagenomic data, further supporting metaproteomics as a fundamental approach to characterize the human GM metabolic functions and activities.

Metabolic and microbial signatures in rat hepatocellular carcinoma treated with caffeic acid and chlorogenic acid

Hepatocellular carcinoma (HCC) treatment remains lack of effective chemopreventive agents, therefore it is very attractive and urgent to discover novel anti-HCC drugs. In the present study, the effects of chlorogenic acid (ChA) and caffeic acid (CaA) on HCC induced by diethylnitrosamine (DEN) were evaluated. ChA or CaA could reduce the histopathological changes and liver injury markers, such as alanine transarninase, aspartate aminotransferase, alkaline phosphatase, total bile acid, total cholesterol, high density lipoprotein cholesterol and low density lipoprotein cholesterol. The underlying mechanisms were investigated by a data integration strategy based on correlation analyses of metabonomics data and 16 S rRNA gene sequencing data. ChA or CaA could inhibit the increase of Rumincoccaceae UCG-004 and reduction of Lachnospiraceae incertae sedis, and Prevotella 9 in HCC rats. The principal component analysis and partial least squares discriminant analysis were applied to reveal the metabolic differences among these groups. 28 different metabolites showed a trend to return to normal in both CaA and ChA treatment. Among them, Bilirubin, L-Tyrosine, L-Methionine and Ethanolamine were correlated increased Rumincoccaceae UCG-004 and decreased of Lachnospiraceae incertae sedis and Prevotella 9. These correlations could be identified as metabolic and microbial signatures of HCC onset and potential therapeutic targets.

Chlorogenic Acid Ameliorates Experimental Colitis by Promoting Growth of Akkermansia in Mice

Chlorogenic acid (ChA)—one of the most abundant polyphenol compounds in the human diet—exerts anti-inflammatory activities. The aim of this study was to investigate the effect of ChA on gut microbiota in ulcerative colitis (UC). Colitis was induced by 2.5% dextran sulfate sodium (DSS) in C57BL/6 mice, which were on a control diet or diet with ChA (1 mM). The histopathological changes and inflammation were evaluated. Fecal samples were analyzed by 16S rRNA gene sequencing. ChA attenuated several effects of DSS-induced colitis, including weight loss, increased disease activity index, and improved mucosal damage. Moreover, ChA could significantly suppress the secretion of IFNγ, TNFα, and IL-6 and the colonic infiltration of F4/80⁺ macrophages, CD3⁺ T cells, and CD177⁺ neutrophils via inhibition of the active NF-κB signaling pathway. In addition, ChA decreased the proportion of Firmicutes and Bacteroidetes. ChA also enhanced a reduction in fecal microbiota diversity in DSS treated mice. Interestingly, ChA treatment markedly increased the proportion of the mucin-degrading bacterium Akkermansia in colitis mice. ChA acted as the intestine-modifying gut microbial community structure, resulting in a lower intestinal and systemic inflammation and also improving the course of the DSS-induced colitis, which is associated with a proportional increase in Akkermansia.

The gut microbiota: A key factor in the therapeutic effects of (poly)phenols

(Poly)phenols (PPs) constitute a large family of phytochemicals with high chemical diversity that are known to be active principles of plant-derived nutraceuticals and herbal medicinal products. Their pharmacological activity, however, is difficult to demonstrate due to their mild physiological effects, and to the large inter-individual variability observed. Many PPs have little bioavailability and reach the colon almost unaltered. There they encounter the gut microbes resulting in a two-way interaction in which PPs modulate the gut microbiota composition, and the intestinal microbes catabolize the ingested PPs to release metabolites that are often more active and better absorbed than the native phenolic compounds. The type and quantity of the PP metabolites produced in humans depend on the gut microbiota composition and function, and different metabotypes have been identified. However, not all the metabolites have the same biological activity, and therefore the final health effects of dietary PPs depend on the gut microbiota composition. Stratification in clinical trials according to individuals' metabotypes is necessary to fully understand the health effects of PPs. In this review, we present and discuss the most significant and updated knowledge regarding the reciprocal interrelation of the gut microbiota with dietary PPs as a key factor that modulates the health effects of these compounds. The review will focus in those PPs that are known to be metabolized by gut microbiota resulting in bioactive metabolites.

Interactions of gut microbiota with dietary polyphenols and consequences to human health

PURPOSE OF REVIEW

Dietary (poly)phenolic compounds have received attention over the last 20 years as antioxidants with preventive properties against chronic diseases. However, the evidence of these effects in clinical trials is weak, mainly because of a considerable interindividual variability. Polyphenols bioavailability is low, and gut microbiota metabolize them into simpler metabolites. As gut microbiota vary among individuals, such interindividual variability should be considered as a moderating factor in clinical trials. In this review, we show evidence of interactions with gut microbiota that help understanding polyphenols' health effects.

RECENT FINDINGS

Recent studies indicate that dietary polyphenols are relevant in the modulation of gut microbiota and that these microorganisms convert polyphenols into active and bioavailable metabolites; hence, variations in gut microbiota can affect polyphenol activity.

SUMMARY

The results show that study participants' stratification by their polyphenol-metabolizing phenotypes would be necessary for clinical trials as specific metabotypes produce the bioactive metabolites responsible for the health effects. Metabotypes can also reflect the gut microbiota composition and metabolic status, and could be biomarkers of the potential polyphenol health effects mediated through gut microbiota.