Curcumin, Quercetin, Catechins and Metabolic Diseases: The Role of Gut Microbiota

Abstract

Polyphenols (PPs) are the naturally occurring bioactive components in fruits and vegetables, and they are the most abundant antioxidant in the human diet. Studies are suggesting that ingestion of PPs might be helpful to ameliorate metabolic syndromes that may contribute in the prevention of several chronic disorders like diabetes, obesity, hypertension, and colon cancer. PPs have structural diversity which impacts their bioavailability as they accumulate in the large intestine and are extensively metabolized through gut microbiota (GM). Intestinal microbiota transforms PPs into their metabolites to make them bioactive. Interestingly, not only GM act on PPs to metabolize them but PPs also modulate the composition of GM. Thus, change in GM from pathogenic to beneficial ones may be helpful to ameliorate gut health and associated diseases. However, to overcome the low bioavailability of PPs, various approaches have been developed to improve their solubility and transportation through the gut. In this review, we present evidence supporting the structural changes that occur after metabolic reactions in PPs (curcumin, quercetin, and catechins) and their effect on GM composition that leads to improving overall gut health and helping to ameliorate metabolic disorders.

Keywords: bioavailability; biotransformation; gut health; metabolic syndrome; plant polyphenols.

Figure 1

Major dietary sources of polyphenols and potential gut microbiota-associated benefits.

Figure 2

Major dietary sources of polyphenols and potential gut microbiota-associated benefits.

Figure 3

Reciprocal interaction between curcumin and GM. Biotransformation of curcumin occurs due to GM that convert it into several metabolites through pathways like demethylation, reduction, acetylation, hydroxylation, and demethoxylation. These metabolites associated with showing biological activities such as antioxidant, anti-inflammatory, anti-tumoral, and neuroprotective activity. Whereas, GM modulation alters the microbial abundance, diversity, and composition, which also exerts health benefits, indirectly. GM: gut microbiota.

Figure 4

Biotransformation of quercetin into metabolites by gut microbiota (mainly by Bacteroides fragilis, Eubacterium ramulus, C. perfringens) and their benefits in gut.

Figure 5

The metabolic pathway and common metabolites of (˗)-Epicatechin-3-O-gallate and their modulatory effects on human gut: Eggerthella lenta and Flavonifractor plautii are mainly responsible for the biotransformation of dietary catechins. GM: gut microbiota.

Figure 6

Summary of the factors affecting the bioavailability of polyphenols.