The Dietary Fiber Pectin: Health Benefits and Potential for the Treatment of Allergies by Modulation of Gut Microbiota

Abstract

Purpose of review: The incidence of allergies is increasing and has been associated with several environmental factors including westernized diets. Changes in environment and nutrition can result in dysbiosis of the skin, gut, and lung microbiota altering the production of microbial metabolites, which may in turn generate epigenetic modifications. The present review addresses studies on pectin-mediated effects on allergies, including the immune modulating mechanisms by bacterial metabolites.

Recent findings: Recently, microbiota have gained attention as target for allergy intervention, especially with prebiotics, that are able to stimulate the growth and activity of certain microorganisms. Dietary fibers, which cannot be digested in the gastrointestinal tract, can alter the gut microbiota and lead to increased local and systemic concentrations of gut microbiota-derived short chain fatty acids (SCFAs). These can promote the generation of peripheral regulatory T cells (T_reg) by epigenetic modulation and suppress the inflammatory function of dendritic cells (DCs) by transcriptional modulation. The dietary fiber pectin (a plant-derived polysaccharide commonly used as gelling agent and dietary supplement) can alter the ratio of Firmicutes to Bacteroidetes in gut and lung microbiota, increasing the concentrations of SCFAs in feces and sera, and reducing the development of airway inflammation by suppressing DC function. Pectin has shown immunomodulatory effects on allergies, although the underlying mechanisms still need to be elucidated. It has been suggested that the different types of pectin may exert direct and/or indirect immunomodulatory effects through different mechanisms. However, little is known about the relation of certain pectin structures to allergies.

Keywords: Allergy; Dietary fiber; Microbiota; Pectin; Prebiotics; SCFA.

Fig. 1

Dietary fibers (overview). Dietary fibers are polymers mainly derived from edible parts of plants, certain types of animals or analogous carbohydrates that are neither digested nor absorbed in the human intestine. They can be divided into carbohydrates and non-carbohydrates (e.g., lignin). Carbohydrate fibers can be further subdivided in non-digestible oligosaccharides or polysaccharides such as non-starch-, resistant starch-, or dextran polysaccharides

Fig. 2

Pectin structure and health benefits. Pectin consists of a linear backbone of at least 65% galacturonic acid (GalA) that can be methyl-esterified at the carboxyl groups present at C-6. The ratio of esterified to non-esterified GalA groups is termed the degree of esterification (DE). Pectin are classified as high methoxy pectin (HMP) with DE > 50% or low methoxy pectin (LMP) with DE < 50%

Fig. 3

Immune modulation by pectin. Immune modulation by dietary fibers can either be indirectly mediated by their fermentation into short chain fatty acids (SCFAs) or directly caused by the pectin, e.g., via the blockage of the pro-inflammatory TLR2/1 pathway. Several positive health effects are associated with consumption of pectin such as maintaining the intestinal barrier, immune modulation like the activation of immune cells (T, B, NK cells), and the inhibition of inflammatory responses

Fig. 4

Immune modulation by pectin-derived SCFAs. Pectin fermentation by gut microbiota leads to the production of SCFAs. Different genera can generate different SCFAs. For example, acetate can be produced by many different genera; propionate is mainly produced by Bacteroidetes and Firmicutes, while butyrate is mainly produced by Clostridia species. SCFA bind “metabolite-sensing” G-protein-coupled receptors such as GPR41, GPR43, GPR109A, and olfactory receptor (Olfr)-78. These receptors promote the gut homeostasis and the regulation of inflammatory responses. GPRs and their metabolites influence T_reg activation, epithelial integrity, gut homeostasis, DC biology, and IgA antibody responses. Through their inhibition of HDAC expression or function, SCFAs also influence gene transcription in many cells and tissues