In vitro modulation of the human gastrointestinal microbial community by plant-derived polysaccharide-rich dietary supplements

Abstract

The use of prebiotics is a possible strategy to manage and steer the complex gut microbial community towards a health-promoting composition (Gastrointestinal Resource Management). In this study, the Simulator of the Human Intestinal Microbial Ecosystem was used to investigate the effects of two commercially-available plant polysaccharide supplements on the structure, composition and metabolism of an in vitro cultured colon microbial community.

Microbial analyses showed both a bifidogenic (up to + 1.3 log cfu/mL) and a lactobacillogenic (up to + 0.9 log cfu/mL) effect during treatment with the dietary supplements. Quantitative PCR confirmed that the increase of Bifidobacteria spp. was statistically significant (P < 0.05) in all of the colon compartments and showed a significant increase of the bacteroides–prevotella group concentration (+ 0.6 log cells/ml) in the compartment simulating the proximal colon. Denaturant gradient gel electrophoresis analyses and a relative ecological interpretation, in combination with sugar and short-chain fatty acids quantification, provided evidence of a positive effect of both the tested products. Overall, the treatment period was associated with (i) good and selective fermentability of the polysaccharide supplements along the entire colon; (ii) positive and selective bifidogenic effect; (iii) the possibility of enhancing species belonging to Bacteroidetes, a phylum recently associated with body weight management.

Introduction

The human intestinal microbial ecosystem is responsible for numerous processes involved in host health, such as extraction of energy from indigestible compounds, stimulation of the gut immune system and the synthesis of essential vitamins. On the other hand, specific microbial community assemblages may also be risk factors contributing to disease states (e.g. allergies, bowel inflammation and obesity) (Turnbaugh et al., 2007, Leser and Mølbak, 2009, Possemiers et al., 2009 and references within).

In recent years, many research efforts have focused on what has been recently defined as Gastrointestinal Resource Management (GRM), i.e. the management of the complex gut microbiota and its metabolism with the aim of improving the host health (Cummings and Macfarlane, 1991, Macfarlane and Macfarlane, 1997, Manning and Gibson, 2004, Possemiers et al., 2009). One approach to achieve this goal is the ingestion of prebiotics to selectively influence the colonic microbial community composition and activity (Gibson et al, 2004). The prebiotics currently used in the functional food industry are oligosaccharides such as lactulose, fructo-oligosaccharides (FOS), inulin, galacto-oligosaccharides (GOS) or arabinoxylan-oligosaccharides (AXOS) (Manning and Gibson, 2004, Sanchez et al., 2009). Most of these compounds are predominantly fermented in the proximal colon (with the exception of AXOS - Grootaert et al., 2009), where the microbiota is known to have a saccharolytic metabolism (Macfarlane et al., 1992, Macfarlane and Macfarlane, 1997, Smith and Macfarlane, 1997). Consequently, there is a great interest in finding different prebiotics or mixtures of prebiotics that could exert a biological activity throughout the entire colon and reduce the occurrence of chronic colonic diseases (for example, Crohn's disease and colorectal cancer) (Baumgart and Sandborn, 2007, Inoue et al., 2007). With this aim, specific studies have been conducted to identify potential key ingredients in numerous medicinal plants known for their ancient uses as healing remedies (Eshun and He 2004). Among them, Aloe vera, larch and seaweed have been correlated with several positive effects in the human body (i.e. decreased ammonia absorption, immune modulation, possible anti-metastatic activity, and increased short-chain fatty acids (SCFAs) production), and it has been suggested that the carbohydrates found in these plants are indeed the biologically active components (Table 1) (Kelly, 1999, Robinson et al., 2001, Kim et al., 2002, Pogribna et al., 2008).

The aim of the present study was to evaluate the effect of two commercially-available plant polysaccharide supplements (glyconutrients) on the structure, composition and metabolism of the resident microbial community in the different areas of the colon (i.e. ascending, transverse and descending colon). The two products contained a combination of larch arabinogalactan (Larix occidentalis), rice starch, Aloe vera gel extract or gel powder and wakame algae extract (Undaria pinnatifida fucoidans) and two different gums (ghatti and tragacanth). For this purpose, the Simulator of Human Intestinal Microbial Ecosystem (SHIME) was used. This in vitro system has already been shown to be a useful model for nutrition studies investigating intestinal microbial composition and activity (De Boever et al., 2000, Van de Wiele et al., 2004, Decroos et al., 2006, Van de Wiele et al., 2007, Marzorati et al., 2009).