Fructans: prebiotics and immunomodulators

Fructans are natural fructose polymers that are used for their prebiotic and health improving properties in functional foods. Although the immunomodulatory effects of fructans on animal cells are known, their mode of action has only recently been unraveled. It was found that inulin-type fructans act as signals in animals, stimulating immune cell activity through Toll Like Receptor (TLR)° mediated signaling. This review summarizes recent progress in the area with focus on possible fructan signaling and downstream signaling events. Intriguingly, synergistic effects with phenolic compounds are often observed. Fructans and their fermentation products (short chain fatty acids and hydrogen gas) lead to a more reduced cellular status and a modulation of the immune system, aiming at disease prevention. Moreover, evidence is accumulating that fructans may alleviate inflammatory symptoms in diseased subjects. In conclusion, fructans are of interest in functional foods because of their prebiotic, antioxidant and immunomodulatory properties. © 2014 Elsevier Ltd.status: publishe

Disease prevention by natural antioxidants and prebiotics acting as ROS scavengers in the gastrointestinal tract

Natural antioxidants derived from plants become increasingly popular as functional food and feed ingredients. This viewpoint article highlights the emerging antioxidant character of natural non-structural carbohydrates, with focus on those plant-derived compounds that have dual antioxidative and prebiotic properties. In parallel to more indirect action mechanisms, it is proposed here that such compounds are involved in direct ROS scavenging processes in plants, in food and in the gastrointestinal tract, counteracting oxidative stress and preventing pathogen outbreaks and the development of ROS related diseases.status: publishe

Fructans as Immunomodulatory and Antiviral Agents: The Case of Echinacea

Throughout history, medicinal purposes of plants have been studied, documented, and acknowledged as an integral part of human healthcare systems. The development of modern medicine still relies largely on this historical knowledge of the use and preparation of plants and their extracts. Further research into the human microbiome highlights the interaction between immunomodulatory responses and plant-derived, prebiotic compounds. One such group of compounds includes the inulin-type fructans (ITFs), which may also act as signaling molecules and antioxidants. These multifunctional compounds occur in a small proportion of plants, many of which have recognized medicinal properties. Echinacea is a well-known medicinal plant and products derived from it are sold globally for its cold- and flu-preventative and general health-promoting properties. Despite the well-documented phytochemical profile of Echinacea plants and products, little research has looked into the possible role of ITFs in these products. This review aims to highlight the occurrence of ITFs in Echinacea derived formulations and the potential role they play in immunomodulation.status: Published onlin

Plant sugars are crucial players in the oxidative challenge during abiotic stress. Extending the traditional concept

Plants suffering from abiotic stress are commonly facing an enhanced accumulation of reactive oxygen species (ROS) with damaging as well as signalling effects at organellar and cellular levels. The outcome of an environmental challenge highly depends on the delicate balance between ROS production and scavenging by both enzymatic and metabolic antioxidants. However, this traditional classification is in need of renewal and reform, as it is becoming increasingly clear that soluble sugars such as disaccharides, raffinose family oligosaccharides (RFOs) and fructans – next to their associated metabolic enzymes – are strongly related to stress-induced ROS accumulation in plants. Therefore, this review aims at extending the current concept of antioxidants functioning during abiotic stress, with special focus on the emanate role of sugars as true ROS scavengers. Examples are given based on their cellular location, as different organelles seem to exploit distinct mechanisms. Moreover, the vacuole comes into the picture as important player in the ROS signalling network of plants. Elucidating the interplay between the mechanisms controlling ROS signalling during abiotic stress will facilitate the development of strategies to enhance crop tolerance to stressful environmental conditions.status: publishe

Towards understanding vacuolar antioxidant mechanisms: a role for fructans?

Recent in vitro, in vivo and theoretical experiments strongly suggest that sugar-(like) molecules counteract oxidative stress by acting as genuine ROS scavengers. A concept was proposed to include the vacuole as a part of the cellular antioxidant network. According to this view sugars and sugar-like vacuolar compounds work in concert with vacuolar phenolic compounds and the “classic” cytosolic antioxidant mechanisms. Among the biologically relevant ROS (H2O2, O2•- and •OH), hydroxyl radicals are the most reactive and dangerous species since there are no enzymatic systems known to neutralize them in any living beings. Therefore, it is important to study in more detail the radical reactions between •OH and different biomolecules, including sugars. Here, we used Fenton reactions to compare the •OH scavenging capacities of a range of natural vacuolar compounds to establish relationships between antioxidant capacity and chemical structure and to unravel the mechanisms of •OH-carbohydrate reactions. The in vitro work on the •OH scavenging capacity of sugars and phenolic compounds revealed a correlation between structure and •OH scavenging capacity. The number and position of C=C type of linkages in phenolic compounds greatly influences antioxidant properties. Importantly, the splitting of disaccharides and oligosaccharides emerged as a predominant outcome of the •OH-carbohydrate interaction. Moreover, non-enzymatic synthesis of new fructan oligosaccharides was found starting from 1-kestotriose. Based on these and previous findings, a working model is proposed describing the putative radical reactions involving fructans and secondary metabolites at the inner side of the tonoplast and in the vacuolar lumen.status: publishe

Fructans and their potential role as paradoxical antioxidants in Echinacea products

On the one hand, fructans, fructose-based oligo- and polysaccharides, are well-known multifunctional carbohydrates that show prebiotic, immunodulatory and antioxidant effects. On the other hand, Echinacea preparations are used on a wide scale in a preventive way, stimulating native immunity. Here we demonstrate that 5 commercially available Echinacea preparations contain inulin-type fructans. The total antioxidant capacity and the DNA protective capacity under oxidative stress were compared to each other and to carbohydrate only fractions. Although not always consistent among all the products tested, our data suggest that inulin-type fructans may represent one important component in these Echinacea products, potentially contributing to immunomodulatory and antioxidant effects. However, prooxidant effects can not be excluded in some preparations. Further research into the effects of sample preparation, degree of polymerization and concentration of the inulin-type fructans, the nature and concentration of polyphenolic compounds, the relative proportions of inulin/polyphenols and the importance of inulin/polyphenolic complexes are warranted.status: Published onlin

Sugars as hydroxyl radical scavengers: proof-of-concept by studying the fate of sucralose in Arabidopsis

Substantial formation of reactive oxygen species (ROS) is inevitable in aerobic life forms. Due to their extremely high reactivity and short lifetime, hydroxyl radicals are a special case, because cells have not developed enzymes to detoxify these most dangerous ROS. Thus, scavenging of hydroxyl radicals may only occur by accumulation of higher levels of simple organic compounds. Previous studies have demonstrated that plant-derived sugars show hydroxyl radical scavenging capabilities during Fenton reactions with Fe(2+) and hydrogen peroxide in vitro, leading to formation of less detrimental sugar radicals that may be subject of regeneration to non-radical carbohydrates in vivo. Here, we provide further evidence for the occurrence of such radical reactions with sugars in planta, by following the fate of sucralose, an artificial analog of sucrose, in Arabidopsis tissues. The expected sucralose recombination and degradation products were detected in both normal and stressed plant tissues. Oxidation products of endogenous sugars were also assessed in planta for Arabidopsis and barley, and were shown to increase in abundance relative to the non-oxidized precursor during oxidative stress conditions. We concluded that such non-enzymatic reactions with hydroxyl radicals form an integral part of plant antioxidant mechanisms contributing to cellular ROS homeostasis, and may be more important than generally assumed. This is discussed in relation to the recently proposed roles for Fe(2+) and hydrogen peroxide in processes leading to the origin of metabolism and the origin of life.status: publishe

Sub-cellular fractionation and gel-based proteomics of Haberlea rhodopensis: a promising approach to open the black box of resurrection plants

International audienceHaberlea rhodopensis (Gesneriacea) belongs to the group of the resurrection plants. Their ability to survive extreme desiccation ren ders them excellent models to study plant response to dehydration. Plant metabolic networks are very complex and subcellular proteomics has proven to be a powerful approach to gain functional knowledge about the subcellular compartments. Here we present a protocol for the simultaneous isolation of pure and intact chloroplasts and mitochondria from Haberlea rhodopensis with subsequent gel-based proteomics including BN PAGE and 2-D gel electrophoresis. Differential detergent – based solubilization of chloroplast membranes allows separation of distinct activities in sub-organellar compartments and contributes for drastic reduction in overall sample complexity improving resolution and sensitivity of further proteomic analyses

Climate extreme effects on the chemical composition of temperate grassland species under ambient and elevated <tex>CO_{2}$</tex> : a comparison of fructan and non-fructan accumulators

Elevated CO(2) concentrations and extreme climate events, are two increasing components of the ongoing global climatic change factors, may alter plant chemical composition and thereby their economic and ecological characteristics, e.g. nutritional quality and decomposition rates. To investigate the impact of climate extremes on tissue quality, four temperate grassland species: the fructan accumulating grasses Lolium perenne, Poa pratensis, and the nitrogen (N) fixing legumes Medicago lupulina and Lotus corniculatus were subjected to water deficit at elevated temperature (+3°C), under ambient CO(2) (392 ppm) and elevated CO(2) (620 ppm). As a general observation, the effects of the climate extreme were larger and more ubiquitous in combination with elevated CO(2). The imposed climate extreme increased non-structural carbohydrate and phenolics in all species, whereas it increased lignin in legumes and decreased tannins in grasses. However, there was no significant effect of climate extreme on structural carbohydrates, proteins, lipids and mineral contents and stoichiometric ratios. In combination with elevated CO(2), climate extreme elicited larger increases in fructan and sucrose content in the grasses without affecting the total carbohydrate content, while it significantly increased total carbohydrates in legumes. The accumulation of carbohydrates in legumes was accompanied by higher activity of sucrose phosphate synthase, sucrose synthase and ADP-Glc pyrophosphorylase. In the legumes, elevated CO(2) in combination with climate extreme reduced protein, phosphorus (P) and magnesium (Mg) contents and the total element:N ratio and it increased phenol, lignin, tannin, carbon (C), nitrogen (N) contents and C:N, C:P and N:P ratios. On the other hand, the tissue composition of the fructan accumulating grasses was not affected at this level, in line with recent views that fructans contribute to cellular homeostasis under stress. It is speculated that quality losses will be less prominent in grasses (fructan accumulators) than legumes under climate extreme and its combination with elevated CO(2) conditions

Climate Extreme Effects on the Chemical Composition of Temperate Grassland Species under Ambient and Elevated CO2: A Comparison of Fructan and Non-Fructan Accumulators

Elevated CO2 concentrations and extreme climate events, are two increasing components of the ongoing global climatic change factors, may alter plant chemical composition and thereby their economic and ecological characteristics, e.g. nutritional quality and decomposition rates. To investigate the impact of climate extremes on tissue quality, four temperate grassland species: the fructan accumulating grasses Lolium perenne, Poa pratensis, and the nitrogen (N) fixing legumes Medicago lupulina and Lotus corniculatus were subjected to water deficit at elevated temperature (+3°C), under ambient CO2 (392 ppm) and elevated CO2 (620 ppm). As a general observation, the effects of the climate extreme were larger and more ubiquitous in combination with elevated CO2. The imposed climate extreme increased non-structural carbohydrate and phenolics in all species, whereas it increased lignin in legumes and decreased tannins in grasses. However, there was no significant effect of climate extreme on structural carbohydrates, proteins, lipids and mineral contents and stoichiometric ratios. In combination with elevated CO2, climate extreme elicited larger increases in fructan and sucrose content in the grasses without affecting the total carbohydrate content, while it significantly increased total carbohydrates in legumes. The accumulation of carbohydrates in legumes was accompanied by higher activity of sucrose phosphate synthase, sucrose synthase and ADP-Glc pyrophosphorylase. In the legumes, elevated CO2 in combination with climate extreme reduced protein, phosphorus (P) and magnesium (Mg) contents and the total element:N ratio and it increased phenol, lignin, tannin, carbon (C), nitrogen (N) contents and C:N, C:P and N:P ratios. On the other hand, the tissue composition of the fructan accumulating grasses was not affected at this level, in line with recent views that fructans contribute to cellular homeostasis under stress. It is speculated that quality losses will be less prominent in grasses (fructan accumulators) than legumes under climate extreme and its combination with elevated CO2 conditions.status: publishe