Sébastien Holvoet

Dietary polyphenols in the prevention and treatment of allergic diseases

Allergic disorders encompass skin, food and respiratory allergies. Sensitization to a normally harmless allergen results in the immune system being biased to a predominant T‐helper type 2 response. Re‐exposure to the same allergen leads to a robust secretion of allergy‐related mediators that eventually triggers symptoms. Our understanding of these disorders has enabled the search of therapeutic approaches that can either modulate the sensitization process or impact on allergic mediators, thus helping manage allergic symptoms. Polyphenols are one such class of compounds that are found in foods and plant sources and have been investigated for their anti‐allergic effect in different disease models and in human clinical trials. Their anti‐inflammatory profile is known to impact on the recruitment of immune cells to the skin and in preventing the development of secondary infections following disruption of the skin barrier. The interaction of polyphenols with proteins can modulate the process of allergic sensitization and their direct effect on allergic effector cells such as mast cells inhibit mediator release, resulting in the alleviation of symptoms. In addition, their endogenous anti‐oxidant ability limits the extent of cellular injury from free radicals during the allergic insult. Overall, polyphenols hold promise as anti‐allergy agents capable of influencing multiple biological pathways and immune cell functions in the allergic immune response and deserve further investigation. The objective of the current review is to summarize the key findings and progress made in studying polyphenols as anti‐allergic ingredients. Special emphasis is placed in this review to highlight key physiological, cellular and signalling pathways implicated in the mechanism of action of different polyphenols in the context of allergic disorders and their manifestations.

Polyphenol‐enriched apple extract attenuates food allergy in mice

Background The immune system may be modulated with nutrition to prevent the development or to treat the symptoms of allergy. Among other foods, consumption of apples has been linked to reduced incidence of atopic dermatitis and respiratory allergy.

Lactococcus lactis NCC 2287 Alleviates Food Allergic Manifestations in Sensitized Mice by Reducing IL-13 Expression Specifically in the Ileum

Objective. Utilizing a food allergy murine model, we have investigated the intrinsic antiallergic potential of the Lactococcus lactis NCC 2287 strain. Methods. BALB/c mice were sensitized at weekly intervals with ovalbumin (OVA) plus cholera toxin (CT) by the oral route for 7 weeks. In this model, an oral challenge with a high dose of OVA at the end of the sensitization period leads to clinical symptoms. Lactococcus lactis NCC 2287 was given to mice via the drinking water during sensitization (prevention phase) or after sensitization (management phase). Results. Lactococcus lactis NCC 2287 administration to sensitized mice strikingly reduced allergic manifestations in the management phase upon challenge, when compared to control mice. No preventive effect was observed with the strain. Lactococcus lactis NCC 2287 significantly decreased relative expression levels of the Th-2 cytokine, IL-13, and associated chemokines CCL11 (eotaxin-1) and CCL17 (TARC) in the ileum. No effect was observed in the jejunum. Conclusion/Significance. These results taken together designate Lactococcus lactis NCC 2287 as a candidate probiotic strain appropriate in the management of allergic symptoms.

Characterization of Candidate Anti-Allergic Probiotic Strains in a Model of Th2-Skewed Human Peripheral Blood Mononuclear Cells

Background: Pre-clinical and clinical studies have evaluated the efficacy of probiotics in allergy. However, predictive in vitro systems for rational strain selection are still missing. Methods: We developed a novel in vitro screening system for the characterization of probiotics with anti-allergic potential. In this model, human peripheral blood mononuclear cells (PBMC) from healthy donors (n = 68) were skewed towards a Th2 cytokine phenotype by culture with IL-4 and anti-CD40, to resemble cells from allergic donors. Th2-skewed cells were then co-cultured with probiotics; a total of 35 strains were tested. Levels of IFN-γ, IL-10, IL-5 and 7 additional cytokines in culture supernatants were determined by ELISA or multiplex assay. Gene expression was assessed by real-time PCR. For validation, splenocytes from ovalbumin-primed mice and PBMC from grass-allergic donors were restimulated with respective antigen and co-cultured with probiotics, and cytokine profiles were correlated. Results: Culture with IL-4 and anti-CD40 antibody induced secretion of IL-5 from PBMC, indicative of induction of a Th2 phenotype. Cytokine profiles induced by probiotics were strain specific even though species- and genus-specific clustering was observed for many strains by principal component analysis. This was paralleled by mRNA levels of the corresponding genes such as increased Tbet and reduced GATA-3 gene expression. Cytokine profiles induced by probiotics in PBMC stimulated with IL-4 and anti-CD40 correlated with those obtained from allergen-stimulated murine splenocytes or human PBMC from grass-allergic donors. Conclusions: Cytokine profiling of probiotic strains with IL-4-/anti-CD40-stimulated PBMC allowed to determine the effect of probiotics on Th2-skewed cells and thus to classify probiotic strains with anti-allergic potential.

Bifidobacterium bifidum NCC 453 Promotes Tolerance Induction in Murine Models of Sublingual Immunotherapy

Background:Enhancing clinical efficacy remains a major goal in allergen-specific immunotherapy. In this study, we tested three strains of bifidobacteria as candidate adjuvants for sublingual allergy vaccines. Methods:Probiotic candidates were evaluated in human monocyte-derived dendritic cell (h-DC) maturation and CD4+ T-cell polarization in vitro models and further tested in murine models of sublingual immunotherapy in BALB/c mice sensitized to either ovalbumin or birch pollen. Results:Bifidobacterium adolescentis, B. bifidum and B. longum induced h-DC maturation and polarized naïve CD4+ T cells toward interferon-γ and interleukin-10 production. B. bifidum increased CD25high, Foxp3+ cells within CD4+ T lymphocytes and was the most potent inducer of interferon-γ in Th2-skewed peripheral blood mononuclear cells and h-DC T-cell cocultures. It also induced a significant decrease in airway hyperresponsiveness in BALB/c mice sensitized to ovalbumin. Sublingual administration of B. bifidum together with recombinant Bet v 1 enhanced tolerance induction in BALB/c mice sensitized to birch pollen, with a downregulation of both airway hyperresponsiveness, lung inflammation and Bet v 1-specific Th2 responses. Conclusions: Due to its capacity to reorient established Th2 responses toward Th1/regulatory T-cell profiles, B. bifidum represents a valid candidate adjuvant for specific immunotherapy of type I allergies.

Beneficial effect of Lactococcus lactis NCC 2287 in a murine model of eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a severe inflammatory disease of the esophagus which is characterized histologically by an eosinophilic infiltration into the esophageal tissue. The efficacy of probiotics in the context of atopic diseases has been well investigated but, to date, there has been no study which has evaluated probiotic effects on EoE inflammation. This study sought to identify a probiotic which improves esophageal inflammation in experimental EoE.

Identification of epicatechin as one of the key bioactive constituents of polyphenol-enriched extracts that demonstrate an anti-allergic effect in a murine model of food allergy

Polyphenols are naturally derived bioactive compounds with numerous reported health benefits. We have previously reported on the beneficial effect of a polyphenol-enriched apple extract in a murine model of food allergy. The objectives of the present study were to elucidate the class of bioactive polyphenols that exhibit a beneficial anti-allergic effect and to assess whether the protective effect matches the in vivo bioavailable metabolite concentrations. Female BALB/c mice were sensitised to ovalbumin (OVA) following the protocol of a well-established murine model of food allergy. They were fed diets containing polyphenol-enriched extracts or purified epicatechin for 8 d after the last sensitisation. The sensitised mice were orally challenged with OVA after the intervention. The allergy symptoms, in addition to allergen-specific serum Ig concentrations and gene expression profiles in the intestine, of the control and treated mice were compared. Plasma samples were collected to compare the concentrations of bioavailable epicatechin metabolites in the treatment groups. Polyphenol-enriched fruit extracts containing epicatechin exhibited a significant anti-allergic effect in vivo. This effect was unambiguously attributed to epicatechin, as oral administration of this purified polyphenol to sensitised mice by inclusion in their diet modulated allergy symptoms in a dose-dependent manner. Immune parameters were also affected by the administration of epicatechin. Bioavailability measurements in plasma indicated that the attenuation of allergy symptoms could be due to the higher concentrations of bioavailable epicatechin metabolites. In conclusion, epicatechin is a key bioactive polyphenol that has the ability to modulate allergy outcomes in sensitised mice.

Long term reduction in food allergy susceptibility in mice by combining breastfeeding‐induced tolerance and TGF‐β enriched formula after weaning

Oral tolerance induction in early life is a promising approach for food allergy prevention. Its success requires the identification of factors necessary for its persistence.

Increased IL-5 and IL-13 cytokine level in ex vivo stimulated whole blood cells from grass pollen allergic donors correlate with seasonal exposure.

There is a need for simple and physiological assays to characterize the immune status of allergic individuals. Whole blood samples from 15 adult subjects (10 with positive clinical history to grass pollen and 5 with negative clinical history) were obtained before the start (April 2010) and during the middle of the grass pollen season (June 2010). The investigators were blinded to the allergic status of the subjects. A skin prick test (SPT) to grass pollen was carried out at the end of the study. Cytokines (IL-5, IL-13, IL-10 and IFNγ) and activation of T-lymphocytes were determined after ex vivo culture of whole blood cells. IL-5, IL-10 and IL-13 cytokines were significantly elevated in allergic individuals during the middle of the season (p≤0.02) compared to the start. This assay can be a valuable tool in clinical trials especially in pediatric population where limited quantities of blood are available to study immune responses.

Identification of epicatechin as the bioactive constituent in polyphenol enriched extracts that demonstrate a beneficial effect on allergic symptoms

Background Polyphenols are naturally derived bioactive compounds that have been attributed numerous health benefits. We have previously characterized the beneficial effect of a polyphenol enriched apple extract in a murine model of food allergy. The objective of the current study was to elucidate the class of bioactive polyphenols that are implicated in the beneficial anti-allergic effect of polyphenol enriched extracts. Methods