The protective role of liver X receptor (LXR) during fumonisin B1-induced hepatotoxicity.

Fumonisin B1 (FB1), a congener of fumonisins produced by Fusarium species, is the most abundant and most toxicologically active fumonisin. FB1 causes severe mycotoxicosis in animals, including nephrotoxicity, hepatotoxicity, and disruption of the intestinal barrier. However, mechanisms associated with FB1 toxicity are still unclear. Preliminary studies have highlighted the role of liver X receptors (LXRs) during FB1 exposure. LXRs belong to the nuclear receptor family and control the expression of genes involved in cholesterol and lipid homeostasis. In this context, the toxicity of FB1 was compared in female wild-type (LXR+/+) and LXRα,ß double knockout (LXR-/-) mice in the absence or presence of FB1 (10 mg/kg body weight/day) for 28 days. Exposure to FB1 supplemented in the mice's drinking water resulted in more pronounced hepatotoxicity in LXR-/- mice compared to LXR+/+ mice, as indicated by hepatic transaminase levels (ALT, AST) and hepatic inflammatory and fibrotic lesions. Next, the effect of FB1 exposure on the liver transcriptome was investigated. FB1 exposure led to a specific transcriptional response in LXR-/- mice that included altered cholesterol and bile acid homeostasis. ELISA showed that these effects were associated with an elevated FB1 concentration in the plasma of LXR-/- mice, suggesting that LXRs participate in intestinal absorption and/or clearance of the toxin. In summary, this study demonstrates an important role of LXRs in protecting the liver against FB1-induced toxicity, suggesting an alternative mechanism not related to the inhibition of sphingolipid synthesis for mycotoxin toxicity.

Deficient tryptophan catabolism along the kynurenine pathway reveals that the epididymis is in a unique tolerogenic state.

Indoleamine 2,3-dioxygenase (IDO) is the first and rate-limiting enzyme of tryptophan catabolism through the kynurenine pathway. Intriguingly, IDO is constitutively and highly expressed in the mammalian epididymis in contrast to most other tissues where IDO is induced by proinflammatory cytokines, such as interferons. To gain insight into the role of IDO in the physiology of the mammalian epididymis, we studied both wild type and Ido1(-/-)-deficient mice. In the caput epididymis of Ido1(-/-) animals, the lack of IDO activity was not compensated by other tryptophan-catabolizing enzymes and led to the loss of kynurenine production. The absence of IDO generated an inflammatory state in the caput epididymis as revealed by an increased accumulation of various inflammation markers. The absence of IDO also increased the tryptophan content of the caput epididymis and generated a parallel increase in caput epididymal protein content as a consequence of deficient proteasomal activity. Surprisingly, the lack of IDO expression had no noticeable impact on overall male fertility but did induce highly significant increases in both the number and the percentage of abnormal spermatozoa. These changes coincided with a significant decrease in white blood cell count in epididymal fluid compared with wild type mice. These data provide support for IDO playing a hitherto unsuspected role in sperm quality control in the epididymis involving the ubiquitination of defective spermatozoa and their subsequent removal.

Impact of perinatal prebiotic consumption on gestating mice and their offspring: a preliminary report.

To assess the impact of prebiotic supplementation during gestation and fetal and early neonatal life, gestating BALB/cj dam mice were fed either a control or a prebiotic (galacto-oligosaccharides-inulin, 9:1 ratio)-enriched diet throughout pregnancy and lactation, and allowed to nurse their pups until weaning. At the time of weaning, male offspring mice were separated from their mothers, weaned to the same solid diet as their dam and their growth was monitored until killed 48 d after weaning. Prebiotic treatment affected neither the body-weight gain nor the food intake of pregnant mice. In contrast, at the time of weaning, pups that had been nursed by prebiotic-fed dams had a higher body weight (11.0 (se 1.2) g) than pups born from control dams (9.8 (se 0.9) g). At 48 d after weaning, significantly higher values were observed for colon length and muscle mass in the offspring of prebiotic-fed dams (1.2 (se 0.1) cm/cm and 5.7 (se 1.8) mg/g, respectively), compared with control offspring (1.1 (se 0.1) cm/cm and 2.9 (se 0.9) mg/g, respectively), without any difference in spleen and stomach weight, or serum leptin concentration. The present preliminary study suggests that altering the fibre content of the maternal diet during both pregnancy and lactation enhances offspring growth, through an effect on intestinal and muscle mass rather than fat mass accretion.

Tissular Genomic Responses to Oral FB1 Exposure in Pigs.

Fumonisin B1 (FB1) is a widespread mycotoxin produced by fungal Fusarium species-mainly in maize, one of the plants most commonly used for food and feed. Pigs and horses are the animal species most susceptible to this mycotoxin. FB1 exposure can cause highly diverse clinical symptoms, including hepatotoxicity, immunotoxicity, and intestinal barrier function disturbance. Inhibition of ceramide synthetase is a well-understood ubiquitous molecular mechanism of FB1 toxicity, but other more tissue-specific effects remain to be elucidated. To investigate the effects of FB1 in different exposed tissues, we cross-analyzed the transcriptomes of fours organs: liver, jejunum, jejunal Peyer's patches, and spleen. During a four-week study period, pigs were fed a control diet or a FB1-contaminated diet (10 mg/kg feed). In response to oral FB1 exposure, we observed common biological processes in the four organs, including predominant and recurrent processes (extracellular matrix organization, integrin activation, granulocyte chemotaxis, neutrophil migration, and lipid and sterol homeostasis), as well as more tissue-specific processes that appeared to be related to lipid outcomes (cell cycle regulation in jejunum, and gluconeogenesis in liver).

Identification of Signaling Pathways Targeted by the Food Contaminant FB1: Transcriptome and Kinome Analysis of Samples from Pig Liver and Intestine.

SCOPE: Fumonisin B1 (FB1) is a mycotoxin produced by Fusarium species. In mammals, this toxin causes widespread organ-specific damage; it promotes hepatotoxicity, is immunotoxic, alters intestinal functions etc. Despite its inhibitory effect on de novo ceramide synthesis, its molecular mechanism of action and toxicity is not totally elucidated. METHODS AND RESULTS: To explore the mechanism of FB1 toxicity, we analyzed the transcriptome and the kinome of two organs targeted by FB1: the liver and the jejunum. Pigs were fed for 4 weeks a control diet or a FB1-contaminated diet (10 mg/kg). As expected, FB1-exposed pigs gained less weight and displayed a higher sphinganine/sphingosine ratio. Comparison of the transcriptomes and the kinomes of treated versus control pigs showed striking differences. Among the disrupted pathways in liver and jejunum, we highlight Protein Kinase B (AKT) / Phosphatase and tensin homolog (PTEN) at the intersection of the FB1-modulated pathways. CONCLUSION: Most of the effects of FB1 are mediated by the regulation of ceramide level, which influences protein phosphatase 2 (PP2A) and the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway. This pathway might be a new target to counteract toxic effect of Fumonisin B1, which is one of the most spread food contaminant in the world.

Pattern recognition receptors in the gut: analysis of their expression along the intestinal tract and the crypt/villus axis.

Pattern recognition receptors (PRRs) play a critical role in the detection of microorganisms and the induction of inflammatory and immune responses. Using PCR and Western-blot analysis, this study investigated the differential expression in the intestine of 14 PRRs and nine associated cytokines. Thirty-two pigs were used to determine the expression of these markers (1) along the proximal/distal axis of the small intestine (duodenum, jejunum, and ileum) and (2) between the intestinal segments and their respective lymphoid organs (Peyer's patches [PP] and mesenteric lymph nodes [MLN]). Six additional animals were used to quantify the expression of these genes along the crypt/villus axis of jejunum, using microdissected samples. Most genes showed increased expression (1) in the distal than in the proximal parts of the small intestine (TLR3, 5, RIG-I, IL-1ß, IL-8, and IFN-γ); (2) in lymphoid organs (TLR1, 2, 6, 9, 10, IL-10, TNF-α), especially the MLN (TLR4, 7, 8, NOD1, NOD2, NALP3, IFN-α, IL-6, IL-12, and TGF-ß), than in intestinal segments. The analysis along the crypt/villus identified: (1) genes with higher expression in lamina propria (TLR1, 2, 4, 9, NOD1, NOD2, IL-1ß, IL-10, TGF-ß, TNF-α) and (2) genes with higher expression in the villus (TLR3, 5, 6, RIG-I, IL-6). These results highlight the differential expression of PRRs and cytokines along the proximal/distal and the crypt/villus axis of the intestine, contributing to a fine analysis of the complex functional architecture of the small intestine and should be related to the gut microbiota.

Perinatal and postweaning exposure to galactooligosaccharides/inulin prebiotics induced biomarkers linked to tolerance mechanism in a mouse model of strong allergic sensitization.

Food allergies are increasing, and no treatment exists, thus enhancing interest in prebiotic strategies. This study aimed to analyze the preventive effects of prebiotic feeding during perinatal and postweaning periods in a mouse model of allergy by studying biomarkers related to tolerance (IgG2a, IgA, IFN-γ, TGF-ß, and IL-10), to allergy (IgE, IgG1, IL-4, IL-17, symptoms), and to microbiota (propionate and MyD88). Balb/c mice, both dams and their pups, were fed a diet supplemented with (+Prb) or without (-Prb) GOS/inulin prebiotics. Mice were then sensitized with allergens. Regardless of diet, sensitized mice exhibited similar levels of IgE, IgG1, CD-23, IL-4, IL-17, and symptoms. However, in comparison to -Prb-sensitized mice, +Prb-sensitized mice displayed higher concentrations of total IgG2a (6669 ± 1788 vs 3696 ± 1326 fluorescence units, p < 0.005), specific IgA (285 ± 26 vs 156 ± 9 fluorescence units, p < 0.01), IFN-γ (3194 ± 424 vs 1853 ± 434 pg/mL, p < 0.01), IL-10 (777 ± 87 vs 95 ± 136 pg/mL, p < 0.005), TGF-ß (4853 ± 1959 vs 243 ± 444 pg/mL, p < 0.01), MyD88 (0.033 ± 0.019 vs 0.009 ± 0.004 relative expression, p < 0.01), and propionate (4.15 ± 0.8 vs 2.9 ± 1.15 µmol, p < 0.05). In a mouse model of allergy, prebiotic exposure during perinatal and postweaning periods induced the highest expression of biomarkers related to tolerance without affecting biomarkers related to allergy.

Wheat gliadins modified by deamidation are more efficient than native gliadins in inducing a Th2 response in Balb/c mice experimentally sensitized to wheat allergens.

SCOPE: Wheat gluten proteins such as gliadins constitute major food allergens. Gluten can be modified industrially by deamidation which increases its solubility and enhances its use as a food ingredient. Sensitization to deamidated gluten has been reported to cause severe allergic reactions with anaphylaxis. The aim of this study was therefore to compare the sensitization and elicitation potentials of native (NG) and deamidated (DG) gliadins. The reactivity pattern of mice IgE was also compared with that of DG-allergic patients. METHODS AND RESULTS: The ability of DG to sensitize Balb/c mice using intra-peritoneal administration with aluminium hydroxide as an adjuvant, and to elicit an allergic response after a challenge, was tested in comparison with NG. Mice sensitized with DG secreted higher levels of total IgE, IL-4, gliadin-specific IgE and IgG1 than mice sensitized with NG. By contrast, mice sensitized with NG produced higher levels of gliadin-specific IgG2a and INFγ. After a challenge, histamine levels were higher in mice sensitised with DG. CONCLUSIONS: DG can sensitize mice much more efficiently than NG. Moreover, this mouse model of allergy to DG revealed an IgE reactivity pattern against purified gliadins which was very similar to that of DG-allergic patients.

Exposure to a galactooligosaccharides/inulin prebiotic mix at different developmental time points differentially modulates immune responses in mice.

Prebiotics constitute emerging tools to alleviate immune pathologies. This study aimed to evaluate the effect of prebiotic exposure during perinatal and postweaning periods on immune and gut regulations. Mice were fed either a galactooligosaccharides/inulin prebiotic mix-enriched diet or a control diet during the perinatal and/or postweaning periods. Biomarkers related to gut barrier function (SCFA, heat shock proteins, zonula occludens protein-1, and mucin-2) and immune mechanisms (IgA, IgE, IgG1, IgG2a, IL-10, TGF-ß, IL-4, IL-17A, and IFN-γ) were analyzed. The milk of dams fed the prebiotic diet was more concentrated in both IgA and TGF-ß when prebiotics were introduced during both the perinatal and postweaning periods; IL-10, IgA, and IgG2a were increased in pups; and expression of intestinal markers was more pronounced. Postweaning exposure to prebiotics alone induced higher INF-γ and TGF-ß levels, whereas IgA levels fell. Combined exposure periods (perinatal/postweaning) to prebiotics increased tolerance-related immunoglobulins in pups and reinforced gut barrier functions.

Probiotics, prebiotics, and synbiotics: impact on the gut immune system and allergic reactions.

Probiotics and prebiotics, alone or together (synbiotics), can influence the intestinal microbiota and modulate the immune response. They may therefore be tools that can prevent or alleviate certain pathologies involving the gut immune system, such as allergies for which no treatment is yet available. This review focuses first on the definitions of probiotics, prebiotics, and synbiotics and key cells in the gut immune system. It then discusses their effects on mucosal immune stimulation. Experimental findings suggest that different probiotic species have similar effects on innate immunity by improving the mechanisms of pathogen destruction. On the contrary, their impacts seem to be variable on the adaptive immune system. Prebiotics can also exert an influence on the gut immune system via the stimulation of the autochthonous bacteria metabolism. Finally, this review focuses on the effects of food supplements on allergy. Different studies performed in humans or rodents have supported a potential role for selected probiotics and prebiotics in reducing some allergic parameters. Probiotic effects on allergy treatment are unclear, especially in human studies. However, they are potentially effective at short-term for prevention when they are administered in perinatal conditions. A clinical study performed with an infant cohort revealed a beneficial effect of prebiotics in preventing allergic manifestations at long-term. Further studies are nonetheless essential to confirm these findings. Food supplements offer potential tools for the prevention or treatment of allergy, but insufficient evidence is available at present to recommend their use in clinical practice.