Fermentation Kinetics of Selected Dietary Fibers by Human Small Intestinal Microbiota Depend on the Type of Fiber and Subject.

SCOPE: An underexplored topic is the investigation of health effects of dietary fibers via modulation of human small intestine (SI) microbiota. A few previous studies hint at fermentation of some dietary fibers in the distal SI of humans and pigs. Here the potential of human SI microbiota to degrade dietary fibers and produce metabolites in vitro is investigated. METHODS AND RESULTS: Fructans, galacto-oligosaccharides, lemon pectins, and isomalto/malto-polysaccharides are subjected to in vitro batch fermentations inoculated with ileostomy effluent from five subjects. Fiber degradation products, formation of bacterial metabolites, and microbiota composition are determined over time. Galacto- and fructo-oligosaccharides are rapidly utilized by the SI microbiota of all subjects. At 5h of fermentation, 31%-82% of galacto-oligosaccharides and 29%-89% fructo-oligosaccharides (degree of polymerization DP4-8) are utilized. Breakdown of fructo-oligosaccharides/inulin DP ≥ 10, lemon pectin, and iso-malto/maltopolysaccharides only started after 7h incubation. Degradation of different fibers result in production of mainly acetate, and changed microbiota composition over time. CONCLUSION: Human SI microbiota have hydrolytic potential for prebiotic galacto- and fructo-oligosaccharides. In contrast, the higher molecular weight fibers inulin, lemon pectin, and iso-malto/maltopolysaccharides show slow fermentation rate. Fiber degradation kinetics and microbiota responses are subject dependent, therefore personalized nutritional fiber based strategies are required.

No effect of 25-hydroxyvitamin D supplementation on the skeletal muscle transcriptome in vitamin D deficient frail older adults.

OBJECTIVE: Vitamin D deficiency is common among older adults and has been linked to muscle weakness. Vitamin D supplementation has been proposed as a strategy to improve muscle function in older adults. The aim of this study was to investigate the effect of calcifediol (25-hydroxycholecalciferol) on whole genome gene expression in skeletal muscle of vitamin D deficient frail older adults. METHODS: A double-blind placebo-controlled trial was conducted in vitamin D deficient frail older adults (aged above 65), characterized by blood 25-hydroxycholecalciferol concentrations between 20 and 50 nmol/L. Subjects were randomized across the placebo group and the calcifediol group (10 µg per day). Muscle biopsies were obtained before and after 6 months of calcifediol (n = 10) or placebo (n = 12) supplementation and subjected to whole genome gene expression profiling using Affymetrix HuGene 2.1ST arrays. RESULTS: Expression of the vitamin D receptor gene was virtually undetectable in human skeletal muscle biopsies, with Ct values exceeding 30. Blood 25-hydroxycholecalciferol levels were significantly higher after calcifediol supplementation (87.3 ± 20.6 nmol/L) than after placebo (43.8 ± 14.1 nmol/L). No significant difference between treatment groups was observed on strength outcomes. The whole transcriptome effects of calcifediol and placebo were very weak, as indicated by the fact that correcting for multiple testing using false discovery rate did not yield any differentially expressed genes using any reasonable cut-offs (all q-values ~ 1). P-values were uniformly distributed across all genes, suggesting that low p-values are likely to be false positives. Partial least squares-discriminant analysis and principle component analysis was unable to separate treatment groups. CONCLUSION: Calcifediol supplementation did not significantly affect the skeletal muscle transcriptome in frail older adults. Our findings indicate that vitamin D supplementation has no effects on skeletal muscle gene expression, suggesting that skeletal muscle may not be a direct target of vitamin D in older adults. TRIAL REGISTRATION: This study was registered at clinicaltrials.gov as NCT02349282 on January 28, 2015.

ANGPTL4 promotes bile acid absorption during taurocholic acid supplementation via a mechanism dependent on the gut microbiota.

Angiopoietin-like 4 (ANGPTL4) raises plasma triglyceride levels by inhibiting lipoprotein lipase. A set of compounds that are able to reduce plasma triglyceride levels are bile acids (BA). Because BA have been shown to decrease ANGPTL4 secretion by intestinal cells, we hypothesized that BA lower plasma triglycerides (partly) via ANGPTL4. To test that hypothesis, wild-type and Angptl4-/- mice were fed chow supplemented with taurocholic acid (TCA) for seven days. TCA supplementation effectively lowered plasma triglycerides in wild-type and Angptl4-/- mice, indicating that ANGPTL4 is not required for plasma triglyceride-lowering by BA. Intriguingly, however, plasma and hepatic BA concentrations were significantly lower in TCA-supplemented Angptl4-/- mice than in TCA-supplemented wild-type mice. These changes in the Angptl4-/- mice were accompanied by lower BA levels in ileal scrapings and decreased expression of FXR-target genes in the ileum, including the BA transporter Slc10a2. By contrast, faecal excretion of specifically primary BA was higher in the Angptl4-/- mice, suggesting that loss of ANGPTL4 impairs intestinal BA absorption. Since the gut microbiota converts primary BA into secondary BA, elevated excretion of primary BA in Angptl4-/- mice may reflect differences in gut microbial composition and/or functionality. Indeed, colonic microbial composition was markedly different between Angptl4-/- and wild-type mice. Suppression of the gut bacteria using antibiotics abolished differences in plasma, hepatic, and faecal BA levels between TCA-supplemented Angptl4-/- and wild-type mice. In conclusion, 1) ANGPTL4 is not involved in the triglyceride-lowering effect of BA; 2) ANGPTL4 promotes BA absorption during TCA supplementation via a mechanism dependent on the gut microbiota.

The effects of long-term daily folic acid and vitamin B12 supplementation on genome-wide DNA methylation in elderly subjects.

BACKGROUND: Folate and its synthetic form folic acid function as donor of one-carbon units and have been, together with other B-vitamins, implicated in programming of epigenetic processes such as DNA methylation during early development. To what extent regulation of DNA methylation can be altered via B-vitamins later in life, and how this relates to health and disease, is not exactly known. The aim of this study was to identify effects of long-term supplementation with folic acid and vitamin B12 on genome-wide DNA methylation in elderly subjects. This project was part of a randomized, placebo-controlled trial on effects of supplemental intake of folic acid and vitamin B12 on bone fracture incidence (B-vitamins for the PRevention Of Osteoporotic Fractures (B-PROOF) study). Participants with mildly elevated homocysteine levels, aged 65-75 years, were randomly assigned to take 400 µg folic acid and 500 µg vitamin B12 per day or a placebo during an intervention period of 2 years. DNA was isolated from buffy coats, collected before and after intervention, and genome-wide DNA methylation was determined in 87 participants (n = 44 folic acid/vitamin B12, n = 43 placebo) using the Infinium HumanMethylation450 BeadChip. RESULTS: After intervention with folic acid and vitamin B12, 162 (versus 14 in the placebo group) of the 431,312 positions were differentially methylated as compared to baseline. Comparisons of the DNA methylation changes in the participants receiving folic acid and vitamin B12 versus placebo revealed one single differentially methylated position (cg19380919) with a borderline statistical significance. However, based on the analyses of differentially methylated regions (DMRs) consisting of multiple positions, we identified 6 regions that differed statistically significantly between the intervention and placebo group. Pronounced changes were found for regions in the DIRAS3, ARMC8, and NODAL genes, implicated in carcinogenesis and early embryonic development. Furthermore, serum levels of folate and vitamin B12 or plasma homocysteine were related to DNA methylation of 173, 425, and 11 regions, respectively. Interestingly, for several members of the developmental HOX genes, DNA methylation was related to serum levels of folate. CONCLUSIONS: Long-term supplementation with folic acid and vitamin B12 in elderly subjects resulted in effects on DNA methylation of several genes, among which genes implicated in developmental processes.

PPARalpha-mediated effects of dietary lipids on intestinal barrier gene expression.

BACKGROUND: The selective absorption of nutrients and other food constituents in the small intestine is mediated by a group of transport proteins and metabolic enzymes, often collectively called 'intestinal barrier proteins'. An important receptor that mediates the effects of dietary lipids on gene expression is the peroxisome proliferator-activated receptor alpha (PPARalpha), which is abundantly expressed in enterocytes. In this study we examined the effects of acute nutritional activation of PPARalpha on expression of genes encoding intestinal barrier proteins. To this end we used triacylglycerols composed of identical fatty acids in combination with gene expression profiling in wild-type and PPARalpha-null mice. Treatment with the synthetic PPARalpha agonist WY14643 served as reference. RESULTS: We identified 74 barrier genes that were PPARalpha-dependently regulated 6 hours after activation with WY14643. For eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and oleic acid (OA) these numbers were 46, 41, and 19, respectively. The overlap between EPA-, DHA-, and WY14643-regulated genes was considerable, whereas OA treatment showed limited overlap. Functional implications inferred form our data suggested that nutrient-activated PPARalpha regulated transporters and phase I/II metabolic enzymes were involved in a) fatty acid oxidation, b) cholesterol, glucose, and amino acid transport and metabolism, c) intestinal motility, and d) oxidative stress defense. CONCLUSION: We identified intestinal barrier genes that were PPARalpha-dependently regulated after acute activation by fatty acids. This knowledge provides a better understanding of the impact dietary fat has on the barrier function of the gut, identifies PPARalpha as an important factor controlling this key function, and underscores the importance of PPARalpha for nutrient-mediated gene regulation in intestine.

A cholesterol-free, high-fat diet suppresses gene expression of cholesterol transporters in murine small intestine.

Transporters present in the epithelium of the small intestine determine the efficiency by which dietary and biliary cholesterol are taken up into the body and thus control whole-body cholesterol balance. Niemann-Pick C1 Like Protein 1 (Npc1l1) transports cholesterol into the enterocyte, whereas ATP-binding cassette transporters Abca1 and Abcg5/Abcg8 are presumed to be involved in cholesterol efflux from the enterocyte toward plasma HDL and back into the intestinal lumen, respectively. Abca1, Abcg5, and Abcg8 are well-established liver X receptor (LXR) target genes. We examined the effects of a high-fat diet on expression and function of cholesterol transporters in the small intestine in mice. Npc1l1, Abca1, Abcg5, and Abcg8 were all downregulated after 2, 4, and 8 wk on a cholesterol-free, high-fat diet. The high-fat diet did not affect biliary cholesterol secretion but diminished fractional cholesterol absorption from 61 to 42% (P < 0.05). In an acute experiment in which triacylglycerols of unsaturated fatty acids were given by gavage, we found that this downregulation occurs within a 6-h time frame. Studies in LXRalpha-null mice, confirmed by in vitro data, showed that fatty acid-induced downregulation of cholesterol transporters is LXRalpha independent and associated with a posttranslational increase in 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity that reflects induction of cholesterol biosynthesis as well as with a doubling of neutral fecal sterol loss. This study highlights the induction of adaptive changes in small intestinal cholesterol metabolism during exposure to dietary fat.

Effect of synthetic dietary triglycerides: a novel research paradigm for nutrigenomics.

BACKGROUND: The effect of dietary fats on human health and disease are likely mediated by changes in gene expression. Several transcription factors have been shown to respond to fatty acids, including SREBP-1c, NF-kappaB, RXRs, LXRs, FXR, HNF4alpha, and PPARs. However, it is unclear to what extent these transcription factors play a role in gene regulation by dietary fatty acids in vivo. METHODOLOGY/PRINCIPAL FINDINGS: Here, we take advantage of a unique experimental design using synthetic triglycerides composed of one single fatty acid in combination with gene expression profiling to examine the effects of various individual dietary fatty acids on hepatic gene expression in mice. We observed that the number of significantly changed genes and the fold-induction of genes increased with increasing fatty acid chain length and degree of unsaturation. Importantly, almost every single gene regulated by dietary unsaturated fatty acids remained unaltered in mice lacking PPARalpha. In addition, the majority of genes regulated by unsaturated fatty acids, especially docosahexaenoic acid, were also regulated by the specific PPARalpha agonist WY14643. Excellent agreement was found between the effects of unsaturated fatty acids on mouse liver versus cultured rat hepatoma cells. Interestingly, using Nuclear Receptor PamChip(R) Arrays, fatty acid- and WY14643-induced interactions between PPARalpha and coregulators were found to be highly similar, although several PPARalpha-coactivator interactions specific for WY14643 were identified. CONCLUSIONS/SIGNIFICANCE: We conclude that the effects of dietary unsaturated fatty acids on hepatic gene expression are almost entirely mediated by PPARalpha and mimic those of synthetic PPARalpha agonists in terms of regulation of target genes and molecular mechanism. Use of synthetic dietary triglycerides may provide a novel paradigm for nutrigenomics research.

The cholesterol-raising factor from coffee beans, cafestol, as an agonist ligand for the farnesoid and pregnane X receptors.

Cafestol, a diterpene present in unfiltered coffee brews such as Scandinavian boiled, Turkish, and cafetière coffee, is the most potent cholesterol-elevating compound known in the human diet. Several genes involved in cholesterol homeostasis have previously been shown to be targets of cafestol, including cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid biosynthesis. We have examined the mechanism by which cafestol elevates serum lipid levels. Changes in several lipid parameters were observed in cafestol-treated APOE3Leiden mice, including a significant increase in serum triglyceride levels. Microarray analysis of these mice identified alterations in hepatic expression of genes involved in lipid metabolism and detoxification, many of which are regulated by the nuclear hormone receptors farnesoid X receptor (FXR) and pregnane X receptor (PXR). Further studies demonstrate that cafestol is an agonist ligand for FXR and PXR, and that cafestol down-regulates expression of the bile acid homeostatic genes CYP7A1, sterol 12alpha-hydroxylase, and Na(+)-taurocholate cotransporting polypeptide in the liver of wild-type but not FXR null mice. Cafestol did not affect genes known to be up-regulated by FXR in the liver of wild-type mice, but did increase expression of the positive FXR-target genes intestinal bile acid-binding protein and fibroblast growth factor 15 (FGF15) in the intestine. Because FGF15 has recently been shown to function in an enterohepatic regulatory pathway to repress liver expression of bile acid homeostatic genes, its direct induction in the gut may account for indirect effects of cafestol on liver gene expression. PXR-dependent gene regulation of cytochrome P450 3A11 and other targets by cafestol was also only seen in the intestine. Using a double FXR/PXR knockout mouse model, we found that both receptors contribute to the cafestol-dependent induction of intestinal FGF15 gene expression. In conclusion, cafestol acts as an agonist ligand for both FXR and PXR, and this may contribute to its impact on cholesterol homeostasis.