Folate derived from cecal bacterial fermentation does not increase liver folate stores in 28-d folate-depleted male Sprague-Dawley rats

Perinatal folate levels do not influence tumor latency or multiplicity in a model of NF1 associated plexiform-like neurofibromas

OBJECTIVE

In epidemiological and experimental research, high folic acid intake has been demonstrated to accelerate tumor development among populations with genetic and/or molecular susceptibility to cancer. Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder predisposing affected individuals to tumorigenesis, including benign plexiform neurofibromas; however, understanding of factors associated with tumor risk in NF1 patients is limited. Therefore, we investigated whether pregestational folic acid intake modified plexiform-like peripheral nerve sheath tumor risk in a transgenic NF1 murine model.

RESULTS

We observed no significant differences in overall survival according to folate group. Relative to controls (180 days), median survival did not statistically differ in deficient (174 days, P = 0.56) or supplemented (177 days, P = 0.13) folate groups. Dietary folate intake was positively associated with RBC folate levels at weaning, (P = 0.023, 0.0096, and 0.0006 for deficient vs. control, control vs. supplemented, and deficient vs. supplemented groups, respectively). Dorsal root ganglia (DRG), brachial plexi, and sciatic nerves were assessed according to folate group. Mice in the folate deficient group had significantly more enlarged DRG relative to controls (P = 0.044), but no other groups statistically differed. No significant differences for brachial plexi or sciatic nerve enlargement were observed according to folate status.

Bacteria from the gut influence the host micronutrient status

Micronutrient deficiencies or "hidden hunger" remains a serious public health problem in most low- and middle-income countries, with severe consequences for child development. Traditional methods of treatment and prevention, such as supplementation and fortification, have not always proven to be effective and may have undesirable side-effects (i.e., digestive troubles with iron supplementation). Commensal bacteria in the gut may increase bioavailability of specific micronutrients (i.e., minerals), notably by removing anti-nutritional compounds, such as phytates and polyphenols, or by the synthesis of vitamins. Together with the gastrointestinal mucosa, gut microbiota is also the first line of protection against pathogens. It contributes to the reinforcement of the integrity of the intestinal epithelium and to a better absorption of micronutrients. However, its role in micronutrient malnutrition is still poorly understood. Moreover, the bacterial metabolism is also dependent of micronutrients acquired from the gut environment and resident bacteria may compete or collaborate to maintain micronutrient homeostasis. Gut microbiota composition can therefore be modulated by micronutrient availability. This review brings together current knowledge on this two-way relationship between micronutrients and gut microbiota bacteria, with a focus on iron, zinc, vitamin A and folate (vitamin B9), as these deficiencies are public health concerns in a global context.

Faster Short-Chain Fatty Acid Absorption from the Cecum Following Polydextrose Ingestion Increases the Salivary Immunoglobulin A Flow Rate in Rats

Salivary immunoglobulin A (IgA) plays a vital role in preventing upper respiratory tract infections (URTI). In our previous study, we showed that the intake of carbohydrates increases the intestinal levels of short-chain fatty acids (SCFAs), which in turn increase salivary IgA levels. However, the mechanism underlying this phenomenon has not been fully elucidated. In this study, we investigated in rats the effect of polydextrose (PDX) ingestion on salivary IgA level and SCFA concentration in cecal digesta and the portal vein. Five-week-old rats were fed with a fiber-free diet (control) or with 40 g/kg of PDX for 28 days. Compared to the control, ingestion of PDX led to a higher salivary IgA flow rate (p = 0.0013) and a higher concentration of SCFAs in the portal vein (p = 0.004). These two data were positively correlated (r_s = 0.88, p = 0.0002, n = 12). In contrast, the concentration of SCFAs in cecal digesta and cecal digesta viscosity were significantly lower following PDX ingestion, compared to the control (p = 0.008 and 0.05, respectively). These findings suggest that the ingestion of PDX increases the absorption rate of SCFAs in the intestine through PDX-induced fermentation, which is accompanied by an increase in SCFA levels in the blood, and ultimately leads to increased salivary IgA levels.

Genes controlling the activation of natural killer lymphocytes are epigenetically remodeled in intestinal cells from germ-free mice

Remodeling of the gut microbiota is implicated in various metabolic and inflammatory diseases of the gastrointestinal tract. We hypothesized that the gut microbiota affects the DNA methylation profile of intestinal epithelial cells (IECs) which could, in turn, alter intestinal function. In this study, we used mass spectrometry and methylated DNA capture to respectively investigate global and genome-wide DNA methylation of intestinal epithelial cells from germ-free (GF) and conventionally raised mice. In colonic IECs from GF mice, DNA was markedly hypermethylated. This was associated with a dramatic loss of ten-eleven-translocation activity, a lower DNA methyltransferase activity and lower circulating levels of the 1-carbon metabolite, folate. At the gene level, we found an enrichment for differentially methylated regions proximal to genes regulating the cytotoxicity of NK cells (false-discovery rate < 8.9E⁻⁶), notably genes regulating the cross-talk between NK cells and target cells, such as members of the NK group 2 member D ligand superfamily Raet. This distinct epigenetic signature was associated with a marked decrease in Raet1 expression and a loss of CD56⁺/CD45⁺ cells in the intestine of GF mice. Thus, our results indicate that altered activity of methylation-modifying enzymes in GF mice influences the IEC epigenome and modulates the crosstalk between IECs and NK cells. Epigenetic reprogramming of IECs may modulate intestinal function in diseases associated with altered gut microbiota.—Poupeau, A., Garde, C., Sulek, K., Citirikkaya, K., Treebak, J. T., Arumugam, M., Simar, D., Olofsson, L. E., Bäckhed, F., Barrès, R. Genes controlling the activation of natural killer lymphocytes are epigenetically remodeled in intestinal cells from germ-free mice.

Western diet induces colonic nitrergic myenteric neuropathy and dysmotility in mice via saturated fatty acid- and lipopolysaccharide-induced TLR4 signalling

KEY POINTS

A high-fat diet (60% kcal from fat) is associated with motility disorders inducing constipation and loss of nitrergic myenteric neurons in the proximal colon. Gut microbiota dysbiosis, which occurs in response to HFD, contributes to endotoxaemia. High levels of lipopolysaccharide lead to apoptosis in cultured myenteric neurons that express Toll-like receptor 4 (TLR4). Consumption of a Western diet (WD) (35% kcal from fat) for 6 weeks leads to gut microbiota dysbiosis associated with altered bacterial metabolites and increased levels of plasma free fatty acids. These disorders precede the nitrergic myenteric cell loss observed in the proximal colon. Mice lacking TLR4 did not exhibit WD-induced myenteric cell loss and dysmotility. Lipopolysaccharide-induced in vitro enteric neurodegeneration requires the presence of palmitate and may be a result of enhanced NO production. The present study highlights the critical role of plasma saturated free fatty acids that are abundant in the WD with respect to driving enteric neuropathy and colonic dysmotility.

ABSTRACT

The consumption of a high-fat diet (HFD) is associated with myenteric neurodegeneration, which in turn is associated with delayed colonic transit and constipation. We examined the hypothesis that an inherent increase in plasma free fatty acids (FFA) in the HFD together with an HFD-induced alteration in gut microbiota contributes to the pathophysiology of these disorders. C57BL/6 mice were fed a Western diet (WD) (35% kcal from fat enriched in palmitate) or a purified regular diet (16.9% kcal from fat) for 3, 6, 9 and 12 weeks. Gut microbiota dysbiosis was investigated by fecal lipopolysaccharide (LPS) measurement and metabolomics (linear trap quadrupole-Fourier transform mass spectrometer) analysis. Plasma FFA and LPS levels were assessed, in addition to colonic and ileal nitrergic myenteric neuron quantifications and motility. Compared to regular diet-fed control mice, WD-fed mice gained significantly more weight without blood glucose alteration. Dysbiosis was exhibited after 6 weeks of feeding, as reflected by increased fecal LPS and bacterial metabolites and concomitant higher plasma FFA. The numbers of nitrergic myenteric neurons were reduced in the proximal colon after 9 and 12 weeks of WD and this was also associated with delayed colonic transit. WD-fed Toll-like receptor 4 (TLR4)^-/- mice did not exhibit myenteric cell loss or dysmotility. Finally, LPS (0.5-2 ng·ml^-1 ) and palmitate (20 and 30 μm) acted synergistically to induce neuronal cell death in vitro, which was prevented by the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester. In conclusion, WD-feeding results in increased levels of FFA and microbiota that, even in absence of hyperglycaemia or overt endotoxaemia, synergistically induce TLR4-mediated neurodegeneration and dysmotility.

Maternal gut and fetal brain connection: Increased anxiety and reduced social interactions in Wistar rat offspring following peri-conceptional antibiotic exposure

BACKGROUND

A growing body of evidence indicates that gut microbiota characteristics may be closely related to mental dysfunctions. However, no studies have investigated fetal brain development in relation to the maternal gut microbiota, despite the extensive use of antibiotics in obstetric practice.

OBJECTIVE

To determine how periconceptional exposure to SuccinylSulfaThiazole (SST), a non-absorbable antibiotic, can affect behavior in rat offspring. This antibiotic drug has previously been shown to substantially perturb the gut microbiota in rats following a 28-day exposure.

METHODS

Female Wistar rats were divided in two groups: control, or exposed during one month before breeding until gestational day 15 to a diet containing 1% SST. We administered behavioral tests to offspring, i.e., open field (post-natal day 20), social interactions (P25), marble burying (P30), elevated plus maze (P35), and prepulse inhibition of the acoustic startle reflex (sensory gating) (P45).

RESULTS

Both male and female offspring exposed peri-conceptionally to SST showed reduced social interactions, with a decrease of about half in time spent in social interactions compared to controls, reduced exploration of the open arm by 20% in the elevated plus maze test indicating increased anxiety and altered sensorimotor gating, with a 1.5-2-fold decrease in startle inhibition.

CONCLUSION

Maternal periconceptional exposure to SST provokes alterations in offspring behavior in the absence of maternal infection. Because we administered SST, a non-absorbable antibiotic, only to the dam, we conclude that these neurobehavioral alterations in the offspring are related to maternal gut microbiota alterations.

High Dietary Folate in Mice Alters Immune Response and Reduces Survival after Malarial Infection

Malaria is a significant global health issue, with nearly 200 million cases in 2013 alone. Parasites obtain folate from the host or synthesize it de novo. Folate consumption has increased in many populations, prompting concerns regarding potential deleterious consequences of higher intake. The impact of high dietary folate on the host’s immune function and response to malaria has not been examined. Our goal was to determine whether high dietary folate would affect response to malarial infection in a murine model of cerebral malaria. Mice were fed control diets (CD, recommended folate level for rodents) or folic acid-supplemented diets (FASD, 10x recommended level) for 5 weeks before infection with Plasmodium berghei ANKA. Survival, parasitemia, numbers of immune cells and other infection parameters were assessed. FASD mice had reduced survival (p<0.01, Cox proportional hazards) and higher parasitemia (p< 0.01, joint model of parasitemia and survival) compared with CD mice. FASD mice had lower numbers of splenocytes, total T cells, and lower numbers of specific T and NK cell sub-populations, compared with CD mice (p<0.05, linear mixed effects). Increased brain TNFα immunoreactive protein (p<0.01, t-test) and increased liver Abca1 mRNA (p<0.01, t-test), a modulator of TNFα, were observed in FASD mice; these variables correlated positively (r_s = 0.63, p = 0.01). Bcl-xl/Bak mRNA was increased in liver of FASD mice (p<0.01, t-test), suggesting reduced apoptotic potential. We conclude that high dietary folate increases parasite replication, disturbs the immune response and reduces resistance to malaria in mice. These findings have relevance for malaria-endemic regions, when considering anti-folate anti-malarials, food fortification or vitamin supplementation programs.

Perigestational dietary folic acid deficiency protects against medulloblastoma formation in a mouse model of nevoid basal cell carcinoma syndrome

Hereditary nevoid basal cell carcinoma syndrome (NBCCS) is caused by PTCH1 gene mutations that result in diverse neoplasms including medulloblastoma (MB). Epidemiological studies report reduced pediatric brain tumor risks associated with maternal intake of prenatal vitamins containing folic acid (FA) and FA supplements specifically. We hypothesized that low maternal FA intake during the perigestational period would increase MB incidence in a transgenic NBCCS mouse model, which carries an autosomal dominant mutation in the Ptch1 gene. Female wild-type C57BL/6 mice (n = 126) were randomized to 1 of 3 diets with differing FA amounts: 0.3 mg/kg (low), 2.0 mg/kg (control), and 8.0 mg/kg (high) 1 mo prior to mating with Ptch1 (+/-) C57BL/6 males. Females were maintained on the diet until pup weaning; the pups were then aged for tumor development. Compared to the control group, offspring MB incidence was significantly lower in the low FA group (Hazard Ratio = 0.47; 95% confidence interval 0.27-0.80) at 1 yr. No significant difference in incidence was observed between the control and high FA groups. Low maternal perigestational FA levels may decrease MB incidence in mice genetically predisposed to tumor development. Our results could have implications for prenatal FA intake recommendations in the presence of cancer syndromes.

Excessive folate synthesis limits lifespan in the C. elegans: E. coli aging model

Background

Gut microbes influence animal health and thus, are potential targets for interventions that slow aging. Live E. coli provides the nematode worm Caenorhabditis elegans with vital micronutrients, such as folates that cannot be synthesized by animals. However, the microbe also limits C. elegans lifespan. Understanding these interactions may shed light on how intestinal microbes influence mammalian aging.

Results

Serendipitously, we isolated an E. coli mutant that slows C. elegans aging. We identified the disrupted gene to be aroD, which is required to synthesize aromatic compounds in the microbe. Adding back aromatic compounds to the media revealed that the increased C. elegans lifespan was caused by decreased availability of para-aminobenzoic acid, a precursor to folate. Consistent with this result, inhibition of folate synthesis by sulfamethoxazole, a sulfonamide, led to a dose-dependent increase in C. elegans lifespan. As expected, these treatments caused a decrease in bacterial and worm folate levels, as measured by mass spectrometry of intact folates. The folate cycle is essential for cellular biosynthesis. However, bacterial proliferation and C. elegans growth and reproduction were unaffected under the conditions that increased lifespan.

Conclusions

In this animal:microbe system, folates are in excess of that required for biosynthesis. This study suggests that microbial folate synthesis is a pharmacologically accessible target to slow animal aging without detrimental effects.

Dietary fructooligosaccharides and wheat bran elicit specific and dose-dependent gene expression profiles in the proximal colon epithelia of healthy Fischer 344 rats

Proximal colon epithelial gene responses to diets containing increasing levels of dietary fermentable material (FM) from 2 different sources were measured to determine whether gene expression patterns were independent of the source of FM. Male Fischer 344 rats (10/group) were fed for 6 wk a control diet containing 10% (g/g) cellulose (0% FM); or a 2, 5, or 10% wheat bran (WB) diet (1, 2, 5% FM); or a 2, 5, or 8% fructooligosaccharides (FOS) diet (2, 5, 8% FM). WB and FOS were substituted for cellulose to give a final 10% nondigestible material content including FM. Gene responses were relative to expression in rats fed the control diet. The gene response patterns associated with feeding ∼2% FM (5% WB and 2% FOS) were similar (∼10 gene changes ≥ 1.6-fold; P ≤ 0.01) and involved genes associated with transport (Scnn1g, Mt1a), transcription (Zbtb16, Egr1), immunity (Fkbp5), a gut hormone (Retn1β), and lipid metabolism (Scd2, Insig1). These changes were also similar to those associated with 5% FM but only in rats fed the 10% WB diet. In contrast, the 5% FOS diet (~5% FM) was associated with 68 gene expression changes ≥ 1.6-fold (P ≤ 0.01). The diet with the highest level of fermentation (8% FOS, ~8% FM) was associated with 132 changes ≥ 1.6-fold (P ≤ 0.01), including genes associated with transport, cellular proliferation, oncogene and tumor metastasis, the cell cycle, apoptosis, signal transduction, transcript regulation, immunity, gut hormones, and lipid metabolic processes. These results show that both the amount and source of FM determine proximal colon epithelial gene response patterns in rats.

Folate production by probiotic bacteria

Probiotic bacteria, mostly belonging to the genera Lactobacillus and Bifidobacterium, confer a number of health benefits to the host, including vitamin production. With the aim to produce folate-enriched fermented products and/or develop probiotic supplements that accomplish folate biosynthesis in vivo within the colon, bifidobacteria and lactobacilli have been extensively studied for their capability to produce this vitamin. On the basis of physiological studies and genome analysis, wild-type lactobacilli cannot synthesize folate, generally require it for growth, and provide a negative contribution to folate levels in fermented dairy products. Lactobacillus plantarum constitutes an exception among lactobacilli, since it is capable of folate production in presence of para-aminobenzoic acid (pABA) and deserves to be used in animal trials to validate its ability to produce the vitamin in vivo. On the other hand, several folate-producing strains have been selected within the genus Bifidobacterium, with a great variability in the extent of vitamin released in the medium. Most of them belong to the species B. adolescentis and B. pseudocatenulatum, but few folate producing strains are found in the other species as well. Rats fed a probiotic formulation of folate-producing bifidobacteria exhibited increased plasma folate level, confirming that the vitamin is produced in vivo and absorbed. In a human trial, the same supplement raised folate concentration in feces. The use of folate-producing probiotic strains can be regarded as a new perspective in the specific use of probiotics. They could more efficiently confer protection against inflammation and cancer, both exerting the beneficial effects of probiotics and preventing the folate deficiency that is associated with premalignant changes in the colonic epithelia.

Low dietary choline and low dietary riboflavin during pregnancy influence reproductive outcomes and heart development in mice

BACKGROUND

Embryonic development may be compromised by dietary and genetic disruptions in folate metabolism because of the critical role of folate in homocysteine metabolism, methylation, and nucleotide synthesis. Methylenetetrahydrofolate reductase (MTHFR), choline, and riboflavin play distinct roles in homocysteine detoxification and generation of one-carbon donors for methylation. The effect of low dietary choline and riboflavin on pregnancy complications and heart development has not been adequately addressed.

OBJECTIVE

Our goal was to determine whether dietary deficiencies of choline and riboflavin in pregnant mice, with and without mild MTHFR deficiency, affect embryonic development.

DESIGN

Female Mthfr(+/+) and Mthfr(+/-) mice were fed a control diet (CD), a choline-deficient diet (ChDD), or a riboflavin-deficient diet (RbDD) and were then mated with male Mthfr(+/-) mice. Embryos were collected 14.5 d postcoitum and examined for reproductive outcomes and cardiac defects.

RESULTS

Plasma homocysteine was higher in ChDD- than in CD-fed females. Liver MTHFR enzyme activity was greater in ChDD-fed Mthfr(+/+) than in CD-fed Mthfr(+/+) females. The RbDD resulted in a higher percentage of delayed embryos and smaller embryos than did the CD. There were more heart defects, which were all ventricular septal defects, in embryos from the ChDD- and RbDD-fed females than from the CD-fed females. Dietary riboflavin and MTHFR deficiency resulted in decreased left ventricular wall thickness in embryonic hearts compared with embryos from CD-fed Mthfr(+/+) females.

CONCLUSIONS

Low dietary choline and riboflavin affect embryonic growth and cardiac development in mice. Adequate choline and riboflavin may also play a role in the prevention of these pregnancy complications in women.

Administration of folate-producing bifidobacteria enhances folate status in Wistar rats

To develop a probiotic that provides the host with folate, we administered folate-overproducing bifidobacteria (Bifidobacteria adolescentis MB 227, B. adolescentis MB 239, and B. pseudocatenulatum MB 116) to Wistar rats with induced folate deficiency. Four groups of rats were fed a solid, low-folate diet with no supplements, folate-producing bifidobacteria [probiotic (PRO)], oligofructose [prebiotic (PRE)], or PRO plus PRE [symbiotic (SYM)] for 14 d. The SYM group also had a significantly higher (16.4 +/- 3.7 nmol/L) than in the PRO group (9.1 +/- 0.3 nmol/L), which was greater than in the control (4.8 +/- 0.5 nmol/L) and PRE groups (5.3 +/- 1.4 nmol/L). The SYM group also had a significantly higher hepatic folate concentration than in the other groups, whereas the kidney folate concentration did not differ among the groups. In the unsupplemented group, the pH of feces did not change during the trial, whereas diets containing bifidobacteria and/or oligofructose led to significant acidification due to enhanced saccharolytic metabolism. As a consequence of feeding rats PRE, PRO, and SYM diets, lactobacilli and bifidobacteria were significantly greater than in controls, whereas coliforms and enterococci were lower. This experiment showed that B. adolescentis MB 227, B. adolescentis MB 239, and B. pseudocatenulatum MB 116 exert both the beneficial effects of probiotics and produce folate in vivo, positively affecting the folate status of rats. The simultaneous administration of oligofructose and folate-producing bifidobacteria enhance their effectiveness on folate status. This study provides new perspectives on the specific use of probiotics to deliver important vitamins such as folate.

Plasma cobalamin and folate and their metabolic markers methylmalonic acid and total homocysteine among Egyptian children before and after nutritional supplementation with the probiotic bacteria Lactobacillus acidophilus in yoghurt matrix

OBJECTIVE

To evaluate the biopotency of the viable probiotic Lactobacillus acidophilus (La1) in yoghurt matrix consumed by Egyptian children on their plasma vitamin B12 and folate levels, and their metabolic markers methylmalonic acid (MMA) and total homocysteine (t-Hcy).

METHODS

A randomized nutritional supplementation trial (42 days duration) was performed in free-living children of both sexes (11 years old). The La1 in yoghurt matrix was administered to provide 1012 colony-forming units/subject/day. Blood sampling for the analysis of plasma vitamin B12, folate and t-Hcy was performed by standardized methods. Five-hour urine collection was used for the analysis of MMA and t-Hcy.

RESULTS

Initially 33.3% of the children presented with biochemical vitamin B12 deficiency (<208 pg/ml), while one-fifth (21%) were biochemically deficient in folate (<3 ng/ml folate/ml plasma or 0.68 nmol/l). Fifty percent of the children presented with high plasma t-Hcy (>15.0 micromol/l). The daily consumption of the probiotic La1 yoghurt for 42 days significantly improved the mean levels of plasma vitamin B12 (P<0.05) and folate (P<0.01) among the studied children compared with the respective baseline data. On the other hand, the average levels of plasma t-Hcy and urinary MMA decreased significantly (P<0.05) at the termination of the 42-day nutritional supplementation, compared with the respective initial mean levels. The consumption of the probiotic yoghurt was also associated with a significant (chi2=8.0; P<0.01) reduction in the percentage prevalence of anemia (hemoglobin <120 g/l).

CONCLUSION

The long-term ingestion of viable probiotic La1 potentially promoted the overall nutritional status of the studied children.

Folate deficiency during pregnancy impacts on methyl metabolism without affecting global DNA methylation in the rat fetus

The methionine cycle and methyl group metabolism are implicated in the long-term programming of metabolism. Diets deficient in folic acid, methionine and choline have been fed to pregnant rats to examine the effects on amino acid metabolism, choline reserves and DNA methylation in dam and fetuses. Animals were fed folate-deficient, folate-deficient with low methionine, folate-deficient with low choline and folate-deficient, low-methionine, low-choline diets starting 2 weeks before mating. The dams and their fetuses were subsequently killed on day 21 of gestation for analysis. Diets low in methionine reduced fetal and maternal weight. Folate deficiency increased the concentrations of homocysteine, glycine, serine and threonine in the maternal plasma, and this was exacerbated by the low-methionine diets. The changes in the amino acid profile in the fetal serum were similar but less pronounced. This result suggests that fetal metabolism was less perturbed. Folate deficiency increased free choline in the maternal liver at the expense of phosphocholine stores. It has been suggested that a deficiency in methyl donors in the diet during pregnancy may impact on key methylation reactions, including the methylation of DNA. Despite widespread changes in the metabolism of choline and amino acids, there was no change in the global methylation of cytosine in DNA from either maternal or fetal livers. This suggests a more indirect mechanism in which gene–nutrient interactions modify the process of differential methylation during development

Dietary fructooligosaccharides alter the cultivable faecal population of rats but do not stimulate the growth of intestinal bifidobacteria

The effect of fructans on the cultivable faecal community of Bio Breeding rats fed diets containing 5% (m/v) food-grade fructooligosaccharide (FOS) was investigated. Culturing of faecal material using chicory inulin as the sole carbohydrate source revealed the presence of a greater diversity of inulin-utilizing bacterial species in FOS-fed rats as compared with the control rats, although both contained species which effectively utilized inulin. The majority of cultivable inulin-utilizing species fell within the Clostridium coccoides group and Clostridium leptum subgroup, some of which were related to previously cultured butyrate-producing bacteria from the intestines of various animals. The impact of FOS on the growth of the indigenous bifidobacteria community and three inulin-utilizing isolates was assessed using real-time polymerase chain reaction. While dietary FOS was found to stimulate the growth of all three inulin-utilizing isolates, no growth stimulation of the indigenous bifidobacteria community occurred over the duration of the feeding trial.

Maternal folate deficiency affects proliferation, but not apoptosis, in embryonic mouse heart

Low dietary folate and deficiency of methylenetetrahydrofolate reductase (Mthfr) were reported to increase the risk for congenital heart defects, but contributory mechanisms have not been elucidated. Because low folate and absent MTHFR activity were shown to affect proliferation and apoptosis in developing neural tissue, we examined these processes in the myocardium of embryos from Mthfr +/+ and Mthfr +/- mice fed control diets (CD) or folic acid-deficient diets (FADD). Mice consumed the designated diets for 8 wk, from weaning and through pregnancy until they were killed. Embryos were assessed on gestational day 12.5 for myocardial proliferation by 5-bromo-2'-deoxyuridine (BrdU) labeling and for apoptosis by TdT-mediated dUTP nick end labeling staining and caspase 3/7 activity assays. FADD-treated dams had significantly higher resorption rates than CD-treated dams. Embryonic lengths and weights from FADD-treated dams were significantly lower than those from CD-treated dams; the smallest embryos were those of the Mthfr +/- dams that consumed the FADD, with effect of genotype tending to be significant (P = 0.09). The thickness of cardiac ventricular compact walls of embryos from FADD-treated dams was significantly reduced, and embryonic myocardium from FADD-treated dams had significantly fewer BrdU-labeled cells compared with CD-treated dams, with no differences in apoptosis due to the diets. Genotype did not affect proliferation or apoptosis. Our results suggest that proliferation of embryonic myocardium is sensitive to maternal dietary folate and that folate supplementation during pregnancy is important for normal heart development and prevention of heart defects.

Impact of methylenetetrahydrofolate reductase deficiency and low dietary folate on the development of neural tube defects in splotch mice

BACKGROUND

The etiology of neural tube defects (NTDs) is multifactorial, with environmental and genetic determinants. Folate supplementation prevents the majority of NTDs, and a polymorphism in methylenetetrahydrofolate reductase (MTHFR) has become recognized as a genetic risk factor. The mechanisms by which folate affects NTD development are unclear. The Splotch (Sp) mouse is a well-characterized mouse model for studying spontaneous NTDs. To assess the potential interaction between folate metabolism and the Sp mutant in NTD development, we studied mice with both Sp and Mthfr mutations, as well as the interaction between Sp and low dietary folate.

METHODS

Wild-type, single Mthfr+/-mutant, single Sp/+mutant, and double mutant (Mthfr+/-, Sp/+) female mice were mated with males of the same genotype. Embryos were examined for NTDs on gestational day (GD) 13.5. To investigate the effects of folate deficiency on Sp mice, Sp/+female mice were fed a control diet (CD), a moderately folic acid-deficient diet (MFADD), or a severely folic acid-deficient diet (SFADD). They were mated with Sp/+males and the embryos were examined.

RESULTS

There were no differences in the incidence or severity of NTDs in embryos from double-mutant mating pairs compared to those from single Sp mutants. Embryos from Mthfr+/-dams did not exhibit NTDs. Diets deficient in folate did not influence the incidence or severity of NTDs in embryos from Sp/+mice.

CONCLUSIONS

We did not observe an interaction between Sp and Mthfr mutations, or between the Sp mutation and low dietary folate, in NTD development in Splotch mice.

Bacterially synthesized folate and supplemental folic acid are absorbed across the large intestine of piglets

A large pool of folate exists in the large intestine of humans. Preliminary evidence, primarily in vitro, suggests that this folate may be bioavailable. The purpose of this study was to test the hypothesis that supplemental folic acid and bacterially synthesized folate are absorbed across the large intestine of piglets. The pig was used as an animal model because it resembles the human in terms of folate absorption, at least in the small intestine. A tracer of [3H]-folic acid or [3H]-para-aminobenzoic acid ([3H]-PABA), a precursor of bacterially synthesized folate, was injected into the cecum of 11-day-old piglets. Feces and urine were collected for 3 days. Thereafter, piglets were killed, and livers and kidneys harvested. [3H]-Folate was isolated from biological samples by affinity chromatography using immobilized milk folate binding proteins and counted using a scintillation counter. In piglets injected with [3H]-folic acid, the feces, liver, urine and kidneys accounted for 82.1%, 12.3%, 3.9% and 1.7% of recovered [3H]-folate, respectively. In piglets injected with [3H]-PABA, the amount of recovered bacterially synthesized folate in the feces, liver and urine was 85.1%, 0.4% and 14.6%, respectively. Twenty-three percent and 13% of tritium were recovered in samples examined (liver, kidney, fecal and urine) from piglets injected with [3H]-folic acid and [3H]-PABA, respectively. Using our estimates of [3H]-folic acid absorption and the total and percent monoglutamyl folate content of piglet feces, we predict that at least 18% of the dietary folate requirement for the piglet could be met by folate absorption across the large intestine.

Commensal bacteria, redox stress, and colorectal cancer: mechanisms and models

The potential role for commensal bacteria in colorectal carcinogenesis is explored in this review. Most colorectal cancers (CRCs) occur sporadically and arise from the gradual accumulation of mutations in genes regulating cell growth and DNA repair. Genetic mutations followed by clonal selection result in the transformation of normal cells into malignant derivatives. Numerous toxicological effects of colonic bacteria have been reported. However, those recognized as damaging epithelial cell DNA are most easily reconciled with the currently understood genetic basis for sporadic CRC. Thus, we focus on mechanisms by which particular commensal bacteria may convert dietary procarcinogens into DNA damaging agents (e.g., ethanol and heterocyclic amines) or directly generate carcinogens (e.g., fecapentaenes). Although these and other metabolic activities have yet to be linked directly to sporadic CRC, several lines of investigation are reviewed to highlight difficulties and progress in the area. Particular focus is given to commensal bacteria that alter the epithelial redox environment, such as production of oxygen radicals by Enterococcus faecalis or production of hydrogen sulfide by sulfate-reducing bacteria (SRB). Super-oxide-producing E. faecalis has conclusively been shown to cause colonic epithelial cell DNA damage. Though SRB-derived hydrogen sulfide (H(2)S) has not been reported thus far to induce DNA damage or function as a carcinogen, recent data demonstrate that this reductant activates molecular pathways implicated in CRC. These observations combined with evidence that SRB carriage may be genetically encoded evoke a working model that incorporates multifactorial gene-environment interactions that appear to underlie the development of sporadic CRC.

A large pool of available folate exists in the large intestine of human infants and piglets

Many microorganisms in the large intestine are capable of synthesizing folate. Preliminary evidence suggests that this folate may be absorbed. The purpose of the 2 experiments reported herein was to estimate the pool of folate in the feces of human infants and piglets and to ascertain, if absorbed, whether the quantity and form of folate are sufficient to potentially affect the folate status of the host organism. The folate content of milk fed to and of fecal solids collected from exclusively human milk-fed (n = 12) and formula-fed (n = 10) term infants (1-6 mo old) was determined microbiologically before (short-chain folates) and after folate conjugase (total folate) treatment. The folate content of formula fed and of feces collected from 10-d-old piglets (n = 10) was also determined microbiologically. The proportion of 5-methyltetrahydrofolate (5-methylTHF) in feces of human infants and piglets that was monoglutamylated was determined by HPLC analysis. The folate content of fecal solids collected from infants was 93.2 +/- 92.8 nmol/d (mean +/- SD), representing on average 50% (8.0-170.1%) of their mean estimated dietary folate intake. Fecal folate was largely present as short-chain folate (66 +/- 21.3%) with the predominant form being 5-methylTHF, 52.5 +/- 30.1% of which was monoglutamylated. In piglets, the folate content of feces was 301.3 +/- 145.7 nmol/d, representing 36% of their dietary folate intake. Piglet fecal folate was largely present as short-chain folate (68.1 +/- 12.6%) with the predominant species being 5-methylTHF, 29.3 +/- 33.2% of which was monoglutamylated. Collectively, these data suggest that the quantity and form of folate (monoglutamylated) in the large intestine of human infants and piglets are sufficiently large to potentially affect folate status.