Vitamin A exerts its activity at the transcriptional level in the small intestine

Role of Food Antioxidants in Modulating Gut Microbial Communities: Novel Understandings in Intestinal Oxidative Stress Damage and Their Impact on Host Health

Dietary components have an important role on the structure and function of host gut microbial communities. Even though, various dietary components, such as carbohydrates, fats, proteins, fibers, and vitamins, have been studied in depth for their effect on gut microbiomes, little attention has been paid regarding the impact of several food antioxidants on the gut microbiome. The long-term exposure to reactive oxygen species (ROS) can cause microbial dysbiosis which leads to numerous intestinal diseases such as microbiota dysbiosis, intestinal injury, colorectal cancers, enteric infections, and inflammatory bowel diseases. Recently, it has been shown that the food derived antioxidant compounds might protect the host from intestinal oxidative stress via modulating the composition of beneficial microbial species in the gut. The present review summarizes the impact of food antioxidants including antioxidant vitamins, dietary polyphenols, carotenoids, and bioactive peptides on the structure as well as function of host gut microbial communities. Several in vitro, animal model, and clinical studies indicates that food antioxidants might modify the host gut microbial communities and their health status. However, still further clarification is needed as to whether changes in certain microbial species caused by food additives may lead to changes in metabolism and immune function.

Protective Effect of Vitamin A on ARA-C Induced Intestinal Damage in Mice

Background

Cytarabine (ARA-C) has been used for many years in the treatment of patients with leukemia and lymphoma. Gastrointestinal ulceration and mucositis are two of the well-known side effects of ARA-C. We set out to investigate whether vitamin A (VA) can help prevent ARA-C-induced mucosal lesions in mice.

Materials and methods

Mice were divided into 5 groups. Group I (control group) received only saline; group II received ARA-C plus saline; group III received ARA-C plus VA; group IV received ARA-C plus a lipid solution, and group V received VA alone. VA (5000 IU/kg) was administered orally to the mice once daily for 7 days. ARA-C (3.6 mg) was administered intraperitoneally for 5 days to groups II, III and IV, starting on the third day of VA treatment. Intestinal segments from the proximal end of the jejunum of treated mice were isolated.

Results

There was improved mucosal integrity, less necrosis and increased villus length with advanced mucosal proliferation in crypts in the VA plus ARA-C group when compared to the ARA-C groups without VA.

Conclusion

We conclude that VA has a protective effect against ARA-C-induced mucosal damage in mice.

Vitamin A and the epigenome

The epigenetic phenomena refer to heritable changes in gene expression other than those in the DNA sequence, such as DNA methylation and histone modifications. Major research progress in the last few years has provided further proof that environmental factors, including diet and nutrition, can influence physiologic and pathologic processes through epigenetic alterations, which in turn influence gene expression. This influence is termed nutritional epigenetics, and one prominent example is the regulation of gene transcription by vitamin A through interaction to its nuclear receptor. Vitamin A is critical throughout life. Together with its derivatives, it regulates diverse processes including reproduction, embryogenesis, vision, growth, cellular differentiation and proliferation, maintenance of epithelial cellular integrity and immune function. Here we review the epigenetic role of vitamin A in cancer, stem cells differentiation, proliferation, and immunity. The data presented here show that retinoic acid is a potent agent capable of inducing alterations in epigenetic modifications that produce various effects on the phenotype. Medical benefits of vitamin A as an epigenetic modulator, especially with respect to its chronic use as nutritional supplement, should rely on our further understanding of its epigenetic effects during health and disease, as well as through different generations.

Vitamin A Deficiency Impairs Mucin Expression and Suppresses the Mucosal Immune Function of the Respiratory Tract in Chicks

The chicken immune system is immature at the time of hatching. The development of the respiratory immune system after hatching is vital to young chicks. The aim of this study was to investigate the effect of dietary vitamin A supplement levels on respiratory mucin and IgA production in chicks. In this study, 120 one-day-old broiler chicks were randomly divided into 4 groups consisting of three replicates of 10 broilers and subjected to dietary vitamin A supplement levels of 0, 1,500, 6,000, or 12,000 IU/kg for seven days. Compared with control birds, vitamin A supplementation significantly increased the mucin and IgA levels in the bronchoalveolar lavage fluid (BALF) as well as the IgA level in serum. In the lungs, vitamin A supplementation downregulated TNF-α and EGFR mRNA expression. The TGF-β and MUC5AC mRNA expression levels were upregulated by vitamin A supplementation at a dose of 6,000 IU/kg, and the IL-13 mRNA expression level was increased at the 12,000 IU/kg supplement level. Vitamin A deficiency (control) significantly decreased the mRNA expression levels of MUC2, IgA, EGFR, IL-13 and TGF-β in trachea tissue. Histological section analysis revealed that the number of goblet cells in the tracheal epithelium was less in the 0 and 12,000 IU/kg vitamin A supplement groups than in the other groups. In conclusion, vitamin A deficiency suppressed the immunity of the airway by decreasing the IgA and mucin concentrations in neonatal chicks. This study suggested that a suitable level of vitamin A is essential for the secretion of IgA and mucin in the respiratory tract by regulating the gene expression of cytokines and epithelial growth factors.

Host immunity and pathogen strain contribute to intestinal disaccharidase impairment following gut infection

Infection or other inflammatory insults in the small intestine often result in reduced disaccharidase enzyme levels. Using a mouse model of giardiasis, we examined the role of host immunity and pathogen virulence in mediating disaccharidase deficiency postinfection (p.i.). C57BL/6J mice were infected with two strains, WB and GS, of the human parasite Giardia duodenalis. The levels of sucrase, maltase, and lactase decreased in wild-type mice p.i. with the GS strain but not with the WB strain. Both CD4-deficient and SCID mice failed to eliminate the infection and did not exhibit disaccharidase deficiency. β(2)-Microglobulin knockout animals controlled infections similar to wild-type mice but exhibited no decrease in disaccharidase activity. Analysis of cytokine production by spleen and mesenteric lymph node cells showed production of IL-4, IL-10, IL-13, IL-17, IL-22, TNF-α, and IFN-γ p.i. with both WB and GS, with IFN-γ being the dominant cytokine for both parasite strains. Mesenteric lymph node cells produced lower levels of cytokines compared with splenocytes in response to parasite extract, although the overall pattern was similar. These data suggest that T cell responses mediate parasite clearance whereas also contributing to pathogenesis. They also demonstrate that differences in pathogen strain can also determine the outcome of infection and further our understanding of the clinical variation seen in human giardiasis.

Ingestion of potato starch containing esterified phosphorus increases alkaline phosphatase activity in the small intestine in rats

Alkaline phosphatase (ALP) hydrolyzes a variety of monophosphate esters and plays an important role in phosphorus (P) metabolism. Several nutrients in food have been reported to affect intestinal ALP activity in animal models. Previous reports indicated that high levels of P or phosphate in diets decreased intestinal ALP activity in rats. Because potato starch contains considerable amounts of esterified P, unlike other starch-derived plants, we hypothesized that the feeding of potato starch would decrease ALP activity in the intestinal tract. Male Sprague-Dawley rats (7 weeks old) were fed 3 different types of diet containing 60% corn starch or 1 of 2 types of potato starch with different esterified P content for 1 or 5 weeks. Body weight and food intake of each rat were measured every day throughout the experimental periods. At the end of the feeding periods, the small intestine was removed to determine ALP activity in the mucosal tissues. Significant differences were observed in ALP activity in the small intestine between the 2 feeding periods, among the 4 segments of the small intestine, and among the 3 diet groups. Significant positive linear correlations between the amount of P derived from the starch and mucosal ALP activity were obtained in the jejunum and jejunoileum in rats after feeding for 5 weeks. We concluded, contrary to our hypotheses, that the ingestion of potato starch adaptively increases ALP activity in the upper part of the small intestine of growing rats in an esterified P content-dependent manner.

Vitamin A deficiency increases protein catabolism and induces urea cycle enzymes in rats

Chronic vitamin A deficiency induces a substantial delay in the rates of weight and height gain in both humans and experimental animals. This effect has been associated with an impaired nutrient metabolism and loss of body protein. Therefore, we analyzed the effect of vitamin A deficiency on endogenous proteolysis and nitrogen metabolism and its reversibility with all-trans retinoic acid (RA). Male weanling rats, housed in pairs, were pair-fed a vitamin A-deficient (VAD) or control diet until they were 60 d old. A group of deficient rats were further treated with daily intraperitoneal injections of all-trans RA for 10 d. Final body and tissue (i.e. liver and heart) weights were significantly lower and tissue:body weight ratios were similar in VAD rats and in controls. Conversely, the epididymal white fat:body weight ratio and the plasma concentrations of alanine aminotransferase and adiponectin were significantly higher in VAD rats, which also had hepatic macrovesicular lipid accumulations. Plasma and gastrocnemius muscle 3-methylhistidine, urine nitrogen, and plasma and urine urea concentrations were all significantly higher in the VAD group. The expression of the genes encoding urea cycle enzymes and their activities increased in VAD livers. These changes were partially reverted by all-trans RA. We propose that fuel partitioning in vitamin A deficiency may shift from fatty acids to protein catabolism as an energy source. Our results emphasize the importance of vitamin A on the energy balance control system and they provide an explanation for the role of vitamin A in protein turnover, development, and growth.

Carotenoids, retinol, and intestinal barrier function in children from northeastern Brazil

OBJECTIVES

To investigate the association of carotenoids and retinol (vitamin A) with intestinal barrier function in children in an urban community in Fortaleza, northeastern Brazil.

METHODS

Descriptive analysis of serum carotenoids and retinol concentrations with intestinal barrier function in 102 children from an urban community, July 2000 to August 2001.

RESULTS

The weight for height z score (wasting) showed that 19.6% (20/102) had mild malnutrition (-1 to -2 z score). All of the children's serum retinol concentrations were determined and none were severely deficient (< or =0.35 micromol/L), 2.9% (3/102) were moderately (0.36-0.70 micromol/L) deficient, 20.6% (21/102) were mildly (0.71-1.05 micromol/L) deficient; 76.5% (78/102) were vitamin A sufficient (>1.05 micromol/L). The lactulose:mannitol (L/M) ratio was elevated (> or =0.0864) in 49% (47/97) of children when compared with healthy children with normal L/M ratio (<0.0864) in the same geographic area. Serum carotenoids, lutein, beta-cryptoxanthin and beta-carotene showed significant inverse correlations with the L/M ratio, but not lutein after adjusting for age. Acute phase proteins (C-reactive protein and alpha-acid glycoprotein) were significantly inversely correlated with retinol but not with carotenoids. Retinol and retinol-binding protein were not significantly associated with L/M ratio.

CONCLUSIONS

These data suggest a disruption of intestinal barrier function in the paracellular pathway with low serum concentrations of carotenoids. Carotenoids may provide a better marker for disrupted intestinal barrier function than retinol-binding protein or retinol.

Role of retinol in protecting epithelial cell damage induced by Clostridium difficile toxin A

Vitamin A (retinol), a fat-soluble vitamin, is an essential nutrient for the normal functioning of the visual system, epithelial cell integrity and growth, immunity, and reproduction. Our group has investigated the effect of high doses of oral vitamin A on early childhood diarrhea in our prospective community-based studies from Northeast Brazil and found a beneficial role in reducing the mean duration but not incidence of diarrheal episodes. In this study, we explored the role of retinol supplementation in intestinal cell lines following Clostridium difficile toxin A (TxA) challenge. C. difficile is the most common anaerobic pathogen borne with antibiotic-borne diarrhea and pseudomembranous colitis. Since retinol is critical for the integrity of tight junctions and to modulate the cell cycle, we have focused on changes in transepithelial electrical resistance (TEER) in Caco-2, a more differentiated intestinal cell line, and on models of cell proliferation, migration and viability in IEC-6 cells, an undifferentiated crypt cell line, following TxA injury. In this model, retinol therapy reduced apoptosis, improved cell migration and proliferation, and prevented the reduction in TEER, following C. difficile TxA challenge in a glutamine-free medium. These results suggest the role of retinol in protecting intestinal epithelial barrier function from C. difficile TxA enterotoxic damage.

Global effects of vitamin A deficiency on gene expression in rat liver: evidence for hypoandrogenism

Vitamin A (retinol) metabolites are ligands for transcription factors that regulate many genes. The liver is the main storage depot for retinol and plays a role in vitamin A homeostasis. To better understand the effects of vitamin A deficiency on liver gene expression, we produced retinol deficiency in male rats by feeding a diet low in retinol for 53 days after weaning and examined the effects on gene expression in liver using Affymetrix oligonucleotide microarrays. We detected expression of 41% of the 8799 probe sets represented on the RGU-34A GeneChips. Vitamin A deficiency resulted in major changes in liver gene expression: 805 genes (22% of all genes detected) differed at P<or=.05 (false discovery rate <0.143). Genes involved in fatty acid metabolism, peroxisomal function, glycolysis, glutamate metabolism and the urea cycle were altered. The expression of many sexually dimorphic genes was altered toward a feminized or senescent pattern of gene expression in the liver. Retinol deficiency also produces a shift toward increased protein and fat catabolism and decreased fatty acid synthesis.