Vitamin A Sufficient Research Articles

Vitamin A Deficiency Blocks the Initiation of Meiosis of Germ Cells in the Developing Rat Ovary In Vivo1

Vitamin A (retinol) is required for male and female reproduction as well as to support many developmental processes. In the male, meiotic entry of germ cells occurs after birth and throughout adulthood, whereas in the female, the entry into meiosis I occurs during embryonic development. Evidence from cultured embryonic ovaries suggests that the vitamin A metabolite, all-trans retinoic acid (atRA), initiates this process. However, in vivo evidence to support a normal role for atRA in meiotic entry is lacking. The present study demonstrates that although germ cell number is normal in ovaries from both vitamin A-sufficient (VAS) embryos and those that are deficient in atRA, the majority of germ cells in the most severely atRA-deficient group fail to enter meiosis and remain in an undifferentiated state. In contrast, in a group that is only moderately deficient in atRA, a small number of ovarian germ cells enter meiosis (30%) compared with 75% of cells in the VAS control group. The expression of the atRA-responsive gene, Stra8, is reduced by approximately 90% and 50% in the severely and moderately atRA-deficient ovaries, respectively, compared with the VAS controls. These results provide the first in vivo evidence that vitamin A regulates the entry of germ cells into meiosis in the developing ovary.

Effects of vitamin A deficiency on plasma glucose, insulin and leptin in rats

We have observed that vitamin A and its catalytic metabolites synergize with insulin to induce hepatic glucokinase gene expression. It has been known that retinoic acid (RA) can stimulate the expression of phosphoenolpyruvate carboxyl kinase gene. To better understand the role of vitamin A in glucose and lipid homeostasis, Zucker lean (female) rats were fed with vitamin A deficient (VAD) diet (TestDiet, #5822) and vitamin A sufficient (VAS) control diet (TestDiet, #5755) after weaning. When body weight gain stops in VAD group (a sign of vitamin A deficiency), animals were used to access the effect of vitamin A deficiency on glucose and lipid metabolism. All animals were fasted for six hours before their plasma and tissue samples were collected for analysis. To this end, levels of plasma glucose (153 ± 35.1 mg/dl), insulin (0.6 ±0.35 ng/ml), and leptin (1.3 ± 0.64 ng/ml) of VAD rats were all significantly lower than those (glucose, 176 ± 23.1 mg/dl; insulin, 1.3 ± 0.6 ng/ml; 4.0 ± 2.1 ng/ml, all P<0.04)) of VAS fed rats. When VAD rats were fed with VAS diet, the plasma glucose level (150 ± 40 mg/dl) of VAD rats was significantly increased at three days (207 ± 62 mg/dl) and seven days (221 ± 45 mg/dl) after initiation of VAS diet (all P<0.05). At the same time, plasma cholesterol level (49.6 ± 4.4 mg/dl) of VAD rats was also significantly increased at three days (74.6 ± 8.8 mg/dl) and seven days (83.9 ± 9.2 mg/dl) after resuming the VAS diet (all P<0.004). These results demonstrated that vitamin A deficiency can result in the changes of plasma glucose and lipid homeostasis. Further work is warranted to understand the underlying molecular mechanisms.

Isx Participates in the Maintenance of Vitamin A Metabolism by Regulation of β-Carotene 15,15′-Monooxygenase (Bcmo1) Expression

Isx (intestine specific homeobox) is an intestine-specific transcription factor. To elucidate its physiological function, we generated Isx-deficient mice by knocking in the beta-galactosidase gene (LacZ) in the Isx locus (IsxLacZ/LacZ mice). LacZ staining of heterozygous (IsxLacZ/+) mice revealed that Isx was expressed abundantly in intestinal epithelial cells from duodenum to proximal colon. Quantitative mRNA expression profiling of duodenum and jejunum showed that beta-carotene 15,15'-monooxygenase (EC1.14.99.36 Bcmo1) and the class B type I scavenger receptor, which are involved in vitamin A synthesis and carotenoid uptake, respectively, were drastically increased in IsxLacZ/LacZ mice. Although mild vitamin A deficiency decreased Isx expression in duodenum of wild-type (Isx+/+) mice, severe vitamin A deficiency decreased Isx mRNA expression in both duodenum and jejunum of Isx+/+ mice. On the other hand, vitamin A deficiency increased Bcmo1 expression in both duodenum and jejunum of Isx+/+ mice. However, Bcmo1 expression was not increased in duodenum of IsxLacZ/LacZ mice by mild vitamin A deficiency. These data suggest that Isx participates in the maintenance of vitamin A metabolism by regulating Bcmo1 expression in the intestine.

Altered lipid catabolism in the vitamin A deficient liver

The transcriptome pattern of metabolic genes in vitamin A deficient (VAD) liver has been compared to the vitamin A-sufficient (VAS) state using the Mouse 32k oligonucleotide (70mer) array. In VAD liver there was a decrease in expression of genes encoding enzymes of mitochondrial fatty acid (FA) oxidation; these genes included fatty acyl CoA ligase, carnitine o-palmitoyl transferase 1, medium chain acyl-CoA dehydrogenase, 3-ketoacyl CoA thiolase, and citrate synthase. Particularly affected was peroxisome metabolism, as genes encoding enzymes of peroxisomal FA oxidation and transport proteins were differentially expressed. These genes included those encoding acyl-CoA oxidase 1, the peroxisomal bifunctional enzyme, peroxisomal thiolase, and carnitine o-octanoyl transferase, the enzyme involved in shuttling FAs from the peroxisome to the mitochondrion. Most genes that were differentially expressed with chronic vitamin A depletion were responsive to treatment with all- trans retinoic acid (RA). Consistent with the decreased expression of genes involved in FA oxidation, we found an increase in hepatic macrocytic lipid accumulation and triglyceride levels. The relevant nuclear receptor gene that was differentially expressed in the VAD liver was that encoding the peroxisome proliferator-activated receptor (PPAR) alpha, the mRNA levels for which were decreased in VAD liver and increased with all- trans RA treatment. Down regulation of the PPAR alpha gene is the likely cause of the altered expression pattern of the above metabolic genes in VAD liver.

Vitamin A deficiency increases airway resistance following C-fiber stimulation

Vitamin A deficiency (VAD) remains an important problem in the developing world where environmental air pollution is increasing. Because the coincidence of these factors could increase the prevalence of asthma in these regions, airway reactivity to methacholine (MCh), capsaicin, and sulfur dioxide was studied in VAD rats. The impedance to a small volume oscillation was analyzed to determine airway resistance (R(aw)) and lung elastance (H). VAD rats demonstrated larger increases in R(aw) and H after the administration of methacholine, and in R(aw) after administration of capsaicin or sulfur dioxide. The muscarinic receptor-2 (M2R) selective antagonist AFDX-116 enhanced the effect of capsaicin in vitamin A sufficient (VAS) but not VAD rats and retinoic acid-administration partially restored this enhancement. These data indicate that diminished auto-inhibitory muscarinic receptor-2 function contributed to this increased airway responsiveness to pulmonary C-fiber stimulation in VAD rats. If children with VAD also have diminished M2R function, they may be more prone to develop asthma, particularly in the presence of environmental co-factors such as sulfur dioxide.

Vitamin A deficiency alters pulmonary parenchymal collagen and tissue mechanics

The mechanical properties of the pulmonary parenchyma are strongly influenced by the collagen and elastic fibers that course through the alveolar interstitium and interconnect the bronchovascular bundles. Vitamin A deficiency (VAD) produces effacement and remodeling of the alveolar architecture, resulting in alternating areas of alveolar dilatation and collapse. To better understand the mechanical consequences and reversibility of this remodeling process, we have examined how the remodeling of collagen and elastic fibers correlates with the mechanical properties of the lung parenchyma in VAD rats. An oscillatory impulse was applied at different levels of stress on the fiber network and the tissue damping (G), elastance (H), hysteresivity (G/H, eta) were analyzed. At a supra-physiological functional residual capacity, the lung parenchyma of VAD rats exhibited a lower G and H than Vitamin A sufficient (VAS) rats, which was accompanied by a significant decrease in the quantity of parenchymal collagen and collagen fibers. Retinoic acid (RA) administration restored the parenchymal collagen and mechanical properties.

Plasma α1-Acid Glycoprotein Can Be Used to Adjust Inflammation-Induced Hyporetinolemia in Vitamin A-Sufficient, but Not Vitamin A-Deficient or -Supplemented Rats

We examined the association between alpha(1)-acid glycoprotein (AGP), all-trans-retinol (retinol), and albumin concentrations in a longitudinal animal model of IL-6-induced inflammation. Vitamin A-sufficient (VAS) male Sprague-Dawley rats were administered recombinant human IL-6 [n = 4, 65 mug/(kg.d)] or PBS (n = 4) continuously for 7 d via osmotic minipumps. Plasma samples were obtained daily and concentrations of retinol, AGP, albumin, and total protein were measured. Compared with both baseline and controls, retinol and albumin decreased (P < 0.05), AGP increased (P < 0.05), and total protein concentrations were unaffected in IL-6-treated rats. In vitamin A-deficient (VAD) rats, AGP concentrations were significantly lower at all time points and increased only to one-third of that in VAS rats. The AGP cut-off value indicative of inflammation was 0.11 g/L (i.e., 95% upper limit of baseline concentrations). After 20.5 h, there was an inverse linear correlation between AGP concentrations and the relative change in retinol to baseline (y = -0.18x + 0.48, r = -0.84, P < 0.001). However, changes in AGP and albumin were not correlated (P = 0.94). The application of this function to retinol concentrations in rats from separate experiments showed that hyporetinolemia cannot be adjusted using plasma AGP in VAD or vitamin A-supplemented rats. In conclusion, correcting inflammation-induced hyporetinolemia using an acute-phase protein requires longitudinally derived data, knowledge of vitamin A status, and a common underlying mechanism of change.

Vitamin A deficiency alters the pulmonary parenchymal elastic modulus and elastic fiber concentration in rats.

BackgroundBronchial hyperreactivity is influenced by properties of the conducting airways and the surrounding pulmonary parenchyma, which is tethered to the conducting airways. Vitamin A deficiency (VAD) is associated with an increase in airway hyperreactivity in rats and a decrease in the volume density of alveoli and alveolar ducts. To better define the effects of VAD on the mechanical properties of the pulmonary parenchyma, we have studied the elastic modulus, elastic fibers and elastin gene-expression in rats with VAD, which were supplemented with retinoic acid (RA) or remained unsupplemented.MethodsParenchymal mechanics were assessed before and after the administration of carbamylcholine (CCh) by determining the bulk and shear moduli of lungs that that had been removed from rats which were vitamin A deficient or received a control diet. Elastin mRNA and insoluble elastin were quantified and elastic fibers were enumerated using morphometric methods. Additional morphometric studies were performed to assess airway contraction and alveolar distortion.ResultsVAD produced an approximately 2-fold augmentation in the CCh-mediated increase of the bulk modulus and a significant dampening of the increase in shear modulus after CCh, compared to vitamin A sufficient (VAS) rats. RA-supplementation for up to 21 days did not reverse the effects of VAD on the elastic modulus. VAD was also associated with a decrease in the concentration of parenchymal elastic fibers, which was restored and was accompanied by an increase in tropoelastin mRNA after 12 days of RA-treatment. Lung elastin, which was resistant to 0.1 N NaOH at 98°, decreased in VAD and was not restored after 21 days of RA-treatment.ConclusionAlterations in parenchymal mechanics and structure contribute to bronchial hyperreactivity in VAD but they are not reversed by RA-treatment, in contrast to the VAD-related alterations in the airways.

Retinoic acid reverses the airway hyperresponsiveness but not the parenchymal defect that is associated with vitamin A deficiency.

Airway hyperresponsiveness (AHR) is influenced by structural components of the bronchial wall, including the smooth muscle and connective tissue elements and the neuromuscular function. AHR is also influenced by parenchymally derived tethering forces on the bronchial wall, which maintain airway caliber by producing outward radial traction. Our previous work has shown that vitamin A-deficient (VAD) rats exhibit cholinergic hyperresponsiveness and a decrease in the expression and function of the muscarinic-2 receptors (M2R). We hypothesized that if decreases in radial traction from airway or parenchymal structures contributed to the VAD-related increase in AHR, then the radial traction would normalize more slowly than VAD-related alterations in neurotransmitter signaling. Rats remained vitamin A sufficient (VAS) or were rendered VAD and then maintained on the VAD diet in the presence or absence of supplementation with all-trans retinoic acid (RA). VAD was associated with an approximately twofold increase in respiratory resistance and elastance compared with VAS rats. Exposure to RA for 12 days but not 4 days restored resistance and elastance to control (VAS) levels. In VAD rats, AHR was accompanied by decreases in bronchial M2R gene expression and function, which were restored after 12 days of RA supplementation. Subepithelial bronchial elastic fibers were decreased by approximately 50% in VAD rats and were significantly restored by RA. The increase in AHR that is associated with VAD is accompanied by decreases in M2R expression and function that can be restored by RA and a reduction in airway elastic fibers that can be partially restored by RA.

RNA Polymerase II Association with the Phosphoenolpyruvate Carboxykinase (PEPCK) Promoter Is Reduced in Vitamin A–Deficient Mice

Phosphoenolpyruvate carboxykinase (PEPCK) gene expression is decreased in vitamin A-deficient (VAD) mice. However, the underlying molecular mechanism at the PEPCK promoter that contributes to this alteration in gene expression remains unexplained and thus serves as the basis for our investigation in this report. Using liver from vitamin A-sufficient (VAS) and VAD mice in the chromatin immunoprecipitation (ChIP) assay, we determined that histones H3 and H4 were in the acetylated or active state in VAS mice at each of the three retinoic acid response elements (RARE1, RARE2 and RARE3) of the PEPCK promoter. The same acetylation pattern was seen in VAD mice, but with relatively lower levels of acetylated H3 and H4 bound at the region encompassing PEPCK RARE1/RARE2. In ChIP assays conducted with an antibody to RNA polymerase II (RNA Pol II), the association of RNA Pol II with PEPCK RARE1/RARE2 was significantly decreased in vitamin A deficiency. The reduction in RNA Pol II association is indicative of an interruption in the direct interactions of RNA Pol II with the PEPCK promoter, with general transcription factors and/or with coregulator molecules that contribute to the activation of the PEPCK gene. These results increase our understanding of the molecular basis for decreased PEPCK gene expression in VAD mice in vivo and offer additional insight into the regulation of other retinoid-responsive genes.

Marginal vitamin A deficiency in pigs experimentally infected with Trichuris suis: a model for vitamin A inadequacy in children

The development of an experimental model for marginal vitamin A deficiency in humans is of major interest, enabling the elucidation of possible interactions with helminth infections. We established a useful experimental model for human vitamin A deficiency in young pigs; deficiency was induced through a depletion method encompassing both sow and offspring. We report on a 2 × 2 study in which 18-week-old vitamin A deficient pigs and vitamin A sufficient littermates were infected with both of the intestinal nematodes Trichuris suis and Ascaris suum and followed for 14 weeks through 32 weeks of age. Forty-nine pigs were followed with respect to bodyweight, liver biopsies and blood samples for retinol concentration and faecal samples for parasite eggs and worms. Liver and serum concentrations of vitamin A were significantly diminished in the vitamin A deficient (VAD) group as compared to the vitamin A sufficient (VAS) group both before ( P < 0·001) and after inoculation with T. suis and A. suum ( P < 0·02). A significant correlation between retinol content in micro-biopsy needle samples and gross liver content was found ( r = 0·457, n = 48, P = 0·001). The adult T. suis worms in the VAD group were marginally smaller (36·7 vs 40·2 mm; P = 0·08), more orally located (section 2·9 vs 3·9; P = 0·08) and had a higher proportion of males (0·58 vs 0·50; P = 0·08) whereas there were no effects of diet treatment on fecundity. The proportion of pigs with faecal T. suis egg excretion 12 weeks post inoculation (p.i.) was significantly lower in the VAD group compared with the VAS infected group (21 vs 78%; P = 0·036). In addition, faecal T. suis egg excretion was significantly lower in the VAD group at both week 11 ( P = 0·040) and week 12 p.i. ( P = 0·021). Vitamin A deficiency may have altered the functional integrity of the mucosal intestinal epithelium, disrupting the normally delicate attachment of T. suis and leading to the premature termination of infection. However, a possible antagonistic interaction, if verified, should not preclude interventions to improve vitamin A status, i.e., treatment should accompany anthelmintic treatment.

Decreases in retinol and retinol-binding protein during total parenteral nutrition in rats are not due to a vitamin A deficiency

Perfusion feeding in rats induced a decrease in circulating retinol despite an adequate supply of vitamin A. We studied the effect of total parenteral nutrition (TPN) on the retinol specific carrier in rat, analyzing holo-RBP (bound to retinol) and apo-RBP (without retinol) in serum and in liver. Vitamin A-sufficient (A+) and -deficient (A-) rats were characterized in terms of vitamin A and RBP status and then perfused (TPN-A+ and TPN-A-) or orally pair-fed (O-A+ and O-A-) with vitamin A. In A+ rats, a decrease in serum retinol (2.6-fold) and an increase in apo-RBP was concomitant with a massive accumulation of RBP in the liver. In TPN-A rats, both circulating RBP and liver total RBP were decreased. In TPN-A+ rats, there was a decrease in circulating retinol (2.4-fold) in parallel to a decrease of serum and liver RBP protein and mRNA. We provide evidence that infused retinyl palmitate was not responsible for serum retinol and RBP decrease and that retinol depletion was not due to vitamin A deficiency. Whatever the vitamin A status, TPN may induce in rats a down-regulation of hepatic RBP synthesis, which may, at least partially, explain the alteration of retinol and RBP in serum.

Nafenopin-induced peroxisome proliferation in vitamin A deficient rats

Induction of peroxisome proliferator responsive genes is thought to be mediated through binding of a peroxisome proliferator-activated receptor (PPAR) to specific peroxisome proliferator response elements in the upstream region of these genes. Binding of PPAR to the acyl-CoA oxidase promoter requires heterodimerization with the retinoid X receptor (RXR), and subsequent transactivation is strongest when ligands for both PPAR and RXR are present. Therefore, we hypothesized that depletion of ligand for the retinoid receptor would limit the induction of peroxisome proliferation in rats. Hepatic retinol content was reduced by more than 90% by feeding weanling rats a vitamin A deficient (VAD) diet for approximately 3 months. Nafenopin treatment for 7 days induced peroxisomal β-oxidation 18-fold in VAD rats compared with 16-fold in rats fed a vitamin A sufficient (VAS) diet. Nafenopin induced microsomal laurate hydroxylase and mitochondrial β-oxidation to comparable rates of specific activity in both VAD and VAS rats. However, the activities in VAD controls were significantly lower than in VAS controls, so the magnitude of the nafenopin-induced increases was greater in the VAD rats. Relative liver weights were increased nearly 2-fold in both VAS and VAD rats treated with nafenopin. Ultrastructural examination of the livers demonstrated that nafenopin increased the number and size of peroxisomes in both VAD and VAS rats. These data demonstrate that rats with severely depleted vitamin A stores remained responsive to the peroxisome proliferator nafenopin. Whether critical retinoid pools that supply RXR ligand (9- cis-retinoic acid) are spared in the vitamin A deficient rats remains to be determined.