Vitamin A - discovery, metabolism, receptor signaling and effects on bone mass and fracture susceptibility

The first evidence of the existence of vitamin A was the observation 1881 that a substance present in small amounts in milk was necessary for normal development and life. It was not until more than 100 years later that it was understood that vitamin A acts as a hormone through nuclear receptors. Unlike classical hormones, vitamin A cannot be synthesized by the body but needs to be supplied by the food as retinyl esters in animal products and ß-carotene in vegetables and fruits. Globally, vitamin A deficiency is a huge health problem, but in the industrialized world excess of vitamin A has been suggested to be a risk factor for secondary osteoporosis and enhanced susceptibility to fractures. Preclinical studies unequivocally have shown that increased amounts of vitamin A cause decreased cortical bone mass and weaker bones due to enhanced periosteal bone resorption. Initial clinical studies demonstrated a negative association between intake of vitamin A, as well as serum levels of vitamin A, and bone mass and fracture susceptibility. In some studies, these observations have been confirmed, but in other studies no such associations have been observed. One meta-analysis found that both low and high serum levels of vitamin A were associated with increased relative risk of hip fractures. Another meta-analysis also found that low levels of serum vitamin A increased the risk for hip fracture but could not find any association with high serum levels of vitamin A and hip fracture. It is apparent that more clinical studies, including large numbers of incident fractures, are needed to determine which levels of vitamin A that are harmful or beneficial for bone mass and fracture. It is the aim of the present review to describe how vitamin A was discovered and how vitamin A is absorbed, metabolized and is acting as a ligand for nuclear receptors. The effects by vitamin A in preclinical studies are summarized and the clinical investigations studying the effect by vitamin A on bone mass and fracture susceptibility are discussed in detail.

Vitamin A Status Modulates Epithelial Mesenchymal Transition in the Lung: The Role of Furin

Vitamin A deficiency (VAD) induced TGF-β hyperactivation and reduced expression of cell adhesion proteins in the lung, suggesting that the disruption of retinoic acid (RA) signaling leads to epithelial-mesenchymal transition (EMT). To elucidate the role of lung vitamin A status in EMT, several EMT markers and the expression of the proprotein convertase furin, which activates TGF-β, were analyzed in two experimental models. Our in vivo model included control rats, VAD rats, and both control rats and VAD rats, treated with RA. For the in vitro studies, human bronchoalveolar epithelial cells treated with RA were used. Our data show that EMT and furin are induced in VAD rats. Furthermore, furin expression continues to increase much more markedly after treatment of VAD rats with RA. In control rats and cell lines, an acute RA treatment induced a significant increase in furin expression, concomitant with changes in EMT markers. A ChIP assay demonstrated that RA directly regulates furin transcription. These results emphasize the importance of maintaining vitamin A levels within the physiological range since both levels below and above this range can cause adverse effects that, paradoxically, could be similar. The role of furin in EMT is discussed.

Vitamin A homeostasis and cardiometabolic disease in humans: lost in translation?

Vitamin A (retinol) is an essential, fat-soluble vitamin that plays critical roles in embryonic development, vision, immunity, and reproduction. Severe vitamin A deficiency results in profound embryonic dysgenesis, blindness, and infertility. The roles of bioactive vitamin A metabolites in regulating cell proliferation, cellular differentiation, and immune cell function form the basis of their clinical use in the treatment of dermatologic conditions and hematologic malignancies. Increasingly, vitamin A also has been recognized to play important roles in cardiometabolic health, including the regulation of adipogenesis, energy partitioning, and lipoprotein metabolism. While these roles are strongly supported by animal and in vitro studies, they remain poorly understood in human physiology and disease. This review briefly introduces vitamin A biology and presents the key preclinical data that have generated interest in vitamin A as a mediator of cardiometabolic health. The review also summarizes clinical studies performed to date, highlighting the limitations of many of these studies and the ongoing controversies in the field. Finally, additional perspectives are suggested that may help position vitamin A metabolism within a broader biological context and thereby contribute to enhanced understanding of vitamin A's complex roles in clinical cardiometabolic disease.

Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension

AIMS

Vitamin A (VA) deficiency triggers many diseases and is a worldwide nutrition problem. The Retinol acyltransferase (LRAT) is an indicator of VA storage function, and the relationship between LRAT and blood pressure level and the regulation mechanism will be elucidated.

METHODS

160 children aged 6-12 years were included, and the serum VA and, the transcription levels of LRAT and RARs, were measured. Spontaneously hypertensive rats (SHRs) and WKY rats were treated with VA deficiency (VAD) or normal (VAN) fodder for 20 weeks. LRAT, retinoic acid, renin angiotensin system (RAS) biomarkers, and the structure and function of the heart for SHRs were measured.

RESULTS

The serum retinol and serum retinol/BMI levels were lower in children in the low LRAT group (LRAT<P₅₀) compared with the high LRAT group (LRAT≥P₅₀)(0.82 μmol/L vs. 0.94 μmol/L, 0.04 vs. 0.05, all P < .01). Moreover, SBP, DBP, and Ang Ⅱ were lower in the low LRAT group (all P < .01). Compared with VAN-treated SHRs, LRAT, retinoic acid receptor alpha (RARα), ACE2, and Ang (1-7) protein expression levels were decreased, while ACE and AT1R expression levels were increased in VAD SHRs. Notably, heart weight (HW), left ventricle weight, the HW-to-body weight ratio and the left ventricle weight-to-body weight ratio were significantly increased in VAD SHRs compared with those in VAN SHRs (P < .01). Cardiomyocyte hypertrophy and ventricular fibrosis were significantly increased in VAD SHRs compared with those in VAN SHRs (both P < .01).

CONCLUSIONS

LRAT may be an important biomarker of vitamin A deficiency in target organs and may regulate BP by affecting RAS biomarkers.

Adequate vitamin A liver stores estimated by the modified relative dose response test are positively associated with breastfeeding but not vitamin A supplementation in Senegalese urban children 9-23 months old: A comparative cross-sectional study

Vitamin A supplementation (VAS) in 6-59-month-old children is recommended but its sustainability is currently questioned. In Senegal, available data suggest that VAS should be maintained, but geographic and age-related specificities need to be addressed to better implement and target VAS programming. The objective of this comparative cross-sectional study, conducted in urban settings of Dakar, was to compare the vitamin A liver stores (VALS) assessed using the modified-relative dose response (MRDR) test between supplemented and non-supplemented 9-23 month-old children and to study their relationship with VAS. The supplemented group (n = 119) received VAS (either 100 000 UI or 200 000 UI) 2 to 6 months before evaluation while the non-supplemented group (n = 110) had not received VAS during the past 6 months. In addition to MRDR, serum retinol concentrations (SR), and biomarkers of subclinical inflammation were measured. Children's health-related data and feeding patterns were collected. Mean MRDR values (VAS: 0.030 ± 0.017, non-VAS: 0.028 ± 0.016, P = 0.389) and inflammation-adjusted SR (VAS: 1.34 ± 0.37, non-VAS: 1.3 ± 0.35, P = 0.515) of children were adequate. Low prevalence of VALS (VAS: 5.2%, non-VAS: 5.4%) and inflammation-adjusted VAD (VAS: 2.6%, non-VAS: 0.9%) were detected despite high presence of infections and inflammation. Children were mostly still being breastfed (VAS: 85.7%, non-VAS: 77.3%) and complementary feeding indicators were similar in both groups. Only breastfeeding was associated with VALS and was found to reduce by 76% at least, the odds of VAD (adjusted OR = 0.24, 95% CI: 0.07-0.8, P = 0.020). Based on MRDR values, VAS was not related to improved VALS and SR as well as VAD reduction among these children with adequate VALS. Reinforcing breastfeeding advocacy and morbidity prevention/control are essential in this setting. Scaling-back VAS in this subpopulation should be examined regarding the risk of hypervitaminosis A after an evaluation of dietary vitamin A intake sufficiency and a more quantitative assessment of VALS.

Dietary vitamin A deficiency reduces growth performance, immune function of intestine, and alters tight junction proteins of intestine for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

This study was carried out to investigate the effects of dietary vitamin A (VA) on growth performance, antioxidant capacity, digestion, intestinal immune response, and mRNA expression of intestinal tight junction proteins for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Six isonitrogenous and isolipidic experimental diets were formulated to obtain VA levels (317, 1136, 2038, 4142, 7715, 15204 IU/kg diet, respectively). The triplicate groups of fish (average weight of 9.01 ± 0.27 g) were fed twice daily (8:00 and 16:00) for 7 weeks. Based on the broken-line analysis model of WG and LYZ activity, the dietary VA requirement of hybrid grouper were estimated to be 2688.58 and 4096.36 IU/kg diet. The results showed that VA deficiency or excess could reduce Weight gain, specific growth rate, and protein efficiency ratio, and increase feed conversion ratio and hepatosomatic index (P < 0.05). In addition, VA deficiency could reduce the serum activities of acid phosphatase (ACP), superoxide dismutase, and total antioxidant capacity and increase the malondialdehyde content (P < 0.05). VA deficiency also could reduce intestinal activities of ACP, alkaline phosphatase, lysozyme, complement 3, complement 4 contents, and activities of alpha-amylase, lipase, and trypsin (P < 0.05). Meanwhile, VA deficiency could reduce villus height in proximal intestine (PI) and mid intestine (MI), as well as muscle thickness in PI and distal intestine (DI) (P < 0.05). Moreover, VA deficiency could down-regulated antimicrobial peptides (β-defensin, Hepcidin [not in MI and DI], Epinecidin), anti-inflammatory cytokines (interleukin 10 and transforming growth factor β1 [not in DI]), tight junction proteins (occluding and claudin3) mRNA levels in the PI, MI and DI, and up-regulated pro-inflammatory cytokines (tumor necrosis factor α [not in MI] and interleukin 1β [not in MI]), signaling molecules c-Rel and p65 (P < 0.05). Collectively, VA deficiency could reduce growth performance because of a negative effect on intestinal health by depressing digestive abilities, intestinal morphology, immunity and tight junction function in the intestine.

COVID-19: Endogenous Retinoic Acid Theory and Retinoic Acid Depletion Syndrome

This study presents two new concepts and definitions to the medical literature. One of those is "endogenous retinoic acid theory" and the other "retinoic acid depletion syndrome". A new classification will be provided for the immune system: "retinoic acid-dependent component" and "retinoic acid non-dependent component". If this theory is verified, all the diseases where the retinoic acid metabolism is defective and retinoic acid levels are low will be identified and new approaches will be developed fortreating such diseases. When the need for retinoic acids increases, such as acute infection, high fever, severe catabolic process, or chronic antigenic stimulation, cytochrome oxidase enzymes are inhibited by drugs or internal mechanisms. Metabolism and excretion of retinoic acids stored in the liver are prevented. In this way, retinoic acid levels in the blood are raised to therapeutic levels. This is called "Endogenous Retinoic Acid Theory". Retinoic acids also manage their metabolism through feedback mechanisms. Despite compensatory mechanisms, causes such as high fever, serious catabolic process and excessively large viral genome (SARS-CoV-2), excessive use of RIG-I and Type I interferon synthesis pathway using retinoic acid causes emptying of retinoic acid stores. As a result, the RIG-I pathway becomes ineffective, Type I IFN synthesis stops, and the congenital immune system collapses. Then the immune mechanism passes to TLR3, TLR7, TLR8, TLR9, MDA5 and UPS pathways in the monocyte, macrophage, neutrophil and dendritic cells of the adaptive immune defense system that do not require retinoic acid. This leads to excessive TNFα and cytokine discharge from the pathway. With the depletion of retinoic acid stores as a result of this overuse, the immune defense mechanism switches from the congenital immune system to the adaptive immune system, where retinoic acids cannot be used. As a result of this depletion of retinoic acids, the shift of the immune system to the NFκB arm, which causes excessive cytokine release, is called "retinoic acid depletion syndrome". COVID-19 and previously defined sepsis, SIRS and ARDS are each retinoic acid depletion syndrome. We claim that retinoic acid metabolism is defective in most inflammatory diseases, particularly COVID-19 (cytokine storm) sepsis, SIRS and ARDS. Finding a solution to this mechanism will bring a new perspective and treatment approach to such diseases.

Adequate vitamin A rich food consumption and associated factors among lactating mothers visiting child immunization and post-natal clinic at health institutions in Gondar Town, Northwest Ethiopia

BACKGROUND

Vitamin A deficiency is highly prevalent in low-income countries and is a major public health problem worldwide. Lactating mothers are the most vulnerable population group to vitamin A deficiency. Despite this, there is limited study on vitamin A-rich food consumption by lactating mothers in Ethiopia. Therefore, this study aimed to assess adequate vitamin A rich food consumption and associated factors among lactating mothers visiting child immunization and postnatal care centers in health institutions of Gondar Town.

METHODS

An Institution-based cross-sectional study design was employed at a health institution in Gondar Town from February to March 2019, and included 631 study participants. Simple random sampling followed by a systematic sampling technique was used to select participants. The data were collected using the Helen Keller International Food Frequency Questionnaire, entered using Epi-Info 7 statistical software and exported to STATA version 14 for analysis. A multivariable logistic regression analysis was used to identify factors associated with the outcome variable and variables with p-value <0.05 were considered as statistically significant.

RESULT

A total of 624 lactating mothers participated in the study giving a response rate of 98.89%. The study shows adequate consumption of vitamin A-rich food was 38.94% (95% CI: 35%- 43%). Predictors such as attending college diploma and above (AOR = 2.26, 95% CI; 1.02-4.99), having household family size ≤ 3 (AOR = 4.04, 95% CI; 1.60-10.17), being in higher economic class (AOR = 1.93, 95% CI; 1.18-3.14), having dietary diversity score of ≥ 5 (AOR = 1.59, 95% CI; 1.09-2.32) and meal frequency of ≥ 4 (AOR = 1.64, 95% CI; 1.09-2.32) were statistically significant.

CONCLUSION AND RECOMMENDATION

The majority of respondents had inadequate consumption of foods rich in vitamin A. Educational status, family size, wealth index, dietary diversity, and meal frequency were found to be factors that affect adequate consumption of vitamin A-rich foods. Encouraging and educating lactating mothers to consume foods rich in vitamin A is crucial.

Altered nutrient status reprograms host inflammation and metabolic health via gut microbiota

The metabolism of macro- and micronutrients is a complex and highly regulated biological process. An imbalance in the metabolites and their signaling networks can lead to nonresolving inflammation and consequently to the development of chronic inflammatory-associated diseases. Therefore, identifying the accumulated metabolites and altered pathways during inflammatory disorders would not only serve as "real-time" markers but also help in the development of nutritional therapeutics. In this review, we explore recent research that has delved into elucidating the effects of carbohydrate/calorie restriction, protein malnutrition, lipid emulsions and micronutrient deficiencies on metabolic health and inflammation. Moreover, we describe the integrated stress response in terms of amino acid starvation and lipemia and how this modulates new age diseases such as inflammatory bowel disease and atherosclerosis. Lastly, we explain the latest research on metaflammation and inflammaging. This review focuses on multiple signaling pathways, including, but not limited to, the FGF21-β-hydroxybutryate-NLRP3 axis, the GCN2-eIF2α-ATF4 pathway, the von Hippel-Lindau/hypoxia-inducible transcription factor pathway and the TMAO-PERK-FoxO1 axis. Additionally, throughout the review, we explain how the gut microbiota responds to altered nutrient status and also how antimicrobial peptides generated from nutrient-based signaling pathways can modulate the gut microbiota. Collectively, it must be emphasized that metabolic starvation and inflammation are strongly regulated by both environmental (i.e., nutrition, gut microbiome) and nonenvironmental (i.e., genetics) factors, which can influence the susceptibility to inflammatory disorders.

Prevalence of Vitamin A Deficiency among Preschool Children in Ethiopia: A Systematic Review and Meta-Analysis

BACKGROUND

Vitamin A deficiency is a major nutritional concern in lower-income countries. The aim of this systematic review and meta-analysis was to show the magnitude of vitamin A deficiency among preschoolers in Ethiopia.

OBJECTIVE

The present study was aimed at synthesizing qualitatively and quantitatively the existing literature on the prevalence of VAD in preschool children in Ethiopia.

METHODS

Studies were searched through the search engine of Google Scholar, Hinari, MEDLINE/PubMed, Cochrane Library, and Africa-Wide Information. Searching was made using the keywords/MeSH of vitamin A deficiency, xerophthalmia, night blindness, Bitot's spot, retinol, children, and Ethiopia. Data were analyzed and compared with the WHO threshold criteria to declare a public health problem. Heterogeneity among studies was assessed using a Cochran Q test and I 2 statistics. A random-effects model with 95% confidence interval was used for prevalence estimations.

RESULTS

Of the 13 studies included in clinical analysis, 12 of them reported the prevalence of night blindness and/or Bitot's spot among preschool children in Ethiopia which was above WHO cutoff point for the public health problem 1% and 0.5%, respectively. The prevalence of night blindness significantly decreased from moderate public health problem 4.2% (95% CI: 2.8%-5.7%) in a period from 1990 to 2004 to mild public health problem 0.8% (95% CI: 0.6%-1.0%) in a period from 2005 to 2019. Furthermore, statistically insignificant reduction was observed in the prevalence of Bitot's spot in a period from 1990 to 2004, 2.2% (95% CI: 1.3%-3.2%) to 1.8% (95% CI: 1.2%-2.3%) in a period from 2005 to 2019. Among 8 studies on subclinical vitamin A deficiency, 7 of them indicated a severe public health problem (>20%). The prevalence of subclinical vitamin A deficiency decreased from 55.7% (95% CI: 39.8%-71.6%) in a period from 1990 to 2004 to 28.3% (95% CI: 9.8%-46.7%) in a period from 2005 to 2019, but not statistically significant.

CONCLUSIONS

Despite the reduced proportion of night blindness and Bitot's spot, still both clinical and subclinical vitamin A deficiencies remain a public health problem in Ethiopia requiring strengthen intervention through the newly initiated health extension program.

Pro-vitamin A carotenoid content of 48 plantain (Musa AAB genome) cultivars sourced from eastern Democratic Republic of Congo

BACKGROUND

Vitamin A deficiency (VAD) is widespread in sub-Saharan Africa (SSA). Unlike in developed countries, where the main source of vitamin A comes from meat, the diet of poor populations in SSA is largely plant based. It is thus important to identify local / popular plants with higher vitamin A content for combating VAD. Banana (including plantains) is an important staple food crop in this region. The identification and promotion of vitamin A-rich banana cultivars could contribute significantly to the alleviation of VAD in areas heavily dependent on the crop. We assessed pro-vitamin A carotenoid (pVACs) content in the fruit pulp of 48 local plantains from eastern Democratic Republic of Congo, to identify cultivars that could help reduce VAD, especially among young children and women of reproductive age.

RESULTS

Mean pVACs content varied from 175-1756 μg/100 gfw in ripe fruits. Significant increases (P < 0.001) in total pVACs content occurred after ripening in all cultivars except 'UCG II'. Retinol activity equivalents (RAE) in ripe fruits ranged from 12-113 μg/100 gfw. Fifteen plantain cultivars, including 'Adili II', 'Nzirabahima', 'Mayayi', 'Buembe', and 'Sanza Tatu' (associated with RAE values of 44 μg/100 gfw and above) can be considered as good sources of pVACs. Modest consumption (250 or 500 gfw) of the fruit pulp of the five best plantain cultivars at ripening stage 5 meets between 39-71% and 44-81% of vitamin A dietary reference intake (DRI) respectively, for children below 5 years old and women of reproductive age.

CONCLUSION

The 15 best plantain cultivars (especially the top 5) could potentially be introduced / promoted as alternative sources of pro-vitamin A in banana-dependent communities, and help to reduce cases of VAD substantially. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Changes in Intestinal Microbiota Are Associated with Islet Function in a Mouse Model of Dietary Vitamin A Deficiency

AIMS

The underlying mechanisms involved in Vitamin A- (VA-) related changes in glucose metabolic disorders remain unclear. Recent evidence suggests that intestinal microbiota is closely linked to the metabolic syndrome. Here, we explored whether and how intestinal microbiota affects glucose homeostasis in VA-deficient diet-fed mice.

METHODS

Six-week-old male C57BL/6 mice were randomly placed on either a VA-sufficient (VAS) or VA-deficient (VAD) diet for 10 weeks. Subsequently, a subclass of the VAD diet-fed mice was switched to a VA-deficient rescued (VADR) diet for an additional 8 weeks. The glucose metabolic phenotypes of the mice were assessed using glucose tolerance tests and immunohistochemistry staining. Changes in intestinal microbiota were assessed using 16S gene sequencing. The intestinal morphology, intestinal permeability, and inflammatory response activation signaling pathway were assessed using histological staining, western blots, quantitative-PCR, and enzyme-linked immunosorbent assays.

RESULTS

VAD diet-fed mice displayed reduction of tissue VA levels, increased area under the curve (AUC) of glucose challenge, reduced glucose-stimulated insulin secretion, and loss of β cell mass. Redundancy analysis showed intestinal microbiota diversity was significantly associated with AUC of glucose challenge and β cell mass. Redundancy analysis showed intestinal microbiota diversity was significantly associated with AUC of glucose challenge and κB signaling pathway activation. Reintroduction of dietary VA to VAD diet-fed mice restored tissue VA levels, endocrine hormone profiles, and inflammatory response, which are similar to those observed following VAS-controlled changes in intestinal microbiota.

CONCLUSIONS

We found intestinal microbiota effect islet function via controlling intestinal inflammatory phenotype in VAD diet-fed mice. Intestinal microbiota influences could be considered as an additional mechanism for the effect of endocrine function in a VAD diet-driven mouse model.

Modulation of Intestinal Immune and Barrier Functions by Vitamin A: Implications for Current Understanding of Malnutrition and Enteric Infections in Children

The micronutrient vitamin A refers to a group of compounds with pleiotropic effects on human health. These molecules can modulate biological functions, including development, vision, and regulation of the intestinal barrier. The consequences of vitamin A deficiency and supplementation in children from developing countries have been explored for several years. These children live in an environment that is highly contaminated by enteropathogens, which can, in turn, influence vitamin A status. Vitamin A has been described to modulate gene expression, differentiation and function of diverse immune cells; however, the underlying mechanisms are not fully elucidated. This review aims to summarize the most updated advances on elucidating the vitamin A effects targeting intestinal immune and barrier functions, which may help in further understanding the burdens of malnutrition and enteric infections in children. Specifically, by covering both clinical and in vivo/in vitro data, we describe the effects of vitamin A related to gut immune tolerance/homeostasis, intestinal barrier integrity, and responses to enteropathogens in the context of the environmental enteric dysfunction. Some of the gaps in the literature that require further research are also highlighted.

Duration of Retinol Isotope Dilution Studies with Compartmental Modeling Affects Model Complexity, Kinetic Parameters, and Calculated Vitamin A Stores in US Women

Background

Retinol isotope dilution (RID) indirectly estimates vitamin A (VA) status. Multicompartment modeling of RID data is used to refine study designs and equations to calculate VA stores. Previous studies suggest that VA in slowly turning over pools is not traced if follow-up is not long enough; however, shorter RID studies are being investigated. Few long-term models have been published.

Objective

We determined the effect of time on mathematical models of VA kinetics, model parameters, and outcomes.

Methods

In this longitudinal study, women (mean ± SD age: 22 ± 3 y; n = 7) were given 2.0 µmol [14,15]-13C2-retinyl acetate. Blood samples were staggered from 4 h to 152 d; the fraction of dose in serum was modeled with compartmental models. Four model-time categories were created: full models that used all data (median: 137 d; range 97-152 d) and truncated shorter studies of 14, 27, and 52 d (range: 42-62 d). Outcomes included number of compartments to adequately model serum data, kinetic parameters, total traced VA mass, and time-to-dose equilibration. To gain insight into longer follow-up, an additional participant was given 17.5 µmol 13C4-VA, and data were modeled as long as enrichment was above baseline (5 y).

Results

Longer follow-up times affected kinetic parameters and outcomes. Compared with the 14-d models, long-term full models required an additional compartment for adequate fit (14.3% compared with 100%; P = 0.0056) and had longer [median (quartile 1, quartile 3)] whole-body half-life [15.0 d (10.5, 72.6 d) compared with 135 d (115, 199 d); P = 0.0006], time-to-dose equilibration [3.40 d (3.14, 6.75 d) compared with 18.9 d (11.2, 25.7 d); P < 0.0001], and total traced mass [166 µmol VA (162, 252 µmol VA) compared with 476 µmol VA (290, 752 µmol VA); P = 0.0031].

Conclusions

Extended RID sampling alters numerous mathematically modeled, time-dependent outcomes in women. Length of study should be considered when using mathematical models for calculating total-body VA stores or kinetic parameters related to VA turnover. This study is registered at www.clinicaltrials.gov as NCT03248700.

Early Life Vitamin C Deficiency Does Not Alter Morphology of Hippocampal CA1 Pyramidal Neurons or Markers of Synaptic Plasticity in a Guinea Pig Model

Approximately 15% of the Western world population, including pregnant women and their children, is characterized as vitamin C (vitC) deficient. In guinea pigs, early life vitC deficiency causes spatial memory deficits, decreased hippocampal volume and neuron numbers, in otherwise clinically healthy animals. We hypothesized that vitC deficiency leads to decreased brain-derived neurotrophic factor and synaptic plasticity markers in selected brain areas (frontal cortex, hippocampus and striatum) and cause morphological changes in cornu ammonis 1 pyramidal neurons of the hippocampus either through a direct effect or indirectly by increased oxidative stress. Fifty-seven female guinea pigs were allocated to three groups receiving either 1390, 100 or 0–50 mg vitC/kg feed for 11 weeks. Dietary vitC levels were reflected in the plasma, cortical and adrenal gland levels, however, redox imbalance was only present in the adrenal glands allowing for the investigation of a direct influence of vitC deficiency on the chosen parameters in the brain. Synaptic plasticity markers were not affected in the investigated brain areas and no differences in isolated pyramidal neuron morphology was recorded. Based on our findings, it appears that vitC deficiency may primarily elicit impaired neuronal function through increased levels of oxidative stress.

Disturbed Vitamin A Metabolism in Non-Alcoholic Fatty Liver Disease (NAFLD)

Vitamin A is required for important physiological processes, including embryogenesis, vision, cell proliferation and differentiation, immune regulation, and glucose and lipid metabolism. Many of vitamin A’s functions are executed through retinoic acids that activate transcriptional networks controlled by retinoic acid receptors (RARs) and retinoid X receptors (RXRs).The liver plays a central role in vitamin A metabolism: (1) it produces bile supporting efficient intestinal absorption of fat-soluble nutrients like vitamin A; (2) it produces retinol binding protein 4 (RBP4) that distributes vitamin A, as retinol, to peripheral tissues; and (3) it harbors the largest body supply of vitamin A, mostly as retinyl esters, in hepatic stellate cells (HSCs). In times of inadequate dietary intake, the liver maintains stable circulating retinol levels of approximately 2 μmol/L, sufficient to provide the body with this vitamin for months. Liver diseases, in particular those leading to fibrosis and cirrhosis, are associated with impaired vitamin A homeostasis and may lead to vitamin A deficiency. Liver injury triggers HSCs to transdifferentiate to myofibroblasts that produce excessive amounts of extracellular matrix, leading to fibrosis. HSCs lose the retinyl ester stores in this process, ultimately leading to vitamin A deficiency. Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome and is a spectrum of conditions ranging from benign hepatic steatosis to non-alcoholic steatohepatitis (NASH); it may progress to cirrhosis and liver cancer. NASH is projected to be the main cause of liver failure in the near future. Retinoic acids are key regulators of glucose and lipid metabolism in the liver and adipose tissue, but it is unknown whether impaired vitamin A homeostasis contributes to or suppresses the development of NAFLD. A genetic variant of patatin-like phospholipase domain-containing 3 (PNPLA3-I148M) is the most prominent heritable factor associated with NAFLD. Interestingly, PNPLA3 harbors retinyl ester hydrolase activity and PNPLA3-I148M is associated with low serum retinol level, but enhanced retinyl esters in the liver of NAFLD patients. Low circulating retinol in NAFLD may therefore not reflect true “vitamin A deficiency”, but rather disturbed vitamin A metabolism. Here, we summarize current knowledge about vitamin A metabolism in NAFLD and its putative role in the progression of liver disease, as well as the therapeutic potential of vitamin A metabolites.

Marginal vitamin A deficiency facilitates Alzheimer's pathogenesis

Deposition of amyloid β protein (Aβ) to form neuritic plaques in the brain is the unique pathological hallmark of Alzheimer's disease (AD). Aβ is derived from amyloid β precursor protein (APP) by β- and γ-secretase cleavages and turned over by glia in the central nervous system (CNS). Vitamin A deficiency (VAD) has been shown to affect cognitive functions. Marginal vitamin A deficiency (MVAD) is a serious and widespread public health problem among pregnant women and children in developing countries. However, the role of MVAD in the pathogenesis of AD remains elusive. Our study showed that MVAD is approximately twofold more prevalent than VAD in the elderly, and increased cognitive decline is positively correlated with lower VA levels. We found that MVAD, mostly prenatal MVAD, promotes beta-site APP cleaving enzyme 1 (BACE1)-mediated Aβ production and neuritic plaque formation, and significantly exacerbates memory deficits in AD model mice. Supplementing a therapeutic dose of VA rescued the MVAD-induced memory deficits. Taken together, our study demonstrates that MVAD facilitates AD pathogenesis and VA supplementation improves cognitive deficits. These results suggest that VA supplementation might be a potential approach for AD prevention and treatment.

Effect of routine prenatal supplementation on vitamin concentrations in maternal serum and breast milk

OBJECTIVE

The aim of the present study was to assess the effect of multivitamin supplements and their different vitamin A sources on retinol concentrations in serum and colostrum milk of postpartum women.

METHODS

This was a retrospective cross-sectional study composed of healthy postpartum women attending two Brazilian private maternity wards (N = 100). According to the type of multivitamin taken during pregnancy, the women were assigned to one of four groups: control group (CG; n = 25), formulation 1 (F1; n = 25), formulation 2 (F2; n = 25), and formulation 3 (F3; n = 25). Blood and colostrum samples were collected under fasting conditions and retinol was analyzed by high-performance liquid chromatography. Dietary vitamin A was assessed using a food frequency questionnaire. Retinol concentrations <20 μg/dL (<0.70 μmol/L) in serum and <60 μg/dL (2.10 μmol/L) in colostrum were considered indicative of vitamin A deficiency.

RESULTS

Of women in the control group, 12% (n = 3) presented serum retinol levels below the cut-off value for adequacy; this was not observed in the supplemented groups. Evaluating the retinol content in breast milk, supplemented groups F1 and F3 presented 4% (n = 1) of inadequacy cases, whereas F2 presented 40% (n = 10). The concentrations found in the F2 and F3 groups were statistically different (P < 0.05).

CONCLUSIONS

The use of multivitamin supplements containing vitamin A during pregnancy prevents vitamin A deficiency regardless of the source administered. In breast milk, supplementation with β-carotene provided a lower concentration of vitamin A compared with retinol.

Effects of vitamin A deficiency in the postnatal mouse heart: role of hepatic retinoid stores

To determine whether hepatic depletion of vitamin A (VA) stores has an effect on the postnatal heart, studies were carried out with mice lacking liver retinyl ester stores fed either a VA-sufficient (LRVAS) or VA-deficient (LRVAD) diet (to deplete circulating retinol and extrahepatic stores of retinyl esters). There were no observable differences in the weights or gross morphology of hearts from LRVAS or LRVAD mice relative to sex-matched, age-matched, and genetically matched wild-type (WT) controls fed the VAS diet (WTVAS), but changes in the transcription of functionally relevant genes were consistent with a state of VAD in LRVAS and LRVAD ventricles. In silico analysis revealed that 58/67 differentially expressed transcripts identified in a microarray screen are products of genes that have DNA retinoic acid response elements. Flow cytometric analysis revealed a significant and cell-specific increase in the number of proliferating Sca-1 cardiac progenitor cells in LRVAS animals relative to WTVAS controls. Before myocardial infarction, LRVAS and WTVAS mice had similar cardiac systolic function and structure, as measured by echocardiography, but, unexpectedly, repeat echocardiography demonstrated that LRVAS mice had less adverse remodeling by 1 wk after myocardial infarction. Overall, the results demonstrate that the adult heart is responsive to retinoids, and, most notably, reducing hepatic VA stores (while maintaining circulating levels of VA) impacts ventricular gene expression profiles, progenitor cell numbers, and response to injury.

The pleiotropic role of vitamin A in regulating mucosal immunity

The effect of vitamin A on mucosal immunity has never been subjected to extensive studies until recently. We started to work in this area in the early 1970s when we observed that children with protein-calorie malnutrition (PCM) often had defective mucosal immunity, judging from the incidence of respiratory tract infections and diarrhea. We reported that these children had depressed secretory IgA (sIgA) levels in their nasal wash fluids. The IgA level in specimens collected from those superimposed with some degrees of vitamin A deficiency state appeared to be more severely affected. In order to better understand the underlying mechanism associated with this condition, we started to study more detail the deficiency state using experimental vitamin A-deficient rats. From a series of experiments using this animal model, we proposed that vitamin A was needed for transport and/or secretion of sIgA across the mucosa. This conclusion was based on the observation that the secretory component of sIgA synthesized by the epithelial cells of these vitamin A deficient animals was adversely affected as compared to the control animals. From that time onward, much progress has been made by several other groups showing that other mechanisms could also influence the integrity and immune function of the mucosa. For instance, recent studies demonstrated that retinoic acid which is a biologically active form of vitamin A has an essential role in mucosal homeostasis, controlling tolerance and immunity in these non-lymphoid tissues. Such a conclusion was made possible by the availability of sophisticated new molecular biology and genetic engineering techniques together with advances in the field of immunoregulation, e.g., the discovery of dendritic cells (DCs) and T helper cell subsets in 1980s, and the role of Toll-like receptors (TLRs) together with other innate immune regulators in controlling adaptive immune response in the early 1990s. These advances provided considerable new insights into the pleiotropic roles of vitamin A including educating mucosal DCs, differentiation of lymphocyte lineages and imprinting them with mucosal-homing properties as well as in regulating tolerance and immunity. The identification of a novel lymphocyte subpopulation, innate lymphoid cells (ILCs), at the beginning of this century has provided us with an additional insight into a new role of vitamin A in regulating homeostasis at the mucosal surface through influencing ILCs. Another new player that regulates intestinal homeostasis and mucosal immune response is microbiota whose composition is known to vary with vitamin A status. So it appears now that the role of vitamin A on mucosal immunity is far beyond regulating the adaptive Th1-Th2 cell response, but is highly pleiotropic and more complicating, e.g., polarizing the phenotype of mucosal DCs and macrophages, directing gut-homing migration of T and B cells, inducing differentiation of effector T cells and Treg subpopulation, balancing mucosal ILCs subpopulation and influencing the composition of microbiota. In this review, I will attempt to bring together these important advances to provide a comprehensive and contemporary perspective on the role of vitamin A in regulating mucosal immunity.

Hierarchical differentiation competence in response to retinoic acid ensures stem cell maintenance during mouse spermatogenesis

Stem cells ensure tissue homeostasis through the production of differentiating and self-renewing progeny. In some tissues, this is achieved by the function of a definitive stem cell niche. However, the mechanisms that operate in mouse spermatogenesis are unknown because undifferentiated spermatogonia (Aundiff) are motile and intermingle with differentiating cells in an 'open' niche environment of seminiferous tubules. Aundiff include glial cell line-derived neurotrophic factor receptor α1 (GFRα1)(+) and neurogenin 3 (NGN3)(+) subpopulations, both of which retain the ability to self-renew. However, whereas GFRα1(+) cells comprise the homeostatic stem cell pool, NGN3(+) cells show a higher probability to differentiate into KIT(+) spermatogonia by as yet unknown mechanisms. In the present study, by combining fate analysis of pulse-labeled cells and a model of vitamin A deficiency, we demonstrate that retinoic acid (RA), which may periodically increase in concentration in the tubules during the seminiferous epithelial cycle, induced only NGN3(+) cells to differentiate. Comparison of gene expression revealed that retinoic acid receptor γ (Rarg) was predominantly expressed in NGN3(+) cells, but not in GFRα1(+) cells, whereas the expression levels of many other RA response-related genes were similar in the two populations. Ectopic expression of RARγ was sufficient to induce GFRα1(+) cells to directly differentiate to KIT(+) cells without transiting the NGN3(+) state. Therefore, RARγ plays key roles in the differentiation competence of NGN3(+) cells. We propose a novel mechanism of stem cell fate selection in an open niche environment whereby undifferentiated cells show heterogeneous competence to differentiate in response to ubiquitously distributed differentiation-inducing signals.

Vitamin A and dendritic cell differentiation

Vitamin A and its active metabolite retinoic acid are essential for the development and function of many tissues including the immune system. The induction of mucosal homing receptors on T and B cells by mucosal dendritic cells (DC) depends on the presence of vitamin A. Recent studies indicate that also the differentiation of CD11b+ DC subsets in the mucosa as well as the spleen depend on vitamin A signalling. As CD11b+ DC subsets exert non-redundant functions in anti-bacterial and anti-fungal immune responses, defects in CD11b+ DC differentiation will contribute to the clinical problems observed during vitamin A deficiency.

Vitamin A deficiency impairs spatial learning and memory: the mechanism of abnormal CBP-dependent histone acetylation regulated by retinoic acid receptor alpha

Vitamin A (VA) is an essential micronutrient. Numerous studies have confirmed that VA deficiency (VAD) leads to a decline in learning and memory function. Our previous studies have demonstrated that retinoic acid nuclear receptor α (RARα) in the hippocampus plays a crucial role in learning and memory, but the exact mechanism for this process is unclear. Epigenetic modifications, particularly histone acetylation, are involved in nervous system development, learning and memory function, and the pathogenesis of neurodegenerative diseases. Histone acetyltransferases (HATs), such as CREB-binding protein (CBP), E1A-binding protein p300 (p300), and p300/CBP-associated factor (PCAF), are critical for regulating memory function. The current study uses RARα and CBP as examples to study the connections between the RA signaling pathway and histone acetylation modification and to reveal the epigenetic mechanism in VAD-induced learning and memory impairment. This study examined the expression of RARα, HATs, acetylated histone H3/H4, and memory-related genes (Zif268, cFos, FosB), as well as the interaction of RARα and CBP in the hippocampus of 8-week-old rats. Additionally, the changes shown in vivo were further assessed in primary cultured neurons with the inhibition or overexpression of RARα. We found significantly lower levels of histone acetylation in the VAD rats. Furthermore, this downregulation, which impairs learning and memory, is induced by the dysregulation of CBP-dependent histone acetylation that is mediated by RARα. This work provides a solid theoretical foundation and experimental basis for the importance of ensuring sufficient nutritional VA during pregnancy and early life to prevent impairments of learning and memory in adulthood.

[Influence of nutritional patterns on the severity of acne in young adults]

Currently, one of discussed questions of acne etiopathogenesis is alimentary factors, in particular, national dietary habits at different regions and the role of diet. The purpose of this research: from the standpoint of evidence-based medicine to reveal the influence of dietary intake (energy value of the diet, macro- and micronutrients content) on the actual severity of acne in young people. We observed 180 respondents aged 15 to 25 years. The main group included 90 patients with moderate to severe acne, who were treated at the Center for Dermatology and prevention of sexually transmitted diseases in Astana, including 38 girls and 52 boys, mean age 20.5 +/- 4.3 years. The control group consisted of 90 apparently healthy subjects (36 girls and 54 boys, mean age 19.8 +/- 4.2 years) without even a single manifestation of non-inflammatory or inflammatory acne elements. Studying the actual food consumption was carried out by a 24-hour (daily) food recall using specially designed questionnaires and albums.

RESULTS

regular meals with excess energy value significantly contributes to the progression of disease severity in young people with acne [the power of influence in young men was 0.43 (43%), girls--0.42 (42%)], the excess of the normal daily requirements for carbohydrates also significantly affect the severity of acne [the power of influence in young men--0.23 (23%), in girls--0.35 (35%)], lack of vitamin A (retinol) and its provitamin (carotene) significantly affect the severity of acne (the power of influence in young men--0.44 (44%) and 0.42 (42%), respectively, in girls--0.46 (46%) and 0.31 (31%), respectively); in young men with severe acne vitamin D deficiency with a force of 0.3 (30%) significantly potentiates the inflammatory process; lack of zinc in the diet significantly affects the severity of the pathological process in severe forms of acne, the power of influence of this micronutrient in young men--0.44 (44%), women--0.34 (34%).

Vitamin A deficiency impairs adaptive B and T cell responses to a prototype monovalent attenuated human rotavirus vaccine and virulent human rotavirus challenge in a gnotobiotic piglet model

Rotaviruses (RV) are a major cause of gastroenteritis in children. Widespread vitamin A deficiency is associated with reduced efficacy of vaccines and higher incidence of diarrheal infections in children in developing countries. We established a vitamin A deficient (VAD) gnotobiotic piglet model that mimics subclinical vitamin A deficiency in children to study its effects on an oral human rotavirus (HRV) vaccine and virulent HRV challenge. Piglets derived from VAD and vitamin A sufficient (VAS) sows were orally vaccinated with attenuated HRV or mock, with/without supplemental vitamin A and challenged with virulent HRV. Unvaccinated VAD control piglets had significantly lower hepatic vitamin A, higher severity and duration of diarrhea and HRV fecal shedding post-challenge as compared to VAS control pigs. Reduced protection coincided with significantly higher innate (IFNα) cytokine and CD8 T cell frequencies in the blood and intestinal tissues, higher pro-inflammatory (IL12) and 2-3 fold lower anti-inflammatory (IL10) cytokines, in VAD compared to VAS control pigs. Vaccinated VAD pigs had higher diarrhea severity scores compared to vaccinated VAS pigs, which coincided with lower serum IgA HRV antibody titers and significantly lower intestinal IgA antibody secreting cells post-challenge in the former groups suggesting lower anamnestic responses. A trend for higher serum HRV IgG antibodies was observed in VAD vs VAS vaccinated groups post-challenge. The vaccinated VAD (non-vitamin A supplemented) pigs had significantly higher serum IL12 (PID2) and IFNγ (PID6) compared to vaccinated VAS groups suggesting higher Th1 responses in VAD conditions. Furthermore, regulatory T-cell responses were compromised in VAD pigs. Supplemental vitamin A in VAD pigs did not fully restore the dysregulated immune responses to AttHRV vaccine or moderate virulent HRV diarrhea. Our findings suggest that that VAD in children in developing countries may partially contribute to more severe rotavirus infection and lower HRV vaccine efficacy.

Vitamin A regulates hypothalamic-pituitary-adrenal axis status in LOU/C rats

The aim of this study was to explore the involvement of retinoids in the hypoactivity and hyporeactivity to stress of the hypothalamic-pituitary-adrenal (HPA) axis in LOU/C rats. We measured the effects of vitamin A deficiency administered or not with retinoic acid (RA) on plasma corticosterone in standard conditions and in response to restraint stress and on hypothalamic and hippocampal expression of corticosteroid receptors, corticotropin-releasing hormone and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in LOU/C rats. Interestingly, under control conditions, we measured a higher plasma concentration of retinol in LOU/C than in Wistar rats, which could contribute to the lower basal activity of the HPA axis in LOU/C rats. Vitamin A deficiency induced an increased HPA axis activity in LOU/C rats, normalized by RA administration. Compared with LOU/C control rats, vitamin A-deficient rats showed a delayed and heightened corticosterone response to restraint stress. The expression of corticosteroid receptors was strongly decreased by vitamin A deficiency in the hippocampus, which could contribute to a less efficient feedback by corticosterone on HPA axis tone. The expression of 11β-HSD1 was increased by vitamin A deficiency in the hypothalamus (+62.5%) as in the hippocampus (+104.7%), which could lead to a higher production of corticosterone locally and contribute to alteration of the hippocampus. RA supplementation treatment restored corticosterone concentrations and 11β-HSD1 expression to control levels. The high vitamin A status of LOU/C rats could contribute to their low HPA axis activity/reactivity and to a protective effect against 11β-HSD1-mediated deleterious action on cognitive performances during ageing.

Inflammation induced by lipopolysaccharide does not prevent the vitamin A and retinoic acid-induced increase in retinyl ester formation in neonatal rat lungs

Vitamin A (VA) plays an important role in post-natal lung development and maturation. Previously, we have reported that a supplemental dose of VA combined with 10% of all-trans-retinoic acid (VARA) synergistically increases retinol uptake and retinyl ester (RE) storage in neonatal rat lung, while up-regulating several retinoid homeostatic genes including lecithin:retinol acyltransferase (LRAT) and the retinol-binding protein receptor, stimulated by retinoic acid 6 (STRA6). However, whether inflammation has an impact on the expression of these genes and thus compromises the ability of VARA to increase lung RE content is not clear. Neonatal rats, 7- to 8-d-old, were treated with VARA either concurrently with lipopolysaccharide (LPS; Expt 1) or 12 h after LPS administration (Expt 2); in both studies, lung tissue was collected 6 h after VARA treatment, when RE formation is maximal. Inflammation was confirmed by increased IL-6 and chemokine (C–C motif) ligand 2 (CCL2) gene expression in lung at 6 h and C-reactive protein in plasma at 18 h. In both studies, LPS-induced inflammation only slightly reduced, but did not prevent the VARA-induced increase in lung RE. Quantitative RT-PCR showed that co-administration of LPS with VARA slightly attenuated the VARA-induced increase of LRAT mRNA, but not of STRA6 or cytochrome P450 26B1, the predominant RA hydroxylase in lung. By 18 h post-LPS, expression had subsided and none of these genes differed from the level in the control group. Overall, the present results suggest that retinoid homeostatic gene expression is reduced modestly, if at all, by acute LPS-induced inflammation and that VARA is still effective in increasing lung RE under conditions of moderate inflammation.

Changes on metabolic parameters induced by acute cannabinoid administration (CBD, THC) in a rat experimental model of nutritional vitamin A deficiency

INTRODUCTION

Vitamin A deficiency can result from malnutrition, malabsorption of vitamin A, impaired vitamin metabolism associated with liver disease, or chronic debilitating diseases like HIV infection or cancer.

BACKGROUND & AIMS

Cannabis administration has been described as a palliative symptom management therapy in such pathological stages. Therefore, this research aimed to study the effects of acute administration of cannabidiol (CBD) or thetrahydrocannabinol (THC) on the levels of retinol in plasma and in the liver, and biochemical parameters related to lipid and glucose metabolism (cholesterolaemia, triglyceridemia and glycemia) in a rat experimental model of vitamin A deficiency.

METHODS

The experimental animal model of Vitamin A deficiency was developed during a 50-day experimental period in which rats consumed a vitamin A-free diet. Cannabidiol (10 mg/kg body weight) or thetrahydrocannabinol (5 mg/kg body weight) were administered intraperitoneally 2 hours prior to sacrifice of the animals.

RESULTS

The nutritional deficiency caused a significant decrease in plasmatic and liver contents of retinol and biochemical parameters of glycemic, lipidic, and mineral metabolism. Acute intraperitoneal administration of Cannabidiol and thetrahydrocannabinol did not improve the indices of vitamin A status in either control or vitamin A-deficient rats. However, it had a significant effect on specific biochemical parameters such as glucose, triglycerides, and cholesterol.

CONCLUSION

Under our experimental conditions, the reported effects of cannabinoid administration on certain signs of nutritional vitamin A deficiency appeared to be mediated through mechanisms other than changes in retinol metabolism or its mobilization after the acute administration of such compounds.

Correlation of vitamin A nutritional status on alpha-tocopherol in the colostrum of lactating women

The adequate supply of vitamins A and E to newborns is essential. However, factors such as maternal nutritional status and nutrient interaction may limit its bioavailability. The aim of this study was to establish nutritional status for vitamins A and E and evaluate the correlation of retinol on colostrum alpha-tocopherol in lactating women. A total of 103 lactating women were recruited at a Brazilian public maternity hospital. Fasting serum and colostrum samples were collected in the immediate post-partum. Retinol and alpha-tocopherol levels were determined by high-performance liquid chromatography and nutritional status for these vitamins was defined from specific cut-off points for serum and colostrum. Mean serum and colostrum retinol (1.49 µmol L(-1) , 2.18 µmol L(-1) ) and alpha-tocopherol (26.4 µmol L(-1) , 26.1 µmol L(-1) ) indicated satisfactory biochemical status. However, we found a prevalence of subclinical deficiency of vitamin A and vitamin E in serum (15.5% and 16%) and colostrum (50% and 60%). Lactating women with serum retinol ≥ 1.05 µmol L(-1) showed an inverse correlation between serum retinol and alpha-tocopherol concentration in the colostrum (P = 0.008, r = -0.28). This association was not observed in serum level < 1.05 µmol L(-1) . The nutritional status of lactating women for vitamins A and E was adequate, although there is a risk of subclinical deficiency. The negative correlation of serum retinol on alpha-tocopherol concentration in the colostrum must be carefully evaluated in situations of vitamin A supplementation, because alpha-tocopherol bioavailability in maternal milk may be compromised.

Vitamin A modulates the expression of genes involved in iron bioavailability

Iron bioavailability seems to be regulated by vitamin A (VA) but the molecular events involved in this mechanism are not well understood. It is also known that retinoids mediate most of their function via interaction with retinoid receptors, which act as ligand-activated transcription factors controlling the expression of a number of target genes. Here, we evaluated the VA effects on the modulation of the levels of mRNA encoding proteins involved in the iron bioavailability, whether in the intestinal absorption process or in the liver iron metabolism. The expression of genes involved in iron intestinal absorption (divalent metal transporter 1, duodenal cytochrome B, ferroportin 1 FPN1, and ferritin) were evaluated in vitro by treating Caco-2 cells with retinoic acid or in vivo by observing the effects of vitamin A deficiency (VAD) in BALB/C mice. Liver hepcidin and ferritin mRNA levels were upregulated by VAD; however, this condition did not promote any change on the expression of those genes that participate in the iron absorption. Moreover, data from the in vitro analysis showed that VA induced FPN1 gene expression by a hepcidin-independent manner. Therefore, the in vivo results support the idea that VAD may not affect iron absorption but would rather affect iron mobilization mechanisms. On the other hand, our results using Caco-2 cells raises the possibility that VA addition to intestinal epithelium may improve iron absorption through the induction of FPN1 gene expression.

Vitamin A status affects obesity development and hepatic expression of key genes for fuel metabolism in Zucker fatty rats

We hypothesized that vitamin A (VA) status may affect obesity development. Male Zucker lean (ZL) and fatty (ZF) rats after weaning were fed a synthetic VA deficient (VAD) or VA sufficient (VAS) diet for 8 weeks before their plasma parameters and hepatic genes' expression were analyzed. The body mass (BM) of ZL or ZF rats fed the VAD diet was lower than that of their corresponding controls fed the VAS diet at 5 or 2 weeks, respectively. The VAD ZL and ZF rats had less food intake than the VAS rats after 5 weeks. The VAD ZL and ZF rats had lower plasma glucose, triglyceride, insulin, and leptin levels, as well as lower liver glycogen content, net mass of epididymal fat, and liver/BM and epididymal fat/BM ratios (ZL only) than their respective VAS controls. VAD rats had lower hepatic Cyp26a1, Srebp-1c, Fas, Scd1, Me1, Gck, and Pklr (ZL and ZF); and higher Igfbp1 (ZL and ZF), Pck1(ZF only), and G6pc (ZF only) mRNA levels than their respective VAS controls. We conclude that ZL and ZF rats responded differently to dietary VA deficiency. VA status affected obesity development and altered the expression of hepatic genes for fuel metabolism in ZF rats. The mechanisms will help us to combat metabolic diseases.

Glycosylation defects underlying fetal alcohol spectrum disorder: a novel pathogenetic model. "When the wine goes in, strange things come out" - S.T. Coleridge, The Piccolomini

Fetal alcohol spectrum disorder (FASD) is an umbrella term used to describe the craniofacial dysmorphic features, malformations, and disturbances in growth, neurodevelopment and behavior occurring in individuals prenatally exposed to alcohol. Fetal alcohol syndrome (FAS) represents the severe end of this spectrum. Many pathophysiological mechanisms have hitherto been proposed to account for the disrupted growth and morphogenesis seen in FAS. These include impaired cholesterol-modification of the Sonic hedgehog morphogen, retinoic acid deficiency, lipoperoxidative damage due to alcohol-induced reactive oxygen species combined with reduced antioxidant defences, and malfunctioning cell adhesion molecules. In this report, we propose a completely novel concept regarding the pathogenesis of FAS. Based on our observation that transferrin isoelectric focusing (TIEF) - the most widely used screening tool for congenital disorders of glycosylation (CDG) - was transiently abnormal in a newborn with FAS and a confirmed maternal history of gestational alcohol abuse, we came to believe that FAS exemplifies a congenital disorder of glycosylation secondary to alcohol-inflicted disruption of (N-linked) protein glycosylation. Various pieces of evidence were found in the literature to substantiate this hypothesis. This observation implies, among others, that one might need to consider the possibility of maternal alcohol consumption in newborns with transient glycosylation abnormalities. We also present an integrated pathophysiological model of FAS, which incorporates all existing theories mentioned above as well as our novel concept. This model highlights the pivotal role of disrupted isoprenoid metabolism in the origination of FAS.

[Activity of enzymatic detoxification systems in the mice liver under conditions of different retinoid provision]

The activity of cellular components of liver detoxification system was studied under the conditions of the absence of vitamin A stores. It is shown that a decrease of p-hydroxylase and N-demethylase activity of cytochrome P-450 simultaneously with a decrease of glutathione-S-transferase activity takes place in the liver microsomal fraction of vitamin A-deficient animals. At the same time the absence of retinoid stores in knock-out animals influences the decrease of only p-hydroxylase activity of cytochrome P-450 system. The increase in glutathione-S-transferase activity is observed in the liver postmicrosomal fraction in mice, kept on vitamin A-deficient diet, while its parametres in knock-out group animals were not statistically different compared to the control.

Endogenous retinoids in the hair follicle and sebaceous gland

Vitamin A and its derivatives (retinoids) are critically important in the development and maintenance of multiple epithelial tissues, including skin, hair, and sebaceous glands, as shown by the detrimental effects of either vitamin A deficiency or toxicity. Thus, precise levels of retinoic acid (RA, active metabolite) are needed. These precise levels of RA are achieved by regulating several steps in the conversion of dietary vitamin A (retinol) to RA and RA catabolism. This review discusses the localization of RA synthesis to specific sites within the hair follicle and sebaceous gland, including their stem cells, during both homeostasis and disease states. It also discusses what is known about the specific roles of RA within the hair follicle and sebaceous gland. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

Spermatogonia differentiation requires retinoic acid receptor γ

Vitamin A is instrumental to mammalian reproduction. Its metabolite, retinoic acid (RA), acts in a hormone-like manner through binding to and activating three nuclear receptor isotypes, RA receptor (RAR)α (RARA), RARβ, and RARγ (RARG). Here, we show that 1) RARG is expressed by A aligned (A(al)) spermatogonia, as well as during the transition from A(al) to A(1) spermatogonia, which is known to require RA; and 2) ablation of Rarg, either in the whole mouse or specifically in spermatogonia, does not affect meiosis and spermiogenesis but impairs the A(al) to A(1) transition in the course of some of the seminiferous epithelium cycles. Upon ageing, this phenomenon yields seminiferous tubules containing only spermatogonia and Sertoli cells. Altogether, our findings indicate that RARG cell-autonomously transduces, in undifferentiated spermatogonia of adult testes, a RA signal critical for spermatogenesis. During the prepubertal spermatogenic wave, the loss of RARG function can however be compensated by RARA, as indicated by the normal timing of appearance of meiotic cells in Rarg-null testes. Accordingly, RARG- and RARA-selective agonists are both able to stimulate Stra8 expression in wild-type prepubertal testes. Interestingly, inactivation of Rarg does not impair expression of the spermatogonia differentiation markers Kit and Stra8, contrary to vitamin A deficiency. This latter observation supports the notion that the RA-signaling pathway previously shown to operate in Sertoli cells also participates in spermatogonia differentiation.

Retinoic acid metabolism links the periodical differentiation of germ cells with the cycle of Sertoli cells in mouse seminiferous epithelium

Homeostasis of tissues relies on the regulated differentiation of stem cells. In the epithelium of mouse seminiferous tubules, the differentiation process from undifferentiated spermatogonia (A(undiff)), which harbor the stem cell functions, to sperm occurs in a periodical manner, known as the "seminiferous epithelial cycle". To identify the mechanism underlying this periodic differentiation, we investigated the roles of Sertoli cells (the somatic supporting cells) and retinoic acid (RA) in the seminiferous epithelial cycle. Sertoli cells cyclically change their functions in a coordinated manner with germ cell differentiation and support the entire process of spermatogenesis. RA is known to play essential roles in this periodic differentiation, but its precise mode of action and its regulation remains largely obscure. We showed that an experimental increase in RA signaling was capable of both inducing A(undiff) differentiation and resetting the Sertoli cell cycle to the appropriate stage. However, these actions of exogenous RA signaling on A(undiff) and Sertoli cells were strongly interfered by the differentiating germ cells of intimate location. Based on the expression of RA metabolism-related genes among multiple cell types - including germ and Sertoli cells - and their regulation by RA signaling, we propose here that differentiating germ cells play a primary role in modulating the local RA metabolism, which results in the timed differentiation of A(undiff) and the appropriate cycling of Sertoli cells. Similar regulation by differentiating progeny through the modulation of local environment could also be involved in other stem cell systems.

Retinoic acid from retinal pigment epithelium induces T regulatory cells

Primary cultured retinal pigment epithelial (RPE) cells can convert T cells into T regulatory cells (Tregs) through inhibitory factor(s) including transforming growth factor β (TGFβ) in vitro. Retinoic acid (RA) enhances induction of CD4(+) Tregs in the presence of TGFβ. We investigated whether RA produced by RPE cells can promote generation of Tregs. We found that in vitro, RA-treated T cells expressed high levels of Foxp3 in the presence of recombinant TGFβ. In GeneChip analysis, cultured RPE cells constitutively expressed RA-associated molecules such as RA-binding proteins, enzymes, and receptors. RPE from normal mice, but not vitamin A-deficient mice, contained significant levels of TGFβ. RPE-induced Tregs from vitamin A-deficient mice failed to suppress activation of target T cells. Only a few Foxp3(+) T cells were found in intraocular cells from vitamin A-deficient experimental autoimmune uveitis (EAU) mice, whereas expression was higher in cells from normal EAU mice. RA receptor antagonist-pretreated or RA-binding protein-siRNA-transfected RPE cells failed to convert CD4(+) T cells into Tregs. Our data support the hypothesis that RPE cells produce RA, thereby enabling bystander T cells to be converted into Tregs through TGFβ promotion, which can then participate in the establishment of immune tolerance in the eye.

[Biochemical features of cancer cachexia under conditions of different provision with vitamin A]

On the model of tumor growth of Guerin's carcinoma and experimental modeling of vitamin A provision the biochemical characteristics of tumor cachexia in animals with malignant tumors and different vitamin A provision status were studied. It is determined that tumor growth in the body, deprived of vitamin A, is characterized by negative nitrogen balance, decrease of glucose, free fatty acids and ketone bodies level in the blood serum, which indicates the increase of cancer cachexia.

A low vitamin A status increases the susceptibility to cigarette smoke-induced lung emphysema in C57BL/6J mice

Chronic obstructive pulmonary disease (COPD) is characterized by chronic airway inflammation. Cigarette smoke has been considered a major player in the pathogenesis of COPD. The inflamed airways of COPD patients contain several inflammatory cells. Vitamin A metabolites have been implicated in the repair of lung damage. Exposure to cigarette smoke has been shown to depress levels of retinol in lungs of rats. The purpose of this study was to investigate if a low, but not deficient, vitamin A status potentiated susceptibility to the development of cigarette smoke-induced lung emphysema in mice. Mice were bred that were the offspring's of 3 generations of mice that were fed a purified diet containing low levels of vitamin A and exposed to cigarette smoke for 3 months, every weekday. Then, levels of 9-cis, 13-cis, and all-trans retinoic acid, retinol and retinyl palmitate were measured in plasma, liver and right lung lobe. The left lung lobe was used to assess mean linear intercept (Lm), as a measure of smoke-induced lung damage. Average feed intakes were not different between treatment groups. We show that both retinol and retinyl palmitate levels were dramatically decreased in the storage organs of mice on the low vitamin A diet (retinol 2-fold in both lung and liver, and retinyl palmitate 5- fold in lung) which shows that the depletion was successful. However, this treatment did not result in the development of lung emphysema. However, smoke exposure led to a significant increase in Lm in mice with a low vitamin A status compared to the room air-breathing controls. Lung levels of acid retinoids were similar in all mice, irrespective of diet or smoke exposure. Concluding, a low vitamin A status increases the susceptibility to the development of cigarette smoke-induced lung emphysema, possibly because of decreased anti-oxidant capacity in the lungs due to locally reduced retinol and retinyl palmitate levels. These observations indicate that human populations with a low vitamin A status and a high prevalence of smoking may be at increased risk of developing lung emphysema.

Evaluation of status of calcium, magnesium, potassium, and sodium levels in biological samples in children of different age groups with normal vision and night blindness

BACKGROUND

The most common cause of blindness in developing countries is vitamin A deficiency. The World Health Organization (WHO) estimates 13.8 million children have some degree of visual loss related to vitamin A deficiency. The causes of night blindness in children are multifactorial and particular consideration has been given to childhood nutritional deficiency, which is the most common problem found in underdeveloped countries. Such deficiency can result in physiological and pathological processes that in turn influence biological sample composition. Vitamin and mineral deficiency prevents more than two billion people from achieving their full intellectual and physical potential.

METHODS

This study was designed to compare the levels of magnesium (Mg), calcium (Ca), potassium (K), and sodium (Na) in scalp hair, serum, blood, and urine of night blindness children in two age groups, (1-5) and (6-10) years, of both genders comparing them to sex- and age-matched controls. A microwave assisted wet acid digestion procedure was developed as a sample pretreatment for the determination of Mg, Ca, K, and Na in biological samples of children with night blindness. The proposed method was validated by using conventional wet digestion and certified reference samples of hair, serum, blood, and urine. The digests of all biological samples were analysed for Mg, Ca, K, and Na by flame atomic absorption spectrometry (FAAS) using an air/acetylene flame.

RESULTS

The results indicated significantly lower levels of Mg, Ca, and K in the biological samples (blood, serum, and scalp hair) of male and female children with night blindness and higher values of Na compared with control subjects of both genders.

CONCLUSIONS

These data present guidance to clinicians and other professionals investigating deficiency of essential mineral elements in biological samples (scalp hair, serum, and blood) of children with night blindness.

A retinoic acid-dependent network in the foregut controls formation of the mouse lung primordium

The developmental abnormalities associated with disruption of signaling by retinoic acid (RA), the biologically active form of vitamin A, have been known for decades from studies in animal models and humans. These include defects in the respiratory system, such as lung hypoplasia and agenesis. However, the molecular events controlled by RA that lead to formation of the lung primordium from the primitive foregut remain unclear. Here, we present evidence that endogenous RA acts as a major regulatory signal integrating Wnt and Tgfbeta pathways in the control of Fgf10 expression during induction of the mouse primordial lung. We demonstrated that activation of Wnt signaling required for lung formation was dependent on local repression of its antagonist, Dickkopf homolog 1 (Dkk1), by endogenous RA. Moreover, we showed that simultaneously activating Wnt and repressing Tgfbeta allowed induction of both lung buds in RA-deficient foreguts. The data in this study suggest that disruption of Wnt/Tgfbeta/Fgf10 interactions represents the molecular basis for the classically reported failure to form lung buds in vitamin A deficiency.

The impact of common micronutrient deficiencies on iodine and thyroid metabolism: the evidence from human studies

Deficiencies of micronutrients are highly prevalent in low-income countries. Inadequate intake of iodine impairs thyroid function and results in a spectrum of disorders. Other common deficiencies of micronutrients such as iron, selenium, vitamin A, and possibly zinc may interact with iodine nutrition and thyroid function. Randomised controlled intervention trials in iodine- and iron-deficient populations have shown that providing iron along with iodine results in greater improvements in thyroid function and volume than providing iodine alone. Vitamin A supplementation given alone or in combination with iodised salt can have a beneficial impact on thyroid function and thyroid size. Despite numerous studies of the effect of selenium on iodine and thyroid metabolism in animals, most published randomised controlled intervention trials in human populations failed to confirm an impact of selenium supplementation on thyroid metabolism. Little evidence is available on interactions between iodine and zinc metabolism.

Control of oxidative phosphorylation by vitamin A illuminates a fundamental role in mitochondrial energy homoeostasis

The physiology of two metabolites of vitamin A is understood in substantial detail: retinaldehyde functions as the universal chromophore in the vertebrate and invertebrate eye; retinoic acid regulates a set of vertebrate transcription factors, the retinoic acid receptor superfamily. The third member of this retinoid triumvirate is retinol. While functioning as the precursor of retinaldehyde and retinoic acid, a growing body of evidence suggests a far more fundamental role for retinol in signal transduction. Here we show that retinol is essential for the metabolic fitness of mitochondria. When cells were deprived of retinol, respiration and ATP synthesis defaulted to basal levels. They recovered to significantly higher energy output as soon as retinol was restored to physiological concentration, without the need for metabolic conversion to other retinoids. Retinol emerged as an essential cofactor of protein kinase Cdelta (PKCdelta), without which this enzyme failed to be activated in mitochondria. Furthermore, retinol needed to physically bind PKCdelta, because mutation of the retinol binding site rendered PKCdelta unresponsive to Rol, while retaining responsiveness to phorbol ester. The PKCdelta/retinol complex signaled the pyruvate dehydrogenase complex for enhanced flux of pyruvate into the Krebs cycle. The baseline response was reduced in vitamin A-deficient lecithin:retinol acyl transferase-knockout mice, but this was corrected within 3 h by intraperitoneal injection of vitamin A; this suggests that vitamin A is physiologically important. These results illuminate a hitherto unsuspected role of vitamin A in mitochondrial bioenergetics of mammals, acting as a nutritional sensor. As such, retinol is of fundamental importance for energy homeostasis. The data provide a mechanistic explanation to the nearly 100-yr-old question of why vitamin A deficiency causes so many pathologies that are independent of retinoic acid action.

Vitamin A facilitates enteric nervous system precursor migration by reducing Pten accumulation

Hirschsprung disease is a serious disorder of enteric nervous system (ENS) development caused by the failure of ENS precursor migration into the distal bowel. We now demonstrate that retinoic acid (RA) is crucial for GDNF-induced ENS precursor migration, cell polarization and lamellipodia formation, and that vitamin A depletion causes distal bowel aganglionosis in serum retinol-binding-protein-deficient (Rbp4(-/-)) mice. Ret heterozygosity increases the incidence and severity of distal bowel aganglionosis induced by vitamin A deficiency in Rbp4(-/-) animals. Furthermore, RA reduces phosphatase and tensin homolog (Pten) accumulation in migrating cells, whereas Pten overexpression slows ENS precursor migration. Collectively, these data support the hypothesis that vitamin A deficiency is a non-genetic risk factor that increases Hirschsprung disease penetrance and expressivity, suggesting that some cases of Hirschsprung disease might be preventable by optimizing maternal nutrition.

Cystitis, pyelonephritis, and urolithiasis in rats accidentally fed a diet deficient in vitamin A

Female Sprague-Dawley rats (n = 100; age, 3 wk) were fed diets that included a vitamin premix and either albumin or milk powder. Rats fed the albumin diet gained weight more slowly than did the other group. Between 19 and 28 wk of being fed the albumin diet, 12 rats died of bacterial cystitis and pyelonephritis. In addition, 2 more rats from the same dietary group developed peritonitis after ovariohysterectomy. Examination of the 44 rats fed the albumin diet that completed the 34-wk experiment revealed pyelonephritis in 68%, cystitis in 66%, urolithiasis in 27%, and nephrolithiasis in 5%. Squamous metaplasia of the transitional epithelium was present in all 44 rats, although other epithelia were histologically normal. Vitamin A deficiency was diagnosed after analyses of blood and liver samples. Analysis of the vitamin premix revealed approximately 25% of the expected amount of vitamin A. Because the milk powder contained sufficient vitamin A, deficiency did not occur in rats fed the milk powder diet. The major consequences of vitamin A deficiency in the rats were squamous metaplasia, bacterial infection, and calculus formation within the urinary tract. This report illustrates the importance of careful formulation and storage of vitamin premixes used in experimental diets. Vitamin A deficiency should be considered in rats with decreased weight gain and urinary tract disease even if ocular lesions are not present.

Application of a key events dose-response analysis to nutrients: a case study with vitamin A (retinol)

The methodology used to establish tolerable upper intake levels (UL) for nutrients borrows heavily from risk assessment methods used by toxicologists. Empirical data are used to identify intake levels associated with adverse effects, and Uncertainty Factors (UF) are applied to establish ULs, which in turn inform public health decisions and standards. Use of UFs reflects lack of knowledge regarding the biological events that underlie response to the intake of a given nutrient, and also regarding the sources of variability in that response. In this paper, the Key Events Dose-Response Framework (KEDRF) is used to systematically consider the major biological steps that lead from the intake of the preformed vitamin A to excess systemic levels, and subsequently to increased risk of adverse effects. Each step is examined with regard to factors that influence whether there is progression toward the adverse effect of concern. The role of homeostatic mechanisms is discussed, along with the types of research needed to improve understanding of dose-response for vitamin A. This initial analysis illustrates the potential of the KEDRF as a useful analytical tool for integrating current knowledge regarding dose-response, generating questions that will focus future research efforts, and clarifying how improved knowledge and data could be used to reduce reliance on UFs.