Vitamin A inadequacy in socioeconomically disadvantaged pregnant Iowan women as assessed by the modified relative dose response (MRDR) test

Breast Milk Retinol Concentrations Reflect Total Liver Vitamin A Reserves and Dietary Exposure in Thai Lactating Women from Urban and Rural Areas

BACKGROUND

Measuring vitamin A (VA) status during lactation is required to inform dietary recommendations. Limited data exist on VA stores in women.

OBJECTIVES

Our objective was to assess VA status in lactating Thai women by measuring total body VA stores (TBSs), serum and breast milk retinol concentrations, and dietary intake.

METHODS

Lactating women (n = 94), 6-8 wk postpartum, were enrolled from rural (Ayutthaya) and urban (Bangkok) areas. TBSs were measured by the 13C-retinol isotope dilution (RID) technique using 2.0 μmol 13C-retinyl acetate and a single blood sample 14 d post-dose. Natural 13C-enrichment was determined in nonenrolled women (n = 11). Estimated total liver VA reserves (TLRs) were determined using assumptions for lactation. Serum, foremilk, and hindmilk samples were analyzed for retinol by HPLC. Dietary VA intake was assessed by FFQ and 24-h dietary recalls for 3 d. Multiple regression and Pearson correlation were used to evaluate relations.

RESULTS

Median VA intakes were 51.8% of 2003 Thai daily recommendations for lactating women, with the majority from animal-source foods. Many women in Ayutthaya consumed liver weekly. Considering TLRs as 50% TBS, 20% and 11% of mothers in Ayutthaya and Bangkok, respectively, showed deficient reserves (≤0.10 μmol retinol/g). Median (quartile 1, quartile 3) serum [1.58 (1.34, 1.91) and 1.52 (1.30, 1.70) μmol/L] and milk [1.88 (1.29, 2.95) and 1.74 (0.96, 2.26) μmol/L] retinol in Ayutthaya and Bangkok, respectively, were normal. Women with deficient TLRs showed low milk retinol concentrations (≤1.0 μmol/L) and consumed less dietary VA, especially from animal-source foods. Breast milk retinol concentrations, especially hindmilk, demonstrated strong correlation with TBSs and TLRs estimated from the RID test.

CONCLUSIONS

Approximately 15% of Thai lactating women had deficient TLRs. Breast milk retinol concentrations in conjunction with dietary intake records show potential to screen mothers at risk of VA deficiency to guide interventions.The Thai Clinical Trials Registry number is TCTR20160824001 for the work in Thailand.

Vitamin A-fortified rice increases total body vitamin A stores in lactating Thai women measured by retinol isotope dilution: a double-blind, randomized, controlled trial

BACKGROUND

Lactating women are at increased risk for vitamin A (VA) deficiency due to demands for breast milk content and limited hepatic stores for women in some countries. Previously, consumption of triple-fortified rice, which included VA, iron, and zinc, successfully improved the VA status of Thai children in whom their total body VA stores (TBSs) were doubled in 2 mo.

OBJECTIVE

This study assessed the efficacy of consuming VA-fortified rice, which delivered 500 µg retinol activity equivalents (RAEs)/d, on TBSs and estimated total liver VA reserves (TLRs) in Thai lactating women using the retinol isotope dilution (RID) test.

METHODS

A randomized controlled trial was conducted with 70 lactating women (n = 35/group) who received either VA-fortified rice (500 µg RAEs/d) or unfortified rice for 14 wk on weekdays only. Serum retinol concentrations (SRs), C-reactive protein, and TBSs were assessed before and after the intervention. The paired 13C-RID test was used to measure TBSs. After a baseline blood sample, 2.0 µmol [14,15]-13C2-retinyl acetate was administered orally. A follow-up blood sample was drawn 14 d later. The RID test was repeated after the intervention.

RESULTS

TBSs increased significantly (P < 0.05) in the intervention group from 240 (182, 316) to 331 (251, 447) [geometric means (95% CIs)] µmol retinol, and this change in TBSs was significantly higher (P < 0.05) than that in the control group [+52.9 (-74, 453) compared with -4.3 (-106, 275) µmol retinol]. Estimated TLRs indicated a high prevalence of VA deficiency among these lactating women. Initial and final SRs did not differ by group and did not change over the course of the intervention.

CONCLUSION

VA-fortified rice improved the VA status of lactating women by increasing TBSs. A targeted approach to disseminate VA interventions among vulnerable groups should be considered in some contexts. This trial was registered at clinicaltrials.gov as NCT03056625.

Systematic Review and Meta-Analysis of the Relative Dose-Response Tests to Assess Vitamin A Status

Vitamin A (VA) is an essential nutrient often lacking in the diets of people in developing countries. Accurate biomarkers of VA status are vital to inform public health policy and monitor interventions. The relative dose-response (RDR) and modified-RDR (MRDR) tests are semi-quantitative screening tests for VA deficiency that have been used in Demographic and Health Surveys and VA intervention studies. A systematic review and meta-analysis of sensitivity and specificity were conducted to summarize the physiological evidence to support the RDR tests as methods to assess VA status and investigate the impact of different pathological and physiological states on the tests. A total of 190 studies were screened for inclusion, with 21 studies comparing the RDR tests with the gold-standard biomarker, liver VA concentration (68% and 80% sensitivity and 85% and 69% specificity for the RDR and MRDR, respectively). Nearly all studies with VA interventions in VA-deficient populations demonstrated a response of the tests to VA intake that would be expected to improve VA status. The impacts of chronic liver disease, protein malnutrition, age, pregnancy and lactation, infection and inflammation, and various other conditions were examined in 51 studies. The RDR and MRDR tests were reported to have been used in 39 observational studies, and the MRDR has been used in at least 6 national micronutrient surveys. The RDR and MRDR are sensitive tests for determining population VA status and assessing VA interventions. Although they are robust to most physiological and pathological states, caution may be warranted when using the tests in neonates, individuals with chronic liver disease, and those with protein or iron malnutrition. Research on further improvements to the tests to increase accessibility, such as sampling breast milk instead of blood or using intramuscular doses in subjects with malabsorption, will allow wider adoption. This review was registered with PROSPERO as CRD42019124180.

Dynamics of vitamin A uptake, storage, and utilization in vocal fold mucosa

Objective

Extrahepatic vitamin A is housed within organ-specific stellate cells that support local tissue function. These cells have been reported in the vocal fold mucosa (VFM) of the larynx; however, it is unknown how vitamin A reaches and is disseminated among VFM target cells, how VFM storage and utilization vary as a function of total body stores, and how these parameters change in the context of pathology. Therefore, in this study, we investigated fundamental VFM vitamin A uptake and metabolism.

Methods

Using cadaveric tissue and serum from human donors representing the full continuum of clinical vitamin A status, we established a concentration range and analyzed the impact of biologic and clinical covariates on VFM vitamin A. We additionally conducted immunodetection of vitamin A-associated markers and pharmacokinetic profiling of orally dosed α-retinyl ester (a chylomicron tracer) in rats.

Results

Serum vitamin A was a significant predictor of human VFM concentrations, suggesting that VFM stores may be rapidly metabolized in situ and replenished from the circulatory pool. On a vitamin A-sufficient background, dosed α-vitamin A was detected in rat VFM in both ester and alcohol forms, showing that, in addition to plasma retinol and local stellate cell stores, VFM can access and process postprandial retinyl esters from circulating chylomicra. Both α forms were rapidly depleted, confirming the high metabolic demand for vitamin A within VFM.

Conclusion

This thorough physiological analysis validates VFM as an extrahepatic vitamin A repository and characterizes its unique uptake, storage, and utilization phenotype.

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Vocal fold mucosa (VFM) is a bone fide extrahepatic vitamin A repository in the larynx.

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VFM rapidly metabolizes vitamin A and can directly access postprandial retinyl esters from chylomicra.

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The VFM vitamin A uptake, storage, and utilization phenotype appears to be comparable in humans and rats.

Overlapping vitamin A interventions in the United States, Guatemala, Zambia, and South Africa: case studies

Vitamin A (VA) deficiency is a serious public health problem, especially in preschool children who are at risk of increased mortality. In order to address this problem, the World Health Organization recommends periodic high-dose supplementation to children 6-59 months of age in areas of highest risk. Originally, supplementation was meant as a short-term solution until more sustainable interventions could be adopted. Currently, many countries are fortifying commercialized common staple and snack foods with retinyl palmitate. However, in some countries, overlapping programs may lead to excessive intakes. Our review uses case studies in the United States, Guatemala, Zambia, and South Africa to illustrate the potential for excessive intakes in some groups. For example, direct liver analysis from 27 U.S. adult cadavers revealed 33% prevalence of hypervitaminosis A (defined as ≥1 μmol/g liver). In 133 Zambian children, 59% were diagnosed with hypervitaminosis A using a retinol isotope dilution, and 16% had ≥5% total serum VA as retinyl esters, a measure of intoxication. In 40 South African children who frequently consumed liver, 72.5% had ≥5% total serum VA as retinyl esters. All four countries have mandatory fortified foods and a high percentage of supplement users or targeted supplementation to preschool children.

Serum retinyl esters are positively correlated with analyzed total liver vitamin A reserves collected from US adults at time of death

Background

Minimal human data exist on liver vitamin A (VA) compared with serum biomarkers. Cutoffs of 5% and 10% total serum VA as retinyl esters (REs) suggest a VA intoxication diagnosis.

Objectives

We compared total liver VA reserves (TLRs) with the percentage of total serum VA as REs to evaluate hypervitaminosis with the use of US adult autopsy samples. Secondary objectives evaluated serum retinol sensitivity, TLRs among lobes, and hepatic α-retinol concentrations, an α-carotene cleavage product.

Design

Matched serum and liver samples were procured from cadavers (n = 27; mean ± SD age: 70.7 ± 14.9 y; range: 49-101 y). TLRs and α-REs were quantified by ultra-performance liquid chromatography. Pearson correlations showed liver and serum associations. Sensitivity and specificity were calculated for >5%, 7.5%, and 10% total serum VA as REs to predict TLRs and for serum retinol <0.7 and 1 μmol/L to predict deficiency.

Results

Serum RE concentrations were correlated with TLRs (r = 0.497, P < 0.001). Nine subjects (33%) had hypervitaminosis A (≥1.0 μmol VA/g liver), 2 of whom had >7.5% total serum VA as REs; histologic indicators corroborated toxicity at 3 μmol/g liver. No subject had >10% total serum VA as REs. Serum retinol sensitivity to determine deficiency (TLRs <0.1 μmol VA/g) was 83% at 0.7 and 1 μmol/L. Hepatic α-retinol was positively correlated with age (P = 0.047), but removing an outlier nullified significance.

Conclusions

This study evaluated serum REs as a biomarker of VA status against TLRs (gold standard), and abnormal histology suggested that 7.5% total serum VA as REs is diagnostic for toxicity at the individual level in adults. The long-term impact of VA supplements and fortificants on VA status is currently unknown. Considering the high prevalence of hypervitaminotic TLRs in this cohort, and given that many countries are adding preformed VA to processed products, population biomarkers diagnosing hypervitaminosis before toxicity are urgently needed. This trial was registered at clinicaltrials.govas NCT03305042.

Flexible opto-electronics enabled microfluidics systems with cloud connectivity for point-of-care micronutrient analysis

In developing countries, the deployment of medical diagnostic technologies remains a challenge because of infrastructural limitations (e.g. refrigeration, electricity), and paucity of health professionals, distribution centers and transportation systems. Here we demonstrate the technical development and clinical testing of a novel electronics enabled microfluidic paper-based analytical device (EE-μPAD) for quantitative measurement of micronutrient concentrations in decentralized, resource-limited settings. The system performs immune-detection using paper-based microfluidics, instrumented with flexible electronics and optoelectronic sensors in a mechanically robust, ultrathin format comparable in size to a credit card. Autonomous self-calibration, plasma separation, flow monitoring, timing and data storage enable multiple devices to be run simultaneously. Measurements are wirelessly transferred to a mobile phone application that geo-tags the data and transmits it to a remote server for real time tracking of micronutrient deficiencies. Clinical tests of micronutrient levels from whole blood samples (n=95) show comparable sensitivity and specificity to ELISA-based tests. These results demonstrate instantaneous acquisition and global aggregation of diagnostics data using a fully integrated point of care system that will enable rapid and distributed surveillance of disease prevalence and geographical progression.

Vitamin A: biomarkers of nutrition for development

Vitamin A is essential for multiple functions in mammals. Without vitamin A, mammals cannot grow, reproduce, or fight off disease. Because of its numerous functions in humans, biomarkers of vitamin A status are quite diverse. Assessment of liver reserves of vitamin A is considered the gold standard because the liver is the major storage organ. However, this measure is not feasible in human studies. Alternative biomarkers of status can be classified as biological, functional, histologic, and biochemical. Historically, signs of xerophthalmia were used to determine vitamin A deficiency. Before overt clinical damage to the eye, individuals who suffer from vitamin A deficiency are plagued by night blindness and longer vision-restoration times. These types of assessments require large population-based evaluations. Therefore, surrogate biochemical measures of vitamin A status, as defined by liver reserves, have been developed. Serum retinol concentrations are a common method used to evaluate vitamin A deficiency. Serum retinol concentrations are homeostatically controlled until liver reserves are dangerously low. Therefore, other biochemical methods that respond to liver reserves in the marginal category were developed. These included dose-response tests and isotope dilution assays. Dose-response tests work on the principle that apo-retinol-binding protein builds up in the liver as liver reserves become depleted. A challenge dose of vitamin A binds to this protein, and serum concentrations increase within a few hours if liver vitamin A concentrations are low. Isotope dilution assays use stable isotopes as tracers of total body reserves of vitamin A and evaluate a wide range of liver reserves. Resources available and study objectives often dictate the choice of a biomarker.

Serum α- and β-Carotene Concentrations Qualitatively Respond to Sustained Carrot Feeding

β-Carotene is a predominant source of vitamin A in developing countries. Genetically selected “high carotene” carrots could have an impact on the vitamin A and antioxidant status of people if widely adopted. A 3 × 3 crossover study in humans ( n = 10) evaluated the difference in uptake and clearance of α- and β-carotene from carrots genetically selected and traditionally bred to have high, typical, or no carotene. Subjects were fed white (0 mg α- and β-carotene/d), orange (1.8 mg α-carotene and 2.6 mg β-carotene/d), or dark-orange (4 mg α-carotene and 7 mg β-carotene/d) carrots in muffins for 11 d, with a 10-d washout phase between treatments. Serum carotenoid and retinol concentrations were measured by HPLC. C-reactive protein (CRP), an indicator of underlying inflammation or infection which may lower serum retinol, was measured at the beginning of each period. A significant treatment effect occurred for serum α- and β-carotene concentrations ( P < 0.001), and a trend towards a negative effect of subjects’ BMI on concentrations ( P= 0.08). A significant treatment by sequence interaction was observed ( P = 0.038), which was attributable to a difference in serum α- and β-carotene concentrations between carrot treatments in the first period. Serum retinol remained stable for the first 20 d of the intervention and then decreased ( P = 0.02). CRP was not elevated in any subject. High carotene carrots provide more provitamin A carotenoids than the typical store-bought variety, without a change in flavor. The availability of high carotene carrots could readily increase consumption of β-carotene and potentially impact the vitamin A status of those individuals who are deficient or at risk of depletion.

Does social class predict diet quality?

A large body of epidemiologic data show that diet quality follows a socioeconomic gradient. Whereas higher-quality diets are associated with greater affluence, energy-dense diets that are nutrient-poor are preferentially consumed by persons of lower socioeconomic status (SES) and of more limited economic means. As this review demonstrates, whole grains, lean meats, fish, low-fat dairy products, and fresh vegetables and fruit are more likely to be consumed by groups of higher SES. In contrast, the consumption of refined grains and added fats has been associated with lower SES. Although micronutrient intake and, hence, diet quality are affected by SES, little evidence indicates that SES affects either total energy intakes or the macronutrient composition of the diet. The observed associations between SES variables and diet-quality measures can be explained by a variety of potentially causal mechanisms. The disparity in energy costs ($/MJ) between energy-dense and nutrient-dense foods is one such mechanism; easy physical access to low-cost energy-dense foods is another. If higher SES is a causal determinant of diet quality, then the reported associations between diet quality and better health, found in so many epidemiologic studies, may have been confounded by unobserved indexes of social class. Conversely, if limited economic resources are causally linked to low-quality diets, some current strategies for health promotion, based on recommending high-cost foods to low-income people, may prove to be wholly ineffective. Exploring the possible causal relations between SES and diet quality is the purpose of this review.

Evaluation of vitamin A supplementation regimens in Ghanaian postpartum mothers with the use of the modified-relative-dose-response test

BACKGROUND

Vitamin A deficiency is an important public health problem in many developing countries. Women of childbearing age and children are documented as the most affected groups.

OBJECTIVE

The objective was to determine the length of time mothers are protected postpartum against vitamin A depletion after receiving either 400,000 IU vitamin A in 2 divided doses or 200,000 IU as a single dose plus a placebo 24 h apart.

DESIGN

Mothers (n = 168) were recruited by trained fieldworkers 7-10 d after delivery. Modified-relative-dose-response (MRDR) tests were performed at baseline in 167 women, and vitamin A was administered within 6 wk after delivery. The women were randomly assigned to 2 main treatment groups, and each treatment group was divided into 3 follow-up subgroups. Each subgroup was invited back once at month 1, 3, or 5 for a second MRDR test.

RESULTS

The serum retinol concentration and the MRDR value were 1.4 +/- 0.5 micromol/L and 0.048 +/- 0.037, respectively, at baseline. A significant improvement in vitamin A status occurred after vitamin A treatment as assessed by the MRDR test (P < 0.0001). Serum retinol concentrations were not different after vitamin A treatment (P = 0.87).

CONCLUSIONS

The mothers had marginally depleted liver reserves of vitamin A at baseline on the basis of MRDR test results. Liver reserves of vitamin A significantly improved in both treatment groups, and the improvement was maintained for >or= 5 mo.

Assessing vitamin A status: past, present and future

Xerophthalmia classification was traditionally used to identify populations with vitamin A deficiency. Currently, night blindness and dark adaptometry have been proposed as population assessment methods. While eye signs and function tests are still used in areas where vitamin A deficiency is severe, a subclinical vitamin A deficiency is more prevalent. Serum and breast milk retinol concentrations are used to identify vitamin A deficiency risk. However, in healthy individuals, serum retinol concentrations are homeostatically controlled and do not begin to decline until liver reserves of vitamin A are dangerously low. Moreover, serum retinol and retinol binding protein (RBP) concentrations fall during times of infection. The RBP:transthyretin ratio may help to determine if serum retinol concentrations are depressed by infection. Other methods better reflect liver reserves of vitamin A, the "gold" standard. The relative dose response and modified relative dose response tests involve giving a small dose of retinyl or dehydroretinyl ester, respectively, and determining a response in the serum at about 5 h. A new response test where retinoyl beta-glucuronide is administered and the degree of hydrolysis to retinoic acid is measured has been investigated. Unlike isotope dilution tests, the dose response tests lack utility in defining the total body reserve of vitamin A. The deuterated retinol isotope dilution test has been used in several different groups. Recently, a new isotope assay was developed using 13C-retinyl acetate and gas chromatography-combustion-isotope ratio mass spectrometry for analysis. Thus, having many choices of vitamin A assessment methods, laboratory sophistication and resources available will usually dictate which methods are chosen.

Vitamin A in dietary supplements and fortified foods: too much of a good thing?

Vitamin A consumption by many Americans is quite high, in part because of the consumption of fortified foods and the use of vitamin supplements. Most multivitamin supplements provide two or more times the recommended dietary allowance (RDA) for vitamin A because the daily value (DV) is based on 1968 and not current RDAs. Consumption of just one multivitamin often provides excessive vitamin A, the majority of it as preformed vitamin A esters. Given recent epidemiologic evidence that suggests a link between chronic intakes of vitamin A that exceed the RDA and hip fractures, it may be time to reexamine food and supplement fortification policies and to discontinue the clinical practice of prescribing two multivitamins to the elderly and other patients whose needs for certain micronutrients are high.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Increased fibronectin deposition in embryonic hearts of retinol-binding protein-null mice

Precise regulation of retinoid levels is critical for normal heart development. Retinol-binding protein (RBP), an extracellular retinol transporter, is strongly secreted by cardiogenic endoderm. This study addresses whether RBP gene ablation affects heart development. Despite exhibiting an >85% decrease in serum retinol, adult RBP-null mice are viable, breed, and have normal vision when maintained on a vitamin A-sufficient diet. Comparison of RBP-null with wild-type (WT) hearts from embryos at day 9.0 (E9.0) through E12.5 revealed an RBP-null phenotype similar to that of other retinoid-deficient models. At an early stage, RBP-null hearts display retarded trabecular development, which recovers by E9.5. This is accompanied at E9.5 and E10.5 by precocious differentiation of subepicardial cardiac myocytes. Most remarkably, RBP-null hearts display augmented deposition of fibronectin protein in the cardiac jelly at E9.0 through E10.5 and in the outflow tract at E12.5. This phenomenon, which was detected by immunohistochemistry and Western blotting without increased fibronectin transcript levels, is accompanied by increased numbers of mesenchymal cells in the outflow tract but not in the atrioventricular canal. RBP-null cardiac myocytes, especially in the subepicardial layer, display increased cell proliferation. This phenotype may present a model of subclinical retinoid insufficiency characterized by alteration of an extracellular matrix component and altered cellular differentiation and proliferation, changes that may have functional consequences for adult cardiac function. This murine model may have relevance to fetal development in human populations with inadequate retinoid intake.

Vitamin A and iron status are improved by vitamin A and iron supplementation in pregnant Indonesian women

In Indonesia, deficiencies of vitamin A and iron are of public health concern during pregnancy. We sought to determine the effects of vitamin A and iron supplementation on the vitamin A and iron status of pregnant Indonesian women. The women (n = 27) were randomly assigned to four groups. The modified relative dose response (MRDR) test for vitamin A status and hemoglobin, hematocrit and ferritin values were determined at baseline. Thereafter, daily supplements were administered: placebo [Pl] (n = 7), 8.4 micromol vitamin A [A] (n = 7), 1.07 mmol iron [Fe] (n = 5), and 8.4 micromol vitamin A plus 1.07 mmol iron [A + Fe] (n = 8). Post-treatment tests were performed after 8 wk. The MRDR value was reduced, i.e., vitamin A status improved, more markedly by the combination of vitamin A and iron than by either nutrient alone (P = 0.034). The decrease in the MRDR relative to baseline was significant in the A + Fe group (P = 0.008). Iron status was also significantly improved in these women (P < 0.05) with both iron and vitamin A supplementation. The mechanism of the enhancing effect of iron on the vitamin A-induced reduction in the MRDR is not known.

Effect of vitamin A deficiency on cardiovascular function in the rat

Selected parameters of cardiovascular function were evaluated in vitamin A-deficient rats at 70 days of age. Resting heart rate was increased by an average of 100 bpm (21.4+/-2.7%), whereas resting systolic blood pressure was normal in vitamin A-deficient animals. The maximal contractile force developed per milligram weight of tissue by aortic rings excised from vitamin A-deficient animals was reduced in response to high potassium (-25.0+/-8.7%) and phorbol 12,13-dibutyrate (-36.8+/-8.4%) but was only slightly reduced in response to norepinephrine (-17.8+/-11.1%). Intimal rubbing to remove the endothelium had no effect on the loss in contractile responsiveness, and the relaxant response to acetylcholine was similar between control and vitamin A-deficient tissue groups. This suggests that the decrease in contractility of vascular smooth muscle from the vitamin A-deficient rats did not involve altered release of endothelium-derived vasoactive factors. Western blot analysis suggested a reduction in the protein levels of several differentiation markers including alpha-actin (-22%), calponin (-37%), desmin (-37%), and vinculin (-40%), whereas the level of PKCalpha was unchanged from control values. Our findings indicate a significant decrease in contractile responsiveness of aortic smooth muscle of the vitamin A-deficient rat that may be associated with a down regulation in the expression of contractile-related proteins.

Retinol binding protein as a surrogate measure for serum retinol: studies in vitamin A-deficient children from the Republic of the Marshall Islands

BACKGROUND

Serum retinol is transported by retinol binding protein (RBP), which has one high-affinity binding site for retinol; consequently, the molar ratio of retinol to RBP in the circulation is approximately 1 to 1. In vitamin A deficiency (VAD), both serum retinol and RBP decline. However, the retinol-RBP relation has not been well studied in populations with a high incidence of severe VAD.

OBJECTIVE

The purpose of this study was to determine whether RBP is a good surrogate for serum retinol at the very low retinol concentrations encountered in VAD.

DESIGN

The stoichiometric relation between retinol and RBP was studied in 239 Marshallese children: 65 with severe VAD (< or = 0.35 micromol retinol/L), 94 with moderate VAD (0.36-0.70 micromol retinol/L), and 80 with vitamin A sufficiency (> 0.70 micromol retinol/L).

RESULTS

Excellent correlation between retinol and RBP (r = 0.94) was observed across all retinol concentrations. Severe VAD was predicted with 96% sensitivity and 91% specificity on the basis of an RBP cutoff of < or = 0.48 micromol/L, whereas moderate VAD was predicted with 87% sensitivity and 98% specificity on the basis of an RBP cutoff of < or = 0.70 micromol/L.

CONCLUSIONS

The use of RBP results in the classification of essentially the same children with VAD as does retinol, and RBP is an excellent surrogate for serum retinol. Considering the relative ease of measuring RBP with immunodiagnostic kits compared with that of serum retinol by HPLC, the use of RBP concentrations to assess VAD may be particularly advantageous in field settings. Consequently, measuring RBP concentrations may be a practical alternative to measuring serum retinol in population surveys assessing the prevalence of VAD.

Vitamin A status assessment in rats with (13)C(4)-retinyl acetate and gas chromatography/combustion/isotope ratio mass spectrometry

Vitamin A assessment methods that indirectly determine liver reserves are still in development. The deuterated vitamin A assay has been successfully applied in several population groups, but large doses of vitamin A must be used and the gas chromatography/mass spectrometry analysis is not very sensitive. Therefore, 10,11,14,15-(13)C(4)-retinyl acetate was synthesized using a modified Wittig-Horner procedure. Thereafter, female Sprague-Dawley rats (n = 47) were fed a vitamin A-deficient diet and divided into three groups: low (L), moderate (M) and high (H) vitamin A. Groups L, M and H were supplemented with 35, 70 and 350 nmol of unlabeled retinyl acetate/d for 17 d. On d 18, three rats from each group were killed to determine baseline (13)C levels. Serum was prepared, and livers were collected and stored at -70 degrees C until analyzed with HPLC and gas chromatography/combustion/isotope ratio mass spectrometry. The remaining rats were supplemented with 52 nmol of (13)C(4)-retinyl acetate. Rats were killed on d 1, 2, 4 and 10. The calculated and measured values of total body reserves (TBR) of vitamin A were within 7% of each other overall, and the relationship was linear (r = 0.98, P < 0.0001). The calculated mean TBR were 0.49 +/- 0.03, 0.82 +/- 0.007 and 3.72 +/- 0.40 micromol, and the measured mean TBR were 0.50 +/- 0.045, 0.69 +/- 0.10 and 3.6 +/- 0.29 micromol for groups L, M and H, respectively. In contrast, serum retinol concentrations did not show a difference among the dietary groups: 1.32 +/- 0.14, 1.35 +/- 0.17 and 1.28 +/- 0.15 micromol/L for groups L, M and H, respectively (P = 0.25). In conclusion, this method offers more sensitivity than traditional methods and may be applicable to human vitamin A status assessment when TBR estimations are desired.

Retinoids in embryonal development

The key role of vitamin A in embryonal development is reviewed. Special emphasis is given to the physiological action of retinoids, as evident from the retinoid ligand knockout models. Retinoid metabolism in embryonic tissues and teratogenic consequences of retinoid administration at high doses are presented. Physiological and pharmacological actions of retinoids are outlined and explained on the basis of their interactions as ligands of the nuclear retinoid receptors. Immediate target genes and the retinoid response elements of their promoters are summarized. The fundamental role of homeobox genes in embryonal development and the actions of retinoids on their expression are discussed. The similarity of the effects of retinoid ligand knockouts to effects of compound retinoid receptor knockouts on embryogenesis is presented. Although much remains to be clarified, the emerging landscape offers exciting views for future research.

Mild vitamin A deficiency delays fetal lung maturation in the rat

During late pregnancy, the fetal lung stores surfactant in preparation for extrauterine life. Surfactant deficiency, most often due to prematurity, precipitates respiratory distress syndrome (RDS) of the neonate. Although vitamin A (retinol) and retinoic acid have been shown to enhance the synthesis of phospholipid surfactant components, their effect on surfactant-specific proteins is unclear. No attempt has been made to evaluate the consequences of vitamin A restriction on surfactant phospholipid storage or on the expression of the life-essential surfactant protein-B (SP-B). We induced in rats a partial vitamin A deficiency leading to a 30-60% reduction in blood retinol, a status compatible with maintenance of gestation and absence of gross abnormalities in offspring. At term, lung surfactant phospholipids were reduced by 21%, and the major surfactant phospholipid, disaturated phosphatidylcholine (DSPC), was reduced by 27% in vitamin A-deficient (VAD) fetuses. The decrease in surfactant phospholipids and DSPC correlated linearly with plasma retinol, and reached about 50% in fetuses with the lowest retinol concentrations; it was accompanied by reduced expression of the gene for fatty acid synthase, a key enzyme in the synthetic pathway for surfactant-phospholipid lipid precursors. The amounts of SP-A, SP-B, and SP-C messenger RNAs were decreased by 46%, 32%, and 28%, respectively, in VAD fetuses. Consistently, amounts of SP-A and SP-B proteins were diminished as assessed by Western blotting. The proportion of type II cells determined after SP-B labeling was unchanged in VAD as compared with control lungs. Vitamin A deficiency is therefore a cause of lung maturational delay. In view of its rather large incidence in human populations, it may represent an increased risk for RDS and an aggravating factor for prematurity.

Role of retinoids in renal development: pathophysiological implication

Vitamin A closely modulates nephron endowment at birth. It is also required for the development of renal vasculature. Fetal vitamin A status may thus be responsible for most of the variations in nephron number found in the general population, and may play a major role in the intrauterine programming of chronic renal disease and hypertension.

Mild vitamin A deficiency leads to inborn nephron deficit in the rat

BACKGROUND

Vitamin A plays a critical role in fetal organogenesis, and its severe deficiency during pregnancy is known to result in malformations of several organs, including the kidney. However, the consequences of mild vitamin A deficiency (VAD) has received little attention. In the present study, we examined the effect of in utero exposure to mild VAD on renal organogenesis.

METHODS

A rat model of mild VAD compatible with normal gestation was developed. Plasma retinol was determined by reverse phase HPLC in mothers and fetuses. Nephron counting was performed in kidneys of fetuses and pups issued from control and VAD mothers. Metanephroi explanted from 14-day-old fetuses from both groups were cultured in the presence or absence of retinoic acid (RA), and growth and differentiation were assessed. c-ret expression was analyzed from fetuses exposed in utero to VAD or to normal vitamin A status and also in metanephroi grown in culture with or without RA using RT-PCR.

RESULTS

The 50% reduction in circulating vitamin A levels induced by vitamin A deprivation in pregnant rats did not affect the overall fetal development. However, the number of nephrons was reduced by 20% in 21-day-old VAD fetuses. The number of nephrons was closely correlated with circulating vitamin A level in both VAD and control fetuses. Metanephroi taken from VAD fetuses developed to a lesser extent in vitro, but their capacity to respond to exogenous retinoic acid was not altered. Finally, we found that the expression of the proto-oncogene c-ret was modulated according to the retinoid environment.

CONCLUSION

We conclude that vitamin A supply to the fetus is critical in determining the number of nephrons. Data available thus far on the frequency of mild VAD during pregnancy and on the long-term consequences of inborn nephron deficit highlight the clinical relevance of the present study.

A low molar ratio of retinol binding protein to transthyretin indicates vitamin A deficiency during inflammation: studies in rats and a posterior analysis of vitamin A-supplemented children with measles

To assess whether the molar ratio of retinol-binding protein (RBP) to transthyretin (TTR) is of utility in detecting vitamin A (VA) deficiency during inflammation, we analyzed data from a rat model of endotoxin-induced inflammation and from a previously reported randomized, placebo-controlled trial of VA supplementation in children with acute measles. In rats, both marginal VA deficiency and inflammation were independent causes of low plasma RBP (two-way ANOVA, P < 0.001), whereas plasma TTR concentration was reduced only by inflammation (P < 0.001). The molar ratio of plasma RBP to TTR was reduced (by approximately 50%) only in rats with marginal VA deficiency and inflammation (two-way ANOVA interaction, P < 0.01). Serum retinol concentration, C-reactive protein (CRP, an indicator of inflammation) and the RBP:TTR molar ratio were determined in children with acute measles at baseline and 2 wk after subgroups received a placebo or a 210 micromol VA supplement. The ratio of RBP:TTR was selectively reduced in children in the placebo group with low plasma retinol (<0.35 micromol/L) and elevated CRP (>40 mg/L). In children with a low RBP:TTR molar ratio (<0.30) at baseline, the RBP:TTR ratio increased significantly 2 wk later only in the VA-treated subgroup. These analyses provide evidence that, because RBP is differentially reduced in comparison to TTR during VA deficiency, the combined determination of the concentrations of serum RBP and TTR may provide a promising means of detecting VA deficiency during inflammation.

Vitamin A and embryonic development: an overview

Vitamin A is an essential micronutrient throughout the life cycle. Its active form, retinoic acid via retinoid receptors, is involved in signal transduction pathways regulating development. Both the lack and excess of vitamin A during embryonic development result in congenital malformations. Approaches to examine the function of vitamin A in embryonic development have included treatment with excess retinoids and the use of retinoid receptor knock-out mice, which have provided important insights into the complexity of the retinoid signaling system. A recently explored model is the retinoid ligand knock-out, i.e., the vitamin A-deficient embryo. Early development can be successfully examined in the vitamin A-deficient avian embryo, in which bioactive retinoids can rescue the deficient genotype as well as phenotype. In this model it has been possible to unequivocally link the physiological function of vitamin A to development of heart, embryonal circulatory and central nervous systems and the regulation of heart asymmetry. Several developmental genes regulated by endogenous vitamin A during early embryogenesis have been identified. Retinoid receptors and their endogenous ligands, the vitamin A-active forms, are present in the early embryo. It is the developmentally regulated biogeneration of the vitamin A-active forms via distinct spatio-temporal metabolic pathways that is critically linked to the initiation of retinoid signal transduction during embryonic development.

Vitamin A deficiency and maternal-infant transmissions of HIV in two metropolitan areas in the United States

OBJECTIVE

To determine whether vitamin A deficiency is associated with maternal-infant HIV transmission among HIV-infected pregnant women in two United States cities.

METHODS

Third trimester serum vitamin A levels were evaluated using high-performance liquid chromatography in 133 HIV-infected women who delivered livebirths during May 1986 to May 1994 and whose infants had known HIV infection status.

RESULTS

Sixteen per cent (seven out of 44) of the transmitting mothers and 6% (five out of 89) of the non-transmitting mothers had severe vitamin A deficiency (< 0.70 mumol/l; P = 0.05). Maternal-infant transmission was also associated with prematurity < 37 weeks gestation (P = 0.02), and Cesarean section delivery (P = 0.04), CD4 percentage (P = 0.03) and marginally associated with duration of membrane rupture of > or = 4 h (P = 0.06) by univariate analysis. In a multivariate logistic regression model, severe vitamin A deficiency [adjusted odds ratio (AOR), 5.05; 95% confidence interval (CI), 1.20-21.24], Cesarean section delivery (AOR, 3.75; 95% CI, 1.10-12.87), and prematurity (AOR, 2.25; 95% CI, 1.22-4.13) were associated with transmission after adjusting for CD4+ percentage, and duration of membrane rupture.

CONCLUSION

Increased risk of maternal-infant transmission was associated with severe vitamin A deficiency among non-breastfeeding women in these cohorts from the United States.