Vitamin A deficiency, child health, and survival

Vitamin A deficiency compromises the barrier function of the retinal pigment epithelium

A major cause for childhood blindness worldwide is attributed to nutritional vitamin A deficiency. Surprisingly, the molecular basis of the ensuing retinal degeneration has not been well defined. Abundant expression of the retinoid transporter STRA6 in the retinal pigment epithelium (RPE) and homeostatic blood levels of retinol-binding protein delay vitamin A deprivation of the mouse eyes. Hence, genetic dissection of STRA6 makes mice susceptible to nutritional manipulation of ocular retinoid status. We performed RNA-seq analyses and complemented the data with tests of visual physiology, ocular morphology, and retinoid biochemistry to compare eyes with different vitamin A status. Mild ocular vitamin A deficiency decreased transcripts of photoreceptor transduction pathway-related genes and increased transcripts of oxidative stress pathways. The response was associated with impaired visual sensitivity and an accumulation of fluorescent debris in the retina. Severe vitamin A deficiency did not only impair visual perception but also decreased transcripts of genes encoding cell adhesion and cellular junction proteins. This response altered cell morphology, resulted in significant changes in transport pathways of small molecules, and compromised the barrier function of the RPE. Together, our analyses characterize the molecular events underlying nutritional blindness in a novel mouse model and indicate that breakdown of the outer blood-retinal barrier contributes to retinal degeneration and photoreceptor cell death in severe vitamin A deficiency.

Is beta-carotene consumption associated with thyroid hormone levels?

The thyroid hormones play a pivotal role in various physiological processes, including growth, metabolism regulation, and reproduction. While non-modifiable factors are known to impact thyroid function, such as genetics and age, nutritional factors are also important. Diets rich in selenium and iodine are conventionally acknowledged to be beneficial for the production and release of thyroid hormones. Recent studies have suggested a potential link between beta-carotene, a precursor to vitamin A (retinol), and thyroid function. Beta-carotene is known for its antioxidant properties and has been shown to play a role in the prevention of various clinical conditions such as cancer and cardiovascular and neurological diseases. However, its impact on thyroid function is still unclear. Some studies have suggested a positive association between beta-carotene levels and thyroid function, while others have found no significant effect. Conversely, the hormone produced by the thyroid gland, thyroxine, enhances the conversion of beta-carotene to retinol. Furthermore, vitamin A derivatives are being explored as potential therapeutic options for thyroid malignancies. In this review, we highlight the mechanisms through which beta-carotene/retinol and thyroid hormones interact and review the findings of clinical studies examining the association between beta-carotene consumption and thyroid hormone levels. Our review underscores the need for further research to clarify the relationship between beta-carotene and thyroid function.

Vitamin A: a key coordinator of host-microbe interactions in the intestine

The human intestine is home to a dense community of microbiota that plays a key role in human health and disease. Nutrients are essential regulators of both host and microbial physiology and function as key coordinators of host-microbe interactions. Therefore, understanding the specific roles and underlying mechanisms of each nutrient in regulating the host-microbe interactions will be essential in developing new strategies for improving human health through microbiota and nutrient intervention. This review will give a basic overview of the role of vitamin A, an essential micronutrient, on human health, and highlight recent findings on the mechanisms by which it regulates the host-microbe interactions. [BMB Reports 2023; 56(3): 133-139].

Vitamin A: a key coordinator of host-microbe interactions in the intestine

The human intestine is home to a dense community of microbiota that plays a key role in human health and disease. Nutrients are essential regulators of both host and microbial physiology and function as key coordinators of host-microbe interactions. Therefore, understanding the specific roles and underlying mechanisms of each nutrient in regulating the host-microbe interactions will be essential in developing new strategies for improving human health through microbiota and nutrient intervention. This review will give a basic overview of the role of vitamin A, an essential micronutrient, on human health, and highlight recent findings on the mechanisms by which it regulates the host-microbe interactions. [BMB Reports 2023; 56(3): 133-139].

Sensory Analysis of a Processed Food Intended for Vitamin A Supplementation

Provitamin A and pre-formed vitamin A compounds are essential micronutrients for humans. However, vitamin A deficiency (VAD) affects the health status of nearly 50% of populations in Southeast Asia and sub-Saharan Africa and is especially pronounced in preschool children and pregnant women. The objective of this research was to determine an acceptable flavor/ingredient combination to produce a palatable food product that incorporates sweet potatoes, peanut paste, and chickpeas. We sought to determine the acceptability of the three product formulations and to determine the influence of demographic data on ratings for the sensory attributes of each sample. To address VAD issues, three formulations of a product incorporating sweet potato puree (to increase β-carotene content), pure peanut butter (to provide fat for β-carotene absorption), and chickpeas (to provide a complete protein source), were developed: (1) an unflavored control, and two formulations with added natural seasonings: (2) curry-flavored, and (3) pumpkin spice-flavored. Sensory analysis of the three products showed that the curry-flavored product received the highest acceptability in terms of overall liking, flavor, texture, and appearance (p < 0.001). Since the demographic effect was not statistically significant (p > 0.05), it is highly likely that the curry-flavored product can be implemented in other countries or areas with high acceptability.

A multidisciplinary research agenda for the acceptance of Golden Rice

Purpose

The world is facing serious global food security challenges such as the need for sufficient food for a growing population and an exponential growth in nutrient deficiency disorders. Agricultural biotechnology, such as genetically modified (GM) crops, offers itself as a promising solution to address one or more of these issues. Golden Rice (GR) is an example of a GM crop which contains high amount of β-carotene, a compound which is an antioxidant and a precursor of vitamin A. In spite of GR’s promised potential benefits in combating vitamin A deficiency (VAD) disorders it is still not cultivated. This viewpoint paper aims to present the reader with a need for multidisciplinary research agenda, the outcomes of which can contribute towards the acceptance of GR.

Design/methodology/approach

This viewpoint paper is based on an extensive literature review to identify the “gaps” which contributed to low acceptance of GR. This paper presents a systematic discussion on the importance of GR in tackling VAD and discusses controversies around GR and a scientific approach to tackle them.

Findings

The literature review clearly indicates that there is a huge gap in information substantiating the potential of GR for consumers as well as for the farming community. Addressing these issues can substantially increase the acceptance and cultivation of GR. This viewpoint paper proposes food technologists’ and social scientists’ research agenda for GR and further indicates how the involvement of other research disciplines can improve the acceptance of GR.

Originality/value

The literature review indicates the potential of GR in tackling VAD disorders but clearly lacks information to substantiate these arguments. This paper presents authors’ opinions, urging scientists to take up a multidisciplinary research approach to emancipate GR from the clutches of GM food controversies.

Vitamin A deficiency and xerophthalmia in children of a developed country

AIM

We aim (i) to characterise the clinical features of vitamin A deficiency (VAD) in a small cohort of Australian children; (ii) to determine the effects of VAD; and (iii) to quantify the prevalence of ophthalmic review in this group.

METHODS

Data collected from the charts incorporated patient demographics, laboratory results, past medical history, ophthalmic symptoms and dietary history. Outcome measures were (i) occurrence of VAD in our study population; (ii) presence of associated systemic effects and ocular manifestations in those diagnosed with VAD; and (iii) determination of whether children with VAD had an ophthalmology review.

RESULTS

Fifty-two of the 146 children had VAD; their average age was 8.4 years (range 11 days to 18 years old). In this Australian cohort, the most common pre-existing medical conditions in those children whose vitamin A status was investigated were cystic fibrosis, gastro-oesophageal reflux disease, micronutrient deficiency and short gut syndrome. The most common medical conditions affecting children with measured VAD in this cohort include autism, coeliac disease and cystic fibrosis. A significant association was found between VAD and anaemia and serum iron levels. Of the 146 children, 28 had ophthalmology review, of whom 13 had VAD. The most common reason for ophthalmology review was retinopathy of prematurity; there was only one referral for review for xerophthalmia. There was one case of xerophthalmia referred due to microbial keratitis.

CONCLUSION

Vitamin A deficiency and xerophthalmia do exist in children of developed country. The potential for xerophthalmia should be considered, and there should be a consideration of an ophthalmology review.

Ketocarotenoid Production in Soybean Seeds through Metabolic Engineering

The pink or red ketocarotenoids, canthaxanthin and astaxanthin, are used as feed additives in the poultry and aquaculture industries as a source of egg yolk and flesh pigmentation, as farmed animals do not have access to the carotenoid sources of their wild counterparts. Because soybean is already an important component in animal feed, production of these carotenoids in soybean could be a cost-effective means of delivery. In order to characterize the ability of soybean seed to produce carotenoids, soybean cv. Jack was transformed with the crtB gene from Pantoea ananatis, which codes for phytoene synthase, an enzyme which catalyzes the first committed step in the carotenoid pathway. The crtB gene was engineered together in combinations with ketolase genes (crtW from Brevundimonas sp. strain SD212 and bkt1 from Haematococcus pluvialis) to produce ketocarotenoids; all genes were placed under the control of seed-specific promoters. HPLC results showed that canthaxanthin is present in the transgenic seeds at levels up to 52 μg/g dry weight. Transgenic seeds also accumulated other compounds in the carotenoid pathway, such as astaxanthin, lutein, β-carotene, phytoene, α-carotene, lycopene, and β-cryptoxanthin, whereas lutein was the only one of these detected in non-transgenic seeds. The accumulation of astaxanthin, which requires a β-carotene hydroxylase in addition to a β-carotene ketolase, in the transgenic seeds suggests that an endogenous soybean enzyme is able to work in combination with the ketolase transgene. Soybean seeds that accumulate ketocarotenoids could potentially be used in animal feed to reduce or eliminate the need for the costly addition of these compounds.

Global burden of maternal and child undernutrition and micronutrient deficiencies

Maternal and child undernutrition and micronutrient deficiencies affect approximately half of the world's population. These conditions include intrauterine growth restriction (IUGR), low birth weight, protein-energy malnutrition, chronic energy deficit of women, and micronutrient deficiencies. Although the rates of stunting or chronic protein-energy malnutrition are increasing in Africa, the absolute numbers of stunted children are much higher in Asia. The four common micronutrient deficiencies include those of iron, iodine, vitamin A, and zinc. All these conditions are responsible directly or indirectly for more than 50% of all under-5 deaths globally. According to more recent estimates, IUGR, stunting and severe wasting are responsible for one third of under-5 mortality. About 12% of deaths among under-5 children are attributed to the deficiency of the four common micronutrients. Despite tremendous progress in different disciplines and unprecedented improvement with many health indicators, persistently high undernutrition rates are a shame to the society. Human development is not possible without taking care to control undernutrition and micronutrient deficiencies. Poverty, food insecurity, ignorance, lack of appropriate infant and young child feeding practices, heavy burden of infectious illnesses, and poor hygiene and sanitation are factors responsible for the high levels of maternal and child undernutrition in developing countries. These factors can be controlled or removed by scaling up direct nutrition interventions and eliminating the root conditions including female illiteracy, lack of livelihoods, lack of women's empowerment, and poor hygiene and sanitation.

Membrane receptors and transporters involved in the function and transport of vitamin A and its derivatives

The eye is the human organ most sensitive to vitamin A deficiency because of vision's absolute and heavy dependence on vitamin A for light perception. Studies of the molecular basis of vision have provided important insights into the intricate mechanistic details of the function, transport and recycling of vitamin A and its derivatives (retinoid). This review focuses on retinoid-related membrane receptors and transporters. Three kinds of mammalian membrane receptors and transporters are discussed: opsins, best known as vitamin A-based light sensors in vision; ABCA4, an ATP-dependent transporter specializes in the transport of vitamin A derivative; and STRA6, a recently identified membrane receptor that mediates cellular uptake of vitamin A. The evolutionary driving forces for their existence and the wide spectrum of human diseases associated with these proteins are discussed. Lessons learned from the study of the visual system might be useful for understanding retinoid biology and retinoid-related diseases in other organ systems as well. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.

The membrane receptor for plasma retinol-binding protein, a new type of cell-surface receptor

Vitamin A is essential for diverse aspects of life ranging from embryogenesis to the proper functioning of most adult organs. Its derivatives (retinoids) have potent biological activities such as regulating cell growth and differentiation. Plasma retinol-binding protein (RBP) is the specific vitamin A carrier protein in the blood that binds to vitamin A with high affinity and delivers it to target organs. A large amount of evidence has accumulated over the past decades supporting the existence of a cell-surface receptor for RBP that mediates cellular vitamin A uptake. Using an unbiased strategy, this specific cell-surface RBP receptor has been identified as STRA6, a multitransmembrane domain protein with previously unknown function. STRA6 is not homologous to any protein of known function and represents a new type of cell-surface receptor. Consistent with the diverse functions of vitamin A, STRA6 is widely expressed in embryonic development and in adult organ systems. Mutations in human STRA6 are associated with severe pathological phenotypes in many organs such as the eye, brain, heart, and lung. STRA6 binds to RBP with high affinity and mediates vitamin A uptake into cells. This review summarizes the history of the RBP receptor research, its expression in the context of known functions of vitamin A in distinct human organs, structure/function analysis of this new type of membrane receptor, pertinent questions regarding its very existence, and its potential implication in treating human diseases.

Lemon grass (Cymbopogon citratus) ameliorates murine spontaneous ileitis by decreasing lymphocyte recruitment to the inflamed intestine

OBJECTIVE

Aberrant leukocyte migration has been implicated in the pathogenesis of inflammatory bowel disease (IBD). Lemon grass is a natural herb that contains citral, which suppresses lymphocyte expression of gut homing molecules by inhibiting retinoic acid formation. We therefore hypothesized that lemon grass intake could ameliorate excess migration of leukocytes to the inflamed intestine in chronic ileitis.

METHODS

Migration of fluorescence-labeled T cells to microvessels in the ileal mucosa of SAMP1/Yit mice was monitored using intravital microscopy. In some mice, lemon grass solution was administered for two weeks. For evaluation of the effects on chronic ileitis, mice were treated with lemon grass for 26 weeks.

RESULTS

Surface expression of beta7 and CCR9 on T lymphocytes was stronger in SAMP1/Yit mice than in AKR/J mice. Lemon grass treatment attenuated the surface expression of beta7-integrin and CCR9. The number of adherent lymphocytes to microvessels in chronic inflamed ileum was significantly few when lymphocytes were isolated from lemon grass treated mice. Long-term lemon grass treatment improved ileitis in SAMP1/Yit mice, which was assessed by body weight, histological changes and the infiltration of beta7-positive cells.

CONCLUSION

Lemon grass ameliorated ileitis through decreasing lymphocyte migration by inhibiting beta7-expression, suggesting its therapeutic usefulness for IBD.

Neonatal vitamin A deficiency and its impact on acute respiratory infections among preschool Inuit children

OBJECTIVE

To assess if vitamin A concentration in umbilical cord blood is associated with incidence and severity of respiratory infections in preschool Inuit children from Nunavik (Québec, Canada).

METHOD

The medical charts of 305 children were reviewed from 0 to 5 years of age. The association between vitamin A concentration in umbilical cord plasma and the incidence rates of acute otitis media (AOM), lower respiratory tract infections (LRTIs) and hospitalization rates for LRTIs was evaluated using Poisson regression.

RESULTS

Compared to children with vitamin A concentration > or =20 microg/dl, adjusted rate ratios (RR) for children below 20 microg/dl ranged between 1.06-1.62 for AOM, 1.12-1.34 for LRTIs, and 1.09-1.43 for hospitalization for LRTIs. Most RRs were statistically significant for AOM and LRTIs, but not for hospitalization for LRTIs.

CONCLUSION

Neonatal vitamin A deficiency appears to be a significant risk factor for AOM and LRTIs in this population.

Conversion of beta-carotene to retinal pigment

Vitamin A and its active metabolite retinoic acid (RA)(1) play a major role in development, differentiation, and support of various tissues and organs of numerous species. To assure the supply of target tissues with vitamin A, long-lasting stores are built in the liver from which retinol can be transported by a specific protein to the peripheral tissues to be metabolized to either RA or reesterified to form intracellular stores. Vitamin A cannot be synthesized de novo by animals and thus has to be taken up from animal food sources or as provitamin A carotenoids, the latter being converted by central cleavage of the molecule to retinal in the intestine. The recent demonstration that the responsible beta-carotene cleaving enzyme beta,beta-carotene 15,15'-monooxygenase (Bcmo1) is also present in other tissues led to numerous investigations on the molecular structure and function of this enzyme in several species, including the fruit fly, chicken, mouse, and also human. Also a second enzyme, beta,beta-carotene-9',10'-monooxygenase (Bcmo2), which cleaves beta-carotene eccentrically to apo-carotenals has been described. Retinal pigment epithelial cells were shown to contain Bcmo1 and to be able to cleave beta-carotene into retinal in vitro, offering a new pathway for vitamin A production in another tissue than the intestine, possibly explaining the more mild vitamin A deficiency symptoms of two human siblings lacking the retinol-binding protein for the transport of hepatic vitamin A to the target tissues. In addition, alternative ways to combat vitamin A deficiency of specific targets by the supplementation with beta-carotene or even molecular therapies seem to be the future.

The positive impact of red palm oil in school meals on vitamin A status: study in Burkina Faso

Background

Vitamin A (VA) deficiency is widespread in sub-Saharan Africa and school-age children are a vulnerable group. In Burkina Faso, the production and consumption of red palm oil (RPO) is being promoted as a food supplement for VA. The objective of the study was to assess the impact on serum retinol of adding RPO to school lunch in two test zones of Burkina Faso.

Methods

Over one school year, 15 ml RPO was added to individual meals 3 times a week in selected primary schools in two sites. Serum retinol was measured with HPLC at baseline and exactly 12 months later to take account of seasonality. A simple pre-post test design was used in the Kaya area (north-central Burkina), where 239 pupils from 15 intervention schools were randomly selected for the evaluation. In Bogandé (eastern Burkina), 24 schools were randomised for the controlled intervention trial: 8 negative controls (G1) with only the regular school lunch; 8 positive controls (G2) where the pupils received a single VA capsule (60 mg) at the end of the school year; and 8 schools with RPO through the school year (G3). A random sample of 128 pupils in each school group took part in the evaluation.

Results

In Kaya, serum retinol went from 0.77 ± 0.37 μmol/L at baseline to 1.07 ± 0.40 μmol/L one year later (p < 0.001). The rate of low serum retinol (<0.7 μmol/L) declined from 47.2% to 13.1%. In Bogandé, serum retinol increased significantly (p < 0.001) only in the capsule and RPO groups, going from 0.77 ± 0.28 to 0.98 ± 0.33 μmol/L in the former, and from 0.82 ± 0.3 to 0.98 ± 0.33 μmol/L in the latter. The rate of low serum retinol went from 46.1 to 17.1% in the VA capsule group and from 40.4% to 14.9% in the RPO group. VA-deficient children benefited the most from the capsule or RPO. Female sex, age and height-for-age were positively associated with the response to VA capsules or RPO.

Conclusion

RPO given regularly in small amounts appears highly effective in the reduction of VA deficiency. RPO deserves more attention as a food supplement for VA and as a potential source of rural income in Sahelian countries.

Carotene oxygenases: a new family of double bond cleavage enzymes

Beta,beta-carotene 15,15'-monooxygensae (betaCMOOX) is the key enzyme involved in the metabolism of provitamin A carotenoids to retinal. Although the enzyme has been known for >40 y, it has been only within the last 2 y that the cloning and the molecular characterization of the betaCMOOX from several species was reported in literature. New clones of the carotene metabolizing enzyme have emerged, all belonging to the family of double bond cleavage enzymes, suggesting common ancestry. BetaCMOOX cleaves beta,beta-carotene to retinal in an in vitro activity assay; no apo-carotenals were identified. The second enzyme involved in carotenoid metabolism, beta,beta-carotene 9',10'-dioxygenase, is responsible for the excentric cleavage pathway of carotenoids, cleaving beta,beta-carotene to 10'-apo-carotenal and beta-ionone. In an expression overview, the betaCMOOX was detected in duodenum, liver, kidney and in the lungs of chickens. In mice, the mRNA for the central cleavage enzyme was highly expressed in liver, testes, small intestine, and kidney. betaCMOOX expression was highest in epithelial and endothelial structures in both species. These results suggest that the source of vitamin A originates from carotenoids in the corresponding tissues, in addition to retinol supplied from liver stores.

Molecular analysis of vitamin A formation: cloning and characterization of beta-carotene 15,15'-dioxygenases

Beta-carotene 15,15'-dioxygenase cleaves beta-carotene into two molecules of retinal and is the key enzyme in the metabolism of carotene to vitamin A. Although the enzyme has been known for more than 40 years, all attempts to purify the protein to homogeneity or to clone its gene have failed until recently, when the successful cloning and sequencing of cDNAs encoding enzymes with beta-carotene 15,15'-dioxygenase activity from Drosophila (J. von Lintig and K. Vogt, 2000, J. Biol. Chem. 275, 11915-11920) and chicken (A. Wyss et al., 2000, Biochem. Biophys. Res. Commun. 271, 334-336) were reported. Very soon it became clear, that we have cloned two members of a new family of carotenoid cleaving enzymes. Overall homologies are very high, certain amino acid stretches almost identical. Thus, beta-carotene 15,15'-dioxygenase can be considered as evolutionarily well conserved. These findings open up wide perspectives for further analysis of this important biosynthetic pathway, concerning basic and medical research as well as biotechnological aspects related to vitamin A supply, which are discussed here.

Expression pattern and localization of beta,beta-carotene 15,15'-dioxygenase in different tissues

Beta,beta-carotene 15,15'-dioxygenase cleaves beta,beta-carotene into two molecules of retinal, and is the key enzyme in the metabolism of beta,beta-carotene to vitamin A. The enzyme has been known for more than 40 years, yet all attempts to purify the protein to homogeneity have failed. Recently, the successful cloning and sequencing of an enzyme with beta,beta-carotene 15,15'-dioxygenase activity from chicken, as well as from Drosophila, has been reported. Here, we describe in detail our attempt to enrich the chicken beta,beta-carotene 15,15'-dioxygenase to such an extent as to allow determination of partial amino acid sequences, which were then used to design degenerate oligonucleotides. Screening of a chicken duodenal expression library yielded a full-length clone containing a coding sequence of 1578 bp. Functional expression in Escherichia coli and in eukaryotic cell lines confirmed that we had cloned the first vertebrate dioxygenase that cleaves beta,beta-carotene at the central 15,15'-double bond. By performing a sequence homology search, the cDNA sequence of the mouse homologue was found as an expressed sequence tag (EST) in the gene bank. At the amino-acid level, the degree of homology between the chicken and mouse sequences is 81%. Thus beta,beta-carotene 15,15'-dioxygenase can be considered as being an enzyme that is evolutionarily rather well conserved. We established the expression pattern of beta,beta-carotene 15,15'-dioxygenase in chicken and mouse tissues with a combination of Northern blots and in situ hybridization. The mRNA for beta,beta-carotene 15,15'-dioxygenase was localized primarily in duodenal villi, as well as in liver and in tubular structures of lung and kidney. These new findings demonstrate that beta,beta-carotene 15,15'-dioxygenase is also expressed in epithelial structures, where it serves to provide the tissue-specific vitamin A supply.

Micronutrients and infection: interactions and implications with enteric and other infections and future priorities

Symposium presentations have focused on the elegant molecular science and the biologic mechanisms by which micronutrients play critical roles in cellular and humoral immune responses, cellular signaling and function, and even in the evolution of microbial virulence. The concluding session examined the practical issues of how best to evaluate the nutritionally at-risk host, especially in the areas of greatest need-an analytical model of nutrient-immune interactions, implications of nutritional modulation of the immune response for disease, and the implications for international research and child health. This overview illustrated how malnutrition may be a major consequence of early childhood diarrhea and enteric infections, as enteric infections may critically impair intestinal absorptive function with potential long-term consequences for growth and development. The potentially huge, largely undefined DALY (disability-adjusted life years) impact of early childhood diarrheal illnesses demonstrates the importance of quantifying the long-term functional impact of largely preventable nutritional and infectious diseases, especially in children in developing areas.

Cloning and expression of beta,beta-carotene 15,15'-dioxygenase

beta,beta-Carotene 15,15'-dioxygenase cleaves beta-carotene into two molecules of retinal and is therefore the key enzyme in beta-carotene metabolism to vitamin A. In the present study, it was possible to enrich the chicken beta,beta-carotene 15,15'-dioxygenase to such an extent that partial amino acid sequence information could be obtained to design degenerate oligonucleotides. With RT-PCR a cDNA fragment could be obtained and used subsequently in a radioactive screening of a chicken duodenal expression library. We cloned the first eukaryotic beta,beta-carotene 15,15'-dioxygenase which symmetrically cleaves beta-carotene at the 15,15'-double bond.