Retinol is specifically required during midgestation for neonatal survival

Meeting the Vitamin A Requirement: The Efficacy and Importance of β-Carotene in Animal Species

Vitamin A is essential for life in all vertebrate animals. Vitamin A requirement can be met from dietary preformed vitamin A or provitamin A carotenoids, the most important of which is β-carotene. The metabolism of β-carotene, including its intestinal absorption, accumulation in tissues, and conversion to vitamin A, varies widely across animal species and determines the role that β-carotene plays in meeting vitamin A requirement. This review begins with a brief discussion of vitamin A, with an emphasis on species differences in metabolism. A more detailed discussion of β-carotene follows, with a focus on factors impacting bioavailability and its conversion to vitamin A. Finally, the literature on how animals utilize β-carotene is reviewed individually for several species and classes of animals. We conclude that β-carotene conversion to vitamin A is variable and dependent on a number of factors, which are important to consider in the formulation and assessment of diets. Omnivores and herbivores are more efficient at converting β-carotene to vitamin A than carnivores. Absorption and accumulation of β-carotene in tissues vary with species and are poorly understood. More comparative and mechanistic studies are required in this area to improve the understanding of β-carotene metabolism.

Maternal antenatal multiple micronutrient supplementation for long-term health benefits in children: a systematic review and meta-analysis

BACKGROUND

Multiple micronutrient supplementation for pregnant women reduces low birth weight and has been recommended in low- and middle-income countries (LMICs) to improve child survival, growth and health. We aimed to review the evidence from long-term follow-up studies of multiple micronutrient supplementation beginning in the later first or second trimester.

METHODS

We searched systematically for follow-up reports from all trials in a 2015 Cochrane review of multiple micronutrient supplementation in pregnancy. The intervention comprised three or more micronutrients and the comparison group received iron (60 mg) and folic acid (400 μg), where possible. Median gestation of commencement varied from 9 to 23 weeks. Primary outcomes were offspring mortality, height, weight and head circumference, presented as unadjusted differences in means or proportions (intervention minus control). Secondary outcomes included other anthropometry, body composition, blood pressure, and cognitive and lung function.

RESULTS

We found 20 follow-up reports from nine trials (including 88,057 women recruited), six of which used the UNIMMAP supplement designed to provide recommended daily allowances. The age of follow-up ranged from 0 to 9 years. Data for mortality estimates were available from all trials. Meta-analysis showed no difference in mortality (risk difference -0.05 per 1000 livebirths; 95 % CI, -5.25 to 5.15). Six trials investigated anthropometry and found no difference at follow-up in weight-for-age z score (0.02; 95 % CI, -0.03 to 0.07), height-for-age z score (0.01; 95 % CI, -0.04 to 0.06), or head circumference (0.11 cm; 95 % CI, -0.03 to 0.26). No differences were seen in body composition, blood pressure, or respiratory outcomes. No consistent differences were seen in cognitive function scores.

CONCLUSIONS

There is currently no evidence that, compared with iron and folic acid supplementation, routine maternal antenatal multiple micronutrient supplementation improves childhood survival, growth, body composition, blood pressure, respiratory or cognitive outcomes.

Effects of antenatal multiple micronutrient supplementation on lung function in mid-childhood: follow-up of a double-blind randomised controlled trial in Nepal

A randomised trial of prenatal multiple micronutrient supplementation in Nepalese women increased birthweight and weight at 2 years of age in offspring, compared to those born to mothers who only received iron and folic acid supplements. Further follow-up of this cohort provided an opportunity to investigate the effect of antenatal multiple micronutrients on subsequent lung function by measuring spirometry at 7-9 years of age in C: hildren born during the trial. 841 children (80% of the cohort) were seen at mean±sd 8.5±0.4 years. Technically successful spirometry results were obtained in 793 (94.3%) children, 50% of whom had been randomised to micronutrient supplementation. Background characteristics, including anthropometry, were similar in the two allocation groups. Lung function was also similar, mean (95% CI) difference in z-scores (supplementation minus control) was -0.08 (-0.19-0.04), -0.05 (-0.17-0.06) and -0.04 (-0.15-0.07) for forced expiratory volume in 1 s (FEV1), forced vital capacity and FEV1/FVC, respectively. Compared with healthy white children, FEV1 and FVC in the "healthy" Nepalese children were ∼1 (∼13%) z-score lower, with no difference in FEV1/FVC. We conclude that, compared with routine iron and folic acid, multiple micronutrient supplementation during pregnancy has no effect on spirometric lung function in Nepalese children at 8.5 years of age.

Expression of interferon regulatory factor-1 in the mouse cumulus-oocyte complex is negatively related with oocyte maturation

OBJECTIVE

We found previously that interferon regulatory factor (Irf)-1 is a germinal vesicle (GV)-selective gene that highly expressed in GV as compared to metaphase II oocytes. To our knowledge, the function of Irf-1 in oocytes has yet to be examined. The present study was conducted to determine the relationship between retinoic acid (RA) and RA-mediated expression of Irf-1 and the mouse oocyte maturation.

METHODS

Immature cumulus-oocyte-complexes (COCs) were collected from 17-day-old female mice and cultured in vitro for 16 hours in the presence of varying concentrations of RA (0-10 µM). Rate of oocyte maturation and activation was measured. Gene expression was measured by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) and cytokine secretion in the medium was measured by Bio-Plex analysis. Apoptosis was analyzed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.

RESULTS

The rates of oocyte maturation to metaphase II and oocyte activation increased significantly with RA treatment (10 nM-1 µM). With 100 nM RA treatment, lowest level of Irf-1 mRNA and cumulus cell's apoptosis was found. Among 23 cytokines measured by Bio-Plex system, the substantial changes in secretion of tumor necrosis factor-α, macrophage inflammatory protein-1β, eotaxin and interleukin-12 (p40) from COCs in response to RA were detected.

CONCLUSION

We concluded that the maturation of oocytes and Irf-1 expression are negatively correlated, and RA enhances the developmental competence of mouse immature oocytes in vitro by suppressing apoptosis of cumulus cells. Using a mouse model, results of the present study provide insights into improved culture conditions for in vitro oocyte maturation and relevant cytokine production and secretion in assisted reproductive technology.

Vitamins A and E: metabolism, roles and transfer to offspring

Vitamins A and E are essential, naturally occurring, fat-soluble nutrients that are involved in several important biological processes such as immunity, protection against tissue damage, reproduction, growth and development. They are extremely important during the early stages of life and must be transferred adequately to the young during gestation and lactation. The present article presents an overview of their biological functions, metabolism and dynamics of transfer to offspring in mammals. Among other topics, the review focuses on the biochemical aspects of their intestinal absorption, blood transport, tissue uptake, storage and catabolism. It also describes their different roles as well as their use as preventive and therapeutic agents. Finally, the mechanisms involved in their transfer during gestation and lactation are discussed.

Vitamin A deficiency in the late gastrula stage rat embryo results in a one to two vertebral anteriorization that extends throughout the axial skeleton

Vitamin A and its metabolites are known to be involved in patterning the vertebrate embryo. Study of the effect of vitamin A on axial skeletal patterning has been hindered by the fact that deficient embryos do not survive past midgestation. In this study, pregnant vitamin A-deficient rats were maintained on a purified diet containing limiting amounts of all-trans retinoic acid (12 microg atRA/g diet) and given a daily oral bolus dose of retinol starting at embryonic day 0.5, 8.25, 8.5, 8.75, 9.25, 9.5, 9.75, or 10.5. Embryos were recovered at E21.5 for analysis of the skeleton and at earlier times for analysis of select mRNAs. Normal axial skeletal development and patterning were observed in embryos from pregnant animals receiving retinol starting on or before E8.75. Delay of retinol supplementation to E9.5 or later resulted in a marked increase in both occurrence and severity of skeletal malformations, extending from the craniocervical to sacral regions. Embryos from the groups receiving retinol starting at E9.5 and E9.75 had one-vertebral anterior transformations of the cervical, thoracic, lumbar, and sacral vertebrae. Few embryos survived in the E10.5 group, but these embryos yielded the most severe and extensive anteriorization events. The skeletal alterations seen in vitamin A deficiency are associated with posterior shifts in the mesodermal expression of Hoxa-4, Hoxb-3, Hoxd-3, Hoxd-4, and Hoxa-9 mRNAs, whereas the anterior domains of Hoxb-4 and Cdx2 expression are unaltered. This work defines a critical window of development in the late gastrula-stage embryo when vitamin A is essential for normal axial skeletal patterning and shows that vitamin A deficiency causes anterior homeotic transformations extending from the cervical to lumbosacral regions.

The role of vitamin A in mammalian reproduction and embryonic development

Since the late 1980s, there has been an explosion of information on the molecular mechanisms and functions of vitamin A. This review focuses on the essential role of vitamin A in female reproduction and embryonic development and the metabolism of vitamin A (retinol) that results in these functions. Evidence strongly supports that in situ-generated all-trans retinoic acid (atRA) is the functional form of vitamin A in female reproduction and embryonic development. This is supported by the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency with atRA, the block in embryonic development that occurs in retinaldehyde dehydrogenase type 2 null mutant mice, and the essential roles of the retinoic acid receptors, at least in embryogenesis. Early studies of embryos from marginally vitamin A-deficient (VAD) pregnant rats revealed a collection of defects called the vitamin A-deficiency syndrome. The manipulation of all-trans retinoic acid (atRA) levels in the diet of VAD female rats undergoing a reproduction cycle has proved to be an important new tool in deciphering the points of atRA function in early embryos and has provided a means to generate large numbers of embryos at later stages of development with the vitamin A-deficiency syndrome. The essentiality of the retinoid receptors in mediating the activity of atRA is exemplified by the many compound null mutant embryos that now recapitulate both the original vitamin A-deficiency syndrome and exhibit a host of new defects, many of which can also be observed in the VAD-atRA-supported rat embryo model and in retinaldehyde dehydrogenase type 2 (RALDH2) mutant mice. A major task for the future is to elucidate the atRA-dependent pathways that are normally operational in vitamin A-sufficient animals and that are perturbed in deficiency, thus leading to the characteristic VAD phenotypes described above.

Impaired retinol utilization in Adh4 alcohol dehydrogenase mutant mice

Adh4, a member of the mouse alcohol dehydrogenase (ADH) gene family, encodes an enzyme that functions in vitro as a retinol dehydrogenase in the conversion of retinol to retinoic acid, an important developmental signaling molecule. To explore the role of Adh4 in retinoid signaling in vivo, gene targeting was used to create a null mutation at the Adh4 locus. Homozygous Adh4 mutant mice were viable and fertile and demonstrated no obvious defects when maintained on a standard mouse diet. However, when subjected to vitamin A deficiency during gestation, Adh4 mutant mice demonstrated a higher number of stillbirths than did wild-type mice. The proportion of liveborn second generation vitamin A-deficient newborn mice was only 15% for Adh4 mutant mice but 49% for wild-type mice. After retinol administration to vitamin A-deficient dams in order to rescue embryonic development, Adh4 mutant mice demonstrated a higher resorption rate at stage E12.5 (69%), compared with wild-type mice (30%). The relative ability of Adh4 mutant and wild-type mice to metabolize retinol to retinoic acid was measured after administration of a 100-mg/kg dose of retinol. Whereas kidney retinoic acid levels were below the level of detection in all vehicle-treated mice (< 1 pmol/g), retinol treatment resulted in very high kidney retinoic acid levels in wild-type mice (273 pmol/g) but 8-fold lower levels in Adh4 mutant mice (32 pmol/g), indicating a defect in metabolism of retinol to retinoic acid. These findings demonstrate that another retinol dehydrogenase can compensate for a lack of Adh4 when vitamin A is sufficient, but that Adh4 helps optimize retinol utilization under conditions of both retinol deficiency and excess.

ADH1 and ADH4 alcohol/retinol dehydrogenases in the developing adrenal blastema provide evidence for embryonic retinoid endocrine function

Studies on retinoid signaling indicate that much of the regulation of this pathway may involve enzymes that synthesize the active ligand retinoic acid. Alcohol dehydrogenases ADH1 (class I ADH) and ADH4 (class IV ADH) function as retinol dehydrogenases in the oxidation of retinol, a necessary step in the synthesis of retinoic acid from vitamin A. These enzymes as well as retinoic acid have previously been localized in the adult adrenal gland, thus providing evidence that this organ is an endocrine source of retinoic acid. Here, we have examined the involvement of ADH1 and ADH4 in embryonic adrenal function by using transgenic mouse technology and immunohistochemistry. Transgenic mice were generated that contain various portions of the mouse ADH4 promoter and 5'-flanking region fused to lacZ. Embryos harboring a construct containing 9.0 kb of 5'-flanking region displayed very high levels of lacZ expression in the developing adrenal blastemas at embryonic stage E11.5 during the initial phase of mouse adrenal gland development. The presence of endogenous ADH4 protein in stage E11.5 adrenal blastemas was demonstrated by immunohistochemistry, and this was the only site of ADH4 immunodetection in stage E11.5 embryos. Endogenous ADH1 protein was also detected by immunohistochemistry in stage E11.5 adrenal blastemas. ADH1 and ADH4 proteins were detectable at later stages of adrenal development, and both were localized to developing adrenal cortical cells by stage E14.5. The presence of both ADH1 and ADH4 retinol dehydrogenases during the earliest stages of adrenal gland development, combined with our earlier findings of high levels of retinoic acid in the embryonic adrenal gland, suggests that one of the earliest functions of ADH may be to provide an embryonic endocrine source of retinoic acid for growth and development.