Placental vitamin D metabolism and its associations with circulating vitamin D metabolites in pregnant women

High-Dose Vitamin D Supplementation Significantly Affects the Placental Transcriptome

Vitamin D deficiency is a highly prevalent obstetrical concern associated with an increased risk of complications like pre-eclampsia, gestational diabetes, and growth retardation. Vitamin D status in pregnancy is also linked to long-term offspring health, e.g., the risk of obesity, metabolic disease, and neurodevelopmental problems. Despite the suspected role of vitamin D in placental diseases and fetal development, there is limited knowledge on the effect of vitamin D on placental function. Thus, we performed next-generation RNA sequencing, comparing the placental transcriptome from uncomplicated term pregnancies receiving the often-recommended dose of 10 µg vitamin D/day (n = 36) with pregnancies receiving 90 µg/day (n = 34) from late first trimester to delivery. Maternal vitamin D status in the first trimester was also considered. We found that signaling pathways related to cell adhesion, immune function, and neurodevelopment were affected, supporting that increased vitamin D supplementation benefits placental function in established pregnancies without severe vitamin D deficiency, also underlining the importance of vitamin D in brain development. Specific effects of the first trimester vitamin D status and offspring sex were also identified. Further studies are warranted, addressing the optimal vitamin status during pregnancy with a focus on organ-specific vitamin D needs in individual pregnancies.

Evaluation of Vitamin D Status and the Analysis of Risk Factors of Vitamin D Deficiency in Twin Pregnancies

OBJECTIVE

Optimization of maternal vitamin D (VD) status has beneficial effects on pregnancies, but little is known about it of twin pregnancies (TP). Our aim was to promote the current understanding of VD status and its associated factors in TP.

METHODS

We performed liquid chromatography-tandem mass spectrometry to quantify 25-hydroxyvitamin D [25(OH)D] and used the enzyme-linked immunosorbent assay method to detect vitamin D binding protein (VDBP) in 218 singleton pregnancies (SP) and 236 TP.

RESULTS

Levels of 25(OH)D and VDBP were higher in TP than SP. The 25(OH)D, free 25(OH)D, C-3 epimer of 25-hydroxyvitamin D [epi-25(OH)D], and VDBP all increased with gestational progress. Age, body 
mass index, and hemoglobin level were associated with VD deficiency (VDD). Analysis of covariance demonstrated that the 25(OH)D and VDBP of TP and SP still showed differences after adjusting for the above associated factors.

CONCLUSION

Differences in VD status were found in SP and TP, suggesting that the assessment of VD status in TP should be treated with caution. High VDD prevalence is observed among pregnant Chinese women, and it is recommended to promote evaluation for VDD.

Decreased Vitamin D Levels and Altered Placental Vitamin D Gene Expression at High Altitude: Role of Genetic Ancestry

High-altitude hypoxia challenges reproduction; particularly in non-native populations. Although high-altitude residence is associated with vitamin D deficiency, the homeostasis and metabolism of vitamin D in natives and migrants remain unknown. We report that high altitude (3600 m residence) negatively impacted vitamin D levels, with the high-altitude Andeans having the lowest 25-OH-D levels and the high-altitude Europeans having the lowest 1α,25-(OH)2-D levels. There was a significant interaction of genetic ancestry with altitude in the ratio of 1α,25-(OH)2-D to 25-OH-D; with the ratio being significantly lower in Europeans compared to Andeans living at high altitude. Placental gene expression accounted for as much as 50% of circulating vitamin D levels, with CYP2R1 (25-hydroxylase), CYP27B1 (1α-hydroxylase), CYP24A1 (24-hydroxylase), and LRP2 (megalin) as the major determinants of vitamin D levels. High-altitude residents had a greater correlation between circulating vitamin D levels and placental gene expression than low-altitude residents. Placental 7-dehydrocholesterol reductase and vitamin D receptor were upregulated at high altitude in both genetic-ancestry groups, while megalin and 24-hydroxylase were upregulated only in Europeans. Given that vitamin D deficiency and decreased 1α,25-(OH)2-D to 25-OH-D ratios are associated with pregnancy complications, our data support a role for high-altitude-induced vitamin D dysregulation impacting reproductive outcomes, particularly in migrants.

Vitamin D Metabolites: Analytical Challenges and Clinical Relevance

Recent research activities have provided new insights in vitamin D metabolism in various conditions. Furthermore, substantial progress has been made in the analysis of vitamin D metabolites and related biomarkers, such as vitamin D binding protein. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methods are capable of accurately measuring multiple vitamin D metabolites in parallel. Nevertheless, only 25(OH)D and the biologically active form 1,25(OH)2D are routinely measured in clinical practice. While 25(OH)D remains the analyte of choice for the diagnosis of vitamin D deficiency, 1,25(OH)2D is only recommended in a few conditions with a dysregulated D metabolism. 24,25(OH)2D, free and bioavailable 25(OH)D, and the vitamin D metabolite ratio (VMR) have shown promising results, but technical pitfalls in their quantification, limited clinical data and the lack of reference values, impede their use in clinical practice. LC-MS/MS is the preferred method for the measurement of all vitamin D related analytes as it offers high sensitivity and specificity. In particular, 25(OH)D and 24,25(OH)2D can accurately be measured with this technology. When interpreted together, they seem to provide a functional measure of vitamin D metabolism beyond the analysis of 25(OH)D alone. The determination of VDBP, free and bioavailable 25(OH)D is compromised by unresolved analytical issues, lacking reference intervals and insufficient clinical data. Therefore, future research activities should focus on analytical standardization and exploration of their clinical value. This review provides an overview on established and new vitamin D related biomarkers including their pathophysiological role, preanalytical and analytical aspects, expected values, indications and influencing conditions.

Vitamin D in gestational diabetes: a broadened frontier

Vitamin D deficiency is very common among women of reproductive age, even during pregnancy. Different studies have yielded vastly different results regarding whether vitamin D deficiency during pregnancy affects the development and progression of gestational diabetes mellitus (GDM), glycemic control in patients with hyperglycemia, and maternal-fetal outcomes. In addition, concerns, such as the mechanisms underlying the effect of vitamin D deficiency on glucose metabolism during pregnancy, efficacy of vitamin D supplementation in reducing the risk of developing GDM, and recommended supplemental dose of vitamin D, are yet to be elucidated. This article reviewed the latest domestic and international studies in this field, with a focus on the relationship between vitamin D deficiency and GDM, their underlying pathophysiological mechanisms, and the role of vitamin D intervention in the prevention and treatment of GDM. We recommend vitamin D supplementation as soon as possible for all pregnant women with vitamin D deficiency, especially those with GDM.

Maternal and Fetal Genetic Variation in Vitamin D Metabolism and Umbilical Cord Blood 25-Hydroxyvitamin D

CONTEXT

Single nucleotide polymorphisms (SNPs) in vitamin D metabolism pathway genes are associated with circulating 25-hydroxyvitamin D (25(OH)D) in adults. Less is known about the relationships between mother and offspring SNPs and umbilical cord blood 25(OH)D.

OBJECTIVE

(1) To undertake a meta-analysis of the relationships of maternal and offspring SNPs in the vitamin D metabolism pathway and cord blood 25(OH)D in pregnant women including novel data; and (2) to examine these relationships in women who received antenatal cholecalciferol supplementation in a clinical trial.

METHODS

Novel data analysis from an observational mother-offspring cohort study (Southampton Women's Survey) and the MAVIDOS double-blind, randomized, placebo-controlled trial of 1000 IU/day cholecalciferol supplementation in pregnancy, and an electronic literature search of published studies in PubMed up to 31 July 2021. Studies reporting associations between rs12785878 (DHCR7), rs10741657 (CYP2R1), rs6013897 (CYP24A1), or rs2282679 (GC) and cord blood 25(OH)D. One published study was included in addition to the novel data analysis. Associations between both maternal and offspring SNPs at rs2282679 (GC) and rs12785878 (DHCR7), and cord blood 25(OH)D were identified. When maternal genotype was adjusted for offspring genotype, and vice versa, there was persisting evidence for associations with maternal rs12785878 (β [95% CI] 1.6 nmol/L [0.3, 2.8] per common allele), and offspring rs2282679 (β 3.1 nmol/L ]2.0, 4.4] per common allele). Maternal and offspring SNPs at rs1074657 and rs613897 were not associated with cord blood 25(OH)D.

RESULT

Associations between both maternal and offspring SNPs at rs2282679 (GC) and rs12785878 (DHCR7), and cord blood 25(OH)D were identified. When maternal genotype was adjusted for offspring genotype, and vice versa, there was persisting evidence for associations with maternal rs12785878 (β [95% CI] 1.6 nmol/L [0.3, 2.8] per common allele), and offspring rs2282679 (β 3.1 nmol/L ]2.0, 4.4] per common allele). Maternal and offspring SNPs at rs1074657 and rs613897 were not associated with cord blood 25(OH)D.

CONCLUSION

Common genetic variation in the vitamin D metabolism pathway is associated with umbilical cord blood 25(OH)D.

Cubilin, the intrinsic factor-vitamin B12 receptor

Cubilin (CUBN), the intrinsic factor-vitamin B12 receptor is a large endocytic protein involved in various physiological functions: vitamin B12 uptake in the gut; reabsorption of albumin and maturation of vitamin D in the kidney; nutrient delivery during embryonic development. Cubilin is an atypical receptor, peripherally associated to the plasma membrane. The transmembrane proteins amnionless (AMN) and Lrp2/Megalin are the currently known molecular partners contributing to plasma membrane transport and internalization of Cubilin. The role of Cubilin/Amn complex in the handling of vitamin B12 in health and disease has extensively been studied and so is the role of the Cubilin-Lrp2 tandem in renal pathophysiology. Accumulating evidence strongly supports a role of Cubilin in some developmental defects including impaired closure of the neural tube. Are these defects primarily caused by the dysfunction of a specific Cubilin ligand or are they secondary to impaired vitamin B12 or protein uptake? We will present the established Cubilin functions, discuss the developmental data and provide an overview of the emerging implications of Cubilin in the field of cardiovascular disease and cancer pathogenesis.

Placental uptake and metabolism of 25(OH)vitamin D determine its activity within the fetoplacental unit

Pregnancy 25-hydroxyvitamin D [25(OH)D] concentrations are associated with maternal and fetal health outcomes. Using physiological human placental perfusion and villous explants, we investigate the role of the placenta in regulating the relationships between maternal 25(OH)D and fetal physiology. We demonstrate active placental uptake of 25(OH)D₃ by endocytosis, placental metabolism of 25(OH)D₃ into 24,25-dihydroxyvitamin D₃ and active 1,25-dihydroxyvitamin D [1,25(OH)₂D₃], with subsequent release of these metabolites into both the maternal and fetal circulations. Active placental transport of 25(OH)D₃ and synthesis of 1,25(OH)₂D₃ demonstrate that fetal supply is dependent on placental function rather than simply the availability of maternal 25(OH)D₃. We demonstrate that 25(OH)D₃ exposure induces rapid effects on the placental transcriptome and proteome. These map to multiple pathways central to placental function and thereby fetal development, independent of vitamin D transfer. Our data suggest that the underlying epigenetic landscape helps dictate the transcriptional response to vitamin D treatment. This is the first quantitative study demonstrating vitamin D transfer and metabolism by the human placenta, with widespread effects on the placenta itself. These data demonstrate a complex interplay between vitamin D and the placenta and will inform future interventions using vitamin D to support fetal development and maternal adaptations to pregnancy.

Questioning the adequacy of standardized vitamin D supplementation protocol in very low birth weight infants: a prospective cohort study

OBJECTIVES

Preterm infants are at increased risk for vitamin D deficiency (VDD). We aimed to assess the adequacy of standardized vitamin D supplementation protocol in very low birth weight (VLBW) infants. Additionally, vitamin D status of mother/infant couples and the associations between vitamin D status at birth and morbidities of the infants were investigated.

METHODS

In this single-center, prospective cohort study blood samples were collected from 55 mothers just before delivery and from their infants at birth and on the 30th day of life (DOL) for 25 hydroxy vitamin D (25OHD) measurements. Vitamin D was initiated in dose of 160 IU/kg by parenteral nutrition on the first DOL and oral vitamin D supplementation (400 IU/day) was administered when enteral feedings reached 50% of total intake or on the 15th DOL.

RESULTS

The median 25OHD levels of the infants were 16.12 (9.14-20.50) in cord blood and 36.32 (31.10-44.44) in venous blood on the 30th DOL (p<0.01). In 98% of the VLBW infants 25OHD reached sufficient levels on the 30th DOL. None of the mothers had sufficient vitamin D levels (25OHD >30 ng/mL). Maternal 25OHD levels were correlated with the 25OHD levels of the infants in cord blood (r=0.665, p<0.001). There was a significant difference in mean cord 25OHD levels between winter (13.65 ± 5.69 ng/mL) and summer seasons (19.58 ± 11.67 ng/mL) (p=0.021). No association was found between neonatal morbidity and vitamin D status.

CONCLUSIONS

The results clearly show that by utilizing the current supplementation protocol, the majority of VLBW infants with deficient/insufficient serum 25OHD levels reached sufficient levels on the 30th DOL. Furthermore, vitamin D levels in mother/infant couples were found to be highly correlated.

Cord Serum Calcitriol Inversely Correlates with Maternal Blood Pressure in Urinary Tract Infection-Affected Pregnancies: Sex-Dependent Immune Implications

Urinary tract infections (UTI) during pregnancy are frequently associated with hypertensive disorders, increasing the risk of perinatal morbidity. Calcitriol, vitamin D₃’s most active metabolite, has been involved in blood pressure regulation and prevention of UTIs, partially through modulating vasoactive peptides and antimicrobial peptides, like cathelicidin. However, nothing is known regarding the interplay between placental calcitriol, cathelicidin, and maternal blood pressure in UTI-complicated pregnancies. Here, we analyzed the correlation between these parameters in pregnant women with UTI and with normal pregnancy (NP). Umbilical venous serum calcitriol and its precursor calcidiol were significantly elevated in UTI. Regardless of newborn’s sex, we found strong negative correlations between calcitriol and maternal systolic and diastolic blood pressure in the UTI cohort (p < 0.002). In NP, this relationship was observed only in female-carrying mothers. UTI-female placentas showed higher expression of cathelicidin and CYP27B1, the calcitriol activating-enzyme, compared to male and NP samples. Accordingly, cord-serum calcitriol from UTI-female neonates negatively correlated with maternal bacteriuria. Cathelicidin gene expression positively correlated with gestational age in UTI and with newborn anthropometric parameters. Our results suggest that vitamin D deficiency might predispose to maternal cardiovascular risk and perinatal infections especially in male-carrying pregnancies, probably due to lower placental CYP27B1 and cathelicidin expression.

Vitamin D Metabolism and Guidelines for Vitamin D Supplementation

Vitamin D is essential for bone health and is known to be involved in immunomodulation and cell proliferation. Vitamin D status remains a significant health issue worldwide. However, there has been no clear consensus on vitamin D deficiency and its measurement in serum, and clinical practice of vitamin D deficiency treatment remains inconsistent. The major circulating metabolite of vitamin D, 25-hydroxyvitamin D (25(OH)D), is widely used as a biomarker of vitamin D status. Other metabolic pathways are recognised as important to vitamin D function and measurement of other metabolites may become important in the future. The utility of free 25(OH)D rather than total 25(OH)D needs further assessment. Data used to estimate the vitamin D intake required to achieve a serum 25(OH)D concentration were drawn from individual studies which reported dose-response data. The studies differ in their choice of subjects, dose of vitamin D, frequency of dosing regimen and methods used for the measurement of 25(OH)D concentration. Baseline 25(OH)D, body mass index, ethnicity, type of vitamin D (D₂ or D₃) and genetics affect the response of serum 25(OH)D to vitamin D supplementation. The diversity of opinions that exist on this topic are reflected in the guidelines. Government and scientific societies have published their recommendations for vitamin D intake which vary from 400-1000 IU/d (10-25 μg/d) for an average adult. It was not possible to establish a range of serum 25(OH)D concentrations associated with selected non-musculoskeletal health outcomes. To recommend treatment targets, future studies need to be on infants, children, pregnant and lactating women.

Vitamin-D dysregulation in early- and late-onset preeclampsia: A gestational-age matched study

Vitamin D deficiency has been associated with preeclampsia, however, vitamin D supplementation studies have shown equivocal data on amelioration of this disease. We hypothesize that women with preeclampsia have an altered endogenous vitamin D homeostasis that counteracts the beneficial effects of vitamin D supplementation. Our study population consisted of 66 maternal/neonate dyads: 16 early-onset (<34 weeks) preeclampsia (EOP), 16 early-onset controls (EOC), 17 late-onset (≥34 weeks) preeclampsia (LOP), and 17 late-onset controls (LOC). Plasma levels of 25-OH-D and the bioactive metabolite 1α,25-(OH)₂-D were studied by ELISA. Placental expression of vitamin D transporters (cubulin and megalin), metabolic genes (CYP2R1, CYP27B1, CYP24A1), and vitamin D binding protein (GC), were studied by real-time PCR, and the nuclear and cytosolic levels of the vitamin D receptor (VDR) protein were analyzed by immunoblotting. Maternal admission, maternal postpartum, and umbilical cord blood levels of 1α,25-(OH)₂-D and placental nuclear vitamin D receptor protein levels, were significantly lower in EOP compared to EOC. In contrast LOP was characterized by lower 25-OH-D levels in maternal postpartum and cord blood, and decreased placental cubulin expression compared to LOC. Both EOP and LOP showed decreased placental expression of CYP2R1 and GC compared to controls. Multivariable linear regression analysis demonstrated that preeclampsia was a significant predictor of decreased 1α,25-(OH)₂-D levels in early-onset subjects, while maternal BMI, but not preeclampsia, was the main predictor of decreased 25-OH-D in late-onset subjects. The highest positive correlation between the two vitamin D metabolites was observed in LOC umbilical cord blood. Finally, paired analysis of maternal metabolites before and after delivery indicated that women without preeclampsia had better maintenance of vitamin D levels. We conclude that EOP is characterized by decreased bioactivation of vitamin D and VDR in association with fetal growth restriction (FGR). In contrast, LOP is characterized by decreased 25-OH-D levels in association with decreased placental CYP2R1 and cubulin expression; and uncoupling of the 25-OH-D with the 1α,25-(OH)₂-D metabolite.

Gestational hypercalcemia: Prevalence and biochemical profile

Gestational hypercalcemia is associated with an increased risk of maternal, fetal and neonatal morbidity and mortality. Hypercalcemia may develop during pregnancy in individuals who were previously asymptomatic. The increased sensitivity during pregnancy may be related to physiological, gestational alterations in vitamin D and calcium metabolism and may be influenced by gene variants. The prevalence is unknown. We investigated the prevalence of hypercalcemia in trimester 3 (T3) in a population representative prospective cohort study (n = 1832) in South-West Sweden. Women with serum albumin (Alb) adjusted calcium (Ca_Alb) ≥ 2.65 mmol/L in T3 (n = 30) were matched to normo-calcemic controls, and markers of calcium and vitamin D metabolism were investigated in trimester 1 (T1) and T3. Serum concentrations of Ca, phosphate (P), Magnesium (Mg), Alb and creatinine (Cr), parathyroid hormone (PTH; T3 only), vitamin D metabolites (total 25(OH)D, 1,25(OH)₂D, 24,25(OH)₂D, and free 25(OH)D) were analysed in T1 and T3. Ca_Alb (Payne; inter-laboratory difference: UEA = 0.15 + 0.9*UGOT; UEA 2.54 = UGOT 2.65) and estimated glomerular filtration rate (eGFR; modified 4-variable MDRD) and vitamin D metabolites ratios (VMR) were calculated. Normally and non-normally distributed data were presented as mean (SD) or median (95 %CI). Group differences in relationships between vitamin D metabolites and with PTH were investigated with multiple regression analyses. Hypercalcemia in T3 was found in 1.7 % of women. PTH concentrations suggestive of primary hyperparathyroidism was found in 1 woman and none had 25(OH)D or 24,25(OH)₂D concentrations in the toxicity range or suggestive of mutations in the CYP24A1 gene. Ca_Alb was significantly higher in hypercalcemic cases compared to controls in T1 (2.44 (2.30-2.80) vs 2.37 (2.25-2.49) mmol/L) and T3 (2.63 (2.52-2.78) vs 2.46 (2.31-2.58) mmol/L). Serum P was higher among cases than controls in T3 (1.12 (0.16) vs 1.07 (0.18) mmol/L) but not in T1 (1.12 (0.18) and 1.12 (0.16) mmol/L). PTH in T3 was lower in cases (1.6 (1.6-2.8) vs 2.3 (2.1-2.8) pmol/L) but 1,25(OH)₂D concentrations were similar. There were no significant group differences in serum 25(OH)D, free 25(OH)D, 24,25(OH)₂D, Mg, Alb, Cr and eGFR. Regression analyses did not show significant differences between cases and controls in relationships between vitamin D metabolites and with PTH, except for the free 25(OH)D-PTH relationship and a higher free:total 25(OH)D ratio in cases at T1. In conclusion, most common causes of hypercalcemia were excluded in the majority of women. Hypercalcemic women had a relatively high serum 1,25(OH)₂D concentration despite an appropriately suppressed PTH, suggestive of abnormal gestational adaptions.

Epimers of Vitamin D: A Review

In this review, we discuss the sources, formation, metabolism, function, biological activity, and potency of C3-epimers (epimers of vitamin D). We also determine the role of epimerase in vitamin D-binding protein (DBP) and vitamin D receptors (VDR) according to different subcellular localizations. The importance of C3 epimerization and the metabolic pathway of vitamin D at the hydroxyl group have recently been recognized. Here, the hydroxyl group at the C3 position is orientated differently from the alpha to beta orientation in space. However, the details of this epimerization pathway are not yet clearly understood. Even the gene encoding for the enzyme involved in epimerization has not yet been identified. Many published research articles have illustrated the biological activity of C3 epimeric metabolites using an in vitro model, but the studies on in vivo models are substantially inadequate. The metabolic stability of 3-epi-1α,25(OH)₂D3 has been demonstrated to be higher than its primary metabolites. 3-epi-1 alpha, 25 dihydroxyvitamin D3 (3-epi-1α,25(OH)₂D3) is thought to have fewer calcemic effects than non-epimeric forms of vitamin D. Some researchers have observed a larger proportion of total vitamin D as C3-epimers in infants than in adults. Insufficient levels of vitamin D were found in mothers and their newborns when the epimers were not included in the measurement of vitamin D. Oral supplementation of vitamin D has also been found to potentially cause increased production of epimers in mice but not humans. Moreover, routine vitamin D blood tests for healthy adults will not be significantly affected by epimeric interference using LC-MS/MS assays. Recent genetic models also show that the genetic determinants and the potential factors of C3-epimers differ from those of non-C3-epimers.Most commercial immunoassays techniques can lead to inaccurate vitamin D results due to epimeric interference, especially in infants and pregnant women. It is also known that the LC-MS/MS technique can chromatographically separate epimeric and isobaric interference and detect vitamin D metabolites sensitively and accurately. Unfortunately, many labs around the world do not take into account the interference caused by epimers. In this review, various methods and techniques for the analysis of C3-epimers are also discussed. The authors believe that C3-epimers may have an important role to play in clinical research, and further research is warranted.

Calcium Metabolic Disorders in Pregnancy: Primary Hyperparathyroidism, Pregnancy-Induced Osteoporosis, and Vitamin D Deficiency in Pregnancy

Physiologic changes during pregnancy include calcium, phosphate, and calciotropic hormone status. Calcium metabolic disorders are rare in pregnancy and management with close calcium and vitamin D control and supplementation. Primary hyperparathyroidism is mostly asymptomatic and does not affect conception or pregnancy. It requires control of plasma calcium levels. Surgical intervention may be indicated. Data on severe cases are missing. Osteoporosis in or before pregnancy is rare but usually diagnosed from fractures. Medical treatment other than supplementation is contraindicated. Vitamin D deficiency is common and may affect conception and increase complications. Current evidence does not prove vitamin D supplements effective in improving outcomes.

Examining the predictive accuracy of metabolomics for small-for-gestational-age babies: a systematic review

INTRODUCTION

To date, there is no robust enough test to predict small-for-gestational-age (SGA) infants, who are at increased lifelong risk of morbidity and mortality.

OBJECTIVE

To determine the accuracy of metabolomics in predicting SGA babies and elucidate which metabolites are predictive of this condition.

DATA SOURCES

Two independent researchers explored 11 electronic databases and grey literature in February 2018 and November 2018, covering publications from 1998 to 2018. Both researchers performed data extraction and quality assessment independently. A third researcher resolved discrepancies.

STUDY ELIGIBILITY CRITERIA

Cohort or nested case-control studies were included which investigated pregnant women and performed metabolomics analysis to evaluate SGA infants. The primary outcome was birth weight <10th centile-as a surrogate for fetal growth restriction-by population-based or customised charts.

STUDY APPRAISAL AND SYNTHESIS METHODS

Two independent researchers extracted data on study design, obstetric variables and sampling, metabolomics technique, chemical class of metabolites, and prediction accuracy measures. Authors were contacted to provide additional data when necessary.

RESULTS

A total of 9181 references were retrieved. Of these, 273 were duplicate, 8760 were removed by title or abstract, and 133 were excluded by full-text content. Thus, 15 studies were included. Only two studies used the fifth centile as a cut-off, and most reports sampled second-trimester pregnant women. Liquid chromatography coupled to mass spectrometry was the most common metabolomics approach. Untargeted studies in the second trimester provided the largest number of predictive metabolites, using maternal blood or hair. Fatty acids, phosphosphingolipids and amino acids were the most prevalent predictive chemical subclasses.

CONCLUSIONS AND IMPLICATIONS

Significant heterogeneity of participant characteristics and methods employed among studies precluded a meta-analysis. Compounds related to lipid metabolism should be validated up to the second trimester in different settings.

PROSPERO REGISTRATION NUMBER

CRD42018089985.

Megalin mediates 25-hydroxyvitamin D3 actions in human mesenchymal stem cells

Osteoblast differentiation of human mesenchymal stem cells (hMSCs) is stimulated by 1α,25-dihydroxycholecalciferol [1α,25(OH)₂D₃] and 25-hydroxycholecalciferol [25(OH)D₃]; the latter's effects require intracellular hydroxylation to 1α,25(OH)₂D₃. Thus, hMSCs are both a source of and target for 1α,25(OH)₂D₃. Megalin is a transmembrane receptor for serum d-binding protein (DBP) in kidney cells and is required for uptake of the 25(OH)D₃-DBP complex. We tested the hypothesis that megalin is required for D actions in hMSCs with cells from surgically discarded marrow for RT-PCR, for effects of 25(OH)D₃ and 1α,25(OH)₂D₃, for 1α,25(OH)₂D₃ biosynthesis, for osteoblastogenesis, and for small interfering RNA for megalin (si-Meg) and control (si-Ctr). In hMSCs with high constitutive megalin expression, both 1α,25(OH)₂D₃ and 25(OH)D₃ stimulated osteoblastogenesis (P < 0.05), but only 1α,25(OH)₂D₃ did so in hMSCs with lower megalin (lo-Meg, P < 0.001) or in si-Meg cells (P < 0.05). In addition, 1α,25(OH)₂D₃ biosynthesis was significantly lower in lo-Meg (46%, P = 0.034) and in si-Meg (23%, P < 0.001) than each control. Leptin significantly stimulated megalin expression 2.1-fold in lo-Meg cells (P < 0.01). These studies show that megalin is expressed in hMSCs and is required for the biosynthesis of 1α,25(OH)₂D₃ and for the 25(OH)D₃/DBP complex to stimulate vitamin D receptor targets and osteoblastogenesis.-Gao, Y., Zhou, S., Luu, S., Glowacki, J. Megalin mediates 25-hydroxyvitamin D₃ actions in human mesenchymal stem cells.

Maternal vitamin D deficiency and developmental origins of health and disease (DOHaD)

Vitamin D is an essential nutrient that is metabolized in the body to generate an active metabolite (1,25(OH)2D) with hormone-like activity and highly diverse roles in cellular function. Vitamin D deficiency (VDD) is a prevalent but easily preventable nutritional disturbance. Emerging evidence demonstrates the importance of sufficient vitamin D concentrations during fetal life with deficiencies leading to long-term effects into adulthood. Here, we provide a detailed review and perspective of evidence for the role of maternal VDD in offspring long term health, particularly as it relates to Developmental Origins of Health and Disease (DOHaD). We focus on roles in neurobehavioral and cardiometabolic disorders in humans and highlight recent findings from zebrafish and rodent models that probe potential mechanisms linking early life VDD to later life health outcomes. Moreover, we explore evidence implicating epigenetic mechanisms as a mediator of this link. Gaps in our current understanding of how maternal VDD might result in deleterious offspring outcomes later in life are also addressed.

Changes in Micronutrient Intake and Status, Diet Quality and Glucose Tolerance from Preconception to the Second Trimester of Pregnancy

Data on changes in dietary intake and related blood parameters throughout pregnancy are scarce; moreover, few studies have examined their association with glucose homeostasis. Therefore, we monitored intake of folate, vitamin B6, vitamin B12, vitamin D and iron, their status markers, and diet quality from preconception to the second trimester of pregnancy, and we examined whether these dietary factors were associated with glucose homeostasis during pregnancy. We included 105 women aged 18⁻40 years with a desire to get pregnancy or who were already <24 weeks pregnant. Women at increased gestational diabetes (GDM) risk were oversampled. Measurements were scheduled at preconception (n = 67), and 12 (n =53) and 24 weeks of pregnancy (n =66), including a fasting venipuncture, 75-grams oral glucose tolerance test, and completion of a validated food frequency questionnaire. Changes in micronutrient intake and status, and associations between dietary factors and glucose homeostasis, were examined using adjusted repeated measures mixed models. Micronutrient intake of folate, vitamin B6 and vitamin D and related status markers significantly changed throughout pregnancy, which was predominantly due to changes in the intake of supplements. Micronutrient intake or status levels were not associated with glucose homeostasis, except for iron intake (FE µg/day) with fasting glucose (β = -0.069 mmol/L, p = 0.013) and HbA1c (β = -0.4843 mmol, p = 0.002). Diet quality was inversely associated with fasting glucose (β = -0.006 mmol/L for each DHD15-index point, p = 0.017). It was shown that micronutrient intakes and their status markers significantly changed during pregnancy. Only iron intake and diet quality were inversely associated with glucose homeostasis.

Longitudinal changes in serum vitamin D binding protein and free 25-hydroxyvitamin D in a multiracial cohort of pregnant adolescents

Serum free 25-hydroxyvitamin D (25(OH)D) rather than total 25(OH)D may better indicate vitamin D status during pregnancy given the pregnancy-associated increase in serum vitamin D binding protein (DBP) concentration. Our aims were to assess changes in DBP and free 25(OH)D across gestation and to determine whether free compared with total 25(OH)D more strongly correlates with markers of vitamin D and calcium metabolism during pregnancy. This ancillary study included 58 pregnant adolescents (53% African American, 47% White) who completed a vitamin D3 supplementation study in Rochester, NY. Blood was collected at entry, mid-study, and delivery (median 17, 29, and 40 weeks' gestation). Mixed-effects regression was used to test for differences in DBP, directly measured free 25(OH)D, and other serum markers by study visit and race. Free and total 25(OH)D were evaluated in relation to serum PTH, 1,25(OH)2D, 24,25(OH)2D, and calcium. The mean DBP concentration was above nonpregnant reference values at entry and increased across gestation (P < 0.0001). Total 25(OH)D explained most of the variance in free 25(OH)D (r ≥ 0.67; P < 0.0001). Holding total 25(OH)D constant, each 100 mg/L increase in DBP was associated with a 0.4 pg/mL decrease in free 25(OH)D (P < 0.01). The percent free 25(OH)D was inversely related to both DBP and total 25(OH)D at each visit. Regardless of race or visit, total 25(OH)D was a stronger correlate of PTH, 1,25(OH)2D, and 24,25(OH)2D, and neither total nor free 25(OH)D was related to serum calcium. African Americans had lower total 25(OH)D (P <  0.0001), but free 25(OH)D did not significantly differ by race (P =  0.2). In pregnant adolescents, DBP concentration was elevated and inversely associated with percent free 25(OH)D, but measured free 25(OH)D provided no advantage over total 25(OH)D as a predictor of PTH, 1,25(OH)2D, 24,25(OH)2D, or calcium. The clinical relevance of the small racial difference in percent free 25(OH)D requires further investigation.

Cubilin, the Intrinsic Factor-Vitamin B12 Receptor in Development and Disease

Gp280/Intrinsic factor-vitamin B12 receptor/Cubilin (CUBN) is a large endocytic receptor serving multiple functions in vitamin B12 homeostasis, renal reabsorption of protein or toxic substances including albumin, vitamin D-binding protein or cadmium. Cubilin is a peripheral membrane protein consisting of 8 Epidermal Growth Factor (EGF)-like repeats and 27 CUB (defined as Complement C1r/C1s, Uegf, BMP1) domains. This structurally unique protein interacts with at least two molecular partners, Amnionless (AMN) and Lrp2/Megalin. AMN is involved in appropriate plasma membrane transport of Cubilin whereas Lrp2 is essential for efficient internalization of Cubilin and its ligands. Observations gleaned from animal models with Cubn deficiency or human diseases demonstrate the importance of this protein. In this review addressed to basic research and medical scientists, we summarize currently available data on Cubilin and its implication in renal and intestinal biology. We also discuss the role of Cubilin as a modulator of Fgf8 signaling during embryonic development and propose that the Cubilin-Fgf8 interaction may be relevant in human pathology, including in cancer progression, heart or neural tube defects. We finally provide experimental elements suggesting that some aspects of Cubilin physiology might be relevant in drug design.

Longitudinal measures of maternal vitamin D and neonatal body composition

Background/Objectives

Vitamin D status has been associated with fetal growth and offspring’s bone mass in some observational studies. We characterize the trajectory of total maternal serum 25-hydroxyvitamin D [25(OH)D] concentration by race and examine whether vitamin D status is associated with neonatal anthropometry and body composition as assessed by dual energy X-ray absorptiometry (DXA).

Methods

Three longitudinal pregnancy samples from the Memphis site of the Calcium for Preeclampsia Prevention trial (1992-1995) were used. Racial differences in total 25(OH)D trajectories (n=343 women) were tested using an interaction term between blood draw gestational week and race in linear mixed-effects models. Linear regression and linear mixed-effects models estimated adjusted associations between total 25(OH)D concentration with neonatal anthropometry and body composition (n=252 with DXA), including interactions with infant sex and serum calcium.

Results

Total 25(OH)D concentration increased with gestational age but its trajectory over pregnancy did not differ between African-American and Caucasian women. Deficient maternal vitamin D (25(OH)D concentration <20 ng/ml) was associated with lower neonatal total bone mineral density (β −0.009 g/cm²; 95% CI −0.016, −0.002). Among male newborns, deficiency was also associated with lower lean mass (−217 g; −391, −43) and birthweight (−308 g; −540, −76). Deficient maternal vitamin D was also associated with lower ponderal index (β –2.3 kg/m³; 95% CI −4.0, −0.5) among those in the lowest calcium tertile.

Conclusion

Vitamin D deficiency during pregnancy is associated with lower bone density and smaller size at birth in certain subgroups suggesting its importance in fetal development.

Vitamin D binding protein rs7041 genotype alters vitamin D metabolism in pregnant women

Research has identified reduced circulating 25-hydroxyvitamin D [25(OH)D] in individuals with the rs7041 (c.1296T>G) T allele in the vitamin D binding protein gene ( GC); however, the effects of the T allele on vitamin D biomarkers during pregnancy and lactation are unknown. Thus, we examined the metabolic effects of GC rs7041 on vitamin D biomarkers among third-trimester pregnant ( n = 26), lactating ( n = 28), and nonpregnant/nonlactating ( n = 21) women consuming a single amount of vitamin D (511 IU/d) and related nutrients for 10-12 wk. T allele carriers had less circulating 25(OH)D, regardless of reproductive state [thymine-thymine (TT): 80% of guanine-guanine (GG), P = 0.05; guanine-thymine (GT): 85% of GG, P = 0.1]. Among pregnant women, the T allele attenuated the expected increase in vitamin D binding protein (DBP). Specifically, although GG pregnant women exhibited greater DBP (216%, P < 0.0001) than did GG nonpregnant women, that difference was lessened among GT women, and TT pregnant women did not exhibit greater DBP than TT nonpregnant women. Furthermore, TT pregnant women had greater placental 25(OH)D₃ to 24,25-dihydroxyvitamin D ratios (251% of GG, P = 0.07) and less osteocalcin, a bone formation marker, in the cord blood of their neonates (24% of GT, P = 0.02). Overall, the GC rs7041 genotype modified the effects of pregnancy on maternal and placental vitamin D metabolism, with possible functional consequences for fetal bone development and infant health.-Ganz, A. B., Park, H., Malysheva, O. V., Caudill, M. A. Vitamin D binding protein rs7041 genotype alters vitamin D metabolism in pregnant women.