Serum Vitamin D Binding Protein Level Associated with Metabolic Cardiovascular Risk Factors in Women with the Polycystic Ovary Syndrome

Association of rs4588 polymorphism in vitamin D binding protein gene with polycystic ovarian syndrome in Iranian women: a case-control study

OBJECTIVE

Vitamin D deficiency and variations in the vitamin D binding protein (VDBP) gene may play a role in the development of Polycystic ovary syndrome (PCOS). This study aims to investigate the association of the rs4588 polymorphism with PCOS in Iranian women, as well as its association with infertility and recurrent pregnancy loss (RPL) in these patients.

RESULTS

The analysis revealed statistically significant differences in the distributions of genotypes and alleles of the rs4588 polymorphism among the three groups (p < 0.0001). The AC genotype and A allele showed an association with an elevated risk of PCOS and infertility. In this study, no association was found between genotypes and alleles of the rs4588 polymorphism and the risk of RPL in women with PCOS. Subjects with the AA or AC genotype exhibited significantly higher levels of LDL compared to those with the CC genotype.

Vitamin D binding protein correlate with estrogen increase after administration of human chorionic gonadotropin but do not affect ovulation, embryo, or pregnancy outcomes

Background

Vitamin D binding protein (DBP) might increase substantially after ovarian stimulation and hence could be associated with IVF/ICSI outcomes because it determines the fraction of free bioavailable 25(OH) vitamin D. In this study, we aim to determine whether DBP is associated with E2 level after ovarian stimulation and IVF/ICSI outcomes.

Design

Post-hoc analysis of a prospective observational cohort.

Setting

Single-center study.

Participants

2569 women receiving embryo transfer.

Intervention

None.

Main outcome measures

The main outcomes were oocyte and embryo quality as well as pregnancy outcomes.

Results

DBP concentration correlates with E2 on hCG day (=day of inducing ovulation with hCG; correlation coefficient r = 0.118, P<0.001) and E2 x-fold change to baseline level (r = 0.108, P<0.001). DBP is also positively correlated with total 25(OH)D (r = 0.689, R2 = 0.475, P<0.001) and inversely with free 25(OH)D (r=-0.424, R2=0.179, P<0.001), meaning that E2-stimulated DBP synthesis results in a decrease of free 25(OH)D during ovarian stimulation. However, such alteration does not affect IVF/ICSI outcomes when considering confounding factors, such as the number and quality of oocytes nor embryo quality as well as pregnancy outcomes.

Conclusion

DBP concentration correlates with the degree of E2 increase after ovarian stimulation. DBP is also positively correlated with total 25(OH)D and inversely with free 25(OH)D, suggesting that the proportion of free 25(OH)D decreases during ovarian stimulation caused by E2-stimulated DBP synthesis. However, such alteration does not affect clinical IVF/ICSI outcomes.

Parameters for Calcium Metabolism in Women with Polycystic Ovary Syndrome Who Undergo Stimulation with Letrozole: A Prospective Cohort Study

For women with polycystic ovarian syndrome (PCOS) and infertility, stimulation with the aromatase-inhibitor letrozole has been recommended as a first-line for ovulation induction. Calcium-associated signaling has also been a component for other ovulation induction and superovulation medications. This study’s aim was to evaluate parameters of calcium metabolism in PCOS women. In a prospective cohort study, 61 anovulatory, infertile PCOS patients who underwent letrozole stimulation were included. Outcome measures were: follicular maturation after letrozole stimulation; parathyroid hormone (PTH); 25-hydroxyvitamin D3 (25OHD3); serum levels of calcium, phosphorus, magnesium, albumin, and total protein. Successful recruitment of a dominant follicle was achieved in 35 patients (57.4%). Women with and without successful follicular development did not differ in serum levels of PTH (38.4 ± 19.7 vs. 39.6 ± 16.2 pg/mL), 25OHD3 (62.5 ± 32.1 vs. 65.4 ± 30.9 nmol/L), calcium (2.36 ± 0.08 vs. 2.37 ± 0.12 mmol/L), or protein (70.2 ± 13.3 vs. 74.0 ± 3.7 g/L), respectively (p > 0.05). However, women who were not responsive to letrozole for ovulation induction demonstrated higher anti-Müllerian hormone (AMH) levels (9.7 ± 4.7 vs. 5.0 ± 3.2 ng/mL, p = 0.005). In conclusion, the success of letrozole stimulation in women with PCOS is independent from calcium metabolism parameters. However, AMH levels seem predictive of medication resistance.

Distribution of vitamin D-binding protein/group-specific component gene subtypes in Kuwaiti population

BACKGROUND

Vitamin D-binding protein or group-specific component (Gc) is the major plasma carrier protein of Vitamin D. Two single nucleotide polymorphisms, rs7041 (NM_000583.3:c.1296G>T;NP_000574.2:p.Asp432Glu) and rs4588 (c.1307C>A; p.Thr436Lys), in the GC gene result in three major genotypes, that is, GC1F (c.1296T, c.1307C), GC1S (c.1296G, c.1307C), GC2 (c.1296T, c.1307A), and phenotypes such as Gc1F (p.432Asp, p.436Thr), Gc1S (p.432Glu, p.436Thr), and Gc2 (p.432Asp, p.436Lys). Significant variations in the frequencies of GC subtypes (genotypes/phenotypes) are reported in different populations living in different geographical locations, for example, GC1S/Gc1S (c.1296G, c.1307C/p.432Glu, p.436Thr) and GC2/Gc2 (c.1296T, c.1307A/p.432Asp, p.436Lys) are predominant in Caucasians and people living in the northern hemisphere, and GC1F/Gc1F (c.1296T, c.1307C/p.432Asp, p.436Thr) is predominant in Africans. However, frequencies of major GC subtypes are not known in the Kuwaiti population. In this study, we investigated 512 alleles to identify the major GC subtypes in Kuwaiti nationals.

METHODS

Genomic DNA was isolated from blood samples of 128 healthy subjects. DNA regions covering the targeted mutations were amplified by PCR. Amplified DNAs were sequenced by the Sanger method and analyzed for specific mutations to determine the GC genotypes and phenotypes.

RESULTS

The results identified the presence of four GC genotypes/phenotypes namely GC1F/Gc1F (c.1296T, c.1307C/p.432Asp, p.436Thr), GC1S/Gc1S (c.1296G, c.1307C/p.432Glu, p.436Thr), GC2/Gc2 (c.1296T, c.1307A/p.432Asp, p.436Lys), and GC3/Gc3 (c.1296G;c.1307A/p.432Glu, p.436Lys). Among the allelic subtypes (n = 512), GC1S (c.1296G; c.1307C) (n = 270, 52.7%) was predominant, followed by GC1F (c.1296T; c.1307C) (n = 138, 27%), GC2 (c.1296T; c.1307A) (n = 72, 14%), and GC3 (c.1296G; c.1307A) (n = 32, 6.3%). Three common subtypes, that is, GC1F (c.1296T; c.1307C), GC1S (c.1296G; c.1307C), and GC2 (c.1296T; c.1307A) are well documented in the literature, but GC3 (c.1296T; c.1307A) is an uncommon variant found in our study subjects.

CONCLUSION

We found that GC subtype distribution was unique in the Kuwaiti population, with some affinity to Caucasians. Several factors including ancestral origin, migration history, and environmental forces such as solar intensity may be responsible for the unique distribution of GC subtypes in this population.

Association of vitamin D-binding protein and vitamin D3 with insulin and homeostatic model assessment (HOMA-IR) in overweight and obese females

OBJECTIVE

Equivocal association the contribution of 25-hydroxyvitamin D (25(OH)D) and the well-accepted role of vitamin D-binding protein (VDBP) on bioavailability of 25(OH)D or its independent roles, has led to possible association of the VDBP in glucose metabolism. This study was conducted to evaluate the relationships among 25(OH)D, VDBP, glucose/insulin metabolism and homeostatic model assessment (HOMA-IR). Blood samples were collected from 236 obese and overweight women. VDBP and 25(OH)D levels, and biochemical parameters were measured using an enzyme-linked immunosorbent assay (ELISA). An impedance fat analyzer was utilized to acquire the body composition.

RESULTS

Using the multivariate linear regression, a reverse relationship was observed between VDBP and (HOMA-IR), such that women with higher VDBP displayed lower insulin resistance. The relationship was independent of age, body mass index, standardized energy intake and physical activity (p = 0.00). No significant relationship between 25(OH)D levels, FBS, body composition or insulin resistance were observed (p > 0.2). Current study observed that higher level of VDBP may be associated with lower levels of insulin and HOMA-IR, thus the evaluation of VDBP in diverse population groups seems to have significant clinical value in evaluating the prevalence of DM or early stage of glucose intolerance.

Proteomic analysis of human follicular fluid from polycystic ovary syndrome patients

Comparative proteomic profiling of human follicular fluid (HFF) from polycystic ovary syndrome (PCOS) and non-PCOS patients who displayed low levels of fertility was carried out via two-dimensional gel electrophoresis (2-DE) combined with mass spectrometry. HFF, an important reproductive fluid, was used for the proteomic analysis of PCOS patients to determine the effect of PCOS on folliculogenesis. HFF was obtained from 10 women (average age, 35 years) undergoing in vitro fertilization at two hospitals. The proteins of HFF were separated using 2-DE analysis and validated by Western blot assay. Approximately 250 protein spots were separated on the 2-DE gel. Among them, the expression levels of seven proteins were found to change at least 1.5-fold in the PCOS patient group. Three protein spots, albumin, uncharacterized protein 1, and uncharacterized protein 2, were downregulated in PCOS patients. However, four protein spots, gelsolin, vitamin D binding protein, serum albumin, and complement factor B, were upregulated in PCOS patient group. These proteins may serve as a panel of potential pathological biomarkers during fertilization and oocyte development.

Early Pregnancy Vitamin D Binding Protein Is Independently Associated with the Development of Gestational Diabetes: A Retrospective Cohort Study

BACKGROUND

Vitamin D-binding protein (VDBP) has been implicated in several adverse pregnancy outcomes either directly or indirectly via influencing the concentrations of biologically active vitamin D metabolites. However, human studies exploring these metabolites in pregnancy remain sparse. Here, we examine whether VDBP and total, free, and bioavailable 25-hydroxyvitamin D (25(OH)D) metabolites in early pregnancy are associated with subsequent adverse pregnancy outcomes.

METHODS

We conducted a retrospective analysis of 304 pregnant women in early pregnancy (<20 weeks gestation). The demographic characteristics, anthropometric data, and total 25(OH)D were measured and plasma or serum samples were collected and bio-banked. Using these samples, we measured VDBP (polyclonal ELISA) and albumin (automated colorimetry), and calculated free and bioavailable 25(OH)D using validated formulae. Pregnancy outcomes were derived from scanned medical records. Regression models were used to analyse the relationships between vitamin D metabolites in early pregnancy and subsequent pregnancy outcomes (gestational diabetes mellitus (GDM), pre-eclampsia, preterm birth), with adjustment for predetermined clinically relevant maternal factors including age, body mass index (BMI), and ethnicity.

RESULTS

Lower VDBP concentrations were associated with higher glucose levels and a greater likelihood of developing GDM at 26-28 weeks gestation (odds ratio [OR] (95% CI) = 0.98 (0.97,0.99), p = 0.015). This finding remained significant after adjustment for maternal covariates including age, BMI, and ethnicity (β = -0.003, p = 0.03). Lower total, free and bioavailable 25(OH)D, but not VDBP, were associated with a shorter length of gestation, but only the relationship with total 25(OH)D remained significant after adjustment for the above maternal covariates (β = 0.02, p = 0.006).

CONCLUSIONS

This is the first study to examine VDBP, and total, free and bioavailable 25(OH)D in relation to pregnancy outcomes in a well characterised multi-ethnic cohort of pregnant women. Our findings show that VDBP and total 25(OH)D are associated with GDM and length of gestation, respectively; however, further investigations using large-scale prospective studies are needed to confirm our findings.

Vitamin D-Binding Protein in Pregnancy and Reproductive Health

Vitamin D-binding protein (VDBP), the main carrier of vitamin D, has recently been implicated in reproductive health and pregnancy outcomes including endometriosis, polycystic ovary syndrome (PCOS), pre-eclampsia, and gestational diabetes mellitus (GDM). Improved methods for measuring VDBP and an increased understanding of its role in biological processes have led to a number of newly published studies exploring VDBP in the context of pregnancy. Here, we synthesize the available evidence regarding the role of VDBP in reproductive health and pregnancy, and we highlight areas requiring further study. Overall, low levels of maternal serum VDBP concentrations have been associated with infertility, endometriosis, PCOS and spontaneous miscarriage, as well as adverse pregnancy outcomes including GDM, pre-eclampsia, preterm birth and fetal growth restriction. However, increased VDBP concentration in cervicovaginal fluid has been linked to unexplained recurrent pregnancy loss and premature rupture of membranes. Some genetic variants of VDBP have also been associated with these adverse outcomes. Further studies using more accurate VDBP assays and accounting for ethnic variation and potential confounders are needed to clarify whether VDBP is associated with reproductive health and pregnancy outcomes, and the mechanisms underlying these relationships.

Vitamin D binding protein is related to cardiac autonomic function and metabolic status in prediabetes

A putative causal relationship between vitamin D status and glucose metabolism and a direct effect of vitamin D on cardiac autonomic function (CAF) have been suggested. We hypothesized that vitamin D binding protein (DBP), as a transporter of vitamin D, might also influence CAF and the overall metabolic risk. The present study aims to assess the relationship between DBP and CAF and metabolic status in a high-risk population with prediabetes. A total of 174 subjects (mean age 49.1±12.9 years, mean body mass index 30.2±6.2 kg/m²) were divided into 2 groups according to glucose tolerance: 48 with normal glucose tolerance and 126 with prediabetes. Glucose tolerance was assessed during oral glucose tolerance test, applying 2006 World Health Organization criteria. Fasting and postload glucose and immunoreactive insulin were measured (homeostatic model assessment of insulin resistance and homeostatic model assessment of β-cell function were calculated). Anthropometric indexes, blood pressure, hemoglobin A1c, creatinine, lipids, high-sensitivity C-reactive protein, total 25-hydroxyvitamin D, DBP (free 25-hydroxyvitamin D was calculated), and intact parathormone were measured. Body composition was estimated by impedance analysis (InBody 720), whereas tissue advanced glycation end products were assessed by skin autofluorescence (AGE Reader, DiagnOptics, the Netherlands). CAF was evaluated by АNX-3.0 system, applying standard autonomic tests. DBP was found to be elevated in women, as well as in the presence of cardiac autonomic dysfunction and metabolic syndrome. DBP was related to parasympathetic activity in both sexes and in prediabetes; to body fat in women and in prediabetes; and to age and high-density lipoprotein cholesterol in men. Vitamin D deficiency was established in 40.8% of the studied cohort. These results support the hypothesis that DBP is associated with CAF and some metabolic parameters in prediabetes.

Type 2 Diabetes Mellitus, Insulin Resistance, and Vitamin D

PURPOSE OF REVIEW

There is a growing, largely inconsistent, literature on the role of vitamin D in association with type 2 diabetes, insulin resistance/insulin secretion, glycemic indices, and complications of type 2 diabetes. Pathophysiologic, bystander, preventive, and treatment roles of vitamin D have all been proposed. In this focused review, we attempt to organize and clarify our current information in this area.

RECENT FINDINGS

Clinical study interpretation is difficult because of variability in dosage, dosage form, study duration, and populations studied, as well as recently reported normal human polymorphisms in vitamin D synthesis and catabolism, vitamin D-binding protein, and vitamin D receptors in addition to a host of potential epigenetic confounders. Low vitamin D status appears to be associated with type 2 diabetes and most other insulin resistance disorders reported to date. The extraskeletal benefits of supplementation/repletion in these disorders in our species, with a few highlighted exceptions, remain to be established. This focused review attempts to summarize our current knowledge in this burgeoning area through a review of key meta-analyses, observational studies, randomized control trials, and Mendelian randomization studies and will hopefully serve as a guide to indicate future research directions and current best practice.