Simultaneous determination of 12 vitamin D compounds in human serum using online sample preparation and liquid chromatography-tandem mass spectrometry

Accurate Clinical Detection of Vitamin D by Mass Spectrometry: A Review

Vitamin D deficiency is thought to be associated with a wide range of diseases, including diabetes, cancer, depression, neurodegenerative diseases, and cardiovascular and cerebrovascular diseases. This vitamin D deficiency is a global epidemic affecting both developing and developed countries and therefore qualitative and quantitative analysis of vitamin D in a clinical context is essential. Mass spectrometry has played an increasingly important role in the clinical analysis of vitamin D because of its accuracy, sensitivity, specificity, and the ability to detect multiple substances at the same time. Despite their many advantages, mass spectrometry-based methods are not without analytical challenges. Front-end and back-end challenges such as protein precipitation, analyte extraction, derivatization, mass spectrometer functionality, must be carefully considered to provide accurate and robust analysis of vitamin D through a well-designed approach with continuous control by internal and external quality control. Therefore, the aim of this review is to provide a comprehensive overview of the development of mass spectrometry methods for vitamin D accurate analysis, including emphasis on status markers, deleterious effects of biological matrices, derivatization reactions, effects of ionization sources, contribution of epimers, standardization of assays between laboratories.

Optimised liquid chromatography tandem mass spectrometry method for the simultaneous quantification of serum vitamin D analogues while also accounting for epimers and isobars

The accurate quantification of multiple vitamin D analogues simultaneously is challenging. This study set out to use liquid chromatography-tandem mass spectrometry (LC-MS/MS) to develop a method capable of measuring a comprehensive vitamin D profile, encompassing twelve vitamin D analogues (vitamin D2, D3, 25(OH)D2, 25(OH)D3, 1,25(OH)2D2, 1,25(OH)2D3, 24,25(OH)2D2, 24,25(OH)2D3, 3-epi-25(OH)D2, 3-epi-25(OH)D3, 7αC4 and1α(OH)D3) in a single run. Serum samples were prepared using double liquid-liquid extraction and analysed on an Agilent 6460 QQQ LC-MS/MS equipped with a Pursuit 3 Pentafluorophenyl (4.6 x 100 mm, 3 μm) column. Recovery rates for all analytes were above 95 % with a coefficient of variation (CV) below 10 %. The method exhibited good linearity (r > 0.995) and had a range of detection limits between 0.01 and 0.35 ng/mL and quantification limits between 0.15 and 0.96 ng/mL. Repeatability and within-lab precision were acceptable, with CV values below 10 % and 15 %, respectively. Method accuracy was excellent, with a systematic error below 6.60 %. additionally, all analytes-maintained stability for 48 h following sample preparation, and no interferences were observed among co-eluting analytes. Lastly, this method achieved "world-class" status according to the Sigma metric scale specifications, requiring minimal quality control to ensure data quality. This successfully validated method has the potential not only for improving vitamin D profiling procedures but also for aiding in the diagnosis of other genetic disorders where measuring beyond 25(OH)D is crucial.

Maternal Iron and Vitamin D Status during the Second Trimester Is Associated with Third Trimester Depression Symptoms among Pregnant Participants in the APrON Cohort

BACKGROUND

The maternal status of multiple micronutrients during pregnancy and postpartum and their potential associations with maternal health outcomes are largely undescribed.

OBJECTIVES

This study aimed to examine associations between maternal iron and vitamin D status, individually and in combination, on depression symptoms in pregnant individuals.

METHODS

The Alberta Pregnancy Outcomes and Nutrition cohort study included pregnant participants and their children from Calgary and Edmonton, Canada. Iron biomarkers (serum ferritin [SF], soluble transferrin receptor, and hepcidin) were measured via immunoassays and vitamin D [25-hydroxyvitamin D3 (25(OH)D3) and 3-epi-25-hydoxyvitamin D3 (3-epi-25(OH)D3)] metabolites were quantifed using liquid chromatography with tandem mass spectroscopy. Four categories of maternal iron and vitamin D status during the second trimester were conceptualized using concentrations of SF and total 25-hydoxyvitamin D [25(OH)D], respectively. Maternal Edinburgh Postnatal Depression Scale (EPDS) scores during the third trimester (n = 1920) and 3 mo postpartum (n = 1822) were obtained.

RESULTS

Concentrations of maternal 25(OH)D3, 3-epi-25(OH)D3, and the ratio of both metabolites were significantly higher during the second trimester compared with their status at 3 mo postpartum. Higher second trimester maternal concentrations of SF (β: -0.8; 95% confidence interval [CI]: -1.5, -0.01), hepcidin (β: -0.5; 95% CI: -0.9, -0.2), and 25(OH)D3 (β: -0.01; 95% CI: -0.02, -0.004) predicted lower maternal EPDS scores during the third trimester. Pregnant individuals with a low iron (SF <15 μg/L) and replete vitamin D (25(OH)D ≥75 nmol/L) (β: 1.1; 95% CI: 0.03, 2.1) or low iron (SF <15 μg/L) and vitamin D (25(OH)D <75 nmol/L) (β: 2.2; 95% CI: 0.3, 4.2) status during midpregnancy had higher third trimester EPDS scores compared with those that were replete in both micronutrients.

CONCLUSIONS

A higher midpregnancy maternal iron and vitamin D status, independently or in combination, predicted fewer maternal depression symptoms in the third trimester. Concentrations of maternal 25(OH)D3 and 3-epi-25(OH)D3 may be lower in the postpartum period compared with midpregnancy.

Mass Spectrometry Analysis for Clinical Applications: A Review

Mass spectrometry (MS) has become an attractive analytical method in clinical analysis due to its comprehensive advantages of high sensitivity, high specificity and high throughput. Separation techniques coupled MS detection (e.g., LC-MS/MS) have shown unique advantages over immunoassay and have developed as golden criterion for many clinical applications. This review summarizes the characteristics and applications of MS, and emphasizes the high efficiency of MS in clinical research. In addition, this review also put forward further prospects for the future of mass spectrometry technology, including the introduction of miniature MS instruments, point-of-care detection and high-throughput analysis, to achieve better development of MS technology in various fields of clinical application. Moreover, as ambient ionization mass spectrometry (AIMS) requires little or no sample pretreatment and improves the flux of MS, this review also summarizes its potential applications in clinic.

Quantification of 25OHD in serum by ID-LC-MS/MS based on oriented immobilization of antibody on magnetic materials

Magnetic nanomaterials are widely used, but co-adsorption of impurities will lead to saturation. In this study, the aim was to prepare a magnetic nano-immunosorbent material based on orienting immobilization that can purify and separate 25-hydroxyvitamin D (25OHD) from serum and provides a new concept of sample pretreatment technology. Streptococcus protein G (SPG) was modified on the surface of the chitosan magnetic material, and the antibody was oriented immobilized using the ability of SPG to specifically bind to the Fc region of the monoclonal antibody. The antigen-binding domain was fully exposed and made up for the deficiency of the antibody random immobilization. Compared with the antibody in the random binding format, this oriented immobilization strategy can increase the effective activity of the antibody, and the amount of antibody consumed is saved to a quarter of the former. The new method is simple, rapid, and sensitive, without consuming a lot of organic reagents, and can enrich 25OHD after simple protein precipitation. Combining with liquid chromatography-tandem mass spectrometry (LC-MS/MS), the analysis can be completed in less than 30 min. For 25OHD₂ and 25OHD₃, the LOD was 0.021 and 0.017 ng mL^-1, respectively, and the LOQ was 0.070 and 0.058 ng mL^-1, respectively. The results indicated that the magnetic nanomaterials based on oriented immobilization can be applied as an effective, sensitive, and attractive adsorbent to the enrichment of serum 25OHD.

Serum Vitamin D Metabolites by HPLC-MS/MS Combined with Differential Ion Mobility Spectrometry: Aspects of Sample Preparation without Derivatization

In current clinical practice, a thorough understanding of vitamin D metabolism is in high demand both for patients with various diseases and for healthy individuals. Analytical techniques that provide simultaneous measurement of multiple metabolites are preferred. Herein, the development of an HPLC-DMS-MS/MS method for the quantitation of vitamin D compounds (25(OH)D₃, 25(OH)D₂, 1,25(OH)₂D₃, 3-epi-25(OH)D₃, 24,25(OH)₂D₃, and D₃) in serum is described. The selected sample preparation procedure based on the combination of liquid-liquid and solid-phase extraction, which excluded a lengthy derivatization step, was compared with other common approaches. Sensitivity was increased through the implementation of differential ion mobility separation. The proposed assay allowed us to determine the low abundant 1,25(OH)₂D₃ with the detection limit of 10 pg/mL. The validation study showed good linearity (r² > 0.99), a wide analytical range (2.5-75 ng/mL for 25(OH)D₃), and acceptable precision (<7%) for all metabolites. The recovery ranged from 71% to 93% and the matrix effect from 0.80 to 0.95 depending on the metabolite; accuracy determination was performed using DEQAS controls.

Determination of vitamin D3 conjugated metabolites: a complementary view on hydroxylated metabolites

Experts typically define vitamin D deficiency levels by the determination of a circulating 25-hydroxyvitamin D₃-calcifediol prohormone. A large part of the population is characterized by deficient vitamin D levels (calcifediol < 20 ng mL^-1) despite individuals not being affected by any disorder. Cholecalciferol (vitamin D₃) and/or calcifediol supplementation is a common practice for vitamin D-deficient individuals as recommended by international scientific societies and official agencies. In the last few years, several studies have reported the presence of conjugated vitamin D₃ metabolites, mainly glucuronidation and sulfation derivatives, although simultaneous quantitative measurements involving phase I and II vitamin D metabolites have not been carried out. A quantitative method based on tandem mass spectrometry detection is proposed here for the combined determination of phase I and phase II vitamin D₃ metabolites in human serum. As phase I and phase II metabolites are preferentially ionized in different modes, a switching polarity mode was adopted to determine both groups of compounds in serum at high sensitivity levels (pg mL^-1). The validation of this proposal was successfully accomplished by following the Center for Drug Evaluation and Research (CDER) guidelines. Its applicability was tested in a cohort of volunteers with mostly deficient baseline levels. Considering the sulfated form of calcifediol, the sum of its concentrations showed sufficient baseline vitamin D levels in all individuals, suggesting that this could be a novel strategy for vitamin D deficiency definition. Therefore, phase II metabolites are proposed to be included when evaluating the vitamin D status since they provide more information about the overall status of the vitamin D endocrine system. Nevertheless, further studies are required to confirm the biological activity of these conjugated metabolites and the suitability of this strategy for the description of vitamin D deficiency.

A Mathematical Model for Determining the Body's Fluctuating Need for and Synthesis of Active Vitamin D

The process by which 1,25(OH)₂D₃ is synthesized and degraded and how it is transported out of the cell and body is described. The changing demand for the synthesis of 1-25(OH)₂D₃ during different conditions experienced by the body is reviewed. A method of determining 1,25(OH)₂D₃ synthesis and demand, and the percent utilization of 25(OH)D₃ to make 1,25(OH)₂D₃ is presented based on the measurement of the end metabolites of 1,25(OH)₂D₃ and of its immediate precursor, 25(OH)D₃. A mathematical model has been developed to allow the calculation of 1,25(OH)₂ D synthesis, and demand, and the percent utilization of 25(OH)D₃. Simple algebraic equations have been derived which allow the calculation of these new parameters using the concentrations of the end metabolites of 1,25(OH)₂D₃ and its immediate precursor, 25(OH)D₃ in the serum and urine. Vitamin D plays an important role in combating invading bacteria and viruses and in subduing the body's associated inflammatory response. This new approach to evaluating vitamin D status may help clinicians determine 25(OH)D₃ and 1,25(OH)₂D₃ levels needed to suppress bacterial infections, viral replication during new viral infections and the reactivation of latent viruses, and to downregulate the inflammatory responses caused by bacteria and viruses.

A highly sensitive LC-MS/MS method for quantitative determination of 7 vitamin D metabolites in mouse brain tissue

Despite its critical role in neurodevelopment and brain function, vitamin D (vit-D) homeostasis, metabolism, and kinetics within the central nervous system remain largely undetermined. Thus, it is of critical importance to establish an accurate, highly sensitive, and reproducible method to quantitate vit-D in brain tissue. Here, we present a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) method and for the first time, demonstrate detection of seven major vit-D metabolites in brain tissues of C57BL/6J wild-type mice, namely 1,25(OH)₂D₃, 3-epi-1,25(OH)₂D₃, 1,25(OH)₂D₂, 25(OH)D₃, 25(OH)D₂, 24,25(OH)₂D₃, and 24,25(OH)₂D₂. Chromatographic separation was achieved on a pentaflurophenyl column with 3 mM ammonium formate water/methanol [A] and 3 mM ammonium formate methanol/isopropanol [B] mobile phase components. Detection was by positive ion electrospray tandem mass spectrometry with the EVOQ elite triple quadrupole mass spectrometer with an Advance ultra-high-performance liquid chromatograph and online extraction system. Calibration standards of each metabolite prepared in brain matrices were used to validate the detection range, precision, accuracy, and recovery. Isotopically labelled analogues, 1,25(OH)₂D₃-d₃, 25(OH)D₃-c₅, and 24,25(OH)₂D₃-d₆, served as the internal standards for the closest molecular-related metabolite in all measurements. Standards between 1 fg/mL and 10 ng/mL were injected with a resulting linear range between 0.001 and 1 ng, with an LLOD and LLOQ of 1 pg/mL and 12.5 pg/mL, respectively. The intra-/inter-day precision and accuracy for measuring brain vit-D metabolites ranged between 0.12-11.53% and 0.28-9.11%, respectively. Recovery in acetonitrile ranged between 99.09 and 106.92% for all metabolites. Collectively, the sensitivity and efficiency of our method supersedes previously reported protocols used to measure vit-D and to our knowledge, the first protocol to reveal the abundance of 25(OH)D₂, 1,25(OH)D₂, and 24,25(OH)₂D₂, in brain tissue of any species. This technique may be important in supporting the future advancement of pre-clinical research into the function of vit-D in neurophysiological and neuropsychiatric disorders, and neurodegeneration.

Measuring Vitamin D3 Metabolic Status, Comparison between Vitamin D Deficient and Sufficient Individuals

The main branch of vitamin D3 metabolism involves several hydroxylation reactions to obtain mono-, di- and trihydroxylated metabolites, including the circulating and active forms—25(OH)D3 and 1,25(OH)2D3, respectively. However, most clinical trials strictly target the determination of 25(OH)D3 to offer a view of the metabolic status of vitamin D3. Due to the growing interest in expanding this restricted view, we have developed a method for measuring vitamin D3 metabolism by determination of vitamin D3, 25(OH)D3, 24,25(OH)2D3, 1,25(OH)2D3 and 1,24,25(OH)3D3 in human plasma. The method was based on SPE–LC–MS/MS with a large volume injection of human plasma (240 µL). Detection of di- and trihydroxymetabolites, found at the picogram per milliliter level, was attained by the combined action of high preconcentration and clean-up effects. The method allows obtaining information about ratios such as the known vitamin D metabolite ratio (24,25(OH)2D3/25(OH)D3), which can provide complementary views of vitamin D3 metabolic status. The method was applied to a cohort of obese patients and a reference cohort of healthy volunteers to find metabolic correlations between target analytes as well as differences as a function of vitamin D levels within and between cohorts.

Sample preparation techniques for extraction of vitamin D metabolites from non-conventional biological sample matrices prior to LC-MS/MS analysis

The determination of vitamin D metabolites as status marker or for diagnostic purposes is almost entirely conducted from blood serum or plasma. Other biological matrices, however, have also interested researchers, for two main reasons: (1) alternative matrices may allow non-invasive sampling, permit easier sample transfer and require less demanding storage conditions; and (2) the levels of vitamin D metabolites in other body compartments may further aid the understanding of vitamin D metabolism and function. Thus, the development of reliable and efficient sample preparation protocols for sample matrices other than serum/plasma, which will remove potential interferences and selectively extract the targeted metabolites, is of great importance. This review summarizes sample preparation methods for measurement of vitamin D metabolites using liquid chromatography-(tandem)mass spectrometry in more than ten different human tissues, including hair, saliva, adipose tissue, brain and others.

Analysis of vitamin D metabolic markers by mass spectrometry: Recent progress regarding the "gold standard" method and integration into clinical practice

Liquid chromatography/tandem mass spectrometry is firmly established today as the gold standard technique for analysis of vitamin D, both for vitamin D status assessments as well as for measuring complex and intricate vitamin D metabolic fingerprints. While the actual mass spectrometry technology has seen only incremental performance increases in recent years, there have been major, very impactful changes in the front- and back-end of MS-based vitamin D assays; for example, the extension to new types of biological sample matrices analyzed for an increasing number of different vitamin D metabolites, novel sample preparation techniques, new powerful chemical derivatization reagents, as well the continued integration of high resolution mass spectrometers into clinical laboratories, replacing established triple-quadrupole instruments. At the same time, the sustainability of mass spectrometry operation in the vitamin D field is now firmly established through proven analytical harmonization and standardization programs. The present review summarizes the most important of these recent developments.

Simultaneous quantification of fat-soluble vitamins A, 25-hydroxylvitamin D and vitamin E in plasma from children using liquid chromatography coupled to Orbitrap mass spectrometry

The fat-soluble vitamins A, D, E and K are micronutrients essential for physiological activity, metabolism and growth. Accurate and sensitive analytical methods are needed to support growing research into fat-soluble vitamins and their impact on children's growth and health. Here we report the first method for simultaneous quantification of fat-soluble vitamins A (retinol), 25-hydroxylvitamin D₂, 25-hydroxylvitamin D₃, and vitamin E (α-tocopherol) using a Q-Exactive Orbitrap mass spectrometer in high-resolution, parallel reaction monitoring mode. This method can select desired ions with high efficiency, potentially making it superior to triple-quadrupole mass spectrometers that employ multiple reaction monitoring. The proposed method offers excellent accuracy, specificity, and sensitivity, as demonstrated with plasma samples from healthy children.

Vitamin D - current stage of knowledge about analysis and supplementation

Nowadays, topics related to the proper nutrition of the body, which requires a complex of compounds and supplementation of these ingredients have undoubtedly gained popularity, so it should come as no surprise that there is a widespread interest in vitamin D in science, medicine, analytics and nutrition. In the world of developing technologies, new directions of physiological action of this vitamin on the body are being discovered. Issues related to the demand for vitamin D in various populations and its sources in food, the appropriate form of supplementation, safety and toxicity are extremely important. The present manuscript focuses on the concise evaluation of key data in the field of vitamin D. Structure and physicochemical properties, demand and delivery trails, deficiency and its diagnosis, supplementation, interactions of vitamin D with supplements and drugs are discussed. Attention has also been paid to the methods of vitamin D analysis in various matrices, which allow for an accurate and precise quality assessment of dietary supplements, drugs and food products. The presented information allows deeper understanding of the mechanisms responsible for the development of many diseases in the context of vitamin D levels.

Relationship between vitamin D deficiency and psychophysiological variables: a systematic review of the literature

Vitamin D is a fat-soluble vitamin that plays a role not only in calcium homeostasis, but also in several other functions, including cell growth and immune functions, and is considered a neurosteroid. Vitamin D deficiency is highly prevalent worldwide and has been suggested to be associated with an increased risk of emotional disorders. Therefore, the association between vitamin D levels and psychophysiological disorders, such as depression, anxiety, and mood, has been investigated. To list these variables, a bibliographical literature research was conducted in the MEDLINE/PubMed, Web of Science, Scopus, Science Direct and PsycINFO databases, between November and December 2020, with no year limits of publication. The studies involved humans aged between 18 and 59 years without associated diseases. This review presents evidence of the main variables involved in this association, main tools used to verify these variables, and methods used to verify circulating vitamin D levels in populations. Most studies have indicated that the main psychophysiological variables involved with vitamin D levels are depression and anxiety followed by mood, and an association has been observed between increased serum vitamin D levels and reduction in symptoms of depression, anxiety, and mood, and there is a heterogeneity of methods for assessing vitamin D. More studies are clearly needed to improve our understanding of their role in modulating the psychophysiological aspects of vitamin D levels.

Vitamin D in human serum and adipose tissue after supplementation

BACKGROUND

Serum 25-hydroxyvitamin D [25(OH)D] concentration is an indicator of vitamin D exposure, but it is also influenced by clinical characteristics that affect 25(OH)D production and clearance. Vitamin D is the precursor to 25(OH)D but is analytically challenging to measure in biological specimens.

OBJECTIVES

We aimed to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantification of vitamins D3 and D2 in serum and to explore the potential of circulating vitamin D as a biomarker of exposure in supplementation trials.

METHODS

The method was validated using guideline C62-A from the Clinical and Laboratory Standards Institute and was applied in 2 pilot clinical trials of oral vitamin D3 supplementation. Pilot study 1 included 22 adults randomly assigned to placebo or 2000 IU/d. Blood was collected at baseline, 1, 3, 6, and 12 mo. Pilot study 2 included 15 adults randomly assigned to 2000 or 4000 IU/d. Blood and subcutaneous (SUBQ) adipose tissue were collected at baseline and 3 mo.

RESULTS

In study 1, mean change (baseline to 3 mo) in serum vitamin D3 was -0.1 ng/mL in the placebo group and 6.8 ng/mL in the 2000 IU/d group (absolute difference: 6.9; 95% CI: 4.5, 9.3 ng/mL). In study 2, mean change (baseline to 3 mo) in serum vitamin D3 was 10.4 ng/mL in the 2000 IU/d group and 22.2 ng/mL in the 4000 IU/d group (fold difference: 2.15; 95% CI: 1.40, 3.37). Serum and adipose tissue vitamin D3 concentrations were correlated, and the dose-response of vitamin D3 in adipose mirrored that in serum.

CONCLUSIONS

We validated a sensitive, robust, and high-throughput LC-MS/MS method to quantify vitamins D3 and D2 in serum. Serum and SUBQ adipose tissue vitamin D3 concentrations increased proportionally to dose with 3 mo of daily supplementation.These trials were registered at clinicaltrials.gov as NCT00552409 (pilot study 1) and NCT01477034 (pilot study 2).

Simultaneous determination of 24,25- and 25,26-dihydroxyvitamin D3 in serum samples with liquid-chromatography mass spectrometry - A useful tool for the assessment of vitamin D metabolism

Vitamin D status is typically assessed by the measurement of 25-hydroxyvitamin D (25(OH)D). However, in selected patient groups the sole determination of 25(OH)D has been proven insufficient for this purpose. The simultaneous measurement of additional vitamin D metabolites may provide useful information for a better evaluation of the vitamin D status. Therefore, we developed and validated a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of 25(OH)D₃, 25(OH)D₂, 24,25(OH)₂D₃ and additionally 25,26(OH)₂D₃, which was identified with a synthesized pure substance. Pure and deuterated substances were used to prepare calibrators and internal standards for all target metabolites. Pre-analytical sample preparation comprised protein precipitation followed by liquid-liquid-extraction and derivatization with 4-Phenyl-1,2,4-triazole-3,5-dione (PTAD) using 50 µL sample volume. Samples were analyzed on an Agilent HPLC 1260 system equipped with a silica-based Kinetex® 5 µm F5 100 Å core-shell column (150 × 4.6 mm) coupled to a Sciex 4500 mass spectrometer. For all four metabolites, limit of detection (LoD) and limit of quantification (LoQ) ranged from 0.3 to 1.5 nmol/L and 1.0 to 3.1 nmol/L, respectively. Recovery varied between 76.1 % and 84.3 %. Intra- and inter-assay imprecision were <8.6 % and <11.5 %, respectively. The analysis of external and internal quality control samples showed good accuracy for 25(OH)D₃, 25(OH)D₂, 24(R),25(OH)₂D₃ and 25,26(OH)₂D₃. Method comparison studies with human samples that were also analyzed with two other LC-MS/MS methods showed close agreement. Finally, the present method has been shown capable of identifying patients with 24-hydroxylase deficiency, which proves its clinical utility.

3-Epi-25-hydroxyvitamin D3 is a poor substrate for SULT2A1: Analysis of its 3-sulfate in cord plasma and recombinant human SULT2A1 incubate

A variety of metabolites derived from 25-hydroxyvitamin D₃ [25(OH)D₃], including its 3-epimer [Epi-25(OH)D₃] and 3-O-sulfate [25(OH)D₃-3S], is found in human plasma/serum. We hypothesized that the 3-O-sulfate of Epi-25(OH)D₃ [Epi-25(OH)D₃-3S] might be present in plasma/serum. Clarifying this point could improve our understanding of the metabolism of vitamin D₃. In this study, we first carefully analyzed the cord plasma samples by derivatization-assisted liquid chromatography/electrospray ionization-tandem mass spectrometry and demonstrated the occurrence of Epi-25(OH)D₃-3S in the plasma. However, the concentration ratio of Epi-25(OH)D₃-3S to 25(OH)D₃-3S (sulfated form) was infinitely lower than the ratio of Epi-25(OH)D₃ to 25(OH)D₃ (unconjugated form). To determine what caused this result, we next performed an in vitro experiment of the 3-O-sulfation for 25(OH)D₃ and Epi-25(OH)D₃ using the recombinant human sulfotransferase (SULT) 2A1. This in vitro experiment revealed that Epi-25(OH)D₃ is a poor substrate for the 3-O-sulfation catalyzed by SULT2A1 as compared to 25(OH)D₃. This substrate specificity of SULT2A1 would be the main cause for the result obtained from the analysis of the cord plasma samples.

Improved sample preparation method for fast LC-MS/MS analysis of vitamin D metabolites in serum

Despite the fact that more than 90% of vitamin D analysis are performed using immuno-enzymatic techniques, it is liquid chromatography coupled with tandem mass spectrometry that is currently the reference method. It allows for specific and selective analysis of all relevant vitamin D metabolites from a variety of biological materials, including serum or a dried blood spot. This paper presents development of a fast, cheap and high-throughput method of serum sample preparation using protein precipitation. For this purpose, organic solvent is used. Several substances were tested, including acetonitrile, methanol and their mixtures with zinc sulfate. However, the highest recovery values for the vitamin D metabolites were obtained for acetonitrile, with an organic solvent to serum ratio of 8:1. The preparation of a sample is carried out in 96-well plates and takes an hour and a half, together with a derivatization reaction using Cookson-type reagent 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione. Due to the fact that vitamin D metabolites are bound to proteins, the relationship between the content of organic solvent in the sample preparation process and their release from the protein complex was examined. The results indicate that the organic solvent content should be 30-70% in order to completely release the tested compounds from the proteins. In addition, the developed chromatographic method has eliminated false positive signals for the 24,25(OH)₂D₃ metabolite. Total analysis time is 5.5 min., while maintaining resolution necessary to separate the analyzed compounds.

Current trends in the analytical determination of vitamin D

Introduction

Vitamin D is a micronutrient that plays a large role in bone disease, and researchers are now discovering that it also does so in non-skeletal disease, thus making high-quality analytical determination necessary. To make this determination, a series of immunochemical and physical methods are used. These methods present a series of different ways of handling samples as well as different methodologies that bring a series of advantages and limitations based on the scope of work in which the vitamin D analysis methodology is applied. Although the Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) is the gold standard method of analytical vitamin D determination, and is the only one to offer a more complete and accurate view of all metabolites of this vitamin, it is necessary to standardize all the analysis methodologies that allow accurate, reliable and quality analytical determination, since it is essential to obtain results that can reliably be extrapolated to the population, and that can be decisive in assessing a large number of pathologies.

Quantification of fat-soluble vitamins and their metabolites in biological matrices: an updated review

Fat-soluble vitamins (FSVs) are micronutrients essential in maintaining normal physiological function, metabolism and human growth. Ongoing increased awareness regarding FSV concentrations and their impact on human growth along with disease progression warrant the need of developing selective and sensitive analytical methods. LC–MS/MS is currently the method of choice for accurate quantitation of FSVs. However, there are multiple approaches for extraction, separation and calibration of FSVs in biological matrices. This review discusses recent LC–MS/MS methods for the simultaneous quantification of FSVs in biological matrices and summarizes sample pretreatment procedures, chromatographic conditions and calibration approaches. Current challenges and clinical applications in various disease states are also highlighted.

Genetic, environmental and biomarker considerations delineating the regulatory effects of vitamin D on central nervous system function

Studies show that vitamin D (vit-D) (25(OH)D), the bioactive metabolite (1,25(OH)2D3) and vit-D receptors (vit-D receptor; protein disulphide isomerase, family A member 3) are expressed throughout the brain, particularly in regions pivotal to learning and memory. This has led to the paradigm that avoiding vit-D deficiency is important to preserve cognitive function. However, presently, it is not clear if the common clinical measure of serum 25(OH)D serves as a robust surrogate marker for central nervous system (CNS) homeostasis or function. Indeed, recent studies report CNS biosynthesis of endogenous 25(OH)D, the CNS expression of the CYP group of enzymes which catalyse conversion to 1,25(OH)2D3 and thereafter, deactivation. Moreover, in the periphery, there is significant ethnic/genetic heterogeneity in vit-D conversion to 1,25(OH)2D3 and there is a paucity of studies which have actually investigated vit-D kinetics across the cerebrovasculature. Compared with peripheral organs, the CNS also has differential expression of receptors that trigger cellular response to 1,25(OH)2D3 metabolites. To holistically consider the putative association of peripheral (blood) abundance of 25(OH)D on cognitive function, herein, we have reviewed population and genetic studies, pre-clinical and clinical intervention studies and moreover have considered potential confounders of vit-D analysis.

Vitamin D Measurement, the Debates Continue, New Analytes Have Emerged, Developments Have Variable Outcomes

The demand for measurement of vitamin D metabolites for clinical diagnosis and to advance our understanding of the role of vitamin D in human health has significantly increased in the last decade. New developments in technologies employed have enabled the separation and quantification of additional metabolites and interferences. Also, developments of immunoassays have changed the landscape. Programmes and materials for assay standardisation, harmonisation and the expansion of the vitamin D external quality assurance scheme (DEQAS) with the provision of target values as measured by a reference measurement procedure have improved standardisation, quality assurance and comparability of measurements. In this article, we describe developments in the measurement of the commonly analysed vitamin D metabolites in clinical and research practice. We describe current analytical approaches, discuss differences between assays, their origin, and how these may be influenced by physiological and experimental conditions. The value of measuring metabolites beyond 25 hydroxyvitamin D (25(OH)D), the marker of vitamin D status, in routine clinical practice is not yet confirmed. Here we provide an overview of the value and application of the measurement of 1,25 dihydroxyvitamin D, 24,25 dihydroxyvitamin D and free 25OHD in the diagnosis of patients with abnormalities in vitamin D metabolism and for research purposes.

Suitability of stationary phase for LC analysis of biomolecules

Biologically active compounds such as carotenoids/isoprenoids, vitamins, steroids, saponins, sugars, long chain fatty acids, and amino acids play a very important role in coordinating functions in living organisms. Determination of those substances is indispensable in advanced biological sciences. Engineered stationary phase in LC for the analysis of biomolecules has become easier with the development of chromatographic science. In general, C₁₈ column is being used for routine analysis but specific columns are being used for specific molecule. Monolithic columns are found to have higher efficiency than normal column. Among recent introduction, triacontyl stationary phases, designed for the separation of carotenoid isomers, are widely used for the estimation of carotenoids. In comparison to conventional C₁₈ phases, C₃₀ phases exhibited superior shape selectivity for the separation of isomers of carotenoids. It is also found useful for better elution and analysis of tocopherols, vitamin K, sterols, and fatty acids. Vitamin K, E, and their isomers are also successfully resoluted and analyzed by using C₃₀ column. Amino bonded phase column is specifically used for better elution of sugars, whereas phenyl columns are suitable for the separation and analysis of curcuminoids and taxol. Like triacontyl stationary phase, pentafluorophenyl columns are also used for the separation and analysis of carotenoids. Similarly, HILIC column are best suited for sugar analysis. All the stationary phases are made possible to resolute and analyze the target biomolecules better, which are the future of liquid chromatography. The present article focuses on the differential interaction between stationary phase and target biomolecules. The applicability of these stationary phases are reported in different matrices.

Simple Fast Quantification of Cholecalciferol, 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D in Adipose Tissue Using LC-HRMS/MS

Vitamin D metabolism is actively modulated in adipose tissue during obesity. To better investigate this process, we develop a specific LC-HRMS/MS method that can simultaneously quantify three vitamin D metabolites, i.e., cholecalciferol, 25-hydroxyvitamin D₃ (25(OH)D₃), and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) in a complex matrix, such as mouse adipose tissue and plasma. The method uses pretreatment with liquid–liquid or solid–phase extraction followed by derivatization using Amplifex^® reagents to improve metabolite stability and ionization efficiency. Here, the method is optimized by co-eluting stable isotope-labelled internal standards to calibrate each analogue and to spike biological samples. Intra-day and inter-day relative standard deviations were 0.8–6.0% and 2.0–14.4%, respectively for the three derivatized metabolites. The limits of quantification (LoQ) achieved with Amplifex^® derivatization were 0.02 ng/mL, 0.19 ng/mL, and 0.78 ng/mL for 1,25(OH)₂D₃, 25(OH)D₃ and cholecalciferol, respectively. Now, for the first time, 1,25(OH)₂D₃ can be co-quantified with cholecalciferol and 25(OH)D₃ in mouse adipose tissue. This validated method is successfully applied to study the impact of obesity on vitamin D status in mice.

Development of a method for multiple vitamin D metabolite measurements by liquid chromatography coupled with tandem mass spectrometry in dried blood spots

There are two forms of vitamin D which are essential to the human body, i.e. vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). The inactive metabolites of vitamin D are commonly used for quantitative analysis because of their longer half-life, stability, and relatively high blood concentrations. This paper presents the development of a high-throughput and sensitive method for determining four vitamin D metabolites in dried blood spots using liquid chromatography coupled with tandem mass spectrometry. This method allows for the determination of 25(OH)D2 and 25(OH)D3 concentrations, as well as the epimeric form 3-epi-25(OH)D3 and 24,25(OH)2D3. The analyzed material is capillary blood taken from the fingertip, deposited on filter paper. Four different chromatographic columns were tested to separate all compounds, in particular, the epimeric form. The column of choice was F5 (Phenomenex, Torrance, CA, USA). In order to prove the consistency between the results for DBS, used as an alternative biological matrix, and serum, comparative studies of these two materials were carried out in nearly 100 individuals. The results indicated their positive correlation. The evaluation of short-term stability of metabolites in DBS within the month showed no change in metabolite concentration. During the validation, the impact of the matrix on the ionization of the tested compounds was evaluated. Capillary blood and venous blood collected for different anticoagulants were also compared. The smallest differences in the results were obtained for citrate. In order to achieve a limit of quantitation of 0.2 ng ml-1, sample preparation involved derivatization using a Cookson-type reagent, 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD).

SULFATION PATHWAYS: Insights into steroid sulfation and desulfation pathways

Sulfation and desulfation pathways represent highly dynamic ways of shuttling, repressing and re-activating steroid hormones, thus controlling their immense biological potency at the very heart of endocrinology. This theme currently experiences growing research interest from various sides, including, but not limited to, novel insights about phospho-adenosine-5'-phosphosulfate synthase and sulfotransferase function and regulation, novel analytics for steroid conjugate detection and quantification. Within this review, we will also define how sulfation pathways are ripe for drug development strategies, which have translational potential to treat a number of conditions, including chronic inflammatory diseases and steroid-dependent cancers.

Standard addition with internal standardisation as an alternative to using stable isotope labelled internal standards to correct for matrix effects-Comparison and validation using liquid chromatography-​tandem mass spectrometric assay of vitamin D

With mass spectrometric detection in liquid chromatography, co-eluting impurities affect the analyte response due to ion suppression/enhancement. Internal standard calibration method, using co-eluting stable isotope labelled analogue of each analyte as the internal standard, is the most appropriate technique available to correct for these matrix effects. However, this technique is not without drawbacks, proved to be expensive because separate internal standard for each analyte is required, and the labelled compounds are expensive or require synthesising. Traditionally, standard addition method has been used to overcome the matrix effects in atomic spectroscopy and was a well-established method. This paper proposes the same for mass spectrometric detection, and demonstrates that the results are comparable to those with the internal standard method using labelled analogues, for vitamin D assay. As conventional standard addition procedure does not address procedural errors, we propose the inclusion of an additional internal standard (not co-eluting). Recoveries determined on human serum samples show that the proposed method of standard addition yields more accurate results than the internal standardisation using stable isotope labelled analogues. The precision of the proposed method of standard addition is superior to the conventional standard addition method.