Evaluation of short-term storage prior to analysis of vitamin D3 and metabolites in human serum by liquid chromatography coupled to tandem mass spectrometry

Differential seasonal performance of C3-epi-D3 level and proportion on multiple metabolic disorders in patients with type 2 diabetes mellitus

BACKGROUND AND AIM

Recent Mendelian randomization and meta analysis suggest a controversial causality between C3-epimer of 25 hydroxyvitamin D3 (C3-epi-D3) and type 2 diabetes mellitus (T2DM). The clinical evidence regarding the impact of C3-epi-D3 on the progression of T2DM is currently insufficient. This study aims to investigate whether C3-epi-D3 has any effect on metabolic disorders of T2DM patients.

METHODS

A total of 1222 patients with T2DM were prospectively enrolled in this study and followed up every 1 to 2 months for 3 to 6 months. Kidney biomarkers, lipids, electrolytes, and 25 hydroxyvitamin D (25-OHD) metabolites were measured as required during follow-up, to investigate the association of C3-epi-D3 levels and %C3-epi-D3 with metabolic disorders, including dyslipidemia, chronic kidney disease (CKD), and calcium-phosphorus metabolic disorder.

RESULTS

Among these T2DM patients, there were age and seasonal differences in C3-epi-D3 levels (χ2 = 10.419 and 19.609, P = 0.034 and < 0.001), but only seasonal difference in %C3-epi-D3 (χ2 = 79.299, P < 0.001). C3-epi-D3 levels showed an evident correlation with calcium-phosphorus product during autumn and winter (ρ = - 0.336 and - 0.304, both P < 0.001), and was confirmed as an independent factor on calcium-phosphorus metabolic disorder during autumn and winter by subsequent partial correlation analysis (rpartial = - 0.300 and - 0.319, both P < 0.001). Both C3-epi-D3 levels and %C3-epi-D3 showed evident correlation with the severity of chronic kidney disease (CKD) in summer (ρ = 0.344 and 0.445, both P < 0.001). But subsequent multinomial logistic regression confirmed that only %C3-epi-D3 independently associated with moderate CKD severity in summer (OR = 1.348, P < 0.001), as well as serious CKD severity in spring, summer, and autumn (OR = 1.324, 1.342, and 1.698, all P < 0.001). Additionally, no evident correlation was observed between C3-epi-D3 and dyslipidemia.

CONCLUSION

Our study releases a seasonally differential impact of C3-epi-D3 levels and proportions on metabolic disorders of T2DM patients, considering to be potentially related to their pathogenesis of different metabolic disorders. The independent association between %C3-epi-D3 and CKD suggests a potential pathological relevance involving C3-epi-D3 itself.

Development and Validation of Novel HPLC Methods for Quantitative Determination of Vitamin D3 in Tablet Dosage Form

In the present work, an efficient isocratic HPLC method was developed for the precise and accurate estimation of vitamin D3 in tablet form. The chromatographic conditions comprised an L3 silica column (5 µm in particle size, 4.6 mm × 250 mm) with a mobile phase n-hexane/ethyl acetate (85:15 v/v) with a flow rate of 2.0 mL/min and a detection wavelength of 292 nm. The new methodology was validated for accuracy, precision, specificity, robustness, and quantification limits according to an official monograph of USP/BP and ICH guidelines. The peak areas of the six replicates of the homogeneous sample were recorded. The mean value obtained was 67,301, and the relative standard deviation (RSD) was 0.1741. The linearity and range were in the acceptable bounds, i.e., 0.999, which was calculated using regression line analysis. The results show that the method is truly acceptable as the RSD, as the flow rate was 0.81%, while for the mobile phase composition, it was 0.72%, which lies in the acceptable range. The limit of detection (LOD) and the limit of quantification (LOQ) values were 0.0539 µg/mL and 0.1633 µg/mL, respectively. The % RSD of the intra and inter-day precision of the method was deemed acceptable according to the international commission for harmonization guidelines. The developed method has potential to be used for the detection and quantification of vitamin D3 during routine analysis for tablets in dosage form.

C3-epi-25(OH)D3 percentage, not level, may be a potential biomarker to reflect its pathological increase in multiple diseases: a cross-sectional case-control study

National surveys in developed countries have examined the presence of C3-epimer of 25-hydroxyvitamin D3 [C3-epi-25(OH)D3]. However, controversy remains regarding its association with disease occurrence due to its high correlation with 25-hydroxyvitamin D3 [25(OH)D3]. This study aims to investigate whether %C3-epi-25(OH)D3 can serve as an indicator for this relationship with various diseases. A total of 3086 healthy participants and 4120 patients were included in this study. We investigated the association between C3-epi-25(OH)D3 and %C3-epi-25(OH)D3 levels with gender, age, and season; compared the performance of C3-epi-25(OH)D3 and %C3-epi-25(OH)D3 across different disease conditions; and explored the correlation between %C3-epi-25(OH)D3 and various diseases. Results indicated that C3-epi-25(OH)D3 varied significantly by gender, age, and season (z/χ2 = 3.765, 10.163, and 150.975, all P < 0.01), while only season for %C3-epi-25(OH)D3 (χ2 = 233.098, P < 0.001). In contrast to the significant decrease in C3-epi-25(OH)D3, %C3-epi-25(OH)D3 showed a significant increase in 8 out of 11 disease categories (z = 3.464 ~ 11.543, all Padj < 0.05). Similar opposite changes were also observed in most of the investigated 32 specific diseases. Moreover, an elevation in %C3-epi-25(OH)D3 was found to be significantly associated with 29 specific diseases both in univariate analysis (OR = 1.16 ~ 2.10, all P < 0.05) and after adjusting for gender, age, and season (OR = 1.15 ~ 1.50, all P < 0.05). However, after further adjustment for 25(OH)D3 levels, the association remained significant only for 15 specific diseases (OR = 1.11 ~ 1.50, all P < 0.05). Seasonal stratification analysis further supports the consistent association of %C3-epi-25(OH)D3 with disease across all or nearly all four seasons. In conclusion, %C3-epi-25(OH)D3 may better reflect the production of C3-epi-25(OH)D3 in disease conditions, thereby offering a more applicable approach to investigate its association with diseases. However, the interpretation of this relationship may be confounded by 25(OH)D3 as a potential covariate.

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.

Comparison of two LC-MS/MS methods for the quantification of 24,25-dihydroxyvitamin D3 in patients and external quality assurance samples

OBJECTIVES

In-house developed liquid-chromatography mass spectrometry (LC-MS/MS) methods are used more and more frequently for the simultaneous quantification of vitamin D metabolites. Among these, 24,25-dihydroxyvitamin D3 (24,25(OH)₂D₃) is of clinical interest. This study assessed the agreement of this metabolite in two validated in-house LC-MS/MS methods.

METHODS

24,25(OH)₂D₃ was measured in 20 samples from the vitamin D external quality assurance (DEQAS) program and in a mixed cohort of hospital patients samples (n=195) with the LC-MS/MS method at the Medical University of Graz (LC-MS/MS 1) and at the University of Liège (LC-MS/MS 2).

RESULTS

In DEQAS samples, 24,25(OH)₂D₃ results with LC-MS/MS 1 had a proportional bias of 1.0% and a negative systemic difference of -0.05%. LC-MS/MS 2 also showed a proportional bias of 1.0% and the negative systemic bias was -0.22%. Comparing the EQA samples with both methods, no systemic bias was found (0.0%) and the slope was 1%. The mean difference of 195 serum sample measurements between the two LC-MS/MS methods was minimal (-0.2%). Both LC-MS/MS methods showed a constant bias of 0.31 nmol/L and a positive proportional bias of 0.90%, respectively.

CONCLUSIONS

This study is the first to assess the comparability of 24,25(OH)₂D₃ concentrations in a mixed cohort of hospitalized patients with two fully validated in-house LC-MS/MS methods. Despite different sample preparation, chromatographic separation and ionization, both methods showed high precision measurements of 24,25(OH)₂D₃. Furthermore, we demonstrate the improvement of accuracy and precision measurements of 24,25(OH)₂D₃ in serum samples and in the DEQAS program.

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.

Measurement of vitamin D in dried blood spots stored under different temperature conditions

BACKGROUND

As part of the Survey of Health, Ageing and Retirement in Europe (SHARE) study, dried blood spot samples were obtained for measurement of potential biological biomarkers, among those vitamin D. Unfortunately, no studies describe the impact of high temperatures on dried blood spot samples and vitamin D measurements.

MATERIALS AND METHODS

Capillary samples were collected on dried blood spot cards from 40 outpatients (median age 78 years) along with venous blood samples. To mimic the different environmental and temporal challenges during collection and shipment until final storage in the SHARE study, dried blood spot cards were stored at different temperatures, at time span and with/without freeze-thaw. Vitamin D concentrations in venous plasma samples were measured by conventional immunoassay (on Architect i2000SR), while vitamin D concentrations in dried blood spot samples were measured using LC-MS/MS with a well-described extraction method and with relevant calibration and comparison with a reference method.

RESULTS

Vitamin D measured in dried blood spot samples did not differ significantly from venous plasma measurements under the different storage conditions tested. The optimal vitamin D correlation between the two matrices was by storage at either 21°C or 35°C for four days (r = 0.9060 and 0.9026, respectively). Freeze-thaw of the dried blood spot samples did not have any significant effect.

CONCLUSION

We find that vitamin D measured in dried blood spot samples do not differ significantly from venous plasma measurements despite storage at different temperatures and freeze-thaw, which enables the use of dried blood spot in multicentre studies taking place under alternating temperature conditions.

Recommendations on the measurement and the clinical use of vitamin D metabolites and vitamin D binding protein - A position paper from the IFCC Committee on bone metabolism

Vitamin D, an important hormone with a central role in calcium and phosphate homeostasis, is required for bone and muscle development as well as preservation of musculoskeletal function. The most abundant vitamin D metabolite is 25-hydroxyvitamin D [25(OH)D], which is currently considered the best marker to evaluate overall vitamin D status. 25(OH)D is therefore the most commonly measured metabolite in clinical practice. However, several other metabolites, although not broadly measured, are useful in certain clinical situations. Vitamin D and all its metabolites are circulating in blood bound to vitamin D binding protein, (VDBP). This highly polymorphic protein is not only the major transport protein which, along with albumin, binds over 99% of the circulating vitamin D metabolites, but also participates in the transport of the 25(OH)D into the cell via a megalin/cubilin complex. The accurate measurement of 25(OH)D has proved a difficult task. Although a reference method and standardization program are available for 25(OH)D, the other vitamin D metabolites still lack this. Interpretation of results, creation of clinical supplementation, and generation of therapeutic guidelines require not only accurate measurements of vitamin D metabolites, but also the accurate measurements of several other "molecules" related with bone metabolism. IFCC understood this priority and a committee has been established with the task to support and continue the standardization processes of vitamin D metabolites along with other bone-related biomarkers. In this review, we present the position of this IFCC Committee on Bone Metabolism on the latest developments concerning the measurement and standardization of vitamin D metabolites and its binding protein, as well as clinical indications for their measurement and interpretation of the results.

Lyophilization as pre-processing for sample storage in the determination of vitamin D3 and metabolites in serum and plasma

Determination of vitamin D levels in human biological specimens has gained a high relevance over the last decades, essentially because low levels have been associated with several biological disorders. In fact, vitamin D deficiency has become a worldwide health concern covering all ages and genders. The storage of biofluids has to be considered for determination of vitamin D and metabolites in order to fully preserve matrices status. This study attempts to evaluate lyophilization of serum and plasma as a pre-processing step for sample storage prior to quantitative analysis of vitamin D₃ and its main hydroxylated metabolites -25(OH)D₃, 24,25(OH)₂D₃ and 1,25(OH)₂D₃. The protocol including sample lyophilization was characterized in terms of analytical features and compared to the same method, based on SPE-LC-MS/MS, without lyophilization. Sensitivity, precision and accuracy were not affected when we operated with lyophilized serum and plasma and results provided by a set of twenty-four serum samples from DEQAS (Vitamin D External Quality Assessment Scheme) were in agreement with reported concentrations for 25(OH)D₃ and 1,25(OH)₂D₃. A stability study programmed for 9 months allowed ensuring that the concentration of vitamin D₃ and metabolites in lyophilized serum and plasma stored at room temperature was not affected during this period. This research has demonstrated that the quantitation of target metabolites is not under the influence of lyophilization. Therefore, including lyophilization prior to analysis could reduce shipment and storage costs, avoid delays of sample processing, and increase the stability of the target analytes due to an effective quenching process.

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.

Prevalence of vitamin D deficiency and its predictors in the Portuguese population: a nationwide population-based study

Vitamin D deficiency is prevalent worldwide, but its prevalence is unknown in adult Portuguese population. In Portugal, 66% of adults present Vitamin D insufficiency/deficiency. Winter, living in Azores, older age, and obesity were the most important risk factors. It highlights the need of strategies to prevent vitamin D deficiency in Portugal.

OBJECTIVE

To estimate the prevalence and risk factors of vitamin D deficiency in the adult Portuguese population.

METHODS

Adults (≥ 18 years old) from the EpiReumaPt Study (2011-2013) were included. Standardized questionnaires on socio-demographic and lifestyle features were obtained. Serum 25-hydroxyvitamin D [25(OH)D] concentrations were evaluated using ADVIA Centaur VitD competitive immunoassay (Siemens Healthineers) in 2015-2017 as 25 (OH)D Level 0: ≤ 10 ng/mL; Level 1: 11-19 ng/mL; Level 2: 20-29 ng/mL, and Level 3: ≥ 30 ng/mL. Weighted multinomial regression analysis was conducted to evaluate the association between socio-demographic and lifestyle variables and vitamin D status.

RESULTS

Based on weighted analysis, the estimated prevalence of levels of 25(OH)D ≤ 10, < 20, and < 30 ng/mL was 21.2, 66.6, and 96.4%, respectively. The strongest independent predictors of serum 25 (OH)D ≤ 10 ng/mL were living in the Azores archipelagos (OR 9.39; 95%CI 1.27-69.6) and having the blood sample collection in winter (OR 18.53; 95%CI 7.83-43.87) or spring (11.55; 95%CI 5.18-25.74). Other significant predictors included older age (OR 5.65, 95%CI 2.08-15.35), obesity (OR 2.61; 95%CI 1.35-5.08), current smoking (OR 2.33; 95%CI 1.23-4.43), and female gender (OR 1.9, 95%CI 1.1-3.28). Conversely, physical exercise (OR 0.48, 95%CI 0.28-0.81) and occasional alcohol intake (OR 0.48, 95%CI 0.29-0.81) were associated with a lower risk of 25(OH)D ≤ 10 ng/mL.

CONCLUSION

Vitamin D deficiency/insufficiency [25(OH)D < 20 ng/ml] is highly prevalent in Portugal, affecting > 60% of all Portuguese adults, with strong geographical and seasonal variation. This study highlights the need to critically assess the relevance of vitamin D deficiency as a public health problem and the urgent need for a wide and scientifically robust debate about the most appropriate interventions at the individual and societal levels.