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

Simultaneous determination of 25(OH)D2, 25(OH)D3 and 1α,25(OH)2D3 in human serum by derivatization-liquid chromatography-tandem mass spectrometry

An LC-MS/MS method was developed and validated for simultaneously quantifying 25-hydroxyvitamin D2, D3, and 1α,25-dihydroxyvitamin D3 in human serum. Protein in 200 μL serum was precipitated with acetonitrile. After centrifugation, the metabolites were derivatized using (diacetoxyiodo)benzene (PIA) and 4-(4-dimethylaminophenyl)-1,2,4-triazolidine-3,5-dione (DMAT) and then quantified by the LC-MS/MS system. The limits of detection (LODs) for the three substances were 10, 10, and 5 pg/mL, and the limits of quantification (LOQs) were 20, 20, and 10 pg/mL. The standard curves for these compounds showed linear regression coefficients (R2)>0.998 over specific concentration ranges. Recoveries were 94.36 %-102.34 % for 25(OH)D2, 92.43 %-103.41 % for 25(OH)D3, and 88.98 %-94.36 % for 1α,25(OH)2D3. The mean serum levels in 109 subjects (consisting of 61 healthy adult males and 59 healthy adult females) were 2.0 ± 1.5 ng/ml (25(OH)D2), 16.4 ± 6.1 ng/ml (25(OH)D3) and 36.6 ± 15.1 pg/ml (1α, 25(OH)2D3).Derivatization of vitamin D metabolites using PIA and DMAT is useful for rapidly determining the serum 25(OH) D2, 25(OH) D3 and 1α,25(OH)2D3 concentrations simultaneously in human serum.

Assessment of Vitamin D Metabolism Disorders in Hemodialysis Patients

BACKGROUND

Patients with end-stage chronic diseases, especially those undergoing hemodialysis (HD), often experience mineral bone disease (MBD), leading to hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH). Vitamin D deficiency and metabolism disorders are also common, resulting from impaired conversion of 25(OH)D3 to its active form, 1,25(OH)2D3, and reduced inactivation to 24,25(OH)2D3. This study aimed to assess the levels of 25(OH)D2, 25(OH)D3, 24,25(OH)2D3, 3-epi-25(OH)D3, and the vitamin D metabolism ratio (VMR) in patients with maintenance HD.

METHODS

A cross-sectional study was conducted on 66 HD patients (22-90 years, average 61.3 ± 16.4), with a control group of 206 adults without chronic kidney disease (CKD), both without cholecalciferol supplementation.

RESULTS

the HD patients had significantly lower 25(OH)D3 levels (15 ng/mL vs. 22 ng/mL) and higher deficiency rates (69% vs. 39%) compared to the controls. However, both groups showed similarly low levels of optimal vitamin D3. The HD patients had lower 24,25(OH)D3 levels (0.1 vs. 2.1 ng/mL) and a lower VMR (0.9% vs. 9%). 3-epi-25(OH)D3 levels and its ratio to 25(OH)D3 were significantly lower in the HD group. Alphacalcidol supplementation raised 1,25(OH)2D3 levels (30.4 vs. 16.2 pg/mL) without affecting other vitamin D metabolites. The HD patients had higher levels of 25(OH)D2 compared to the controls (0.61 vs. 0.31 ng/mL).

CONCLUSIONS

Vitamin D3 reserves are lower, and both functional deficiency and impaired catabolism of vitamin D3 are present in HD patients compared to the general population. The VMR index is the most sensitive parameter for vitamin D3 deficiency assessment, highlighting the importance of measuring 24,25(OH)D3. Alphacalcidol supplementation increases 1,25(OH)2D3 levels without affecting other vitamin D metabolites. 25(OH)D2 is the only metabolite that was higher in HD patients than the controls.

Ubiquinone (Coenzyme Q-10) Supplementation Influences Exercise-Induced Changes in Serum 25(OH)D3 and the Methyl-Arginine Metabolites: A Double-Blind Randomized Controlled Trial

Researchers have studied the effects of exercise on serum methyl-arginine and vitamin D metabolites; however, the effects of exercise combined with antioxidants are not well documented. Since oxidative stress affects the metabolism of vitamin D and methyl-arginine, we hypothesised that the antioxidant coenzyme Q10 (CoQ10) might modulate exercise-induced changes. A group of twenty-eight healthy men participated in this study and were divided into two groups: an experimental group and a control group. The exercise test was performed until exhaustion, with gradually increasing intensity, before and after the 21-day CoQ10 supplementation. Blood samples were collected before, immediately after, and 3 and 24 h after exercise. CoQ10, vitamin D metabolites, asymmetric dimethylarginine (ADMA), symmetric dimethylarginine, methylarginine, dimethylamine, arginine, citrulline, and ornithine were analysed in serum samples. CoQ10 supplementation caused a 2.76-fold increase in the concentration of serum CoQ10. Conversely, the 25(OH)D3 concentration increased after exercise only in the placebo group. ADMA increased after exercise before supplementation, but a decrease was observed in the CoQ10 supplementation group 24 h after exercise. In conclusion, our data indicate that CoQ10 supplementation modifies the effects of exercise on vitamin D and methyl-arginine metabolism, suggesting its beneficial effects. These findings contribute to the understanding of how antioxidants like CoQ10 can modulate biochemical responses to exercise, potentially offering new insights for enhancing athletic performance and recovery.

An ultra-sensitive and high-throughput trapping-micro-LC-MS method for quantification of circulating vitamin D metabolites and application in multiple sclerosis patients

Quantitative analysis of the biologically-active metabolites of vitamin D (VitD), which are crucial in regulating various physiological and pathological processes, is important for clinical investigations. Liquid chromatography-tandem mass spectrometry (LC-MS) has been widely used for this purpose but existing LC-MS methods face challenges in achieving highly sensitive and accurate quantification of low-abundance VitD metabolites while maintaining high throughput and robustness. Here we developed a novel pipeline that combines a trapping-micro-LC-(T-µLC) with narrow-window-isolation selected-reaction monitoring MS(NWI-SRM) for ultra-sensitive, robust and high-throughput quantification of VitD metabolites in serum samples after derivatization. The selective-trapping and delivery approach efficiently removes matrix components, enabling high-capacity sample loading and enhancing sensitivity, throughput, and robustness. The NWI-SRM further improves the sensitivity by providing high selectivity. The lower limits of quantification (LOQs) achieved were markedly lower than any existing LC-MS methods: 1.0 pg/mL for 1,25(OH)2D3, 5.0 pg/mL for 24,25(OH)2D3, 30 pg/mL for both 25(OH)D2 and 25(OH)D3, all within a 9-min cycle. The method is applied to quantify VitD metabolites from 218 patients with multiple sclerosis. This study revealed negative correlations(r=- 0.44 to - 0.51) between the levels of 25(OH)D2 and all the three D3 metabolites in multiple sclerosis patients.

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.

Seasonal changes in free 25-(OH)D and vitamin D metabolite ratios and their relationship with psychophysical stress markers in male professional football players

Introduction: Novel markers of vitamin D status are currently being investigated, including free 25-(OH)D (25-(OH)DF) and the vitamin D metabolite ratio (24,25-(OH)2D3:25-(OH)D3; VMR). The VMR may provide additional functional information on vitamin D metabolism in athletes. Therefore, the main objective of the current study was to evaluate 25-(OH)DF, bioavailable 25-(OH)D (25-(OH)DB), VMR, and psychophysical stress markers during different training periods over a half-season. The second aim was to assess the association between vitamin D binding protein (VDBP), total and free 25-(OH)D, VMRs, and psychophysical stress markers in professional football players. Moreover, we examined the relationship between 25-(OH)D3 and vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3) to determine if training loads in different training periods influenced the vitamin D metabolome. Methods: Twenty professional football players were tested at six different time points across half a year (V1-June; V2-July; V3-August; V4-October; V5-December; V6-January). Results: Analyses indicated a significant seasonal rhythm for VDBP, and total 25-(OH)D (25-(OH)DT), 25-(OH)DB, 24,25-(OH)2D3, 3-epi-25-(OH)D3, 25-(OH)D3:24,25-(OH)2D3, and 24,25-(OH)2D3:25-(OH)D3 VMRs throughout the training period. No correlation was detected between 25-(OH)DT, 25-(OH)DB, 25-(OH)DF, vitamin D metabolites, VMRs, VDBP, and ferritin, liver enzymes (aspartate transaminase [AST] and alanine transaminase [ALT]), creatine kinase (CK), cortisol, testosterone, and testosterone-to-cortisol ratio (T/C) in each period (V1-V6). However, there was a strong statistically significant correlation between 25-(OH)D3 and 24,25-(OH)D3 in each training period. Conclusion: In conclusion, a seasonal rhythm was present for VDBP, 25-(OH)DT, 25-(OH)DB, vitamin D metabolites (24,25-(OH)2D3, 3-epi-25-(OH)D3), and VMRs (25-(OH)D3:24,25-(OH)2D3, 25-(OH)D3:3-epi-25-(OH)D3). However, no rhythm was detected for 25-(OH)DF and markers of psychophysical stress (ferritin, liver enzymes, CK, testosterone, cortisol, and T/C ratio). Moreover, the relationships between free and total 25-(OH)D with psychophysical stress markers did not demonstrate the superiority of free over total measurements. Furthermore, training loads in different training periods did not affect resting vitamin D metabolite concentrations in football players.

Supplementation with Vitamin D3 Protects against Mitochondrial Dysfunction and Loss of BDNF-Mediated Akt Activity in the Hippocampus during Long-Term Dexamethasone Treatment in Rats

Dexamethasone (DEXA) is a commonly used steroid drug with immunosuppressive and analgesic properties. Unfortunately, long-term exposure to DEXA severely impairs brain function. This study aimed to investigate the effects of vitamin D3 supplementation during chronic DEXA treatment on neurogenesis, mitochondrial energy metabolism, protein levels involved in the BDNF-mediated Akt activity, and specific receptors in the hippocampus. We found reduced serum concentrations of 25-hydroxyvitamin D3 (25(OH)D3), downregulated proBDNF and pAkt, dysregulated glucocorticosteroid and mineralocorticoid receptors, impaired mitochondrial biogenesis, and dysfunctional mitochondria energy metabolism in the DEXA-treated group. In contrast, supplementation with vitamin D3 restored the 25(OH)D3 concentration to a value close to that of the control group. There was an elevation in neurotrophic factor protein level, along with augmented activity of pAkt and increased citrate synthase activity in the hippocampus after vitamin D3 administration in long-term DEXA-treated rats. Our findings demonstrate that vitamin D3 supplementation plays a protective role in the hippocampus and partially mitigates the deleterious effects of long-term DEXA administration. The association between serum 25(OH)D3 concentration and BDNF level in the hippocampus indicates the importance of applying vitamin D3 supplementation to prevent and treat pathological conditions.

Vitamin D and Its Metabolites Status before and during Chemotherapy in Caucasian Breast Cancer Patients

BACKGROUND

The predictive role of vitamin D (VD) in breast cancer (BC) patients' survival is still being investigated. This paper aims to evaluate the changes in VD metabolites during chemotherapy (CTH) and the predictive role of VD status in Caucasian BC patients treated with CTH.

METHODS

Vitamin D and its metabolites were assessed with reference LC-MS/MS methodology in 98 consecutive BC patients starting CHT, after 3 and 6 months, and compared to the control group.

RESULTS

The frequency of VD deficiency in BC patients was greater than in the control group (56.1% vs. 37.2%). After 6 months of CTH, the number of VD-deficient BC patients slightly increased to 60%. The concentrations of VD active forms [25(OH)D2, 25(OH)D3], and catabolites [24,25(OH)2D3 and 3-epi-25(OH)D3] decreased after 3 and 6 months of CTH compared to the baseline values. Strong positive correlations between concentrations of 3-epi-25(OH)D3 and 25(OH)D in both groups were found. Similar correlations were also observed between 24,25(OH)2D3 and 25(OH)D levels. Kaplan-Meier survival analysis showed significantly longer survival in BC patients without deficiency (>20 ng/mL) at baseline (HR = 2.44 (95% CI 1.07-5.59), p = 0.026).

CONCLUSIONS

(1) Our data provide further evidence that BC patients before CTH are more VD-deficient than the general population and this deficiency increases further during CTH treatment, as observed using the reference LC-MS methodology. (2) Presented results show that VD catabolism is not affected in BC patients. (3) The poorer survival in VD-deficient BP patients supports the importance of VD supplementation in BC patients with 25(OH)D levels below 20 ng/mL.

A new method based on dispersive liquid-liquid microextraction for fat-soluble vitamin determination in serum by LC-MS/MS

A green and inexpensive pretreatment known as dispersive liquid-liquid microextraction (DLLME) was developed in this assay coupled with the LC-MS/MS method for routine analysis of fat soluble vitamins (FSVs). The technique was performed with methanol as the dispersive solvent and dichloromethane as the extraction solvent. The extraction phase containing FSVs was evaporated to dryness and reconstituted in a mixture of acetonitrile and water. The influence variables concerning the DLLME procedure were optimized. After that, the method was investigated for its applicability in LC-MS/MS analysis. As a result, the parameters were settled for the optimal conditions during the DLLME process. A cheap and lipid-free substance was found as an alternative to serum to eliminate the matrix effect while preparing the calibrators. The method validation indicated that it was suitable for determining FSVs in serum. Moreover, this method was applied successfully to determine serum samples, which was consistent with the literature. In summary, the DLLME method developed in this report was reliable and more cost-effective than the traditional LC-MS/MS method, and could be applied in the future.

Metabolism of vitamin D is not affected by sport activity

BACKGROUND

Higher levels of physical activity are related to higher 25-(OH)D levels. Total 25-(OH)D (25-(OH)DT) are routinely used in clinical practice to assess vitamin D, however novel biomarkers are currently being investigated as free 25-(OH)D (25-(OH)DF) or vitamin D metabolite ratios (VMRs). The primary aim of our study was to assess 25-(OH)DF, vitamin D metabolites and VMRs in inactive men and athletes. A secondary aim was to check whether regular physical activity influence on vitamin D metabolome. A tertiary aim was to determine the relationship between 25-(OH)DT, 25-(OH)DF, vitamin D binding protein (VDBP), vitamin D metabolites and VMRs in this cohort.

METHODS

A total of 69 participants (27 inactive men, 18 indoor and 24 outdoor athletes) participated in the study. Vitamin D metabolites (25-(OH)DT, 24,25-(OH)2D3, 3-epi-25-(OH)D3, and 1,25-(OH)2D) were assessed using LC-MS/MS. The 25-(OH)DF concentration was calculated based on serum albumin and VDBP levels.

RESULTS

There were no differences in vitamin D metabolites and VMRs between inactive men and between the two groups of athletes. We showed a strong relationship between 25-(OH)DT, 25-(OH)DF and 24,25-(OH)D3, 3-epi-25(OH)D3, 24,25-(OH)2D3:25-(OH)D3 VMR in each group. Analysis showed that 25-(OH)DT, 25-(OH)DF inversely associated with 25-(OH)D3:24,25-(OH)2D3, 25-(OH)D3:3-epi-25-(OH)D3, 1,25-(OH)2D:24,25-(OH)2D3 ratios in inactive men and athletes (indoor and outdoor).

CONCLUSIONS

On the basis of our results, we concluded that regular long-term physical activity has no effect on the concentration of vitamin D metabolites at rest. Furthermore, free vitamin D does not correlate more strongly with vitamin D metabolites and VMRs compared to total.

A Simultaneous Extraction/Derivatization Strategy for Quantitation of Vitamin D in Dried Blood Spots Using LC–MS/MS: Application to Biomarker Study in Subjects Tested for SARS-CoV-2

Vitamin D plays a critical role in bone development and maintenance, and in other physiological functions. The quantitation of endogenous levels of individual vitamin D and its metabolites is crucial for assessing several disease state conditions. With cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) leading to the coronavirus disease 2019 (COVID-19) pandemic, there are several studies that have associated lower levels of serum vitamin D with severity of infection in COVID-19 patients. In this context, we have developed and validated a robust LC–MS/MS method for simultaneous quantitation of vitamin D and its metabolites in human dried blood spot (DBS) obtained from participants tested for COVID-19. The chromatographic separation for vitamin D and metabolites was performed using an ACE Excel C18 PFP column protected with a C18 guard column (Phenomenex, Torrance, CA, USA). The mobile phase consisted of formic acid in water (0.1% v/v) as mobile phase A and formic acid in methanol (0.1% v/v) as mobile phase B, operated at a flow rate of 0.5 mL/min. Analysis was performed utilizing the LC–MS/MS technique. The method was sensitive with a limit of quantification of 0.78 ng/mL for all analytes, and had a large dynamic range (200 ng/mL) with a total run time of 11 min. The inter- and intraday accuracy and precision values met the acceptance criteria per the US Food and Drug Administration guidelines. Blood concentrations of 25(OH)D3, vitamin D3, 25(OH)D2, and vitamin D2 over a range of 2–195.6, 0.5–121.5, 0.6–54.9, and 0.5–23.9 ng/mL, respectively, were quantified in 909 DBS samples. In summary, our developed LC−MS/MS method may be used for quantification of vitamin D and its metabolites in DBS, and may be applied to investigations of the emerging role of these compounds in various physiological processes.

Quantification of 25-hydroxyvitamin D2 and D3 in Mitra® devices with volumetric absorptive microsampling technology (VAMS®) by UHPLC-HRMS for regular vitamin D status monitoring

The numbers of vitamin D inadequacies has reportedly increased in the general population, especially in the Northern hemisphere. However, routine measurement of 25(OH) vitamin D is usually associated with a substantial effort due to the requirement of a venous blood sample taken by medical professionals. Thus, the objective of this work is to develop and validate an easy and minimal-invasive method, using a microsampling technique for autonomous blood collections by medically untrained individuals. The assay enables a simplified monitoring of the vitamin D-status in both, risk group and normal population throughout the year. For this purpose, a simple methanol extraction without derivatization combined with a UHPLC-HRMS method was developed to quantify 25(OH)D2 and 25(OH)D3 in capillary blood. For sample collection, a 20 μl Mitra® device with VAMS® technology is used. By employing the six-fold deuterium-labelled 25(OH)D3 as internal standard, the validated assay provides accurate (<10%) and precise (<11%) results. With a LOQ of 5 ng/ml, the approach also proved sensitive enough to adequately identify potential vitamin D deficiencies (< 12 ng/ml), and proof-of-concept analyses of authentic VAMS® samples (n = 20) yielded test results in the expected blood concentration range. Implementing VAMS® sampling for vitamin D-status monitoring enables a higher frequency due to a simplified, straightforward, and time-effective sample collection. VAMS® assures accurate sample volumes because of its absorptive capacities and, thus, area bias and homogeneity issues associated with conventional DBS are avoided. Regular monitoring of 25(OH)D status throughout the year supports people in high-risk groups for vitamin D-deficiency by early identifying inadequacies and, thus, preventing adverse health consequences.

Relationship Between Metabolites of Vitamin D, Free 25-(OH)D, and Physical Performance in Indoor and Outdoor Athletes

The potential effects of vitamin D in athletes have received considerable attention in the literature. However, little is known about vitamin D metabolites and their association with physical performance in athletes. Therefore, the aim of our study was to determine the relationship between metabolites of vitamin D, vitamin D binding protein (VDBP), free, bioavailable 25-(OH)D, and physical fitness tests in athletes. A total of 40 indoor and outdoor players (16 judoists and 24 football players) participated in the study. Vitamin D metabolites (25-(OH)D, 24,25-(OH)₂D₃, 3-epi-25-(OH)D₃, and 1,25-(OH)₂D) were assessed using LM-MS/MS. Free 25-(OH)D concentration was evaluated by calculation using serum albumin and VDBP levels. Athletic performance was assessed using handgrip and vertical jump. Our study showed a significant correlation between vitamin D metabolites and handgrip strength and vertical jump variables in indoor players. It demonstrated a significant association between 3-epi-25-(OH)D₃ and vertical jump parameters in outdoor players. The results of our study showed relationship between free, bioavailable 25-(OH)D, and vertical jump variables in indoor players. In conclusion, we provide novel information on the vitamin D metabolites and athletic performance in athletes. Based on the results of our study, we concluded that vitamin D metabolites might be involved in skeletal muscle function in relation to athletic performance.

A novel LC-MS/MS method for the simultaneous analysis of selected fat-soluble vitamins in serum obtained from pediatric patients with pneumonia

Several observational studies have reported associations between low levels of fat-soluble vitamins (A, D and E) and the incidence of pneumonia. Whether infection affects or negatively regulates serum vitamin levels remains controversial. Our aims were to develop and validate a simple-pretreatment and fast method to determine the serum levels of selected fat-soluble vitamins, namely vitamin A (retinol), vitamin D (25-OH-D₃, 25-OH-D₂, and 3-epi-25-OH-D₃), and vitamin E (α-tocopherol), in children suffering from pneumonia during the acute phase and after inflammatory marker recovery. The sample preparation procedure involving protein precipitation and filtration was finished in one step, and separation took 8 min per sample. The calibrations were linear, with R² > 0.99. Both the intra-run (n = 6) and inter-run (n = 3) precision (relative standard deviation, RSD%) values were below 14.61%. The spiked recoveries at 3 concentrations ranged from 80.97 to 111.91%. Accuracies were calibrated using both National Institute of Standards and Technology serum (NIST 968f) and external quality assurance (EQA) samples offered by the National Center of Clinical Laboratories of China, and the relative error (RE%) values ranged from -13.17% to 12.53%. Clinical sample analysis revealed that infection did alter the serum retinol concentration and it did not alter the 25-OH-D and α-tocopherol levels in young children with pneumonia.

Bariatric Surgery Induced Changes in Blood Cholesterol Are Modulated by Vitamin D Status

The effect of metabolically active bariatric surgery treatment on lipid metabolism is inconclusive. The authors of this study presume that initial vitamin D status may play a regulating role in influencing the beneficial post-effects of bariatric surgery, especially the lipid profile. The biochemical data obtained from 24 patients who had undergone laparoscopic one-anastomosis gastric bypass (OAGB) at baseline, 3 months before the surgery, at the time of surgery, and 6 months later, demonstrate that vitamin D status influenced the postoperative lipid profile. The baseline established the partition line which divided patients into two groups according to the stated calcidiol initial concentration level of 32 ng/mL. The data shows that OAGB induces a decrease in TG and hsCRP while increasing HDL. Conversely, in patients whose 25(OH)D₃ was below 32 ng/mL TC significantly increased while those above this concentration remained in the normal physiological range. The changes induced by OAGB in TG, glucose, and hsCRP were similar in both groups. Unexpectedly, the surgery did not affect vitamin D metabolites. In conclusion, the results of the study suggest that a higher concentration of serum 25(OH)D₃ may enhance the protective effects of OAGB.

Application of Dried Blood Spots and Serum Samples for the Determination of Vitamin D Metabolites in the Group of Healthy Women and with Hashimoto’s Thyroiditis

Purpose

The relationship between Hashimoto's thyroiditis and vitamin D concentration was already presented in many studies. The aim of this study was to analyze the differences in the concentration of vitamin D metabolites between healthy women and women with Hashimoto's thyroiditis (HT).

Methods

The quantitative analysis of five vitamin D metabolites was carried out using liquid chromatography coupled with tandem mass spectrometry. The analyzed materials were serum and dried blood spots (DBS). The results obtained for the two materials were also compared.

Results

No statistically significant differences were found in the mean concentration of the 25(OH)D3, 25(OH)D2, 24,25(OH)2D3, 1,25(OH)2D3 metabolites between the test and the control groups. However, a strong correlation was found between the 25(OH)D3 and 24,25(OH)2D3 metabolites.

Conclusion

The study showed that healthy women and women with Hashimoto's disease had similar concentration of vitamin D metabolites. Research also proved that DBS is a good alternative to serum. The differences in 25(OH)D concentration were not statistically significant (17.0 and 15.5 ng mL−1 for serum and DBS, respectively). DBS can be successfully used in research on a large group of people, since the process of material collection, as well as sample preparation, is fast and simple. It is also easy to transport and store, and requires small volume of blood.

The Positive Impact of Vitamin D on Glucocorticoid-Dependent Skeletal Muscle Atrophy

(1) The study aimed to investigate whether vitamin D₃ supplementation would positively affect rats with glucocorticoids-induced muscle atrophy as measured by skeletal muscle mass in two experimental conditions: chronic dexamethasone (DEX) administration and a model of the chronic stress response. (2) The study lasted 28 consecutive days and was performed on 45 male Wistar rats randomly divided into six groups. These included two groups treated by abdominal injection of DEX at a dose of 2 mg/kg/day supplemented with vegetable oil (DEX PL; n = 7) or with vitamin D₃ 600 IU/kg/day (DEX SUP; n = 8), respectively, and a control group treated with an abdominal injection of saline (CON; n = 6). In addition, there were two groups of rats chronically stressed by cold water immersion (1 hour/day in a glass box with 1-cm-deep ice/water mixture; temperature ~4 °C), which were supplemented with vegetable oil as a placebo (STR PL; n = 9) or vitamin D₃ at 600 IU/kg/day (STR SUP; n = 9). The last group was of sham-stressed rats (SHM; n = 6). Blood, soleus, extensor digitorum longus, gastrocnemius, tibialis anterior, and quadriceps femoris muscles were collected and weighed. The heart, liver, spleen, and thymus were removed and weighed immediately after sacrifice. The plasma corticosterone (CORT) and vitamin D₃ metabolites were measured. (3) We found elevated CORT levels in both cold water-immersed groups; however, they did not alter body and muscle weight. Body weight and muscle loss occurred in groups with exogenously administered DEX, with the exception of the soleus muscle in rats supplemented with vitamin D₃. Decreased serum 25(OH)D₃ concentrations in DEX-treated rats were observed, and the cold water immersion did not affect vitamin D₃ levels. (4) Our results indicate that DEX-induced muscle loss was abolished in rats supplemented with vitamin D₃, especially in the soleus muscle.

LC-MS/MS analysis of vitamin D3 metabolites in human serum using a salting-out based liquid-liquid extraction and DAPTAD derivatization

LC-MS/MS has recently emerged as the best-practice for simultaneous analysis of vitamin D metabolites. We have developed and validated an LC-MS/MS method for simultaneous quantification of 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3 in human serum. These three metabolites were extracted from 50 μL of serum by acetonitrile protein precipitation followed by salting-out of acetonitrile. DAPTAD (4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione) was used to derivatize the extracted metabolites and their deuterated isotope internal standards. Chromatographic separation was achieved on a UPLC C18 column (Waters® ACQUITY 100 × 2.1 mm, 1.7 µm) utilizing 0.1% formic acid and acetonitrile as mobile phases. Limits of quantification were 1 ng/mL for 25(OH)D3 and 0.1 ng/mL for 24,25(OH)D3 and 3-epi-25(OH)D3. In-house and external Vitamin D External Quality Assessment Scheme (DEQAS) quality control sample analysis revealed satisfactory method accuracy. Within-analytical batch and between analytical batches precision were <15%. Extraction recovery for the three analytes were all ˃ 85% and all showed adequate autosampler, bench-top and freeze-thaw stability. Inter-methodological comparison of 25(OH)D3 results in patient serum samples revealed systematic and proportional differences between our method and DiaSorin® Liaison immunoassay, however a good agreement with an independent LC-MS/MS method was found.

Ultra-Marathon-Induced Increase in Serum Levels of Vitamin D Metabolites: A Double-Blind Randomized Controlled Trial

Purpose: While an increasing number of studies demonstrate the importance of vitamin D for athletic performance, the effects of any type of exercise on vitamin D metabolism are poorly characterized. We aimed to identify the responses of some vitamin D metabolites to ultra-marathon runs. Methods: A repeated-measures design was implemented, in which 27 amateur runners were assigned into two groups: those who received a single dose of vitamin D₃ (150,000 IU) 24 h before the start of the marathon (n = 13) and those (n = 14) who received a placebo. Blood samples were collected 24 h before, immediately after, and 24 h after the run. Results: In both groups of runners, serum 25(OH)D₃, 24,25(OH)₂D₃, and 3-epi-25(OH)D₃ levels significantly increased by 83%, 63%, and 182% after the ultra-marathon, respectively. The increase was most pronounced in the vitamin D group. Body mass and fat mass significantly decreased after the run in both groups. Conclusions: Ultra-marathon induces the mobilization of vitamin D into the blood. Furthermore, the 24,25(OH)₂D₃ and 3-epi-25(OH)D₃ increases imply that the exercise stimulates vitamin D metabolism.