Determination of vitamin D metabolites in various biological samples through an improved chemical derivatization assisted liquid chromatography-tandem mass spectrometry approach

Vitamin D (VD) metabolites are involved in a variety of important metabolic processes and physiological effects in organisms. Profiling of VD metabolites favors a deep understanding of the physiological role of VD. However, VD metabolites are difficult to detect due to their high chemical structural rigidity, structural similarity, and low sensitivities under liquid chromatography-tandem mass spectrometry (LC-MS). Herein, we present a chemical derivatization assisted LC-MS/MS strategy for the detection of VDs, in which 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) is employed to derivatize the conjugated diene of VD metabolites and provides sensitizing reporters for MS detection. After PTAD derivatization, the sensitivities of seven VD metabolites increased by 24-276 folds, with the limits of detection ranging from 3 to 20 pg mL-1. Using this method, we achieved a sensitive and accurate quantification of 7 VD metabolites (vitamin D2, vitamin D3, 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D2, 1,25-dihydroxyvitamin D3, and 1,24,25-trihydroxyvitamin D3) of the VD metabolic pathway in different trace biological samples, including human serum, mouse tissues (namely liver, kidney, lung, and spleen), and cells. We believe that the present method can provide a promising tool for an in-depth analysis of VD metabolism.

A novel caged Cookson-type reagent toward a practical vitamin D derivatization method for mass spectrometric analyses

RATIONALE

25-Hydroxylated vitamin D is the best marker for vitamin D (VD). Due to its low ionization efficiency, a Cookson-type reagent, 1,2,4-triazoline-3,5-dione (TAD), is used to improve the detection/quantification of VD metabolites by liquid chromatography/tandem mass spectrometry (LC/MS/MS). However, the high reactivity of TAD makes its solution stability low and inconvenient for practical use. We here describe the development of a novel caged Cookson-type reagent, and we assess its performances in the quantitative and differential detection of four VD metabolites in serum using LC/MS/MS.

METHODS

Caged 4-(4'-dimethylaminophenyl)-1,2,4-triazoline-3,5-dione (DAPTAD) analogues were prepared from 4-(4'-dimethylaminophenyl)-1,2,4-triazolidine-3,5-dione. Their stability and reactivity were examined. The optimized caged DAPTAD (14-(4-(dimethylamino)phenyl)-9-phenyl-9,10-dihydro-9,10-[1,2]epitriazoloanthracene-13,15-dione, DAP-PA) was used for LC/MS/MS analyses of VD metabolites.

RESULTS

The solution stability of DAP-PA in ethyl acetate dramatically improved compared with that of the non-caged one. We measured the thermal retro-Diels-Alder reaction enabling the release of DAPTAD and found that the derivatization reaction was temperature-dependent. We also determined the detection limit and the lower limit of quantifications for four VD metabolites with DAPTAD derivatization.

CONCLUSIONS

DAP-PA was stable enough for mid- to long-term storage in solution. This advantage shall contribute to the detection and quantification of VD in clinical laboratories, and as such to the broader use of clinical mass spectrometry.

Serum and synovial fluid vitamin D metabolites and rheumatoid arthritis

Vitamin D-deficiency has been linked to inflammatory diseases including rheumatoid arthritis (RA). Studies to date have focused on the impact of serum 25-hydroxyvitamin D3 (25(OH)D3), an inactive form of vitamin D, on RA disease activity and progression. However, anti-inflammatory actions of vitamin D are likely to be mediated at sites of RA disease, namely the inflamed joint, and may involve other vitamin D metabolites notably the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). In the current study serum and synovial fluid samples from n = 20 patients with persistent RA and n = 7 patients with reactive arthritis (ReA) were analysed for multiple vitamin D metabolites. Serum data for RA and ReA patients were compared to healthy controls (HC). There was no significant difference between RA or ReA patients relative to HC for 25(OH)D3, 24,25(OH)2D3, 1,25(OH)2D3 or 25(OH)D2. However, 3-epi-25(OH)D3 was significantly lower in RA and ReA patients compared to HC (p < 0.05). All vitamin D metabolites, apart from 25(OH)D2, were lower in SF compared to serum, and SF 1,25(OH)2D3 was unquantifiable in 13/20 RA and 4/7 ReA samples. SF 25(OH)D3, 3-epi-25(OH)D3 and DBP correlated inversely with swollen joint score, and serum 25(OH)D2 and SF DBP correlated directly with C-reactive protein levels. These data indicate that serum 25(OH)D3 provides only limited insight into the role of vitamin D in RA. Alternative serum metabolites such as 3-epi-25(OH)2D3, and SF metabolites, notably lack of SF 1,25(OH)2D3, may be more closely linked to RA disease severity and progress.

Vitamin D Content of Australian Native Food Plants and Australian-Grown Edible Seaweed

Vitamin D has previously been quantified in some plants and algae, particularly in leaves of the Solanaceae family. We measured the vitamin D content of Australian native food plants and Australian-grown edible seaweed. Using liquid chromatography with triple quadrupole mass spectrometry, 13 samples (including leaf, fruit, and seed) were analyzed in duplicate for vitamin D₂, vitamin D₃, 25-hydroxyvitamin D₂, and 25-hydroxyvitamin D₃. Five samples contained vitamin D₂: raw wattleseed (Acacia victoriae) (0.03 µg/100 g dry weight (DW)); fresh and dried lemon myrtle (Backhousia citriodora) leaves (0.03 and 0.24 µg/100 g DW, respectively); and dried leaves and berries of Tasmanian mountain pepper (Tasmannia lanceolata) (0.67 and 0.05 µg/100 g DW, respectively). Fresh kombu (Lessonia corrugata) contained vitamin D₃ (0.01 µg/100 g DW). Detected amounts were low; however, it is possible that exposure to ultraviolet radiation may increase the vitamin D content of plants and algae if vitamin D precursors are present.

The use of synthetic and natural vitamin D sources in pig diets to improve meat quality and vitamin D content

This study investigated the effects of synthetic and natural sources of vitamin D biofortification in pig diets on pork vitamin D activity and pork quality. One hundred and twenty pigs (60 male, 60 female) were assigned to one of four dietary treatments for a 55 d feeding period. The dietary treatments were (1)50 μg vitamin D₃/kg of feed; (2)50 μg of 25-hydroxvitamin D₃/kg of feed (25-OH-D₃); (3)50 μg vitamin D₂/kg of feed; (4)50 μg vitamin D₂-enriched mushrooms/kg of feed (Mushroom D₂). The pigs offered the 25-OH-D₃ diet exhibited the highest (P < 0.001) serum total 25-hydroxyvitamin D concentration and subsequently exhibited the highest (P < 0.05) Longissimus thoracis (LT) total vitamin D activity. Mushroom D₂ and 25-OH-D₃ supplementation increased pork antioxidant status. The vitamin D₂-enriched mushrooms improved (P < 0.05) pig performance, carcass weight and LT colour. In conclusion, 25-OH-D₃ is the most successful source for increasing pork vitamin D activity, while Mushroom D₂ may be a new avenue to improve animal performance and pork quality.

Skeletal muscle vitamin D in patients with end stage osteoarthritis of the knee

Muscle function is often impaired in patients with knee osteoarthritis (OA), with reduced strength and increased pain. The role of vitamin D and the vitamin D-endocrine pathway in muscle health has recently been placed in the spotlight, with various groups reporting positive effects on muscle development, function and health. Recently, it has been shown that uptake into muscle of the specialized vitamin D binding protein (DBP) is dependent on the endocytic receptor, megalin. Here we analyse circulating vitamin D, and muscle DBP, megalin and the cognate vitamin D receptor (VDR) in patients with knee OA and compare them to asymptomatic controls. Muscle and blood samples were collected from 19 patients with end-stage OA of the knee and 10 age-matched controls. Muscle biopsies from the OA group were performed during knee replacement surgery and a needle biopsy was used on control volunteers. Immunoblots performed with specific antibodies were used to detect the presence of DBP, megalin, VDR (using the specific D-6 antibody) and albumin in the muscle biopsies. Results were correlated with FoxO1, a key regulator of the ubiquitin-proteasome degradation pathway in muscle. There were no differences in circulating levels of 25 (OH) vitamin D3 between the groups, and no subjects were vitamin D deficient. We found increased VDR, DBP and albumin protein in the muscle from patients with OA compared to controls, with no change in muscle megalin expression. Furthermore, DBP levels in the muscle correlated with FoxO1, suggesting an association between muscle protein breakdown and the activation of the vitamin D-endocrine pathway in muscle surrounding an OA affected joint. We show, for the first time, that the factors involved in the vitamin D-endocrine-pathway are present at higher levels in muscles from OA patients compared to asymptomatic controls. This is despite no differences in circulating 25 (OH) vitamin D levels between the groups. These findings indicate the activation of vitamin D pathway in these muscles that may provide a beneficial compensatory stimulation of the repair process in muscles that are subject to inflammatory and proteolytic processes.

Vitamin D₃ and 25-Hydroxyvitamin D₃ Content of Retail White Fish and Eggs in Australia

Dietary vitamin D may compensate for inadequate sun exposure; however, there have been few investigations into the vitamin D content of Australian foods. We measured vitamin D₃ and 25-hydroxyvitamin D₃ (25(OH)D₃) in four species of white fish (barramundi, basa, hoki and king dory), and chicken eggs (cage and free-range), purchased from five Australian cities. Samples included local, imported and wild-caught fish, and eggs of varying size from producers with a range of hen stocking densities. Raw and cooked samples were analysed using high performance liquid chromatography with photodiode array. Limits of reporting were 0.2 and 0.1 μg/100 g for vitamin D₃ and 25(OH)D₃, respectively. The vitamin D₃ content of cooked white fish ranged from <0.1 to 2.3 μg/100 g, and the 25(OH)D₃ content ranged from 0.3 to 0.7 μg/100 g. The vitamin D₃ content of cooked cage eggs ranged from 0.4 to 0.8 μg/100 g, and the 25(OH)D₃ content ranged from 0.4 to 1.2 μg/100 g. The vitamin D₃ content of cooked free-range eggs ranged from 0.3 to 2.2 μg/100 g, and the 25(OH)D₃ content ranged from 0.5 to 0.8 μg/100 g. If, as has been suggested, 25(OH)D₃ has five times greater bioactivity than vitamin D₃, one cooked serve (100 g) of white fish, and one cooked serve of cage or free-range eggs (120 g) may provide 50% or 100%, respectively, of the current guidelines for the adequate intake of vitamin D (5 µg) for Australians aged 1-50 years.

Oral intake of 7-dehydrocholesterol increases vitamin D3 concentrations in the liver and kidney

INTRODUCTION

Due to the high prevalence of vitamin D deficiency, strategies are needed to improve vitamin D status. Food components can affect vitamin D metabolism and have to be considered when estimating the efficacy of vitamin D supplements. 7-dehydrocholesterol (7-DHC) occurs naturally in food, but its impact on vitamin D metabolism has not yet been examined.

METHODS

Three groups of male C57BL/6 mice (n=12 per group) were placed on a diet that contained 0, 2.5 or 5mg 7-DHC per kg diet over a period of 6 weeks. Vitamin D and other sterols in the serum, skin, liver and kidney were quantified by LC-MS/MS. The relative mRNA abundance of hepatic genes encoding vitamin D hydroxylation enzymes and transporters was analyzed by real-time RT-PCR.

RESULTS

We found a substantial dose-dependent increase of non-hydroxylated vitamin D₃ in the liver and kidney of mice fed a diet containing 7-DHC. The vitamin D₃ content in the liver was 2.80±0.61pmol/g, 7.34±4.28pmol/g and 12.9±3.58pmol/g in groups that received 0, 2.5 and 5mg/kg 7-DHC, respectively. In the kidney, the vitamin D₃ content of these groups was 1.78±1.17pmol/g, 3.55±1.06 and 6.36±2.29pmol/g, respectively. The serum and tissue concentrations of 25-hydroxyvitamin D₃ (25(OH)D₃) remained unaffected by 7-DHC. The relative mRNA data provided no plausible mechanism for the observed effects of 7-DHC on vitamin D₃. All groups of mice had similar concentrations of cholesterol, desmosterol and 7-DHC in their serum and tissues.

CONCLUSION

The current findings provide the first evidence that dietary 7-DHC seems to affect vitamin D metabolism. The underlying mechanism remains elusive and needs further investigation.

25-Hydroxyvitamin D assays: Potential interference from other circulating vitamin D metabolites

The vitamin D External Quality Assessment Scheme (DEQAS) for 25-hydroxyvitamin D (25-OHD) has approximately 1100 participants in 53 countries using 26 different methods or variants of methods (October 2014). In April 2015, the scheme was extended to cover 24,25-dihydroxyvitamin D (24,25(OH)₂D). Since 2013, the 25-OHD scheme has been accuracy-based with values assigned by the NIST reference measurement procedure (RMP). DEQAS is uniquely placed to assess the accuracy (bias) and specificity of 25-OHD methods in a routine laboratory setting. Other vitamin D metabolites are known to interfere in 25-OHD assays and DEQAS has distributed samples spiked with 3-epi-25-OHD₃ (52.4nmol/L), 24R,25(OH)₂D₃ (14.4nmol/L) and 24S,25(OH)₂D₃ (57.9nmol/L). The 3-epimer showed a cross reactivity of 56% in a competitive protein binding assay but was not detected in any antibody-based methods. Not all HPLC/UV or LC-MS/MS methods were able to resolve 3-epi-25-OHD₃ from 25-OHD₃ and thus overestimated total 25-OHD. The cross reactivity of 24R,25(OH)₂D₃ (24S,25(OH)₂D₃) ranged from <5% (<5%) to 548% (643%) in ligand binding assays. Both 24-hydroxylated metabolites were resolved by HPLC/UV and LC-MS/MS methods and thus caused no complications in the measurement of 25-OHD. Most antibodies to 25-OHD are known to cross-react with dihydroxylated metabolites but interference in some assays was far greater than expected. This may be related to the anomalous behaviour of exogenously added metabolites in these 25-OHD methods.

Vitamin D fortification of eggs for human health

BACKGROUND

Vitamin D is an essential component of vertebrate nutrition, and epidemiological surveys confirm a chronic vitamin D insufficiency in the human population. Eggs are one of the few natural sources rich in vitamin D, containing both vitamin D₃ (D₃) and 25-hydroxyvitamin D₃ (25(OH)D₃). 25-Hydroxyvitamin D₃ is especially useful because it provides five times the relative biological activity of vitamin D. In order to establish the potential for enrichment of eggs with D₃ and 25(OH)D₃, a total of 162 hens were fed three levels of D₃ in combination with three levels of 25(OH)D₃. Egg yolks were analysed for their D₃ and 25(OH)D₃ contents, and egg production, egg weights and feed efficiencies were recorded.

RESULTS

The contents of D₃ and 25(OH)D₃ in egg yolk increased significantly with increasing dietary concentrations. There were no significant differences in egg mass, egg weight or feed efficiency. Depending on the dietary concentrations used, it was possible to produce eggs with between 100 and 500 IU vitamin D, providing scope to meet the recommended daily requirement of vitamin D for children or adults.

CONCLUSION

The addition of higher levels of D₃ and 25(OH)D₃ produced eggs with sufficient vitamin D to meet the recommended daily requirements of adults and children without any detrimental effect on production parameters.

Serum levels of 3-epi-25-OH-D3 during hypervitaminosis D in clinical practice

CONTEXT

Intoxication from vitamin D supplements has been rarely reported, but nowadays, it occurs more frequently. The presence of the C-3 epimer of 25-hydroxyvitamin D(3) (3-epi-25-OH-D(3)) is highly prevalent in adults, although there is little information regarding its in vivo relevance, if any, especially under pathological conditions.

OBJECTIVE

Our aim was to assess the presence of the 3-epi-25-OH-D(3) in serum samples displaying 25-OH-D(3) concentrations indicative of hypervitaminosis D.

DESIGN, SETTING, PATIENTS, AND MAIN OUTCOME MEASURE

A total of 58 samples displaying a wide range of concentrations of 25-OH-D(3) (>64-439 ng/ml) by ultrafast liquid chromatography were consecutively recruited and reassessed for the presence of 3-epi-25-OH-D(3) using a second chromatographic system. Data from additional biochemical tests performed as part of the patient evaluation were also recorded.

RESULTS

Mean relative contribution of 3-epi-25-OH-D(3) was less than 4%, and concentrations ranged from 2-28.6 ng/ml. Serum levels of the C3 epimer, but not the relative contribution, correlate with serum 25-OH-D(3). Overall, in subjects with 25-OH-D(3) concentrations indicative of hypervitaminosis D, the presence of the C-3 epimer and its levels were apparently unrelated to age, serum markers of renal and liver function, acute-phase reactants, and the presence of hypercalcemia. 3-Epi-25-OH-D(3) did not correlate with PTH, but subjects displaying PTH suppression (<14 pg/ml) showed higher concentrations of 3-epi-25-OH-D(3).

CONCLUSION

The relative contribution of 3-epi-25-D(3) was not significantly altered during hypervitaminosis D, although the absolute levels reached in serum may be biologically relevant. From a clinical viewpoint, although the small size of the group may affect the lack of relationships, the presence of 3-epi-25-OH-D(3) was apparently unrelated to serum markers of renal and liver function, acute-phase reactants, PTH, and the presence of hypercalcemia.

The C-3 epimer of 25-hydroxyvitamin D(3) is present in adult serum

CONTEXT

Epimers have identical molecular structure but differ in stereochemical configuration. It is widely believed that the C-3 epimer of 25-hydroxyvitamin D(3) [3-epi-25(OH)D(3)] is found only in neonates. However, this epimer was recently detected in a limited number of adults. The physiological importance of 3-epi-25(OH)D(3) is uncertain but might affect 25-hydroxyvitamin D test results and thereby reliability of the 25-hydroxyvitamin D(3) [25(OH)D(3)] measurement.

OBJECTIVE

This project describes development of a highly sensitive method for 3-epi-25(OH)D(3) measurement and establishes the prevalence of this epimer in adult clinical serum specimens. DESIGN, SETTING, PARTICIPANTS, AND MAIN OUTCOME MEASURE: Serum 25(OH)D(3), 3-epi-25(OH)D(3), and 25(OH)D(2) concentrations were determined in a cohort of patients (n = 214; age neonate to 80+ yr). High-performance liquid chromatography with ultraviolet detection and high-performance liquid chromatography tandem mass spectrometry with atmospheric pressure chemical ionization equipped with cyanopropyl analytical columns were used to baseline separate and quantitate 25(OH)D(3), 3 epi-25(OH)D(3), and 25(OH)D(2).

RESULTS

The C-3 epimer was detected in 212 of 214 (99%) of samples. Concentrations ranged from 1 to 93 ng/ml for 25(OH)D(3) and 0.1 to 23.7 ng/ml for 3-epi-25(OH)D(3). The relative amounts of epimer to 25(OH)D(3) ranged from 0 to 25.5% (mean 4.75%). The epimer amount increased as 25(OH)D(3) increased in a nonlinear mode. In sera with approximately the same 25(OH)D(3) concentration, the ratio of epimer to 25(OH)D(3) varied, e.g. at 25(OH)D(3) values of 20-22 ng/ml, the ratio varied from 2-8.5%.

CONCLUSION

3-Epi-25(OH)D(3) is present in the majority of human serum specimens. Although this concentration is generally low, further work must investigate the impact of 3-epi-25(OH)D(3) on the various 25-hydroxyvitamin D assays and ultimately what information, if any, C-3 epimer measurement can provide clinically.

25-hydroxyvitamin D3 affects vitamin D status similar to vitamin D3 in pigs--but the meat produced has a lower content of vitamin D

In food databases, the specific contents of vitamin D3 and 25-hydroxyvitamin D3 in food have been implemented in the last 10 years. No consensus has yet been established on the relative activity between the components. Therefore, the objective of the present study was to assess the relative activity of 25-hydroxyvitamin D3 compared to vitamin D3. The design was a parallel study in pigs (n 24), which from an age of 12 weeks until slaughter 11 weeks later were fed approximately 55 microg vitamin D/d, as vitamin D3, in a mixture of vitamin D3 and 25-hydroxyvitamin D3, or 25-hydroxyvitamin D3. The end-points measured were plasma 25-hydroxyvitamin D3, and in the liver and loin the content of vitamin D3 and 25-hydroxyvitamin D3. Vitamin D3 and 25-hydroxyvitamin D3 in the feed did not affect 25-hydroxyvitamin D3 in the plasma, liver or loin differently, while a significant effect was shown on vitamin D3 in the liver and loin (P < 0.001). 25-Hydroxyvitamin D3 in the plasma, liver and loin significantly correlates with the sum of vitamin D3 and 25-hydroxyvitamin D3 in the feed (P < 0.05). Therefore, 25-hydroxyvitamin D3 should be regarded as having the same activity as vitamin D3 in food databases. Sole use of 25-hydroxyvitamin D3 as a vitamin D source in pig feed will produce liver and meat with a negligible content of vitamin D3, while an increased content of vitamin D3 in the feed will produce liver and meat with increased content of both vitamin D3 and 25-hydroxyvitamin D3.

Management of chronic kidney disease mineral-bone disorder

Chronic kidney disease mineral-bone disorder (CKD-MBD) is a systemic disorder of abnormal serum levels of mineral-related biochemistries, abnormal bone, and extraskeletal calcification. Although we have gained understanding on how these components are interrelated, our therapeutic tools remain focused on only one aspect of CKD-MBD at a time. However, the management of these disorders is also interrelated; treatments may help one aspect of the disorder but cause or accelerate another. As such, management remains a major challenge to nephrologists and requires balancing risk and benefit of the various available therapies. Our challenge for the decade ahead is to determine which combinations of therapy can be used safely together to prevent morbidity and mortality in CKD. Furthermore, the pathophysiology that sets these events into motion begins well before the onset of ESRD. Future therapies and guidelines should, therefore, also emphasize the need for earlier detection and management of CKD, shaped by the results of valid clinical trials.

Measurement of vitamin D status: background, clinical use, and methodologies

Vitamin D and its metabolites are crucial to the overall health and well-being of humans and animals, having important functions in calcium homeostasis and bone metabolism. Exposure of the skin to sunlight may provide adequate levels of vitamin D; however, there are numerous reports of vitamin D insufficiency or deficiency. 25-hydroxyvitamin D (calcidiol, 25(OH)D) is regarded as the best measurement of overall vitamin D status. 1,25-dihydroxyvitamin D (calcitriol, 1,25(OH)2D) is the most biologically active vitamin D metabolite. 25(OH)D has higher affinity for vitamin D binding protein (VDBP) than 1,25-dihydroxyvitamin D; whereas, 1,25-dihydroxyvitamin D has higher affinity for the vitamin D receptor (VDR) than 25-hydroxyvitamin D. HPLC and immunoassays allow the determination of vitamin D status, as measured by 25(OH)D, and 1,25(OH)2D. Recently it has been shown that the vitamin D requirements have been underestimated and that vitamin D2 is much less potent than vitamin D3. Future studies will determine the amount of vitamin D3 necessary for optimal health and well-being.

Supplemental vitamin D3 concentration and biological type of steers. II. Tenderness, quality, and residues of beef

Vitamin D3 was orally supplemented to determine the supplemental dose that improved beef tenderness in different cattle breed types. Feedlot steers (n = 142) were arranged in a 4 x 3 factorial arrangement consisting of four levels of supplemental vitamin D3 (0, 0.5, 1, and 5 million IU/steer daily) administered for eight consecutive days antemortem using three biological types (Bos indicus, Bos Taurus-Continental, and Bos Taurus-English). Warner-Bratzler shear force (WBSF) was measured at 3, 7, 10, 14, and 21 d postmortem, and trained sensory analysis was conducted at 7 d postmortem on LM, semimembranosus, gluteus medius, and supraspinatus steaks. Concentrations of vitamin D3 and the metabolites 25-hydroxyvitamin D3, and 1,25-dihydroxyvitamin D3 were determined in the LM, liver, kidney, and plasma. Biological type of cattle did not interact (P > 0.10) with vitamin D3 supplementation for sensory or tenderness traits, suggesting that feeding vitamin D3 for 8 d before slaughter affected the different biological types of cattle similarly. Supplementing steers with 0.5, 1, or 5 million IU/(steer(d) decreased (P < 0.05) LM WBSF at 7, 10, 14, and 21 d postmortem compared with controls, and vitamin D3 treatments of 0.5, 1, and 5 million IU decreased (P < 0.05) semimembranosus WBSF at 3, 7, and 14 d postmortem. In general, vitamin D3-induced improvements in WBSF were most consistent and intense in LM steaks. Sensory panel tenderness was improved (P < 0.05) by all vitamin D3 treatments in LM steaks. Sensory traits ofjuiciness, flavor, connective tissue, and off-flavor were not (P > 0.05) affected by vitamin D3 treatments. All vitamin D3 treatments decreased micro-calpain activity and increased muscle Ca concentrations (P < 0.05). Vitamin D3 concentrations were increased (P < 0.05) by supplementation in all tissues tested (liver, kidney, LM, and plasma); however, cooking steaks to 71 degrees C decreased (P < 0.05) treatment residue effects. The vitamin D metabolite 1,25-dihydroxyvitamin D3 was increased (P < 0.05) only in plasma samples as a result of the vitamin D3 treatments. These results indicate that supplementation with vitamin D3 at 0.5 million IU/steer daily for eight consecutive days before slaughter improved tenderness in steaks from different subprimal cuts by affecting muscle Ca concentrations, micro-calpain activities, and muscle proteolysis, with only a small effect on tissue residues of vitamin D3.

Rapid HPLC method for measurement of vitamin D3 and 25(OH)D3 in blood plasma

The present work describes a novel, simplified high-performance liquid chromatography (HPLC) method for evaluation of vitamin D3 and its 25-hydroxy metabolite in blood plasma. The retrieval of the analytes from the blood plasma matrix is based on a single-step extraction using acetonitrile. The method is specific, sensitive, and ensures good reproducibility. The recovery of the analytes, precision, and reproducibility obtained using the present approach gave results comparable to or better than more complex, laborious, and time-consuming procedures. This method is suitable for evaluation of the host's vitamin D physiological status, as well as for rapid analysis of blood plasma samples in suspected cholecalciferol toxicity. With a significantly shortened time of analysis (10 minutes), the present method allows the possibility for processing of a large number of samples rapidly, efficiently, and at a low cost.

Effect of cholecalciferol-enriched hen feed on egg quality

Eggs are one of the most important sources of vitamin D in the human diet, and their vitamin D content can be further increased by adding more vitamin D to hen feed. To investigate this issue more closely, we performed two feeding experiments. In both, zero egg samples were collected while the hens were fed regular feeds with a vitamin D content of 1720 or 4280 IU/kg. In experiment 1, egg samples were collected 2, 4, 7, 9, 11, 13, 16, 23, and 30 days after beginning the high-cholecalciferol (11 200 IU/kg) feeding period. In experiment 2, samples were collected 2, 4, 6, 8, 13, 28, 56, 84, 112, 140, and 168 days after beginning the high-cholecalciferol (12 000 IU/kg) diet. The egg samples were then assayed for their cholecalciferol content, and some samples, also for the presence of 25-hydroxycholecalciferol by an HPLC method. Further, the vitamin D-fortified eggs were compared with the controls by a sensory evaluation, by conducting fatty acid and functional analyses (emulsion capacity, gel forming capacity, foaming properties) and by measuring eggshell strength. Because vitamin D can be toxic in high doses, we also performed histopathological tests on the hens at the end of experiment 2. The top cholecalciferol contents in egg yolk (ca. 30 microg/100 g) were reached 8-13 days from starting the high-cholecalciferol diet. After 112 days feeding the cholecalciferol content gradually decreased to ca. 22 microg/100 g. When added to eggs as described above, vitamin D did not affect their sensory or functional properties or their fatty acid composition. Moreover, the cholecalciferol levels used in this study appeared not to affect eggshell strength or to be harmful for hens.

Cholecalciferol and 25-hydroxycholecalciferol content of chicken egg yolk as affected by the cholecalciferol content of feed

The predominant source of vitamin D is the synthesis of cholecalciferol in the skin by the action of sunlight; however, due to the relative lack of sunlight, the intake of vitamin D from food is emphasized during winter, especially in the northern countries. Only a few foods (fish, eggs, wild mushrooms, meat, and milk) are natural sources of vitamin D. In addition, the content of vitamin D in foods is generally low, and some groups of people obtain amounts of vitamin D that are too small from their diet. The present study was designed to determine whether it is possible to increase the vitamin D content of egg yolk by giving hens feed containing elevated levels of cholecalciferol. Three cholecalciferol levels were tested: 26.6 (1064), 62.4 (2496), and 216 microgram (8640 IU)/kg feed. Egg yolk samples were taken after 0, 4, 5, and 6 weeks and were assayed for the presence of cholecalciferol and 25-hydroxycholecalciferol using an HPLC method. According to the present study, there was strong positive correlation between cholecalciferol content in poultry feed and cholecalciferol (r = 0. 995) and 25-hydroxycholecalciferol (r = 0.941) content in egg yolk.

Determination of vitamin D3 metabolites: state-of-the-art and trends

The steps involved in the methods for the determination of vitamin D3 metabolites (namely, 25-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3, 24,25-dihydroxyvitamin D3) mainly in clinical samples are critically reviewed. Sample pretreatment (e.g. deproteinization, saponification, liquid liquid and liquid solid extraction, etc.) as a function of both type of sample and detection system, quantitation based on protein saturation and liquid as well as gas chromatography are discussed. The chemical principles on which the methods are based and the derivatization procedures, which facilitate separation and/or detection, are also commented upon. Finally, the future prospects of the research on methods for the determination of these metabolites are outlined.

Bone density, vitamin D status, and disordered bone remodeling in end-stage chronic liver disease

Hepatic osteodystrophy occurs in up to 50% of patients with chronic liver disease (CLD). The aim of this study was to determine the relative contribution of increased resorption and decreased formation to hepatic osteodystrophy by measuring biochemical markers. Twenty-seven patients with advanced CLD (14 female, 13 male) were enrolled. Bone mineral density (BMD), measured at the lumbar spine, and femoral neck, were measured by dual energy X-ray absorptiometry (DXA); bone turnover was assessed using biochemical markers of bone formation and resorption. Based on WHO criteria, osteoporosis and osteopenia were present in 41% and 18% of patients, respectively. All three markers of bone resorption (free deoxypyridinoline, pyridinoline, and hydroxyproline) were increased significantly in patients with CLD. There was a less marked change in the markers of bone formation (osteocalcin, procollagen type 1 peptide, and bone alkaline phosphatase), resulting in a negative uncoupling index in 23/27 (85%) of the patients. Only two (7%) patients had biochemical changes consistent with osteomalacia. The results suggest that increased bone resorption is the predominant cause of hepatic osteodystrophy and therapeutic strategies should be designed to suppress bone resorption, especially in preparation for liver transplantation. Bone biomarkers may be useful alternatives to bone biopsy in evaluating hepatic osteodystrophy.

Identification of 7-dehydrocholesterol, vitamin D3, 25(OH)-vitamin D3 and 1,25(OH)2-vitamin D3 in Solanum glaucophyllum cultures grown in absence of light

Solanum glaucophyllum contains the calciotropic hormone 1, 25-dihydroxy-vitamin D3 (1,25(OH)2D3). The metabolic pathway leading to the formation of 1,25(OH)2D3 in the plant is largely unknown. Specifically, there is controversy about the participation of a photolytic reaction in the generation of vitamin D3 and its metabolites. To investigate the requirement for light, S. glaucophyllum tissue (callus) and cell suspension cultures grown under strict conditions of darkness were extracted with chloroform/methanol (1:2, v/v) followed by purification of the lipidic fraction by Sephadex LH-20 and high-performance liquid chromatography. HPLC peaks with elution times similar to those of authentic samples of 7-dehydrocholesterol, vitamin D3, 25(OH)D3 and 1,25(OH)2D3 were detected. The presence of 1,25(OH)2D3 was also evidenced by [3H]1,25(OH)2D3 competitive binding analysis using the chick hormone intestinal receptor. Furthermore, 7-dehydrocholesterol, vitamin D3, 25(OH)D3 and 1,25(OH)2D3 were unequivocally identified by mass spectrometry. Incubation of control samples of 7-dehydrocholesterol under the same conditions as S. glaucophyllum cultures did not result in vitamin D3 formation, excluding the influence of light in these experiments. The results suggest that a synthetic route of vitamin D3 compounds independent of light operates in Solanum glaucophyllum cultured in vitro.

Vitamin D levels in noninstitutionalized children with cerebral palsy

Calcitriol (1,25-dihydroxy vitamin D) is an important hormone in calcium and phosphate metabolism. Levels of calcitriol and its precursor, 25-hydroxy vitamin D (calcidiol), were measured in a heterogeneous group of 125 noninstitutionalized children and adolescents with spastic cerebral palsy. Levels of each were correlated with: (1) clinical factors including mobility, prior fracture, and use of anticonvulsants; (2) nutrition and growth parameters including skinfolds, body mass index, and use of vitamin supplements; and (3) other serum analyses including osteocalcin as a marker of bone formation, calcium, and alkaline phosphatase. Levels of calcidiol and calcitriol did not correlate with any of the various clinical, nutritional, or growth parameters examined. The prevalence of low (< 10 ng/mL) levels of calcidiol was significant (19%), and dependent on the season of the year in which the level was measured. In contrast, less than 2% of the patients were found to have a low (< 20 pg/mL) level of calcitriol and the mean was comparable to normal pediatric subjects. Levels of calcitriol are maintained in noninstitutionalized children with cerebral palsy despite anticonvulsants, poor nutrition, and calcidiol levels that vary greatly with the seasons.

Measurement of vitamin D and its metabolites (calcidiol and calcitriol) and their clinical significance

The serum concentration of vitamin D will only give information about the recent exposure to either nutritional vitamin D or to recent vitamin D production in the skin. Within hours vitamin D is removed from the circulation and reappears again a few hours later as 25(OH)D. Measurements of vitamin D therefore are not useful to judge the vitamin D status of man. Plasma concentrations of 25-hydroxyvitamin D (25(OH)D) are the best markers of imminent or existing vitamin D deficiency. Suboptimal vitamin D supply (or 25(OH)D plasma concentrations) are observed in most European countries and North America from November to April. Vitamin D substitution is recommended to persons with a serum concentration of 25(OH)D below 50 nmol/L (20 micrograms/L). Plasma concentrations of 1,25(OH)2D3 (calcitriol) depend mainly on renal function, concentrations of intact PTH and the supply of the organism with calcium and phosphate. High PTH, low calcium and low phosphate supply are the main stimulators of the production of calcitriol. Vitamin D substitution, or if necessary, therapy with active vitamin D metabolites or analogs, e.g. calcitriol or alfacalcidol, are often necessary in hypercalcemic persons with low serum concentrations of calcitriol, e.g. in patients with renal failure. Disorders with low or high vitamin D metabolite concentrations in serum are described in this paper.

Vitamin D3 and its metabolites in the tomato plant

The tomato plant has been demonstrated to have vitamin D-like activity. The activity was present in the leaves but not in the fruit of the plant. The chloroform extract of the leaves (containing free vitamin D and its metabolites) and the ethanol extract of the residue (containing the glycosidic forms) were partially purified by column chromatography. The fractions corresponding to authentic vitamin D3, 25-hydroxy vitamin D3 and 1,25-dihydroxy vitamin D3 were tested for biological activity and analysed by HPLC. The results indicate that the plant contains vitamin D3, 25-hydroxy vitamin D3 and 1,25-dihydroxy vitamin D3 and their glycosidic forms. Free vitamin D3 was observed to be the major active principle and the concentration of the free forms of the metabolites was higher than the corresponding glycosides.

[Extraction and purification of the three major vitamin D metabolites using C18 and NH2 cartridges and measurement of 25-hydroxyvitamin D]

In this study, the three major vitamin D metabolites: 25-hydroxyvitamin D [25(OH)D], 24,25-dihydroxy-vitamin D [24,25(OH)2D], 1,25-dihydroxyvitamin D [1,25(OH)2D] were clearly separated using a NH2 cartridge after acetonitrile and C18 cartridge extraction. In the NH2 cartridge purification procedure, 25(OH)D was eluted with hexane/dichloromethane (50:50), 24,25(OH)2D was eluted with hexane/dichloromethane (20:80) and 1,25(OH)2D was eluted with hexane/isopropanol (75:25). Contamination of each fraction with two other metabolites were less than 1.4%. Recoveries of added 3H-25(OH)D, 3H-24,25-(OH)2D and 3H-1,25(OH)2D were 73.2 +/- 2.45%, 60.0 +/- 2.98% and 63.5 +/- 3.37%, respectively. Using the 25(OH)D fraction after the NH2 cartridge procedure, we measured 25(OH)D using a competitive protein binding assay. The intra- (n = 10) and interassay (n = 8) coefficients of variation were 4.60-8.41% and 6.62-16.4%, respectively. Analytical recovery of added 25(OH)D was in the range of 81.2-130%. The 25(OH)D values were 17.4 +/- 6.02 ng/ml (mean +/- SD) in serum from 110 healthy volunteer collected in May. The correlation of 25(OH)D values was good between cartridge purification and high performance liquid chromatography (HPLC) purification. (gamma = -0.38 + 1.03x, r = 0.953, n = 36). This purification using a simple cartridge procedure was suitable for the measurement of 25(OH)D, and preferable to the time-consuming HPLC purification.

Subterranean mole-rats naturally have an impoverished calciol status, yet synthesize calciol metabolites and calbindins

Mole-rats (Family Bathyergidae) have no obvious source of calciol. They live in an environment devoid of sunlight and consume a herbivorous diet. Calciol status, metabolism and expression were examined in six species of Bathyergids. Serum levels of calcidiol in all species were < 5 micrograms/l and those of calcitriol were low (18.0 +/- 11.0 (SD) ng/l, N = 57) when compared to other rodents. Within 72 h of injecting animals with tritium-labelled calciol, most of the labelled prohormone had been metabolized to more polar metabolites. Three times more tritium-labelled calcitriol (19.3 +/- 2.9%) was present than (24R)-hydroxycalcidiol (6.2 +/- 10%). The natural absence of detectable circulating concentrations of calcidiol and the threefold greater amount of calcitriol to (24R)-hydroxycalcidiol produced indicate that calciol naturally is in short supply. Calciol-dependent calbindins were absent in the duodenum. Calbindin-D28k was present in the Purkinje cells of the cerebellum and in some collecting ducts and proximal and distal convoluted tubules of the kidney. Calbindin-D9k also was present but was localized uniquely in the juxtaglomerular cells of the five southern African species. These data confirm that Bathyergid mole-rats naturally have an impoverished calciol status. Despite the presence of calbindins in renal tissues, the functional importance of this hormone in calbindin synthesis and other normal mole-rat physiology is not known.

Quantification and kinetics of 25-hydroxyvitamin D3 by isotope dilution liquid chromatography/thermospray mass spectrometry

A liquid chromatography/thermospray mass spectrometry method has been developed and used to measure the plasma levels and half-life of 25-hydroxyvitamin D3 in adults. The mean plasma levels of 25-hydroxyvitamin D3 averaged 40 ng ml-1 (n = 4) in summer and 30 ng ml-1 (n = 6) in winter. The method was also used to determine the half-life of serum 25-hydroxyvitamin D3 in subjects maintained on either high or low-fiber diets who had been given an intravenous infusion of (6,19,19-2H3)25-hydroxyvitamin D3 sufficient to label 5% of their estimated body pools. The half-life was determined to be 10.4 days (n = 4), which is approximately 50% of the currently accepted value of 19 days, determined using radiolabeled methods. This difference may be due to kinetic isotope effects arising as a result of the tritiated compounds being labeled at sites that undergo Cyt-P450-catalyzed oxidations.

The relationship between endogenous oestradiol and vitamin D3 metabolites in serum and follicular fluid during ovarian stimulation for in-vitro fertilization and embryo transfer

The present study was undertaken to examine the effect of circulating oestradiol on serum levels of 25-hydroxyvitamin D3 (25-OHD3), 24,25-dihydroxyvitamin D3[24,25-(OH)2D3], and 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] during gonadotrophin-induced ovarian stimulation in 10 healthy women undergoing in-vitro fertilization and embryo transfer (IVF). The presence of these metabolites in the follicular fluid was also investigated. Plasma oestradiol increased from 25 +/- 3.2 (mean +/- SE) pg/ml before initiation of treatment to 2563 +/- 328 pg/ml on the day of injection of human chorionic gonadotrophin (HCG) and 1641 +/- 299 pg/ml on the day of ovum retrieval (P < 0.01). Serum levels of 1,25-(OH)2D3 increased from 32.0 +/- 1.9 (mean +/- SE) pg/ml to 46.6 +/- 8.1 and 48.5 +/- 7.7 pg/ml (P < 0.05) on the day of HCG and ovum retrieval, respectively. No changes in blood levels of 25-OHD3 and 24,25-(OH)2D3 were found. The presence of vitamin D metabolites in follicular fluid is documented herein for the first time. All three metabolites were present in the follicular fluid but were significantly lower than in the concurrent serum (P < 0.01). A highly significant correlation was found between serum and follicular fluid levels: r = 0.787, P < 0.001 for 1,25-(OH)2D3; r = 0.738, P < 0.01 for 25-OHD3; and r = 0.751, P < 0.01 for 24,25-(OH)2D3. Our results suggest that raised levels of circulating oestradiol during gonadotrophin-induced ovarian stimulation are associated with a significant increase of serum 1,25-(OH)2D3.

Production and specificity of antisera raised against 25-hydroxyvitamin D3-[C-3]-bovine serum albumin conjugates

In order to obtain specific antisera for use in the enzyme immunoassay of 25-hydroxyvitamin D3, three hapten-carrier conjugates having different lengths of bridges at the C-3 position were prepared from 25-hydroxyvitamin D3 by coupling with bovine serum albumin using the active ester method. The specificity of anti-25-hydroxyvitamin D3 antisera elicited in rabbits was tested by a cross-reaction study with closely related secosterols and by measuring the plasma levels of 25-hydroxyvitamin D3 by means of radioimmunoassay using tritium-labeled antigen. The results indicated that the specificity of the antisera obtained is higher than that of vitamin D-binding protein, and that some of these antisera are suitable for enzyme immunoassay.

Analysis of vitamin D and its metabolites using thermospray liquid chromatography/mass spectrometry

A new method is described for the analysis of vitamin D and its metabolites utilizing thermospray (TSP) mass spectrometry as an on-line detector for high performance liquid chromatography. Ionization conditions were optimized for use with isocratic reversed phase chromatography. TSP mass spectrometry was employed in series with a UV absorbance detector to facilitate comparisons between the two methods of detection. Positive ion TSP mass spectra were recorded for vitamin D2, vitamin D3, 25-hydroxyvitamin D3 (25(OH)D3), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3). The spectra contained protonated molecular ions, ammonium adduct ions and fragment ions due to the loss of one or more molecules of water. A comparison of quantitative precision was made by determining UV absorbance and TSP standard curves for vitamin D3 using two different methods: (1) External standard method with post-column (post UV detector) addition of ammonium acetate. (2) As (1) but using the method of internal standards with a closely eluting internal standard (vitamin D2). In each case the quantitative precision (correlation coefficient) for UV absorbance detection was superior owing to intrinsic instability of the TSP ion beam. A stable isotopically labelled internal standard was employed in the development of an assay for 1,25(OH)2D3. The assay was used to quantify in vitro enzymic conversion of 25(OH)D3 to 1,25(OH)2D3 in guinea pig and sheep renal mitochondrial incubations. TSP LC/MS was also applied to analysis of an extract of human blood plasma in which D3 and each of its principal metabolites were identified in a single analysis.

Synthesis of a reagent for fluorescence-labeling of vitamin D and its use in assaying vitamin D metabolites

The fluorogenic dienophile 1,2,4-triazoline-3,5-dione with a highly fluorescent quinoxalinone group at the 4-position (DMEQ-TAD) was synthesized and exploited as a reagent to assay vitamin D metabolites. 25-Hydroxyvitamin D3, 1 alpha,25-dihydroxyvitamin D3, and 24(R),25-dihydroxyvitamin D3 reacted quantitatively with DMEQ-TAD when the two substrates were mixed in dichloromethane at room temperature to yield the corresponding 6,19-cycloadduct. The reaction was very fast so that 1 alpha,25-dihydroxyvitamin D3 at a concentration as low as 10(-8) M could be quantitatively labeled with the fluorescent reagent within 30 min at room temperature. With this reagent, down to 10 fmol of vitamin D metabolites could be quantified linearly. The detection limit of the labeled vitamin D using high-performance liquid chromatography was usually about 1 fmol. Thus, it was shown in a model system that the fluorometric method using the new reagent (DMEQ-TAD) can be applied to the assay of the three major vitamin D metabolites in 1 ml of plasma. This is the first practical fluorometric method for assaying the active vitamin D metabolite.

25-Hydroxyvitamin D and vitamin D in human milk: effects of supplementation and season

Breast-milk 25-hydroxyvitamin D (25-[OH]D) and vitamin D were measured in mothers supplemented with 2000 or 1000 IU (50 or 25 micrograms) of vitamin D/d or with no supplementation. Fore- and hindmilk samples were collected at two stages of lactation (8 and 15 or 20 wk after delivery) and at different seasons. Season affected the levels of 25-(OH)D and vitamin D. The 25-(OH)D levels were higher in hind- than in foremilk. Supplementation had no effect on vitamin D levels. Milk 25-(OH)D levels of mothers receiving either 1000 or 2000 IU (25 or 50 micrograms) vitamin D/d were significantly higher than those of unsupplemented mothers in February and April. In theory, supplementation with 2000 IU (50 micrograms) vitamin D should have increased the calculated antirachitic activity of the milk in winter to the levels of unsupplemented mothers in September; however, responses varied widely among individuals.

Vitamin D supply to the rat fetus and neonate

The prevention of neonatal rickets by oral supplementation with vitamin D2 (ergocalciferol) has tended to obscure our ignorance of the natural mechanism by which young mammals receive an adequate supply of vitamin D. To investigate the possibility of specific intrauterine transfer and storage of vitamin D in fetal tissues, vitamin D-deficient female rats were given depot injections of 3H- or 14C-labeled vitamin D3 (cholecalciferol) before mating and the 3H-labeled animals were killed at stages during the last third of gestation. Analysis of lipid extracts from whole fetuses revealed a linear increase in the concentration of 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, and D3 itself between days 14 and 19 of gestation. During this period the elimination half-time of 3H-labeled molecules in maternal plasma fell from 27.1 to 4.4 d, suggesting that a specific mechanism was transferring vitamin D molecules into the fetuses. The vitamin was stored predominantly as 25-hydroxyvitamin D3 and 24,25-dihydroxyvitamin D3, with the highest concentrations in fetal muscle. Immediately after birth, pups from 3H- and 14C-labeled mothers were exchanged and later killed after 1-3 wk of suckling. Analysis of total lipid extracts for 3H and 14C content determined the relative contributions of vitamin D supplied before birth via the placenta and after birth in the maternal milk. The vitamin D content of the rat milk was relatively high, between 1.0 and 3.5 micrograms/liter. Nevertheless, the supply of vitamin D in utero, rather than from milk, was the main determinant of vitamin D status in early neonatal life. This is the first indication in a mammal of a specific transfer mechanism that allows the fetus to accumulate vitamin D from the mother during the last third of gestation.

Suppression of rat hepatic vitamin D-25-hydroxylase by cholecalciferol, but not by 25-hydroxy- or 1,25-dihydroxymetabolites

Hepatic vitamin D-25-hydroxylase activity is greater in vitamin D-depleted than replete animals. We investigated whether vitamin D itself or a metabolite of vitamin D was responsible for modulating the activity of vitamin D-25-hydroxylase. Accordingly, we repleted vitamin D-depleted rats with subcutaneous injections of 2600, 520, and 130 pmoles of cholecalciferol (D3), 25-hydroxycholecalciferol (25(OH)D3), and 1,25-dihydroxycholecalciferol (1,25(OH)2D3), respectively, for up to 3 weeks. Repletion resulted in accelerated weight gain and in increased activity of gut mucosal alkaline phosphatase. Using an improved assay to measure vitamin D-25-hydroxylase activity in liver homogenates, we found 78% reduction (P less than 0.001) in the D3-repleted group, maximal by 1 week, in contrast to no change in those groups treated with D3 metabolites. D3, 25(OH)D3, and D3-esters remaining in livers at the time of assay were estimated in a parallel experiment using [3H]D3-repleted rats. Residual D3 accounted for only a 9% dilution of substrate in the assay. 25(OH)D3 was present in the liver at concentrations two orders of magnitude lower than the amount required to inhibit vitamin D-25-hydroxylase activity in vitro. D3 esters had no inhibitory effect in vitro at 250-fold excess of that found in the repleted rat liver. Vitamin D appears to modulate its D-25-hydroxylase activity in biological systems by a mechanism other than feedback inhibition by 25(OH)D3, 1,25(OH)2D3, or D3-esters.

Rapid automated high-performance liquid chromatographic assay for ercalcidiol and calcidiol (25-hydroxyvitamins D2 and D3) using trans-calcidiol as an ultraviolet-absorbing internal standard

A system is described using high-performance liquid chromatography to separate and quantify, by spectrophotometry in a simple one-stage procedure, ercalcidiol (25-hydroxyvitamin D2) and calcidiol (25-hydroxyvitamin D3). The novel feature of the method is the employment of an ultraviolet-absorbing internal standard to monitor recovery. This has the advantage of permitting total automation of the quantification by eliminating the need for radioactivity counting. The method gives results that compare well with those obtained in other systems and has particular application in clinical studies where rapid separate determination of ercalcidiol and calcidiol is required.

Hypercalcemia and osteoclast proliferation in adult T-cell leukemia

Eighteen autopsy cases of adult T-cell leukemia (ATL) were investigated clinicopathologically. Thirteen of the patients had hypercalcemia during their clinical course. Nine of the thirteen had a high level of serum calcium at the terminal stage, even after extensive chemotherapy. Microscopic examination of the bone revealed proliferation of osteoclasts and bone resorption in eight patients. No osteoclast proliferation or bone resorption was found in the other nine normocalcemic patients. The infiltration of ATL cells was observed in only two patients--one was hypercalcemic and the other, normocalcemic. The factors affecting the serum calcium level were examined in two hypercalcemic patients. Hypercalcemia could not be accounted for by parathyroid hormone or prostaglandins E levels, which were in the normal range, or by 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, which were low. Our findings are consistent with the mechanism proposed by several investigators, that the malignant T-lymphocytes produced an osteoclast-activating-factor-like substance that caused osteoclast proliferation and hypercalcemia.

Vitamin D3 metabolites in amniotic fluid in relation with maternal and fetal sera in term pregnancies

The concentration of 25-hydroxyvitamin D3 (25(OH)D3), 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) were determined in amniotic fluid, fetal cord serum and maternal serum in 26 cases of elective cesarean sections at term. All the women had a normal pregnancy and did not get any vitamin D fortified preparations. The samples were collected during December 1982-April 1983, at 37-40 weeks of pregnancy. The respective levels (+/- S.D.) of 25(OH)D3, 24,25(OH)2D3 and 1,25(OH)2D3 in maternal serum were: 18.03 +/- 10.8 ng/ml, 1.473 +/- 1.562 ng/ml and 36 +/- 21.5 pg/ml; in fetal cord serum: 13.15 +/- 8.3 ng/ml, 0.9 +/- 0.76 ng/ml and 29.2 +/- 18.55 pg/ml and in amniotic fluid: 0.732 +/- 0.508 ng/ml, 0.212 +/- 0.104 ng/ml and 14.3 +/- 10.0 pg/ml. The levels of the three metabolites in maternal and fetal cord serum were not statistically different. There was a statistically significant correlation between maternal and fetal serum levels of 25(OH)D3 and 24,25(OH)2D3 (r = 0.79, p less than 0.01 and r = 0.743, p less than 0.01 respectively). No significant correlation was found in 1,25(OH)2D3 levels between maternal and fetal cord sera. This lack of correlation may well be in agreement with the recent findings of Kouppala, et al. who demonstrated that the fetus contributes to its own pool of 1,25(OH)2D3. A significant difference was found between maternal serum and amniotic fluid levels of the three metabolites. A statistically significant difference was also found between fetal serum levels of 25(OH)D3 and 24,25(OH)2D3 and amniotic fluid levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Levels of active metabolites of vitamin D3 in the callus of fracture repair in chicks

The levels of the active metabolites of vitamin D were measured in the callus and in the epiphyseal growth plate of chicks given radioactive cholecalciferol during fracture healing. Those levels were correlated with the histological findings. Three groups of chicks were studied: a control group with no fracture, chicks with fractures fixed by Kirschner wire, and chicks with unfixed fractures. A significant increase in the levels of the active metabolites was found in the callus during the first few days after fracture. The levels of 25-hydroxycholecalciferol [25(OH)D3] and of 24,25-dihydroxycholecalciferol [24,25(OH)2D3] were higher when there was no fixation, while those of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] were higher after fixation. The concentrations of these metabolites in the proximal epiphysis of the tibia were similar to those found in the callus. Based on these findings it is suggested that the active metabolites of vitamin D are directly involved in the process of fracture repair.

Studies on the measurement of 25-hydroxy vitamin D in human saliva

A competitive protein-binding assay for 25-hydroxy vitamin D (25-OHD) in saliva has been established by adaptation of that previously described for 25-OHD in serum (Fairney et al. 1979). Random values of salivary 25-OHD in patients attending hospital for venesection showed a wide range of results (105-1000 pg/ml, n 55). These values corresponded to 1.2% of the total serum values with which they showed a significant relation (r 0.45, P less than 0.001). There was no relation between salivary 25-OHD and measured serum free 25-OHD in eighteen pairs of saliva and serum studied. Studies in two individuals showed that salivary 25-OHD values varied throughout the day and that a vitamin D load (19.5 micrograms), given as pickled herrings at lunch, produced a marked rise in 25-OHD values 5-8 h later. Diurnal profile studies of salivary 25-OHD in Caucasian and Asian 11-year-old male schoolchildren showed lower values in Asian children eating a vegetarian diet, and a significant variation with time and ethnic group (P less than 0.001). It is concluded that 25-OHD is present in saliva and that the values vary throughout the day. The values obtained may relate to dietary intake of vitamin D and the subject's ethnic origin.

Lack of evidence for existence of vitamin D and 25-hydroxyvitamin D sulfates in human breast and cow's milk

The presence of water-soluble vitamin D and 25-OH-D sulfates in human breast and cow's milk was studied. We first confirmed that synthetic vitamin D2 and D3 sulfates could not be hydrolyzed by alkali but by acid. Breast or cow's milk was separated into milk whey containing water-soluble components and milk curd containing crude proteins and lipophilic components. The separated milk whey and curd were hydrolyzed by acid or alkali and each lipid extract was subjected to HPLC analysis. Neither peak due to vitamin D and 25-OH-D was observed in the chromatograms of acid- and alkali-hydrolyzed milk whey, whereas the peaks due to vitamin D3 and 25-OH-D3 were found in the chromatograms of both acid- and alkali-hydrolyzed milk curd and there was no significant difference between the respective peak heights. The eluates corresponding to the respective peaks observed on the latter's chromatograms were collected and subjected to UV, HPLC, GC-MS and GLC to identify the existence of vitamin D3 and 25-OH-D3, respectively. We concluded from these results that neither breast nor cow's milk contained water-soluble vitamin D and 25-OH-D sulfates, whereas they contained fat-soluble vitamin D3 and 25-OH-D3. The concentrations of vitamin D3 and 25-OH-D3 in breast milk were about 125 and 350 ng/liter, while those in cow's milk were about 420 and 270 ng/liter, respectively. The experiments on the transfer of 3H-D3 and 3H-25-OH-D3 perorally dosed to lactating rats into suckling pups through their milk also supported the above conclusion.

Estimation of vitamin D3 and 25-hydroxyvitamin D3 in muscle and adipose tissue of rats and man

An assay is described based on a high pressure liquid chromatography system for measurement of vitamin D3 and 25-hydroxyvitamin D3 concentration in adipose tissue and muscle. The sensitivity of the assay is less than 1 ng/g of tissue. Neither vitamin D3 nor 25-hydroxyvitamin D3 were found in tissues of vitamin D-deficient rats using this method. 25-Hydroxyvitamin D3 could not be detected in adipose tissue and very little was found in muscle of normal rats. The mean vitamin D3 concentrations in 15 samples of human perirenal adipose tissue was 45.3 ng/g +/- 22.2 (SD) and in 6 samples of axillary tissue 115.6 ng/g +/- 52.4 (SD). Human adipose tissue contains a substantial amount of vitamin D3 and its contribution to the maintenance of vitamin D status is discussed.

Tissue distribution of 7-dehydrocholesterol, vitamin D3 and 25-hydroxyvitamin D3 in several species of fishes

A high-performance liquid chromatographic (HPLC) method for simultaneous determination of 7-dehydrocholesterol (7-DHC), vitamin D3 and 25-hydroxyvitamin D3 (25-OH-D3) in tissues of fishes was established, and using this method the tissue distribution of the sterols in lamprey (Entosphenus japonicus), great blue shark (Prionace glauca), skipjack (Katsuwonus pelamis) and albacore (Thunnus alalunga) was investigated. The results are summarized in the following: Although the alimentary canal, gall bladder and roe of lamprey and the alimentary canal of great blue shark contained comparatively high levels of 7-DHC (higher than 2,000 ng/wet tissue g), the other tissues of lamprey and great blue shark and all tissues of skipjack and albacore contained only low levels of 7-DHC (lower than 1,000 ng/g). There was no significant correlation between the levels of 7-DHC and vitamin D3. The contents of 7-DHC in the skin of skipjack and albacore were only 1/1,000 of those in the skin of rats. Although the contents of vitamin D3 in the liver of skipjack and albacore were extremely high (41,240 and 21,000 ng/g, respectively), those in the skin were very low (454 and 257 ng/g, respectively). 25-OH-D3 was detected in the viscera of skipjack, but the levels were not very high (lower than 150 ng/g). These levels were not significantly correlated with those of vitamin D3. The results suggest that large quantities of vitamin D3 in the liver of skipjack and albacore are supplied by other biosynthetic routes or by intake of vitamin D3 rather than by photochemical biosynthesis.

Relationships among vitamin D, 25-hydroxyvitamin D, and vitamin D-binding protein concentrations in the plasma and milk of human subjects

We measured plasma and milk concentrations of vitamin D2, vitamin D3, 25-hydroxyvitamin D2 (25OHD2), 25-hydroxyvitamin D3 (25OHD3), and vitamin D-binding protein (DBP) in a group of lactating women. All vitamin D compounds were quantitated using competitive protein binding assay, while DBP concentrations were determined by rocket electrophoresis. Vitamin D3 was the most abundant vitamin D compound in human milk, followed by vitamin D2, 25OHD3, and, finally, 25OHD2. The average vitamin D activity in milk was between 33-68 IU/liter, depending on the criterion of biological activity used. DBP concentrations in milk were approximately 3% of those in plasma. Significant relationships were found between plasma and milk levels for all vitamin D compounds. The milk to blood concentration ratio was greatest for vitamin D2, followed by vitamin D3, 25OHD2, and 25OHD3. (Thus, the parent compounds gained access into milk in a much more efficient fashion than their 25-hydroxy metabolites. It is postulated that this differential translocation is controlled by the DBP in the circulation.) There was no significant correlation between plasma and milk DBP concentrations, nor were milk DBP concentrations related to the vitamin D content of milk. This investigation supports the concept that the nutritional status of lactating mothers affects the vitamin D sterol potential of her milk which, in turn, would likely have an effect on the vitamin D status of her nursing infant.