Measurement of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2 and 25,26-dihydroxyvitamin D2 in a single plasma sample by mass fragmentography

A specific and sensitive assay for the measurement of the concentration of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D2 and 25,26-dihydroxyvitamin D2 in a single plasma sample is described, using stable isotope dilution mass fragmentography. After addition of appropriate deuterium-labelled internal standards, plasma samples were treated with acetonitrile to precipitate protein, and vitamin D metabolites were extracted on prepacked microparticulate reverse-phase cartridges. Further purification was achieved using straight-phase cartridges and high-performance liquid chromatography. Gas chromatography-mass spectrometry was carried out after appropriate derivatisation of samples and standards. The method has been evaluated in terms of specificity, recovery of added standards, and reproducibility.

Bone mineral content, serum vitamin D metabolite concentrations, and ultraviolet B light exposure in infants fed human milk with and without vitamin D2 supplements

OBJECTIVE

To monitor ultraviolet B light exposure in human milk-fed infants both with and without supplemental vitamin D2, and to measure longitudinally the bone mineral content, growth, and serum concentrations of calcium, phosphorus, 25-hydroxyvitamin D3, 25-hydroxyvitamin D2, 1,25-dihydroxyvitamin D, and parathyroid hormone.

DESIGN

Longitudinal, randomized, double-blind, placebo-controlled study of 6 months' duration.

SETTING

Patients from private pediatric practice, Madison, Wisconsin.

PATIENTS

Sequential sampling of 46 human milk-fed white infants; 24 received 400 IU/day of vitamin D2, and 22 received placebo. An additional 12 patients were followed who received standard infant formula. Eighty-three percent of patients completed a full 6 months of the study.

MEASUREMENTS AND RESULTS

Ultraviolet B light exposure and measurements of growth did not differ between groups. At 6 months, the human milk groups did not differ significantly in bone mineral content or serum concentrations of parathyroid hormone or 1,25-dihydroxyvitamin D, although total 25-hydroxyvitamin D values were significantly less in the unsupplemented human milk group (23.53 +/- 9.94 vs 36.96 +/- 11.86 ng/ml; p less than 0.01). However, 25-hydroxyvitamin D3 serum concentrations were significantly higher in the unsupplemented human milk-fed group compared with the supplemented group (21.77 +/- 9.73 vs 11.74 +/- 10.27 ng/ml, p less than 0.01) by 6 months of age.

CONCLUSION

Unsupplemented, human milk-fed infants had no evidence of vitamin D deficiency during the first 6 months of life.

Bone disease in chronic childhood cholestasis. I. Vitamin D absorption and metabolism

Metabolic bone disease is common in children and adults with chronic cholestasis. We evaluated baseline vitamin D (vitamin D2 and D3), 25-OH vitamin D2 and D3, 1,25(OH)2 vitamin D, vitamin D-binding protein, bone mineral content and dietary mineral content in six children (mean age: 12.1 years) with cholestasis since infancy. Absorption of 25-OH vitamin D3 and vitamin D2 was evaluated by measuring serial serum concentrations after a test dose. Bone mineral content was reduced by greater than 2 S.D. in five of six subjects compared to age-specific controls; none had radiographic evidence of rickets but all had osteopenia. Dietary Ca and P content in the subjects was comparable to the recommended daily allowance for age-specific children. Baseline serum vitamin D2 concentrations were undetectable in all but one cholestatic subject despite oral supplementation with 2,500 to 50,000 IU per day vitamin D2. Baseline serum 25-OH vitamin D was 33.2 +/- 6.0 ng per ml (mean +/- S.E.) and comparable to our laboratory norms (15 to 50 ng per ml). Serum 1,25(OH)2 vitamin D and "free" 1,25(OH)2 vitamin D were both significantly (p less than 0.05) reduced compared to controls. A significantly blunted rise and reduced area under the absorption curve (both p less than 0.001) after 1,000 IU per kg vitamin D2 was found in cholestatic children (0.8 ng +/- 0.5 ng per ml and 18.0 +/- 14.3 ng hr per ml, respectively) compared to controls (59.5 +/- 10.0 ng per ml and 1,780 +/- 253 ng hr per ml, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of starvation and sampling time on plasma alkaline phosphatase activity and calcium homeostasis in the rat

The effect of starvation and sampling time on plasma alkaline phosphatase activity, total plasma calcium concentration and whole blood ionized calcium concentration was determined in the rat. Starvation caused a significant fall in total and ionized calcium concentrations as well as in alkaline phosphatase activity. These changes were accompanied by a fall in whole blood pH and an increase in the anion gap and a decrease in urinary excretion of calcium. These indices were restored to normal following refeeding. There was no change in serum 25-OH vitamin D concentrations following starvation for 3 days. Alkaline phosphatase activity showed a pattern compatible with the presence of a circadian rhythm when sampling took place between 0800 and 1800 h. Total and ionized calcium concentrations did not show such a rhythm when animals were fed the present diet.

The measurement of vitamins D2 and D3 and seven major metabolites in a single sample of human plasma using gas chromatography/mass spectrometry

Selected ion monitoring of vitamin D metabolites has previously been described but there has been only one detailed description of the measurement by gas chromatography/mass spectrometry (GC/MS) of a number of metabolites in a single plasma sample. We describe here a GC/MS method, using stable isotope labelled internal standards, which allows the estimation of vitamins D2 and D3, and their 25-hydroxy, 24,25-dihydroxy and 25,26-dihydroxy metabolites in a single 2 ml sample of plasma, although more is needed for the measurement of 1,25-dihydroxyvitamin D3. Plasma was extracted on Bond Elut C18 cartridges and initial fractionation carried out on Sep-Pak SIL. Straight-phase high-performance liquid chromatography was required for separation of polyhydroxylated metabolites prior to GC/MS using an LKB 2091 mass spectrometer with conventional packed columns. n-Butylboronate esters were formed across vicinal hydroxyls, followed by formation of trimethylsilyl ethers using trimethylsilylimidazole. The [M - 90 - 15]+ ion for each compound was monitored. Deuterated internal standards were not available for all metabolites and it was necessary to use (2H6)D3 and (2H6)25OHD3 as standards for the measurement of D2 and D3, and 25OHD3 and 25OHD2, respectively, and (2H6)24,25(OH)2D3 as a standard for 24,25(OH)2D3 and 25,26(OH)2D2. Although the [M - 90 - 15]+ ion of 24,25(OH)2D and 25,26(OH)2D has the same mass: charge ratio, derivatives of these compounds are completely separated in the GC system used. The intra-assay precision for all these assays is usually less than 5%.

Vitamin D metabolism in biliary atresia: intestinal absorptions of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3

In children with biliary atresia, defective intestinal absorption of vitamin D and impaired hepatic uptake and 25-hydroxylation of vitamin D lead to a deficiency of vitamin D and rickets. We recently observed severe rickets in a 3-year-old boy with corrected biliary atresia resulting in jaundice, despite oral treatment with 1 alpha-hydroxyvitamin D3 (1 alpha-OHD3) or 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. He had low 25-hydroxyvitamin D (25-OHD) and high 1,25-(OH)2D serum levels. Intramuscular vitamin D2 administration produced radiological and biochemical evidence of recovery. Oral 1,25-(OH)2D3 (0.1 microgram/kg) and 25-OHD3 (10 micrograms/kg) tolerance tests were done to assess the ability to absorb vitamin D and the effectiveness of using these drugs orally. Eleven children with corrected biliary atresia, aged 9 months to 7 years, were studied. In oral 1,25-(OH)2D3 tolerance tests, the increments above the baseline serum levels of 1,25-(OH)2D were 140.7 +/- 27.4 pg/ml in nonjaundiced patients (n = 5). In jaundiced patients (n = 3), 1,25-(OH)2D3 absorption in two patients with high basal 1,25-(OH)2D values was lower than that of nonjaundiced patients; however, the absorption in the third patient with a low basal value was similar to that of nonjaundiced patients. In oral 25-OHD3 tolerance tests, the mean increase of serum 25-OHD was 48.9 +/- 30.6 ng/ml in nonjaundiced patients (n = 5) and 23.7 +/- 9.5 ng/ml in jaundiced patients (n = 4), the peak serum 25-OHD levels being reached 6-12 h after 25-OHD3 loading.(ABSTRACT TRUNCATED AT 250 WORDS)

The plasma binding protein for vitamin D is a site of discrimination against vitamin D-2 compounds by the chick

The binding of 25-hydroxy-[26,27-3H]vitamin D-3 and 25-hydroxy-[26,27-3H]vitamin D-2 to the vitamin D binding protein in the plasma of both rats and chicks has been studied. In the case of rats, sucrose density gradient analysis, competitive displacement, and Scatchard analysis demonstrate that 25-hydroxyvitamin D-3 and 25-hydroxyvitamin D-2 are bound equally well to the vitamin D binding protein. In contrast, 25-hydroxyvitamin D-2 is poorly bound, while 25-hydroxyvitamin D-3 is tightly bound to the vitamin D binding protein in chick plasma. On the other hand, the chick intestinal receptor binds 1,25-dihydroxyvitamin D-2 and 1,25-dihydroxyvitamin D-3 equally well with a KD of 7.10(-11) M for both compounds. These results strongly suggest that the failure of the plasma transport protein in chicks to bind the vitamin D-2 compounds may be responsible for their relative ineffectiveness in these animals.

Comparisons between two receptor assays for 1,25-dihydroxyvitamin D

We present a competitive protein binding assay (CPBA) for 1,25(OH)2D employing 1,25(OH)2D receptor from calf thymus, which was compared with a CPBA-employing receptor from rachitic chick intestine. The thymus receptor assay was more sensitive, specific and precise than the intestinal receptor assay. The thymus receptor assay measured both 1,25(OH)2D2 and 1,25(OH)2D3 with equal affinity, whereas 1,25(OH)2D2 was 1.1 times less potent than 1,25(OH)2D3 in the displacement from the chick intestinal receptor. Mean serum values of 1,25(OH)2D in normal subjects, post-menopausal women, pregnant women, and patients with chronic renal failure measured by the two assay systems did not differ. Furthermore, both assays showed that 1,25(OH)2D was unchanged in post-menopausal women after treatment with vitamin D2 or vitamin D3, 4000 IU/day for 8 weeks. We conclude that the high sensitivity of the thymus receptor and the equal affinity for the D2 and D3 analogue make the thymus receptor assay a reliable alternative to the chick intestinal receptor assay.

Correlation between concentrations of humoral antibodies and vitamin D nutritional status: a survey study

The vitamin D nutritional status and the plasma concentrations of IgG, IgA, IgM and total immunoglobulins were determined in 2052 Saudi subjects. It was observed that females had significantly lower 25-hydroxyvitamin D levels than males and children had lower levels than adults. The mean levels of IgG and IgM were significantly higher in females than in males and those in adults higher than in children. There was a highly significant positive correlation between the concentrations of the circulating form of vitamin D, 25-OHD, and IgG levels in the overall population, in children and in adults. When these groups were classified into males and females the correlation was significant only for females. The significance and importance of this correlation between vitamin D nutritional status and IgG is as yet unknown. The possible clinical relevance of this study's findings are discussed.

Plasma calcemic hormones in mature female reindeer, Rangifer tarandus

The plasma calcemic hormones in mature female reindeer were measured during the major portion of the antler growth cycle, between the months of March and November. Blood samples were collected every 2 months, a total of five samples each from eight reindeer. Plasma levels of 25-hydroxyvitamin D, PTH, and osteocalcin were found to increase progressively from May through July and decline thereafter except 1,25-dihydroxyvitamin D level which peaked in September. No change in plasma total Ca was observed at any time of the year. Plasma estradiol level was elevated in March only. All animals grew and shed antlers between April and February. This suggests that during the antler growth period when the deer undergoes cyclic bone loss, corresponding changes in plasma calcemic hormones occur, which may account for the reported skeletal bone changes seen during the growth of the antler.

Dietary assessment of maternal vitamin D intake and correlation with maternal and neonatal serum vitamin D concentrations at delivery

Maternal and cord blood 25-hydroxy vitamin D concentrations are positively and significantly correlated. If an easily obtainable maternal dietary history could be used to predict maternal and secondarily cord blood vitamin D status, it would be a useful means of assessing the vitamin D adequacy of the newborn. Therefore, a single assessment of maternal dietary vitamin D intake during the last trimester of pregnancy was correlated with maternal and newborn serum vitamin D concentration. Neither the correlation between maternal dietary history of vitamin D intake and maternal serum 25-hydroxy vitamin D level nor between maternal dietary history and cord blood 25-hydroxy vitamin D level was significant. These data indicate that a single maternal dietary history is an inadequate method of predicting neonatal vitamin status at delivery.

Interactions between 1,25-dihydroxyvitamin D3 and vitamin D2: effects of pharmacologic doses in normal individuals

To determine whether the administration of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) affects the conversion of a pharmacologic dose of vitamin D2 to 25-hydroxyvitamin D (25OHD), 20 normal subjects received two separate doses of vitamin D2--one with and the other without the concomitant administration of 1,25(OH)2D3. Serum 1,25(OH)2D rose in response to 1,25(OH)2D3 administration and fell when vitamin D2 was given alone. Serum osteocalcin rose in response to 1,25(OH)2D3 administration. Serum 25OHD rose in response to vitamin D2 administration regardless of whether the subjects also received 1,25(OH)2D3. The data from this study in humans support the suggestion that the effects of 1,25(OH)2D3 on serum 25OHD concentrations are mediated through mechanisms other than impairment of production.

Intermittent high-dose vitamin D prophylaxis during infancy: effect on vitamin D metabolites, calcium, and phosphorus

In infants receiving intermittent high dose vitamin D prophylaxis (600,000 IU ergocalciferol per dose orally) every 3-5 mo, the serum concentrations of vitamin D metabolites, calcium (Ca), and phosphorus (P) were determined before and 2 wk after each dose. The 25-hydroxyvitamin D (OHD) concentrations increased to well above normal but the values returned to the normal range before each subsequent dose. The 24,25- and 25,26-dihydroxyvitamin D ([OH]2D) levels followed a pattern similar to that of 25-OHD, and both were closely related to the latter (r = 0.85, p less than 0.005, and r = 0.84, p less than 0.005, respectively). The 1,25-(OH)2D concentrations did not vary in a consistent pattern and remained largely within the normal range. All infants had normal Ca levels before the first dose but 14 infants (34%) later had one or both Ca values above the upper normal limit of 2.80 mmol/L (2.81-3.32 mmol/L), indicating that the vitamin D doses were excessive despite the lack of accumulative increases in serum vitamin D concentrations.

Parity and vitamin D metabolites

Twenty-five hydroxycalciferol (25-OHD), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcium (Ca), phosphorus (P), alkaline phosphatase, and total protein were estimated in 86 Saudi pregnant women. They were divided into two groups, group I, parity 5 or more, and group II, parity 4 or less. The mean level of 25-OHD was 10.4 (S.D. 6.5) ng/ml in group I, and for group II 8.2 (6.1) ng/ml with no significant statistical difference between the groups. 1,25(OH)2D mean levels, in group I 45.5 (S.D. 30.2) ng/ml and in group II 36.9 (S.D. 27.1) pg/ml, also showed no significant difference. Levels of vitamin D metabolites were comparable with non-pregnant levels in Saudi Arabia but lower than others reported in Western populations. We found no effect of increasing parity on levels of vitamin D metabolites in our study.

Calcium, vitamin D-endocrine system, and parathyroid hormone in black and white males

The serum and urinary calcium, 25-hydroxyvitamin D (25OHD), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), and parathyroid hormone (PTH) were studied in healthy black and white males living in Belgium, and the results were compared to data in blacks of similar age living in Zaïre. Dietary calcium and vitamin D were estimated in a sub-sample of blacks and whites examined in Belgium. Compared to whites (9.51 +/- 0.28 mg%) serum calcium was somewhat lower in blacks (9.26 +/- 0.27 mg% in Belgium; 9.19 +/- 0.48 mg% in Zaïre). The 24 hour urinary calcium excretion averaged 215.0 +/- 16.7 mg% in whites and was higher (P less than 0.05 or less) than in blacks (115 +/- 71 mg% in Belgium; 36 +/- 33 mg% in Zaïre). The serum 25OHD levels were similar in whites and blacks evaluated in Zaïre, both being higher (P less than 0.05 or less) than in blacks living in Belgium. In the latter blacks, an inverse correlation was observed between the 25OHD level and the duration of the stay in a temperate climate. Parathyroid hormone levels were slightly higher in blacks living in Belgium than in the other two groups of subjects. The serum levels of 1,25(OH)2D3 and human vitamin D-binding protein were similar in the three groups of subjects. Dietary calcium averaged 541 +/- 152 mg/day in blacks and was significantly (P less than 0.001) less than in whites (1,203 +/- 508 mg/day), whereas no significant difference was observed in dietary vitamin D intake between blacks and whites. It is concluded that calcium intake is low in blacks but stimulation of parathyroid hormone and 1,25(OH)2D3 required to achieve normocalcemia does not occur.

Effect of vitamin D2 and vitamin D3 on the serum concentrations of 1,25(OH)2D2, and 1,25(OH)2D3 in normal subjects

Serum concentrations of vitamin D2 and vitamin D3 metabolites were measured in 19 normal subjects before and during treatment with either vitamin D2 or vitamin D3, 4000 IU per day for 8 weeks. Vitamin D2 treatment increased the serum concentration of 1,25(OH)2D2, but a corresponding decrease in 1,25(OH)2D3 resulted in an unchanged serum concentration of total 1,25(OH)2D. During treatment with vitamin D3, the serum concentration of 1,25(OH)2D metabolites was unchanged. We conclude that the production of 1,25(OH)2D is tightly regulated and that 1 alpha-hydroxylase does not discriminate between D2 and D3 metabolites in normal subjects.

Treatment effects of parenteral vitamins in total parenteral nutrition patients

To determine the prevalence of abnormal vitamin levels in an adult hospitalized population requiring total parenteral nutrition (TPN) and to assess the effect of routine parenteral vitamin therapy on vitamin levels, we studied 35 general surgical patients. Assays for 12 vitamins were performed both before and after a standard 10-day course of TPN. Patients were given nothing by mouth. The first 25 patients received a daily parenteral vitamin mixture tailored to the recommendations of the Nutrition Advisory Group of The American Medical Association (maintenance dose). The final 10 patients were given a parenteral multivitamin dose providing substantially greater amounts of most vitamins (repletion dose). Only 58% (190/324) of pre-TPN vitamin levels were normal, 25% were low, and 17% were high. No patient had fewer than two abnormal baseline levels. Vitamin levels did not correlate with serum albumin, body weight, or nitrogen balance. After 10 days of treatment, only 39% of low pre-TPN vitamin levels improved; most (45/62) of the low posttreatment levels were low at baseline. The higher repletion dose resulted in a significantly (p less than 0.01) greater percent increase in vitamin A, C, and pyridoxine levels. The prevalence of abnormal vitamin levels in this population is high (42%). Standard parenteral vitamin therapy leads to marginal improvement in abnormally low pre-TPN vitamin levels.

Effect of aging on vitamin D stores and bone density in women

It has been suggested that the decrease in vitamin D stores with aging is a contributory cause of age-related osteoporosis. We studied this question by measuring bone mineral density (BMD) of the mid-radius, distal radius, and lumbar spine assessed by single and dual photon absorptiometry in 122 women, aged 33-94 years, selected from a random sample of Rochester, MN residents. We measured serum 25-hydroxyvitamin D (25OHD), the major storage form of vitamin D, as well as 25OHD3 (representing both endogenous and exogenous sources of vitamin D), and 25OHD2 (representing only exogenous sources). Both baseline serum total 25OHD (r = -0.29, P less than 0.001) and the metabolite 25OHD3 (r = -0.41, P less than 0.001), were negatively associated with age at baseline. After adjusting for the effect of age by multiple regression analysis, there was no association between serum levels of 25OHD2, 25OHD3, or total 25OHD and BMD for any of the three skeletal scanning sites. Thus, in a northern American population we cannot demonstrate that reduced bioavailability of vitamin D plays a major role in age-related bone loss.

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.

The influence of progressive hyperinsulinemia on duodenal calcium absorption in the rat

Using an in situ loop technique, we studied the influence of moderate hyperinsulinemia on the bidirectional fluxes [lumen-to-plasma (LP), plasma-to-lumen (PL)] and on the net absorption of calcium (Ca) in the duodenum of the rat. Under hyperinsulinemic euglycemic clamp conditions, three different steady-state plasma insulin levels (66 +/- 16, 187 +/- 13, 263 +/- 24 microU/mL) were maintained by intravenous (IV) infusion of either 20, 40, or 60 mU/h of insulin. LP flux and net Ca absorption (CaA) increased significantly under all, while the PL flux was not changed by any of the three insulin doses. Under 40 and 60 mU/h of IV insulin, the individual plasma insulin levels and LP fluxes were positively and significantly correlated, suggesting a dose-dependent action of insulin on duodenal CaA. No significant changes were seen in plasma somatostatinlike immunoreactivity (SLI), parathyroid hormone (PTH), and serum Ca, while serum inorganic phosphate (Pi) and 1,25(OH)2 vitamin D levels fell with increasing doses of IV insulin. It is concluded for the rat that physiologic degrees of hyperinsulinemia enhance duodenal CaA by an as yet unknown mechanism, this action seems to be independent of PTH and, the role of 1,25(OH)2 vitamin D in this context is poorly understood.

Vitamin D deficiency in women with femoral neck fracture

Calcium (Ca) metabolism, with particular reference to serum vitamin D metabolites, was investigated in 40 women with femoral neck fracture (mean age 77.1 +/- 8.6 yr). All the patients were ambulant before the fracture; eight were long-term geriatric in-patients. Serum total and ionised calcium and serum albumin levels were significantly lower, and serum parathormone (PTH) levels significantly higher in fracture patients than in controls. Both serum 25-OH-D and 1,25-(OH)2D were significantly lower in fracture patients than in controls. We concluded that vitamin D, serum PTH and calcium levels should be checked with greater frequency in patients at high risk for osteoporosis and osteomalacia before they reach the age of 70.

Hypercalcemia in infants with congenital hypothyroidism and its relation to vitamin D and thyroid hormones

The circulating concentrations of calcium, phosphorus, and vitamin D metabolites were measured in 25 infants (fifteen to 30 days of age) with congenital hypothyroidism before treatment or during the first 6 months of thyroxine therapy. Five of the children before treatment and four during the early 3 months of treatment had mild hypercalcemia (10.8 to 12.4 mg/dl). Hypercalcemia before treatment did not appear to be related to the vitamin D status of the infant nor to an alteration in vitamin D metabolism, but to the presence of a residual thyroid secretion. In contrast, hypercalcemia during thyroxine therapy was related to vitamin D supplementation, even though the serum calcium concentration could not be correlated with the circulating concentration of any of the vitamin D metabolites assayed and obvious changes in vitamin D metabolism could not be demonstrated.