A method for simultaneous determination of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 in human plasma by using two steps of high-performance liquid chromatography

A method for simultaneous determination of 25-hydroxyvitamin D2 (25-OH-D2) and 25-hydroxyvitamin D3 (25-OH-D3) in human plasma has been developed by using two steps of high-performance liquid chromatography (HPLC). Lipids extracted from 0.51 ml of human plasma were first subjected to the preparative HPLC using a Nucleosil 5C18 column (reversed-phase type) and a 25-OH-D fraction containing 25-OH-D2 and 25-OH-D3 was separated. The separated fraction was subsequently subjected to the analytical HPLC using a Zorbax SIL column (straight-phase type). Since the peaks corresponding to 25-OH-D2 and 25-OH-D3 were clearly separated from one another on the chromatogram of the analytical HPLC, the metabolites could be simultaneously determined by estimating the respective peak heights. When the fractions corresponding to the respective peaks were separately collected by repeatedly applying rather large quantities of human plasma and were subjected to gas chromatography-mass spectrometry (GC-MS), they were identified as containing 25-OH-D2 and 25-OH-D3, respectively. The proposed method was applied to plasma samples of human adults taking 400 I.U./day of vitamin D2 for 8 weeks and the values were 22.5 +/- 8.1 ng/ml for 25-OH-D3 and 11.5 +/- 1.8 ng/ml for 25-OH-D2 (mean +/- S.D.), respectively.

Plasma levels of vitamin D metabolites in the bovine species during the perinatal period

Plasma vitamin D metabolites (25-OH D; 24,25-(OH)2D and 1,25-(OH)2D) were measured simultaneously in the blood plasma samples of young cows and their calves. Four of the calves were chronically catheterized in utero at least 2 weeks before the expected time of parturition. No significant hypocalcaemia occurred in the dams at calving. Plasma vitamin D metabolites showed no significant variations for 2 weeks before and 4 days after calving. But rapid changes in plasma 1,25-(OH)2D concentrations were observed in one calf during the first 48 postnatal hours. Before birth, the maternal and foetal concentrations of either 1,25-(OH)2D or 24,25-(OH)2D were positively correlated. 25-(OH) D (13 ng/ml), 24,25-(OH)2D (1 ng/ml) and 1,25-(OH)2D (76 pg/ml) were detected in one foetal plasma collected 35 days before term.

Seasonal changes in the activity of serum alkaline phosphatase

This paper reports a seasonal variation in alkaline phosphatase (ALP) levels in the serum, with low values occurring in summer and high in winter. These variations were found both in indoor and outdoor workers and in a group of elderly women in a long-stay ward. The seasonal change in ALP was in the opposite direction to the seasonal change in the serum levels of 25-hydroxyvitamin D. No such change was seen in the serum levels of gamma-glutamyltransferase. It is suggested that the seasonal change in plasma ALP could be due to changes in the bone isoenzyme. Serum levels of calcium remained unchanged; the change in ALP may reflect a homeostatic mechanism controlling plasma calcium, which compensates for seasonal variations in vitamin D supply.

Serum levels of 25-hydroxyvitamin D in postmenopausal osteoporosis

Serum concentrations of 25-hydroxy-vitamin D were measured in a group of women with symptomatic postmenopausal osteoporosis, assessed by bone biopsy. A competitive protein binding assay was used, which included a chromatographic step. Accurate surveys of dietary or therapeutic vitamin D intake and light environment were obtained in each patient. Women with severe postmenopausal osteoporosis were found to have significantly (P less than 0.001) higher serum levels of 25-hydroxyvitamin D than age-matched normal women, the mean values being 27.5 ng/ml (+/- 13.6 SD) and 9.2 ng/ml (+/-5.7), respectively. The authors hypothesize that the reduction in 1,25-dihydroxyvitamin D, recently reported in postmenopausal osteoporotic women, might be responsible for the increased serum levels of 25-hydroxyvitamin D through an inadequate product inhibition of liver vitamin D 25-hydroxylase.

Induction of bone resorption by parathyroid hormone in congenital malignant osteopetrosis

A male patient, afflicted with malignant congenital osteopetrosis, was studied over a 5 year period. Hypocalcemia (less than 8 mg/dl) with lack of an appropriate increase in serum immunoreactive parathyroid hormone (iPTH) prevailed at all times. Under a calcium restricted diet, a 6-hour infusion of parathyroid extract normalized serum calcium, and increased the urinary hydroxyproline excretion suggesting that bone resorption had been induced. A second attempt to induce resorption was made by infusing a synthetic amino terminal fragment of bovine PTH over a period of 3 weeks at the dose of 1.5 units/kg/hr. This infusion evoked an increase in serum calcium (8.1 to 10.5 mg/dl), urinary calcium (0.03 to 0.65 mg/g creatinine) and urinary hydroxyproline (160 to 372 mg/g creatinine); and urinary hydroxyproline (160 to 372 mg/g creatinine); increases which were reversed by calcitonin administration. Iliac crest bone biopsies were obtained before and on the last day of the 3-week infusion. Quantitative comparison of the two specimens showed that, during PTH infusion, there was a 23% decrease in bone volume due to the increase in marrow space, a 93% increase in the number of osteoclasts and 136% increment in the osteoclastic resorption surface. Electron microscopic examination of the osteoclasts in the first tissue sample showed no evidence of ruffled borders, while in the second biopsy, numerous cytoplasmic processes indicative of resorptive activity were visible at the matrix-cell interface. It is proposed that, in our patient, the osteopetrotic phenotype is the consequence of an abnormality in the interaction between PTH and osteoclasts that may be related to the synthesis of a physiologically "defective" PTH.

Impaired 24,25-dihydroxyvitamin D production in anephric human and pig

Plasma 25-hydroxyvitamin D and 24, 25-dihydroxy-vitamin D [24,25-(OH)(2)D] concentrations were measured in normal and chronically dialyzed anephric humans and pigs. Measurement of the 24, 25-(OH)(2)D was preceded by three purification steps involving one Sephadex LH-20 column and two high-pressure liquid chromatographic columns. The final high-pressure liquid chromatography step involved resolution of 25-hydroxy-vitamin D(3)-26,23 lactone and 25,26-dihydroxy-vitamin D(2) from 24,25-dihydroxyvitamin D(2) and 24,25-dihydroxyvitamin D(3) [24,25-(OH)(2)D(3)]. The total 25-hydroxyvitamin D [25-hydroxyvitamin D(2) plus 25-hydroxyvitamin D(3) (25-OHD(3))] was 31.7+/-3.6 ng/ml in the plasma of eight anephric human subjects and 40.1+/-3.7 ng/ml in five normal human subjects. Six of the eight anephric patients had undetectable (<0.2 ng/ml) 24,25-(OH)(2)D concentrations. Two of the eight patients had very low (0.51 and 0.41 ng/ml), but detectable, 24,25-dihydroxyvitamin D(2). The normal human volunteers had plasma 24,25-(OH)(2)D concentrations of 2.8+/-0.7 ng/ml. Chronically dialyzed anephric and normal pigs were given intramuscular injections of massive amounts (5 x 10(6) IU) of vitamin D(3) immediately after surgery (day 0) and again on day 7. In anephric pigs, plasma 25-OHD(3) progressively rose from 12+/-4 ng/ml on day 0 to 705+/-62 ng/ml on day 10. The 25-OHD(3) concentrations in normal pigs rose from 8+/-2 ng/ml on day 0 to 439+/-64 ng/ml on day 10. Plasma 25-OHD(3) was higher in anephrics throughout the experiment, and concentrations were significantly higher (P < 0.05) on days 9 and 10. Plasma 24,25-(OH)(2)D(3) concentrations declined progressively in anephric pigs from 3.6+/-0.6 ng/ml on day 0 to 3.2+/-0.7 ng/ml on day 2. During days 4-10, plasma 24,25-(OH)(2)D(3) was not apparent until plasma 25-OHD(3) was >400 ng/ml. In control pigs, plasma 24,25-(OH)(2)D(3) was elevated from 4.3+/-0.6 ng/ml on day 0 to 178+/-2.7 ng/ml on day 3. Plasma 24,25-(OH)(2)D(3) was significantly higher (P < 0.05) in controls on days 1-8. At the end of the experiment (day 10), 24,25-(OH)(2)D(3) concentrations were similar and not significantly different in both groups (87.0+/-18.4 ng/ml in anephric and 110.3+/-32.1 ng/ml in normal pigs). The identity of the 24,25-(OH)(2)D(3) isolated from anephric pig plasma was confirmed by mass spectroscopy. Our data suggest that anephric humans receiving normal dietary levels of vitamin D(3) have little or no ability to produce 24,25-(OH)(2)D. However, we have shown that pigs produce 24,25-(OH)(2)D(3) when plasma 25-OHD(3) is extremely high (>400 ng/ml).

The estimation of vitamin D and some metabolites in human plasma by mass fragmentography

A mass fragmentographic assay for vitamin D3, 25-hydroxyvitamin D3, 25-hydroxyvitamin D2 and 24,25-dihydroxyvitamin D3 is described. After extraction of plasma with methanol and dichloromethane, Lipidex 5000 chromatography was used to separate the plasma extract into three fractions (a vitamin D fraction, a 25-hydroxyvitamin D fraction and a 24,25-dihydroxyvitamin D fraction). Cholesterol was removed from the vitamin D fractio by thin-layer chromatography. :After addition of vitamin D2 to each fraction, isotachysterol trimethylsilyl ethers were formed. Recoveries prior to gas chromatography-mass spectrometry were assessed by the use of tritiated standards added to the plasma before extraction. Using this procedure, normal ranges were established (vitamin D3: 3--17.7, 25-hydroxyvitamin D3: 5.9--35.2, 25-hydroxyvitamin D2: 0.6---1.0 and 24,25-dihydroxyvitamin D3: 0.6--2.9 micrograms/l).

The effect of elevated prolactin levels on plasma 1,25-dihydroxyvitamin D and intestinal absorption of calcium

Because of evidence in experimental animals that prolactin stimulates production of 1,25-dihydroxyvitamin D, we evaluated several indices of calcium metabolism in patients who had hyperprolactinemia due to functioning pituitary adenomas and in normal age-matched controls. Plasma levels of 1,25-dihydroxyvitamin D in hyperprolactinemic patients were in the normal range (15 to 24 pg/ml versus 15 5o 75 pg/ml in controls). Intestinal absorption of calcium, plasma levels of immunoreactive parathyroid hormone, and serum values for calcium, phosphorus, and alkaline phosphatase were similar in patients and controls. We conclude that prolactin probably has no effect on plasma 1,25-dihydroxyvitamin D levels or calcium metabolism in man.

Assay for vitamin D2 and vitamin D3 in plasma of dairy cows: changes after massive dosing of vitamin D3

A sensitive, precise assay for vitamin D in plasma is described. Three to five milliliters of plasma were extracted with methanol:methylene chloride (2:1). The lipid extract was chromatographed on Sephadex LH-20 and then on lipidex-5000 columns. After high pressure liquid chromatography with a reverse phase chromatographic system, vitamin D2 and vitamin D3 were quantitated by ultraviolet absorbance. We used this assay system for monitoring daily changes of vitamin D3 in plasma of two Jersey cows after four intramuscular doses (15 x 10(6) IU) of vitamin D3 administered at weekly intervals. Basal vitamin D in plasma was 3.2 +/- .99 ng/ml with a range of 1.7 to 4.9 ng/ml. Vitamin D3 in plasma remained relatively low (10 to 45 ng/ml) the week after the first vitamin D3 injection. Vitamin D3 was high (130 to 234 ng/ml) after the second, third, and fourth injections. Vitamin D3 decreased steadily to 88 ng/ml by 38 days after the fourth vitamin D3 injection. Phosphorus in plasma increased sharply to a plateau at 9.5 mg/100 ml during the week after the second vitamin D3 injection and returned to normal (4.5 mg/100 ml) at the end of the experiment. Calcium, however, gradually increased to 14.0 mg/100 ml 20 days after the fourth vitamin D3 injection. Both animals remained hypercalcemic (calcium 11.5 mg/100 ml) during the experiment.

Determination of vitamin D and its metabolites in plasma from normal and anephric man

A multiple assay capable of reliably determining vitamins D(2) and D(3) (ergocalciferol and cholecalciferol), 25(OH)D(2) (25-hydroxyvitamin D(2)) and 25(OH)D(3) (25-hydroxyvitamin D(3)), 24,25(OH)(2)D (24,25-dihydroxyvitamin D), 25,26(OH)(2)D (25,26-dihydroxyvitamin D) and 1,25(OH)(2)D (1,25-dihydroxyvitamin D) in a single 3-5ml sample of human plasma was developed. The procedure involves methanol/methylene chloride extraction of plasma lipids followed by separation of the metabolites and purification from interfering contaminants by batch elution chromatography on Sephadex LH-20 and Lipidex 5000 and by h.p.l.c. (high-pressure liquid chromatography). Vitamins D(2) and D(3) and 25(OH)D(2) and 25(OH)D(3) are quantified by h.p.l.c. by using u.v. detection, comparing their peak heights with those of standards. 24,25(OH)(2)D and 25,26(OH)(2)D are measured by competitive protein-binding assay with diluted plasma from vitamin D-deficient rats. 1,25(OH)(2)D is measured by competitive protein-binding assay with diluted cytosol from vitamin D-deficient chick intestine. Values in normal human plasma samples taken in February are: vitamin D 3.5+/-2.5ng/ml; 25(OH)D 31.6+/-9.3ng/ml; 24,25(OH)(2)D 3.5+/-1.4ng/ml; 25,26(OH)(2)D 0.7+/-0.5ng/ml; 1,25(OH)(2)D 31+/-9pg/ml (means+/-s.d.). Values in two normal human plasma samples taken in February after 1 week of high sun exposure are: vitamin D 27.1+/-7.9ng/ml; 25(OH)D 56.8+/-4.2ng/ml; 24,25(OH)(2)D 4.3+/-1.6ng/ml; 25,26(OH)(2)D 0.5+/-0.2ng/ml. Values in anephric-human plasma are: vitamin D 2.7+/-0.8ng/ml; 25(OH)D 36.4+/-16.5ng/ml; 24,25(OH)(2)D 1.9+/-1.3ng/ml; 25,26(OH)(2)D 0.6+/-0.3ng/ml; 1,25(OH)(2)D was undetectable.

Simultaneous measurement of serum 25-hydroxycholecalciferol and 25-hydroxyergocalciferol

A method for the selective measurement of serum 25-hydroxycholecalciferol and 25-hydroxyergocalciferol has been developed. The two hydroxysecosteroids were measured in a control group and in a group of ambulatory patients treated chronically with anticonvulsant drugs. In both groups the serum levels of 25-hydroxycholecalciferol and 25-hydroxyergocalciferol followed a log normal distribution. No significant difference could be elicited between the control and the treated groups for either hydroxysecosteroid. Furthermore the data shows how important is the dietary source of vitamin D in our environment.

The relevance of 25-hydroxycalciferol measurements in sera of patients with renal failure

Iliac crest biopsies and serum specimens were obtained from 36 non-dialyzed uraemic patients. The mean serum 25-hydroxycalciferol concentration of the patients was lower than that of normal subjects and a significant correlation was found between 25-hydroxycalciferol values and the severity of osteomalacia. Parathyroid osteopathy was significantly correlated with serum immunoreactive parathyroid hormone but not with serum 25-hydroxycalciferol values. While normal serum 25-hydroxycalciferol concentrations in uraemic patients do not exclude the presence of osteomalacia, a low concentration is virtually diagnostic of this disorder.

Diet, sunlight, and 25-hydroxy vitamin D in healthy children and adults

In 110 white West Midlands children serum 25-hydroxy vitamin D (25-OHD) concentrations showed a pronounced seasonal variation, the values being highest in August and lowest in February. The concentrations correlated significantly both with recorded sunlight and with seasonal ultraviolet energy of the sunlight. Children who had had a seaside holiday the previous summer had a higher mean 25-OHD concentration than those who had not had a summer holiday away from home. Correlation between vitamin D intake and serum 25-OHD concentration was not significant.

A familial syndrome of decrease in sensitivity to 1,25-dihydroxyvitamin D

Typical features of hereditary vitamin D-dependent (pseudovitamin D-deficient) rickets were observed beginning at ages 20 and 5 months in a brother and sister. Both had calcium malabsorption correctable with high doses of 25-hydroxyvitamin D. During periods of hypocalcemia they both manifested secondary hyperparathyroidism with hypophosphatemia and high serum concentrations of endogenously produced 1,25-dihydroxyvitamin D. In each, normalization of serum calcium concentration and resolution of osteomalacia were obtained with continuous administration of high doses of ergocalciferol or high doses of 1,25-dihydroxycholecalciferol. Chemical features of vitamin D deficiency were corrected in the presence of high circulating concentrations of 1,25-dihydroxyvitamin D2, produced endogenously, or of 1,25-dihydroxyvitamin D3, administered by mouth. Serum concentrations of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D, and 1,25-dihydroxyvitamin D were normal in five first degree relatives. We conclude that in these five first degree relatives. We conclude that in these siblings, rickets and osteomalacia resulted from a hereditary decreased sensitivity to 1,25-dihydroxyvitamin D at the intestine and perhaps other vitamin D target tissues.

Assay of vitamins D2 and D3, and 25-hydroxyvitamins D2 and D3 in human plasma by high-performance liquid chromatography

I describe a new assay that is capable of measuring vitamin D2, vitamin D3, 25-hydroxyvitamin D2, and 25-hydroxyvitamin D3 in 2 ml of plasma or serum. Plasma is extracted by the Bligh and Dyer technique [Can. J. Biochem. Physiol. 37, 911 (1959)], the lipid component is fractionated by two high-performance liquid-chromatographic systems based upon adsorption and reversed-phase chromatography, and each of the four vitamin D metabolites is measured by its absorbance at 254 nm. The method has a sensitivity limit of 0.5 mug/liter of plasma. The identity of metabolite peaks was confirmed by mass spectrometry, ultraviolet absorption spectrophotometry, and rechromatography, and there was good correlation (r=0.84) between plasma 25-hydroxyvitamin D as measured by the present method and by a protein binding assay developed in our laboratory. Mean concentrations of vitamin D and 25-hydroxyvitamin D in normal adults (n=25) in December were 2.2 +/- 1.1 (SD) and 16 +/- 3.9 (SD) mug/liter, respectively. 25-Hyroxyvitamin D2 made up 31% of the total 25-hydroxyvitamin D. Patients receiving pharmacological doses of vitamin D had values for vitamin D and 25-hydroxyvitamin D that were 10- to 100-fold normal. This method provides a rapid, reliable physico-chemical assay that appears to have advantages over existing protein binding assays and can be used to measure circulating vitamin D.

Elevation of serum 25-hydroxycalciferol levels in androgen-treated and ultraviolet-irradiated rats

Administration of 4-8 mg testosterone propionate significantly raised 25-hydroxycalciferol levels in the ultraviolet irradiated rats compared to the ultraviolet irradiated controls, but failed to influence serum 25-hydroxycalciferol levels in the non-irradiated animals. Estradiol benzoate and progesterone did not influence serum 25-hydroxycalciferol levels regardless of the ultraviolet irradiation. These findings implicate that testosterone enhances vitamin D biosynthesis induced by ultraviolet irradiation in rats, in accordance with the clinical observation that males often show higher levels of serum 25-hydroxycalciferol than females.

Radioimmunoassay of the binding protein for vitamin D and its metabolites in human serum: concentrations in normal subjects and patients with disorders of mineral homeostasis

A radioimmunoassay for the binding protein for vitamin D and its metabolites (DBP) has been developed. Suitable rabbit anti-DBP antiserum was elicited after primary and one booster injection. Anti-DBP antisera, as well as antigroup-specific component antisera, produced a single, monospecific line of percipitation when reacted against purified DBP and human serum. DBP was iodinated with 125I and 125I-DBP was purified by gel filtration on Sephadex G-200. Binding of 125I-DBP by 20 nl of rabbit anti-DBP antisera was approximately 50% and was sharply competed for by 0.4-4.0 ng of DBP standard. Displacement of 125I-DBP by human serum dilutions or standard DBP gave identical curves, and only weak competition was observed with old and new world primate sera. Apo- and holo-DBP possessed indistinguishable immunoreactivity. The assay detects DBP in 1-10 nl of human serum with reasonable accuracy and with reasonable intra- and interassay precision. The mean serum concentration (+/- SEM) for a group of 40 normal adults was 525 +/- 24 mug/ml and no sex difference was observed. Higher levels were found in sera from pregnant women and women receiving oral contraceptives, and decreased concentrations were observed in premature cord and hypoproteinemic sera. No significant correlation between serum DBP levels and serum 25-hydroxycalciferol levels was found, and the DBP content of sera from vitamin D-deprived and vitamin D-treated subjects was indistinguishable from that of normal adults. DBP accounts for 6- of the alpha globulin in normal human serum. Considering the normal serum content of the parent vitamin and its metabolites to be approximately 0.1-0.2 mum, these immunoassay data confirm previous saturation analyses of human serum antiricketic sterol-binding capacity and suggest that greater than 95% of DBP circulates as the apoprotein under normal conditions.

1,25-Dihydroxyvitamin D in biological fluids: a simplified and sensitive assay

A competitive binding assay for 1,25-dihydroxyvitamin D [1,25-(OH2D] in plasma has been developed in which intestinal cytosol preparations from rachitic chicks are used as the binding protein. A new method of extraction and two new chromatographic procedures are used for this assay. The method is sensitive to as little as 10 picograms of 1,25-(OH)2D, and triplicate assays can be done on 5 milliliters of plasma. This assay shows that in the plasma of normal adult subjects there is a 1,25-(OH)2D concentration of 29 +/- 2 picograms per milliliter, while none can be detected in the plasma of nephrectomized subjects and end-stage renal failure patients.

Human serum binding capacity and affinity for 25-hydroxyergocalciferol and 25-hydroxycholecalciferol

25-Hydroxyvitamin D-binding capacity and affinity were studied in human cord, adult, and maternal sera, and in sera from women receiving oral contraceptives, by in vitro satuaration analyses employing dextran-coated charcoal to adsorb unbound sterol. 25-Hydroxyergocalciferol and 25-hydroxycholecalciferol were equipotent in their ability to displace 3H 25-hydroxycholecalciferol from human serum binding sites. At 0C, the apparent dissociation constant for the serum binding of 25-hydroxycholecalciferol was low (Kd=8x 10-10M). Cord and adult sera had a similar 25-hydroxycholecalciferol binding capacity (1.8 x 10-6M), but the binding capacity of maternal sera and the sera from women receiving oral contraceptives was significantly higher. At physiological serum concentrations of 25-hydroxyvitamin D (5 x 10-8M), only 2-3% of human serum 25-hydroxyvitamin D-bindig sites are occupied.