Free 25-hydroxyvitamin D levels are normal in subjects with liver disease and reduced total 25-hydroxyvitamin D levels.

We determined the free fraction of 25-dihydroxyvitamin D (25OHD) in the serum of subjects with clinical evidence of liver disease and correlated these measurements to the levels of vitamin D binding protein and albumin. These subjects when compared to normal individuals had lower total 25OHD levels, higher percent free 25OHD levels, but equivalent free 25OHD levels. These subjects also had reduced vitamin D binding protein and albumin concentrations. The total concentration of 25OHD correlated positively with both vitamin D binding protein and albumin, whereas the percent free 25OHD correlated negatively with vitamin D binding protein and albumin. The free 25OHD levels did not correlate with either vitamin D binding protein or albumin. We conclude that total vitamin D metabolite measurements may be misleading in the evaluation of the vitamin D status of patients with liver disease, and recommend that free 25OHD levels also be determined before making a diagnosis of vitamin D deficiency.     

Elevated 1,25-dihydroxyvitamin D plasma levels in normal human pregnancy and lactation.

Plasma 1,25-dihydroxyvitamin D levels are elevated in early pregnancy and continue to increase throughout pregnancy. They remain elevated postpartum in lactating women. The elevated levels probably represent a physiological response to increased calcium requirements.     

Radioimmunoassay for 1,25-dihydroxyvitamin D in serum or plasma

For this sensitive RIA for 1 alpha,25-dihydroxyvitamin D, we used antibodies to 1 alpha,25-dihydroxycholecalciferol-3-hemisuccinate conjugated to bovine serum albumin, raised in rabbits. These antibodies show a high affinity for 1 alpha,25-dihydroxyvitamin D3 but cross react with other vitamin D metabolites as well. Extraction and liquid chromatography are required to isolate the 1 alpha,25-dihydroxyvitamin D from human serum or plasma with benzene (analytical recovery, 96%) and chromatographed by "high-performance" liquid chromatography on a silica column. The sensitivity of the assay is 2 pg/tube. The between-assay CV is 12.6% (means = 61.8 ng/L, n = 27) and the within-assay CV is 7.4% (means = 61.8 ng/L, n = 15). The reference interval, obtained from data on serum of healthy persons, is 51.8 +/- 15.1 ng/L (means +/- SD, n = 91), with no sex-related difference. Patients with chronic renal failure have lower concentrations in serum, and patients suffering from calcium nephrolithiasis have increased concentrations. Our assay offers the advantage of a relatively short prepurification procedure and the production of large amounts of stable gamma-globulins that can be used for several years without loss of binding properties.     

Physiologic regulation of the serum concentration of 1,25-dihydroxyvitamin D by phosphorus in normal men.

We asked this question: in normal humans, is either a normal dietary intake or normal serum concentration of phosphorus a determinant of the serum concentration of 1,25(OH)2D? In seven normal men whose dietary phosphorus was decreased from 2,300 to 625 mg/d, each intake for 8-9 d, under strictly controlled, normal metabolic conditions, we measured serum concentrations of 1,25(OH)2D daily, and concentrations of phosphorus hourly throughout a 24-h period, before and after restriction. Decreasing dietary phosphorus induced: (a) a 58% increase in serum levels of 1,25(OH)2D; (b) a 35% decrease in serum levels of phosphorus measured in the afternoon; (c) a 12% decrease in the 24-h mean serum level of phosphorus; but, (d) no decrease in morning fasting levels of phosphorus. Serum concentrations of 1,25(OH)2D varied inversely and significantly with 24-h mean concentrations of phosphorus (r = -0.77, P less than 0.001). When these data are combined with those of our prior study in which dietary phosphorus was varied over an extreme range, the relationship between serum levels of 1,25(OH)2D and 24-h mean serum levels of phosphorus is even stronger (r = -0.90, P less than 0.001). In the aggregate, the results demonstrate that in normal men, dietary phosphorus throughout a normal range and beyond, can finely regulate the renal production and serum concentration of 1,25(OH)2D, and provide evidence that this regulation is mediated by fine modulation of the serum concentration of phosphorus.     

Polychlorinated biphenyl serum levels in pregnant subjects with diabetes

OBJECTIVE--Polychlorinated biphenyls (PCBs) are persistent pollutants that are ubiquitous in the food chain; detectable amounts are in the blood of nearly everyone. Their effect on humans at background levels of exposure is an area of active investigation. Increased blood levels of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin), a PCB-like compound, have recently been reported among subjects with diabetes, suggesting that PCB levels could be similarly elevated. To test this hypothesis, we examined a group of pregnant women whose serum PCB levels had been measured and whose diabetes status had been previously recorded. RESEARCH DESIGN AND METHODS--Using stored serum from a large birth cohort study, we conducted a cross-sectional study of 2,245 pregnant women, of whom 44 had diabetes (primarily type 1) and 2,201 were control subjects. RESULTS--The adjusted mean serum level of PCBs among the subjects with diabetes was 30% higher than in the control subjects (P = 0.0002), and the relationship of PCB level to adjusted odds of diabetes was linear. CONCLUSIONS--The possibility exists that PCBs and diabetes are causality related; alternatively, the pharmacokinetics of PCBs could be altered among patients with diabetes. At any event, if the association is replicated in other studies, increased serum levels of PCBs in subjects with diabetes or their offspring may put them at increased risk of PCB-induced changes in thyroid metabolism or neurodevelopment.     

Seasonal and age-related differences in serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and parathyroid hormone in patients from Western Norway

Abstract

Objective. The aim of this study was to investigate the seasonal and age-related variation of vitamin D and PTH serum concentrations in a large general patient population in Western Norway. Design. A retrospective study was conducted at the Hormone laboratory, Haukeland University Hospital, Bergen, Norway. All analyses of 25-hydroxyvitamin D (25(OH)D) (n = 8325), 1,25-dihydroxyvitamin D (1,25(OH)₂D) (n = 4509) and PTH (n = 4203) requested from private practitioners from 2005 to 2008 were included. All three analytes were available in 1551 subjects. Subjects. Mean age of the study population was 49.8 years and 70.9% of the samples were from women. Results. The highest concentrations of 25(OH)D and 1,25(OH)₂D were observed in July–September. In April 43% of the studied population had 25(OH)D concentrations below 50 nmol/L. There was a positive correlation between 25(OH)D and 1,25(OH)₂D (p < 0.001). The levels of 25(OH)D and PTH were negatively correlated (p < 0.001) while 1,25(OH)₂D and PTH showed a weak positive correlation (p = 0.015). We observed higher concentrations of 25(OH)D (p = 0.003) and lower 1,25(OH)₂D levels (p < 0.001) in the older age groups. PTH increased throughout the whole age span (p < 0.001). Conclusion. We observed a seasonal variation in 25(OH)D and 1,25(OH)₂D with low serum concentrations during winter/early spring while PTH showed an inverse pattern. Higher levels of PTH in winter and the elderly may reflect an impaired vitamin D status that may affect calcium homeostasis and bone health.     

Stimulation of 1,25-dihydroxyvitamin D production by parathyroid hormone and dibutyryl 3',5'-cyclic AMP in normal subjects, hypoparathyroidism and pseudohypoparathyroidism

Parathyroid extract (PTE) or synthetic 1-34 human parathyroid hormone (1-34 hPTH) was injected intravenously as a bolus in 4 normal subjects, 4 patients with PTH deficient hypoparathyroidism (HP) and 3 patients with pseudohypoparathyroidism (PHP). In normal subjects and HP, plasma 1,25(OH)2D was markedly increased at 6 hr and reached the peak at 12 or 14 hr after administration of 200 units of PTE or 20 to 30 micrograms of 1-34hPTH. On the other hand, 500 units of PTE or 20 micrograms of 1-34hPTH failed to increase plasma 1,25(OH)2D in PHP. However, 2.5 mg/kg of dibutyryl cAMP remarkably increased plasma 1,25(OH)2D in a patient with PHP. Maximal increments of plasma 1,25(OH)2D in 3 patients with HP(21.7 +/- 5.6 pg/ml, mean +/- S.D.) were nearly as high as in normal subjects (20.6 +/- 7.0 pg/ml), whereas those in 3 patients with PHP (2.3 +/- 2.3 pg/ml) were distinctly lower than in normal subjects or HP. It is suggested that 1,25(OH)2D production by PTH is intact in HP, but is impaired in PHP mainly due to a defect in the activation of adenylate cyclase system.     

Determinants of the serum concentration of 1,25-dihydroxyvitamin D in primary hyperparathyroidism

1. The serum concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were measured in 44 patients with primary hyperparathyroidism. 2. In 14 patients the serum concentration of 1,25-dihydroxyvitamin D was greater than normal (142-337 pmol/l). One patient had a subnormal concentration of 1,25-dihydroxyvitamin D (36 pmol/l) but no other evidence of vitamin D deficiency. 3. The possible biological determinants of the serum concentration of 1,25-dihydroxyvitamin D were sought by multivariate analysis of relevant variables. The serum concentration of 1,25-dihydroxyvitamin D was found to be significantly and positively correlated with the serum concentrations of 25-hydroxyvitamin D (P less than 0.001) and parathyroid hormone (P less than 0.003), and with the glomerular filtration rate (P less than 0.03), and negatively correlated with the serum concentrations of calcium (P less than 0.02) and phosphate (P = 0.055) (multiple R = 0.638, P less than 0.002). 4. In primary hyperparathyroidism the major determinant of serum 1,25-dihydroxyvitamin D is the availability of precursor 25-hydroxyvitamin D. 5. The finding that serum 1,25-dihydroxyvitamin D is commonly normal in patients with primary hyperparathyroidism despite an adequate state of vitamin D nutrition, can be explained in terms of the constraining influences of hypercalcaemia and variable degrees of renal dysfunction on the biosynthesis of 1,25-dihydroxyvitamin D.     

糖尿病肾病患者血清1，25-二羟维生素D3水平及临床意义

目的探讨血清1,25-二羟维生素D。水平在糖尿病肾病（diabeticnephropathy,DN）进展中的作用。方法131例2型糖尿病患者分为单纯糖尿病组（DM组）30例、早期DN组（EDN组）32例、临床DN组（CDN组）35例与DN终末期组（ESDN组）34例,选择体检健康者30例为对照组,各组采用ELISA法检测血清1,25-二羟维生素D3和25-羟维生素D。水平。结果糖尿病及DN各组血清1,25-二羟维生素D3及25-羟维生素D。水平均明显低于对照组（P〈0．01）,且随DN逐渐进展二者水平均逐渐降低（P〈0．05）;糖尿病患者血清1,25-二羟维生素D3水平与尿微量白蛋白排泄率呈负相关（r=0．452,P=0．034）,与肾小球滤过率呈正相关（r=0．390,P=0．006）。结论血清1,25-二羟维生素D3水平检测可能有利于DN的早期发现和病情判断。     

慢性肾病患者血1,25-二羟基维生素D3水平变化

目的 研究慢性肾病(CKD)患者血1,25-二羟基维生素D3(维生素D3)水平异常与肾功能受累程度的关系.方法 研究对象包括150例健康对照者和101例CKD患者,检测其血维生素D3、甲状旁腺素、钙、磷、肌酐、清蛋白及尿素氮水平,计算肾小球滤过率(GFR).结果 与对照组相比,第4~5期患者的血维生素D3水平显著降低(P<0.05),第3~5期患者的血甲状旁腺素(PTH)、肌酐及尿素氮(BUN)水平显著升高(P<0.05),第4~5期患者的血磷水平显著升高(P<0.05),各期CKD患者的清蛋白水平均显著降低(P<0.05),仅第5期CKD患者的血钙浓度显著降低(P<0.05).血维生素D3水平与血PTH、尿素氮及肌酐水平呈负线性相关关系,与血钙、清蛋白及GFR水平呈正线性相关关系.结论 第4~5期CKD患者缺乏维生素D3,说明只有当肾功能受损严重时,CKD患者血维生素D3水平才会出现明显异常.此外,本研究还表明CKD患者血维生素D3水平与其他肾功能相关生化指标存在一定的相关性.     

Production, degradation, and circulating levels of 1,25-dihydroxyvitamin D in health and in chronic glucocorticoid excess.

The decreased intestinal absorption of calcium and accelerated bone loss associated with chronic glucocorticoid excess may be mediated by changes in vitamin D metabolism, leading to decreased availability of circulating 1,25-dihydroxyvitamin D. This hypothesis was examined in 14 patients with either endogenous or exogenous glucocorticoid excess. Analysis of paired serum samples (mean +/- SE) in 13 patients during euglucocorticoidism and during hyperglucocorticoidism showed that glucocorticoid excess resulted in small decreases of plasma 25-hydroxy-vitamin D concentrations (22 +/- 2- 18 +/- 2 ng/ml; P < 0.05) but no significant changes in plasma 1,25-dihydroxyvitamin D (32 +/- 8- 23 +/- 6 pg/ml) or serum immunoreactive parathyroid hormone (21 +/- 2- 18 +/- 2 muleq/ml). Additionally, we studied plasma kinetics of [3H]1,25-dihydroxyvitamin D3 after intravenous bolus administration in 10 hyperglucocorticoid patients and in 14 normal controls. Assessment with a three-compartment model showed no significant abnormalities in production rates (hyperglucocorticoid patients 1.2 +/- 0.3 micrograms/d, controls 1.5 +/- 0.2 micrograms/d) or metabolic clearance rates (hyperglucocorticoid patients, 18 +/- 2%; controls, 14 +/- 2%) or feces (hyperglucocorticoid patients, 60 +/- 9%, controls, 54 +/- 6%). We conclude that glucocorticoid excess does not effect plasma levels, production, or degradation of 1,25(OH)2D in humans. Thus, other mechanisms must be postulated to explain satisfactorily the abnormalities of bone structure and intestinal calcium absorption that may occur after chronic glucocorticoid therapy.     

Defective binding and function of 1,25-dihydroxyvitamin D3 receptors in peripheral mononuclear cells of patients with end-organ resistance to 1,25-dihydroxyvitamin D.

Lectin-induced DNA synthesis by peripheral mononuclear cells from 17 normal donors was inhibited (40-60%) by 1,25-dihydroxyvitamin D3 (1,25[OH]2D3) at physiological concentrations (10(-10)-10(-9) M). The lymphocytes acquire specific receptors for 1,25(OH)2D3 upon activation by the lectins. This process precedes the inhibitory effect of 1,25(OH)2D3. We studied lymphocytes from six patients from four different kindreds with the syndrome of hereditary end-organ resistance to 1,25(OH)2D (the so-called vitamin D-dependent rickets type II). In five patients (three kindreds) peripheral blood mononuclear cells did not acquire receptors for 1,25(OH)2D3 upon phytohemagglutinin-induced activation. Moreover, in contrast to normal lymphocytes, the mitogenic stimulation of these patients' lymphocytes by phytohemagglutinin and concanavalin A was not inhibited by 1,25(OH)2D3. Activated lymphocytes of the sixth patient from a fourth kindred exhibited normal binding of [3H]1,25(OH)2D3 but the hormone failed to inhibit the mitogenic stimulation. A similar pattern of the vitamin D effector system was previously observed in fibroblasts cultured from skin biopsies of the same group of patients. The conclusions from these findings are: (a) the inhibition of mitogenic stimulation by 1,25(OH)2D3 is mediated by specific functional receptors to the hormone; and (b) the receptors for 1,25(OH)2D3 in mononuclear cells are probably controlled genetically by the same mechanisms as the effector system in well-characterized target organs of the hormone, such as intestine and kidney.     

1,25-二羟维生素D3治疗对早期糖尿病肾病炎性因子的影响

目的 探讨早期糖尿病肾病( diabetic nephropathy,DN)患者体内1,25-二羟维生素D3与血清炎性因子水平的变化,观察1,25-二羟维生素D3对早期DN患者相关炎性因子的影响.方法 2型糖尿病患者238例中无蛋白尿者100例为DM组,初诊早期DN者138例为DN组,DN组再随机分为治疗组和对照组各69例.在血糖、血压稳定1周后治疗组给予常规治疗+骨化三醇胶丸,对照组给予常规治疗,2组疗程均为3个月.比较各组患者1,25-二羟维生素D3、24 h尿蛋白定量及相关炎性因子的变化.结果 治疗前DN组1,25-二羟维生素D3水平低于DM组(P＜0.05),白细胞介素-6、肿瘤坏死因子-α、血浆纤溶酶原激活物抑制物-1及尿结缔组织生长因子水平均高于DM组(P＜0.05);治疗后DN治疗组上述炎性因子水平及24 h尿蛋白定量均较治疗前降低(P＜0.05),1,25-二羟维生素D3水平升高(P＜0.05),对照组治疗前、后各指标比较差异均无统计学意义(P＞0.05).结论 早期DN患者1,25-二羟维生素D3缺乏,炎性因子水平高,补充骨化三醇胶丸可改善患者炎症状态.     

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.     

Comparison of a cytosol radioreceptor assay with a radioimmunoassay for 1,25-dihydroxyvitamin D in serum or plasma

Human plasma and serum levels for 1 alpha,25-dihydroxyvitamin D were determined by a cytosol radioreceptor assay (RRA) and a radioimmunoassay (RIA). For both assays, 1.5 ml of human serum or plasma is used. Prior to RRA or RIA, extraction with benzene is performed followed by 'high-performance' liquid chromatography (HPLC) on a silica column (25 X 0.46 cm) with hexane/isopropanol (9/1 by vol), to isolate 1 alpha,25-dihydroxyvitamin D from the other vitamin D metabolites. The cytosol receptor was isolated from the intestine of healthy chickens. The antisera were raised in rabbits to 1 alpha,25-dihydroxyvitamin D3-3-hemisuccinate coupled to bovine serum albumin. The standard curves for RRA and RIA are prepared with 1 alpha,25-dihydroxyvitamin D3. 1 alpha,25-dihydroxy[3H]vitamin D3 of high spec act (158 kCi/mol) is used as tracer. The reactants are incubated for 16 h at 4 degrees C. Then, bound and free ligand are separated after the addition of dextran-coated charcoal. Both assays have a sensitivity of 2 pg/tube. The cytosol receptor and the antibodies have about the same absolute affinity for 1 alpha,25-dihydroxyvitamin D3 but the cytosol receptor has a higher relative affinity for 1 alpha,25-dihydroxyvitamin D3 (compared with other vitamin D metabolites). Reproducibility and precision are better for the RIA. The between- and within-assay CVs are 16.0% (mean = 58.7 ng/l, n = 16) and 11.2% (mean = 52.1 ng/l, n = 15), respectively, for RRA and 12.6% (mean = 61.8 ng/l, n = 27) and 7.4% (mean = 61.8 ng/l, n = 15), respectively using RIA. Reference values obtained by both assays on healthy males and healthy premenopausal females are the same for both sexes; 53.9 +/- 31.0 ng/l (n = 46) using RRA and 51.8 +/- 30.2 ng/l (n = 91) for RIA (mean +/- 2 SD).     

A comparison of automated methods for the quantitation of serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D

OBJECTIVE: To compare automated platforms with the routinely used methods in our clinical laboratory for the quantitation of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D]. METHOD: The NEXgen Four and Triturus ELISA platforms, utilizing the IDS enzyme immunoassay (EIA) kit for 25(OH)D, and the DiaSorin Liaison 25(OH)D methods were compared with the DiaSorin radio immunoassay (RIA) kit. The NEXgen Four and the Triturus, utilizing IDS EIA for 1,25(OH)2D, were compared with the thymus radioreceptor assay (RRA) for measurement of 1,25(OH)2D. RESULTS: NEXgen correlated best with DiaSorin RIA (r(2)=0.652). NEXgen correlated best with the thymus RRA method (r(2)=0.541). Imprecision CV values for NEXgen 1,25(OH)2D were 2.8-9.4% within-run and 10.2-13.9% between-run compared with a between-run precision of 14.0-16.9% with the thymus RRA method. CONCLUSION: NEXgen correlated best with DiaSorin RIA for measurement of 25(OH)D. NEXgen correlated best and demonstrated better precision than thymus RRA for quantitation of 1,25(OH)2D.