Hypovitaminosis D in a normal, apparently healthy urban European population

Serum 25 OH Vitamin D (25 OH D) concentrations generally vary with latitude, season, and the composition of the population studied. There is a growing recognition that rather than a seasonal specific decline in serum 25 OH Vitamin D, a significant proportion of the population may exhibit asymtomatic subclinical Vitamin D insufficiency. Vitamin D insufficiency has been described in populations at risk, such as nursing home residents and the homebound elderly. We assessed a population of normal, apparently healthy volunteers at a single European urban center for 25 OH Vitamin D sufficiency. Serum 25 OH D concentrations were determined using an automated LIAISON((R)) 25 OH Vitamin D assay. For the purposes of this study, Vitamin D insufficiency was defined as a serum 25 OH Vitamin D concentration of <15 ng/mL. Of the total population (n = 126) 34% exhibited 25 OH Vitamin D concentrations of <15 ng/ml. The mean +/- S.D. serum 25 OH Vitamin D concentration among the total, sufficient, and insufficient populations was 19.4 +/- 7.7, 23.6 +/- 6.4, and 12.1 +/- 2.3 ng/mL. From these data, we conclude that 25 OH Vitamin D insufficiency is more common than previously thought, and is not restricted to high-risk groups.     

Lipid status association with 25-hydroxy vitamin D: Cross sectional study of end stage renal disease patients

BackgroundSome observational studies indicate an association of 25-hydroxy vitamin D (25(OH)D) insufficiency and atherogenic cholesterol concentrations. The aim of this study was to investigate relationship between 25(OH)D concentrations and lipid parameters in end stage renal disease (ESRD) patients, separately for predialysis, hemodialysis and peritoneal dialysis patients.MethodsWe have adjusted 25(OH)D concentrations for seasonal variability with cosinor analysis, and performed all further analysis using these corrected 25(OH)D concentrations. Concentrations of 25(OH)D and the lipid parameters were determined in 214 ESRD patients and 50 control group participants. The analysis included the measurement of 25(OH)D by HPLC, apolipoprotein (Apo) AI, ApoB and Lp(a) by nephelometry, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG) by spectrophotometry and manually calculated ApoB/ApoAI and LDL-C/HDL-C ratio.ResultsESRD patients with adjusted 25(OH)D concentrations of 50 nmol/L had significantly higher TC (P = 0.005) and ApoAI (P = 0.049). Significantly higher HDLC (P = 0.011) and ApoAI (P = 0.020) were found in hemodialysis patients with the 25(OH)D concentrations of 50 nmol/L. The other analyzed lipid parameters differed significantly between predialysis, hemodialysis and peritoneal dialysis patients with 25(OH)D concentrations of < 50 nmol/L.ConclusionsOur study indicate the significant relationship between 25(OH)D repletion and optimal concentrations of lipid parameters in ESRD patients. Further research is necessary to explain whether joint evaluation of vitamin D status and lipid abnormalities could improve cardiovascular outcome in ESRD patients.     

Low Maternal Vitamin D Status during the Second Trimester of Pregnancy: A Cross-Sectional Study in Wuxi,China

BackgroundVitamin D deficiency is common in pregnant women, but an optimal serum vitamin D level during pregnancy has not been determined and remains an area of active research. Vitamin D data from large populations of pregnant Chinese women are still limited.ObjectiveTo evaluate the vitamin D status of women in Eastern China during the second trimester of pregnancy.MethodsA hospital-based, cross-sectional, observational study. Serum 25-hydroxyvitamin D [25(OH)D] concentration was measured in samples from 5823 pregnant women in Wuxi City, China (latitude: 31.5o N), from January 2011 to June 2012.ResultsThe median serum 25(OH)D concentration was 34.0 nmol/L [2.5 nmol/L 25(OH)D = 1 ng/mL 25(OH)D]. Vitamin D deficiency [defined as 25(OH)D < 30 nmol/L according to the Institute of Medicine (National Academy of Sciences, Washington, D.C., USA)] or inadequacy [25(OH)D of 30–49.9 nmol/L] was identified in 40.7% and 38.0% of the women, respectively. Only 0.9% had a 25(OH)D level ≥ 80.0 nmol/L, which is the concentration recommended as adequate by the Endocrine Society (Washington, D.C., USA). Compared with older women, younger women were more likely to be deficient in vitamin D. There were significant differences in the 25(OH)D levels according to season. The 25(OH)D levels reached peak values in September and were correlated with (r = 0.337, P < 0.001), and fluctuated with, average monthly air temperatures.ConclusionsThere is a high prevalence of Vitamin D deficiency among pregnant Chinese women, and 25(OH)D levels varied according to season and air temperature. The results of this study also suggest that currently there is a big gap between the levels of Vitamin D detected in pregnant Chinese women and the levels recommended by the Endocrine Society.     

Elevated serum 25(OH)D concentrations, vitamin D, and calcium intakes are associated with reduced adipocyte size in women

Recent studies have suggested a beneficial effect of vitamin D and calcium on adipocyte metabolism and the metabolic profile. Our objective was to examine associations of vitamin D intake, calcium and dairy products as well as serum 25(OH)D concentration with adiposity measures and adipocyte size in women. Omental and subcutaneous adipose tissue samples were obtained from 43 women undergoing gynecological surgeries. Adipocyte size was measured using adipocyte suspensions from collagenase-digested fat tissues. Total and visceral adiposity were assessed by dual-energy X-ray absorptiometry and computed tomography, respectively. Serum 25(OH)D was measured by radioimmmunoassay. Dietary intakes were assessed using a food frequency questionnaire. Women consuming two or more dairy product portions daily had smaller adipocytes in the omental depot compared to women consuming less than two portions daily (79 ± 12 vs. 94 ± 16 μm, P ≤ 0.01). Dietary intakes of calcium (r = -0.55) and vitamin D (r = -0.43) as well as serum 25(OH)D (r = -0.35) were also inversely and significantly associated with omental adipocyte size (P ≤ 0.05 for all). Dietary vitamin D intake was inversely associated with visceral adipose tissue area (r = -0.34, P ≤ 0.05). Serum 25(OH)D was also inversely associated with visceral adipose tissue area (r = -0.32) as well as with total adipose tissue area (r = -0.44), subcutaneous adipose tissue area (r = -0.36), BMI (r =-0.43) and total body fat mass (r = -0.41, P ≤ 0.05 for all). In conclusion, elevated dietary vitamin D intake and serum 25(OH)D values are related to lower visceral adiposity and omental adipocyte size in women.     

Atrial natriuretic hormone secretion in patients with renal failure

To study the effects of volume overload and renal failure on plasma levels of immunoreactive atrial natriuretic hormone (IR-ANH), we measured levels of this hormone in normal subjects, in patients with advanced chronic renal failure (CRF) with and without clinically evident volume overload, and in patients with end-stage renal disease (ESRD) treated with chronic hemodialysis. The levels were 13 +/- 2 pmol/l in normal volunteers, 77 +/- 24 pmol/l in patients with CRF without volume overload, and 219 +/- 50 pmol/l in patients with CRF and clinically evident volume overload (analysis of variance, p less than 0.001, alpha = 0.05 compared to normals). In patients with ESRD, the levels of IR-ANH were 145 +/- 46 pmol/l before dialysis and decreased to 87 +/- 31 after dialysis (p less than 0.025). No correlation was found between the decrease in IR-ANH levels and the decrease in weight during dialysis. A significant positive correlation was found between the IR-ANH levels and blood urea nitrogen in patients with CRF (r = 0.658, p less than 0.01). Volume overload appears to be the most important stimulatory factor for ANH secretion in renal failure patients but other mechanisms, especially a decrease in metabolic clearance, may also contribute to elevated plasma levels. The increased secretion of ANH in patients with renal failure may be an important adaptive response to volume overload and hypertension.     

Cell specificity and properties of the C-3 epimerization of Vitamin D3 metabolites

It is well documented that Vitamin D3 metabolites and synthetic analogs are metabolized to their epimers of the hydroxyl group at C-3 of the A-ring. We investigated the C-3 epimerization of Vitamin D3 metabolites in various cultured cells and basic properties of the enzyme responsible for the C-3 epimerization. 1alpha,25-Dihydroxyvitamin D3 [1alpha,25(OH)2D3], 25-hydroxyvitamin D3 [25(OH)D3] and 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] were metabolized to the respective C-3 epimers in UMR-106 (rat osteosarcoma), MG-63 (human osteosarcoma), Caco-2 (human colon adenocarcinoma), LLC-PK1 (porcine kidney) and HepG2 (human hepatoblastoma)] cells, although the differences existed in the amount of each C-3 epimer formed with different cell types. In terms of maximum velocity (Vmax) and Michaelis constant (Km) values for the C-3 epimerization in microsome fraction of UMR-106 cells, 25(OH)D3 exhibited the highest specificity for the C-3 epimerization among 1alpha,25(OH)2D3, 25(OH)D3 and 24,25(OH)2D3. C-3 epimerization activity was not inhibited by various cytochrome P450 inhibitors and antiserum against NADPH cytochrome P450 reductase. Neither CYP24, CYP27A1, CYP27B1 nor 3(alpha --> beta) -hydroxysteroid epimerase (HSE) catalyzed the C-3 epimerization in vitro. Based on these results, the enzyme responsible for the C-3 epimerization of Vitamin D3 are thought to be different from already-known cytochrome P450-related Vitamin D metabolic enzymes and HSE.     

Regulation of serum 1,25(OH)2 vitamin D3 levels by fibroblast growth factor 23 is mediated by FGF receptors 3 and 4

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone implicated in the pathogenesis of several hypophosphatemic disorders. FGF23 causes hypophosphatemia by decreasing the expression of sodium phosphate cotransporters (NaPi-2a and NaPi-2c) and decreasing serum 1,25(OH)(2)Vitamin D(3) levels. We previously showed that FGFR1 is the predominant receptor for the hypophosphatemic actions of FGF23 by decreasing renal NaPi-2a and 2c expression while the receptors regulating 1,25(OH)(2)Vitamin D(3) levels remained elusive. To determine the FGFRs regulating 1,25(OH)(2)Vitamin D(3) levels, we studied FGFR3(-/-)FGFR4(-/-) mice as these mice have shortened life span and are growth retarded similar to FGF23(-/-) and Klotho(-/-) mice. Baseline serum 1,25(OH)(2)Vitamin D(3) levels were elevated in the FGFR3(-/-)FGFR4(-/-) mice compared with wild-type mice (102.2 ± 14.8 vs. 266.0 ± 34.0 pmol/l; P = 0.001) as were the serum levels of FGF23. Administration of recombinant FGF23 had no effect on serum 1,25(OH)(2)Vitamin D(3) in the FGFR3(-/-)FGFR4(-/-) mice (173.4 ± 32.7 vs. 219.7 ± 56.5 pmol/l; vehicle vs. FGF23) while it reduced serum 1,25(OH)(2)Vitamin D(3) levels in wild-type mice. Administration of FGF23 to FGFR3(-/-)FGFR4(-/-) mice resulted in a decrease in serum parathyroid hormone (PTH) levels and an increase in serum phosphorus levels mediated by increased renal phosphate reabsorption. These data indicate that FGFR3 and 4 are the receptors that regulate serum 1,25(OH)(2)Vitamin D(3) levels in response to FGF23. In addition, when 1,25(OH)(2)Vitamin D(3) levels are not affected by FGF23, as in FGFR3(-/-)FGFR4(-/-) mice, a reduction in PTH can override the effects of FGF23 on renal phosphate transport.     

类风湿关节炎患者血清维生素D水平与疾病活动度相关

目的:探讨类风湿关节炎(Rheumatoid arthritis,RA)患者血清维生素D(25(OH)D)水平与疾病活动度的关系。方法:总共纳入180例RA患者,同时纳入60例年龄、性别相匹配的健康对照。检测所有参与者的血清25(OH)D水平及所有RA患者C反应蛋白和血沉。同时获取RA患者晨僵时间、疼痛视觉模拟表评分、乏力视觉模拟表评分、压痛关节数、肿胀关节数、健康评估量表得分、情绪变化量表得分等。利用RA患者28个关节疾病活动评分(Disease activity score in 28 joints,DAS28)评估RA疾病活动度。结果:相对于健康对照组(43.89±16.28 ng/m L),RA患者的血清25(OH)D明显降低(28.52±8.95 ng/m L)(P=0.000)。RA患者的血清25(OH)D水平越低,压痛关节数、肿胀关节数越多(P=0.043,r=-0.132;P=0.017,r=-0.177),血沉、C反应蛋白越高(P=0.018,r=-0.177;P=0.007,r=-0.200),同时DAS28评分越高(P=0.007,r=-0.201);患者的晨僵时间、疼痛评分、乏力评分、健康评估量表得分及情绪量表得分与血清维生素D水平负相关(P=0.043,r=-0.151;P=0.019,r=-0.175;P=0.006,r=-0.205;P=0.048,r=-0.147;P=0.017,r=-0.178)。结论:RA患者血清维生素D普遍缺乏,并且与RA患者疾病活动度负相关。     

Sex-specific role of CYP24A1 rs2762939 in the risk of essential hypertension based on the serum vitamin D and total renin concentrations

CYP24A1, Vitamin D 24-hydroxylase catabolizes 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D to 24-hydroxylated vitamin D products. It is widely known that low Vitamin D can lead to increased renal renin and angiotensin II production, consequently elevating blood pressure or development of essential hypertension (EH). We have conducted an investigation on hypertensives and controls to evaluate the association of the gene variant, CYP24A1 rs2762939 and 25(OH)D in an Indian population with EH. On gender-based stratification, with multivariate logistic analysis after adjustment for covariates, the CYP24A1 rs2762939 CC variant showed a higher risk of EH in males (aOR = 3.141, CI 1.164–8.478, P = .024) while females illustrated an inverse association with EH (aOR = 0.398, CI 0.172–0.092, P = .031). The 25(OH)D levels among the three genotypes of hypertensives substantiate these results. Our results clearly suggest that gender, CYP24A1 rs2762939, and Vitamin D status may play a significant role in disease susceptibility towards EH in Indian population.     

The anomalous behaviour of exogenous 25-hydroxyvitamin D in competitive binding assays

The Vitamin D International External Quality Assessment Scheme (DEQAS) was established in 1989 to monitor the performance of assays for 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D (I,25(OH)₂D). This is achieved through the quarterly distribution of five samples of human serum. Results are used to calculate an All-Laboratory Trimmed Mean and a Method Mean for each of the methods used by participants. In July 2005, participants were asked to assay serum to which 50.9 nmol of either 25-OHD₃ or 25-OHD₂ had been added as ethanolic solutions. The final concentration of ethanol in the serum was 0.7%. The distribution also included a sample of the original serum (OS) containing 0.7% pure ethanol. The percentage recoveries of exogenous 25-OHD₃ (R1) and 25-OHD₂ (R2) were calculated for each method. Results (OS nM, R1 and R2) were as follows: DiaSorin RIA (n = 53); 39.2, 82.1%, 83.3%, DiaSorin Liason (n = 16); 36.8, 81.4%, 88.6%, IDS RIA (n = 21); 36.4, 54.2%, 29.1%, IDS OCTEIA (n = 16); 47.3, 78.8%, 56.4%, Nichols Advantage (n = 21); 58.9, 46.4%, 43.2%, HPLC (n = 9); 42.6, 112.2%, 97.1%, LC–MS (n = 4); 34.0, 111.5%, 118.1%. The IDS RIA and Nichols assays gave unexpectedly low recoveries. This does not appear to be a calibration problem or the effect of ethanol.     

Vitamin D and prevention of colorectal cancer

BACKGROUND: Inadequate photosynthesis or oral intake of Vitamin D are associated with high incidence rates of colorectal cancer, but the dose-response relationship has not been adequately studied. METHODS: Dose-response gradients from observational studies of Vitamin D intake and serum 25-hydroxyvitamin D were plotted as trend lines. The point on each linear trend line corresponding to an odds ratio of 0.50 provided the prediagnostic Vitamin D intake or 25-hydroxyvitamin D concentration associated with 50% lower risk compared to <100IU/day Vitamin D or <13ng/ml serum 25-hydroxyvitamin D. Medians of these values were determined. RESULTS: Overall, individuals with >or=1000IU/day oral Vitamin D (p<0.0001) or >or=33ng/ml (82nmol/l) serum 25-hydroxyvitamin D (p<0.01) had 50% lower incidence of colorectal cancer compared to reference values. CONCLUSIONS: Intake of 1000IU/day of Vitamin D, half the safe upper intake established by the National Academy of Sciences, was associated with 50% lower risk. Serum 25-hydroxyvitamin D of 33ng/ml, which is known to be safe, also was associated with 50% lower risk. Prompt public health action is needed to increase intake of Vitamin D(3) to 1000IU/day, and to raise 25-hydroxyvitamin D by encouraging a modest duration of sunlight exposure.     

25-Hydroxyvitamin D levels of children are inversely related to adiposity assessed by body mass index

Vitamin D deficiency is associated with wide range of pathologies. Some evidences have shown that low vitamin D circulating levels in children and adolescent are related to fat mass and obesity. The objectives of the present study were to characterize vitamin D status in children and adolescents and to determine if serum 25-hydroxyvitamin D (25(OH)D) concentration is related to adiposity assessed by body mass index (BMI). Serum 25(OH)D levels were measured by LIAISON method in 471 children and adolescents (2 to 18 years age) and analyzed according to gender, pubertal period, age, and BMI. An overall prevalence of 25(OH)D insufficiency and deficiency was present in the 67.1%. Lower 25(OH)D levels were found in females (25.56 ± 14.03 vs 29.71 ± 17.10 ng ml^?1; P = 0.004) and pubertal children (25.52 ± 13.97 vs 29.21 ± 16.83 ng ml^?1; P = 0.011). In addition, an inverse relation of BMI and age on 25(OH)D concentrations was observed in children. In conclusion, low vitamin D status was highly prevalent among children and adolescents. Of note, a non-lineal regression model showed that 39.6% of vitamin D levels variability was explained by BMI. These results indicate that adiposity assessed by BMI impacts vitamin D status.     

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.     

Contribution of adipose tissue to plasma 25-hydroxyvitamin D concentrations during weight loss following gastric bypass surgery

Roux-en-y gastric bypass (RYGB) surgery is associated with dramatic improvements in obesity-related comorbidity, but also with nutritional deficiencies. Vitamin D concentrations are depressed in the severely obese, but the impact of weight loss via RYGB is unknown. We determined associations between adiposity and systemic 25-hydroxyvitamin D (25(OH)D) during weight loss and the immediate and longer-term effects of RYGB. Plasma 25(OH)D concentrations and fat mass (FAT) were determined by immunoassay and air displacement plethysmography, respectively, at 0 (before RYGB surgery), and at 1, 6, and 24 months in severely obese white and African American (AA) women (n = 20). Decreases in adiposity were observed at 1, 6, and 24 months following RYGB (P < 0.05). Plasma 25(OH)D concentrations increased at 1 month (P = 0.004); a decreasing trend occurred over the remainder months after surgery (P = 0.02). Despite temporary improvement in vitamin D status, a high prevalence of vitamin D insufficiency was observed (76, 71, 67, and 82%, at baseline, 1, 6, and 24 months, respectively), and plasma 25(OH)D concentrations were lower in AA compared to white patients (P < 0.05). Strong positive baseline and 1 month cross-sectional correlations between FAT and plasma 25(OH)D were observed, which remained after adjustment for age and race subgroup (β = 0.76 and 0.61, respectively, P = 0.02). In conclusion, 25(OH)D concentrations increased temporarily and then decreased during the 24 months following RYGB. The acute increase and the positive associations observed between adipose tissue mass and systemic 25(OH)D concentrations suggest storage in adipose tissue and release during weight loss.     

Serum 25-hydroxyvitamin D levels are not associated with impaired postural sway in community-dwelling older women: a 6-year follow-up study

Objectives:A positive association between levels of blood 25-hydroxyvitamin D (25[OH]D), an index of vitamin D status, and physical balance has been reported from cross-sectional studies, but longitudinal studies are rare. The present study aimed to test the hypothesis that low serum 25(OH)D levels are longitudinally associated with impaired postural sway over a 6-year follow-up period in older women.Methods:The present cohort consisted of 392 community-dwelling Japanese women aged ≥69 years. Baseline examinations included serum 25(OH)D and physical performance tests, including postural sway velocity. Standing postural sway was evaluated by measuring gravity-center sway velocity. Follow-up physical performance tests were conducted 6 years later.Results:Mean subject age and serum 25(OH)D levels were 73.3 years (SD 3.7) and 61.0 nmol/L (SD 16.9), respectively. No significant association was found between 25(OH)D levels and changes in postural sway velocity (adjusted P for trend=0.72). Women with 25(OH)D <30 nmol/L tended to have lower Δpostural sway velocity than those with 25(OH)D ≥30 nmol/L (mean, -0.59 vs 0.37 cm/s, respectively; adjusted P=0.13).Conclusions:Vitamin D levels are not longitudinally associated with impaired postural sway in older women. Further longitudinal studies are needed to corroborate the results of this study.     

Determinants of circulating 1,25-dihydroxyvitamin D3 levels: the role of renal synthesis and catabolism of vitamin D

Details of the molecular mechanisms determining levels of the secosteroid, 1,25-dihydroxyvitamin D(3) (1,25D) remain to be elucidated. The current paradigm for the control of serum 1,25D levels is the tight regulation of renal 25-hydroxyvitamin D-1alpha-hydroxlase (CYP27B1) activity by a number of physiological factors. 1,25D production is also regulated by the cytochrome P450 enzyme, 25-hydroxyvitamin D-24-hydroxylase (CYP24), which through side chain hydroxylation reactions, inactivates 1,25D. We have recently demonstrated that renal CYP27B1 and CYP24 expression contribute equally to regulating serum 1,25D levels. We now describe the contribution of renal Vitamin D receptor (VDR) expression in determining serum 1,25D levels. Serum 1,25D levels were decreased when the dietary calcium intake was increased. We measured mRNA levels for CYP27B1, CYP24 and VDR receptor in kidney RNA extracts from animals fed diets containing different levels of calcium, ranging from 0.05 to 1%. Serum 1,25D levels were negatively correlated with renal CYP24 mRNA levels (R2 = 0.35, P < 0.01) while renal VDR is positively correlated with renal CYP24 mRNA (R2 = 0.80, P < 0.001). However, only renal VDR mRNA remained a significant determinant of renal CYP24 expression when both these variables were included in multiple linear regression analysis (multiple R2 = 0.89, P < 0.001). These findings suggest that kidney CYP24 activity acts in concert with kidney CYP27B1 to control serum 1,25D levels and that serum 1,25D stimulates renal CYP24 expression by acting through the renal VDR.     

The assessment of circulating 25(OH)D and 1,25(OH)2D: Where we are and where we are going

The field of Vitamin D assay technology has progressed significantly over the past 4 decades. Further, the clinical utility of these measurements has moved from esoteric into mainstream clinical diagnosis. This movement has been fueled by the realization that Vitamin D is involved in bodily systems beyond skeletal integrity. The clinical assay techniques for circulating 25(OH)D and 1,25(OH)₂D have progressed away from competitive protein binding assay (CPBAs) that utilize tritium reporters to radioimmunoassay (RIAs) that utilize both I¹²⁵ and chemiluminescent reporters. These advances have allowed direct serum analysis of 25(OH)D in an automated format that provides a huge sample throughput. Detection of circulating 25(OH)D can also be achieved utilizing direct high-performance liquid chromatographic (HPLC) or liquid chromatography coupled with mass spectrometry (LC–MS) techniques. These methods are accurate, however, they require expensive equipment and restrict sample throughput in the large clinical laboratory. Direct serum detection of 1,25(OH)₂D is unlikely to occur for many reasons as a sample pre-purification will always be required. However, a semi-automated chemiluminescent detection system with automated sample preparation is in final development for the determination of circulating 1,25(OH)₂D. These advances will allow both 25(OH)D and 1,25(OH)₂D to be detected in an accurate, rapid fashion to meet the clinical demands we see emerging.     

Radioimmunoassay of CRF-like material in rat plasma: validation of the method

The availability of antibodies against the ovine corticotropin releasing factor (CRF), which cross-react with a CRF-like immunoreactivity (CRF-LI) in the rat, has enabled us to develop a radioimmunoassay (RIA) for rat CRF-LI in plasma and crude hypothalamic extracts. 125I-Tyr CRF 1-41 was used as the tracer, and synthetic ovine CRF as the reference hormone. The precision profile of the assay indicates a high degree of reproducibility except for the lower dose range. The minimum detectable dose was 20 pg/tube. This assay can detect differences in plasma CRF-LI levels after various manipulations that simultaneously alter the ACTH levels in plasma. A wide range of CRF concentrations has been found in plasma of normal rats. Caution should be exercised in the interpretation of the values obtained since an ovine RIA system was used.     

Vitamin D status and response to Vitamin D(3) in obese vs. non-obese African American children

Background: Serum 25‐hydroxyvitamin D (25(OH)D) is low in obese adults. Objective: To examine serum 25(OH)D in obese (BMI >95th percentile for age) vs. non‐obese (BMI = 5th–75th percentile for age) 6–10‐year‐old African American children and compare their differences in therapeutic response to vitamin D supplementation. Methods and Procedures: In an open label non‐randomized pre‐post comparison 21 obese (OB) and 20 non‐obese (non‐OB) subjects matched for age, sex, skin color, and pubertal maturation were treated with 400 IU of vitamin D₃ daily for 1 month. Serum 25(OH)D, 1,25‐dihydroxyvitamin D (1,25(OH)₂D), parathyroid hormone (PTH), leptin, and markers of bone turnover (serum bone‐specific alkaline phosphatase (BSAP), osteocalcin (OC), and urine n ‐telopeptide cross‐links of type 1 collagen (urine NTX)) were measured. Vitamin D deficiency was defined as serum 25(OH)D ≤20 ng/ml and insufficiency as 21–29 ng/ml respectively. Results: Vitamin D deficiency occurred in 12/21 (57%) OB vs. 8/20 (40%) non‐OB at baseline (P = 0.35) and persisted in 5/21 (24%) OB vs. 2/18 (11%) non‐OB (P = 0.42) after treatment. When the cohort was stratified by the baseline levels of 25(OH)D, there were differences in the response to treatment in the obese and non‐obese cohorts. Discussion: Vitamin D deficiency was common among OB and non‐OB preadolescent African American children, and 400 IU of vitamin D₃ (2× the recommended adequate intake) daily for 1 month was inadequate to raise their blood levels of 25(OH)D to ≥30 ng/ml.     

A role for the cytoskeleton in renal vitamin D metabolism

Conversion of circulating 25-hydroxyvitamin D3 (25(OH)D3) to its active metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) occurs in the renal tubule mitochondrion. Recent reports have implicated the cytoskeleton in certain other steroid metabolizing cells as a mediator of a rate-limiting mitochondrial transport step. Whilst the activity of the renal converting enzyme, a typical steroid hydroxylase, is known to be regulated closely by a number of well studied factors, no information is available to indicate whether an analogous transport step is relevant to the regulation of vitamin D metabolism. Cytochalasin B and vinblastine were used as chemical antagonists of the microfilamentous and microtubular elements of the cytoskeleton. Both agents inhibited the conversion of 25(OH)D3 to 1,25(OH)2D3 by isolated vitamin D-deficient chick renal tubules in a dose-dependent manner. At the concentrations required to inhibit 25(OH)D3-1 alpha-hydroxylase activity in whole cells, these agents inhibited neither isolated mitochondrial 1,25(OH)2D3 production, nor 24,25(OH)2D3 synthesis by vitamin D-replete tubules. The cytoskeletal antagonists were found to increase the content of labelled 1,25(OH)2D3 and 25(OH)D3 in a mitochondrial fraction prepared by Percoll fractionation of tubule cells pre-exposed to the antagonists and labelled 25(OH)D3 substrate. The data suggest that disruption of the cytoskeleton may result in inhibition of transport of newly synthesised 1,25(OH)2D3 out of the mitochondrion and through the cell, and accumulating 1,25(OH)2D3 may oppose its further synthesis. This is consistent with a transport process mediated by the cytoskeleton being involved in the regulation of renal vitamin D metabolism.