Vitamin D Status among Thai School Children and the Association with 1,25-Dihydroxyvitamin D and Parathyroid Hormone Levels

In several low latitude countries, vitamin D deficiency is emerging as a public health issue. Adequate vitamin D is essential for bone health in rapidly growing children. In the Thai population, little is known about serum 25-hydroxyvitamin D [25(OH)D] status of infants and children. Moreover, the association between 25(OH)D and the biological active form of 1,25-dihydroxyvitamin D [1,25(OH)]₂D is not clear. The specific aims of this study were to characterize circulating serum 25(OH)D, 1,25(OH)₂D and their determinants including parathyroid hormone (PTH), age, sex, height and body mass index (BMI) in 529 school-aged Thai children aged 6–14 y. Adjusted linear regression analysis was performed to examine the impact of age and BMI, and its interaction with sex, on serum 25(OH)D concentrations and 1,25(OH)₂D concentrations. Serum 25(OH)D, 1,25(OH)₂D and PTH concentrations (geometric mean ± geometric SD) were 72.7±1.2 nmol/L, 199.1±1.3 pmol/L and 35.0±1.5 ng/L, respectively. Only 4% (21 of 529) participants had a serum 25(OH)D level below 50 nmol/L. There was statistically significant evidence for an interaction between sex and age with regard to 25(OH)D concentrations. Specifically, 25(OH)D concentrations were 19% higher in males. Moreover, females experienced a statistically significant 4% decline in serum 25(OH)D levels for each increasing year of age (P = 0.001); no decline was seen in male participants with increasing age (P = 0.93). When BMI, age, sex, height and serum 25(OH)D were individually regressed on 1,25(OH)₂D, height and sex were associated with 1,25(OH)₂D with females exhibiting statistically significantly higher serum 1,25(OH)₂D levels compared with males (P<0.001). Serum 1,25(OH)₂D among our sample of children exhibiting fairly sufficient vitamin D status were higher than previous reports suggesting an adaptive mechanism to maximize calcium absorption.     

Vitamin D-Binding Protein Levels in Female Patients with Primary Hyperparathyroidism

ObjectiveTo determine whether low levels of vitamin D-binding protein (DBP) are related to 25-hydroxyvitamin D (25[OH]D) deficiency in female patients with primary hyperparathyroidism (PHPT).MethodsTwenty-five female patients with PHPT (serum calcium level >10.2 mg/dL and intact parathyroid hormone (iPTH) level >66 pg/mL) and 25 healthy age- and body mass index-matched female control subjects were xaminod. Serum calcium and iPTH levels were determined by commercial laboratories. Levels of 25(OH)D and 1,25-dihydroxyvitamin D (1,25[OH]₂D) were determined by radioimmunoassay, and DBP level was determined by enzyme-linked immunosorbent assay.ResultsSerum iPTH and calcium levels were higher in PHPT patients than control subjects (P<.001). Levels of 25(OH)D, albumin, and DBP were lower in the serum of PHPT patients than control subjects (P<.01). There were no significant differences in 1,25(OH)₂D and free 25(OH) D levels between PHPT patients and control subjects. DBP level was inversely correlated with calcium (r = -0.47; P<.01) and iPTH (r = −0.31; P<.05) levels. The 25(OH)D level correlated positively with both DBP (r = 0.28; P <.05) and albumin (r = 0.44; P<.05) levels.ConclusionsBoth serum 25(OH)D and DBP levels were lower in female patients with PHPT compared with control subjects. We suggest that a low DBP level contributes to the low 25(OH)D level observed in female PHPT patients. The etiology of the decrease in DBP and its relationship to calcium, 25(OH)D, and PTH levels require further investigation. (Endocr Pract. 2013;19:609-613)     

Independent Association of Circulating Vitamin D Metabolites with Anemia Risk in Patients Scheduled for Cardiac Surgery

Background

Preoperative anemia is considered an independent risk factor of poor clinical outcome in cardiac surgical patients. Low vitamin D status may increase anemia risk.

Methods

We investigated 3,615 consecutive patients scheduled for cardiac surgery to determine the association between preoperative anemia (hemoglobin [Hb] <12.5 g/dL) and circulating levels of the vitamin D metabolites 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25[OH]₂D).

Results

Of the study cohort, 27.8 % met the criteria for anemia. In patients with deficient 25OHD levels (<30 nmol/l) mean Hb concentrations were 0.5 g/dL lower than in patients with adequate 25OHD levels (50.0–125 nmol/l; P<0.001). Regarding 1,25(OH)₂D, mean Hb concentrations were 1.2 g/dL lower in the lowest 1,25(OH)₂D category (<40 pmol/l) than in the highest 1,25(OH)₂D category (>70 pmol/l; P<0.001). In multivariable–adjusted logistic regression analyses, the odds ratios for anemia of the lowest categories of 25OHD and 1,25(OH)₂D were 1.48 (95%CI:1.19-1.83) and 2.35 (95%CI:1.86-2.97), compared with patients who had adequate 25OHD levels and 1,25(OH)₂D values in the highest category, respectively. Anemia risk was greatest in patients with dual deficiency of 25OHD and 1,25(OH)₂D (multivariable-adjusted OR = 3.60 (95%CI:2.40-5.40). Prevalence of deficient 25OHD levels was highest in anemia of nutrient deficiency, whereas low 1,25(OH)₂D levels were most frequent in anemia of chronic kidney disease.

Conclusion

This cross-sectional study demonstrates an independent inverse association between vitamin D status and anemia risk. If confirmed in clinical trials, preoperative administration of vitamin D or activated vitamin D (in case of chronic kidney disease) would be a promising strategy to prevent anemia in patients scheduled for cardiac surgery.     

Altered Calcium and Vitamin D Homeostasis in First-Time Calcium Kidney Stone-Formers

Background

Elevated serum 1,25-dihydroxyvitamin D (1,25(OH)₂D) concentrations have been reported among cohorts of recurrent calcium (Ca) kidney stone-formers and implicated in the pathogenesis of hypercalciuria. Variations in Ca and vitamin D metabolism, and excretion of urinary solutes among first-time male and female Ca stone-formers in the community, however, have not been defined.

Methods

In a 4-year community-based study we measured serum Ca, phosphorus (P), 25-hydroxyvitamin D (25(OH)D), 1,25(OH)₂D, 24,25-dihydroxyvitamin D (24,25(OH)₂D), parathyroid hormone (PTH), and fibroblast growth factor-23 (FGF-23) concentrations in first-time Ca stone-formers and age- and gender frequency-matched controls.

Results

Serum Ca and 1,25(OH)₂D were increased in Ca stone-formers compared to controls (P = 0.01 and P = 0.001). Stone-formers had a lower serum 24,25(OH)₂D/25(OH)D ratio compared to controls (P = 0.008). Serum PTH and FGF-23 concentrations were similar in the groups. Urine Ca excretion was similar in the two groups (P = 0.82). In controls, positive associations between serum 25(OH)D and 24,25(OH)₂D, FGF-23 and fractional phosphate excretion, and negative associations between serum Ca and PTH, and FGF-23 and 1,25(OH)₂D were observed. In SF associations between FGF-23 and fractional phosphate excretion, and FGF-23 and 1,25(OH)₂D, were not observed. 1,25(OH)₂D concentrations associated more weakly with FGF-23 in SF compared with C (P <0.05).

Conclusions

Quantitative differences in serum Ca and 1,25(OH)₂D and reductions in 24-hydroxylation of vitamin D metabolites are present in first-time SF and might contribute to first-time stone risk.     

Reduced Parathyroid Hormone-Stimulated 1,25-Dihydroxyvitamin D Production in Vitamin D Sufficient Postmenoposual Women with Low Bone Mass and Idiopathic Secondary Hyperparathyroidism

ObjectiveDistinguishing secondary hyperparathyroidism (sHPT) from eucalcemic primary hyperparathyroidism (EC-pHPT) is important. The objective of this study was to measure parathyroid hormone (PTH)-stimulated production of 1α,25-dihydroxyvitamin D (1,25[OH]₂D) in early postmenopausal patients with idiopathic sHPT, who also fit the criteria for EC-pHPT, compared to age-matched controls.MethodsIn this pilot case-control study, postmenopausal women aged 44 to 55 years with normal serum calcium (Ca), glomerular filtration rate (GFR) ≥65 mL/min, and 25-hydroxyvitamin D (25[OH]D) ≥75 nmol/L (30 ng/mL) were given an 8 hour infusion of PTH(1-34), 12 pmol/kg/h. Patients (n = 5) had elevated PTH, normal 1,25(OH)₂D, and no hypercalciuria. Controls (n = 5) had normal PTH. At baseline, 4, and 8 hours, serum Ca, creatinine (Cr), phosphorus (P), 1,25(OH)₂D, fibroblast growth factor (FGF23), and 24,25(OH)₂D as well as urine Ca, P, Cr, and cAMP/GFR were measured. The fractional excretion of calcium (FeCa) and tubular reabsorption of phosphorus (TMP)/GFR were calculated.ResultsPatients had lower 1,25(OH)₂D levels (± SD) than controls at 4 (39.8 ± 6.9 versus 58.8 ± 6.7; P = .002) and 8 hours (56.4 ± 9.2 versus 105 ± 2.3; P = .003) of PTH infusion, attenuated after adjusting for higher body mass index (BMI) in patients (P = .05, .04), respectively. The 24,25(OH)2D levels were lower in patients than controls (1.9 ± 0.6 versus 3.4 ± 0.6, respectively; P = .007). No differences were seen in serum Ca or P, urine cAMP/GFR, TRP/GFR, FeCa, or PTH suppression at 8 hours (patients 50%, controls 64%).ConclusionVitamin D sufficient patients who fit the criteria for EC-pHPT had reduced PTH-stimulated 1,25(OH)₂D compared to controls, partially attributable to their higher BMI. Other causes of reduced 1,25(OH)₂D production ruled out were excessive catabolism of vitamin D metabolites, elevated FGF23, and CYP27B1 mutation. Elevated BMI and idiopathic reduced PTH-stimulated 1,25(OH)₂D production should be considered in the differential of sHPT. (Endocr Pract. 2013;19:91-99)     

Vitamin D substrate–product relationship in idiopathic hypercalciuria

Absorptive hypercalciuria (AH) is associated with elevated levels of 1,25-dihydroxyvitamin D (1,25(OH)₂D). While no increase of 1,25(OH)₂D after oral administration of 25-hydroxyvitamin D (25OHD) at high doses has been claimed in normal subjects, a substrate–product relationship has been reported in normal children, young people after UV irradiation, older persons, postmenopausal women, primary hyperparathyroidism, renal failure, osteomalacia, and sarcoidosis. No data of this relationship in AH is available. To investigate 25OHD-1,25(OH)₂D substrate–product relationship in AH, 161 AH patients (mean age 60.9 ± 11.7 years) and 110 age- and sex-matched controls (mean age 61.5 ± 12.4 years) were studied. In 57 controls and 52 AH subjects 25OHD-1,25(OH)₂D relationship in basal conditions and after 2-week oral 25OHD (25 μg/day) administration were evaluated. In basal conditions 25OHD and 1,25(OH)₂D were correlated in both, controls and AH; 25OHD treatment was followed by an increase in serum 25OHD and 1,25(OH)₂D in both groups. However, delta responses of 25OHD and 1,25(OH)₂D to 25OHD were higher in AH suggesting an enhanced activity of 1α-hydroxylase. In conclusion, the higher response of 1,25(OH)₂D after oral 25OHD in AH patients suggests a differential capacity between both groups in handling the increases in 1,25(OH)₂D.     

Serum 25-Hydroxyvitamin D Deficiency; A Risk Factor for Chronic Kidney Disease in Ambulatory Indigent Patients

ObjectiveTo assess whether 25-hydroxyvitamin D (25[OH]D) deficiency is a risk factor for chronic kidney disease (CKD) in ambulatory indigent patients.MethodsData for all serum 25(OH)D concentrations measured during 2010 in our ambulatory nondialysis-dependent patients were analyzed along with CKD-related parameters. Patients were stratified into groups based on 25(OH)D levels of < 10, 10 to 19, 20 to 29, and ≥ 30 ng/mL. CKD was defined by estimated glomerular filtration rate (eGFR; Chronic Kidney Disease-Epidemiology Collaboration [CKD-EPI] equation) and abnormal urine protein to creatinine ratios. CKD-associated parameters included serum parathyroid hormone (PTH), 1,25-dihydroxyvitamin D (1,25[OH]₂D), alkaline phosphatase, albumin, corrected calcium, and total CO₂ levels.ResultsA total of 2,811 patients had 25(OH)D levels measured. Patients with 25(OH)D levels < 10 ng/mL had significantly increased relative risk (RR) of an eGFR < 15 mL/min/1.73 m² (RR, 4.0), an eGFR of 15 to 29 mL/min/1.73 m² (RR, 2.6), urine protein to creatinine ratio > 3.5 g/g (RR, 5.6), and serum PTH > 100 pg/mL (RR, 2.8) compared to patients with a 25(OH)D level ≥ 30 ng/mL. Patients with 25(OH)D levels of 10 to19 ng/mL had significantly increased RR of a urine protein to creatinine ratio > 3.5 g/g (RR,4.8) and serum PTH > 100 pg/mL (RR, 1.5) compared to patients with 25(OH)D levels ≥ 30 ng/mL.Conclusion25(OH)D deficiency (< 10 ng/mL) was associated with reduced eGFR, nephrotic-range proteinuria, and increased PTH levels in our population of ambulatory urban indigent patients. (Endocr Pract. 2014;20:236-243)     

Simplified method for the determination of 25-hydroxy and 1α,25-dihydroxy metabolites of vitamins D2 and D3 in human plasma application to nutritional studies

A simplified method for the determination of 25-hydroxy and 1α,25-dihydroxy metabolites of vitamins D₂ and D₃ in human plasma was developed. Plasma samples were deproteinizated and applied to a Bond Elut C₁₈ OH cartridge to separate 25-hydroxyvitamin D (25-OH-D) and 1α-25-dihydroxyvitamin D [1,25(OH)₂D] fractions. The 25-OH-D fraction was purified by a Bond Elut C₁₈ cartridge and 25-OH-D₂ and 25-OH-D₃ were assayed by HPLC using a Zorbax SIL column. The 1,25(OH)₂D fraction obtained above was subsequently applied to HPLC using a Zorbax SIL column to separate 1,25(OH)₂D₂ and 1,25(OH)₂D₃ fractions which were determined by a radioreceptor assay (RRA) using calf thymus receptor. The method was applied to nutritional studies.     

Influence of ultraviolet B radiation on vitamin D3 metabolism in vitamin D3-resistant New World primates

We investigated the occurrence of rickets in adolescent tamarins (Saguinus imperator) residing at the Los Angeles Zoo. Compared to tamarins in the same colony without clinical evidence of bone disease (N = 6), rachitic platyrrhines (N = 3) had a decrease in their serum calcium concentration (P < .05). The affected tamarins also had lower serum 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) levels than did nonaffected colony mates, but 2–10-fold higher concentrations than in Old World primates of a comparable developmental stage. New World primates in many different genera are known to exhibit target organ resistance to the active vitamin D₃ metabolite, 1,25-(OH)₂D₃, compensated by maintenance of high circulating concentrations of 1,25-(OH)₂D₃. The relatively low serum 1,25-(OH)₂D₃ concentration in rachitic tamarins and ultraviolet B radiation deficient environment of these primates suggested that bone disease may be linked to a deficiency in substrate for 1,25-(OH)₂D₃, 25 hydroxyvtamin D₃ (25-OHD₃). Chronic exposure of platyrrhines in three different vitamin D resistant genera to an artificial UVB source resulted in 1) a significant increase in the mean serum 25-OHD₃ (P < .001) and 1,25-(OH)₂D₃ (P < .02) level over that encountered in platyrrhines not exposed to UVB; and 2) prevention of rachitic bone disease in irradiated individuals. These data further show that the serum 25-OHD₃ and 1,25-OH₂D₃ levels are positively correlated in vitamin D-resistant platyrrhines (r = 0.64; P= .0014) and suggest that a compromise in cutaneous vitamin D₃ production by means of UVB deprivation may limit necessary 1,25-(OH)₂D₃ production. © 1992 Wiley-Liss, Inc.     

Expressions of polypeptide: N-acetylgalactosaminyltransferase in leukemia cell lines during 1,25-dihydroxyvitamin D3 induced differentiation

The effect of 1,25-dihydroxyvitamin D3 [1,25(OH)₂D3] on two leukemia cell lines, K562 and SHI-1, and its relation to the expression of different subtypes of polypeptide: N-acetylgalactosaminyltransferase (pp-GalNAc-T) was studied. With morphological and cell flow-cytometric method, it was found that 1,25(OH)₂D3 induced the differentiation of both leukemia cell lines toward monocytic lineage, but not affected the cell growth and apoptosis. The expressions of different subtypes of pp-GalNAc-T, the initial glycosyltransferase in O-glycan synthesis, were studied with RT-PCR before and after the treatment of different concentrations of 1,25(OH)₂D3. Among fourteen subtypes of pp-GalNAc-T (T1 ∼ T14), K562 cells obviously expressed pp-GalNAc-T2, T4, T5, T7 (T2 was the highest) and SHI-1 cells apparently expressed pp-GalNAcT1, T2, T3 and T4 (T4 was the highest) only. After K562 cells were treated 1, 25(OH)₂D3 for 72 h, pp-GalNAc-T2, T4, T5, T7 were increased in a dose dependent manner. In contrast, pp-GalNAc-T1 and T2, especially T1, were up-regulated in SHI-1 cells by 1,25(OH)₂D3, but T3 was unchanged and T4 was down-regulated. The different alterations of pp-GalNAc-Ts in these two cell lines were probably related to the different structural changes of O-glycans during 1,25(OH)₂D3 induced differentiation.     

Vitamin D Metabolites and Their Association with Calcium,Phosphorus, and PTH Concentrations,Severity of Illness,and Mortality in Hospitalized Equine Neonates

Background

Hypocalcemia is a frequent abnormality that has been associated with disease severity and outcome in hospitalized foals. However, the pathogenesis of equine neonatal hypocalcemia is poorly understood. Hypovitaminosis D in critically ill people has been linked to hypocalcemia and mortality; however, information on vitamin D metabolites and their association with clinical findings and outcome in critically ill foals is lacking. The goal of this study was to determine the prevalence of vitamin D deficiency (hypovitaminosis D) and its association with serum calcium, phosphorus, and parathyroid hormone (PTH) concentrations, disease severity, and mortality in hospitalized newborn foals.

Methods and Results

One hundred newborn foals ≤72 hours old divided into hospitalized (n = 83; 59 septic, 24 sick non-septic [SNS]) and healthy (n = 17) groups were included. Blood samples were collected on admission to measure serum 25-hydroxyvitamin D₃ [25(OH)D₃], 1,25-dihydroxyvitamin D₃ [1,25(OH) ₂D₃], and PTH concentrations. Data were analyzed by nonparametric methods and univariate logistic regression. The prevalence of hypovitaminosis D [defined as 25(OH)D₃ <9.51 ng/mL] was 63% for hospitalized, 64% for septic, and 63% for SNS foals. Serum 25(OH)D₃ and 1,25(OH) ₂D₃ concentrations were significantly lower in septic and SNS compared to healthy foals (P<0.0001; P = 0.037). Septic foals had significantly lower calcium and higher phosphorus and PTH concentrations than healthy and SNS foals (P<0.05). In hospitalized and septic foals, low 1,25(OH)₂D₃ concentrations were associated with increased PTH but not with calcium or phosphorus concentrations. Septic foals with 25(OH)D₃ <9.51 ng/mL and 1,25(OH) ₂D₃ <7.09 pmol/L were more likely to die (OR=3.62; 95% CI = 1.1-12.40; OR = 5.41; 95% CI = 1.19-24.52, respectively).

Conclusions

Low 25(OH)D₃ and 1,25(OH)₂D₃ concentrations are associated with disease severity and mortality in hospitalized foals. Vitamin D deficiency may contribute to a pro-inflammatory state in equine perinatal diseases. Hypocalcemia and hyperphosphatemia together with decreased 1,25(OH)₂D₃ but increased PTH concentrations in septic foals indicates that PTH resistance may be associated with the development of these abnormalities.     

Treatment with 50000 IU Vitamin D2 Every Other Week and Effect on Serum 25-Hydroxyvitamin D2, 25-Hydroxyvitamin D3, and Total 25-Hydroxyvitamin D in Aclinical Setting

ObjectiveTo examine the effect of 50 000 IU-vitamin D₂ supplementation in a clinical setting on serum total 25-hydroxyvitamin D (25[OH]D), 25-hydroxyvitamin D₂ (25[OH]D₂), and 25-hydroxyvitamin D₃ (25[OH]D₃).MethodsThis retrospective cohort study was performed in an urban tertiary referral hospital in Boston, Massachusetts. Patients who had been prescribed 50 000 IU vitamin D₂ repletion and maintenance programs were identified through a search of our electronic medical record. Baseline and follow-up total serum 25(OH)D, 25(OH)D₂, and 25(OH)D₃ levels were compared.ResultsWe examined the medical records of 48 patients who had been prescribed 50 000 IU vitamin D₂ in our clinic. Mean ± standard deviation baseline total 25(OH) D was 31.0 ± 10.6 ng/mL and rose to 48.3 ± 13.4 ng/mL after treatment (P <.001). 25(OH)D₂ increased from 4.2 ± 4.3 ng/mL to 34.6 ± 12.3 ng/mL after treatment (P <.001), for an average of 158 days (range, 35-735 days). Serum 25(OH)D3 decreased from 26.8 ± 10.8 ng/mL to 13.7 ± 7.9 ng/mL (P <.001).ConclusionsFifty thousand IU vitamin D₂ repletion and maintenance therapy substantially increases total 25(OH)D and 25(OH)D2 despite a decrease in serum 25(OH)D3. This treatment program is an appropriate and effective strategy to treat and prevent vitamin D deficiency.(Endocr Pract. 2012;18:399-402)     

Prediagnostic plasma vitamin D metabolites and mortality among patients with prostate cancer

Background

Laboratory evidence suggests that vitamin D might influence prostate cancer prognosis.

Methodology/Principal Findings

We examined the associations between prediagnostic plasma levels of 25(OH)vitamin D [25(OH)D] and 1,25(OH)₂vitamin D [1,25(OH)₂D] and mortality among 1822 participants of the Health Professionals Follow-up Study and Physicians'' Health Study who were diagnosed with prostate cancer. Cox proportional hazards models were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) of total mortality (n = 595) and lethal prostate cancer (death from prostate cancer or development of bone metastases; n = 202). In models adjusted for age at diagnosis, BMI, physical activity, and smoking, we observed a HR of 1.22 (95% CI: 0.97, 1.54) for total mortality, comparing men in the lowest to the highest quartile of 25(OH)D. There was no association between 1,25(OH)₂D and total mortality. Men with the lowest 25(OH)D quartile were more likely to die of their cancer (HR: 1.59; 95% CI: 1.06, 2.39) compared to those in the highest quartile (P_trend = 0.006). This association was largely explained by the association between low 25(OH)D levels and advanced cancer stage and higher Gleason score, suggesting that these variables may mediate the influence of 25(OH)D on prognosis. The association also tended to be stronger among patients with samples collected within five years of cancer diagnosis. 1,25(OH)₂D levels were not associated with lethal prostate cancer.

Conclusions/Significance

Although potential bias of less advanced disease due to more screening activity among men with high 25(OH)D levels cannot be ruled out, higher prediagnostic plasma 25(OH)D might be associated with improved prostate cancer prognosis.     

Serum concentrations of 1,25-dihydroxyvitamin D3 in Platyrrhini and Catarrhini: A phylogenetic appraisal

We measured the serum concentration of 25-hydroxyvitamin D₃ (25-OH-D₃) and 1,25-dihydroxyvitamin D₃ (1,25-[OH]₂-D₃) in 23 different Platyrrhines from four different genera and in 21 Catarrhines from six different genera in residence at the Los Angeles Zoo. The mean (±S.E.) serum concentration of 1,25-(OH)₂-D₃ was significantly greater in Platyrrhines (810 ± 119 pg/ml) than in Catarrhines (61 ± 5 pg/ml), suggesting that high circulating concentrations of the active vitamin D hormone were a characteristic of New World primates in both the Cebidae and Callitrichidae family. This increase in the serum concentration of 1,25-(OH)₂-D₃ is probably an adaptational response on the part of Platyrrhini to offset a relative decrease in the concentration of specific receptor for 1,25-(OH)₂-D₃ in target tissues for the hormone.     

Plasma 25-hydroxycholecalciferol and 1,25-dihydroxycholecalciferol concentrations are decreased in hind limb unloaded Dahl salt-sensitive female rats

Plasma 1,25-dihydroxyvitamin D (1,25-(OH)₂D) concentration was shown to decrease during bed rest in several studies when baseline plasma 25-hydroxyvitamin D (25-OHD) concentration was sub-optimal. Dahl salt-sensitive female (S) rats, but not Dahl salt-resistant female (R) rats, demonstrated a 50% decrease in plasma 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) concentration after 28 days of hind limb unloading (HU, disuse model) during low salt intake (0.3%). We tested the vitamin D endocrine system response of female S rats to hind limb unloading during high salt intake (2%, twice that of standard rat chow to mimic salt intake in the USA). Hind limb unloading resulted in lower plasma 25-OHD₃ concentrations in S-HU rats than in R-HU rats (P < 0.05) and greater urinary loss of 25-OHD₃ by S-HU rats than by S rats (P < 0.05). Plasma 1,25-(OH)₂D₃ concentration of S-HU rats was half that of S rats, but was unchanged in R-HU rats. The association of low plasma 25-OHD concentration with decrease in plasma 1,25-(OH)₂D concentration of hind limb unloaded rats and of bed rest participants (published studies) suggests that low vitamin D status might be a risk factor for decrease in plasma vitamin D hormone concentration during long-term immobilization or bed rest.     

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.     

Supplemental vitamin D increases serum cytokines in those with initially low 25-hydroxyvitamin D: A randomized,double blind,placebo-controlled study

The purpose of this study was to determine if vitamin D status before supplementation influences the cytokine response after supplemental vitamin D. Forty-six reportedly healthy adults (mean(SD); age, 32(7) y; body mass index (BMI), 25.3(4.5) kg/m²; serum 25-hydroxyvitamin D (25(OH)D), 34.8(12.2) ng/mL) were randomly assigned (double blind) to one of three groups: (1) placebo (n = 15), or supplemental vitamin D (cholecalciferol) at (2) 4000 (n = 14) or (3) 8000 IU (n = 17). Supplements were taken daily for 35 days. Fasting blood samples were obtained before (Baseline, Bsl) and 35-days after (35-d) supplementation. Serum 25(OH)D, 1,25-dihydroxyvitamin D (1,25(OH)D), cytokines, and intact parathyroid hormone with calcium were measured in each blood sample. Supplemental vitamin D increased serum 25(OH)D (4000 IU, ≈29%; 8000 IU, ≈57%) and 1,25(OH)D (4000 IU, ≈12%; 8000 IU, ≈38%) without altering intact parathyroid hormone or calcium. The vitamin D metabolite increases in the supplemental vitamin D groups (n = 31) were dependent on initial levels as serum 25(OH)D (r = −0.63, p < 0.05) and 1,25(OH)D (r = −0.45, p < 0.05) at Bsl correlated with their increases after supplementation. Supplemental vitamin D increased interferon (IFN)-γ and interleukin (IL)-10 in subjects that were vitamin D insufficient (serum 25(OH)D < 29 ng/mL) compared to sufficient (serum 25(OH)D ⩾ 30 ng/mL) at Bsl. We conclude that supplemental vitamin D increase a pro- and anti-inflammatory cytokine in those with initially low serum 25(OH)D.     

Modulation of 1alpha,25-dihydroxyvitamin D3-membrane associated, rapid response steroid binding protein expression in mouse odontoblasts by 1alpha,25-(OH)2D3

The rapid, nongenomic effects of 1alpha,25-dihydroxyvitamin D3 (1alpha,25-(OH)2D3 have been related to a 1,25D3-membrane associated, rapid response steroid binding protein or 1,25D3-[MARRS]bp, with a molecular weight of 65 kDa, in several tissues and species. Currently, no information is available concerning the nongenomic responses to 1alpha,25-(OH)2D3 in dental tissues. In order to investigate the expression of 1,25D3-[MARRS]bp in dental cells, in the presence or absence of 1alpha,25-(OH)2D3, we have used rabbit polyclonal antibodies directed against the N-terminus of the 1,25D3-[MARRS]bp (Ab099) that recognizes the 1alpha,25-(OH)2D3 binding protein in chick intestinal basolateral membranes and a mouse odontoblast-like cell line (MO6-G3). Western blotting and flow cytometric analyses with Ab099 specifically detected 1,25D3-[MARRS]bp in MO6-G3 cells. Moreover, 1,25D3-[MARRS]bp was up-regulated, in vivo, in differentiated dental cells. Electron microscopic analysis confirmed the plasma membrane localization of this binding protein and also showed its intracellular presence. Incubation of MO6-G3 cells with different doses of 1alpha,25-(OH)2D3 for 36 h resulted in an inhibition of 1,25D3-[MARRS]bp expression with a maximal effect at 50 nM steroid. In addition, the culture media of MO6-G3 cells contains immunoreactive 1,25D3-[MARRS]bp. Immunogold positive membrane vesicle-like structures are present in the extracellular matrix of MO6-G3 cells. Altogether, these results indicate that the 1,25D3-[MARRS]bp expression in MO6-G3 cells is modulated by 1alpha,25-(OH)2D3. In conclusion, this 1alpha,25-(OH)2D3 binding protein could play an important role in the rapid, nongenomic responses to 1alpha,25-(OH)2D3 in dental cells.     

Enhanced effects of guggulsterone plus 1,25(OH)2D3 on 3T3-L1 adipocytes

Guggulsterone (GS) and 1,25-dihydroxyvitamin D3 [1,25(OH)₂D₃] have been shown to influence adipogenesis in 3T3-L1 cells. We investigated the ability of GS and 1,25(OH)₂D₃, alone and in combination to inhibit adipogenesis and induce apoptosis in 3T3-L1 adipocytes. Maturing preadipocytes were treated with 1,25(OH)₂D₃ in combination with GS for 6 days during differentiation. GS and 1,25(OH)₂D₃ each inhibited lipid accumulation, but the combination potentiated the inhibition of lipid accumulation. Apoptosis was increased by 1,25(OH)₂D₃ while GS had no effect, but GS + 1,25(OH)₂D₃ increased apoptosis more than either compound alone. Furthermore, GS + 1,25(OH)₂D₃ caused a potentiated decrease in the expression of aP2 and farnesoid X receptor expression more than either compound alone. In addition, 1,25(OH)₂D₃ increased vitamin D receptor expression after 6 days, while GS had no effect. GS + 1,25(OH)₂D₃, however, caused a potentiated increase in the expression of VDR. These findings show that GS potentiates 1,25(OH)₂D₃’s anti-adipogenic and pro-apoptotic effects in maturing 3T3-L1 preadipocytes.     

Evaluation of vitamin D3 metabolites in Callithrix jacchus (common marmoset)

Vitamin D₃ (cholecalciferol) is endogenously produced in the skin of primates when exposed to the appropriate wavelengths of ultraviolet light (UV-B). Common marmosets (Callithrix jacchus) maintained indoors require dietary provision of vitamin D₃ due to lack of sunlight exposure. The minimum dietary vitamin D₃ requirement and the maximum amount of vitamin D₃ that can be metabolized by marmosets is unknown. Observations of metabolic bone disease and gastrointestinal malabsorption have led to wide variation in dietary vitamin D₃ provision amongst research institutions, with resulting variation in circulating 25-hydroxyvitamin D₃ (25(OH)D₃), the accepted marker for vitamin D sufficiency/deficiency. Multiple studies have reported serum 25(OH)D₃ in captive marmosets, but 25(OH)D₃ is not the final product of vitamin D₃ metabolism. In addition to serum 25(OH)D_3, we measured the most physiologically active metabolite, 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃), and the less well understood metabolite, 24,25-dihydroxyvitamin D₃ (24,25(OH)₂D₃) to characterize the marmoset's ability to metabolize dietary vitamin D₃. We present vitamin D₃ metabolite and related serum chemistry value colony reference ranges in marmosets provided diets with 26,367 (Colony A, N = 113) or 8,888 (Colony B, N = 52) international units (IU) of dietary vitamin D₃ per kilogram of dry matter. Colony A marmosets had higher serum 25(OH)D₃ (426 ng/ml [SD 200] vs. 215 ng/ml [SD 113]) and 24,25(OH)₂D₃ (53 ng/ml [SD 35] vs. 7 ng/ml [SD 5]). There was no difference in serum 1,25(OH)₂D₃ between the colonies. Serum 1,25(OH)₂D₃ increased and 25(OH)D₃ decreased with age, but the effect was weak. Marmosets tightly regulate metabolism of dietary vitamin D₃ into the active metabolite 1,25(OH)₂D₃; excess 25(OH)D₃ is metabolized into 24,25(OH)₂D₃. This ability explains the tolerance of high levels of dietary vitamin D₃ by marmosets, however, our data suggest that these high dietary levels are not required.