Advantages of paper chromatography as a preparative step in the assay of 1,25-dihydroxyvitamin D

Seasonal variation in vitamin D₃ levels is paralleled by changes in the peripheral blood human T cell compartment

It is well-recognized that vitamin D₃ has immune-modulatory properties and that the variation in ultraviolet (UV) exposure affects vitamin D₃ status. Here, we investigated if and to what extent seasonality of vitamin D₃ levels are associated with changes in T cell numbers and phenotypes. Every three months during the course of the entire year, human PBMC and whole blood from 15 healthy subjects were sampled and analyzed using flow cytometry. We observed that elevated serum 25(OH)D₃ and 1,25(OH)₂D₃ levels in summer were associated with a higher number of peripheral CD4⁺ and CD8⁺ T cells. In addition, an increase in naïve CD4⁺CD45RA⁺ T cells with a reciprocal drop in memory CD4⁺CD45RO⁺ T cells was observed. The increase in CD4⁺CD45RA⁺ T cell count was a result of heightened proliferative capacity rather than recent thymic emigration of T cells. The percentage of Treg dropped in summer, but not the absolute Treg numbers. Notably, in the Treg population, the levels of forkhead box protein 3 (Foxp3) expression were increased in summer. Skin, gut and lymphoid tissue homing potential was increased during summer as well, exemplified by increased CCR4, CCR6, CLA, CCR9 and CCR7 levels. Also, in summer, CD4⁺ and CD8⁺ T cells revealed a reduced capacity to produce pro-inflammatory cytokines. In conclusion, seasonal variation in vitamin D₃ status in vivo throughout the year is associated with changes in the human peripheral T cell compartment and may as such explain some of the seasonal variation in immune status which has been observed previously. Given that the current observations are limited to healthy adult males, larger population-based studies would be useful to validate these findings.

Regulation of cytokine responses by seasonality of vitamin D status in healthy individuals

The immune modulating capacity of vitamin D(3) is well-recognized. Ultra-violet (UV) exposure determines production of vitamin D(3) in vivo and varies through the course of the year, especially in temperate regions. However, it is not known whether the human innate immune response differs due to seasonality. To validate the seasonal effects of vitamin D(3) , the effect of 1,25(OH)(2) D(3) on peripheral blood mononuclear cells (PBMC) cytokine response was first determined in vitro. 1,25(OH)(2) D(3) decreased interleukin (IL)-6 and tumour necrosis factor (TNF)-α release by PBMC stimulated with tripalmitoyl-S-glycerylcysteine (Pam3Cys) or lipopolysaccharide (LPS). Subsequently, ex-vivo stimulation studies were performed in 15 healthy volunteers through the course of the four seasons of the year. PBMC were isolated and stimulated with Toll-like receptor (TLR)-2 and TLR-4 ligands Pam3Cys and LPS, respectively. Circulating concentrations of 25(OH)D(3) and 1,25(OH)(2) D(3) were higher during summer (P<0·05) and a down-regulation of TLR-4-mediated IL-1β, IL-6, TNF-α, interferon (IFN)-γ and IL-10 production in summer was observed compared to winter (P<0·05). The variation in cytokine response upon TLR-2 (Pam3Cys) stimulation was moderate throughout the four seasons. The repressed cytokine production during the summer months could be explained partly by the reduced cell-membrane expression of TLRs. Physiological variation in vitamin D(3) status through the four seasons of the year can lead to alteration in the innate immune responses. Elevated vitamin D(3) level in vivo is associated with down-regulation of cytokine response through diminished surface expression of pattern recognition receptors.

Melatonin synthesis under calcium constraint in gilthead sea bream (Sparus auratus L.)

Brain or blood plasma melatonin was analysed as a measure for pineal melatonin production in sea bream. Access to calcium was limited by diluting the seawater to 2.5 per thousand and removing calcium from the diet or by prolonged feeding of vitamin D-deficient diet. Interactions/relations between melatonin and calcium balance and the hypercalcemic endocrines PTHrP and calcitriol were assessed. Restricting calcium availability in both water and diet had no effect on plasma melatonin, but when calcium was low in the water or absent from food, increased and decreased plasma melatonin was observed, respectively. Fish on a vitamin D-deficient diet (D- fish) showed decreased plasma calcitriol levels and remained normocalcemic. Decreased brain melatonin was found at all sampling times (10-22 weeks) in the D- fish compared to the controls. A positive correlation between plasma Ca2+ and plasma melatonin was found (R(2)=0.19; N=41; P <0.01) and brain melatonin was negatively correlated with plasma PTHrP (R(2)=0.78; N=4; P <0.05). The positive correlation between plasma levels of melatonin and Ca2+ provides evidence that melatonin synthesis is influenced by plasma Ca2+. The decreased melatonin production in the D- fish points to direct or indirect involvement of calcitriol in melatonin synthesis by the pineal organ in teleosts. The hypercalcemic factors PTHrP and calcitriol appeared to be negatively correlated with melatonin and this substantiates an involvement of melatonin in modulating the endocrine response to cope with hypocalcemia. It further points to the importance of Ca2+ in melatonin physiology.

Expression of the novel epithelial Ca2+ channel ECaC1 in rat pancreatic islets

The epithelial Ca2+ channel, ECaC1, is primarily expressed in the apical membrane of vitamin D-responsive tissues. This study characterizes for the first time the presence of this novel channel in pancreatic tissue by reverse transcriptase-polymerase chain reaction and immunohistochemistry. In addition, the expression of ECaC1 was investigated in an animal model for Type 2 diabetes mellitus, the Zucker diabetic fatty (ZDF) rat. Identical staining patterns for ECaC1 and insulin were observed, whereas no co-localization of ECaC1 with glucagon was found. ECaC1, insulin, and prohormone convertase 1 (a neuroendocrine endoprotease expressed in secretory granules) showed a similar punctate staining. ECaC1 co-localized with the Ca2+ binding protein calbindin-D(28K) in the beta-cells. Furthermore, in contrast to wild-type rats, in ZDF rats aging led to a progressive decrease in both insulin and ECaC1 staining. Plasma 1,25-dihydroxyvitamin D3 levels were similar in both control and ZDF rats and decreased with aging. Taken together, our findings indicate that this novel Ca2+ channel may play a role in the regulation of endocrine Ca2+ homeostasis.

Extraction of fat-soluble vitamins

An overview of the different extraction procedures of fat-soluble vitamins from human fluids, foods and pharmaceutical preparations is presented. Methods using organic solvent extraction (both liquid-liquid and solid-liquid extraction), supercritical fluid extraction and solid-phase extraction for the different types of both vitamins and matrices are discussed.

Osteopenia in insulin-dependent diabetes mellitus; prevalence and aspects of pathophysiology

The objective was to evaluate the prevalence and severity of osteopenia in patients with uncomplicated insulin-dependent diabetes mellitus (IDDM) and to obtain more information on the pathophysiology of diabetic osteopenia. In 35 patients with uncomplicated IDDM (21 men and 14 women; age 37.6+/-9.9 yr; duration of disease 8.5+/-3.5 years) bone mineral density was measured by dual energy X-ray absorptiometry (DEXA). In addition, markers of bone formation [plasma insulin-like growth factor I (IGF-I), serum alkaline phosphatase (ALP), serum bone alkaline phosphatase (BAP) and serum osteocalcin] and bone resorption [urinary excretion of calcium and of the cross-linked N-telopeptide of type 1 collagen, both corrected for the excretion of creatinine] were measured in the diabetic patients and in 33 healthy controls, matched for sex, age, height, weight and body mass index (BMI). In 67% of the diabetic men and 57% of the diabetic women osteopenia of the femoral neck and/or the lumbar spine (T-value < or = -1 SD) was present. Fourteen percent of the male patients, but none of the female patients, met the criteria for osteoporosis (T-value < or = -2.5 SD). In the whole group of diabetic patients the mean plasma IGF-I level tended to be lower (p<0.10) as compared to that in the controls. In the diabetic patients with femoral neck osteopenia, the mean plasma IGF-I level was significantly lower (p<0.05) than in those without osteopenia at this site. There were no differences in the mean serum ALP, BAP and osteocalcin levels between the diabetic patients and the controls, nor between the diabetic patients with and without femoral neck osteopenia. Considering only the male diabetic patients, significantly lower mean plasma IGF-I (-26%), serum ALP (-24%) and serum osteocalcin (-38%) levels were present in the patients with femoral neck osteopenia than in those without osteopenia at this site, suggesting lowered bone formation. The bone resorption markers were similar in all (sub)groups of diabetic patients and not different between diabetic patients and controls. Bone mineral density (BMD) did not correlate with plasma levels of glycosylated hemoglobin (HbA1c). BMD values were not related to any of the bone resorption or formation markers, except for plasma IGF-I both in the femoral neck (r=+0.38, p=0.026) and the lumbar spine (r=+0.34, p=0.043). Our data demonstrate that at least in male patients with IDDM, osteopenia is the consequence of a lowered bone formation with a predominance of bone resorption over formation.

Female sex hormone replacement therapy increases serum free 1,25-dihydroxyvitamin D3: a 1-year prospective study

OBJECTIVE

Currently, hormone replacement therapy is applied successfully to reduce post-menopausal bone resorption. However, the exact mechanism by which oestrogen exerts its effect has not yet been fully elucidated. In order to determine whether changes in the biologically active 1,25-dihydroxyvitamin D3 may be of importance in this process, the concentrations of both total and free 1,25-dihydroxyvitamin D3 in serum were assessed.

DESIGN

In 36 post-menopausal women the effect of hormone replacement therapy, with a combination of 17 beta-oestradiol and norethisterone acetate, on the serum levels of total and free 1,25-dihydroxyvitamin D3 was studied after 0, 3, 6 and 12 cycles.

MEASUREMENTS

The total concentration of 1,25-dihydroxyvitamin D3 in serum was assessed using a radioreceptor assay after diethylether extraction of the samples followed by paper chromatography. The free fraction of 1,25-dihydroxyvitamin D3 was measured using symmetric dialysis. The free 1,25 dihydroxyvitamin D3 concentration was calculated by multiplying the total concentration by the free fraction.

RESULTS

During therapy, mean serum total 1,25-dihydroxyvitamin D3 concentrations (+/- SD) were 106.4 pmol/l (+/- 27.5), 155.0 pmol/l (+/- 49.5), 176.7 pmol/l (+/- 70.0) and 161.1 pmol/l (+/- 55.3) at 0, 3, 6 and 12 cycles, respectively. Serum free 1,25-dihydroxyvitamin D3 concentrations were 68 fmol/l (+/- 22), 107 fmol/l (+/- 35), 120 fmol/l (+/- 43) and 108 fmol/l (+/- 37), respectively. Baseline values of both total and free 1,25-dihydroxyvitamin D3 were significantly lower than those during therapy at all time (P < or = 0.001).

CONCLUSION

Both the serum total 1,25-dihydroxyvitamin D3 and the serum free 1,25-dihydroxyvitamin D3 concentrations are increased during combined 17 beta-oestradiol and norethisterone acetate therapy for a year. Assuming that the free concentration 1,25-dihydroxyvitamin D3 reflects the biologically active fraction, this rise may in part explain the preventive effect of hormone replacement therapy on osteoporosis.

Determination of non-protein-bound plasma 1,25-dihydroxyvitamin D by symmetric (rate) dialysis

Most of the total circulating 1,25-dihydroxyvitamin D (1,25(OH)2D) is bound to plasma proteins, mainly vitamin D-binding protein (DBP) and albumin. Only a small fraction in plasma exists in the free form. It is widely assumed that the non-protein-bound free hormone reflects the biologically active fraction. We describe a dialysis method for the determination of plasma free 1,25(OH)2D which is relatively easy to perform. In this symmetric or "rate" dialysis method, identical samples are placed at both sides of a membrane. At one side, tritiated 1,25(OH)2D is added and the rate of transfer of this tritiated 1,25(OH)2D through a dialysis membrane is directly related to the free fraction of plasma 1,25(OH)2D. This method is much less susceptible toward tracer impurities than indirect equilibrium dialysis and centrifugal ultrafiltration. Moreover, it requires much less tracer. The intraassay coefficient of variation for the determination of the free fraction is 1.0%; the interassay variation is 7.7%. Comparison of the free fraction of 23 samples assessed with both centrifugal ultrafiltration and symmetric dialysis showed much higher values using the former method. No significant correlation between the two methods was found. The free fraction of 1,25(OH)2D in normal subjects as assessed with symmetric dialysis ranges from 0.049 to 0.103%.

Hormone replacement therapy increases serum 1,25-dihydroxyvitamin D: A 2-year prospective study

Osteoporosis is a common disorder in postmenopausal women, which is probably due to decreased ovarian function. Currently, hormone replacement therapy (HRT), involving administration of estrogen and progestogen, is successfully applied to reduce bone resorption. We studied the effect of HRT on 23 postmenopausal women. This consisted of a combination of 17 beta-estradiol and dydrogesterone, on the serum level of 1,25-dihydroxyvitamin D (1,25(OH)2D) after 0, 6, 12, and 24 months. We found mean serum concentrations (+/- SD) of 1,25(OH)2D of 130.5 pmol/liter (46.1), 152.7 pmol/liter (45.1), 170.8 pmol/liter (64.0), and 155.2 pmol/liter (59.7), respectively. The baseline values in these women were found to be significantly lower than those during therapy (P < or = 0.005). No statistically significant differences were observed when comparing the estrogen-only phase with the combined estrogen-progestogen phase. It is concluded that HRT results in an increase in the serum 1,25(OH)2D concentration which lasts for at least 2 years. This increase may partly explain the preventive effect of HRT on osteoporosis. Furthermore, these results suggest that dydrogesterone does not influence the estrogen-induced changes in serum 1,25(OH)2D concentration.