Increased catabolism of 25-hydroxyvitamin D in patients with partial gastrectomy and elevated 1,25-dihydroxyvitamin D levels. Implications for metabolic bone disease

Vitamin D Metabolites: Analytical Challenges and Clinical Relevance

Recent research activities have provided new insights in vitamin D metabolism in various conditions. Furthermore, substantial progress has been made in the analysis of vitamin D metabolites and related biomarkers, such as vitamin D binding protein. Liquid chromatography tandem mass spectrometric (LC-MS/MS) methods are capable of accurately measuring multiple vitamin D metabolites in parallel. Nevertheless, only 25(OH)D and the biologically active form 1,25(OH)2D are routinely measured in clinical practice. While 25(OH)D remains the analyte of choice for the diagnosis of vitamin D deficiency, 1,25(OH)2D is only recommended in a few conditions with a dysregulated D metabolism. 24,25(OH)2D, free and bioavailable 25(OH)D, and the vitamin D metabolite ratio (VMR) have shown promising results, but technical pitfalls in their quantification, limited clinical data and the lack of reference values, impede their use in clinical practice. LC-MS/MS is the preferred method for the measurement of all vitamin D related analytes as it offers high sensitivity and specificity. In particular, 25(OH)D and 24,25(OH)2D can accurately be measured with this technology. When interpreted together, they seem to provide a functional measure of vitamin D metabolism beyond the analysis of 25(OH)D alone. The determination of VDBP, free and bioavailable 25(OH)D is compromised by unresolved analytical issues, lacking reference intervals and insufficient clinical data. Therefore, future research activities should focus on analytical standardization and exploration of their clinical value. This review provides an overview on established and new vitamin D related biomarkers including their pathophysiological role, preanalytical and analytical aspects, expected values, indications and influencing conditions.

Predicting the acute-phase response fever risk in bisphosphonate-naive osteoporotic patients receiving their first dose of zoledronate

INTRODUCTION

To devise a precise and efficient tool for predicting the individualized risk of acute-phase response (APR) in bisphosphonate (BP)-naive osteoporotic (OP) patients, receiving their first intravenous dose of zoledronate (ZOL).

METHODS

The baseline clinical and laboratory data of 475 consecutive BP-naive OP patients, who received their first intravenous dose of ZOL between March 2016 and March 2021 in the Affiliated Kunshan Hospital of Jiangsu University, were chosen for analysis. Univariate and multivariable logistic regression models were generated to establish candidate predictors of APR fever risk, using three distinct fever thresholds, namely, 37.3 °C (model A), 38.0 °C (model B), and 38.5 °C (model C). Next, using predictor regression coefficients, three fever-threshold nomograms were developed. Discrimination, calibration, and clinical usefulness of each predicting models were then assessed using the area under the curve (AUC), calibration curve (CC), and decision curve analysis (DCA). The internal and external model validations were then performed.

RESULTS

The stable predictors were age, serum 25-hydroxy vitamin D, serum total calcium, and peripheral blood erythrocytes count. These were negatively associated with the APR fever risk. The AUCs of models A, B, and C were 0.828 (95% confidence intervals [CI], 0.782 to 0.874), 0.825 (95% CI, 0.767 to 0.883), and 0.879 (95% CI, 0.824 to 0.934), respectively. Good agreement was observed between the predictions and observations in the CCs of all three nomograms.

CONCLUSIONS

This study developed and validated nomogram prediction models that can predict APR fever risk in BP-naive OP patients receiving their first infusion of ZOL.

Increased calcium intake is associated lower serum 25-hydroxyvitamin D levels in subjects with adequate vitamin D intake: a population-based observational study

BACKGROUND

There are indications that an increased intake of calcium has a vitamin D sparing effect, which might be explained by a decreased catabolism of 25-hydroxyvitamin D (25(OH)D). However, there are only a few studies where this has been examined.

METHOD

In the seventh survey of the Tromsø study, serum 25(OH)D and parathyroid hormone were measured, and questionnaires on calcium and vitamin D intakes filled in.

RESULTS

There were significant interactions between sex, calcium and vitamin D intakes regarding serum 25(OH)D level. The analyses were therefore done stratified. In males there was, regardless of vitamin D intake, a significant decrease in serum 25(OH)D with increasing calcium intake. The difference in serum 25(OH)D between those with the highest and lowest calcium intakes was approximately 10%. In the females, there was in subjects with low vitamin D intake (< 7 μg/d) a significant increase in serum 25(OH)D with increasing calcium intake, which could not be explained by secondary hyperparathyroidism. In females with higher vitamin D intakes, increasing calcium intake was associated with lower serum 25(OH)D levels.

CONCLUSIONS

There is, at least in subjects with an adequate vitamin D intake, a negative association between calcium intake and serum 25(OH)D.

Vitamin D expenditure is not altered in pregnancy and lactation despite changes in vitamin D metabolite concentrations

Pregnancy and lactation are associated with changes in vitamin D and calcium metabolism but the impact of these changes on vitamin D expenditure is unknown. We measured plasma 25(OH)D₃ half-life with a stable-isotope tracer and investigated relationships with vitamin D metabolites in pregnant, lactating and ‘non-pregnant, non-lactating’ (NPNL) women. Vitamin D metabolites, vitamin D binding protein (DBP), PTH and 25(OH)D₃ half-life were measured in third-trimester pregnant women (n22) and repeated during lactation 12 weeks post-partum (n14) and twice in NPNL women (n23 and n10, respectively) in rural Gambia where calcium intakes are low with little seasonality in UVB-exposure. 25(OH)D₃ half-life was not significantly different between groups (mean(SD): 20.6(6.8), 22.6(7.7), 18.0(4.7) and 17.7(9.5) days in pregnant, lactating and NPNL women, respectively). Plasma 25(OH)D₃, 1,25(OH)₂D, and DBP were higher in pregnancy, and calculated free-25(OH)D₃ and PTH were lower (P < 0.05). In lactation, 25(OH)D₃ and 24,25(OH)₂D₃ were lower compared to pregnant (P < 0.001, P = 0.02) and NPNL women (P = 0.04, P = 0.07). Significant associations were observed between half-life and 25(OH)D₃ (+ve) in pregnancy, and in all groups between 25(OH)D₃ and free-25(OH)D₃ (+ve) and PTH and 25(OH)D₃ (−ve) (P < 0.0001). These data suggest that adaptive changes in pregnancy and lactation occur that prevent pronounced changes in vitamin D expenditure.

Predictors of 25(OH)D half-life and plasma 25(OH)D concentration in The Gambia and the UK

Predictors of 25(OH)D3 half-life were factors associated with vitamin D metabolism, but were different between people in The Gambia and the UK. Country was the strongest predictor of plasma 25(OH)D concentration, probably as a marker of UVB exposure. 25(OH)D3 half-life may be applied as a tool to investigate vitamin D expenditure.

INTRODUCTION

The aim of this study was to investigate predictors of 25(OH)D3 half-life and plasma 25(OH)D concentration.

METHODS

Plasma half-life of an oral tracer dose of deuterated-25(OH)D3 was measured in healthy men aged 24-39 years, resident in The Gambia, West Africa (n = 18) and in the UK during the winter (n = 18), countries that differ in calcium intake and vitamin D status. Plasma and urinary markers of vitamin D, calcium, phosphate and bone metabolism, nutrient intakes and anthropometry were measured.

RESULTS

Normally distributed data are presented as mean (SD) and non-normal data as geometric mean (95% CI). Gambian compared to UK men had higher plasma concentrations of 25(OH)D (69 (13) vs. 29 (11) nmol/L; P < 0.0001); 1,25(OH)2D (181 (165, 197) vs. 120 (109, 132) pmol/L; P < 0.01); and parathyroid hormone (PTH) (50 (42, 60) vs. 33 (27, 39); P < 0.0001). There was no difference in 25(OH)D3 half-life (14.7 (3.5) days vs. 15.6 (2.5) days) between countries (P = 0.2). In multivariate analyses, 25(OH)D, 1,25(OH)2D, vitamin D binding protein and albumin-adjusted calcium (Caalb) explained 79% of variance in 25(OH)D3 half-life in Gambians, but no significant predictors were found in UK participants. For the countries combined, Caalb, PTH and plasma phosphate explained 39 % of half-life variability. 1,25(OH)2D, weight, PTH and country explained 81% of variability in 25(OH)D concentration; however, country alone explained 74%.

CONCLUSION

Factors known to affect 25(OH)D metabolism predict 25(OH)D3 half-life, but these differed between countries. Country predicted 25(OH)D, probably as a proxy measure for UVB exposure and vitamin D supply. This study supports the use of 25(OH)D half-life to investigate vitamin D metabolism.

Adjuvant therapy with high dose vitamin D following primary treatment of melanoma at high risk of recurrence: a placebo controlled randomised phase II trial (ANZMTG 02.09 Mel-D)

BACKGROUND

Patients with primary cutaneous melanomas that are ulcerated and >2 mm in thickness, >4 mm in thickness and those with nodal micrometastases at diagnosis, have few options for adjuvant treatment. Recent studies have suggested a role for vitamin D to delay melanoma recurrence and improve overall prognosis.

METHODS/DESIGN

This is a pilot placebo-controlled randomised phase II trial to assess the feasibility, safety and toxicity of an oral loading dose of Vitamin D (500,000 IU) followed by an oral dose of 50,000 IU of Vitamin D monthly for 2 years in patients who have been treated for cutaneous melanoma by wide excision of the primary. Patients aged 18-79 years who have completed primary surgical treatment and have Stage IIb, IIc, IIIa (N1a, N2a) or IIIb (N1a, N2a) disease are eligible for randomisation 2:1 to active treatment or placebo. The primary endpoints are sufficiency of dose, adherence to study medication and safety of the drug. The secondary endpoints are participation and progression free survival. The study has been approved by the Ethics Review Committee (RPAH Zone) of the Sydney Local Health District, protocol number X09-0138.

DISCUSSION

Effective, non-toxic adjuvant therapy for high risk primary melanoma is not currently available. Favorable outcomes of this phase II study will form the basis for a multi-centre phase III study to assess whether the addition of oral high-dose vitamin D therapy in patients who have completed primary treatment for melanoma and are at high risk of recurrence will: 1. prolong time to recurrence within 5 years 2. improve overall survival at 5 years and 3. be both safe and tolerable. 62 patients have been randomised since the study commenced in December 2010. Target accrual for the study has been met with 75 patients randomised between December 2010 and August 2014.The Mel-D trial is conducted by the Australia and New Zealand Melanoma Trials Group (ANZMTG 02.09) TRIAL REGISTRATION: Australia and New Zealand Clinical Trials Registry (ANZCTR) ACTRN12609000351213.

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.

Modulation of vitamin d status and dietary calcium affects bone mineral density and mineral metabolism in göttingen minipigs

Calcium and vitamin D deficiency impairs bone health and may cause rickets in children and osteomalacia in adults. Large animal models are useful to study experimental osteopathies and associated metabolic changes. We intended to modulate vitamin D status and induce nutritional osteomalacia in minipigs. The control group (n = 9) was fed a semisynthetic reference diet with 6 g calcium and 6,500 IU vitamin D₃/kg and the experimental group (n = 10) the same diet but with only 2 g calcium/kg and without vitamin D. After 15 months, the deficient animals were in negative calcium balance, having lost bone mineral density significantly (means ± SEM) with −51.2 ± 14.7 mg/cm³ in contrast to controls (−2.3 ± 11.8 mg/cm³), whose calcium balance remained positive. Their osteoid surface was significantly higher, typical of osteomalacia. Their plasma 25(OH)D dropped significantly from 60.1 ± 11.4 nmol/L to 15.3 ± 3.4 nmol/L within 10 months, whereas that of the control group on the reference diet rose. Urinary phosphorus excretion and plasma 1,25-dihydroxyvitamin D concentrations were significantly higher and final plasma calcium significantly lower than in controls. We conclude that the minipig is a promising large animal model to induce nutritional osteomalacia and to study the time course of hypovitaminosis D and associated functional effects.

Influence of gastrectomy on cortical and cancellous bones in rats

The aim of the present study was to examine the influence of gastrectomy (GX) on cortical and cancellous bones in rats. Twenty male Sprague-Dawley rats were randomized into the two groups of 10 animals each: a sham operation (control) group and a GX group. Seven weeks after surgery, the bone mineral content and density (BMC and BMD, resp.) and the mechanical strength of the femur were determined, and bone histomorphometric analyses were performed on the tibia. GX induced decreases in the BMC, BMD, ultimate force, work to failure, and stiffness of the femoral distal metaphysis and the BMC, BMD, and ultimate force of the femoral diaphysis. GX induced a decrease in cancellous bone mass, characterized by an increased osteoid thickness, osteoid surface, osteoid volume, and bone formation. GX also induced a decrease in cortical bone mass, characterized by increased endocortical bone resorption. The GX induced reductions in the bone mass and strength parameters were greater in cancellous bone than in cortical bone. The present study showed that the response of bone formation, resorption, and osteoid parameters to GX and the degree of GX-induced osteopenia and the deterioration of bone strength appeared to differ between cortical and cancellous bones in rats.

Plasma appearance and disappearance of an oral dose of 25-hydroxyvitamin D2 in healthy adults

25-Hydroxyvitamin D (25(OH)D) half-life is a potential biomarker for investigating vitamin D metabolism and requirements. We performed a pilot study to assess the approach and practical feasibility of measuring 25(OH)D half-life after an oral dose. A total of twelve healthy Gambian men aged 18–23 years were divided into two groups to investigate the rate and timing of (1) absorption and (2) plasma disappearance after an 80 nmol oral dose of 25(OH)D₂. Fasting blood samples were collected at baseline and, in the first group, every 2 h post-dose for 12 h, at 24 h, 48 h and on day 15. In the second group, fasting blood samples were collected on days 3, 4, 5, 6, 9, 12, 15, 18 and 21. Urine was collected for 2 h after the first morning void at baseline and on day 15. 25(OH)D₂ plasma concentration was measured by ultra-performance liquid chromatography-tandem MS/MS and corrected for baseline. Biomarkers of vitamin D, Ca and P metabolism were measured at baseline and on day 15. The peak plasma concentration of 25(OH)D₂ was 9·6 (sd 0·9) nmol/l at 4·4 (sd 1·8) h. The terminal slope of 25(OH)D₂ disappearance was identified to commence from day 6. The terminal half-life of plasma 25(OH)D₂ was 13·4 (sd 2·7) d. There were no significant differences in plasma 25(OH)D₃, total 1,25(OH)₂D, parathyroid hormone, P, Ca and ionised Ca and urinary Ca and P between baseline and day 15 and between the two groups. The present study provides data on the plasma response to oral 25(OH)D₂ that will underpin and contribute to the further development of studies to investigate 25(OH)D half-life.

Comparison of metabolism of vitamins D2 and D3 in children with nutritional rickets

Children with calcium-deficiency rickets may have increased vitamin D requirements and respond differently to vitamin D(2) and vitamin D(3). Our objective was to compare the metabolism of vitamins D(2) and D(3) in rachitic and control children. We administered an oral single dose of vitamin D(2) or D(3) of 1.25 mg to 49 Nigerian children--28 with active rickets and 21 healthy controls. The primary outcome measure was the incremental change in vitamin D metabolites. Baseline serum 25-hydroxyvitamin D [25(OH)D] concentrations ranged from 7 to 24 and 15 to 34 ng/mL in rachitic and control children, respectively (p < .001), whereas baseline 1,25-dihydroxyvitamin D [1,25(OH)(2)D] values (mean ± SD) were 224 ± 72 and 121 ± 34 pg/mL, respectively (p < .001), and baseline 24,25-dihydroxyvitamin D [24,25(OH)(2)D] values were 1.13 ± 0.59 and 4.03 ± 1.33 ng/mL, respectively (p < .001). The peak increment in 25(OH)D was on day 3 and was similar with vitamins D(2) and D(3) in children with rickets (29 ± 17 and 25 ± 11 ng/mL, respectively) and in control children (33 ± 13 and 31 ± 16 ng/mL, respectively). 1,25(OH)(2)D rose significantly (p < .001) and similarly (p = .18) on day 3 by 166 ± 80 and 209 ± 83 pg/mL after vitamin D(2) and D(3) administration, respectively, in children with rickets. By contrast, control children had no significant increase in 1,25(OH)(2)D (19 ± 28 and 16 ± 38 pg/mL after vitamin D(2) and D(3) administration, respectively). We conclude that in the short term, vitamins D(2) and D(3) similarly increase serum 25(OH)D concentrations in rachitic and healthy children. A marked increase in 1,25(OH)(2)D in response to vitamin D distinguishes children with putative dietary calcium-deficiency rickets from healthy children, consistent with increased vitamin D requirements in children with calcium-deficiency rickets. © 2010 American Society for Bone and Mineral Research.

Vitamin D nutrition and bone disease in adults

The consequences of vitamin D deficiency upon the skeleton are well known and management in the absence of renal failure is relatively straightforward. Vitamin D, either by mouth or parenterally will correct the deficiency and heal the osteomalacia. The mechanisms underlying the causation of vitamin D deficiency are now better understood and indicate the importance of underlying calcium malabsorption and secondary hyperparathyroidism leading to 1,25(OH)2D-induced catabolism of 25(OH)D and possibly also of vitamin D itself. In such situations, e.g., gastrointestinal and pancreaticobiliary disease, calcium supplementation in addition to vitamin D is indicated. The reasons behind nutritional vitamin D deficiency and the possible role of meat in protecting from osteomalacia await further elucidation, but from epidemiological studies, calcium deficiency, per se, is not implicated in the etiopathogenesis. The concept of vitamin D insufficiency is poorly understood, and difficult to define since a single value or close range of serum 25(OH)D values is unlikely to predict the needs of all subjects. Oral calcium intake and renal function are also likely to be relevant to the level of 25(OH)D which is found to be sufficient or insufficient for any given individual to maintain a normal serum calcium level without secondary hyperparathyroidism. There is increasing evidence that vitamin D insufficiency, by leading to sustained hyperparathyroidism, is prejudicial to the skeleton, particularly cortical bone. Since it is without symptoms until fractures occur, it should be actively sought in those clinical situations now recognized as contributing to risk. It can only be identified by the periodic measurement of serum 25(OH)D and the calcitropic hormones PTH and 1,25(OH)2D. In addition, BMD should be measured in a predominantly cortical site such as the proximal forearm, as well as the more conventional sites of spine and hip. The implications of these recommendations are an increase in the use of assays for PTH and vitamin D metabolites in the groups of subjects discussed in this review. Patients with chronic malabsorption states might reasonably be expected to have measurements performed twice-yearly. When vitamin D insufficiency is found, treatment with either vitamin D, calcium or both will be necessary, depending on the etiology of the insufficiency state in the inividual. In some malabsorptive states, calcium malabsorption is the cause of hyperparathyroidism and oral calcium alone can be used to reverse excess PTH activity in those with an adequate state of vitamin D nutrition. However, even in those vitamin D replete individuals, vitamin D catabolism will be enhanced and a small additional oral dose of vitamin D can do no harm. Regular monitoring of PTH and vitamin D metabolites will remain a necessity to ensure continued efficacy of treatment. Current recommendations for dietary supplements of vitamin D are clearly inadequate [61]. There is compelling evidence for supplements of 800 IU per day in the elderly and other high risk populations. Such a dose is safe and without side effects. The available evidence suggests that this should be combined with calcium supplements of 1200 mg/day [19] and that the current UK recommendations for a daily calcium intake of 700 mg contrast with those from the USA at 1,200 mg for people over 50 years old. Physicians need to be aware of both the small but important problem of vitamin D depletion and osteomalacia with its sometimes ambiguous presentation, and the more common but covert vitamin D (and calcium) insufficiency with its widespread and varied clinical associations.