Ivo Jans

Time-related increase of biochemical markers of bone turnover in androgen-deficient male rats

Bone loss during androgen deficiency has been associated with accelerated bone turnover and imbalance between bone formation and resorption but the relative increase of both phenomena is not well described. Serum osteocalcin as marker of bone formation and urinary excretion of pyridinoline (PYD) and deoxypyridinoline (DPD) as markers of bone resorption were measured in both orchidectomized (ORCH, n = 8) and sham-operated (SHAM, n = 8) aged (12-month-old) male rats from 2 days before until 66 days after surgery. PYD and DPD were significantly higher in the ORCH group compared to the SHAM group starting from 21 days after surgery until the end of the experiment. Serum osteocalcin was only significantly increased in the ORCH group at 30 and 40 days. The maximal increase of serum osteocalcin was also smaller than the increase in PYD and DPD (30% versus 74% and 112%, respectively). The two markers of bone resorption were correlated with osteocalcin (r = 0.63 for PYD and r = 0.71 for DPD). Based on these results, we conclude that (1) bone resorption, as measured by PYD and DPD, increased during androgen deficiency; (2) moreover, the increase of bone resorption, as measured by DPD and PYD, was followed by a more moderate increase in bone formation as measured by serum osteocalcin, supporting the hypothesis that androgen deficiency causes accelerated bone turnover and imbalance between bone resorption and bone formation.

Vitamin D metabolites in childhood nephrotic syndrome

We measured serum levels of total and ionised calcium, phosphate, intact parathyroid hormone, 25-hydroxyvitamin D [25(OH)D], 1,25-dihydroxyvitamin D [1,25(OH)2D] and the vitamin D binding protein (DBP) in 14 children with idiopathic nephrotic syndrome and 10 healthy, age-matched controls. In all nephrotics serum DBP levels were below the normal range. Serum 25(OH)D was below 7 ng/ml in 10 of 14 nephrotic children and in the low normal range in the remaining 4 patients. The average serum 1,25(OH)2D levels were lower in the nephrotic patients than in the controls. However, free 1,25(OH)2D levels were normal in the nephrotic patients. Both serum 25(OH)D and 1,25(OH)2D correlated positively with the concentration of DBP There was a significant negative correlation between serum DBP levels and the urinary protein excretion and a significant positive correlation between the urinary excretions of DBP and albumin. From this study it can be concluded that the nephrotic child is capable of maintaining appropriate serum concentrations of free calcitriol despite important urinary losses of both substrate and bound calcitriol.

Active vitamin D (1,25-dihydroxyvitamin D) and bone health in middle-aged and elderly men: The European Male Aging Study (EMAS)

CONTEXT There is little information on the potential impact of serum 1,25-dihydroxyvitamin D [1,25(OH)2D] on bone health including turnover. OBJECTIVE The objective of the study was to determine the influence of 1,25(OH)2D and 25-hydroxyvitamin D [25(OH)D] on bone health in middle-aged and older European men. DESIGN, SETTING, AND PARTICIPANTS Men aged 40-79 years were recruited from population registers in 8 European centers. Subjects completed questionnaires that included questions concerning lifestyle and were invited to attend for quantitative ultrasound (QUS) of the heel, assessment of height and weight, and a fasting blood sample from which 1,25(OH)2D, 25(OH)D, and PTH were measured. 1,25(OH)2D was measured using liquid chromatography tandem mass spectrometry. Bone markers serum N-terminal propeptide of type 1 procollagen (P1NP) and crosslinks (β-cTX) were also measured. Dual-energy x-ray absorptiometry (DXA) of the hip and lumbar spine was performed in 2 centers. MAIN OUTCOME MEASURE(S) QUS of the heel, bone markers P1NP and β-cTX, and DXA of the hip and lumbar spine were measured. RESULTS A total of 2783 men, mean age 60.0 years (SD 11.0) were included in the analysis. After adjustment for age and center, 1,25(OH)2D was positively associated with 25(OH)D but not with PTH. 25(OH)D was negatively associated with PTH. After adjustment for age, center, height, weight, lifestyle factors, and season, 1,25(OH)2D was associated negatively with QUS and DXA parameters and associated positively with β-cTX. 1,25(OH)2D was not correlated with P1NP. 25(OH)D was positively associated with the QUS and DXA parameters but not related to either bone turnover marker. Subjects with both high 1,25(OH)2D (upper tertile) and low 25(OH)D (lower tertile) had the lowest QUS and DXA parameters and the highest β-cTX levels. CONCLUSIONS Serum 1,25(OH)2D is associated with higher bone turnover and poorer bone health despite being positively related to 25(OH)D. A combination of high 1,25(OH)2D and low 25(OH)D is associated with the poorest bone health.

Calcium and bone homeostasis in heterozygous carriers of CYP24A1 mutations: A cross-sectional study.

BACKGROUND Bi-allelic CYP24A1 mutations can cause idiopathic infantile hypercalcemia (IIH), adult-onset nephrocalcinosis, and possibly bone metabolism disturbances. It is currently unclear if heterozygous carriers experience clinical problems or biochemical abnormalities. Our objective is to gain insight in the biochemical profile and health problems in CYP24A1 heterozygotes. STUDY DESIGN Cross-sectional evaluation of participants. Data of previously reported carriers are reviewed. SETTING AND PARTICIPANTS Outpatient clinic of a tertiary care hospital. Participants were eight family members of an infant with a well-characterized homozygous CYP24A1 mutation c.1186C>T p.(Arg396Trp). OUTCOMES Serum vitamin D metabolites. Symptoms or biochemical signs of hypercalcemia, hypercalciuria or nephrocalcinosis. Bone health in heterozygous as compared to wild type (WT) subjects. MEASUREMENTS Genotyping by Sanger sequencing; vitamin D metabolites by liquid chromatography tandem mass spectrometry; renal, calcium and bone markers by biochemical analyses; presence of nephrocalcinosis by renal ultrasound; bone health by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. RESULTS Six participants were heterozygous carriers of the mutation. None of the heterozygous subjects had experienced IIH. One had a documented history of nephrolithiasis, two others had complaints compatible with this diagnosis. No major differences between WT and heterozygous subjects were found regarding bone health, serum or urinary calcium or 25OHD/24,25(OH)2D ratio. Literature reports on three out of 33 heterozygous cases suffering from IIH. In all three, the 25OHD/24,25(OH)2D ratio was highly elevated. Nephrocalcinosis was frequently reported in family members of IIH cases. LIMITATIONS Small sample size, lack of a large control group. CONCLUSIONS Our and literature data suggest that most heterozygous CYP24A1 mutation carriers have a normal 25OHD/24,25(OH)2D ratio, are usually asymptomatic and have a normal skeletal status but may possibly be at increased risk of nephrocalcinosis. A review of the available literature suggests that an elevated 25OHD/24,25(OH)2D ratio may be associated with symptoms of IHH, irrespective of carrier status.

Higher 25(OH)D2 Is Associated With Lower 25(OH)D3 and 1,25(OH)2D3

CONTEXT Despite common use of supplemental vitamin D2 in clinical practice, the associations of serum vitamin D2 concentrations with other vitamin D metabolites and total vitamin D are unclear. OBJECTIVE The aim of the study was to measure vitamin D2 and D3 levels and examine their associations with each other and with total vitamin D. DESIGN We performed a cross-sectional analysis of 679 randomly selected participants from the Osteoporotic Fractures in Men Study. 25-Hydroxyvitamin D2 [25(OH)D2], 25(OH)D3, 1,25-dihydroxyvitamin D2 [1,25(OH)2D2], and 1,25(OH)2D3 were measured using liquid chromatography-tandem mass spectrometry and were summed to obtain total 25(OH)D and 1,25(OH)2D. Associations between all metabolites (D2, D3, and total levels) were examined using Wilcoxon rank-sum tests and Spearman correlations. RESULTS 25(OH)D2 and 1,25(OH)2D2 were detectable in 189 (27.8%) and 178 (26.2%) of the men, respectively. Higher 25(OH)D2 levels did not correlate with higher total 25(OH)D (r = 0.10; P = .17), although median total 25(OH)D was slightly higher in those with detectable vs undetectable 25(OH)D2 (25.8 vs 24.3 ng/mL; P < .001). 25(OH)D2 was not positively associated with total 1,25(OH)2D levels (r = -0.11; P = .13), and median 1,25(OH)2D level was not higher in those with detectable vs undetectable 25(OH)D2. Higher 25(OH)D2 was associated with lower 25(OH)D3 (r = -0.35; P < .001) and 1,25(OH)2D3 (r = -0.32; P < .001), with median levels of both D3 metabolites 18-35% higher when D2 metabolites were undetectable. CONCLUSIONS In a cohort of older men, 25(OH)D2 is associated with lower levels of 25(OH)D3 and 1,25(OH)2D3, suggesting that vitamin D2 may decrease the availability of D3 and may not increase calcitriol levels.

Associations of 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D With Bone Mineral Density, Bone Mineral Density Change, and Incident Nonvertebral Fracture

Relationships between 1,25‐dihydroxyvitamin D (1,25(OH)2D) and skeletal outcomes are uncertain. We examined the associations of 1,25(OH)2D with bone mineral density (BMD), BMD change, and incident non‐vertebral fractures in a cohort of older men and compared them with those of 25‐hydroxyvitamin D (25OHD). The study population included 1000 men (aged 74.6 ± 6.2 years) in the Osteoporotic Fractures in Men (MrOS) study, of which 537 men had longitudinal dual‐energy X‐ray absorptiometry (DXA) data (4.5 years of follow‐up). A case‐cohort design and Cox proportional hazards models were used to test the association between vitamin D metabolite levels and incident nonvertebral and hip fractures. Linear regression models were used to estimate the association between vitamin D measures and baseline BMD and BMD change. Interactions between 25OHD and 1,25(OH)2D were tested for each outcome. Over an average follow‐up of 5.1 years, 432 men experienced incident nonvertebral fractures, including 81 hip fractures. Higher 25OHD was associated with higher baseline BMD, slower BMD loss, and lower hip fracture risk. Conversely, men with higher 1,25(OH)2D had lower baseline BMD. 1,25(OH)2D was not associated with BMD loss or nonvertebral fracture. Compared with higher levels of calcitriol, the risk of hip fracture was higher in men with the lowest 1,25(OH)2D levels (8.70 to 51.60 pg/mL) after adjustment for baseline hip BMD (hazard ratio [HR] = 1.99, 95% confidence interval [CI] 1.19–3.33). Adjustment of 1,25(OH)2D data for 25OHD (and vice versa) had little effect on the associations observed but did attenuate the hip fracture association of both vitamin D metabolites. In older men, higher 1,25(OH)2D was associated with lower baseline BMD but was not related to the rate of bone loss or nonvertebral fracture risk. However, with BMD adjustment, a protective association for hip fracture was found with higher 1,25(OH)2D. The associations of 25OHD with skeletal outcomes were generally stronger than those for 1,25(OH)2D. These results do not support the hypothesis that measures of 1,25(OH)2D improve the ability to predict adverse skeletal outcomes when 25OHD measures are available.

Need for Estradiol Assays With a Lower Functional Sensitivity in Clinical Studies Examining Postmenopausal Women Treated With Aromatase Inhibitors

TO THE EDITOR: In their recently published study, Folkerd et al found that in postmenopausal women with early estrogen receptor– positive breast cancer who are treated with aromatase inhibitors (AIs), suppressed levels of estradiol and estrone sulfate are related to body mass index. If confirmed, this observation is of great interest, not only because it would explain why treatment with an AI results in a better outcome compared with tamoxifen in lean patients but not in obese patients, but also because it might open the way toward individualized AI treatment by adapting the dose of AIs on the basis of the plasma estradiol and estrone sulfate concentration. Although the measurement of AIs using mass spectrometry is not so difficult, the measurement of estrogens, particularly estradiol, is quite challenging. As reported by the authors, most on-treatment values for estradiol were below 3 pmol/L, which was the “conventional sensitivity” limit of the assay used. Conventional sensitivity was defined by the authors as the 95% CI of the zero standard, which corresponds more or less to the limit of blank (LoB) as defined by the Clinical and Laboratory Standards Institute. The LoB is the highest apparent analyte concentration that is expected to be found when replicates of a sample containing no analyte are tested. The limit of detection is the lowest analyte concentration likely to be reliably distinguished from the LoB and at which detection is feasible. The limit of quantitation, which is defined as the lowest concentration at which the analyte can not only be reliably detected but also measured with an acceptable degree of imprecision, is usually significantly higher (and cannot be lower) than the LoB and the limit of detection. Functional sensitivity is usually defined as the concentration that results in a coefficient of variation (CV) of 20%. The authors reported a between-run CV of 12% for a concentration of 37 pmol/L for their estradiol assay, suggesting that the functional sensitivity of their assay is significantly higher than 3 pmol/L, given that the CV increases exponentially around the limit of quantitation. Such a functional sensitivity is insufficient to allow a reliable quantification of estradiol concentrations in individual postmenopausal women who are treated with AIs. For estrone sulfate, there is a similar problem, although to a lesser extent. The functional sensitivity is most likely also significantly higher than 15 pmol/L, given that the authors reported a CV of 11% at 130 pmol/L, but in contrast to estradiol, a majority of on-treatment values were above the conventional sensitivity defined by the authors. Toexaminetherelationbetweenestrogenconcentration,bodymass index, and outcome, and to open the way toward individualized AI treatment, clinical studies should use estrogen assays with a better functional sensitivity, particularly for estradiol. Unfortunately, the only estradiol assays that currently have a functional sensitivity of less than 3 pmol/L are labor-intensivemassspectrometrymethodsthatrequireextensivesample pretreatmentincludingliquid/liquidextraction.Asimplemassspectrometrymethodnotrequiring liquid/liquidextraction,derivatization,or large volumes of serum (eg, 500 L) is therefore needed.

Arthralgia induced by endocrine treatment for breast cancer: A prospective study of serum levels of insulin like growth factor-I, its binding protein and oestrogens

BACKGROUND Aromatase inhibitors (AIs) frequently induce or enhance musculoskeletal problems (AI-induced musculoskeletal syndrome (AIMSS)) which sometimes are debilitating. Apart from low oestrogen levels, underlying mechanisms are unknown and likely multiple. We previously hypothesised a role for the growth hormone/insulin like growth factor-I (IGF-I) axis. Here, we report the effect of tamoxifen and AI on IGF-I, IGF binding protein-3 (IGFBP-3) and oestrogen levels from a prospective study. MATERIALS AND METHODS Postmenopausal women with an early breast cancer scheduled to start adjuvant endocrine therapy with an AI or tamoxifen were recruited. A rheumatologic questionnaire was completed and serum was collected for assessment of IGF-I, IGFBP-3 and oestrogen levels. Re-evaluation was done after 3, 6 and 1 2months of therapy. RESULTS 84 patients started on tamoxifen (n=42) or an AI (n=42). 66% of the latter group experienced worsening of pre-existing or de novo complaints in joint and/or muscle, compared to 29% of tamoxifen-treated patients. AI therapy resulted in elevated IGF-I levels with a statistically significant increase at 6months (p=0.0088), whereas tamoxifen users were characterised by a decrease in IGF-I levels at all follow-up times (p<0.0004). No effect on IGFBP-3 was seen in the latter group. AI-users, however, showed decreased IGFBP-3 levels at 12 months (p=0.0467). AIMSS was characterised by a decrease in IGFBP-3 levels (p=0.0007) and a trend towards increased IGF-I/IGFBP-3 ratio (p=0.0710). CONCLUSION These findings provide preliminary evidence that AI-induced musculoskeletal symptoms are associated with changes in the growth hormone (GH)/IGF-I axis.

Serum β-2 microglobulin is a marker of high bone remodelling in elderly women

Abstract β -2 microglobulin ( β 2m), the water soluble extrinsic light chain of class I MHC, has been recently isolated from the adult bone culture medium. Serum β 2m plays a role as a bone-derived growth factor regulating both osteoblast and osteoclast cell activity. Serum β 2m has been proposed as a bone remodeling biological marker in high bone turnover conditions. The purpose of our study was to determine the relationship between β 2m and vitamin D status in post-menopausal women. We have studied 44 healthy women from 20 to 80 years with normal hepatic and renal function, without diabetes mellitus and/or inflammatory, tumoral or infectious diseases. We measured the serum levels of calcium, phosphorus, parathyroid hormone (PTH), vitamin D binding protein (DBP), 25-OHD 3 (calcidiol), 1,25(OH) 2 D 3 (calcitriol) and β 2m. Serum β 2m levels increased with age ( r =0.54, P β 2m (1.76±0.22 mg/l vs. 1.35±0.2 mg/l, P P 3 (7.5±2.3 ng/ml vs. 18.2±2.5 ng/ml, P β 2m were negatively correlated with 25-OHD 3 ( r =−0.34, P r =−0.45, P r =0.48, P β 2m as a regulator of bone metabolism and its potential use as a marker of high bone turnover in post-menopausal women, specially in elderly women with vitamin D deficiency and secondary hyperparathyroidism.

1β,25-Dihydroxyvitamin D3: A new vitamin D metabolite in human serum

BACKGROUND The measurement of 1α,25(OH)2D3 in human serum poses a true challenge as concentrations are very low and structurally similar metabolites can interfere. MATERIALS AND METHODS During optimization of our in-house LC-MSMS method for serum 1α,25(OH)2D3 a previously co-eluting isobaric interference was separated. The isobar was identified as 1β,25(OH)2D3 by comparing retention time and fragmentation spectra to standards (other isobaric dihydroxylated vitamin D3 analogs). 1β,25(OH)2D3 showed specific cluster formation (water), not present in 1α,25(OH)2D3. 1β,25(OH)2D3 was measured in serum of apparently healthy human volunteers (n=20), patients with high serum 25-hydroxyvitamin D [25(OH)D] concentrations (>50ng/mL) (n=33 among which 4 with very high levels (>150ng/mL)) and patients with kidney failure (n=68; 39 stage 1-3, 29 stage 4-5). Pearsons r was calculated for correlations and Mann-Whitney statistic to compare group medians. RESULTS Median serum 1β,25(OH)2D3 was 11pg/mL in apparently healthy volunteers and increased to 20pg/mL for serum 25(OH)D concentrations above 80ng/mL (n=22) (p<0.0001). 1β,25(OH)2D3 concentrations were significantly correlated to serum 25(OH)D concentrations (r=0.85) for the combined results from healthy volunteers and patient sera (n=53) (p<0.0001). For patients with kidney failure, median serum 1β,25(OH)2D3 was 7pg/mL and not different from the median level in healthy volunteers (p=0.06). The median concentration did not vary with different stages. CONCLUSIONS We present evidence for the widespread presence of 1β,25(OH)2D3, a new vitamin D metabolite, in human serum. The level increases with rising serum 25(OH)D concentrations and is particularly high in patients with very high 25(OH)D levels. We previously demonstrated that 1β,25(OH)2D3 is a poor genomic agonist but a potent non-genomic antagonist of 1α,25(OH)2D3. The clinical implications of the presence of this analog therefore require further exploration.