Acute C-Terminal Crosslinking Telopeptide of Type I Collagen (CTX-1) Suppression with Milk Calcium or Calcium Carbonate Is Independent of Visceral Fat in a Randomized Crossover Study in Lean and Overweight Postmenopausal Women.

BACKGROUND: Postmenopausal women with higher visceral adipose tissue (VAT) present with suppressed bone resorption (lower C-terminal crosslinking telopeptide of type I collagen; CTX-1) and turnover (lower osteocalcin) but whether this blunts the effect of calcium is unknown. OBJECTIVES: The primary outcome of this study was the effect of VAT on changes in CTX-1 after intake of 2 forms of calcium. Secondary outcomes included changes in parathyroid hormone (PTH), serum calcium, phosphorus, and alkaline phosphatase (ALP). METHODS: Randomized open three period crossover trial conducted between 2017 and 2019 at the University of South Australia among 77 lean and overweight postmenopausal women (53-79 y) with BMI <25 kg/m2 and >27 kg/m2, respectively. Participants received a single dose of milk (1000 mg calcium), calcium carbonate tablet (1000 mg calcium), and fruit juice (no calcium) in random order with a 7-d washout period. Blood samples were collected at baseline and hourly for 5 h. Data was analyzed by repeated measures ANOVA of log-transformed data. RESULTS: At baseline, women with higher VAT had significantly lower CTX-1 and higher PTH (44% lower and 30% higher, respectively, between Q4 and Q1, P < 0.0001). VAT had no influence on the acute changes in CTX-1 or PTH with calcium or juice. A suppression of 44% in CTX-1 was seen with calcium carbonate and milk and a suppression of 18% with juice. PTH was suppressed more with calcium carbonate (47%) compared to milk (22%). Milk calcium reduced PTH and CTX-1 at 2 h, whereas calcium carbonate reduced PTH in 1 h. The suppression in CTX-1 was slower with lowest concentrations at 4-5 h. CONCLUSIONS: Intake of 1000 mg calcium from milk or from calcium carbonate is effective in acutely suppressing bone resorption in postmenopausal women irrespective of visceral fat. This trial is registered at http://www.ANZCTR.org.au/ACTRN12617000779370.aspx as ACTRN 12617000779370).

Acute C-Terminal Crosslinking Telopeptide of Type I Collagen (CTX-1) Suppression with Milk Calcium or Calcium Carbonate Is Independent of Visceral Fat in a Randomized Crossover Study in Lean and Overweight Postmenopausal Women.

BACKGROUND: Postmenopausal women with higher visceral adipose tissue (VAT) present with suppressed bone resorption (lower C-terminal crosslinking telopeptide of type I collagen; CTX-1) and turnover (lower osteocalcin) but whether this blunts the effect of calcium is unknown. OBJECTIVES: The primary outcome of this study was the effect of VAT on changes in CTX-1 after intake of 2 forms of calcium. Secondary outcomes included changes in parathyroid hormone (PTH), serum calcium, phosphorus, and alkaline phosphatase (ALP). METHODS: Randomized open three period crossover trial conducted between 2017 and 2019 at the University of South Australia among 77 lean and overweight postmenopausal women (53-79 y) with BMI <25 kg/m2 and >27 kg/m2, respectively. Participants received a single dose of milk (1000 mg calcium), calcium carbonate tablet (1000 mg calcium), and fruit juice (no calcium) in random order with a 7-d washout period. Blood samples were collected at baseline and hourly for 5 h. Data was analyzed by repeated measures ANOVA of log-transformed data. RESULTS: At baseline, women with higher VAT had significantly lower CTX-1 and higher PTH (44% lower and 30% higher, respectively, between Q4 and Q1, P < 0.0001). VAT had no influence on the acute changes in CTX-1 or PTH with calcium or juice. A suppression of 44% in CTX-1 was seen with calcium carbonate and milk and a suppression of 18% with juice. PTH was suppressed more with calcium carbonate (47%) compared to milk (22%). Milk calcium reduced PTH and CTX-1 at 2 h, whereas calcium carbonate reduced PTH in 1 h. The suppression in CTX-1 was slower with lowest concentrations at 4-5 h. CONCLUSIONS: Intake of 1000 mg calcium from milk or from calcium carbonate is effective in acutely suppressing bone resorption in postmenopausal women irrespective of visceral fat. This trial is registered at http://www.ANZCTR.org.au/ACTRN12617000779370.aspx as ACTRN 12617000779370).

Adiposity and estrogen receptor-positive, postmenopausal breast cancer risk: Quantification of the mediating effects of fasting insulin and free estradiol.

Adiposity increases estrogen receptor (ER)-positive postmenopausal breast cancer risk. While mechanisms underlying this relationship are uncertain, dysregulated sex-steroid hormone production and insulin signaling are likely pathways. Our aim was to quantify mediating effects of fasting insulin and free estradiol in the adiposity and ER-positive postmenopausal breast cancer association. We used data from a case-cohort study of sex hormones and insulin signaling nested within the Melbourne Collaborative Cohort Study. Eligible women, at baseline, were not diagnosed with cancer, were postmenopausal, did not use hormone therapy and had no history of diabetes or diabetes medication use. Women with ER-negative disease or breast cancer diagnosis within the first follow-up year were excluded. We analyzed the study as a cumulative sampling case-control study with 149 cases and 1,029 controls. Missing values for insulin and free estradiol were multiply imputed with chained equations. Interventional direct (IDE) and indirect (IIE) effects were estimated using regression-based multiple-mediator approach. For women with body mass index (BMI) >30 kg/m2 compared to women with BMI 18.5-25 kg/m2 , the risk ratio (RR) of breast cancer was 1.75 (95% confidence interval [CI] 1.05-2.91). The estimated IDE (RR) not through the mediators was 1.03 (95% CI 0.43-2.48). Percentage mediated effect through free estradiol was 72% (IIE-RR 1.56; 95% CI 1.11-2.19). There was no evidence for an indirect effect through insulin (IIE-RR 1.12; 95% CI 0.68-1.84; 28% mediated). Our results suggest that circulating free estradiol plays an important mediating role in the adiposity-breast cancer relationship but does not explain all of the association.

The associations of anthropometric, behavioural and sociodemographic factors with circulating concentrations of IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3 in a pooled analysis of 16,024 men from 22 studies.

Insulin-like growth factors (IGFs) and insulin-like growth factor binding proteins (IGFBPs) have been implicated in the aetiology of several cancers. To better understand whether anthropometric, behavioural and sociodemographic factors may play a role in cancer risk via IGF signalling, we examined the cross-sectional associations of these exposures with circulating concentrations of IGFs (IGF-I and IGF-II) and IGFBPs (IGFBP-1, IGFBP-2 and IGFBP-3). The Endogenous Hormones, Nutritional Biomarkers and Prostate Cancer Collaborative Group dataset includes individual participant data from 16,024 male controls (i.e. without prostate cancer) aged 22-89 years from 22 prospective studies. Geometric means of protein concentrations were estimated using analysis of variance, adjusted for relevant covariates. Older age was associated with higher concentrations of IGFBP-1 and IGFBP-2 and lower concentrations of IGF-I, IGF-II and IGFBP-3. Higher body mass index was associated with lower concentrations of IGFBP-1 and IGFBP-2. Taller height was associated with higher concentrations of IGF-I and IGFBP-3 and lower concentrations of IGFBP-1. Smokers had higher concentrations of IGFBP-1 and IGFBP-2 and lower concentrations of IGFBP-3 than nonsmokers. Higher alcohol consumption was associated with higher concentrations of IGF-II and lower concentrations of IGF-I and IGFBP-2. African Americans had lower concentrations of IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3 and Hispanics had lower IGF-I, IGF-II and IGFBP-3 than non-Hispanic whites. These findings indicate that a range of anthropometric, behavioural and sociodemographic factors are associated with circulating concentrations of IGFs and IGFBPs in men, which will lead to a greater understanding of the mechanisms through which these factors influence cancer risk.

A multicenter study to evaluate harmonization of assays for N-terminal propeptide of type I procollagen (PINP): a report from the IFCC-IOF Joint Committee for Bone Metabolism.

Background Biochemical bone turnover markers (BTM) are useful tools to assess bone remodeling at the cellular level. N-terminal propeptide of type I procollagen (PINP) has been recommended as a reference marker for bone formation in research studies. Methods We describe the results of a multicenter study for routine clinical laboratory assays for PINP in serum and plasma. Four centers (Athens, Greece [GR], Copenhagen, Denmark [DK], Liege, Belgium [BE] and Sheffield, United Kingdom [UK]) collected serum and plasma (EDTA) samples from 796 patients presenting to osteoporosis clinics. Specimens were analyzed in duplicate with each of the available routine clinical laboratory methods according to the manufacturers' instructions. Passing-Bablok regressions, Bland-Altman plots, V-shape evaluation method and the concordance correlation coefficient for PINP values between serum and plasma specimens and between methods were used to determine the agreement between results. A generalized linear model was employed to identify possible variables that affected the relationship between the methods. Results We showed that both EDTA plasma and serum were suitable for PINP determination. We observed a significant proportional bias between Orion radioimmunoassay and the automated methods for PINP (Roche Cobas and IDS iSYS), which both gave very similar results. The multivariate model did not improve the excellent correlation that was observed between the methods. Conclusions Harmonization of PINP assays is possible by applying a correction factor or correctly assigning the values of the calibrators. This work will benefit from further collaboration between assays manufacturers and clinical laboratory professionals.

Combination breast cancer chemotherapy with doxorubicin and cyclophosphamide damages bone and bone marrow in a female rat model.

PURPOSE: Anthracyclines (including doxorubicin) are still the backbone of commonly used breast cancer chemotherapy regimens. Despite increasing use of doxorubicin and cyclophosphamide (AC) combinations for treating breast cancer, their potential to cause adverse skeletal effects remains unclear. METHODS: This study examined the effects of treatments with the AC regimen on bone and bone marrow in adult female rats. RESULTS: AC treatment for four cycles (weekly intravenous injection of 2 mg/kg doxorubicin and 20 mg/kg cyclophosphamide) resulted in a reduced volume of trabecular bone at the metaphysis, which was associated with reduced serum levels of 25-hydroxy vitamin D3 and alkaline phosphatase. Reductions in densities of osteocytes and bone lining cells were also observed. In addition, bone marrow was severely damaged, including a severe reduction in bone marrow cellularity and an increase in marrow adipocyte content. Accompanying these changes, there were increases in mRNA expression of adipogenesis regulatory genes (PPARγ and FABP4) and an inflammatory cytokine (TNFα) in metaphysis bone and bone marrow. CONCLUSIONS: This study indicates that AC chemotherapy may induce some bone loss, due to reduced bone formation, and bone marrow damage, due to increased marrow adiposity. Preventive strategies for preserving the bone and bone marrow microenvironment during anthracycline chemotherapy warrant further investigation.

Vitamin D: can you have too much of a good thing in chronic kidney disease?

Recommendation of vitamin D supplements is common although there is little information regarding the definition of the upper limit of safety. Kusunoki et al. now publish interesting data of a novel mechanism by which excess 25-hydroxyvitamin D exerts adverse effects on the kidney, using unilateral ureteral obstruction in the mouse as a model of kidney disease. Their report provides a new mechanism to be assessed as a surrogate measure of vitamin D toxicity that may be clinically relevant.

Acute effect of a supplemented milk drink on bone metabolism in healthy postmenopausal women is influenced by the metabolic syndrome.

BACKGROUND: Dietary factors acutely influence the rate of bone resorption, as demonstrated by changes in serum bone resorption markers. Dietary calcium exerts its effect by reducing parathyroid hormone levels while other components induce gut incretin hormones both of which reduce bone resorption markers. The impact of dietary calcium on bone turnover when energy metabolism is modulated such as in metabolic syndrome has not been explored. This study was designed investigate whether metabolic syndrome or a greater amount of visceral fat influences the impact of dietary calcium on bone turnover. METHODS: The influence of the metabolic syndrome on effects of dietary calcium on bone turnover in community dwelling postmenopausal women was studied. Twenty five volunteers consumed 200 mL of low fat milk with additional 560 mg calcium (one serve of Milo®) in the evening on one occasion. Fasting morning serum biochemistry before and after the milk drink with lumber spine bone density, bone mineral content, fat and lean mass using dual energy X-ray absorptiometry (DXA) and waist circumference were measured. The women were divided into 2 groups using the waist measurement of 88 cm, as a criterion of metabolic syndrome. Student's t tests were used to determine significant differences between the 2 groups. RESULTS: The lumbar spine mineral content was higher in women with metabolic syndrome. After consuming the milk drink, serum bone resorption marker C terminal telopeptide (CTX) was suppressed to a significant extent in women with metabolic syndrome compared to those without. CONCLUSIONS: The results suggests that dietary calcium may exert a greater suppression of bone resorption in post-menopausal women with metabolic syndrome than healthy women. Despite substantial evidence for close links between energy metabolism and bone metabolism this is the first report suggesting visceral fat or metabolic syndrome may influence the effects of dietary calcium on bone metabolism.

A meta-analysis of reference markers of bone turnover for prediction of fracture.

The aim of this report was to summarize the clinical performance of two reference bone turnover markers (BTMs) in the prediction of fracture risk. We used an updated systematic review to examine the performance characteristics of serum procollagen type I N propeptide (s-PINP) and serum C-terminal cross-linking telopeptide of type I collagen (s-CTX) in fracture risk prediction in untreated individuals in prospective cohort studies. We excluded cross-sectional studies. Ten potentially eligible publications were identified and six included in the meta-analysis. There was a significant association between s-PINP and the risk of fracture. The hazard ratio per SD increase in s-PINP (gradient of risk [GR]) was 1.23 (95 % CI 1.09-1.39) for men and women combined unadjusted for bone mineral density. There was also a significant association between s-CTX and risk of fracture, GR = 1.18 (95 % CI 1.05-1.34) unadjusted for bone mineral density. For the outcome of hip fracture, the association between s-CTX and risk of fracture was slightly higher, 1.23 (95 % CI 1.04-1.47). Thus, there is a modest but significant association between BTMs and risk of future fractures.

Efficacy and mechanisms of action of vitamin D in experimental polyarthritis.

Vitamin D (vit D) status has been linked to the occurrence and severity of auto-immune and inflammatory diseases. This study evaluates the effects of vit D status on adoptive transfer of adjuvant-induced arthritis (ATA). Rats maintained on diets replete or deficient in vit D3 received arthritogenic thoracic duct cells and were monitored for severity of arthritis. CD45(+) cells obtained by collagenase digestion of hind-paw synovium-rich tissues (SRTs) were analysed to observe the effects of dietary vit D3 on the inflammatory process. Arthritis was more severe in vitamin D-deficient (vit-D(-)) rats compared with vitamin D-replete (vit-D(+)) rats. Resolution was delayed in vit-D(-) rats compared with vit-D(+) rats, or rats fed standard chow. During the acute phase of ATA, numbers of CD45(+) cells were significantly increased in the SRTs of vit-D(-) rats compared with vit-D(+) rats. This increase involved T-cells, polymorphonuclear leukocytes, macrophages, dendritic cells (DCs) and MHC II(hi) cells that resemble activated monocytes. A major difference between the dietary groups was that most DCs at the peak of inflammation in vit-D(-) rats were CD4(-), whereas in convalescent vit-D(+) rats most expressed CD4. Multiple categories of genes expressed by DCs differed between deficient and replete rats, with deficiency being associated with relative upregulation of certain pro-inflammatory genes and replete status being associated with upregulation of genes associated with resolution of inflammation. The findings indicate that ATA is more severe and prolonged in vit-D deficiency, that vit-D deficiency promotes accumulation of CD4(-) DCs in synovium during ATA and that a gene-expression profile is likely to contribute to the observed increased severity and duration of arthritis.

Second to fourth digit ratio (2D:4D) and concentrations of circulating sex hormones in adulthood.

BACKGROUND: The second to fourth digit ratio (2D:4D) is used as a marker of prenatal sex hormone exposure. The objective of this study was to examine whether circulating concentrations of sex hormones and SHBG measured in adulthood was associated with 2D:4D. METHODS: This analysis was based on a random sample from the Melbourne Collaborative Cohort Study. The sample consisted of of 1036 men and 620 post-menopausal women aged between 39 and 70 at the time of blood draw. Concentrations of circulating sex hormones were measured from plasma collected at baseline (1990-1994), while digit length was measured from hand photocopies taken during a recent follow-up (2003-2009). The outcome measures were circulating concentrations of testosterone, oestradiol, dehydroepiandrosterone sulphate, androstenedione, Sex Hormone Binding Globulin, androstenediol glucoronide for men only and oestrone sulphate for women only. Free testosterone and oestradiol were estimated using standard formulae derived empirically. Predicted geometric mean hormone concentrations (for tertiles of 2D:4D) and conditional correlation coefficients (for continuous 2D:4D) were obtained using mixed effects linear regression models. RESULTS: No strong associations were observed between 2D:4D measures and circulating concentrations of hormones for men or women. For males, right 2D:4D was weakly inversely associated with circulating testosterone (predicted geometric mean testosterone was 15.9 and 15.0 nmol/L for the lowest and highest tertiles of male right 2D:4D respectively (P-trend = 0.04). There was a similar weak association between male right 2D:4D and the ratio of testosterone to oestradiol. These associations were not evident in analyses of continuous 2D:4D. CONCLUSIONS: There were no strong associations between any adult circulating concentration of sex hormone or SHGB and 2D:4D. These results contribute to the growing body of evidence indicating that 2D:4D is unrelated to adult sex hormone concentrations.

International Osteoporosis Foundation and International Federation of Clinical Chemistry and Laboratory Medicine position on bone marker standards in osteoporosis.

The International Osteoporosis Foundation (IOF) and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Working Group on Bone Marker Standards (WG-BMS) has evaluated the clinical potential of bone turnover markers (BTMs) in the prediction of fracture risk and for monitoring treatment. Research evidence suggests that BTMs may provide information on fracture risk independently from BMD, so that fracture risk prediction might be enhanced by their inclusion in assessment algorithms. The potential use of BTMs to predict the response to treatments for osteoporosis in the individual patient is also of great interest. Treatment-induced changes in specific markers account for a substantial proportion of fracture risk reduction. However, there is still a need for stronger evidence on which to base practice in both situations. IOF/IFCC recommends one bone formation marker (serum procollagen type I N propeptide, s-PINP) and one bone resorption marker (serum C-terminal cross-linking telopeptide of type I collagen, s-CTX) to be used as reference markers and measured by standardised assays in observational and intervention studies in order to enlarge the international experience of the application of markers to clinical medicine and to help resolve uncertainties over their clinical use.

Vitamin D insufficiency in Aboriginal Australians.

OBJECTIVE: To investigate the adequacy of vitamin D status in a South Australian Aboriginal population, and to examine the relationship between serum 25-hydroxyvitamin D (25-OHD) levels and biochemical variables of calcium and bone mineral homeostasis, as well as other factors which may influence vitamin D synthesis, storage and metabolism. DESIGN, SETTING AND PARTICIPANTS: A single-visit, observational study of 58 adults from two Aboriginal community-controlled health services in Adelaide and Yalata, South Australia. Participants were recruited between May 2008 and December 2009. MAIN OUTCOME MEASURES: Serum levels of 25-OHD, parathyroid hormone (PTH), fasting glucose and fasting C-terminal telopeptides of type I collagen (ß-CTx). RESULTS: Serum 25-OHD levels showed clear seasonal variation, being higher in summer (P < 0.001). The overall mean level was 56.8 nmol/L (SD, 22.1), which is below the recommended target level of 60 nmol/L. Serum 25-OHD levels correlated significantly with ß-CTx (P = 0.03), but not with age, body mass index (BMI), PTH levels or levels of fasting glucose. A significant association was found between BMI and PTH levels (P = 0.001). A significant inverse association between serum 25-OHD levels and BMI, observed in other studies, was not found in our study. CONCLUSIONS: Vitamin D insufficiency is highly prevalent in this population of adult Aboriginal Australians, with low mean values found in all seasons other than summer.

Visceral Fat Is a Negative Determinant of Bone Health in Obese Postmenopausal Women.

The protective effect of obesity on bone health has been challenged by studies that link visceral adiposity to poor bone microarchitecture in young obese men and women. In postmenopausal women, the role of visceral adipose tissue (VAT) on bone turnover markers (BTMs) has not been investigated. The aim was to investigate the impact of VAT on BTMs, total bone mineral density (BMD), vitamin D metabolites and parathyroid levels (1-84 PTH) levels in postmenopausal women. A total of 76 lean and overweight women (without osteoporosis) underwent VAT measurements by dual-energy X-ray absorptiometry (iDXA). Blood samples were analyzed for serum C-terminal telopeptide of type 1 collagen (CTX-1), osteocalcin, bone-specific alkaline phosphatase (bone ALP), 1-84 PTH and vitamin D (25 hydroxyvitamin D, 25(OH)D) levels. VAT volumes ranged from 91 to 3392 cm3 and body mass index (BMI) ranged from 18.3 to 53.9 kg/m2. Women in the highest VAT quartile had significantly lower CTX-1, 25(OH)D, osteocalcin and the highest BMD (p < 0.05, for all). While VAT positively associated with BMD, after controlling for BMI, VAT was a negative predictor of BMD (ß = 0.368, p < 0.05). VAT was an independent negative predictor of CTX-1 (ß = -0.263, p < 0.05) and osteocalcin levels (ß = -0.277, p < 0.05). Among all measures of adiposity, VAT was the strongest independent determinant of BMD and BTMs. In clinical settings, VAT, and not BMI, may be a sensitive predictor of bone health in obese women.

Obesity, vitamin D status and physical activity: 1,25(OH)2D as a potential marker of vitamin D deficiency in obese subjects.

BACKGROUND: Obesity has been regarded to be protective against fracture in spite of its association with low levels of vitamin D. Vitamin D is the key regulator of bone metabolism and its deficiency contributes to higher level of parathyroid hormone (PTH), leading to the activation of bone turnover. METHODS: We studied 161 subjects of which 65 were young healthy subjects and 96 were elderly subjects. We measured creatinine, 25(OH)D, 1,25(OH)2D, PTH, albumin, and calcium plasma levels, we evaluated physical activity, and we calculated BMI. A sub-cohort of elderly subjects also underwent DXA scans. RESULTS: Overweight and obese subjects, as well as underweight ones, had lower levels of vitamin D but normal serum concentrations of 1,25(OH)2D and PTH was higher in underweight and obese subjects. Moreover, we found a nonlinear relationship between body mass index (BMI) and PTH with a significant U-shaped exponential regression. Regardless of BMI, 25(OH)D mean levels were higher in subjects who practice physical activity. CONCLUSIONS: These findings suggest that physical activity and BMI had a significant effect on the metabolism of bone and vitamin D, but the effect of BMI was different in underweight, normal weight or obese subjects. In obesity the real vitamin D deficiency could be estimate by serum 1,25(OH)2D concentrations whose lower levels contribute to the higher PTH production and consequently to bone loss and to a greater fracture risk.

Widespread vitamin D deficiency and its sex-specific association with adiposity in Chinese children and adolescents.

OBJECTIVES: Vitamin D is involved in various physiologic and pathologic processes in the human body. The aim of this study was to determine the prevalence of vitamin D deficiency and the association of adiposity indicators with 25-hydroxyvitamin D (25[OH]D) in Chinese children and adolescents. METHODS: This was a population-based, nationwide, multicenter cross-sectional study involving 10 696 participants (51.2% boys) 6 to 18 y of age. Total body fat mass was assessed by dual-energy x-ray absorptiometry, and measures of body mass index (BMI), fat mass index (FMI), fat mass percentage (FMP), and plasma 25(OH)D concentrations were obtained. RESULTS: The adjusted mean of 25(OH)D was 39.3 nmol/L for all participants, 40.7 nmol/L for boys, and 37.9 nmol/L for girls. Of the children, 30% had vitamin D deficiency (25[OH]D <30 nmol/L) and 80% had vitamin D insufficiency (25[OH]D <50 nmol/L). The prevalence rates of vitamin D deficiency and insufficiency were higher in girls (31%, 83.4%, respectively) than in boys (22.8%, 78.7%, respectively). An L-shape relationship between age and 25(OH)D was observed in all children, with a threshold age of 14 y. Also, there was an inverted U-shaped association of BMI with 25(OH)D, and multivariable linear models shown FMI and FMP were inversely associated with 25(OH)D concentrations, particularly in boys (ß = -0.86 and -0.83, respectively, all P < 0.05). CONCLUSIONS: Vitamin D deficiency was widespread and its sex-specific association with an excess of body fat in Chinese children and adolescents. The findings indicate that targeted screening and treatment guidelines may be useful.

Circulating steroid hormone concentrations in postmenopausal women in relation to body size and composition.

Steroid hormones are associated with the risk of postmenopausal breast cancer and evidence suggests that increased concentrations of oestrogens from peripheral aromatisation in adipose tissue partly explains the association between body mass index (BMI) and risk of postmenopausal breast cancer. This study examined the associations between circulating concentrations of steroid hormones and anthropometric measurements in a sample of naturally postmenopausal women from the Melbourne Collaborative Cohort Study, not using hormone replacement therapy. We measured plasma concentration of total oestradiol, oestrone sulphate, dehydroepiandrosterone sulphate, androstenedione, testosterone and sex hormone binding globulin (SHBG) and calculated concentration of free oestradiol. Body measurements included height, weight, BMI, waist circumference, fat mass and fat-free mass, the last two estimated by bioelectrical impedance analysis. BMI was positively associated with both oestrogens and androgens and negatively with SHBG. Fat mass was the principal measure responsible for the association observed between body size and total oestradiol. The associations between oestrone sulphate and androgens and body size were mainly with waist circumference. The associations between oestrogens and body size were close to null for the first 6 years since menopause and became positive thereafter. Our results are compatible with the hypothesis that after the menopause excess fat mass increases oestrogen concentrations through the peripheral aromatisation of androgens in adipose tissue. This effect requires around 6 years to be detectable by way of circulating steroid hormone levels.

Calcium malabsorption does not cause secondary hyperparathyroidism.

We challenge the widespread assumption that malabsorption of calcium per se causes secondary hyperparathyroidism. Serum parathyroid hormone (PTH) does not rise at the menopause despite the fall in calcium absorption, nor is it raised in osteoporotic women with vertebral fractures despite their low calcium absorption. The age-related rise in serum PTH can be accounted for by the age-related fall in serum 25(OH)D and/or decline in renal function with consequent loss of the calcemic action of vitamin D on bone. The reference interval for serum PTH is established in the fasting state when it is at the top of its diurnal cycle and is maintaining serum ionized calcium at the expense of bone to meet the calcium being lost through skin, bowel, and kidneys. There is no evidence that the fasting PTH is influenced by the previous day's intake or absorption of calcium, although it can be lowered by a large evening calcium supplement. Malabsorption of calcium-like dietary calcium deficiency-is a risk factor for osteoporosis because it reduces or prevents the normal food-related daytime fall in PTH and bone resorption, not because it causes secondary hyperparathyroidism.

Amylin inhibits bone resorption while the calcitonin receptor controls bone formation in vivo.

Amylin is a member of the calcitonin family of hormones cosecreted with insulin by pancreatic beta cells. Cell culture assays suggest that amylin could affect bone formation and bone resorption, this latter function after its binding to the calcitonin receptor (CALCR). Here we show that Amylin inactivation leads to a low bone mass due to an increase in bone resorption, whereas bone formation is unaffected. In vitro, amylin inhibits fusion of mononucleated osteoclast precursors into multinucleated osteoclasts in an ERK1/2-dependent manner. Although Amylin +/- mice like Amylin-deficient mice display a low bone mass phenotype and increased bone resorption, Calcr +/- mice display a high bone mass due to an increase in bone formation. Moreover, compound heterozygote mice for Calcr and Amylin inactivation displayed bone abnormalities observed in both Calcr +/- and Amylin +/- mice, thereby ruling out that amylin uses CALCR to inhibit osteoclastogenesis in vivo. Thus, amylin is a physiological regulator of bone resorption that acts through an unidentified receptor.

The Late Osteoblast/Preosteocyte Cell Line MLO-A5 Displays Mesenchymal Lineage Plasticity In Vitro and In Vivo.

The process of osteoblast switching to alternative mesenchymal phenotypes is incompletely understood. In this study, we tested the ability of the osteoblast/preosteocyte osteogenic cell line, MLO-A5, to also differentiate into either adipocytes or chondrocytes. MLO-A5 cells expressed a subset of skeletal stem cell markers, including Sca-1, CD44, CD73, CD146, and CD166. Confluent cultures of cells underwent differentiation within 3 days upon the addition of osteogenic medium. The same cultures were capable of undergoing adipogenic and chondrogenic differentiation under lineage-appropriate culture conditions, evidenced by lineage-specific gene expression analysis by real-time reverse-transcription-PCR, and by Oil Red O and alcian blue (pH 2.5) staining, respectively. Subcutaneous implantation of MLO-A5 cells in a gel foam into NOD SCID mice resulted in a woven bone-like structure containing embedded osteocytes and regions of cartilage-like tissue, which stained positive with both alcian blue (pH 2.5) and safranin O. Together, our findings show that MLO-A5 cells, despite being a strongly osteogenic cell line, exhibit characteristics of skeletal stem cells and display mesenchymal lineage plasticity in vitro and in vivo. These unique characteristics suggest that this cell line is a useful model with which to study aging and disease-related changes to the mesenchymal lineage composition of bone.