Post-menopausal women with rheumatoid arthritis who are treated with raloxifene or alendronate or glucocorticoids have lower serum undercarboxylated osteocalcin levels

Exogenous and endogenous determinants of vitamin K status in cystic fibrosis

Cystic fibrosis (CF) patients are at high risk for vitamin K deficiency. The effects of vitamin K supplementation are very ambiguous. Therefore, we aimed to define the determinants of vitamin K deficiency in a large cohort of supplemented - 146 (86.9%) and non-supplemented - 22 (13.1%) CF patients. Vitamin K status was assessed using prothrombin inducted by vitamin K absence (PIVKA-II) and undercarboxylated osteocalcin (u-OC). The pathological PIVKA-II concentration (≥ 2 ng/ml) and abnormal percentage of osteocalcin (≥ 20%) were found in 72 (42.8%) and 60 (35.7%) subjects, respectively. We found that liver involvement, diabetes, and glucocorticoid therapy were potential risk factors for vitamin K deficiency. Pathological concentrations of PIVKA-II occurred more frequently in patients with pancreatic insufficiency and those who have two severe mutations in both alleles of the CFTR gene. Pathological percentage of u-OC was found more frequently in adult CF patients and those not receiving vitamin K. However, it seems that there are no good predictive factors of vitamin K deficiency in CF patients in everyday clinical care. Early vitamin K supplementation in CF patients seems to be warranted. It is impossible to clearly determine the supplementation dose. Therefore, constant monitoring of vitamin K status seems to be justified.

Comparison of the effect of 18-month daily teriparatide administration on patients with rheumatoid arthritis and postmenopausal osteoporosis patients

Patients with rheumatoid arthritis showed greater response to 18-month administration of daily teriparatide especially in the increase of bone formation markers at 1 month and femoral neck bone mineral density at 18 months compared to postmenopausal osteoporosis patients.

INTRODUCTION

The aim of this study was to evaluate the effects of 18-month administration of daily teriparatide (TPTD) in osteoporosis patients with rheumatoid arthritis (RA) by comparing that of postmenopausal osteoporosis patients (Porosis).

METHODS

The effects of TPTD were examined between RA (n = 70; age 68.4 years; disease activity score assessing 28 joints with CRP [DAS28-CRP] 2.8; rheumatoid factor [RF] positivity 75.5 %) with 77.1 % of prior bisphosphonate (BP), 84.3 % of oral prednisolone (PSL) (4.4 mg/day at baseline), 25.7 % of biologics, and Porosis (n = 62; age 71.3 years) with 77.4 % of prior BP.

RESULTS

Femoral neck (FN) bone mineral density (BMD) increase at 18 months was significantly greater in RA compared to Porosis (4.7 vs. 0.7 %, P = 0.038), whereas it was 9.7 versus 7.9 % (P = 0.736) in the lumbar spine (LS). The increase of bone formation markers (bone alkaline phosphatase [bone ALP] and N-terminal type I procollagen propeptide [PINP]) at 1 month were all significantly greater in RA compared to Porosis. A multivariate logistic regression analysis revealed that the significant indicator of 18-month BMD increase in RA was a 3-month increase of under-carboxylated osteocalcin (ucOC) for LS (β = 0.446, P = 0.005) and baseline ucOC for FN (β = 0.554, P = 0.001), in which both showed significant negative correlation with baseline PSL dose.

CONCLUSIONS

RA showed greater response to daily TPTD administration, especially in the increase of bone formation markers at 1 month and FN BMD increase at 18 months compared to Porosis.

In vivo analysis of the contribution of bone resorption to the control of glucose metabolism in mice

Osteocalcin is a hormone produced in bones by osteoblasts and regulating energy metabolism. While osteocalcin exists in two forms, γ-carboxylated and undercarboxylated only the latter appears to function as a hormone in vivo. It has been proposed recently that osteoclasts, the bone-resorbing cells, are responsible of decarboxylating, i.e. activating osteocalcin. To address the role of osteoclasts in the maintenance of energy metabolism we analyzed mutant mouse strains harboring either an increase or a decrease in osteoclasts number. Osteoprotegerin-deficient mice that are characterized by an increase in the number of osteoclasts demonstrate an increase in serum levels of undercarboxylated osteocalcin and are significantly more glucose tolerant than WT animals. Conversely, osteoclasts ablation in mice results in a decrease in serum undercarboxylated osteocalcin levels and in reduced glucose tolerance. These results support the notion that osteoclasts are controlling glucose metabolism at least in part through the regulation of osteocalcin decarboxylation.

Endocrine actions of osteocalcin

Osteocalcin is the most abundant noncollagenous protein of bone matrix. Once transcribed, this protein undergoes posttranslational modifications within osteoblastic cells before its secretion, including the carboxylation of three glutamic residues in glutamic acid, which is essential for hydroxyapatite binding and deposition in the extracellular matrix of bone. Recent provocative data from experimental observations in mice showed that the circulating undercarboxylated fraction of osteocalcin increases insulin secretion and sensitivity, lowers blood glucose, and decreases visceral fat in both genders, while it enhances testosterone production by the testes in males. Moreover, both total and undercarboxylated osteocalcins increase following physical activity with potential positive effects on glucose tolerance. Despite that these evidences have been only in part confirmed in humans, further prospective investigations are needed to definitively establish the endocrine role of osteocalcin both in the general population and cohorts of patients with diabetes or other metabolic disorders.

Bone turnover markers: use in osteoporosis

Biochemical markers of bone turnover (bone turnover markers, BTMs) can be used to study changes in bone remodelling in osteoporosis. Investigators and clinicians should be aware of the appropriate sample collection and storage conditions for optimum measurements of these markers. Improvements in the variability of BTM measurements have resulted from the development of assays for automated analysers, and from international consensus regarding their use. Appropriate reference intervals should be used for the optimum interpretation of results. BTMs can provide information that is useful for the management of patients with osteoporosis, for both the initial clinical assessment and for guiding and monitoring of treatment. BTMs are clinically useful to determine possible causes of secondary osteoporosis by identifying patients with high bone turnover and rapid bone loss. In the follow-up of treatment response, BTM levels respond rapidly to both anabolic and antiresorptive treatments. BTM changes can also be used for understanding the mechanism of action of drugs in development and identifying the correct dose; they are also potentially useful as surrogate biomarkers for fracture.