Changes in the carboxyl-terminal propeptide of type I procollagen and other markers of bone formation upon five days of bed rest

The specificities, influencing factors, and medical implications of bone circadian rhythms

Physiological processes within the human body are regulated in approximately 24-h cycles known as circadian rhythms, serving to adapt to environmental changes. Bone rhythms play pivotal roles in bone development, metabolism, mineralization, and remodeling processes. Bone rhythms exhibit cell specificity, and different cells in bone display various expressions of clock genes. Multiple environmental factors, including light, feeding, exercise, and temperature, affect bone diurnal rhythms through the sympathetic nervous system and various hormones. Disruptions in bone diurnal rhythms contribute to the onset of skeletal disorders such as osteoporosis, osteoarthritis and skeletal hypoplasia. Conversely, these bone diseases can be effectively treated when aimed at the circadian clock in bone cells, including the rhythmic expressions of clock genes and drug targets. In this review, we describe the unique circadian rhythms in physiological activities of various bone cells. Then we summarize the factors synchronizing the diurnal rhythms of bone with the underlying mechanisms. Based on the review, we aim to build an overall understanding of the diurnal rhythms in bone and summarize the new preventive and therapeutic strategies for bone disorders.

Time of day of exercise does not affect the beneficial effect of exercise on bone structure in older female rats

Background: Circadian clock genes are expressed in bone and biomarkers of bone resorption and formation exhibit diurnal patterns in animals and humans. Disruption of the diurnal rhythms may affect the balance of bone turnover and compromise the beneficial effects of exercise on bone. Objective: This study investigated whether the time of day of exercise alters bone metabolism in a rodent model. We hypothesized that exercise during the active phase results in greater bone mass than exercise during the rest phase in older female rats. Methods: Fifty-five, female 12-month-old Sprague Dawley rats were randomly assigned to four treatment groups (n = 13-14/group). Rats were subjected to no exercise or 2 h of involuntary exercise at 9 m/min and 5 days/wk for 15 weeks using motor-driven running wheels at Zeitgeber time (ZT) 4-6 (rest phase), 12-14 (early active phase), or 22-24 (late active phase). ZT 0 is defined as light on, the start of the rest phase. A red lamp was used at minimal intensity during the active, dark phase exercise period, i.e., ZT 12-14 and 22-24. Bone structure, body composition, and bone-related cytokines in serum and gene expression in bone were measured. Data were analyzed using one-way ANOVA followed by Tukey-Kramer post hoc contrasts. Results: Exercise at different ZT did not affect body weight, fat mass, lean mass, the serum bone biomarkers, bone structural or mechanical parameters, or expression of circadian genes. Exercise pooled exercise data from different ZT were compared to the No-Exercise data (a priori contrast) increased serum IGF-1 and irisin concentrations, compared to No-Exercise. Exercise increased tibial bone volume/total volume (p = 0.01), connectivity density (p = 0.04), and decreased structural model index (p = 0.02). Exercise did not affect expression of circadian genes. Conclusion: These data indicate that exercise is beneficial to bone structure and that the time of day of exercise does not alter the beneficial effect of exercise on bone in older female rats.

Delayed inhibition of collagen deposition by targeting bone morphogenetic protein 1 promotes recovery after spinal cord injury

Fibrotic scars appear after spinal cord injury (SCI) and are mainly composed of fibroblasts and excess extracellular matrix (ECM), including different types of collagen. The temporal and spatial distribution and role of excess collagens and ECM after SCI are not yet fully understood. Here, we identified that the procollagen type I C-terminal propeptide (PICP), a marker of collagen type I deposition, and bone morphogenetic protein 1 (BMP1), a secreted procollagen c-proteinase (PCP) for type I collagen maturation, were significantly elevatedin cerebrospinal fluid of patients with SCI compared with healthy controls, and were associated with spinal cord compression and neurological symptoms. We revealed the deposition of type I collagen in the area damaged by SCI in mice and confirmed that BMP1 was the only expressed PCP and induced collagen deposition. Furthermore, transforming growth factor-β (TGF-β), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) can activate the expression of BMP1. However, inhibition of BMP1 at the acute phase eliminated fibrotic scars in the damaged area and inhibited activation and enrichment of astrocytes, which made the damage difficult to repair and increased hematoma. Unexpectedly, knockdown of Bmp1 by adeno-associated virus or the inhibition of BMP1 biological function by specific inhibitors and monoclonal antibodies at different time points after injury led to distinct therapeutic effects. Only delayed inhibition of BMP1 improved axonal regeneration and myelin repair at the subacute stage post-injury, and led to the recovery of motor function, suggesting that scarring had a dual effect. Early inhibition of the scarring was not conducive to limiting inflammation, while excessive scar formation inhibited the growth of axons. After SCI, the collagen deposition indicators increased in both human cerebrospinal fluid and mouse spinal cord. Therefore, suppression of BMP1 during the subacute phase improves nerve function after SCI and is a potential target for scar reduction.

Bone adaptation and osteoporosis prevention in hibernating mammals

Hibernating bears and rodents have evolved mechanisms to prevent disuse osteoporosis during the prolonged physical inactivity that occurs during hibernation. Serum markers and histological indices of bone remodeling in bears indicate reduced bone turnover during hibernation, which is consistent with organismal energy conservation. Calcium homeostasis is maintained by balanced bone resorption and formation since hibernating bears do not eat, drink, urinate, or defecate. Reduced and balanced bone remodeling protect bear bone structure and strength during hibernation, unlike the disuse osteoporosis that occurs in humans and other animals during prolonged physical inactivity. Conversely, some hibernating rodents show varying degrees of bone loss such as osteocytic osteolysis, trabecular loss, and cortical thinning. However, no negative effects of hibernation on bone strength in rodents have been found. More than 5000 genes in bear bone tissue are differentially expressed during hibernation, highlighting the complexity of hibernation induced changes in bone. A complete picture of the mechanisms that regulate bone metabolism in hibernators still alludes us, but existing data suggest a role for endocrine and paracrine factors such as cocaine- and amphetamine-regulated transcript (CART) and endocannabinoid ligands like 2-arachidonoyl glycerol (2-AG) in decreasing bone remodeling during hibernation. Hibernating bears and rodents evolved the capacity to preserve bone strength during long periods of physical inactivity, which contributes to their survival and propagation by allowing physically activity (foraging, escaping predators, and mating) without risk of bone fracture following hibernation. Understanding the biological mechanisms regulating bone metabolism in hibernators may inform novel treatment strategies for osteoporosis in humans.

A Systematic Review of the Circadian Rhythm of Bone Markers in Blood

There exists a marked circadian variation for several bone markers (BM), which is influenced by endogenous as well as exogenous factors including hormones, physical activity, and fasting. Consequently, was the aim of this review to provide an overview of the knowledge of the circadian variation of BM and which factors influence this rhythmicity. A systematic search of PubMed was performed for studies evaluating the circadian variation of BM and which factors influence this rhythmicity. The studies were screened for eligibility by a set of predetermined criteria including a list of relevant BM and a minimum study duration of 24 h with at least 3 blood samples of which two should be at least 6 h apart. In total were 29 papers included. There exists a marked circadian variation for most BM including Carboxy-terminal Cross-Linked Telopeptide of Type I Collagen (CTX) and osteocalcin (OC) with nighttime or early morning peak. Pro-collagen Type I N-terminal Propeptide (PINP) and PTH also showed circadian rhythm but with less amplitude. The inter-osteoblast-osteoclast regulatory markers such as OPG, RANKL, FGF23, and sclerostin showed no circadian rhythm. The markers were differently affected by exogenous factors like fasting, which greatly reduced the circadian variation of CTX but did not affect PINP or OC. The marked circadian variation and the factors which influence the rhythmicity, e.g., fasting are of great consequence when measuring BM. To reduce variation and heighten validity should circadian variation and fasting be kept in mind when measuring BM.

Viewpoint on the role of tissue maintenance in ageing: focus on biomarkers of bone, cartilage, muscle, and brain tissue maintenance

Specific hallmarks are thought to underlie the ageing process and age-related functional decline. In this viewpoint, we put forward the hypothesis that disturbances in the process of tissue maintenance are an important common denominator that may lie in between specific hallmarks of ageing (i.e. damage and responses to damage) and their ultimate (patho)physiological consequences (i.e. functional decline and age-related disease). As a first step towards verifying or falsifying this hypothesis, it will be important to measure biomarkers of tissue maintenance in future studies in different study populations. The main aim of the current paper is to discuss potential biomarkers of tissue maintenance that could be used in such future studies. Among the many tissues that could have been chosen to explore our hypothesis, to keep the paper manageable, we chose to focus on a selected number of tissues, namely bone, cartilage, muscle, and the brain, which are important for mobility and cognition and affected in several common age-related diseases, including osteoporosis, osteoarthritis, sarcopenia, and neurodegenerative diseases. Furthermore, we discuss the advantages and limitations of potential biomarkers for use in (pre)clinical studies. The proposed biomarkers should be validated in future research, for example by measuring these in humans with different rates of ageing.

The 24-hour serum profiles of bone markers in healthy older men and women

The process of bone turnover displays variations over 24 h, with C-terminal cross-linked telopeptide of type 1 collagen (CTX) and osteocalcin exhibiting a nadir in the afternoon and a peak in the night. In contrast, N-terminal propeptide of type 1 procollagen (P1NP) did not display an apparent 24-hour rhythm. Other emerging novel biomarkers of bone, sclerostin and Dickkopf-related protein 1 (DKK1), are markers of osteocyte activity with limited data available regarding their 24-hour profiles. In this study, we aimed to extend available data on 24-hour profiles of CTX, osteocalcin, and P1NP and to assess the 24-hour profiles of sclerostin and DKK1 in healthy older men and women and to compare these between men and women. We measured these five bone markers in EDTA plasma collected every 4 h during 24 h in 37 healthy older men and women (range 52-76 years). Differences between time points were determined using repeated measures ANOVA and cosinor analyses were performed to determine circadian rhythmicity. The circadian rhythm of CTX was confirmed by the cosinor model, with women showing larger amplitude compared to men. Osteocalcin showed higher levels during nighttime compared to daytime in both men and women. For P1NP levels we observed a small but significant increase in the night in men. Sclerostin and DKK1 did not show a circadian rhythm, but sclerostin levels differed between time points. Because of the large intraindividual variation, DKK1 as measured in this study cannot be considered a reliable marker for diagnostic or research purposes. In conclusion, when measuring CTX, osteocalcin, P1NP, or sclerostin either in clinical practice or in a research setting, one should consider the 24-hour profiles of these bone markers.

The Role of Circadian Rhythms in Muscular and Osseous Physiology and Their Regulation by Nutrition and Exercise

The mammalian circadian clock regulates the day and night cycles of various physiological functions. The circadian clock system consists of a central clock in the suprachiasmatic nucleus (SCN) of the hypothalamus and peripheral clocks in peripheral tissues. According to the results of circadian transcriptomic studies in several tissues, the majority of rhythmic genes are expressed in a tissue-specific manner and are influenced by tissue-specific circadian rhythms. Here we review the diurnal variations of musculoskeletal functions and discuss the impact of the circadian clock on homeostasis in skeletal muscle and bone. Peripheral clocks are controlled by not only photic stimulation from the central clock in the SCN but also by external cues, such as feeding and exercise. In this review, we discuss the effects of feeding and exercise on the circadian clock and diurnal variation of musculoskeletal functions. We also discuss the therapeutic potential of chrono-nutrition and chrono-exercise on circadian disturbances and the failure of homeostasis in skeletal muscle and bone.

Serum N-terminal telopeptide of type I collagen as an early marker of fracture nonunion in rabbits

The aim of the present study was to establish an experimental animal model of fracture nonunion, and to investigate the changes in serum biomarker concentrations in fracture nonunion. A total of 20 purebred New Zealand rabbits were divided into two group: A bone defect group and a bone fracture group. In the bone defect group, a 15-mm section of bone (including the periosteum) was removed from the mid-radius, and the medullary cavities were closed with bone wax. In the bone fracture group, the mid-radius was fractured. X-rays were taken and blood samples were collected preoperatively and at 2, 3, 4, 5, 6, 7, 8, 10 and 12 weeks after the surgical procedure. The serum concentrations of osteocalcin (OC) and bone-specific alkaline phosphatase (BSAP) served as markers of bone formation, and those of C-terminal telopeptide of type I collagen (CTX), N-terminal telopeptide of type I collagen (NTX) and tartrate-resistant acid phosphatase 5b (TRACP 5b) served as markers of bone resorption. The concentration levels of the markers were measured using a biotin double-antibody sandwich enzyme-linked immunosorbent assay. In the bone defect group, bone callus was observed on X-ray at 2 weeks in three rabbits and the bone calluses stabilized at 5 weeks; however, none of the bones had healed at 8 weeks. In the bone fracture group, the fracture line was distorted at 2 weeks and bone calluses formed at 6-8 weeks. In the bone defect group, the serum BSAP and TRACP 5b concentrations increased following the surgical procedure, peaked at 4 weeks, began to decrease at 5 weeks and stabilized after 6 weeks. The serum OC concentrations did not change significantly following the surgical procedure. The serum CTX concentrations fluctuated during the first 4 weeks, peaked at 5 weeks, then decreased and stabilized after 6 weeks. The serum NTX concentrations fluctuated during the first 4 weeks, were significantly lower at 5 weeks compared with the other time points and stabilized after 6 weeks. These results suggested that a bone nonunion model can be established in New Zealand rabbits by resecting a 15-mm section of bone from the mid-radius prior to bone wax blocking. Measurement of the serum BSAP, CTX, NTX, and TRACP 5b concentrations may be useful for the early detection of bone nonunion. The serum NTX concentrations changed significantly in rabbits with bone nonunion. Further studies are required in order to determine the feasibility of using serum NTX concentrations for the early diagnosis of bone nonunion.

Comparison in bone turnover markers during early healing of femoral neck fracture and trochanteric fracture in elderly patients

Healing of fractures is different for each bone and bone turnover markers may reflect the fracture healing process. The purpose of this study was to determine the characteristic changes in bone turnover markers during the fracture healing process. The subjects were consecutive patients with femoral neck or trochanteric fracture who underwent surgery and achieved bone union. There were a total of 39 patients, including 33 women and 6 men. There were 18 patients (16 women and 2 men) with femoral neck fracture and 21 patients (17 women and 4 men) with trochanteric fracture. Serum bone-specific alkaline phosphatase (BAP) was measured as a bone formation marker. Urine and serum levels of N-terminal telopeptide of type I collagen (NTX), as well as urine levels of C-terminal telopeptide of type I collagen (CTX) and deoxypyridinoline (DPD), were measured as markers of bone resorption. All bone turnover markers showed similar changes in patients with either type of fracture, but significantly higher levels of both bone formation and resorption markers were observed in trochanteric fracture patients than in neck fracture patients. BAP showed similar levels at one week after surgery and then increased. Bone resorption markers were increased after surgery in patients with either fracture. The markers reached their peak values at three weeks (BAP and urinary NTX), five weeks (serum NTX and DPD), and 2–3 weeks (CTX) after surgery. The increase in bone turnover markers after hip fracture surgery and the subsequent decrease may reflect increased bone formation and remodeling during the healing process. Both fractures had a similar bone turnover marker profile, but the extent of the changes differed between femoral neck and trochanteric fractures.

Recent advances in the use of serological bone formation markers to monitor callus development and fracture healing

The failure of an osseous fracture to heal, or the development of a nonunion, is common; however, current diagnostic measures lack the capability of early and reliable detection of such events. Analyses of radiographic imaging and clinical examination, in combination, remain the gold standard for diagnosis; however, these methods are not reliable for early detection. Delayed diagnosis of a nonunion is costly from both the patient and treatment standpoints. In response, repeated efforts have been made to identify bone metabolic markers as diagnostic or prognostic tools for monitoring bone healing. Thus far, the evidence regarding a correlation between the kinetics of most bone metabolic markers and nonunion is very limited. With the aim of classifying the role of biological pathways of bone metabolism and of understanding bone conditions in the development of osteoporosis, advances have been made in our knowledge of the molecular basis of bone remodeling, fracture healing, and its failure. Procollagen type I amino-terminal propeptide has been shown to be a reliable bone formation marker in osteoporosis therapy and its kinetics during fracture healing has been recently described. In this article, we suggest that procollagen type I amino-terminal propeptide presents a good opportunity for early detection of nonunion. We also review the role and potential of serum PINP, as well as other markers, as indications of fracture healing.

Early changes in bone specific turnover markers during the healing process after vertebral fracture

BACKGROUND

The present study measured longitudinal changes in bone turnover markers in elderly patients with vertebral fracture and investigated the relationship among bone turnover markers, duration of bed rest and bone mineral density (BMD).

METHODS

Criteria for patient selection were 50 years in age and older, and presence of VF. Serum bone-specific alkaline phosphatase (BAP) was measured as a marker of bone formation. Urinary crosslinked N-terminal telopeptides of type I collagen (NTX) was measured as a marker of bone resorption. In principle, samples were collected just after injury, within 24 h, and 1, 2, 3, 5 and 8 weeks after. We also measured duration of bed rest and BMD.

RESULTS

The study population consisted of 42 cases. The average BMD of the lumbar vertebrae was 0.670 ± 0.174 g/cm2. Bed rest period was 17.9 ± 8.8 days. BAP showed significantly higher values at 2 and 3 weeks compared with the baseline value. Thereafter, BAP progressively decreased until 8 weeks. Urinary NTX was increased soon after the onset of pain with the same patterns in BAP. Urinary NTX values reached a peak at 3 weeks, and then they kept significantly higher values until 8 weeks. The peak value of serum BAP was affected by the duration of bed rest, although that of the urinary NTX was not. The peak values of serum BAP and urinary NTX showed negative correlations with the initial BMD values.

CONCLUSIONS

Bone turnover markers remained higher at 8 weeks, even patients symptom was healed after VF. Bone turnover markers were affected on physical activity and BMD.

Parathyroid hormone may maintain bone formation in hibernating black bears (Ursus americanus) to prevent disuse osteoporosis

Mechanical unloading of bone causes an imbalance in bone formation and resorption leading to bone loss and increased fracture risk. Black bears(Ursus americanus) are inactive for up to six months during hibernation, yet bone mineral content and strength do not decrease with disuse or aging. To test whether hibernating bears have biological mechanisms to prevent disuse osteoporosis, we measured the serum concentrations of hormones and growth factors involved in bone metabolism and correlated them with the serum concentration of a bone formation marker (osteocalcin). Serum was obtained from black bears over a 7-month duration that included periods of activity and inactivity. Both resorption and formation markers increased during hibernation, suggesting high bone turnover occurred during inactivity. However, bone formation appeared to be balanced with bone resorption. The serum concentration of parathyroid hormone (PTH) was higher in the hibernation(P=0.35) and post-hibernation (P=0.006) seasons relative to pre-hibernation levels. Serum leptin was lower (P<0.004)post-hibernation relative to pre-hibernation and hibernation periods. Insulin-like growth factor I (IGF-I) decreased (P<0.0001) during hibernation relative to pre-hibernation and reached its highest value during remobilization. There was no difference (P=0.64) in 25-OH vitamin D between the three seasons. Serum osteocalcin (bone formation marker) was significantly correlated with PTH, but not with leptin, IGF-I or 25-OH vitamin D. Osteocalcin and PTH were positively correlated when samples from all seasons were pooled and when only hibernation samples were considered, raising the possibility that the anabolic actions of PTH help maintain bone formation to prevent disuse osteoporosis. Prostaglandin E2 (PGE2)release from MC3T3 osteoblastic cells was significantly affected by treatment with bear serum from different seasons (i.e. hibernation versus active periods). The seasonal changes in PGE2 release showed trends similar to the seasonal changes in serum IGF-I. Since both PGE2 and IGF-I are associated with collagenous bone formation, it is possible that seasonal changes in a circulating factor influence IGF-I levels in vivo in bears and PGE2 release in osteoblastic cells in vitro. The significant decrease in serum leptin following arousal from hibernation may promote bone formation during remobilization, assuming there is a similar decrease in intracerebroventricular leptin. These findings support the idea that seasonal changes in the concentration of circulating molecules help regulate bone formation activity and may be important for preventing disuse osteoporosis in bears.

Immobilization induces a very rapid increase in osteoclast activity

We studied in a randomized, strictly controlled cross-over design, the effects of 6 days 6 degrees head-down tilt bed rest (HDT) in eight male healthy subjects in our metabolic ward. The study consisted of two periods (phases) of 11 days each in order to allow for the test subjects being their own controls. Both study phases were identical with respect to environmental conditions, study protocol and diet. Two days before arriving in the metabolic ward the subjects started with a diet. The diet was continued in the metabolic ward. The metabolic ward period (1l days) was divided into three parts: 4 ambulatory days, 6 days either HDT or control and 1 recovery day. Continuous urine collection started on the first day in the metabolic ward to analyze calcium excretion and bone resorption markers. On the 2nd ambulatory day in the metabolic ward and on the 5th day in HDT or control blood was drawn to analyze serum calcium, parathyroid hormone, and bone formation markers. Urinary calcium excretion was, as early as the first day in immobilization, increased (p<0.01). CTX- and NTX-excretion stayed unchanged in the first 24 h in HDT compared to the control. But already on the 2nd day of immobilization, both bone resorption markers significantly increased. We conclude from these results--pronounced rise of bone resorption markers--that already 24 h of immobilization induce a significant rise in osteoclast activity in healthy subjects. Thus, it appears possible to use short-term bed rest studies as a first step for the development of countermeasures to immobilization.

Urinary excretion of type I collagen cross-linked N-telopeptide and serum bone-specific alkaline phosphatase analysis to determine the correlation of age and back-pain related changes in elderly women

We evaluated bone turnover using biochemical markers in 273 women over 60 years of age with suspected osteoporosis. Their age range was 60-96 years, with an average of 72.7 years. Patients with disorders that might affect bone metabolism were excluded. Those complaining of back pain within 6 months before or after examination were assigned to the back-pain group. Serum bone-specific alkaline phosphatase (BAP) was measured as a bone formation marker, and the urinary N-terminal telopeptide of type I collagen (NTX) was measured as a bone resorption marker. Both BAP and NTX levels increased in individuals over 60 years of age; moreover, these markers were significantly higher in subjects aged over 80 years. Among elderly patients, both BAP and NTX levels were significantly higher in those with back pain than in those without, and in a similar way were observed to increase in parallel with age from the 60-year point. We found that both NTX and BAP increased with aging, and that the increase in these bone turnover markers was closely related to back pain. We also showed that NTX and BAP levels increased significantly in women over 80 years, and specifically in patients with back pain.

Connective tissue responses in acute community-acquired pneumonia

Circulating connective tissue components including the aminoterminal propeptides of type III collagen (PIIINP), type I collagen (PINP) and hyaluronan were determined in patients hospitalised for pneumonia of suspected bacterial origin. Ninety patients were included, 64 of these were followed prospectively for up to 21 days after initiation of therapy. Serum PIIINP was determined by RIA, s-PINP by ELISA, and s-hyaluronan by a radiometric assay. S-PIIINP rose significantly above the zero value within 24 h in both pneumococcal pneumonia (T0: 5.3 microg/l, 95% CI: 2.7-8.1 microg/l vs. T1: 6.7 microg/l, 95% CI: 3.8-9.1, P<0.01) and in pneumonia of unknown aetiology (T0: 4.0 microg/l, 95% CI: 3.6-4.8 vs. T1: 4.5 microg/l, 95% CI: 3.8-5.1, P<0.05) followed by a gradual decline. At T1, S-PIIINP was higher in pneumococcal pneumonia compared with pneumonia of unknown aetiology (P<0.05). By contrast, s-PINP tended to decline within 24 h in both pneumococcal pneumonia (T1: 30 microg/l, 95% CI: 23-40, ns) and in pneumonia of unknown aetiology (T1: 32 microg/l, 95% CI: 22-42, ns) followed by a steady increase. The PINP antigen size distribution remained constant throughout the follow-up period. S-hyaluronan in pneumococcal pneumonia paralleled s-PIIINP reaching a peak value on day 1 (121 microg/l, 95% CI: 65-191, P=0.38). There was a positive correlation between s-PIIINP and C-reactive protein (CRP). The study demonstrates, that community-acquired pneumonia elicits a differentiated mesenchymal response, which is turned down in response to successful antibiotic therapy.

Circadian variation in the serum concentration of C-terminal telopeptide of type I collagen (serum CTx): effects of gender, age, menopausal status, posture, daylight, serum cortisol, and fasting

We examined the diurnal variation in serum concentration of C-terminal telopeptide of type I collagen (serum CrossLaps, sCTx) under various conditions. The studies included a total of 100 individuals. Blood samples were collected every 3 h over 27 h. sCTx levels varied over the 24 h with a maximum at about 05:00 in the morning and a minimum of about 14:00 in the afternoon. The variation had a magnitude of about +/-40% around the 24 h mean and was similar in premenopausal and early and late postmenopausal women with normal and low bone mass. Furthermore, it was not affected by 5 days of bed-rest, by absence of a normal diurnal variation in cortisol production, or by absence of a normal light cycle (blindness). Nasal salmon calcitonin, an antiresorptive drug used for treatment of osteoporosis, was not able to break the circadian pattern whether the treatment was administered in the morning or the evening. The only parameter that showed a pronounced influence on the circadian variation was fasting, which reduced the variation significantly to about one fourth. From a practical point of view the results of this study demonstrate that samples for sCTx should be taken in the fasting state.

Space Flight Is Associated with Rapid Decreases of Undercarboxylated Osteocalcin and Increases of Markers of Bone Resorption without Changes in Their Circadian Variation: Observations in Two Cosmonauts

Background: Microgravity induces bone loss by mechanism(s) that remain largely unknown.

Methods: We measured biochemical markers related to bone remodeling in two cosmonauts before, during, and after 21- and 180-day space flights, respectively.

Results: During both flights, type I procollagen propeptide and bone alkaline phosphatase decreased as early as 8 days after launch. Undercarboxylated osteocalcin percentage increased early and remained high during both flights. Vitamin K supplementation restored carboxylation of osteocalcin during the long-term flight. Urinary and serum C-telopeptide of type I collagen (CTX) increased as early as day 8 of the flights; the increase was greater in serum than in urine. Pyridinoline, free deoxypyridinoline, and N-telopeptide increased less than CTX during the short-term space flight. The circadian rhythm of bone resorption assessed by urine CTX and free deoxypyridinoline was not altered by microgravity.

Conclusion: Vitamin K metabolism or action and bone remodeling may be altered in cosmonauts.

Weight gain reverses bone turnover and restores circadian variation of bone resorption in anorexic patients

OBJECTIVE

The present study was conducted in order to describe the variations and circadian rhythm of biochemical markers of bone remodelling at baseline and after weight gain in patients with anorexia nervosa (AN).

SUBJECTS

We studied 9 women (mean age 21 years, range: 16-30) with established AN who remained amenorrhoeic during the study and with a low body mass index (BMI) after refeeding and 6 female controls (mean age 20 years, range, 18-24 and BMI: 20.6 +/- 1.1 kg/m2). Refeeding was not associated with any other intervention or treatment, especially oestrogen replacement or hormonal contraception. Serum levels of oestradiol remained below 70 pmol/l before and after refeeding.

MEASUREMENTS

During the study, PTH and 25-hydroxyvitamin D measurements were performed. Markers of bone formation: serum intact osteocalcin (iBGP) and serum intact BGP + fragments (iBGP+F) and markers of bone resorption: urine C-teloptide of type I collagen (uCTX) and serum C-telopeptide ofvtype 1 collagen (s-CTX) were measured.

RESULTS

At baseline, PTH and 25 OH-vitamin D concentrations were within the normal range in AN patients and no significant variation was observed after refeeding. Bone formation markers were found to be significantly different at baseline between AN patients and controls. After refeeding, iBGP and iBGP+F levels increased by 172% and 154%, respectively, to values no different from controls. Intact BGP and iBGP+F exhibited a significant circadian variation in controls (P < 0.05 and P < 0.002, respectively), whereas we did not find any such circadian rhythm in AN patients. After refeeding no significant circadian variation was observed; however, iGBP+F tended to peak in early morning and exhibited a nadir in the afternoon. At baseline, sCTX was 2-fold higher in AN patients than in controls. After weight gain sCTX decreased significantly and reached control values. Refeeding induced a non-significant 40% decrease in uCTX. We found positive correlations between uCTX and the 24-h mean value of sCTX levels (r2 = 0.93, P < 0.0001) and between uCTX and the mean value of sCTX peak levels at 0800 h (r2 = 0.65, P < 0.0003). Serum CTX exhibited a significant circadian variation in controls (P < 0.001) with a peak at 0800 h and a nadir at 1600 h with a 60% decrease between peak and nadir values. We found that anorexia nervosa suppressed the sCTX circadian variation which was restored by refeeding. We found a significant non-linear relationship between BMI and sCTX/iBGP ratio in AN (r2 = 0.6, P < 0.0001), thus illustrating the influence of nutritional status on bone remodelling.

CONCLUSIONS

In this study we found that weight gain, related to refeeding only, reversed the anorexia nervosa-induced uncoupling of bone remodelling and restored circadian variation of a bone resorption marker.

Biochemical markers of bone turnover

Biochemical markers of bone turnover that are specific to bone allow study of the subtle changes in bone turnover associated with osteoporosis. They have been evaluated in Paget's disease of the bone and chronic renal failure. This review focuses on the use of biochemical markers of bone turnover in osteoporosis. The data in this review period are numerous and varied due to the growing interest in the use of biochemical markers of bone turnover in clinical practice. The data provide support for the use of the newer bone turnover markers for monitoring treatment of osteoporosis, if care is taken to minimize sources of variability.

Lack of effectiveness of bed rest for sciatica

BACKGROUND AND METHODS

Bed rest is widely advocated for sciatica, but its effectiveness has not been established. To study the effectiveness of bed rest in patients with a lumbosacral radicular syndrome of sufficient severity to justify treatment with bed rest for two weeks, we randomly assigned 183 subjects to either bed rest or watchful waiting for this period. The primary outcome measures were the investigator's and patient's global assessments of improvement after 2 and 12 weeks, and the secondary outcome measures were changes in functional status and in pain scores (after 2, 3, and 12 weeks), absenteeism from work, and the need for surgical intervention. Neither the investigators who assessed the outcomes nor those involved in data entry and analysis were aware of the patients' treatment assignments.

RESULTS

After two weeks, 64 of the 92 patients in the bed-rest group (70 percent) reported improvement, as compared with 59 of the 91 patients in the control (watchful-waiting) group (65 percent) (adjusted odds ratio for improvement in the bed-rest group, 1.2; 95 percent confidence interval, 0.6 to 2.3). After 12 weeks, 87 percent of the patients in both groups reported improvement. The results of assessments of the intensity of pain, the bothersomeness of symptoms, and functional status revealed no significant differences between the two groups. The extent of absenteeism from work and rates of surgical intervention were similar in the two groups.

CONCLUSIONS

Among patients with symptoms and signs of a lumbosacral radicular syndrome, bed rest is not a more effective therapy than watchful waiting.

Time-dependent changes of serum carboxy-terminal peptide of type I procollagen and carboxy-terminal telopeptide of type I collagen concentrations in patients with acute myocardial infarction after successful reperfusion: correlation with left ventricular volume indices

To test the hypothesis that in patients with acute myocardial infarction (AMI), changes in the concentrations of the serum carboxy-terminal peptide of type I procollagen (PICP) and the carboxy-terminal telopeptide of type I collagen (ICTP) reflect extracellular matrix reformation and degradation, respectively, in the infarct healing processes, we measured these serum concentrations by RIA and compared their values with left ventricular (LV) indices obtained by left ventriculography. We studied 13 consecutive patients with their first AMI who underwent successful reperfusion. Blood samples were taken the day of admission and on days 2, 3, 4, 5, 7, and 14. LV volume indices were determined at 1 month after AMI, when LV remodeling was almost completed. The serum concentrations of both PICP and ICTP changed in a time-dependent manner. The average serum PICP concentration was lower than 1 SD below the mean control values on days 2 and 3 and increased thereafter, returning to the lower end of the control range at day 14. The area under the curve (AUC) for PICP was significantly correlated with the LV end systolic (ES) and end diastolic (ED) volume indices and LV ejection fraction for the first 14 days after AMI. The serum PICP on days 5–14 was inversely correlated or tended to be correlated with the LVES and LVED volume indices. The average serum ICTP concentrations on admission were within the control range, began to increase on day 2, and reached maximal concentrations on day 5, remaining at a plateau concentration until day 14. Although the AUC of ICTP for 14 days, the ICTP concentrations on days 1 and 14, and the minimal and maximal concentrations were significantly correlated with creatine kinase (CK) release and the period from AMI onset to the peak CK time, the concentrations were not significantly correlated with any LV indices except for the concentration on day 4, which was weakly correlated with the LVES volume index. The serum concentrations of PICP showed a significant time-dependent change that correlated with LV indices, indicating that PICP may provide additional information for evaluating the healing process because it affects LV remodeling after AMI. Although the serum concentration of ICTP changed in association with CK release, the ICTP concentration was found to be a poor indicator for LV indices.

Evaluation of a nonhuman primate model to study circadian rhythms of calcium metabolism

We evaluated primate models for the study of circadian rhythms in calcium and bone metabolism. Blood and urine were collected from two cynomolgus macaques every 4 h for 24 h. Studies were initiated at three different clock times to separate the effects of repeated experimental sampling from circadian effects. Also, samples were collected from seven monkeys at times of expected maxima and minima. Some parameters exhibited the expected circadian rhythm with increases at night (serum total calcium) or in the early morning (urinary collagen cross-links). Others displayed the effects of the experimental procedure, either increasing (urinary creatinine and phosphorus) or decreasing (osteocalcin, urinary calcium) with repeated sampling. Serum phosphorus, cortisol, and type I procollagen were influenced by both clock time and experimental procedures. Alkaline phosphatase and parathyroid hormone did not show any differences with time or sampling. This data is consistent with findings in humans that bone resorption increases at night and that endogenous corticosteroids decrease bone formation. The usefulness of the monkey model is limited by the physiological stress of sample collection in these subjects.

Decrease of bone formation in adult women with fragility fractures

OBJECTIVES

To compare bone mineral density (BMD) and some markers of bone metabolism in women with fragility fractures and in normal age-matched subjects.

METHODS

A 100 women with at least one vertebral deformity > 25%, and 219 age-, BMI- and parity-matched healthy women, were recruited for the study. In all the patients fractures were symptomatic and occurred at least 1 year before densitometric measurement. Forearm bone mineral density (BMD) as well as biochemical assessment of some markers of bone turnover were measured in all the subjects.

RESULTS

BMD was significantly lower in the fracture than in the control group (0.326 +/- 0.073 vs. 0.379 +/- 0.079; P < 0.001). Fractured women showed alkaline phosphatase (ALP) and osteocalcin (OC) serum levels significantly lower than controls, while no differences were found in fasting urinary calcium and hydroxyproline excretion. Women without fractures showed a significant correlation between ALP and both age and years since menopause (YSM). Such a correlation is lacking in the fracture group.

CONCLUSIONS

Women with vertebral deformities likely due to a fracture had a forearm BMD and markers of bone formation lower than normal. Whether low bone density is due to a low peak of bone mass or to an increased postmenopausal bone loss sustained by an uncoupling between the two bone remodelling processes is still unclear.

Circadian variation in bone resorption is not related to serum cortisol

Serum osteocalcin, serum procollagen type I carboxyterminal propeptide (sPICP), and the urinary excretion of pyridinium crosslinks (biochemical markers of bone formation and resorption) all exhibit a circadian variation with a peak during the night. This study was performed to investigate the influence of the endogenous circadian rhythm in cortisol on the biochemical markers of bone turnover. Participants included 11 patients substituted with hydrocortisone due to either hypopituitarism (n = 7) or bilateral adrenalectomy (n = 4). Their daily tablet intake of hydrocortisone was divided in four equal doses in order to abrogate the known circadian variation in cortisol. 24 healthy postmenopausal women served as controls. The study design was performed over 24 h, with blood samples taken every 3 h, and urine collected in 3 h aliquots. Urinary pyridinium crosslinks (Pyr/ Cr, D-Pyr/Cr), serum osteocalcin (sOC), and serum PICP were measured. Patients without a circadian variation in cortisol had normal circadian variation in the urinary excretion of pyridinium crosslinks and sPICP, but no circadian rhythm in serum osteocalcin. We conclude that the etiology of the circadian rhythm in the biochemical markers of bone turnover is still unknown. This study indicates that the circadian variation in sOC can be controlled by the endogenous circadian variation in serum cortisol, whereas this hormone does not control the circadian variation in either the serum PICP or the urinary excretion in pyridinium crosslinks.

Different responses of bone alkaline phosphatase isoforms during recombinant insulin-like growth factor-I (IGF-I) and during growth hormone therapy in adults with growth hormone deficiency

We studied serum bone alkaline phosphatase (ALP) isoforms and other markers of bone turnover in growth hormone-deficient (GHD) adults (n = 22). The patients were followed during 1 week of insulin-like growth factor-I (IGF-I) administration, 40 micrograms/kg of body weight/day (n = 6), and during 24 months of growth hormone (GH) therapy, 0.125 IU/kg of body weight/week for the first month, and then 0.250 IU/kg of body weight/week (n = 20). Six ALP isoforms were separated and quantified by high-performance liquid chromatography: one bone/intestinal, two bone (B1, B22), and three liver ALP isoforms. At baseline, the mean levels of B1, B22, and osteocalcin were higher in GHD adults than in healthy adults. After 2 week of IGF-I administration and 1 month of GH therapy, only B1 was decreased. We suggest that the initial decrease of B1 during GH therapy could be an effect of endocrine IGF-I action mediated by GH. After 3 months of GH therapy, both B1 and B2 increased as compared with placebo. Osteocalcin, carboxy-terminal propeptide of type I procollagen (PICP), cross-linked carboxy-terminal telopeptide of type I collagen (ICTP), and urinary pyridinoline cross-links/creatinine ratio increased during GH therapy. PICP increased significantly before bone ALP and osteocalcin, indicating early stimulation of type I collagen synthesis as previously demonstrated by in vitro models. Different responses of the bone ALP isoforms during IGF-I and during GH therapy suggest different regulations in vivo.

Morning or evening administration of nasal calcitonin? Effects on biochemical markers of bone turnover

The purpose of this study was to examine the effect of intranasal salmon calcitonin (sCT) administration (200 IE), given either in the morning (8:00) or evening (21:00), on the known circadian variation in biochemical markers of bone turnover. An open, placebo-controlled, randomized, crossover study, with three 24 h studies of blood samples drawn every third hour and urine collected in 3 h aliquots was undertaken. Subjects consisted of nine healthy postmenopausal women, aged 58 +/- 7 years. Urinary CrossLaps (a measure of bone resorption) was measured by ELISA and corrected for creatinine (Cr). Serum osteocalcin (sOC) was measured by radioimmunoassay (RIA). The first 24 h study was performed without intervention. Prior to this control study the participants were randomized to either morning (8:00) or evening (21:00) sCT (200 IE). sCT administrations were given 4-5 days prior to and during the second study. After a washing-out period of 2 weeks the participants were given 200 IE of sCT at the reverse time of the day 5 days prior to and during the third study. At all timepoints, urinary CrossLaps/Cr exhibited a significant (p < 0.001) circadian rhythm with its zenith in early morning and nadir in late afternoon. Both morning and evening administration of sCT significantly decreased the urinary excretion of CrossLaps/Cr approximately 3-6 h after administration with a subsequent rebound effect. sOC did not exhibit a significant circadian variation and was not affected by the calcitonin. The 24 h mean urinary CrossLaps/Cr and sOC remained unchanged. Both morning and evening sCT significantly decreased the urinary excretion of CrossLaps/Cr 3-6 h after administration, with a rebound effect approximately 12 h later. However, the present study does not indicate that neither evening nor twice-daily administration is superior to morning administration.