Regulation of plasma osteocalcin by corticosterone and norepinephrine during restraint stress

Sympathetic Neurostress Drives Osteoblastic Exosomal MiR-21 Transfer to Disrupt Bone Homeostasis and Promote Osteopenia

Innervation and extracellular vesicle secretion co-exist in the local tissue microenvironment for message transfer, but whether they are interconnected to regulate organ homeostasis remains unknown. Sympatho-adrenergic activation is implicated in stress-induced depression and leads to bone loss, but the mechanisms and therapeutics are incompletely elucidated. Here, it is revealed that sympathetic neurostress through the β_1/2 -adrenergic receptor (β1/2-AR) signaling triggers the transcription response of a microRNA, miR-21, in osteoblasts, which is transferred to osteoclast progenitors via exosomes for dictating osteoclastogenesis. After confirming that miR-21 deficiency retards the β1/2-AR agonist isoproterenol (ISO)-induced osteopenia, it is shown that the pharmacological inhibition of exosome release by two clinically-relevant drugs, dimethyl amiloride and omeprazole, suppresses osteoblastic miR-21 transfer and ameliorates bone loss under both ISO and chronic variable stress (CVS)-induced depression conditions. A targeted delivery approach to specifically silence osteoblastic miR-21 is further applied, which is effective in rescuing the bone remodeling balance and ameliorating ISO- and CVS-induced osteopenias. These results decipher a previously unrecognized paradigm that neural cues drive exosomal microRNA communication to regulate organ homeostasis and help to establish feasible strategies to counteract bone loss under psychological stresses.

Serum osteocalcin is associated with subjective stress in people with depression and type 2 diabetes

BACKGROUND

Low serum osteocalcin is a risk factor for type 2 diabetes mellitus (T2DM), and osteocalcin release from bone is associated with an acute stress response in mice. Both diabetes and stress are associated with depression. Here, we assess relationships between serum osteocalcin, depression and subjective stress in people with T2DM.

METHODS

Participants with T2DM (HbA1c above 6.4 %, impaired fasting glucose or impaired glucose tolerance) were assessed for a major depressive episode using the research version of the Structured Clinical Interview for DSM-5 depression criteria (SCID-5RV). Subjective stress over the past month was assessed using the Perceived Stress Scale (PSS). Serum carboxylated (cOCN) and fully decarboxylated (dcOCN) osteocalcin were assayed from fasting morning blood by commercial enzyme-linked immunosorbent assay.

RESULTS

Among 95 participants (mean age 62.4 ± 9.9, 51 % women), 22 % were experiencing a depressive episode (9 men, 12 women). The presence of a depressive episode was not associated with dcOCN or cOCN concentrations; however, higher concentrations of cOCN were associated with higher PSS scores in participants with depression (r = 0.585, p = 0.005). In an analysis of covariance model controlling for age, sex, body mass index, glycemic control (glycosylated hemoglobin), insulin resistance (homeostatic model), depression, and antidepressant use, cOCN was associated with PSS scores (F=10.302, p = 0.002), and this relationship was stronger in those with depression (depression × cOCN interaction F=4.978, p = 0.028). Although associations between dcOCN concentrations and PSS scores did not reach significance, the same trend seen with cOCN concentrations was observed in participants with depression for dcOCN (r=0.365, p=0.10), and for a depression × dcOCN interaction associated with PSS scores in the whole group (F=2.165, p = 0.15).

CONCLUSIONS

Osteocalcin is a neuroendocrine marker associated with perceived chronic stress among people with T2DM experiencing a depressive episode.

Neuropeptide Y Regulation of Energy Partitioning and Bone Mass During Cold Exposure

The maintenance of whole body energy homeostasis is critical to survival and mechanisms exist whereby an organism can adapt to its environment and the stresses placed upon it. Environmental temperature and thermogenesis are key components known to affect energy balance. However, little is known about how these processes are balanced against the overall energy balance. We show that even mild cold exposure has a significant effect on energy expenditure and UCP-1 levels which increase by 43% and 400%, respectively, when wild-type (WT) mice at thermoneutral (29 °C) were compared to mice at room temperature (22 °C) conditions. Interestingly, bone mass was lower in cold-stressed WT mice with significant reductions in femoral bone mineral content (- 19%) and bone volume (- 13%). Importantly, these cold-induced skeletal changes were absent in mice lacking NPY, one of the main controllers of energy homeostasis, highlighting the critical role of NPY in this process. However, energy expenditure was significantly greater in cold-exposed NPY null mice, indicating that suppression of non-thermogenic tissues, like bone, contributes to the adaptive responses to cold exposure. Altogether, this work identifies NPY as being crucial in coordinating energy and bone homeostasis where it suppresses energy expenditure, UCP-1 levels and lowers bone mass under conditions of cold exposure.

Osteocalcin in acute stress response: from the perspective of cardiac diseases

Osteocalcin is an osteoblast-derived peptide mainly found in the bone matrix but also in circulation. A recent investigation suggested that osteocalcin mediated acute stress response (ASR) by inhibiting parasympathetic tone in mice and humans. We propose a hypothesis that osteocalcin is regulated by the skeleton movement and glucocorticoids, and inhibition of the parasympathetic tone by osteocalcin may indicate a therapeutic target in the treatment of acute myocardial infarction (AMI).

Mediation of the Acute Stress Response by the Skeleton

We hypothesized that bone evolved, in part, to enhance the ability of bony vertebrates to escape danger in the wild. In support of this notion, we show here that a bone-derived signal is necessary to develop an acute stress response (ASR). Indeed, exposure to various types of stressors in mice, rats (rodents), and humans leads to a rapid and selective surge of circulating bioactive osteocalcin because stressors favor the uptake by osteoblasts of glutamate, which prevents inactivation of osteocalcin prior to its secretion. Osteocalcin permits manifestations of the ASR to unfold by signaling in post-synaptic parasympathetic neurons to inhibit their activity, thereby leaving the sympathetic tone unopposed. Like wild-type animals, adrenalectomized rodents and adrenal-insufficient patients can develop an ASR, and genetic studies suggest that this is due to their high circulating osteocalcin levels. We propose that osteocalcin defines a bony-vertebrate-specific endocrine mediation of the ASR.

Evaluation of Short and Long Term Cold Stress Challenge of Nerve Grow Factor, Brain-Derived Neurotrophic Factor, Osteocalcin and Oxytocin mRNA Expression in BAT, Brain, Bone and Reproductive Tissue of Male Mice Using Real-Time PCR and Linear Correlation Analysis

The correlation between the Ngf/p75ntr-Ntrk1 and Bdnf, Osteocalcin-Ost/Gprc6a and Oxytocin-Oxt/Oxtr genes, was challenged investigating their mRNA levels in 3 months-old mice after cold-stress (CS). Uncoupling protein-1 (Ucp-1) was used as positive control. Control mice were maintained at room temperature T = 25°C, CS mice were maintained at T = 4°C for 6 h and 5-days (N = 15 mice). RT-PCR experiments showed that Ucp-1 and Ngf genes were up-regulated after 6 h CS in brown adipose tissues (BAT), respectively, by 2 and 1.5-folds; Ucp-1 was upregulated also after 5-days, while Ngfr (p75ntr) and Ntrk1 genes were downregulated after 6 h and 5-days CS in BAT. NGF and P75NTR were upregulated in bone and testis following 5-days, and P75NTR in testis after 6 h CS. Bdnf was instead up-regulated in bone following 5-days CS and down-regulated in testis. OST was upregulated by 16 and 3-fold in bone and BAT, respectively, following 5-days CS. Gprc6a was upregulated after 6 h in brain, while Bglap (Ost) gene was downregulated. Oxt gene was upregulated by 5-fold following 5-days CS in bone. Oxtr was upregulated by 0.5 and 0.3-fold, respectively, following 6 h and 5-days CS in brain. Oxtr and Oxt were downregulated in testis and in BAT. The changes in the expression levels of control genes vs. genes following 6 h and 5-days CS were correlated in all tissues, but not in BAT. Correlation in BAT was improved eliminating Ngfr (p75ntr) data. The correlation in brain was lost eliminating Oxtr data. In sum, Ucp-1 potentiation in BAT after cold stress is associated with early Ngf-response in the same tissue and trophic action in bone and testis. In contrast, BDNF exerts bone and neuroprotective effects. Similarly to Ucp-1, Bglap (Ost) signaling is enhanced in bone and BAT while it may exert local neuroprotective effects thought its receptor. Ngfr (p75ntr) regulates the adaptation to CS through a feed-back loop in BAT. Oxtr regulates the gene-response to CS through a feed-forward loop in brain. Overall these results expand the understanding of the physiology of these molecules under metabolic thermogenesis.

Uncoupling protein-1 is protective of bone mass under mild cold stress conditions

Brown adipose tissue (BAT), largely controlled by the sympathetic nervous system (SNS), has the ability to dissipate energy in the form of heat through the actions of uncoupling protein-1 (UCP-1), thereby critically influencing energy expenditure. Besides BAT, the SNS also strongly influences bone, and recent studies have demonstrated a positive correlation between BAT activity and bone mass, albeit the interactions between BAT and bone remain unclear. Here we show that UCP-1 is critical for protecting bone mass in mice under conditions of permanent mild cold stress for this species (22°C). UCP-1^-/- mice housed at 22°C showed significantly lower cancellous bone mass, with lower trabecular number and thickness, a lower bone formation rate and mineralising surface, but unaltered osteoclast number, compared to wild type mice housed at the same temperature. UCP-1^-/- mice also displayed shorter femurs than wild types, with smaller cortical periosteal and endocortical perimeters. Importantly, these altered bone phenotypes were not observed when UCP-1^-/- and wild type mice were housed in thermo-neutral conditions (29°C), indicating a UCP-1 dependent support of bone mass and bone formation at the lower temperature. Furthermore, at 22°C UCP-1^-/- mice showed elevated hypothalamic expression of neuropeptide Y (NPY) relative to wild type, which is consistent with the lower bone formation and mass of UCP-1^-/- mice at 22°C caused by the catabolic effects of hypothalamic NPY-induced SNS modulation. The results from this study suggest that during mild cold stress, when BAT-dependent thermogenesis is required, UCP-1 activity exerts a protective effect on bone mass possibly through alterations in central NPY pathways known to regulate SNS activity.

Altered Ethanol Consumption in Osteocalcin Null Mutant Mice

Osteocalcin (OC) is an abundant extracellular calcium-binding protein synthesized by osteoblasts. Although most OC is bound to hydroxyapatite mineral during bone formation, a consistent amount is released directly to circulation. Plasma OC (pOC) levels are highly sensitive to stressful stimuli that alter stress-responsive hormones, such as glucocorticoids (cortisol or corticosterone) and the catecholamines norepinephrine and epinephrine. To gain a better understanding of the apparent relationship of OC to the effects of ethanol (EtOH) and the stress responses, we compared mice that have OC (WT [OC+/+] and HET [OC+/-]) with OC null mutants (KO [OC-/-]), which have no OC in either plasma or in bone. One experiment included chronic unpredictable stress, a second was conducted in the absence of any known stressors other than EtOH, while a third imposed a more severe acute immobilization stress in addition to EtOH consumption. The data obtained confirmed significant differences in EtOH consumption in mice that previously experienced various stressful stimuli. We also determined that adrenal tyrosine-hydroxylase expression was inversely proportional to EtOH consumption and tended to be lower in KO than in WT. Data suggest that OC possesses the ability to modulate the adrenal gene expression of the catecholamine synthetic pathway. This modulation may be responsible for differences in EtOH consumption under stress.

Chronic Mild Stress Causes Bone Loss via an Osteoblast-Specific Glucocorticoid-Dependent Mechanism

Chronic stress and depression are associated with alterations in the hypothalamic-pituitary-adrenal signaling cascade and considered a risk factor for bone loss and fractures. However, the mechanisms underlying the association between stress and poor bone health are unclear. Using a transgenic (tg) mouse model in which glucocorticoid signaling is selectively disrupted in mature osteoblasts and osteocytes [11β-hydroxysteroid-dehydrogenase type 2 (HSD2)OB-tg mice], the present study examines the impact of chronic stress on skeletal metabolism and structure. Eight-week-old male and female HSD2OB-tg mice and their wild-type (WT) littermates were exposed to chronic mild stress (CMS) for the duration of 4 weeks. At the endpoint, L3 vertebrae and tibiae were analyzed by micro-computed tomography and histomorphometry, and bone turnover was measured biochemically. Compared with nonstressed controls, exposure to CMS caused an approximately threefold increase in serum corticosterone concentrations in WT and HSD2OB-tg mice of both genders. Compared with controls, CMS resulted in loss of vertebral trabecular bone mass in male WT mice but not in male HSD2OB-tg littermates. Furthermore, both tibial cortical area and area fraction were reduced in stressed WT but not in stressed HSD2OB-tg male mice. Osteoclast activity and bone resorption marker were increased in WT males following CMS, features absent in HSD2OB-tg males. Interestingly, CMS had little effect on vertebral and long-bone structural parameters in female mice. We conclude that in male mice, bone loss during CMS is mediated via enhanced glucocorticoid signaling in osteoblasts (and osteocytes) and subsequent activation of osteoclasts. Female mice appear resistant to the skeletal effects of CMS.

Update on primary ovarian insufficiency

PURPOSE OF REVIEW

Despite an incidence of 1% among women under the age of 40, primary ovarian insufficiency (POI) is still poorly understood. As the variable cause and presentation of POI complicate its management, a standard regimen for treatment remains to be established. However, emerging research has provided new insight on current mainstays of treatment as well as novel management approaches and therapeutic interventions.

RECENT FINDINGS

Recent clinical trials in women with POI indicate that the widely used regimen of transdermal estradiol and medroxyprogesterone acetate restores bone mineral density to a level equal to women with normal ovarian function. Further research verifies that compounded bioidentical hormones and androgen supplementation are inadequate in treating POI and lowering risk for long-term sequelae. Additionally, assessing changes in bone turnover markers may be useful for monitoring bone mineral density. Alternative therapies such as acupuncture, dehydroepiandrosterone, and bupropion may be effective in treating the effects of estrogen deficiency at some level, but require further investigation.

SUMMARY

Recent updates show promise in improving management methods and reducing risk of long-term sequelae. Additional research that expands upon the most current literature is critical to achieve an evidence-based standard of best practice.

Mastication as a Stress-Coping Behavior

Exposure to chronic stress induces various physical and mental effects that may ultimately lead to disease. Stress-related disease has become a global health problem. Mastication (chewing) is an effective behavior for coping with stress, likely due to the alterations chewing causes in the activity of the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Mastication under stressful conditions attenuates stress-induced increases in plasma corticosterone and catecholamines, as well as the expression of stress-related substances, such as neurotrophic factors and nitric oxide. Further, chewing reduces stress-induced changes in central nervous system morphology, especially in the hippocampus and hypothalamus. In rodents, chewing or biting on wooden sticks during exposure to various stressors reduces stress-induced gastric ulcer formation and attenuates spatial cognitive dysfunction, anxiety-like behavior, and bone loss. In humans, some studies demonstrate that chewing gum during exposure to stress decreases plasma and salivary cortisol levels and reduces mental stress, although other studies report no such effect. Here, we discuss the neuronal mechanisms that underline the interactions between masticatory function and stress-coping behaviors in animals and humans.

Osteocalcin, but not deoxypyridinoline, increases in response to isoflurane-induced anaesthesia in young female guinea pigs

The effect of the inhaled anaesthetic isoflurane was investigated on bone biomarkers, both during maturation and on minerals and glucose postpartum. Female guinea pigs (n = 10) were anaesthetized during maturation (5 and 9 weeks) and postpartum (26 weeks of age) with isoflurane during dual-energy X-ray absorptiometry scanning. Blood collection was performed at all ages before and after anaesthesia for measurement of plasma osteocalcin (OC), total deoxypyridinoline (tDPD), and cortisol. Postpartum measurements also included: blood ions, acid-base parameters and glucose, plasma minerals, total alkaline phosphatase (tALP), and albumin. Plasma OC concentration almost doubled after exposure to isoflurane at 5 weeks (30.1 ± 5.0-57.9 ± 11.2 nmol/L, p < 0.001) and at 9 weeks (29.1 ± 7.5-62.9 ± 15.9 nmol/L, p < 0.001), but did not change postpartum (3.7 ± 3.3-4.3 ± 3.9 nmol/L, p = 0.88). There was no effect of isoflurane exposure on plasma tDPD at any age. Plasma cortisol increased after exposure to isoflurane at 9 weeks (1859.6 ± 383.2-2748.0 ± 235.3 nmol/L, p < 0.01) and postpartum (3376.7 ± 322.2-4091.6 ± 195.6 nmol/L, p < 0.001) but not at 5 weeks (2088.3 ± 326.4-2464.1 ± 538.0 nmol/L, p > 0.05). Blood ionized Ca(2+), Na(+) and plasma total Ca did not change, whereas plasma albumin decreased, and inorganic phosphate (PO4) and Cl(-) increased upon exposure to isoflurane. Isoflurane decreased tALP (43.2 ± 6.6-40.2 ± 5.9 IU/L, p = 0.01) and increased glucose (7.5 ± 0.6-10.9 ± 1.7 mmol/L, p < 0.0001) postpartum. Isoflurane inflates the assessment of a bone-derived biomarker, OC, during rapid growth, but not following pregnancy when formation is very low. Measurements prior to anaesthesia are recommended to reflect normal metabolism.

Tooth loss early in life accelerates age-related bone deterioration in mice

Both osteoporosis and tooth loss are health concerns that affect many older people. Osteoporosis is a common skeletal disease of the elderly, characterized by low bone mass and microstructural deterioration of bone tissue. Chronic mild stress is a risk factor for osteoporosis. Many studies showed that tooth loss induced neurological alterations through activation of a stress hormone, corticosterone, in mice. In this study, we tested the hypothesis that tooth loss early in life may accelerate age-related bone deterioration using a mouse model. Male senescence-accelerated mouse strain P8 (SAMP8) mice were randomly divided into control and toothless groups. Removal of the upper molar teeth was performed at one month of age. Bone response was evaluated at 2, 5 and 9 months of age. Tooth loss early in life caused a significant increase in circulating corticosterone level with age. Osteoblast bone formation was suppressed and osteoclast bone resorption was activated in the toothless mice. Trabecular bone volume fraction of the vertebra and femur was decreased in the toothless mice with age. The bone quality was reduced in the toothless mice at 5 and 9 months of age, compared with the age-matched control mice. These findings indicate that tooth loss early in life impairs the dynamic homeostasis of the bone formation and bone resorption, leading to reduced bone strength with age. Long-term tooth loss may have a cumulative detrimental effect on bone health. It is important to take appropriate measures to treat tooth loss in older people for preventing and/or treating senile osteoporosis.

The antidepressant bupropion exerts alleviating properties in an ovariectomized osteoporotic rat model

AIM

Depression is a risk factor for impaired bone mass and micro-architecture, but several antidepressants were found to increase the incidence of osteoporotic fractures. In the present study we used ovariectomized (OVX) rats as a model of osteoporosis to investigate the effects of the antidepressant bupropion on the femoral bones.

METHODS

OVX animals were treated with bupropion (30, 60 mg·kg(-1)·d(-1)) for six weeks. Bone turnover biomarkers (urinary DPD/Cr ratio, serum BALP, OC, TRAcP 5b, CTX and sRANKL levels) and inflammatory cytokines (TNF-α, IL-1β and IL-6) were determined using ELISA. Inductively coupled plasma mass spectroscopy (ICP-MS) was used to determine the femoral bone mineral concentrations. The cortical and trabecular morphometric parameters of femoral bones were determined using micro-CT scan and histopathology.

RESULTS

In OVX rats, the levels of bone turnover biomarkers and inflammatory cytokines were significantly elevated and femoral bone Ca(2+) and PO4(3-) concentrations were significantly reduced. Moreover, cortical and trabecular morphometric parameters and histopathology of femoral bones were severely altered by ovariectomy. Bupropion dose-dependently inhibited the increases in bone turnover biomarkers and inflammatory cytokines. OVX rats treated with the high dose of bupropion showed normal mineral concentrations in femoral bones. The altered morphometric parameters and histopathology of femoral bones were markedly attenuated by the treatment.

CONCLUSION

Bupropion exerts osteo-protective action in OVX rats through suppressing osteoclastogenesis-inducing factors and inflammation, which stabilize the osteoclasts and decrease bone matrix degradation or resorption.

Effects of Active Mastication on Chronic Stress-Induced Bone Loss in Mice

Chronic psychologic stress increases corticosterone levels, which decreases bone density. Active mastication or chewing attenuates stress-induced increases in corticosterone. We evaluated whether active mastication attenuates chronic stress-induced bone loss in mice. Male C57BL/6 (B6) mice were randomly divided into control, stress, and stress/chewing groups. Stress was induced by placing mice in a ventilated restraint tube (60 min, 2x/day, 4 weeks). The stress/chewing group was given a wooden stick to chew during the experimental period. Quantitative micro-computed tomography, histologic analysis, and biochemical markers were used to evaluate the bone response. The stress/chewing group exhibited significantly attenuated stress-induced increases in serum corticosterone levels, suppressed bone formation, enhanced bone resorption, and decreased trabecular bone mass in the vertebrae and distal femurs, compared with mice in the stress group. Active mastication during exposure to chronic stress alleviated chronic stress-induced bone density loss in B6 mice. Active mastication during chronic psychologic stress may thus be an effective strategy to prevent and/or treat chronic stress-related osteopenia.

Chewing ameliorates chronic mild stress-induced bone loss in senescence-accelerated mouse (SAMP8), a murine model of senile osteoporosis

Chronic mild stress is a risk factor for osteoporosis and chewing inhibits the stress response. We examined the effect of chewing on chronic stress-induced bone loss and bone microstructural deterioration in mice. The senescence-accelerated mouse strain P8 (SAMP8) was randomly divided into control, stress, and stress with chewing groups of fifteen animals each. Mice in the stress and stress with chewing groups were placed in a ventilated restraint tube for 60minutes, twice a day for 4weeks. The restrained mice were simultaneously subjected daily to one of the following stressors: water immersion, physical shaking and flashing lights. Mice in the stress with chewing group were allowed to chew a wooden stick during the experimental period. After the experiment, the bone response was evaluated using quantitative micro computed tomography, bone histomorphometry, and biochemical markers. Exposure of SAMP8 mice to chronic stress resulted in significant increase of the blood corticosterone and noradrenaline levels, and adrenal weight. The bone resorption was activated and the bone formation was suppressed. Trabecular bone volume and trabecular number were decreased in both the vertebra and distal femur of the stress group. Chewing under chronic stress prevented the increase in the blood corticosterone and noradrenaline levels, attenuated the reduced bone formation and increased bone resorption, improved the trabecular bone loss and bone microstructural deterioration induced by chronic mild stress. These findings indicate that chewing can ameliorate chronic stress-induced bone loss in SAMP8 mice. Thus, chewing may represent a useful method preventing and/or treating chronic stress-related osteoporosis.

Decreased sensory responses in osteocalcin null mutant mice imply neuropeptide function

Osteocalcin, the most abundant member of the family of extracellular mineral binding gamma-carboxyglutamic acid proteins is synthesized primarily by osteoblasts. Its affinity for calcium ions is believed to limit bone mineralization. Several of the numerous hormones that regulate synthesis of osteocalcin, including glucocorticoids and parathyroid hormone, are also affected by stressful stimuli that require energy for an appropriate response. Based on our observations of OC responding to stressful sensory stimuli, the expression of OC in mouse and rat sensory ganglia was confirmed. It was thus hypothesized that the behavioral responses of the OC knockout mouse to stressful sensory stimuli would be abnormal. To test this hypothesis, behaviors related to sensory aspects of the stress response were quantified in nine groups of mice, aged 4-14 months, comparing knockout with their wild-type counterparts in six distinctly different behavioral tests. Resulting data indicated the following statistically significant differences: open field grooming frequency following saline injection, wild-type > knockout; paw stimulation with Von Frey fibers, knockout < wild-type; balance beam, knockout mobility < WT; thermal sensitivity to heat (tail flick), knockout < wild-type; and cold, knockout < wild-type. Insignificant differences in hanging wire test indicate that these responses are unrelated to reduced muscle strength. Each of these disparate environmental stimuli provided data indicating alterations of responses in knockout mice that suggest participation of osteocalcin in transmission of information about those sensory stimuli.

Ethanol and stress activate catecholamine synthesis in the adrenal: effects on bone

Ethanol consumption and mental stress activate the sympathetic nervous system, which can adversely affect bone. We compared six groups of 10 young adult rats, three with and three without 2 h daily restraint stress. Two groups consumed food and water ad libitum, two received food and 6% (w/v) ethanol as drinking water, and two received the amount of food consumed by ethanol rats the previous day plus water ad libitum (pairfed). After 6 weeks, rats were killed. Plasma, femurs, lumbar vertebrae, and adrenals were harvested. Femoral dimensions were measured and biomechanical properties were tested by three-point bending. Plasma osteocalcin, vertebral osteocalcin mRNA levels, and adrenomedullary tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT) mRNA levels were quantified. Daily restraint decreased weight gain and femoral length compared to dietary controls, and appeared to partially preserve bone strength, especially in calorie-restricted pairfed rats. Femoral strength was significantly affected by treatment in that bones of pairfed controls were weakest, ethanol drinkers were intermediate, and ad libitum restrained were strongest. Femoral yield load, displacement, and work at yield load were negatively correlated with TH and DBH mRNA levels, but not PNMT, suggesting a negative influence of norepinephrine. Plasma osteocalcin and dry weight of lumbar 3-5 vertebrae were unaffected; however, osteocalcin mRNA in second lumbar vertebrae was positively correlated with TH, DBH, and PNMT levels. Ethanol consumption at this level had little effect on femur morphology or strength. In contrast, the data suggested possible stimulation rather than inhibition of vertebral bone formation.

Differing effects of acute and chronic stressors on plasma osteocalcin and leptin in rats

Stressor activation of the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis can have profound effects on bone and also appetite and metabolism. We tested in rats the response of plasma osteocalcin (pOC, a bone biomarker that is acutely stress responsive), corticosterone, and leptin to (1) ethanol consumption (5% w/v) in a liquid diet (compared with ad libitum and pair-fed rats), (2) acute restraint, and (3) acute (once, 1 h) and (4) chronic (1 h/day for 7 weeks) social aggression. Basal pOC concentration did not differ with ethanol diet or social interaction, but was elevated by both foot restraint immobilization (Imo) and restraint in wire mesh cylinders (WMR). As previously reported for chronic Imo, ingestion of ethanol blunted the pOC response to Imo. Plasma corticosterone concentration was increased by acute WMR and acute social interaction but was unaltered by chronic social interaction. Plasma leptin concentration was markedly increased by Imo in ad libitum fed, but only slightly in ethanol or pair-fed rats. In contrast, the data reflect significant differences between acute and chronic stressor effects since chronic social stress had little effect on pOC or plasma corticosterone, but tended to decrease leptin level in relation to dominance. Lack of significant impact of prolonged ethanol intake or social aggression suggests physiological adaptation.

Depression induces bone loss through stimulation of the sympathetic nervous system

Major depression is associated with low bone mass and increased incidence of osteoporotic fractures. However, causality between depression and bone loss has not been established. Here, we show that mice subjected to chronic mild stress (CMS), an established model of depression in rodents, display behavioral depression accompanied by impaired bone mass and structure, as portrayed by decreases in trabecular bone volume density, trabecular number, and trabecular connectivity density assessed in the distal femoral metaphysis and L3 vertebral body. Bone remodeling analysis revealed that the CMS-induced skeletal deficiency is accompanied by restrained bone formation resulting from reduced osteoblast number. Antidepressant therapy, which prevents the behavioral responses to CMS, completely inhibits the decrease in bone formation and markedly attenuates the CMS-induced bone loss. The depression-triggered bone loss is associated with a substantial increase in bone norepinephrine levels and can be blocked by the beta-adrenergic antagonist propranolol, suggesting that the sympathetic nervous system mediates the skeletal effects of stress-induced depression. These results define a linkage among depression, excessive adrenergic activity, and reduced bone formation, thus demonstrating an interaction among behavioral responses, the brain, and the skeleton, which leads to impaired bone structure. Together with the common occurrence of depression and bone loss in the aging population, the present data implicate depression as a potential major risk factor for osteoporosis and the associated increase in fracture incidence.

Ethanol consumption increases rat stress hormones and adrenomedullary gene expression

Numerous reports document altered drinking behavior following acute stressors but few describe physiological responses to acute stress of chronic ethanol consuming subjects. We tested rats' responses to 120-min foot restraint immobilization (Immo) after 1 week of liquid diet containing 5% wt/vol ethanol (ethanol-fed). Controls consumed isocaloric liquid diet ad libitum (adlib-fed) or in amounts equal to that of ethanol-fed subjects on the previous day (pair-fed). Each rat was implanted with a tail artery cannula on day 7 to allow remote blood collection before and during Immo on day 8. Plasma epinephrine (Epi); norepinephrine (NE); corticosterone (Cort); prolactin (PRL); adrenomedullary gene expression of catecholamine biosynthetic enzymes tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine-N-methyl transferase (PNMT); and TH protein levels were measured. Ethanol-fed rats had two to threefold higher basal plasma Epi and NE and tended to have increased Cort compared to adlib-fed or pair-fed rats. Immo increased Epi and NE in ethanol-fed rats more than twofold above those observed in controls, and also increased Cort more in ethanol-fed than in control rats. PRL was marginally affected. Ethanol potentiated the normal immobilization-induced increase in adrenomedullary TH, DBH, and PNMT messenger RNA (mRNA). TH protein increased only in ethanol-fed rats. Increased plasma catecholamine levels, adrenomedullary gene expression, and TH protein concentration in nonimmobilized ethanol-fed rats strongly suggest that ethanol consumption was itself a stressor, which potentiated the subsequent response to acute Immo. Moreover, the observed interaction of ethanol and stress on plasma catecholamine levels illustrates the importance of minimizing additional stressful stimuli when investigating ethanol's physiological effects.

The hormonal and inflammatory responses to pelvic reconstructive surgery following major trauma

Patients undergoing trauma sustain an initial injury followed by further physiological challenges during surgery. Plasma osteocalcin (OC), a marker of osteoblastic activity, declines after major surgery. Increased cortisol secretion, and other components of the perioperative stress response, may play a role in mediating this response. We have examined the osteocalcin, hormonal and cytokine responses in twenty patients undergoing post-traumatic pelvic reconstruction surgery. We measured plasma osteocalcin, serum cortisol, bone specific alkaline phosphatase (BSAP), IL-6, IL-8, IL-10, plasma epinephrine and norepinephrine concentrations for up to 3 days after surgery. We recorded an increase in IL-6, IL-10 and epinephrine concentrations perioperatively and a fall in OC and BSAP concentrations. There were no significant changes in cortisol or IL-8 concentrations. Patients undergoing pelvic reconstruction surgery following trauma have a preserved inflammatory and catecholamine response but the cortisol response may be obtunded. Osteocalcin concentrations are affected by factors other than glucocorticoids.

Spaceflight affects bone formation in rhesus monkeys: a histological and cell culture study

Using analyses of iliac crest cell and tissue, back-scattered electron imaging, and biochemical techniques, we characterized the effects of a 14-day spaceflight (Bion 11) on bone structure and bone formation in two 3- to 4-yr-old male rhesus monkeys compared with eight age-matched Earth-control monkeys. We found that postflight bone volume was 35% lower than preflight values in flight monkeys. This was associated with reduced osteoid (-40%) and mineralizing (-32%) surfaces and decreased bone formation rate (-53%). Moreover, flight monkeys exhibited trends to lower values of mineralization profile in iliac bone (back-scattered electron imaging) and to decreased osteocalcin serum levels (P = 0.08). The initial number of trabecular bone cells yielded in cultures did not differ in flight and control animals before or after the flight. However, osteoblastic cell proliferation was markedly lower in postflight vs. preflight at 9 and 14 days of culture in one flight monkey. This study suggests that a 14-day spaceflight reduces iliac bone formation, osteoblastic activity, and/or recruitment in young rhesus monkeys, resulting in decreased trabecular bone volume.

Osteocalcin and the hormonal, inflammatory and metabolic response to major orthopaedic surgery

Plasma osteocalcin, a marker of osteoblastic activity, decreases after major abdominal and gynaecological surgery. Increased cortisol secretion and other hormonal and inflammatory components of the peri-operative stress response may play a role in mediating this response. We assessed the effects of three different anaesthetic techniques on peri-operative osteocalcin concentrations. Thirty-six female patients undergoing elective total hip replacement were randomly assigned to receive propofol, propofol plus 'three-in-one' block or etomidate as part of a general anaesthetic technique. We measured plasma osteocalcin and serum cortisol, bone specific alkaline phosphatase, interleukin-6, plasma epinephrine, norepinephrine, plasma glucose and cystatin C concentrations for up to 3 days after surgery. Etomidate successfully inhibited the cortisol response to surgery but plasma osteocalcin declined in all patients. This was accompanied by increased plasma catecholamines, interleukin-6 and glucose concentrations, and decreased cystatin C-values. Inhibition of the cortisol response to surgery failed to prevent a decrease in plasma osteocalcin concentrations after surgery, suggesting that other factors such as cytokines or catecholamines may play a significant role.

Repeated immobilization stress reduces rat vertebral bone growth and osteocalcin

We previously showed that psychological stressors alter plasma levels of osteocalcin (pOC), a bone-specific mineral binding protein, in ways that differ with the type of stressor. To determine effects of chronic stress, we examined vertebrae, pOC, and corticosterone levels from conscious rats subjected to foot-restraint immobilization (Immo) daily for 1-42 times. After 40-42 Immo, basal pOC was decreased by 25% compared with unstressed rats, and the subsequent rise in pOC during Immo was blunted. Corticosterone was elevated 10-fold during Immo. Immo for seven times did not change vertebral OC concentration, but caused a slight decrease in calcium and phosphorous concentrations in younger rats. Rats Immo for 42 times exhibited reduced body weight, vertebral weight, and vertebral OC concentration but no significant differences in vertebral mineral concentrations. Body fat content was visibly decreased. We do not know the source of or the stimulus for the initial rise in pOC. We conclude that both decreased growth and bone OC concentration are due to repeatedly elevated stress hormones.

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.

Increases in osteocalcin after ovariectomy are amplified by LPS injection: strain differences in bone remodelling

1. LPS (Escherichia coli serotype 0111:B4, 300 micrograms/mouse IP) increases serum osteocalcin in normal female C57B16 mice from 2 to 6 hr after its injection, with peak levels at 2-4 hr after LPS. 2. Both basal and LPS-stimulated serum osteocalcin were markedly inhibited by dexamethasone (10 mg/kg IP). 3. When observed 3 hr after LPS injection, serum osteocalcin was increased by ovariectomy (OVX) (with respect to sham-operated mice) and this increase was amplified in LPS-treated mice. This increase in osteocalcin was maximal 14 days after OVX, whereas urinary deoxypyridinoline cross-link levels were increased at all observation times (11-28 days). 4. All these changes were also observed in Balb/c mice but their magnitudes were consistently lower than those in C57B16 mice. 5. We propose that, (1) osteocalcin is a useful marker of bone remodelling in mice and the precision of measurement of changes in its levels after OVX is increased by LPS treatment and (2) C57B16 mice give greater magnitude and more consistent changes in both serum osteocalcin and urinary deoxypyridinoline cross-links after OVX, and may be a better strain for development of an in vivo model of post-menopausal osteoporosis.