Biochemical markers for assessment of calcium economy and bone metabolism: application in clinical trials from pharmaceutical agents to nutritional products.

Nutrition plays an important role in osteoporosis prevention and treatment. Substantial progress in both laboratory analyses and clinical use of biochemical markers has modified the strategy of anti-osteoporotic drug development. The present review examines the use of biochemical markers in clinical research aimed at characterising the influence of foods or nutrients on bone metabolism. The two types of markers are: (i) specific hormonal factors related to bone; and (ii) bone turnover markers (BTM) that reflect bone cell metabolism. Of the former, vitamin D metabolites, parathyroid hormone, and insulin-like growth factor-I indicate responses to variations in the supply of bone-related nutrients, such as vitamin D, Ca, inorganic phosphate and protein. Thus modification in bone remodelling, the key process upon which both pharmaceutical agents and nutrients exert their anti-catabolic or anabolic actions, is revealed. Circulating BTM reflect either osteoclastic resorption or osteoblastic formation. Intervention with pharmacological agents showed that early changes in BTM predicted bone loss and subsequent osteoporotic fracture risk. New trials have documented the influence of nutrition on bone-tropic hormonal factors and BTM in adults, including situations of body-weight change, such as anorexia nervosa, and weight loss by obese subjects. In osteoporosis-prevention studies involving dietary manipulation, randomised cross-over trials are best suited to evaluate influences on bone metabolism, and insight into effects on bone metabolism may be gained within a relatively short time when biochemical markers are monitored.

Dairy in adulthood: from foods to nutrient interactions on bone and skeletal muscle health.

The risk of fragility fractures exponentially increases with aging. Reduced mass and strength of both bone in osteoporosis and skeletal muscle in sarcopenia play a key role in the age-related incidence of fragility fractures. Undernutrition is often observed in the elderly, particularly in those subjects experiencing osteoporotic fractures, more likely as a cause than a consequence. Calcium (Ca), inorganic phosphate (Pi), vitamin D, and protein are nutrients that impact bone and skeletal muscle integrity. Deficiency in the supply of these nutrients increases with aging. Dairy foods are rich in Ca, Pi, and proteins and in many countries are fortified with vitamin D. Dairy foods are important souces of these nutrients and go a long way to meeting the recommendations, which increase with aging. This review emphaszes the interactions between these 4 nutrients, which, along with physical activity, act through cellular and physiological pathways favoring the maintenance of both bone and skeletal muscle structure and function.

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

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

Cbfa1-independent decrease in osteoblast proliferation, osteopenia, and persistent embryonic eye vascularization in mice deficient in Lrp5, a Wnt coreceptor.

The low-density lipoprotein receptor-related protein (Lrp)-5 functions as a Wnt coreceptor. Here we show that mice with a targeted disruption of Lrp5 develop a low bone mass phenotype. In vivo and in vitro analyses indicate that this phenotype becomes evident postnatally, and demonstrate that it is secondary to decreased osteoblast proliferation and function in a Cbfa1-independent manner. Lrp5 is expressed in osteoblasts and is required for optimal Wnt signaling in osteoblasts. In addition, Lrp5-deficient mice display persistent embryonic eye vascularization due to a failure of macrophage-induced endothelial cell apoptosis. These results implicate Wnt proteins in the postnatal control of vascular regression and bone formation, two functions affected in many diseases. Moreover, these features recapitulate human osteoporosis-pseudoglioma syndrome, caused by LRP5 inactivation.

Energy requirements in hospitalized elderly people.

OBJECTIVES: To estimate energy intake and energy expenditure (EE) in elderly hospitalized patients recovering from an acute illness. DESIGN: Cross-sectional evaluation of the disparity between energy intake and expenditure. PARTICIPANTS: Ninety geriatric patients (mean age+/-standard deviation 79.7+/-7.5) admitted to acute care or rehabilitation units. MEASUREMENTS: Patients' energy intake and resting EE (REE) were measured over a 3-day period. Blood samples were taken to determine C-reactive protein (CRP), creatinine, and albumin concentrations and to check renal function. RESULTS: Energy intake was higher than REE by a factor of 1.29, but it was lower than the energy requirement. Energy intake, adjusted for differences in body weight, was independent of sex, highest in those who were malnourished (defined as a body mass index (BMI) <21), and lowest in patients who scored poorly on the Mini-Mental State Examination. Energy intake and REE were independent of plasma CRP, creatinine, and albumin concentrations, as well as the initial diagnosis. REE was similar in men and women, at 18.8 kcal/kg per day. REE was 21.4 kcal/kg per day in patients with a BMI of 21 or less and 18.4 kcal/kg per day in those with a BMI greater than 21 kg/m2. The Harris-Benedict equation accurately predicted mean REE. CONCLUSION: The mean REE of the geriatric patients studied was 18.8 kcal/kg per day, whereas energy intake was just sufficient to cover minimal requirements. Thus, hospitalized elderly patients are likely to benefit from higher calorie intake.

Trabecular bone microarchitecture is related to the number of risk factors and etiology in osteoporotic men.

Microarchitecture of trabecular bone is a very important component of bone quality in osteoporosis and a determinant of vertebral fracture in men with low bone mineral density (BMD). In contrast to women, male osteoporosis is, in most cases, secondary. The relationships between microarchitecture and different risk factors have never been evaluated in men. About 152 men with low BMD at the lumbar spine or hip (BMD, T-score < -2.5) were included in this study. Risk factors were: age, BMI, alcohol intake, corticosteroid therapy, hypogonadism, and chronic diseases. Transiliac bone biopsies were obtained and histomorphometry was done on an image analyzer; the following parameters were measured: cortical thickness (Ct.Th), trabecular bone volume (BV/TV), trabecular thickness (Tb.Th), separation (Tb.Sp) and number (Tb.N), interconnectivity Index (ICI), star volume of the bone marrow, and strut analysis with node and free-end count. The 50 men with two risk factors had a lower BMD, lower Ct.Th and a significant higher star volume than those with one factor or idiopathic osteoporosis. The 26 men with at least three risk factors, had a lower BMD, a reduction of BV/TV and Ct.Th and a marked disorganization of the trabecular network (increased Tb.Sp, ICI, star volume, and free-end to free-end struts). The prevalence of vertebral fractures was higher in these patients. When the main risk factor was considered, a marked decrease in trabecular bone connectivity was observed in hypogonadic men. In osteoporotic men, higher the number of risk factors, lower the connectivity of trabecular network and higher the vertebral fracture risk.

Bigenic Cre/loxP, puDeltatk conditional genetic ablation.

Genetic ablation experiments are used to resolve problems regarding cell lineages and the in vivo function of certain groups of cells. We describe a two-component conditional ablation technology using a mouse carrying an X-linked puDeltatk transgene, which is only activated in cells expressing Cre. Ablation of the Cre-expressing cells can be temporally regulated by the time of ganciclovir (GCV) administration. This strategy was demonstrated using a Col2Cre transgenic line. Differentiating chondrocytes in bigenic animals could be ablated at different developmental stages resulting in disorganized growth plates and dwarfism. Macrocephaly, macroglossia and umbilical hernia were also observed in ablated 18.5 dpc embryos. Crosses between the puDeltatk selector transgenic line and existing cre lines will facilitate numerous temporally regulated tissue-specific ablation experiments.

LRP5 mutations in osteoporosis-pseudoglioma syndrome and high-bone-mass disorders.

The LDL receptor-related protein 5 (LRP5) is a member of the LDL receptor family, which also includes the VLDL receptor and the apolipoprotein E receptor 2. The LRP5 is a co-receptor of Wnt located on the osteoblast membrane between two other receptors, Frizzled and Kremen. Frizzled and LRP5 bind to Wnt, thereby stabilizing beta-catenin and activating bone formation. When the dickkopf protein (Dkk) binds to Kremen and LRP5, this last undergoes internalization and therefore becomes unable to bind Wnt; this leads to degradation of beta-catenin and to inhibition of bone formation. In humans, loss of LRP5 function causes osteoporosis-pseudoglioma syndrome, which is characterized by congenital blindness and extremely severe childhood-onset osteoporosis (lumbar spine Z-score often < -4) with fractures. The G171V mutation prevents Dkk from binding to LRP5, thereby increasing LRP5 function; the result is high bone mass due to uncoupling of bone formation and resorption. The Z-scores in this condition can exceed +6 at the hip and spine. The LRP5 and Wnt/beta-catenin reflect the level of bone formation and play a central role in bone mass accrual and normal distribution. Furthermore, LRP5 may contribute to mediate mechanical loads within bone tissue. Identification of the Wnt/beta-catenin pathway is a breakthrough in the elucidation of pathophysiological mechanisms affecting bone tissue and suggests new treatment targets for patients with osteoporosis or specific malignant conditions such as myeloma and sclerotic bone metastases.

Reversible skeletal abnormalities in gamma-glutamyl transpeptidase-deficient mice.

Gamma-glutamyl transpeptidase (GGT) is a widely distributed ectopeptidase responsible for the degradation of glutathione in the gamma-glutamyl cycle. This cycle is implicated in the metabolism of cysteine, and absence of GGT causes a severe intracellular decrease in this amino acid. GGT-deficient (GGT-/-) mice have multiple metabolic abnormalities and are dwarf. We show here that this latter phenotype is due to a decreased of the growth plate cartilage total height resulting from a proliferative defect of chondrocytes. In addition, analysis of vertebrae and tibiae of GGT-/- mice revealed a severe osteopenia. Histomorphometric studies showed that this low bone mass phenotype results from an increased osteoclast number and activity as well as from a marked decrease in osteoblast activity. Interestingly, neither osteoblasts, osteoclasts, nor chondrocytes express GGT, suggesting that the observed defects are secondary to other abnormalities. N-acetylcysteine supplementation has been shown to reverse the metabolic abnormalities of the GGT-/- mice and in particular to restore the level of IGF-1 and sex steroids in these mice. Consistent with these previous observations, N-acetylcysteine treatment of GGT-/- mice ameliorates their skeletal abnormalities by normalizing chondrocytes proliferation and osteoblastic function. In contrast, resorbtion parameters are only partially normalized in GGT-/- N-acetylcysteine-treated mice, suggesting that GGT regulates osteoclast biology at least partly independently of these hormones. These results establish the importance of cysteine metabolism for the regulation of bone remodeling and longitudinal growth.

Atypical pattern of acute severe shoulder pain: contribution of sonography.

A patient presented with an atypical pattern of acute severe shoulder pain. Sonography elucidated the mechanism of the pain and allowed effective treatment. The patient was unable not only to move her shoulder but also to flex and to extend her elbow. Sonography showed a calcific deposit in the subscapularis tendon with local edema displacing the long head of the biceps tendon out of the bicipital groove. Local injection of a glucocorticoid under ultrasonographic control was followed within 7 days by subsidence of the subscapularis tendon edema and by a return of the long head of the biceps tendon to its normal position in the bicipital groove.

The absorptiometry T-score: influence of selection of the reference population and related considerations for everyday practice.

OBJECTIVES: The WHO definition of osteoporosis is based on T-scores, which are calculated from mean bone mineral density values in reference populations composed of young adults. The definition of this reference population is a key-point. METHODS: We compared lumbar spine T-scores in three reference populations of young adults, one from the US and two from France. RESULTS: Reference values were higher in the American population than in the two French populations. As a result, the prevalence of a T-score indicating osteoporosis in a population of 2887 patients aged 20-87 years (mean age, 62.4 +/- 9.5 years) was 32% with the American reference population and 22% and 24% with the two French populations. Thus, about 25% and 32% of patients classified as having osteoporosis with the American reference population did not have osteoporosis with the two French reference populations, respectively. There was no significant difference between the prevalences obtained with the two French populations. CONCLUSIONS: Reference populations of young adults should be representative of the population of each country, for each measurement site, gender, and ethnic group. When evaluating individuals, in addition to the clinical setting and T-score, age should be taken into account. The Z-score remains useful.

Labyrinthectomy decreases bone mineral density in the femoral metaphysis in rats.

To determine whether the vestibular system could influence bone remodeling in rats, we measured bone mineral density with dual energy X-rays absorptiometry before and 30 days after bilateral labyrinthectomy. Comparatively to intact control rats, labyrinthectomized animals showed a reduced bone mineral density in distal femoral metaphysis (p = 0.007): the variations between D0 and D30 were +3.0% for controls and -13.9% for labyrinthectomized rats. No significant difference between the 2 groups was observed in the whole body mineral density. These results suggest that the peripheral vestibular apparatus is a modulator of bone mass and more specifically in weight bearing bone. We discuss possible mechanisms of this vestibular influence probably mediated by the sympathetic nervous system.

[Physiopathology of osteoporosis]. / Physiopathologie de l'ostéoporose.

PURPOSE: The pathophysiology of osteoporosis has seen many recent progress especially with the use of genetically modified animal models. CURRENT KNOWLEDGE AND KEY POINTS: Among many discoveries, one can notice the crucial role of LRP5, GH, IGF-1 and the sex hormones receptors in the acquisition of the peak bone mass, the control of bone remodeling by the sympathetic nervous system and his implication as a transmitter of mechanical loading in bone. Also, the role of estrogen and androgen receptors as well as the aromatase is specified according to sexes. The role of growth plate's chondrocytes in the installation of the trabecular bone network is better and better demonstrated. The greater periosteal apposition in men, mediated by androgens receptor, seems to explain the greatest radial growth and so the greatest bone resistance to mechanical strains like a lower fracture rate in men compared to women. The bone microarchitecture and quality explain an important part of the mechanical properties of bones and why considering the same bone mass one bone is breaking and another one not. FUTURE PROSPECTS AND PROJECTS: Many therapeutic applications should finalize the discovery of these new bone cells signalisation pathways.

Novel LRP5 gene mutation in a patient with osteoporosis-pseudoglioma syndrome.

Osteoporosis-pseudoglioma syndrome (OPPG) is a rare autosomal recessive disorder characterised by severe juvenile-onset osteoporosis and congenital or early-onset blindness. This serious illness is due to mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) that is a major actor in pathways involved in bone remodelling. Here, we report a novel frameshift mutation identified in a 22 year-old Tunisian boy of a consanguineous family. This patient had low bone mineral density (BMD), experienced multiple fractures during childhood and suffered ocular alterations with blindness. Direct DNA sequencing showed a homozygous 5 base pair insertion in exon 5 of the LRP5 gene. This new mutation is located in the first EGF-like domain and gives rise to a truncated protein of 384 amino acids. The functional significance of this mutation clearly indicates a loss-of-function mutation of the LRP5 gene leading to the observed OPPG phenotype. Rheumatologists must be aware of LRP5 gene that in addition to being a major gene in the mendelian disease that is OPPG syndrome seems to be involved in osteoporosis in the general population through some of its polymorphisms.

Extraspinal sciatica revealing late metastatic disease from parotid carcinoma.

Sciatica is a clinical symptom usually caused by a disk herniation and less often by other conditions such as tumors, infections, or inflammatory diseases. We report the case of a woman in whom sciatica led to the identification of a large pelvic metastasis from a carcinoma of the parotid gland.

Fibrillin-1 and -2 differentially modulate endogenous TGF-ß and BMP bioavailability during bone formation.

Extracellular regulation of signaling by transforming growth factor (TGF)-ß family members is emerging as a key aspect of organ formation and tissue remodeling. In this study, we demonstrate that fibrillin-1 and -2, the structural components of extracellular microfibrils, differentially regulate TGF-ß and bone morphogenetic protein (BMP) bioavailability in bone. Fibrillin-2-null (Fbn2(-/-)) mice display a low bone mass phenotype that is associated with reduced bone formation in vivo and impaired osteoblast maturation in vitro. This Fbn2(-/-) phenotype is accounted for by improper activation of latent TGF-ß that selectively blunts expression of osterix, the transcriptional regulator of osteoblast maturation, and collagen I, the structural template for bone mineralization. Cultured osteoblasts from Fbn1(-/-) mice exhibit improper latent TGF-ß activation as well, but mature faster because of increased availability of otherwise matrix-bound BMPs. Additional in vitro evidence excludes a direct role of microfibrils in supporting mineral deposition. Together, these findings identify the extracellular microfibrils as critical regulators of bone formation through the modulation of endogenous TGF-ß and BMP signaling.

Bone tissue and hyperhomocysteinemia.

Bone tissue quality is determined not only by multiple architectural variables, but also by the mechanical properties of collagen type 1. Homocysteinuria is a genetic disease whose manifestations include severe hyperhomocysteinemia and decreased bone strength. The effects of smaller homocysteine elevations on bone tissue are difficult to demonstrate in clinical studies. Studies in animals and in humans suggest that homocysteine may weaken collagen crosslinks and, if present in large amounts, interfere with bone remodeling. Whether routine homocysteine assays should be performed to detect bone frailty remains unclear. In clinical practice, the focus should be on identifying patients with potential causes of homocysteine elevation (e.g., medications), who should then be given vitamin D and folic acid supplementation if needed. This approach may improve not only bone health, but also vascular and general health.

Treatment and management of osteoporosis-pseudoglioma syndrome.

Osteoporosis-pseudoglioma syndrome (OPPG; MIM 259770) is a very rare genetic disorder with an autosomal recessive mode of inheritance, characterized by congenital or infancy-onset visual loss and skeletal fragility, diagnosed during childhood. This syndrome can lead to severe disability and chronic bone pain. Low-density lipoprotein receptor-related protein 5 (LRP5) is the gene mutated and inactivated in OPPG, and plays a pivotal role in bone accrual and skeletal remodeling by controlling bone formation through activators, such as Wnt proteins, or inhibitors, such as DKK1. OPPG should be differentiated from osteogenesis imperfecta and child abuse by clinicians. Eye examination, coupled to bone phenotype and research of LRP5 mutation, are key points to diagnose OPPG. Chronic pain should be managed correctly in this syndrome with severe functional disability. Bisphosphonates allows fracture prevention, the catch-up of bone mineral density and improvement in mobility in children with OPPG. New drugs favoring osteoblast function and osteoclast inhibition are potential candidates in the treatment of OPPG.