Bone histomorphometry in male idiopathic osteoporosis

Understanding the characteristics of idiopathic osteoporosis by a systematic review and meta-analysis

PURPOSE

To understand the pathophysiology of idiopathic osteoporosis (IOP) better, we conducted a systematic review and meta-analysis of bone mineral density (BMD), hormones, and bone turnover markers (BTMs) between IOP patients and healthy controls.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, an appropriate search query was created, and three databases, including PubMed, ScienceDirect, and Google Scholar, were searched for screening relevant original articles. Feasible information, both qualitative and quantitative, was extracted and used to conduct meta-analyses. Publication bias and heterogeneity among studies were evaluated using appropriate statistical tools.

RESULTS

A total of 21 studies were included in the meta-analysis. There was reduced BMD at the lumbar spine (LS) (pooled: SDM: -2.38, p-value: 0.0001), femoral neck (FN) (pooled: SDM: -1.75 p-value: 0.0001), total hip (TH) (pooled: SDM: -1.825, p-value: 0.0001) and distal radius (DR) (pooled: SDM of -0.476, p-value: 0.0001), of which LS was the most affected site. There was no significant change in BTMs compared with healthy controls. Total estradiol (SDM: -1.357, p-value: 0.003) was reduced, and parathyroid hormone (PTH) (SDM: 1.51, p-value: 0.03) and sex hormone-binding globulin (SHBG) (SDM: 1.454, p-value: 0.0001) were elevated in IOP patients compared with healthy controls.

CONCLUSION

Our meta-analysis, the first of its kind on IOP, defines it as showing BMD decline maximally at LS compared with healthy controls without any alterations in the BTMs. Further studies are required to understand gender differences and the significance of altered hormonal profiles in this condition.

Correlation of bone mineral density using the dual energy x-ray absorptiometry and the magnetic resonance imaging of the lumbar spine in Indian patients

Background

Dual-energy x-ray absorptiometry (DEXA) scan is extensively used to diagnose osteoporosis. But surprisingly, osteoporosis remains an underdiagnosed condition with many fragility fracture patients who have failed to undergo DEXA or received concomitant treatment for osteoporosis. Magnetic resonance imaging (MRI) of the lumbar spine is a routine radiological investigation bring done for low back pain. MRI can detect changes in the bone marrow signal intensity on the standard T1-weighted images. This correlation can be explored to measure osteoporosis in elderly and post-menopausal patients. The present study aims to find any correlation of bone mineral density using the DEXA and MRI of the lumbar spine in Indian patients.

Methods

Five regions of interest (ROI) of size 130-180 mm2 were placed in the vertebral body in the mid-sagittal section and parasagittal sections on either side (four in L1-L4 and one outside body) of elderly patients who underwent MRI for back pain. They also underwent a DEXA scan for osteoporosis. Signal to Noise Ratio (SNR) was calculated by dividing the mean signal intensity obtained for each vertebra by the standard deviation of the noise. Similarly, SNR was measured for 24 controls. An MRI-based "M score" was calculated by getting the difference in SNR patients to SNR controls and then dividing it by the control's standard deviation (SD). Correlation between the T score on DEXA and M scores on MRI was found out.

Results

With the M score greater than or equal to 2.82, the sensitivity was 87.5%, and the specificity was 76.5%. M scores negatively correlated with the T score. With the increase in the T score, the M score decreased. The Spearman correlation coefficient for the spine T score was -0.651, with a p-value of <0.001, and the hip T score was -0.428, with a p-value of 0.013.

Conclusion

Our study indicates that MRI investigations are helpful in Osteoporosis assessments. Even though MRI may not replace DEXA, it can give insight into elderly patients who get an MRI routinely for back pain. It may also have a prognostic value.

Aging and Bone Metabolism

Changes in bone architecture and metabolism with aging increase the likelihood of osteoporosis and fracture. Age-onset osteoporosis is multifactorial, with contributory extrinsic and intrinsic factors including certain medical problems, specific prescription drugs, estrogen loss, secondary hyperparathyroidism, microenvironmental and cellular alterations in bone tissue, and mechanical unloading or immobilization. At the histological level, there are changes in trabecular and cortical bone as well as marrow cellularity, lineage switching of mesenchymal stem cells to an adipogenic fate, inadequate transduction of signals during skeletal loading, and predisposition toward senescent cell accumulation with production of a senescence-associated secretory phenotype. Cumulatively, these changes result in bone remodeling abnormalities that over time cause net bone loss typically seen in older adults. Age-related osteoporosis is a geriatric syndrome due to the multiple etiologies that converge upon the skeleton to produce the ultimate phenotypic changes that manifest as bone fragility. Bone tissue is dynamic but with tendencies toward poor osteoblastic bone formation and relative osteoclastic bone resorption with aging. Interactions with other aging physiologic systems, such as muscle, may also confer detrimental effects on the aging skeleton. Conversely, individuals who maintain their BMD experience a lower risk of fractures, disability, and mortality, suggesting that this phenotype may be a marker of successful aging. © 2023 American Physiological Society. Compr Physiol 13:4355-4386, 2023.

Women’s lifetime reproductive profiles and frailty among aging individuals in the USA and the Philippines

Frailty, particularly traits which are related to sex steroid hormone production, results from the age-associated decline in function considered to be part of the typical aging process. This process may vary with influences including environmental, biological, or lifestyle factors. An area of concern that has received relatively little attention is the impact of cumulative lifetime changes in sex steroid hormones related to the traits we see that typify the human aging process. Women’s lifetime reproductive profiles include menstrual/ovulatory cycles, gestation, and lactation, all of which respond to changes in sex steroid hormone levels. Here, we review data on reproductive profiles and risks of frailty among post-menopausal women. In the current study, our team collected reproductive histories of women to determine the estimated number of lifetime reproductive cycles (ELC). We interviewed 44 women in the USA and 67 women in the Philippines aged 65 years plus to obtain data on reproductive cycles, pregnancy, and breastfeeding. Participants completed several frailty tasks including grip strength, a sit-to-stand test, and gait speed. While ELC was not associated with frailty in the US population, higher ELC was associated with lower frailty among the Philippine population. The current study should be considered as an exploratory project investigating field-friendly methods to use when considering lifetime reproductive histories and the influence on the aging process.

Large-scale osteocyte lacunar morphological analysis of transiliac bone in normal and osteoporotic premenopausal women

Bone's ability to adapt is governed by the network of embedded osteocytes, which inhabit individual pores called lacunae. The morphology of these lacunae and their resident osteocytes are known to change with age and diseases such as postmenopausal osteoporosis. However, it is unclear whether alterations in lacunar morphology are present in younger populations with osteoporosis. To investigate this, we implemented a previously validated methodology to image and quantify the three-dimensional morphometries of lacunae on a large scale with ultra-high-resolution micro-computed tomography (microCT) in transiliac bone biopsies from three groups of premenopausal women: control n = 39; idiopathic osteoporosis (IOP) n = 45; idiopathic low BMD (ILBMD) n = 19. Lacunar morphometric parameters were measured in both trabecular and cortical bone such as lacunar density (Lc.N/BV), lacunar volume (Lc.V), and lacunar sphericity (Lc.Sr). These were then compared against each other and also with previously measured tissue morphometries such as bone volume density (BV/TV), trabecular separation (Tb.Sp), trabecular number (Tb.N), and others. We detected no differences in lacunar morphology between the IOP, ILBMD and healthy premenopausal women. In contrast, we did find significant differences between lacunar morphologies including Lc.N/BV, Lc. V, and Lc. Sr in cortical and trabecular regions within all three groups (p < 0.001), which was consistent with our previous findings on a subgroup of the healthy group. Furthermore, we discovered strong correlations between Lc. Sr from trabecular regions with the measured BV/TV (R = -0.90, p < 0.05). The findings and comprehensive lacunar dataset we present here will be a crucial foundation for future investigations of the relationship between osteocyte lacunar morphology and disease.

Diffusion-weighted magnetic resonance imaging of mandibular bone marrow: do apparent diffusion coefficient values of the cervical vertebrae and mandible correlate with age?

OBJECTIVES

The objective of this investigation was to assess the correlation between the mandible and cervical vertebrae bone marrow apparent diffusion coefficient (ADC), obtained by diffusion-weighted magnetic resonance imaging (DWI), with age; to verify the correlation between ADC values from the mandible and the cervical vertebrae; to describe and assess the differences between ADC values obtained from DWI examinations of distinct mandible areas as well as cervical vertebrae.

METHODS

Thirty imaging examinations with DWI for that included the mandible and C1, C2, C3, and C4 vertebrae in the same examination were included. ADC values were collected from 7 distinct areas in the mandible and the cervical vertebrae. Differences between ADC values and non-parametric correlations were performed.

RESULTS

A total of 270 regions were assessed. No significant difference was found between ADC values of all areas tested. An inverse correlation was found between C2, C3, and C4 vertebrae ADC values and age. The significant correlation of anatomic area ADC values and age were presented as graphics to verify if the linear trend of ADC values and age are in accordance with the literature CONCLUSIONS: The mandible area that most correlates with the cervical vertebrae, using ADC values, is the posterior trabecular area, below the inferior molars. Also, C2, C3, and C4 vertebrae ADC values inversely correlate with age, which demonstrates the bone qualitative changes in bone composition. ADC values may be useful for the qualitative assessment of bone quality to screen patients at osteoporosis risk.

How to manage osteoporosis before the age of 50

This narrative review discusses several aspects of the management of osteoporosis in patients under 50 years of age. Peak bone mass is genetically determined but can also be affected by lifestyle factors. Puberty constitutes a vulnerable period. Idiopathic osteoporosis is a rare, heterogeneous condition in young adults due in part to decreased osteoblast function and deficient bone acquisition. There are no evidence-based treatment recommendations. Drugs use can be proposed to elderly patients at very high risk. Diagnosis and management of osteoporosis in the young can be challenging, in particular in the absence of a manifest secondary cause. Young adults with low bone mineral density (BMD) do not necessarily have osteoporosis and it is important to avoid unnecessary treatment. A determination of BMD is recommended for premenopausal women who have had a fragility fracture or who have secondary causes of osteoporosis: secondary causes of excessive bone loss need to be excluded and treatment should be targeted. Adequate calcium, vitamin D, and a healthy lifestyle should be recommended. In the absence of fractures, conservative management is generally sufficient, but in rare cases, such as chemotherapy-induced osteoporosis, antiresorptive medication can be used. Osteoporosis in young men is most often of secondary origin and hypogonadism is a major cause; testosterone replacement therapy will improve BMD in these patients. Diabetes is characterized by major alterations in bone quality, implying that medical therapy should be started sooner than for other causes of osteoporosis. Primary hyperparathyroidism, hyperthyroidism, Cushing's syndrome and growth hormone deficiency or excess affect cortical bone more often than trabecular bone.

Sensitivity and specificity assessment of DWI and ADC for the diagnosis of osteoporosis in postmenopausal patients

OBJECTIVE

In this study, we prospectively investigated the diagnostic capability of diffusion-weighted magnetic resonance imaging (DWI) in assessing vertebral marrow changes in postmenopausal women with osteoporosis.

MATERIALS AND METHODS

Sixty postmenopausal women (mean age 60.2 ± 6.11 years) underwent both dual-energy X-ray absorptiometry (DEXA) of the spine and MRI. Results were acquired from each patient's L2 to L4, for a total of 180 lumbar vertebrae. Based on bone mineral density (BMD) measurements obtained from DEXA, the vertebrae were divided into three groups as follows: normal (n = 52), osteopenic (n = 92), and osteoporotic (n = 36). DWI of the vertebral body was performed to assess the apparent diffusion coefficient (ADC). The ADC outcomes were compared among the three groups and correlated with BMD.

RESULTS

ADC values (× 10^-6 mm²/s) were significantly lower in the osteoporotic group (135.67 ± 44.10) in comparison to the normal group (561.85 ± 190.37) (P = 0.0001). The results showed a positive correlation between ADC and BMD values (r = 0.748, P = 0.0001). In receiver operating characteristic (ROC) analysis, the area under the curve for DWI was 0.912 (P = 0.001). A cut-off value of 400 mm²/s for the diagnosis of osteoporosis; had sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of 90.90%, 83.34%, 88.89%, 93.75%, and 76.93%, respectively.

CONCLUSION

ADC values correlated positively with BMD in women. DWI can allow quantitative evaluation of bone marrow changes and osteoporosis in postmenopausal women.

Abaloparatide improves cortical geometry and trabecular microarchitecture and increases vertebral and femoral neck strength in a rat model of male osteoporosis

Androgen deficiency is a leading cause of male osteoporosis, with bone loss driven by an inadequate level of bone formation relative to the extent of bone resorption. Abaloparatide, an osteoanabolic PTH receptor agonist used to treat women with postmenopausal osteoporosis at high risk for fracture, increases bone formation and bone strength in estrogen-deficient animals without increasing bone resorption. This study examined the effects of abaloparatide on bone formation, bone mass, and bone strength in androgen-deficient orchiectomized (ORX) rats, a male osteoporosis model. Four-month-old Sprague-Dawley rats underwent ORX or sham surgery. Eight weeks later, sham-operated rats received vehicle (saline; n = 10) while ORX rats (n = 10/group) received vehicle (Veh) or abaloparatide at 5 or 25 μg/kg (ABL5 or ABL25) by daily s.c. injection for 8 weeks, followed by sacrifice. Dynamic bone histomorphometry indicated that the tibial diaphysis of one or both abaloparatide groups had higher periosteal mineralizing surface, intracortical bone formation rate (BFR), endocortical BFR, and cortical thickness vs Veh controls. Vertebral trabecular BFR was also higher in both abaloparatide groups vs Veh, and the ABL25 group had higher trabecular osteoblast surface without increased osteoclast surface. By micro-CT, the vertebra and distal femur of both abaloparatide-groups had improved trabecular bone volume and micro-architecture, and the femur diaphysis of the ABL25 group had greater cortical thickness with no increase in porosity vs Veh. Biomechanical testing indicated that both abaloparatide-groups had stronger vertebrae and femoral necks vs Veh controls. These findings provide preclinical support for evaluating abaloparatide as an investigational treatment for male osteoporosis.

Abaloparatide, a novel osteoanabolic PTHrP analog, increases cortical and trabecular bone mass and architecture in orchiectomized rats by increasing bone formation without increasing bone resorption

Male osteoporosis can occur with advanced age and with hypogonadism, with increased bone resorption and/or inadequate bone formation contributing to reduced bone mass and increased fracture risk. Abaloparatide is a selective PTH receptor agonist that increases bone formation and bone mass in postmenopausal women with osteoporosis and in estrogen-deficient animals. The current study evaluated the effects of abaloparatide in orchiectomized (ORX) rats, a model of male osteoporosis. Four-month-old Sprague-Dawley rats underwent ORX or sham surgery; 8 weeks later the ORX groups exhibited relative osteopenia vs sham controls, based on dual X-ray absorptiometry (DXA) and/or peripheral quantitative computed tomography (pQCT) assessments at the total body, lumbar spine, femur, and tibia. ORX rats (n = 10/group) were then injected daily (s.c.) for 8 weeks with vehicle or abaloparatide at 5 (ABL5) or 25 μg/kg/d (ABL25). Sham controls (n = 10) received s.c. vehicle. DXA and pQCT showed that one or both abaloparatide groups gained more areal and volumetric BMD at all sites analyzed compared with vehicle controls, leading to substantial or complete reversal of ORX-induced BMD deficits. pQCT also indicated greater gains in tibial cortical thickness in both abaloparatide groups versus vehicle controls. Tibial bone histomorphometry showed greater trabecular bone formation and bone volume and improved micro-architecture with abaloparatide, with no increase in osteoclasts. Abaloparatide also led to significant improvements in the balance of biochemical bone formation markers versus bone resorption markers, which correlated with BMD changes. These findings suggest that abaloparatide may have therapeutic benefits in men with osteoporosis.

Proceedings of the 2018 Santa Fe Bone Symposium: Advances in the Management of Osteoporosis

The Santa Fe Bone Symposium is an annual meeting devoted to clinical applications of recent advances in skeletal research. The 19th Santa Fe Bone Symposium convened August 3-4, 2018, in Santa Fe, New Mexico, USA. Attendees included physicians of many specialties, fellows in training, advanced practice providers, clinical researchers, and bone density technologists. The format consisted of lectures, case presentations by endocrinology fellows, and panel discussions, with all involving extensive interactive discussions. Topics were diverse, including an evolutionary history of calcium homeostasis, osteoporosis treatment in the very old, optimizing outcomes with orthopedic surgery, microbiome and bone, new strategies for combination and sequential therapy of osteoporosis, exercise as medicine, manifestations of parathyroid hormone excess and deficiency, parathyroid hormone as a therapeutic agent, cell senescence and bone health, and managing patients outside clinical practice guidelines. The National Bone Health Alliance conducted a premeeting on development of fracture liaison services. A workshop was devoted to Bone Health TeleECHO (Bone Health Extension for Community Healthcare Outcomes), a strategy of ongoing medical education for healthcare professions to expand capacity to deliver best practice skeletal healthcare in underserved communities and reduce the osteoporosis treatment gap.

Bone histomorphometry in transiliac biopsies from 48 normal, healthy men

Investigators and clinicians use bone histomorphometry data from iliac bone biopsies to study bone abnormalities in diseased patients, and to understand the safety and effectiveness of pharmaceutical interventions. This requires access to a high quality normal data-set to be used for comparisons, a resource that has not been adequate to date. The objective of this work is to present static and dynamic bone histomorphometry data from transilial bone biopsies performed on 48 healthy males, evenly distributed between ages 45 and 75. In addition, we compared these results with results from our earlier study in normal postmenopausal women (Recker et al., 1988 [1]). The data include bone density and anthropometric measurements, micro-CT, and a collection of serum biochemical measurements. We found that several of the histomorphometry variables were correlated with serum measurements, i.e. serum testosterone and sex hormone-binding globulin (SHBG). Micro-CT variables were correlated with the static histomorphometry variables, and were very similar. Age-related changes were observed for both histomorphometry and Micro-CT, but were surprisingly small in most cases. Comparisons with our previously reported histomorphometry data from normal women were surprisingly similar, but there was a significant age by gender interaction in the wall thickness (W.Th) measurements, i.e. there was a small increase in this variable with age in men, and a significant decline with age in women. The population selected for this study, and the prior study in normal women, were carefully chosen so as to rule out the presence of clinical, life-style or other confounding factors. While the cohort chosen herein was a convenience sample, and not a population-based sample, we believe it can be used as a reference standard with proper precautions in its interpretation and in its comparisons with diseased populations.

Aberrant tryptophan transport in cultured fibroblast from patients with Male Idiopathic Osteoporosis: An in vitro study

It has been demonstrated, that long-term chronic tryptophan deficiency, results in decreased serotonin synthesis, which may lead to low bone mass and low bone formation. Findings from studies in male patients with idiopathic osteoporosis suggested a decreased transport of tryptophan in erythrocytes of osteoporotic patients, indicating that serotonin system defects may be involved in the etiology of low bone mass. Tryptophan is the precursor of serotonin, and a disturbed transport of tryptophan is implicated in altered serotonin synthesis. However, no study has investigated the tryptophan transport kinetics in MIO patients. The aim of this study is to investigate the kinetic parameters of tryptophan transport in fibroblasts derived from MIO patients compared to age and sex matched controls. Fibroblast cells were cultured from skin biopsies obtained from 14 patients diagnosed with Male Idiopathic Osteoporosis and from 13 healthy age-sex matched controls, without a diagnosis of osteoporosis. Transport of the amino acid tryptophan across the cell membrane was measured by the cluster tray method. The kinetic parameters, maximal transport capacity (V_max) and affinity constant (K_m) were determined by using the Lineweaver-Burke plot equation. The results of this study have shown a significantly lower mean value for V_max (p = 0.0138) and lower K_m mean value (p = 0.0009) of tryptophan transport in fibroblasts of MIO patients compared to the control group. A lower V_max implied a decreased tryptophan transport availability in MIO patients. In conclusion, reduced cellular tryptophan availability in MIO patients might result in reduced brain serotonin synthesis and its endogenous levels in peripheral tissues, and this may contribute to low bone mass/formation. The findings of the present study could contribute to the etiology of idiopathic osteoporosis and for the development of novel approaches for diagnosis, treatment and management strategies of MIO.

Evaluation of MR Spectroscopy and Diffusion-Weighted MRI in Postmenopausal Bone Strength

AIM

To prospectively investigate the role of MR spectroscopy (MRS) and diffusion-weighted magnetic resonance imaging (DWI) in assessing vertebral marrow changes in postmenopausal women.

MATERIALS AND METHODS

Fifty postmenopausal women, who underwent dual-energy x-ray absorptiometry of the spine, were divided into three bone density groups (normal, osteopenia, and osteoporosis) based on T-score. Both MRS and DWI of the L3 vertebral body were performed to calculate the marrow fat content and apparent diffusion coefficient (ADC). The results were compared between three groups and correlated with BMD.

RESULTS

Vertebral marrow fat content was significantly increased in the osteoporotic group when compared with that of the osteopenic group and the normal bone density group. ADC values in the osteoporotic, osteopenic, and normal bone density groups were 338, 408 and 464, respectively, with statistically significant differences (P < 0.001). A statistically significant positive correlation between T-scores and ADC existed (r=0.694, p value <0.001). The vertebral marrow fat content was negatively correlated to the bone density (r=-0.455, p< 0.001) and to marrow ADC (r= -0.302, p < 0.05).

CONCLUSION

The postmenopausal women with osteoporosis exhibited a corresponding increase in vertebral marrow fat content as the bone density decreased. Marrow fat content and ADC were related to the bone density. MRS and DWI are helpful in evaluating the bone marrow changes in postmenopausal women.

From histology to micro-CT: Measuring and modeling resorption cavities and their relation to bone competence

The process of bone remodelling plays an essential role in the emergence and maintenance of bone geometry and its internal structure. Osteoclasts are one of the three main bone cell types that play a crucial role in the bone remodelling cycle. At the microstructural level, osteoclasts create bone deficits by eroding resorption cavities. Understanding how these cavities impair the mechanical quality of the bone is not only relevant in quantifying the impact of resorption cavities in healthy bone and normal aging, but maybe even more so in quantifying their role in metabolic bone diseases. Metabolic bone diseases and their treatment are both known to affect the bone remodelling cycle; hence, the bone mechanical competence can and will be affected. However, the current knowledge of the precise dimensions of these cavities and their effect on bone competence is rather limited. This is not surprising considering the difficulties in deriving three-dimensional (3D) properties from two-dimensional (2D) histological sections. The measurement difficulties are reflected in the evaluation of how resorption cavities affect bone competence. Although detailed 3D models are generally being used to quantify the mechanical impact of the cavities, the representation of the cavities themselves has basically been limited to simplified shapes and averaged cavity properties. Qualitatively, these models indicate that cavity size and location are important, and that the effect of cavities is larger than can be expected from simple bone loss. In summary, the dimensions of osteoclast resorption cavities were until recently estimated from 2D measures; hence, a careful interpretation of resorption cavity dimensions is necessary. More effort needs to go into correctly quantifying resorption cavities using modern 3D imaging techniques like micro-computed tomography (micro-CT) and synchrotron radiation CT. Osteoclast resorption cavities affect bone competence. The structure-function relationships have been analysed using computational models that, on one hand, provide rather detailed information on trabecular bone structure, but on the other incorporate rather crude assumptions on cavity dimensions. The use of high-resolution representations and parametric descriptions could be potential routes to improve the quantitative fidelity of these models.

Mouse models of telomere dysfunction phenocopy skeletal changes found in human age-related osteoporosis

A major medical challenge in the elderly is osteoporosis and the high risk of fracture. Telomere dysfunction is a cause of cellular senescence and telomere shortening, which occurs with age in cells from most human tissues, including bone. Telomere defects contribute to the pathogenesis of two progeroid disorders characterized by premature osteoporosis, Werner syndrome and dyskeratosis congenital. It is hypothesized that telomere shortening contributes to bone aging. We evaluated the skeletal phenotypes of mice with disrupted telomere maintenance mechanisms as models for human bone aging, including mutants in Werner helicase (Wrn^−/−), telomerase (Terc^−/−) and Wrn^−/−Terc^−/− double mutants. Compared with young wild-type (WT) mice, micro-computerized tomography analysis revealed that young Terc^−/− and Wrn^−/−Terc^−/− mice have decreased trabecular bone volume, trabecular number and trabecular thickness, as well as increased trabecular spacing. In cortical bone, young Terc^−/− and Wrn^−/−Terc^−/− mice have increased cortical thinning, and increased porosity relative to age-matched WT mice. These trabecular and cortical changes were accelerated with age in Terc^−/− and Wrn^−/−Terc^−/− mice compared with older WT mice. Histological quantification of osteoblasts in aged mice showed a similar number of osteoblasts in all genotypes; however, significant decreases in osteoid, mineralization surface, mineral apposition rate and bone formation rate in older Terc^−/− and Wrn^−/−Terc^−/− bone suggest that osteoblast dysfunction is a prominent feature of precocious aging in these mice. Except in the Wrn^−/− single mutant, osteoclast number did not increase in any genotype. Significant alterations in mechanical parameters (structure model index, degree of anistrophy and moment of inertia) of the Terc^−/− and Wrn^−/−Terc^−/− femurs compared with WT mice were also observed. Young Wrn^−/−Terc^−/− mice had a statistically significant increase in bone-marrow fat content compared with young WT mice, which remained elevated in aged double mutants. Taken together, our results suggest that Terc^−/− and Wrn^−/−Terc^−/− mutants recapitulate the human bone aging phenotype and are useful models for studying age-related osteoporosis.

Intravenous treatment with ibandronate normalizes bone matrix mineralization and reduces cortical porosity after two years in male osteoporosis: a paired biopsy study

The spectrum of therapeutic options and the amount of clinical trials for male osteoporosis (mOP) is lower than those for postmenopausal osteoporosis. Therefore, we examined the effects of 24 months of ibandronate (IBN) treatment (3 mg/3 mL intravenously every 3 months) on bone material quality in 19 subjects with mOP within an open-label, single-center, prospective phase III study (Eudract number 2006-006692-20). Patients (median age [25th, 75th percentiles] 53.0 [44.5; 57.0] years) were included if they had low bone mineral density (BMD) and/or at least one low trauma fracture and no secondary cause of osteoporosis. The primary endpoint was to evaluate IBN effects on cancellous (Cn.) and cortical (Ct.) bone mineralization density distribution (BMDD) based on quantitative backscattered electron imaging (qBEI) of paired transiliacal bone biopsies (baseline, 24 months). Secondary endpoints included changes in areal bone mineral density (BMD by dual-energy X-ray absorptiometry [DXA]) and serum markers of bone turnover including type I collagen peptides CrossLaps (CTX), procollagen type 1 amino-terminal propeptide (P1NP), and osteocalcin (OC). At baseline, cancellous bone matrix mineralization from mOP was lower than published reference data (mean degree of mineralization Cn.CaMean -1.8%, p < 0.01). IBN treatment increased calcium concentrations versus baseline (Cn.CaMean +2.4%, Ct.CaMean, +3.0% both p < 0.01), and reduced heterogeneity of mineralization (Cn.CaWidth -14%, p = 0.044; Ct.CaWidth, -16%, p = 0.001), leading to cancellous BMDD within normal range. IBN treatment was associated with a decrease in porosity of mineralized cortical tissue (-25%, p = 0.01); increases in BMD at the lumbar spine, the femoral neck, and the total hip (+3.3%, +1.9%, and +5.6%, respectively, p ≤ 0.01); and reductions in CTX (-37.5%), P1NP (-44.4%), and OC (-36.3%, all p < 0.01). Our BMDD findings are in line with the reduction of bone turnover markers and the increase in BMD by IBN in our patients and suggest that the latter mainly reflects the increase in matrix mineralization and the reduction of cortical porosity in this cohort with mOP.

Idiopathic osteoporosis in men

Over the last decade, the increasingly significant problem of osteoporosis in men has begun to receive much more attention than in the past. In particular, recent observations from large scale population studies in males led to an advance in the understanding of morphologic basis of growth, maintenance and loss of bone in men, as well as new insights about the pathophysiology and treatment of this disorder. While fracture risk consistently increases after age 65 in men (with up to 50 % of cases due to secondary etiologies), osteoporosis and fractures may also occur in young or middle aged males in the absence of an identifiable etiology. For this category (so called idiopathic osteoporosis), there are still major gaps in knowledge, particularly concerning the etiology and the clinical management. This article provides a summary of recent developments in the acquisition and maintenance of bone strength in men, as well as new insights about the pathogenesis, diagnosis, and treatment of idiopathic osteoporosis.

Teriparatide for idiopathic osteoporosis in premenopausal women: a pilot study

CONTEXT

Premenopausal women with idiopathic osteoporosis (IOP) have abnormal cortical and trabecular bone microarchitecture.

OBJECTIVE

The purpose of this study was to test the hypotheses that teriparatide increases bone mineral density (BMD) and bone formation and improves trabecular microarchitecture and stiffness in women with IOP.

DESIGN

This was an open-label pilot study.

SETTING

The setting was a tertiary care referral center.

PATIENTS

Participants were 21 premenopausal women with unexplained fragility fractures or low BMD.

INTERVENTION

Teriparatide was administered at 20 μg daily for 18 to 24 months.

MAIN OUTCOME MEASURES

The primary endpoint was within-subject percent change in lumbar spine BMD. Secondary endpoints included percent change in hip and forearm BMD, transiliac biopsy parameters (trabecular bone volume, microarchitecture, stiffness, and adipocytes), serum N-terminal propeptide of procollagen type 1 (P1NP), and C-telopeptide.

RESULTS

BMD increased at the spine (10.8 ± 8.3% [SD]), total hip (6.2 ± 5.6%), and femoral neck (7.6 ± 3.4%) (all P < .001). Serum P1NP doubled by 1 month, peaked at 6 months, and returned to baseline by 18 to 24 months. Transiliac biopsies demonstrated significant increases in cortical width and porosity and trabecular bone volume and number increased, mirrored by a 71% increase in trabecular bone stiffness (P < .02-.001). Adipocyte area, perimeter, and volume/marrow volume decreased, with no change in adipocyte number. Four women had no increase in BMD and a blunted, delayed increase in serum P1NP. Nonresponders had markedly lower baseline bone formation rate (0.002 ± 0.001 vs 0.011 ± 0.006 mm²/mm/y; P < .001) and higher serum IGF-1 (208 ± 54 vs 157± 44 ng/mL; P = .03).

CONCLUSIONS

Teriparatide was associated with increased spine and hip BMD and improved trabecular microarchitecture and stiffness at the iliac crest in the majority of women with IOP.

Bone material properties in premenopausal women with idiopathic osteoporosis

Idiopathic osteoporosis (IOP) in premenopausal women is characterized by fragility fractures at low or normal bone mineral density (BMD) in otherwise healthy women with normal gonadal function. Histomorphometric analysis of transiliac bone biopsy samples has revealed microarchitectural deterioration of cancellous bone and thinner cortices. To examine bone material quality, we measured the bone mineralization density distribution (BMDD) in biopsy samples by quantitative backscattered electron imaging (qBEI), and mineral/matrix ratio, mineral crystallinity/maturity, relative proteoglycan content, and collagen cross-link ratio at actively bone forming trabecular surfaces by Raman microspectroscopy and Fourier transform infrared microspectroscopy (FTIRM) techniques. The study groups included: premenopausal women with idiopathic fractures (IOP, n = 45), or idiopathic low BMD (Z-score ≤ -2.0 at spine and/or hip) but no fractures (ILBMD, n = 19), and healthy controls (CONTROL, n = 38). BMDD of cancellous bone showed slightly lower mineral content in IOP (both the average degree of mineralization of cancellous bone [Cn.Ca(Mean) ] and mode calcium concentration [Cn.Ca(Peak) ] are 1.4% lower) and in ILBMD (both are 1.6% lower, p < 0.05) versus CONTROL, but no difference between IOP and ILBMD. Similar differences were found when affected groups were combined versus CONTROL. The differences remained significant after adjustment for cancellous mineralizing surface (MS/BS), suggesting that the reduced mineralization of bone matrix cannot be completely accounted for by differences in bone turnover. Raman microspectroscopy and FTIRM analysis at forming bone surfaces showed no differences between combined IOP/ILBMD groups versus CONTROL, with the exceptions of increased proteoglycan content per mineral content and increased collagen cross-link ratio. When the two affected subgroups were considered individually, mineral/matrix ratio and collagen cross-link ratio were higher in IOP than ILBMD. In conclusion, our findings suggest that bone material properties differ between premenopausal women with IOP/ILBMD and normal controls. In particular, the altered collagen properties at sites of active bone formation support the hypothesis that affected women have osteoblast dysfunction that may play a role in bone fragility.

Premenopausal women with idiopathic low-trauma fractures and/or low bone mineral density

INTRODUCTION

In men, idiopathic osteoporosis (IOP) is often associated with low serum insulin-like growth factor (IGF-1) and reduced bone formation. The characteristics of premenopausal women with IOP are not well defined. We aimed to define the clinical, reproductive, and biochemical characteristics of premenopausal women with unexplained osteoporosis.

METHODS

This is a cross-sectional study of 64 women with unexplained osteoporosis, 45 with fragility fractures, 19 with low bone mineral density (BMD; Z-score less than or equal to -2.0) and 40 normal controls. The following are the main outcome measures: clinical and anthropometric characteristics, reproductive history, BMD, gonadal and calciotropic hormones, IGF-1, and bone turnover markers (BTMs).

RESULTS

Subjects had lower BMI and BMD than controls, but serum and urinary calcium, serum estradiol, vitamin D metabolites, IGF-1, and most BTMs were similar. Serum parathyroid hormone (PTH) and the resorption marker, tartrate-resistant acid phosphatase (TRAP5b), were significantly higher in both groups of subjects than controls and directly associated in all groups. Serum IGF-1 and all BTMs were directly associated in controls, but the association was not significant after controlling for age. There was no relationship between serum IGF-1 and BTMs in subjects. There were few differences between women with fractures and low BMD.

CONCLUSIONS

Higher serum TRAP5b and PTH suggest that increased bone turnover, possibly related to subclinical secondary hyperparathyroidism could contribute to the pathogenesis of IOP. The absence of differences between women with fractures and those with very low BMD indicates that this distinction may not be clinically useful to categorize young women with osteoporosis.

Abnormal bone microarchitecture and evidence of osteoblast dysfunction in premenopausal women with idiopathic osteoporosis

CONTEXT

Idiopathic osteoporosis (IOP) in premenopausal women is an uncommon disorder of uncertain pathogenesis in which fragility fractures occur in otherwise healthy women with intact gonadal function. It is unclear whether women with idiopathic low bone mineral density and no history of fragility fractures have osteoporosis.

OBJECTIVE

The objective of the study was to elucidate the microarchitectural and remodeling features of premenopausal women with IOP.

DESIGN

We performed transiliac biopsies after tetracycline labeling in 104 women: 45 with fragility fractures (IOP), 19 with idiopathic low bone mineral density (Z score ≤-2.0) and 40 controls. Biopsies were analyzed by two-dimensional quantitative histomorphometry and three-dimensional microcomputed tomography. Bone stiffness was estimated using finite element analysis.

RESULTS

Compared with controls, affected women had thinner cortices; fewer, thinner, more widely separated, and heterogeneously distributed trabeculae; reduced stiffness; and lower osteoid width and mean wall width. All parameters were indistinguishable between women with IOP and idiopathic low bone mineral density. Although there were no group differences in dynamic histomorphometric remodeling parameters, serum calciotropic hormones, bone turnover markers, or IGF-I, subjects in the lowest tertile of bone formation rate had significantly lower osteoid and wall width, more severely disrupted microarchitecture, lower stiffness, and higher serum IGF-I than those in the upper two tertiles, suggesting that women with low turnover IOP have osteoblast dysfunction with resistance to IGF-I. Subjects with high bone turnover had significantly higher serum 1,25 dihydroxyvitamin D levels and a nonsignificant trend toward higher serum PTH and urinary calcium excretion.

CONCLUSIONS

These results suggest that the diagnosis of IOP should not require a history of fracture. Women with IOP may have high, normal or low bone turnover; those with low bone turnover have the most marked deficits in microarchitecture and stiffness. These results also suggest that the pathogenesis of idiopathic osteoporosis is heterogeneous and may differ according to remodeling activity.

Trabecular bone microstructure and local gene expression in iliac crest biopsies of men with idiopathic osteoporosis

Male idiopathic osteoporosis (MIO) is a metabolic bone disease that is characterized by low bone mass, microstructural alterations, and increased fracture risk in otherwise healthy men. Although the detailed pathophysiology of MIO has yet to be clarified, evidence increasingly suggests an osteoblastic defect as the underlying cause. In this study we tested the hypothesis that the expression profile of certain osteoblastic or osteoblast-related genes (ie, WNT10B, RUNX2, Osterix, Osteocalcin, SOST, RANKL, and OPG) is different in iliac crest biopsies of MIO patients when compared with healthy controls. Furthermore, we investigated the relation of local gene expression characteristics with histomorphometric, microstructural, and clinical features. Following written informed consent and diligent clinical patient characterization, iliac crest biopsies were performed in nine men. While RNA extraction, reverse-transcription, and real-time polymerase chain reactions (PCRs) were performed on one biopsy, a second biopsy of each patient was submitted for histomorphometry and micro-computed tomography (µCT). Age-matched bone samples from forensic autopsies served as controls. MIO patients displayed significantly reduced WNT10B, RUNX2, RANKL, and SOST expression. Performing µCT for the first time in MIO biopsies, we found significant decreases in trabecular number and connectivity density. Trabecular separation was increased significantly, but trabecular thickness was similar in both groups. Histomorphometry revealed decreased BV/TV and osteoid volume and fewer osteoclasts in MIO. By providing evidence for reduced local WNT10B, RUNX2, and RANKL gene expression and histomorphometric low turnover, our data support the osteoblast dysfunction model discussed for MIO. Further, MIO seems to lead to a different microstructural pathology than age-related bone loss.

Fragility fractures in men with idiopathic osteoporosis are associated with undermineralization of the bone matrix without evidence of increased bone turnover

The pathogenesis of primary osteoporosis in younger individuals is still elusive. An important determinant of the biomechanical competence of bone is its material quality. In this retrospective study we evaluated bone material quality based on quantitative backscattered electron imaging to assess bone mineralization density distribution (BMDD) in bone biopsies of 25 male patients (aged 18-61 years) who sustained fragility fractures but were otherwise healthy. BMDD of cancellous bone was compared with previously established adult reference data. Complementary information was obtained by bone histomorphometry. The histomorphometric results showed a paucity of osteoblasts and osteoclasts on the bone surface in the majority of patients. BMDD revealed a significant shift to lower mineralization densities for cancellous bone values: CaMean (weighted mean Ca content, -5.9%), CaPeak (mode of the BMDD, -5.6%), and CaHigh (portion of fully mineralized bone, -76.8%) were decreased compared to normative reference; CaWidth (heterogeneity in mineralization, +18.5%) and CaLow (portion of low mineralized bone, +68.8; all P < 0.001) were significantly increased. The shift toward lower mineral content in the bone matrix in combination with reduced indices of bone formation and bone resorption suggests an inherent mineralization defect leading to undermineralized bone matrix, which might contribute to the susceptibility to fragility fractures of the patients. The alteration in bone material might be related to osteoblastic dysfunction and seems fundamentally different from that in high bone turnover osteoporosis with a negative bone balance.

Heterogeneity of biological bone markers in idiopathic male osteoporosis

In men with idiopathic osteoporosis, histomorphometric studies reported both increased resorption and decreased remodeling. We aimed at examine bone remodeling in these patients by biological marker measurement. We compared pre-treatment carboxy-terminal cross-linking telopeptide of type I collagen (CTX) and bone alkaline phosphatase (bALP) levels in 49 men, mean age 59 ± 14 year, with idiopathic osteoporosis with fractures (40 patients) or osteoporosis diagnosed by densitometry (9 patients) with 50 age-matched controls. The influence of baseline remodeling level on alendronate efficacy was studied. Bone remodeling markers (CTX and bALP) did not significantly differ between patients and controls and were correlated in both groups. There was no correlation between these markers, vitamin D and PTH levels. Twenty-one patients underwent repeat densitometry after 1 year of alendronate (70 mg/week). Mean annual BMD increase, spine +4.1 ± 3.9%, and hip +1.5 ± 1.2% showed no correlation with baseline CTX. Bone remodeling is very heterogeneous and formation and resorption remain biologically coupled in both idiopathic male osteoporosis and controls. Baseline remodeling level does not affect the action of alendronate on BMD.

Associations between amino acids and bone mineral density in men with idiopathic osteoporosis

Idiopathic osteoporosis in middle-aged men is characterized by low-level bone formation. Inhibited anabolism may be involved in the pathogenesis of the disease and amino acids may be of importance. In the present study fasting amino acid profiles in plasma and erythrocytes were determined in 22 male idiopathic osteoporosis (MIO) patients and in 20 age-matched healthy men and associated with bone mineral density, bone histomorphometry and hormones. The osteoporotic patients had normal plasma essential amino acids but increased non-essential amino acids (p=0.001), particularly glutamine and glycine. The ratio essential/non-essential amino acids, an index of protein nutritional status, was decreased in the MIO patients (0.59 (0.04) μmol/l, mean (SD)), compared to controls (0.66 (0.05), p=0.001). In the MIO patients, the ratio essential/non-essential plasma amino acids (r=0.60, p=0.003) was positively correlated with lumbar spine bone mineral density. The erythrocyte amino acids represent a large proportion of the free amino acids in blood. A novel finding was the lower levels of erythrocyte tryptophan in MIO (12 (2) μmol/l) compared to controls (16 (3), p=0.001) and decreased erythrocyte/plasma ratio (0.28 (0.07) vs. 0.33, (0.06), p<0.01), suggesting an altered amino acid transport of tryptophan between plasma and erythrocytes. In the combined group of MIO and control men (n=42), bone mineral density was positively correlated with erythrocyte tryptophan in both the lumbar spine (r=0.45, p=0.003) and femoral neck (r=0.56, p<0.001). The bone histomorphometric variables wall thickness, trabecular thickness and mineral apposition rate were all positively associated with erythrocyte tryptophan levels in the MIO patients. In the combined group of MIO and controls, a multiple regression analysis showed that erythrocyte tryptophan could explain 22% of the variation of lumbar spine and 30% of the variation in femoral neck bone mineral density. We conclude that men with idiopathic osteoporosis have changes in free amino acid profiles which indicate their altered utilization. The correlations between tryptophan and bone mineral density and bone histomorphometry suggest a link between tryptophan and osteoblast function which may be important for bone health.

A perspective on male osteoporosis

Osteoporosis and fragility fracture become common with advancing age in men. The incidence of osteoporosis-related fracture is similar to myocardial infarction and exceeds that of lung and prostate carcinoma combined. These fractures cause substantial morbidity, and the mortality following hip fracture is greater in men than in women. A decline in sex steroids and glucocorticoid and alcohol use, among other factors, contribute to bone loss and fracture risk. Approaches to reduce fracture risk in men are very similar to that in women - recognising and addressing muscle weakness/falls risk and optimising nutrition, with emphasis on calcium and vitamin D and medications when appropriate. Despite the high prevalence, osteoporosis remains largely undiagnosed and undertreated. Hopefully, increased recognition of male osteoporosis by health-care providers and the men themselves, in combination with recent consensus recommendations for treatment based on fracture-risk estimation, will reduce the burden of fragility fracture in men.