Pathogenesis and natural course of primary osteoporosis

Avicularin Alleviates Osteoporosis in Ovariectomized Mice by Inhibiting Osteoclastogenesis through NF-κB Pathway Inhibition

Osteoporosis (OP) is mainly manifested by bone loss and bone degeneration. OP is considered a risk factor for pathological fractures, as well as impacts the health of middle-aged and elderly individuals. Drug therapy remains the main treatment scheme for OP; however, its efficacy is limited and has been associated with serious side effects. Therefore, it is important to develop new, effective, and safe treatment methods for OP. Avicularin (AL) is a flavonoid and quercetin derivative from various plants. Our study showed that AL disrupts osteoclast activation and resorptive function via inhibition of the RANKL-induced osteoclast differentiation together with the resorption capacity of bone marrow-derived macrophages (BMMs). Hence, AL prevents the activation and resorptive activity of osteoclasts. The results of qPCR showed that genes related to osteoclasts exhibited downregulated expression after AL treatment. Furthermore, AL inhibited RANKL-induced phosphorylation as well as degradation of the inhibitor IκBα of the NF-κB pathway, together with P65 phosphorylation in BMMs. We used an OP mouse model that was established by ovariectomy (OVX). Relative to untreated OP mice, mice that received AL treatment showed a significant increase in bone mineral density; however, the expression of TRAP, NFATC1, mmp9, and CTX-1 was significantly reduced. These results indicate that AL disrupts osteoclastogenesis via inhibition of the NF-κB pathway, which in turn improves OVX-induced OP.

Bisphosphonate-enoxacin inhibit osteoclast formation and function by abrogating RANKL-induced JNK signalling pathways during osteoporosis treatment

Osteoporosis is an age‐related disease characterized by low mineral density, compromised bone strength and increased risk of fragility fracture. Most agents for treating osteoporosis focus primarily on anti‐resorption by inhibiting osteoclast activity. Bisphosphonate (BP) is a potent anti‐resorptive agent that has been used clinically for decades and is proven to be effective. However, BP has a variety of side effects and is far from being an ideal anti‐osteoporosis agent. BP selectively binds to calcium crystals, which are subsequently taken up or released by osteoclasts. Based on the action of BP, we previously demonstrated the inhibitory effect of a novel bone‐targeting BP derivative, bisphosphonate‐enoxacin (BE). In the current study, we used bone marrow‐derived osteoclast cultures to further assess the inhibitory effect of BE on osteoclastogenesis and employed reverse transcription PCR and real‐time PCR to examine expression of osteoclast‐specific genes. Additionally, we used bone resorption and F‐actin immunofluorescence assays to evaluate the effect of BE on osteoclast function and investigated the potential mechanisms affecting osteoclast differentiation and function in vitro. Furthermore, an ovariectomized (OVX) rat model was established to evaluate the therapeutic effects of BE on preventing bone loss. Results showed that BE exerted potent inhibitory effects on osteoclast formation and bone resorption by specifically abrogating RANKL‐induced JNK signalling, and that it preserved OVX rat bone mass in vivo without any notable side effects. Collectively, these results indicated that the BP derivative BE may have significant potential as a treatment for osteoporosis and other osteolytic diseases.

Gastrointestinal calcium absorption and dietary calcium load: relationships with bone remodelling in vertebral osteoporosis

Patients with vertebral osteoporosis have a wide range of bone loss rates, bone remodelling rates and capacities for gastrointestinal (GI) calcium absorption. To test the hypothesis that variations in GI absorptive capacity determine rates of bone loss or remodelling, we have sought relationships between calcium absorption or vitamin D metabolite levels on the one hand and rates of cancellous and cortical bone loss (measured by serial quantitative computed tomography in the radius; n = 25) or indices of bone remodelling in tetracycline-prelabelled transiliac biopsies (n = 41) on the other, in a sequential untreated group. Calcium absorption (net and true) was measured in 18-day balances and by a two-isotope deconvolution method (fractional absorption and maximum absorption rate, MAR). There was no significant seasonal effect on any of these four measures of calcium absorption (variance ratio, F = 0.52-1.61, p > 0.1) or on 1,25-dihydroxyvitamin D levels (F = 0.13, p > 0.1; range 11-69 pg/ml), notwithstanding the expected seasonal effect on 25-hydroxyvitamin D levels (mean 18.7 ng/ml, zenith mid July, semi-amplitude 7.5 ng/ml; F = 6.82, p < 0.01). Neither this metabolite nor 1,25-dihydroxyvitamin D correlated with any index of calcium absorption (p > 0.1). No measure of calcium absorption (or intake) had a significant relationship with radial cortical or cancellous bone loss (p all > 0.1) but cancellous bone loss was associated with the rate of endogenous calcium excretion (r = 0.50, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal variations in iliac trabecular bone formation in vertebral osteoporosis

The histologic heterogeneity of osteoporosis relative to normal controls has attracted great interest. There has been controversy as to whether patients with high turnover osteoporosis may convert to a normal or low turnover form, and vice versa. We have studied 44 patients over 12 years by dynamic histomorphometry and 85Sr kinetics+calcium balance performed within 60 days in 20 patients (Group 1) and 75-808 days apart in the remainder (Group 2). In the first group, the histologic tissue level bone formation rate (BFR/BV or BFR/BS) was predictive of the 85Sr measurements of bone formation (r = 0.66 P < 0.01). There was no statistically significant correlation in Group 2 and the regression coefficients were significantly different (P = 0.01). Periodic regression was used to determine if seasonal changes were responsible for this loss of correlation; none was found that was of statistical significance. No systematic changes with time in bone formation were found in Group 2 during the period of observation; nor were consistent secular changes detected when the data for both groups were examined according to procedure date. In conclusion, bone formation may change with time in postmenopausal osteoporosis. Evidence that these changes are systematic was not found and this has implications for the design of treatment studies.

Estimated long-term effect of calcitonin treatment in acute osteoporotic spine fractures

A 12-month prospective controlled study was conducted in 28 patients with acute osteoporotic spine fractures to evaluate and compare the effect of calcitonin treatment and cyclical hormone replacement therapy on forearm bone mineral content (BMC) and bone turnover. We established two treatment groups and a control group of women with postmenopausal osteoporosis (n = 28). Group A (n = 10) received 100 U of calcitonin by subcutaneous self-application on alternate days and oral calcium (Ca) for 6-8 weeks. Group B (n = 10) received cyclical estrogen/gestagen replacement therapy over 12 months and oral calcium. The control group (n = 8) received analgetic treatment and 500 mg Ca daily. BMC was measured by single photon absorptiometry (SPA) with I 125 before and 6 and 12 months after the onset of the therapies. Ca, phosphorus (P), alkaline phosphatase, and 2-hour urinary OH-proline excretion were measured to classify bone turnover. One year after the onset of the two therapies, forearm BMC measured by SPA showed a significant increase in the group under hormone replacement therapy (P less than 0.025) as well as in the calcitonin group (P less than 0.05), although the latter underwent treatment only over a short period (6-8 weeks). In the same period, BMC decreased significantly in the control group (P less than 0.025). These results demonstrate that short-term calcitonin treatment over 6-8 weeks is as effective as long-term hormone replacement therapy, both therapies increasing forearm BMC measured by SPA.

Reduced bone mass in daughters of women with osteoporosis

To determine whether premenopausal daughters of women with postmenopausal osteoporosis have lower bone mass than other women of the same age, we measured the bone mineral content of the lumbar spine and femoral neck and midshaft, using dual-photon absorptiometry, in 25 postmenopausal women with osteoporotic compression fractures and in 32 of their premenopausal daughters; we then compared the results with those in normal controls. As compared with normal postmenopausal women, women with osteoporosis had lower bone mineral content in the lumbar spine, femoral neck, and femoral midshaft by 33, 24, and 15 percent, respectively (P less than 0.001 for each comparison by the one-tailed t-test). As compared with normal premenopausal women, the daughters of women with osteoporosis had lower bone mineral content at these sites by 7, 5, and 3 percent, respectively (P = 0.03, 0.07, and 0.15, respectively, by the one-tailed t-test). In terms of a standardized score, we calculated that the mean (+/- SEM) relative deficits in bone mineral content in the daughters of women with osteoporosis were 58 +/- 18 percent (lumbar spine) and 34 +/- 16 percent (femoral neck) of the relative deficits in their mothers. We conclude that daughters of women with osteoporosis have reduced bone mass in the lumbar spine and perhaps in the femoral neck; this reduction in bone mass may put them at increased risk for fractures. We also conclude that postmenopausal osteoporosis may result partly from a relatively low peak bone mass rather than from excessive loss of bone.

1,25-Dihydroxyvitamin D stimulation test for osteoblast function in normal and osteoporotic postmenopausal women

The cause of bone loss in postmenopausal osteoporosis--decreased bone formation or increased bone resorption--is controversial. Synthesis of bone--Gla protein (BGP), a specific osteoblast product, is stimulated by 1,25-dihydroxyvitamin D3 [1,25(OH)2D] in vitro. Thus, increases in serum BGP levels during 1,25(OH)2D administration might provide a useful dynamic index of osteoblast function. We compared 14 postmenopausal osteoporotic women with 12 age-matched postmenopausal normal women before and during 6 d of 1,25(OH)2D administration (2.0 micrograms/d). Serum BGP levels were similar at baseline and increased during treatment in both groups (P less than 0.001). However, trend analysis showed a greater (P less than 0.01) increase in the osteoporotic women. These data do not support the hypothesis that defective osteoblast function is the major cause of bone loss in postmenopausal osteoporosis.

Bone histological heterogeneity in postmenopausal osteoporosis: a sequential histomorphometric study

We studied sequential bone biopsies performed at 6 to 24 month intervals from 14 untreated osteoporotic women (64 +/- 7). Subgroups were defined, respectively, by increased osteoclastic resorption surfaces and decreased osteoblastic surfaces +/- 2 S.D. Normal values were obtained from bone biopsy of 23 normal women (61 +/- 8). When patients were divided into subgroups according to the above criteria the first biopsy showed that 3 out of the 14 patients had high resorption surfaces and 6 had low osteoblastic surfaces. Eight patients spontaneously changed during the study. In 2 patients there was a change in resorption surfaces, in 3 in osteoblastic surfaces and in 3 a change in both osteoblastic and resorption surfaces was observed. Considering the first or second bone biopsy results the patient variance was higher than the control subject's variance; however the variance between the first and second bone biopsy of one patient was not different from the variance inside the group of patients. The average intraindividual variation of the parameters on sequential biopsies was of the same order as the one we previously observed on simultaneous bone biopsies of normal and hemodialyzed patients. We concluded that if osteoporosis is a heterogeneous disorder, subgroups cannot be definitively defined on the basis of cellular parameters of bone remodelling assessed on bone biopsies.

The origin of osteoclasts: evidence, clinical implications and investigative challenges of an extra-skeletal source

Recent evidence for an extraskeletal origin of osteoclasts and the historical record of the genesis of osteoclasts are examined critically. Reviews of the structure, function and development of osteoclasts from mononuclear precursors, the local regulation of bone resorption and the coupling of bone formation to preceding resorption are presented as a background for discussing the clinical implications for management of osteolytic bone diseases. The roles of osteoclasts and macrophages as phagocytes are compared and contrasted, and recent evidence for macrophage heterogeneity resulting from site-specific monoblastic precursors is reviewed. The implications of these recent developments in macrophage biology are extrapolated to osteoclasts and the existence of site-specific, extraskeletal osteoclast precursors is proposed. Finally, the investigative challenges inherent in these perspectives are discussed.

Bone formation and resorption as the determinants of trabecular bone volume in postmenopausal osteoporosis

Histomorphometry has been applied to trabecular bone samples obtained post-mortem from young and old women without known bone disease and to bone biopsy specimens from patients with postmenopausal osteoporosis. Bone volume was significantly lower in the old than young controls and significantly lower again in the osteoporotics. The loss of bone with age associated with a rise in surface resorption but no change in forming surface, and the further loss in osteoporotics was associated with a further rise in resorption and a small non-significant fall in forming surfaces. It is suggested that trabecular bone volume is determined by the relation between total forming surface on the one hand and percent surface resorption on the other, and this relationship is expressed in mathematical terms. Age-related bone loss (simple osteoporosis) in women is accounted for by increased resorption, and accelerated osteoporosis is mainly due to a further increase in resorption.