Vitamin D binding protein sequesters monomeric actin in the circulation of the rat.

Plasma vitamin D binding protein (DBP) may scavenge actin released during cell lysis. We examined the plasma disappearance and tissue appearance of 125I-DBP, 125I-G-actin, and the DBP-G-actin complex after their intravenous administration to rats. The plasma disappearance of DBP and DBP-actin were indistinguishable, with rapid initial (t1/2 = 2.6 h) and slower second (t1/2 = 7 h) slopes. After 125I-G-actin (nanomole) injection, plasma disappearance paralleled that of DBP and DBP-actin. All injected actin was associated with DBP, without evidence of free actin, actin-gelsolin complexes or actin oligomers. Tissue appearances of 125I-apo-DBP (apo) or holo-DBP were similar, with highest accumulations in perfused liver, kidney, and skeletal muscle. Although more complex phenomena (plasma entry of F-actin and intracellular actin binding proteins) would occur in vivo after cell lysis, our results suggest a role for DBP in the sequestration and disposition of actin monomers in the circulation.

Long-term effects of raloxifene on bone mineral density, bone turnover, and serum lipid levels in early postmenopausal women: three-year data from 2 double-blind, randomized, placebo-controlled trials.

BACKGROUND: In postmenopausal women, raloxifene hydrochloride has favorable effects on bone and lipid metabolism and does not stimulate reproductive tissues. The studies reported herein evaluated the long-term (3-year) effects of raloxifene treatment on bone mineral density (BMD), serum lipid levels, and drug tolerability in healthy postmenopausal women. METHODS: A total of 1145 healthy European and North American postmenopausal women aged 45 through 60 years were enrolled in 2 parallel, double-blind, randomized, placebo-controlled trials of identical design and randomly assigned to receive raloxifene hydrochloride, 30, 60, or 150 mg, or placebo daily; all groups received 400 to 600 mg of elemental calcium. Assessments included measurements for BMD by dual-energy x-ray absorptiometry, markers of bone turnover, and serum lipid levels. RESULTS: Lumbar spine BMD changed from baseline to 36 months as follows: placebo (mean percentage change + SE), -1. 32% +0.22%; raloxifene, 30 mg, 0.71% +0.23%; raloxifene, 60 mg, 1. 28% +0.23%; and raloxifene, 150 mg, 1.20% +0.24%. Comparable BMD changes were observed in the hip and total body. Biochemical markers of bone turnover were suppressed by raloxifene to normal premenopausal ranges through 3 years. Serum low-density lipoprotein cholesterol was reduced 7% to 12% below baseline through 3 years. Study withdrawals due to any reason (37%) and withdrawals due to adverse events (14%) were not different among groups. The only significant adverse effect of therapy was hot flashes (25% in the 60-mg raloxifene group vs 18% in the placebo group); hot flashes were typically reported as mild and were not associated with study withdrawal (1.7% for 60-mg raloxifene vs 2.4% for placebo). CONCLUSIONS: Raloxifene preserves BMD at important skeletal sites, lowers serum low-density lipoprotein cholesterol levels, and has a tolerability profile comparable to placebo. These results indicate a favorable benefit-risk profile of raloxifene for long-term use in healthy postmenopausal women. Arch Intern Med. 2000;160:3444-3450.

Improved assessment of lumbar vertebral body strength using supine lateral dual-energy x-ray absorptiometry.

Clinical and biomechanical investigations indicate that assessment of vertebral body bone mineral density (BMD) by anteroposterior dual-energy x-ray absorptiometry (DXA) is a useful index of vertebral body strength and fracture risk in osteoporosis. However, inclusion of non-force-bearing and small-force-bearing mineralized structures, such as the posterior elements and aortic calcifications, in the measurement of anterior BMD obscures the assessment of vertebral body mass by this technique. Indeed, such interference is particularly severe in the presence of posterior element degeneration or previous spinal surgery. Recent anatomic studies illustrate that the lateral view provides unobstructed visualization of the L3, L4, and possibly L2 vertebral bodies, suggesting that supine lateral BMD may more accurately assess vertebral body fracture risk. We evaluated this hypothesis in a blinded using human cadaver spines to compare the value of supine lateral and anteroposterior BMD in assessing vertebral body fracture force, average compressive stress, maximum stored strain energy, and strain at failure. Both measures of BMD significantly correlate with these biomechanical measures. However, statistical comparison of the methods using multiple and stepwise regression reveals that supine lateral BMD provides a better assessment of the vertebral body fracture properties than anteroposterior BMD. The enhanced predictive value of supine lateral BMD occurs because of the variable contribution of posterior element mineral to the anteroposterior BMD measurement. Evaluation to test the utility of supine lateral BMD for the assessment of fracture risk and a fracture threshold in patients with osteoporosis is therefore recommended.

A controlled trial of raloxifene (LY139481) HCl: impact on bone turnover and serum lipid profile in healthy postmenopausal women.

This randomized, double-blind, placebo-controlled, multicenter, 8-week study evaluated short-term effects of raloxifene on bone turnover, serum lipids, and endometrium in healthy, postmenopausal women. A total of 251 women received either placebo, raloxifene HCl 200 or 600 mg/day, or conjugated estrogens (Premarin, 0.625 mg/day). Bone turnover (serum alkaline phosphatase, serum osteocalcin, urinary pyridinoline cross-links, urinary calcium excretion, urinary hydroxyproline) and serum lipids (total serum cholesterol, high- and low-density lipoprotein cholesterol [HDL-C and LDL-C]) were evaluated at weeks 0, 2, 4, and 8. Endometrial biopsies were performed at weeks 0 and 8. Treatment groups were compared for each parameter for baseline-to-endpoint changes. The estrogen and raloxifene groups experienced similar decreases in serum alkaline phosphatase (range 10-11%), serum osteocalcin (range 21-26%), urinary pyridinoline cross-links (range 20-26%), and urinary calcium excretion (range 45-72%). These decreases differed significantly compared with placebo-treated subjects for all markers except serum osteocalcin, the raloxifene HCl 200 mg group. LDL-C decreased significantly in the estrogen and both raloxifene groups (range 5-9%) compared with placebo-treated subjects. HDL-C increased significantly in the estrogen group (16%) but was unchanged in the raloxifene groups. HDL-C:LDL-C ratios increased significantly in the estrogen and raloxifene groups (range 9-29%). Serum cholesterol decreased significantly in both raloxifene groups (range 4-8%) but was unchanged in the estrogen group. Uterine biopsies of raloxifene-treated subjects showed no change in the endometrium during this short-term treatment. Biopsies of the estrogen group showed significant endometrial stimulation. The only adverse event possibly related to raloxifene was vasodilatation (hot flashes) which was most common in the raloxifene HCl 600 mg group. Study results indicate that raloxifene may provide beneficial effects to bone and serum lipids in humans without uterine stimulatory effects.

Contribution of raloxifene and calcium and vitamin D3 supplementation to the increase of the degree of mineralization of bone in postmenopausal women.

Raloxifene has been shown to increase bone mineral density and reduce the risk of vertebral fracture in postmenopausal women with osteoporosis. In this study, we report the results of the first prospective longitudinal study to evaluate the mean degree of mineralization of bone (MDMB) in a group of patients enrolled in the Multiple Outcomes of Raloxifene Evaluation trial. Patients were randomly assigned to one of three treatment groups: placebo (n = 24), raloxifene 60 mg/d (RLX60; n = 22), or raloxifene 120 mg/d (RLX120; n = 18). All patients received daily calcium (500 mg) and vitamin D(3) (400-600 IU) supplementation for the duration of the study. Iliac crest biopsies were taken at baseline and after 2 yr of treatment. Quantitative microradiography was used to analyze the biopsy specimens and revealed a statistically significant (P < 0.05) mean percentage increase in total MDMB of 7.0, 5.3, and 5% for RLX60-, RLX120-, and placebo-treated patients, respectively, compared with baseline. Raloxifene treatment was found to shift the distribution of total bone mineral to higher values of MDMB (RLX60, 29%; RLX120, 8%) with greater heterogeneity, compared with placebo. The profile of MDMB observed in biopsies after treatment with placebo and raloxifene, compared with baseline, closely resembles physiological premenopausal bone.

Secondary osteoporosis. Diagnostic considerations.

This article discusses the important secondary causes of osteoporosis that contribute significantly to bone loss and that seem to increase fracture risk, including hypogonadism, endogenous and exogenous thyroxine excess, hyperparathyroidism, malignancies, gastrointestinal diseases, medications, vices, and connective tissue diseases.

Clinical utility of bone mass measurements in adults: consensus of an international panel. The Society for Clinical Densitometry.

Low bone mass predicts future fracture risk as well as high cholesterol or high blood pressure can predict the risk of heart disease or stroke. Prevention of the first fracture should be a clinical goal. In patients without fractures, osteopenia and osteoporosis can be diagnosed based on the extent of reduction in bone mass below mean peak bone mass of young healthy individuals. As bone mass decreases, fracture risk increases exponentially. Clinical situations in which an assessment of bone mass and fracture risk affects therapeutic decisions include estrogen deficiency, vertebral abnormalities, radiographic osteopenia, asymptomatic primary hyperparathyroidism, and long-term corticosteroid therapy. Serial measurements can also be used to monitor the effects of osteoporosis treatments. The appropriate technique and skeletal site for bone mass measurements should be chosen based on the patient's circumstances and the precision of measurement. A clinical interpretation can enhance the value of computer-generated bone mass measurement reports and improve decision making.

Receptors for and bioresponses to 1,25-dihydroxyvitamin D in a human colon carcinoma cell line (HT-29).

Human colon carcinoma (HT-29) cells were examined for their capacity to bind and respond to 1,25-dihydroxycholecalciferol [1,25-(OH)2D3]. These cells are known to differentiate and increase their population doubling time when galactose is substituted for glucose in their media. High-affinity and specific binding of 1,25-(OH)2[3H]D3 was observed in extracts of these cells grown in glucose. The binder sedimented in sucrose gradients and eluted from DEAE-cellulose columns in a manner indistinguishable from rabbit intestinal 1,25-(OH)2D3-receptor. Smaller amounts of this binder were seen in HT-29 cells grown in galactose. Both glucose-fed and galactose-fed cells exhibited a dose-dependent decrease in growth rate on exposure to 10(-12) to 10(-6) mol/L 1,25-(OH)2D3. Ultrastructural examination of galactose-fed and glucose + 1,25-(OH)2D3-treated cells showed enterocytic differentiation and features that were not distinguishable between these groups. Sucrase activity was higher in galactose-fed cells and did not change with 1,25-(OH)2D3 treatment. However, the lower sucrase activity in glucose-fed cells increased after exposure to 10(-8) mol/L 1,25-(OH)2D3. These results indicate receptor content and bioresponsivity to 1,25-(OH)2D3 in a human enterocytic cell line, suggesting that it will be a useful model for the study of the mechanisms of action of this sterol.

The role of imaging and in situ biomechanical testing in assessing pedicle screw pull-out strength.

STUDY DESIGN: This study determined the predictive ability of quantitative computed tomography, dual energy x-ray absorptiometry, pedicular geometry, and mechanical testing in assessing the strength of pedicle screw fixation in an in vitro mechanical test of intra-pedicular screw fixation in the human cadaveric lumbar spine. OBJECTIVE: To test several hypotheses regarding the relative predictive value of densitometry, pedicular geometry, and mechanical testing in describing pedicle screw pull-out. SUMMARY OF BACKGROUND DATA: Previous investigations have suggested that mechanical testing, geometry, and densitometry, determined by quantitative computed tomography or dual energy x-ray absorptiometry, predict the strength of the screw-bone system. However, no study has compared the relative predictive value of these techniques. METHODS: Forty-nine pedicle screw cyclic-combined flexion-extension moment-axial pull-out tests were performed on human cadaveric lumbar vertebrae. The predictive ability of quantitative computed tomography, dual energy x-ray absorptiometry, insertional torque, in situ stiffness, and pedicular geometry was assessed using multiple regression. RESULTS: Several variables correlated to force at failure. However, multiple regression analysis showed that bone mineral density of the pedicle determined by quantitative computed tomography, insertional torque, and in situ stiffness when used in combination resulted in the strongest prediction of pull-out force. No other measures provided additional predictive ability in the presence of these measures. CONCLUSIONS: Pedicle density determined by quantitative computed tomography when used with insertional torque and in situ stiffness provides the strongest predictive ability of screw pull-out. Geometric measures of the pedicle and density determined by dual energy x-ray absorptiometry do not provide additional predictive ability in the presence of these measures.

Strength and stability of posterior lumbar interbody fusion. Comparison of titanium fiber mesh implant and tricortical bone graft.

STUDY DESIGN: A paired comparison was done of the bending flexibility and compression strength of tricortical bone graft and titanium fiber mesh implants in a human cadaver model of posterior lumbar interbody fusion. OBJECTIVES: To test the hypothesis that a titanium fiber mesh implant and a tricortical bone graft provide adequate and equal mechanical strength and stability in posterior lumbar interbody fusion constructs. SUMMARY OF BACKGROUND DATA: Although studies of posterior lumbar interbody fusion constructs have been performed, the authors are unaware of any study in which the strength and stability of a titanium fiber mesh implant are compared with those of tricortical bone graft for posterior lumbar interbody fusion in the human cadaver lumbar spine. METHODS: Changes in neutral zone and range of motion were measured in a bending flexibility test before and after placement of posterior lumbar interbody fusion constructs. Tricortical bone graft and titanium fiber mesh implant construct stability than were compared in a paired analysis. The constructs than were loaded to failure to evaluate construct strength as a function of graft material and bone mineral density. RESULTS: The posterior lumbar interbody fusion procedure produced statistically significant decreases in neutral zone when compared with the intact spine. No statistically significant differences in neutral zone, range of motion, or strength were detected between the two implants. Construct strength correlated strongly with bone mineral density. CONCLUSIONS: Posterior lumbar interbody fusion procedures result in equal or improved acute stability for titanium fiber mesh implants and tricortical bone graft implants when used without additional posterior stabilization.

Structural effects of raloxifene on the proximal femur: results from the multiple outcomes of raloxifene evaluation trial.

INTRODUCTION: Raloxifene improves spine bone mineral density (BMD), and its ability to reduce vertebral fractures by 40-50% suggests that it increases vertebral strength. Positive effects on hip BMD suggest a similar strengthening of the hip, but dimensional ambiguities in BMD by dual energy x-ray absorptiometry (DXA) make it difficult to infer strength effects directly. Hip fractures may be too infrequent to evaluate in practical clinical trials; even the Multiple Outcomes of Raloxifene Evaluation (MORE) study with 7,705 subjects was insufficiently powered to show a comparable reduction in hip fractures. METHODS: An alternative evaluation of hip DXA data in structural terms should provide more direct evidence of treatment effects on hip strength. Hip scans from a subset of the MORE study, including 4,806 postmenopausal women with osteoporosis randomized to daily oral doses of placebo, 60 mg, or 120 mg of raloxifene were reanalyzed by the hip structure analysis (HSA) method. Scans acquired at baseline, 1, 2, and 3 years were evaluated to extract BMD and cross-sectional geometry across the narrowest point on the neck (NN), the intertrochanteric region (IT), and the proximal shaft 1.5 times the minimum neck width distal to the intersection of the neck and shaft axes. RESULTS: While femur outer diameter expanded during follow-up at all three regions, there were no differences in expansion between groups; treatment influenced mainly the amount and distribution of bone within cross-sections. Effects were similar at the two dose levels at the NN region although the 120 mg dose produced a greater effect on section modulus (SM) at the IT region and on BMD, bone cross-sectional area (CSA), SM, average cortical thickness (CT), and buckling ratio (BR) at the shaft region. Compared with placebo after 3 years, treatment groups showed 0.4-2% higher BMD, CSA, SM, and CT and 1-2% lower BR. The smallest treatment effects were evident at the shaft at 60 mg. CONCLUSIONS: We conclude that raloxifene does not influence periosteal apposition in the proximal femur but it nevertheless produces small but significant improvement in resistance to axial and bending stresses (CSA and SM, respectively) at all analyzed regions. The significant reductions in buckling ratio suggest that additional strength loss due to cortical instability is also ameliorated by treatment.

Severe osteoporosis in men.

OBJECTIVE: To evaluate men with severe osteoporosis for pathogenetic factors and to review the reported features of primary osteoporosis in men. DESIGN: Case series and clinical review. PATIENTS: 47 men consecutively referred to a metabolic bone center because of atraumatic (or minimally traumatic) fractures (91%) or radiographic osteopenia (9%). MEASUREMENTS: Clinical assessment, radiographs, chemical analyses of serum and urine, hormone assays, skeletal densitometry, and histomorphometry of iliac crest biopsy specimens. RESULTS: 27 of the 47 men (57%) had vertebral fractures, and 16 (34%) had appendicular fractures. Causal factors identified in 30 men (64%) included glucocorticosteroid treatment (8 men); hypogonadism (7 men); excessive alcohol consumption (7 men); and anticonvulsant use, osteomalacia, severe hyperthyroidism, or bone marrow neoplasia (8 men). Seventeen men (36%) had no medical conditions or known risk factors associated with bone disease. Spinal mineral density was well below the mean value for healthy young men in 94% of the patients with primary osteoporosis tested. Examination of biopsy specimens from 13 of 17 men with primary osteoporosis showed reduced trabecular bone volumes, normal bone formation rates, and slightly increased resorption surfaces. Fasting hypercalciuria was seen in some men (41%). In the primary osteoporosis group, eight men were followed serially (range of follow-up, 6 months to 9 years) while they were receiving a nonpharmacologic regimen (diet and activity); the mean axial bone mineral density of these men increased slightly. CONCLUSIONS: A thorough evaluation for identifiable causes of severe osteoporosis in men is warranted because definable pathogenetic factors are seen in many cases. A few men with severe osteoporosis have primary or idiopathic osteoporosis. Primary osteoporosis in men is probably caused by many factors because heterogeneous clinical, laboratory, and histologic features were seen in our series and in those of others. Further studies of primary osteoporosis are needed to define the course of the disease, to identify pathogenetic mechanisms, and to develop therapeutic interventions.

Angiopathic consequences of saturating the plasma scavenger system for actin.

Two plasma proteins, vitamin D-binding protein (actin monomer sequestrant) and gelsolin (actin polymer severing), have been found in association with actin in plasma from ill humans and during experimental injury. In vitro, these are the only plasma proteins that display a high affinity for actin. We infused increasing amounts of globular actin intravenously to rats to evaluate its disposition in plasma and tissues. Intravascular filament formation, microthrombi, and endothelial injury were observed, especially in the pulmonary circulation. These pathological changes were not observed when the globular actin in the infusate had been preincubated with the vitamin D-binding protein in vitro. Complexes of actin with both proteins were found in the plasma, suggesting a saturable, plasma actin-binding system in vivo. Our findings suggest that in vivo saturation of these proteins' actin-binding capacities may serve as a paradigm for pulmonary vascular disorders seen during widespread tissue trauma and cell lysis.

The relationship of health-related quality of life to prevalent and incident vertebral fractures in postmenopausal women with osteoporosis: results from the Multiple Outcomes of Raloxifene Evaluation Study.

OBJECTIVE: To examine the effect of both prevalent and incident vertebral fractures on health-related quality of life (HRQOL) in postmenopausal women with osteoporosis and to characterize the effect of prevalent vertebral fractures on HRQOL with respect to number, location, severity, and adjacency. METHODS: Participants were a subset of women (n = 1,395, mean age 68.5 years) from the Multiple Outcomes of Raloxifene Evaluation trial who had low bone mineral density and/or prevalent vertebral fractures. Vertebral fractures were measured by radiography at baseline, 2 years, and 3 years. HRQOL was assessed using the Osteoporosis Assessment Questionnaire (OPAQ), a validated disease-targeted instrument, at baseline and annually for 3 years. RESULTS: Both prevalent and incident radiographic vertebral fractures were associated with decreased HRQOL. At baseline, women with a prevalent vertebral fracture had significantly lower OPAQ scores on physical function, emotional status, clinical symptoms, and overall HRQOL compared with women without a prevalent fracture (all P < 0.01). HRQOL scores were lower with each subsequent fracture. The effect of prevalent vertebral fracture was dependent on the location within the spine and was strongest in the lumbar region (L1-L4). Incident vertebral fractures significantly decreased OPAQ scores on physical function, emotional status, clinical symptoms, and overall HRQOL (all P < 0.001). CONCLUSION: Our findings demonstrate the importance of treating postmenopausal women who have prevalent vertebral fractures to prevent further decreases in HRQOL associated with subsequent incident vertebral fracture.

Effects of raloxifene on fracture severity in postmenopausal women with osteoporosis: results from the MORE study. Multiple Outcomes of Raloxifene Evaluation.

Raloxifene reduces the risk of new vertebral fractures, but its effect on the severity of these new fractures has not been determined. The MORE (Multiple Outcomes of Raloxifene Evaluation) trial studied the effects of placebo, raloxifene 60 or 120 mg/day in 7,705 postmenopausal women with osteoporosis. Radiologists assessed new vertebral fractures from radiographs and graded the fracture severity as normal (no fracture) or mild, moderate or severe. New clinical vertebral fractures were defined as new vertebral fractures associated with symptoms, such as back pain, and confirmed in radiographs. In the total study population, the majority (76.4%) of the women who experienced clinical vertebral fractures were diagnosed with new moderate/severe vertebral fractures. In turn, women with moderate/severe vertebral fractures in the overall population were more likely to experience clinical symptoms suggestive of fracture than were women who had new mild-only vertebral fractures. The incidence of new mild-only and moderate/severe fractures was the same in women without prevalent vertebral fractures, but the incidence of new moderate/severe fractures was 2 to 3 times higher than that for new mild-only fractures in women with prevalent vertebral fractures. Raloxifene 60 mg/day decreased the risk of at least 1 new moderate/severe vertebral fracture by 61% in women without prevalent vertebral fractures [RR 0.39 (95% CI 0.17, 0.69)], and by 37% in women with prevalent vertebral fractures [RR 0.63 (95% CI 0.49, 0.83)] at 3 years. The risk reductions for at least 1 new moderate/severe vertebral fracture were not significantly different between the raloxifene doses, in women with and without prevalent vertebral fractures. The effects of raloxifene on significantly decreasing the risk of new moderate/severe vertebral fractures may explain the risk reduction for new painful clinical vertebral fractures observed with raloxifene, and is particularly important in postmenopausal women with severe osteoporosis who are at higher risk for moderate or severe fractures.