Effects of dietary nutrients and food groups on bone loss from the proximal femur in men and women in the 7th and 8th decades of age

PAMM: a redox regulatory protein that modulates osteoclast differentiation

The central role of reactive oxygen species (ROS) in osteoclast differentiation and in bone homeostasis prompted us to characterize the redox regulatory system of osteoclasts. In this report, we describe the expression and functional characterization of PAMM, a CXXC motif-containing peroxiredoxin 2-like protein expressed in bone marrow monocytes on stimulation with M-CSF and RANKL. Expression of wild-type (but not C to G mutants of the CXXC domain) PAMM in HEK293 cells results in an increased GSH/GSSG ratio, indicating a shift toward a more reduced environment. Expression of PAMM in RAW264.7 monocytes protected cells from hydrogen peroxide-induced oxidative stress, indicating that PAMM regulates cellular redox status. RANKL stimulation of RAW 264.7 cells caused a decrease in the GSH/GSSG ratio (reflecting a complementary increase in ROS). In addition, RANKL-induced osteoclast formation requires phosphorylation and translocation of NF-kappaB and c-Jun. In stably transfected RAW 264.7 cells, PAMM overexpression prevented the reduction of GSH/GSSG induced by RANKL. Concurrently, PAMM expression completely abolished RANKL-induced p100 NF-kappaB and c-Jun activation, as well as osteoclast formation. We conclude that PAMM is a redox regulatory protein that modulates osteoclast differentiation in vitro. PAMM expression may affect bone resorption in vivo and help to maintain bone mass.

Low urine pH and acid excretion do not predict bone fractures or the loss of bone mineral density: a prospective cohort study

Background

The acid-ash hypothesis, the alkaline diet, and related products are marketed to the general public. Websites, lay literature, and direct mail marketing encourage people to measure their urine pH to assess their health status and their risk of osteoporosis.

The objectives of this study were to determine whether 1) low urine pH, or 2) acid excretion in urine [sulfate + chloride + 1.8x phosphate + organic acids] minus [sodium + potassium + 2x calcium + 2x magnesium mEq] in fasting morning urine predict: a) fragility fractures; and b) five-year change of bone mineral density (BMD) in adults.

Methods

Design: Cohort study: the prospective population-based Canadian Multicentre Osteoporosis Study. Multiple logistic regression was used to examine associations between acid excretion (urine pH and urine acid excretion) in fasting morning with the incidence of fractures (6804 person years). Multiple linear regression was used to examine associations between acid excretion with changes in BMD over 5-years at three sites: lumbar spine, femoral neck, and total hip (n = 651). Potential confounders controlled included: age, gender, family history of osteoporosis, physical activity, smoking, calcium intake, vitamin D status, estrogen status, medications, renal function, urine creatinine, body mass index, and change of body mass index.

Results

There were no associations between either urine pH or acid excretion and either the incidence of fractures or change of BMD after adjustment for confounders.

Conclusion

Urine pH and urine acid excretion do not predict osteoporosis risk.

Phosphate decreases urine calcium and increases calcium balance: a meta-analysis of the osteoporosis acid-ash diet hypothesis

Background

The acid-ash hypothesis posits that increased excretion of "acidic" ions derived from the diet, such as phosphate, contributes to net acidic ion excretion, urine calcium excretion, demineralization of bone, and osteoporosis. The public is advised by various media to follow an alkaline diet to lower their acidic ion intakes. The objectives of this meta-analysis were to quantify the contribution of phosphate to bone loss in healthy adult subjects; specifically, a) to assess the effect of supplemental dietary phosphate on urine calcium, calcium balance, and markers of bone metabolism; and to assess whether these affects are altered by the b) level of calcium intake, c) the degree of protonation of the phosphate.

Methods

Literature was identified through computerized searches regarding phosphate with surrogate and/or direct markers of bone health, and was assessed for methodological quality. Multiple linear regression analyses, weighted for sample size, were used to combine the study results. Tests of interaction included stratification by calcium intake and degree of protonation of the phosphate supplement.

Results

Twelve studies including 30 intervention arms manipulated 269 subjects' phosphate intakes. Three studies reported net acid excretion. All of the meta-analyses demonstrated significant decreases in urine calcium excretion in response to phosphate supplements whether the calcium intake was high or low, regardless of the degree of protonation of the phosphate supplement. None of the meta-analyses revealed lower calcium balance in response to increased phosphate intakes, whether the calcium intake was high or low, or the composition of the phosphate supplement.

Conclusion

All of the findings from this meta-analysis were contrary to the acid ash hypothesis. Higher phosphate intakes were associated with decreased urine calcium and increased calcium retention. This meta-analysis did not find evidence that phosphate intake contributes to demineralization of bone or to bone calcium excretion in the urine. Dietary advice that dairy products, meats, and grains are detrimental to bone health due to "acidic" phosphate content needs reassessment. There is no evidence that higher phosphate intakes are detrimental to bone health.

The effect of including quantitative heel ultrasound in models for estimation of 10-year absolute risk of fracture

The role of quantitative ultrasound (QUS) in clinical practice is debatable. An unanswered question is that whether combining QUS and BMD measurements could improve the prediction of fracture risk. We examined this in a sample of men and women in the European Prospective Investigation into Cancer (EPIC)-Norfolk who had both heel QUS and hip DXA between 1995 and 1997 and were followed for any incident fracture up to 2007. From 1455 participants (703 men) aged 65-76 years at baseline, 79 developed a fracture over 10.3+/-1.4 years of follow-up. Two separate sex-stratified Cox proportional-hazard models were used including clinical risk factors and total hip BMD. Heel broadband ultrasound attenuation (BUA) was also included in the second model. Global measures of model fit, area under ROC curve, and the Hosmer-Lemeshow statistic showed relative superiority of the model including BUA. Using each model, we calculated 10-year absolute risk of fracture for all participants and categorized them in groups of < 5%, 5% to < 15%, and > or = 15%. Comparison of groupings showed a total re-classification of 16.6% of participants after inclusion of BUA with the greatest re-classification (30.7%) among the group with intermediate risk. Adding a QUS measurement to models based on clinical risk factors and BMD improves the predictive power of models and suggests that further attention should be paid to QUS as a clinical tool for fracture risk assessment.

Natural history and correlates of hip BMD loss with aging in men of African ancestry: the Tobago Bone Health Study

Little is known about the magnitude, pattern, and determinants of bone loss with advancing age among men, particularly among those of African descent. We examined the rate of decline in hip BMD and identified factors associated with BMD loss among 1478 Afro-Caribbean men >or=40 yr of age. BMD was measured at baseline and after an average of 4.4 yr by DXA. The rate of decline in femoral neck BMD was 0.29 +/- 0.81%/yr in the total sample (p < 0.0001). However, a U-shaped relationship between advancing age and the rate of decline in BMD was observed. The rate of decline in BMD at the femoral neck was -0.38 +/- 0.77%/yr among men 40-44 yr of age, decelerated to -0.15 +/- 0.81%/yr among men 50-54 yr of age, and then accelerated to -0.52 +/- 0.90%/yr among those 75+ yr of age (all p < 0.003). Men who lost >or=5% of their body weight during follow-up had significantly greater BMD loss than those who remained weight stable or gained weight (p < 0.0001). The relationship between weight loss and BMD loss was more pronounced among men who were older and leaner at study entry (p < 0.03). We also observed a strong impact of advanced prostate cancer and its treatment with androgen deprivation on BMD loss. Men of African ancestry experience substantial BMD loss with advancing age that seems to be comparable to the rate of loss among white men in other studies. Additional studies are needed to better define the natural history and factors underlying bone loss with aging in men of African ancestry.

Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash diet hypothesis

BACKGROUND

The acid-ash diet hypothesis of osteoporosis suggests that acid from the modern diet causes a demineralization of the skeleton, and mobilized bone calcium is excreted. A systematic approach has not been used to summarize the findings of the numerous studies about the hypothesis.

OBJECTIVES

The purpose of this meta-analysis was to estimate the quantity of net acid excretion and calciuria associated with the modern diet, to assess the association between acid excretion and calcium excretion, and to assess the influence of urine preservatives on calcium measurement.

DESIGN

We systematically searched for trials of the acid-ash hypothesis and conducted a meta-analysis.

RESULTS

Twenty-five of 105 studies met the inclusion criteria. The estimated quantity of net acid excretion from the weighted average of the control diets from 11 studies was 47 mEq/d. The increase in urinary calcium with a change in renal net acid excretion depended on whether the urine was acidic or alkaline (P < 0.001). A significant linear relation was observed between net acid excretion and calcium excretion for both acidic and alkaline urine (P < 0.001). The estimated change in urine calcium associated with a change of 47 mEq of net acid excretion in acidic urine was 1.6 mmol/d (66 mg/d) of calcium.

CONCLUSION

Evidence suggests a linear association between changes in calcium excretion in response to experimental changes in net acid excretion. However, this finding is not evidence that the source of the excreted calcium is bone or that this calciuria contributes to the development of osteoporosis.

Vitamin A: is it a risk factor for osteoporosis and bone fracture?

Results from observational studies of the association between vitamin A intake or serum concentration and bone mineral density or fracture are mixed. The inconsistencies may be due, in part, to difficulties in obtaining an accurate assessment of vitamin A intake or status. Serum retinol is a poor measure of vitamin A status because it is subject to homeostatic control. Stable-isotope-dilution methodology gives a validated assessment of the total-body and liver vitamin A stores and is recommended in future studies on vitamin A status and osteoporosis. The potential for exacerbating an already serious public health problem with intakes of vitamin A currently considered safe indicates further research into this matter is warranted.

Association between change in bone mineral density and decline in usual walking speed in elderly community-dwelling Japanese women during 2 years of follow-up

OBJECTIVES

To investigate the association between change in bone mineral density (BMD) and change in usual walking speed in elderly community-living Japanese women during 2 years of follow-up.

DESIGN

Longitudinal cohort study.

SETTING

Community-based.

PARTICIPANTS

A total of 182 women aged 70 to 84 who completed a baseline survey and a follow-up survey 2 years later.

MEASUREMENTS

An interview, anthropometric measurements, blood analysis, and physical performance tests were performed at baseline and at follow-up 2 years later. BMD was evaluated using dual-energy X-ray absorptiometry measured at the forearm. Annual percentage changes in BMD and usual walking speed during the 2-year follow-up period were calculated; annual percentage changes in BMD were summarized in quartiles. The association between annual bone loss rate and decline in usual walking speed was analyzed using multiple linear regression adjusted for changes in muscle strength, balance capability, and other potential confounders.

RESULTS

Change in BMD was significantly related to change in usual walking speed during the 2-year follow-up. After multivariate adjustment, usual walking speed declined significantly more in elderly women whose BMD decreased (-3.5% change in walking speed in the first quartile of percentage change in BMD and -3.1% in the second quartile) than in women whose BMD increased (+1.5% in fourth quartile).

CONCLUSION

Elderly women whose BMD decreased had a significantly greater decline in usual walking speed than women whose BMD increased, even after multivariate adjustment of potential confounders.

Bone turnover and nutritional status in Crohn's disease: relationship to circulating mononuclear cell function and response to fish oil and antioxidants

Crohn's disease is associated with osteoporosis, malnutrition and altered function of peripheral blood mononuclear cells (PBMC). The responses of circulating immune cells and extra-intestinal manifestations to increased inflammatory activity and to modulation by dietary supplementation are uncertain. The relationships between disease status, bone turnover and body mass and composition, PBMC function and fatty acid availability have been investigated in patients with Crohn's disease. The availability of n-3 and n-6 PUFA is altered in adult patients and interferon (IFN)-γ production by PBMC is lower. Increased inflammatory activity is associated with increased bone resorption in adult patients and decreased body mass in paediatric patients. In healthy male subjects there is a proportionate relationship between supplementary intake of EPA and DHA (0.3–2.0 g as fish oil/d) in combination with antioxidants (vitamins A, C and E and Se) and incorporation into plasma phospholipids and PBMC, and a non-linear relationship with PBMC synthesis of TNF-α, IL-6 and prostaglandin E2 (decrease) and IFN-γ (increase). In adults with Crohn's disease high-dose fish oil (2.7 g EPA+DHA/d) in combination with antioxidants (vitamins A, C and E and Se) increases the EPA and DHA content of PBMC and decreases the production of IFN-γ by PBMC, but is not associated with effects on bone turnover or nutritional status.

Geographic and other determinants of BMD change in European men and women at the hip and spine. a population-based study from the Network in Europe for Male Osteoporosis (NEMO)

INTRODUCTION

While the determinants of BMD change have been studied in women, there have been few longitudinal studies in men. As part of the Network in Europe for Male Osteoporosis (NEMO) study, data were analysed from 1337 men and 1722 women aged 50-86y (mean=67 years) from 13 centres across Europe to assess determinants of BMD change and between-gender contrasts.

METHODS

BMD was measured at the femoral neck, trochanter and/or L2-L4 spine on 2 occasions 0.8-8 years apart (mean=3.5 years) using DXA densitometers manufactured by Hologic (n=6), Lunar (n=5) and Norland (n=2). Each was cross-calibrated using the European Spine Phantom and annual rates of BMD change (g/cm(2)/year) were calculated from the standardised paired BMD values. The EPOS risk factor questionnaire was administered at baseline.

RESULTS

In multivariate linear regression models, there were large between centre differences in the mean rates of BMD change in all 3 sites for both genders (P<0.0001) with the standard deviation of the between centre heterogeneity in the adjusted means being 0.005 g/cm(2)/year at the femoral neck. The overall adjusted mean annual rates of BMD change in g/cm(2)/year (95% CI) pooled across centres by random effects meta-analysis in men were: femoral neck -0.005 (-0.009, -0.001); trochanter -0.003 (-0.006, -0.001); and spine 0.000 (-0.004, 0.004). In women the respective estimates were: -0.007 (-0.009, -0.005); -0.004 (-0.006, -0.003); and -0.005 (-0.008, -0.001). The I(2) statistic for heterogeneity was between 81% and 94%, indicating strong evidence of between centre heterogeneity. Higher baseline BMD value was associated with subsequent greater decline in BMD (P<0.001). Preserved BMD was associated with higher baseline body weight in all 3 sites in men (P<0.012) but not in women. Weight gain preserved BMD (P<0.039) in all 3 sites for both genders, except the male spine. Increasing age was associated with faster BMD decline at the trochanter in both genders (P<0.026) and with a slower rate of decline at the female spine (P=0.002). Effects of lifestyle, physical activity, medications, and reproductive factors were not consistent across sites or between genders.

CONCLUSION

These results show major geographic variations in rates of BMD change in men and women over 50 years of age across diverse European populations and demonstrate that body weight and weight gain are key determinants of BMD change in men.

Follicle-stimulating hormone stimulates TNF production from immune cells to enhance osteoblast and osteoclast formation

Declining estrogen production after menopause causes osteoporosis in which the resorption of bone exceeds the increase in bone formation. We recently found that mice deficient in the beta-subunit of follicle-stimulating hormone (FSHbeta) are protected from bone loss despite severe estrogen deficiency. Here we show that FSHbeta-deficient mice have lowered TNFalpha levels. However, TNFalpha-deficient mice are resistant to hypogonadal bone loss despite having elevated FSH, suggesting that TNFalpha is critical to the effect of FSH on bone mass. We find that FSH directly stimulates TNFalpha production from bone marrow granulocytes and macrophages. We also explore how TNFalpha up-regulation induces bone loss. By modeling the known actions of TNFalpha, we attribute the high-turnover bone loss to an expanded osteoclast precursor pool, together with enhanced osteoblast formation. TNFalpha inhibits osteoblastogenesis in the presence of ascorbic acid in culture medium, but in its absence this effect becomes stimulatory; thus, ascorbic acid reverses the true action of TNFalpha. Likewise, ascorbic acid blunts the effects of TNFalpha in stimulating osteoclast formation. We propose that hypogonadal bone loss is caused, at least in part, by enhanced FSH secretion, which in turn increases TNFalpha production to expand the number of bone marrow osteoclast precursors. Ascorbic acid may prevent FSH-induced hypogonadal bone loss by modulating the catabolic actions of TNFalpha.

Fruit and vegetable intakes and bone mineral status: a cross sectional study in 5 age and sex cohorts

BACKGROUND

Evidence is increasing for positive effects of fruit and vegetable intakes on bone health. However, most of the studies to date were conducted in adults, and few reports included adolescents.

OBJECTIVE

We explored the association between bone mineral status and fruit and vegetable intakes in adolescent boys and girls (aged 16-18 y), young women (aged 23-37 y), and older men and women (aged 60-83 y).

DESIGN

Bone mineral measurements of the whole body, hip, and spine were made in all subjects by using dual-energy X-ray absorptiometry. Information on health and lifestyle and physical activity was obtained by questionnaire. Fruit, vegetable, and nutrient intakes were ascertained from 7-d food diaries.

RESULTS

In adolescent boys and girls and older women, significant positive associations were observed between spine size-adjusted bone mineral content (SA-BMC) and fruit intake. In boys only, femoral neck SA-BMC was also significantly and positively associated with the intakes of both fruit and dietary vitamin C. No significant associations were found in the young women or older men, or between bone measurements and intake of vegetables alone (after adjustments) in any of the groups.

CONCLUSIONS

Higher fruit and vegetable intakes may have positive effects on bone mineral status in both younger and older age groups, especially at the spine and femoral neck. The specific mechanisms remain to be ascertained, but vitamin C, other fruit-specific antioxidants, and lifestyle may play a role.

A Nutrient Density Standard for Vegetables and Fruits: Nutrients per Calorie and Nutrients per Unit Cost

OBJECTIVES

The Dietary Guidelines for Americans 2005 recommended that consumers give priority to nutrient-dense foods, those that contain substantial amounts of key nutrients in relation to the dietary energy they provide. This study developed a scoring system to estimate the nutritional adequacy of vegetables and fruits, on a per weight, per calorie, and per unit cost basis.

DATA

We used a French national food composition database for 637 foods, including 129 vegetables and fruits. Mean national retail prices were obtained for each food.

METHODS

The nutrient adequacy score was defined as the mean of percent daily values for 16 nutrients, based on 100 g of food. The nutrient density score and the nutrient-to-price ratio were the mean of percent daily values for 16 nutrients, expressed per 100 kcal and per 1 euro of food, respectively. Relationships between energy density of vegetables and fruits, nutrient adequacy score, nutrient density score, and nutrient-to-price ratio were tested using linear regression.

RESULTS

Energy density and nutrient density score were negatively correlated, confirming the widely accepted notion that energy-dense foods tend to be nutrient-poor. As expected, fruits and vegetables had the highest nutrient density score because they were nutrient-rich in relation to their low energy content. They also had a relatively high nutrient-to-price ratio, showing that they provided nutrients at a reasonable cost when compared with other foods.

CONCLUSIONS

Foods ranked differently when nutritional adequacy was calculated per weight (nutrient adequacy score), per calorie (nutrient density score), or per unit cost (nutrient-to-price ratio). The present results showed that although fruits and vegetables are an expensive source of dietary energy, they provide key nutrients at a reasonable cost.

Lifecourse study of bone health at age 49-51 years: the Newcastle thousand families cohort study

OBJECTIVE

To quantify the direct and indirect effects of fetal (position in family, weight, and social class at birth), childhood (breast feeding, growth, infections, and social class in childhood, age at menarche), and adult life (social class, alcohol consumption, smoking, diet, reproductive history, exercise, hormone replacement therapy use), and adult size (height, weight) on bone health at age 49-51 years, as measured by bone mineral density, total scanned bone area of the hip and lumbar spine, and femoral neck shaft angle.

DESIGN

Follow up study of the Newcastle thousand families birth cohort established in 1947.

PARTICIPANTS

171 men and 218 women who attended for dual energy x ray absorptiometry scanning.

MAIN RESULTS

Fetal life explained around 6% of variation in adult bone mineral density for men, but accounted for less than 1% for women. Adult lifestyle, including effects mediated through adult weight accounted for over 10% of variation in density for men and around 6% for women. Almost half of variation in bone area for men was explained by early life. However, most of this was mediated through achieved adult height and weight. In women, less than 5% of variation in bone area was accounted for by early life, after adjusting for adult size. Most of the variation in each of the indicators for both sexes was contributed either directly or indirectly by adult lifestyle and achieved adult height and weight.

CONCLUSIONS

The effect of fetal life on bone health in adulthood seems to be mediated through achieved adult height.

Spontaneous fractures in the mouse mutant sfx are caused by deletion of the gulonolactone oxidase gene, causing vitamin C deficiency

Using a mouse mutant that fractures spontaneously and dies at a very young age, we identified that a deletion of the GULO gene, which is involved in the synthesis of vitamin C, is the cause of impaired osteoblast differentiation, reduced bone formation, and development of spontaneous fractures.

INTRODUCTION

A major public health problem worldwide, osteoporosis is a disease characterized by inadequate bone mass necessary for mechanical support, resulting in bone fracture. To identify the genetic basis for osteoporotic fractures, we used a mouse model that develops spontaneous fractures (sfx) at a very early age.

MATERIALS AND METHODS

Skeletal phenotype of the sfx phenotype was evaluated by DXA using PIXImus instrumentation and by dynamic histomorphometry. The sfx gene was identified using various molecular genetic approaches, including fine mapping and sequencing of candidate genes, whole genome microarray, and PCR amplification of candidate genes using cDNA and genomic DNA as templates. Gene expression of selected candidate genes was performed using real-time PCR analysis. Osteoblast differentiation was measured by bone marrow stromal cell nodule assay.

RESULTS

Femur and tibial BMD were reduced by 27% and 36%, respectively, in sfx mice at 5 weeks of age. Histomorphometric analyses of bones from sfx mice revealed that bone formation rate is reduced by >90% and is caused by impairment of differentiated functions of osteoblasts. The sfx gene was fine mapped to a 2 MB region containing approximately 30 genes in chromosome 14. By using various molecular genetic approaches, we identified that deletion of the gulonolactone oxidase (GULO) gene, which is involved in the synthesis of ascorbic acid, is responsible for the sfx phenotype. We established that ascorbic acid deficiency caused by deletion of the GULO gene (38,146-bp region) contributes to fractures and premature death because the sfx phenotype can be corrected in vivo by treating sfx mice with ascorbic acid and because osteoblasts derived from sfx mice are only able to form mineralized nodules when treated with ascorbic acid. Treatment of bone marrow stromal cells derived from sfx/sfx mice in vitro with ascorbic acid increased expression levels of type I collagen, alkaline phosphatase, and osteocalcin several-fold.

CONCLUSION

The sfx is a mutation of the GULO gene, which leads to ascorbic acid deficiency, impaired osteoblast cell function, and fractures in affected mice. Based on these and other findings, we propose that ascorbic acid is essential for the maintenance of differentiated functions of osteoblasts and other cell types.

Racial differences in rate of decline in bone mass in older men: the Baltimore men's osteoporosis study

Older black men have higher adjusted BMD than older white men. Using data from a longitudinal cohort study of older men followed for a mean of 18.8 +/- 6.5 (SD) months, we found that older black men have a higher rate of decline in femoral neck and total hip BMD and femoral neck BMAD than older white men.

INTRODUCTION

Older black men have higher adjusted BMD compared with older white men. The difference in BMD may be caused by having attained higher peak bone mass as young adults and/or having a slower rate of decline in bone mass as adults. There are few published longitudinal data on change in bone mass in older white men and no published data for older black men.

MATERIALS AND METHODS

Three hundred forty-nine white men and 119 black men 65 of age (mean age, 75 +/- 5.7 and 72 +/- 5.6 years, respectively) who participated in the longitudinal component of the Baltimore Men's Osteoporosis Study returned for a second visit after a mean of 18.8 +/- 6.5 (SD) months and were not taking medications used to treat low bone mass at either visit. BMD was measured at the femoral neck and total hip by Hologic-certified technicians using a QDR 2000 at the baseline visit (V1) and QDR 4500 at the first follow-up visit (V2). Participants also completed self-administered and interviewer-administered questionnaires and underwent standardized clinic examinations. Bone mineral apparent density (BMAD) at the femoral neck was calculated as an estimate of volumetric BMD. Annual crude and multiple variable adjusted percent changes in BMD and BMAD were calculated.

RESULTS

In univariate analyses, black men had lower percent decline in femoral neck and total hip BMD and femoral neck BMAD than white men. In addition, older age at baseline, lower baseline weight, current smoking, and lower baseline BMD were associated with greater percent decline per year in femoral neck BMD; older age at baseline, current smoking, and lower baseline BMD were associated with greater percent decline per year in total hip BMD; and older age at baseline and lower baseline femoral neck BMAD were associated with greater percent decline per year in femoral neck BMAD. Racial differences in bone loss persisted in multiple variable models that controlled for other factors associated with change in BMD and BMAD.

CONCLUSIONS

Older black men seem to lose bone mass at a slower rate than older white men. These differences in the rate of bone loss may account, in part, for the racial disparities in BMD and BMAD and risk of osteoporotic fractures among older men.

Osteoporosis: the role of micronutrients

Osteoporosis and low bone mass are currently estimated to be a major public health threat. Adequate nutrition plays a major role in the prevention and treatment of osteoporosis; the micronutrients of greatest importance are calcium and vitamin D. Calcium has been shown to have beneficial effects on bone mass at all ages, although the results are not always consistent. Higher doses than the current US recommendation (600 IU) of vitamin D in the elderly (age > or = 65 y) may actually be required for optimal bone health (800-1000 IU/d). The elderly can clearly benefit from increased vitamin D intakes; however, the potential importance of vitamin D in peak bone mass is just being investigated. Vitamin D has been related to falls, with supplementation reducing the number of falls. There are clear fracture benefits demonstrated in randomized clinical trials of calcium and vitamin D supplementation. The other micronutrient needs for optimizing bone health can be easily met by a healthy diet that is high in fruits and vegetables to ensure adequate intakes for magnesium, potassium, vitamin C, vitamin K, and other potentially important nutrients. Healthcare professionals need to be aware of the importance of adequate calcium and vitamin D intakes (easily monitored by serum 25(OH)D) for optimal bone health, as well as the prevention of falls and fractures. In addition, a healthy diet that includes 5 servings a day of fruits and vegetables should optimize the intake of micronutrients required for bone health.

Regulation of human osteoclast differentiation by thioredoxin binding protein-2 and redox-sensitive signaling

Differential expression of TBP-2 and Trx-1 occurs during osteoclastogenesis. Adenoviral overexpression of TBP-2 in osteoclast precursors inhibits Trx-1 expression, osteoclast formation, and AP-1 binding activity. TBP-2 and Trx-1 are key regulators of osteoclastogenesis.

INTRODUCTION

Thioredoxin binding protein-2 (TBP-2) negatively regulates thioredoxin-1 (Trx-1), a key endogenous modulator of cellular redox and signaling. In gene array analysis, we found that TBP-2 expression was reduced during human osteoclast differentiation compared with macrophage differentiation. Our aim was to determine the roles of TBP-2 and Trx-1 in human osteoclastogenesis and RANKL signaling.

MATERIALS AND METHODS

Osteoclasts or macrophages were generated from colony-forming unit-granulocyte macrophage (CFU-GM) precursors treated with sRANKL and macrophage-colony-stimulating factor (M-CSF), or M-CSF alone, respectively. Expression of TBP-2 and Trx-1 was quantified by real-time PCR and Western analysis. Adenoviral gene transfer was used to overexpress TBP-2 in precursors. NF-kappaB and activator protein 1 (AP-1) signaling was assessed with EMSA.

RESULTS

In the presence of sRANKL, expression of TBP-2 was decreased, whereas Trx-1 expression was increased. The antioxidant N-acetylcysteine reversed this pattern and markedly inhibited osteoclastogenesis. Adenoviral overexpression of human TBP-2 in precursors inhibited osteoclastogenesis and Trx-1 expression, inhibited sRANKL-induced DNA binding of AP-1, but enhanced sRANKL-induced DNA binding of NF-kappaB.

CONCLUSIONS

These data support significant roles for TBP-2 and the Trx system in osteoclast differentiation that are mediated by redox regulation of AP-1 transcription. A likely mechanism of stress signal induction of bone resorption is provided. Modulators of the Trx system such as antioxidants have potential as antiresorptive therapies.