Large-scale genome-wide linkage analysis for loci linked to BMD at different skeletal sites in extreme selected sibships

Few genome-wide linkage studies of osteoporosis have been conducted in the Asian population. We performed a genome-wide scan involving 3093 adult siblings with at least one sib-pair extremely concordant or discordant for hip BMD. Our results indicated four genome-wide significant QTLs for BMD. In comparison with 12 previous reported linkage studies, we reveal novel linkage regions that have reaching global significance.

INTRODUCTION

The genetic basis for osteoporosis has been firmly established, but efforts to identify genes associated with this complex trait have been incomplete, especially in Asian populations. The purpose of this study was to identify quantitative trait loci (QTLs) for BMD in a Chinese population.

MATERIALS AND METHODS

We performed a genome-wide scan involving 3093 siblings 25-64 years of age from 941 families, with at least one sib-pair extreme concordant or discordant for total hip BMD from a large community-based cohort (n = 23,327) in Anhui, China. Linkage analysis was performed on BMD residuals adjusted for age, height, weight, occupation, cigarette smoking, physical activity, and alcohol consumption using the revised Haseman-Elston regression-based linkage model.

RESULTS

Our results revealed significant QTLs on chromosome 7p21.2 for femoral neck BMD (LOD = 3.68) and on chromosome 2q24.3 for total hip BMD (LOD = 3.65). Suggestive linkage regions were found to overlap among different skeletal sites on chromosomes 2q, 7p, and 16q. Sex-specific linkage analysis further revealed a significant QTL for lumbar spine BMD on chromosome 13q21.1 (LOD = 3.62) in women only. When performing multivariate linkage analysis by combining BMDs at four skeletal sites (i.e., whole body, total hip, femoral neck, and lumbar spine BMD), an additional significant QTL was found at chromosome 5q21.2 (LOD = 4.56). None of these significant QTLs found in our study overlapped with major QTLs reported by other studies.

CONCLUSIONS

This study reveals four novel QTLs in a Chinese population and suggests that BMD at different skeletal sites may also share common genetic determinants.

Response rate of bone mineral density to teriparatide in postmenopausal women with osteoporosis

PURPOSE

It is desirable for clinicians to know what bone mineral density (BMD) response they can expect in women treated with osteoporosis therapies. The focus of this analysis was to determine what percentage of women attained a lumbar spine BMD response to teriparatide that equaled or exceeded the least significant change (LSC) value of 3%.

METHODS

Data from three clinical trials involving postmenopausal women with osteoporosis were examined. The Fracture Prevention Trial was a double-blinded, placebo-controlled clinical trial examining the safety and efficacy of teriparatide 20 and 40 microg/day. The other two trials were double-blinded, head-to-head comparisons of alendronate 10 mg/day and teriparatide 20 or 40 microg/day, respectively. Only treatment-compliant women who had lumbar spine BMD measurements at all specified time points in these trials were included. For reference, we also examined the percentage of women with lumbar spine BMD responses to alendronate. Hip BMD responses that equaled or exceeded 3% were also examined.

RESULTS

According to the LSC criteria, 91% of the teriparatide 20 microg/day group and 94% of the teriparatide 40 microg/day group were lumbar spine BMD responders at 18 months in the Fracture Prevention Trial. In the teriparatide 20 microg/alendronate head-to-head trial, 94% of women receiving teriparatide had a lumbar spine BMD response that equaled or exceeded the 3% criterion at 18 months compared to 75% of those receiving alendronate 10 mg/day (p < 0.01). In the teriparatide 40 microg/day group of the other head-to-head trial, 92% of women achieved the 3% criterion for the lumbar spine at 12 months compared to 69% of those receiving alendronate 10 mg/day (p < 0.01). The median 3-month change in amino-terminal extension peptide of procollagen type 1 [PINP] in women who had a lumbar spine BMD response to teriparatide at 18 months was larger than in women who did not have a lumbar spine BMD response. However, the median 3-month PINP change in lumbar spine BMD nonresponders still exceeded the LSC value of 10 microg/L. Although the percentage of teriparatide-treated women with a hip BMD response that met the 3% criterion was significantly greater than for placebo, there was no significant difference between the percentage of teriparatide 20 microg/day and alendronate 10 mg/day responders in the comparison trial. The baseline characteristics of teriparatide lumbar spine responders and nonresponders were similar.

CONCLUSION

This analysis demonstrates that the vast majority of treatment-compliant postmenopausal women with osteoporosis and minimal prior bisphosphonate exposure have a lumbar spine BMD response to teriparatide that meets or exceeds the LSC. The characteristics of teriparatide responders and nonresponders were not significantly different; thus, we were unable to discern any characteristics that could be used to identify potential nonresponders.

Congenic mice provide in vivo evidence for a genetic locus that modulates serum insulin-like growth factor-I and bone acquisition

We identified quantitative trait loci (QTL) that determined the genetic variance in serum IGF-I through genome-wide scanning of mice derived from C57BL/6J(B6) x C3H/HeJ(C3H) intercrosses. One QTL (Igf1s2), on mouse chromosome 10 (Chr10), produces a 15% increase in serum IGF-I in B6C3 F2 mice carrying c3 alleles at that position. We constructed a congenic mouse, B6.C3H-10 (10T), by backcrossing c3 alleles from this 57-Mb region into B6 for 10 generations. 10T mice have higher serum and skeletal IGF-I, greater trabecular bone volume fraction, more trabeculae, and a higher number of osteoclasts at 16 wk, compared with B6 (P < 0.05). Nested congenic sublines generated from further backcrossing of 10T allowed for recombination and produced four smaller sublines with significantly increased serum IGF-I at 16 wk (i.e. 10-4, 10-7, 10-10, and 10-13), compared with B6 (P < 0.0003), and three smaller sublines that showed no differences in IGF-I vs. age- and gender-matched B6 mice. Like 10T, the 10-4 nested sublines at 16 wk had higher femoral mineral (P < 0.0001) and greater trabecular connectivity density with significantly more trabeculae than B6 (P < 0.01). Thus, by comprehensive phenotyping, we were able to narrow the QTL to an 18.3-Mb region containing approximately 148 genes, including Igf1 and Elk-3(ETS domain protein). Allelic differences in the Igf1s2 QTL produce a phenotype characterized by increased serum IGF-I and greater peak bone density. Congenic mice establish proof of concept of shared genetic determinants for both circulating IGF-I and bone acquisition.

Short-term changes in bone turnover markers and bone mineral density response to parathyroid hormone in postmenopausal women with osteoporosis

CONTEXT

Treatment of osteoporotic women with PTH increases biochemical markers of bone turnover, increases axial bone mineral density (BMD), and reduces fracture risk.

OBJECTIVE

Our objective was to determine the relationship between levels of baseline turnover before PTH therapy and short-term changes in turnover during PTH therapy and subsequent changes in areal and volumetric BMD.

DESIGN AND SETTING

We conducted a randomized, placebo-controlled trial at four academic centers.

PATIENTS

Patients included 238 postmenopausal women with low hip or spine BMD.

INTERVENTION

Subjects were randomized to sc PTH (1-84), 100 mug/d (119 women), for 1 yr.

MAIN OUTCOME MEASURE

Bone turnover markers were measured in fasting blood samples collected before therapy and after 1 and 3 months. Areal and volumetric BMD at the spine and hip were assessed by dual-energy x-ray absorptiometry and quantitative computed tomography (QCT) after 1 yr of therapy.

RESULTS

Among women treated with PTH alone, the relationships between baseline turnover and 1-yr changes in dual-energy x-ray absorptiometry and QCT BMD were inconsistent. Greater 1- and 3-month increases in turnover, particularly the formation marker N-propeptide of type I collagen, were associated with greater increases in areal BMD. When volumetric hip and spine BMD were assessed by QCT, greater short-term increases in turnover were even more positively associated with 1-yr increases in BMD. Each sd increase in the 3-month change of N-propeptide of type I collagen was associated with an a 21% greater increase in QCT spine trabecular BMD.

CONCLUSIONS

Greater short-term changes in turnover with PTH therapy are associated with greater 1-yr increases in spine and hip BMD among postmenopausal osteoporotic women.

Impaired bone anabolic response to parathyroid hormone in Fgf2-/- and Fgf2+/- mice

Since parathyroid hormone (PTH) increased FGF2 mRNA and protein expression in osteoblasts, and serum FGF-2 was increased in osteoporotic patients treated with PTH, we assessed whether the anabolic effect of PTH was impaired in Fgf2-/- mice. Eight-week-old Fgf2+/+ and Fgf2-/- male mice were treated with rhPTH 1-34 (80mug/kg) for 4 weeks. Micro-CT and histomorphometry demonstrated that PTH significantly increased parameters of bone formation in femurs from Fgf2+/+ mice but the changes were smaller and not significant in Fgf2-/- mice. IGF-1 was significantly reduced in serum from PTH-treated Fgf2-/- mice. DEXA analysis of femurs from Fgf2+/+, Fgf2+/-, and Fgf2-/- mice treated with rhPTH (160mug/kg) for 10 days showed that PTH significantly increased femoral BMD in Fgf2+/+ by 18%; by only 3% in Fgf2+/- mice and reduced by 3% in Fgf2-/- mice. We conclude that endogenous Fgf2 is important for maximum bone anabolic effect of PTH in mice.

Relation of body composition, fat mass, and serum lipids to osteoporotic fractures and bone mineral density in Chinese men and women

BACKGROUND

Higher fat mass may be an independent risk factor for osteoporosis and osteoporotic fractures.

OBJECTIVE

We aimed to determine the independent contribution of fat mass to osteoporosis and to estimate the risk of osteoporotic fractures in relation to body weight, lean mass, and other confounders.

DESIGN

This was a community-based, cross-sectional study of 7137 men, 4585 premenopausal women, and 2248 postmenopausal women aged 25-64 y. Total-body and hip bone mineral content (BMC) and bone mineral density (BMD) and body composition were measured by dual-energy X-ray absorptiometry. Serum lipids were measured. Sex- and menopause-specific multiple generalized linear models were applied.

RESULTS

Across 5-kg strata of body weight, fat mass was significantly inversely associated with BMC in the whole body and total hip. When we compared the highest quartile with the lowest quartile of percentage fat mass in men, premenopausal women, and postmenopausal women, the adjusted odds ratios (95% CIs) of osteoporosis defined by hip BMD were 5.2 (2.1, 13.2), 5.0 (1.7, 15.1), and 6.9 (4.3, 11.2), respectively. Significant linear trends existed for higher risks of osteoporosis, osteopenia, and nonspine fractures with higher percentage fat mass. Significant negative relations were found between whole-body BMC and cholesterol, triacylglycerol, LDL, and the ratio of HDL to LDL in all groups.

CONCLUSIONS

Risks of osteoporosis, osteopenia, and nonspine fractures were significantly higher for subjects with higher percentage body fat independent of body weight, physical activity, and age. Thus, fat mass has a negative effect on bone mass in contrast with the positive effect of weight-bearing itself.

Relationship between insulin-like growth factor I, dehydroepiandrosterone sulfate and proresorptive cytokines and bone density in cystic fibrosis

INTRODUCTION

Patients with cystic fibrosis (CF) are known to be at risk for early osteoporosis, and the mechanisms that mediate bone loss are still being delineated. The aim of the present investigation was to investigate if a correlation exists in these patients between skeletal measurements by dual-energy x-ray absorptiometry (DXA) and two anabolic factors, dehydroepiandrosterone (DHEA) and insulin-like growth factor I (IGF-I), and proresorptive factors such as the cytokines interleukin-1beta, tumor necrosis factor alpha, and interleukin-6.

METHODS

We studied 32 outpatients (18 females; mean age: 26.2+/-7.9 years) at a tertiary care medical center. The subjects had venous samples obtained, underwent anthropometric and bone mineral density (BMD) measurements, and completed a health survey. Serum IGF-I concentrations were below the age-adjusted mean in 78% of the participants, and DHEA sulfate (DHEAS) concentrations were low in 72%. Serum concentrations of all cytokines were on the low side of normal; nonetheless, there was a modest inverse correlation between IL-1beta and BMD at all sites.

RESULTS

In univariate analyses, IGF-I and DHEAS were significant correlates of BMD or bone mineral content. In final multivariate models controlling for anthropometric and other variables of relevance to bone density, only IGF-I was identified as a significant independent skeletal predictor. While alterations in DHEAS, IGF-I, and specific cytokines may contribute to skeletal deficits in patients with CF, of these factors a low IGF-I concentration appears to be most strongly correlated with BMD.

CONCLUSIONS

These findings may have therapeutic implications for enhancing bone density in these patients.

Effects of iron ions, protons and X rays on human lens cell differentiation

We have investigated molecular changes in cultured differentiating human lens epithelial cells exposed to high-energy accelerated iron-ion beams as well as to protons and X rays. In this paper, we present results on the effects of radiation on gene families that include or are related to DNA damage, cell cycle regulators, cell adhesion molecules, and cell cytoskeletal function. A limited microarray survey with a panel of cell cycle-regulated genes illustrates that irradiation with protons altered the gene expression pattern of human lens epithelial cells. A focus of our work is CDKN1A (p21(CIP1/WAF1)), a protein that we demonstrate here has a role in several pathways functionally related to LET-responsive radiation damage. We quantitatively assessed RNA and protein expression in a time course before and after single 4-Gy radiation doses and demonstrated that transcription and translation of CDKN1A are both temporally regulated after exposure. Furthermore, we show qualitative differences in the distribution of CDKN1A immunofluorescence signals after exposure to X rays, protons or iron ions, suggesting that LET effects likely play a role in the misregulation of gene function in these cells. A model of molecular and cellular events is proposed to account for precataractous changes in the human lens after exposure to low- or high-LET radiations.

Antibiotic uptake by plants from soil fertilized with animal manure

Antibiotics are commonly added to animal feed as supplements to promote growth of food animals. However, absorption of antibiotics in the animal gut is not complete and as a result substantial amounts of antibiotics are excreted in urine and feces that end up in manure. Manure is used worldwide not only as a source of plant nutrients but also as a source of organic matter to improve soil quality especially in organic and sustainable agriculture. Greenhouse studies were conducted to determine whether or not plants grown in manure-applied soil absorb antibiotics present in manure. The test crops were corn (Zea mays L.), green onion (Allium cepa L.), and cabbage (Brassica oleracea L. Capitata group). All three crops absorbed chlortetracycline but not tylosin. The concentrations of chlortetracycline in plant tissues were small (2-17 ng g(-1) fresh weight), but these concentrations increased with increasing amount of antibiotics present in the manure. This study points out the potential human health risks associated with consumption of fresh vegetables grown in soil amended with antibiotic laden manures. The risks may be higher for people who are allergic to antibiotics and there is also the possibility of enhanced antimicrobial resistance as a result of human consumption of these vegetables.

Variation in genes involved in the RANKL/RANK/OPG bone remodeling pathway are associated with bone mineral density at different skeletal sites in men

In order to assess the contribution of polymorphisms in the RANKL (TNFSF11), RANK (TNFRSF11A) and OPG (TNFRSF11B) genes to variations in bone mineral density (BMD), a population-based cohort with 1,120 extreme low hip BMD cases or extreme high hip BMD controls was genotyped on five SNPs. We further explored the associations between these genetic variations and forearm BMDs by genotyping 266 offspring and 309 available parents from 160 nuclear families. A family-based association test was used. Significantly positive associations were found for A163G polymorphisms in the promoter regions of the OPG gene, a missense substitution in exon 7 (Ala192Val) of the RANK gene and rs9594782 SNP in the 5' UTR of the RANKL gene with BMD in men only. Men with TC/CC genotypes of the rs9594782 SNP had a 2.1 times higher risk of extremely low hip BMD (P = 0.004), and lower whole body BMD (P < 0.001). Subjects with the TC genotype of the Ala192Val polymorphism had a 40% reduced risk of having extremely low hip BMD (P < 0.01), and higher whole body BMD (P < 0.01). Subjects with the GG genotype of the A163G polymorphism had a 70% reduced risk of having extremely low hip BMD (P < 0.05), and higher whole body BMD (P < 0.01). Significant gene-gene interactions were also observed among the OPG, RANK and RANKL genes. Our findings suggest that genetic variation in genes involved in the RANKL/RANK/OPG bone remodeling pathway are strongly associated with BMD at different skeletal sites in adult men, but not in women.

Genetic differences in the IGF-I gene among inbred strains of mice with different serum IGF-I levels

There is significant heterogeneity in serum IGF-I concentrations among normal healthy individuals across all ages and among inbred strains of mice. C3H/HeJ (C3H) mice have 30% higher serum IGF-I concentrations over a lifetime than C57BL/6J (B6), even though body size and length are identical. The underlying mechanism for this disparity remains unknown although several possibilities exist including altered GH secretion, resistance to GH action, or impaired IGF-I secretion from the liver or peripheral tissues. To study this further, we evaluated mRNA levels of pituitary GH, and of IGF-I, GH receptor (GHR) and acid-labile subunit (ALS) in liver and skeletal muscle of male C3H and B6 strains. mRNA levels of hepatic IGF-I paralleled serum IGF-I levels, whereas pituitary GH mRNA expression was significantly lower in C3H than B6. In addition, reduced hepatic mRNA levels of ALS and GHR in B6 suggests hepatic GH resistance in B6. In contrast, mRNA levels of IGF-I and GHR in skeletal muscle were not different between B6 and C3H. There was a single sequence repeat polymorphism (SSR) in the promoter region of both GHR and IGF-I genes in mice; the SSR in the IGF-I gene was significantly different between the two strains. The SSR in the IGF-I gene corresponds to the E2F binding site, which is critical for regulating IGF-I gene expression. These results suggest that the SSR in the promoter region of the IGF-I gene may be partially responsible for differences in serum IGF-I levels between B6 and C3H strains.

Older women track and field athletes have enhanced calcaneal stiffness

Vigorous weight-bearing exercise is recommended to women as a method of osteoporosis prevention. This study examined older women athletes to see if they indeed were less likely to develop osteoporosis than those in the general population, and to investigate which factors could have contributed to these results. One hundred and thirty-nine women 40-88 years old, all competitors in a USA National Masters Track and Field Championships, volunteered for the study. Masters refers to competitors > or =40 years old. Their calcaneal stiffness (SI) was measured by a Lunar Achilles+ ultrasonometer. Subjects were also measured for height and weight, and completed a questionnaire on exercise history, diet, lifestyle factors, medical and menopausal issues, and use of hormone replacement therapy (HRT). The women, mean age 57.3 years, had an overall average SI of 99.5 (T-score = 0.04) which is equivalent to that of a 20-year-old woman and 20.8% higher than expected for women of their age. Their median SI remained not different from expected peak bone SI until the age of 70. For analysis, this cohort of women was divided into two groups: premenopausal and postmenopausal athletes. The SI of both groups was correlated with the earliest age at which they had first participated in sports or exercises that impart moderate to high strain rates to the lower limbs and with current participation in high impact track and field events. Variables correlated with SI in the general population, such as weight, HRT, previous fracture, hysterectomy, and current menopausal status, did not predict SI in this cohort. In conclusion, women competing in Masters track and field at the national level had calcaneal stiffness substantially higher than expected for women of their age in the general population, and their participation in vigorous sports and activities, either currently or at a younger age, was predictive of this association.

Insulin-like growth factor-I and parathyroid hormone: potential new therapeutic agents for the treatment of osteoporosis

Millions of men and women worldwide are afflicted by osteoporosis. As this number is projected to increase over the next half century, attempts to forestall the disease process are being tested. Conventional therapies centre on maintaining bone mineral density (BMD) by blocking bone resorption. However, there is a growing need for drugs that can stimulate new bone formation (anabolic agents), thereby reducing future fracture risk. Both parathyroid hormone (PTH) and insulin like growth factor-I (IGF-I) have been the subject of numerous animal and human studies to determine whether these peptides have promise for the treatment of low bone mass. Although the mechanisms of action for these agents are not well delineated, each protein can activate the osteoblast and thereby enhance bone mass. The effects of these drugs on the osteoclast are less well defined. At the current time, there is considerably more interest in PTH than IGF-I, for several reasons. Firstly, animal studies with PTH are more impressive in terms of histomorphometry and biomechanics than IGF-I; secondly, PTH is specific for the skeleton whereas IGF-I is ubiquitous; and thirdly, human studies with PTH have been relatively devoid of significant side-effects. Large scale Phase III trials are now underway in the US and Europe. It is anticipated that at least one of these peptides may prove to have a role in the prevention and treatment of osteoporosis.

Phosphorus leaching at cold temperatures as affected by wastewater application and soil phosphorus levels

Land application of wastewater in the northern-tier United States during winter months has been suggested as a means to reduce cost of building storage lagoons. A study was initiated in 1996 to assess land application of potato-processing wastewater on a 120-ha field at Park Rapids, MN. One objective of this study was to evaluate the effects of soil P levels and temperature on P leaching in soil columns. In this paper, we report the P sorption, desorption, and leaching characteristics of a high-P (>200 mg kg(-1)) and a low-P (<25 mg kg(-1)) surface soil from the wastewater irrigation site. The leaching experiment was done with wastewater at 4 +/- 2 or 10 +/- 2 degrees C. The high-P soil resulted in an equilibrium P concentration of 8.0 mg L(-1) compared with 0.14 mg L(-1) for the low-P soil. When low-P wastewater was applied to the high-P soil, the soil acted as a P source, and the total phosphorus (TP) concentration in the leachate was 3.5 times higher than the input TP concentration (C0). When high-P wastewater was applied to the high-P soil, the soil acted as a P sink retarding the TP concentration in the leachate by 80%. Phosphorus desorption was higher at 10 degrees C compared with 4 degrees C. The results showed that depending on P levels of the soil and the wastewater, reduction or increase in leachate P will occur below the surface soil. However, further mobility of this P under field conditions will depend on the volume and rate of percolating water as well as the sorption-desorption characteristics of the subsoil.

Prostate carcinoma cells that have resided in bone have an upregulated IGF-I axis

BACKGROUND

Prostate cancer (PC) has a propensity to metastasize to the skeleton, inducing an osteoblastic response in the host. Recent epidemiological studies have suggested that circulating IGF-I may be important for both the pathogenesis and dissemination of PC. We have postulated that tumor secreted IGF-I in conjunction with endogenous IGF-I contributes to the osteoblastic phenotype characteristic of metastatic PC.

METHODS

To test this thesis we studied the established LNCaP PC progression model consisting of three genetically related human PC cell lines.

RESULTS

Using RIA, we found serum-free conditioned media (CM) of LNCaP and C4-2 had no measurable IGF-I, whereas IGF-I was easily detected in CM from C4-2B cells at 24 hr (i.e., 1.8 +/- 0.53 ng/mg cell protein). Real-time PCR of IGF-I mRNA showed that C4-2B expressed 100-fold more IGF-I mRNA than LNCaP cells. In addition, C4-2B expression of IGF-I mRNA was substantially increased in the presence of exogenous IGF-I to nearly twofold. While IGFBP-3 and IGFBP-1 were not detectable in the CM of any PC line, all cells secreted IGFBP-2. C4-2B cells produced 40% more IGFBP-2 than LNCaP or C4-2 cells (C4-2B at 167 +/- 43 ng/mg cell protein). RANKL, a product of bone stromal cells, was also differentially expressed: LNCaP had threefold higher RANKL mRNA compared to C4-2 and C4-2B and at least equivalent protein expression.

CONCLUSIONS

Our results suggest that PC cells that have metastasized to bone have an upregulated IGF-I regulatory system. This suggests an activated IGF-I axis contributes to the host-PC interaction in promoting osteoblastic metastases.

An investigation of the predictors of bone mineral density and response to therapy with alendronate in osteoporotic men

Male osteoporosis is an important disease, with 25-30% of all hip fractures occurring in men. In a recent randomized, placebo-controlled study of osteoporotic males, alendronate 10 mg daily for 2 yr led to significant increments in bone mineral density (BMD), of a similar magnitude to those observed in postmenopausal women. In this study, specimens collected at intervals during the recent trial of alendronate in male osteoporosis, from 197 of the original 241 participants, were assayed for testosterone, estradiol, IGF-I, IGF binding protein 3 (IGFBP-3), bone-specific alkaline phosphatase [BSAP (serum)], and N-telopeptide of type I collagen corrected for creatinine [NTx (urine)]. Together with fracture and densitometry data from the original study, relationships were examined between BMD and serum IGF-I, IGFBP-3, testosterone, estradiol, BSAP, and urine NTx, both at baseline and during treatment with alendronate, to gain possible insights into the pathogenesis of male osteoporosis. Statistically significant (P <or= 0.05) associations were documented, at baseline, between the presence of vertebral fracture and each of serum IGF-I, serum IGFBP-3, serum free testosterone, total spine BMD, and total body BMD. No statistically significant correlations were observed between any of the baseline variables (IGF-I, IGFBP-3, estradiol, testosterone, and presence of vertebral fracture) and the BMD response to alendronate at any site. In a multivariate analysis, used to identify possible combinations of factors capable of predicting baseline BMD or response to alendronate, statistically significant (P <or= 0.01) relationships were seen, at baseline, between BMD and body mass index, age, and prior fracture. However, no statistically significant relationships were seen between any of the baseline variables (age, body mass index, testosterone, estradiol, IGF-I, IGFBP-3, and prior fracture) and change in BMD at any site. These data suggest that among men with osteoporosis it is not possible to identify patients who would be particularly good candidates for therapy with alendronate on the basis of biochemical or hormonal markers. Alendronate therapy appears to benefit osteoporotic males equally, irrespective of baseline serum testosterone, estradiol, IGF-I, or markers of bone turnover.

Congenic mice reveal sex-specific genetic regulation of femoral structure and strength

Genetic linkage studies in C3H/HeJ (C3H) and C57BL/6J (B6) mice identified several chromosomal locations or quantitative trait loci (QTL) linked to femoral volumetric bone mineral density (vBMD). From QTL identified on chromosomes (chr) 1, 4, 6, 13, and 18, five congenic mouse strains were developed. In each of these mice, genomic DNA from the QTL region of the donor C3H strain was transferred into the recipient B6 strain. Here we report the effects of donated C3H QTL on femoral structure, cortical vBMD and bending strength. Femoral structure was quantified by the polar moment of inertia (Ip) at the mid-diaphysis, which reflects the bending or torsional rigidity of the femur. Although the C3H progenitor mice have a smaller Ip than B6 progenitor mice, the congenic mice carrying the C3H segment at Chr 4 had significantly increased Ip in both males and females, giving these mice stronger femora. In female mice from the congenic Chr 1 strain, Ip was increased whereas male mice from the Chr 1 strain had smaller femoral cross-sections and significantly reduced Ip. This sex-specific effect on femoral structure was seen to a lesser extent in Chr 18 congenic mice. In addition, cortical vBMD was measured using peripheral quantitative computed tomography. Cortical vBMD was similar among most congenic strains except in Chr 6 congenic mice, where cortical vBMD was significantly less in females, but not in males. We conclude that (1) chromosomal QTL from C3H mice, which are genetically linked to total femoral vBMD, also regulate femoral structure; (2) the QTL on Chr 4 improves femoral structure and strength; (3) QTL on Chr 1 and 18 impart sex-specific effects on femoral structure; and (4) the QTL on Chr 6 imparts a sex-specific effect on cortical vBMD and femoral strength.

Skeletal unloading induces resistance to insulin-like growth factor I on bone formation

Skeletal unloading results in an inhibition of bone formation associated with a decrease in osteoblast number, impaired mineralization of bone, and altered proliferation and differentiation of osteoprogenitor cells. Although such changes are likely to be mediated by multiple factors, resistance to the growth-promoting action of insulin-like growth factor I (IGF-I) has been hypothesized to play an important role. To determine whether skeletal unloading induces resistance to IGF-I on bone formation, we examined the response of unloaded (hindlimb elevation) and normally loaded tibia and femur to IGF-I administration. To eliminate the variable of endogenous growth hormone production and secretion during exogenous IGF-I administration, we used growth hormone-deficient dwarf rats (dw-4). The rats were given IGF-I (2.5 mg/kg/day) or vehicle during 7 and 14 days of unloading or normal loading. This significantly increased the serum level of IGF-I in both the normally loaded and unloaded rats. Unloading did not affect the serum level of IGF-I in the vehicle-treated rats. IGF-I markedly increased periosteal bone formation at the tibiofibular junction of normally loaded rats. Unloading decreased bone formation in the vehicle-treated rats, and blocked the ability of IGF-I to increase bone formation. On the other hand, IGF-I increased periosteal bone formation at the midpoint of the humerus (normally loaded in this model) in both hindlimb-elevated and normally loaded rats. IGF-I significantly increased osteogenic colony number, total ALP activity, and total mineralization in bone marrow osteoprogenitor (BMOp) cells of normally loaded rats. Unloading reduced these parameters in the vehicle-treated rats, and blocked the stimulation by IGF-I. Furthermore, IGF-I administration (10 ng/ml) in vitro significantly increased cell proliferation of the BMOp cells isolated from normally loaded bone, but not that of cells from unloaded bone. These results indicate that skeletal unloading induces resistance to IGF-I on bone formation.

Factors related to the use of bone densitometry: survey responses of 494 primary care physicians in New England

Large population-based surveys have shown that approximately 30% of people over age 65 years have osteoporosis and that 17% of the population over 65 years will sustain a fracture during their lifetime. Many people with osteoporosis are never being evaluated even though effective treatments are available. We examined why primary care physicians order few bone mineral density scans. We conducted a cross-sectional survey of primary care physicians practicing in any of the six New England states. Target physician specialties included internal medicine, general practitioners/family physicians, and obstetrician-gynecologists who had a facsimile number listed with the American Medical Association. Demographics, practice characteristics, use of bone densitometry, and attitudes regarding osteoporosis, bone densitometry and health maintenance were assessed by questionnaire. Twelve percent (n=494) of the physicians responded to the questionnaire. Respondents were similar to non-respondents with respect to years of practice, training and geographical state, though they were more likely to be female (p < or =0.05). Respondents had a mean age of 51 years, and 51% were trained in internal medicine, 25% in general practice/family practice and 24% in obstetrics-gynecology. The mean number of self-reported bone densitometry referrals per month was 10+/-11, and 25% of respondents reported that they referred fewer than 4 patients per month. In adjusted logistic models, factors significantly associated with referring fewer than 4 patients per month were: training in internal medicine (odds ratio (OR) 2.0, 95% confidence interval (CI) 1.0-3.9) or general practice/family practice (OR 2.6, 95% CI 1.3-5.2) versus obstetrics-gynecology; practicing in an urban setting (OR 2.5, 95% CI 1.3-4.9) or rural/small town setting (OR 2.2, 95% CI 1.2-4.1) versus a suburban setting; spending less than 50% of professional time in patient care (OR 4.0, 95% CI 1.7-9.5); seeing the lowest proportion of postmenopausal women (OR 2.5., 95% CI 1.2-5.3); the belief that calcium and vitamin D are adequate to treat osteoporosis (OR 2.1, 95% CI 1.0-4.5); and the belief that osteoporosis treatment should not be based on bone density results (OR 3.2, 95% CI 1.7-6.1). Potentially modifiable physician beliefs and a number of practice characteristics are associated with low referral rates for bone densitometry. Educational strategies aimed at improving the use of bone density testing should consider these factors.

Insulin-like growth factor binding proteins 4 and 5 and bone mineral density in elderly men and women

Insulin-like growth factor-1 (IGF-I) plays a central role in the maintenance of bone mass. To test whether two major IGF-I binding proteins, IGFBP-4 and IGFBP-5, are related to bone mineral density (BMD), we studied a sample of the Framingham Offspring Cohort participants (99 men and 101 women, ages 60-87). Serum levels of IGF-I, IGFBP-4, and IGFBP-5 were measured by previously validated radioimmunoassays (CVs approximately 10%). BMDs of the proximal femur and lumbar spine were measured using a Lunar DPX-L densitometer. In males, but not females, IGF-I and IGFBP-5 were inversely associated with age (r = 0.34 and r = -0.28, respectively; P <0.01), while IGFBP-4 levels were positively associated with age (P <0.01). Multivariate means for BMD (adjusted for age, body mass index, height, smoking, and in women, estrogen use) were computed across quartiles of IGFBP-4 and IGFBP-5 and IGFBP-4/IGFBP-5 ratio. In women, but not men, IGFBP-5 was positively associated with femoral neck BMD (P = 0.03), however, after statistical adjustment for IGF-I, this association was no longer significant. No other associations were observed for BMD at any other site. Further study is necessary for elucidation of the gender differences in the possible influence of IGF system components on bone mass.

IGF-I regulates osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand in vitro and OPG in vivo

IGF-I, a ubiquitous polypeptide, plays a key role in longitudinal bone growth and acquisition. The most predominant effect of skeletal IGF-I is acceleration of the differentiation program for osteoblasts. However, in vivo studies using recombinant human (rh) IGF-I and/or rhGH have demonstrated stimulation of both bone formation and resorption, thereby potentially limiting the usefulness of these peptides in the treatment of osteoporosis. In this study, we hypothesized that IGF-I modulates bone resorption by regulating expression of osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB (RANK) ligand (RANKL) in bone cells. Using Northern analysis in ST2 cells, we found that human IGF-I suppressed OPG mRNA in a time- and dose-dependent manner: 100 micro g/LIGF-I (13 nM) decreased OPG expression by 37.0 +/- 1.8% (P < 0.002). The half maximal inhibitory dose of IGF-I was reached at 50 micro g/liter ( approximately 6.5 nM) with no effect of IGF-I on OPG message stability. Conditioned media from ST2 cells confirmed that IGF-I decreased secreted OPG, reducing levels by 42%, from 12.1-7 ng/ml at 48 h (P < 0.05). Similarly, IGF-I at 100 micro g/liter (13 nM) increased RANKL mRNA expression to 353 +/- 74% above untreated cells as assessed by real-time PCR. In vivo, low doses of rhGH when administered to elderly postmenopausal women only modestly raised serum IGF-I (to concentrations of 18-26 nM) and did not affect circulating OPG concentrations; however, administration of rhIGF-I (30 micro g/kg.d) for 1 yr to older women resulted in a significant increase in serum IGF-I (to concentrations of 39-45 nM) and a 20% reduction in serum OPG (P < 0.05). In summary, we conclude that IGF-I in a dose- and time-dependent manner regulates OPG and RANKL in vitro and in vivo. These data suggest IGF-I may act as a coupling factor in bone remodeling by activating both bone formation and bone resorption; the latter effect appears to be mediated through the OPG/RANKL system in bone.

Genetics and bone. Using the mouse to understand man

The rationale for use of inbred strains of mice in bone research is well recognized and includes: a) practical factors (economics of scale, rapid development of adult status, pre-existing knowledge, down-sized technologies) and b) proven methodologies for genetic studies (polygenic trait analyses, mapping tools, genomic sequencing, methods for gene manipulation). Initial investigations of inbred strains of mice showed that femoral and lumbar vertebral volumetric bone mineral density (BMD, mg/mm(3)) by pQCT varied in excess of 50% for femurs and 9% in vertebral BMD. Two strains - low BMD C57BL/6J (B6) mice and high BMD C3H/HeJ (C3H) - were investigated for insights to their BMD diversity. B6C3F2 females derived from intercrossing B6C3F1s were raised to adult skeletal status at 4 months, then necropsied for phenotyping of bone and genotyping of genomic DNA. 1000 F2 females were genotyped for PCR product polymorphisms on all 19 autosomes at approximately 15 cM. Genome wide analyses for genotype-phenotype correlations showed 10 chromosomes (Chrs) carried genes for femoral and 7 Chrs for vertebral BMD. LOD scores ranged from 2.90 to 24.4, and percent of F2 variance accounted for ranged from 1 to 10%. Analyses of main effects revealed both dominant-recessive and additive inheritance patterns. Both progenitor strains carried alleles with positive and negative effects on BMD of each bone sites. A remarkable array of additonal skeletal phenotypes (femur and vertebral geometry, strength measures, serum markers) also proved polygenic in nature, with complex segregation patterns. Verification of BMD quantitative trait loci (QTLs) was undertaken by creating congenic B6 strains carrying individual QTL regions from C3H. Following 6 cycles of backcrossing a QTL-containing region from C3H to the B6 strain, N6F2 congenic strain mice were aged to 4 months, then genotyped for the QTL region and phenotyped for skeletal traits. Comparison of mice homozygous for C3H alleles versus homozygous for B6 alleles in the QTL regions showed that femoral BMD increased or decreased significantly in congenic strains, as was predicted from F2 data. Gender differences specific to BMD QTLs have been revealed, as have more than 30 additional phenotypes associated with cortical and trabecular structural parameters and biomechanical properties.

Reconsidering the effects of antiresorptive therapies in reducing osteoporotic fracture

Concepts of what constitutes osteoporosis have evolved from the single criterion of low bone mass to a more inclusive consideration of bone strength, based on both quantity and quality. The evidence driving this shift is drawn from many sources. For example, recent studies of bone geometry have shown what engineers have always known: material properties and structural strength are inseparable. Genetic factors also argue against a one-dimensional (ID) view of osteoporosis. Large-scale family studies present a strong case for genetic influences on bone mass and predisposition to fracture. The contribution of aging to fracture risk has long been known, but we are only now beginning to understand what happens to bone remodeling and microstructure in an aging skeleton. The recognition that osteoporosis is far more complex than previously thought suggests that factors in addition to bone mineral density (BMD) may be useful for evaluating bone fragility and therapeutic effectiveness. Although assessment of BMD is noninvasive and widely available, the degree of increase in BMD alone fails to account for the broader effectiveness of antiresorptive agents in reducing the risk of fractures related to osteoporosis. Indeed, the very multiplicity of factors that determine fracture risk implies that response to therapy may be equally complex. Studies of response to antiresorptive agents and the cellular processes they induce are at best preliminary at this time. Although new technologies have been applied to studying bone microarchitecture, their invasive nature limits wide use. New methods are needed to provide insight into the causes and effects of bone fragility. The definition of osteoporosis, meanwhile, must still be considered a work in progress.

Growth hormone administration and exercise effects on muscle fiber type and diameter in moderately frail older people

OBJECTIVE

Reduced muscle mass and strength are characteristic findings of growth hormone deficiency (GHD) and aging. We evaluated measures of muscle strength, muscle fiber type, and cross sectional area in response to treatment with recombinant human growth hormone (rhGH) with or without a structured resistance exercise program in frail older subjects.

DESIGN

Placebo-controlled, randomized, double blind trial.

SETTING

Outpatient clinical research center at an urban university-affiliated teaching hospital.

PARTICIPANTS

Thirty-one consenting older subjects (mean age 71.3 +/- 4.5 years) recruited as a subset of a larger project evaluating rhGH and exercise in older people, who underwent 62 quadricep-muscle biopsies.

INTERVENTION

Random assignment to a 6-month course of one of four protocols: rhGH administered subcutaneously daily at bedtime, rhGH and a structured resistance exercise program, structured resistance exercise with placebo injections, or placebo injections only.

MEASUREMENTS

Muscle biopsy specimens were obtained from the vastus lateralis muscle. Isokinetic dynamometry strength tests were used to monitor individual progress and to adjust the weights used in the exercise program. Serum insulin-like growth factor-I (IGF-I) was measured and body composition was measured using a Hologic QDR 1000W dual X-ray densitometer.

RESULTS

The administration of rhGH resulted in significant increase in circulating IGF-I levels in the individuals receiving rhGH treatment. Muscle strength increased significantly in both the rhGH/exercise (+55.6%, P =.0004) as well as the exercise alone (+47.8%, P =.0005) groups. There was a significant increase in the proportion of type 2 fibers between baseline and six months in the combined rhGH treated subjects versus those not receiving rhGH (P =.027).

CONCLUSIONS

Our results are encouraging in that they suggest an effect of growth hormone on a specific aging-correlated deficit. IGF-I was increased by administrating rhGH and muscle strength was increased by exercise. The administration of rhGH to frail older individuals in this study resulted in significant changes in the proportions of fiber types. Whether changes in fiber cross-sectional area or absolute number occur with long-term growth hormone administration requires further study.

Quantitative trait loci for femoral and lumbar vertebral bone mineral density in C57BL/6J and C3H/HeJ inbred strains of mice

Significant differences in vertebral (9%) and femoral (50%) adult bone mineral density (BMD) between the C57BL/6J (B6) and C3H/HeJ (C3H) inbred strains of mice have been subjected to genetic analyses for quantitative trait loci (QTL). Nine hundred eighty-six B6C3F2 females were analyzed to gain insight into the number of genes that regulate peak BMD and their locations. Femurs and lumbar vertebrae were isolated from 4-month-old B6C3F2 females at skeletal maturity and then BMD was determined by peripheral quantitative computed tomography (pQCT). Estimates of BMD heritability were 83% for femurs and 72% for vertebrae. Genomic DNA from F2 progeny was screened for 107 polymerase chain reaction (PCR)-based markers discriminating B6 and C3H alleles on all 19 autosomes. The regression analyses of markers on BMD revealed ten chromosomes (1, 2, 4, 6, 11, 12, 13, 14, 16, and 18) carrying QTLs for femurs and seven chromosomes (1, 4, 7, 9, 11, 14, and 18) carrying QTLs for vertebrae, each with log10 of the odds ratio (LOD) scores of 2.8 or better. The QTLs on chromosomes (Chrs) 2, 6, 12, 13, and 16 were unique to femurs, whereas the QTLs on Chrs 7 and 9 were unique to vertebrae. When the two bone sites had a QTL on the same chromosome, the same marker had the highest, although different, LOD score. A pairwise comparison by analysis of variance (ANOVA) did not reveal significant gene x gene interactions between QTLs for either bone site. BMD variance accounted for by individual QTLs ranged from 1% to 10%. Collectively, the BMD QTLs for femurs accounted for 35.1% and for vertebrae accounted for 23.7 % of the F2 population variances in these bones. When mice were homozygous c3/c3 in the QTL region, 8 of the 10 QTLs increased, while the remaining two QTLs on Chrs 6 and 12 decreased, femoral BMD. Similarly, when mice were homozygous c3/c3 in the QTL region for the vertebrae, five of the seven QTLs increased, while two QTLs on Chrs 7 and 9 decreased, BMD. These findings show the genetic complexity of BMD with multiple genes participating in its regulation. Although 5 of the 12 QTLs are considered to be skeleton-wide loci and commonly affect both femurs and vertebrae, each of the bone sites also exhibited unique QTLs. Thus, the BMD phenotype can be partitioned into its genetic components and the effects of these loci on normal bone biology can be determined. Importantly, the BMD QTLs that we have identified are in regions of the mouse genome that have known human homology, and the QTLs will become useful experimental tools for mechanistic and therapeutic analyses of bone regulatory genes.