Bone mineral density discordance and exploration of one of its causes

Discordances between hip and spine areal density T-score values are common and incompletely understood. In a cohort of 1157 postmenopausal women, discordances of greater than 10% occurred in 91%, with spine bone mineral density (BMD) T-scores significantly less negative than femoral neck (FN) T-scores (p<0.001). However, when T-scores based on bone mineral content (BMC) rather than BMD were used, the mean discordance was not significantly different from 0. This was largely because BMC at the FN had seemingly declined with age less rapidly than had BMD at that site. This can be explained by age-related areal expansion at the hip, which would be missed in the reported BMD output. One consequence is that if BMC-based T-scores are used to classify patients, substantially fewer individuals would have been judged osteoporotic in this cohort (two-thirds fewer for spine and three-fourths fewer for hip).

Linkage and association between CA repeat polymorphism of the TNFR2 gene and obesity phenotypes in two independent Caucasian populations

Previously, our group has reported a suggestive linkage evidence of 1p36 with body mass index (BMI) (LOD = 2.09). The tumor necrosis factor receptor 2 (TNFR2) at 1p36 is an excellent positional and functional candidate gene for obesity. In this study, we have investigated the linkage and association between the TNFR2 gene and obesity phenotypes in two large independent samples, using the quantitative transmission disequilibrium tests (QTDT). The first group was made up of 1,836 individuals from 79 multi-generation pedigrees. The second group was a randomly ascertained set of 636 individuals from 157 US Caucasian nuclear families. Obesity phenotypes tested include BMI, fat mass, and percentage fat mass (PFM). A significant result (P = 0.0056) was observed for linkage with BMI in the sample of the multigenerational pedigrees. Our data support the TNFR2 gene as a quantitative trait locus (QTL) underlying BMI variation in the Caucasian populations.

Transmenopausal changes in the trabecular bone structure

INTRODUCTION

Post-menopausal osteoporosis is a disorder of excess skeletal fragility, due partly to changes in bone microstructure. Menopause is known to result in bone loss and reduction in bone mechanical strength. However, the mechanism and nature of microstructural changes at menopause need more detailed description and analyses. The overall hypothesis for this analysis is that the variables describing trabecular bone micro-architecture will be affected by changes in the hormonal status of women just prior to, and early after, last menses, and that volumetric bone density, and trabecular structure will decline significantly. The study was designed to capture true longitudinal transmenopausal changes in three-dimensional (3-D) trabecular bone architecture. Currently, minimal data exist regarding these features.

MATERIALS AND METHODS

Transilial biopsies specimens were obtained from healthy pre-menopausal women (age >46), and repeated at 12 months after the last menstrual period. Bone architecture was quantified in 38 paired specimens using micro-computed tomography (micro-CT-40, Scanco) techniques. Bone biopsies were embedded for histomorphomteric analyses and parts of the analyses have been published elsewhere. Embedded bone biopsies were scanned at 30-mum resolution such that the region of interest was similar to that in the two-dimensional (2-D) histomorphometric analyses. Paired t-tests were used to compare the pre- and post-menopausal bone structural data from each technique.

RESULTS

There was good correlation between standard histomorphometric (2-D) and micro-CT (3-D) measurements. Most of the variables characterizing bone structure in post-menopausal women (from micro-CT) significantly decreased (BV/TV, trabecular number, apparent and tissue density). In addition, both trabecular spacing (Tb.S) and the structure model index (SMI) increased in the post-menopausal women suggesting transformation of trabecular bone from plate- to rod-like structure. The 3-D trabecular connectivity density (Conn.D) was negatively correlated with activation frequency (Ac.f).

CONCLUSIONS

These data suggest that 3-D micro-CT measurements (longitudinal) are comparable to those of standard histomorphometry, and that most of the bone structural measurements are sensitive to changes in women's hormonal status across menopause.

Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial

BACKGROUND

Numerous observational studies have found supplemental calcium and vitamin D to be associated with reduced risk of common cancers. However, interventional studies to test this effect are lacking.

OBJECTIVE

The purpose of this analysis was to determine the efficacy of calcium alone and calcium plus vitamin D in reducing incident cancer risk of all types.

DESIGN

This was a 4-y, population-based, double-blind, randomized placebo-controlled trial. The primary outcome was fracture incidence, and the principal secondary outcome was cancer incidence. The subjects were 1179 community-dwelling women randomly selected from the population of healthy postmenopausal women aged >55 y in a 9-county rural area of Nebraska centered at latitude 41.4 degrees N. Subjects were randomly assigned to receive 1400-1500 mg supplemental calcium/d alone (Ca-only), supplemental calcium plus 1100 IU vitamin D3/d (Ca + D), or placebo.

RESULTS

When analyzed by intention to treat, cancer incidence was lower in the Ca + D women than in the placebo control subjects (P < 0.03). With the use of logistic regression, the unadjusted relative risks (RR) of incident cancer in the Ca + D and Ca-only groups were 0.402 (P = 0.01) and 0.532 (P = 0.06), respectively. When analysis was confined to cancers diagnosed after the first 12 mo, RR for the Ca + D group fell to 0.232 (CI: 0.09, 0.60; P < 0.005) but did not change significantly for the Ca-only group. In multiple logistic regression models, both treatment and serum 25-hydroxyvitamin D concentrations were significant, independent predictors of cancer risk.

CONCLUSIONS

Improving calcium and vitamin D nutritional status substantially reduces all-cancer risk in postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00352170.

Factors influencing skeletal maturation at diagnosis of paediatric Cushing's disease

BACKGROUND/AIMS

Growth retardation is a recognised complication of paediatric Cushing's disease (CD), but there are few published data on skeletal maturation at diagnosis. We assessed factors contributing to skeletal maturation in patients with paediatric CD.

PATIENTS/METHODS

17 patients, 12 males, 5 females (median age 12.1 years, range 5.8-17.4) were studied. The bone age (BA) of each child was determined by a single observer using the TW3 RUS method. BA delay, i.e. the difference between chronological age (CA) and BA, was compared with clinical and biochemical variables.

RESULTS

BA delay was present in 15/17 patients (mean delay 2.0 years, range -0.5 to 4.1 years) and correlated negatively with height SDS (r = -0.70, p < 0.01) and positively with duration of symptoms (r = 0.48, p = 0.05) and CA (r = 0.48, p = 0.05). No relationships were found with midnight cortisol, ACTH, DHEA-S or cortisol suppression during the low-dose dexamethasone suppression test.

CONCLUSIONS

BA in most children with CD was delayed and related to length of symptoms and height SDS at diagnosis. Early diagnosis will reduce delay in skeletal maturation and thus contribute to optimal catch-up growth.

Linear growth and body mass index in pediatric patients with Cushing's disease or simple obesity

BACKGROUND

Increasing prevalence of childhood obesity has resulted in an accelerating rate of referrals of overweight patients to pediatric clinics for exclusion of endocrine or metabolic etiologies. The exclusion of Cushing's disease (CD) requires complex and potentially invasive investigations.

OBJECTIVE

To evaluate the sensitivity of accurate measurements of height, weight and body mass index (BMI) in discriminating between simple obesity and CD.

METHODS AND PATIENTS

Height, weight and BMI were measured at diagnosis in 25 patients with CD; 14 males, 11 females, mean age 12.9 yr (6.4-17.8) and 41 patients with simple obesity (SO), defined as BMI >2.0 SD; 20 males, 21 females, mean age 9.4 yr (3.5-15.6).

RESULTS

Mean (+/-SE) BMI SDS in the CD patients was 2.41+/-0.5 and in the SO patients 3.71+/-1.3. Height SDS in the CD patients was -1.88+/-0.24 and in the SO patients 1.18+/-0.19 (p<0.05). The mean (+/-SE) BMI SDS to height SDS ratio was significantly decreased in the CD compared with the SO patients; -1.81+/-0.54 vs +0.90+/-1.17 (p<0.0001).

CONCLUSIONS

Simple, accurate measurement of height and BMI SDS values provides a quick, and sensitive diagnostic discriminator in pediatric patients with CD or SO, thus potentially avoiding complex investigations.

Vitamin D Status in a Rural Postmenopausal Female Population

BACKGROUND

Inadequate vitamin D nutritional status is increasingly recognized as common in North American and European populations, but the extent of the shortfall and the parameters of the distribution for populations of interest remain uncertain.

PURPOSE

To report the distribution of values for serum 25-hydroxyvitamin D [25(OH)D] in a population of rural postmenopausal women, together with quantification of factors related to vitamin D status.

SETTING

Nine largely agrarian counties in eastern Nebraska (approximately 41 degrees N).

PARTICIPANTS

A population-based sample of 1,179 women 55 years of age and older recruited into a four-year trial of calcium and vitamin D supplementation.

METHODS

Baseline biochemical, dietary, and anthropometric measurements obtained on entry into trial.

RESULTS

Serum 25(OH)D concentration at baseline varied cyclically with season, with the solar cycle explaining 2.9% of the total variance (P < 0.001). Mean seasonally adjusted 25(OH)D concentration was 71.1 nmol/L. Serum 25(OH)D also exhibited the expected inverse curvilinear relationship with serum parathyroid hormone (PTH), with the inflection point of the curve located at approximately 80 nmol/L. Supplements containing vitamin D were regularly taken by 59% of the cohort (median dose: 200 IU/d). Nevertheless, approximately 4% of all women had values below the laboratory reference range and more than two-thirds fell below 80 nmol/L. Seasonally adjusted serum 25(OH)D concentration was positively correlated with the size of daily vitamin D supplement dose, and negatively with age, weight, and body mass index (P < 0.01 for all). In stepwise multiple linear regression models, weight, age, and supplement dose were independently correlated with seasonally adjusted serum 25(OH)D, and together explained 19% of the total variance of adjusted 25(OH)D concentration. Women taking supplements had only one-sixth the chance of having a 25(OH)D value below the reference limit of the assay, compared to women who did not use supplements.

CONCLUSIONS

Approximately two-thirds of this rural population fell below 80 nmol/L, a value considered to be the lower end of the optimal range. Based on the slope of 25(OH)D on supplement dose observed in these women, it would require an additional vitamin D input of nearly 2000 IU/d to reach the goal of an RDA for vitamin D, i.e., to bring 97.5% of the cohort to levels of 80 nmol/L or higher.

Benefits of screening in von Hippel-Lindau disease--comparison of morbidity associated with initial tumours in affected parents and children

Von Hippel-Lindau (VHL) is a rare autosomal dominant syndrome characterised by the association of retinal and CNS haemangioblastomas, phaeochromocytoma and renal cell carcinoma. If a child of an affected parent has inherited a VHL mutation or the parent's mutation cannot be identified, then clinical screening is recommended. We report the clinical features in three parent-offspring pairs where the parents have presented clinically with renal cell carcinoma, phaeochromocytoma, cerebellar haemangioblastoma and retinal haemangioma, and the children have undergone pre-symptomatic screening. During the first screening a 13-year-old boy was diagnosed with bilateral phaeochromocytoma and later developed an endolymphatic sac tumour at 19 years. A right phaeochromocytoma was found in a 12-year-old girl who was screened from the age of 4 years and in a 13-year-old boy screened from 5 years of age. All children were asymptomatic at the time of diagnosis. These families demonstrate that clinical screening of children at risk of VHL can detect tumours before the first symptoms arise with a consequent reduction in morbidity. These observations strongly support the recommendation to undertake screening of the children of VHL patients.

CA repeat polymorphism of the TNFR2 gene is not associated with bone mineral density in two independent Caucasian populations

Osteoporosis has a strong genetic component, but the genes involved are poorly defined. Genome-wide scans in multiple populations have identified chromosome 1p36 as one region linked to bone mineral density (BMD). The tumor necrosis factor receptor 2 (TNFR2) at 1p36 is a positional and functional candidate gene in osteoporosis. In this study, we conducted linkage and association tests between the CA repeat polymorphism of the TNFR2 gene and BMD in two large independent samples using the quantitative transmission disequilibrium test (QTDT) program. The first group of subjects was composed of 1836 individuals from 79 multigeneration pedigrees. The second group was a randomly ascertained set of 636 individuals from 157 nuclear families. We found no evidence of association or linkage for spine or hip BMD in the samples of the multigenerational pedigrees or nuclear families. Through testing for association and for linkage, our data do not support the TNFR2 gene as a QTL underlying hip or spine BMD variation in our Caucasian populations.

Calcium supplementation does not augment bone gain in young women consuming diets moderately low in calcium

In earlier observational work, the dietary calcium:protein ratio was directly related to bone accrual in healthy postadolescent women. In this study, we sought to test the hypothesis that augmented calcium intake would increase postadolescent skeletal consolidation, using a double-blind, randomized, placebo-controlled design. We recruited 152 healthy young women (age 23.1 +/- 2.7 y, BMI 22.5 +/- 3.0 kg/m2); their usual diets, as assessed by 7-d food diaries, were low in calcium (605 +/- 181 mg/d; 15.1 +/- 4.5 mmol/d) and in the calcium:protein ratio (10.1 +/- 2.0 mg/g). The subjects were randomly assigned to supplemental calcium [500 mg calcium (12.5 mmol) as the carbonate, 3 times/d, with meals] or placebo capsules identical in appearance; all participants also took a daily multivitamin, and they were followed for up to 36 mo with bone densitometry (dual energy X-ray absorptiometry; DXA) at 6-mo intervals. A total of 121 subjects remained in the study for at least 12 mo (median time in the study, 35 mo), with a mean compliance level (observed/expected tablet consumption) of 87.7%. DXA data for these 121 subjects indicated modest but significant mean rates of increase (i.e., 0.24 to 1.10%/y) in bone mineral content (BMC; total body, total hip, and lumbar spine) and in lumbar spine bone mineral density (BMD) but no change in total hip BMD. None of these rates of change differed by group, i.e., calcium supplementation did not have any measurable effect on bone mass accrual. By midstudy, the calcium content of the subjects' usual diets for both groups had risen by approximately 15%. The combined effect of improved intakes of dietary calcium and the small amount of calcium added by the multivitamin tablets resulted in a mean calcium intake for the control group > 800 mg (20 mmol)/d, possibly at or near the threshold beyond which additional calcium has no further effect on bone accrual.

A genome-wide linkage scan for bone mineral density in an extended sample: evidence for linkage on 11q23 and Xq27

BACKGROUND

Osteoporosis is a major public health problem, mainly quantified by low bone mineral density (BMD). The majority of BMD variation is determined by genetic effects. A pilot whole genome linkage scan (WGS) was previously reported in 53 white pedigrees with 630 subjects. Several genomic regions were suggested to be linked to BMD variation.

OBJECTIVE

To substantiate these previous findings and detect new genomic regions.

METHODS

A WGS was conducted on an extended sample where the size was almost tripled (1816 subjects from 79 pedigrees). All the subjects were genotyped with 451 microsatellite markers spaced approximately 8.1 cM apart across the human genome. Two point and multipoint linkage analyses were carried out using the variance component method.

RESULTS

The strongest linkage signal was obtained on Xq27 with two point LOD scores of 4.30 for wrist BMD, and 2.57 for hip BMD, respectively. Another important region was 11q23, which achieved a maximum LOD score of 3.13 for spine BMD in multipoint analyses, confirming the results on this region in two earlier independent studies. Suggestive linkage evidence was also found on 7p14 and 20p12.

CONCLUSIONS

Together with the findings from other studies, the current study has further delineated the genetic basis of bone mass and highlights the importance of increasing sample size to confirm linkage findings and to identify new regions of linkage.

Potassium Intake and the Calcium Economy

BACKGROUND

Dietary potassium intake (K) lowers urinary calcium (Ca) excretion and, in short-term studies, may improve Ca balance.

PURPOSE

Our objective was to assess K effects on the Ca economy under steady-state conditions.

DESIGN

8-day, inpatient metabolic studies of nitrogen, phosphorus, and Ca balance, combined with dual isotopic Ca tracer kinetics studies. Study diet matched to prestudy nutrient intakes.

SUBJECTS

191 single women studied from 1-5 times at approximately 5-year intervals, for a total of 644 inpatient studies. Median age at time of study: 50.2 yrs; 301 studies were performed postmenopausally without hormone replacement; 343 were either premenopausal or postmenopausal but on estrogen replacement therapy.

RESULTS

Dietary K was highly significantly associated with urinary Ca excretion, with a coefficient of -0.0109 mmol urine Ca/mmol diet K. However, dietary K was negatively correlated with dual-tracer Ca absorption (coefficient for Ca absorption fraction: -0.00094/mmol dietary K), and was not associated with urine Ca after adjustment for Ca absorption.

CONCLUSION

While a high K diet (i.e., one rich in fruits, vegetables, and dairy products) has multiple health benefits and clearly lowers urine Ca, it does not seem to exert any appreciable net influence on the Ca economy, largely because the reduced calciuria is offset by reduction of intestinal absorption. We note, however, that since the high K intakes in our studies come more from milk and meat than from fruits and vegetables, we cannot exclude a possible balance effect for different food sources of K.

Bone mineral density at diagnosis and following successful treatment of pediatric Cushing's disease

Bone mineral density (BMD) is frequently reduced in children and adolescents with Cushing's disease (CD), but there is little follow-up data after cure. BMD was determined by dual energy X-ray absorptiometry (DEXA) in two groups of patients with CD. Group 1 comprised 8 patients, 5 males and 3 females, aged 12.4 yr (8.2-16.8), assessed at diagnosis. Group 2 comprised 11 subjects, 6 males and 5 females, diagnosed at age 13.3 yr (6.4-17.4), cured by transsphenoidal surgery (TSS) (no.=7) or TSS + pituitary irradiation (no.=4). They had measurement of BMD, at mean age of 18.3 yr (11.1-28.5), i.e. 4.5 yr (0.8-11.4) after cure. Four patients, mean age 20.2 yr (17.6-22.4), had repeated DEXA'scans, 1-4 times, for up to 5.8 yr. After cure, GH deficiency was present in 9 patients and treated with hGH in 8. In Group 1, patients' L2-L4 volumetric (v)BMD Z-score was variable with a mean of -1.04 (-3.21-0.11). L2-L4 vBMD Z-score values correlated negatively with midnight cortisol (p < 0.05). In Group 2, mean L2-L4 vBMD was -0.38 (-1.0-0.13); and in 7/11, mean femoral neck (FN) areal (a)BMD Z-score was 0.14 (-1.62-2.46). FN aBMD Z-score was higher than L2-L4 aBMD Z-score (p < 0.05). In patients with repeated scans, mean change in L2-L4 vBMD Z-score was 0.20 (-0.15-0.45), and mean change in FN aBMD Z-score 0.03 (-0.53-0.38). These findings show variability of BMD at diagnosis and near normal BMD after cure of pediatric CD, suggesting that with appropriate replacement of pituitary hormone deficiency normal peak bone mass is achievable.

Genetic dissection of human stature in a large sample of multiplex pedigrees

Recently, we reported a whole genome scan on a sample of 630 Caucasian subjects from 53 human pedigrees. Several genomic regions were suggested to be linked to height. In an attempt to confirm the identified genomic regions, as well as to identify new genomic regions linked to height, we conducted a whole genome linkage study on an extended sample of 1,816 subjects from 79 pedigrees, which includes the 53 pedigrees containing the original 630 subjects from our previous whole genome study and an additional 128 new subjects, and 26 further pedigrees containing 1,058 subjects. Several regions achieved suggestive linkage signals, such as 9q22.32 [MLS (multipoint LOD score) = 2.74], 9q34.3 [MLS = 2.66], Xq24 [two-point LOD score = 2.64 at the marker DXS8067], and 7p14.2 [MLS = 2.05]. The importance of the above regions is supported either by other whole genome studies or by candidate genes within these regions relevant to linear growth or pathogenesis of short stature. In addition, this study has tentatively confirmed the Xq24 region's linkage to height, as this region was also detected in the previous whole genome study. To date, our study has achieved the largest sample size in the field of genetic linkage studies of human height. Together with the findings of other studies, the current study has further delineated the genetic basis of human stature.

Race and sex differences and contribution of height: A study on bone size in healthy Caucasians and Chinese

Osteoporosis is characterized by a loss of bone strength, of which bone size (BS) is an important determinant. However, studies on the factors determining BS are relatively few. The present study evaluated the independent effects of height, age, weight, sex, and race on areal BS at the hip and spine, measured by dual-energy X-ray absorptiometry, while focusing on the differential contributions of height to BS across sex, race, and skeletal site. The subjects were aged 40 years or older, including 763 Chinese (384 males and 379 females) from Shanghai, People's Republic of China, and 424 Caucasians (188 males and 236 females) from Omaha, Nebraska. Basically, Caucasians had significantly larger BS than Chinese. After adjusting for height, age, and weight, the Chinese had similar spine BS, but significantly larger intertrochanter BS in both sexes and larger total hip BS in females compared with Caucasians. Males had significantly larger BS than females before and after adjustment in both ethnic groups. The effects of age, weight, and race varied, depending on skeletal site. As expected, height had major effects on BS variation in both sexes and races. Height tended to account for larger BS variation at the spine than at the hip (except for Chinese females), and larger BS variation in Caucasians than in Chinese of the same sex (except for the trochanter in females). We conclude that height is a major predictor for BS, and its contributions vary across sex, race, and skeletal site.

Determinants of endogenous calcium entry into the gut

BACKGROUND

In addition to food sources, calcium enters the gut by way of digestive secretions and shed mucosa. In health, such entry is as large as or larger than urinary calcium excretion. Because calcium absorption is inefficient, most of this endogenous intestinal calcium is excreted.

OBJECTIVE

Our aim was to determine the dietary, anthropometric, and physiologic determinants of calcium entering the digestive stream from endogenous sources.

DESIGN

Multiple regression modeling of intake and excretion data was used with 553 metabolic balance and kinetics studies performed in 190 midlife, white women.

RESULTS

Endogenous intestinal calcium averaged 3.29 +/- 0.83 mmol/d. Multiple regression models explaining variation in this endogenous intestinal calcium were developed with use of dietary intake, anthropometric, and serum mineral variables. All 3 groups of predictor variables individually explained up to 22% of the variation in measured values for endogenous intestinal calcium. A composite model, incorporating all 3 groups explained 29% of the variation, with phosphorus and meat protein intakes, height, weight, and serum calcium and phosphorus concentrations all independently entering the model. Phosphorus intake dominated over all the other predictors, explaining 20% of the variance all by itself, with endogenous intestinal calcium rising by 0.037 mmol for every 1 mmol of phosphorus ingested. Meat protein (but not nonmeat protein) was the only other significant dietary contributor, exhibiting a negative coefficient.

CONCLUSION

As a first approximation, the amount of endogenous calcium entering the digestive stream rises with body size and with the amount of phosphorus-rich food consumed.

Bone remodeling increases substantially in the years after menopause and remains increased in older osteoporosis patients

Bone remodeling rates (Ac.f) were measured in transilial biopsy specimens from 50 healthy premenopausal women before and 1 year after menopause, in 34 healthy women 13 years past menopause, and in 89 women with untreated osteoporosis. Ac.f nearly doubled 1 year after menopause, tripled 13 years after menopause, and remained elevated in women with osteoporosis.

INTRODUCTION

Increased bone remodeling rates are associated with increased skeletal fragility independent of bone mass, partially accounting for the age-related increase in fracture risk in women that is independent of bone loss. We examined bone remodeling rates before and after menopause and in women with osteoporosis by measurements of activation frequency (Ac.f, #/year) in transilial bone biopsy specimens.

MATERIALS AND METHODS

We recruited 75 women, > 46 years old, who had premenopausal estradiol and gonadotropin levels and regular menses. During 9.5 years of observation, 50 women experienced normal menopause and had 2 transilial bone biopsy specimens after tetracycline labeling, one at the beginning of observation and the second 12 months after the last menses, when serum follicle-stimulating hormone (FSH) was > 75 mIU/ml and serum estradiol was < 20 pg/ml. Ac.f was also computed for a group of older healthy postmenopausal women and a group of women with untreated osteoporosis studied earlier by the same biopsy (Bx) and labeling protocol.

RESULTS

Median Ac.f rose from 0.13/year to 0.24/year (p < 0.001) across menopause and was greater still in the older normals (p < 0.008) than in the second Bx. Ac.f was not significantly greater in the osteoporosis patients than in the older postmenopausal normals.

CONCLUSION

Bone remodeling rates double at menopause, triple 13 years later, and remain elevated in osteoporosis. This change contributes to increases in age-related skeletal fragility in women.

Girls on a high-calcium diet gain weight at the same rate as girls on a normal diet: A pilot study

OBJECTIVE

To determine whether pubertal girls assigned to calcium-rich diets or their usual calcium intakes differ significantly in weight gain.

DESIGN

This is a pilot study conducted on data from an experimental research project.

SUBJECTS/SETTING

The sample included 59 girls, 9 years of age, from Omaha metropolitan communities.

INTERVENTION

Participants were randomly assigned to a calcium-rich diet supplying at least 1,500 mg of calcium per day or their usual diet.

MAIN OUTCOME MEASURE

The outcome measure was change in weight during 2 years of study.

STATISTICAL ANALYSES

Data were analyzed using descriptive statistics, Mann-Whitney U, t tests of paired and independent samples, and analysis of covariance.

RESULTS

The girls in the calcium-rich diet group had a mean (+/-standard deviation) calcium intake of 1,656+/-191 mg/day, whereas the girls on their usual diets averaged 961+/-268 mg/day. Although the participants in the treatment group consumed nearly twice as much dietary calcium--primarily from dairy foods--they did not have greater increases in body weight, body mass index, or fat or lean mass than the control group. These findings held when the data were grouped by tertile of calcium intake. Compared with girls on their usual diets, the girls who consumed the calcium-rich diet also significantly increased their intake of essential nutrients.

CONCLUSION

We conclude that calcium-rich diets do not cause excessive weight gain in pubertal girls but do contribute positively to overall nutrition. These findings provide support for programs to promote calcium-rich diets, which are critical for attaining peak bone mass.

A follow-up linkage study for bone size variation in an extended sample

Bone size, which has strong genetic determination, is an important determinant of bone strength and a risk factor of osteoporotic fractures. We previously reported an approximately 10-cm genome-wide linkage scan in 630 subjects from 53 US Caucasian pedigrees. The strongest evidence of linkage was obtained on chromosome 17q22 near the marker D17S787, with a two-point LOD score of 3.98 and a multipoint maximum LOD score (MLS) of 3.01. Additionally, suggestive linkages (1.54 < MLS < 2.83) were found at the other four chromosomal regions. In the present study, with an attempt to further examine our previous findings, we perform a follow-up linkage analysis in an expanded sample of 79 pedigrees with 1816 subjects. The total sample contains >80,000 informative relative pairs for linkage analyses, including 3846 sib pairs. Fifteen markers covering the above five promising regions are genotyped, narrowing the average genomic distance from approximately 10 to 5 cm. In the total 79 pedigrees, support of linkage was achieved for the wrist bone size at 17q22 with a two-point LOD score of 2.27 (P = 0.0006) and MLS of 1.78 (P = 0.002). The genomic region 17q22 includes COL1A1, a strong candidate gene that is significantly associated with osteoporotic fracture risk. Our data suggest that this region is promising for further exploratory studies.

A second-stage genome scan for QTLs influencing BMD variation

Low bone mineral density (BMD) is a major risk factor for osteoporotic fracture. To identify genomic regions harboring quantitative trait loci (QTLs) contributing to BMD variation, we performed a two-stage genome screen. The first stage involved genotyping of a sample of 53 pedigrees with 630 individuals using 400 microsatellite markers spaced at approximately 10-cM intervals throughout the genome. Ten genomic regions with multi- and/or two-point LOD scores greater than 1.5 were observed. In the present second-stage study, 60 microsatellite markers, with a mean spacing of about 5 cM, were genotyped in these regions in an expanded sample of 79 pedigrees that contained 1816 subjects. Each pedigree was ascertained through a proband with extreme BMD at the hip or spine. BMD at the spine (L1-4), hip (the femoral neck, trochanter, and intertrochanteric region), and wrist (the ultradistal region) was measured by dual-energy X-ray absorptiometry (DXA) and was adjusted for age, sex, height, and weight. Two-point and multipoint linkage analyses were performed for each BMD site using statistical genetic methods that are implemented in the computer package SOLAR. Several regions (7q11, 10q26, 12q13, and 12q24) achieved LOD scores in excess of 1 in the second-stage followup study. The current results replicate some of our previous linkage findings and also highlight some of the difficulties facing microsatellite linkage mapping for complex human diseases.

Genome scan for QTLs underlying bone size variation at 10 refined skeletal sites: genetic heterogeneity and the significance of phenotype refinement

To identify quantitative trait loci (QTLs) underlying variation in bone size, we conducted a whole-genome linkage scan in 53 pedigrees with 630 subjects using 380 microsatellite markers. Lumbar area 1, 2, 3, and 4 at the spine, femoral neck, trochanter, intertrochanter areas at the hip, ultradistal, mid-distal, and one-third distal areas at the wrist were measured by dual-energy X-ray absorptiometry (DXA), and adjusted for age, height, weight, and sex. Two-point and multipoint linkage analyses were performed for skeletal bone size at each site and their composite measurements using the SOLAR package. Two chromosomal regions (1q22 and 10q21) were identified with significant evidence of linkage (LOD > 4.32) to one-third distal area, and three were identified with suggestive evidence of linkage (LOD > 2.93) to bone size in one skeletal site. Our results indicated that the low power of QTLs mapping for composite phenotypic measurements may result from genetic heterogeneity of complex traits.

A follow-up linkage study for quantitative trait loci contributing to obesity-related phenotypes

We have recently reported a whole-genome scan in a sample of 630 subjects from 53 extended pedigrees, in which several genomic regions that may contain quantitative trait loci (QTLs) for obesity were suggested. In the present study, with an attempt to confirm our previous findings, we performed a follow-up linkage study in an expanded sample of 79 pedigrees with 1816 subjects (including expanded previous 53 pedigrees and 26 newly recruited pedigrees containing 1058 subjects). A new set of microsatellite markers spanning previously identified regions were selected, with the average genomic distance narrowed from approximately 10 cM to approximately 5 cM in this study. Using a variance component method, we performed two- and multipoint linkage analyses in the following three sample sets: expanded previous 53 pedigrees (758 subjects), 26 new pedigrees, and 79 total pedigrees. For body mass index, analyses of the expanded 53 pedigrees attained a LOD score of 2.32 near marker D1S468 in two-point analysis and a maximum LOD score (MLS) of 2.21 in multipoint analysis; 2q14 near marker D2S347 attained a LOD score of 3.42 in two-point analysis and a MLS of 3.93 in multipoint analysis. The linkage peaks at 1p36 and 2q14 were further supported in the analyses of all 79 pedigrees, with multipoint MLS being 1.38 and 0.90, respectively. For fat mass, genomic region 6q27 achieved a LOD score of 1.24 in two-point analysis and an MLS of 0.92 in multipoint analysis in all 79 pedigrees. Our data support that 1p36, 2q14, and 6q27 are promising regions that may harbor QTLs for obesity phenotypes.

Linkage and association of the CA repeat polymorphism of the IL6 gene, obesity-related phenotypes, and bone mineral density (BMD) in two independent Caucasian populations

Genetic factors play an important role in osteoporosis and obesity, two serious public health problems in the world. We investigated the relationships between obesity-related phenotypes, bone mineral density (BMD) and the CA repeat polymorphism of the IL6 gene in two large independent samples using the quantitative transmission disequilibrium test (QTDT). The first sample consisted of 1,816 individuals from 79 multigenerational pedigrees. Each pedigree was identified through a proband with BMD Z-scores </=-1.28 at the hip or spine. The second sample was a randomly ascertained set of 636 individuals from 157 nuclear families. Ten alleles containing 9-18 CA repeats were identified in our Caucasian populations. For body mass index (BMI), fat mass and percentage fat mass (PFM), highly significant (P<0.01) or significant (P<0.05) results were found for linkage in our sample of nuclear families and for association in the multigenerational pedigrees. We also observed weak evidence for linkage (P=0.069) with spine BMD and for association with hip BMD in the sample of multigenerational pedigrees. Our results suggest that genetic variation in or near the IL6 locus may be involved in the etiology of obesity and osteoporosis.

Several genomic regions potentially containing QTLs for bone size variation were identified in a whole-genome linkage scan

Bone size is an important determinant of osteoporotic fractures. For a sample of 53 pedigrees that contains more than 10,000 relative pairs informative for linkage analyses, we performed a whole-genome linkage scan using 380 microsatellite markers to identify genomic regions that may contain QTLs of bone size (two dimensional measurement by dual energy X-ray absorptiometry). We conducted two- and multi-point linkage analyses. Several potentially important genomic regions were identified. For example, the genomic region 17q23 may contain a QTL for wrist (ultra distal) bone size variation; a LOD score of 3.98 is achieved at D17S787 in two-point analyses and a maximum LOD score (MLS) of 3.01 is achieved in multi-point analyses in 17q23. 19p13 may contain a QTL for hip bone size variation; a LOD score of 1.99 is achieved at D19S226 in two-point analyses and a MLS of 2.83 is achieved in 19p13 in multi-point analyses. The genomic region identified on chromosome 17 for wrist bone size seems to be consistent with that identified for femur head width variation in an earlier whole-genome scan study. The genomic regions identified in this study and an earlier investigation on one-dimensional bone size measurement by radiography are compared. The two studies may form a basis for further exploration with larger samples and/or denser markers for confirmation and fine mapping studies to eventually identify major functional genes and the associated etiology for osteoporosis.

Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol

BACKGROUND

The cholecalciferol inputs required to achieve or maintain any given serum 25-hydroxycholecalciferol concentration are not known, particularly within ranges comparable to the probable physiologic supply of the vitamin.

OBJECTIVES

The objectives were to establish the quantitative relation between steady state cholecalciferol input and the resulting serum 25-hydroxycholecalciferol concentration and to estimate the proportion of the daily requirement during winter that is met by cholecalciferol reserves in body tissue stores.

DESIGN

Cholecalciferol was administered daily in controlled oral doses labeled at 0, 25, 125, and 250 micro g cholecalciferol for approximately 20 wk during the winter to 67 men living in Omaha (41.2 degrees N latitude). The time course of serum 25-hydroxycholecalciferol concentration was measured at intervals over the course of treatment.

RESULTS

From a mean baseline value of 70.3 nmol/L, equilibrium concentrations of serum 25-hydroxycholecalciferol changed during the winter months in direct proportion to the dose, with a slope of approximately 0.70 nmol/L for each additional 1 micro g cholecalciferol input. The calculated oral input required to sustain the serum 25-hydroxycholecalciferol concentration present before the study (ie, in the autumn) was 12.5 micro g (500 IU)/d, whereas the total amount from all sources (supplement, food, tissue stores) needed to sustain the starting 25-hydroxycholecalciferol concentration was estimated at approximately 96 micro g (approximately 3800 IU)/d. By difference, the tissue stores provided approximately 78-82 micro g/d.

CONCLUSIONS

Healthy men seem to use 3000-5000 IU cholecalciferol/d, apparently meeting > 80% of their winter cholecalciferol need with cutaneously synthesized accumulations from solar sources during the preceding summer months. Current recommended vitamin D inputs are inadequate to maintain serum 25-hydroxycholecalciferol concentration in the absence of substantial cutaneous production of vitamin D.

A whole-genome linkage scan suggests several genomic regions potentially containing QTLs underlying the variation of stature

Human height is a complex trait under the control of both genetic and environment factors. In order to identify genomic regions underlying the variation of stature, we performed a whole-genome linkage analysis on a sample of 53 human pedigrees containing 1,249 sib pairs, 1,098 grandparent-grandchildren pairs, 1,993 avuncular pairs, and 1,172 first-cousin pairs. Several genomic regions were suggested by our study to be linked with human height variation. These regions include 5q31 at 144 cM from pter on chromosome 5 (with a maximum LOD score of 2.14 in multipoint linkage analyses), Xp22 at the marker DXS1060, and Xq25 at DXS1001 on the X chromosome (with LOD scores of 1.95 and 1.91, respectively, in two-point linkage analyses). Noticeably, Xp22 happens to be the very region where a newly identified gene underlying idiopathic short stature, SHOX, maps. Based on our findings, further confirmation and fine-mapping studies are to be pursued on expanded samples and/or with denser markers for eventual identification of major functional genes involved in human height variation.

A whole-genome linkage scan suggests several genomic regions potentially containing quantitative trait Loci for osteoporosis

Osteoporosis is an important health problem, particularly in the elderly women. Bone mineral density (BMD) is a major determinant of osteoporosis. For a sample of 53 pedigrees that contain 1249 sibling pairs, 1098 grandparent-grandchildren pairs, and 2589 first cousin pairs, we performed a whole- genome linkage scan using 380 microsatellite markers to identify genomic regions that may contain quantitative trait loci (QTL) of BMD. Each pedigree was ascertained through a proband with BMD values belonging to the bottom 10% of the population. We conducted two-point and multipoint linkage analyses. Several potentially important genomic regions were suggested. For example, the genomic region near the marker D10S1651 may contain a QTL for hip BMD variation (with two-point analysis LOD score of 1.97 and multipoint analysis LOD score of 2.29). The genomic regions near the markers D4S413 and D12S1723 may contain QTLs for spine BMD variation (with two-point analysis LOD score of 2.12 and 2.17 and multipoint analysis LOD score of 3.08 and 2.96, respectively). The genomic regions identified in this and some earlier reports are compared for exploration in extension studies with larger samples and/or denser markers for confirmation and fine mapping to eventually identify major functional genes involved in osteoporosis.

Decline in muscle mass with age in women: a longitudinal study using an indirect measure

Muscle mass is known to decline with age, but only limited longitudinal data exist to quantify the rate of loss. Using 24-hour urine creatinine, corrected for the contribution of dietary meat intake, we assessed the change with age prospectively in 107 women who provided a minimum of 3 sets of measurements spanning an average interval of 11.9 years, centered around age 55 years. The rate of change in 24-hour urine creatinine at that age averaged -0.94%/yr (95% confidence interval [CI], -1.24% to -0.64%/yr; P <.001). Change in creatinine excretion was directly correlated with change in weight (P <.01), with those gaining weight tending to gain both lean and fat mass. The rate of change in creatinine excretion with age in our subjects is similar to that described in published cross-sectional studies on age-related change in total body potassium and in longitudinal studies using (40)K and dual-energy xray absorptiometry. Our study is the largest longitudinal study reported to date and provides, perhaps, a more secure basis for estimating muscle mass change with age than has been available heretofore.

A genomewide linkage scan for quantitative-trait loci for obesity phenotypes

Obesity is an increasingly serious health problem in the world. Body mass index (BMI), percentage fat mass, and body fat mass are important indices of obesity. For a sample of pedigrees that contains >10,000 relative pairs (including 1,249 sib pairs) that are useful for linkage analyses, we performed a whole-genome linkage scan, using 380 microsatellite markers to identify genomic regions that may contain quantitative-trait loci (QTLs) for obesity. Each pedigree was ascertained through a proband who has extremely low bone mass, which translates into a low BMI. A major QTL for BMI was identified on 2q14 near the marker D2S347 with a LOD score of 4.04 in two-point analysis and a maximum LOD score (MLS) of 4.44 in multipoint analysis. The genomic region near 2q14 also achieved an MLS >2.0 for percentage of fat mass and body fat mass. For the putative QTL on 2q14, as much as 28.2% of BMI variation (after adjustment for age and sex) may be attributable to this locus. In addition, several other genomic regions that may contain obesity-related QTLs are suggested. For example, 1p36 near the marker D1S468 may contain a QTL for BMI variation, with a LOD score of 2.75 in two-point analysis and an MLS of 2.09 in multipoint analysis. The genomic regions identified in this and earlier reports are compared for further exploration in extension studies that use larger samples and/or denser markers for confirmation and fine-mapping studies, to eventually identify major functional genes involved in obesity.

Calcium and weight: clinical studies

Data from six observational studies and three controlled trials in which calcium intake was the independent variable (and either bone mass or blood pressure the original outcome variable) have been reanalyzed to evaluate the effect of calcium intake on body weight and body fat. Analysis reveals a consistent effect of higher calcium intakes, expressed as lower body fat and/or body weight, and reduced weight gain at midlife. Similarly, studies relating nutrient intake to body composition report negative associations between calcium intake and body weight at midlife and between calcium and body fat accumulation during childhood. There is a fairly consistent effect size, with each 300 mg increment in regular calcium intake associated with approximately 1 kg less body fat in children and 2.5-3.0 kg lower body weight in adults. Taken together these data suggest that increasing calcium intake by the equivalent of two dairy servings per day could reduce the risk of overweight substantially, perhaps by as much as 70 percent.

Relevance of the genes for bone mass variation to susceptibility to osteoporotic fractures and its implications to gene search for complex human diseases

We investigate the relevance of the genetic determination of bone mineral density (BMD) variation to that of differential risk to osteoporotic fractures (OF). The high heritability (h(2)) of BMD and the significant phenotypic correlations between high BMD and low risk to OF are well known. Little is reported on h(2) for OF. Extensive molecular genetic studies aimed at uncovering genes for differential risks to OF have focussed on BMD as a surrogate phenotype. However, the relevance of the genetic determination of BMD to that of OF is unknown. This relevance can be characterized by genetic correlation between BMD and OF. For 50 Caucasian pedigrees, we estimated that h(2) at the hip is 0.65 (P < 0.0001) for BMD and 0.53 (P < 0.05) for OF; however, the genetic correlation between BMD and OF is nonsignificant (P > 0.45) and less than 1% of additive genetic variance is shared between them. Hence, most genes found important for BMD may not be relevant to OF at the hip. The phenotypic correlation between high BMD and low risk to OF at the hip (approximately -0.30) is largely due to an environmental correlation (rho(E) = -0.73, P < 0.0001). The search for genes for OF should start with a significant h(2) for OF and should include risk factors (besides BMD) that are genetically correlated with OF. All genes found important for various risk factors must be tested for their relevance to OF. Ideally, employing OF per se as a direct phenotype for gene hunting and testing can ensure the importance and direct relevance of the genes found for the risk of OF. This study may have significant implications for the common practice of gene search for complex diseases through underlying risk factors (usually quantitative traits).

Evidence for a major gene for bone mineral density/content in human pedigrees identified via probands with extreme bone mineral density

Bone mineral content (BMC) and/or bone mineral density (BMD, i.e. BMC scaled by bone size) are major determinants for osteoporosis, which is a serious health problem. The major determinant of variation in BMD/BMC is genetic. The few studies now available are inconsistent in the identification and/or even in the existence of major gene(s) for BMD/BMC. In 51 human pedigrees with 941 individuals (526 measured for phenotypes) identified via probands with extreme BMD values, we performed complex segregation analyses to test the existence of a genetic locus with a major effect on BMD/BMC variation. We analyzed BMD and BMC at the spine, hip and wrist jointly by employing, as the study phenotype, factor scores (FS) of the principle component that explains approximately 75% of the total BMD/BMC variation at the three sites. The results indicate that a major gene exists with a codominant effect that is responsible for approximately 16% of the FS variation when adjusted for significant effects of sex, body weight and age. A significant genotype-x-sex-x-age interaction was found, which may explain approximately 14% of the FS variation after adjusting for body weight. Testing of various models did not provide support for shared familial environmental effects but suggested the existence of residual polygenic effects, which may explain approximately 50% of the FS variation when adjusting for sex, body weight and age. This study indicates a promising aspect of studies to identify a major gene for BMD/BMC variation in our pedigrees identified via extreme probands.

Differences in bone mineral density, bone mineral content, and bone areal size in fracturing and non-fracturing women, and their interrelationships at the spine and hip

Osteoporotic fractures are a major public health problem, particularly in women. Bone mineral density (BMD), bone mineral content (BMC), and bone size have been regarded as important determinants of osteoporotic fractures. In 1449 women over age 30 years, we studied the detailed relationship, at the spine and hip, between BMD, BMC, and bone areal size (all measured by dual-energy X-ray absorptiometry) and compared their relative magnitudes in fracturing and non-fracturing individuals. We find that, (1) BMD and BMC are significantly higher at the spine and hip in non-fracturing women. Bone areal size is significantly larger at the spine in non-fracturing women; however, the significance disappears when adjustment is made for the significant difference of height (stature) between fracturing and non-fracturing women. In contrast to the spine, bone areal size is always significantly largerin fracturing women at the hip. (2) The relationship among BMD, BMC, and bone areal size is different at the spine and hip. Specifically, at the spine, BMD increases with bone areal size linearly. At the hip, BMD has a quadratic relationship with bone areal size, so that BMD increases at lower bone areal sizes, then (after an intermediate zone of values) decreases with increasing bone areal size. However, BMD adjusted for BMC always decreases with increasing bone areal size, as expected by the definition of BMD. With no adjustment for BMC, the increase in BMD with bone areal size is due to a more rapid increase of BMC than increasing bone areal size, thus explaining the observations of association of both larger BMD and larger bone areal size with stronger bone. (3) At the spine, 86.2% of BMD variation is attributable to BMC and 12.6% to bone areal size. At the hip, 98.0% of BMD variation is due to BMC and 1.1% due to bone areal size. The current study may be important in understanding the relationship among BMD, BMC, and bone size as risk determinants of osteoporotic fractures.

Is population bone mineral density variation linked to the marker D11S987 on chromosome 11q12-13?

Our purpose is to test linkage of human chromosome 11q12-13 to BMD variation. Chromosome 11q12-13 has been linked to three BMD-related phenotypes that are inherited as Mendelian traits in human pedigrees: an autosomal dominant high bone mass trait, autosomal recessive osteoporosis pseudoglioma, and autosomal recessive osteopetrosis. A sibling pair study with 374 sibships showed significant linkage of D11S987 to normal BMD variation, with a maximum logarithm of odds score of 3.5. However, a subsequent linkage study with a total of 595 sibling pairs demonstrated reduced significance for linkage of D11S987 to bone mineral density variation, with a logarithm of odds score less than 2.2. We genotyped five markers in a genomic region of approximately 27 cM centering on D11S987 and measured bone mineral density and other traits (weight, etc.) for 635 individuals from 53 human pedigrees. Each of these pedigrees was ascertained through a proband with bone mineral density Z-scores less than -1.28 at the hip or spine. Adjusting for age, sex, and weight as covariates, we performed two-point and multipoint linkage analyses using the variance component linkage analysis method implemented in Sequential Oligogenic Linkage Analysis Routines. We found little evidence of linkage of these five markers to bone mineral density at the spine, hip, wrist and total body bone mineral content. The maximum logarithm of odds score at these five markers was 0.25, and the maximum logarithm of odds score at D11S987 was 0.15. Therefore, although we cannot exclude the linkage of D11S987 region to bone mineral density variation, there is no evidence for linkage of the marker D11S987 on human chromosome 11q12-13 to bone mineral density variation in our study population.

Chemistry of the diazeniumdiolates. 3. Photoreactivity

We have found O(2)-substituted diazeniumdiolates, compounds of structure R(2)N-N(O)=NOR' that are under development for various possible pharmaceutical uses, to be rather photosensitive. With R = ethyl and R' = methyl, benzyl, or 2-nitrobenzyl, the observed product distributions suggest that two primary pathways are operative. A minor pathway involves the extrusion of nitrous oxide (N(2)O) with simultaneous generation of R(2)N(*) and R'O(*), which may then form amines, aldehydes, and alcohols. The major reaction pathway is an interesting photochemical cleavage of the N=N bond to form a nitrosamine (R(2)NN=O) and an oxygen-substituted nitrene (R'ON). The intermediacy of the O-nitrene was inferred from the production of abundant oxime, via rearrangement of the O-nitrene to a C-nitroso compound (R'ON --> O=NR'), and subsequent tautomerization to the more stable oxime. Involvement of the O-nitrene was confirmed by trapping with 2,3-dimethyl-2-butene to form the aziridine and with oxygen to generate the nitrate ester. 2-Nitro substitution on the benzyl derivative had surprisingly little effect on the reaction course. For each compound examined, minor amounts of nitric oxide (NO), presumably produced by secondary photolysis of the nitrosamine, were observed. Time-resolved infrared experiments provided additional support for the above reaction pathways and confirmed that the nitrosamine is a primary photoproduct. We have also found that the relative contributions of the reaction pathways can be altered in certain derivatives. For example, when R' = 2,4-dinitrophenyl, the contribution of the nitrosamine/O-nitrene-forming pathway was diminished. Pharmacological implications of these results are discussed.

Chemistry of the diazeniumdiolates. 2. Kinetics and mechanism of dissociation to nitric oxide in aqueous solution

Diazeniumdiolate ions of structure R(2)N[N(O)NO](-) (1) are of pharmacological interest because they spontaneously generate the natural bioregulatory species, nitric oxide (NO), when dissolved in aqueous media. Here we report the kinetic details for four representative reactivity patterns: (a) straightforward dissociation of the otherwise unfunctionalized diethylamine derivative 2 (anion 1, where R = Et) to diethylamine and NO; (b) results for the zwitterionic piperazin-1-yl analogue 4, for which the protonation state of the neighboring basic amine site is an important determinant of dissociation rate; (c) data for 5, a diazeniumdiolate derived from the polyamine spermine, whose complex rate equation can include terms for a variety of medium effects; and (d) the outcome for triamine 6 (R = CH(2)CH(2)NH(3)(+)), the most stable structure 1 ion identified to date. All of these dissociations are acid-catalyzed, with equilibrium protonation of the substrate preceding release of NO. Specific rate constants and pK(a) values for 2-6 have been determined from pH/rate profiles. Additionally, a hypsochromic shift (from approximately 250 to approximately 230 nm) was observed on acidifying these ions, allowing determination of a separate pK(a) for each substrate. For 6, the pK(a) value obtained kinetically was 2-3 pK(a) units higher than the value obtained from the spectral shift. Comparison of the ultraviolet spectra for 6 at various pH values with those for O- and N-alkylated diazeniumdiolates suggests that protonation at the R(2)N nitrogen initiates dissociation to NO at physiological pH, with a second protonation (at oxygen) accounting for both the spectral change and the enhanced dissociation rate at pH <4. Our results help to explain the previously noted variability in dissociation rate of 5, whose half-life we found to increase by an order of magnitude when its concentration was raised from near-zero to 1 mM, and provide mechanistic insight into the factors that govern dissociation rates among diazeniumdiolates of importance as pharmacologic progenitors of NO.

Hormones, weight change and menopause

OBJECTIVE

To determine total body weight change occurring in women at mid-life, specifically with respect to occurrence of menopause and use of estrogen.

DESIGN

Retrospective analysis of body weight measurements accumulated in two cohorts of healthy women participating in studies of skeletal metabolism.

SUBJECTS

Cohort 1: 191 healthy nuns enrolled in a prospective study of osteoporosis risk, aged 35-45 in 1967; cohort 2: 75 women aged 46 or older and still menstruating, enrolled in 1988 in a study of bone cell dynamics across menopause. Roughly one-third of each group received hormone replacement after menopause.

MEASUREMENTS

Body weight and height, age, menstrual status and use of estrogen replacement. Cohort 1: 608 measurements at 5 y intervals spanning a period from 17 y before to 22 y after menopause; cohort 2: 1180 measurements at 6-month intervals spanning a period from 5 y prior to 5 y after menopause.

RESULTS

In cohort 1 weight rose as a linear function of age (both chronological and menopausal), both before and after cessation of ovarian function, at a rate of approximately 0.43% y(-1). Neither the menopausal transition nor the use of estrogen had an appreciable effect on this rate of gain. In cohort 2 the rate of gain seemed to diminish slightly at menopause. As with cohort 1, hormone replacement (or its absence) had no appreciable effect on weight.

CONCLUSIONS

The long-term, total body weight trajectory at mid-life is not influenced appreciably by either cessation of ovarian function or by hormone replacement.

The secondary amine/nitric oxide complex ion R(2)N[N(O)NO](-) as nucleophile and leaving group in S9N)Ar reactions

Ions of structure R(2)N[N(O)NO](-) and their alkylation products have seen increasing use as nitric oxide (NO)-generating agents for biomedical research applications. Here we show that such diazeniumdiolate anions can readily displace halide from a variety of electrophilic aza- or nitroaromatic substrates to form O(2)-arylated derivatives of structure R(2)N-N(O)=N-OAr. The site of arylation and the cis arrangement of the oxygens were confirmed by X-ray crystallography. Displacement by various nucleophiles showed R(2)N[N(O)NO](-) to be a reasonably good leaving group, with rate constants for displacement by hydroxide, methoxide, and isopropylamine that were between those of chloride and fluoride in the S(N)Ar reactions we surveyed. The Meisenheimer intermediate could be spectrally observed. These O(2)-aryl diazeniumdiolates proved capable of reacting with the nucleophilic sulfur of the HIV-1 p7 nucleocapsid protein's zinc finger assembly to eject the zinc, disrupting a structural motif critical to viral replication and suggesting possible utility in the drug discovery realm.

Characterization of genetic and lifestyle factors for determining variation in body mass index, fat mass, percentage of fat mass, and lean mass

In this study, we simultaneously characterized genetic and lifestyle factors (exercise, smoking, and alcohol consumption) in determining variation in body mass index (BMI), fat mass, percentage of fat mass (PFM), and lean mass while adjusting for the effects of age and sex. Six hundred fifty-eight Caucasian individuals from 48 pedigrees were studied for BMI. Among these individuals, 289 from 38 pedigrees were studied for fat mass, PFM, and lean mass measured by dual X-ray absorptiometry (DXA). After adjusting for age, sex, and lifestyle factors, the heritabilities (h(2)) of BMI, fat mass, PFM, and lean mass ranged from 0.52 to 0.57 with associated standard errors ranging from 0.09 to 0.14. After accounting for significant sex and age effects, exercise had significant effects for all the phenotypes studied, and the effects of smoking and alcohol consumption were not significant. Therefore, significant proportions of variation in BMI, fat mass, PFM, and lean mass were under genetic control, and exercise had a significant effect in reducing BMI, fat mass, and PFM and in increasing lean mass. This study warrants further genetic linkage analyses to search for genes for the obesity-related phenotypes measured by DXA in our population.

Calcium intake and body weight

Five clinical studies of calcium intake, designed with a primary skeletal end point, were reevaluated to explore associations between calcium intake and body weight. All subjects were women, clustered in three main age groups: 3rd, 5th, and 8th decades. Total sample size was 780. Four of the studies were observational; two were cross-sectional, in which body mass index was regressed against entry level calcium intake; and two were longitudinal, in which change in weight over time was regressed against calcium intake. One study was a double-blind, placebo-controlled, randomized trial of calcium supplementation, in which change in weight during the course of study was evaluated as a function of treatment status. Significant negative associations between calcium intake and weight were found for all three age groups, and the odds ratio for being overweight (body mass index, >26) was 2.25 for young women in the lower half of the calcium intakes of their respective study groups (P: < 0.02). Relative to placebo, the calcium-treated subjects in the controlled trial exhibited a significant weight loss across nearly 4 yr of observation. Estimates of the relationship indicate that a 1000-mg calcium intake difference is associated with an 8-kg difference in mean body weight and that calcium intake explains approximately 3% of the variance in body weight.

Determination of bone mineral density of the hip and spine in human pedigrees by genetic and life-style factors

In 40 human pedigrees with 563 subjects, we evaluated the contribution of genetic and life-style factors (exercise, smoking, and alcohol consumption) and the interactions between non-genetic factors in determining bone mineral density (BMD) of the hip and spine. In our analysis, we adjusted for age, weight, height, menopausal status in females, life-style factors, and the significant interactions among these factors. For the spine and hip BMD, heritabilities (h(2)) (+/- SE) were, respectively, 0.68 (0.21) and 0.86 (0.28) in males and 0.64 (0.13) and 0.67 (0.14) in females. Exercise had significant beneficial effects for male spine BMD and female hip BMD. Alcohol consumption experienced in our sample had significant beneficial effects on hip BMD in both sexes. Although the main effect of smoking was not significant, there were significant interaction effects between smoking and other important factors (e.g., exercise, weight, alcohol consumption). For example, for female spine BMD, exercise had significant beneficial effects in smokers; however, its effect in non-smokers was non-significant. This result indicates that exercise may reduce deleterious effects of smoking (if any) on BMD, but may have minor effects in increasing BMD in non-smokers. The various interaction effects among risk factors explicitly revealed here for the first time indicate that the detailed effects and direction of individual risk factors may depend on the presence and magnitude of other factors. Weight invariably affected BMD of the hip and spine in both sexes. Age effects were significant for hip BMD, but not for male spine BMD.

Association of estrogen receptor-alpha genotypes with body mass index in normal healthy postmenopausal Caucasian women

Several lines of evidence suggest the importance of the estrogen receptor (ER) in determining body mass index (BMI). Our purpose was to investigate whether genetic polymorphisms at the restriction enzyme PvuII site of the ER-alpha gene locus are associated with BMI variation. Data on BMI, age, and ER-alpha genotypes were obtained from 108 healthy midwestern U.S. postmenopausal Caucasian women. The study subjects were unrelated and aged 65 yr and over (mean age +/- SD, 73.4 +/- 5.1 yr), with an average BMI of 25.25 (SD, 4.04). The ER-alpha genotypes were obtained by PCR followed by restriction enzyme PvuII digestion. We found that in our study subjects the ER-alpha genotypes are significantly associated with BMI (by ANOVA, P = 0.04), explaining about 6.2% of the BMI variation in our study sample. The allelic effects of this locus on BMI are approximately additive. In our sample, individuals of the PP and Pp genotypes have, respectively, 11.4% and 4.8% higher BMI than individuals of the pp genotype. There is a significant ER-alpha genotype by age interaction, so that in our sample PP individuals tend to gain weight with age, whereas Pp and pp individuals tend to lose weight with age. Therefore, the ER-alpha polymorphisms are associated with BMI variation in healthy postmenopausal Caucasian women aged 65 yr and over. Our result is consistent with some recent findings suggesting the potential effects of the ER on BMI. The importance of the ER-alpha genotypes in other populations and other age groups needs to be demonstrated. Although the results of the ER-alpha genotype by age interaction are obtained here from cross-sectional data, direct confirmation may come from longitudinal studies in which individuals are measured multiple times over several years. The importance of the ER-alpha genotypes on BMI should be confirmed by further studies using methods robust to the potential problem of population substructuring that may confound the conclusions of population association studies.

Genetic determination of Colles' fracture and differential bone mass in women with and without Colles' fracture

Osteoporotic fractures (OFs) are a major public health problem. Direct evidence of the importance and, particularly, the magnitude of genetic determination of OF per se is essentially nonexistent. Colles' fractures (CFs) are a common type of OF. In a metropolitan white female population in the midwestern United States, we found significant genetic determination of CF. The prevalence (K) of CF is, respectively, 11.8% (+/- SE 0.7%) in 2471 proband women aged 65.55 years (0.21), 4.4% (0.3%) in 3803 sisters of the probands, and 14.6% (0.7%) in their mothers. The recurrence risk (K0), the probability that a woman will suffer CF if her mother has suffered CF is 0.155 (0.017). The recurrence risk (Ks), the probability that a sister of a proband woman will suffer CF given that her proband sister has suffered CF is 0.084 (0.012). The relative risk lambda (the ratio of the recurrence risk to K), which measures the degree of genetic determination of complex diseases such as CF, is 1.312 (0.145; lambda 0) for a woman with an affected mother and 1.885 (0.276; lambda s) for a woman with an affected sister. A lambda-value significantly greater than 1.0 indicates genetic determination of CF. The terms lambda 0 and lambda s are related to the genetic variances of CF. These parameters translate into a significant and moderately high heritability (0.254 [0.118]) for CF. These parameters were estimated by a maximum likelihood method that we developed, which provides a general tool for characterizing genetic determination of complex diseases. In addition, we found that women without CF had significantly higher bone mass (adjusted for important covariates such as age, weight, etc.) than women with CF.

Conversion of a polysaccharide to nitric oxide-releasing form. Dual-mechanism anticoagulant activity of diazeniumdiolated heparin

We describe heparin/diazeniumdiolate conjugates that generate nitric oxide (NO) at physiological pH. Like the heparin from which they were prepared, they inhibit thrombin-induced blood coagulation. Unlike heparin, they can also inhibit and reverse ADP-induced platelet aggregation (as expected for an NO-releasing agent), suggesting potential utility as dual-action antithrombotics.

Esterase-sensitive nitric oxide donors of the diazeniumdiolate family: in vitro antileukemic activity

We have designed a novel prodrug class that is stable in neutral aqueous media but releases bioactive nitric oxide (NO) on metabolism by esterase. Diazeniumdiolates of structure R(2)N-N(O)=N-OR', in which R' = Na, were reacted with BrCH(2)OAc to convert the spontaneously NO-releasing salts 1a (R(2)N = diethylamino) and 1b (R(2)N = pyrrolidino) to prodrugs 2a (AcOM-DEA/NO) and 2b (AcOM-PYRRO/NO), respectively, where R' = CH(2)OAc. In contrast to anions 1a and 1b (half-lives in pH 7.4 phosphate at 37 degrees C of 2 min and 3 s, respectively), 2a and 2b showed only minimal decomposition after 16 h under these conditions. Very rapid hydrolysis occurred in the presence of porcine liver esterase, however, with free anion 1a being observed as an intermediate in the esterase-induced generation of NO from 2a. The potential utility of this prodrug class is illustrated with a comparison of 1 and 2 as antiproliferative agents in NO-sensitive human leukemia cell lines HL-60 and U937. While the 72-h IC(50)'s for 1a and 1b (which generate NO throughout the medium) in HL-60 cell cultures were >600 microM, those of 2a and 2b were 8.3 and 6.4 microM, respectively. This result is consistent with our hypothesis that 2 is selectively hydrolyzed to 1 and thence to NO intracellularly. For U937 cells, the 72-h IC(50) for both 2a and 2b was 53 microM. By contrast, relatively high antiproliferative IC(50)'s (>100 microM in U937 cells) were observed for analogues in which R' = CH(2)CH(2)SC(O)Me, from which acetyl and 2-mercaptoethyl groups must be successively cleaved to free the NO-releasing diazeniumdiolate function. Within 24 h at initial concentrations of 50 microM, 2a and 2b induced apoptosis in 50% and 57% of the HL-60 cells, respectively (35% and 40% of the U937 cells, respectively). The data reveal significant in vitro antileukemic activity on the part of these novel compounds. Moreover, their substantial ease-of-handling advantages over the anionic diazeniumdiolates from which they are derived suggest their use as convenient agents for probing the biological roles of NO.

A prospective study of quantitative ultrasound in children and adolescents

The accrual of optimal bone mass during childhood and adolescence is essential for the formation of a skeleton that will meet structural needs throughout life. Assessing bone health of children is becoming increasingly important in order to identify those who require interventions, and quantitative ultrasound (QUS) has appeal for these assessments. The purpose of this prospective study was to characterize changes in QUS values in 328 healthy children and adolescents over a 3-yr period. Measurements of QUS, height, weight, nutrient intake, fracture history, and Tanner stage were made at baseline and 3 yr later. Both females and males experienced significant increases in QUS values during the study. The rate of change of QUS peaked at an earlier age in females than in males, and maximum accumulation rates in both genders occurred at ages at which highest accumulation rates are seen with densitometry. Females exhibited higher QUS values than males during puberty, also similar to results for dual X-ray absorptiometry (DXA). This is the first report of prospective data of QUS in children and adolescents. Our findings that QUS values change during childhood and adolescence in a manner similar to DXA values, the "gold standard," provide support for the validity of using QUS to assess bone health in children and adolescents.

The effect of low-dose continuous estrogen and progesterone therapy with calcium and vitamin D on bone in elderly women. A randomized, controlled trial

BACKGROUND

Hormone replacement therapy (HRT), the mainstay of osteoporosis prevention, is limited because of dose-related risks, side effects, and patient acceptance. The bone-sparing efficacy and tolerability of the lowest available doses of HRT have not been adequately studied in elderly women.

OBJECTIVE

To determine the bone-sparing effect of continuous low-dose HRT in elderly women.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

University osteoporosis research and clinical center.

PATIENTS

128 healthy white women (age > 65 years) with low bone mass recruited by word of mouth and by local advertisement. The principal eligibility criterion was spinal bone mineral density of 0.90 g/cm2 or less.

INTERVENTION

Continuous therapy with conjugated equine estrogen, 0.3 mg/d, and medroxyprogesterone, 2.5 mg/d, or matching placebo. Sufficient calcium supplementation was given to bring all calcium intakes above 1000 mg/d in both groups; supplemental oral 25-hydroxyvitamin D was given to maintain serum 25-hydroxyvitamin D levels of at least 75 nmol/L in both groups.

MEASUREMENTS

Bone mineral density of the spine, hip, total body, and forearm; serum total alkaline phosphatase and serum osteocalcin levels at 6-month intervals; and 24-hour urine creatinine and hydroxyproline excretion at baseline, 12 months, and 42 months.

RESULTS

During 3.5 years of observation, spinal bone mineral density increased by 3.5% (P < 0.001) in an intention-to-treat analysis and by 5.2% among patients with greater than 90% adherence to therapy. Significant increases were seen in total-body and forearm bone density (P < 0.01). Symptoms related to HRT (breast tenderness, spotting, pelvic discomfort, and mood changes) were mild and short-lived.

CONCLUSIONS

Continuous low-dose HRT with conjugated equine estrogen and oral medroxyprogesterone combined with adequate calcium and vitamin D provides a bone-sparing effect that is similar or superior to that provided by other, higher-dose HRT regimens in elderly women. This combination is well tolerated by most patients.