Calcitriol and Bone Mass Accumulation in Females During Puberty

Adolescence is characterized by rapid skeletal development and high demands for bone minerals. Though the stimulative effect of calcitriol on intestinal calcium and phosphorus absorption is well understood, its effect on bone development is not completely clear. It may be directly involved in the facilitation of calcium economy during this critical phase of skeletal development. Therefore, we evaluated the serum concentrations of calcitriol in relation to skeletal development in a cross-sectional study of 178 healthy Caucasian females during different pubertal stages, extending from childhood to young adulthood. In addition, a subsample of 57 younger girls was followed for a 1-year period to evaluate the association among serum calcitriol, nutrition parameters (dietary calcium, phosphorus, and vitamin D), bone mass accumulation, and biochemical markers of bone turnover. The serum calcitriol concentration in a cross-sectional sample was the highest during pubertal growth spurt (sexual maturity index 3–4, age 11–13 years) (ANOVA: F = 2.4945; P= 0.0329). This correlated to the peak skeletal calcium accretion (g/year) and bone mass accumulation in total body and forearm. In a longitudinal sample, there was a positive association between annual change in TBBMC (P= 0.0255); TBBMD (P= 0.0168); proximal radius (1/3 distance from styloid process) BMC (P= 0.0096); BMD (P= 0.0541), and baseline calcitriol level in forward stepwise regression analyses. The results of the forward stepwise regression analyses with serum calcitriol as a dependent variable and different serum, urinary, and dietary parameters measured at baseline (age 11 years, n = 114) and after 1 year (age 12 years, n = 57) showed that osteocalcin was positively associated with calcitriol in both years; more so in a second year (P= 0.0514, P < 0.0001, respectively). Dietary vitamin D and phosphorus showed negative association with serum calcitriol at age 11, and dietary Ca and P were selected at age 12. The results of this study show that calcitriol is a significant correlate of bone mass accumulation during pubertal growth, presumably in response to the high requirements for calcium during this critical phase of skeletal development. Received: 5 June 1996 / Accepted: 31 December 1996     

Biochemical Responses of Bone Metabolism to 1,25-Dihydroxyvitamin D Administration in Black and White Women

The basis for the racial difference in bone mass between black and white women is not known. Lower bone turnover, better renal calcium conservation, and decreased sensitivity to parathyroid hormone (PTH) have been proposed as explanations. A dynamic comparison of osteoblast function, utilizing stimulation by 1,25-dihydroxyvitamin D [1,25(OH)₂D], has not been tested between these two ethnic groups. We compared well-matched black (n= 15) and white (n= 15) premenopausal women, before and during 5 days of 1,25(OH)₂D administration (1.0 μg/day) in order to assess dynamic indices of bone metabolism. As expected, at baseline, black women had lower levels of serum 25-hydroxyvitamin D and biochemical markers of bone turnover with slightly higher levels of PTH. Black women also had superior renal calcium conservation than white women at baseline. In response to 1,25(OH)₂D administration, black women had a slightly greater increase in serum calcium and greater decrement in PTH. Moreover, black women showed a lesser increment in urinary calcium than white women and a more robust increase in two markers of bone formation – osteocalcin and carboxyterminal propeptide of type 1 procollagen – than white women. There were no changes in bone resorption indices in either race upon 1,25(OH)₂D administration. These data provide preliminary evidence that black women conserve calcium more efficiently under both static and dynamic conditions, and also appear to have better osteoblastic functional reserve than white women. Received: 22 June 1999 / Accepted: 6 September 1999     

Effects of Postmenopausal Hormone Replacement Therapy With and Without Vitamin D3 on Circulating Levels of 25-Hydroxyvitamin D and 1,25-Dihydroxyvitamin D

The effects of postmenopausal hormone replacement therapy (HRT) and vitamin D₃ on vitamin D metabolites (25OHD and 1,25(OH)₂D) were studied in a population-based prospective 1-year study. The serum concentrations of intact parathyroid hormone (PTH), calcium, and phosphate were also studied. A total of 72 women were randomized into four treatment groups: HRT group (sequential combination of 2 mg estradiol valerate and 1 mg cyproterone acetate), Vit D₃ group (vitamin D₃ 300 IU/day + calcium lactate 500 mg/day), HRT + Vit D₃ group (both above) and placebo group (calcium lactate 500 mg/day). Serum samples were taken in March–April, when vitamin D formation from sunlight in Finland is minimal after the dark winter. Serum concentrations of 25OHD increased in the Vit D₃ group (33.5%, P < 0.001) and in the HRT + Vit D₃ group (38.2%, P < 0.001) but had not changed significantly in the HRT and placebo groups at the 1-year follow-up examination. Serum concentrations of calcitriol (1,25(OH)₂D) increased, however, only in the HRT group (23.7%, P < 0.05), and remained unchanged in other groups. Serum concentrations of PTH decreased by 23.2% (P < 0.05) in the placebo group, but did not change significantly in the other three groups. The concentrations of serum calcium increased in the nonhormone groups (P < 0.001), whereas serum phosphate concentrations decreased in the hormone groups (P < 0.05 and 0.001). Our results confirm the positive effect of 1 year of HRT on serum calcitriol. Vitamin D₃ supplementation increased 25OHD concentrations, but did not affect calcitriol concentrations even though the initial levels were low. Interestingly, the combination of HRT and vitamin D₃ did not increase serum calcitriol concentrations as much as HRT alone. Received: 14 June 1996 / Accepted: 17 June 1997     

In Vivo Treatment with Calcitriol (1,25(OH)2D3) Reverses Age-Dependent Alterations of Intestinal Calcium Uptake in Rat Enterocytes

The vitamin D endocrine system has been involved in the impairment of intestinal calcium absorption during aging. Alterations in the nongenomic mechanism of calcitriol (1,25-dihydroxy-vitamin D₃; [1,25(OH)₂D₃] have been recently evidenced. In enterocytes isolated from aged rats, 1,25(OH)₂D₃ stimulation of Ca²⁺ channels through the cAMP/PKA pathway is blunted. We have now investigated whether in vivo administration of calcitriol to senescent rats reverses the absence of hormonal effects in isolated intestinal cells. In enterocytes from 20–24-month-old rats given 1,25(OH)₂D₃ for 3 days (30 ng/100 g bw/day), calcitriol (10⁻¹⁰ M, 3–5 minutes) stimulated Ca²⁺ uptake and intracellular cAMP to the same degree and protein quinase A (PKA) activity to a lesser degree than in enterocytes from young animals. Significantly higher basal levels of cAMP and PKA detected in enterocytes from old rats were not affected by prior injection of animals with 1,25(OH)₂D₃. When the aged rats were injected with 25(OH)D₃, similar Ca²⁺ influx, cAMP, and PKA responses to in vitro stimulation with calcitriol were obtained. 1,25(OH)₂D₃-dependent changes in Ca²⁺ uptake by enterocytes from both young and old rats treated with calcitriol were totally suppressed by the cAMP antagonist Rp-cAMPS, whereas the response to the agonist Sp-cAMPS was markedly depressed in aged animals. These results suggest that intestinal resistance to nongenomic 1,25(OH)₂D₃ stimulation of duodenal cell Ca²⁺ uptake develops in rats upon aging and show that in vivo administration of 1,25(OH)₂D₃ or its precursor to senescent rats restores the ability of the hormone to stimulate duodenal cell calcium influx through the cAMP messenger system. Received: 26 December 1997 / Accepted: 12 May 1998     

High Bone Turnover is Associated with Low Bone Mass and Spinal Fracture in Postmenopausal Women

A group of 366 healthy, white postmenopausal women, aged 50–81 years, mean age 66 years, were selected from the screened population of Scandinavians who were part of a multicenter study of the efficacy of tiludronate, a new bisphosphonate, in established postmenopausal osteoporosis. Eighty-eight women had a lumbar spine bone mineral density (BMD) above 0.860 g/cm², and 278 women had a BMD below 0.860 g/cm². Spinal fracture was diagnosed from lateral spine X-ray studies and defined as at least 20% height reduction (wedge, compression, or endplate fracture) in at least one vertebra (T4–L4). Bone resorption was assessed by measurement of the urinary excretion of type I collagen degradation products by the CrossLaps™ enzyme-linked immunoassay (ELISA). Bone formation was assessed by ELISA measurement of the N-terminal-mid-fragment as well as the intact serum osteocalcin (OC_N-MID), thus omitting the influence of the instability of osteocalcin caused by the labile 6 amino acid C-terminal sequence. The women were divided into groups with high or low bone turnover according to the concentrations of urinary CrossLaps™ or OC_N-MID. Women in the quartiles with the highest concentrations of CrossLaps [519 ± 119 μg/mmol (SD)] or OC_N-MID [44.6 ± 7.5 ng/ml (SD)] had 10–16% lower spinal BMD compared with women in the lowest quartiles (CrossLaps 170 ± 48 μg/mmol (SD), and OC_N-MID [22.1 ± 3.0 ng/ml (SD)] (P < 0.0004). The prevalences of spinal fracture were 25 to 29% in the lowest quartiles, whereas the prevalences in the highest quartiles were almost double—53–54% (P < 0.006). If the women were subgrouped according to spinal BMD and prevalence of spinal fracture, corresponding results were found. Women with a BMD less than 0.860 g/cm², without or with spinal fracture (n = 136 and n = 142), had 36–43% higher concentration of CrossLaps (P= 0.0001) and 11–15% higher concentration of OC_N-MID (P < 0.02), as compared with women with a BMD above 0.860 g/cm² and no spinal fracture (n = 84). In conclusion, the results indicate a strong association among high bone turnover, low bone mass, and prevalence of spinal fracture, which supports the theory that high bone turnover is a risk factor for spinal fracture and osteoporosis. Received: 29 February 1996 / Accepted: 9 August 1996     

Calcium Supplementation Suppresses Bone Resorption in Early Postmenopausal Women

In order to establish whether calcium supplementation suppresses bone resorption in early postmenopausal women and whether any response is related to calcium absorption status, we studied 22 healthy women (median age 52 years) all within 5 years of the menopause. Urine was collected between 9.00 p.m. and 9.00 a.m., and 9.00 a.m. and 9.00 p.m., (2 days) and a fasting blood and spot urine sample was obtained at 9 a.m. On the first day, 5 μCi of ⁴⁵Ca in 250 ml water with 20 mg calcium carrier as the chloride was given at 9.00 a.m. and a further blood sample was obtained at 10.00 a.m. to measure calcium absorption. A 1 g calcium load was given at 9.00 p.m., immediately before the second 24-hour urine collection. There was a rise in plasma ionized calcium (1.18 ± 0.010 mmol/liter versus 1.21 ± 0.011 mmol/liter, P < 0.01) and a fall in plasma PTH (4.2 ± 0.34 pmol/liter versus 3.5 ± 0.31 pmol/liter, P < 0.01) from baseline after the calcium load, and a trend for the magnitude of the change in PTH to be inversely related to calcium absorption (r =−0.33, P= 0.13). In the fasting spot urine samples, there were falls in hydroxyproline (OHPr/Cr; 14.6 ± 0.71 versus 12.6 ± 0.83, P < 0.001), pyridinoline (Pyr/Cr; 75 ± 2.8 versus 70 ± 3.5, P < 0.05), and deoxypyridinoline (Dpd/Cr; 22.7 ± 1.2 versus 19.5 ± 1.1, P < 0.005) after the calcium load. The calcium load suppressed urinary Dpd/Cr between 9.00 p.m. and 9.00 a.m. (P < 0.005), but not between 9.00 a.m. and 9.00 p.m. We conclude that acute administration of a 1 g calcium load suppresses bone resorption in early postmenopausal women, probably by decreasing PTH secretion. Received: 2 December 1996 / Accepted: 21 May 1997     

Biochemical Markers of Bone Turnover Reflect Femoral Bone Loss in Elderly Women

Although over 90% of hip fractures occur in patients over age 70, few data are available on femoral bone loss in this age group. To examine the relationship between biochemical markers of bone turnover and femoral bone loss in the elderly, 36 female and 17 male, healthy, community-dwelling elderly over age 65 (mean ± SD age: women 71 ± 4 years, men 75 ± 5 years) were followed for 3 years. Annual bone mineral density measurements of the hip and lumbar spine by dual-energy x-ray absorptiometry (DXA) were obtained and biochemical markers of bone resorption (urinary N-telopeptide crosslinks, free pyridinoline, total pyridinoline, total deoxypyridinoline, and hydroxyproline) and bone formation (serum osteocalcin, bone-specific alkaline phosphatase) were obtained at the end of year 3. In elderly women, longitudinal bone loss at the total hip was negatively correlated with markers of bone resorption (r =−0.39 to −0.52, P < 0.05), bone formation (r =−0.38, P < 0.05), and age (r =−0.39, P < 0.05). Markers of bone resorption were correlated with markers of bone formation (r = 0.63 to 0.74, P < 0.01). In multiple regression analysis, urinary N-telopeptide crosslinks (marker of resorption), serum osteocalcin (marker of formation), and serum parathyroid hormone explained 43% of the variability of bone loss at the total hip in women. These parameters were not related to bone loss in men. We conclude that femoral bone loss increases with age in women over 65. Measurements of specific biochemical markers of bone turnover are correlated with longitudinal bone loss in elderly women. These markers may help identify women at greatest risk for bone loss who would benefit most from therapeutic interventions. Received: 28 January 1996 / Accepted: 3 May 1996     

Geographic Differences in Bone Turnover: Data from a Multinational Study in Healthy Postmenopausal Women

Biochemical markers of bone metabolism (bone markers) are used increasingly to monitor response to therapy and may be predictors of bone loss and fractures. The relationship between fracture rates, which differ between countries, and the rate of bone turnover has not been examined. Therefore, we explored the geographic variability of bone turnover in a selected, healthy study population of 619 postmenopausal women, ages 40–61, participating in a clinical trial of raloxifene hydrochloride for osteoporosis prevention. The subjects were distributed among 38 investigative sites in 10 countries (9–211 subjects/country) on four continents (North America, n = 277, Europe, n = 168, Australia, n = 125, and Africa, n = 49). Specimens for serum osteocalcin (OC), bone-specific alkaline phosphatase (BSAP), and urine type I collagen fragment/urinary creatinine ratio (CTX) were handled in a uniform fashion and assayed in a central laboratory. Mean levels of OC (P < 0.001), BSAP (P= 0.006), and CTX (P < 0.001) varied significantly by country (ANOVA), with the lowest values typically in German and Spanish subjects and the highest in American and Canadian subjects. The consistent pattern and wide ranges of mean bone marker values (OC 1.6-fold, BSAP 1.7-fold, CTX 3.1-fold) between countries suggest clinically significant differences in bone turnover. Geographic differences in bone markers were not explained by the determined potential confounders of age, years posthysterectomy, total serum cholesterol, and serum follicle stimulating hormone (FSH). We conclude that bone marker values vary substantially by country in this selected study population, suggesting systematic geographic differences in bone metabolism that potentially relate to osteoporotic fracture rates. Received: 28 November 1997 / Accepted: 23 March 1998     

Systematic Review of Randomized Trials of the Effect of Exercise on Bone Mass in Pre- and Postmenopausal Women

Studies of the effect of exercise programs on bone mass appear inconsistent. Our objective was to systematically review and meta-analyze randomized trials of the effect of exercise on bone mass in pre- and postmenopausal women. A computerized MEDLINE search was conducted for the years 1966–1997. Thirty-five randomized trials were identified. Meta-analytic methods were used to statistically pool results of studies of the effect of impact (e.g., aerobics) and non-impact (e.g., weight training) exercise on the lumbar spine and femoral neck. The most studied bone site was the lumbar spine in postmenopausal women (15 studies), where both impact [1.6% bone loss prevented, 95% confidence intervals (CI): 1.0%–2.2%] and non-impact (1.0%, 95% CI: 0.4%–1.6%) exercise programs had a positive effect. Results for the lumbar spine in premenopausal women (eight studies) were similar: 1.5% (95% CI: 0.6%–2.4%) less bone loss (or net gain) after impact exercise and 1.2% (95% CI: 0.7%–1.7%) after non-impact exercise. Impact exercise programs appeared to have a positive effect at the femoral neck in postmenopausal women (five studies), 1.0% (95% CI: 0.4%–1.6%) bone loss prevented, and possibly in premenopausal women, 0.9% (95% CI: −0.2%–2.0%) bone loss prevented. There were too few trials to draw conclusions from meta-analyses of the effect of nonimpact exercise on the neck of femur. This systematic review of randomized trials shows that both impact and non-impact exercise have a positive effect at the lumbar spine in pre- and postmenopausal women. Impact exercise probably has a positive effect at the femoral neck. More studies are required to determine the optimal intensity and type of exercise. Received: 11 May 1999 / Accepted: 18 January 2000     

Prediction of Bone Loss Rate in Healthy Postmenopausal Women

Prevention of fractures is the only way to drastically reduce osteoporosis-related health expenditures. In order to optimize the cost/benefit ratio of a strategy of prevention, it is essential to identify, as early as possible, women who will develop fractures later in their life. Therefore, and since postmenopausal bone loss is an asymptomatic process, screening procedures should detect, at the time of the menopause, women whose postmenopausal bone loss is higher than the mean, and will, a couple of years later, exhibit a low mineral content and a subsequent high risk for fractures. For 3 years we have followed a cohort of 92 healthy women who had undergone menopause less than 36 months previously. By a multivariate discriminant analysis based on the differences in lumbar bone density, assessed by dual photon absorptiometry, and in a few routine biochemical parameters (serum phosphorus, estrone, androstenedione, and urine calcium) observed during the first 6 months of the study, we have been able to correctly predict the rate of spinal bone loss, observed at the end of the 3 years, in 76% of the subjects. All of the women who presented a bone loss higher than 10% over the 3 years were correctly isolated by our discriminant functions after 6 months of follow-up. We conclude that a measurement of lumbar bone mineral density coupled with a few routine biochemical determinations, repeated twice at a 6-month interval in healthy postmenopausal women, can isolate 100% of postmenopausal ``fast bone losers' with an overall specificity of 76%. Received: 22 December 1995 / Accepted: 23 September 1996     

Comparison of Calcitriol Treatment with Etidronate–Calcitriol and Calcitonin–Calcitriol Combinations in Turkish Women with Postmenopausal Osteoporosis: A Prospective Study

Calcitriol has been widely used in the management of osteoporosis, but its efficiency is a matter of controversy. It is not known whether combinations of calcitriol and antiresorptive agents such as etidronate and calcitonin are superior to calcitriol alone in the treatment of postmenopausal osteoporosis. To make this determination, 30 Turkish women with postmenopausal osteoporosis between 45 and 68 years of age were randomized to receive either intermittent cyclical etidronate (400 mg/day, for 14 days) followed by 60 days of cyclical calcitriol therapy 0.25 μg twice daily (group 1; n= 10), or calcitriol 0.25 μg twice daily (group 2; n= 10), or calcitriol 0.25 μg/day in combination with 100 IU intranasal salmon calcitonin taken every other day (group 3; n= 10) through a 1-year period. Bone mineral density (BMD) of lumbar spine (L2 to L4) was determined for each patient by dual-photon absorptiometry (¹⁵³Gd) at baseline, after 6 months, and at the end of the study. There was no significant difference among groups with respect to mean spinal BMD at baseline, after 6, and after 12 months. No significant spinal BMD changes occurred in any group from baseline, after 6 months, and after 12 months. Four patients in groups 1 and 2 and five patients in group 3 developed hypercalcemia at least once during therapy. Hypercalciuria occurred at least once in 9, 10, and 7 patients in groups 1, 2, and 3, respectively. One patient in group 2 developed a renal stone at the end of the study. Mean urine hydroxyproline levels did not change significantly in any group with respect to baseline. The data suggest that one-year treatment with calcitriol, given either alone or in combination with antiresorptive agents, does not improve spinal BMD in Turkish women with postmenopausal osteoporosis, and is associated with a high rate of adverse events. Received: 4 October 1996 / Accepted: 31 December 1996     

The Effect of Intermittent Slow-Release Sodium Fluoride and Continuous Calcium Citrate Therapy on Calcitropic Hormones, Biochemical Markers of Bone Metabolism, and Blood Chemistry in Postmenopausal Osteoporosis

A detailed examination of calcitropic hormones and biochemical markers of bone turnover, serum chemistry, and blood hematology was performed in 75 postmenopausal women allocated to two groups: placebo plus calcium citrate (400 mg Ca B.I.D.) (n = 36) or intermittent slow-release sodium fluoride (SRNaF, 25 mg B.I.D.) plus calcium citrate (n = 39). After 2 years of therapy, a significant reduction in serum immunoreactive parathyroid hormone (PTH) was seen for both groups (43 ± 18 SD–30 ± 11 ng/liter, in placebo and 46 ± 24–36 ± 10, in SRNaF P < 0.0001 for both groups). Serum 1,25(OH)₂D significantly fell in placebo-treated patients (91 ± 31–75 ± 34 pmol/liter, P= 0.001) but did not change for SRNaF-treated patients. This difference in response between placebo and SRNaF-treated groups was significant, P= 0.005. Urinary hydroxyproline significantly declined during treatment in both groups (130 ± 61–76 ± 38 μmol/day, for placebo and 138 ± 84–84 ± 38 for SRNaF, P= 0.001). Similar decreases in urinary N-telopeptide of type I collagen were also observed for both groups (305 ± 192–252 ± 197 nmoles BCE/day for placebo and 356 ± 230–220 ± 197, P= 0.0001 for SRNaF). Serum carboxyterminal propeptide of type I collagen (PICP) declined significantly in both the placebo and SRNaF groups (118 ± 38–101 ± 36 μg/liter, and 116 ± 47–105 ± 39, P= 0.0027). Serum osteocalcin did not change significantly for either group, but bone-specific alkaline phosphatase (BS-ALPase), another marker of bone formation, demonstrated a significant fall in the placebo group at 2 years of therapy (16.2 ± 6.7 U/liter–12.1 ± 3.5, P= 0.009) and a small increase in the SRNaF-treated patients (13.0 ± 4.1–15.0 ± 4.5). The observed difference in response of BS-ALPase between the placebo and treated groups was significant (P= 0.007). There were no significant changes within or between treatment groups for blood hematology or serum chemistries. Mean values for all parameters remained within established normal ranges. These findings suggest that administration of calcium citrate inhibited PTH secretion and thereby reduced bone resorption in both groups, indicated by a decline in serum PTH, urinary hydroxyproline, and N-telopeptide. A low turnover state of bone may have been produced in the placebo group taking calcium citrate alone, since serum PICP, BS-ALPase, and 1,25(OH)₂D also decreased. The addition of SRNaF prevented serum 1,25(OH)₂D from falling by an unknown mechanism. However, its anabolic action on the skeleton was best reflected by changes in BS-ALPase. Moreover, SRNaF appeared to exert no deleterious effects on blood chemistries or hematology during 2 years of administration. Received: 28 January 1996 / Accepted: 25 April 1997     

Risk of Calcium Oxalate Nephrolithiasis after Calcium or Combined Calcium and Calcitriol Supplementation in Postmenopausal Women

Although calcium supplementation can cause hypercalciuria, the risk of nephrolithiasis has been shown to decrease rather than increase among subjects who had a higher calcium intake. Hypercalciuria is also a well-established side effect of calcitriol administration. However, the risk of nephrolithiasis is not well defined. The present study was undertaken to prospectively determine the effect of calcium with or without calcitriol on physicochemical risk factors associated with calcium oxalate nephrolithiasis in Thai postmenopausal women with osteoporosis. Subjects consisted of 53 Thai women more than 10 years postmenopausal who were randomly allocated to receive 750 mg of calcium carbonate supplement alone (n= 28) or 750 mg of calcium carbonate plus 0.5 mg calcitriol (n= 25) daily. Mean ± SEM for age was 65.3 ± 1.1 years, body weight 53.5 ± 1.3 kg. Urine samples for biochemical assays were collected at baseline and 3 months after treatment. Supersaturation for calcium oxalate stone formation was assessed from the 24 h urine constituents by the Tiselius’s index, AP(CaOx). Three months of calcium supplement alone resulted in a modest, but not significant, increase in urinary calcium (baseline, 2.90 ± 0.43 mmol/day; after treatment 3.58 ± 0.54 mmol/day) with no change in urinary oxalate, citrate or magnesium. In contrast, calcium together with calcitriol caused a significant increase in urinary calcium (baseline, 2.87 ± 0.41 mmol/day; after treatment, 4.08 ± 0.57 mmol/day; p<0.05). No significant change in other urine constituents after treatment with calcium and calcitriol was detected. Therefore, AP(CaOx) did not significantly increase either after calcium alone (baseline, 1.17 ± 0.39; after treatment, 1.36 ± 0.28) or after calcium plus calcitriol (baseline, 1.09 ± 0.17; after treatment, 1.09 ± 0.19). However, after treatments, 12 subjects (23%) – 6 receiving calcium supplement alone and 6 receiving calcium plus calcitriol supplement – had high AP(CaOx) values (greater than the upper limit of 95% CI for AP(CaOx) derived from non-stone-forming Thai women). The post-treatment/baseline ratio was 3.21 ± 0.74 for urinary calcium, 1.01 ± 0.19 for urinary oxalate, and 2.23 ± 0.42 (median 1.15) for AP(CaOx). The post-treatment/baseline ratio of calcium, but not for urinary oxalate, had a significant correlation with the post-treatment/baseline ratio of AP(CaOx). Our findings suggest that the alteration in the risk of calcium oxalate nephrolithiasis based on urinary composition is related to the alteration in urinary calcium. The risk of calcium oxalate nephrolithiasis does not increase significantly after calcium or combined calcium and calcitriol supplement in the majority of postmenopausal women with osteoporosis. Received: 10 March 1999 / Accepted: 16 November 1999     

The Effectiveness of Cyclic and Continuous Oral Clodronate Therapy on Bone Density and Markers in Osteopenic Postmenopausal Women

Bisphosphonates have been used effectively to treat established osteoporosis and prevent postmenopausal bone loss. However, the optimal manner of its administration—whether cyclic or continuous—has not been well established. This study investigated the efficacy of cyclic and continuous oral administration of clodronate in 54 newly identified osteopenic postmenopausal women in a randomized, double-blind, crossover fashion. The participants were randomly separated into two groups. The cyclic group (n = 29) received 800 mg twice daily of oral clodronate for 2 weeks every 3 months for the first 12 months followed by placebo for the second 12 months. The continuous group (n = 25) received placebo in the first 12 months and ingested 400 mg of clodronate once daily for the second 12 months. The urinary amino-terminal (NTX™) and carboxy-terminal (CrossLaps™) cross-linked fragments of type I collagen, both markers of bone resorption, showed a marked decrease (25–50%) with both regimens during the period of active treatment. In the cyclic group, the levels of these two markers increased in the second 12 months with placebo, but did not return to the baseline completely. However, bone mineral density (BMD), determined by dual-energy X-ray absorptiometry (DXA), showed no significant change of BMD at various sites after 1 year of active treatment in both groups. Thoracic and lumbar spine X-ray showed no new vertebral fracture in either group after 2 years of treatment. With the two treatment protocols in this study, oral clodronate was effective in decreasing postmenopausal bone resorption, causing no significant changes in BMD at various sites. Received: 16 April 1997 / Accepted: 1 October 1998     

Association of Methylenetetrahydrofolate Reductase (MTHFR) Polymorphism with Bone Mineral Density in Postmenopausal Japanese Women

The pathogenesis of osteoporosis is controlled by genetic and environmental factors. Considering the high prevalence of osteoporosis in homocystinuria, abnormal homocysteine metabolism would contribute to the pathogenesis of osteoporosis. It is known that the polymorphism of methylenetetrahydrofolate reductase (MTHFR), the enzyme catalyzing the reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, correlates with hyperhomocysteinemia. In this study, we examined the association of this polymorphism with bone mineral density (BMD). BMD was measured by dual-energy X-ray absorptiometry (DXA) in 307 postmenopausal women. MTHFR A/V polymorphism was analyzed using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP). We compared BMD, clinical characteristics, and bone metabolic markers among MTHFR groups (AA, AV, VV). The groups did not differ in terms of baseline data. The values of lumbar spine BMD and total body BMD were as follows: lumbar spine: AA, 0.91 ± 0.18, AV, 0.88 ± 0.16, VV, 0.84 ± 0.14 g/cm²; total body: AA, 0.97 ± 0.11, AV, 0.96 ± 0.11, VV, 0.93 ± 0.09 g/cm². In the VV genotype, lumbar spine BMD values were significantly lower than those of the women with the AA genotype (P= 0.016) and total body BMD was significantly lower than those of the women with AA genotype (P= 0.03) and AV genotype (P= 0.04). This is the first report that suggests that the VV genotype of MTHFR is one of the genetic risk factors for low BMD. Received: 29 March 1999 / Accepted: 20 September 1999     

Resistive Training Maintains Bone Mineral Density in Postmenopausal Women

We examined the effects of a total body resistive training program (RT) on total and regional bone mineral density (BMD) in older women. Twenty-seven healthy postmenopausal women (mean age 62 ± 1 years) participated in a strength training program three times/week for 16 weeks. Strength was assessed before and after training by either one or three repetition maximum (1RM and 3RM) tests. Both upper and lower body strength significantly increased by 36–65% and 32–98%, respectively, after training. There was a small but significant decrease in body weight and body mass index after training (P < 0.05), with no change in the waist-to-hip ratio. BMD, assessed by dual-energy X-ray absorptiometry, did not change over the duration of the training period in the anterioposterior spine (L₂–L₄), femoral neck, Ward's triangle, and greater trochanter. BMD of the total body, lateral spine (B₂–B₄), and the regions of the radius (1/3 radius and ultradistal radius) also did not fall in subsets of these women. Muscular strength of both the leg and chest press were significantly associated with L₂–L₄, femoral neck, Ward's triangle, and greater trochanter BMD (range r = 0.57–0.84, all P < 0.005). Markers of bone turnover, namely, bone-specific alkaline phosphatase, osteocalcin, and urinary aminoterminal cross-linked telopeptide of type I collagen did not change significantly. In conclusion, a resistive training program maintains BMD and improves muscular strength in healthy, older women. This may be important in preventing the negative health outcomes associated with the age-related loss of bone density. Received 5 June 1996 / Accepted: 26 June 1997     

Increased Serum Levels of N-Telopeptides (NTx) of Bone Collagen in Postmenopausal Nigerian Women

Serum levels of cross-linked N-telopeptides (NTx) of bone collagen, alkaline phosphatase (ALP), and intact parathyroid hormone (PTH) were determined in 64 premenopausal (PRM) and 86 postmenopausal (PSM) women living in northern Nigeria. Serum NTx values were correlated with ALP activity (r = 0.31–0.58, P < 0.01) and PTH (0.32–0.35, P < 0.01)) in all of the subjects studied, and were also related to age (−0.47, P < 0.001) and body mass index (−0.45, P < 0.001) in PRM women. Menopause had the effect of increasing the circulating concentrations of NTx and ALP activity by 15% (P= 0.001) and 11% (P= 0.02), respectively; however, serum levels of PTH were not different between these two groups of women. Compared with Caucasian counterparts matched for age and body mass index, PSM Nigerian women had significantly increased circulating concentrations of NTx (21.7 versus 16.2 nmol BCE/liter, P= 0.01) and demonstrated a trend towards higher ALP activities and PTH levels. These results indicate that (1) discrete reference intervals should be defined for biochemical markers of bone metabolism in African populations, (2) Nigerian women have relatively higher rates of bone turnover, and (3) further investigation of the implications of increased serum NTx should be undertaken using physical methods such as dual X-ray absorptiometry (DXA) and bone ultrasound attenuation. Received: 16 September 1998 / Accepted: 10 January 1999     

The Response to Calcitriol Therapy in Postmenopausal Osteoporotic Women is a Function of Initial Calcium Absorptive Status

Calcitriol is used in the treatment of osteoporosis but the indications for its use have not been clearly defined. Because it stimulates calcium absorption, we have tended to select osteoporotic patients with low calcium absorption for this therapy and now report the results. We measured the hourly fractional rate of calcium absorption (α) with ⁴⁵Ca and fasting urinary calcium/creatinine (Ca/Cr) and hydroxyproline/creatinine (OHPr/Cr) in 103 postmenopausal women aged 68 (0.67SE) years with vertebral compression fractures (77) or forearm or vertebral bone density below the young normal range (26). They were given 0.25 μg daily of calcitriol (Rocaltrol, Roche, Basle, Switzerland) with a 1 g calcium supplement daily for 6–12 weeks, when the biochemical tests were repeated. Initial OHPr/Cr was inversely related to initial α (P= 0.001) and positively to initial Ca/Cr (P < 0.001). α rose on therapy from 0.47 (0.018) to 0.59 (0.018) per hour (P < 0.001) and OHPr/Cr fell in the whole group from 19.1 (0.83) to 13.8 (0.58) (P < 0.001). The change in α on therapy (corrected for the ``regression to the mean effect') was inversely related to initial α (P < 0.001) as was the change in OHPr/Cr (P= 0.001). There was no relationship, however, between initial Ca/Cr and either the rise in α or the fall in OHPr/Cr on therapy. The data support the concept that low calcium absorption is a cause of negative calcium balance in postmenopausal osteoporosis and that the effectiveness of calcitriol therapy is inversely related to the initial rate of calcium absorption. Received: 16 August 1996 / Accepted: 5 March 1997     

Bone Mineral Density and Biochemical Markers of Bone Turnover in Peri- and Postmenopausal Women

Bone mineral density (BMD) measured by densitometry is the elective parameter for the diagnosis of osteopenia and osteoporosis. Biochemical markers have been proposed as sensitive indicators of high bone turnover and for monitoring response to antiresorptive treatment. We conducted a retrospective study to investigate the values of biochemical markers of bone metabolism with a view to early diagnosis of osteoporosis and monitoring of hormone replacement and calcitonin therapy. The subjects were 415 women, mean age 51 ± 8 years (43–62 years) in peri- and postmenopause, recruited at the Menopause Center of Obstetrics and Gynecology Department of Siena University and divided in five groups. Bone densitometry was performed in all subjects and blood samples were taken for assayed biochemical markers, that is, [osteocalcin (OC), parathyroid hormone (PTH), type 1 procollagen (PICP), and calcitonin (CT)]. Three groups of women were divided into two subgroups: those with normal and those with low BMD (<1 SD). Basal concentrations of PCP1, OC, PTH, and CT were compared in the various groups. Two groups of postmenopausal women with BMD below the normal were treated with estrogen replacement therapy and unmodified eel calcitonin. We evaluated whether some of these biochemical markers of bone turnover could help identify women with low BMD and whether they could be useful for monitoring the results of antiresorptive therapies. Markers of bone formation (PICP and OC) make it possible to distinguish women with high turnover who are at risk for osteoporosis from women with low turnover in menopause. A good correlation was also found between changes in levels of these markers and changes in BMD during treatments, which suggests that the PICP and OC would be useful for monitoring response to antiresorptive therapy. Received: 29 March 1998 / Accepted: 2 November 1999     

1,25-Dihydroxyvitamin D3 Promotes Vitamin K2 Metabolism in Human Osteoblasts

It has been reported that vitamin K₂ (menaquinone-4) promoted 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃)-induced mineralization and enhanced γ-carboxyglutamic acid (Gla)-containing osteocalcin accumulation in cultured human osteoblasts. In the present study, we investigated whether menaquinone-4 (MK-4) was metabolized in human osteoblasts to act as a cofactor of γ-glutamyl carboxylase. Both conversions of MK-4 to MK-4 2,3-epoxide (epoxide) and epoxide to MK-4 were observed in cell extracts of cultured human osteoblasts. The effect of 1,25(OH)₂D₃ and warfarin on the vitamin K cycle to cultured osteoblasts were examined. With the addition of 1 nM 1,25(OH)₂D₃ or 25 μM warfarin in cultured osteoblasts, the yield of epoxide from MK-4 increased. However, the conversion of epoxide to MK-4 was strongly inhibited by the addition of warfarin (2.5–25 μM), whereas it was almost not inhibited by 1,25(OH)₂D₃ (0.1–10 nM). To clarify the mechanism for this phenomenon, a cell-free assay system was studied. Osteoblast microsomes were incubated with 10 μM epoxide in the presence or absence of warfarin and 1,25(OH)₂D₃. Epoxide reductase, one of the enzymes in the vitamin K cycle was strongly inhibited by warfarin (2.5–25 μM), whereas it was not affected by 1,25(OH)₂D₃ (0.1–1 nM). Moreover, there was no effect of pretreatment of osteoblasts with 1 nM 1,25(OH)₂D₃ on the activity of epoxide reductase. However, the activity of epoxidase, that is the γ-glutamyl carboxylase was induced by the pretreatment of osteoblasts with 1 nM 1,25(OH)₂D₃. In the present study, it was demonstrated that the vitamin K metabolic cycle functions in human osteoblasts as well as in the liver, the post-translational mechanism, by which 1,25(OH)₂D₃ caused mineralization in cooperation with vitamin K₂ was clarified. Received: 20 September 2000 / Accepted: 19 February 2001