Trabecular bone score in kidney transplant recipients.

SUMMARY: It is uncertain whether bone mineral density (BMD) can accurately predict fracture in kidney transplant recipients. Trabecular bone score (TBS) provides information independent of BMD. Kidney transplant recipients had abnormal bone texture as measured by lumbar spine TBS, and a lower TBS was associated with incident fractures in recipients. INTRODUCTION: Trabecular bone score (TBS) is a texture measure derived from dual energy X-ray absorptiometry (DXA) lumbar spine images, providing information independent of bone mineral density. We assessed characteristics associated with TBS and fracture outcomes in kidney transplant recipients. METHODS: We included 327 kidney transplant recipients from Manitoba, Canada, who received a post-transplant DXA (median 106 days post-transplant). We matched each kidney transplant recipient (mean age 45 years, 39% men) to three controls from the general population (matched on age, sex, and DXA date). Lumbar spine (L1-L4) DXA images were used to derive TBS. Non-traumatic incident fracture (excluding hand, foot, and craniofacial) (n = 31) was assessed during a mean follow-up of 6.6 years. We used multivariable linear regression models to test predictors of TBS, and multivariable Cox proportional hazard regression was used to estimate hazard ratios (HRs) per standard deviation decrease in TBS to express the gradient of risk. RESULTS: Compared to the general population, kidney transplant recipients had a significantly lower lumbar spine TBS (1.365 ± 0.129 versus 1.406 ± 0.125, P < 0.001). Multivariable linear regression revealed that receipt of a kidney transplant was associated with a significantly lower mean TBS compared to controls (-0.0369, 95% confidence interval [95% CI] -0.0537 to -0.0202). TBS was associated with fractures independent of the Fracture Risk Assessment score including BMD (adjusted HR per standard deviation decrease in TBS 1.64, 95% CI 1.15-2.36). CONCLUSION: Kidney transplant recipients had abnormal bone texture as assessed by TBS and a lower lumbar spine TBS was associated with fractures in recipients.

Risk factors for low bone mass in healthy 40-60 year old women: a systematic review of the literature.

UNLABELLED: Based on a systematic review of the literature, only low body weight and menopausal status can be considered with confidence, as important risk factors for low BMD in healthy 40-60 year old women. The use of body weight to identify high risk women may reduce unnecessary BMD testing in this age group. INTRODUCTION: BMD testing of perimenopausal women is increasing but may be unnecessary as fracture risk is low. Appropriate assessment among younger women requires identification of risk factors for low BMD specific to this population. METHODS: We conducted a systematic literature review of risk factors for low BMD in healthy women aged 40-60 years. Articles were retrieved from six databases and reviewed for eligibility and methodological quality. A grade for overall strength of evidence for each risk factor was assigned. RESULTS: There was good evidence that low body weight and post-menopausal status are risk factors for low BMD. There was good or fair evidence that alcohol and caffeine intake, and reproductive history are not risk factors. There was inconsistent or insufficient evidence for the effect of calcium intake, physical activity, smoking, age at menarche, history of amenorrhea, family history of OP, race and current age on BMD. CONCLUSIONS: Based on current evidence in Caucasians, we suggest that, in healthy women aged 40-60 years, only those with a low body weight (< 70 kg) be selected for BMD testing. Further research is necessary to determine optimal race-specific discriminatory weight cut-offs and to evaluate the risk factors for which there was inconclusive evidence.

An evaluation of several biochemical markers for bone formation and resorption in a protocol utilizing cyclical parathyroid hormone and calcitonin therapy for osteoporosis.

Female patients (n = 20) with osteoporosis, aged 66 +/- 5 yr were studied during a 24-h infusion of parathyroid hormone (PTH [1-34]) at a rate of 0.5 IU equivalents/kg.h, and then during a 28-d period of subcutaneous injections, at a dose of 800 IU equivalents per day. Thereafter half the patients received subcutaneous injections of calcitonin, 75 U/d for 42 d, and all patients were followed to the end of a 90-d cycle. Biochemical markers of bone formation (serum alkaline phosphatase, osteocalcin, and the carboxy-terminal extension peptide of pro-collagen 1) and bone resorption (fasting urine calcium, hydroxyproline, and deoxypyridinoline) were compared during treatment by the intravenous and subcutaneous route of PTH administration, and subsequently during calcitonin therapy. During intravenous PTH infusion there were significant reductions in all three bone formation markers, despite expected rises in urinary calcium and hydroxyproline. By contrast, the circulating markers of bone formation increased rapidly by > 100% of baseline values during daily PTH injections (P < 0.001). Significant increases in bone resorption markers were only seen at the end of the 28 d of injections, but were < 100% over baseline values, (P < 0.05). Quantitative bone histomorphometry from biopsies obtained after 28 d of PTH treatment confirmed that bone formation at both the cellular and tissue levels were two to five times higher than similar indices measured in a control group of biopsies from untreated osteoporotic women. Subsequent treatment of these patients with calcitonin showed no significant changes in the biochemical markers of bone formation and only a modest attenuation of bone resorption. Thus, PTH infusion may inhibit bone formation, as judged by circulating biochemical markers, whereas daily injections confirm the potent anabolic actions of the hormone. Sequential calcitonin therapy does not appear to act synergistically with PTH in cyclical therapeutic protocols.

Long-term dalteparin in pregnancy not associated with a decrease in bone mineral density: substudy of a randomized controlled trial.

BACKGROUND: The risk of decreased bone mineral density (BMD) with prophylactic dose long-term low-molecular-weight heparin (LMWH) is unknown. OBJECTIVES: We sought to determine whether long-term prophylactic dalteparin in pregnancy leads to loss of BMD. PATIENTS/METHODS: Patients in a substudy of an ongoing multicenter randomized trial investigating the effect of antepartum dalteparin prophylaxis on pregnancy outcomes in thrombophilic pregnant women were randomized to either dalteparin 5000 U s.c. daily until 20 weeks and then 5,000 U s.c. q12 h until >37 weeks or to the control group. The primary outcome was absolute spine BMD at six weeks postpartum. RESULTS: Of 77 patients eligible for the BMD substudy, 62 were analyzed. 33 patients received a mean of 212 days of dalteparin in the intervention group. 29 patients received a mean of 38 days of postpartum dalteparin in the control group. There was no difference in mean BMD between the intervention (1.11 g cm(-2)) and the control groups (1.14 g cm(-2)). Similarly, there was no difference in T-scores; the difference of -0.34 (95% confidence interval -0.93 to +0.25) in favor of the control group excludes a clinically important increase in fracture risk. CONCLUSIONS: Our results suggest that the use of long-term prophylactic dalteparin in pregnancy is not associated with a significant decrease in BMD. CLINICAL TRIAL REGISTRATION: ISRCTN87441504 at http://www.controlled-trials.com.

Aluminum intoxication in vitamin D-deficient rats: studies of bone aluminum localization and histomorphometry before and after vitamin D repletion.

Aluminum accumulation by both dialysis patients and nonuremic patients, requiring chronic total parenteral nutrition, may be an etiological factor in the development of severe osteomalacia. To study the role of aluminum toxicity in bone, further experiments have been conducted in the nonuremic, vitamin D-deficient rat. Weanling rats were raised on vitamin D-deficient diets, and half received parenteral aluminum (5 mg/wk), for 30 days. In the first experiment low doses of 25-OH cholecalciferol (500 ng/week) were given subcutaneously for a further 30 days. Control rats were maintained on a similar protocol, but were supplemented with cholecalciferol (5 micrograms/week) from the outset until sacrifice at 60 days. In the second experiment a single bolus of cholecalciferol (5 micrograms) was given to study short-term changes in serum biochemistry and bone histology at 96 hr. Quantitative bone histomorphometric analyses of the proximal tibial metaphysis were made in all experimental groups. In the experimental vitamin D-deficient group, with the highest bone aluminum content (as assessed by extraction of whole bone aluminum), X-ray microanalysis was performed to determine the distribution of aluminum in bone tissue and bone cell organelles. The results showed that control rats treated with prolonged aluminum therapy (30 mg over 60 days) had evidence of both reduced osteoid matrix synthesis and mineralization. However, in vitamin D-deficient rats, there was no evidence that aluminum exacerbated the osteomalacic lesion, even though there was histochemical evidence of aluminum deposition at the bone-osteoid interface.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid small-animal dual-energy X-ray absorptiometry using digital radiography.

Although dual-energy X-ray absorptiometry (DEXA) is an established technique for clinical assessment of areal bone mineral density (BMD), the spatial resolution, signal-to-noise ratio, scan time, and availability of clinical DEXA systems may be limiting factors for small-animal investigations using a large number of specimens. To avoid these limitations, we have implemented a clinical digital radiography system to perform rapid area DEXA analysis on in vitro rat bone specimens. A crossed step-wedge (comprised of epoxy-based materials that mimic the radiographic properties of tissue and bone) was used to calibrate the system. Digital radiographs of bone specimens (pelvis, spine, femur, and tibia from sham-ovariectomized [SHAM] and ovariectomized [OVX] rats) were obtained at 40 kilovolt peak (kVp) and 125 kVp, and the resulting areal BMD values were compared with those obtained with a clinical fan-beam DEXA system (Hologics QDR 4500). Our investigation indicates that the cross-wedge calibrated (CWC) DEXA technique provides high-precision measurements of bone mineral content (BMC; CV = 0.6%) and BMD (CV = 0.8%) within a short acquisition time (<30 s). Areal BMD measurements reported by the CWC-DEXA system are within 8.5% of those reported by a clinical fan-beam scanner, and BMC values are within 5% of the known value of test specimens. In an in vivo application, the CWC-DEXA system is capable of reporting significant differences between study groups (SHAM and OVX) that are not reported by a clinical fan-beam DEXA system, because of the reduced variance and improved object segmentation provided by the CWC-DEXA system.

Nuclear localization of the type 1 PTH/PTHrP receptor in rat tissues.

The localization of PTH/PTH-related peptide (PTHrP) receptor (PTHR) has traditionally been performed by autoradiography. Specific polyclonal antibodies to peptides unique to the PTHR are now available, which allow a more precise localization of the receptor in cells and tissues. We optimized the IHC procedure for the rat PTHR using 5-microm sections of paraffin-embedded rat kidney, liver, small intestine, uterus, and ovary. Adjacent sections were analyzed for the presence of PTHR mRNA (by in situ hybridization) and PTHrP peptide. A typical pattern of staining for both receptor protein and mRNA was observed in kidney in cells lining the proximal tubules and collecting ducts. In uterus and gut, the receptor and its mRNA are present in smooth muscle layers (PTHrP target) and in glandular cuboidal cells and surface columnar epithelium. This suggests that PTH, or more likely PTHrP, plays a role in surface/secretory epithelia that is as yet undefined. In the ovary, PTHR was readily detectable in the thecal layer of large antral follicles and oocytes, and was present in the cytoplasm and/or nucleus of granulosa cells, regions that also contained receptor transcripts. PTHR protein and mRNA were found in the liver in large hepatocytes radiating outward from central veins. Immunoreactive cells were also present around the periphery of the liver but not within two or three cell layers of the surface. Clear nuclear localization of the receptor protein was present in liver cells in addition to the expected cytoplasmic/peripheral staining. PTHR immunoreactivity was present in the nucleus of some cells in every tissue examined. RT-PCR confirmed the presence of PTHR transcripts in these same tissues. Examination of the hindlimbs of PTHR gene-ablated mice showed no reaction to this antibody, whereas hindlimbs from their wild-type littermates stained positively. The results emphasize that the PTHR is highly expressed in diverse tissues and, in addition, show that the receptor protein itself can be localized to the cell nucleus. Nuclear localization of the receptor suggests that there is a role for PTH and/or PTHrP in the regulation of nuclear events, either on the physical environment (nucleoskeleton) or directly on gene expression.

The addition of a raloxifene analog (LY117018) allows for reduced PTH(1-34) dosing during reversal of osteopenia in ovariectomized rats.

To test the hypothesis that an antiresorptive agent might reduce the dosing requirement for an anabolic drug during reversal of osteopenia due to estrogen deficiency, the following experiment was conducted in 6-month-old female rats. Ovariectomy or sham surgery was performed and the following six experimental groups were studied. Untreated (SHAM) or ovariectomized (OVX) animals served as control groups. Four weeks post-OVX, osteopenic rats (now 7 months old), were treated in one of four experimental protocols: human parathyroid hormone (hPTH(1-34)), 80 microg/kg/day, given by subcutaneous injection 5 days/week; a selective estrogen receptor modulator (SERM), raloxifene analog LY117018 (RA), 3 mg/kg/day, given by gavage 5 days/week; and two combinations of LY117018 at the same dose and frequency with hPTH(1-34) (same dose, 5 times/week) and a reduced dosing interval of hPTH(1-34) (same dose, 2 times/week). After 12 weeks of treatment, the four experimental groups were sacrificed at age 10 months. SHAM and OVX controls were also studied at 7 and 10 months of age. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry at four skeletal sites: two mixed cortical/trabecular sites (femur and tibia) and two predominantly trabecular sites (lumbar spine and pelvis). The differences in BMD were consistent at all four sites. RA alone maintained BMD at all skeletal sites, but the results were not significantly improved over OVX controls, at age 10 months. hPTH(1-34) injections given 5 days/week resulted in BMD increments significantly higher than in either OVX or SHAM controls (p < 0.001). While the RA did not enhance the anabolic effects of full doses of hPTH(1-34), the addition of RA treatment to twice-weekly hPTH(1-34) dosing resulted in BMD increments at all four skeletal sites that were similar to the more intensive anabolic regimen of hPTH(1-34) therapy given 5 times/week. Therefore, an antiresorptive agent such as SERMs may potentially reduce the pharmacologic doses of PTH needed to reverse estrogen deficiency-induced osteopenia.

The response of vertebral bone mineral density during the treatment of osteoporosis with sodium fluoride.

Forty-eight female patients with postmenopausal osteoporotic vertebral compression fractures were treated with sodium fluoride and calcium supplements; their response to treatment was documented by sequential measurements of vertebral and forearm bone mineral density (BMD). During treatment 25 patients developed significant side-effects due to fluoride, and ultimately, 18 patients (37%) were intolerant of the drug after 17.3 +/- 7.3 (+/- SD) months. The remaining patients were followed for 29.4 +/- 9.6 months. By linear regression analysis, 69% of patients had a positive slope of vertebral BMD vs. time of greater than 0.0017 g/cm2.month (range, 0.0017-0.01) and were classified as treatment responders. The increment in vertebral BMD above the baseline value over time was described by the relationship delta BMD (g/cm2.month) = 0.042 + 0.0053 x months, equivalent to a rate of 8.4%/yr. Because the rates of increasing BMD were very variable, it was difficult to determine in individual patients the point at which a positive response to treatment had occurred; by calculating the 95% confidence target BMD by which the BMD must rise above the initial value before discounting the imprecision of the measurements (0.062 g/cm2), only 70% of responders were identified by 12 months. The total cumulative dose of sodium fluoride (31.3 +/- 16.4 g) was significantly higher in patients classified as responders than in the nonresponders (20.6 +/- 13.4 g; P less than 0.05), probably because of differences in side-effects between the two groups. In contrast, forearm BMD fell significantly in the responders by an average of 7.7%/yr, suggesting the possibility of a preferential improvement in axial bone density at the expense of cortical bone. Thus, the majority of patients treated with fluoride respond with increasing vertebral BMD, but it may take 12-24 months to identify these individually.

Differential effects of inhaled budesonide and oral prednisolone on serum osteocalcin.

Inhaled glucocorticosteroids have been developed for the treatment of asthma in an attempt to minimize the suppression of endogenous adrenal function that complicates oral or injected steroid usage, but it is unclear whether this strategy leads to reduced systemic complications in other areas, such as the skeleton. In this study we evaluated serum osteocalcin levels as a marker of skeletal metabolism in healthy volunteers treated with oral and inhaled steroids alone and in response to an oral calcitriol stimulation test. Forty subjects, aged 33 +/- 9 (mean +/- SD) yr were randomized to receive either high or low dose oral prednisolone (40 vs. 10 mg/day) or inhaled budesonide (3.2 vs. 0.8 mg/day). Each dose of budesonide is known to have a greater antiasthmatic potency than the dose of prednisolone with which it was compared. In addition 10 control subjects received placebos containing no active steroid drugs. During the second week of treatment, half of the subjects in each of the 4 steroid-treated groups and all subjects in the control group received oral calcitriol (2.0 micrograms/day). There was a marked dose-dependent reduction in serum cortisol levels, but this reduction was significantly less pronounced during budesonide treatment, such that low dose budesonide was without effect. During the first week of steroid therapy there were significant dose-dependent reductions in serum osteocalcin (P = 0.003), but this reduction was not significantly different between budesonide and prednisolone treatments. In response to calcitriol, serum osteocalcin increased by 35% in the control group (P = 0.06). Osteocalcin levels increased by 56% and 50% in the low dose budesonide and prednisolone groups and by 106% in the high dose budesonide group, but did not change in the high dose prednisolone group. The osteocalcin response to calcitriol was significantly higher in the budesonide groups (P = 0.03, by analysis of variance). High dose prednisolone caused increases in serum 1,25-dihydroxyvitamin D3 (P less than 0.02), urinary calcium excretion (P = 0.07), and urinary hydroxyproline (P less than 0.01). None of these changes was seen during budesonide therapy. There are as yet no data for these variables after long term use of inhaled budesonide in asthmatic patients, but our acute studies suggest that this potent topical glucocorticoid may have considerably less impact on the skeleton than oral prednisolone, even if used at doses high enough to suppress endogenous adrenal function.

A comparison of the in vivo biochemical responses to exogenous parathyroid hormone-(1-34) [PTH-(1-34)] and PTH-related peptide-(1-34) in man.

PTH-related peptide (PTHrP) is one of the etiological factors associated with hypercalcemia of malignancy in humans and rodents. In both in vivo and in vitro animal systems its actions mimic those of PTH; however, its bioactivity in humans has not previously been assessed. Therefore, we compared the actions of the synthetic human (h) analogs hPTHrP-(1-34) and hPTH-(1-34) when given by iv infusion to 15 healthy subjects, aged 25 +/- 3 yr. Three 12-h test infusions were given to each subject in the order: hPTH-(1-34) at a dose of 8 pmol/kg.h, an equimolar dose (8 pmol/kg.h) of PTHrP-(1-34) (low dose), and a 10-fold higher dose (80 pmol/kg.h) of hPTHrP-(1-34) (high dose). PTH infusion resulted in significant increases from basal values in serum total ionized calcium, urinary phosphate and cAMP, and serum 1,25-dihydroxyvitamin D3 [1,25-(OH)2d3]. No significant increases from basal values in any of these variables were observed during low dose PTHrP infusion. However, a 10-fold higher dose of PTHrP significantly increased serum calcium from 2.36 +/- 0.07 to 2.63 +/- 0.16 mmol/L (P less than 0.003), ionized calcium from 1.22 +/- 0.03 to 1.39 +/- 0.09 mmol/L (P less than 0.003), urinary phosphate from 0.21 +/- 0.19 to 0.31 +/- 0.16 mmol/L glomerular filtrate (P less than 0.05), urinary cAMP from 37 +/- 18 to 53 +/- 28 nmol/L glomerular filtrate (P less than 0.01), and serum 1,25-(OH)2D3 from 29.8 +/- 12.1 to 46.0 +/- 20.3 pmol/L (P less than 0.01). For each variable these changes were statistically equivalent to the increases observed during PTH infusion. The molar concentrations of circulating immunoreactive PTH-(1-34) and PTHrP-(1-34) (at the higher dose) achieved during infusion were at a ratio of 1:3. These results suggest that the in vivo actions of synthetic hPTHrP-(1-34) are comparable to those of hPTH-(1-34), but its biological activity after infusion may be less than that of hPTH-(1-34). Moreover, the increased concentrations of serum 1,25-(OH)2D3 observed with administration of hPTHrP-(1-34) are unlike the changes seen in hypercalcemia of malignancy in which levels of this vitamin D metabolite are frequently depressed.

A randomized controlled trial to compare the efficacy of cyclical parathyroid hormone versus cyclical parathyroid hormone and sequential calcitonin to improve bone mass in postmenopausal women with osteoporosis.

Short cycles of human (h) PTH-(1-34) may have an anabolic effect to increase bone mass in patients with osteoporosis. As PTH also stimulates bone resorption, it is theoretically possible to enhance the anabolic effects of PTH by using a sequential antiresorptive agent in the treatment cycle. To test this hypothesis, 30 women with osteoporosis, aged 67 +/- 8 yr, completed a 2-yr protocol that comprised 28-day courses of hPTH-(1-34) (800 U) given by daily sc injections; each course was repeated at 3-month intervals. By random allocation, patients either received sequential calcitonin (CT) immediately following the cycle of hPTH-(1-34) (75 U/day, sc; PTH + CT; n = 16) or placebo CT (PTH alone; n = 14) for 42 days. Baseline bone mineral density (BMD) at the lumbar spine site revealed t scores of -3.7 +/- 1.2 (+/-SD) for the PTH alone group and -3.0 +/- 1.4 for the PTH + CT groups, who had 2.0 +/- 2.3 and 1.8 +/- 2.4 vertebral fractures, respectively, at entry to the study. At the end of the 2 yr, the lumbar spine BMD increased from 0.720 +/- 0.130 to 0.793 +/- 0.177 g/cm2 (10.2%) in the PTH group and from 0.760 +/- 0.168 to 0.820 +/- 0.149 g/cm2 (7.9%) in the PTH + CT group. These changes were significant over time in both groups (P < 0.001). Although the final 2-yr lumbar spine BMD was not significantly different between the two treatment groups, those patients receiving sequential CT injections gained bone mass at a consistently slower rate. Changes in BMD at the femoral neck averaged +2.4% and -1.8% in the PTH and PTH + CT groups, respectively, neither of which was significant. In the group receiving only cyclical hPTH-(1-34), the observed 2-yr vertebral fracture incidence was 4.5 compared to 23.0/100 patient yr in the PTH + CT group (P = 0.078). During the first two cycles, changes in biochemical markers of bone formation (serum total alkaline phosphatase, bone-specific alkaline phosphatase, and osteocalcin) and bone resorption (fasting urinary hydroxyproline and N-telopeptide excretion) were significantly increased over pretreatment values after 28 days of hPTH-(1-34) injections (P < 0.05 to P < 0.01 for both groups). Even end of cycle values remained elevated over the study baseline across time (P < 0.01). There were no significant differences for any outcome parameter between the two treatment groups. We conclude that short cycles (28 days) of daily hPTH-(1-34) injections result in significant increases in lumbar spine BMD, without significant changes in cortical bone mass at the femoral neck. Very low incident vertebral fracture rates were documented over 2 yr. However, there is no evidence that sequential antiresorptive therapy with CT is of any benefit over that conferred by cyclical PTH alone.

Enhancement of bone mass in osteoporotic women with parathyroid hormone followed by alendronate.

Treatment of osteoporosis with PTH causes a marked increase in vertebral bone mineral density (BMD). However, this effect is rapidly reversed when the treatment is stopped. The purpose of the present study was to determine whether the bisphosphonate alendronate could preserve or enhance bone density in patients previously treated with PTH. Sixty-six postmenopausal osteoporotic women were treated for 1 yr with 50, 75, or 100 microg recombinant human PTH-(1-84) or placebo, and then were given 10 mg alendronate daily for an additional year. BMD was measured in the femoral neck, lumbar spine, and whole body. Markers of bone turnover included skeletal alkaline phosphatase, osteocalcin, and N-telopeptide. During the first year, changes in BMD (mean +/- SD) in women receiving PTH (all doses combined) were 7.1 +/- 5.6% (spine), 0.3 +/- 6.2% (femoral neck), and -2.3 +/- 3.3% (total body). After switching to alendronate for 1 yr in women who previously had received PTH, mean changes in BMD were 13.4 +/- 6.4% (spine), 4.4 +/- 7.2% (femoral neck), and 2.6 +/- 3.1% (whole body). In the subgroup of patients who had received the highest dose of PTH, the mean increase in vertebral BMD was 14.6 +/- 7.9%. All markers of bone turnover increased during treatment with PTH and decreased to below baseline after 1 yr of alendronate. In conclusion, sequential treatment of osteoporosis with PTH and alendronate results in an increase in vertebral bone density that is considerably more than has been reported with alendronate or estrogens alone. This combination of drugs may be a useful approach to maximizing bone density in women with vertebral osteoporosis.

Comparison of the pharmacokinetics of parenteral parathyroid hormone-(1-34) [PTH-(1-34)] and PTH-related peptide-(1-34) in healthy young humans.

The amino-terminal fragments of human PTH [hPTH-(1-34)] and PTH-related peptide [PTHrP-(1-34)] appear to be equipotent in several rodent models. However, continuous i.v. infusions of these peptides to young human volunteers suggested that a 10-fold higher molar dose of PTHrP was required to produce comparable circulating levels of the peptide and biochemical responses similar to PTH. As PTHrP has a wide variety of target tissues in mammalian species and may, therefore, play a paracrine, rather than an endocrine, hormonal role in vivo, we evaluated whether enhanced metabolic clearance of injected PTHrP might explain its apparently reduced potency as a PTH-like hormone. Ten healthy subjects [age, 25 +/- 9 (+/- SD) yr] received in random order either hPTH-(1-34) or hPTHrP-(1-34) given by bolus i.v. injections in a dose of 10.7 nmol. Measurements of plasma immunoreactive peptide indicated a comparable volume of distribution for each, but the apparent t1/2 (8.3 +/- 1.6 min) and plasma clearance (4.0 +/- 1.4 L/min) for hPTHrP were significantly (P < 0.05) accelerated compared to those of hPTH (t1/2, 10.2 +/- 0.5 min; clearance, 2.0 +/- 0.4 L/min). Peak plasma cAMP levels were 9-fold lower in response to hPTHrP (29.5 +/- 19 vs. 190 +/- 63 pmol/L; P < 0.01), and increases in urinary cAMP excretion were 5-fold lower (2.1 +/- 1.1 vs. 11.2 +/- 3.7 nmol/mmol creatinine; P < 0.01). No major differences were observed in the urinary excretion of phosphate, calcium, or sodium between the two peptides. Although hPTHrP-(1-34) has a 2-fold higher MCR than hPTH-(1-34), this may not explain the more than 5-fold lower plasma or urinary cAMP response to PTHrP in humans. The comparable effects of PTH and PTHrP on urinary phosphate, calcium, and sodium may indicate a non-cAMP-dependent pathway for these responses, although the intracellular pool of cAMP generated to either peptide, and thus the local target tissue response, could not be estimated in the present study.

Bone aluminum and histomorphometric features of renal osteodystrophy.

To evaluate the relationship between aluminum and the characteristics of bone disease in uremia, bone aluminum content and quantitative histomorphometric analysis of bone were evaluated in bone biopsies from 59 uremic patients undergoing maintenance hemodialysis. Biopsies were classified as showing 1) pure osteomalacia (OM) in 23 cases, 2) osteitis fibrosa (OF) in 13, 3) mixed in 7, and 4) mild lesions in 16. There were no significant differences in levels of serum calcium or alkaline phosphatase between the groups, but serum phosphorus levels were slightly higher in those with OF. Serum immunoreactive parathyroid hormone levels were greater in the patients with OF and mixed lesions than in patients with OM or mild lesions (P less than 0.01). Bone aluminum exceeded normal in all groups (P less than 0.01), with values of 175 +/- 18 mg/kg dry wt in OM patients, 46 +/- 7 of OF patients, 81 +/- 29 in mixed subjects, and 67 +/- 7 in patients with mild lesions. Bone aluminum was significantly higher in the OM patients than in any other group (P less than 0.01); also, bone aluminum correlated with the quantitative measure of unmineralized osteoid in OM (r = 0.67; P less than 0.001); no correlations existed for the other groups. There were inverse correlations between bone aluminum and the serum immunoreactive parathyroid hormone (r = -0.35; P less than 0.01) and resorbing surface on biopsy (r = -0.44; P less than 0.001). Bone aluminum correlated with the duration of hemodialysis in patients with OF with mixed and mild lesions (r = 0.49); no relation was seen in OM patients, and bone aluminum was higher for the duration of dialysis, suggesting that aluminum may accumulate more rapidly in OM subjects. These findings are consistent with but do not prove the hypothesis that aluminum plays a pathogenic role in dialysis osteomalacia; the mechanism by which aluminum accumulates remains unknown.

Comparison of the biochemical responses to human parathyroid hormone-(1-31)NH2 and hPTH-(1-34) in healthy humans.

The 1-31 fragment of human PTH [hPTH-(1-31)NH2] has been shown, like hPTH-(1-34), to have anabolic effects on the skeletons of ovariectomized rats when given intermittently, but, unlike hPTH-(1-34), it does so without affecting serum calcium concentrations and does not activate the protein kinase C second messenger pathway in some target cells. To investigate the biochemical responses to hPTH-(1-31) in humans, we have directly compared it to hPTH-(1-34) during the course of slow infusions of each. Ten healthy adults, five men and five women, aged 26+/-5 yr (range, 22-37), each received 8-h continuous infusions of 8 pmol/kg.h hPTH-(1-34) and hPTH-(1-31) given in random order at least 2 weeks apart. During the infusions there were significant increases in both plasma and urinary cAMP (P < 0.05), but there were no differences in the responses between the two peptides (P = 0.362 for plasma; P = 0.987 for urine). There were also significant phosphaturic and natriuretic responses to the two peptides, which again were not different between peptides. During the infusion of hPTH-(1-34) serum ionized calcium (Ca2+) increased from 1.21+/-0.033 to 1.29+/-0.046 mmol/L (P < 0.01), and endogenous hPTH-(1-84) decreased from 29.6+/-9 to 15.0+/-5.7 pg/mL (P < 0.01), such that there was a negative correlation between them (r2 = 0.45). However, when hPTH-(1-31) was infused, neither serum Ca2+ (1.24+/-0.03 vs. 1.25+/-0.03) nor hPTH-(1-84) (26.8+/-5 vs. 30.7+/-12 pg/mL) was affected. Circulating concentrations of 1,25-dihydroxyvitamin D3 increased from 92+/-42 to 131+/-63 pmol/L (P < 0.05) during infusion of hPTH-(1-34) and from 92+/-27 to 110+/-42 pmol/L (P = NS) during hPTH-(1-31) infusion. There was also a significant increase in the urinary measure of type I collagen degradation of aminoterminal telopeptides from 78+/-45 to 101+/-51 nmol/mmol creatinine (P < 0.05) when hPTH-(1-34) was infused, but it was not affected (68+/-30 vs. 66+/-24 nmol/mmol creatinine) by hPTH-(1-31). Therefore, hPTH-(1-31) appears to be equivalent and equipotent to hPTH-(1-34) in the release of cAMP from target tissues and the renal handling of phosphate and sodium. However, at the doses employed, it does not increase serum calcium, is a weaker stimulator of the 25-hydroxyvitamin D-1alpha-hydroxylase, and does not induce rapid bone resorption.

Regional variation of insulin-like growth factor-I gene expression in mature rat bone and cartilage.

Regulation of long bone growth by growth hormone and other endocrine factors is mediated by the local synthesis of IGF-I in the growth plate. Recent evidence suggests that different regions of the growth plate exhibit variable growth rates. To investigate whether IGF-I gene expression in the growth plate differs in relation to growth, we examined the distribution of IGF-I mRNA and peptide using in situ hybridization and immunohistochemistry, respectively, in the tibiae of 18-week-old rats (n = 6). Osteoblasts were identified by osteocalcin immunoreactivity, and osteoclasts by tartrate-resistant acid phosphatase (TRAP) histochemistry. The abundance of IGF-I mRNA in growth plate chondrocytes was quantified by counting the autoradiographic signal associated with each cell. IGF-I mRNA was identified in chondrocytes of both the proliferative and hypertrophic zones of the growth plate. Cells in the marginal regions of both zones contained significantly more IGF-I mRNA than those in the central region (p < 0.05). In addition, IGF-I mRNA levels were greater in the periphery of the growth plate on the medial side of the tibia (p < 0.05) in which there was more active growth than the lateral side. IGF-I immunoreactivity was present predominantly in the hypertrophic zone chondrocytes and no regional differences in its distribution were observed. IGF-I mRNA and peptide were also identified in periosteal fibroblasts, notably at sites of muscle attachment to bone, and in osteoblasts at active sites of bone remodelling in the periosteal, endocortical, and endosteal bone envelopes. In the TRAP-positive osteoclasts, IGF-I immunoreactivity, but not IGF-I mRNA, was detected. In addition, both IGF-I mRNA and peptide were identified in the hemopoietic cells of the metaphyseal bone marrow, whereas only IGF-I immunoreactivity was detectable in the diaphysis. We conclude that, in the tibiae of mature rats: (i) IGF-I gene expression in the growth plate is related to its growth and/or synthetic activity; and (ii) the presence of IGF-I in osteoblasts and osteoclasts suggests its involvement in active bone growth and remodeling.

Regional migratory osteoporosis of the lower extremities with vertebral osteoporosis.

Regional migratory osteoporosis is a disorder of unknown etiology, characterized by successive episodes of joint pain, accompanied by localized osteoporosis. The disorder affects the lower limbs, usually the region of the foot, knee, or hip, and each episode usually lasts several months and is followed by spontaneous recovery. This disorder has not previously been reported to cause episodes of vertebral osteoporosis. We describe three patients in whom regional osteoporosis, involving the lower limbs, was associated with simultaneous vertebral osteoporosis indistinguishable from idiopathic osteoporosis. These cases suggest that this disorder might be responsible for some cases of apparent idiopathic spinal osteoporosis.

Histomorphometric evidence for increased bone turnover without change in cortical thickness or porosity after 2 years of cyclical hPTH(1-34) therapy in women with severe osteoporosis.

Parathyroid hormone (PTH) increases trabecular but may decrease cortical bone mass during treatment of postmenopausal osteoporosis. In a 2-year trial, PTH, with or without sequential calcitonin (CT), was given to 29 osteoporotic women (mean age 67 +/- 7 years), in 3-month cycles [28 days hPTH(1-34), 50 microg/day, +/-42 days CT, 75 units/day, 20 days "free"]. Over 2 years, lumbar spine bone mineral density measurements increased an average of 10%. Paired iliac crest biopsies were obtained 28 days and 2 years after starting the trial. The addition of CT made no difference to changes seen with cyclical PTH alone. Thus, the histomorphometric analyses for all 29 treated patients were compared with a separate group of biopsies from untreated osteoporotic control patients (n = 15). No significant increments in total bone volume or trabecular architecture were seen over 2 years of cyclical PTH treatment, although the light microscopic appearance of bone was normal. At the level of the bone remodeling unit, a twofold increase in total trabecular erosion surface over the control measurements was observed within the first 28 days of PTH treatment (10 +/- 5 vs. 5 +/- 3% trabecular surface, p < 0.01), which was sustained over 2 years. Trabecular bone formation rates (surface referent) were 11 +/- 7 microm(3)/microm(2)/year in control patients and threefold higher in treated patients both acutely (31 +/- 31 microm(3)/microm(2)/year, p < 0.01) and after 2 years (33 +/- 43 microm(3)/microm(2)/year, p < 0. 05). The activation frequency of trabecular remodeling was threefold higher than controls through 2 years of treatment (p < 0.05). The mean wall thickness of completed osteons after 2 years of treatment was significantly larger than controls (28 +/- 7 vs. 22 +/- 5 microm, p < 0.01), suggesting a positive remodeling balance, as well as the histomorphometric evidence of increased bone turnover and the increased resorption surfaces. Over 2 years of cyclical PTH therapy, cortical thickness remained significantly higher than controls (680 +/- 202 vs 552 +/- 218 microm, p < 0.05), without significant changes in cortical porosity. Thus, the histomorphometric changes during cyclical PTH therapy in patients with severe osteoporosis are consistent with increased trabecular bone turnover and a positive remodeling balance, with no evidence for detrimental changes in cortical bone.

Comparison of the response of pelvic and proximal tibial cancellous bone in rat to ovariectomy with estrogen replacement.

In this study, we found that the trabecular architecture of the rat pelvis has similarities to that of human iliac crest. Although we made no direct comparisons between the estrogen deficiency-induced rat osteopenia model and postmenopausal histomorphometry of iliac crest, we attempted to determine whether the rat pelvis might be appropriate to study changes in bone modeling and in situ changes in osteoblast protein expression. Three groups of young, sexually mature rats (12 weeks of age, each group comprising six animals) were either ovariectomized (ovx) and treated with 17beta-estradiol (ovx + E), vehicle (ovx), or sham-operated (sham). Histomorphometric variables were quantitated in the pelvis and compared with proximal tibial metaphysis in the three groups. Immunocytochemical localization of osteocalcin was also evaluated in the two skeletal sites. There was a greater reduction in bone volume of the proximal tibial metaphysis of ovx rats than in the pelvis of ovx rats when compared with sham-operated animals (p < 0.01), although bone formation rates were significantly higher at the pelvic site than tibial metaphysis (p < 0.01). The more rapid loss of bone between the tibia and pelvis may reflect differences in longitudinal growth in young rats, but the other intersite differences in bone remodeling consequent to ovx were at least as well demonstrated in the pelvic trabecular structure. Because ex vivo removal of the rat pelvis is simple, and provides a larger histomorphometric section with which to evaluate dynamic changes in metabolic bone disease, we suggest that this site may be useful in studies of osteopenia in the sexually mature female rat. Immunocytochemical demonstration of osteocalcin in trabecular surface osteoblasts was excellent in both sites. These results suggest that the rat pelvis is as accessible for histological study as the more conventional appendicular sites. When compared with the proximal tibial metaphysis, the rat pelvis (1) has a more homogeneous trabecular structure; (2) has more than twice as much trabecular bone area to sample; (3) has no open epiphyseal growth cartilages; (4) loses trabecular bone half as rapidly after ovx; (5) displays a greater increase in bone turnover after ovx; and (6) is the same anatomic site that is sampled in humans. We have also shown that the pelvis is a suitable site to demonstrate immunocytochemistry for osteoblast-derived proteins.