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.     

Iliac bone biopsies at the time of periarticular stress fractures during fluoride therapy: comparison with pretreatment biopsies

We attempted to establish whether systemic changes in trabecular bone explain the development of stress fractures in the lower limbs during fluoride therapy for osteoporosis. To this end we compared transiliac bone biopsies obtained before treatment with those taken around the time of stress fractures after 14.3 +/- 10.9 (SD) months of therapy in six patients (group A). Biopsies from a comparable group of six patients without stress fractures at the time of the second biopsy (after 11.9 +/- 2.7 months of treatment) served for comparison (group B). The biopsies were processed undecalcified and examined by routine histomorphometry. The second biopsies did not show any significant improvement in mean bone volume or trabecular architecture. Although the second biopsies in group A had increased erosion surfaces (p less than 0.05) and greater osteoid volume (p less than 0.05), group B biopsies showed no difference in erosion surfaces but an increase in all osteoid parameters: osteoid volume (p less than 0.05), osteoid surface (p less than 0.05), and osteoid seam thickness (p less than 0.01). We reached the following conclusions: (1) the combination of increased erosion and replacement of removed bone by as yet unmineralized osteoid in the stress fracture group must have weakened bone and allowed the development of stress fractures. (2) Stress fracture patients may have mounted a less vigorous osteoblast response to fluoride than non-stress fracture patients. Under these conditions microfractures are likely to heal poorly and propagate to develop into full stress fractures. (3) Renal failure is a contraindication to fluoride therapy.     

Analysis of the effects of growth hormone, voluntary exercise, and food restriction on diaphyseal bone in female F344 rats.

The aim of this study is to examine the effects of growth hormone, exercise, and weight loss due to food restriction on tibial diaphyseal bone and on tibial muscle mass. Thirteen-month-old female F344 rats were divided into six groups: group 1, baseline controls (B); group 2, age-matched controls (C); group 3, GH treated (GH); group 4, voluntary wheel running exercise (EX); group 5, GH + EX; and group 6, food restricted (FR). The dose of GH was 2.5 mg recombinant human (rh) GH/kg body weight/day, 5 days per week, given in two divided doses of 1.25 mg at 9-10 A.M. and 4-5 P.M. Food-restricted rats were fed 60% of the mean food intake of the age-matched controls. All animals except the baseline controls were killed after 4.5 months. The baseline controls were killed at the beginning of the study. Growth hormone increased the body weight and tibial muscle mass of the rats markedly, while EX caused only a slight decrease in body weight and partially inhibited the increase caused by GH in the GH + EX group. Food restriction greatly decreased body weight below that of age-matched controls, but neither FR nor EX had a significant effect on the mass of the muscles around the tibia. Growth hormone and EX independently increased tibial diaphyseal cortical bone area (p < 0.0001, p < 0.0001), cortical thickness (p < 0.0001, p < 0.0001), cortical bone mineral content (p < 0.0001, p < 0.0001), periosteal perimeter (p < 0.0001, p < 0.0001), and bone strength-strain index (SSI) (p < 0.0001, p < 0.0001). The effects of GH were more marked and resulted in a greater increase in the weight of the mid tibial diaphysis (p < 0.0001). The combination of GH and EX produced additive effects on many of the tibial diaphyseal parameters, including bone SSI. GH + EX, but not GH or EX alone, caused a significant increase in endocortical perimeter (p < 0.0001). In the FR rats, cortical bone area and cortical mineral content increased above the baseline level (p < 0.001, p < 0.0001) but were below the levels for age-matched controls (p < 0.0001, p < 0.0001). In addition, marrow area, endocortical perimeter, and endocortical bone formation rate increased significantly in the FR rats (p < 0.01, p < 0.0001, p < 0.0001). Three-point bending test of right tibial diaphysis resulted in maximum force (Fmax) values that reflected the group differences in indices of tibial diaphyseal bone mass, except that GH + EX did not produce additive effect on Fmax. The latter showed good correlation with left tibial diaphyseal SSI (r = 0.857, p < 0.0001), and both indices of bone strength correlated well with tibial muscle mass (r = 0.771, Fmax; r = 0.700, SSI; p < 0.0001). GH increased serum IGF-I (p < 0.0001), and the increase was partially reduced by EX. Serum osteocalcin was increased by GH with or without EX (p < 0.01, p < 0.01), and FR or EX alone did not alter serum IGF-I and osteocalcin levels. The bone anabolic effects of GH with or without EX may relate, in part, to increased load on bone from tibial muscles and body weight, which were increased by the hormone. The osteogenic effect of EX with or without GH may relate, in part, to increased frequency of muscle load on bone as EX decreased body weight (p < 0.05), but had no significant effect on tibial muscle mass. The enhanced loss of endocortical bone by FR may relate, in part, to decreased load on bone due to low body weight (p < 0.0001), as FR did not cause a significant decrease in tibial muscle mass (p = 0.357). The roles of humoral and local factors in the bone changes observed remain to be established.     

Growth hormone, insulin-like growth factors and their binding proteins in adult hemodialysis patients treated with recombinant human growth hormone.

BACKGROUND: Growth deficiency and malnutrition in uremic children are often caused by malfunction of the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis and can be corrected by treatment with GH. The purpose of this study was to evaluate the levels of GH, IGF-I and II and their binding proteins compared to changes in body composition in adult, enfeebled, uremic patients in chronic hemodialysis (HD), treated for 6 months with recombinant human growth hormone (rhGH). METHODS: 31 patients were included in a controlled, randomized, double-blinded study using either 4 IU/m2/day of rhGH or placebo injected subcutaneously every evening for 6 months. RESULTS: Fasting levels of GH were normal at start and increased significantly from 2.2 to 13.5 microg/l (p = 0.01) within the first 4 months of rhGH treatment. Before treatment IGF-I was at the upper limit of normal range (130 to 220 microg/l) in both groups, and it increased significantly from 213 to 348 microg/l (p = 0.01) during rhGH treatment. IGF-II was above the normal range in both groups, and remained unchanged throughout. IGFBP-1 decreased in the rhGH-treated group from 53.1 to 24.7 microg/l (p = 0.004), while IGFBP-3 increased from 5620 to 7100 microg/l (p = 0.004). The molar ratio of IGF-I/IGFBP-3 increased significantly from 14 to 25% (p = 0.01), while the ratio decreased in the placebo group (p = 0.01). During the treatment with rhGH the patients increased their lean body mass (= muscle mass) by a median of 3.18 kg (range 0.82 to 5.12 kg) (p = 0.0001) while their fat mass decreased by a median of 3.33 kg (range 0.18 to 5.82 kg) (p = 0.004). Total body mass (= weight) remained stable. No significant changes were observed in the placebo group. CONCLUSION: The baseline GH and IGF-I concentrations were normal in malnourished HD patients. When treated with rhGH in a dosage as used in growth-retarded uremic children, IGF-I increased to the levels seen in acromegalic persons. IGF-I increased more than IGFBP-3 whereby its biological activity obviously improved. This was reflected in an increased muscle mass and a decreased fat mass. The rhGH treatment was well tolerated.     

Effect of long-term growth hormone treatment on bone mass and bone metabolism in growth hormone-deficient men.

Long-term GH treatment in GH-deficient men resulted in a continuous increase in bone turnover as shown by histomorphometry. BMD continuously increased in all regions of interest, but more in the regions with predominantly cortical bone. INTRODUCTION: Adults with growth hormone (GH) deficiency have reduced rates of bone turnover and subnormal BMD. GH treatment is effective in enhancing bone turnover as shown by biochemical markers and bone histomorphometric studies. However, it is uncertain whether long-term treatment will result in higher bone mass. In this study, we present BMD and histomorphometric data on 5 years of GH treatment in GH-deficient men. MATERIALS AND METHODS: Thirty-eight adult men with childhood onset GH deficiency (20-35 years) were included in the study. Twenty-six of these had multiple pituitary hormone deficiencies and were on stable conventional hormone replacement. BMC (total body) and BMD (lumbar spine and hip) were measured before and after 1, 2, 3, 4, and 5 years of treatment. BMD in various regions of the total body was calculated by computer software (head, trunk, arms, and legs). Transiliac bone biopsies were obtained before and after 1 and 5 years of GH treatment. RESULTS: Total body BMC increased 18% after 5 years of treatment. This increase was observed in all regions of interest: head, 13.7%; trunk, 27.8%; arms, 24.4%; legs, 13.8%. BMD also increased in all separately measured regions: lumbar spine, 9%; femoral neck, 11%; femoral trochanter, 16%. Lumbar spine area significantly increased (p=0.0002). Histomorphometric data showed increased osteoid surface (p<0.02), osteoid volume (p<0.01), and activation frequency (p<0.006), but trabecular bone volume did not increase significantly. Qualitative assessment of the cortical bone showed endosteal and periosteal bone formation. CONCLUSIONS: In conclusion, GH considerably increases BMC after long-term treatment. The combination of BMD and histomorphometric data suggests that GH has a greater effect on cortical than on trabecular bone.     

Bone histomorphometry of renal osteodystrophy in diabetic patients

Bone biopsies and plasma parathyroid hormone (PTH) from 27 diabetic dialysis patients were compared to biopsies and PTH levels from matched patients without diabetes to determine if PTH has a role in preserving bone mass in diabetic renal osteodystrophy. Significantly lower values were present in the diabetic group for mineralized bone area (p less than 0.003), osteoblastic osteoid (p less than 0.01), resorptive surface (p less than 0.001), fibrosis (p less than 0.005), bone apposition rate (p less than 0.01), bone formation rate (BMU level) (p less than 0.04), and plasma PTH (p less than 0.05). Bone-surface aluminum was higher in the diabetic group (44 +/- 5% vs. 20 +/- 5%, p less than 0.005). Linear regression analysis revealed significant positive correlations of mineralized bone area with time on dialysis, bone formation rate, bone resorption, and PTH only in the group without diabetes. While both groups had significant positive correlations of PTH with osteoblastic osteoid and bone resorption, only in the nondiabetic group was there a positive correlation of PTH with bone apposition and bone formation rate (BMU level), observations suggesting that the lower bone formation in the diabetic patients may have arisen in part from a failure of PTH to promote bone mineralization. We conclude that relatively low PTH levels and high bone aluminum in diabetic patients with chronic renal failure may be responsible in part for low bone mass when compared to uremic patients without diabetes.     

The bone formation defect in idiopathic juvenile osteoporosis is surface-specific

We have previously shown that idiopathic juvenile osteoporosis (IJO) is characterized by a decreased cancellous bone volume and a very low bone formation rate on cancellous surfaces. Whether IJO similarly affects cortical bone is unknown. We therefore compared tetracycline double-labeled transfixing iliac-crest bone biopsies from eight children with typical clinical features of IJO (six girls; age 10-12 years) and from nine children (four girls; age 9-12 years) without metabolic bone disease. No differences in intracortical remodeling activity were detected. Both structural parameters reflecting intracortical remodeling (cortical porosity, active canal diameter, and quiescent canal diameter) and bone surface-based metabolic parameters (osteoid, osteoblast, mineralizing, osteoclast and eroded surfaces, and bone formation rate) were similar in IJO patients and controls (p > 0.2 each, t-test). Although the internal cortex of the biopsy was thinner in IJO patients than in controls (660 +/- 170 microm vs. 980 +/- 320 microm; p = 0.02), there was no difference in the width of the external cortex (p = 0.36). In growing children, both cortices exhibit an external modeling drift. Therefore, the difference in internal cortical width point to a decreased modeling activity on the endocortical surface of the internal cortex. In fact, bone formation rate on this surface was 48% lower in IJO patients than in controls (82 +/- 45 microm(3)/microm(2) per year vs. 159 +/- 162 microm(3)/microm(2) per year). However, this difference did not achieve statistical significance (p = 0.21) due to the high variability of bone formation rate on modeling surfaces. The disturbance of bone remodeling in IJO is limited to cancellous bone, but there may be a modeling defect affecting the internal cortex. Thus, the process causing IJO appears to mainly affect bone surfaces that are in contact with the bone marrow cavity.     

The effects of growth hormone replacement therapy on bone metabolism in adult-onset growth hormone deficiency: a 2-year open randomized controlled multicenter trial.

Adult hypopituitary patients with growth hormone deficiency (GHD) show a significant decrease in bone mass and an increased fracture rate. Replacement therapy with GH increases bone turnover. Most of the long-term data on bone mineral content (BMC) and bone mineral density (BMD) have been acquired in open, noncontrolled trials involving limited numbers of patients. To determine whether long-term GH therapy is beneficial for bone despite the increased bone turnover, 100 patients (59 men and 41 women), aged 25-65 years (mean, 49.7 years) with adult-onset GHD were randomized to treatment with GH (40 men and 28 women; mean dose, 0.18 IU/kg per week) or to a nontreated control group (19 men and 13 women) for 24 months. Despite a similar increase in parameters of bone turnover (osteocalcin [OC], procollagen type I carboxy-terminal propeptide [PICP], and pyridinolines ([PYD]) in male and female GH-treated patients compared with controls, the effects on BMC and BMD as evaluated by dual-energy X-ray absorptiometry were gender specific. A significant increase in spine BMC and BMD and total hip BMD and a decrease in BMD at the ultradistal radius over time was observed in male GH-treated patients compared with the evolution in controls (mean +/- SEM change at 24 months: +6.8 +/- 1.1% and p = 0.009, +5.1 +/- 0.8% and p = 0.005, +3.5 +/- 0.7% and p = 0.02, and -2.6 +/- 0.8% and p = 0.008, respectively). No significant treatment effects were observed in female patients. Despite the increase in the total remodeling space induced by GH treatment, prolonged GH therapy in adult-onset GHD has a positive effect on bone balance, maintaining bone mass in women, and even increasing it in men over a 2 year-period.     

Growth hormone increases bone mineral content in postmenopausal osteoporosis: a randomized placebo-controlled trial.

Eighty osteoporotic, postmenopausal women, 50-70 years of age, with ongoing estrogen therapy (HRT), were randomized to recombinant human growth hormone (GH), 1.0 U or 2.5 U/day, subcutaneous, versus placebo. This study was double-blinded and lasted for 18 months. The placebo group then stopped the injections, but both GH groups continued for a total of 3 years with GH and followed for 5 years. Calcium (750 mg) and vitamin D (400 U) were given to all patients. Bone mineral density and bone mineral content were measured with DXA. At 18 months, when the double-blind phase was terminated, total body bone mineral content was highest in the GH 2.5 U group (p = 0.04 vs. placebo). At 3 years, when GH was discontinued, total body and femoral neck bone mineral content had increased in both GH-treated groups (NS between groups). At 4-year follow-up, total body and lumbar spine bone mineral content increased 5% and 14%, respectively, for GH 2.5 U (p = 0.01 and p = 0.0006 vs. placebo). Femoral neck bone mineral density increased 5% and bone mineral content 13% for GH 2.5 U (p = 0.01 vs. GH 1.0 U). At 5-year follow-up, no differences in bone mineral density or bone mineral content were seen between groups. Bone markers showed increased turnover. Three fractures occurred in the GH 1.0 U group. No subjects dropped out. Side effects were rare. In conclusion, bone mineral content increased to 14% with GH treatment on top of HRT and calcium/vitamin D in postmenopausal women with osteoporosis. There seems to be a delayed, extended, and dose-dependent effect of GH on bone. Thus, GH could be used as an anabolic agent in osteoporosis.     

Decreased in vitro osteoblast proliferation and low turnover bone disease in nonuremic proteinuric patients

Patients with proteinuria, even those with normal glomerular filtration rate, often present abnormal bone histology. We evaluated bone histology and the in vitro proliferation of osteoblasts in samples obtained from 17 proteinuric patients with primary glomerulopathies. Histomorphometric analysis of bone biopsies was performed, and bone fragments were obtained for osteoblast culture, in which we evaluated cell proliferation. In comparison to controls, patients presented lower trabecular bone volume (20.9+/-14.5% vs 26.8+/-5.9%; P=0.0008); lower trabecular number (1.7+/-0.2/mm vs 2.0+/-0.3/mm; P=0.004); and greater trabecular separation (475.5+/-96.4 microm vs 368.3+/-86.2 microm, P=0.0002). We also found alterations in bone formation and resorption: lower osteoid volume (0.9+/-0.7% vs 2.0+/-1.4%; P=0.0022); lower osteoid thickness (6.4+/-2.8 microm vs 11.5+/-3.2 microm; P<0.0001); less mineralizing surface (4.6+/-3.1% vs 13.5+/-6.0%; P<0.0001); lower bone formation rate (0.03+/-0.04 microm(3)/microm(2)/day vs 0.09+/-0.05 microm(3)/microm(2)/day; P<0.0001); and greater osteoclast surface (0.35+/-0.6 vs 0.05+/-0.1%, P=0.0016). Mean in vitro osteoblast proliferation was lower in patients than in controls (910.2+/-437.1 vs 2261.0+/-1121.0 d.p.m./well, P=0.0016). Serum concentrations of 25-hydroxyvitamin-D(3) correlated negatively with proteinuria and positively with in vitro osteoblast proliferation. Our results demonstrate that nonuremic proteinuric glomerulonephritic patients present bone structure disorder, low bone formation and high bone resorption, as well as low osteoblast proliferation.     

Hormone replacement therapy prevents osteoclastic hyperactivity: A histomorphometric study in early postmenopausal women.

In a randomized, double blind, clinical prospective trial comprising 35 women treated with either hormone replacement therapy (HRT) (cyclic estradiol/norethisterone acetate) or placebo we performed histomorphometric studies on paired bone biopsies obtained before and after 2 years of treatment. Untreated women developed a progressively more negative balance at individual bone multicellular units (BMUs) (i.e., wall thickness-erosion depth) (2.2 +/- 1.7 microm vs. -5.7 +/- 1.4 microm; p < 0.01), while women on HRT displayed preservation of bone balance (2.4 +/- 2.4 microm vs. 2.5 +/- 2.5 microm; NS). No significant differences in wall thickness between the two groups were demonstrable, but the untreated women developed a pronounced increase in erosion depth over 2 years (46.9 +/- 1.8 microm vs. 52.0 +/- 1.9 microm; p < 0.05), while the HRT group revealed no change (47.8 +/- 2.7 microm vs. 44.6 +/- 1.7 microm; NS). Furthermore, the placebo group displayed an increased osteoclastic erosion depth (17.8 +/- 1.6 microm vs. 25.0 +/- 1.7 microm; p < 0.001), compared with unchanged values in the HRT group (20.0 +/- 1.6 microm vs. 16.9 +/- 1.4 microm/day; NS). While the placebo group revealed a slight increase in volume referent resorption rate (35 +/- 8% vs. 38 +/- 8%; NS) the HRT group revealed a pronounced decrease (46 +/- 8% vs. 28 +/- 5%; p < 0.05). No significant changes in marrow star volume (an index of trabecular perforations) were demonstrable in either group. Our results demonstrate that bone remodeling in early postmenopausal women is characterized by progressive osteoclastic hyperactivity, which is reduced by cyclic HRT. This reduction of resorptive activity at the BMU level after HRT seems to precede the reduction in activation frequency demonstrated in previous studies on older postmenopausal women.     

Differences in bone turnover and intact PTH levels between African American and Caucasian patients with end-stage renal disease

BACKGROUND: Evidence derived from healthy subjects suggests that African Americans have higher serum parathyroid hormone (PTH) levels and decreased bone responsiveness to PTH than Caucasians. African American patients with end-stage renal disease (ESRD) also have higher serum PTH than Caucasians. Studies that correlate intact PTH (iPTH) levels with bone turnover in ESRD patients were performed in a predominantly Caucasian population. METHODS: In this study, serum iPTH and bone histomorphometric data were analyzed for racial differences in 76 ESRD patients (Caucasian = 48, African Americans = 28). Bone turnover was determined by histomorphometric measurement of activation frequency in all patients. RESULTS: Age, duration of dialysis, and calcium and phosphorus levels were similar between the two groups. iPTH levels (pg/mL; mean +/- SE) were significantly higher in the African American group (534 +/- 79 vs. 270 +/- 46, P < 0.01). Also, alkaline phosphatase levels (IU/L) were significantly higher in the African American group (162 +/- 31 vs. 144 +/- 43, P < 0.01). Correlations between PTH levels and activation frequency were r = 0.60, P < 0.01 in Caucasians and r = 0.22, P = NS in African Americans. The mean PTH level in African American patients with histologic findings of low bone turnover was 460 +/- 115 vs. 168 +/- 41 in Caucasian patients with similar bone turnover (P < 0.01). In patients with low bone turnover, African Americans had significantly higher osteoid volume and thickness, number of osteoblasts and osteoclasts, erosion surface, peritrabecular fibrosis, and single-label surface than Caucasians. However, erosion depth, bone formation rate per osteoblast and mineralization apposition rate were similar between the two groups. CONCLUSION: There is no correlation between iPTH and bone turnover in African Americans with ESRD. A substantial number of African American patients with low bone turnover have very high serum PTH levels. Bone histomorphometric results reveal differences in remodeling dynamics and responses to PTH between African American and Caucasian patients. Further studies utilizing newer PTH measurement assays are needed to better delineate the correlation between PTH and bone turnover in the various racial groups.     

Fewer bone histomorphometric abnormalities with intermittent than with continuous slow-release sodium fluoride therapy

To help resolve the uncertainty whether sodium fluoride (NaF) therapy should be given intermittently or continuously, we examined iliac crest bone biopsies (before and after treatment) and fragility fracture rates in 35 intermittently treated (group I) and 69 continuously treated (group C) patients; all received calcium. The following statistically significant results were obtained. Reduction in vertebral fracture rate was similar in the two groups. Trabecular thickness and the structurally more important mineralized thickness increased only in group I. Group I also accumulated less excess osteoid (surface, volume). Mean osteoid thickness did not change in either group because of a bimodal distribution of wide seams with osteoblasts and double tetracycline labels, and thin seams without osteoblasts or labels. Osteoid was lamellar. Osteoid in abnormal sites (within bone marrow or bone, or around osteocytes) was found less frequently in group I. Adjusted apposition rate declined and mineralization lag time increased in both groups because of extended unlabelled osteoid seams. Erosion surface increased only in group C. Hook and/or tunnel erosion was seen less frequently in group I; it was closely associated with osteoid in abnormal sites and correlated with osteoid surface. Extended osteoid surface may have forced osteoclasts to hollow out trabeculae, leaving the empty osteoid shell in marrow. Excess osteoid volume and eroded surface and osteoid and erosion in abnormal sites correlated with bone fragility in group C. We conclude that intermittent therapy is to be preferred because it (1) increased mineralized trabecular thickness, (2) did not cause excessive osteoid accumulation and erosion, (3) showed less osteoid and erosion in abnormal sites and (4) led to a similar reduction in the vertebral fracture rate as did continuous treatment. The question of whether intermittency of therapy has some other effect independent of the cumulative dose of fluoride administered cannot be answered by this study.     

Bone remodeling rate and remodeling balance are not co-regulated in adulthood: implications for the use of activation frequency as an index of remodeling rate.

Use of activation frequency as a measure of remodeling rate assumes co-regulation of remodeling rate and remodeling balance. In iliac crest biopsy specimens from 57 healthy subjects 19-80 yr of age, no correlations were shown between these variables, an observation that challenges the use of activation frequency as an estimate of remodeling rate. INTRODUCTION: The histomorphometric derivation of activation frequency assumes that the remodeling rate is dependent on the duration of the remodeling cycle and the amount of bone formed in individual remodeling units. This implies that remodeling balance and remodeling rate are co-regulated. We tested this assumption in normal human adult cancellous bone. MATERIALS AND METHODS: Relationships between indices of bone formation at the basic multicellular unit (BMU) level (wall width and mineral apposition rate) and indices of remodeling rate (mineralizing perimeter and osteoid perimeter) were examined in iliac crest biopsies obtained from 57 healthy adults (24 men) 19-80 yr of age. RESULTS: Univariate analysis revealed a negative correlation between wall width and osteoid perimeter (r = -0.38; p = 0.0004), but there was no correlation between wall width and mineralizing perimeter or between mineral apposition rate and either mineralizing or osteoid perimeter. After adjustment for age and sex, the association between wall width and osteoid perimeter was no longer observed. Both wall width and mineral apposition rate correlated negatively with age (r = -0.75, p < 0.0001 and r = -0.27, p = 0.05, respectively). CONCLUSIONS: Our results indicate that remodeling balance and remodeling rate are not co-regulated in adult human bone. Activation frequency, as currently derived from histomorphometric variables, may therefore be unreliable as an indicator of remodeling rate.     

Homologous growth hormone accelerates healing of segmental bone defects

The effect of homologous recombinant porcine growth hormone (r-pGH) on secondary fracture healing was investigated in a diaphyseal defect of the tibia in Yucatan micropigs. A 1 cm defect of the tibia was created surgically and stabilized with an AO 3.5 mm DCP plate. The treatment group (12 animals) received 100 microg of r-pGH per kilogram of body weight subcutaneously once per day, whereas the control pigs (12 animals) received 1 mL of sodium chloride as placebo. For evaluation of the GH-axis, serum levels of insulin-like growth factor-I (IGF-I) were sampled every fourth day. The animals were killed 6 weeks after surgery. Quantitative computed tomography (qCT) was performed to determine bone mineral density (BMD) and bone mineral content (BMC) of the defect zone. The torsional stiffness and the torsional failure load were measured by destructive torsional testing of the defect and contralateral tibiae. qCT measurements revealed a significant increase in the BMC of the defect zone in the treatment group compared with controls (GH BMC = 2833 +/- 679 mg, placebo BMC = 2215 +/- 636 mg; p < 0.05), whereas the BMD values were similar in both groups (GH BMD = 668 +/- 60 mg/mm(2), placebo BMD = 629 +/- 52 mg/mm(2), p = 0.12). Torsional failure load was 70% higher and torsional stiffness 83% higher in the treatment group than in the control group (p < 0.05). The mean serum level of IGF-I in the treatment group increased to 382% of the preoperative basal level and decreased to 69% in the control group, and this difference was highly significant (p < 0.001). Our data indicate that daily administration of recombinant GH leads to an increase of serum IGF-I levels and stimulates secondary fracture healing, resulting in increased mechanical strength and stiffness of the callus.     

A randomized study on the effects of estrogen/gestagen or high dose oral calcium on trabecular bone remodeling in postmenopausal osteoporosis

Thirty-seven patients with postmenopausal crush fracture osteoporosis were randomized to oral cyclic estrogen/gestagen (n = 20) or oral calcium (2000 mg elemental calcium per day) (n = 17). Fourteen in each group completed 1 year of treatment. Iliac crest bone biopsies were obtained after intravital double labeling with tetracycline before and after treatment in 10 patients on estrogen/gestagen and 11 patients on calcium. In the estrogen/gestagen group the activation frequency in trabecular bone decreased from 0.52 + 0.11 (SEM) year-1 to 0.27 + 0.08 year-1 (p less than 0.01). No significant changes were found in resorption or formation periods. The osteoid surfaces and the mineralizing surfaces decreased (p less than 0.05), whereas the decrease in eroded surfaces was insignificant. Furthermore, no significant changes were observed in final resorption depth, wall thickness or bone balance per remodeling cycle. Serum alkaline phosphatase and renal hydroxyproline excretion decreased during treatment (p less than 0.002), whereas the lumbar bone mineral content (BMC) increased (p less than 0.01). In the calcium group the extent and thickness of osteoid surfaces decreased (p less than 0.05) without significant changes in activation frequency. Serum alkaline phosphatase and renal hydroxyproline excretion decreased during treatment (p less than 0.02). No significant changes were observed in lumbar BMC or the other histomorphometric parameters. The study supports that the positive effect of estrogen/gestagen on BMC can be explained by a reduction in the activation frequency of new remodeling cycles leading to a decreased remodeling space and an increase in mean bone age. There is no evidence of a positive balance per remodeling cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The evolution of osteomalacia in the rat with acute aluminum toxicity

Aluminum toxicity is the presumed cause of aluminum-associated osteomalacia. In animal models, osteomalacia has been produced after a prolonged course of aluminum. In the present study, rats with renal failure received 20 mg intraperitoneal aluminum during a 2 day period. This model allows sequential observations in the development of osteomalacia. Rats were sacrificed and studied 5, 12, 25, and 40 days after aluminum administration. No differences were observed in serum calcium, phosphorus, or creatinine as a consequence of aluminum administration. Compared with control rats, parathyroid hormone was decreased at 12 and 25 days. A direct correlation was present between plasma and bone aluminum at 12 days (r = 0.92, p less than 0.01), 25 days (r = 0.85, p less than 0.005), and 40 days (r = 0.88, p less than 0.001) but not 5 days after aluminum administration. Plasma aluminum peaked at 5 days (727 +/- 89 micrograms/liter, mean +/- SEM) and bone aluminum at 40 days (273 +/- 40 micrograms/g). Aluminum had profound effect on bone histology. At 5 days there was a decrease in osteoblast surface and osteoid surface; at 12 days osteoblast surface and osteoid surface returned to normal but osteoclast surface decreased. Subsequently there was a progressive increase in osteoid surface and osteoid volume. Bone formation rate measured at 12, 25, and 40 days was decreased at these intervals. In conclusion, (1) high plasma aluminum may be directly toxic to the osteoblast; (2) progressive osteoid accumulation is secondary to matrix (osteoid) deposition, which exceeds the depressed bone formation rate; (3) the progressive decrease in plasma aluminum and increase in bone aluminum suggest that bone has a high affinity for aluminum but may have a relatively slow rate of uptake at any given time; (4) aluminum may directly decrease parathyroid hormone; (5) the correlation between plasma and bone aluminum suggest an exchange is present; and (6) aluminum toxicity may independently affect the osteoblast and bone mineralization.     

Bone mineral density and histology in distal renal tubular acidosis

BACKGROUND: Chronic metabolic acidosis in distal renal tubular acidosis (RTA) has been implicated in the pathogenesis of enhanced bone resorption and osteopenia, resulting in a loss of bone mineral content. However, histomorphometric and bone densitometric studies of patients who suffered from long-standing distal RTA have rarely been done. METHODS: A cross-sectional study to determine the alterations of bone mineral density (BMD) and histology was done in 14 nonazotemic RTA patients (11 females and 3 males) who had never received alkaline therapy before enrolling into this study. The mean age was 32.7 +/- 11.9 years. BMD measurements and transiliac bone biopsy were done in all patients. Blood chemistries, intact parathyroid hormone level, and a 24-hour urine collection for the determination of urinary calcium, phosphate, sodium, and potassium were obtained from the RTA patients at the time of bone biopsy. Data from 28 age-, sex-, and body mass index-matched, normal controls who were residents in the same area were also obtained. RESULTS: Urinary excretion of calcium was 2.05 +/- 1.59 mmol/day. No patient had hypercalciuria. The serum intact parathyroid hormone level was 15.92 +/- 8.48 pg/mL. RTA patients had lower BMD in most areas when compared with normal controls. There were two patients who suffered from a pathologic fracture at the femur. Bone histomorphometry from RTA patients shows a significantly decreased bone formation rate (0.02 +/- 0.02 vs. 0.07 +/- 0.045 microm(3)/microm(2)/day, P < 0.05), not significantly decreased osteoblastic surface (0.78 +/- 1.03% vs. 2.6 +/- 1.1%) and osteoclastic surface (0.05 +/- 0.03 vs. 0.13 +/- 0.23%), but significantly increased osteoid surface (31.47 +/- 24.52 vs. 5.79 +/- 4.39%, P < 0.05) and osteoid volume (2.95 +/- 3.09 vs. 0.92 +/- 1.05%, P < 0.05) when compared with those of normal controls. There was no difference in osteoid thickness (10.65 +/- 6.10 vs. 8.69 +/- 2.14 microm). Only one distal RTA patient who had a marked increase in osteoid thickness justified the diagnosis of osteomalacia. CONCLUSIONS: This study demonstrates that low bone mass is common in distal RTA patients. Chronic metabolic acidosis results in suppression of bone formation and resorption, which in turn may contribute to the development of low bone mass in distal RTA patients. Although minor elevations in osteoid surface and osteoid volume are found among distal RTA patients, overt osteomalacia is not the predominant bone lesion.     

Osteocalcin, iPTH, alkaline phosphatase and hand X-ray scores as predictive indices of histomorphometric parameters in renal osteodystrophy

To evaluate the relationship between hyperparathyroid bone X-ray lesion, biochemical parameters and bone histology in chronic renal failure, 59 patients (52 +/- 14.9 years; Crs 4.7 +/- 2.2 mg/dl, mean +/- SD) on conservative treatment and 103 (48 +/- 14 years) on hemodialysis (from 48.4 +/- 36.7 months) were studied. Right-hand X-ray was carried out for evaluation of the scores (0-3) of acroosteolysis (score A) and subperiosteal resorption (score B). Serum iPTH, osteocalcin and alkaline phosphatase (AP) were measured. In addition in a subset of 53 patients, 30 in predialysis and 23 in dialysis, a bone biopsy was performed for histomorphometry. In predialysis the scores A and B correlated with bone GLA protein (BGP) (p less than 0.01), AP (p less than 0.05) and osteoid surface (p less than 0.05) and 0.01 respectively). In hemodialysis the same level of significant correlation (p less than 0.001) was found between the scores and the three humoral parameters. Score A correlated with active osteoblastic surface and active resorption surface while score B correlated with active osteoblastic surface (p less than 0.01), osteoid surface and active resorption surface (p less than 0.05). Multiple regression analysis carried out to establish the predictive variables of bone histologic lesions (active resorption surface and active osteoblastic surface) singled out BGP in predialysis and AP and the two scores in dialysis. We conclude that serum BGP, as compared to PTH and AP, prevails as a valid marker of hyperparathyroid bone lesion in predialysis, while in dialysis it does not seem to add further information to that carried by other variables.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone substitution increases gene expression of members of the IGF family in cortical bone from women with adult onset growth hormone deficiency--relationship with bone turn-over

OBJECTIVE: To investigate the effects of growth hormone (GH) replacement therapy on bone matrix gene expression of insulin-like growth factors (IGFs) and markers of bone metabolism in women with adult-onset GH deficiency (GHD). DESIGN AND METHODS: Nineteen women, mean age 45 (range 24-56) years, were included in a double-blind, placebo-controlled parallel group study for 12 months. Biochemical markers were measured at baseline, 6 and 12 months. Bone biopsies were obtained and BMD was measured at baseline and after 12 months. RESULTS: Maximum responses were observed after 6 and 12 months, for bone resorptive and bone formative markers respectively. GH therapy enhanced gene expression in cortical bone of IGFs, GH-and calcitonin-receptor (CR) and osteoprotegerin (OPG), however with the most pronounced effects on CR and IGF-I. Changes in IGF-I gene expression during longitudinal follow-up were significantly correlated with changes in both circulating IGF-I (r = 0.82, p < 0.05), changes in markers of enhanced osteoclastic activity, measured both locally in bone (CR, r = 0.87, p < 0.01) and in serum (CTX-I, r = 0.86, p < 0.05), as well as serum bone ALP (r = 0.96, p < 0.01). CONCLUSIONS: This study indicates that both liver- and bone-derived IGF-I may be significant in mediating the effects of GH on bone metabolism in humans.