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.     

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.     

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.     

Antero-postero differences in cortical thickness and cortical porosity of T12 to L5 vertebral bodies

OBJECTIVE: This study will investigate interrelationships between the cortical shell and cancellous bone trabecular thickness, in vertebral bodies. METHODS: One hundred and sixty vertebral bodies from T12 to L5 were obtained at autopsy. The average age of the cohort was 59.3+/-22.1 years (range = 20-94 years). Cortical thickness, cortical porosity and trabecular thickness from the adjacent cancellous bone were measured. RESULTS: At the mid-vertebral body anterior cortical thickness was significantly greater than posterior cortical thickness (524 +/- 352 vs. 370 +/- 283 microm, respectively, P < 0.0001) and mid-anterior cortical porosity was significantly less than mid-posterior cortical porosity (24 +/- 14% vs. 32 +/- 16%, respectively, P < 0.0001). There were no anterior/posterior differences in trabecular thickness of the cancellous bone adjacent to the cortical walls. CONCLUSION: This study provides a novel perspective of T12 to L5 vertebral body bone, where measurement of cortical thickness and cortical porosity in a cohort of skeletally normal individuals revealed structural differences between load bearing anterior and posterior cortical walls. The data suggest that modulators of change to vertebral body bone may affect the cortical and trabecular bone differently. The relationships between cortical and cancellous bone suggest that the middle sectors of the vertebral body play a critical role in load bearing.     

Reduced bone formation and relatively increased bone resorption in absorptive hypercalciuria

Absorptive hypercalciuria (AH), a common stone-forming condition characterized biochemically by intestinal hyperabsorption of calcium and hypercalciuria may be associated with bone loss. In AH type I (AH-1), hypercalciuria persists despite restriction in dietary calcium intake. We therefore hypothesized that the skeleton may contribute to the hypercalciuria in this subgroup of patients. Histomorphometric analysis of iliac crest biopsies were performed on nine stone-formers with AH-1 and on nine matched normal subjects. After stabilization on a stone-prevention diet, calcium homeostasis in the stone formers was then evaluated on inpatient constant metabolic diet before and after short-term blockade of bone resorption by alendronate (10 mg daily, 17 days total). Compared with controls, the stone-formers had lower indices of bone formation (osteoblast surface/bone surface 1.8+/-2.1 vs 3.0+/-1.5%, P=0.04; wall thickness 35.8+/-6.9 vs 47.2+/-7.6%, P=0.001) and relatively higher bone resorption (osteoclast surface/bone surface 0.4+/-0.2 vs 0.2+/-0.2%, P=0.05). In the stone-formers, a short-term course of alendronate treatment corrected fasting urinary calcium (0.14+/-0.06 to 0.06+/-0.04 mg Ca/mg Cr, P=0.001) and marginally reduced 24-h urinary calcium by 48 mg/day (P=0.06). Increased intestinal calcium absorption and hypercalciuria persisted, but estimated calcium balance improved (P=0.007). Our results suggest that the hypercalciuria of AH-1 originates primarily from intestinal hyperabsorption of calcium, but bone resorption in excess of bone formation may contribute.     

Effect of aluminum and parathyroid hormone on osteoblasts and bone mineralization in chronic renal failure

Bone aluminum, quantitative bone histology, and plasma parathyroid hormone (PTH) were compared in 29 patients undergoing chronic hemodialysis. Histologic techniques included double tetracycline labeling and histochemical identification of osteoclasts and osteoblasts. Bone aluminum was measured chemically by flameless atomic absorption spectrophotometry, and histochemically. When measured chemically, the bone aluminum was 67 +/- 46 (SD) mg/kg dry weight (normal 2.4 +/- 1.2 mg/kg); histochemically, aluminum was present at 2.9 +/- 4.4% of trabecular surface. The biochemical and histochemical results agreed well (r = 0.80, P less than 0.001). No double tetracycline labels were seen at the mineralization front where aluminum was deposited, indicating cessation of mineralization at these sites. The osteoblast surface correlated positively with plasma PTH (r = 0.67, P less than 0.001) and negatively with bone aluminum level (r = -0.42, P less than 0.05). Multiple linear regression showed a correlation of aluminum with osteoblasts additional to that of PTH, consistent with a direct effect of aluminum in depressing osteoblast numbers. Though a relationship between PTH and chemically determined bone aluminum level could not be demonstrated, there was a negative correlation between osteoclast count and aluminum, and the nine patients with severe hyperparathyroid bone disease had lower chemically determined aluminum levels than the other patients. These results suggest that aluminum (a) directly inhibits mineralization, (b) is associated with decreased PTH activity and hence osteoblast numbers, and (c) directly reduces osteoblast numbers. In addition to inducing severe, resistant osteomalacia, aluminum appears to contribute to the mild osteomalacia commonly seen in renal failure, characterized by extensive thin osteoid and low tetracycline and osteoblast surfaces.     

ACE genotype and ACE inhibitors induced renoprotection in chronic proteinuric nephropathies1

ACE genotype and ACE induced renoprotection in chronic proteinuric nephropathies. BACKGROUND: Whether angiotensin-converting enzyme (ACE) gene polymorphism affects disease progression and response to ACE inhibitor therapy in nondiabetic proteinuric nephropathies is not clearly established. METHODS: The relationship between insertion/deletion (I/D) genotypes and proteinuria, rate of glomerular filtration rate decline (DeltaGFR)-centrally evaluated by repeated measures of iohexol plasma clearance-and incidence of end-stage renal disease (ESRD) was prospectively evaluated in 212 patients with nondiabetic proteinuric chronic nephropathies enrolled in the Ramipril Efficacy in Nephropathy (REIN) trial, where patients were randomly assigned to ramipril or conventional treatment. RESULTS: The DeltaGFR +/- SEM (-0.38 +/- 0.09 vs. -0.50 +/- 0.08 vs. -0.36 +/- 0.06 mL/min/1.73 m2 per month) and incidence of ESRD (19 vs. 22 vs. 25%) in the three subgroups with the II, ID, and DD genotypes, respectively, were comparable. Of note, DeltaGFR (-0.28 +/- 0.07 vs. -0.43 +/- 0.09 mL/min/1.73 m2 per month) and incidence of ESRD [14% vs. 36%, P = 0.04, RR (95% CI), 2.62 (1.02 to 6.71)] were lower in ramipril than in conventionally treated patients in the DD genotype, but not in the II and ID genotype. Either at univariate (P = 0.04) or at multivariate (P = 0.01) analysis, ramipril significantly predicted a lower incidence of events in DD, but not in II and ID patients. At three months, ramipril decreased proteinuria more effectively in DD (-38.2%) than in the II (-26.7%) or ID (-19.2%) genotype. In DD (but not in II or ID) ramipril-treated patients, a short-term reduction in proteinuria correlated with DeltaGFR over the entire follow-up period (P = 0.02, r = -0.41). CONCLUSIONS: In nondiabetic proteinuric nephropathies, the ACE I/D polymorphism does not predict disease progression, but is a strong predictor of ACE inhibition-associated renoprotection in that proteinuria, DeltaGFR, and progression to ESRD are effectively reduced in patients with the DD, but not in those with the II or ID genotype.     

Ascorbic Acid Deficiency, Iron Overload and Alcohol Abuse Underlie the Severe Osteoporosis in Black African Patients with Hip Fractures — A Bone Histomorphometric Study

Osteoporosis and femoral neck fractures (FNF) are uncommon in black Africans although osteoporosis accompanying iron overload (from traditional beer brewed in iron containers) associated with ascorbic acid deficiency (oxidative catabolism by iron) has been described from sub-Saharan Africa. This study describes histomorphometric findings of iliac crest bone biopsies and serum biochemical markers of iron overload and of alcohol abuse and ascorbic acid levels in 50 black patients with FNFs (29 M, 21 F), age 62 years (40–95) years (median [min-max]), and in age- and gender-matched black controls. We found evidence of iron overload in 88% of patients and elevated markers of alcohol abuse in 72%. Significant correlations between markers of iron overload and of alcohol abuse reflect a close association between the two toxins. Patients had higher levels of iron markers, i.e., siderin deposits in bone marrow (P < 0.0001), chemical non-heme bone iron (P = 0.012), and serum ferritin (P = 0.017) than controls did. Leukocyte ascorbic acid levels were lower (P = 0.0008) than in controls. The alcohol marker mean red blood cell volume was elevated (P = 0.002) but not liver enzymes or uric acid. Bone volume, trabecular thickness, and trabecular number were lower, and trabecular separation was greater in patients than in controls, all at P < 0.0005; volume, surface, and thickness of osteoid were lower and eroded surface was greater, all at P < 0.0001. There was no osteomalacia. Ascorbic acid deficiency accounted significantly for decrease in bone volume and trabecular number, and increase in trabecular separation, osteoid surface, and eroded surface; iron overload accounted for a reduction in mineral apposition rate. Alcohol markers correlated negatively with osteoblast surface and positively with eroded surface. Relative to reported data in white FNF patients, the osteoporosis was more severe, showed lower osteoid variables and greater eroded surface; FNFs occurred 12 years earlier and were more common among men. We conclude that the osteoporosis underlying FNFs in black Africans is severe, with marked uncoupling of resorption and formation in favor of resorption. All three factors—ascorbic acid deficiency, iron overload, and alcohol abuse—contributed to the osteoporosis, in that order.     

Stainable aluminum and not aluminum content reflects bone histology in dialyzed patients

Quantitative evaluation of stainable bone aluminum and measurement of bone aluminum content were done in 55 patients on chronic maintenance dialysis. All patients underwent bone biopsies. Histomorphometry of static and dynamic parameters of bone structure, bone formation and resorption, and quantitation of stainable bone aluminum at the osteoid-bone interface were performed. In addition, bone aluminum content was measured by atomic absorption spectrophotometry. Bone aluminum content was elevated in all patients (81 +/- 9.6 vs. 18 +/- 6 micrograms/g dry wt) and stainable aluminum was found in 47% of them. All patients with predominant low-turnover osteomalacia or adynamic bone disease displayed stainable bone aluminum. In contrast, stainable bone aluminum was not present in individuals with predominant-hyperparathyroid bone disease. Patients with stainable aluminum had lower bone mass (P less than 0.05), higher volume and surface of lamellar osteoid (P less than 0.01), less volume and surface of woven osteoid (P less than 0.05 and P less than 0.01), lower osteoblastic and osteoclastic indices (P less than 0.01), less doubly labelled osteoid seams, lower mineral apposition rate and lower bone formation rates (P less than 0.05 to P less than 0.01). Stainable aluminum correlated with volume of lamellar osteoid and cellular parameters of bone formation and resorption, mineral apposition rate, and bone formation rates (P less than 0.05 to P less than 0.001). In contrast, bone aluminum content correlated with volume of lamellar osteoid only (P less than 0.001). These findings indicate that stainable aluminum at the mineralization front and not aluminum content of bone reflects the histopathologic changes found in bone of dialyzed patients.     

Aluminum deposition in the bone of patients with chronic renal failure--detection of aluminum accumulation without signs of aluminum toxicity in bone using acid solochrome azurine

In this study, the sensitivity of the aurine tricarboxylic acid (ATA) and acid solochrome azurine (ASA) stain for aluminum were compared under special consideration of the relationship to bone histology in renal osteodystrophy. Al deposition in iliac crest bone biopsies taken from 78 patients with chronic renal failure (CRF) was assessed histochemically using the ATA and ASA stain; the Al accumulation was correlated with bone histology and histomorphometry. Significantly more Al was detectable with the ASA method on trabecular bone surfaces and cement lines (18 +/- 20% vs 4 +/- 12% on surfaces; 13 +/- 18% vs 0.4 +/- 1.3% on cement lines). In 31 cases in which ATA yielded negative results, ASA in contrast indicated Al deposits on up to 20% of the trabecular bone surface. The specimens with more Al on the trabecular bone surface had a significantly higher osteoid volume and osteoid surface. With ATA, these differences were observed at a staining of > or = 10% of the trabecular surface, with ASA at a staining of > or = 40% of the trabecular surface. Therefore, it seems to be possible to detect a very low Al deposition, without any Al-induced changes in bone morphology or signs of Al toxicity in the bone using the ASA method. By contrast, a positive ATA stain is mainly found in biopsies with typical signs of Al-induced changes of histomorphometric bone parameters. We, therefore, recommend the routine use of the ASA stain to detect Al deposition in bone.     

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.     

Antiproteinuric effect of losartan in non-diabetic renal disease is not dependent on ACE insertion/deletion polymorphism

BACKGROUND: The antiproteinuric effect of angiotensin-converting enzyme (ACE) inhibitors appears to vary depending on the ACE insertion (I)/deletion (D) genotype in non-diabetic nephropathy. This interaction may be overcome by using an angiotensin II receptor blocker. We evaluated the short-term antiproteinuric effect of losartan according to the ACE I/D genotype in patients with non-diabetic proteinuric renal diseases. METHODS: Ninety-nine (II/ID/DD: 36/52/11) non-diabetic patients with overt proteinuria were enrolled. The patients received losartan 50 mg daily followed by 100 mg in two treatment periods each lasting 12 weeks. Clinical parameters including proteinuria were measured at baseline and at the end of each period. RESULTS: At baseline each genotype (II/ID/DD) had comparable mean arterial blood pressure (mean +/- SD) 103.2 +/- 11.1/102.7 +/- 10.6/104.1 +/- 15.3; proteinuria (geometric mean, 95% CI, mg/day) 1,839 (1,518-2,227)/1,998 (1,683-2,372)/1,613 (1,072-2,427), and creatinine clearance (ml/min/1.73 m(2)) 65.7 +/- 28.4/63.2 +/- 27.8/68.8 +/- 25.3, respectively. Both doses of losartan significantly lowered blood pressure and proteinuria (p < 0.05 vs. baseline), and losartan 100 mg was more effective than 50 mg in reducing proteinuria (52.5 +/- 29.0 vs. 40.5 +/- 30.8%, respectively, p = 0.001). No differences in the antiproteinuric effect of losartan was observed among the ACE I/D genotype. Losartan 100 mg demonstrated a comparable degree of mean arterial pressure (mean +/- SD, %) (II/ID/DD, 13.3 +/- 7.6/10.8 +/- 9.8/13.0 +/- 11.6, respectively, p = NS) and proteinuria reduction (mean, 95% CI) among the three genotypes (51.4% (40.3-62.5%)/53.4% (45.5-61.4%)/51.4% (40.0-63.8%), respectively, p = NS). CONCLUSION: Our data suggest that losartan provides a similar short-term antiproteinuric response for all three genotypes of ACE I/D genotype in non-diabetic proteinuric chronic renal disease.     

Deficient bone formation in idiopathic juvenile osteoporosis: a histomorphometric study of cancellous iliac bone.

Idiopathic juvenile osteoporosis (IJO), a rare cause of osteoporosis in children, is characterized by the occurrence of vertebral and metaphyseal fractures. Little is known about the histopathogenesis of IJO. We analyzed by quantitative histomorphometry iliac crest biopsies from 9 IJO patients (age, 10.0-12.3 years; 7 girls) after tetracycline labeling. Results were compared with identically processed samples from 12 age-matched children without metabolic bone disease and 11 patients with osteogenesis imperfecta type I. Compared with healthy controls, cancellous bone volume (BV) was markedly decreased in IJO patients (mean [SD]: 10.0% [3.1%] vs. 24.4% [3.8%]), because of a 34% reduction in trabecular thickness (Tb.Th) and a 37% lower trabecular number (Tb.N; p < 0.0001 each; unpaired t-test). Bone formation rate (BFR) per bone surface was decreased to 38% of the level in controls (p = 0.0006). This was partly caused by decreased recruitment of remodeling units, as shown by a trend toward lower activation frequency (54% of the control value; p = 0.08). Importantly, osteoblast team performance also was impaired, as evidenced by a decreased wall thickness (W.Th; 70% of the control value; p < 0.0001). Reconstruction of the formative sites revealed that osteoblast team performance was abnormally low even before mineralization started at a given site. No evidence was found for increased bone resorption. Compared with children with osteogenesis imperfecta (OI), IJO patients had a similarly decreased cancellous BV but a much lower bone turnover. These results suggest a pathogenetic model for IJO, in which impaired osteoblast team performance decreases the ability of cancellous bone to adapt to the increasing mechanical needs during growth. This will finally result in load failure at sites where cancellous bone is essential for stability.     

Comparison of trabecular bone microarchitecture and remodeling in glucocorticoid-induced and postmenopausal osteoporosis.

Long-term treatment with glucocorticoids (GCs) leads to a rapid bone loss and to a greater risk of fractures. To evaluate the specific effects of this treatment on cancellous bone remodeling, structure, and microarchitecture, we compared 22 transiliac biopsy specimens taken in postmenopausal women (65 +/- 6 years) receiving GCs (> or = 7.5 mg/day, for at least 6 months) and 22 biopsy specimens taken in age-matched women with postmenopausal osteoporosis (PMOP), all untreated and having either at least one vertebral fracture or a T score < -2.5 SD. On these biopsy specimens, we measured static and dynamic parameters reflecting trabecular bone formation and resorption. Also, we performed the strut analysis and evaluated the trabecular bone pattern factor (TBPf), Euler number/tissue volume (E/TV), interconnectivity index (ICI), and marrow star volume (MaSV). Glucocorticoid-induced osteoporosis (GIOP), when compared with PMOP, was characterized by lower bone volume (BV/TV), trabecular thickness (Tb.Th), wall thickness (W.Th), osteoid thickness (O.Th), bone formation rate/bone surface (BFR/BS), adjusted mineral apposition rate/bone surface (Aj.AR/BS), and higher ICI and resorption parameters. After adjustment for BV/TV, the W.Th remained significantly lower in GIOP (p < 0.0001). The active formation period [FP(a+)] was not different. Patients with GIOP were divided into two groups: high cumulative dose GCs (HGCs; 23.7 +/- 9.7 g) and low cumulative dose GCs (LGCs; 2.7 +/- 1.2 g). HGC when compared with LGC was characterized by lower W.Th (p < 0.05), BV/TV (p < 0.001), Tb.Th (p < 0.05), trabecular number (Tb.N; p < 0.05), FP(a+)(p < 0.05), and nodes (p < 0.05), and higher E/TV (p < 0.05), ICI (p < 0.005), and TBPf (p < 0.05). When HGC was compared with PMOP, the results were similar except for the MaSV, which was significantly higher (p < 0.005). In summary, GIOP was characterized by lower formation and higher resorption than in PMOP, already present after LGC. With HGCs, these changes were associated with a more dramatic bone loss caused by a major loss of trabecular connectivity.     

The skeletal response to estrogen is impaired in female but not in male steroid receptor coactivator (SRC)-1 knock out mice

Estrogen (E) is critical for the maintenance of bone mass in both female and male mice and steroid receptor coactivator (SRC)-1 has been shown to be important for mediating E effects on bone, at least in female mice. In the present study, we defined the skeletal phenotype of male SRC-1 knock out (KO) mice and compared it with their female littermates. Further, to determine the role of SRC-1 in mediating effects of E on bone in male mice, we examined the skeletal effects of gonadectomy (gnx) with or without E replacement in male mice and placed these findings in the context of our previous studies in female SRC-1 KO mice. Analysis of a large group of male (WT, n=67; SRC-1 KO, n=56) and female (WT, n=66; SRC-1 KO, n=70) mice showed a significant decrease in trabecular volumetric bone mineral density (vBMD) in SRC-1 KO mice compared to their WT littermates in both genders (male SRC-1 KO, 275+/-3 vs. WT, 295+/-3 mg/cm(3), P<0.001; female SRC-1 KO, 210+/-2 vs. WT, 221+/-2 mg/cm(3), P<0.001). Following gnx and E replacement (10 microg/kg/day), we previously demonstrated that SRC-1 KO female mice have a defect in E action in trabecular, but not in cortical bone. In contrast, we now demonstrate that the same dose of E administered to gnx'd male SRC-1 KO mice was sufficient to prevent trabecular bone loss in these mice. For example, in WT female mice, gnx followed by E replacement maintained spine BMD (1.2+/-3.4% vs. baseline) as compared to gnx without E replacement (-12.7+/-2.6%, P<0.001 vs. sham); this effect of E was absent in SRC-1 KO female mice. By contrast, the identical dose of E was equally effective in maintaining spine BMD in E-treated gnx'd male WT (-5.2+/-5.1% vs. baseline) and male SRC-1 KO (-5.4+/-5.3%) mice, respectively, as compared to gnx'd mice without E treatment (WT, -17.6+/-2.5%, P=0.02; SRC-1 KO, -28.6+/-2.6%, P<0.001 vs. sham). E treatment was effective in suppressing cancellous bone turnover in both gnx'd WT and SRC-1 KO male mice as determined by significant reductions in osteoblast and osteoclast numbers; however, in female mice, E treatment only suppressed bone turnover in WT but not in SRC-1 KO mice. Collectively, these findings demonstrate that loss of SRC-1 results in trabecular osteopenia in male and female mice, but in contrast to female mice, this is not due to any detectable resistance to E action in trabecular bone in male SRC-1 KO mice.     

Association of sex hormone status with the bone loss of renal transplant patients.

BACKGROUND: Bone loss is an important problem in renal transplantation recipients. The role of sex hormones in this setting has not been previously addressed. The objective was to investigate whether sex hormone status is associated with bone mass loss in renal transplant recipients. METHODS: Thirty patients (16 men and 14 women, of which eight were post-menopausal) were studied by bone densitometry and bone biopsy. In women, serum oestradiol levels and menopausal status were determined; in men, serum testosterone levels were assessed. RESULTS: Mean age was 48+/-11 years. Time on dialysis was 13+/-17 months, and time since transplantation was 125+/-67 months. Thirteen patients were on cyclosporine A (CsA) monotherapy, 12 on azathioprine plus prednisolone (PRED) dual therapy, and five on CsA, azathioprine and PRED triple therapy. In men, serum testosterone levels were 19.7+/-6.8 nmol/l (mean+/-SD). In pre-menopausal women, oestradiol serum levels were 209(128-289) pmol/l (median (percentiles 25-75%)), and in post-menopausal women 93(54-299) pmol/l (non-significant). Univariate analysis in women demonstrated that serum oestradiol levels were positively correlated with Z scores of osteoblast surface (r=0.70, P=0.005), osteoid surface (r=0.75, P=0.002) and trabecular wall thickness (r=0.68, P=0.008). In men, a weak correlation was seen between serum testosterone levels and the cumulative dose of PRED (r=-0.52, P=0.06). In the multivariate analysis, two models of multiple regression were employed (one for women and one for men), considering the densitometric and histomorphometric variables (Z scores) as dependent variables. Serum testosterone in men did not predict any of the densitometric nor histomorphometric variables analysed, while serum oestradiol in women was an independent predictor for the osteoblast surface (r=0.81, P=0.003), osteoid surface (r=0.82, P=0.009) and trabecular wall thickness (r=0.54, P=0.05). CONCLUSIONS: In female renal transplant recipients, serum oestradiol levels independently predict the bone status, while in men, factors other than testosterone seem to influence bone loss. Our results give rise to the hypothesis that sex hormone replacement therapy may play a role in prevention and/or treatment of the bone loss in women following renal transplantation.     

Effect of fluoride on aluminum-induced bone disease in rats with renal failure.

Aluminum (Al) accumulation in renal failure is an etiological factor in the pathogenesis of low turnover bone disease. Aluminum-induced impairment of mineralization has been related to a reduced extent of active bone-forming surface. The present study investigated the effect of fluoride, a potent stimulator of osteoblast number, on the toxicity of aluminum in rats with renal failure (Nx). Following a large parenteral aluminum load (3.2 mg/kg x day) over a period of nine weeks, bone histomorphometry of vertebral cancellous bone revealed a severe low-turnover osteodystrophy as evidenced by a fall in osteoblastic osteoid surfaces and mineral apposition rates. Concurrent administration of fluoride [20 mg/liter (F20) or 40 mg/liter (F40) supplied with the drinking water] resulted in a significant increase in the number of osteoblasts (Nx+Al+F40 vs. Nx+Al, 33.75 +/- 2.83 vs. 1.81 +/- 0.43 mm-1, P less than 0.001) together with an overall reduced deposition of aluminum in bone (469.3 +/- 24.6 vs. 592.2 +/- 28.3 micrograms/g, P less than 0.01). However, there was an increase in the fraction of osteoid surface exhibiting stainable aluminum at the bone-osteoid interface (70.7 +/- 7.1 vs. 44.3 +/- 6.0%, P less than 0.005). Fluoride-exposed rats accumulated a significantly larger osteoid volume, suggesting an exacerbation of the osteomalacic lesion, and furthermore, dynamic histomorphometric parameters remained depressed. These results indicate that fluoride has a distinct effect on the pattern of aluminum deposition in bone. In addition, fluoride antagonizes the aluminum-induced reduction in osteoblast number but provides no amelioration of the impaired mineralization in aluminum-intoxicated rats. Thus, in this model a decrease in the extent of osteoblast surface does not account for the development of aluminum-related bone disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

Genetic regulation of cortical and trabecular bone strength and microstructure in inbred strains of mice.

The inbred strains of mice C57BL/6J (B6) and C3H/HeJ (C3H) have very different femoral peak bone densities and may serve as models for studying the genetic regulation of bone mass. Our objective was to further define the bone biomechanics and microstructure of these two inbred strains. Microarchitecture of the proximal femur, femoral midshaft, and lumbar vertebrae were evaluated in three dimensions using microcomputed tomography (microCT) with an isotropic voxel size of 17 microm. Mineralization of the distal femur was determined using quantitative back-scatter electron (BSE) imaging. MicroCT images suggested that C3H mice had thicker femoral and vertebral cortices compared with B6. The C3H bone tissue also was more highly mineralized. However, C3H mice had few trabeculae in the vertebral bodies, femoral neck, and greater trochanter. The trabecular number (Tb.N) in the C3H vertebral bodies was about half of that in B6 vertebrae (2.8(-1) +/- 0.1 mm(-1) vs. 5.1(-1) +/- 0.2 mm(-1); p < 0.0001). The thick, more highly mineralized femoral cortex of C3H mice resulted in greater bending strength of the femoral diaphysis (62.1 +/- 1.2N vs. 27.4 +/- 0.5N, p < 0.0001). In contrast, strengths of the lumbar vertebra were not significantly different between inbred strains (p = 0.5), presumably because the thicker cortices were combined with inferior trabecular structure in the vertebrae of C3H mice. These results indicate that C3H mice benefit from alleles that enhance femoral strength but paradoxically are deficient in trabecular bone structure in the lumbar vertebrae.     

Bone histology and bone mineral density after correction of acidosis in distal renal tubular acidosis

BACKGROUND: The association between chronic metabolic acidosis and alterations in bone cell functions has been demonstrated in vitro and in animal studies. However, the causal role of acidosis and the effects of alkaline therapy on bone histology and bone mineral density in chronic metabolic acidosis have never been systematically demonstrated in humans. This study was conducted to examine the alterations in bone mineral density and bone histology before and after correction of acidosis among patients with distal renal tubular acidosis (dRTA) METHODS: Correction of metabolic acidosis by potassium citrate was done in non-azotemic dRTA patients, 6 females and 4 males, who had never received long-term alkaline therapy before enrolling into this study. Blood chemistries, serum intact parathyroid hormone, and 24-hour urine collection for the determination of urinary calcium, phosphate, sodium, potassium, bone mineral density determination, and transiliac bone biopsy were done in all patients at baseline and after one year of potassium citrate therapy. RESULTS: Significant elevations in serum bicarbonate (16.5 +/- 3.0 vs. 24.6 +/- 2.8 mEq/L, P < 0.05) and urinary potassium excretion (35.2 +/- 7.9 vs. 55.4 +/-3.5 mEq/L, P < 0.05) were observed after potassium citrate therapy. No significant alterations in other serum and urine electrolytes were found after the therapy. Serum intact parathyroid hormone level was also significantly elevated after one year of treatment (12.8 +/- 7.3 vs. 26.2 +/- 8.7 pg/mL, P < 0.05). Bone formation rate was significantly suppressed at baseline and was normalized by the treatment (0.02 +/- 0.02 vs. 0.06 +/- 0.03 microm(3)/microm(2)/day, P < 0.05). There were non-significant elevations in trabecular bone volume, osteoblastic and osteoclastic numbers. Bone mineral densities in dRTA patients were also significantly decreased below normal values in most studied areas at baseline and were significantly elevated at the trochanter of femur (0.677 +/- 0.136 vs. 0.748 +/- 0.144 g/c m(2), P < 0.05) and total femur (0.898 +/- 0.166 vs. 0.976 +/- 0.154 g/c m(2), P < 0.05) after the treatment. CONCLUSIONS: This study demonstrates that alkaline therapy corrects abnormal bone cell function and elevates bone mineral density in dRTA patients, indicating the causal role of acidosis in the alterations of bone cell functions and reduction in bone mineral density. Parathyroid gland activity also may be involved in the adaptation of the body to chronic metabolic acidosis.     

Bone remodeling at the endocortical surface of the human femoral neck: a mechanism for regional cortical thinning in cases of hip fracture.

Endocortical remodeling and wall thickness (W.Th.) were measured in femoral neck bone from 12 female fracture cases (81.3 +/- 1.5 years) and 12 sex-matched controls (81.9 +/- 1.9 years). Regionally, osteoid and eroded surface were increased, whereas W.Th. was reduced. These processes likely contribute to cortical bone loss seen in hip fracture. INTRODUCTION: Because periosteal expression of alkaline phosphatase was similar between cases and controls, we hypothesized that the mechanism causing the marked femoral neck cortical thinning associated with hip fracture may be net endocortical bone loss. METHODS: Twelve female cases of femoral neck fracture (mean age = 81.3 +/- 1.5 years) and 12 age- and sex-matched postmortem controls (mean age = 81.9 +/- 1.9 years) were included in the study. Samples of their femoral neck bone were embedded in methyl methacrylate, sectioned at 10 microm, and stained with Solochrome cyanine R and Goldner's trichrome for the detection of osteoid (%OS/BS) and resorption surfaces (%ES/BS) respectively. In addition, wall thickness (W.Th.) and lamellar thickness (Lm.Th.) data were also collected from identifiable endocortical bone packets as a measure of formative potential. RESULTS AND CONCLUSIONS: %OS/BS was significantly elevated in the anterior (control = 3.4 +/- 0.7: fracture = 11.0 +/- 2.3; p = 0.0001), inferior (3.4 +/- 1.0: 9.9 +/- 3.0; p = 0.0009), and posterior quadrants (3.2 +/- 0.8: 9.1 +/- 2.3; p = 0.0021). Only for anterior region was increased %ES/BS demonstrated in the fracture group (2.8 +/- 0.6: 5.3 +/- 0.7; p = 0.055). W.Th. (mm) was reduced only in the inferior region of the fracture cases (control = 33.7 +/- 1.2: fracture = 30.6 +/- 0.9; p = 0.013), whereas Lm.Th. was also reduced inferiorly (control = 2.7 +/- 0.08: fracture = 2.5 +/- 0.08; p = 0.042). These data suggest that an endocortical remodeling imbalance involving reduced bone formation within inferior region coupled with elevated anterior resorption may make an important contribution to the cortical thinning observed in cases of femoral neck fracture.