A stochastic analysis of iliac trabecular bone dynamics

Published normal histomorphometric data were used to derive distributions of thicknesses of trabecular plates and completed bone remodelling units (the basic multicellular unit carrying out bone remodelling, the BMU, when completed is termed a structural unit BSU). A stochastic model was set up to investigate the predictions of current BMU theory. Each of 100 trabecular "thicknesses" was drawn from the appropriate normal distribution using a pseudorandom number generator. Each day, each of its two surfaces when quiescent was assumed to have a 1:900 chance of initiating a remodelling cycle. Resorption (active, 12 days; reversal phase, 27 days) was followed by formation (94 +/- 35 days) and resulted in BMU balance when resorption depth was 36.8 +/- 9.2 micron. Fenestration (thickness less than 0) was assumed to lead to permanent loss of the trabecula. The original model unrealistically increased its mean trabecular thickness as thin trabeculae were lost. This was corrected by assuming that thin trabeculae had greater osteoblastic stimulation and a consequent tendency to thicken, perhaps due to higher mechanical loading. Over 20 years, 14% of trabeculae were lost when the BMU balance was exact and the distribution of trabecular thicknesses was unchanged. About one-half of fenestrations were due to deeper-than-average resorption cavities developing in thin trabeculae, and the remainder to coincident remodelling on both surfaces. A 10% fall in osteoblast lifespan resulted in an additional 36.7% loss of trabecular bone volume and mean trabecular thickness fell to 83.1 micron, compatible with Courpron's data. Simulating more rapid mechanisms of bone loss, approximately 50% of trabeculae could be lost after ten years by the arrest of bone formation; the doubling of resorption depth with unchanged bone formation; and a doubling in the rate of initiation of new BMUs with unchanged bone formation rate, all three followed by complete recovery of BMU balance after only two years. In each case, mean trabecular thickness fell only transiently but trabeculae continued to be lost after recovery. Prolonged osteoblast life span was the most likely explanation for the increased mean trabecular thicknesses and trabecular bone volumes seen in patients with osteoporosis, when treated with sodium fluoride plus calcium supplements or daily injections of parathyroid peptide hPTH 1-34.     

Structural and histomorphometric studies of iliac crest trabecular and cortical bone in autosomal dominant osteopetrosis: a study of two radiological types

Cylindrical iliac crest biopsies were obtained from 16 patients with autosomal dominant osteopetrosis after intravital double labeling with tetracycline, and compared with normal age- and sex-matched controls. Ten patients had the radiological type I (5 women, 5 men, aged 17-62 years, mean 42) characterized by diffuse, symmetrical osteosclerosis and enlarged thickness of the cranial vault. Six patients had type II (2 women, 4 men, aged 22-44 years, mean 36), where "Rugger Jersey Spine" and endobone are characteristic findings. Structural studies of cortical and trabecular bone were performed, and trabecular bone resorption and formation rates were studied using dynamic histomorphometry. The total biopsy length (C. Wi) were increased in type I (p less than 0.05), and unchanged in type II. Both types showed increased cortical width (Ct. Wi) (p less than 0.01 and p less than 0.05, respectively), and decreased fractional width of cancellous bone (Cn.Wi/C.Wi) (p less than 0.01 and p less than 0.05). The fractional trabecular bone volume (BV/TV) and trabecular thickness (Tb. Th) were both significantly increased in type I (p less than 0.05), while resorptive and formative indices of trabecular bone remodeling were normal. No difference was found in trabecular bone balance, which was slightly positive in both patients and controls. In type II osteopetrosis the eroded surfaces (OS/BS) were significantly increased (p less than 0.01), as was the total resorptive period RP) (p less than 0.05). The resorption depth (R.D.) was normal, while the resorption rate (MRR) was insignificantly decreased. Many big multinucleated osteoclasts were seen in this type suggesting defective resorptive function.(ABSTRACT TRUNCATED AT 250 WORDS)     

Primary hyperparathyroidism: iliac crest trabecular bone volume, structure, remodeling, and balance evaluated by histomorphometric methods.

Iliac bone biopsies from 69 patients (48 females, 21 males; median age 58 years; range 17-79 years) with primary hyperparathyroidism (PHP) were examined, and static histomorphometric parameters compared to 30 age- and sex-matched normal controls. The control group for the dynamic parameters constituted 20 sex-matched younger normal controls. Fractional volume of trabecular bone was normal, but the trabeculae were thinner (p less than 0.05) in PHP. The structural parameters marrow space star volume, intertrabecular distance, and mean trabecular plate density were not significantly different in PHP patients compared to normal controls, but the age-related increase, for females, in marrow space star volume and decrease, for both sexes, in mean plate density observed in the controls were not noticed in the PHP group. Trabecular bone remodeling was found significantly increased in the PHP patients reflected by increased extension of eroded (p less than 0.001), osteoid (p less than 0.001), and labeled surfaces (p less than 0.05). The activation frequency was increased by approximately 50% (p less than 0.001). Neither PHP patients nor controls showed age-related decrease in trabecular thickness, and accordingly in both groups the bone balance per remodeling cycle was very close to and not significantly different from zero. Normal postmenopausal women (age greater than or equal to 50 yr) had lower trabecular bone volume (p less than 0.001) and higher intertrabecular distance than normal pre-menopausal women (age less than 50 yr).(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationships between calcium and phosphorus homeostasis, parathyroid hormone levels, bone aluminum, and bone histomorphometry in patients on maintenance hemodialysis

Serum biochemistry related to calcium and phosphorus homeostasis and parathyroid function was studied together with bone histomorphometry after double-labeling with tetracycline and staining for aluminum in 17 patients without symptoms of bone disease, treated with maintenance hemodialysis for at least 6 months. A close correlation was found between the serum level of parathyroid hormone (PTH) and bone resorption surfaces and bone formation rates, both at tissue and basic multicellular unit (BMU) levels. The patients could be divided into a high turnover group with a normal mineralization process and a low turnover group with markedly defective mineralization. The second group was further characterized by lower PTH and higher fractional aluminum-stained trabecular bone surfaces. For the whole patient material, the fractional aluminum-stained surfaces related inversely to tetracycline-labeled surfaces and to bone formation rates at both BMU and tissue levels, but not to the time on dialysis or to the cumulative ingested amount of aluminum hydroxide. The data provide evidence that PTH or PTH-related factors, besides activating bone remodeling, directly enhance bone formation in dialysis patients and that aluminum incorporation into bone is associated with a progressive disturbance of bone mineralization.     

Contrasting microanatomy of idiopathic and corticosteroid-induced osteoporosis

Previous studies of microanatomic changes in normal bone with age have suggested that underlying differences in bone remodeling between male subjects and female subjects give rise to different patterns of bone loss. The relationship between microanatomic and histologic levels of organization are herein examined in two groups of osteoporotic subjects, one with idiopathic and the other with corticosteroid-induced osteoporosis. Using tissue from the iliac crest, total trabecular surface and trabecular width and number were measured, together with bone volume and static and dynamic indices of formation (osteoid surface, seam width, mean wall thickness, lamellar thickness, calcification fronts, and mineralization rate) and resorption (total resorption cavities and osteoclast incidence). The results suggest that while a similar loss of trabecular bone volume is common to both groups, there is a marked distinction in the distribution of the remaining bony tissue and indices of remodeling. A decline in trabecular number accompanied by a relative increase in resorption characterized both sexes with primary osteoporosis, whereas a decline in trabecular width associated with depressed formation was the predominant feature in the secondary disease. Thus trabecular attenuation is principally the manifestation of depressed formation, while trabecular discontinuity is primarily the manifestation of bone resorption.     

Continuous infusion of 1,25-dihydroxyvitamin D3 stimulates bone turnover in the normal young mouse

The effects of continuous administration of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on mineral and bone metabolism have been examined in the normal mouse. Four doses (0.05-0.25 micrograms/kg/day) of 1,25(OH)2D3 were infused continuously for 4 weeks in 21-day-old intact animals. Mineral and skeletal changes were evaluated by analytical methods and by histomorphometric analysis of endosteal bone formation and resorption parameters. All doses of 1,25(OH)2D3 increased the fractional osteoclastic surface and the osteoclast number in conjunction with increased hydroxyproline excretion. 1,25(OH)2D3 induced a dose-dependent elevation of the calcification rate, reduction of the mean osteoid seam thickness, and shortening of the mineralization lag time. In addition, there was a dose-related increase in the extent of tetracycline double-labeled osteoid surface and a concurrent rise in the fractional osteoblastic surface associated with elevated serum alkaline phosphatase levels. Increased bone formation appeared to have been balanced by increased bone resorption since the trabecular bone volume remained unchanged. Except at the highest dose given, serum calcium and phosphate concentrations remained normal in spite of increased bone mobilization and presumably enhanced intestinal absorption of minerals. Urinary cAMP and TmP/GFR remained normal, suggesting that parathormone secretion was not altered. The results show that continuous 1,25(OH)2D3 infusion in the young mouse produces a dose-dependent stimulation of bone mineralization rate in response to increased osteoclastic bone resorption. The data indicate that 1,25(OH)2D3 can regulate bone turnover as well as mineral homeostasis in the young mouse.     

Bone changes after alcohol abuse

In this study bone morphometric findings in 19 heavy or moderate drinkers are compared with those in 43 non-drinkers (22 non-osteoporotic patients with osteo-arthritis (OA) and 21 osteoporotic patients with femoral neck fractures (FNFs). Transiliac bone biopsy specimens were examined for assessment of trabecular bone volume and thickness, bone resorption and formation, osteoid seam length and width and the mineralization front by quantitative histomorphometry and microradiography. Trabecular bone volume and thickness were significantly diminished in the drinking group when compared with those in the 22 non-drinking patients with OA (P less than 0,005 and P less than 0,0001 respectively). Bone formation was significantly lower in the drinkers than in the OA group (P less than 0,0005), and bone resorption was significantly greater in the drinkers than in the OA (P less than 0,005) and FNF (P less than 0,01) groups. In heavy drinkers bone formation was significantly lower (P less than 0,05) than in moderate drinkers. The extent of the mineralization front was significantly lower in the drinking group than in the OA (P less than 0,005) and FNF (P less than 0,0005) groups. Osteoid seam length and width did not differ in the three groups. The presence of abnormal liver function test results did not significantly affect any of the parameters. It is concluded that alcohol abuse is associated with: (i) uncoupling of bone resorption and bone formation; (ii) reduced trabecular bone volume and thickness; and (iii) a mild mineralization defect.     

Bone histology in adults with aseptic necrosis. Histomorphometric evaluation of iliac biopsies in seventy-seven patients

We studied the bone histology by histomorphometric methods in transiliac bone-biopsy specimens from seventy-seven adult patients with aseptic osteonecrosis and normal kidney function. The trabecular bone volume, trabecular osteoid volume, trabecular osteoid surfaces, thickness index of osteoid seams, total resorption surfaces, calcification rate, tetracycline-labeled surfaces, and bone-formation rate at the basic multicellular unit level and at the tissue level were determined. Histological evidence of osteomalacia was found in nine patients, of whom four were alcoholics. In the remaining sixty-eight patients--fifteen treated with corticosteroids, twenty-nine alcoholics, and twenty-four who did not have any detectable etiological factor--a common histomorphometric profile was found. This consisted morphologically of a reduction in trabecular bone volume and in the thickness of osteoid seams, and dynamically of a reduction in calcification rate and in total labeled surfaces. All of these changes suggested a marked decrease in osteoblastic appositional rate and in bone-formation rate at the cell and tissue levels. This could induce a healing defect of microfractures and thus facilitate subchondral fractures. Clinical Relevance: This histological study indicated that non-apparent bone disease--either osteoporosis or osteomalacia--may underlie aseptic osteonecrosis in almost all patients, and be found even when blood and urinary biochemical parameters, usually reflecting bone-remodeling, are normal. An iliac-crest bone biopsy with static and dynamic histomorphometric study is the appropriate method for detecting these abnormalities. These results are of importance for understanding the pathophysiological mechanisms underlying osteonecrosis as well as its prevention and treatment.     

A theoretical analysis of long-term bisphosphonate effects on trabecular bone volume and microdamage

Bisphosphonates increase bone mass and reduce fracture risk, but their anti-resorptive action may lead to increases in fatigue microdamage. To investigate how bisphosphonate effects influence changes in bone volume and microdamage in the long term, a strain-adaptive model of bone remodeling and microdamage balance was developed for a continuum-level volume of postmenopausal trabecular bone by invoking Frost's mechanostat hypothesis. Both disuse and fatigue microdamage were assumed to stimulate the activation frequency of basic multicellular units (BMUs) such that bone remodeling served to remove excess bone mass and microdamage. Bisphosphonate effects were simulated as follows: low, intermediate, high, or complete suppression of BMU activation frequency either without a change in resorption by the BMU or with an independent decrease in resorption while the bone formation process was unaffected (i.e., formation initially exceeded resorption). Of the bisphosphonate effects, a reduction in resorption relative to formation dictated the long-term gain in bone volume while the potency of activation frequency suppression controlled the rate of gain. A plateau in the bone mass gain that typically occurs in clinical studies of bisphosphonate treatment was predicted by the model because the resultant reduction in strain forced bone formation by the BMU to decrease over time until it matched the reduction in BMU resorption. A greater suppression of activation frequency proportionally increased microdamage, but the accumulation was limited over the long term as long as remodeling was incompletely suppressed. The results of the model suggest creating bisphosphonates that provide minimal suppression of remodeling and a large decrease in BMU resorption because this would minimize damage accumulation and increase bone mass, respectively.     

Increased cancellous bone in the femoral neck of patients with coxarthrosis (hip osteoarthritis): a positive remodeling imbalance favoring bone formation

Osteoporosis is caused by an imbalance between bone resorption and formation which results in an absolute reduction in bone mass. In a previous study we highlighted a condition, osteoarthritis of the hip (coxarthrosis, cOA), where an imbalance between resorption and formation provided beneficial effects in the form of an absolute increase in bone mass. We demonstrated that the femoral neck in patients with cOA had increased cancellous bone area, connectivity and trabecular thickness which might contribute to the protection against fracture associated with the condition. The aim of the present study was to analyze forming and resorbing surfaces in coxarthritic cancellous bone to assess whether increased formation or reduced resorption could be responsible for these structural changes. Whole cross-sectional femoral neck biopsies were obtained from 11 patients with cOA and histomorphometric parameters compared with 14 age- and sex-matched cadaveric controls. The ratio of osteoid surface to bone surface was 121% ( p<0.001) higher in the cases but there was no significant difference in resorptive surface. The percentage osteoid volume to bone volume (%OV/BV; +270%, p<0.001) and osteoid width (O.Wi; +127%, p<0.001) were also higher in the cases. This study suggests that the increased cancellous bone mass seen in cases of cOA is due to increased bone formation rather than decreased bone resorption. Investigation of the cellular and biochemical basis for these changes might provide new insights into the pathogenesis of osteoarthritis and highlight novel biological mechanisms regulating bone multicellular unit (BMU) balance that could be relevant to developing new interventions against hip and other osteoporotic fractures.     

Bone tissue response to four-month antiorthostatic bedrest: A bone histomorphometric study

Summary A histomorphometric analysis were made on iliac crest biopsies from eight healthy male volunteers submitted to a 4-month antiorthostatic bedrest. Bone mass and bone cell parameters, reflecting resorption and formation activities, were measured before and after the bedrest period. Trabecular bone volume and mean cortical thickness were not modified despite a decreased number of trabeculae and nonsignificant increase of the trabecular thickness; total and active resorption surfaces and the number of osteollast per mm² of trabecular surfaces do not vary significantly. Osteoid thickness does not vary but we found a reduced osteoid surface and a nonsignificant decreased osteoid volume. Our results suggest that bone architecture may be more affected by the reduction of mechanical forces than the bone mass. These modifications were supposed to be the result of an accelerated bone turnover in the early stage of immobilization. In this study, we failed to find disuse osteoporosis; however, we must point out that the new organization of the trabecutae could affect the bone mechanical properties.     

Abnormalities in bone mineral density and bone histology in thalassemia.

This study demonstrated that there was extensive iron staining on trabecular surface and marked reduction in trabecular bone volume without significant alteration in bone formation and bone resorption rates as well as significant reduction in bone mineral density in 18 thalassemic patients. Serum IGF-I was reduced and may modulate the reduction of bone mass. INTRODUCTION: Bone histomorphometric studies in thalassemia to show alterations in bone histology and their relationship to biochemical parameters are very limited. Therefore, this study was systematically conducted to determine the alterations in thalassemia patients. METHODS: Serum biochemical parameters, trans-iliac crest bone biopsy, and determination of bone mineral density of femur and lumbar spine were done in 18 thalassemic patients (10 females and 8 males). RESULTS: Serum osteocalcin, carboxy terminal teleopeptide fragment of type I collagen, and parathyroid hormone levels were within normal limits, but serum 25(OH) vitamin D (19.3 +/- 1.6 ng/ml) and 1,25(OH)2 vitamin D (33.77 +/- 1.51 pg/ml) levels were decreased. Serum insulin-like growth factor I (IGF-I; 145.2 +/- 20 ng/ml) was suppressed, whereas serum ferritin (1366.6 +/- 253.9 ng/ml) was markedly elevated. Reduced bone mineral density was found in all studied areas. Trabecular bone volume was significantly decreased (16.65 +/- 1.12%), whereas bone formation rate, eroded surface, and other bone histomorphometric parameters were within normal limits. The trabecular bone volume varied significantly with bone mineral density of total femur (r = 0.48, p = 0.04). There was an extensive stainable iron surface on the mineral front (9-60%). Significant correlation between serum IGF-I, serum ferritin, stainable iron surface, and bone mineral density, lumbar spine, and total femur were found. Serum IGF-I correlated with trabecular bone volume (r = 0.6, p = 0.03), inversely with both serum ferritin level (r = -0.6, p < 0.01), and inversely with stainable iron surface (r = -0.53, p = 0.02). Multiple regression analysis demonstrated that IGF-I was the only independent variable that determined bone mineral density of lumbar spine and total femur. CONCLUSION: Low bone mineral density and reduced trabecular bone volume with extensive iron deposition are the predominant findings in thalassemic patients. There was no evidence of increased bone resorption or mineralization defect. A reduction in circulatory IGF-I may modulate the reduction of bone mass.     

Metabolic bone disease with and without osteomalacia after intestinal bypass surgery: a bone histomorphometric study

We performed iliac bone histomorphometry after in vivo double tetracycline labeling 3-14 years after intestinal bypass surgery for obesity in 21 patients, selected because of clinical suspicion of metabolic bone disease, and compared the results with those of 40 age-matched normal control subjects. Osteomalacia defined by rigorous kinetic criteria was found in six cases, histologic features of secondary hyperparathyroidism without significantly impaired mineralization in one case, and possible osteomalacia masked by impaired matrix synthesis in one case. In the patients with definite osteomalacia, nonfracture bone pain was more frequent, corrected plasma calcium lower, plasma alkaline phosphatase and magnesium higher, and secondary hyperparathyroidism more severe than in the other patients. In the patients without osteomalacia there was a 24.5% reduction in trabecular bone volume compared to the controls; in contrast to age-related bone loss and post-menopausal osteoporosis, this was due mainly to reduction in the thickness rather than the density of trabecular plates. About two-thirds of the reduction in trabecular thickness was due to reduction in interstitial bone thickness, representing the cumulative effect of increased depth of osteoclastic resorption cavities, probably due in part to secondary hyperparathyroidism. About one-third of the reduction in trabecular thickness was the result of reduced mean wall thickness, representing insufficient osteoblastic matrix synthesis, probably due in part to malabsorption of an unidentified nutrient necessary for normal bone health. Resorption indices were not increased at the time of the biopsy, but there were persistent defects in the recruitment and activity of osteoblasts. Clinically significant bone loss after intestinal shunt surgery, as in several other clinical situations, results from the combined effects of an unsustained increase in bone resorption and a sustained decrease in bone formation.     

Effects of a one-year administration of phosphate and intermittent calcitonin on bone-forming and bone-resorbing cells in involutional osteoporosis: A histomorphometric study

Summary The bone histomorphometric effects of intermittent phosphate and calcitonin therapy during 1 year were analyzed in 15 involutional osteoporotic patients. Phosphate was administered continuously (1.5 g/day) and calcitonin was injected during 5 days every third week (50 IU/day). The bone cell response was analyzed in two separate groups, according to the amount of trabecular bone present in the iliac bone biopsy: patients with trabecular bone volume (TBV) beyond the histomorphometric spontaneous fracture threshold (0.16 mm3/mm3) (group 1; 11 patients) and patients with TBV above this threshold (group 2; 4 patients). In group 1, the treatment significantly increased TBV from 0.113±0.025 to 0.156±0.046 mm3/mm3 by thickening the existing trabeculae rather than by creating new trabeculae; stimulation of bone formation rate (+50%) and significant reduction in active trabecular resorption surfaces (from 0.021±0.013 to 0.010±0.006 mm2/mm2;P<.05) may have led to positive bone balance. In group 2, TBV was not changed because of the treatment's relative inefficiency for reducing the bone-resorbing cell activity, leading to likely persistent negative bone balance. Cortical thickness did not change in either group. This study confirms the positive effectiveness of continuous treatment with phosphate and intermittent calcitonin during 1 year on bone balance in involutional osteoporosis with low amount of bone. The lack of response in patients with normal amount of bone must be verified before raising the hypothesis of different bone cell activity and before anticipating the therapeutic response according to local bone mass besides bone remodeling status in osteoporosis.     

Decreased bone formation in osteoporotic patients compared with age-matched controls

Summary In order to study trabecular bone remodeling in postmenopausal osteoporosis we compared bone biopsies of 44 osteoporotic women aged 50–70 to those of 23 nonosteoporotic women, matched for age, who had a bone biopsy during anesthesia for knee arthritis. Trabecular bone volume, mean wall thickness, osteoblastic surfaces, labeled surfaces, and bone formation rate were decreased in osteoporotic women compared with control women. The osteoclast number and the osteoclastic surfaces were the same in the two groups. The normal distribution of the histomorphometric static parameters in osteoporotic patients did not allow the separation of subgroups. These data indicate that decreased bone formations is a major contributing factor leading to trabecular bone loss in postmenopausal osteoporosis.     

In vivo inhibition of osteoblastic metalloproteinases leads to increased trabecular bone mass.

Mice specifically overexpressing TIMP-1 in osteoblasts have been generated to investigate the role of MMPs in bone in vivo. These mice displayed increased trabecular bone volume and decreased bone turnover. This model provides evidence of the role played by the MMPs in bone remodeling and balance. INTRODUCTION: Although it has been suggested that the matrix metalloproteinases (MMPs) may play a role in initiating the bone resorption process in vitro, there is no evidence that they play any role in in vivo bone maintenance. MATERIALS AND METHODS: We used an artificial promoter specifically driving cells of the osteoblastic lineage to overexpress the tissue inhibitor of MMPs (TIMP-1) cDNA in mice. Densitometric analysis, using DXA and pQCT, and static and dynamic histomorphometry were used to evaluate the bone phenotype both in male and female transgenic mice. We evaluated osteoblastic differentiation using a primary osteoblast culture and osteoclast activity using an ex vivo organ culture. RESULTS AND CONCLUSION: We showed that at 1 and 2.5 months of age, only the female mice exhibited a bone phenotype. These mice displayed specific increases in the BMD and bone volume of trabecular bone. This increase was accompanied by decreased trabecular separation, suggesting a decrease in bone resorption. Using an ex vivo resorption assay, we demonstrated that parathyroid hormone (PTH)-stimulated bone resorption was reduced in these mice. Evaluation of the bone histomorphometric dynamic parameters showed that the mineralizing surfaces and bone formation rate were both reduced. There was no change in the mineralization lag time or number of osteocyte lacunae. Using primary osteoblast culture and molecular analysis, we showed that the differentiation and function of osteoblasts from transgenic mice were normal, but that the ex vivo formation of mineralized nodules was delayed. This model is the first to show that in vivo MMPs play a role in bone remodeling and bone balance. Moreover, our data suggest that MMP activity could be involved in the hormonal regulation of bone resorption by osteoblasts.     

Bone histomorphometric changes after liver transplantation for chronic cholestatic liver disease.

Thirty-three patients with cholestatic liver disease underwent histomorphometric assessment of paired bone biopsy specimens at time of orthotopic liver transplantation (OLT) and 4 months thereafter. At 4 months after OLT, bone metabolism improved, with bone formation increasing to normal and no change in bone resorption. Early post-transplant bone loss may be attributed to an additional insult to bone formation early after transplantation. INTRODUCTION: Patients with advanced liver disease, especially chronic cholestasis, often have osteopenia, which worsens early after orthotopic liver transplantation (OLT) before starting to recover. The changes in bone metabolism leading to this rapid loss of bone after OLT, and to its recovery, are poorly defined. MATERIALS AND METHODS: In thirty-three patients with advanced chronic cholestatic liver disease, tetracycline-labeled bone biopsy specimens were analyzed prospectively at time of OLT and at 4 months after OLT, as part of a randomized trial to study the efficacy of calcitonin on post-transplant bone loss. Hierarchical cluster analysis of histomorphometric parameters was performed in an attempt to establish the functional grouping of individual histomorphometric parameters before and after OLT. RESULTS AND CONCLUSIONS: Results showed that from the time of OLT to 4 months after OLT, bone mineral density of the lumbar spine and histomorphometric parameters of bone volume decreased, consistent with early post-transplant bone loss. Histomorphometric resorption parameters were increased before OLT, with no change after OLT. Histomorphometric formation parameters increased from low values before OLT to normal values at 4 months after OLT, with the exception of mean wall thickness values, which further decreased after OLT, suggesting an additional insult to bone formation during the study period. Histomorphometric changes after OLT were similar in female and male patients, pre- and postmenopausal women, and in patients treated and not treated with calcitonin. Hierarchical cluster analysis suggested that before OLT, bone resorption was functioning independently of bone formation, but that by 4 months after OLT, their coupled relationship had improved. Therefore, despite post-transplant bone loss, by 4 months after OLT, bone metabolism had improved, with increased bone formation and more coupled bone balance, as suggested by hierarchical cluster analysis.     

Tetracyclines Inhibit Rat Osteoclast Formation and Activity In Vitro and Affect Bone Turnover in Young Rats In Vivo

An experiment was designed to investigate whether systemic administration of tetracyclines (TCs) as bone fluorochrome labels could interfere with bone modeling in vivo and inhibit osteoclast formation and activity in vitro. Cell cultures of rat bone marrow macrophages revealed that TC and oxytetracycline inhibited osteoclastogenesis and bone resorption and stimulated apoptosis. Forty rats in five groups were treated with saline, calcein green, alizarin red S, TC, or oxytetracycline. Their tibias were used for histomorphometric analysis, including bone static, dynamic, and resorption parameters in the tibial proximal metaphysis. No significant differences in bone volume per tissue volume, trabecular number, trabecular thickness, trabecular separation, bone formation rate per bone surface, mineralizing surface, or mineral apposition rate were observed. TC or oxytetracycline decreased eroded surface, number of osteoclasts per bone perimeter, and osteoclast surface per bone surface by about 50%. The results demonstrated that TC and oxytetracycline inhibit rat osteoclast formation and activity in vitro, and histomorphometric parameters involved in bone turnover may be affected by the use of oxytetracycline and TC as fluorescent bone labels in vivo.     

Mechanisms underlying the effects of phosphate and calcitonin on bone histology in postmenopausal osteoporosis

The aim of this study was to evaluate the mechanism underlying the beneficial effect of phosphate combined with calcitonin on trabecular bone mass in postmenopausal osteoporosis. Histomorphometric parameters of trabecular bone formation and resorption were assessed blindly on sections from tetracycline-labeled iliac crest bone biopsies from 44 women with postmenopausal osteoporosis obtained before and after 6 months of treatment with phosphate (n = 9), calcitonin (n = 13), combined therapy (n = 13), or double placebos (n = 9). Treatment with phosphate (1.5 g/day) increased the osteoblastic surface in correlation with the fractional trabecular surface with double tetracycline labeling. The mean wall thickness of the basic structural units increased significantly only in the two groups of patients treated with phosphate. Thus, oral phosphate therapy stimulated bone formation by increasing both the bone-forming surfaces and bone matrix production. The mean interstitial bone thickness, which is inversely related to the depth of resorbing cavities, was increased in the two groups treated with calcitonin (50 IU X 5 days every third week), indicating that calcitonin therapy partially inhibited the resorbing activity of osteoclasts. The combination of calcitonin and phosphate produced a reduction in bone resorption associated with a stimulation of bone matrix production. This effect resulted in a 22.1% increase in the thickness of the trabeculae and a 31.1% increase in trabecular bone volume. The data show that calcitonin combined with phosphate increased the trabecular bone volume in postmenopausal osteoporosis through reduction of bone resorption associated with stimulation of bone formation along the trabecular bone surface.     

Stimulation of bone formation in osteoporosis patients treated with fluoride associated with increased DNA synthesis by osteoblastic cells in vitro.

In this study we evaluated whether the fluoride-induced increased bone formation in osteoporosis is mediated by stimulation of bone cell proliferation and/or differentiation. We analyzed the kinetics of DNA synthesis and the phenotypic features of osteoblastic cells isolated from the trabecular bone surface in relationship to histomorphometric indices of bone formation evaluated on the same bone biopsy in 12 osteoporotic patients treated with fluoride. Osteoblastic cells isolated from patients with a higher than normal bone formation rate, increased mean wall thickness of trabecular bone packets, and high trabecular bone volume after fluoride therapy displayed a higher than normal rate of DNA synthesis in vitro. The peak of [3H]thymidine incorporation into DNA, the maximal DNA synthesis, and the area under the growth curve of osteoblastic cells isolated from these patients were higher than the values in normal bone cells obtained from age-matched controls. By contrast, in vitro parameters of osteoblastic cell proliferation were not different from normal in fluoride-treated osteoporosis patients in whom bone formation was not increased, although the duration of treatment and bone fluoride content were not different. Parameters of bone cell proliferation in vitro were increased in correlation with the mean wall thickness, and the latter correlated with the trabecular bone volume, indicating that the augmentation of bone formation and bone volume induced by fluoride was paralleled by an increased proliferation of osteoblastic cells. Basal osteocalcin production (corrected for cell protein) and alkaline phosphatase activity in vitro were comparable, and the response to 1,25-dihydroxyvitamin D3 (10 nmol/liter, 48 h) was not different in normal osteoblastic cells and in cells from fluoride-treated osteoporosis patients whether they had high or normal bone formation. The results show that the fluoride-induced increased bone formation in osteoporotic patients is associated with an increased in vitro proliferative capacity of osteoblastic cells lining the trabecular bone surface, whereas parameters of osteoblast differentiation are not affected. The data also suggest that induction of a higher than normal bone cell proliferation is prerequisite for the stimulation of bone formation by fluoride.