Calcified cartilage differs in patients with end-stage primary osteoarthritis and secondary osteoarthritis due to rheumatoid arthritis of the hip joint.

OBJECTIVES: Despite distinct aetiologies, the end-stages of primary osteoarthritis (OA) and secondary OA are described by common radiological features. However, the morphology of the bone-cartilage unit may differ depending on the pathogenesis. In this cross-sectional study, we aimed to investigate the histological differences in the bone-cartilage unit of the femoral head between patients with primary OA and secondary OA due to rheumatoid arthritis (RA). METHOD: Femoral heads were obtained from 12 patients with primary OA, six patients with secondary OA due to RA, and 12 control subjects. The femoral heads were investigated using stereological methods to ensure unbiased quantification. RESULTS: The volume (mean difference [95% confidence interval]) (2.1 [0.5;3.8] cm3, p = 0.016) and thickness (413 [78.9;747] µm, p = 0.029) of the articular cartilage and the thickness of the calcified cartilage (56.4 [0.4;113] µm, p = 0.017) were larger in patients with primary OA than in patients with secondary OA due to RA. Femoral head volume (1.2 [-3.6;6.1] cm3, p = 0.598), bone volume fraction (-1.1 [-2.8;5.1] cm3, p = 0.553), subchondral bone thickness (-2.5 [-212;207] µm, p = 0.980), and osteophyte area (25.3 [-53.6;104] cm2, p = 0.506) did not differ between patients. CONCLUSION: The thicker calcified cartilage in primary OA preceding the loss of articular cartilage can be attributed to endochondral ossification. Patients with secondary OA due to RA had severely thinner calcified cartilage as the pathogenesis is driven by inflammation and is characterized by a generalized and more severe loss of articular cartilage.

Local bone loss in patients with anti-citrullinated peptide antibody and arthralgia, evaluated with high-resolution peripheral quantitative computed tomography.

OBJECTIVE: To investigate bone changes in the metacarpophalangeal (MCP) joints of anti-citrullinated peptide antibody (ACPA)-positive patients with arthralgia, but not arthritis, compared to healthy controls. METHOD: Using a cross-sectional study design, patients were recruited from hospitals and private care rheumatologists, and controls from a test subject website. All subjects underwent medical history interview, clinical examination, and biochemical screening including ACPA. Patients with positive ACPA, arthralgia, and no rheumatic disease were included. Controls without a history or signs of rheumatological disease or positive ACPA were included. A 2.7-cm-long region around the second and third MCP joints was evaluated using high-resolution peripheral quantitative computed tomography with a voxel size of 82 µm. RESULTS: Twenty-nine ACPA-positive patients and 29 healthy controls were evaluated. Trabecular volumetric bone mineral density and bone volume fraction did not differ between the groups. In addition, the cortical bone was not affected in patients, as we found no difference in average cortical thickness and cortical bone area between the groups. In contrast, the trabeculae were significantly (p < 0.05) thinner in both second and third MCP heads compared with controls, whereas trabecular number and trabecular separation did not differ between the groups. No erosions were demonstrated and the number of non-specific breaks did not differ between the groups. CONCLUSION: Trabecular bone changes were observed in ACPA-positive patients with arthralgia compared with healthy controls. The results may reflect inflammatory up-regulated trabecular bone resorption leading to early bone loss before the onset of clinical arthritis.

Pantoprazole, a proton pump inhibitor, does not prevent botulinum toxin induced disuse osteopenia in mice.

OBJECTIVES: Pantoprazole is a proton pump inhibitor that has been shown to inhibit bone resorption. The aim of the study was to investigate whether pantoprazole can prevent development of botulinum toxin (BTX)-induced disuse osteopenia in mice. METHODS: Forty-eight 16-week-old female C57BL/6J mice were randomized into 4 groups (n=12): Base, Ctrl, BTX, and BTX+Pan. The Base group was euthanized at study start. The BTX and BTX+Pan groups were immobilized by injections with BTX in one hind limb. The BTX+Pan group was injected i.p. daily with 100 mg pantoprazole per kg bodyweight. The mice were euthanized after 3 weeks of treatment. The skeletal status was investigated by DEXA, µCT, mechanical testing, dynamic bone histomorphometry, and RT-qPCR. The bone sites investigated were tibia, femur, L5 vertebra, and humerus. RESULTS: Injections of BTX induced a pronounced and significant loss of bone density, microstructure, and strength in the immobilized hind limb. Furthermore, the localized intramuscular injections of BTX lead to a slight loss of bone and bone strength at the L5 vertebra and humerus. Treatment with pantoprazole did not have any bone protective or deleterious effects. CONCLUSION: Pantoprazole was unable to prevent the development of BTX induced disuse osteopenia in skeletally mature female C57BL/6J mice.

Alterations in gene expression precede sarcopenia and osteopenia in botulinum toxin immobilized mice.

OBJECTIVES: To investigate alteration of bone and muscle gene expression at different time points during 3 weeks of botulinum toxin (BTX) induced immobilization and how this correlate with conventional analysis of bone and muscle. METHODS: Thirty-five 16-week-old female C57BL/6-mice were investigated; 15 were injected with BTX, 15 served as age-matched controls, and 5 as baseline. 5 BTX-injected and 5 control mice were euthanized after 1, 2, and 3 weeks. Analysis included RT-qPCR, dynamic bone histomorphometry, DEXA, µCT, mechanical testing, and muscle cell cross-sectional-area (CSA). RESULTS: Genes related to osteoblasts were expressed at a lower level after 1 week, but not after 2 and 3 weeks of disuse. Moreover, genes related to osteoclasts were expressed at a higher level after 1 and 2 weeks of disuse, whereafter they approached the level of the controls. Genes related to muscle atrophy were upregulated 1 and 2 weeks after the BTX-injection, but not after 3 weeks. In contrast, deterioration of bone microstructure and strength, and reduction in muscle cell CSA were most evident after 3 weeks of disuse. CONCLUSIONS: Gene expression should be investigated during the first two weeks of immobilization, whereas changes in bone microstructure and muscle cell CSA are most prominent after 3 weeks of immobilization.

Age-related changes in vertebral and iliac crest 3D bone microstructure--differences and similarities.

UNLABELLED: Age-related changes of vertebra and iliac crest 3D microstructure were investigated, and we showed that they were in general similar. The 95th percentile of vertebral trabecular thickness distribution increased with age for women. Surprisingly, vertebral and iliac crest bone microstructure was only weakly correlated (r = 0.38 to 0.75), despite the overall similar age-related changes. INTRODUCTION: The purposes of the study were to determine the age-related changes in iliac and vertebral bone microstructure for women and men over a large age range and to investigate the relationship between the bone microstructure at these skeletal sites. METHODS: Matched sets of transiliac crest bone biopsies and lumbar vertebral body (L2) specimens from 41 women (19-96 years) and 39 men (23-95 years) were micro-computed tomography (µCT) scanned, and the 3D microstructure was quantified. RESULTS: For both women and men, bone volume per total volume (BV/TV), connectivity density (CD), and trabecular number (Tb.N) decreased significantly, while structure model index (SMI) and trabecular separation (Tb.Sp) increased significantly with age at either skeletal site. Vertebral trabecular thickness (Tb.Th) was independent of age for both women and men, while iliac Tb.Th decreased significantly with age for men, but not for women. In general, the vertebral and iliac age-related changes were similar. The 95th percentile of the Tb.Th distribution increased significantly with age for women but was independent of age for men at the vertebral body, while it was independent of age for either sex at the iliac crest. The Tb.Th probability density functions at the two skeletal sites became significantly more similar with age for women, but not for men. The microstructural parameters at the iliac crest and the vertebral bodies were only moderately correlated from r = 0.38 for SMI in women to r = 0.75 for Tb.Sp in men. CONCLUSION: Age-related changes in vertebral and iliac bone microstructure were in general similar. The iliac and vertebral Tb.Th distributions became more similar with age for women. Despite the overall similar age-related changes in trabecular bone microstructure, the vertebral and iliac bone microstructural measures were only weakly correlated (r = 0.38 to 0.75).

Growth hormone mitigates loss of periosteal bone formation and muscle mass in disuse osteopenic rats.

Growth hormone (GH) is a potent anabolic agent capable of increasing both bone and muscle mass. The aim was to investigate whether GH could counteract disuse-induced loss of bone and muscle mass in a rat model. Paralysis was induced by injecting 4 IU Botox (BTX) into the muscles of the right hind limb. Sixty female Wistar rats, 14 weeks old, were divided into the following groups: baseline, controls, BTX, BTX+GH, and GH. GH was given at a dosage of 5 mg/kg/d for 4 weeks. Compared with controls, BTX resulted in lower periosteal bone formation rate (BFR/BS,-79%, P<0.001), bone mineral density (aBMD, -13%, P<0.001), trabecular bone volume (BV/TV, -26%, P<0.05), and mid-femoral bone strength (-12%, P<0.05). In addition, BTX reduced rectus femoris muscle mass (-69%, P<0.001) and muscle cell cross sectional area (CSA) (-73%, P<0.001) compared with controls. GH counteracted disuse-induced losses of periosteal BFR/BS (2-fold increase vs. BTX, P<0.001), whereas no effect on aBMD, trabecular BV/TV, or bone strength was found. In addition, GH partly prevented loss of muscle mass (+29% vs. BTX, P<0.001), and tended to prevent loss of muscle CSA (+11%, P=0.064). In conclusion, GH mitigates disuse-induced loss of periosteal BFR/BS at the mid-femur and rectus femoris muscle mass.

Application of design-based stereology for estimation of absolute volume and surface area of the articular and calcified cartilage compartments of undecalcified human femoral heads.

Design-based stereological methods using systematic uniform random sampling, the Cavalieri estimator and vertical sections are used to investigate undecalcified human femoral heads. Ten entire human femoral heads, obtained from normal women and normal men, were systematically sampled and thin undecalcified vertical sections were obtained. Absolute volumes and surface areas of the entire femoral head, the articular cartilage and the calcified cartilage compartments were estimated. In addition, the average thickness of the articular cartilage and the calcified cartilage were calculated. The stereological procedures applied to the human femoral heads resulted in average coefficient of errors, which were 0.03-0.06 for the volume estimates and 0.03-0.04 for the surface area estimates. We conclude that design-based stereology using the Cavalieri estimator and vertical sections can successfully be used in large undecalcified tissue specimens, like the human femoral head, to estimate the absolute volume and surface area of macroscopic as well as of microscopic tissue compartments. The application of well-known design-based stereological methods carries potential advantage for investigating the pathology in inflammatory and degenerative joint diseases.

No effect of risedronate on articular cartilage damage in the Dunkin Hartley guinea pig model of osteoarthritis.

OBJECTIVES: To investigate whether treatment with a bisphosphonate would influence the subchondral bone plate stiffness and the development of cartilage damage in Dunkin Hartley guinea pigs, which develop osteoarthritis (OA) spontaneously. METHOD: Fifty-six 3-month-old male Dunkin Hartley guinea pigs were randomized into a baseline group and six groups receiving either the bisphosphonate risedronate (30 µg/kg) or vehicle five times a week for 6, 12, or 24 weeks. The medial condyle of the right stifle joint was investigated by histology, using the Osteoarthritis Research Society International (OARSI) score, along with static and dynamic histomorphometry. The subchondral bone plate of the left tibia was tested mechanically with indentation testing. Degradation products of C-terminal telopeptides of type II collagen (CTX-II) were measured in serum. RESULTS: The OARSI score did not differ between risedronate-treated and control animals at any time point. The fraction of bone surfaces covered with osteoclasts (Oc.S/BS) was significantly suppressed in risedronate-treated animals at all time points, as were the fractions of mineralizing surfaces (MS/BS) and osteoid-covered surfaces (OS/BS), and also serum CTX-II. This was accompanied by a significant increase in the epiphyseal content of calcified tissue and in the thickness of the subchondral bone plate. However, this did not result in a stiffer subchondral bone at any time point. DISCUSSION: The risedronate treatment inhibited osteoclastic resorption of calcified cartilage in the primary spongiosa under the epiphyseal growth plate, explaining the risedronate-mediated decrease in CTX-II. Moreover, the serum CTX-II level was not related to the OA-induced articular cartilage degradation seen in this model. CONCLUSIONS: Risedronate did not influence the OARSI score and subchondral plate stiffness, but decreased serum CTX-II in Dunkin Hartley guinea pigs.

Relationship between articular cartilage damage and subchondral bone properties and meniscal ossification in the Dunkin Hartley guinea pig model of osteoarthritis.

OBJECTIVES: To describe the age-related changes of articular cartilage, subchondral bone morphology, and stiffness. Furthermore, to investigate whether subchondral bone histological and mechanical properties and meniscal histological properties are related to articular cartilage damage in the Dunkin Hartley guinea pig model of osteoarthritis (OA). METHODS: Forty male Dunkin Hartley guinea pigs aged 2, 6, 9, and 12 months were studied. The right stifle joints and the left menisci were embedded undecalcified and the tibial articular cartilage and subchondral bone and the menisci were examined using histology. The stiffness of the left tibial subchondral bone was determined with indentation testing. RESULTS: The Osteoarthritis Research Society International (OARSI) grade of the osteoarthritic cartilage lesions of the medial (p < 0.001) and lateral (p < 0.001) condyle and the ossification of the medial (p < 0.001) and lateral (p < 0.001) meniscus increased significantly with age and was significantly more pronounced at the medial condyle than at the lateral condyle. The grade of the osteoarthritic cartilage lesions was significantly correlated (r = 0.78, p < 0.001) with the meniscal ossification, weakly correlated (r = 0.34, p < 0.007) with the subchondral bone plate thickness, and not correlated with the subchondral bone density (r = -0.010, p = 0.94) and the subchondral bone stiffness (r = -0.13, p = 0.30). CONCLUSION: The meniscal ossification observed in Dunkin Hartley guinea pigs may play an important role in the pathogenesis of OA in these animals.

CARGEL Bioscaffold improves cartilage repair tissue after bone marrow stimulation in a minipig model.

PURPOSE: To gain knowledge of the repair tissue in critically sized cartilage defects using bone marrow stimulation combined with CARGEL Bioscaffold (CB) compared with bone marrow stimulation (BMS) alone in a validated animal model. METHODS: Six adult Göttingen minipigs received two chondral defects in each knee. The knees were randomized to either BMS combined with CB or BMS alone. The animals were euthanized after 6 months. Follow-up consisted of histomorphometry, immunohistochemistry, semiquantitative scoring of the repair tissue (ICRS II), and µCT of the trabecular bone beneath the defect. RESULTS: There was significantly more fibrocartilage (80% vs 64%, p = 0.04) and a trend towards less fibrous tissue (15% vs 30%, p = 0.05) in the defects treated with CB. Hyaline cartilage was only seen in one defect treated with CB and none treated with BMS alone. For histological semiquantitative score (ICRS II), defects treated with CB scored lower on subchondral bone (69 vs. 44, p = 0.04). No significant differences were seen on the other parameters of the ICRS II. Immunohistochemistry revealed a trend towards more positive staining for collagen type II in the CB group (p = 0.08). µCT demonstrated thicker trabeculae (p = 0.029) and a higher bone material density (p = 0.028) in defects treated with CB. CONCLUSION: Treatment of cartilage injuries with CARGEL Bioscaffold seems to lead to an improved repair tissue and a more pronounced subchondral bone response compared with bone marrow stimulation alone. However, the CARGEL Bioscaffold treatment did not lead to formation of hyaline cartilage.

Modeling-based bone formation transforms trabeculae to cortical bone in the sclerotic areas in Buschke-Ollendorff syndrome. A case study of two females with LEMD3 variants.

Buschke-Ollendorff syndrome is a rare autosomal dominant condition caused by pathogenic variants in LEMD3 and characterized by connective tissue nevi and sclerotic bone abnormalities known as osteopoikilosis. The bone phenotype in Buschke-Ollendorff syndrome including osteopoikilosis remains unclear. We investigated bone turnover markers, pelvis and crura X-rays; lumbar spine and femoral neck DXA; bone activity by NaF-PET/CT, bone structure by µCT and dynamic histomorphometry in adults with Buschke-Ollendorff syndrome. Two women aged 25 and 47 years with a BMI of 30 and 32 kg/m2, respectively, were included in the investigation. Bone turnover markers were within normal range. aBMD Z-scores were comparable to that of controls in the lumbar spine and increased at the hip. Radiographies exposed spotted areas in crura and pelvis, and NaF-PET/CT exposed abnormal pattern of irregular shaped NaF uptake in the entire skeleton. In both biopsies, µCT showed trabecular structure comparable to that of controls with stellate shaped sclerotic noduli within the cavity and on the endocortex. Histomorphometric analyses of the sclerotic lesions revealed compact lamellar bone with a normal bone remodeling rate, but partly replaced by modeling-based bone formation. Woven bone was not observed in the nodules. Therefore, while bone turnover and BMD were largely within normal reference range in patients with the Buschke-Ollendorff syndrome, osteosclerotic lesions appear to emerge due to modeling-based bone formation with secondary bone remodeling. These observations indicate that LEMD3 may be important for the activation of bone lining cells leading to modeling-based bone formation.

Three-dimensional microstructural properties of regenerated mineralizing tissue after PTH (1-34) treatment in a rabbit tibial lengthening model.

UNLABELLED: Since the approval of parathyroid hormone (PTH) as treatment for osteoporosis, PTH has increasingly been investigated for bone repair and regeneration. The aim of the study was to investigate the effects of intermittent PTH treatment on the microstructure of regenerated mineralizing tissue after distraction osteogenesis in rabbits. After tibial mid-diaphyseal osteotomy the callus was distracted 1 mm/day for 10 days. 72 rabbits were divided in to 3 groups, which daily received a PTH (1-34) 25 microg/kg injection for 30 days; a saline injection for 10 days and a PTH injection for 20 days; or a saline injection for 30 days. The microstructure of the regenerate was assessed by micro computed tomography (microCT). In all 51 obtained specimens were evaluated morphometrically using three different volumes of interests. The results showed that treatment with PTH during distraction osteogenesis resulted in a significantly higher trabecular number, a more isotropic trabecular orientation, a higher connectivity density, and a higher mineralizing tissue mass. We also found that distraction calluses treated with PTH were more mature than the non-treated. CONCLUSION: treatment with PTH resulted in an enhanced microstructure of the newly regenerated mineralizing tissue indicating that PTH has a potential role as a stimulating agent during distraction osteogenesis.

The orphan nuclear receptor SHP utilizes conserved LXXLL-related motifs for interactions with ligand-activated estrogen receptors.

SHP (short heterodimer partner) is an unusual orphan nuclear receptor consisting only of a ligand-binding domain, and it exhibits unique features of interaction with conventional nuclear receptors. While the mechanistic basis of these interactions has remained enigmatic, SHP has been suggested to inhibit nuclear receptor activation by at least three alternatives; inhibition of DNA binding via dimerization, direct antagonism of coactivator function via competition, and possibly transrepression via recruitment of putative corepressors. We now show that SHP binds directly to estrogen receptors via LXXLL-related motifs. Similar motifs, referred to as NR (nuclear receptor) boxes, are usually critical for the binding of coactivators to the ligand-regulated activation domain AF-2 within nuclear receptors. In concordance with the NR box dependency, SHP requires the intact AF-2 domain of agonist-bound estrogen receptors for interaction. Mutations within the ligand-binding domain helix 12, or binding of antagonistic ligands, which are known to result in an incomplete AF-2 surface, abolish interactions with SHP. Supporting the idea that SHP directly antagonizes receptor activation via AF-2 binding, we demonstrate that SHP variants, carrying either interaction-defective NR box mutations or a deletion of the repressor domain, have lost the capacity to inhibit agonist-dependent transcriptional estrogen receptor activation. Furthermore, our studies indicate that SHP may function as a cofactor via the formation of ternary complexes with dimeric receptors on DNA. These novel insights provide a mechanistic explanation for the inhibitory role of SHP in nuclear receptor signaling, and they may explain how SHP functions as a negative coregulator or corepressor for ligand-activated receptors, a novel and unique function for an orphan nuclear receptor.

The anabolic effect of PTH on bone is attenuated by simultaneous glucocorticoid treatment.

Glucocorticoids (GC) are used for the treatment of a wide spectrum of diseases because of their potent anti-inflammatory and immunosuppressive effects, and they are serious and common causes of secondary osteoporosis. Administration of intermittent parathyroid hormone (PTH) may induce formation of new bone and may counteract the bone loss induced by GC treatment. Effects of simultaneous PTH and GC treatment were investigated on bone biomechanics, static and dynamic histomorphometry, and bone metabolism. Twenty-seven-month-old female rats were divided randomly into the following groups: baseline, vehicle, PTH, GC, and PTH + GC. PTH (1-34) 25 mug/kg and GC (methylprednisolone) 2.5 mg/kg were injected subcutaneously each day for a treatment period of 8 weeks. The rats were labeled with fluorochromes 3 times during the experiment. Bone sections were studied by fluorescence microscopy. The PTH injections resulted in a 5-fold increase in cancellous bone volume. At the proximal tibia, PTH induced a pronounced formation of new cancellous bone which originated from the endocortical bone surfaces and from thin trabeculae. Formation and modeling of connections between trabeculae were observed. Similar but less pronounced structural changes were seen in the PTH + GC group. The compressive strength of the cancellous bone was increased by 6-fold in the PTH group compared with the vehicle group. GC partially inhibited the increase in compressive strength induced by PTH. Concerning cortical bone, PTH induced a pronounced increase in the endocortical bone formation rate (BFR) and a smaller increase in periosteal BFR. The combination of PTH + GC resulted in a partial inhibition of the PTH-induced increase in bone formation. Serum-osteocalcin was increased by 65% in the PTH group and reduced by 39% in the GC group. The pronounced anabolic effect of PTH injections on the endocortical and trabecular bone surfaces and less pronounced anabolic effect on periosteal surfaces were partially inhibited, but not prevented, by simultaneous GC treatment in old rats. Both cortical and cancellous bone possessed full mechanical competence after treatment with PTH + GC.

Age- and gender-related differences in vertebral bone mass, density, and strength.

This study was designed to evaluate age- and gender-related differences in vertebral bone mass, density, and strength by dual-energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT), peripheral QCT (pQCT), ash measurements, and biomechanical testing. The material comprised human lumbar vertebral bodies (L3) from 51 females and 50 males (age-range: 18-96 years). The results showed that females had significantly lower vertebral body bone mass (ash weight) than males at any given age. The decline in bone mass with age was parallel for females and males. The different bone density measurements-cancellous ash density, total vertebral body ash density, DXA bone mineral density, QCT, and pQCT-showed no gender-related difference concerning numeric value or changes with age. Morphometrical measurements showed that females had smaller vertebral bodies (volumes) than males. Hence the females had significantly smaller cross-sectional area (CSA) of L3 than males (11.6 cm2 and 14.4 cm2, respectively). This led to females having lower maximum compressive load (N) than males at all ages, whereas maximum compressive stress (load/CSA) showed no gender-related difference. In conclusion, females have lower vertebral body bone mass than males at any given age, due to smaller vertebral bodies. Hence, maximum compressive load (strength not corrected for size) was lower in females. Vertebral body cancellous bone density and total-vertebral body density were equal when comparing genders, and no gender differences were found in the size-corrected strength: maximum compressive stress. The decrease with age in vertebral body compressive strength decrease was twice as large as the age decrease in density.

Sequential treatment with basic fibroblast growth factor and parathyroid hormone restores lost cancellous bone mass and strength in the proximal tibia of aged ovariectomized rats.

This study was designed to determine whether sequential treatment with basic fibroblast growth factor (bFGF) and parathyroid hormone (PTH) can restore lost cancellous bone mass and strength at a severely osteopenic skeletal site in aged ovariectomized (OVX) rats. Female Sprague-Dawley rats were subjected to sham surgery or ovariectomy at 3 months of age and maintained untreated for the first year after surgery. At 15 months of age, groups of baseline control and OVX rats were killed and catheters were inserted in the jugular veins of all remaining rats. Two groups of OVX rats were injected intravenously (iv) daily with bFGF for 14 days at a dose of 200 microg/kg body weight. At the end of bFGF treatment, one group was killed whereas the other group was subjected to 8 weeks of treatment with synthetic human PTH 1-34 [hPTH(1-34)] consisting of subcutaneous (sc) injections 5 days/week at a dose of 80 microg/kg. Another group of OVX rats was treated iv with vehicle for 2 weeks followed by treatment with PTH alone for 8 weeks. Other groups of sham-operated control rats and OVX rats were treated iv and sc with vehicle alone. The right proximal tibia from each rat was processed undecalcified for quantitative bone histomorphometry and the left proximal tibia was subjected to biomechanical testing. Baseline and vehicle-treated OVX rats were severely osteopenic because their tibial cancellous bone volumes were less than 5% compared with mean values of 20.3% and 15.0% in baseline and vehicle-treated control rats, respectively. Treatment of OVX rats for 2 weeks with bFGF alone did not significantly increase tibial cancellous bone volume but induced marked increases in osteoid volume, osteoblast surface, and osteoid surface. Sequential treatment of aged OVX rats with bFGF and PTH increased tibial cancellous bone volume (15.1%) and load to failure to at least the level of vehicle-treated control rats. Tibial cancellous bone volume (10.8%) and load to failure also were significantly increased by treatment with PTH alone, and these variables were not significantly different from those of OVX rats treated with bFGF + PTH. However, tibial ash density was significantly greater in OVX rats treated sequentially with bFGF and PTH compared with OVX rats treated with PTH alone. Our findings suggest that sequential treatment with bFGF and PTH may be useful for restoration of lost cancellous bone in the severely osteopenic, estrogen-deplete skeleton, but it cannot be concluded with certainty that this sequential treatment has a greater bone restorative effect than treatment with PTH alone.

Parathyroid hormone increases bone formation and improves mineral balance in vitamin D-deficient female rats.

The present study was designed to investigate whether enhanced bone formation due to intermittent PTH administration is dependent on vitamin D metabolites. Forty-eight female Sprague-Dawley rats were randomized into four groups: 1) vitamin D-sufficient, saline-injected (+D Sal); 2) vitamin D-sufficient, human (h) PTH-(1-38)-treated (+D PTH); 3) vitamin D-deficient, saline-injected (-D Sal); and 4) vitamin D-deficient, hPTH-(1-38)-treated (-D PTH) animals. The -D diet contained 2% calcium (Ca), 1.25% phosphorus (P), and 20% lactose to maintain normocalcemia and normophosphatemia despite vitamin D deficiency. The +D diet contained 0.8% Ca, 0.5% P, 20% lactose, and 1000 IU/kg vitamin D. After 45 days of either diet, the rats were injected with 50 microg/kg BW PTH or saline, s.c., daily for 2 weeks. Serum Ca, Mg, P, albumin, and creatinine were similar in all groups. PTH administration decreased endogenous PTH concentrations in the -D PTH compared with those in the - D Sal group. Serum alkaline phosphatase activity, bone mass measurements, dual energy x-ray absortiometric analysis of mineral density, and mechanical testing values in vertebrae and femora of the -D Sal animals did not significantly differ from those in +D Sal animals. Moreover, in both diet groups, PTH improved bone biochemical activity (as assessed by serum alkaline phosphatase), bone mass, mineral density, and biomechanical properties. These results indicate that mineral supply, more than vitamin D itself, may be important for normal bone mineralization and to enable PTH to enhance bone formation. A balance study performed during the last 3 days of the experiment revealed that PTH increased apparent intestinal magnesium absorption in the +D group only. Ca and P retention, however, were augmented in both diet groups after PTH treatment. In conclusion, in normocalcemic and normophosphatemic -D rats, PTH treatment reduced the increased endogenous hormone concentration and improved Ca and P retention. Furthermore, PTH may have a vitamin D-dependent influence on intestinal magnesium absorption. Finally, short term PTH treatment is anabolic in bone of vitamin D-deficient rats when adequate mineral amounts are provided in the diet.

Sequential treatment with basic fibroblast growth factor and PTH is more efficacious than treatment with PTH alone for increasing vertebral bone mass and strength in osteopenic ovariectomized rats.

The study was designed 1) to determine whether treatment with basic fibroblast growth factor (bFGF) and PTH is more efficacious than treatment with PTH alone for increasing bone mass and strength and improving trabecular microarchitecture in osteopenic ovariectomized rats, and 2) to assess whether prior and concurrent administration of the antiresorptive agents estrogen and risedronate suppresses the bone anabolic response to treatment with bFGF alone and sequential treatment with bFGF and PTH. Three-month-old female Sprague Dawley rats were ovariectomized (OVX) or sham-operated (sham) and maintained untreated for 1 yr. Baseline sham and OVX rats were killed at this time (15 months of age). Groups of rats were injected sc with estrogen (10 microg/kg, 4 d/wk), risedronate (5 microg/kg, 2 d/wk), or vehicle. At the end of the second week of antiresorptive treatment, catheters were inserted into the jugular veins of all rats, and vehicle or bFGF at a dose of 250 microg/kg was injected daily for 14 d. Three groups of rats were killed at the end of bFGF treatment. The remaining rats were continued on their respective antiresorptive therapy and injected sc with vehicle or synthetic human PTH-(1-34) at a dose of 80 microg/kg, 5 d/wk, for 8 wk. Lumbar vertebrae were processed for cancellous bone histomorphometry and biomechanical testing. Ovariectomy resulted in a decrease in vertebral bone mass and strength. Treatment of OVX rats for 14 d with bFGF markedly increased osteoblast surface, osteoid surface, and osteoid volume compared with vehicle treatment of sham and OVX rats. Furthermore, osteoid bridges were observed extending between preexisting trabeculae in bFGF-treated OVX rats. Prior and concurrent administration of estrogen and risedronate did not suppress these bone anabolic effects of bFGF. Treatment of OVX rats with PTH alone increased vertebral cancellous bone mass and strength to the level of vehicle-treated sham rats. Sequential treatment of OVX rats with bFGF and PTH further augmented vertebral bone mass and strength to a level above that observed in OVX rats treated with PTH alone. The improvements in bone mass and strength were associated with an increase in trabecular thickness in OVX rats treated with PTH alone and with an increase in trabecular thickness and node to terminus ratio, an index of trabecular connectivity, in OVX rats treated sequentially with bFGF and PTH. Cotreatment with estrogen and risedronate did not suppress the anabolic response of bone to bFGF and PTH. In fact, a trend for an even greater increase in cancellous bone mass and node to terminus ratio was observed in OVX rats treated with risedronate, bFGF, and PTH. These findings indicate that sequential treatment with bFGF and PTH is more efficacious than treatment with PTH alone for increasing bone mass and strength and improving trabecular microarchitecture in osteopenic OVX rats.

Predicting human vertebral bone strength by vertebral static histomorphometry.

The study investigates the relationship between static histomorphometry and bone strength of human lumbar vertebral bone. The ability of vertebral histomorphometry to predict vertebral bone strength was compared with that of vertebral densitometry, and also with histomorphometry and bone strength of iliac crest bone biopsies. The material comprised matched sets of second lumbar vertebrae, third lumbar vertebrae, and two iliac crest bone biopsies from each of 21 women (19--96 years) and 24 men (23--95 years). One of the iliac crest biopsies and 9-mm-thick mediolateral slices of half of each of the entire vertebral bodies (L-2) were used for histomorphometry. The other iliac crest biopsies and the L-3 were destructively tested by compression. High correlation was found between BV/TV or Tb.Sp and vertebral bone strength (absolute value of r = 0.86 in both cases). Addition of Tb.Th significantly improved the correlation between BV/TV and bone strength, and the addition of bone space star volume significantly improved the correlation between Tb.Sp and bone strength (from absolute value of r = 0.86 to absolute value of r = 0.89 in both cases). Bone structure (connectivity density) was not capable of improving the prediction of bone strength of the vertebral body. The correlations between BV/TV of L-2 and bone strength of L-3 were comparable with the correlation obtained by quantitative computed tomography (QCT), peripheral QCT (pQCT), and dual-energy X-ray absorptrometry (DEXA) of L-3 and bone strength of L-3. The iliac crest was found to have low predictive power of vertebral bone strength (iliac BV/TV: r = 0.62; iliac bone strength: r = 0.67). No gender-related differences were found in any of the relationships. It was shown that trabecular bone volume BV/TV and mean trabecular plate separation Tb.Sp are good predictors of vertebral bone strength. The ability of histomorphometry to predict vertebral bone strength was comparable to that of densitometry. Bone structure assessed by connectivity density did not improve the correlation between static histomorphometric measures and vertebral bone strength. No gender-related differences were found in any of the relationships. Neither static histomorphometry nor biomechanical testing of iliac crest bone biopsies is a good predictor of vertebral bone strength.

Quantification of remodeling parameter sensitivity--assessed by a computer simulation model.

During normal aging and menopause, cancellous bone is lost at all skeletal sites due to remodeling-related factors: negative formation balance; temporarily increased remodeling space; and osteoclastic perforations. The relative importance of the various factors in inducing bone mass loss and perforations is still controversial. We have previously used a computer simulation model to describe the effect of several bone remodeling parameters on vertebral cancellous bone loss. The model focused on two different scenarios for the menopause and three different treatment regimens. The aim of the present study was to extend the previous study by quantifying remodeling parameter sensitivity for changes in the bone mass with the use of the computer model we had previously formulated. The menopause scenario, with increased activation frequency and increased resorption depth, was chosen as the base case scenario, and the following parameters were investigated in the sensitivity analysis: activation frequency; formation balance; resorption depth; and critical trabecular thickness. Simulations were performed for a period of 20 years starting at the age of 48 years. The analysis showed that the number of perforations and the perforation-related mass loss both exhibited a large sensitivity toward variations in the final resorption depth. However, the formation balance was the factor that was responsible for the greater part of the bone mass loss. The computer model allowed us to quantify the sensitivity of different output variables with respect to changes in some of the model parameters. This can give information about the biological mechanisms responsible for bone mass loss around the surgically induced or natural menopause and also provide an indication of the type of treatment that would be most useful in preventing the deterioration of the cancellous network.