Sclerostin deficiency in humans

Sclerosteosis and van Buchem disease are two rare bone sclerosing dysplasias caused by genetic defects in the synthesis of sclerostin. In this article we review the demographic, clinical, biochemical, radiological, and histological characteristics of patients with sclerosteosis and van Buchem disease that led to a better understanding of the role of sclerostin in bone metabolism in humans and we discuss the relevance of these findings for the development of new therapeutics for the treatment of patients with osteoporosis.

Sclerostin: recent advances and clinical implications

PURPOSE OF REVIEW

Discovery of the Wnt signaling pathway and understanding the central role of osteocyte in skeletal homeostasis have been the major advances in skeletal biology over the past decade. Sclerostin, secreted mainly (but not exclusively) by osteocytes, has emerged as a key player in skeletal homeostasis. This review highlights the most relevant recent advances.

RECENT FINDINGS

Sclerostin by inhibiting Wnt signaling pathway decreases bone formation and osteoblast differentiation and promotes osteoblast apoptosis. Ability to measure serum sclerostin levels better clarified the role of sclerostin in various physiologic and pathologic states. Early clinical trials with antibodies to sclerostin have produced robust increases in bone mineral density, and fracture prevention trials are underway.

SUMMARY

Since the discovery of Wnt signaling pathway and sclerostin's association with high bone mass, there has been a remarkable progress. Clinical trials with fracture endpoints, already underway, should expand osteoanabolic therapeutic horizon in the very near future. Measurement of sclerostin levels in a number of conditions has advanced our knowledge about pathophysiology of skeletal and nonskeletal disorders in an altogether new light.

[Features of fluor intoxication development in patients with nondifferentiated connective tissue dysplasia and physical therapy methods for these patients]

The article covers results of studies concerning time of fluorosis development in patients with signs of connective tissue dysplasia syndrome (CTDS). if compared with patients without CTDS, and of studies concerning hyperostosis coefficient in accordance with presence or absence of CTDS. Efficiency of physical therapy and balneotherapy for these patients are also reported by the authors.

Sclerostin: therapeutic horizons based upon its actions

Inactivating mutations of the SOST gene cause a reduction in sclerostin levels and are associated with high bone mass. The clinical phenotypes, sclerosteosis and van Buchem's disease, were described in 1950s. Much later, it was learned that both diseases are due to loss-of-function mutations in the SOST gene. As a regulator of an important osteoanabolic pathway, Wnt, inactivation of SOST leads to a stimulation of the pathway it regulates. The high bone mass in patients with either sclerosteosis or van Buchem's disease is associated with unusual skeletal strength; they do not fracture. Knowledge of this molecule and its actions led rather quickly to the development of anti-sclerostin antibodies that lead to marked increases in bone mass in both animals and human subjects. Blocking sclerostin action with anti-sclerostin antibodies is a promising new therapeutic approach to osteoanabolic therapy of osteoporosis.

'Sink or swim': an evaluation of the clinical characteristics of individuals with high bone mass

SUMMARY

High bone mineral density on routine dual energy X-ray absorptiometry (DXA) may indicate an underlying skeletal dysplasia. Two hundred fifty-eight individuals with unexplained high bone mass (HBM), 236 relatives (41% with HBM) and 58 spouses were studied. Cases could not float, had mandible enlargement, extra bone, broad frames, larger shoe sizes and increased body mass index (BMI). HBM cases may harbour an underlying genetic disorder.

INTRODUCTION

High bone mineral density is a sporadic incidental finding on routine DXA scanning of apparently asymptomatic individuals. Such individuals may have an underlying skeletal dysplasia, as seen in LRP5 mutations. We aimed to characterize unexplained HBM and determine the potential for an underlying skeletal dysplasia.

METHODS

Two hundred fifty-eight individuals with unexplained HBM (defined as L1 Z-score ≥ +3.2 plus total hip Z-score ≥ +1.2, or total hip Z-score ≥ +3.2) were recruited from 15 UK centres, by screening 335,115 DXA scans. Unexplained HBM affected 0.181% of DXA scans. Next 236 relatives were recruited of whom 94 (41%) had HBM (defined as L1 Z-score + total hip Z-score ≥ +3.2). Fifty-eight spouses were also recruited together with the unaffected relatives as controls. Phenotypes of cases and controls, obtained from clinical assessment, were compared using random-effects linear and logistic regression models, clustered by family, adjusted for confounders, including age and sex.

RESULTS

Individuals with unexplained HBM had an excess of sinking when swimming (7.11 [3.65, 13.84], p < 0.001; adjusted odds ratio with 95% confidence interval shown), mandible enlargement (4.16 [2.34, 7.39], p < 0.001), extra bone at tendon/ligament insertions (2.07 [1.13, 3.78], p = 0.018) and broad frame (3.55 [2.12, 5.95], p < 0.001). HBM cases also had a larger shoe size (mean difference 0.4 [0.1, 0.7] UK sizes, p = 0.009) and increased BMI (mean difference 2.2 [1.3, 3.1] kg/m(2), p < 0.001).

CONCLUSION

Individuals with unexplained HBM have an excess of clinical characteristics associated with skeletal dysplasia and their relatives are commonly affected, suggesting many may harbour an underlying genetic disorder affecting bone mass.

[Medium-term results of anatomic straight-shaft IMAGE implantation in primary hip joint endoprosthetics--a prospective study]

AIM

The IMAGE prosthesis was developed with the objective of proximal load induction to avoid stress shielding and proximal bone resorption. In this study patients were followed clinically and radiologically with a special emphasis on osteointegration of the shaft in the proximal and distal regions. In addition, the reconstruction of the bony geometry of the proximal humerus was investigated.

METHOD

95 consecutive patients (mean age: 61.1 years) with an IMAGE shaft were followed up prospectively over five years after primary hip arthroplasty. Radiologically, the osteointegration was appraised on the basis of the parameters cortical bone hypertrophy, radiolucent lines, shaft sintering and the position of the rotational centre. The clinical parameters assessed were the Harris hip score (HSS) and the WOMAC score.

RESULTS

In Dorr C configuration no distal cortical bone hypertrophy was visible, in contrast to 19% in types A and B. By means of this criterion in 81% of the cases, a metaphyseal anchoring can be assumed. In 20% of the cases proximal and in 11.1% distal radiolucent lines were found. In only 3.3 % of the patients were the radiolucent lines due to unwanted distal osteointegration. In most cases the reasons were PE wear and metallosis. In 18.8% a distal anchoring was visible. Sintering (in total 18 prostheses) was greatest in Dorr C configuration and high-grade osteoporosis. The difference in offset reconstruction was 4.23 mm on average. In reconstruction of the rotational centre the variability was between 2.0 and 6.9 mm. 94.13 points were attained in the HHS and 10.13 points in the WOMAC score. Specific complications related to the implantation were not observed.

CONCLUSIONS

Proximal stress transmission can be supported and the danger of stress shielding can be reduced by means of an appropriate design of a prosthetic stem. Distal corticoid hypertrophy was found in only 19% of the patients with the prosthesis model investigated as compared to 60% having prostheses with distal femoral anchoring. The medium-term clinical results are excellent, so that the shaft appears suitable for primary as well as secondary osteoarthritis of the hip joint.

Rheumatological manifestations in diabetes mellitus

Rheumatological manifestations of Diabetes Mellitus may be classified in: non articular, articular and bone conditions. Among non articular conditions, diabetic cheiroarthropathy, frequent in type I diabetes, the most important disorder related to limited joint mobility, results in stiff skin and joint contractures. Adhesive capsulitis of the shoulder, flexor tenosynovitis, and Duputryen's and Peyronie's diseases are also linked to limited joint mobility. Diffuse skeletal hyperostosis, due to calcification at entheses, is frequent and early, particularly in type 2 diabetes. Neuropathies cause some non articular conditions, mainly neuropathic arthritis, a destructive bone and joint condition more common in type I diabetes. Algodistrophy, shoulder-hand and entrapment syndromes are also frequent. Mononeuropathy causes diabetic amyotrophy, characterised by painless muscle weakness. Among muscle conditions, diabetic muscle infarction is a rare, sometimes severe, condition. Among articular conditions, osteoarthritis is frequent and early in diabetes, in which also chondrocalcinosis and gout occur. Rheumatoid arthritis (RA) and diabetes I have a common genetic background and the presence of diabetes gives to RA an unfavourable prognosis. Among bone conditions, osteopenia and osteoporosis may occur early in type 1 diabetes. Contrarily, in type 2 diabetes, bone mineral density is similar or, sometimes, higher than in non diabetic subjects, probably due to hyperinsulinemia.

SOST/sclerostin, an osteocyte-derived negative regulator of bone formation

Sclerosteosis and Van Buchem disease are two closely related bone disorders characterized by progressive bone thickening due to increased bone formation. Sclerosteosis is associated with mutations in the SOST gene and Van Buchem disease with a 52 kb deletion downstream of the SOST gene that probably affects transcription of the gene. Expression of the gene product sclerostin in bone is restricted to osteocytes and it is a negative regulator of bone formation. It inhibits BMP-stimulated bone formation, but cannot antagonize all BMP responses. The exclusive bone phenotype of good quality of patients with sclerosteosis and Van Buchem disease and the specific localization of sclerostin make it an attractive target for the development of bone forming therapeutics.

Calvarial hyperostosis syndrome in two bullmastiffs

Two bullmastiffs with calvarial hyperostosis syndrome are described and are the first documented examples in females. The clinical and radiologic features were similar to those previously reported in males. Magnetic resonance (MR) imaging findings have not previously been reported. One dog underwent MR imaging and abnormalities included thickening of the frontal bones with loss of normal fat signal and changes in the overlying soft tissues. In one of the dogs, long bone changes were seen in the femora and resembled those seen with craniomandibular osteopathy.

Microarray analysis of proliferative and hypertrophic growth plate zones identifies differentiation markers and signal pathways

Longitudinal bone growth results from coordination of proliferation and hypertrophy of chondrocytes, calcification of the matrix, vascular invasion, and completion of endochondral bone formation in the growth plate. Although proliferative and hypertrophic chondrocytes are well characterized histomorphologically, the understanding of factors governing this transition is not fully explained. Our hypothesis was that significant differential gene expression exists between proliferative and hypertrophic chondrocytes that may provide clues to the regulation of this transition at the transcriptional level. Normal Sprague-Dawley rat growth plate chondrocytes from the proliferative zone (PZ) and hypertrophic zone (HZ) were isolated by laser capture microdissection and then subjected to microarray analysis. Confirmation of the differential expression of selected genes was done by in situ hybridization and quantitative reverse transcription (RT) polymerase chain reaction (PCR). A total of 40 transcripts showed at least twofold greater expression in the PZ compared to HZ at both 6 and 7 weeks of age, while 52 transcripts showed twofold greater expression in the HZ compared to PZ at these time points. Many of the differentially expressed genes in each zone had very high levels of expression and thus were classified as "enriched transcripts" for that zone. The PZ-enriched transcripts included fibromodulin, proline arginine-rich end leucine-rich repeat protein, lactate dehydrogenase, and enolase 1 alpha. In contrast, HZ-enriched transcripts included collagen I, protein kinase (lysine deficient 4), proteasome (prosome, macropain) activator subunit 4, prostaglandin I2 synthase, and integrin-binding sialoprotein, matrix metalloproteinase 13 (MMP13), and collagen X. Other genes were highly expressed in cells from both zones, including collagen II, aggrecan, cartilage oligomeric protein, cartilage link protein, laminin receptor, and eukaryotic translocation elongation factor. Functional classification of the PZ-enriched transcripts showed an increased percentage of genes expressed in nuclear cell cycle and transcription functions. In contrast, the HZ-enriched transcripts were more involved in extracellular structure and membrane receptor and transporter functions. Pathway analysis indicated that transforming growth factor beta and parathyroid hormone-related protein (PTHrP) pathways were important in both zones, and bone morphogenic protein pathway played a role in the HZ. It is likely that these differentially expressed genes are involved in regulation of the transition from proliferation to differentiation functions in the growth plate.

Argon plasma surgery for treatment of inferior turbinate hypertrophy: a long-term follow-up in 157 patients

Chronic nasal obstruction is a common disorder, mostly caused by hypertrophic inferior turbinates. In cases of nonresponse to conservative medical management, the surgical reduction of the inferior turbinates is often required. Surgical techniques for the reduction of hyperplastic nasal turbinates include monopolar or bipolar coagulation, partial or total reduction of the turbinates with a conchotome or scissors and laser surgery with Nd:YAG, CO(2) or KTP. Argon plasma coagulation (APC) is a new, innovative technique in otorhinolaryngology which is based on high-frequency electrocoagulation with an argon gas source. The fast and short surgery times, the absence of hemorrhagic complications and, in rhinosurgery, the complete abstention from any kind of nasal packing are remarkable. Between March and November 2000, a group of 157 patients with symptoms of nasal obstruction due to hypertrophic inferior turbinates were treated using APC, at the Otorhinolaryngology Surgery Department of the Hospital of Dolo (Venice). The follow-up period was 24 months. Rhinomanometry was performed to objectively measure the nasal obstruction and to verify the postoperative improvement. The Student t test was used for statistical data. After 24 months, 87% (p < 0.001) of the patients reported to have a better nasal airflow than before the operation. None of the patients needed a nasal packing after APC surgery. The indication, advantages, complications, controversies and long-term results of the treatment with APC in rhinosurgery are reviewed and discussed.

Recent progress in the molecular genetics of sclerosing bone dysplasias

Bone mineral density is a quantitative trait influenced by both genetic and environmental factors. Epidemiological and twin studies have shown heritability for the variance of bone density of up to 80%. The role of genetic factors in bone homeostasis also is clearly illustrated by the existence of an extended group of genetic conditions associated with an abnormal bone density. These conditions are mainly monogenic in that they are caused by mutations in one gene. Recent developments in molecular genetics and genomics have resulted in a dramatically increased power to identify such disease-causing genes. The group of conditions with increased bone density has been poorly studied and understood at the molecular genetic level but recently for some of them, major breakthroughs have been made. These findings will make the molecular analysis of such patients an additional tool in diagnostics and in genetic counseling.

Diffuse idiopathic skeletal hyperostosis causes artificially elevated lumbar bone mineral density measured by dual X-ray absorptiometry

A 76-yr-old man with bilateral total hip arthroplasties was referred for a baseline bone mineral density (BMD) measurement. The L1-L4 lumbar bone density revealed a density above the upper expected value for a young individual (i.e., T-score > 2.5) with large intervertebral variation, while the forearm study revealed an osteoporotic measurement. Lumbar spine radiographs demonstrated abundant, flowing ossification of the anterior spinal ligament, predominantly at L3, consistent with diffuse idiopathic skeletal hyperostosis, which accounted for the increased BMD.

Influence of retinyl acetate on osteochondral junction chondrocytes in C3H and balb mice

OBJECTIVE

To establish the pathophysiology of retinoid induced hyperostosis.

METHODS

Radiographical, histological, ultrastructural, and immunohistochemical features of retinoid induced hyperostosis were evaluated using C3H-Heston mice and Balb mice.

RESULTS

Dose dependent and progressive ossification was noted at extraosseous sites of both mouse strains. New bone formation was seen not only in the extraosseous tissues, but subchondral bone showed prominent proliferation. Major histopathological abnormalities appeared to take place in the chondrocytes near the osteochondral junctions, and some of the metaplastic chondrocytes near the osteochondral junction expressed osteocalcin and type I collagen, extracellular molecules normally present in bone. Species dependent responsiveness was also noted.

CONCLUSION

Longterm administration of retinoids may induce an aberrant differentiation of the articular and entheseal chondrocytes near the osteochondral junctions, and the affected cells appeared to produce extracellular components including osteocalcin and type I collagen.

Connective tissue and joint disease in diabetes mellitus

Connective tissue is ubiquitous and subject to alterations that result in changes in the extracellular matrix of vessels and tissues leading to the long-term complications of diabetes. This article reviews only those abnormalities of interstitial connective tissue involving skeleton, joints, skin, and periarticular tissues. Abnormalities in the skin and periarticular tissues result in syndromes limiting joint movement, including limited joint mobility, Dupuytren disease, flexor tenosynovitis, carpal tunnel syndrome, stiff-hand syndrome, and shoulder-hand reflex dystrophy. Of these, only limited joint mobility and stiff-hand syndrome occur exclusively in patients with diabetes. In all of these conditions, advanced glycation end products are thought to form as a result of nonenzymatic reaction of glucose with proteins, causing stiffening.

Sapho syndrome with femoral hyperostosis. Two case-reports

A characteristic manifestation of SAPHO syndrome is hyperostosis, which most typically affects the sternoclavicular joints. Two cases of SAPHO syndrome with painful hyperostosis of the femur are reported. This misleading localization can lead to delays in the diagnosis and treatment.

Hearing impairment in Engelmann disease

There are several hyperostosis diseases of the skull that are accompanied by hearing impairment. In this article a case of Engelmann disease is presented. Currently > 130 cases of Engelmann disease are reported in literature. About 18% of these cases reported hearing impairment, but it is possible that this figure may be higher, because many of the authors concentrated on other aspects of the disease and made no reference to hearing loss in their reports. The etiology of deafness is the narrowing of the internal auditory canals cause by bony encroachment on nerves and vessels. This lends to progressive perceptive hearing loss and narrowing of the tympanic cavities. The result is fixation or adhesion of ossicle to tympanic walls, and narrowing of the bony part of auditory tubes, which causes serous otitis media.

[Physical exercise and the skeleton]

The skeleton provides more than only a framework for the body. Bone is a calcified conjunctive tissue sensitive to various mechanical stimuli, mainly to those resulting from gravity and muscular contractions. Numerous animal and human studies demonstrate the importance of weight-bearing physical activity as well as mechanical loading for maintaining skeletal integrity. Lack of weight-bearing activity is dangerous for the skeleton: a decrease in bone mineral density (BMD) has been demonstrated in animals and humans under conditions of weightlessness or immobilization. Other studies have also reported a lower vertebral BMD among young amenorrheic athletes than among athletes with regular cycles and/or non athletes. The main factor responsible for this lower BMD in the amenorrheic athletes is the persistent low level of endogenous estrogen observed among these women. However this does not represent a premature and irreversible loss of bone mass since the resumption of menses following a decrease in training is the primary factor for a significant increase in vertebral BMD in these formerly amenorrheic athletes. A weight-bearing exercise is likely to be more beneficial at weight-bearing than at non weight-bearing sites, and hypogonadism resulting from very intensive training and exercise is more detrimental to trabecular than cortical bone. Bone deficit at non weight-bearing sites may be attenuated by maintenance of body weight. Nevertheless the etiology of "stress fractures" among athletes remains poorly understood, and the exact relationship between soft tissue mass and BMD is not clear. Osteoporosis, the most common bone disorder in France, is a pathological condition associated with increased loss of bone mass, resulting in a greater risk of fracture. Although symptoms of osteoporosis do not generally occur until after menopause, recent evidence suggests that bone loss starts much earlier in life. Therefore osteoporosis might be prevented by increasing peak bone mass and/or by slowering bone loss after menopause. Exercise such as resistance training or weight-bearing activities like running or walking have an osteogenic effect on increasing BMD in young people, and the decrease in BMD is slower in exercised than in non-exercised post-menopausal women. Nevertheless the influence of the length and of the intensity of such physical activities remain to be determined.

Osteophyte formation in the vertebral column: a review of the etiologic factors--Part II

Osteophyte formation in the vertebral column is a well documented phenomenon that is poorly understood. The most commonly identified etiologic factors are degeneration and altered mechanics of the spine, either of which in turn have been considered to be a result of the natural aging process or the pathogenesis of spinal disease. In Part I [Contemporary Orthopaedics, 29(1): 31-37, 1994], the process of osteophyte formation was reviewed. In Part II, the sequential and consequential changes from the finely interwoven events of aging, degeneration, mechanical instability, and disease are described.

Muscular strength in idiopathic haemihypertrophy

Nine patients (age 8.9, range 6.5 to 9.5 years) with idiopathic haemihypertrophy were followed at six month intervals for two years. The isometric voluntary contraction strength of the elbow flexors and knee extensors was measured bilaterally, and expressed per unit of muscle and bone cross sectional area of the upper arm (elbow flexors) and of the mid thigh (knee extensors). In absolute terms, the hypertrophic side was always stronger, and the increase in strength was strongly correlated with the increase in limb size bilaterally (P less than 0.01). The hypertrophic limb always exerted greater isometric strength, but if strength was standardized for an anthropometric estimate of upper arm and mid thigh cross sectional area, the normal and hypertrophic side were not significantly different. The limb length discrepancy, when expressed in percentage, remained constant at approximately 3%.

Eighth cranial nerve dysfunction in hyperostosis cranialis interna

Hyperostosis cranialis interna is a recently described autosomal dominant bone disorder characterised by hyperostosis and osteosclerosis confined to the skull, especially the calvarium and the skull base. In the affected family members, we found variable simultaneous involvement of cranial nerves I, II, VII and VIII from late childhood onwards, most likely due to nerve entrapment. Auditory and vestibular functions were followed in 3 young family members for 8 years. At the first examination, pure tone audiograms were normal in all 3 cases and case 1 showed no caloric response in the right ear. During follow-up, this ear developed severe hearing loss progressing to deafness. The left ear showed transient sensorineural hearing loss and a temporarily diminished caloric response. Similar observations were made in case 2. Both cases showed abnormal brain stem auditory-evoked responses during and after the sudden hearing loss, in which initially only wave I was preserved and later on wave V returned with significantly prolonged I-V interval. The latter phenomenon was also observed in case 3 on both sides in the presence of normal audiograms during and after transient unilateral facial nerve paralysis, which was accompanied by bilateral diminished caloric responses.

[Hip and spinal ossification enthesopathies induced by etretinate therapy in peripheral psoriatic arthritis]

The occurrence of ossifying enthesopathy during treatment with synthetic retinoids (etretinate, isotretinoin and acitretin) is a side-effect more and more frequently recorded. The authors report here a new case in a patient with a severe psoriatic arthritis. This observation is characterized by the size of ossifications on hips and lumbar spine which appeared after two years of etretinate therapy. The interest of this observation lies in the fact that ossifications occurred while the patient was treated with long-term corticotherapy. The disease for which retinoids are prescribed does not seem to influence the occurrence of those lesions and it is likely that the responsibility of these molecules is entire. Lesions are enthesitis ossification. They are frequent during these treatments (average of 70%) after an average time of 24 to 36 months for etretinate and of 10 months for isotretinoin. Lesions are asymptomatic in about 50% of the cases. After discontinuation of treatment, lesions become quiescent and does not disappear. Growth hormone or abnormalities in vitamin A metabolism could play a role in the physiopathology of lesions.

Hyperostosis and fixed partial denture pontics: report of 16 patients and review of literature

A total of 19 hyperostoses underlying mandibular posterior fixed partial dentures were observed in 16 patients. In three patients the lesions were bilateral. Histologic examination of hyperostoses from eight patients showed that they were composed essentially of hyperplastic lamellar bone. Radiographic and clinical evidence suggested that subpontic hyperostoses are chronic, slow growing lesions with an exclusive predilection for the mandibular molar-premolar site. They appear to have variable growth rates and attain widely variable maximum size. The etiology of subpontic hyperostoses is unknown, but it is possible that inflammation, trauma, mandibular and occlusal function, and genetic factors, either individually or in combination, play a role in the initiation and development of these lesions. Subpontic hyperostoses have potential periodontal and restorative implications that may require their surgical removal.

Haemodynamic pathogenesis of vascular-bone syndromes in congenital vascular defects

This work is devoted to the haemodynamic pathogenesis of congenital vascular-bone syndromes. It is based on our studies of 209 patients suffering from angio-osteohypertrophic and angio-osteohypotrophic syndromes as regards the species and anatomopathological forms of the vascular defects, the haemodynamics, tissue metabolism and changes in the tubular bones. Establishing the haemodynamic pathogenesis of congenital vascular-bone syndromes in vascular defects is very important in determining the principles of their surgical treatment. It offers the possibility of a correct choice of operative tactics and techniques in these severe vascular diseases, which in many cases lead to disability and cardiovascular insufficiency.

Hyperostosis induced by the bisphosphonate (2-PEBP) in the oophorectomized rat

To prevent the high turnover bone remodeling associated with acute estrogen deficiency, the bisphosphonate [2-(2-pyridinyl) ethylidene-BP] (2-PEBP) was administered to oophorectomized (OX) rats. Three groups of 15 rats each (250 g) were studied. Group (Gp) A was sham operated, Gp B was OX, and Gp C received 2-PEBP (1.72 mg/kg/day) intraperitoneally for 3 days commencing 4 days postoophorectomy. Oophorectomy was confirmed with serum estradiol measurements. Blood samples were collected on days -7, 0, 7, 14, 21, and 28 for ionized calcium (Ca2+), PTH, and serum bone gla protein (BGP). Rats received tetracycline for bone histomorphometric labeling. All results were compared to Gp A. Body weight increased significantly in Gps B and C (P less than 0.005 by day 28). There was no significant difference in Ca2+, and PTH levels in Gps B and C were similar to Gp A. BGP levels were significantly higher on day 28 in Gp B (P less than 0.05). In Gp C, BGP levels were significantly decreased on days 7, 21, and 28 (P less than 0.03). Gp B revealed increased bone turnover without loss of bone volume (BV/TV). BV/TV was significantly increased in Gp C despite a decrease in parameters of bone formation and normal osteoclast number. In conclusion, 2-PEBP in the OX rat inhibited bone resorption more than formation with resultant hyperostosis. Serum BGP appeared to be a good marker of the changes observed on bone histomorphometry.