Lawrence G. Raisz

Fractures Attributable to Osteoporosis: Report from the National Osteoporosis Foundation

To assess the cost‐effectiveness of interventions to prevent osteoporosis, it is necessary to estimate total health care expenditures for the treatment of osteoporotic fractures. Resources utilized for the treatment of many diseases can be estimated from secondary databases using relevant diagnosis codes, but such codes do not indicate which fractures are osteoporotic in nature. Therefore, a panel of experts was convened to make judgments about the probabilities that fractures of different types might be related to osteoporosis according to patient age, gender, and race. A three‐round Delphi process was applied to estimate the proportion of fractures related to osteoporosis (i.e., the osteoporosis attribution probabilities) in 72 categories comprised of four specific fracture types (hip, spine, forearm, all other sites combined) stratified by three age groups (45–64 years, 65–84 years, 85 years and older), three racial groups (white, black, all others), and both genders (female, male). It was estimated that at least 90% of all hip and spine fractures among elderly white women should be attributed to osteoporosis. Much smaller proportions of the other fractures were attributed to osteoporosis. Regardless of fracture type, attribution probabilities were less for men than women and generally less for non‐whites than whites. These probabilities will be used to estimate the total direct medical costs associated with osteoporosis‐related fractures in the United States.

Direct Stimulation of Bone Resorption by Thyroid Hormones

Although hypercalcemia, osteoporosis, and increased bone turnover are associated with thyrotoxicosis, no direct effects of thyroid hormones on bone metabolism have been reported previously in organ culture. We have now demonstrated that prolonged treatment with thyroxine (T4) or triiodothyronine (T3) can directly increase bone resorption in cultured fetal rat long bones as measured by the release of previously incorporated 45Ca. T4 and T3 at 1 muM to 10 nM increased 45Ca release by 10-60% of total bone 45Ca during 5 days of culture. The medium contained 4 mg/ml of bovine serum albumin to which 90% of T4 and T3 were bound, so that free concentrations were less than 0.1 muM. The response to T4 and T3 was inhibited by cortisol (1 muM) and calcitonin (100 mU/ml). Indomethacin did not inhibit T4 response suggesting that T4 stimulation of bone resorption was not mediated by increased prostaglandin synthesis by the cultured bone. Matrix resorption was demonstrated by a decrease in extracted dry weight and hydroxyproline concentration of treated bones and by histologic examination which also showed increased osteoclast activity. The effects of thyroid hormones were not only slower than those of other potent stimulators of osteoclastic bone resorption (parathyroid hormone, vitamin D metabolites, osteoclast activating factor, and prostaglandins), but the maximum response was not as great. We conclude that T4 and T3 can directly stimulate bone resorption in vitro at concentrations approaching those which occur in thyrotoxicosis. This effect may explain the disturbances of calcium metabolism seen in hyperthyroidism.

Prostaglandin synthesis by fetal rat bone in vitro: evidence for a role of prostacyclin.

Prostaglandin synthesis by fetal rat bones was examined by thin-layer chromatography of culture media after preincubation with labeled arachidonic acid. Cultures in rabbit complement (non-heat inactivated serum) were compared with cultures in heat-inactivated serum or cultures treated with indomethacin. The major complement-dependent products were PGE2, PGF2 alpha and 6-keto-PGF1 alpha, the metabolite of prostacyclin (PGI2). Since PGI2 had not been previously identified in bone its ability to stimulate bone resorption was tested. Repeated addition of PGI2 stimulated release of previously incorporated 45Ca from fetal rat long bones in both short-term and long-term cultures at concentrations of 10(-5) to 10(-9)M. Because of the short half life of PGI2 in solution at neutral pH, we tested a sulfur analog, thiaprostacyclin (S-PGI2) which was found to be a stimulator of bone resorption at concentrations of 10(-5) to 10(-6)M. These studies suggest that endogenous PGI2 production may play a role in bone metabolism. Since vessels produce PGI2 it is possible that PGI2 release may be responsible for the frequent association between vascular invasion and resorption of bone or calcified cartilage in physiologic remodeling and pathologic osteolysis.

Ovariectomy enhances and estrogen replacement inhibits the activity of bone marrow factors that stimulate prostaglandin production in cultured mouse calvariae.

To examine PG production in estrogen deficiency, we studied effects on cultured neonatal mouse calvariae of bone marrow supernatants (MSup) from sham-operated (SHAM), ovariectomized (OVX), or 17 beta-estradiol (OVX+E)-treated mice. MSups were obtained 3 wk after OVX when bone density had decreased significantly. 10-60% MSup increased medium PGE2 and levels of mRNA for inducible and constitutive prostaglandin G/H synthase (PGHS-2 and PGHS-1) and cytosolic phospholipase A2 in calvarial cultures. OVX MSups had twofold greater effects on PGHS-2 and medium PGE2 than other MSups. IL-1 receptor antagonist and anti-IL-1 alpha neutralizing antibody decreased MSup-stimulated PGHS-2 mRNA and PGE2 levels and diminished differences among OVX, sham-operated, and OVX+E groups. In contrast, antibodies to IL-1 beta, IL-6, IL-11, and TNF alpha had little effect. There were no significant differences in IL-1 alpha concentrations or IL-1 alpha mRNA levels in MSups or marrow cells. PGHS-2 mRNA in freshly isolated tibiae from OVX mice was slightly greater than from sham-operated. We conclude that bone marrow factors can increase PG production through stimulation of PGHS-2; that OVX increases and estrogen decreases activity of these factors; and that IL-1 alpha activity, together with additional unknown factors, mediates the differential MSup effects.

Fracture incidence in postmenopausal women with primary hyperparathyroidism

BACKGROUNDnThe association of bone loss and increased fractures in postmenopausal women with minimally symptomatic hyperparathyroidism has not been clearly defined. This study was done to determine the frequency of fractures in postmenopausal women with hyperparathyroidism.nnnMETHODSnForty-six postmenopausal women who had undergone parathyroidectomy for hyperparathyroidism during a 5-year period (1986 to 1991) were interviewed, and their medical records were examined to determine their fracture history. Forty-four postmenopausal women without hyperparathyroidism were contacted by random digit dialing and interviewed as controls.nnnRESULTSnThe groups were comparable with regard to age, weight, height, race, and age at menopause. Medical conditions and medication use were also similar, except for more reports of hypothyroidism in the hyperparathyroidism group (p = 0.05). Only 13% of women presented for treatment because of bone concerns, either fractures (9%) or low bone density (4%). However, on interview, 48% of the patients with hyperparathyroidism reported fractures compared with 25% of the controls (p = 0.02), a difference that remained even when those presenting with bone disease were excluded (p = 0.05). Of those with fractures, multiple fractures occurred in 36% of patients with hyperparathyroidism compared with 9% of controls and generally occurred after minor rather than major trauma (92% versus 45%, p = 0.002). Appendicular skeletal sites were reported for 86% of hyperparathyroidism groups and 92% of control groups fractures. Moreover, 50% of patients with hyperparathyroidism reported height loss compared with 27% of the control group (p = 0.05).nnnCONCLUSIONSnThis study shows that postmenopausal women with hyperparathyroidism reported more fractures and height loss than the control group, even when patients with hyperparathyroidism who presented because of bone disease were excluded.

Bone resorptive factor produced by osteosarcoma cells with osteoblastic features is PGE2.

Summary Conditioned media from osteosarcoma clonal cell lines possess potent bone resorbing activity, assayed by measuring 45Ca release from prelabelled fetal rat bones. The resorbing activity correlated closely with the presence of osteoblastic features, such as elevated alkaline phosphatase and receptors for parathyroid hormone. Dialysis, organic solvent extraction, cyclooxygenase inhibition, thin layer chromatography of media from 14C-arachidonate-incubated cells and radioimmunoassay showed that the resorptive activity was due to PGE2. PGE2 was also produced by osteoblast-enriched rat calvaria cells. These findings support the hypothesis that osteoblastic cells participate in the local control of bone resorption via prostaglandin release.

Early effects of parathyroid hormone and thyrocalcitonin on bone in organ culture.

BONE resorption is stimulated by parathyroid hormone (PTH), but the effect can be inhibited by actinomycin D both in vitro1,2 and in vivo2,3. These findings led to the suggestion that the action of PTH on bone depends on new RNA being synthesized. PTH, however, has a rapid and direct effect on the release of calcium ions from mitochondria which is presumably not mediated by the synthesis of new RNA4, and partial effects of PTH on the mobilization of calcium ions from bone have been detected in the presence of actinomycin D1,3,5. To clarify the relationship between the effect on the transport of calcium ions and that on the synthesis of RNA we investigated the early response of foetal bone in organ culture. The technique used also provided an opportunity to investigate the early effects of the hypocalcaemic hormone, thyrocalcitonin, which inhibits the resorption of bone in organ culture6.

Stimulation of undermineralized matrix formation by 1,25 dihydroxyvitamin D3 in long bones of rats

SummaryWe previously reported that pharmacologic doses of 1,25 dihydroxyvitamin D3 (1,25-(OH)2D3) given for 2–3 days, inhibited osteoblastic collagen synthesis in young rats. In this study, we tested the effects of 5, 25, and 125 ng of 1,25(OH)2D3 injected subcutaneously into 6-week-old rats for 12 or 18 days. In rats given 125 ng, cortical bone of distal half femurs exhibited decreased calcium (Ca) content but dry weight and hydroxyproline (Hyp) content were no different from control. Trabecular bone Ca was not different from control but dry weight and Hyp were increased. When cortical and trabecular bone were combined, there was a decrease in Ca, an increase in Hyp, and a 50% decrease in Ca:Hyp. Fluorescent labels given after 8 days of treatment were either diffuse or absent in calcified sections from rats given 125 ng, indicating impaired mineralization. The 25 and 125 ng doses produced hypercalcemia with normal serum phosphate. There was a dose-related increase in serum immunoreactive bone gla protein (BGP) and serum 1,25(OH)2D3 and a decrease in serum 25 (OH)D3. At the 5 ng dose, no adverse effects were seen on body growth. With 25 ng and 125 ng, growth was inhibited. Increased serum urea nitrogen and histologic evidence of nephrocalcinosis occurred at the 125 ng dose. When 125 ng was given for 12 days and then withdrawn for 6 days, systemic toxicity decreased and bone Hyp and Ca increased so that Ca:Hyp remained low and comparable to that of rats treated with 1,25(OH)2D3 continuously We conclude that pharmacologic doses of 1,25(OH)2D3 stimulate trabecular bone matrix formation but produce impairment of mineralization, despite a high Ca×Pi product.

Effect of sex steroids on bone collagen synthesis in vitro

SummaryAlthough sex steroids are known to affect skeletal metabolism, their effects on bone collagen synthesis have not been studied. We have examined the direct effects of progesterone, 17β estradiol, testosterone, 5α dihydrotestosterone and dehydroepiandrosterone on bone collagen and noncollagen protein synthesis in cultures of calvaria obtained from 21-day fetal rats. Bones were incubated for 24 to 168 h and3H-proline was added for the last 2 h of culture. Incorporation of the label into collagenase-digestible protein (CDP)1 and noncollagen protein (NCP) was determined using repurified bacterial collagenase.Progesterone caused a dose dependent inhibition of the labeling of CDP at concentrations of 3×10−7M to 10−5M after 96 h of culture. A smaller inhibitory effect was observed on NCP. The inhibitory effect was slow in onset and persisted when bones were incubated for 48 h with progesterone and then transferred to control medium for 48 h. Progesterone also inhibited the incorporation of3H-thymidine and3H-uridine into fetal rat calvaria.After 24 h of culture, 17β estradiol and testosterone had no effects on the labeling of CDP and NCP. After 96 h, 17β estradiol had a small and inconsistent stimulatory effect on the labeling of CDP but testosterone had no effect. Neither hormone altered the inhibitory effects of parathyroid hormone, cortisol and progesterone. Dihydrotestosterone and dehydroepiandrosterone had no effects after 24 h and 96 h of culture. 17β estradiol, testosterone and dihydrotestosterone did not affect the incorporation of3H-uridine or3H-thymidine into fetal rat calvaria.Our studies indicate that progesterone is an inhibitor of bone collagen synthesis and estrogens and androgens are not major regulators of bone formation in vitro.

Effect of somatomedin and growth hormone on bone collagen synthesis in vitro

Abstract Although pituitary hormones, particularly growth hormone (GH), are known to influence skeletal growth, there is no evidence for a direct effect of GH or GH-dependent factors (somatomedins) on bone as opposed to cartilage. We have examined the effects of GH, a somatomedin (Sm) preparation, and serum from intact and hypophysectomized rats on bone collagen synthesis in cultures of 21-day fetal rat calvaria. Collagen synthesis and non-collagen protein synthesis were measured by the incorporation of 3H-proline into collagenase-digestible (CDP) and noncollagen protein (NCP). Bovine and rat GH caused a small inhibition in the incorporation of labeled proline into CDP which was not dose related. Sm in doses of 18–540 mU/ml increased the incorporation of proline into CDP up to three-fold after 24 hr in culture. Sm also had a smaller and more variable stimulatory effect on the labeling of NCP. The effects of Sm were maximal after 3 hr of treatment and were maintained for 96 hr. Sm (60 mU/ml) and insulin (10−8 M) had effects of similar magnitude and were not additive. The addition of 10% serum from hypophysectomized rats stimulated the labeling of both CDP and NCP, but serum from rats with intact pituitaries had a greater effect. Treatment of hypophysectomized rats with thyroxine, corticosterone, and GH. did not increase the bone collagen synthesis stimulating activity of the serum, although GH treatment did increase serum Sm activity by a pig cartilage assay. The results indicate that GH dose not stimulate bone collagen synthesis directly. However, they suggest that the pituitary gland either releases or stimulates the production of factors which stimulate bone collagen synthesis. Sm may be such a factor, but sulfation activity and bone collagen synthesis stimulating activity may be dissociable.