Biomedical subjects

T M Murray

Publications and source records attributed to T M Murray.

At least 19 recordsLinked to original sources

PubMed1996

Prevention and management of osteoporosis: consensus statements from the Scientific Advisory Board of the Osteoporosis Society of Canada. 4. Calcium nutrition and osteoporosis.

OBJECTIVE: To recommend appropriate levels of calcium intake in light of the most recent studies. OPTIONS: Dietary calcium intake, calcium supplementation, calcium and vitamin D supplementation; ovarian hormone therapy in postmenopausal women. OUTCOMES: Fracture and loss of bone mineral density in osteoporosis; increased bone mass, prevention of fractures and improved quality of life associated with osteoporosis prevention. EVIDENCE: Relevant clinical studies and reports were examined, in particular those published since the 1988 Osteoporosis Society of Canada position paper on calcium nutrition. Only studies in humans were considered, including controlled, randomized trials and prospective studies, using bone mass and fractures as end-points. Studies in early and later phases of skeletal growth were noted. The analysis was designed to eliminate menopause as a confounding variable. VALUES: Preventing osteoporosis and maximizing quality of life were given a high value. BENEFITS, HARMS AND COSTS: Adequate calcium nutrition increases bone mineral density during skeletal growth and prevents bone loss and osteoporotic fractures in the elderly. Risks associated with high dietary calcium intake are low, and a recent study extends this conclusion to the risk of kidney stones. Lactase-deficient patients may substitute yogurt and lactase-treated milk for cow's milk. True milk allergy is probably rare; its promotion of diabetes mellitus in susceptible people is being studied. RECOMMENDATIONS: Current recommended intakes of calcium are too low. Revised intake guidelines designed to reduce bone loss and protect against osteoporotic fractures are suggested. Canadians should attempt to meet their calcium requirements principally through food sources. Pharmaceutical calcium supplements and a dietician's advice should be considered where dietary preferences or lactase deficiency restrict consumption of dairy foods. Further research is necessary before recommending the general use of calcium supplements by adolescents. Calcium supplementation cannot substitute for hormone therapy in the prevention of postmenopausal bone loss and fractures. Adequate amounts of vitamin D are necessary for optimal calcium absorption and bone health. Elderly people and those who use heavy sun screens should have a dietary intake of 400 to 800 IU of vitamin D per day.

Aged↗

PubMed1996

Prevention and management of osteoporosis: consensus statements from the Scientific Advisory Board of the Osteoporosis Society of Canada. 7. Fluoride therapy for osteoporosis.

OBJECTIVE: To present the latest findings on the use of fluoride in the treatment of osteoporosis. OPTIONS: Plain sodium fluoride (NaF), enteric-coated sodium fluoride (EC-NaF), sodium monofluorophosphate (Na2FPO4), slow-release sodium fluoride (SR-NaF); fluoride with a calcium supplement. OUTCOMES: Fracture and loss of bone mineral density in osteoporosis; increased bone mass, prevention of fractures and improved quality of life associated with treatment. EVIDENCE: Relevant clinical studies and reports were examined, with an emphasis on recent prospective, randomized, controlled trials. Clinical practices in European countries were also considered. VALUES: Reducing fractures, increasing bone mineral density and minimizing side effects of treatment were given a high value. BENEFITS, HARMS AND COSTS: NaF therapy stimulates bone formation and may be effective in preventing osteoporotic fractures. It may be an acceptable alternative treatment to estrogen or bisphosphonate therapy and useful in premenopausal and corticosteroid-induced osteoporosis and in some patients with mild osteogenesis imperfecta. Toxic effects are dependent on formulation and dosage. They include a range of gastrointestinal and musculoskeletal conditions. EC-NaF is associated with less toxicity than plain NaF; its gastrointestinal toxicity is negligible. Na2FPO4 has no gastrointestinal toxicity, but can give rise to skeletal toxicity. SR-NaF appears to have no side effects when given intermittently. Carcinogenicity has not been found in vivo with fluoride therapy, despite in vitro results. RECOMMENDATIONS: New data indicate that fluoride therapy should be re-evaluated as a potentially effective treatment of osteoporosis with minimal side effects. More studies are needed of slow-release fluoride formulations, intermittent treatment schedules and calcium supplementation of fluoride. Studies should be undertaken to see if it is advantageous to initiate treatment with antiresorptive agents before or in combination with fluoride. Conclusive data have not been presented regarding the benefit of any specific type of calcium supplement. Further studies on the basic mechanism of action of fluoride on the skeleton are necessary to evaluate fluoride's potential to stimulate bone formation therapeutically.

Aged↗

PubMed1996

Normal parathyroid hormone responsiveness of bone-derived cells from a patient with pseudohypoparathyroidism.

Pseudohypoparathyroidism (PHP) is characterized by a lack of response to parathyroid hormone (PTH); however, normal skeletal responsiveness to PTH in some patients with PHP type Ia was previously suggested on the basis of clinical observations. To test this hypothesis, we measured cyclic adenosine monophosphate (cAMP) production in response to various agonists in bone-derived osteoblast-like (OBL) cells from trabecular explants obtained from an iliac crest biopsy of a 25-year-old woman with PHP. The patient was proved to have PHP type Ia on the basis of Albright's hereditary osteodystrophy and decreased activity of stimulatory guanine nucleotide-binding protein (Gs) in erythrocytes. Responsiveness of the patient's OBL cells was compared with OBL cells from eight subjects aged 18-39 years who had no evidence of metabolic bone disease. OBL cells from the patient responded to the following agonists (expressed in multiples of elevation of cAMP, stimulated/basal, mean +/- SE, n = 3): PTH, 3.8 +/- 0.3; forskolin, 8.2 +/- 0.2; and cholera toxin, 56.8 +/- 10.0. These responses were not significantly different from those of control OBL cells: PTH, 4.5 +/- 1.1 (range 2.4-7.5); forskolin, 7.7 +/- 1.4; and cholera toxin, 57.9 +/- 16.2. The normal cholera toxin response indicated the presence of functional Gs. Bone cells from patients with PHP type Ia may exhibit a normal PTH receptor-coupled adenylyl cyclase system in vitro despite clinical evidence of impaired hormone-responsive adenylyl cyclase in other tissues, including the kidney. Skeletal responsiveness to PTH may explain the long periods of spontaneous normocalcemia observed in this patient.

Adenylyl Cyclases↗

PubMed1996

Positive interaction between 17 beta-Estradiol and parathyroid hormone in normal human osteoblasts cultured long term in the presence of dexamethasone.

We previously developed two models of human osteoblasts with distinct differentiation stages using cells derived from iliac crest trabecular bone explants cultured long term in the presence (HOB + DEX) and absence (HOB - DEX) of 10 nM dexamethasone (DEX) (Wong et al., J Bone Miner Res 1990;5:803). Using these models from 36 subjects aged 41-80 years, we examined the effects of 17 beta-estradiol (E2) on cell proliferation, osteocalcin (OC) production, alkaline phosphatase (ALP) and basal and parathyroid hormone (PTH)-stimulated adenylate cyclase activities, as well as the steady-state mRNA levels of ALP, collagen type I(COLL), OC, and receptors for E2 (ER) and PTH (PTHr). E2 alone had no effect on [3H]thymidine uptake in (HOB - DEX) cells but appeared to stimulate the uptake in (HOB + DEX) cells in a dose-dependent manner, with maximum effect at 10(-10)M (p < 0.05). However, in the presence of 10(-6)M PTH, E2 inhibited the uptake in (HOB - DEX) cells (ANOVA, KW = 18.95, p < 0.005) but stimulated the uptake in (HOB + DEX) cells (KW = 13.52, p < 0.025). E2 decreased the amount of osteocalcin in culture media from both (HOB - DEX) and (HOB + DEX) cells (p < 0.05). PTH alone or E2, alone or in combination with 10(-9)M PTH, had no effect on ALP activity in (HOB - DEX) cells. In contrast, in (HOB + DEX) cells, E2 + PTH but not E2 alone, had biphasic effects on ALP activity, with maximum stimulation observed at 10(-11) and 10(-10)M E2, and a return to basal levels at 10(-9)M E2. E2 decreased basal adenylate cyclase activities in a dose-dependent manner in (HOB + DEX) but not (HOB - DEX) cells (KW = 13.48, p < 0.05). In (HOB + DEX) cells, E2 had biphasic effects on PTH-stimulated adenylate cyclase activity, with significant stimulation observed at 10(-10)M (p < 0.05). While E2 had no significant effect on osteoblastic marker mRNA levels in (HOB - DEX) cells, it decreased osteocalcin and stimulated PTHr mRNA levels in (HOB + DEX) cells. Thus, in our human osteoblastic cell models, estrogen regulated metabolic function largely in the more differentiated cells, by modifying the effects of PTH.

Adenylyl Cyclases↗

PubMed1996

Immunohistochemical localization of the estrogen receptor in human osteoblastic SaOS-2 cells: association of receptor levels with alkaline phosphatase activity.

We have previously shown that the combination of estrogen (E2) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] enhanced alkaline phosphatase (ALP) activity in human osteosarcoma SaOS-2 cells which had been grown in the presence of 10 nmol/L dexamethasone (SaOS + DEX cells). To determine whether this increase in ALP activity was associated with changes in receptor protein levels for E2 (ER) in individual SaOS + DEX cells, a monoclonal antibody to ER and a histochemical stain for ALP were used localize the expression of these proteins in fixed cells. Western and Northern blot analyses were used to determine whether E2 and 1,25(OH)2D3 affected immunoreactive ER protein and mRNA levels, respectively. Our results showed that immunohistochemical staining for ER was primarily nuclear, whereas histochemical staining for ALP was cytosolic. Treatment of cells with 1,25(OH)2D3, E2, or E2 + 1,25(OH)2D3 increased the levels of both ER and ALP activity, as visualized by enhanced cellular staining. Western analyses showed that 1,25(OH)2D3 and E2, separately and in combination, significantly increased ER protein levels. 1,25(OH)2D3 enhanced ER levels in a dose-dependent manner [analysis of variance (ANOVA), F = 3.91, p < 0.05]; this effect was augmented by E2 (ANOVA, F = 5.98, p < 0.005). In comparison, 17 alpha-E2 + 1,25(OH)2D3 and tamoxifen + 17 beta-E2 + 1,25(OH)2D3 did not increase ER levels compared with those obtained with 17 beta-E2 + 1,25(OH)2D3. ER mRNA levels were not significantly increased by E2, 1,25(OH)2D3, or E2 + 1,25(OH)2D3 together. In contrast, in a population of SaOS cells which had been in culture longer (approximately 40 passages more) than the previous cells, E2 + 1,25(OH)2D3 did not enhance ALP activity or ER levels above those obtained with 1,25(OH)2D3 alone. These results showed that in responsive SaOS cells, E2 enhanced both the stimulatory effects of 1,25(OH)2D3 on ALP activity and the activation of ER. Thus changes in ALP activity are associated with changes in ER levels in SaOS + DEX cells.

Alkaline Phosphatase↗

PubMed1996

Effects of 1alpha,25-dihydroxy-16ene, 23yne-vitamin D3 on osteoblastic function in human osteosarcoma SaOS-2 cells: differentiation-stage dependence and modulation by 17-beta estradiol.

We compared the separate effects of 1alpha,25-dihydroxyvitamin D3 (1alpha,25(OH)2D3) and its analog, 1alpha,25-dihydroxy-16ene,23yne-vitamin D3 (1alpha25(OH)2-16ene,23yne-D3), as well as their interactions with 17-beta estradiol (E2) in our human osteosarcoma SaOS-2 cell models representing two stages of differentiation, the SaOS+DEX and SaOS-DEX cells. SaOS+DEX cells have been previously shown to express higher PTH-stimulated adenylate cyclase (PTH-AC) and basal alkaline phosphatase (ALP) activities compared with SaOS-DEX cells. ALP: In SaOS+DEX cells, 0.1 nmol/L analog, but not 1alpha,25(OH)2D3, increased ALP activity 1.7-fold (p < 0.05). Instead, 1 nmol/L 1alpha,25(OH)2D3 increased ALP 1.4-fold (p < 0.05). In these cells, E2 enhanced 1alpha,25(OH)2D3-stimulated ALP activity (ANOVA, F = 51.22, p <0.0001), while inhibiting the effect of the analog. [3H]-Thymidine uptake: In SaOS+DEX cells, 1alpha,25(OH)2D3 had biphasic effects (ANOVA, F = 13.08, p < 0.0001), which were not altered by E2. In contrast, the analog was stimulatory only with E2 (ANOVA, F = 3.59, p < 0.025). Osteocalcin (OC): 1alpha,25(OH)2D3 and its analog stimulated OC production in SaOS-DEX cells with smaller effects in SaOS+DEX cells. In SaOS-DEX cells, E2 enhanced the effect of 1alpha,25(OH)2D3, but not that of the analog. PTH-AC: In SaOS-DEX cells, 100 nmol/L analog inhibited PTH-AC activities by 50% (p < 0.01), whereas 1alpha,25(OH)2D3 had little effect. In SaOS+DEX cells, both compounds inhibited PTH-AC approximately 35%. E2 inhibited the effect of the analog in SaOS-DEX cells, but enhanced the effects of both compounds in SaOS+DEX cells. These results show that the analog 1alpha,25(OH)2-16ene,23yne-D3 was effective in regulating osteoblastic function; its effects were modulated by E2 and dependent upon the stage of osteoblast differentiation.

Adenylyl Cyclases↗

PubMed1996

17 beta-oestradiol enhances the stimulatory effect of 1,25-dihydroxyvitamin D3 on alkaline phosphatase activity in human osteosarcoma SaOS-2 cells in a differentiation-dependent manner.

We tested the effect of osteoblastic differentiation on the interactive effects of 17 beta-oestradiol (E2) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on alkaline phosphatase activity. As cell models we utilized the more differentiated human osteosarcoma (SaOS) cells that had been cultured for 6 days in medium containing 10 nM dexamethasone (Dex) (SaOS+Dex cells) and the less differentiated cells cultured in the absence of Dex (SaOS-Dex cells). The cells were challenged with 1,25(OH)2D3 in the presence or absence of Dex for 24 h and then with E2 for an additional 24 h. In SaOS-Dex cells, alkaline phosphatase activity remained constant over the 48-h period and was not significantly affected by E2, 1,25(OH)2D3 or 1,25(OH)2D3+E2 treatment. On the other hand, in SaOS+Dex cells, 1,25(OH)2D3 and E2+1,25(OH)2D3 stimulated alkaline phosphatase activity (ANOVA, F = 154.2, P < 0.0001) with the maximal response at 48 h (P < 0.01). In SaOS+Dex cells, 1,25(OH)2D3 had dose-dependent stimulatory effects which were strongly enhanced by 10 nM E2 (ANOVA, F = 46.0, P < 0.001). Studies on dose-dependent effects of E2, in the presence or absence of 100 nM 1,25(OH)2D3, revealed that in the presence of 1,25(OH)2D3, the E2 dose-response curve was biphasic in SaOS+Dex cells (ANOVA, F = 3.40, P < 0.005), with maximum stimulation at 10 nM E2 (P < 0.01). The specificity of E2 was verified using the inactive 17 alpha-oestradiol and the oestrogen antagonist, tamoxifen. These data indicate that E2 and 1,25(OH)2D3 have positive interactive effects on alkaline phosphatase activity in human osteoblasts, and suggest that the expression of this interaction is dependent on the stage of differentiation of the cells.

Alkaline Phosphatase↗

PubMed1996

Mechanisms of bone loss.

We have seen rapid and important advances in the understanding of bone resorption processes at the cellular and molecular levels. Indeed, the field of molecular and cellular biology of bone is proliferating at a virtually exponential rate. Osteoclastic bone resorption, the major process involved in Type 1 osteoporosis, is the target of several pharmacological agents for the treatment of osteoporosis, and is the potential target of several agents that are proposed for the treatment of osteoporosis. This review will focus on (1) the factors known or postulated to affect bone loss; (2) the function of the differentiated osteoclast and the pharmacological effects on osteoclast function; (3) the processes involved in the generation and differentiation of mature osteoclasts and, again, the pharmacological implications of these processes.

Adult↗

PubMed1995

Age-dependent expression of osteoblastic phenotypic markers in normal human osteoblasts cultured long-term in the presence of dexamethasone.

We have previously shown that osteoblasts derived from trabecular bone explants and cultured long term in 10 nM dexamethasone ((HOB + DEX) cells) exhibited properties consistent with a more differentiated phenotype compared with those grown in the absence of dexamethasone ((HOB-DEX) cells). To characterize these two cell models further, we measured the steady-state mRNA levels of the phenotypic markers alkaline phosphatase (ALP), collagen type I (COLL) and osteocalcin (OC), OC production, and the activities of ALP and parathyroid hormone (PTH)-stimulated adenylate cyclase. These findings were then correlated with the age and sex of the bone donors. Long-term culture in dexamethasone significantly increased ALP and OC mRNA levels and the activities of ALP and PTH-stimulated adenylate cyclase but not OC production, in (HOB + DEX) compared with (HOB-DEX) cells (p < 0.05). When the data were examined with respect to the age of the bone donor, age-dependent differences in the expression and responses to dexamethasone were apparent. ALP and PTH-stimulated adenylate cyclase activities decreased with increasing age of the bone donor in (HOB-DEX) and (HOB + DEX) cells (p < 0.05). There were no significant correlations between phenotypic marker mRNA levels and bone donor age in (HOB-DEX) and ((HOB + DEX) cells. All age-dependent decreases in ALP and PTH-stimulated cyclase activities were enhanced in the (HOB + DEX) cells. However, when the data were examined according to the sex of the bone donor, there were no differences in mRNA levels, OC production, or ALP and cyclase activities between cells from male and female donors. These results indicate an age dependence in the expression of osteoblastic markers in human bone cells at different stages of differentiation: thus osteoblastic cultures derived from older donors are likely to contain fewer osteoprogenitor cells, lower levels of glucocorticoid receptors or represent more differentiated osteoblasts compared with those derived from younger donors.

Adenylyl Cyclases↗

PubMed1995

Hockey helmets, face masks, and injurious behavior.

OBJECTIVE: To educate physicians about factors that contribute to injurious behaviors in ice hockey and to propose that the medical community play a role in advocating change within the sport. METHODS: A review of relevant literature on the topic was conducted, with information drawn from scientific journal publications, conference proceeding, theses, and newspaper publications. RESULTS: The introduction of mandatory head and facial protection has been effective in virtually eliminating ocular, facial, and dental injuries in youth hockey, but it has also been problematically linked with an increase in catastrophic spinal injuries. Players adopt a false sense of security when donning the equipment, leading them to take excessive and unwarranted risks because of the protection they are supposedly afforded. The addition of these protective devices has also altered how officials perceive game situations, leading them to be more lenient in administering penalties. The net result has been an increase in illegal and injurious behaviors, such as checking from behind. CONCLUSION: Physician advocacy may play an important role in effecting change within the sport.

Athletic Injuries↗

PubMed1994

Carboxyl-terminal parathyroid hormone peptide (53-84) elevates alkaline phosphatase and osteocalcin mRNA levels in SaOS-2 cells.

Previous findings in our laboratory have shown that hPTH-(53-84) stimulates alkaline phosphatase activity in dexamethasone-treated ROS 17/2.8 cells. In the present study, we examined the effects of hPTH-(53-84) and hPTH-(1-34) on the expressions of alkaline phosphatase, osteocalcin, and collagen type I mRNA levels in the human osteosarcoma cell line SaOS-2. The effect of hPTH-(53-84) on alkaline phosphatase and osteocalcin message levels was dose dependent (ANOVA, p < 0.005 and p < 0.001, respectively), with significant stimulation observed at 10 nM. Treatment with 10 nM hPTH-(53-84) for 24 h resulted in significant 2- and 1.4-fold increases in mRNA levels for alkaline phosphatase and osteocalcin, respectively (p < 0.05), but had no effect on collagen type I expression. The increased alkaline phosphatase mRNA levels was associated with a 1.5-fold increase in enzyme activity (p < 0.05). In contrast, under similar incubation conditions, hPTH-(1-34) had no significant effects on alkaline phosphatase or osteocalcin mRNA levels. On the other hand, hPTH-(1-34) had dose-dependent stimulatory effects on collagen type I mRNA levels (ANOVA, p < 0.001), 10 nM hPTH-(1-34) stimulating collagen type I expression 1.6-fold (p < 0.05). The results indicate that carboxyl-terminal hPTH-(53-84) has direct and unique biologic effects in human osteoblast-like cells in culture.

Alkaline Phosphatase↗

PubMed1994

In vitro study of osteoblastic cells from patients with idiopathic osteoporosis and comparison with cells from non-osteoporotic controls.

We have examined bone cells derived from iliac crest trabecular explants of 30 patients with idiopathic osteoporosis and 45 control subjects in order to determine whether intrinsic abnormalities in osteoblast function may contribute to the decreased bone formation observed in this disease. Bone cells isolated from all subjects expressed several in vitro characteristics of the osteoblast phenotype including adenylate cyclase responsiveness to parathyroid hormone (PTH) and prostaglandin E1 (PGE1), basal and 1,25(OH)2D3-stimulated alkaline phosphatase activity and osteocalcin production. Results were compared amongst three subject groups; young controls less than 40 years old, older controls over 40 years old, and osteoporotics. Osteoporotic cells were found in general to be fully active in vitro. There were no differences between osteoporotic and control cells in their basal levels of adenylate cyclase, or alkaline phosphatase, in their growth rates, or cell morphology. The cyclic AMP (cAMP) response to PTH was significantly lower in osteoporotic cells (71%, p < 0.01) and older control cells (64%, p < 0.005) relative to the response in cells from younger controls, suggesting that the decreased responsiveness in osteoporotic cells was due to subject age rather than the osteoporotic state. At the same time, the cAMP responses to PGE1 and cholera toxin were similar in cells from all three subject groups. The response to forskolin was reduced to about 40% in osteoporotic cells compared with controls, but this was not mirrored by similar differences in the responses to PTH, PGE1 or cholera toxin, suggesting that the availability of catalytic subunits is not rate-limiting in these cells. 1,25(OH)2D3-stimulated osteocalcin production was 220% higher in osteoporotics than in older controls, but the numbers tested were small and the difference did not reach significance. The one significant abnormality we observed in osteoporotic cells was in alkaline phosphatase activity: 1,25(OH)2D3-stimulated alkaline phosphatase activity was twofold higher in osteoporotics than in younger (p < 0.05), older (p < 0.05) and pooled controls (p < 0.025). The significance of this finding is unknown, but we postulate that it may reflect an intrinsic abnormality in osteoblast function in patients with idiopathic osteoporosis.

Adolescent↗

PubMed1994

17 beta-estradiol and parathyroid hormone potentiate each other's stimulatory effects on alkaline phosphatase activity in SaOS-2 cells in a differentiation-dependent manner.

We studied the effects of 17 beta-estradiol (E2) and PTH on alkaline phosphatase activity in SaOS-2 cells that had been passaged and grown continually in the presence (SaOS + Dex) or absence (SaOS - Dex) of 10(-8) M dexamethasone (Dex). We showed that the more differentiated SaOS + Dex cells had higher alkaline phosphatase activity and PTH-responsive adenylate cyclase than the less differentiated SaOS - Dex cells. In SaOS - Dex cells, E2 or PTH (1 x 10(-11)-1 x 10(-6) M) had no effect on alkaline phosphatase activity. On the other hand, in SaOS + Dex cells, PTH and E2 each had small but very significant stimulatory effects on alkaline phosphatase activity. The combined effects of PTH and E2 resulted in potentiation which was dose dependent for PTH and E2. 17 alpha-estradiol and tamoxifen (1 x 10(-11)-1 x 10(-6) M) had no effect on PTH-stimulated alkaline phosphatase activity in SaOS + Dex cells, but the latter inhibited the E2 effect, clearly demonstrating its specificity. In conclusion, we have shown that in more differentiated osteoblastic cells, E2 and PTH have interactive effects on alkaline phosphatase activity.

Adenylyl Cyclases↗

PubMed1993

Pseudohypoparathyroidism with osteitis fibrosa cystica: direct demonstration of skeletal responsiveness to parathyroid hormone in cells cultured from bone.

A young girl had tibial osteotomies at age 14 for genu valgum and then had recurrent tibial cysts over a number of years. Hypocalcemia and hyperphosphatemia were first noted at age 21. The diagnosis of pseudohypoparathyroidism was made at age 28, when elevated plasma PTH was detected. Clinical and biochemical features, including a PTH response test and assay of RBC Gs, established the diagnosis of pseudohypoparathyroidism type 1b. Failure to suppress plasma PTH with vitamin D therapy led to an exacerbation of her cystic bone disease; there were widespread lytic lesions radiologically, most of which took up [99mTc]diphosphonate on bone scan. Microradioscopy revealed evidence of resorption of phalangeal tufts. Bone biopsy showed osteitis fibrosa cystica. During an orthopedic procedure, trabecular bone fragments were taken from her right humerus, and bone-derived cells cultured using an explant technique. The cultured cells were osteoblast-like in morphology, fully responsive to PTH, cholera toxin, forskolin, and PGE1 in vitro, and had an alkaline phosphatase and osteocalcin response to 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Following this examination of skeletal responsiveness, attempts were made to suppress the elevated plasma PTH levels and symptomatic bone disease by optimizing therapy with oral 1,25-(OH)2D3. When bone pain associated with the cystic bone disease failed to resolve, the patient underwent total parathyroidectomy, following which the bone pain gradually resolved. This is the first direct demonstration of PTH responsiveness in cultured bone cells in the syndrome of pseudohypoparathyroidism with osteitis fibrosa cystica.

Adenylyl Cyclases↗

PubMed1993

Age-related changes in hepatic and splenic insulin receptors and serum insulin and glucose levels in inbred mice.

Inbred mice of strains A/J, DBA/1J, and SJL/J were housed and aged in our animal colony, and parameters of carbohydrate metabolism were assessed at various ages. The patterns of age-related change were both organ- and strain-specific. Age-related changes in two of the strains were associated with relative carbohydrate intolerance. Common to all three strains was a biphasic pattern of change in hepatic insulin receptor number, with a decrease in early life and a return to earlier levels late in life. In both A/J and DBA/1J mice, there was a sharp increase in serum insulin level (twofold to 9.7-fold) that corresponded to the decrease in hepatic insulin receptors and was associated with hyperglycemia; no significant change in serum insulin or glucose levels was seen in SJL/J mice, despite a similar biphasic pattern in hepatic insulin receptor concentration. Age-related changes in splenic insulin receptors resembled changes in the liver in A/J and SJL/J mice, ie, there were synchronous biphasic age-related patterns. This was not the case in the spleens of DBA/1J mice, in which we did not observe age-related changes. There was no change in insulin receptor affinity with age, nor was there any difference in affinity between tissues or mouse strains. The pattern of change in hepatic insulin receptors and serum insulin levels was more complex than has been previously recognized. We do not know the mechanisms responsible for this complex pattern, but it must involve at least two discrete age-related events.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1991

Dexamethasone-treated ROS 17/2.8 rat osteosarcoma cells are responsive to human carboxylterminal parathyroid hormone peptide hPTH (53-84): stimulation of alkaline phosphatase.

We tested the effects of various parathyroid hormone (PTH) peptides on alkaline phosphatase (ALP) activity in the osteoblastic cell line ROS 17/2.8. In dexamethasone-treated ROS 17/2.8 cells there was a dose-related increase in ALP activity due to treatment with hPTH (53-84). ALP activity was stimulated by 10 nM hPTH (53-84) by a mean of 1.51 +/- 0.07-fold (P less than 0.001) in nine experiments, whereas the same dose of bPTH (1-34) and bPTH (1-84) inhibited enzyme activity to 0.36 +/- 0.02-fold (P less than 0.001) and 0.37 +/- 0.03-fold (P less than 0.001), respectively. Significant stimulation of ALP activity occurred with doses of hPTH (53-84) as low as 0.01 nM. There was no stimulation of enzyme activity by hPTH (53-84) in the absence of dexamethasone; the maximum ALP response to hPTH (53-84) occurred between 96 and 144 hours, and no significant effect was seen at time periods less than 96 hours. The optimum dose of dexamethasone required to enable the response to hPTH (53-84) was 10 nM. Carboxylterminal PTH fragments had a specific stimulatory effect on ALP activity in dexamethasone-treated ROS 17/2.8 cells, but the aminoterminal PTH effect appeared to be dominant, as the equimolar combination of bPTH (1-34) and hPTH (53-84) resulted in inhibition of ALP activity. Thus, in order for the effects of carboxylterminal fragments to be manifest, the cells would have to be stimulated under conditions in which the aminoterminal receptor is unoccupied; this could occur under some in vivo conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗

PubMed1990

Long-term effects of physiologic concentrations of dexamethasone on human bone-derived cells.

Bone cells derived from human trabecular explants display osteoblastic features. We examined the modulation of alkaline phosphatase activity and cAMP production as the result of exposing trabecular explants to physiologic concentrations of dexamethasone for 4 weeks during cellular outgrowth and subculture. Cells treated with dexamethasone were observed to grow generally more slowly than control cells. Cells appeared larger and more polygonal, and staining for alkaline phosphatase was more intense in the dexamethasone-exposed cultures. There was a progressive increase in cellular PTH responsiveness with increasing duration of exposure of cells to dexamethasone. Cells grown for 6 weeks in 3 x 10(-8) M dexamethasone had a 10-fold increase in PTH-stimulated cyclic AMP accumulation. Dexamethasone-treated cells also had a significantly increased alkaline phosphatase activity. 1,25-(OH)2D3-stimulated alkaline phosphatase activity was increased approximately 20-fold. cAMP responses were significantly increased to PTH (21.7-fold), PGE1 (2.67-fold), and forskolin (4.81-fold), but not to cholera toxin. Dexamethasone-treated cells also had a mean decrease in 1,25-(OH)2D3-stimulated osteocalcin production to 26.2% of control values (p less than 0.001). Hydrocortisone treatment gave rise to similar effects but of smaller magnitude than those of dexamethasone. Testosterone did not have a significant effect on alkaline phosphatase activity or cAMP production. Skin fibroblasts showed a significant enhancement of alkaline phosphatase activity in response to dexamethasone, but of a much smaller magnitude than in bone cells. The phenotypic changes induced by long-term culture in dexamethasone are consistent with the promotion of a more differentiated osteoblastic phenotype.

Adenylyl Cyclases↗

PubMed1990

Fluoride-induced fractures: relation to osteogenic effect.

The possible effects of fluoride in inducing fractures were studied in 61 patients treated with sodium fluoride (NaF), 40-60 mg daily in combination with calcium and vitamin D. Nine patients developed the fluoride-(F) related lower extremity pain syndrome. Four other patients had stress fractures associated with trauma. Seven of the 61 patients had 10 upper femur fractures of which 5 were stress fractures. The bone mineral mass of the central skeleton including the hips was measured by neutron activation and the results expressed as a calcium bone index (CaBI) which normalizes the results to that of young adults of the same body size (normal range 0.75-1.2). At the time of hip fracture, 4 patients with a minimal increase in bone mass (mean delta CaBI 0.01) had 4 femur fractures and 3 patients with a marked increase (mean delta CaBI 0.24) had 6. The 7 patients with upper femur fractures at 4 years had a significantly higher bone fluoride retention, 30 mg/g Ca compared with 23.9 mg/g Ca for the other 54 (p less than 0.02) and were older, 73.1 versus 64.2 years (p less than 0.01). Using all 61 fluoride-treated patients, femur fractures/patient were significantly correlated to bone fluoride (p less than 0.05) and to age (p less than 0.05). By partial correlation, only the correlation between hip fractures/patient and bone fluoride remained significant after controlling for the effect of age (p less than 0.05). These results suggest that fluoride therapy may be implicated in the pathogenesis of hip fractures which may occur in treated patients despite a rapid, marked increase in bone mass. The lower extremity pain syndrome is not frequently associated with stress fractures in this study.

Aged↗