Glucocorticoids increase osteoblast-like bone cell response to 1,25(OH)2D3

Tumor necrosis factor alpha decreases 1,25-dihydroxyvitamin D3 receptors in osteoblastic ROS 17/2.8 cells

Bone remodeling is a complex process regulated by systemic hormones, local cytokines, and growth factors. One cytokine, tumor necrosis factor alpha (TNF-alpha), is known to have potent inhibitory effects on osteoblast matrix protein production and to stimulate osteoclast recruitment. We have previously shown that TNF-alpha inhibits 1,25-(OH)2D3-stimulated synthesis of bone gla protein (BGP), an abundant and osteoblast-specific matrix constituent. We hypothesized that the mechanism of TNF-alpha action included inhibition of intracellular 1,25-(OH)2D3 receptor (VDR) number or function. To test this, the osteoblastic cell line ROS 17/2.8 was cultured in the presence or absence of TNF-alpha (100 ng/ml), and binding of [3H]1,25-(OH)2D3 to 0.3 M KCl extracts of cytosol was measured by equilibrium assay. Specific [3H]1,25-(OH)2D3 binding decreased 70%, 25 h after addition of TNF-alpha. The decrease in [3H]1,25-(OH)2D3 binding was seen by 18 h, was sustained throughout the 72 h culture period, and was greater in low-density cultures. Scatchard analysis confirmed that TNF-alpha (100 ng/ml for 24 h) caused a decrease in the number of binding sites without change in VDR affinity. Northern analysis with a VDR riboprobe revealed that the decrease in VDR occurred without a change in the 4.4 kb steady-state VDR mRNA [VDR/cyclophilin mRNA signal ratio: control, 2.25; TNF-alpha, 2.24 (24 h), 2.17 (40 h), n = 2 flasks/time point]. These results suggest that TNF-alpha action on osteoblastic cells includes an inhibitory effect on VDR number at a point distal to the synthesis of VDR mRNA.

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.

Glucocorticoid-induced osteoporosis

Glucocorticoid induced osteoporosis (GC-OP) is the most important form of all secondary osteoporoses. Mainly from in vitro and animal studies a lot of information exists concerning the underlying pathogenetic mechanisms. Some findings are still controversial but it is generally accepted that the three most important mechanisms are inhibition of osteoblastic matrix formation, stimulation of osteoclastic bone resorption and deterioration of intestinal calcium resorption with consecutive mild secondary hyperparathyroidism. In the individual patients the time between the beginning of corticoid therapy and clinical manifestation of osteoporosis varies considerably. If there is really a threshold dosage of corticoids is still debated. Besides dosage and duration of steroids age, sex, other risk factors of osteoporosis and underlying disease may be important factors. In contrast to the clinical prominence of GC-OP only little experience exists in counteracting the detrimental effects of corticoids on bone tissue. For pure prevention it seems reasonable to overcome intestinal calcium malabsorption by calcium or vitamin D. Concerning treatment of manifest GC-OP we studied the effect of salmon calcitonin (sCT) in patients with chronic obstructive lung disease. 18 patients injected themselves 100 U sCT every second day subcutaneously while 18 randomized patients served as untreated controls. There was a significant pain reduction in the sCT group and after six months the mineral content of the distal radius had increased by 2.7% despite a daily mean intake of 16.2 mgs prednisone during that time. In the control group (mean daily prednisone dose 16.8 mgs) the mineral content decreased with 3.5% on the average (p less than 0.001).

Effects of ascorbic acid on alkaline phosphatase activity and hormone responsiveness in the osteoblastic osteosarcoma cell line UMR-106

L-ascorbic acid at physiological concentrations (10 micrograms/ml) increased alkaline phosphatase activity in the osteoblastlike rat osteosarcoma cell line, UMR-106. The increase was dose-dependent and detectable at 6 hours after the addition of 100 micrograms/ml ascorbic acid to the medium. Treatment of the cells with 100 micrograms/ml ascorbic acid potentiated the response of cAMP to both PTH and PGE1, while cell growth was inhibited. Furthermore, the number of colonies formed by the cells grown in the soft agar was significantly reduced by increasing concentrations of ascorbic acid. These results indicate that ascorbic acid might play some role in the differentiation of osteoblasts.

Differential effect of hydrocortisone on eosinophil and neutrophil proliferation

Glucocorticosteroid therapy results in an increase in the number of circulating neutrophils and a decrease in the number of eosinophils. Utilizing the double layer soft agar technique, we examined the effect of physiologic to pharmacologic concentrations of hydrocortisone on the proliferation of human neutrophil progenitors and eosinophil progenitors from peripheral blood and bone marrow. When peripheral blood cultures were studied, eosinophil proliferation was inhibited in a dose-responsive fashion with 10(-8) - 10(-5) M hydrocortisone succinate, and comprised 49 +/- 4% of the colonies in control cultures and only 4 +/- 1% (P less than 0.01) at pharmacologic levels of hydrocortisone (10(-5) M). The number of neutrophil colonies, on the other hand, increased by 31% when 10(-5) M hydrocortisone was added to cultures. In order for corticosteroids to exert this effect, it was necessary to add them within 24 h of the initiation of culture. The effect of hydrocortisone on granulocyte proliferation could not be blocked by progesterone, a structurally analogous steroid. To determine whether hydrocortisone was acting directly on the progenitor cell or via an effector cell, its effect on modulating cell populations and stimulating-factor production was studied. Removal of E-rosetting cells and/or adherent cells did not affect the inhibition of eosinophil colony growth or the enhancement of neutrophil colony growth. Furthermore, addition of the potent inhibitor of T cell function, cyclosporin A, failed to affect eosinophil colony frequency, suggesting that inhibition of T cell function was an unlikely explanation for the observed hydrocortisone effect. Leukocyte conditioned media (LCM), derived from peripheral blood mononuclear cells incubated with hydrocortisone, was devoid of both neutrophil and eosinophil colony-stimulating activity, whereas a control LCM stimulated both neutrophil and eosinophil proliferation. The data suggest that the observed hydrocortisone effect on granulocyte colony formation is unlikely to be mediated by an intermediary, and that hydrocortisone acts directly on progenitor cells.

Effect of oral 1,25-dihydroxyvitamin D and calcium on glucocorticoid-induced osteopenia in patients with rheumatic diseases

Twenty-three rheumatic disease patients with glucocorticoid-induced osteopenia (defined by measurement of forearm bone mass) completed an 18-month double-blind, randomized study to assess the effect of oral calcium and 1,25-dihydroxyvitamin D (1,25-OH2D) or calcium and placebo on bone and mineral metabolism. Intestinal 47Ca absorption was increased (P less than 0.05) and serum parathyroid hormone levels were suppressed (P less than 0.01) by 1,25-OH2D (mean dose 0.4 micrograms/day); however, no significant gain in forearm bone mass occurred, and bone fractures were frequent in both groups. In the 1,25-OH2D group, histomorphometric analysis of iliac crest biopsy specimens demonstrated a decrease in osteoclasts/mm2 of trabecular bone (P less than 0.05) and parameters of osteoblastic activity (P less than 0.05), indicating that 1,25-OH2D reduced both bone resorption and formation. We conclude that 1,25-OH2D should not be used for treatment of glucocorticoid-induced osteopenia. Since patients receiving calcium and placebo did not exhibit a loss of forearm bone mass, elemental calcium supplementation of 500 mg daily might be useful to maintain skeletal mass in patients receiving long-term glucocorticord therapy.

Glucocorticoids increase the 1,25(OH)2D3 receptor concentration in rat osteogenic sarcoma cells

We have used cultured osteoblastlike rat osteogenic sarcoma cells (ROS 17/2) which have receptors for 1,25(OH)2D3 and for glucocorticoids, and have examined the modulation of the 1,25(OH)2D3 receptor by the potent glucocorticoid triamcinolone acetonide. We report that triamcinolone acetonide caused an increase of the 1,25(OH)2D3 receptor concentration in these cells but it did not affect the affinity of the receptor to 1,25(OH)2D3; this phenomenon occurred in a dose-dependent fashion for triamcinolone (10(-9) to 10(-7) M) with a maximum increase of 1,25(OH)2D3 receptor concentration of approximately equal to twofold. During the culture period, the 1,25(OH)2D3 receptor concentration was altered both in untreated as well as in triamcinolone-treated cells, being highest at the early logarithmic phase and diminished progressively as cells approached confluence. However, throughout the culture period, the 1,25(OH)2D3 receptor concentration was higher in the triamcinolone-treated cells.

Effects of 1 alpha,25-dihydroxyvitamin D3 and glucocorticoids on the growth of rat and mouse osteoblast-like bone cells

The effects of 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) and its interaction with glucocorticoids to regulate bone cell growth were studied in osteoblast-like (OH) cell cultures. Owing to our earlier findings that species difference and cell density at the time of treatment modified hormonal responses, comparisons were made between rat and mouse cells and sparse and dense cultures. 1,25(OH)2D3 inhibited cell proliferation in both species regardless of cell density. The magnitude of inhibition was larger in mouse cells, but the sensitivity to 1,25(OH)2D3 was the same for both species. Other metabolites, 25(OH)D3 and 24R,25(OH)2D3, were greater than 100-fold less potent than 1,25(OH)2D3 even in serum-free medium, which is similar to their ratio of affinity for the 1,25(OH)2D3 receptor. Dexamethasone, as previously shown, inhibited sparse and dense mouse cell cultures and sparse rat cell cultures while stimulating dense rat cell cultures to grow. The inhibitory actions of 1,25(OH)2D3 were not additive to the inhibitory dexamethasone effects. However, 1,25(OH)2D3 addition resulted in attenuation of the stimulatory effect of dexamethasone. These responses to 1,25(OH)2D3 and dexamethasone were dependent on cell density and not selective attachment of certain cell types at either plating density. In conclusion, the findings demonstrated that 1,25(OH)2D3 exerts an inhibiting action on both mouse and rat bone cell proliferation. This effect must be reconciled with the in vivo beneficial actions of 1,25(OH)2D3 on bone metabolism. Also, the likelihood of decreased cell number must be considered when biochemical activities are assessed after vitamin D treatment in vitro.

Effects of phosphate and 1,25(OH)2D3 on in vitro bone collagen synthesis in the hypophosphatemic mouse

Calvarial bones from hypophosphatemic (Hyp) mice and normal littermates were cultured in a chemically defined medium to determine: (a) the effect of medium phosphate (Pi) concentration (1, 2, and 3 mM) on collagen synthesis; (b) the effect of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] (10(-12)M-10(-7)M) on collagen synthesis; and (c) whether bone responsiveness to 1,25(OH)2D3 was affected by changes in medium Pi concentration. Bone collagen synthesis was evaluated by measuring [ 3H ]hydroxyproline formation. The distribution of labeled hydroxyproline between bone explant and culture medium (total and dialyzable fraction) was studied. These experiments confirm that 1,25(OH)2D3 inhibits specifically bone collagen synthesis in vitro. We did not detect any effect of medium Pi concentration on basal collagen synthesis but were able to demonstrate that lowering medium Pi concentration increased the 1,25(OH)2D3-induced inhibition of collagen synthesis. Bones from both genotypes responded to 1,25(OH)2D3, but modulation of this response by changes in Pi concentration was altered in Hyp bone as, in contrast to normal bone, its response to 1,25(OH)2D3 was unaffected when medium Pi concentration was decreased from 3 to 2 mM. These findings support the hypothesis of an altered response of bone to 1,25(OH)2D3 in the Hyp mouse.

Studies on osteoporosis VII. Effect of 17 beta-hydroxy-4-estren-3-one 17-decanoate on experimental osteoporosis

Total body neutron activation analysis was employed to measure total calcium in C3H/St (Ha) female mice. Ninety-nine percent of total body calcium is in bone and loss of calcium was used as an index of osteoporosis. Heparin (500 U/kg B.I.D.) treatment for three months resulted in significant osteoporosis. 17 beta-Hydroxy-4-estren-3-one 17-decanoate 1.5 mg/kg or 4 mg/kg twice monthly prevented this heparin accelerated osteoporosis. The results suggest that 17 beta-hydroxy-4-estren-3-one 17-decanoate may be capable of preventing bone loss and partially increasing bone mass in patients exposed to osteoporosis inducing regimens.

Effects of hydrochlorothiazide and dietary sodium restriction on calcium metabolism in corticosteroid treated patients

The effect of treatment with hydrochlorothiazide (HCT) and dietary sodium restriction on calcium economy in glucocorticoid-treated patients was investigated. Fractional 47Ca intestinal absorption (FCaA) and fractional urinary calcium excretion (FCaEx) were measured in six normal individuals and in ten patients receiving glucocorticoids for chronic obstructive pulmonary disease before and after 60 days of treatment with a 50 mEq sodium diet and HCT 50 mg twice daily. FCaA was significantly decreased on glucocorticoid-treated patients (27.5 +/- 4.3%) when compared to normal individuals (41.8 +/- 2.8%, p less than 0.005). A significant increase in FCaA to 38.9 +/- 4.8%, (P less than .05) was seen in glucocorticoid-treated patients after treatment with HCT and dietary sodium restriction. Baseline FCaEx was higher in glucocorticoid-treated patients than in the normal subjects. A significant decrease in FCaEx after dietary sodium restriction and thiazide administration occurred in both normal (0.99 +/- 0.28% before vs. 0.69 +/- 0.30% after; p less than .025) and glucocorticoid-treated patients (1.46 +/- 0.19% before vs. 0.73 +/- 0.13% after p; less than 0.025). These data suggest that dietary sodium restriction and HCT therapy may improve total body calcium economy in glucocorticoid-treated patients by increasing intestinal calcium absorption and decreasing urinary calcium excretion.