Evidence for coordinated regulation of osteoblast function by 1,25-dihydroxyvitamin D3 and parathyroid hormone

AbstractFrom several animal studies and clinical observations it became evident that at target tissue level 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and parathyroid hormone (PTH) must act in an interrelated manner. In the present study we examined the interaction between 1,25-(OH)2D3 and PTH in the target cell of these hormones in bone, the osteoblast. In addition we studied the role of PTH-activated signal pathways. The three osteoblastic cell lines UMR 106, ROS 172.8 and MG-63 were used as model systems. In UMR 106 cells 1,25-(OH)2D3 and PTH caused a synergistic up-regulation of the vitamin D receptor (VDR) which was accompanied by a synergistic induction of VDR mRNA expression whereas in both ROS 172.8 and MG-63 cells no interaction was observed. In UMR 106 cells the effect of PTH on homologous up-regulation of VDR could be mimicked by the cAMP agonist forskolin and by dibutyrylic-CAMP. Phorbol ester activation of protein kinase C reduced basal as well as 1,25-(OH)2D3-induced up-regulation of VDR. 1,25-(OH)2D3 induced 24-hydroxylase activity in UMR 106 and MG 63 cells and, in contrast to VDR regulation, in both cell lines PTH and 1,25-(OH)2D3 synergistically induce 24-hydroxylase activity. Similar to VDR regulation the effect of PTH was mimicked by activation of cAMP production whereas protein kinase C activation reduced the induction by 1,25-(OH)2D3 Finally, we examined the interaction with respect to osteocalcin synthesis. In ROS 172.8 and MG-63 cells 1,25-(OH)2D3 stimulated osteocalcin production. In ROS 172.8 cells PTH as well as stimulation of cAMP production by forskolin enhanced 1,25-(OH)2D3-induced osteocalcin production whereas, as we have shown previously, activation of protein kinase C does not change 1,25-(OH)2D3- stimulated osteocalcin production. In MG-63 cells neither PTH nor forskolin significantly changed 1,25-(OH)2D3 induction of osteocalcin synthesis. From the present study it can be concluded that indeed at target cell level 1,25-(OH)2D3 and PTH act in a coordinated manner. On basis of the potentiation of 1,25-(OH)2D3 action by PTH in osteoblasts together with the previously reported inhibition of PTH-stimulated cAMP production by 1,25-(OH)2D3 we postulate a negative feedback-loop at target cell level. The activation of the cAMP pathway results in an enhancement of the 1,25-(OH)2D3 action whereas the protein kinase C pathway attenuates the 1,25-(OH)2D3 action. Finally, the present study provides a basis for the indications from in vivo observations about an interrelated action of 1,25-(OH)2D3 and PTH at the target cell. More generally it demonstrates on the basis of analyses of endogenous cellular responses evidence for an interplay between receptor-activated pathways of peptide and steroid hormones

Vitamin D: A modulator of cell proliferation and differentiation

Abstract 1,25-Dihydroxyvitamin D3, [1,25(OH)2D3], the biologically most active metabolite of vitamin D3, is involved in the regulation of calcium homeostasis and bone metabolism. Recently, receptors for 1,25(OH)2D3 have also been shown in cells and tissues not directly related to calcium homeostasis. Experimental data obtained with leukemic and cancer cell lines, both in vitro and in vivo, showed the effects of 1,25(OH)2D3 on cell differentiation and proliferation. However, high doses of the sterol have to be used to observe these effects. Additional studies are needed to establish whether 1,25(OH)2D3 or suitable analogues have a therapeutic potential in malignant diseases without unacceptable toxicity like the development of hypercalcemia

Modulation by epidermal growth factor of the basal 1,25(OH)2D3 receptor level and the heterologous up-regulation of the 1,25(OH)2D3 receptor in clonal osteoblast-like cells

The effects of epidermal growth factor (EGF) on basal 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) receptor level and on parathyroid hormone (PTH)-induced 1,25-(OH)2D3 (OH)2D3 receptor up-regulation were studied in the phenotypically osteoblastic cell line UMR 106. EGF in concentrations exceeding 0.1 ng/ml reduced the number of 1,25(OH)2D3 binding sites without changing the binding affinity. Maximal reduction was 30% at about 1 ng/ml. This reduction was independent of a change in cAMP content. EGF dose-dependently attenuated both PTH-induced 1,25(OH)2D3 receptor up-regulation and PTH-stimulated cAMP production without and effect on the ED50 of the PTH effects. For both PTH responses the IC50 and the maximal effective dose were similar, 0.1 ng/ml an 1 ng/ml EGF, respectively. Reduction was first seen at 0.01 ng/ml EGF. At this concentration. EGF reduced PTH-stimulated 1,25-(OH)2D3 receptor binding without an inhibition of the cAMP response. Time-course studies with 1 ng/ml EGF revealed that at 2 h preincubation EGF reduced the heterologous up regulation by PTH, and maximal inhibition was seen after 4 h. In contrast, PTH-stimulated cAMP production was just significantly inhibited only after 6 h, with 60% inhibition after 24 h preincubation. The effects of prostaglandin E2 and forskolin on both 1,25(OH)2D3 binding and cAMP production were inhibited in a similar fashion. On the other hand, dibutyryl cAMP- and 3-isobutyl-1-methylxanthinestimulated 1,25(OH)2D3 binding were not affected by EGF. Taken together, our results demonstrate that EGF reduces both the basal number of 1,25(OH)2D3 binding sites and the heterologous up-regulation of the 1,25(OH)2D3 receptor. The current data suggest that EGF reduces heterologous upregulation of the 1,25(OH)2D3 receptor independent of as well as dependent on the cAMP messenger system. The EGF effect is not primarily located at the PTH receptor, at cAMP phosphodiesterase, or at protein kinase A level

Single and multigland disease in primary hyperparathyroidism: Clinical follow-up, histopathology, and flow cytometric DNA analysis

Two-hundred seventy-four patients with primary hyperparathyroidism had selective removal of enlarged parathyroid glands. Biopsies were taken from all parathyroid glands. Normal-size glands were not resected irrespective of their histological appearance. After a mean follow-up of 13.5 years the rates of persistent and recurrent hyperparathyroidism were, respectively, 3.6% and 0.7%. Transient and permanent hypoparathyroidism occurred in 24% and 2.5% of the patients. The microscopic appearance of enlarged glands and of biopsies taken from normal-size glands were reviewed by two pathologists. Normal parathyroid glands were distinguished from abnormal glands fairly accurately (sensitivity 93%, specificity 80%). Microscopic classification of abnormal parathyroid glands as adenomas or hyperplastic glands correlated poorly with the gross classification as single or multigland disease. Flow cytometric DNA analysis of paraffin embedded parathyroid tissue showed significant differences for DNA index, % S-phase and % G2M (p<0.001). Differentiating single from multigland disease by means of DNA analysis was not possible. In conclusion, removal of only enlarged parathyroid glands results in acceptable rates of persistent and recurrent hyperparathyroidism. Biopsies should only be taken sparingly to prevent transient and permanent hypoparathyroidism. Microscopic examination and flow cytometric DNA analysis can differentiate normal from abnormal parathyroid glands but are unable to differentiate abnormal glands into single or multigland disease

Inhibition of insulin- and insulin-like growth factor-I-stimulated growth of human breast cancer cells by 1,25-dihydroxyvitamin D3 and the vitamin D3 analogue EB1089

1, 25 Dihydroxyvitamin D3 (1,25-(OH)2D3) and a number of synthetic vitamin D3 analogues with low calcaemic activity, have been shown to inhibit breast cancer cell growth in vitro as well as in vivo. The purpose of the present study was to investigate a possible interaction of 1, 25-(OH)2D3 and the vitamin D3 analogue EB1089 with the insulin-IGF-I regulatory system. The oestrogen receptor-positive MCF-7 human breast cancer cells used in this study are able to grow autonomously and their growth is stimulated by insulin. In order to avoid interference of IGF-binding proteins (IGF-BPs), we used an analogue of IGF-I, long R3 IGF-I, which stimulated MCF-7 cell growth similar to insulin. The growth stimulation by insulin and by long R3 IGF-I was completely inhibited by 1,25-(OH)2D3 and EB1089. Autonomous growth was also inhibited by 1,25-(OH)2D3 and EB1089. The analogue EB1089 was active at 50 times lower concentrations than 1,25-(OH)2D3. It was shown that growth inhibition was not achieved through downregulation of insulin and IGF-I binding after 48 h. Paradoxically, after prolonged treatment (8 days), an upregulation of insulin and IGF-I binding was observed. Two possible intracellular mediators of the insulin-IGF mitogenic signal are C-FOS and mitogen-activated protein (MAP) kinase. Insulin-induced C-FOS mRNA was inhibited by 1,25-(OH)2D3, suggesting that it could be involved in the growth inhibition by 1,25-(OH)2D3. MAP kinase activation appeared not to be involved in growth stimulation by both insulin and IGF-I. Together, the present study demonstrates that vitamin D3 compounds can block the mitogenic activity of insulin and IGF-I, which may contribute to their tumour suppressive activity observed in vivo. Copyrigh

Vertebral deformities and functional impairment in men and women

Abstract The objective of this study was to assess the prevalence and health effects of vertebral deformities i

Beta-Blocking Agents and Electroconvulsive Therapy

In this review we want to summarize the results of the placebo-controlled randomized clinical trials with betablocking adrenergic agents during electroconvulsive therapy (ECT), and review the effect on seizure duration and cardiovascular variables. We sea

The Relationship of Early Sleep Improvement With Response to Pharmacotherapy in Unipolar Psychotic Depression

BACKGROUND: Since insomnia and depression are interrelated, improved sleep early in antidepressant pharmacotherapy may predict a positive treatment outcome. We investigated whether early insomnia improvement (EII) predicted treatment outcome in psychotic depression (PD) and examined if there was an interaction effect between EII and treatment type to assess if findings were treatment-specific. METHODS: This study is a secondary analysis of a randomized trial comparing 7 weeks treatment with the antidepressants venlafaxine, imipramine and venlafaxine plus the antipsychotic quetiapine in PD ( n = 114). Early insomnia improvement, defined as ≥20% reduced insomnia after 2 weeks, was assessed by the Hamilton Rating Scale for Depression (HAM-D-17). Associations between EII and treatment outcome were examined using logistic regressions. Subsequently, we added interaction terms between EII and treatment type to assess interaction effects. The predictive value of EII was compared with early response on overall depression (≥20% reduced HAM-D-17 score after 2 weeks). RESULTS: EII was associated with response (odds ratio [OR], 7.9; 95% confidence interval [CI], 2.7-23.4; P = &lt;0.001), remission of depression (OR, 6.1; 95% CI, 1.6-22.3; P = 0.009), and remission of psychosis (OR, 4.1; 95% CI, 1.6-10.9; P = 0.004). We found no interaction effects between EII and treatment type on depression outcome. Early insomnia improvement and early response on overall depression had a comparable predictive ability for treatment outcome. CONCLUSIONS: Early insomnia improvement was associated with a positive outcome in pharmacotherapy of PD, regardless of the medication type. Future studies are needed to confirm our findings and to examine the generalizability of EII as predictor in treatment of depression.</p