Dexamethasone enhances In vitro vascular calcification by promoting osteoblastic differentiation of vascular smooth muscle cells.
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Vascular calcification is often associated with atherosclerotic lesions. Moreover, the process of atherosclerotic calcification has several features similar to the mineralization of skeletal tissue. Therefore, we hypothesized that vascular smooth muscle cells might acquire osteoblastic characteristics during the development of atherosclerotic lesions. In the present study, we investigated the effect of dexamethasone (Dex), which is well known to be a potent stimulator of osteoblastic differentiation in vitro, on vascular calcification by using an in vitro calcification model. We demonstrated that Dex increased bovine vascular smooth muscle cell (BVSMC) calcification in a dose- and time-dependent manner. Dex also enhanced several phenotypic markers of osteoblasts, such as alkaline phosphatase activity, procollagen type I carboxy-terminal peptide production, and cAMP responses to parathyroid hormone in BVSMCs. We also examined the effects of Dex on human osteoblast-like (Saos-2) cells and compared its effects on BVSMCs and Saos-2 cells. The effects of Dex on alkaline phosphatase activity and the cAMP response to parathyroid hormone in BVSMCs were less prominent than those in Saos-2 cells. Interestingly, we detected that Osf2/Cbfa1, a key transcription factor in osteoblastic differentiation, was expressed in both BVSMCs and Saos-2 cells and that Dex increased the gene expression of both transcription factors. These findings suggest that Dex may enhance osteoblastic differentiation of BVSMCs in vitro. (+info)
The relaxant effects of parathyroid hormone(1-34) and parathyroid hormone-related protein(1-34) on ovine reticulo-ruminal smooth muscle in vivo.
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The motility of the reticulo-rumen has been measured in trained, conscious sheep using inflated balloons temporarily introduced to selected regions of that forestomach. The frequency and amplitude of the contractions of the reticulum and both the A and B waves of contraction of the rumen were measured under the same conditions before, during and after the administration of an i.v. bolus of either parathyroid hormone (PTH(1-34)) or PTH-related protein (PTHrP(1-34)) followed by its i.v. infusion. These two peptides are known to share a common receptor in other organs, e.g. the kidney. In this study they both showed an inhibitory effect on reticulo-ruminal motility. The effect of PTHrP(1-34) on the rate of ruminal blood flow was also examined and a significant reduction observed, after a transient increase. The secretion of endogenous PTH(1-34) was stimulated by a 32% reduction in the plasma calcium ion concentration induced by an i.v. infusion of sodium citrate. Associated with this were significant reductions in reticulo-ruminal motility, e.g. the reduction in the mean amplitude of the reticular contractions reflected the reduction in plasma calcium ion concentration. When the PTH(1-34)/PTHrP(1-34) receptor was blocked with [Asn10,Leu11,D-Trp12]PTHrP(7-34) before and during the induction of hypocalcaemia, all but one of the parameters of reticulo-ruminal motility were normalized. Indeed, by the day following the administration of this blocking agent, all these parameters had returned to their normal range. It is concluded that stimulation of the PTH(1-34)/PTHrP(1-34) receptor in reticulo-ruminal smooth muscle reduces the motility of this tissue and may play a role in the depression of motility of the digestive tract which is characteristic of clinical milk fever in the dairy cow. (+info)
Intrinsic limitations to unilateral parathyroid exploration.
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OBJECTIVE: To evaluate a method of limited parathyroid exploration for primary hyperparathyroidism. SUMMARY BACKGROUND DATA: Although preoperative localization of parathyroid adenomas has become sensitive enough for clinical practice, it has not achieved success as the basis for limited parathyroid exploration, because multiglandular disease is routinely underdiagnosed. The rapid intraoperative parathyroid hormone assay is sensitive for multiglandular disease, because hormone levels will not fall within 10 minutes of adenoma removal if additional abnormal tissue is present. A combination technique in which the exploration is limited according to the localization studies and the success is confirmed with the parathyroid hormone assay has promise for producing a high rate of curative limited parathyroid explorations. METHODS: Forty-eight consecutive patients with primary hyperparathyroidism and indications for surgery underwent preoperative localization. After tests, 45 patients underwent unilateral parathyroid exploration and confirmation of the success of unilateral exploration during surgery using the rapid parathyroid hormone assay. The intraoperative management of these patients and their follow-up to 3 months was recorded. RESULTS: Thirty-two of the 48 patients (67%) had successful unilateral exploration as gauged by a marked drop in parathyroid hormone levels during the procedure and by 3-month clinical follow-up. Of the 16 patients who ultimately underwent bilateral exploration, 7 had parathyroid hormone levels that did not fall after adenoma removal. Of these seven, five were found to have a second adenoma and two had slow metabolism of hormone with no additional abnormal tissue found. In 5 of the 16 patients, bilateral exploration was performed for erroneous localization. Four additional patients underwent bilateral exploration for improved exposure or negative results on localization tests. CONCLUSIONS: These results show that unilateral parathyroid exploration is limited by the intrinsic 15% rate of multiglandular primary hyperparathyroidism, combined with the imperfections of preoperative localizing techniques. Although an 85% rate of unilateral exploration can theoretically be obtained for unselected cases, the other vagaries of the technique make a 70% rate a more reasonable expectation. (+info)
Effects of rat fetuin on stimulation of bone resorption in the presence of parathyroid hormone.
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Rat fetuin, which is the rat counterpart of human alpha 2-HS glycoprotein and bovine fetuin, is only detectable in calcified tissues such as bone matrices and dentin, and bone cells such as osteoblasts and osteocytes immunohistochemically. The effect of this protein on bone resorption was examined to study its physiological role in bone metabolism. Rat fetuin increased bone resorption in the presence of low concentrations of parathyroid hormone (PTH), but it had no activity on bone resorption without PTH. The increase in bone resorption by PTH and PTH plus rat fetuin was inhibited by the addition of chymostatin, an inhibitor for cathepsin L. Moreover, we found that when type I collagen from rat was preincubated with rat fetuin, the digestion of rat type I collagen by cathepsin L was increased. These findings suggest that rat fetuin present in bone matrix is important in bone resorption. (+info)
Vitamin D receptor genotype influences parathyroid hormone and calcitriol levels in predialysis patients.
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BACKGROUND: BsmI vitamin D receptor (VDR) gene polymorphism has been associated with the severity of hyperparathyroidism in patients on hemodialysis. The aim of this study was to analyze the influence of this polymorphism on parathyroid function and serum calcitriol levels in patients with different degrees of chronic renal failure (CRF) before dialysis. METHODS: A total of 248 CRF patients, divided into three groups according to creatinine clearance (CCr; mild CRF group> 60 to 35 to 10 to 2.5 mmol/liter and serum phosphorus levels of> 1.6 mmol/liter or who needed phosphorus binding agents were excluded. The statistical analysis was done with the general factorial analysis of variance entering first PTH and then calcitriol as the dependent variable; the genotype (BB, Bb and bb), sex and CCr group were defined as factors; and covariables included serum calcium, serum phosphorus, 1/creatinine versus time slope, PTH when calcitriol was the dependent variable, and calcitriol when PTH was the dependent variable. RESULTS: When serum PTH levels were entered as the dependent variable, serum calcium, CCr group, and the interaction of genotype with the CCr group were found to be significant factors (P = 0.025, P <0.001 and P = 0.039, respectively). When serum calcitriol levels were entered as the dependent variable, genotype, the interaction of genotype with CCr, the CCr group, and the 1/creatine versus time slope were found to be significant (P = 0.027, P = 0.028, P <0.001 and P = 0.044, respectively). The marginal means of PTH, adjusted with the general factorial analysis of variance across the three groups were: (a) mild CRF group, BB 5.3 pmol/liter (CI 0 to 13.8), Bb 5.5 pmol/liter (CI 2 to 9), bb 5.4 pmol/liter (CI 0.6 to 10.2); (b) moderate CRF group, BB 6.2 pmol/liter (CI 1.5 to 10.9), Bb 7.8 pmol/liter (CI 5.3 to 10.3), bb 7.5 pmol/liter (CI 4.8 to 10.1); (c) severe CRF group, BB 9.3 pmol/liter (CI 4.2 to 14.3), Bb 17.1 pmol/liter (CI 13.9 to 20.2), bb 21.9 pmol/liter (CI 18.7 to 25.2). The marginal means of calcitriol adjusted with the general factorial analysis of variance across the three groups were: (a) mild CRF group, BB 47 pg/ml (CI 37 to 57), Bb 40.9 pg/ml (CI 37 to 44.8), bb 32.6 pg/ml (CI 26.8 to 38. 4); (b) moderate CRF group, BB 24.1 pg/ml (CI 18.3 to 29.8), Bb 26.6 pg/ml (CI 23.5 to 29.7), bb 25.3 pg/ml (CI 22 to 28.6); (c) severe CRF group, BB 27.4 pg/ml (CI 21.3 to 33.5), Bb 19.4 pg/ml (CI 15.5 to 23.2), bb 20.4 pg/ml (CI 16.1 to 24.7). CONCLUSION: The progression of hyperparathyroidism is slower in predialysis patients with BB genotypes than in the other genotypes. Also, calcitriol levels are less reduced in the BB genotype, which may act to lessen the severity of secondary hyperparathyroidism. (+info)
Potent antitumor effects mediated by local expression of the mature form of the interferon-gamma inducing factor, interleukin-18 (IL-18).
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IL-18 is produced during the acute immune response by macrophages and immature dendritic cells. IL-18 receptors are induced on T cells and NK cells by IL-12 and together they enhance a cellular immune response. We constructed retroviral and adenoviral vectors encoding the mature bioactive murine IL-18 in order to examine their immune and antitumor effects in murine tumor models. Secretion of bioactive IL-18 from murine tumor cells was facilitated by transfecting them with recombinant viral vectors carrying the prepro leader sequence of human parathyroid hormone fused to the 5' end of the mature murine IL-18 cDNA. Direct injection of the IL-18 recombinant adenoviral vector (Ad.PTH.IL-18) into an established MCA205 murine fibrosarcoma completely eradicated tumor in all animals with concomitant induction of protective systemic immunity. Co-administration of systemic IL-12 provided synergistic antitumor effects when combined with peritumoral injections of Ad.PTH.IL-18 without apparent side-effects as we observed with systemic administration of IL-18. Depletion of asialo GM-1+ cells completely abrogated the antitumor effects of Ad.PTH.IL-18, suggesting a major role for NK cells in mediating the anti-tumor effects of IL-18. Peritumoral injection of Ad.PTH.IL-18 was also associated with reduced numbers of CD8+ cells found within the tumor (HBSS versus Ad.PTH.IL-18, P < 0.0001). This suggests that IL-18 could be utilized as an alternative cancer gene therapy especially when combined with systemic administration of IL-12. (+info)
Antagonistic effects of vitamin D and parathyroid hormone on lipoprotein lipase in cultured adipocytes.
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The effects of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) (calcitriol) and parathyroid hormone (PTH) on synthesis and secretion of lipoprotein lipase (LPL) were studied in 3T3-L1 adipocytes. Expression of the vitamin D receptor was demonstrated by saturation kinetics with radiolabeled calcitriol. Incubation with calcitriol (10(-8) M) for up to 4 d resulted in a time-dependent significant increase in heparin-releasable LPL activity (LPLa) accompanied by a significant increase in LPL mRNA. In contrast, incubation with intact (1-84) PTH (10(-6) to 10(-9) M) produced a time- and dose-dependent significant decrease in LPLa, but no change in LPL mRNA. The effect of PTH (24-h incubation, 10(-8) M) could be prevented by the calcium channel blocker verapamil. Coincubation with both calcitriol and PTH at equimolar concentration (10(-8) M) resulted in an increase in LPLa and LPL mRNA. These data indicate an antagonistic role for calcitriol and PTH in the regulation of LPL, possibly mediated by intracellular calcium, which may contribute to the alterations in lipoprotein metabolism occurring in uremia. (+info)
Inhibition of osteoblast-specific transcription factor Cbfa1 by the cAMP pathway in osteoblastic cells. Ubiquitin/proteasome-dependent regulation.
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The cAMP pathway, a major intracellular pathway mediating parathyroid hormone signal, regulates osteoblastic function. Parathyroid hormone (through activation of protein kinase A) has also been shown to stimulate ubiquitin/proteasome activity in osteoblasts. Since the osteoblast-specific transcription factor Osf2/Cbfa1 is important for differentiation of osteoblastic cells, we examined the roles of the cAMP and ubiquitin/proteasome pathways in regulation of Cbfa1. In the osteoblastic cell line, MC3T3-E1, continuous treatment with cAMP elevating agents inhibited both osteoblastic differentiation based on alkaline phosphatase assay and DNA binding ability of Cbfa1 based on a gel retardation assay. Cbfa1 inhibition was paralleled by an inhibitory effect of forskolin on Cbfa1-regulated genes. Northern and Western blot analyses suggested that the inhibition of Cbfa1 by forskolin was mainly at the protein level. Pretreatment with proteasome inhibitors prior to forskolin treatment reversed the effect of forskolin. Furthermore, addition of proteasome inhibitors to forskolin-pretreated samples resulted in recovery of Cbfa1 protein levels and accumulation of polyubiquitinated forms of Cbfa1, indicating a role for the proteasome pathway in the degradation of Cbfa1. These results suggest that suppression of osteoblastic function by the cAMP pathway is through proteolytic degradation of Cbfa1 involving a ubiquitin/proteasome-dependent mechanism. (+info)