Comparing conventional gauze therapy to vacuum-assisted closure wound therapy: a prospective randomised trial.

BACKGROUND: Vacuum-assisted closure wound therapy (vacuum therapy) has been used in our department since 1997 as a tool to bridge the period between debridement and definite surgical closure in full-thickness wounds. We performed a prospective randomised clinical trial to compare the efficacy of vacuum therapy to conventional moist gauze therapy in this stage of wound treatment. METHODS: Treatment efficacy was assessed by semi-quantitative scoring of the wound conditions (signs of rubor, calor, exudate and fibrinous slough) and by wound surface area measurements. Tissue biopsies were performed to quantify the bacterial load. Besides this, the duration until 'ready for surgical therapy' and complications encountered during therapy and postoperatively were recorded. RESULTS: Fifty-four patients were included (vacuum n=29, conventional n=25). With vacuum therapy, healthier wound conditions were observed. Furthermore, a tendency towards a shorter duration of therapy was found, which was most prominent in late-treated wounds. In addition, the wound surface area reduced significantly faster with vacuum therapy. Surprisingly, these results were obtained without a decrease in the number of bacteria colonising the wound. Complications were minor, except for one case of septicaemia and one case of increased tissue necrosis, which compelled us to stop vacuum therapy. For the treatment of full-thickness wounds, vacuum therapy has proven to be a valid wound healing modality.

An economic evaluation of the use of TNP on full-thickness wounds.

OBJECTIVE: Topical negative pressure (TNP) (vacuum therapy) is frequently used in the management of acute, traumatic, infected and chronic full-thickness wounds. This prospective clinical randomised trial compared the costs of TNP with conventional therapy (moist gauze) in the management of full-thickness wounds that required surgical closure. METHOD: The direct medical costs of the total number of resources needed to achieve a healthy, granulating wound bed that was 'ready for surgical therapy' were calculated. RESULTS: Fifty-four patients admitted to a department of plastic and reconstructive surgery were recruited into the trial. Cost analysis showed significantly higher mean material expenses for wounds treated with TNP (414euros+/-229euros [SD]) compared with conventional therapy (15euros+/-11euros; p<0.0001 ), but significantly lower mean nursing expenses (33euros+/-31 euros and 83euros+/-58euros forTNP and conventional therapy respectively; p<0.0001). Hospitalisation costs were lower in theTNP group (1788euros+/-1060euros) than in the conventional treatment group (2467euros+/-1336euros; p<0.043) due to an on average shorter duration until they were'ready for surgical therapy'. There was no significant difference in total costs per patient between the two therapies (2235euros+/-1301euros for TNP versus 2565euros+/-1384euros for conventional therapy). CONCLUSION: TNP had higher material costs. However, these were compensated by the lower number of time-consuming dressing changes and the shorter duration until they were 'ready for surgical therapy', resulting in the therapy being equally as expensive as conventional moist gauze. DECLARATION OF INTEREST: This work was partly supported by the Plastic and Reconstructive Surgery Esser Foundation, and KCI Medical, Houten,The Netherlands. The authors have no conflicts of interest.

Moderate cholecalciferol supplementation depresses intestinal calcium absorption in growing dogs.

Hormonal regulation of calcium (Ca) absorption was investigated in a cholecalciferol (vitamin D(3))-supplemented group (hVitD) vs. a control group (cVitD) of growing Great Danes (100 vs. 12.5 micro g vitamin D(3)/kg diet). Although Ca intakes did not differ, fractional Ca absorption was significantly lower in the hVitD group than in the cVitD group. There were no differences in plasma concentrations of Ca, inorganic phosphate, parathyroid hormone, growth hormone or insulin-like growth factor I between groups. Plasma 25-hydroxycholecalciferol [25(OH)D(3)] concentrations were maintained in the hVitD dogs at the same levels as in the cVitD dogs due to increased turnover of 25(OH)D(3) into 24,25-dihydroxycholecalciferol [24,25(OH)(2)D(3)] and 1,25-dihydroxycholecalciferol [1,25(OH)(2)D(3)]. In hVitD dogs, the greater plasma 24,25(OH)(2)D(3) concentration and the enhanced metabolic clearance rate (MCR) of 1,25(OH)(2)D(3) indicated upregulated 24-hydroxylase activity. The increased MCR of 1,25(OH)(2)D(3) decreased plasma 1,25(OH)(2)D(3) concentrations. In hVitD dogs, the greater production rate of 1,25(OH)(2)D(3) was consistent with the 12.9-fold greater renal 1alpha-hydroxylase gene expression compared with cVitD dogs and compensated to a certain extent for the accelerated MCR of 1,25(OH)(2)D(3). The moderately decreased plasma 1,25(OH)(2)D(3) concentration can only partially explain the decreased Ca absorption in the hVitD dogs. Intestinal vitamin D receptor concentrations did not differ between groups and did not account for the decreased Ca absorption. We suggest that 24,25(OH)(2)D(3) may downregulate Ca absorption.

Vitamin D and vitamin D analogs in cancer treatment.

The secosteroid hormone 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) is a key player in the regulation of bone mineralization and calcium homeostasis. In addition, 1,25-(OH)2D3 has antiproliferative and prodifferentiation effects on various cells in vitro and in vivo. The growth-inhibitory properties of 1,25-(OH)2D3 could be harnessed in the treatment of cancer. However, its use as an anti-cancer drug is limited because of the calcemic effects of pharmacological doses. In an attempt to dissociate the antiproliferative and calcemic effects, numerous vitamin D3 analogs were developed. The mechanisms by which 1,25-(OH)2D3 and 1,25-(OH)2D3 analogs exert their growth-inhibitory effects are not clear but include effects on cell differentiation, apoptosis, cell cycle regulation, metastases, and angiogenesis. In the current review aspects involved in the tumor suppressive activity of 1,25-(OH)2D3 and 1,25-(OH)2D3 analogs will be addressed. The use of vitamin D3 compounds, alone or in combination with other drugs, in cancer treatment and the potential drawbacks will also be discussed.

Structure and function of GC79/TRPS1, a novel androgen-repressible apoptosis gene.

Expression of death-signaling genes induces many biochemical cascades resulting in elimination of cells via apoptosis or programmed cell death. GC79/TRPS1 is a novel apoptosis associated gene that encodes a multitype zinc finger GATA-type transcription factor. Expression of GC79/TRPS1 is repressed in the rat ventral prostate and significantly elevated after androgen withdrawal by castration. Castration leads to regression of the prostate caused by apoptosis of androgen-dependent prostate cells. Prostate cancer consists of androgen-dependent and androgen-independent cells. The androgen-independent cells, usually present in the prostate of advanced prostate cancer patients do not have the ability to undergo apoptosis after androgen withdrawal. GC79/TRPS1 expression in androgen-dependent prostate cancer cells is repressed by androgens, while GC79/TRPS1 expression is hardly detectable in androgen-independent prostate cancer cells under cell culture conditions. This suggests that lack of GC79/TRPS1 expression could be a mechanism for the inability to induce the apoptotic pathway in androgen-independent prostate cancer cells after androgen withdrawal. This review will focus on the current knowlegde of the structure and function of GC79/TRPS1, a novel androgen-repressible apoptosis gene.

Vitamin D control of osteoblast function and bone extracellular matrix mineralization.

Vitamin D is the major regulator of calcium homeostasis and protects the organism from calcium deficiency via effects on the intestine, kidney, parathyroid gland, and bone. Disturbances in the vitamin D endocrine system (e.g., vitamin D-dependent rickets type I and type II), result in profound effects on the mineralization of bone. Recent studies with vitamin D receptor knockout mice also show effects on bone. It is questioned whether vitamin D has a direct effect on bone formation and mineralization. In rickets and particular vitamin D receptor knockout mice, calcium supplementation restores bone mineralization. However, the vitamin D receptor is present in osteoblasts, and vitamin D affects the expression of various genes in osteoblasts. This review focuses on the role of vitamin D in the control of osteoblast function and discusses the current knowledge of the direct effects of vitamin D on mineralization. Moreover, the role of vitamin D metabolism and the mechanism of action of vitamin D and interaction with other hormones and factors are discussed.

24,25-Dihydroxyvitamin D(3) and bone metabolism.

The 1alpha-hydroxylated metabolite of 25-hydroxyvitamin D(3), 1,25-dihydroxyvitamin D(3), is the biologically most active metabolite of vitamin D. The 24-hydroxylated metabolites were generally considered as degradation products of a catabolic pathway finally leading to excretion of calcitroic acid. Studies with analogues fluorinated at the C-24 position did not indicate a physiological function for 24R,25(OH)(2)D(3). Nevertheless throughout the years various studies showed biologic effects of other metabolites than 1alpha,25(OH)(2)D(3). In particular the metabolite 24R,25(OH)(2)D(3) has been functionally analyzed, e.g. with respect to a role in normal chicken egg hatchability and effects on chondrocytes in the resting zone of cartilage. Numerous studies have shown the presence of the vitamin D receptor in bone cells and effects of 1alpha,25(OH)(2)D(3) on bone and bone cells. Also for 24R,25(OH)(2)D(3) studies have been performed focusing on effects on bone and bone cells. The purpose of this review is to summarize the data regarding 24R,25(OH)(2)D(3) and bone and to evaluate its role in bone biology.

Anti-tumor effects of 1,25-dihydroxyvitamin D3 and vitamin D analogs.

The role of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) as a regulator of cell growth and differentiation is well recognized. Currently, 1, 25-(OH)2D3 and vitamin D analogs are being evaluated for their therapeutic potential in the treatment of hyperproliferative disorders like cancer. In the present review, we will discuss several processes that might be involved in 1,25-(OH)2D3- and vitamin D analog-mediated suppression of cancer cell growth. The effects on tumor cell proliferation, differentiation, apoptosis, angiogenesis, metastases, and parathyroid hormone-related peptide secretion will be highlighted. In addition, combination therapy with other tumor effec tive drugs will be addressed. Furtermore, we will focus on the potential drawbacks and the possible side effects of vitamin D compounds in the treatment of cancer.

Distinct effects on the conformation of estrogen receptor alpha and beta by both the antiestrogens ICI 164,384 and ICI 182,780 leading to opposite effects on receptor stability.

Tissue-specific effects of 17beta-estradiol (E(2)) and synthetic estrogen receptor (ER) ligands on target gene regulation might, at least partly, be explained by a selective ligand-induced conformational change of their receptors (ERalpha and ERbeta). In this study, the effects of E(2) and the synthetic ER ligands tamoxifen (TAM), ICI 164,384, and ICI 182,780 on the conformation of ERalpha and ERbeta were examined using limited proteolytic digestion analysis. We found that E(2) induced a conformational change of ERalpha resulting in the protection of a 30-kDa product, whereas TAM protected a 28-kDa fragment. Strikingly, the ERalpha conformational change induced by both ICI 164,384 and ICI 182,780 did not result in protection but rather seems to induce a ligand concentration-dependent increase in proteolytic degradation of the 30- and 28-kDa products. Incubation of ERbeta with E(2) resulted in an increased protection of a 30-kDa fragment, whereas with TAM protection of a 29-kDa fragment was observed. In contrast to the situation with ERalpha, ICI 164,384 and ICI 182,780 incubation induced the protection in a manner similar to 30-kDa fragment E(2). In addition, the ICI compounds also induced in a dose-dependent manner the preservation of a 32-kDa fragment. Our observations demonstrate that ICI 164,384 and ICI 182,780 have distinct effects on the conformation of ERalpha and ERbeta, resulting in receptor subtype-selective opposite effects on receptor stability in vitro.

Evidence for involvement of 17beta-estradiol in intestinal calcium absorption independent of 1,25-dihydroxyvitamin D3 level in the Rat.

The sex steroid 17beta-estradiol (17beta-E2) has a broad range of actions, including effects on calcium and bone metabolism. This study with 3-month-old Brown Norway rats was designed to investigate the role of 17beta-E2 in the regulation of calcium homeostasis. Rats were divided in four groups, sham-operated, ovariectomized (OVX), and OVX supplemented with either a 0.025-mg or 0.05-mg 17beta-E2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17beta-E2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Supplementation with either one of the 17beta-E2 dosages resulted in an 80% reduction of 1,25(OH)2D3 and only a 20% reduction in 25-hydroxyvitamin D3 levels. OVX, as well as supplementation with 17beta-E2, did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH)2D3 levels were also significantly decreased in the 17beta-E2-supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal calcium absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH)2D3 serum level was increased, OVX resulted in a significant decrease in intestinal calcium absorption in the duodenum. Despite the strongly reduced 1,25(OH)2D3 levels (18. 1 +/- 2.1 and 16.4 +/- 2.2 pmol/l compared with 143.5 +/- 29 pmol/l for the OVX group), the OVX-induced decrease in calcium absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17beta-E2. None of the treatments resulted in a significant change in calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17beta-E2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17beta-E2 is positively involved in intestinal calcium absorption, and the data strengthen the assertion that 17beta-E2 exerts this effect independent of 1,25(OH)2D3. In general, 17beta-E2 not only affects bone turnover but also calcium homeostasis via an effect on intestinal calcium absorption. (J Bone Miner Res 1999;14:57-64)

Regulation of osteocalcin production and bone resorption by 1,25-dihydroxyvitamin D3 in mouse long bones: interaction with the bone-derived growth factors TGF-beta and IGF-I.

Bone cells produce multiple growth factors that have effects on bone metabolism and can be incorporated into the bone matrix. Interplay between these bone-derived growth factors and calciotropic hormones has been demonstrated in cultured bone cells. The present study was designed to extend these observations by examining the interactions between either transforming growth factor-beta (TGF-beta) or insulin-like growth factor-I (IGF-I) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in a mouse long bone culture model with respect to osteocalcin production and bone resorption. In contrast to the stimulation in rat and human, in the fetal mouse long bone cultures, 1,25(OH)2D3 caused a dose-dependent inhibition of osteocalcin production. Both the osteocalcin content in the culture medium and in the extracts of the long bones was reduced by 1,25(OH)2D3. This effect was not specific for fetal bone because 1,25(OH)2D3 also reduced osteocalcin production by the neonatal mouse osteoblast cell line MC3T3. TGF-beta inhibited whereas IGF-I dose-dependently increased osteocalcin production in mouse long bones. The combination of TGF-beta and 1,25(OH)2D3 did not result in a significantly different effect compared with each of these compounds alone. The IGF-I effect was completely blocked by 1,25(OH)2D3. In the same long bones as used for the osteocalcin measurements, we performed bone resorption analyses. Opposite to its effect on osteocalcin, 1,25(OH)2D3 dose-dependently stimulated bone resorption. TGF-beta reduced and IGF-I did not change basal (i.e., in the absence of hormones) bone resorption. Our results show that 1,25(OH)2D3-enhanced bone resorption is dose-dependently inhibited by TGF-beta and IGF-I. Regression analysis demonstrated a significant negative correlation between 1,25(OH)2D3-induced bone resorption and osteocalcin production. The specificity for their effect on 1,25(OH)2D3-stimulated bone resorption was assessed by testing the effects of TGF-beta and IGF-I in combination with parathyroid hormone (PTH). Like 1,25(OH)2D3, PTH dose-dependently stimulates bone resorption. However, PTH-stimulated bone resorption was not affected by TGF-beta. Like 1,25(OH)2D3-stimulated bone resorption, IGF-I inhibited the PTH effect but at a 10-fold higher concentration compared with 1,25(OH)2D3. In conclusion, the present study demonstrates growth factor-specific interactions with 1,25(OH)2D3 in the control of osteocalcin production and bone. With respect to bone resorption, these interactions are also hormone specific. The present data thereby support and extend the previous observations that interactions between 1,25(OH)2D3 and bone-derived growth factors play an important role in the control of bone metabolism. These data together with the fact that TGF-beta and IGF-I are present in the bone matrix and potentially can be released during bone resorption support the concept that growth factors may control the effects of calciotropic hormones in bone in a localized and possibly temporal manner. Finally, in contrast to human and rat, in mice 1,25(OH)2D3 reduces osteocalcin production and this reduction is paralleled by stimulation of bone resorption by 1,25(OH)2D3. These data thereby show a dissociation between osteocalcin production and bone resorption.

Consequences of vitamin D receptor regulation for the 1,25-dihydroxyvitamin D3-induced 24-hydroxylase activity in osteoblast-like cells: initiation of the C24-oxidation pathway.

A direct relationship between vitamin D receptor (VDR) level and target cell responsiveness to 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) has been shown in osteoblast-like cell lines. However, we previously found an inverse relationship between the TGF beta-induced VDR up-regulation and subsequent 1,25-(OH)2D3-induced biological responses. A clear inhibition of the 1,25-(OH)2D3-induced stimulation of osteocalcin and osteopontin expression was observed. A biological response that has formerly been shown to be coupled to VDR level is 24-hydroxylase activity. This enzyme initiates the C24 oxidation of the side-chain, followed by cleavage and ultimate metabolic clearance of both 25-(OH)D3 and its metabolite 1,25-(OH)2D3. With UMR 106 (rat) and MG 63 (human) osteoblast-like cells, we show that after preincubation with TGF beta, which causes an increase in VDR level, 1,25-(OH)2D3 induction of 24-hydroxylase activity is also stimulated. In addition, we provide evidence that variations in VDR level induced by other means (PTH, EGF, medium change) are also closely associated with 1,25-(OH)2D3-induced 24-hydroxylase activity. Furthermore, we show that in MG 63 cells, but not in UMR 106 cells, TGF beta itself was able to increase the activity of the enzyme 24-hydroxylase. As 24-hydroxylation is the initial step in the further C24 oxidation of 1,25-(OH)2D3, our results indicate a close coupling of VDR level and the degradation of its ligand, 1,25-(OH)2D3. This mechanism may provide an important regulatory feedback in the action of 1,25-(OH)2D3 at target tissue/cell level.

Differential effects of 1,25-dihydroxyvitamin D3-analogs on osteoblast-like cells and on in vitro bone resorption.

Although numerous studies have shown potent antiproliferative and differentiation-inducing effects of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) and its analogs on cells not directly related to bone metabolism, only few reports focussed on the effects of these analogs on bone. We compared the action of several recently developed analogs with that of 1,25-(OH)2D3 on human (MG-63) and rat (ROS 17/2.8) osteoblast-like cells and on in vitro bone resorption. In MG-63 cells the analogs EB1089 and KH1060 were about 166,000 and 14,000 times more potent than 1,25-(OH)2D3 in stimulating type I procollagen and 100 and 6,000 times more potent in stimulating osteocalcin production, respectively. Also in ROS 17/2.8 cells EB1089 and KH1060 were most potent in inducing osteocalcin synthesis. In vitro bone resorption was 2.3 and 17.5 times more potently stimulated by EB1089 and KH1060, respectively. In MG-63 cells, 1,25-(OH)2D3 and the analogs inhibited cell proliferation, whereas both 1,25-(OH)2D3 and the analogs stimulated the growth of ROS 17/2.8 cells. Differences in potency could neither be explained by affinity for the vitamin D receptor nor by a differential involvement of protein kinase C in the action of the analogs. Together, these data show that also in bone the analogs EB1089 and KH1060 are more potent than 1,25-(OH)2D3 but that the potency of the analogs compared to 1,25-(OH)2D3 is dependent on the biological response. On the basis of these observations it can be concluded that the reported reduced calcemic effect in vivo is not the result of a decreased responsiveness of bone to these analogs. Lastly, in view of eventual clinical application of 1,25-(OH)2D3-analogs, the observed stimulation of in vitro bone resorption and growth of an osteosarcoma cell line warrant in vivo studies to further examine these effects.

Antiestrogens inhibit in vitro bone resorption stimulated by 1,25-dihydroxyvitamin D3 and the vitamin D3 analogs EB1089 and KH1060.

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) has been shown to inhibit breast cancer cell growth both in vitro and in vivo. A major drawback is that high doses of 1,25-(OH)2D3 are needed which may result in undesirable side effects like the development of hypercalcemia and an increased risk of bone metastases due to the stimulation of bone resorption by 1,25-(OH)2D3. Several newly developed 1,25-(OH)2D3 analogs have a reduced calcemic activity, but their direct effects on bone resorption have not yet been examined. Presently, the antiestrogen tamoxifen is the most important endocrine therapy for breast cancer. Recent studies have demonstrated the benefit of the combination tamoxifen and 1,25-(OH)2D3/analogs for the inhibition of breast cancer cell growth. Besides inhibition of breast cancer growth tamoxifen appeared to have beneficial effects on bone. The purpose of the present study was to investigate the effect of tamoxifen on 1,25-(OH)2D3- and analogs (EB1089 and KH1060)-stimulated bone resorption in an in vitro model. Bone resorption was stimulated by 1,25-(OH)2D3 and analogs in a dose-dependent manner with KH1060 and EB1089 being more potent and 1,25-(OH)2D3. Tamoxifen caused a strong dose-dependent inhibition (70% at 10 microM) of 1,25-(OH)2D3- and EB1089-stimulated bone resorption. KH1060-stimulated bone resorption was also inhibited by tamoxifen but to a lesser extent (36%). Also the pure antiestrogen ICI164,384 but not 17 beta-estradiol inhibited 1,25-(OH)2D3-stimulated bone resorption. Together, this study demonstrates that tamoxifen considerably reduces 1,25-(OH)2D3/analogs-stimulated bone resorption and therefore may be useful to reduce the risk of bone metastases. This together with the observed beneficial effects on breast cancer cell growth indicates that tamoxifen together with 1,25-(OH)2D3/analogs is an interesting combination for the treatment of breast cancer. The mechanism of the bone resorption inhibitory action is not yet known but seems to be independent of the estrogen pathway.

Inhibition of breast cancer cell growth by combined treatment with vitamin D3 analogues and tamoxifen.

The steroid hormone 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] has potential to be used as an antitumor agent, but its clinical application is restricted by the strong calcemic activity. Therefore, new vitamin D3 analogues are developed with increased growth inhibitory and reduced calcemic activity. In the present study, we have examined the antiproliferative effects of four novel vitamin D3 analogues (CB966, EB1089, KH1060, and 22-oxa-calcitriol) on breast cancer cells, either alone or in combination with the antiestrogen tamoxifen. The estrogen-dependent ZR-75-1 and estrogen-responsive MCF-7 cell lines were used as a model. It was shown that, with EB1089 and KH1060, the same growth inhibitory effect as 1,25-(OH)2D3 could be reached at up to 100-fold lower concentrations, whereas CD966 and 22-oxa-calcitriol were nearly equipotent with 1,25-(OH)2D3. The growth inhibition by the vitamin D3 compounds could be augmented by combined treatment with tamoxifen. At the maximal effective concentrations of the vitamin D3 compounds, the effect of combined treatment was addictive (MCF-7 cells) or less than additive (ZR-75-1 cells). Tamoxifen increased the sensitivity of the cells to the vitamin D3 compounds 2- to 4000-fold, which was expressed by a shift to lower median effective concentration values. Thereby, the vitamin D3 compounds may be used at even lower dosages in combination therapy with tamoxifen. A major problem of tamoxifen therapy is the development of tamoxifen resistance. We have observed that tamoxifen-resistant clones of ZR-75-1 cells retain their response to the vitamin D3 compounds. Regulation of the growth-related oncogene c-myc (mRNA level) and the estrogen receptor (protein level) were studied but appeared not to be related to the antiproliferative action of the vitamin D3 compounds. Together, our data point to a potential benefit of combination therapy with 1,25-(OH)2D3 or vitamin D3 analogues and tamoxifen for the treatment of breast cancer.

Transforming growth factor beta-induced dissociation between vitamin D receptor level and 1,25-dihydroxyvitamin D3 action in osteoblast-like cells.

In the present study the interaction between a locally produced factor in bone, transforming growth factor beta (TGF beta) and a systemic regulator of bone metabolism, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was investigated. In rat (UMR 106, ROS 17/2.8) and human (MG-63) osteoblastic cell lines and in isolated fetal rat osteoblasts TGF beta caused a comparable increase in vitamin D receptor (VDR) level. A maximum was observed after 6 h at 1 ng/ml TGF beta. Scatchard analysis revealed that up-regulation of VDR is due to an increase in receptor number and not to a change in affinity. This was supported by Northern blot analysis which showed a dose- and time-dependent increase in VDR mRNA by TGF beta. To assess the significance of the TGF beta-induced increase in VDR level for 1,25-(OH)2D3 effects cells were preincubated with TGF for 4 h (causing a 2-3-fold increase of the VDR level) and subsequently incubated with 1,25-(OH)2D3 for 4 h and 24 h. TGF beta preincubation potently inhibited subsequent 1,25-(OH)2D3 stimulation of osteocalcin production in both ROS 17/2.8 and MG-63 cells on protein as well as mRNA level. A similar inhibition by TGF beta was observed on the 1,25-(OH)2D3-induced increase in osteopontin mRNA. The current study demonstrates dissociation between regulation of VDR level and modulation of two 1,25-(OH)2D3 biological responses by TGF beta in osteoblast-like cell lines of different origin. This dissociation shows that, besides interaction at VDR level also at other levels in the cell interaction(s) exist between TGF beta and 1,25-(OH)2D3. Besides, these data emphasize the potential importance of the interplay of locally produced factors and systemic calciotrophic hormones in the regulation of bone metabolism.

Peritoneal macrophages from patients on continuous ambulatory peritoneal dialysis show a differential secretion of prostanoids and interleukin-1 beta.

In vitro secretion of the prostanoids PGE2 and PGI2 and of the cytokine IL-1 beta by peritoneal macrophages obtained from CAPD patients during episodes of peritonitis and infection free periods, was determined, after culturing with or without 5 micrograms/ml of LPS. The release of PGE2 and PGI2 as measured by its stable metabolite 6-keto-PGF alpha was determined in 10 episodes of peritonitis and 10 infection free periods. IL-1 beta release was determined in 14 episodes of peritonitis and 20 infection free periods. PGI2 release from macrophages declined sharply during peritonitis both in the absence and presence of LPS in the culture medium (p less than 0.005). A tendency to decreased PGE2 release was found during peritonitis, when macrophages were cultured in the absence of LPS. In the presence of LPS, the same amounts of PGE2 were released during peritonitis and during an infection free period. On the other hand, peritoneal macrophages released significantly more IL-1 beta during peritonitis as compared to an infection free period, provided that the cells were in vitro stimulated with LPS. In view of the interregulatory effects between prostanoids and macrophage cytokines in their production, these findings may indicate that the impaired release of PGI2 during peritonitis has allowed the macrophages to secrete more IL-1 beta after in vitro stimulation with LPS. This implies that PGI2 and PGE2 may play a distinct role in the regulation of cytokine secretion by these cells.

Evidence for the functional involvement of protein kinase C in the action of 1,25-dihydroxyvitamin D3 in bone.

In the present study the involvement of protein kinase C in the action of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) on osteoblast-like cells and in the stimulation of in vitro bone resorption by 1,25(OH)2D3 was examined. Incubation for 24 h with 1,25(OH)2D3 potently stimulated osteocalcin synthesis by ROS 17/2.8 cells. This stimulation was inhibited (30-70% inhibition) by 25 microM of the protein kinase C (PKC) inhibitors 1-O-hexadecyl-2-O-methyl-rac-glycerol (AMG) and sphingosine without affecting basal osteocalcin synthesis. 1,25(OH)2D3-stimulated osteocalcin secretion by nontransformed isolated fetal rat osteoblasts was also inhibited (30-55%) by AMG. Also, AMG inhibited 10(-9) M 1,25(OH)2D3-induced up-regulation of vitamin D receptor in ROS 17/2.8 cells. Activation of PKC with phorbol 12-myristate 13-acetate (PMA) did not cause an increase in osteocalcin secretion, while only a small increase in cellular content of osteocalcin in ROS 17/2.8 cells was observed. Addition of PMA together with 1,25(OH)2D3 did not change the response to 1,25(OH)2D3. The PKC inhibitors were not toxic for the cells. 1,25(OH)2D3 did not stimulate diacylglycerol production in ROS 17/2.8 cells up to 5 min after administration. However, 4- and 24-h incubation with 10 nM 1,25(OH)2D3 increased phorbol ester binding in ROS 17/2.8 cells. 1,25(OH)2D3 potently stimulated bone resorption after 3 and 6 days of culture in fetal mouse long bones and calvaria. Both the PKC inhibitors AMG (25 microM) and staurosporine (50 nM) strongly inhibited (60-86% inhibition) 1,25(OH)2D3-stimulated bone resorption without affecting basal 45Ca release. These effects were not due to a cytotoxic effect of both PKC inhibitors. Nor is it likely that the effects of AMG and staurosporine are due to inhibition of cell proliferation as hydroxyurea did not affect 1,25(OH)2D3-stimulated bone resorption. The inhibition of 1,25(OH)2D3-stimulated bone resorption by PKC inhibitors suggests that besides osteocalcin synthesis PKC is also involved in other responses of 1,25(OH)2D3 in bone. 1,25(OH)2D3 does not directly activate PKC via an increase in diacylglycerol production but more likely via an increase in PKC. Together, the present study demonstrates a functional involvement of PKC in the action of 1,25(OH)2D3 in bone and bone cells which may have consequences for the development of 1,25(OH)2D3 analogs, e.g. with less hypercalcemic and relatively more antiproliferative activity.

Regulation of 1,25-dihydroxyvitamin D3 receptor gene expression by parathyroid hormone and cAMP-agonists.

We studied the effect of parathyroid hormone (PTH) and activation of the cAMP signal pathway on vitamin D receptor (VDR) mRNA levels in the phenotypically osteoblast cell line UMR 106. PTH caused a time- and dose-dependent increase of the VDR mRNA content with a maximum after 2 h. After 24 h the VDR mRNA level in PTH-treated cells returned to control level. In contrast, the 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-induced increase in VDR mRNA did not decline after 24 h. Inhibition of transcription with actinomycin D (10 micrograms/ml) completely abolished the PTH-induced increase of VDR mRNA and inhibition of translation with cycloheximide (1 microgram/ml) resulted in superinduction of VDR mRNA. The role of cAMP in the induction of VDR mRNA was studied with several agents acting via the cAMP pathway. Incubation for 2 and 4 h with forskolin, Bt2cAMP, PTHrP or prostaglandin E2 caused an increase in the level of VDR mRNA comparable to that caused by PTH. The calcium ionophore A23187 did not affect VDR mRNA level. The present study demonstrates that PTH and activation of the cAMP signal pathway cause up-regulation of VDR via induction of VDR gene expression. The effect of cAMP on the VDR gene is suggestive for a cAMP responsive element in the VDR gene.