Immunophenotyping of mast cells: a sensitive and specific diagnostic tool for systemic mastocytosis.

INTRODUCTION: The diagnosis of systemic mastocytosis (SM) is based on a combination of major and minor criteria. Flow cytometric detection of aberrant expression of CD2 and/or CD25 on CD117-positive mast cells is one of the minor criteria used. In the present study we examined the sensitivity and specificity of mast cell immunophenotyping in the diagnosis of SM. MATERIAL AND METHODS: Patients were 36 persons with SM diagnosed according to WHO criteria. Controls were 31 patients without SM. Immunophenotyping was performed according to published guidelines. RESULTS: All patients with SM were positive for CD2 and/or CD25. All patients without SM , except one, were negative for these markers. The sensitivity for immunophenotyping was 100%, the specificity 91%. The positive and negative predictive values were 97% and 100% respectively. CONCLUSION: Immunophenotyping of bone marrow derived mast cells is not only a very sensitive but also a very specific method to diagnose SM with high positive and negative predictive value.

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.

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.

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.