Effects of 1alpha,25-dihydroxy-16ene, 23yne-vitamin D3 on osteoblastic function in human osteosarcoma SaOS-2 cells: differentiation-stage dependence and modulation by 17-beta estradiol

Human cells with osteogenic potential in bone tissue research

Bone regeneration after injury or after surgical bone removal due to disease is a serious medical challenge. A variety of materials are being tested to replace a missing bone or tooth. Regeneration requires cells capable of proliferation and differentiation in bone tissue. Although there are many possible human cell types available for use as a model for each phase of this process, no cell type is ideal for each phase. Osteosarcoma cells are preferred for initial adhesion assays due to their easy cultivation and fast proliferation, but they are not suitable for subsequent differentiation testing due to their cancer origin and genetic differences from normal bone tissue. Mesenchymal stem cells are more suitable for biocompatibility testing, because they mimic natural conditions in healthy bone, but they proliferate more slowly, soon undergo senescence, and some subpopulations may exhibit weak osteodifferentiation. Primary human osteoblasts provide relevant results in evaluating the effect of biomaterials on cellular activity; however, their resources are limited for the same reasons, like for mesenchymal stem cells. This review article provides an overview of cell models for biocompatibility testing of materials used in bone tissue research.

The Synthesis and Biological Evaluation of D-Ring-Modified Vitamin D Analogues

The vitamin D₃ structure consists of the A-ring, a linker originating from the B-ring, C-ring, D-ring, and side-chain moieties. Each unit has its unique role in expressing the biological activities of vitamin D₃. Many efforts have been made to date to assess the possible clinical use of vitamin D. Some organic chemists focused on the D-ring structure of vitamin D and synthesized D-ring-modified vitamin D analogues, and their biological activities were studied. This review summarizes the synthetic methodologies of D-ring-modified vitamin D analogues, except for seco-D, and their preliminary biological profiles.

Polydatin Induces Differentiation and Radiation Sensitivity in Human Osteosarcoma Cells and Parallel Secretion through Lipid Metabolite Secretion

Osteosarcoma is a bone cancer characterized by the production of osteoid tissue and immature bone from mesenchymal cells. Osteosarcoma mainly affects long bones (femur is most frequently site) and occur in children and young adults with greater incidence. Here, we investigated the role accomplished by polydatin, a natural antioxidative compound, in promoting osteogenic differentiation alone or after radiation therapy on osteosarcoma cells. In vitro, polydatin significantly induced cell cycle arrest in S-phase and enhanced bone alkaline phosphatase activity. Moreover, the differentiation process was paralleled by the activation of Wnt-β-catenin pathway. In combination with radiotherapy, the pretreatment with polydatin promoted a radiosensitizing effect on osteosarcoma cancer cells as demonstrated by the upregulation of osteogenic markers and reduced clonogenic survival of tumor cells. Additionally, we analyzed, by mass spectrometry, the secretion of sphingolipid, ceramides, and their metabolites in osteosarcoma cells treated with polydatin. Overall, our results demonstrate that polydatin, through the secretion of sphingolipids and ceramide, induced osteogenic differentiation, alone and in the presence of ionizing therapy. Future investigations are needed to validate the use of polydatin in clinical practice as a potentiating agent of radiotherapy-induced anticancer effects.

Vitamin D Receptor Signaling and Cancer

The vitamin D receptor (VDR) binds the secosteroid hormone 1,25(OH)₂D₃ with high affinity and regulates gene programs that control a serum calcium levels, as well as cell proliferation and differentiation. A significant focus has been to exploit the VDR in cancer settings. Although preclinical studies have been strongly encouraging, to date clinical trials have delivered equivocal findings that have paused the clinical translation of these compounds. However, it is entirely possible that mining of genomic data will help to refine precisely what are the key anticancer actions of vitamin D compounds and where these can be used most effectively.

Cytokine, Chemokine, and Growth Factor Profile Characterization of Undifferentiated and Osteoinduced Human Adipose-Derived Stem Cells

Bone is the second most manipulated tissue after blood. Adipose-derived stem cells (ASCs) may become a convenient source of MSC for bone regenerative protocols. Surprisingly, little is known about the most significant biomolecules these cells produce and release after being osteoinduced. Therefore, the present study aimed at dosing 13 candidates chosen among the most representative cytokines, chemokines, and growth factors within the conditioned media of osteodifferentiated and undifferentiated ASCs. Two acknowledged osteoblastic cell models, that is, MG-63 and SaOs-2 cells, were compared. Notably, IL-6, IL-8, MCP-1, and VEGF were highly produced and detectable in ASCs. In addition, while IL-6 and IL-8 seemed to be significantly induced by the osteogenic medium, no such effect was seen for MCP-1 and VEGF. Overall SaOS-2 had a poor expression profile, which may be consistent with the more differentiated phenotype of SaOs-2 compared to ASCs and MG-63. Instead, in maintaining medium, MG-63 displayed a very rich production of IL-12, MCP-1, IP-10, and VEGF, which were significantly reduced in osteogenic conditions, with the only exception of MCP-1. The high expression of MCP-1 and VEGF, even after the osteogenic commitment, may support the usage of ASCs in bone regenerative protocols by recruiting both osteoblasts and osteoclasts of the host.

Proinsulin C-peptide modulates the expression of ERK1/2, type I collagen and RANKL in human osteoblast-like cells (Saos-2)

A lower bone mass accompanied by a higher bone fragility with increased risk of fracture are observed in individuals with type 1 diabetes mellitus. Low C-peptide levels are associated with low lumbar mineral density in postmenopausal woman. In this work, we investigated the role of C-peptide on the osteoblast cell biology in vitro. We examined intracellular pathways and we found that C peptide activates ERK1/2 in human osteoblast-like cells (Saos-2). We also observed that proinsulin C-peptide prevents a reduction of type I collagen expression and decreases, in combination with insulin, receptor activator of nuclear factor-κB (RANKL) levels. In this work we show for the first time that Cpeptide activates a specific intracellular pathway in osteoblasts and it modulates the expression of protein involved in bone remodeling. Our results suggest that both C-peptide may have a role in bone metabolism. Further studies are needing to fully clarify its role.

Effect of raloxifene and its interaction with human PTH on bone formation

We studied the of effects raloxifene alone or in combination with human PTH (hPTH) 1-34 in mineralizing cultures of SaOS-2 cells. Raloxifene (10(-8)-10(-6) M) increased bone nodule formation in cultures of SaOS-2 cells when added intermittently from day 8 to day 17. A single 24-h treatment with 10(-8) M hPTH (1-34) at day 8 reduced the nodule area by 75.6% at day 17, and raloxifene added concomitantly with hPTH (1-34) reduced this inhibitory effect in a dose-dependent manner. Raloxifene also reduced the hPTH (1-34)-induced inhibition of alkaline phosphatase (ALP) activity. The 10-fold stimulation of c-fos mRNA expression by hPTH (1-34) was not influenced by raloxifene co-treatment. The protein kinase A (PKA) inhibitor 6-22 amide (1.7 nM) and the protein kinase C (PKC) inhibitor-bisindolylmaleimide 1 (10 nM) did not influence the separate effects of PTH and raloxifene on mineralized bone nodule formation. This is the first report on the interaction of PTH and raloxifene in an osteoblast culture system.

Prolonged culture of HOS 58 human osteosarcoma cells with 1,25-(OH)2-D3, TGF-beta, and dexamethasone reveals physiological regulation of alkaline phosphatase, dissociated osteocalcin gene expression, and protein synthesis and lack of mineralization

Cultured rodent osteoblastic cells reiterate the phenotypic differentiation and maturation of osteoblasts seen in vivo. As previously shown, the human osteosarcoma cell line HOS 58 represents a differentiated stage of osteoblast development. The potential of HOS 58 for still further in vitro differentiation suggests the line can serve as a model of osteoblast maturation. Using this cell line, we have investigated the influence of 1,25-(OH)2-D3 (D3), TGF-beta and Dexamethasone (Dex) on proliferation and on the protein and mRNA levels of alkaline phosphatase (AP), procollagen 1 (Col 1), and osteocalcin (Oc), as well as mineralization during 28 days in culture. AP mRNA and protein were highly expressed throughout the culture period with further increase of protein AP activity at constant gene expression levels. A differentiation inhibiting effect of either TGF-beta or Dex was seen. Col 1 was investigated without the use of ascorbic acid and showed only minor changes during culture time or stimulation. The gene expression for Oc increased continually whereas protein synthesis peaked at confluence and decreased thereafter. TGF-beta and Dex treatments decreased Oc mRNA and protein levels. Stimulation by D3 was maximal at day 7 with a decrease thereafter. HOS 58 cells showed no mineralization capacity when stimulated with different agents, as measured by energy-dispersive X-ray microanalysis. This was not due to absence of Cbfa1 expression. In conclusion, the HOS 58 osteosarcoma cell line represents a differentiated cell line with highly expressed and physiologically regulated AP expression during further differentiation in culture. We observed a dissociation between osteocalcin gene expression and protein secretion which may contribute to the lack of mineralization in this cell line.

A non-calcemic analog of 1 alpha,25 dihydroxy vitamin D(3) (JKF) upregulates the induction of creatine kinase B by 17 beta estradiol in osteoblast-like ROS 17/2.8 cells and in rat diaphysis

We have reported that multiple treatments with so-called 'non-hypercalcemic' analogs of 1 alpha,25(OH)(2) vitamin D(3) (1,25(OH)(2)D(3)) stimulate the specific activity of creatine kinase BB (CK) in ROS 17/2.8 osteoblast-like cells, and that pretreatment with these analogs upregulates responsiveness and sensitivity to 17 beta estradiol (E(2)) for the induction of CK. However, since the analogs showed toxicity in vivo, we have now studied the action of a demonstrably non-calcemic hybrid analog of vitamin D in ROS 17/2.8 cells, and prepubertal rats. The analog JKF was designed to separate its calcemic activity from other biological activities by combining a calcemic-lowering 1-hydroxymethyl group with a potentiating C, D-ring side chain modification including 24 difluoronation. Treatment with 1 pM JKF alone significantly stimulated CK specific activity at 4 h by 30+/-10%. However after three daily pretreatments, JKF upregulated the extent of induction by 30 nM E(2) by 33% at 1 pM and by 97% at 1 nM; the E(2) dose needed for a significant stimulation of CK activity was lowered to 30 pM. The action of the SERMS tamoxifen, tamoxifen methiodide and raloxifene, at 3 microM, was also upregulated by three daily pretreatments with 1 nM JKF; unexpectedly, this pretreatment prevented the inhibition of E(2) stimulation by the SERMS. Upregulation of E(2) action by 1 nM JKF was inhibited by 1 nM ZK159222, an inhibitor of the nuclear action of 1,25(OH)(2)D(3). In vivo, three daily injections of 0.05 ng/g body weight of JKF augmented the response of prepubertal female rat diaphysis and epiphysis to E(2). Therefore, demonstrably non-calcemic analogs of 1,25(OH)(2)D(3) may have potential for use in combination with estrogens or SERMS in the prevention and/or treatment of metabolic bone diseases such as postmenopausal osteoporosis.

Vitamin D compounds exert anti-apoptotic effects in human osteosarcoma cells in vitro

Several studies have demonstrated that vitamin D regulates growth and differentiation in bone cells in vitro. In addition, in vivo studies have shown that vitamin D stimulates bone formation, increases the number of osteoblast precursor cells and prevents bone mineral loss. These observations indicate that vitamin D may have anabolic effects on bone, and thus therapeutic potential in the treatment of osteoporosis. However, little is known about the effects of vitamin D on apoptosis in bone cells and about the contribution of this process to the effect of vitamin D on bone mineral loss. To investigate this aspect in more detail, we studied the effect of 1alpha,25(OH)(2)D(3) and a series of analogues on apoptosis in human osteosarcoma cells. No significant induction of apoptosis was observed with any of the compounds after a 5 day treatment period. In contrast, some of the analogues showed a tendency to protect the cells from undergoing apoptosis. This anti-apoptotic effect of vitamin D was further confirmed by the ability of 1alpha,25(OH)(2)D(3) to suppress camptothecin- and staurosporin-induced DNA fragmentation in the cells. In cultures treated simultaneously with 1alpha,25(OH)(2)D(3) in combination with camptothecin or staurosporin, the level of DNA fragmentation was markedly reduced compared with cultures treated with camptothecin or staurosporin alone. On the basis of the present results, it is therefore concluded that vitamin D displays anti-apoptotic effects in human osteoblast-like osteosarcoma cells in vitro. This observation suggests that besides regulating growth and differentiation, vitamin D exerts its anabolic effects on bone by protecting osteoblastic cells from undergoing apoptosis.

The biological activities of 1alpha,25-dihydroxyvitamin D3 and its synthetic analog 1alpha,25-dihydroxy-16-ene-vitamin D3 in normal human osteoblastic cells and human osteosarcoma SaOS-2 cells are modulated by 17-beta estradiol and dependent on stage of differentiation

We compared the effects of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] and its analog, 1alpha,25-dihydroxy-16-ene-vitamin D3 [1alpha,25(OH)2-16-ene-D3], as well as their interactions with 17-beta estradiol (E2) on osteoblastic function in our human normal (HOB) and osteosarcoma SaOS-2 cell models representing two different stages of differentiation, the more differentiated HOB+DEX cells and SaOS+DEX cells, and the corresponding less differentiated HOB-DEX and SaOS-DEX cells. The differential effects of 1alpha,25(OH)2D3 and 1alpha,25(OH)2-16-ene-D3 and the modulation by E2 on ALP activity in HOB-DEX and HOB+DEX cells were small but significant. The most significant effects were seen in SaOS+DEX cells, in which 1alpha,25(OH)2-16-ene-D3 was 100-fold more potent than 1alpha,25(OH)2D3, the maximal enhancement being exerted at 0.1 nM and 10 nM, respectively. E2 enhanced the stimulatory effects of both compounds, with ALP being increased 2-fold at 0.1 nM (p<0.001). Osteocalcin (OC) production in HOB-DEX cells was stimulated 1.3 to 1.4-fold by 1alpha,25(OH)2D3 and 1alpha,25(OH)2-16-ene-D3 at a concentration of 0.01 nM, with E2 inhibiting the effect of 1alpha,25(OH)2-16-ene-D3. In SaOS-DEX and SaOS+DEX cells, 1alpha,25(OH)2D3 and 1alpha,25(OH)2-16-ene-D3 stimulated OC production 1.6-fold at 0.1 nM with E2 slightly enhancing the effect of 1alpha,25(OH)2D3. Western blot analysis of 1alpha,25(OH)2D3 receptor (VDR) levels showed that in SaOS+DEX cells, the effect of 1alpha,25(OH)2D3 was larger than that of 1alpha,25(OH)2-16-ene-D3. These results show that 1alpha,25(OH)2-16-ene-D3 is biologically active in human osteoblasts.

"Non-hypercalcemic" analogs of 1alpha,25 dihydroxy vitamin D augment the induction of creatine kinase B by estrogen and selective estrogen receptor modulators (SERMS) in osteoblast-like cells and rat skeletal organs

We have demonstrated previously that daily treatments for 3 days with the so-called "non-hypercalcemic" analogs of 1alpha,25 dihydroxy vitamin D in ROS 17/2.8 osteoblast-like cells, stimulate the specific activity of creatine kinase BB (CK), and that such treatment with these analogs followed by a single treatment with gonadal steroids, upregulates responsiveness and sensitivity to estradiol 17beta (E(2)) for the induction of CK. This study was designed to determine if these same "non-hypercalcemic" vitamin D analogs could upregulate in vivo the response to E(2) and whether substitution of selective estrogen receptor modulators (SERMS) for E(2) would result in the same upregulation. We found that one week or 2 weeks pretreatment of prepubertal rats with vitamin D analogs led to increased induction of CK by E(2) and by the SERMS tamoxifen, tamoxifen methiodide and raloxifene, in epiphysis and diaphysis of the femur but not in the uterus. However, in contrast to their antiestrogenic activity in the uterus, there was no inhibition of E(2) action by the SERMS in skeletal tissues. The induction of mRNA for ckb in ROS 17/2.8 cells by E(2) or SERMS was demonstrated only after vitamin D pretreatment; there was no inhibition of E(2) induction by SERMS. Antagonists of vitamin D dependent calcium transport (transcaltachia) did not inhibit stimulation by vitamin D analogs. These results support the involvement of a nuclear mechanism in the upregulation of induction of CK by E(2), which may be due, in part, to the ability of vitamin D to increase estrogen receptor(s).

Nonhypercalcemic analogs of vitamin D stimulate creatine kinase B activity in osteoblast-like ROS 17/2.8 cells and up-regulate their responsiveness to estrogens

We have reported that pretreatment with 1 alpha, 25(OH)2D3(1, 25) up-regulates responsiveness and sensitivity to 17 beta estradiol (E2) in osteoblast-like cells, as measured by parallel stimulation of [3H]thymidine incorporation into DNA and the specific activity of creatine kinase BB (CK). Increased responsiveness was correlated with increased E2 receptor concentration. In this study, we have extended these observations to new nonhypercalcemic analogs of 1,25. We compared the analogs hexafluoro vitamin D3 (FL), and the side chain modified derivatives: EB 1089 (EB), CB 1093 (CB) and MC 1288 (MC) with 1,25 and 25 (OH)D3(25 D3). Treatment with 30 nM E2 for 4 h stimulated CK activity in ROS 17/2-8 cells by 40%; there was no further increase after 3 daily additions of E2. Treatment by 3 daily additions, at 1 nM, of all analogs except 25 D3 caused a 2-3-fold increase in CK specific activity. This schedule of treatment also upregulated the response to 4 h exposure to 30 nM E2 by 30-70% above the response to vitamin D analogs alone, and by up to 2 fold compared to E2 without pretreatment. At 1 pM, the analogs doubled CK activity, and, except for 1,25, upregulated the response to E2 to levels characteristic of each analog. Pretreatment with vitamin D analogs also increased the sensitivity to E2 by lowering the dose for a comparable response to E2 by one or two orders of magnitude. Stimulation of specific activity of CK by the analogs was paralleled by increases in the steady state level of mRNA for CKB, but not in its half life. Whereas pretreatment by vehicle followed by E2 for 2 h was unable to increase CKB mRNA, pretreatment with the analogs made possible detection of mRNA responsiveness to E2. These results add to the evidence for the interaction of estrogens and antiestrogens with vitamin D metabolites in regulation of bone growth in vitro. They also strengthen the potential for treatment of bone loss, as occurs in postmenopausal osteoporosis, by a combination of nonhypercalcemic vitamin D analogs and estrogens.