Dexamethasone and retinoic acid differentially regulate growth and differentiation in an immortalised human clonal bone marrow stromal cell line with osteoblastic characteristics

Effect of cAMP Signaling Regulation in Osteogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells

The successful implementation of adipose-derived mesenchymal stem cells (ADSCs) in bone regeneration depends on efficient osteogenic differentiation. However, a literature survey and our own experience demonstrated that current differentiation methods are not effective enough. Since the differentiation of mesenchymal stem cells (MSCs) into osteoblasts and adipocytes can be regulated by cyclic adenosine monophosphate (cAMP) signaling, we investigated the effects of cAMP activator, forskolin, and inhibitor, SQ 22,536, on the early and late osteogenic differentiation of ADSCs cultured in spheroids or in a monolayer. Intracellular cAMP concentration, protein kinase A (PKA) activity, and inhibitor of DNA binding 2 (ID2) expression examination confirmed cAMP up- and downregulation. cAMP upregulation inhibited the cell cycle and protected ADSCs from osteogenic medium (OM)-induced apoptosis. Surprisingly, the upregulation of cAMP level at the early stages of osteogenic differentiation downregulated the expression of osteogenic markers RUNX2, Osterix, and IBSP, which was more significant in spheroids, and it is used for the more efficient commitment of ADSCs into preosteoblasts, according to the previously reported protocol. However, cAMP upregulation in a culture of ADSCs in spheroids resulted in significantly increased osteocalcin production and mineralization. Thus, undifferentiated and predifferentiated ADSCs respond differently to cAMP pathway stimulation in terms of osteogenesis, which might explain the ambiguous results from the literature.

Exploring Poly(Ethylene Glycol)-Poly(Trimethylene Carbonate) Nanoparticles as Carriers of Hydrophobic Drugs to Modulate Osteoblastic Activity

Current treatment options for bone-related disorders rely on a systemic administration of therapeutic agents that possess low solubility and intracellular bioavailability, as well as a high pharmacokinetic variability, which in turn lead to major off-target side effects. Hence, there is an unmet need of developing drug delivery systems that can improve the clinical efficacy of such therapeutic agents. Nanoparticle delivery systems might serve as promising carriers of hydrophobic molecules. Here, we propose 2 nanoparticle-based delivery systems based on monomethoxy poly(ethylene glycol)-poly(trimethyl carbonate) (mPEG-PTMC) and poly(lactide-co-glycolide) for the intracellular controlled release of a small hydrophobic drug (dexamethasone) to osteoblast cells in vitro. mPEG-PTMC self-assembles into stable nanoparticles in the absence of surfactant and shows a greater entrapment capacity of dexamethasone, while assuring bioactivity in MC3T3-E1 and bone marrow stromal cells cultured under apoptotic and osteogenic conditions, respectively. The mPEG-PTMC nanoparticles represent a potential vector for the intracellular delivery of hydrophobic drugs in the framework of bone-related diseases.

Patient-reported health outcomes for severe knee osteoarthritis after conservative treatment with an intra-articular cell-free formulation for articular cartilage regeneration combined with usual medical care vs. usual medical care alone: A randomized controlled trial

Osteoarthritis (OA) is a major public health problem characterized by joint pain, fatigue, functional limitation and decreased quality of life of the patient, which results in increased use of healthcare services and high economical costs. A promising novel bioactive cell-free formulation (BIOF2) for cartilage regeneration has recently been tested in pre-clinical and clinical trials, and has demonstrated a success rate similar to that of total joint arthroplasty for the treatment of severe knee OA. The present study evaluated the efficacy of treatment with BIOF2, by including it within a conservative regimen of 'usual medical care' of knee OA, and whether its efficacy was affected in subgroups of patients presenting with comorbidities that exacerbate OA. A prospective, randomized, 2-arm parallel group phase III clinical trial was conducted, which included 105 patients in the 'usual medical care' group (paracetamol/NSAIDs and general care provided by the family physician) and 107 patients in the BIOF2 group (usual medical care + intra-articular BIOF2 application at 0, 1 and 2 months). Two aspects were evaluated at 0, 6 and 12 months: i) Minimal clinically important improvement (MCII), based on 30% improvement of pain from the baseline; and ii) the Patient Acceptable Symptom State (PASS), a questionnaire that determines patient well-being thresholds for articular pain and function. Adverse effects and regular NSAID use were registered. At 12 months, BIOF-2 treatment produced MCII in 70% of the patients and >50% achieved PASS. Excluding the patients with class 2 obesity or malalignment conditions (genu varum or genu valgum >20 degrees), the experimental treatment produced MCII and PASS in 100 and 92% of patients, respectively, compared with 25 and 8% in the group of usual medical care (P<0.001). No patient with malalignment and treatment with BIOF2 achieved PASS. Notably, there were no serious adverse effects. To conclude, BIOF2 is a safe therapeutic alternative that is easy to implement together with usual medical care for knee OA. Trial registration: Cuban Public Registry of Clinical Trials (RPCEC) Database RPCEC00000277. Retrospectively registered June, 2018.

Retinoic acid increases the effect of bone morphogenetic protein type 2 on osteogenic differentiation of human adipose-derived stem cells

BACKGROUND

Bone morphogenetic protein type 2 (BMP-2) and retinoic acid (RA) are osteoinductive factors that stimulate endogenous mechanisms of bone repair which can be applied on management of osseous defects in oral and maxillofacial fields.

OBJECTIVE

Considering the different results of RA on osteogenesis and its possible use to substitute/potency BMP-2 effects, this study evaluated the outcomes of BMP-2, RA, and BMP-2+RA treatments on in vitro osteogenic differentiation of human adipose-derived stem cells (ASCs) and the signaling pathway(s) involved.

MATERIAL AND METHODS

ASCs were treated every other day with basic osteogenic medium (OM) alone or supplemented with BMP-2, RA, or BMP-2+RA. Alkaline phosphatase (ALP) activity was determined using the r-nitrophenol method. Extracellular matrix mineralization was evaluated using von Kossa staining and calcium quantification. Expression of osteonectin and osteocalcin mRNA were determined using qPCR. Smad1, Smad4, phosphorylated Smad1/5/8, BMP-4, and BMP-7 proteins expressions were analyzed using western blotting. Signaling pathway was evaluated using the IPA® software.

RESULTS

RA promoted the highest ALP activity at days 7, 14, 21, and 28, in comparison to BMP-2 and BMP-2+RA. BMP-2+RA best stimulated phosphorylated Smad1/5/8 protein expression at day 7 and Smad4 expression at days 7, 14, 21, and 28. Osteocalcin and osteonectin mRNA expressions were best stimulated by BMP-2+RA at day 7. Matrix mineralization was most improved by BMP-2+RA at days 12 and 32. Additionally, BMP-2+RA promoted the highest BMP signaling pathway activation at days 7 and 14, and demonstrated more activation of differentiation of bone-forming cells than OM alone.

CONCLUSIONS

In summary, RA increased the effect of BMP-2 on osteogenic differentiation of human ASCs.

Effect of donor variation on osteogenesis and vasculogenesis in hydrogel cocultures

To introduce a functional vascular network into tissue-engineered bone equivalents, human endothelial colony forming cells (ECFCs) and multipotent mesenchymal stromal cells (MSCs) can be cocultured. Here, we studied the impact of donor variation of human bone marrow-derived MSCs and cord blood-derived ECFCs on vasculogenesis and osteogenesis using a 3D in vitro coculture model. Further, to make the step towards cocultures consisting of cells derived from a single donor, we tested how induced pluripotent stem cell (iPSC)-derived human endothelial cells (iECs) performed in coculture models. Cocultures with varying combinations of human donors of MSCs, ECFCs, or iECs were prepared in Matrigel. The constructs were cultured in an osteogenic differentiation medium. Following a 10-day culture period, the length of the prevascular structures and osteogenic differentiation were evaluated for up to 21 days of culture. The particular combination of MSC and ECFC donors influenced the vasculogenic properties significantly and induced variation in osteogenic potential. In addition, the use of iECs in the cocultures resulted in prevascular structure formation in osteogenically differentiated constructs. Together, these results showed that close attention to the source of primary cells, such as ECFCs and MSCs, is critical to address variability in vasculogenic and osteogenic potential. The 3D coculture model appeared to successfully generate prevascularized constructs and were sufficient in exceeding the ~200 μm diffusion limit. In addition, iPSC-derived cell lineages may decrease variability by providing a larger and potentially more uniform source of cells for future preclinical and clinical applications.

Transdifferentiation of adipocytes to osteoblasts: potential for orthopaedic treatment

OBJECTIVES

As both adipocytes and osteoblasts originate from the same pool of mesenchymal stem cells, increasing clinical evidence has emerged of the plasticity between the two lineages. For instance, the downregulation of osteoblast differentiation and upregulation of adipogenesis are common features of conditions such as multiple myeloma, obesity and drug-induced bone loss in diabetes mellitus. However, despite in-vitro and in-vivo observations of adipocyte transdifferentiation into osteoblasts, little is known of the underlying mechanisms.

KEY FINDINGS

This review summarises the current knowledge of this particular transdifferentiation process whereby the Wnt/β-catenin signalling pathway and Runx2 overexpression have been postulated to play a critical role.

SUMMARY

Furthermore, due to the possibility of a novel therapy in the treatment of bone conditions, a number of agents with the potential to induce adipo-to-osteoblast transdifferentiation have been investigated such as all-trans retinoic acid, bone morphogenetic protein-9 and vascular endothelial growth factor.

Ginsenoside Rg1 promotes osteogenic differentiation of rBMSCs and healing of rat tibial fractures through regulation of GR-dependent BMP-2/SMAD signaling

Fracture healing is closely related to the number and activity of bone marrow mesenchymal stem cells (BMSCs) near the fracture site. The present study was to investigate the effect of Rg1 on osteogenic differentiation of cultured BMSCs and related mechanisms and on the fracture healing in a fracture model. In vitro experiments showed that Rg1 promoted the proliferation and osteogenic differentiation of BMSCs. Western blot analyses demonstrated that Rg1 promoted osteogenic differentiation of BMSCs through the glucocorticoid receptor (GR)-dependent BMP-2/Smad signaling pathway. In vivo, X-ray examination showed that callus growth in rats treated with Rg1 was substantially faster than that in control rats after fracture. The results of H&E and Safranin-O/Fast Green staining revealed that, compared with controls, rats in the Rg1 treatment group had a significantly higher proportion of trabecular bone but a much lower proportion of fibers and cartilage components inside the callus. Micro-CT suggested that bone mineral density (BMD), percent bone volume (BV/TV), trabecular number (Tb.N), and trabecular thickness (Tb.Th) were significantly increased in the treatment group, whereas trabecular separation (Tb.Sp) was significantly reduced. Thus, Rg1 promotes osteogenic differentiation by activating the GR/BMP-2 signaling pathway, enhances bone calcification, and ultimately accelerates the fracture healing in rats.

Effect of retinoic acid and vitamin D3 on osteoblast differentiation and activity in aging

Several studies have evidenced that in aging, osteoblast functional activity is impaired: osteoblast proliferation is slower and matrix deposition is less efficient. Because peroxisome-proliferator-activated receptor γ2 (PPARγ2) and fatty acids are important inhibitory signals in osteoblast development, we have investigated in human primary osteoblasts obtained from patients of different ages, the influence of retinoic acid and calcitriol on enzymes involved in differentiative (PPARγ2, β-catenin, and insulin-like growth factor 1) and metabolic (carnitine palmitoyltransferase 1) intracellular pathways, and on transglutaminase 2, as enzyme fundamental for stabilizing the newly deposited extracellular matrix in bone. Retinoic acid and calcitriol influenced, respectively, proliferation and differentiation of osteoblasts, and an increase in PPARγ2 expression was observed following retinoic acid administration, whereas a decrease was observed following calcitriol administration. Aging widely influenced all parameters analyzed (the proliferation, differentiation, and new matrix deposition are significantly reduced in aged osteoblasts), with the exception of PPARγ2, which we found to be constitutively overexpressed and not modulated by retinoic acid or calcitriol administration. Our findings show the impaired ability of aged osteoblasts to perform adequate functional response and draw attention to the therapeutic approaches for bone healing in elderly patients.

FGF-2 induces the proliferation of human periodontal ligament cells and modulates their osteoblastic phenotype by affecting Runx2 expression in the presence and absence of osteogenic inducers

The exact phenotype of human periodontal ligament cells (hPDLCs) remains a controversial area. Basic fibroblast growth factor (FGF-2) exhibits various functions and its effect on hPDLCs is also controversial. Therefore, the present study examined the effect of FGF-2 on the growth and osteoblastic phenotype of hPDLCs with or without osteogenic inducers (dexamethasone and β-glycerophosphate). FGF-2 was added to defined growth culture medium and osteogenic inductive culture medium. Cell proliferation, osteogenic differentiation and mineralization were measured. The selected differentiation markers, Runx2, collagen type I, α1 (Col1a1), osteocalcin (OCN) and epidermal growth factor receptor (EGFR), were investigated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Runx2 and OCN protein expression was measured by western blotting. FGF-2 significantly increased the proliferation of hPDLCs, but did not affect alkaline phosphatase activity. RT-qPCR analysis revealed enhanced mRNA expression of Runx2, OCN and EGFR, but suppressed Col1a1 gene expression in the absence of osteogenic inducers, whereas all these gene levels had no clear trend in their presence. The Runx2 protein expression was clearly increased, but the OCN protein level showed no evident trend. The mineralization assay demonstrated that FGF-2 inhibited mineralized matrix deposition with osteogenic inducers. These results suggested that FGF-2 induces the growth of immature hPDLCs, which is a competitive inhibitor of epithelial downgrowth, and suppresses their differentiation into mineralized tissue by affecting Runx2 expression. Therefore, this may lead to the acceleration of periodontal regeneration.

Optimized osteogenic differentiation protocol from R1 mouse embryonic stem cells in vitro

Embryonic stem cells (ESCs) are a unique model that allows the study of molecular pathways underlying commitment and differentiation. One such lineage is osteoblasts, which are responsible for forming bone tissue in the body. There are many osteogenic differentiation protocols in the literature utilizing different soluble factors. The goal of the present study was to increase the efficacy of our osteogenic differentiation protocol from R1 cells. We have studied the effects of the addition of the following factors: dexamethasone, retinoic acid, and peroxisome-proliferator-activated receptor-gamma inhibitor, which have been reported to enhance osteogenesis. We found that among the 6 different protocols that were tested, the addition of retinoic acid with later addition of dexamethasone gives the most enrichment of osteogenic lineage cells. Thus, our findings provide valuable guidelines for culture condition to differentiate mouse R1 ESCs to osteoblastic cells in vitro.

The effect of nitrogen containing bisphosphonates, zoledronate and alendronate, on the production of pro-angiogenic factors by osteoblastic cells

Bisphosphonates (BPs) have been shown to influence angiogenesis. This may contribute to BP-associated side-effects such as osteonecrosis of the jaw (ONJ) or atypical femoral fractures (AFF). The effect of BPs on the production of angiogenic factors by osteoblasts is unclear. The aims were to investigate the effect of (1) alendronate on circulating angiogenic factors; vascular endothelial growth factor (VEGF) and angiopoietin-1 (ANG-1) in vivo and (2) zoledronate and alendronate on the production of VEGF and ANG-1 by osteoblasts in vitro. We studied 18 post-menopausal women with T score⩽-2 randomized to calcium/vitamin D only (control arm, n=8) or calcium/vitamin D and alendronate 70mg weekly (treatment arm, n=10). Circulating concentrations of VEGF and ANG-1 were measured at baseline, 3, 6 and 12months. Two human osteoblastic cell lines (MG-63 and HCC1) and a murine osteocytic cell line (MLO-Y4) were treated with zoledronate or alendronate at concentrations of 10(-12)-10(-6)M. VEGF and ANG-1 were measured in the cell culture supernatant. We observed a trend towards a decline in VEGF and ANG-1 at 6 and 12months following treatment with alendronate (p=0.08). Production of VEGF and ANG-1 by the MG-63 and HCC1 cells decreased significantly by 34-39% (p<0.01) following treatment with zoledronate (10(-9)-10(-6)M). Treatment of the MG-63 cells with alendronate (10(-7) and 10(-6)) led to a smaller decrease (25-28%) in VEGF (p<0.05). Zoledronate (10(-10)-10(-)(6)M) suppressed the production of ANG-1 by MG-63 cells with a decrease of 43-49% (p<0.01). Co-treatment with calcitriol (10(-8)M) partially reversed this zoledronate-induced inhibition. BPs suppress osteoblastic production of angiogenic factors. This may explain, in part, the pathogenesis of the BP-associated side-effects.

Retinoic acid regulates commitment of undifferentiated mesenchymal stem cells into osteoblasts and adipocytes

Evidence indicates that the balance between osteoblastogenesis and adipogenesis of mesenchymal stem cells (MSCs) is regulated by several hormones, growth factors, and their downstream signaling cascades. Previous studies suggest that retinoic acid (RA) plays a role in osteoblastogenesis and adipogenesis. However, it is unknown whether RA regulates commitment of MSCs into osteoblasts and adipocytes. In this study, we investigated the role of RA in differentiation of MSCs using the C3H10T1/2 cell line. RA stimulated activity and expression of alkaline phosphatase (ALP) and upregulated activity of the ALP gene promoter. The effects of RA were further enhanced by bone morphogenetic protein 2 (BMP2) and resultant Smad signaling. Furthermore, overexpression of Runx2 and Msx2, critical transcription factors for bone formation and BMP2-dependent osteoblastogenesis, enhanced RA-dependent ALP activity. In view of these findings, RA likely stimulates osteoblast differentiation through the BMP2-Smad-Runx2/Msx2 pathway. In contrast, RA markedly inhibited BMP2-induced adipocyte differentiation, suppressing expression of peroxisome proliferator-activated receptor-γ (PPARγ), CCAAT/enhancer-binding protein (C/EBP)α and C/EBPδ, and inhibiting adipogenic function of C/EBPβ, C/EBPδ, and PPARγ. In conclusion, our data suggest that RA regulates commitment of MSCs into osteoblasts and adipocytes by controlling transcriptional regulators.

Effects of low-intensity electromagnetic fields on the proliferation and differentiation of cultured mouse bone marrow stromal cells

BACKGROUND

Electromagnetic fields (EMFs) used in stem-cell tissue engineering can help elucidate their biological principles.

OBJECTIVE

The aim of this study was to investigate the effects of low-intensity EMFs on cell proliferation, differentiation, and cycle in mouse bone marrow stromal cells (BMSCs) and the in vivo effects of EMFs on BMSC.

METHODS

Harvested BMSCs were cultured for 3 generations and divided into 4 groups. The methylthiotetrazole (MTT) assay was used to evaluate cell proliferation, and alkaline phosphatase activity was measured via a colorimetric assay on the 3rd, 7th, and 10th days. Changes in cell cycle also were analyzed on the 7th day, and bone nodule formation was analyzed on the 12th day. Additionally, the expression of the collagen I gene was examined by reverse transcription-polymerase chain reaction (RT-PCR) on the 10th day. The BMSCs of the irradiated group and the control group were transplanted into cortical bone of different mice femurs separately, with poly(lactic-co-glycolic acid) (PLGA) serving as a scaffold. After 4 and 8 weeks, bone the bone specimens of mice were sliced and stained by hematoxylin and eosin separately.

RESULTS

The results showed that EMFs (0.5 mT, 50 Hz) accelerated cellular proliferation, enhanced cellular differentiation, and increased the percentage of cells in the G(2)/M+S (postsynthetic gap 2 period/mitotic phase + S phase) of the stimulation. The EMF-exposed groups had significantly higher collagen I messenger RNA levels than the control group. The EMF + osteogenic medium-treated group readily formed bone nodules. Hematoxylin and eosin staining showed a clear flaking of bone tissue in the irradiated group.

CONCLUSION

Irradiation of BMSCs with low-intensity EMFs (0.5 mT, 50 Hz) increased cell proliferation and induced cell differentiation. The results of this study did not establish a stricter animal model for studying osteogenesis, and only short-term results were investigated. Further study of the mechanism of EMF is needed.

Effects of VEGF and FGF-2 on proliferation and differentiation of human periodontal ligament stem cells

Human periodontal ligament stem cells (PDLSCs) from extracted third molar teeth are a type of adult stem cell originating from dental tissue. PDLSCs are known to have a self-renewal capacity and multi-lineage differentiation potential. Vascular endothelial growth factor (VEGF), an angiogenic/vasculogenic factor, has been shown to stimulate endothelial cell mitogenesis and cell migration. Another growth factor, fibroblast growth factor-2 (FGF-2), a mitogenic factor, enhances osteogenesis in mesenchymal stem cells (MSCs). This study examines the effects of VEGF and FGF-2 on PDLSCs in vitro and in vivo compared with those on bone marrow stem cells (BMSCs) as a positive control. Treatment of PDLSCs with VEGF increases the accumulation of calcium nodules, alkaline phosphatase (ALP) activity and the formation of hard tissue and up-regulates the mRNA level of runt-related transcription factor 2 (Runx2). In contrast, FGF-2 enhances the proliferation of PDLSCs in vitro in cell culture, where it significantly decreases calcium accumulation and ALP activity and down-regulates the expression of osteogenic gene markers (i.e., Runx2, ALP, type I collagen) involved in osteogenic induction. We have also transplanted PDLSCs with hydroxyapatite/tricalcium phosphate particles (HA/TCP) as carriers for each factor (VEGF, FGF-2) into nude mice and, after 8 weeks, observed the in vivo formation of hard tissue at the dorsal surface. Based on our results, we suggest that VEGF has positive effects on odonto-/osteogenic differentiation in vitro and on the formation of mineralized structure in vivo. FGF-2 might be a powerful promoter of the proliferation of progenitor cells in hard tissue regeneration but exogenous FGF-2 might inhibit terminal differentiation.

Enhancement of osteogenic gene expression for the differentiation of human periosteal derived cells

The osteogenic differentiation of progenitor populations allows analysis of cell functionality as well as creating a platform for investigating stem cells for bone tissue engineering. Protocols used for osteogenic differentiation of progenitor cells are often identical to those detailed for bone marrow mesenchymal stem cells, however this may be flawed due to cell populations residing in different niches and being in distinct stages of differentiation. We herein describe the individual and combined effects of known osteo-inductive agents; dexamethasone (Dex), 1,25-dihydroxyvitamin D3 (VitD3), all trans-retinoic acid (atRA), cyclic AMP (cAMP) and bone morphogenic protein 2 (BMP2) in combination with fetal bovine serum (FBS) on osteogenesis of human periosteal derived cells (hPDCs). The addition of Dex&FBS was essential for the transition of hPDCs to an ALP positive cell population. Subsequently, atRA, Dex&FBS and BMP2 were required for the expression of transcription factors governing osteogenesis and hence differentiation towards a mature osteoblast. It is also hypothesized that Dex has no direct effect on the differentiation of hPDCs, instead its effect is to augment differentiation in combination with other factors. These data provide a comprehensive assessment of known osteogenic factors, in a novel multiplex system, to evaluate their effect on progenitor cell differentiation.

Fate of bone marrow-derived stromal cells after intraperitoneal infusion or implantation into femoral bone defects in the host animal

The fate of intraperitoneally injected or implanted male rat bone marrow-derived stromal cells inside female sibling host animals was traced using Y-chromosome-sensitive PCR. When injected intraperitoneally, Y-chromosome-positive cells were found in all studied organs: heart muscle, lung, thymus, liver, spleen, kidney, skin, and femoral bone marrow with a few exceptions regardless of whether they had gone through osteogenic differentiation or not. In the implant experiments, expanded donor cells were seeded on poly(lactide-co-glycolide) scaffolds and grown under three different conditions (no additives, in osteogenic media for one or two weeks) prior to implantation into corticomedullar femoral defects. Although the impact of osteogenic in vitro cell differentiation on cell migration was more obvious in the implantation experiments than in the intraperitoneal experiments, the donor cells stay alive when injected intraperitoneally or grown in an implant and migrate inside the host. However, when the implants contained bioactive glass, no signs of Y-chromosomal DNA were observed in all studied organs including the implants indicating that the cells had been eliminated.

Retinoic acid enhances osteogenesis in cranial suture-derived mesenchymal cells: potential mechanisms of retinoid-induced craniosynostosis

BACKGROUND

In utero retinoid exposure results in numerous craniofacial malformations, including craniosynostosis. Although many malformations associated with retinoic acid syndrome are associated with neural crest defects, the specific mechanisms of retinoid-induced craniosynostosis remain unclear. The authors used the culture of mouse cranial suture-derived mesenchymal cells to probe the potential cellular mechanisms of this teratogen to better elucidate mechanisms of retinoid-induced suture fusion.

METHODS

Genes associated with retinoid signaling were assayed in fusing (posterofrontal) and patent (sagittal, coronal) sutures by quantitative real-time polymerase chain reaction. Cultures of mouse suture-derived mesenchymal cells from the posterofrontal suture were established from 4-day-old mice. Cells were cultured with all-trans retinoic acid (1 and 5 muM). Proliferation, osteogenic differentiation, and specific gene expression were assessed.

RESULTS

Mouse sutures were found to express genes necessary for retinoic acid synthesis, binding, and signal transduction, demonstrated by quantitative real-time polymerase chain reaction (Raldh1, Raldh2, Raldh3, and Rbp4). These genes were not found to be differentially expressed in fusing as compared with patent cranial sutures in vivo. Addition of retinoic acid enhanced the osteogenic differentiation of suture-derived mesenchymal cells in vitro, including up-regulation of alkaline phosphatase activity and Runx2 expression. Contemporaneously, cellular proliferation was repressed, as shown by proliferative cell nuclear antigen expression. The pro-osteogenic effect of retinoic acid was accompanied by increased gene expression of several hedgehog and bone morphogenetic protein ligands.

CONCLUSIONS

Retinoic acid represses proliferation and enhances osteogenic differentiation of suture-derived mesenchymal cells. These in vitro data suggest that retinoid exposure may lead to premature cranial suture fusion by means of enhanced osteogenesis and hedgehog and bone morphogenetic protein signaling.

Ex vivo culturing of stromal cells with dexamethasone-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles promotes ectopic bone formation

Recently, our group has proposed a combinatorial strategy in tissue engineering principles employing carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles (CMCht/PAMAM) towards the intracellular release and regimented supply of dexamethasone (Dex) aimed at controlling stem cell osteogenic differentiation in the absence of typical osteogenic inducers, in vivo. In this work, we have investigated if the Dex-loaded CMCht/PAMAM dendrimer nanoparticles could play a crucial role in the regulation of osteogenesis, in vivo. Macroporous hydroxyapatite (HA) scaffolds were seeded with rat bone marrow stromal cells (RBMSCs), whose cells were expanded in MEM medium supplemented with 0.01 mg ml(-1) Dex-loaded CMCht/PAMAM dendrimer nanoparticles and implanted subcutaneously on the back of rats for 2 and 4 weeks. HA porous ceramics without RBMSCs and RBMSCs/HA scaffold constructs seeded with cells expanded in the presence and absence of 10(-8) M Dex were used as controls. The effect of initial cell number seeded in the HA scaffolds on the bone-forming ability of the constructs was also investigated. Qualitative and quantitative new bone formation was evaluated in a non-destructive manner using micro-computed tomography analyses of the explants. Haematoxylin and Eosin stained implant sections were also used for the histomorphometrical analysis. Toluidine blue staining was carried out to investigate the synthesis of proteoglycan extracellular matrix. In addition, alkaline phosphatase and osteocalcin levels in the explants were also quantified, since these markers denote osteogenic differentiation. At 4 weeks post-implantation results have shown that the novel Dex-loaded carboxymethylchitosan/poly(amidoamine) dendrimer nanoparticles may be beneficial as an intracellular nanocarrier, supplying Dex in a regimented manner and promoting superior ectopic de novo bone formation.

Osteogenic differentiation of stem cells derived from human periodontal ligaments and pulp of human exfoliated deciduous teeth

Multipotent stem cells derived from periodontal ligaments (PDLSC) and pulp of human exfoliated deciduous teeth (SHED) represent promising cell sources for bone regeneration. Recent studies have demonstrated that retinoic acid (RA) and dexamethasone (Dex) induce osteogenesis of postnatal stem cells. The objective of this study was to examine the effects of RA and Dex on the proliferation and osteogenic differentiation of SHED and PDLSC and to compare the osteogenic characteristics of SHED and PDLSC under RA treatment. SHED and PDLSC were treated with serum-free medium either alone or supplemented with RA or Dex for 21 days. The proliferation of SHED and PDLSC was significantly inhibited by both RA and Dex. RA significantly upregulated gene expression and the activity of alkaline phosphatase in SHED and PDLSC. Positive Alizarin red and von Kossa staining of calcium deposition was seen on the RA-treated SHED and PDLSC after 21 days of culture. The influences of RA on the osteogenic differentiation of SHED and PDLSC were significantly stronger than with Dex. Supplementation with insulin enhanced RA-induced osteogenic differentiation of SHED. Thus, RA is an effective inducer of osteogenic differentiation of SHED and PDLSC, whereas RA treatment in combination with insulin supplementation might be a better option for inducing osteogenic differentiation. Significantly higher cell proliferation of PDLSC results in greater calcium deposition after 3-week culture, suggesting that PDLSC is a better osteogenic stem cell source. This study provides valuable information for efficiently producing osteogenically differentiated SHED or PDLSC for in vivo bone regeneration.

Effect of dexamethasone on differentiation of multipotent stromal cells from human adipose tissue

Effect of dexamethasone on differentiation of multipotent stromal cells from human adipose tissue was evaluated. Addition of dexamethasone to growth medium resulted in active adipogenesis. Addition of dexamethasone to the osteogenic medium (containing active vitamin D3 form as the main inductor) led to simultaneous realization of the adipogenic and osteogenic potencies of multipotent stromal cells of the adipose tissue. Hence, the quality of the transplant on the basis of predifferentiated multipotent stromal cells from the adipose tissue for bone tissue repair can be deteriorated by dexamethasone directing some cells to adipogenic development.

In vitro differentiation of human calvarial suture derived cells with and without dexamethasone does not induce in vivo-like expression

Osteogenic supplements are a requirement for osteoblastic cell differentiation during in vitro culture of human calvarial suture-derived cell populations. We investigated the ability of ascorbic acid and beta-glycerophosphate with and without the addition of dexamethasone to stimulate in vivo-like osteoblastic differentiation. Cells were isolated from unfused and prematurely fused suture tissue from patients with syndromic and non-syndromic craniosynostosis and cultured in each osteogenic medium for varying lengths of time. The effect of media supplementation was investigated with respect to the ability of cells to form mineralised bone nodules and the expression of five osteodifferentiation marker genes (COL1A1, ALP, BSP, OC and RUNX2), and five genes that are differentially expressed during human premature suture fusion (GPC3, RBP4, C1QTNF3, WIF1 and FGF2). Cells from unfused sutures responded more slowly to osteogenic media but formed comparable bone nodules to fused suture-derived cells after 16 days of culture in either osteogenic media. However, gene expression differed between unfused and fused suture-derived cells, as did expression in each osteogenic medium. When compared to expression in the explant tissue of origin, neither medium induced a level or profile of gene expression similar to that seen in vivo. Overall, our results demonstrate that cells from the same suture that are isolated during different stages of morphogenesis in vivo, despite being de-differentiated to a similar level in vitro, respond uniquely and differently to each osteogenic medium. Further, we suggest that neither cell culture medium recapitulates differentiation via activation of the same genetic cascades as occurs in vivo.

Effect of anti-inflammatory agents on the integration of autogenous bone graft and bovine bone devitalized matrix in rats

PURPOSE: To study the repair of bone defect filled with autograft or bovine bone devitalized matrix in rats under anti-inflammatory action. METHODS: Two hundred and forty Wistar rats were distributed to two groups of 120 animals each. A 2mm-diameter defect was created in the femoral diaphysis. Animals of Group I had the bone defect filled with autograft and those of Group II, with bovine bone devitalized matrix. Animals of each group were redistributed to four subgroups according to the intramuscular administration of anti-inflammatory drug or saline solution: A - diclofenac sodium; B - dexamethasone; C - meloxicam; D - saline solution. Evaluation periods were 7, 14 and 30 days. Histological evaluation consisted of quantifying the inflammatory process, the bone neoformation, the collagen formation and the presence of macrophages. RESULTS: Animals of Group I did not show significant difference considering inflammatory reaction. Significant and progressive increase of bone neoformation was observed in both groups. The animals that received meloxicam and autograft showed less collagen formation at 14 and 30 days. The number of macrophages was higher in Group II than in Group I. The animals treated with dexamethasone and saline solution did not show statistically significant difference. CONCLUSIONS: Diclofenac sodium and meloxicam delayed bone graft repair and dexamethasone did not interfere in it.

Encapsulation and osteoinduction of human periodontal ligament fibroblasts in chitosan–hydroxyapatite microspheres

Periodontal ligament cells play a crucial role in the regeneration of periodontal tissues and an undifferentiated mesenchymal cell subset is thought to exist within this population. The aim of this study was to assess the osteogenic differentiation potential of human periodontal ligament fibroblasts (hPDLFs) in three dimensional (3D)-osteogenic culture environment following encapsulation in chitosan-hydroxyapatite (C/HA) microspheres with the size range of 350-450 microm. Human PDLF cultures were established and three experimental groups were formed: (i) two-dimensional (2D)-culture as single cell monolayer, (ii) 3D-static culture of C/HA encapsulated hPDLFs, and (iii) 3D-dynamic culture of C/HA encapsulated hPDLFs in a rotating wall vessel bioreactor. The cells were cultured in standard culture medium supplemented with beta-glycerophosphate, dexamethasone, and ascorbic acid. After 21 days, immunohistochemistry was performed using antibodies against osteonectin, osteopontin, bone-sialoprotein, and osteocalcin as osteogenic differentiation markers. Phase-contrast and scanning electron microscopy observations were used for histological and morphological evaluation. The combined effects of osteoinductive medium and HA-containing composite microsphere material on encapsulated hPDLFs resulted in the transformation of a considerable portion of the cells into osteoblastic lineage at the end of the experiments. Results demonstrate the ability of hPDLFs to undergo osteogenic differentiation upon induction in vitro, both under 2D and 3D culture conditions. C/HA microspheres in microgravity bioreactor may serve as a suitable 3D environment to support the osteogenic differentiation of human PDLFs, in vitro.

The effects of various irradiation doses on the growth and differentiation of marrow-derived human mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are progenitors of mesenchymal tissues including bones. Irradiation can damage the osteogenic activity of human marrow by suppressing osteoblasts leading to post-irradiation osteoporosis. However, the effect of therapeutic irradiation on MSC remains unexplored. We investigated the effects of various doses of X-ray irradiation on human MSC (hMSC) by measuring its post-irradiation proliferation and differentiation activities. Standard immunophenotypes and differentiating functions of the MSC were determined. Irradiation inhibited proliferation of hMSC up to two wk post-irradiation but thereafter, those residual surviving cells regained their normal proliferation rate. Bone forming activity as reflected by alkaline phosphatase (ALP) and calcium deposition were both reduced in a dose-dependent fashion. Maximum suppressive effect on osteogenic activity was noted in MSC treated with high-dose irradiation (12 Gy). Adipocyte percentage was also reduced by 50% in cultures that received >4 Gy. Attempts to protect the irradiated cells with 1 microM all-trans retinoic acid did not show any beneficial effect on MSC proliferation and differentiation. The direct impairment of proliferation and osteogenic differentiation potential of MSC by irradiation may contribute partly to the post-transplant osteoporosis.

Osteogenic differentiation of human marrow-derived mesenchymal stem cells

Bone marrow-derived mesenchymal stem cells (MSCs) are adherent cells that differentiate into chondroblasts, osteoblasts and adipocytes. In this short review, we summarize the molecular mechanisms that are known to control osteoblast differentiation and osteogenic potential of MSCs in vitro. We discuss the advances made in gene-based therapy to promote osteogenic differentiation of MSCs and the perspectives for an optimal use of MSCs for bone tissue regeneration or repair. One important challenge at the present time is to identify factors and pathways that promote osteogenic commitment of MSCs in order to use MSCs with functional potential for optimal bone repair in humans. In this context, genomic and proteomic analyses may help to identify molecules that could be used to promote osteogenic differentiation of human MSCs. In the future this may lead to selective therapeutic strategies for tissue engineering application in bone regeneration and repair in humans.

Dexamethasone's enhancement of osteoblastic markers in human periodontal ligament cells is associated with inhibition of collagenase expression

Although dexamethasone (Dex) substantially enhances the osteoblastic phenotype in osteogenic cells, including human periodontal ligament (PDL) cells, the basis for this response remains poorly understood. Since the accretion of a collagenous matrix is important for an osteoblastic response and dexamethasone is known to decrease collagenase expression, we examined whether osteoblastic differentiation mediated by Dex is linked to a decrease in collagenase expression in PDL cells. Early passage human PDL cells were exposed to Dex, or ascorbic acid (AA) or beta-glycerophosphate (betaGP) alone, or in various combinations in serum-free media for 3 or 5 days. Cells exposed to Dex alone or any combinations of treatments that included Dex demonstrated increased core binding factor alpha 1 (Cbfa1), alkaline phosphatase (AP), osteonectin (ON), osteopontin (OP), bone sialoprotein (BSP) and collagen I (alpha1) expression when compared to control cells or those exposed to AA or betaGP. The induction of these osteoblastic markers was accompanied by a decrease in collagenase-1 expression. Collagenase activity showed a statistically significant strong negative relationship to Cbfa1 (Pearson's r=-0.97), AP (r=-0.87), OP (r=-0.95) and BSP (r=-0.82) in 5-day cultures, and moderately strong relationship to ON (r=-0.74) from 3 days culture. Dex also produced a dose-dependent increase in AP that was paralleled by a decrease in collagenase activity (r=-0.98). Addition of collagenase inhibitors increased AP expression while concomitantly suppressing collagenase activity. Conversely, addition of exogenous collagenase decreased the AP phenotype of the cells, which was more marked in the absence then in the presence of Dex. The findings indicate that Dex enhances specific markers of osteoblastic differentiation in PDL cells by decreasing collagenase expression, and suggest that endogenous collagenase may regulate osteoblastic differentiation of these cells.

The effects of dexamethasone and dehydroepiandrosterone (DHEA) on cytokines and receptor expression in a human osteoblastic cell line: potential steroid-sparing role for DHEA

Osteoporosis and associated fractures are the most common and debilitating complication of glucocorticoid use. The use of alternative anti-inflammatory agents without the deleterious skeletal effects of glucocorticoids is needed. Dehydroepiandrosterone (DHEA) may have immunomodulatory as well as positive effects on bone. For our further understanding of the mechanisms of action of DHEA, as a steroid-sparing agent, we investigated and compared the effects of dexamethasone (DEX) and DHEA on the regulation of the downstream effector pathway of osteoclastogenesis; RANKL/OPG and a range of inflammatory/pro-resorbing cytokines and receptors using a human clonal osteoblastic cell line. The cells were treated with DEX, DHEA, and androstenedione (ANDI). The mRNA expression of RANKL and OPG was determined by real-time PCR after overnight incubation. The regulation of a broad spectrum of cytokines by DEX and DHEA was also investigated using a human cytokine/growth factor and receptor gene array consisting of 268 cytokine-related cDNAs. To confirm some of the gene expression changes, protein production was measured by ELISA. RANKL expression and RANKL/OPG ratio were increased by DEX. This effect was reversed by co-treatment with both DHEA or ANDI. Several pro-inflammatory/resorptive cytokines including IL-6, IL-4, IFN-gamma, macrophage inhibitory factor (MIF) were down-regulated not only by DEX but also by DHEA. In contrast to DEX, DHEA did not lead to suppression of growth factors including vascular endothelial growth factor (VEGF), fibroblast growth factor-5 (FGF-5), insulin-like growth factor-binding protein3 (IGF-BP3). Several new target genes previously documented to influence bone formation were up-regulated by DHEA such as Notch 2, insulin receptor, thrombin receptor (PAR1). The data suggest that DHEA has immunomodulatory properties without the catabolic effects on bone remodeling, observed with glucocorticoid use. DHEA may thus prove useful as a steroid-sparing agent in the management of inflammatory disorders such as SLE or rheumatoid arthritis. Further in vivo studies are indicated.

Inhibition of Histone Acetylation as a Tool in Bone Tissue Engineering

Our approach to bone tissue engineering is the in vitro expansion and osteogenic differentiation of bone marrow-derived human mesenchymal stem cells (hMSCs) and their subsequent implantation on porous ceramic materials. Current osteogenic differentiation protocols use dexamethasone to initiate the osteogenic process, thus ignoring the multiple signaling pathways that control osteogenesis in vivo. Supporting osteogenesis at multiple stages might further enhance the bone-forming capacity of hMSCs. As reported previously, inhibition of so-called histone deacetylases (HDACs) stimulates osteoblast maturation, and in this report, we investigated whether trichostatin A (TSA), a widely used HDAC inhibitor, can be implemented in bone tissue engineering. We confirmed that TSA treatment of hMSCs results in increased expression of alkaline phosphatase (ALP) with concomitant increase in mineralization. Flow cytometry demonstrated that TSA increases the percentage of ALP-positive hMSCs as well as their average ALP expression level, but the robustness of the response differs between donors. Unfortunately, TSA has a profound negative effect on cell proliferation, so we investigated whether hMSCs respond to TSA after reaching confluence. Confluent hMSCs on tissue culture plastic displayed enhanced ALP expression. Therefore, we seeded TSA-treated hMSCs onto ceramic particles and analyzed ectopic bone formation upon implantation in immune-deficient mice. Unfortunately, TSA-treated hMSCs did not display better bone formation in vivo than control cells. Finally, we observed that TSA treatment strongly enhanced bone formation of ex vivo cultured mouse calvaria, which warrants further exploration of TSA in bone tissue engineering.

Functions of vitamin D, retinoic acid, and dexamethasone in mouse adipose-derived mesenchymal cells

Adipose-derived mesenchymal cells (AMCs) offer great promise for tissue engineering of bone. Previously, 1,25-dihydroxyvitamin D3, retinoic acid (RA), and dexamethasone had been shown to promote osteogenesis in bone marrow-derived mesenchymal cells (BMSCs). To study the osteogenic characteristics of mouse AMCs, we applied these 3 hormones alone and in combination to the AMCs and examined markers of osteogenic differentiation. Interestingly, vitamin D and RA demonstrated a consistent, dose-dependent enhancement of osteogenesis and upregulated osteoblast specific markers including osteopontin and osteocalcin. However, in AMCs, dexamethasone clearly inhibited osteogenic differentiation in a dose dependent fashion and greatly increased the adipogenic marker peroxisome proliferator activated receptor gamma (PPAgamma). In summary, we show in vitro that vitamin D and RA are potential candidates to serve as enhancers of osteogenesis of AMCs and may be incorporated into future cell-based strategies for bone tissue engineering.

Osteogenic induction of human periodontal ligament fibroblasts under two- and three-dimensional culture conditions

Human periodontal ligament fibroblasts (hPDLF) play a key role in the regeneration of periodontal compartment during guided tissue regeneration procedures. This property is attributed to the progenitor cell subsets residing in the area. The aim of this study was to investigate whether hPDLFs could undergo an osteogenic differentiation under two- and three-dimensional (2D and 3D) culture conditions upon osteogenic induction. hPDLFs were isolated from six healthy donors, cultured, and expanded according to standard protocols. Then, three osteogenic culture conditions (dexamethasone, ascorbic acid, and beta-glycerophosphate) were established: 1) 2D culture as single-cell monolayer, 2) 3D-static culture on mineralized poly(DL-lactic-co-glycolic acid) (PLGA) scaffold, and 3) 3D culture on mineralized PLGA scaffold inside the NASA-approved bioreactor stimulating microgravity conditions. After 21 days of osteogenic induction, the majority of monolayer cultures had undergone differentiation toward osteogenic lineage, as indicated by morphological changes, mineralization assay, and some phenotypical properties. However, immunohistochemistry revealed that the scaffold cultures expressed higher levels of osteogenic marker proteins compared with that of the monolayers. Secondly, hPDLF-PLGA constructs in bioreactor showed an increased expression of osteopontin and osteocalcin compared with that of static 3D culture after 21 days. Results indicate that human periodontal ligament contains a subpopulation of cells capable of undergoing osteogenic differentiation and presumably contributing to regeneration of bone defects in the adjacent area. Human PDLF-seeded mineralized PLGA scaffold in microgravity bioreactor may be used to support osteogenic differentiation in vitro. Thus, this system may offer new potential benefits as a tool for periodontal tissue engineering.

Human osteoblast precursors produce extracellular adenosine, which modulates their secretion of IL-6 and osteoprotegerin

We showed that human osteoprogenitor cells produced adenosine and expressed ecto-5'-nucleotidase and all four adenosine receptor subtypes. Adenosine stimulated IL-6 but inhibited osteoprotegerin secretion, suggesting that adenosine is a newly described regulator of progenitor cell function.

INTRODUCTION

Maintaining skeletal homeostasis relies on there being a balance between bone formation and resorption; an imbalance between these processes can lead to diseases such as osteoporosis and rheumatoid arthritis. Recent reports showed that locally produced ATP, acting through P2 receptors, has pronounced effects on bone formation. However, ATP can be enzymatically cleaved to adenosine that has little or no activity at P2 receptors but mediates its action through the P1 family of receptors. We studied whether adenosine may also have an important role in controlling bone cell differentiation and function.

MATERIALS AND METHODS

Extracellular adenosine levels were analyzed by high-performance liquid chromatography in HCC1 and bone marrow stromal (BMS) cells. Ecto-5'-nucleotidase (CD73) expression and activity was determined by RT-PCR, immunocytochemistry, and the cleavage of etheno-AMP to ethenoadenosine. Adenosine receptor expression and activity were determined by RT-PCR and cAMP measurements. The effects of adenosine receptor agonists on IL-6, osteoprotegerin (OPG), and RANKL expression were determined by ELISA and QRT-PCR.

RESULTS

HCC1 and BMS cells produce adenosine and express CD73 and all four adenosine receptor subtypes. The A2b receptor was shown to be functionally dominant in HCC1 cells, as determined by cAMP production and in its stimulation of IL-6 secretion. Adenosine receptor agonism also inhibited OPG secretion and OPG but not RANKL mRNA expression.

CONCLUSIONS

Our findings show that HCC1 and primary BMS cells produce adenosine, express CD73 and all four adenosine receptor subtypes. In HCC1 cells, adenosine has a potent stimulatory action on IL-6 secretion but an inhibitory action on OPG expression. These data show for the first time that adenosine may be an important regulator of progenitor cell differentiation and hence an important local contributor to the regulation of bone formation and resorption.

Proliferation and osteogenic differentiation of mesenchymal stem cells cultured onto three different polymers in vitro

In this study, the osteoinductive and cell-binding properties of three different resorbable polymers were evaluated by human mesenchymal stem cells (MSCs). MSCs were isolated, expanded, and cultivated onto resorbable D,D,L,L-polylactide (PLLA), collagen I/III, and polygalactin-910/polydioxanone (PGPD) scaffolds in vitro. To evaluate the influence of dexamethasone, ascorbic acid, and beta-glycerolphosphate (DAG) on osteoblast differentiation, MSCs were incubated in a DAG-enriched medium. After a 28-day period in vitro, the cellular loaded polymers were digested enzymatically by papain and HCl. The Ca(2+) content of the biomembranes was evaluated by an o-kresolphthalein-complexon reaction via photometer. A PicoGreen assay was performed for dsDNA quantification. Significant differences between the number of adherent MSCs were documented (collagen > PLLA > PGPD). Compared to the initial number of adherent cells, all biomaterials induced a significant decrease in cellular adherence after 28 days in vitro. The presence of DAG-enriched culture medium stimulated the cellular proliferation for PLLA and slightly for PGPD, whereas cell proliferation was inhibited when MSCs were cultivated onto collagen I/III. In comparison with the control groups, all biomaterials (PLLA, PGPD, and collagen I/III) showed a significant increase in local Ca(2+) accumulation under DAG stimulation after 28 days in vitro. Furthermore, collagen I/III and PLLA scaffolds showed osteoinductive properties without DAG stimulation. These results were verified by immunocytochemical stainings against osteoblast-typical markers (osteopontin and alkaline phosphatase) and completed by calcified matrix detection (von Kossa staining). MSCs were identified by CD105 and CD13 antigen expression. Corresponding to an absence of CD34, CD45, and collagen II expression, we found no chondrogenic or hematopoietic cell differentiation. The results indicate significant differences for the proliferation, differentiation, adherence, and Ca(2+) accumulation between the tested polymers in a MSC culture.

Interactive effects of cadmium and all-trans-retinoic acid on the induction of forelimb ectrodactyly in C57BL/6 mice

BACKGROUND

Most toxicological studies have tested single chemical agents at relatively high doses, and fewer studies have addressed the toxic effects of chemical interactions. It is important to understand the toxicity of chemical mixtures in order to assess the more realistic risks of environmental and occupational exposures. A number of chemicals are known to induce a predominantly postaxial forelimb ectrodactyly in C57BL/6 mice, including acetazolamide, ethanol, cadmium, valproic acid, carbon dioxide, dimethadione, phenytoin, and 13-cis-retinoic acid and all-trans-retinoic acid (RA). In the present study, the interactive effects of coadministration of cadmium and RA on developing limbs were investigated.

METHODS

Pregnant C57BL/6 mice were treated with different intraperitoneal (IP) doses of cadmium chloride (CdCl2) and/or RA on gestational day (GD) 9.5, and fetuses were collected on GD 18 and double stained for examination of skeletal defects.

RESULTS

When RA was given simultaneously with cadmium, a significant increase in the incidence and severity of forelimb ectrodactyly (predominantly postaxial) was observed compared to the results with corresponding doses of cadmium or RA alone. When mice were exposed to subthreshold doses of both cadmium (0.5 mg/kg) and RA (1 mg/kg), the combined treatment exceeded the threshold, resulting in forelimb ectrodactyly in 19% of the fetuses. Moreover, coadministration of cadmium and RA at doses exceeding the respective thresholds showed a synergistic effect, that is, 92% of fetuses were found with the forelimb defect as opposed to 10% if the response were additive.

CONCLUSIONS

The findings demonstrate that concurrent exposure to these teratogens can have a synergistic effect and that subteratogenic doses may combine to exceed a threshold.

Comparison of fetal and adult marrow stromal cells in osteogenesis with and without glucocorticoids

To better understand the potential use of fetal marrow stromal cells (MSCs) in bone tissue engineering, we compared the ability of these cells with those of adult MSCs with respect to osteoblasts differentiation in the presence or absence of glucocorticoids. Cells were grown for 3-4 weeks in basal medium or supplemented with 100 nM dexamethasone (DEX, a synthetic glucocorticoid analog) or with 50 microM L-ascorbate and 10 mM glycerol-2-phosphate (AS+GP) or with AS+GP+DEX. At various time points in culture, the following parameters were compared between fetal and adult MSCs: cell morphology, cell proliferation, alkaline phosphatase activity, calcium (45Ca) uptake, von Kossa staining, and glucocorticoids receptor expression were analyzed. Compared with adult MSCs, fetal cells showed a less dramatic change to cuboidal morphology in DEX-containing media. Fetal MSCs in all media conditions showed higher proliferation rates and lower alkaline phosphatase activities (p < 0.001) than adult cells. Both fetal and adult MSCs responded similarly in DEX-containing media with respect to suppressing cell proliferation, stimulating alkaline phosphatase activity, and consistently accumulating calcium (usually higher in fetal cells) with subsequent formation of mineralized matrix when compared with cells cultured in AS+GP. Our findings further implicate the requirement of glucocorticoids in osteogenesis. In conclusion, compared with adult MSCs, fetal cells showed greater ability in sustaining cell proliferation and calcium uptake suggesting that they may be useful for bone tissue repair.

Dexamethasone and basic-fibroblast growth factor regulate markers of mineralization in cementoblasts in vitro

BACKGROUND

The aim of this study was to determine the effects of basic-fibroblast growth factor (b-FGF) and/or dexamethasone (Dex) on cementoblasts in vitro.

METHODS

Murine cementoblasts were treated as follows: 1) 5% FBS (fetal bovine serum) + ascorbic acid (AA, 50 microg/ml, control); 2) 5% FBS + Dex (10(7)M) + AA; 3) 5% FBS + b-FGF (50 ng/ml)+AA; or 4) 5% FBS + Dex (10(7) M) + b-FGF (50 ng/ml)+AA and then evaluated by Northern analysis for changes in specific genes and by von Kossa stain for changes in mineral nodule formation.

RESULTS

Mitotic activity: b-FGF stimulated DNA synthesis significantly versus negative control. Gene expression: osteocalcin (OCN): Dex or b-FGF or the combination resulted in a decrease in expression versus control. Bone sialoprotein (BSP): Dex increased expression of BSP mRNA levels, b-FGF decreased transcript for BSP at 6 and 24 hours. Long-term (8 days) Dex, b-FGF, or Dex plus b-FGF caused a decrease in BSP expression versus control; osteopontin (OPN): both Dex and b-FGF increased transcripts for OPN seen by 6 hours, with a greater increase noted with b-FGF versus Dex. No apparent additive effect of Dex with b-FGF was noted; matrix gamma-carboxyglutamic acid protein (MGP): b-FGF induced transcripts for MGP and addition of Dex increased this effect, while Dex alone had no effect on expression. Biomineralization: Dex increased cementoblast- mediated biomineralization, while b-FGF blocked this activity, and addition of Dex to b-FGF did not alter FGF associated inhibition.

CONCLUSION

Dex and FGF alone and in combination alter cementoblast behavior, but additional studies are required to determine whether these factors have beneficial effects at the clinical level.

Bone Morphogenetic Protein 2 and Retinoic Acid Acceleratein VivoBone Formation, Osteoclast Recruitment, and Bone Turnover

Reconstruction of craniofacial defects presents a substantial biomedical burden, and requires complex surgery. Interestingly, children after age 2 years and adults are unable to heal large skull defects. This nonhealing paradigm provides an excellent model system for craniofacial skeletal tissueengineering strategies. Previous studies have documented the in vivo osteogenic potential of adipose-derived stromal (ADS) cells and bone marrow-derived stromal (BMS) cells. This study investigates the ability to accelerate in vivo osteogenesis on ex vivo recombinant human bone morphogenetic protein 2 (BMP-2) and retinoic acid stimulation. Mouse osteoblasts, ADS cells, and BMS cells were seeded onto apatite-coated PLGA scaffolds, stimulated with rhBMP-2 and retinoic acid ex vivo for 4 weeks, and subsequently implanted into critically sized (4 mm) calvarial defects. Samples were harvested after 2, 4, 8, and 12 weeks. Areas of complete bony bridging were noted as early as 2 weeks in vivo; however, osteoclasts were attracted to the scaffold as identified by calcitonin receptor staining and tartrate-resistant acid phosphatase activity staining. Although the optimal method of in vitro osteogenic priming for mesenchymal cells remains unknown, these results provide evidence that BMP-2 and retinoic acid stimulation of multipotent cells ex vivo can subsequently induce significant quantities of bone formation within a short time period in vivo.

Novel Starch-Based Scaffolds for Bone Tissue Engineering: Cytotoxicity, Cell Culture, and Protein Expression

Starch-based biomaterials and scaffolds have been proposed for several biomedical applications. In the present work new scaffolds based on a 50/50 (wt%) blend of corn starch/ethylene-vinyl alcohol (SEVA-C) were studied. These scaffolds were processed by a melt-based technology, which has been used before with other starch-based materials but never with SEVA-C. Scanning electron microscopy (SEM) observation showed that the developed porous structures were 60% porous with pore size between 200 and 900 microm and a reasonable degree of interconnectivity. Moreover, scaffolds presented a compressive modulus of 117.50 +/- 3.7 MPa and a compressive strength of 20.8 +/- 2.4 MPa. Cytotoxicity evaluation was performed according to ISO/EN 10993 part 5 guidelines, and revealed that the developed scaffolds were nontoxic and did not inhibit cell growth. Direct contact assays were also carried out by use of a cell line of human osteoblast-like cells (SaOS-2). Cells were seeded (3 x 10(5) per scaffold) and allowed to grow for 4 weeks at 37 degrees C, in a humidified atmosphere containing 5% CO(2). Total protein assay showed that the cells were able to grow for the 4 weeks of the experiment. These data were further confirmed by SEM. Moreover, a cell viability assay (MTS test) demonstrated that cells were perfectly viable after the 4 weeks of culture, showing the adequacy of the developed structure in supporting them. Finally, Western blot analysis revealed that osteopontin was being actively expressed by the cells, which, in association with collagen deposition observed by SEM, seems to indicate that bone extracellular matrix was being deposited. Consequently it is believed that starch-based scaffolds should be considered as an alternative for bone tissue-engineering applications in the near future.