Dexamethasone induces caspase activation in murine osteoblastic MC3T3-E1 cells

Lycii radicis cortex inhibits glucocorticoid‑induced bone loss by downregulating Runx2 and BMP‑2 expression

Lycii radicis cortex (LRC) has been used to regulate high blood pressure, body temperature, pain and bone disorders in East Asia. Glucocorticoids (GCs), also known as steroids, are potent immunity regulators widely used in the treatment of inflammatory diseases. However, despite their effectiveness, GC usage is strictly controlled due to severe side‑effects, such as osteoporosis. However, further research is required as to date, at least to the best of our knowledge, there is no appropriate model to overcome secondary osteoporosis as a side‑effect of GC use. Thus, the aim of the present study was to establish an experimental model of osteoporosis induced by GC. Furthermore, the present study aimed to establish the research methodology for medical evaluations of the effectiveness and side‑effects of GCs. A secondary osteoporosis animal model was established, and the animals were divided into two groups as follows: The allergic contact dermatitis (ACD)‑induced group and the non‑ACD‑induced group. In the ACD‑induced group, a GC topical application group was compared with a GC subcutaneous injection group. The results revealed that the presence of ACD affected the induction of GC‑mediated osteoporosis. Therefore, the group exhibiting induced ACD that was treated with a topical application of GC was selected for examining the side‑effects of GCs. The effects of LRC on secondary osteoporosis were confirmed in vivo and in vitro. The results indicated that LRC regulated dexamethasone‑induced osteoblast apoptotic markers, including caspase‑6, caspase‑9, X‑linked inhibitor of apoptosis, apoptosis inhibitor 1 and apoptosis inhibitor 2, and increased the expression of osteoblast differentiation‑related genes, such as Runt‑related transcription factor 2 and bone morphogenetic protein 2 in the MC3T3E‑1 cell line. LRC also significantly reduced GC‑induced osteoporosis and exerted anti‑inflammatory effects in vivo. In addition, LRC inhibited the reduction of calbindin‑D28k in the kidney. Overall, the results of the present study suggest that the use of LRC alleviates GC‑induced secondary osteoporosis.

Allicin inhibits osteoblast apoptosis and steroid-induced necrosis of femoral head progression by activating the PI3K/AKT pathway

Steroid-induced avascular necrosis of the femoral head (SANFH) is a major complication of long-term or excessive clinical use of glucocorticoids. Allicin is a classical ingredient extracted from garlic and has many functions such as anti-apoptosis and antibacterial effects. The purpose of this study was to investigate the effect and the mechanism of allicin on apoptosis of osteoblasts induced by dexamethasone (Dex) and SANFH in rats. In vitro, we performed CCK-8, western blotting, TUNEL and other experiments, and the results of these experiments showed that allicin could inhibit the Dex-induced abnormal expression of C-caspase3, C-caspase9, Bax, cytochrome C and Bcl-2 by activating the PI3K/AKT pathway. In vivo, the results of micro-CT, hematoxylin-eosin staining and immunohistochemical analysis suggested that allicin could effectively inhibit the progress of SANFH in rats. In summary, our experiments indicate that allicin is a potential drug for the treatment of SANFH.

Repertoire of Structure-Activity-Based Novel Modified Peptides Elicits Enhanced Osteogenic Potential

Biologically active peptides in milk proteins can be used as effective dietary supplements for management of bone-associated issues including osteoporosis. A bioactive peptide derived from milk, viz. VLPVPQK/PepC, has been validated previously from our lab for its osteoanabolic action. In this study, we report 14 novel variants of PepC, designed in silico, based on the structure-activity relationship, aiming to enhance its osteogenic effect that holds tremendous therapeutic utility for bone-related injuries. PepC was computationally modified at seven positions of its original sequence, resulting in 14 modified synthetic peptides for functional predictions and in vitro assessment by comparative analysis of modified peptides by PepC for improved ability in osteogenic functional assays (proliferation potential, antioxidant ability, gene and protein expression, cytotoxic effect, bone mineralization) using calvarial osteoblasts. For most peptides with the highest Peptide7 response relative to PepC (p < 0.05), enhanced osteoanabolic response was observed. Further observations on Peptide7 have therefore been investigated in depth (qPCR, immunoblotting, LCMS/MS, and PCA analysis). Peptide7 displayed a rise in the expression of osteogenes (Osterix, Opg, Bmp2, and Runx2, p < 0.05) and protein (Runx2 and Bmp2, p < 0.05). Besides, LCMS/MS findings suggest Peptide7 escapes intestinal peptidases degradation. Experimental evidence supports an improved osteological reaction to newly modified peptides and hence exploitation in the preparation of functional foods or supplements.

Effects of denosumab on bone mineral density and bone turnover markers in rheumatoid arthritis patients switching from bisphosphonates

BACKGROUND

To compare the efficacy of 12-month denosumab treatment on bone mineral density (BMD) and bone turnover markers (BTMs) between treatment-naïve osteoporosis patients with rheumatoid arthritis (RA) and those with previous bisphosphonate (BP) therapy.

METHODS

A total of 36 RA patients with osteoporosis completed 12-month follow-up. Twenty-five patients were osteoporotic treatment-naïve (naïve group), and 11 patients were previously treated with BPs (switch group) (average 7.9 years). BMD and BTMs were measured before and 6 and 12 months after treatment.

RESULTS

BTM levels were higher in the naïve group at baseline. However, the same level of suppression was achieved at 6 months in both groups. Spine BMD increased significantly in both groups. There was no significant difference in the mean percent changes of BMD of the spine (naïve group: 6.8 ± 0.8, switch group: 5.1 ± 1.5), femoral neck (2.9 ± 1.4, 2.9 ± 1.3), and total hip (1.7 ± 0.9, 1.4 ± 1.1) between these two groups at 12 months.

CONCLUSIONS

The effects of denosumab on BMD and BTMs of the switch group after long-term BP treatment are comparable to those of the naïve group in RA patients. Thus, switching BPs to denosumab is one of the useful options to treat osteoporosis with RA.

Haem oxygenase-1 induction prevents glucocorticoid-induced osteoblast apoptosis through activation of extracellular signal-regulated kinase1/2 signalling pathway

Background

High-dose glucocorticoid (GC) therapy always causes osteoporosis partly by inducing osteoblast apoptosis. However, the underlying mechanisms of GC-induced apoptosis remain elusive. Haem oxygenase-1 (HO-1) is a cytoprotective protein that rescues cells from H₂O₂ or high glucose-induced apoptosis. In bone metabolism, HO-1 also participates in osteoclast and osteoblast differentiation.

Objective

The present study aimed to investigate the protective role of HO-1 against GC-induced osteoblast apoptosis and to elucidate the underlying mechanism.

Methods

Mouse osteoblastic MC3T3-E1 cells were treated with dexamethasone (Dex) for 24 h in the presence or absence of cobalt (III) protoporphyrin IX chloride (CoPP, an inducer of HO-1). In some experiments, U0126 was added to the culture 1 h before CoPP treatment. The induction of apoptosis was determined by flow cytometry. Cell viability was evaluated using a cell counting kit-8 (CCK-8) assay. The expression levels of Bax and bcl-2 were measured by real-time polymerase chain reaction and Western blot. HO-1, extracellular signal-regulated kinase (ERK)-1/2 and pERK1/2 protein levels were measured by Western blot analysis.

Results

Dex promoted apoptosis and inhibited cell viability in MC3T3-E1 cells. In addition, Dex significantly increased Bax expression and reduced Bcl-2 expression. The expression of HO-1 was also reduced after Dex treatment. HO-1 induction by CoPP significantly attenuated Dex-induced apoptosis as evidenced by Annexin V/PI staining. The mRNA expression level of antiapoptotic gene Bcl-2 was also increased after CoPP treatment. Moreover, CoPP treatment increased the phosphorylation of ERK1/2. U0126, an inhibitor of ERK activation, significantly abrogated the protective effects of CoPP.

Conclusion

Our results demonstrate that HO-1 induction by CoPP can attenuate Dex-induced apoptosis of mouse osteoblastic MC3T3-E1 cells. The antiapoptotic effect of HO-1 induction may be correlated with the activation of ERK1/2 signalling pathway. The translational potential of this article: HO-1 induction by CoPP can prevent GC-induced osteoblast apoptosis. Our findings will highlight the therapeutic potential of HO-1 induction in GC-induced osteoporosis.

Metformin Ameliorates Periapical Lesions through Suppression of Hypoxia-induced Apoptosis of Osteoblasts

INTRODUCTION

Intramuscular injection of metformin has been shown to inhibit the progression of periapical lesions in rats by decreasing the number of receptor activator of nuclear factor-κβ ligand- and tartrate-resistant acid phosphatase-positive cells. In this study, we investigated the effect of metformin on hypoxia-induced apoptosis of osteoblasts and the therapeutic activity of intracanal metformin in induced periapical lesions in rats.

METHODS

The influence of metformin on hypoxia-induced mitochondrial superoxide production in human osteoblasts was examined by using MitoSOX (Invitrogen, Carlsbad, CA) fluorescence dye signaling. The release of cytochrome c from mitochondria and the cleavage of procaspase-9 and poly(adenosine diphosphate-ribose) polymerase were evaluated by Western blot analysis. Apoptotic cell fraction was assessed by DNA content flow cytometry. In a rat model of induced periapical lesions, the effect of intracanal metformin on disease progression was appraised by 2-dimensional radiography and micro-computed tomographic imaging. Oxidative lesions and apoptotic activity of osteoblasts in vivo were estimated, respectively, by 8-hydroxy-2'-deoxyguanosine staining and terminal deoxynucleotidyl transferase dUTP nick end labeling.

RESULTS

Metformin inhibited hypoxia-enhanced mitochondrial superoxide production in osteoblasts. Metformin suppressed hypoxia-induced cytochrome c release from mitochondria and the cleavage of procaspase-9 and poly(adenosine diphosphate-ribose) polymerase. Metformin repressed hypoxia-augmented apoptotic cell fraction. In a rat model, intracanal metformin diminished the size of periapical lesions and the oxidative damage and apoptotic activity in osteoblasts.

CONCLUSIONS

Hypoxia increased oxidative stress in osteoblasts and enhanced cell death through activation of the mitochondrial pathway of apoptosis. Metformin attenuated the oxidative and cytotoxic action of hypoxia. The therapeutic effect of metformin on periapical lesions is partially caused by its antioxidative activity.

Luteolin attenuates glucocorticoid-induced osteoporosis by regulating ERK/Lrp-5/GSK-3β signaling pathway in vivo and in vitro

Glucocorticoid-induced osteoporosis (GIO) is a secondary osteoporosis with extensive use of glucocorticoids (GCs). GCs can increase bone fragility and fracture via inhibiting osteoblastic proliferation and differentiation. Luteolin (LUT), a kind of plant flavonoid, has been reported to exhibit the antioxidant activity, but the effects of LUT on GIO still remain unclear. This study aimed to investigate the effects of LUT on GIO both in vivo and in vitro and elaborate the potential molecular mechanisms. LUT increased the superoxide dismutase activity, glutathione level and decreased reactive oxygen species (ROS) level and lactate dehydrogenase release in GIO. Meanwhile, LUT decreased caspase-3, caspase-9, and Bax protein expressions and increased Bcl-2 protein expression in GIO. LUT increased the ratio of osteoprotegerin (OPG)/receptor activator of nuclear factor-κB Ligand (RANKL) messenger RNA (mRNA) expression and mRNA expression levels of osteogenic markers, including runt-related transcription factor 2, osterix, collagen type I, and osteocalcin. LUT also enhanced the extracellular signal-regulated kinases (ERK) phosphorylation, glycogen synthase kinase 3β (GSK-3β) phosphorylation, mRNA expression levels of lipoprotein-receptor-related protein 5 (Lrp-5) and β-catenin. Further study revealed that Lrp-5 small interfering RNA (siRNA )and ERK-siRNA reduced the effects of LUT on GSK-3β phosphorylation, alkaline phosphatase (ALP) activity and the ratio of OPG/RANKL mRNA expression. Moreover, ERK-siRNA decreased Lrp-5 mRNA expression in vitro. These results indicated that LUT promoted proliferation by attenuating oxidative stress and promoted osteoblastic differentiation by regulating the ERK/Lrp-5/GSK-3β pathway in GIO. This study may bring to light the possible mechanisms involved in the action of LUT in GIO treatment, and benefit for further research on GIO.

Echinacoside suppresses dexamethasone-induced growth inhibition and apoptosis in osteoblastic MC3T3-E1 cells

Glucocorticoids (GCs) are widely used to treat chronic diseases. Prolonged and/or overdose administration of GCs has many side-effects to human health including GC-induced osteoporosis (GIOP). In this investigation, the objective was to assess the influence that echinacoside (ECH) exerts upon dexamethasone-treated murine osteoblastic MC3T3-E1 cells. We found that ECH (5, 10, 20 and 40 mg/l) inhibited dexamethasone (1,000 nM)-suppressed cell viability as demonstrated by Cell Counting Kit-8 (CCK-8) assay. The dose of 10 mg/l was selected for the following experiments because this dose had a better effect than the dose of 5 mg/l, and the doses >10 mg/l had a similar effect as this dose. ECH (10 mg/l) or pifithrin-α (PFT-α) (a p53 inhibitor, 20 µM) suppressed dexamethasone-induced MC3T3-E1 apoptosis as illustrated by Annexin V/propidium iodide (PI) double-labeling flow cytometry analysis. ECH or PFT-α treatment also alleviated dexamethasone's action of inhibiting Bcl-2 expression as well as dexamethasone's action of stimulating on the expression of p53 and Bax. Moreover, lentivirus mediated-p53 overexpression reversed the effects of ECH in dexamethasone-treated MC3T3-E1 cells, suggesting that ECH induced anti-apoptotic effects in dexamethasone-treated osteoblasts via p53-dependent pathway. In summary, ECH has a protective effect against osteoblastic cell apoptosis induced by dexamethasone, suggesting that ECH may have potentials for clinical application in the treatment of GIOP.

Dexamethasone-induced production of reactive oxygen species promotes apoptosis via endoplasmic reticulum stress and autophagy in MC3T3-E1 cells

Apoptosis of osteoblasts, triggered by prolonged or excessive use of glucocorticoids (GCs), has been identified as a dominant contributor to the development of osteoporosis and osteonecrosis. However, the molecular mechanisms underlying GC‑induced apoptosis are multifaceted and remain to be fully elucidated. The present study aimed to explore the correlation between dexamethasone (DEX)‑induced reactive oxygen species (ROS), autophagy and apoptosis in MC3T3‑E1 osteoblast‑like cells. Cell viability was assessed using a Cell Counting Kit‑8 assay, and flow cytometry was performed to assess cellular apoptosis, cell cycle and ROS production. Immunofluorescence and western blot analysis were respectively used to detect autophagic vacuoles and the expression of proteins, including cyclin D kinase (CDK)2, poly[ADP ribose] polymerase, caspase‑3, activating transcription factor (ATF)4, CCAAT/enhancer‑binding protein homologous protein (CHOP), Beclin1, microtubule‑associated proteins 1A/1B light chain (LC)3B and P62. It was revealed that DEX not only reduced cell viability, but also promoted apoptosis via the activation of endoplasmic reticulum (ER) stress. In addition, DEX induced cell cycle arrest at G0/G1 phase via inhibition of the expression of CDK2, and the production of ROS was activated. Of note, the DEX‑mediated changes in viability and apoptosis were attenuated in MC3T3‑E1 cells after treatment with 3‑methyladenine, which is an autophagy inhibitor. Treatment with the antioxidant N‑acetylcysteine abolished the effect of DEX on the proliferation, apoptosis, ER stress and autophagy of MC3T3‑E1 cells. In conclusion, the present results indicated that DEX promoted the production of ROS, which enhanced apoptosis through activation of autophagy and ER stress in MC3T3-E1 cells.

Fludarabine inhibits STAT1-mediated up-regulation of caspase-3 expression in dexamethasone-induced osteoblasts apoptosis and slows the progression of steroid-induced avascular necrosis of the femoral head in rats

Steroid-induced avascular necrosis of the femoral head (SANFH) is a major limitation of long-term or excessive clinical administration of glucocorticoids. Fludarabine, which is a compound used to treat various hematological malignancies, such as chronic lymphocytic leukemia, acts by down-regulating signal transducer and activator of transcription 1 (STAT1) by inhibiting STAT1 phosphorylation in both normal and cancer cells. This study assessed the effects of fludarabine in vitro (primary murine osteoblasts) and in vivo (rat SANFH model). In vitro, pretreatment with fludarabine significantly inhibited Dexamethasone (Dex)-induced apoptosis in osteoblasts, which was examined by TUNEL staining. Treatment with Dex caused a remarkable decrease in the expression of Bcl-2; an increase in cytochrome c release; activation of BAX, caspase-9, and caspase-3; and an obvious enhancement in STAT1 phosphorylation. However, treatment resulted in the up-regulation of caspase-3 expression. Enhanced P-STAT1 activity and up-regulation of caspase-3 expression were also observed in osteoblasts. In vivo, the subchondral trabeculae in fludarabine-treated rats exhibited less bone loss and a lower ratio of empty lacunae. Taken together, our results suggest that STAT1-mediated up-regulation of caspase-3 is involved in osteoblast apoptosis induced by Dex and indicates that fludarabine may serve as a potential agent for the treatment of SANFH.

Salidroside inhibits steroid-induced avascular necrosis of the femoral head via the PI3K/Akt signaling pathway: In vitro and in vivo studies

Dexamethasone (Dex) and other glucocorticoids are widely used to treat serious infections and immunological diseases, however they may cause steroid-induced avascular necrosis of the femoral head (SANFH). Salidroside (Sal) has demonstrated an anti-apoptotic effect on neurocytes by activating the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. In the present study, primary osteoblasts were used in vitro and in rats in vivo to determine the anti-apoptotic effect of Sal on SANFH. The result of the present study demonstrated that pretreatment with Sal increased the cell survival rate while decreasing the cell apoptosis and lactate dehydrogenase release rate. Additionally, Sal also caused the reduction of TUNEL positive cells in TUNEL staining assay. Sal decreased the expression of cleaved caspase-3, cleaved caspase-9, apoptosis regulator BAX and cytochrome C, while it increased the expression of B cell lymphoma-2 and phosphorylated-Akt in Dex-induced osteoblasts. In vivo Sal protected against SANFH in rats by decreasing the percentage of empty lacunae. The present study demonstrated that Sal alleviated Dex-induced osteoblast apoptosis by activating the PI3K/Akt signaling pathway and downregulating caspase-3 expression in osteoblasts. Sal also protected against SANFH in a rat model of SANFH by decreasing the percentage of empty lacunae. The inhibition of the mitochondrial apoptosis pathway was also involved. Further research is required to determine the full underlying mechanisms by which Sal has an effect.

Raman spectroscopy differentiates between sensitive and resistant multiple myeloma cell lines

Current methods for identifying neoplastic cells and discerning them from their normal counterparts are often nonspecific and biologically perturbing. Here, we show that single-cell micro-Raman spectroscopy can be used to discriminate between resistant and sensitive multiple myeloma cell lines based on their highly reproducible biomolecular spectral signatures. In order to demonstrate robustness of the proposed approach, we used two different cell lines of multiple myeloma, namely MM.1S and U266B1, and their counterparts MM.1R and U266/BTZ-R subtypes, resistant to dexamethasone and bortezomib, respectively. Then, micro-Raman spectroscopy provides an easily accurate and noninvasive method for cancer detection for both research and clinical environments. Characteristic peaks, mostly due to different DNA/RNA ratio, nucleic acids, lipids and protein concentrations, allow for discerning the sensitive and resistant subtypes. We also explored principal component analysis (PCA) for resistant cell identification and classification. Sensitive and resistant cells form distinct clusters that can be defined using just two principal components. The identification of drug-resistant cells by confocal micro-Raman spectroscopy is thus proposed as a clinical tool to assess the development of resistance to glucocorticoids and proteasome inhibitors in myeloma cells.

Puerarin attenuates glucocorticoid-induced apoptosis of hFOB1.19 cells through the JNK- and Akt-mediated mitochondrial apoptotic pathways

Puerarin is an active component of Pueraria lobata, which is a commonly used Chinese herbal medicine for the treatment of osteoporosis. The present study aimed to evaluate the osteoprotective effect of puerarin on glucocorticoid (GC)-induced apoptosis of osteoblasts in vitro. The effects of puerarin on dexamethasone (DEX)-induced cell apoptosis were assessed using enzyme-linked immunosorbent assay and a terminal deoxynucleotidyl transferase dUTP nick-end labeling assay, and found that the viability of hFOB1.19 cells was significantly increased following exposure to between 10⁻⁶ and 10⁻¹⁰ M puerarin, with a maximal anti-apoptotic effect at a concentration of 10⁻⁸ M. In addition, compared with the control group, puerarin upregulated the transcription and protein levels of B-cell lymphoma-2 and downregulated B-cell-associated X protein in the hFOB1.19 cells. Puerarin attenuated the DEX-induced release of cytochrome c and cleavage of caspase-3, and treatment with puerarin inhibited the c-Jun N-terminal kinase (JNK) pathway and activated the phosphoinositide 3-kinase (PI3K)/Akt pathway in the hFOB1.19 cells. Furthermore, the Akt inhibitor, LY294002, partly eliminated the protective effect of puerarin on DEX-induced apoptosis, and puerarin combined with the JNK inhibitor, SP600125, suppressed DEX-induced apoptosis to a lesser extent than in the cells treated with SP600125 alone. These results suggested that the JNK and PI3K/Akt signaling pathways mediate the inhibitory effects of puerarin on apoptosis in the hFOB1.19 cells. In conclusion, puerarin prevented DEX-induced apoptosis of hFOB1.19 cells via inhibition of the JNK pathway and activation of the PI3K/Akt signaling pathway in the cells, dependent on the mitochondrial apoptotic pathway. These results support puerarin as a promising target in the treatment of GC-induced osteoporosis.

Switching of oral bisphosphonates to denosumab in chronic glucocorticoid users: a 12-month randomized controlled trial

OBJECTIVES

To evaluate the effect of switching from oral bisphosphonates to denosumab on bone mineral density (BMD) in long-term glucocorticoid users.

METHODS

Adult patients who were receiving long-term prednisolone (≥2.5 mg/day for ≥1 year) and oral bisphosphonates (≥2 years) were recruited. Participants were randomized to either continue oral bisphosphonates or switch to denosumab (60 mg subcutaneously every 6 months) for 12 months. Serial BMD (lumbar spine, hip) and bone turnover markers (serum osteocalcin, P1NP, β-CTX) were measured.

RESULTS

42 women were recruited (age 54.7±12.9 years; 21 shifted to denosumab and 21 continued on bisphosphonates). The duration of prednisolone therapy was 101±66.3 months and the daily dose was 4.4±2.1 mg. Baseline demographic data, osteoporosis risk factors, and BMD at various sites were similar between the two groups of patients. At month 12, BMD of the spine and hip increased by +3.4±0.9% (p=0.002) and +1.4±0.6% (p=0.03), respectively, in the denosumab group; whereas the corresponding change was +1.5±0.4% (p=0.001) and +0.80±0.5% (p=0.12) in the bisphosphonate group. The spinal BMD at month 12 was significantly higher in the denosumab than bisphosphonate group after adjustment for baseline BMD and β-CTX values, and other confounding factors (p=0.01). Bone turnover markers (β-CTX and P1NP) were more strongly suppressed by denosumab than the bisphosphonates. Minor infections were more common in denosumab-treated patients while other adverse events occurred at similar frequencies between the two groups.

CONCLUSIONS

In patients receiving long-term glucocorticoids, switching from oral bisphosphonates to denosumab resulted in greater gain of the spinal BMD and suppression of bone turnover markers after 12 months of therapy. The results have to be confirmed by a larger clinical trial with fracture as endpoint.

Protective effects of total saponins of panax notoginseng on steroid-induced avascular necrosis of the femoral head in vivo and in vitro

This research was designed to investigate the protective effects of TSPN on steroid-induced avascular necrosis of the femoral head (ANFH) and the likely mechanisms of those effects. As an in vivo study, TSPN was shown to be protective against steroid-induced ANFH due to the upregulation of VEGF-A. Furthermore, TSPN attenuated the apoptosis of osteocytes and reduced the expression of Caspase-3 relative to the model group. As an in vitro study, TSPN exerted a concentration-dependent protective effect against apoptosis in MC3T3-E1 cells. Moreover, TSPN (at a dose of 100 μg/mL) significantly reversed the dexamethasone-induced augmentation of Caspase-3 expression and activity. Therefore, our study demonstrated that TSPN had a protective effect against steroid-induced ANFH that was related to the upregulation of VEGF-A and the inhibition of apoptosis and Caspase-3 activation.

Dexamethasone and 1,25-dihydroxyvitamin D3 reduce oxidative stress-related DNA damage in differentiating osteoblasts

The process of osteoblast differentiation is regulated by several factors, including RUNX2. Recent reports suggest an involvement of RUNX2 in DNA damage response (DDR), which is important due to association of differentiation with oxidative stress. In the present work we explore the influence of two RUNX2 modifiers, dexamethasone (DEX) and 1,25-dihydroxyvitamin D3 (1,25-D3), in DDR in differentiating MC3T3-E1 preosteoblasts challenged by oxidative stress. The process of differentiation was associated with reactive oxygen species (ROS) production and tert-butyl hydroperoxide (TBH) reduced the rate of differentiation. The activity of alkaline phosphatase (ALP), a marker of the process of osteoblasts differentiation, increased in a time-dependent manner and TBH further increased this activity. This may indicate that additional oxidative stress, induced by TBH, may accelerate the differentiation process. The cells displayed changes in the sensitivity to TBH in the course of differentiation. DEX increased ALP activity, but 1,25-D3 had no effect on it. These results suggest that DEX might stimulate the process of preosteoblasts differentiation. Finally, we observed a protective effect of DEX and 1,25-D3 against DNA damage induced by TBH, except the day 24 of differentiation, when DEX increased the extent of TBH-induced DNA damage. We conclude that oxidative stress is associated with osteoblasts differentiation and induce DDR, which may be modulated by RUNX2-modifiers, DEX and 1,25-D3.

Protective effect of Korean Red Ginseng against glucocorticoid-induced osteoporosis in vitro and in vivo

Background

Glucocorticoids (GCs) are commonly used in many chemotherapeutic protocols and play an important role in the normal regulation of bone remodeling. However, the prolonged use of GCs results in osteoporosis, which is partially due to apoptosis of osteoblasts and osteocytes. In this study, effects of Korean Red Ginseng (KRG) on GC-treated murine osteoblastic MC3T3-E1 cells and a GC-induced osteoporosis mouse model were investigated.

Methods

MC3T3-E1 cells were exposed to dexamethasone (Dex) with or without KRG and cell viability was measured by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. Real-time polymerase chain reaction was performed to evaluate the apoptotic gene expression; osteogenic gene expression and alkaline phosphatase (ALP) activity were also measured. Western blotting was performed to evaluate the mitogen-activated protein kinase (MAPK) proteins. A GC-induced osteoporosis animal model was used for in vivo study.

Results and conclusion

The MTT assay revealed that Korean Red Ginseng (KRG) prevents loss of cell viability caused by Dex-induced apoptosis in MC3T3E1 cells. Real-time polymerase chain reaction data showed that groups treated with both Dex and KRG exhibited lower mRNA levels of caspase-3 and -9, whereas the mRNA levels of Bcl2, IAPs, and XIAP increased. Moreover, groups treated with both Dex and KRG demonstrated increased mRNA levels of ALP, RUNX2, and bone morphogenic proteins as well as increased ALP activity in MC3T3-E1 cells, compared to cells treated with Dex only. In addition, KRG increased protein kinase B (AKT) phosphorylation and decreased c-Jun N-terminal kinase (JNK) phosphorylation. Moreover, microcomputed tomography analysis of the femurs showed that GC implantation caused trabecular bone loss. However, a significant reduction of bone loss was observed in the KRG-treated group. These results suggest that the molecular mechanism of KRG in the GC-induced apoptosis may lead to the development of therapeutic strategies to prevent and/or delay osteoporosis.

STAT1-caspase 3 pathway in the apoptotic process associated with steroid-induced necrosis of the femoral head

Osteocyte apoptosis is the main manifestation of steroid-induced avascular necrosis of the femoral head (SANFH). STAT1 and caspase 3 participate in the process of apoptosis and STAT1 upregulates the expression of caspase 3. We examined the relationship between the STAT1-caspase 3 pathway and apoptosis in SANFH. All specimens were divided into four groups: the negative control group, Ficat I-II group, Ficat III group, and Ficat IV-V group, and examined histologically, with a TUNEL assay, immunohistochemically, with a caspase 3 activity assay, with ELISAs of STAT1 and phospo-STAT1 (p-STAT1), with a western blotting analysis of p-STAT1 and with real-time RT-PCR. The proportion of empty lacunae increased significantly with the development of SANFH. The proportion of TUNEL-positive cells and immunohistochemical analysis of caspase 3 also increased significantly, although the Ficat I-II group did not differ significantly from the negative control group. Immunohistochemical analysis of STAT1 and p-STAT1, caspase 3 activity all showed significant differences among the groups. An ELISA and a western blotting analysis of p-STAT1 showed significant differences among the groups. An ELISA of STAT1, real-time RT-PCR analysis of caspase 3 and STAT1 all showed significant differences among the groups except between the Ficat I-II and negative control groups. The correlation analysis showed strong positive relationships between the proportion of empty lacunae and the proportion of TUNEL-positive cells between caspase 3 activity and the proportion of TUNEL-positive cells and between the levels of p-STAT1 protein and caspase 3 mRNA. The apoptotic process in SANFH develops with the upregulated expression of caspase 3 via the expression and activation of STAT1. The STATI-caspase 3 pathway plays a critical role in the development of SANFH.

Involvement of reactive oxygen species in osteoblastic differentiation of MC3T3-E1 cells accompanied by mitochondrial morphological dynamics

Bone remodeling is regulated by local factors that regulate bone-forming osteoblasts and bone-resorbing osteoclasts, in addition to hormonal activity. Recent studies have shown that reactive oxygen species (ROS) act as an intracellular signal mediator for osteoclast differentiation. However the role of ROS on osteoblast differentiation is poorly understood. Here, we investigated the impact of ROS on osteoblastic differentiation of MC3T3-E1 cells. Osteogenic induction resulted in notable enhancement of mineralization and expression of osteogenic marker gene alkaline phosphatase, which were accompanied by an increase in ROS production. Additionally, we found that mitochondrial morphology dynamically changed from tubular reticulum to fragmented structures during the differentiation, suggesting that mitochondrial morphological transition is a novel osteoblast differentiation index. The antioxidant N-acetyl cysteine prevented not only ROS production but also mineralization and mitochondrial fragmentation. It is therefore suggested that the ROS-dependent signaling pathways play a role in osteoblast differentiation accompanied by mitochondrial morphological transition.

Interleukin-6 and JAK2/STAT3 signaling mediate the reversion of dexamethasone resistance after dexamethasone withdrawal in 7TD1 multiple myeloma cells

We previously reported the establishment and characteristics of a DXM-resistant cell line (7TD1-DXM) generated from the IL6-dependent mouse B cell hybridoma, 7TD1 cell line. After withdrawing DXM from 7TD1-DXM cells over 90 days, DXM significantly inhibited the cell growth and induced apoptosis in the cells (7TD1-WD) compared with 7TD1-DXM cells. Additionally, IL-6 reversed while IL-6 antibody and AG490 enhanced the effects of growth inhibition and apoptosis induced by DXM in 7TD1-WD cells. Our study demonstrates that 7TD1-DXM cells become resensitized to DXM after DXM withdrawal, and IL-6 and JAK2/STAT3 pathways may regulate the phenomenon.

TXNIP is highly regulated in bone biopsies from patients with endogenous Cushing's syndrome and related to bone turnover

OBJECTIVE

Patients with endogenous Cushing's Syndrome (CS), as long-time treated patients with exogenous glucocorticoids (GCs), have severe systemic manifestations including secondary osteoporosis and low-energy fractures. The aim of the present study was to investigate the functional role of TXNIP in bone with focus on osteoblast (OB) differentiation and OB-mediated osteoclast activity and function in vitro.

DESIGN AND METHODS

Nine bone biopsies from CS before and after surgical treatment were screened for expressional candidate genes. Microarray analyses revealed that the gene encoding TXNIP ranked among the most upregulated genes. Subsequent in vitro and in vivo studies were performed.

RESULTS

We found that TXNIP gene in bone is downregulated in CS following surgical treatment. Furthermore, our in vivo data indicate novel associations between thioredoxin and TXNIP. Our in vitro studies showed that silencing TXNIP in OBs was followed by increased differentiation and expression and secretion of osteocalcin as well as enhanced activity of alkaline phosphatase. Moreover, treating osteoclasts with silenced TXNIP OB media showed an increased osteoclast activity.

CONCLUSIONS

TXNIP expression in bone is highly regulated during the treatment of active CS, and by GC in bone cells in vitro. Our data indicate that TXNIP may mediate some of the detrimental effects of GC on OB function as well as modulate OB-mediated osteoclastogenesis by regulating the OPG/RANKL ratio.

Fisetin prevents fluoride- and dexamethasone-induced oxidative damage in osteoblast and hippocampal cells

Fluoride intoxication and dexamethasone treatment produce deleterious effects in bone and brain. The aim of this study was to evaluate the effect of fluoride (F) and dexamethasone (Dex) co-exposure on oxidative stress and apoptosis in osteoblast-like MC3T3-E1 and hippocampal HT22 cell lines. Co-exposure to F and Dex resulted in a concentration-dependent decrease in cell viability, induction of apoptosis and increased generation of reactive oxygen species (ROS) and nitric oxide (NO) following 72 h of incubation. Fluoride-induced apoptosis in MC3T3-E1 and HT22 cells was attenuated by catalase and L-NNMA, indicating a role for H2O2 and NO as mediators of cytotoxicity. Dexamethasone-induced apoptosis was associated with H2O2 generation in both cell lines and it was attenuated during co-incubation with catalase. These data indicate that co-exposure to F and Dex amplifies their respective cytotoxicity in H2O2- and NO-dependent manner. As flavonoid fisetin prevented F- and Dex-induced cytotoxicity the potential role of this product in pharmacology and diet may be considered.

The pharmacological effects of morroniside and loganin isolated from Liuweidihuang Wan, on MC3T3-E1 cells

Liuweidihuang wan (LW), initially a well-known formula for curing "wu chi wu ruan", is commonly used nowadays for clinical treatment of postmenopausal osteoporosis (PO), but the identity of the effective substance(s) remains unclear. The present study was designed to evaluate the effects of morroniside and loganin isolated from LW on the proliferation, differentiation and apoptosis of MC3T3-E1 cells, as well as the possible mechanism of action. Morroniside and loganin had no effects on the proliferation of MC3T3-E1 cells, but both susbtances could improve the activity of alkaline phosphatase (ALP), and increase the contents of collagen type I and osteocalcin. Simultaneously, the mRNA expression of caspase-3, capase-9, RANKL was down-regulated and that of bcl-2 was up-regulated, which partially explains the anti-osteoporosis mechanism in MC3T3-E1 cells. In conclusion, morroniside and loganin may directly promote the differentiation and inhibit the apoptosis of MC3T3-E1 cells, and accordingly indirectly reduce bone resorption, which makes them promising natural drugs leads for treating PO in the near future.

The PI3K/Akt/FOXO3a/p27Kip1 signaling contributes to anti-inflammatory drug-suppressed proliferation of human osteoblasts

Akt has been reported to suppress p27(Kip1) promoter activity through Forkhead box O (FOXO) in different kinds of cells. Previous studies indicated that anti-inflammatory drugs up-regulated p27(Kip1), and this effect might play an important role in anti-inflammatory drug-induced cell cycle arrest of human osteoblasts (hOBs). In this study, we hypothesized that these drugs might increase p27(Kip1) expression in hOBs by altering the Akt/FOXO signaling. We tested this hypothesis by examining the influences of three anti-inflammatory drugs on the levels and/or activities of Akt, FOXO and p27(Kip1) as well as the relationship between these factors and proliferation of hOBs. We tested the effects of indomethacin (10(-5) and 10(-4)M), celecoxib (10(-6) and 10(-5)M), and dexamethasone (10(-7) and 10(-6)M) using PI3K inhibitor, LY294002 (10(-5)M) as the basis of comparison. The three drugs suppressed the canonical level of phosphorylated Akt in hOBs. This was accompanied by elevated FOXO3a level and increased promoter activity, mRNA expression and protein level of p27(Kip1). Furthermore, the anti-inflammatory drugs suppressed the EGF-induced increases in proliferation, phosphorylation, and nucleus translocation of Akt. Simultaneously, they suppressed EGF-induced decreases of FOXO3a nucleus accumulation and p27(Kip1) mRNA expression. On the other hand, FOXO silencing significantly attenuated the drug-induced up-regulation of p27(Kip1) and suppression of proliferation in hOBs. To the best of our knowledge, this study represents the first to demonstrate that Akt/FOXO3a/p27(Kip1) pathway contributes to suppression of hOB proliferation by anti-inflammatory drugs. We suggest that anti-inflammatory drugs suppress hOB proliferation, at least partly, through inactivating Akt, activating FOXO3a, and eventually up-regulating p27(Kip1) expression.

Oscillatory perfusion culture of CaP-based tissue engineering bone with and without dexamethasone

Dexamethasone, a powerful osteogenic agent for osteoblast differentiation, has been suggested to have synergistic effects when applied together with perfusion culture. As ceramic scaffolds are widely used clinically and oscillatory flow well replicates the natural physical conditions, the biological effects of dexamethasone on oscillatory perfusion culture of CaP-based tissue engineering bone were investigated in this study. Mouse osteoblast-like cells, MC 3T3-E1, were seeded onto porous ceramic scaffolds using the oscillatory perfusion method. The seeded constructs were then either cultured by a static method or an oscillatory perfusion method at different flow rates continuously for 6 days with and without dexamethasone. The cell proliferation, early osteogenic effects, and viability were subsequently evaluated. The results showed that the oscillatory flow could enhance early osteogenesis of osteoblast-like cells in three-dimensional culture on ceramic scaffolds, with a peak function at the flow rate of 0.5 mL/min. The cell viability was significantly higher and more uniform in the perfusion groups than in the static culture groups. The uniformity decreased as the perfusion rates decreased. However, dexamethasone seems to have had no significant effects in any of the groups. Our results suggest that dexamethasone is not an efficient osteogenic supplement during perfusion culture on CaP ceramic scaffolds, and predifferentiation before seeding or additional osteogenic factors should be considered for such cultures.

Regulation of bim in glucocorticoid-mediated osteoblast apoptosis

Osteoblasts undergo apoptosis both in vitro and in vivo in response to high dose glucocorticoid (GC) treatment. However, the molecular mechanisms remain elusive, hindering the prevention and treatment of this side-effect. Apoptosis was induced by dexamethasone (Dex) in murine MBA-15.4 osteoblasts within 24-48 h of treatment. We found dose- and time-dependent upregulation of Bim protein, a pro-apoptotic Bcl-2 family member, with highest levels at 24-48 h for 1 microM Dex. This was also observed in primary human bone marrow stromal cells. Bim is subjected to stringent transcriptional and post-translational regulation in osteoblasts. Bim mRNA was upregulated in response to 1 microM Dex; both cycloheximide and the GC receptor antagonist, RU486, prevented Dex-induction of Bim protein, indicating transcriptional regulation involving the GC receptor. The proteasome inhibitor, MG132, potently increased Bim protein levels. Bim was also upregulated in osteoblasts undergoing apoptosis in response to serum deprivation and matrix detachment. Gene silencing experiments show that short interference RNA (siRNA) specific for Bim or the downstream effector Bax both reduced apoptosis induced by Dex in osteoblastic cells. These findings suggest that Bim is a novel regulator of osteoblast apoptosis and may be a therapeutic target.

Effect of strontium ranelate on hydrogen peroxide-induced apoptosis of CRL-11372 cells

In vitro and in vivo studies have proven strontium to be an osteoinductive trace element. The effect of strontium ranelate (SR) on H(2)O(2)-induced apoptosis of CRL-11372 cells and optimization of its anti-apoptotic dose were the aims of this study. After 1 h of pretreatment with SR 1 microM, 50 microM, 100 microM, 500 microM, and 1,000 microM concentrations, CRL-11372 osteoblasts were exposed to 100 microM H(2)O(2) for periods of 6-12 h. The same experiments were repeated without H(2)O(2). The apoptotic index and viability of cells were assessed quantitatively with a fluorescent dye and qualitatively with agarose gel electrophoresis. Concentrations of 1-100 microM of SR with a 6-h treatment and only 1 microM concentration with a 12-h treatment inhibited the apoptotic effect of H(2)O(2) on cultured osteoblasts significantly (P < 0.05). SR was shown to inhibit H(2)O(2)-induced apoptosis of CRL-11372 cells in a dose-dependent manner.

Detection of apoptosis of bone cells in vitro

Studies during the last decade demonstrated that apoptosis is as important as mitosis for the growth and maintenance of the skeleton and provided information on the significance and molecular regulation of apoptosis of bone cells. It is now known that: (1) all osteoclasts die by apoptosis after completing a bone resorption cycle; (2) the majority of osteoblasts also die, whereas the remainder become lining cells or osteocytes; and (3) osteocytes, although long-living cells, also can die prematurely. Furthermore, mounting evidence indicates that systemic hormones, local growth factors, cytokines, and pharmacological agents, as well as mechanical forces regulate the rate of bone cell apoptosis. This chapter summarizes the methods developed in the last few years to examine apoptosis of cultured bone cells and identify the signaling pathways and molecules involved in apoptosis regulation by diverse skeletal stimuli.

Effects of anti-inflammatory drugs on proliferation, cytotoxicity and osteogenesis in bone marrow mesenchymal stem cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) were found to suppress proliferation and induce cell death in cultured osteoblasts, and steroids were found to decrease the osteogenesis potential of mesenchymal stem cells. In this study, we further tested the effects of anti-inflammatory drugs (AIDs) on the functions of bone marrow mesenchymal stem cells (BMSCs). The BMSCs from mice (D1-cells) and humans (hBMSCs) were treated with dexamethasone (10(-7) to 10(-6) M), cyclooxygenase-2 (COX-2) selective NSAIDs (10(-6) to 10(-5) M) and non-selective NSAIDs (10(-5) to 10(-4) M). Drug effects on proliferation, cell cycle kinetics, cytotoxicity and mRNA and protein expressions of cell cycle regulators were tested. The osteogenesis potential of D1-cells were evaluated by testing mRNA expressions of type Ialpha collagen and osteocalcin 2-8 days after treatments, and testing mineralization 1-3 weeks after treatments. The results showed that all the tested drugs suppressed proliferation and arrested cell cycle of D1-cells, but no significant cytotoxic effects was found. Prostaglandin E1, E2 and F2alpha couldn't rescue the effects of AIDs on proliferation. The p27kip1 expression was up-regulated by indomethacin, celecoxib and dexamethasone in both D1-cells and hBMSCs. Higher concentrations of indomethacin and dexamethasone also up-regulated p21Cip1/Waf1 expression in hBMSCs, and so did celecoxib on D1-cells. Expressions of cyclin E1 and E2 were down-regulated by these AIDs in D-cells, while only cyclin E2 was down-regulated by dexamethasone in hBMSCs. All the tested NSAIDs revealed no obvious detrimental effects on osteogenic differentiation of D1-cells. These results suggest that the proliferation suppression of AIDs on BMSCs may act via affecting expressions of cell cycle regulators, but not prostaglandin-related mechanisms.

Vanadate prevents glucocorticoid-induced apoptosis of osteoblasts in vitro and osteocytes in vivo

Skeletal mass is maintained by a balance between formation and resorption, cell proliferation and apoptosis. In vitro, glucocorticoids (GCs) decrease extracellular signal-regulated kinases (ERK) activation by mitogens, thus inhibiting osteoblast proliferation. Both ERK activity and proliferation are restored by co-treatment with the protein tyrosine phosphatase inhibitor, vanadate. Since ERK signalling may also be anti-apoptotic, we explored the effects of vanadate on GC-induced apoptosis in vitro and in vivo. Apoptosis in MBA-15.4 pre-osteoblasts increased from 6 h and remained up to eightfold higher through 6 days of 10(- 6) M dexamethasone (Dex) treatment. Co-incubation with 10(- 7) M vanadate markedly reduced apoptosis at all time points. Vanadate also prevented GC-induced poly-ADP-ribose polymerase cleavage. We assessed the transcriptional profiles of seven anti-apoptotic proteins (Bcl-2, Bcl-X(L), inhibitors of apoptosis protein-1 (IAP-1), IAP-2, X-linked IAP (XIAP), Fas-associated death-domain-like IL-1beta-converting enzyme-inhibitory protein (FLIP(Long)) and FLIP(Short)) in osteoblasts subjected to various stimuli using real-time quantitative PCR. Although these anti-apoptotic genes responded to different mitogenic conditions, Dex failed to repress their expression, and in fact significantly up-regulated Bcl-X(L), IAP-2 and XIAP. Dex may therefore induce apoptosis by up-regulating pro-apoptotic gene expression. We have previously demonstrated that rats treated with GC develop low formation osteoporosis (bone histomorphometry and DEXA) and skeletal fragility (breaking strength) that were largely prevented by co-treatment with vanadate. We report here that vertebrae from rats treated with 3.5 mg/kg per day methylprednisolone for 9 weeks showed increased incidence of terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end-labelling-positive apoptotic osteocytes, which was reduced by vanadate co-treatment. We conclude that vanadate prevents GC-induced apoptosis of pre-osteoblasts in vitro and osteocytes in vivo, and this may contribute to its bone-sparing effects in vivo.

l-Carnitine protects against apoptosis of murine MC3T3-E1 osteoblastic cells

L-carnitine (LC), an amino acid with a major role in cellular energy metabolism, has positive effects on bone metabolism. However, the effect of LC on apoptosis of osteoblast in vitro has not been reported. The aim of this study was to investigate the action of LC on apoptosis of mouse osteoblastic cell line MC3T3-E1. Cell apoptosis was measured by sandwich-enzyme-immunoassay. Release of cytochrome c from mitochondria into cytosol and Bcl-2, Bax protein levels were determined by Western blot analysis. The enzyme substrate was used to assess the activation of caspase-3 and caspase-9. LC inhibited MC3T3-E1 cell apoptosis induced by serum deprivation. Our study also shows that LC decreased cytochrome c release and caspase-3 and caspase-9 activation in serum-deprived MC3T3-E1 cells. Furthermore, LC protected against MC3T3-E1 cell apoptosis induced by the glucocorticoid (GC) dexamethasone (Dex).

Selective regulation of bone cell apoptosis by translational isoforms of the glucocorticoid receptor

Glucocorticoids are widely used in the treatment of inflammatory and other diseases. However, high-dose or chronic administration often triggers troublesome side effects such as metabolic syndrome and osteoporosis. We recently described that one glucocorticoid receptor gene produces eight translational glucocorticoid receptor isoforms that have distinct gene-regulatory abilities. We show here that specific, but not all, glucocorticoid receptor isoforms induced apoptosis in human osteosarcoma U-2 OS bone cells. Whole human genome microarray analysis revealed that the majority of the glucocorticoid target genes were selectively regulated by specific glucocorticoid receptor isoforms. Real-time PCR experiments confirmed that proapoptotic enzymes necessary for cell death, granzyme A and caspase-6, were induced by specific glucocorticoid receptor isoforms. Chromatin immunoprecipitation assays further suggested that glucocorticoid receptor isoform-dependent induction of proapoptotic genes was likely due to selective coregulator recruitment and chromatin modification. Interestingly, the capabilities to transrepress proinflammatory genes were similar among glucocorticoid receptor isoforms. Together, these findings provide new evidence that translational glucocorticoid receptor isoforms can elicit distinct glucocorticoid responses and may be useful for the development of safe glucocorticoids with reduced side effects.

Apelin stimulates proliferation and suppresses apoptosis of mouse osteoblastic cell line MC3T3-E1 via JNK and PI3-K/Akt signaling pathways

The aim of this study was to investigate the effects of apelin on proliferation and apoptosis of mouse osteoblastic MC3T3-E1 cells. APJ was expressed in MC3T3-E1 cells. Apelin did not affect Runx2 expression, alkaline phosphatase (ALP) activity, osteocalcin and type I collagen secretion, suggesting that it has no effect on osteoblastic differentiation of MC3T3-E1 cells. However, apelin stimulated MC3T3-E1 cell proliferation and inhibited cell apoptosis induced by serum deprivation. Our study also shows that apelin decreased cytochrome c release and caspase-3, capase-8 and caspase-9 activation in serum-deprived MC3T3-E1 cells. Apelin activated c-Jun N-terminal kinase (JNK) and Akt (phosphatidylinositol 3-kinase downstream effector), and the JNK inhibitor SP600125, the phosphatidylinositol 3-kinase (PI3-K) inhibitor LY294002 or the Akt inhibitor 1L-6-hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate (HIMO) inhibited its effects on proliferation and serum deprivation-induced apoptosis. Furthermore, apelin protected against apoptosis induced by the glucocorticoid dexamethasone or TNF-alpha. Apelin stimulates proliferation and suppresses serum deprivation-induced apoptosis of MC3T3-E1 cells and these actions are mediated via JNK and PI3-K/Akt signaling pathways.

Synthesis and Biological Evaluation of Heteroaryldiamides and Heteroaryldiamines as Cytotoxic Agents, Apoptosis Inducers and Caspase-3 Activators

The work described here involved the synthesis and biological evaluation of new heteroaryldiamides and heteroaryldiamines. A new general model in which the structures can be adjusted has been applied in this study. Three different structural units can be distinguished: a central nucleus and two symmetric terminal units. The central element is either an aliphatic chain of varying length and flexibility, piperazine, or a polyamine nucleus. However, the terminal units are pyridine, quinoline, indole, benzene or pyrido[2,3-d]pyrimidine with different substituents. The antitumoural activities of the compounds were evaluated in vitro by examining their cytotoxic effects against human breast, colon, and bladder cancer cell lines. Compounds that showed cytotoxic activity were subjected to both apoptosis and caspase-3 assays. With regard to selectivity, the cytotoxicity was also determined in cell cultures of two nontumoural lines. The most promising compounds are 4c, 5c and 7, which are amino-pyridinium, quinolyl-N-oxide, and pyridyl derivatives, respectively, and these reveal a significant in vitro cytotoxicity in at least two of the three cell lines tested. These compounds induced apoptosis and also produced a rapid dose-dependent increase in the caspase-3 level in HT-29 cells. Other encouraging profiles were found, such as those presented by 1k and 8d, which are cytotoxic and apoptotic but do not provoke an increase in the level of caspase-3, or those presented by 2f, 3c and 4a, which are slightly cytotoxic but do not show any other significant activity. The different types of behaviour of each compound are not necessarily parallel in the three cell lines tested.

Ghrelin stimulates proliferation and differentiation and inhibits apoptosis in osteoblastic MC3T3-E1 cells

Ghrelin is a 28-amino-acid peptide identified in the stomach as an endogenous ligand of the growth hormone secretagogue receptor (GHS-R) that strongly stimulates the release of growth hormone at the hypothalamus and pituitary level. Although GHS-Rs are expressed in a variety of peripheral tissues, little is known about its effect on bone independent of GH/IGF-1 axis. This study was undertaken to investigate whether ghrelin exerts a direct effect on osteoblasts. We identified mRNA and protein expression of GHS-R in primary osteoblasts as well as a number of osteoblastic cell lines, including MC3T3-E1, ROS 17/2.8, UMR-106, MG63, and SaOS2 cells. Treatment of ghrelin (10(-11) to 10(-7) M) to MC3T3-E1 cells showed dose-dependent stimulation of proliferation, which was abrogated by treatment with [d-Lys]-GHRP-6 (10(-3) M), a selective antagonist of the ghrelin receptor. Ghrelin activated ERK1/2 MAPK and pretreatment with MAPK kinase inhibitors, PD98059 attenuated the ghrelin-induced cell proliferation. Ghrelin also inhibited TNFalpha-induced apoptosis and suppressed caspase-3 activation that occurs in response to TNFalpha as well as during in vitro differentiation process. Moreover, ghrelin treatment enhanced in vitro osteoblast differentiation as evidenced by matrix mineralization, alkaline phosphatase activity, and osteoblast-specific gene expression. These results suggest that ghrelin promotes proliferation and differentiation and inhibits apoptosis of osteoblasts.

Regulation of apoptosis in osteoclasts and osteoblastic cells

In postnatal life, the skeleton undergoes continuous remodeling in which osteoclasts resorb aged or damaged bone, leaving space for osteoblasts to make new bone. The balance of proliferation, differentiation, and apoptosis of bone cells determines the size of osteoclast or osteoblast populations at any given time. Bone cells constantly receive signals from adjacent cells, hormones, and bone matrix that regulate their proliferation, activity, and survival. Thus, the amount of bone and its microarchitecture before and after the menopause or following therapeutic intervention with drugs, such as sex hormones, glucocorticoids, parathyroid hormone, and bisphosphonates, is determined in part by effects of these on survival of osteoclasts, osteoblasts, and osteocytes. Understanding the mechanisms and regulation of bone cell apoptosis will enhance our knowledge of bone cell function and help us to develop better therapeutics for the management of osteoporosis and other bone diseases.

Caspase-independent cell death?

Many cells die with apoptotic morphology and with documented activation of an effector caspase, but there are also many exceptions. Cells frequently display activation of other proteases, including granzymes, lysosomal cathepsins, matrix metalloproteinases, and proteasomal proteases, and others display morphologies that are not fully consistent with classical apoptosis. In some experimental situations, evidence of caspase-dependent death is indirect, demonstrating that the cell can activate caspases rather than that it does. In other situations, such as involution of mammary or prostate tissue, many cells display autophagic or other morphology different from apoptosis, and there is considerable evidence for the activation of a lysosomal system. Prior to total collapse and necrosis, cells that are in trouble can activate numerous physiological pathways toward self-destruction. Intrinsic or extrinsic routes to effector caspase activation are frequently the most rapid and efficient. If neither of these routes is immediately available, owing to mutation, genetic manipulation, inhibitor, or the biology of the cell, other routes may be followed, leading to variant forms of cell death that may display one or more characteristics of apoptosis. Experimental and therapeutic procedures must account for this possibility.

On the link between Bcl-2 family proteins and glucocorticoid-induced apoptosis

As immunosuppressive agents, glucocorticoids (GCs) act by inhibiting the expression of cytokines and adhesion molecules at the transcriptional and post-transcriptional levels. In addition, GCs exerted their effects by modulating apoptosis. In view of the central role of the Bcl-2 family protein in regulating apoptosis, it was tempting to speculate that GCs modulated apoptosis through modulation of the expression of proapoptotic (Bax, Bcl-X(S), Bak) and prosurvival (Bcl-2, Bcl-X(L), Bcl-w) Bcl-2 family members. Prosurvival Bcl-2 family members in various cell types antagonized GC-induced apoptosis, thereby suggesting a causal relationship between GC-induced apoptosis and Bcl-2 proteins. The antagonism of apoptosis afforded by prosurvival Bcl-2 proteins appeared to be specific for the GCs, as Bcl-2 and Bcl-x(L) blocked GC-induced apoptosis in T cell hybridomas but did not affect Fas or activation-induced apoptosis. Although it is speculated that GC-induced apoptosis may be mediated through the activation of proapoptotic Bcl-2 proteins, recent findings suggest that this may vary depending on the conditions and the cell types used. The mechanism by which Bcl-2 inhibited GC-induced apoptosis remains uncertain. It was suggested that Bcl-2 acted on outer mitochondrial membranes to preserve their function. Bcl-2 overexpression also inhibited GC-induced apoptotic events, including caspase activation and mitochondrial dysfunction. The cross-talk of the GC receptors with other secondary messengers could lead to modulation of the activity of Bcl-2 proteins through modification of their phosphorylation status, without ruling out the possibility of a physical interaction between activated GR with Bcl-2 proteins.